阅读说明：本技术 用于具有多种产物的分隔壁塔和双分隔壁塔的先进过程控制方案 (Advanced process control scheme for divided wall and double divided wall columns with multiple products ) 是由 R·皮什切克 P·德胡格 D·A·霍坎森 E·克鲁文 于 2019-08-20 设计创作，主要内容包括：提供用于改进在单个塔内包括一个或多个分隔壁的分离系统的过程控制的系统和方法。已经发现,通过基于能量平衡而非质量平衡控制分隔壁塔,可实现改进的过程控制。能量平衡可部分基于控制塔的第一分隔部分内的进料侧上的多个位置的温度进行。使用基于进料侧上的多个位置的温度控制的能量平衡可促进分隔壁塔的运行保持在单一的相空间区域内,所述相空间可合适地近似为线性模型。这可允许常规过程控制器管理操纵变量和被控变量。除控制进料侧上的多个位置的温度外,还可使用多个其它特征作为操纵变量或被控变量。任选地,多变量控制器可用于提供塔的进一步改进的控制。(Systems and methods are provided for improving process control of a separation system including one or more dividing walls within a single column. It has been found that by controlling the dividing wall column based on energy balance rather than mass balance, improved process control can be achieved. The energy balance may be based in part on controlling the temperature at a plurality of locations on the feed side within the first divided portion of the column. The use of energy balance based on temperature control at multiple locations on the feed side can facilitate maintaining operation of the divided wall column within a single phase space region, which can be suitably approximated as a linear model. This may allow a conventional process controller to manage manipulated and controlled variables. In addition to controlling the temperature at various locations on the feed side, various other characteristics may be used as manipulated or controlled variables. Optionally, a multivariable controller may be used to provide further improved control of the column.)

1. A process for separating a feed into a plurality of products, comprising:

feeding a feed comprising i)1 vol% or more of one or more light components, ii)1 vol% or more of one or more heavy components, or iii) a combination of i) and ii) into a feed inlet volume defined in the distillation column by a first dividing wall and a second dividing wall, the feed inlet volume being in fluid communication with the top common volume and with the bottom common volume;

maintaining a bottom feed inlet temperature in the feed inlet volume between a first temperature and a second temperature during the passing, the bottom feed inlet temperature measured at a location at least two theoretical stages above the split feed vapor stream, the first temperature and the second temperature being greater than the final boiling point of the one or more light components;

maintaining a top feed inlet temperature in the feed inlet volume between a third temperature and a fourth temperature during the passing, the top feed inlet temperature measured at a location at least two theoretical stages below the split flow of feed liquid, the third temperature and the fourth temperature being less than the initial boiling point of the one or more heavy components;

withdrawing a first product stream from a first partitioned volume of the distillation column, the first partitioned volume located in a first column zone defined in part by a first partition wall, the first product stream comprising at least a portion of the one or more light components;

withdrawing a second product having a lower volatility to normal boiling point than the first product stream from a second divided volume of the distillation column, the second divided volume located in a second column zone bounded in part by a second dividing wall;

withdrawing a third product stream from a third partitioned volume of the distillation column having a lower volatility based on normal boiling point than the second product stream, the third partitioned volume being located in the first column zone, the third product stream comprising at least a portion of the one or more heavy components;

withdrawing a bottoms product stream from the bottom common volume; and

an overhead product stream is withdrawn from above the top packed bed of the distillation column,

wherein the concentration of the one or more light components at the feed vapor split is less than 0.1 volume percent and the concentration of the one or more heavy components at the feed liquid split is less than 0.1 volume percent.

2. A process for separating a feed into a plurality of products, comprising:

feeding a feed comprising i)1 vol% or more of one or more light components, ii)1 vol% or more of one or more heavy components, or iii) a combination of i) and ii) into a feed inlet volume defined in the distillation column by a first dividing wall and a second dividing wall, the feed inlet volume being in fluid communication with the top common volume and with the bottom common volume;

maintaining a bottom feed inlet temperature in the feed inlet volume between a first temperature and a second temperature during the passing, the bottom feed inlet temperature measured at a location at least two theoretical stages above the split feed vapor stream, the first temperature and the second temperature being greater than the final boiling point of the one or more light components;

maintaining a top feed inlet temperature in the feed inlet volume between a third temperature and a fourth temperature during the passing, the top feed inlet temperature measured at a location at least two theoretical stages below the split flow of feed liquid, the third temperature and the fourth temperature being less than the initial boiling point of the one or more heavy components;

withdrawing a first product stream from a first partitioned volume of the distillation column, the first partitioned volume located in a first column zone defined in part by a first partition wall, the first product stream comprising at least a portion of the one or more light components;

withdrawing a second product having a lower volatility based on normal boiling point than the first product stream from a second partitioned volume of the distillation column, the second partitioned volume located in a second column zone bounded in part by a second partitioned wall, the second product stream comprising at least a portion of the one or more heavy components;

withdrawing a bottoms product stream from the bottom common volume; and

an overhead product stream is withdrawn from above the top packed bed of the distillation column,

wherein the concentration of the one or more light components at the feed vapor split is less than 0.1 volume percent and the concentration of the one or more heavy components at the feed liquid split is less than 0.1 volume percent.

3. A process for separating a feed into a plurality of products, comprising:

feeding a feed comprising i)1 vol% or more of one or more light components, ii)1 vol% or more of one or more heavy components, or iii) a combination of i) and ii) into a feed inlet volume defined in the distillation column by a first dividing wall and a second dividing wall, the feed inlet volume being in fluid communication with the top common volume and with the bottom common volume;

maintaining a bottom feed inlet temperature in the feed inlet volume between a first temperature and a second temperature during the passing, the bottom feed inlet temperature measured at a location at least two theoretical stages above the split feed vapor stream, the first temperature and the second temperature being greater than the final boiling point of the one or more light components;

maintaining a top feed inlet temperature in the feed inlet volume between a third temperature and a fourth temperature during the passing, the top feed inlet temperature measured at a location at least two theoretical stages below the split flow of feed liquid, the third temperature and the fourth temperature being less than the initial boiling point of the one or more heavy components;

withdrawing a first product stream from a first partitioned volume of the distillation column, the first partitioned volume located in a first column zone defined in part by a first partition wall, the first product stream comprising at least a portion of the one or more light components;

withdrawing a second product having a lower volatility to normal boiling point than the first product stream from a second divided volume of the distillation column, the second divided volume located in a second column zone bounded in part by a second dividing wall;

withdrawing a third product stream having a lower volatility to normal boiling point than the second product stream from a third partitioned volume of the distillation column, the third partitioned volume located in the first column zone;

withdrawing a fourth product stream from a fourth segregated volume of the distillation column having a lower volatility based on normal boiling point than the third product stream, the fourth segregated volume being located in the second column zone, the fourth product stream comprising at least a portion of the one or more heavy components;

withdrawing a bottoms product stream from the bottom common volume; and

an overhead product stream is withdrawn from above the top packed bed of the distillation column,

wherein the concentration of the one or more light components at the feed vapor split is less than 0.1 volume percent and the concentration of the one or more heavy components at the feed liquid split is less than 0.1 volume percent.

4. The process according to any one of the preceding claims, wherein the interior of the distillation column comprises two or less liquid partial streams and two or less vapor partial streams.

5. The process according to any one of the preceding claims, wherein said feedstock comprises 10 vol% or more of said one or more light components, or wherein said feedstock comprises 10 vol% or more of said one or more heavy components, or a combination thereof.

6. The process according to any one of the preceding claims, wherein at least one of the bottom feed inlet temperature and the top feed inlet temperature comprises a pressure compensated temperature.

7. The method according to any of the preceding claims, further comprising:

taking out a feed reflux extract above the feed liquid split stream;

splitting the feed reflux production in a feed reflux splitter to form at least a first portion of the feed reflux production and a second portion of the feed reflux production, the splitting based on the feed reflux splitter location;

returning a first portion of the feed reflux production above the feed side of the split feed liquid stream; and

a second portion of the feed reflux withdrawal is returned above the product side of the feed liquid split.

8. The method of claim 7, wherein maintaining the bottom feed inlet temperature comprises:

measuring the bottom feed inlet temperature;

determining the flow rate of the first portion of the returned feed reflux production; and

based on the measured bottom feed inlet temperature and the measured flow rate of the first portion of the feed return production returned, the feed return flow splitter position is changed to maintain the bottom feed inlet temperature between the third temperature and the fourth temperature.

9. The process according to any of the preceding claims, wherein maintaining the bottom feed inlet temperature further comprises:

measuring the flow rate of the feed; analyzing the feed to determine the amount of the one or more light components, the one or more heavy components, or a combination thereof; and

changing the set point for the bottom feed inlet temperature based on the measured flow rate, the analyzed amount of the one or more light components, the analyzed amount of the one or more heavy components, or a combination thereof.

10. The process according to any of the preceding claims, wherein maintaining the top feed inlet temperature comprises: measuring the top feed inlet temperature; and varying the overhead temperature based on control of the overhead internal reflux to maintain the top feed inlet temperature between the first temperature and the second temperature.

11. The process according to any of the preceding claims, wherein maintaining the bottom feed temperature, the top feed temperature, or a combination thereof comprises:

inputting at least one of the measured bottom feed inlet temperature and the measured top feed inlet temperature into a multivariable controller;

inputting a plurality of additional measurements to the multivariable controller, the plurality of additional measurements comprising at least the measured feed flow rate; and

varying at least one of the feed reflux draw, the feed reflux splitter position, and the reboiler duty based on one or more of the measured bottom feed inlet temperature, the measured top feed inlet temperature, the measured feed flow rate, and additional measurements.

12. The process of claim 11, wherein the plurality of additional measurements comprise one or more product temperatures associated with the top product stream, the bottom product stream, the first product stream, the second product stream, and the third product stream, and wherein at least one of the top internal reflux and the reboiler duty is varied based on the one or more product temperatures.

13. The process of any of the above claims, wherein withdrawing the first product stream further comprises:

determining a set point for a first draw tray temperature, a first draw tray draw rate, or a combination thereof;

the first draw tray temperature is maintained based on at least the determined setpoint of the first draw tray temperature and two or more of the first draw tray top reflux, the first draw tray bottom reflux, and the first draw tray draw rate.

14. The method of claim 13, further comprising:

measuring a plurality of temperatures of a draw stream from a first draw tray; and

changing a set point for the first draw tray temperature, the first draw tray draw rate, or a combination thereof based on the plurality of measured temperatures of the draw stream from the first draw tray.

15. The process according to any one of the preceding claims, wherein withdrawing the second product stream further comprises:

determining a set point for a second draw tray temperature, a second draw tray draw rate, or a combination thereof;

maintaining the second draw tray temperature based on at least the determined setpoint of the second draw tray temperature and two or more of the second draw tray top reflux, the second draw tray bottom reflux, and the second draw tray draw rate.

16. The method of claim 15, further comprising:

measuring a plurality of temperatures of a draw stream from a second draw tray; and

changing a set point for the second draw tray temperature, a second draw tray draw rate, or a combination thereof based on the plurality of measured temperatures of the draw stream from the second draw tray.

17. The process of any of claims 1 or 3-16, wherein withdrawing the third product stream further comprises:

determining a set point for a third draw tray temperature, a third draw tray draw rate, or a combination thereof;

maintaining the third draw tray temperature based on at least the determined set point for the third draw tray temperature and two or more of the third draw tray top reflux, the third draw tray bottom reflux, and the third draw tray draw rate.

18. The method of claim 17, further comprising:

measuring a plurality of temperatures of a draw stream from a third draw tray; and

changing a set point for the third draw tray temperature, a third draw tray draw rate, or a combination thereof based on the plurality of measured temperatures of the draw stream from the third draw tray.

19. The method according to any one of the preceding claims, wherein analyzing the feed comprises sampling the feed to obtain a sample and analyzing the sample using a gas chromatograph.

20. The method of any of the above claims, further comprising:

determining a target overhead temperature in the distillation column; and maintaining the target overhead temperature based on the change in internal reflux.

21. The method according to any one of claims 1 or 4 to 20, further comprising

A fourth product stream having a lower volatility based on normal boiling point than the third product stream is withdrawn from a fourth partitioned volume of the distillation column, the fourth partitioned volume being located in the second column zone.

22. The method according to any of the preceding claims, wherein at least one of the first dividing wall and the second dividing wall comprises a plurality of substantially parallel dividing wall sections, at least one of the plurality of substantially parallel dividing wall sections being horizontally offset with respect to at least one other of the plurality of substantially parallel dividing wall sections.

23. A system for separating a feed into a plurality of products, comprising:

a distillation column comprising a top common volume, a bottom common volume, an intermediate volume, and a column wall;

a reboiler in the bottom common volume comprising a reboiler duty controller;

a first dividing wall and a second dividing wall in the intermediate volume, the first dividing wall and the second dividing wall defining a feed inlet volume, a feed vapor split stream, and a feed liquid split stream, the first dividing wall and the column wall defining a first column zone comprising a first plurality of divided volumes, the second dividing wall and the column wall defining a second column zone comprising a second plurality of divided volumes;

a first reflux splitter in fluid communication with the overhead common volume via a reflux take-off, a first reflux return above the first column zone, and a second reflux return above the second column zone;

a feed reflux splitter in fluid communication with the distillation column in the volume above the feed liquid split via a feed reflux draw, a first feed reflux return and a second feed reflux return above the feed inlet volume;

a feed inlet top temperature sensor located at least two theoretical stages below the feed liquid stream;

a feed inlet bottom temperature sensor located at least two theoretical stages above the feed vapor split;

a feed inlet in fluid communication with the feed inlet volume, the feed inlet comprising a feed analyzer;

at least one top outlet in fluid communication with the top common volume or with the volume above the top packed bed;

at least one bottom outlet in fluid communication with the bottom common volume;

a first outlet in fluid communication with a first separation volume of the first plurality of separation volumes;

a second outlet in fluid communication with a second separation volume of the second plurality of separation volumes;

a third outlet in fluid communication with a third separation volume of the first plurality of separation volumes, the third outlet having an elevation lower than an elevation of the first outlet; and

a multivariable controller in communication with at least the feed top inlet temperature sensor, the feed bottom inlet temperature sensor, the feed analyzer, the multivariable controller configured to provide input communication to at least one of the reboiler duty controller, the feed reflux production controller, and the feed reflux splitter based on one or more of the feed top inlet temperature, the feed bottom inlet temperature, and the analyzed feed composition.

24. The system of claim 23, wherein the multivariable controller further receives communication with a plurality of additional temperature sensors, including a first outlet temperature sensor, a second outlet temperature sensor, a third outlet temperature sensor, a top outlet temperature sensor, and a bottom outlet temperature sensor, the multivariable controller configured to provide input communication to the reboiler duty controller based on the one or more additional temperature sensors.

25. The system according to claim 23 or 24, wherein said multivariable controller further receives communication with a feed top pressure sensor and a feed bottom pressure sensor, control of at least one of the top feed inlet temperature and the bottom feed inlet temperature being based on pressure-sensitive temperatures.

FIELD

Systems and methods for separation using a distillation column having multiple dividing walls are provided. The system and method includes a process control scheme.

Background

Distillation columns or towers are one of the structures that are common in a refinery environment. Distillation columns are used to separate multiple product streams from an input stream at a refinery using reduced or minimized footprint. In addition, distillation columns are valuable for the separation of products having adjacent, similar, and/or overlapping boiling ranges.

A Divided Wall Column (DWC) is a distillation column comprising a vertical dividing wall separating a feed zone from one or more side product draw zones. DWC techniques can reduce the amount of equipment and/or energy required to achieve one or more desired separations. The dividing wall can be used to separate the volume for receiving the input feed to the column from the location for withdrawing the product stream, thereby reducing product contamination. Additionally or alternatively, the separation wall may be used to create separate compartments to remove multiple product streams having a high purity of greater than 99 wt.%.

While Divided Wall Columns (DWCs) may provide the advantage of reducing energy consumption and/or space occupation in refineries, difficulties remain in the implementation of divided wall column technology when multiple divided walls are present in a single column structure. In fact, operating DWCs in a refinery or chemical plant environment requires the ability to control primarily the operation of the column using process control techniques. Process control techniques typically involve running the process in a region of an operating phase space (operating phase space) where the response of the controlled variable to the movement of the manipulated variable can be reasonably approximated as a linear response. For many types of processes, process control techniques can be implemented in a relatively straightforward manner. However, it remains a challenge to maintain DWCs with multiple divider walls in a stable operating zone using process control techniques. While the amount of operator intervention may be increased, it is preferable to find systems and methods that can improve the operation of DWCs using process control techniques.

Us patent 6,551,465 describes a dividing wall column control system. In this control system, the rate at which overhead liquid is returned to the column is set by monitoring the temperature at the top of the product dividing wall section. The side draw product withdrawal rate is set by monitoring the temperature at the bottom of the product dividing wall section.

SUMMARY

In various aspects, methods of separating a feed into multiple products are provided. The process can include feeding a feed comprising i)1 vol% or more of one or more light components, ii)1 vol% or more of one or more heavy components, or iii) a combination of i) and ii) into a feed inlet volume defined in a distillation column by a first dividing wall and a second dividing wall. The feed inlet volume may be in fluid communication with the top common volume and in fluid communication with the bottom common volume. During the conveying, a bottom feed inlet temperature within the feed inlet volume may be maintained between the first temperature and the second temperature. The bottom feed inlet temperature may be measured, for example, at a location at least two theoretical stages above the feed vapor split. The first temperature and the second temperature may be greater than the final boiling point of the one or more light components. Additionally or alternatively, the top feed inlet temperature within the feed inlet volume may be maintained between the third temperature and the fourth temperature during the conveying. The top feed inlet temperature may be measured, for example, at a location at least two theoretical stages below the feed liquid split. The third temperature and the fourth temperature may be less than the initial boiling point of the one or more heavy components. Product streams may then be withdrawn from various partitioned volumes within the distillation column. In the product stream, a first product stream may include at least a portion of the one or more light components, while another product stream from the partitioned volume may include at least a portion of the one or more heavy components. Additionally, a bottom product stream and an overhead product stream may be withdrawn from the bottom common volume and the top common volume, respectively. During the passing, the concentration of the one or more light components at the feed vapor split may be less than 0.1 vol% and/or the concentration of the one or more heavy components at the feed liquid split may be less than 0.1 vol%.

In various aspects, systems for implementing such separations may also be provided.

Brief Description of Drawings

FIG. 1 shows an example of a divided wall column configuration capable of separating at least five products from a feed, with two vapor split streams and two liquid split streams within the column.

FIG. 2 shows one example of controllers, sensors and other analyzers that may be used in conjunction with a divided wall column configuration similar to that shown in FIG. 1.

Detailed description of the invention

I. Overview

In various aspects, systems and methods are provided for improving process control of a separation system including one or more dividing walls within a single column. It has been found that by controlling the dividing wall column based on energy balance rather than mass balance, improved process control can be achieved. The energy balance may be based in part on controlling the temperature at a plurality of locations on the feed side within the first divided portion of the column. The use of energy balance based on temperature control at multiple locations on the feed side can facilitate maintaining operation of the divided wall column within a single phase space region, which can be suitably approximated as a linear model. This may allow a conventional process controller to manage manipulated and controlled variables. In addition to controlling the temperature at various locations on the feed side, various other characteristics may be used as manipulated or controlled variables.

One of the difficulties with conventional process control methods for producing divided wall columns of four or more products is maintaining the operation of the DWC within a single phase space region. Using conventional mass balance control methods for distillation columns, the goal of column operation is to operate the column to achieve the desired output at each product location. However, in a divided wall column, there may be different temperatures on opposite sides of the divided wall. Thus, attempting to manage a column containing a dividing wall based on the mass balance of the feed vs product can result in unpredictable behavior. For example, in a conventional distillation column, if too much feed is fractionated into intermediates, a conventional mass balance response may be to lower the temperature. However, this may not produce the desired results in columns having dividing walls. In columns having a feed inlet volume separated from the intermediate product by a dividing wall, the potential cause of excess product at the product withdrawal location is due to improper separation of feed in the feed inlet volume. In particular, the initial portion of the column receiving the feed (i.e., the feed inlet volume) is generally expected to split the feed based on boiling range, some lighter components are expected to exit above the liquid split, and some heavier components are expected to exit below the liquid split. If the light components exit below the liquid split, there may be excess product at the product withdrawal location. However, attempts to cool the product location did not solve this problem, and in fact made it worse by causing a corresponding decrease in temperature in the feed inlet volume on the opposite side of the dividing wall. Similar problems can occur when heavy components exit above the liquid split. Thus, in a control method based on mass balance, it is possible for the column to enter such a phase space region: where attempting to "correct" the amount of product at the intermediate location may cause the column to move further away from the desired operating zone.

It has been found that by maintaining the energy balance within the column, control of DWCs can be improved. Rather than attempting to balance output product production versus input feed, the DWC may be controlled based on maintaining desired or target temperatures at various locations within the DWC. In particular, the temperature near the top and bottom of the feed inlet volume can be controlled to prevent light components from exiting below the vapor split and to prevent heavy components from exiting above the liquid split. By controlling the temperature in the column to achieve the target value and the target product purity, the operation of the column can be maintained in the desired phase space region. Optionally, one or more of the target temperatures and/or the temperature used to control the controller may correspond to a pressure compensation temperature to account for the effect of pressure on the volatility of the components within the column.

As an example, the feed may contain 1 vol% or more of one or more light components (or 10 vol% or more) and/or 1 vol% or more of one or more heavy components (or 10 vol% or more). The one or more light components, if present, correspond to components that make up a portion of the column intermediate (i.e., not a portion of the column overhead). Similarly, the heavy component or components, if present, correspond to components that form part of different intermediates of the column. In various aspects, the one or more light components can be prevented from exiting the feed inlet volume via a vapor split at the bottom of a dividing wall defining the feed inlet volume when the column is operated. Additionally or alternatively, the one or more heavy components may be prevented from exiting the feed inlet volume via a liquid split at the top of a partition wall defining the feed inlet volume. This may correspond, for example, to limiting the amount of the one or more light components at the vapor split to 0.1 volume percent or less of the composition at the vapor split. Similarly, the amount of the one or more heavy components may be limited to 0.1 volume percent or less of the composition at the liquid split.

Other variables that may be manipulated and/or controlled in order to control the multiple temperatures in the feed inlet volume include, but are not limited to, overhead temperature, reboiler or heater duty, temperature of the cut point for one or more product withdrawals (product draws), withdrawal rate for one or more product withdrawals, feed flow, bottoms flow, overhead internal reflux, overhead, bottoms level, and reflux drum level. Additionally, feed and/or product composition may be analyzed as a further input source. For example, control of reboiler duty and overhead internal reflux can allow control of temperature at various locations within the column, including within the feed inlet volume.

In addition to using energy balance, at least a portion of the manipulated variables and controlled variables may be correlated using a multivariable controller. The multivariable controller may allow for selection of various input values from the beginning of the decision on how to implement energy balancing. For example, it may be desirable to set the reboiler duty based on the temperature within the feed inlet volume rather than selecting the reboiler duty based on the bottom temperature. The amount of internal reflux at one or more locations can also be controlled by a multivariable controller in order to control the temperature at the top and bottom of the feed inlet volume. One difficulty for operators operating towers using energy balance control schemes is that increased energy is typically used. By managing multiple variables using a multivariable controller, the amount of energy required to operate the tower based on energy balance may be reduced or minimized.

General dividing wall column configuration and operation

To facilitate the explanation of the control scheme for a divided wall column, an overview of a general divided wall column configuration is provided.

In various aspects, configurations and/or methods as described herein can be used to produce 5 or more products (or 4 or more products, or 6 or more products) from a divided wall column containing a plurality of divided walls. Optionally, such a configuration may include up to two vapor splits and two liquid splits. The reduction or minimization of the number of vapor and/or liquid split streams in a divided wall column configuration is beneficial because each split stream corresponds to a location where the streams must be managed to equalize pressure at the split point. Thus, the reduction or minimization of the number of splits may reduce the number of restrictions on the flows within the system and reduce the complexity of design and operation. It is noted that when counting the number of products, the top product and the bottom product from the divided wall column may correspond to the products withdrawn from a common packed bed within the divided wall column. With respect to the bottoms, it is noted that at least a portion of the bottoms can generally be recycled as part of the reboiler loop to provide additional heat to the distillation column. Additionally, configurations and/or methods may also be provided for columns that include a single dividing wall, such as columns that produce 4 products.

In some aspects, production of 5 or more products from a divided wall column containing two or more divided walls may require maintaining a temperature differential across at least one divided wall of at least 10 ℃, or at least 20 ℃, or at least 25 ℃, such as at most 35 ℃ or possibly higher. Maintaining a temperature differential across at least one dividing wall can allow for the removal of products having different boiling ranges at similar heights or elevations in the column while still achieving the desired purity.

In some aspects, by having different packing types and sizes on opposite sides of the dividing wall, the production of 5 or more products from the dividing wall column can be facilitated. The use of different packing types and sizes is a design consideration to optimize the column design to improve or maximize utilization and reduce or minimize the amount of waste. The pressure drop, capacity and packing efficiency of each horizontally adjacent packed bed section can vary due to the use of different packing types and sizes. This can result in the ratio of gas mass flow to cross-sectional area varying within various sections of the divided wall column.

In some aspects, 5 or more products can be produced from a divided wall column while operating the column at a pressure of 100kPa or greater, or 150kPa or greater, while still having a maximum of 2 liquid split streams and 2 vapor split streams. It is sometimes beneficial to operate the column at higher pressures.

It has been found desirable during operation of a distillation column that the packed beds in the divided volumes from which the side-draw products are withdrawn have substantially equal percent flooding. When the distillation column is operated at substantially equal percent flooding, a target percent flooding can be determined that is within a threshold amount of the percent flooding of any packed bed in the partitioned volume from which the side-draw product is withdrawn. It is noted that in some aspects, trays can be used in place of packed beds within a divided wall column. To simplify the present description, packed beds are described herein to illustrate the invention.

In some aspects, the distillation column can be designed to have approximately equal average percent flooding in each divided (i.e., adjacent) section of the packed bed. The divided sections are separated from each other by a partition wall. Designing approximately equal percent flooding for each partition is expected to maintain a constant vapor flow split and maximize the total hydraulic capacity of the column to account for the increase in feed flow since each packed bed in the partition volume has a similar amount of remaining capacity. This may allow different packing types and sizes to be used for each column section depending on separation requirements. Additionally or alternatively, operating at approximately equal percent flooding may allow flexibility in processing feeds having different compositions, as the pressure drop across the packed bed may have reduced or minimized variability as the amount of compounds of a particular boiling range varies with the feed. This is in contrast to attempts to run distillation based on control of gas flow within one or more partitioned volumes defined by dividing walls, which may limit packing selection of horizontally adjacent packed beds to similar packing types and sizes. In this discussion, operating with approximately equal average percent vapor flooding in adjacent packed beds is defined as operating with average percent vapor flooding values that differ by less than 10%. One potential benefit of operating with approximately equal average vapor flood percentage values is that this may allow the divided wall columns to maintain substantially similar vapor split ratios when operating at significantly different column feed rates. A significantly different feed rate is defined as the first feed rate differing from the second feed rate by 25% or more. A substantially similar vapor split ratio is defined as the first vapor split ratio differing from the second vapor split ratio by less than 10% for the same vapor split.

In some aspects related to configurations in which at least four products are produced by a divided wall column, at least one of the dividing walls can correspond to a plurality of dividing wall segments, wherein at least one of the dividing wall segments is horizontally offset or staggered relative to at least one other of the dividing wall segments. Having offset wall segments can change the relative cross-sections of the partitioned volume/tower region defined by the plurality of wall segments. This helps to maintain a constant percentage of flooded volume through each packed bed by varying the total volume available for flooding (flooding) within a given packed bed. Additionally or alternatively, the use of offset wall configurations may provide an increased amount of available packed bed volume within the distillation column compared to configurations involving a single, coherent dividing wall having an oblique section (angled section). For example, the staggered or offset position of the staggered walls may be located within the column internals, such as within chimney trays (chimney tray). Locating the staggered locations within the column internals reduces or minimizes any potential effect of wall staggering on fluid flow within the column. Staggered locations within the column internals may also reduce or minimize the amount of volume not occupied by the packed bed. Dividing wall towers (DWCs) with angled dividing walls may result in designs with greater waste volumes than DWCs using staggered dividing walls. For example, DWC configurations using sloped or angled divider walls typically do not have a packed bed adjacent to the sloped portion of the divider wall. This can result in a large portion of the column volume being empty.

In some aspects, the plurality of dividing walls may allow for multiple products to be withdrawn from each divided volume while reducing or minimizing the packed bed height between the multiple products. In a conventional distillation column, the products withdrawn from adjacent levels in the column generally correspond to products having overlapping or adjacent boiling ranges. By establishing separate volumes for the removal of the side-draw product, product of higher purity can be removed from the separate volumes. For example, a distillation column comprising two dividing walls may have a feed inlet volume and multiple dividing volumes separate from a central volume for product withdrawal. If three side-draw products are desired in addition to the top product and the bottom product, two of the three side-draw products can be removed from the divided volume defined in part by the first dividing wall (corresponding to the first column zone) and the remaining side-draw product can be removed from the divided volume defined in part by the second dividing wall (corresponding to the second column zone). In these aspects, the withdrawal position can be configured such that the side-draw product withdrawn from the second column section can have a boiling range corresponding to the boiling range between the products withdrawn from the second column section. This configuration may reduce or minimize the number of equivalent trays required to achieve the desired separation between products. This configuration is expected to reduce the height of the packed bed located between the two side-draw product withdrawal locations in the first column zone. For example, depending on the variation in relative volatility between vertically adjacent side-draw products, the packed bed between product withdrawal locations in the first column zone may correspond to 5 equivalent trays or less, rather than the typical need for at least 10 equivalent trays required for proper separation of the products.

Operation with an approximately constant percent flooding in the divided volume can be contrasted with conventional strategies for operating divided wall columns. Examples of conventional strategies for dividing wall column operation include operation at constant gas mass flow rate/cross-sectional ratio in the divided volume, which does not take full advantage of column capacity, efficiency, or allow for different types of packing and sizes to be used for each divided section.

Definition of

In this discussion, a dividing wall is defined as a dividing wall or other barrier that impedes fluid flow disposed/passing substantially parallel to/through the central axis of the distillation column. The dividing wall can intersect the inner wall of the distillation column (referred to as the column wall) at one or more locations, such as at two locations. The height of the dividing wall may be generally less than the internal height of the distillation column.

In this discussion, a divided volume is defined as the volume within a distillation column bounded laterally by at least one dividing wall and either the column wall or a second dividing wall. This is different from a common volume within a distillation column, which refers to a volume spanning substantially the entire internal cross-section of the distillation column at a height/elevation corresponding to the common volume. The separation volume has substantially no fluid communication transversely across the separation wall. Rather, any fluid communication between the separate volumes separated by the dividing wall is indirect-based on fluid communication via, for example, the upper or lower common volumes. The vertical boundaries of the separation volume are based on the packed bed and other associated internals in the divided wall column. In this discussion, the vertical boundary of the separation volume is defined as the top of a liquid distributor tray (or other flow distributor) located above the packed bed to the bottom of a chimney tray, liquid withdrawal tray, or another structure suitable for product withdrawal, below the same packed bed. If no liquid/flow distributor is present above the packed bed, the separation volume starts at the top of the packed bed. If there is no chimney tray or other equivalent structure below the packed bed, the separation volume ends with the structure that starts the next separation volume. It is noted that the separation volumes in a divided wall column need not be contiguous under these conditions. It is further noted that the feed inlet volume may not correspond to the separation volume. For example, the feed inlet volume may correspond to the volume between the chimney tray and the flow distributor. Finally, it is noted that the packed bed and the relevant internals may not correspond to a separation volume in this definition if a portion of the relevant internals exceeds the dividing wall. For example, two sections of adjacent packed beds may be separated by a dividing wall, but may share a common chimney tray below the location of the dividing wall. This type of internal piece arrangement is outside the definition of the separation volume.

In this discussion, a column section corresponds to a column section defined in part by the lateral boundaries formed by the dividing walls, with the top and bottom thereof defined by the top and bottom of the respective dividing wall. For a section bounded on multiple sides by a dividing wall, a lowest elevation top (lowest elevation top) and a highest elevation bottom may be used to define the section. The column section may comprise one or more divided volumes.

In this discussion, a liquid split is defined as a position corresponding to the top of a dividing wall where two horizontally adjacent packed beds are separated and the flow of liquid into the top of these beds is manipulated to achieve the desired component separation in each packed bed. In this discussion, the vapor split is defined as the position corresponding to the bottom of the dividing wall where two horizontally adjacent packed beds are separated and the vapor ratio to each side of the dividing wall is set by the design of the column internals.

In this discussion, the packed bed is defined according to conventional definitions. Thus, the packed bed has a volume available to contain fluid between the particles/structures and/or within the pores in the packed bed. It is mentioned that the total volume of the packed bed corresponds to this available volume. In this discussion, the percent vapor flood (percent vapor flow) of a packed bed is defined as the volume percent relative to the liquid flood point defined by the Fractionation Research, Inc. In this discussion, the target percent flooding corresponds to a value for comparison to the percent flooding of the packed bed within the partitioned volume in the distillation column.

In this discussion, the side-draw product refers to the distillation product except for the product taken from the top common volume or the bottom common volume.

In this discussion, reference to boiling points or boiling points corresponds toSuch as a cut point determined according to ASTM D2887, or according to ASTM D86 and/or ASTM D7169 if ASTM D2887 is not suitable for the sample properties. Reference to the "Tx" cut point refers to the fractional weight "x" from which a sample can be distilled at a given temperature. For example, the T10 cut corresponds to a temperature at which 10 wt.% of the sample can be distilled. In this discussion, compounds corresponding to light ends (i.e., C) are included₁To C₄Compounds) may be described based on the carbon number of the hydrocarbons included in the fraction according to common practice of those skilled in the art. For example, is described as C₄The boiling range to 200 ℃ represents an endpoint low enough to include C₄The boiling range of the hydrocarbon. Similarly, corresponding to C₁To C₄The boiling range of the light fraction of compounds may have a sufficiently low endpoint to include methane and a sufficiently high endpoint to include C₄A hydrocarbon.

In this discussion, the two product streams may be compared based on the volatility of the streams as determined by the normal boiling point. In this discussion, comparing the volatility of two streams based on standard boiling points is defined as comparing streams based on the T50 boiling points of the streams at standard conditions (i.e., 1atm or 100 kPa-a). A first stream is defined as having a lower volatility than a second stream if the T50 boiling point of the first stream is higher than the corresponding T50 boiling point of the second stream.

In this discussion, fluid communication may refer to direct fluid communication or indirect fluid communication. Indirect fluid communication refers to the ability of fluid to pass from a first volume to a second volume via an intermediate volume.

In this discussion, the term "substantially parallel" means that one wall/wall section is oriented within 10 ° or less of parallel to the axis or another wall/wall section.

In this discussion, the opposite position of the partition wall is defined as the position adjacent to the partition wall on the opposite side of the partition wall at a given position.

Basic control scheme

In various aspects, the basic control scheme can be used to control a distillation column comprising one or more dividing walls, such as a Double Dividing Wall Column (DDWC) or a column having Multiple Dividing Walls (MDWC). The basic control scheme appears to be different for different column operations, depending on the feed composition, the amount of product stream, and the availability of lights for pressure control. However, such a basic control scheme may be based on various control principles. Control principles may include, but are not limited to, control of the temperature in the feed inlet volume; controlling the internal reflux of the tower top; controlling the purity of the product; control of reboiler heat duty; and control of column or column bottoms liquid level. In some aspects, multivariable controllers can be used to facilitate managing so many control principles. In addition to simplifying management, it has been found that a multivariable controller can reduce the energy requirements for operating a column that includes one or more dividing walls, such as two dividing walls or multiple dividing walls.

The basic control scheme of DWC may be based on a process controller, such as a proportional-integral-derivative controller or another convenient type of controller. Such controllers may typically receive a single input which is then used to determine a single output signal. The foundation

Regardless of the nature of the feed, a common element in the basic control of DWC is a stable separation control in the feed inlet volume (i.e. on the feed side of the dividing wall). This control prevents light key components from slipping down below the wall and heavy key components from escaping above the wall. With this basic control scheme in mind, successful completion of this 100% of the time can facilitate the success of model-based multivariable controllers.

In various aspects, maintaining steady state separation in the feed inlet volume can be based on an energy balance control scheme. Material balance control schemes often do not perform well enough.

A. Feed inlet volume separation control

Maintaining adequate control over the separation in the feed inlet volume is the starting point for the basic control scheme to operate. This may correspond to maintaining temperature control of at least two locations within the feed inlet volume. One position corresponds to a position at least two theoretical stages below the liquid split (i.e. the top of the wall), such as 2 to 5 stages below the liquid split. This may be referred to as the top feed inlet temperature. The second position corresponds to a position at least two theoretical stages above the vapor split, such as 2 to 5 stages above the vapor split. This may be referred to as the bottom feed inlet temperature.

Various control options are possible for controlling the top feed inlet temperature and the bottom feed inlet temperature. For example, in some aspects, the top feed inlet temperature can be influenced and/or stabilized by overhead product quality control, upper side stream product quality control, or a combination thereof. In these aspects, there may not be a basic control scheme to control the top feed inlet temperature. Instead, a model-based multivariable controller may manage one or more controls to maintain a desired top feed inlet temperature. Alternatively, the top feed temperature can be incorporated into the base control scheme by using the top feed temperature as one of the constraints of reboiler duty control.

One example of a control option for controlling the bottom feed inlet temperature may be based on the control of the internal reflux to the feed side of the wall defining the feed inlet volume. The feed reflux production may be withdrawn above a liquid split stream defining the feed inlet volume. The feed return flow splitter can then be used to control the amount of liquid returned over the opposite side of the dividing wall by the returning liquid vs returned to a position above the feed inlet volume. This can provide control over the amount of cooling that occurs in the feed inlet volume. According to this aspect, this may be used to facilitate control of the top feed inlet temperature and/or the bottom feed inlet temperature.

In some aspects, the flow of reflux from the reflux splitter to the feed inlet volume can be monitored by a suitable method, such as by using a full aperture ultrasonic flow meter. In these aspects, the flow meter may include at least three probes (pick-ups) for measuring flow. Fewer probes and/or different types of flow meters may lead to inaccurate flow measurements due to the bubbling nature of the reflux line, which may be close to boiling flow.

B. Product purity control

In a divided wall column, such as a double divided wall column, the column can produce a variety of products. The purity of one or more products (and optionally the purity of each product) can be controlled based in part on the withdrawal rate at the product location, internal reflux below the product withdrawal location, and/or information regarding changes in the input feed to the feed inlet volume.

In various aspects, the internal reflux to the feed side of the wall can be calculated. This is generally equal to the measured external reflux flow to the feed side of the wall. Optionally, if the reflux is heated by pumping to provide pressure to the reflux (e.g., reflux to the product side of the wall), a temperature sensor may be used to calculate the reduction in internal reflux caused by heating. An internal return flow controller for the portion of the feed return flow returning above the feed side of the wall can reset the position of the return flow splitter (i.e., can determine the amount of return flow delivered above the feed inlet volume). The set point of the internal reflux flow controller can be reset, for example, based on a pressure compensation value that determines the bottom feed inlet temperature.

In aspects where product purity is controlled based in part on the reflux below the product withdrawal location, internal reflux below the product take-off tray can be calculated. This can be determined, for example, by subtracting the withdrawal rate from the internal reflux above the withdrawal tray. For a product take-off tray located in a wall segment (i.e., a dividing volume), the internal reflux to the product take-off side of the wall can first be calculated to determine the reflux only in the dividing volume associated with product take-off.

After calculating the internal reflux below the production tray, the internal reflux flow below the production tray may be used as a process variable for a controller that controls the internal reflux below the production tray. This controller can reset the production rate controller to control product production. With respect to the set point of the internal reflux below the production tray, a pressure compensated temperature controller for the fractionation point related to the quality of the produced product can be used to reset the set point of the internal reflux controller below the production tray.

In some aspects, a divided wall column can have a significant withdrawal rate for product near the middle of the column. But for higher or lower side stream products, in some aspects, the withdrawal rate may provide insufficient control authority over the tight control of internal reflux below the withdrawal tray. In other words, the effect of production rate on temperature may not be sufficient to provide the required level of temperature control. In such aspects, the multivariable controller may optionally manipulate production rate rather than the base control temperature setpoint. This is beneficial to avoid the situation where model prediction error is introduced into the multivariable controller due to the lack of ability of the base control to maintain temperature at or near the product withdrawal location.

In addition to the above, it is beneficial in some aspects that the basic control scheme uses feed information in determining product production. For example, when there are significant and abrupt changes in feed rate and feed composition, it is beneficial to provide a dynamically compensated material balance feed forward control of the affected product production while the basic control. It is noted that this may preferably be bypassed when controlling the product quality using multivariable model-based control instead of basic control.

C. Tower top control

In various aspects, it is beneficial that the pressure within the column be stable under all conditions, including storms that cause internal reflux fluctuations. Since the overall control uses energy balance control, pressure disturbances may cause the entire control scheme to cycle.

In some aspects, the initial step for overhead control may be to calculate and control the column internal reflux using the overhead temperature, external reflux flow rate, and reflux temperature. The overhead stream composition can be controlled by resetting the temperature controller for internal reflux control.

Additional details regarding pressure control may depend on the nature of the components in the overhead section. For example, some overhead sections may include flooded, drumless overhead condensers. In some aspects, the overhead take-off rate may be large enough to achieve adequate overhead pressure control authority. In such an aspect, a) a reflux ratio control valve may be used to control internal reflux; b) a pressure compensated tray temperature controller for overhead product quality control can reset the set point of the internal ratio controller; and c) the overhead pressure controller can reset the set point for overhead product withdrawal. Optionally, adding an external reflux flow as a feed forward to the pressure control can further improve process control stability.

In other aspects, the overhead take-off may not provide sufficient control authority over overhead pressure control. In such an aspect, a) a backflow control valve may be used to control internal backflow; and b) the overhead pressure controller can reset the internal reflux ratio controller set point. Feed forward to pressure control has limited validity due to the small flow taken overhead. In addition, a pressure compensated tray temperature controller for overhead product quality control can reset the set point for overhead product production. This control scheme performs poorly in terms of top product quality control, but it is beneficial to maintain a constant pressure in the column.

In still other aspects, the overhead assembly can include a partial overhead condenser having a small vapor product stream and a reflux drum. In such aspects, pressure control can be achieved by manipulating the small vapor product stream flow rate. If the liquid withdrawal rate from the top of the column is large enough to achieve sufficient liquid level control authority of the reflux drum, a) a reflux control valve is used to control internal reflux; b) the pressure compensated tray temperature controller for overhead product quality control may manipulate the set point of the internal reflux ratio controller; and c) the reflux drum level controller can reset the overhead liquid product flow controller. Alternatively, if overhead production does not provide sufficient control authority over reflux drum level control, the level control can be handled as part of a model-based multivariable controller. In such an alternative aspect, the multivariable controller can manipulate the internal reflux (which manipulates the flow of the external reflux) and the overhead liquid product. Additionally, if the model-based multivariable controller is not enabled, the internal reflux ratio controller may be manipulated by the backup tank level controller.

D. Reboiler heat duty control

The reboiler heat duty is calculated as a process variable and used in the heat duty controller to manipulate the final handle (ultimate handle) which manipulates the heating medium sent to the reboiler.

The reboiler heat duty can be manipulated by a model-based multivariable controller to handle the varying constraints in the divided wall column. When no such control is provided, the reboiler heat duty set point can be manipulated in relation to the bottoms quality by a pressure compensated tray temperature control. However, in divided wall columns, bottoms quality control may not be a constraint control on heat demand. In such a case, an override (override) controller may be required to provide sufficient heat to adequately fractionate at higher locations in the column. Alternatively, in aspects where a multivariable controller is not used, the pressure compensated temperature at a higher location in the column may reset the heat load set point.

E. Liquid level control at the bottom of a tower

The bottom draw rate controller set point can typically be reset by the bottom level controller. In the case of a model-based multivariable controller linking the towers together, the tower bottom flow can be directly manipulated by it. Multivariable controllers are also beneficial where the feed contains a reduced or minimized amount of bottoms material.

F. Model-based multivariable control for divided wall column

In various aspects, a multivariable controller can be used to coordinate control of multiple variables within a divided wall column. The use of multiple variable controllers can provide a way for the interaction of information and/or control structures from different sections of the column and allow multiple variables to be considered and/or selected from the time a set point for a variable (e.g., reboiler heat duty cycle) is selected.

In some aspects, a model-based multivariable controller may be configured to interact with a plurality of manipulated variables (independent variables), a plurality of controlled variables (dependent variables), and optionally one or more independent feedforward or disturbance variables.

As one example, the manipulated variables may include, but are not limited to, overhead pressure; reboiler heat duty; a bottom feed inlet temperature control setpoint; one or more base control setpoint for the product for the cut point temperature controller (e.g., setpoint for all cut point temperature controllers); the withdrawal rate of the product when the base control tray temperature control is unsuccessful; feed flow (this may alternatively be a feed forward/disturbance variable); the bottoms product flow (if the bottoms level is included in the model-based multivariable controller); and overhead internal reflux and overheads (as in the aspect where the column includes a reflux drum).

Feed forward or disturbance variables may include, but are not limited to, column feed composition based on output values from a feed analyzer, such as a gas chromatograph; and tower feed rate (if not manipulated by a model-based multivariable controller).

Controlled variables may include, but are not limited to, top feed inlet temperature; based on the analyzer, the product production composition; sensitive tray temperatures where the underlying control tray temperature is not established; bottom liquid level (if included); reflux drum level (if a reflux drum is present) or overhead condenser level; column delta pressure as flooding constraint; and various additional column constraints such as controller outputs and/or valve positions.

It is noted that the restriction of variables by the top feed inlet temperature and the bottom feed inlet temperature is important to ensure that the light key components cannot slide down below the wall defining the feed inlet volume and/or that the heavy key components cannot escape from above the wall defining the feed inlet volume. It is also noted that reboiler duty is not necessarily related to column bottom separation, but affects many multivariable dependent variables.

According to aspects, a multi-variable controller may be used to facilitate manipulation and/or control of a variable set or variables that are not normally considered to interact under a base control method. An operational model of the multivariable controller may be formed based on the manipulated variables, disturbance variables, and controlled variables that are deemed to interact best. As one example, the reboiler heat duty (manipulated variable) may be set based on considerations of temperature inputs from a number of temperatures throughout the column. Additionally, changes in the feed detected by the feed analyzer may also be considered when selecting the reboiler heat duty. Based on these changes in reboiler heat duty, the multivariable controller can also change the set point associated with one or more reflux splitters to maintain one or more temperatures at a target value even if additional heat is added to the column bottom. More generally, any desired combination of manipulated variables, disturbance variables, and controlled variables may be incorporated into the model of the multivariable controller in order to manage the divided wall column as described herein.

The basic control scheme itself stabilizes the separation. It is designed such that the entire DWC looks like a classical distillation column with linear behavior to a multivariable controller. But due to many interactions, basic control is often unable to run DWCs efficiently. In various aspects, model-based multivariable control can be used to control heat input and product composition to meet specifications while conserving energy and efficiency. Properly designed base controls and properly designed multivariable controls may benefit the successful and efficient operation of the DWC.

In various aspects, the multivariable controller can be said to receive communication with one or more sensors and/or controllers within the divided wall column. Receive communications are defined as being capable of receiving signal communications from sensors and/or controllers. Additionally, a multivariable controller can communicate with one or more controller inputs to provide input regarding a setpoint of the controller.

G. Instrumented

To provide information about the temperature, pressure, composition, flow rate and/or other values within the divided wall column, various instruments can be used. Examples of instruments may include, but are not limited to, a) a feed analyzer for feed forward control of product take-off trays and heat input; b) an impurity analyzer associated with one or more product streams (such as possibly all product streams) for product quality control; c) a composition analyzer for the return flow from the return flow splitter; d) a tower top pressure sensor; e) a tower top temperature sensor; f) a return temperature sensor; g) a level indicator of the top drum (if present); h) a liquid level indicator at the bottom of the tower; i) an instrument capable of calculating the heat input from the reboiler (e.g., using flow and temperature measurements to determine the heat input from the reboiler in a MW or another power plant); j) a full aperture ultrasonic flow meter with multiple probes (pick-ups) for the return flow to the feed inlet volume; and k) temperature sensors and optionally pressure sensors for fractional point control at sensitive temperature locations. This may include temperature sensing of temperatures, such as top feed inlet temperature and bottom feed inlet temperature. Additionally or alternatively, one or more temperature sensors may be associated with each product fraction as part of product purity control, such as 3 temperature sensors per product fraction. For products that can tolerate higher impurity levels, such as 5 vol% or higher impurity levels, a single thermocouple may be sufficient. Optionally, a temperature sensor may also be associated with the pressure sensor in order to calculate a pressure-sensitive temperature value.

V. variations of packed beds on opposite sides of the dividing wall

Conventionally, the flow on either side of a divided wall column has been managed by limiting the nature and type of the differences on opposite sides of the divided wall. As an example, a conventional divided wall column uses the same type of packed bed throughout the column. By using the same type of packing and matching the depth of the packed bed across the dividing wall, the pressure drop across the dividing wall can be similar, so that the fluid flow in the volume defined by the dividing wall is relatively predictable.

Unlike conventional configurations, in various aspects, a divided wall column may be used that allows for differing fluid properties on opposite sides of the divided wall in at least some locations. Structurally, the variation in fluid properties may be achieved by including structures with different pressure drops on opposite sides of the dividing wall. For example, instead of providing packed beds of similar packing type, size and depth on both sides of the partition wall, the packed beds on opposite sides of the partition wall may be varied. The packed bed differential on opposite sides of the dividing wall near the top of the wall can eventually be balanced by other differentials near the bottom of the dividing wall. Note that above the top of the divider wall (or below the bottom of the divider wall), any pressure differential will subside because there is no structure to hold the pressure differential.

Another type of variation that contributes to having dissimilar fluid properties on opposite sides of the dividing wall may correspond to a variation in the cross-sectional area of the divided volume on opposite sides of the wall while reducing or minimizing the amount of waste generated in the column. Varying the cross-sectional area may vary the relative pressure drop across the dividing wall. For example, in a column zone having a constant cross-sectional area, if all beds in the column zone have the same packing type, size, and cross-sectional area, the pressure drop across each packed bed may depend primarily on the depth of the bed. However, if the cross-sectional area of one of the packed beds is larger while maintaining the same packing/packing density/bed depth, the total pressure drop across the packed bed is lower due to the increased area available to accommodate the flow.

In some aspects, the maintenance of temperature differentials on opposite sides of a divider wall may be facilitated or enhanced by using a divider wall with enhanced insulating properties, such as a divider wall comprised of two wall structures separated by a wall gap. The wall gap may correspond to an air gap, a vacuum gap, or another convenient type of gap that may reduce or minimize heat transfer between wall structures. In aspects where the dividing wall corresponds to a chord between two points on the circumferential inner wall of the column, the wall structures may be separated by a wall gap along the full length of the wall. Any convenient gap size may be used between the spaced wall structures, such as a wall gap of 0.3 inches (0.7 cm) to 3.0 inches (7.6 cm), or 0.5 inches (1.2 cm) to 2.0 inches (5.1 cm).

VI. raw materials

Any convenient type of feed suitable for separation in a conventional distillation column and/or multiple columns may be separated using a divided wall column. Examples of suitable feeds for separation may include, but are not limited to, hydrocarbon (or hydrocarbon-like) feeds. The hydrocarbonaceous feed can include a feed having one or more heteroatoms other than carbon or hydrogen. Examples of hydrocarbon-like compounds include, but are not limited to, oxygenates (such as alcohols, esters, and ethers), nitrogen-containing compounds (such as amines), and sulfur-containing compounds (such as mercaptans). It is noted that such heteroatoms may be contained in a ring structure, such as a cyclic ether or thiophene.

In some aspects, a suitable feed (or other fraction) may have a boiling range that includes light fractions. For example, the lower end of the boiling range may be sufficiently low to include C₁Hydrocarbons, or low enough to include C₂Hydrocarbons (but not including C)₁Hydrocarbons) or low enough to include C₃Hydrocarbons (but not including C)₂Hydrocarbons) or low enough to include C₄Hydrocarbons (but not including C)₃Hydrocarbons). For example, a feed (or other fraction) including various types of light ends may have C₁To 350 ℃, or C₁To 270 deg.C,Or C₁To 200 ℃ or C₁A boiling range defined by the initial boiling point to the T90 cut point to 150 ℃. As another example, include C₂The hydrocarbon feed (or other fraction) may have C₂To 350 ℃, or C₂To 270 ℃ or C₂To 200 ℃ or C₂A boiling range defined by the initial boiling point to the T90 cut point to 150 ℃. As yet another example, C is included₃The hydrocarbon feed (or other fraction) may have C₃To 350 ℃, or C₃To 270 ℃ or C₃To 200 ℃ or C₃A boiling range defined by the initial boiling point to the T90 cut point to 150 ℃. As yet another example, C is included₄The hydrocarbon feed (or other fraction) may have C₄To 350 ℃, or C₄To 270 ℃ or C₄To 200 ℃ or C₄A boiling range defined by the initial boiling point to the T90 cut point to 150 ℃. As yet another example, C is included₅The hydrocarbon feed (or other fraction) may have C₅To 350 ℃, or C₅To 270 ℃ or C₅To 200 ℃ or C₅A boiling range defined by the initial boiling point to the T90 cut point to 150 ℃.

In other aspects, suitable feeds may have a T10 cut point of at least 60 ℃, or at least 90 ℃, or at least 120 ℃. In some aspects, suitable feeds may have a T90 cut point of 350 ℃ or less, or 300 ℃ or less, or 270 ℃ or less, or 200 ℃ or less, or 150 ℃ or less. For example, a suitable feed may have a T10/T90 distillation range of at least 60 ℃ to 150 ℃ or less, or at least 60 ℃ to 200 ℃ or less, or at least 60 ℃ to 300 ℃ or less, or at least 90 ℃ to 200 ℃ or less, or at least 90 ℃ to 270 ℃ or less, or at least 120 ℃ to 300 ℃ or less, or at least 120 ℃ to 350 ℃ or less. It is noted that feeds with higher T90 cut points may be suitable for separation, as such higher boiling portions of the feed may form "bottoms" fractions, while lower boiling portions correspond to products withdrawn from the various separation volumes.

As an example, the feed consists mainly of benzene, toluene, xylene, and light and heavy components as impurities. The corresponding separation can yield at least 5 products corresponding to light ends, heavy ends and products substantially corresponding to benzene, toluene and xylene. Such separation may be carried out in a divided wall column separator having two dividing walls, with the benzene, toluene and mixed xylene products being withdrawn from different divided volumes in the column region bounded by the dividing walls and the inner walls of the column.

As another example, a suitable feed may correspond to a feed comprising hydrocarbons (or hydrocarbon-like compounds) containing 6 or more carbons per compound. In such an example, a dividing wall distillation column may be used to form 6 products. The top product may correspond to C₉Or lighter products, while the bottom product may correspond to C₁₈Or heavier products. The separation volume from one column zone can be used for taking out C₁₀–C₁₁Products and C₁₄–C₁₅Product, while the separate volume from the second column zone can be used for C removal₁₂–C₁₃Products and C₁₆–C₁₇And (3) obtaining the product.

Configuration example

Fig. 1 schematically shows an example of the configuration of a divided wall column comprising two divided walls. The partition wall in fig. 1 corresponds to a wall made of a plurality of wall segments, wherein at least one wall segment is horizontally offset with respect to the other wall segments.

In fig. 1, the fractionation column includes a top common volume 110, a bottom common volume 190, and a plurality of other volumes in an intermediate volume 150. The start of the top common volume 110 is indicated by the elevation indicator 111 and the start of the bottom common volume 190 is indicated by the elevation indicator 191.

The bottom common volume 190 includes a bottom product draw 195 for providing a product stream that is at least partially sent to a reboiler (not shown) for heating to maintain the temperature of the fractionation column. The heated product stream is returned to the fractionation column via reboiler return 193. Any convenient type of reboiler return port 193 can be used including, but not limited to, a rinse nozzle, a conduit distributor, a vane distributor, or a baffle distributor.

The top common volume 110 includes an optional embedded overhead condenser 113 and a top product draw 115 to remove the lowest boiling product from the feed. Optionally, multiple product draw ports for different boiling ranges may be included as part of the common top volume 110. For product extraction ports other than bottom product extraction port 195, various additional internal structures may be associated with the product removal location. For example, for the overhead product withdrawal port 115, the liquid for withdrawal is collected in a chimney tray 120. A portion of the liquid becomes the withdrawn product 115 and the remainder is returned 117 to the liquid distributor 127 for further distillation. The liquid portion returning to 117 the liquid distributor 127 passes down into the packed bed 130 where it can contact the ascending heated vapor. This may result in partial vaporization of the descending liquid and may also result in partial condensation of the ascending vapor. The ascending vapor may continue to move upward until the vapor condenses and is withdrawn as part of the product draw, or until the vapor exits via a vapor phase withdrawal location (not shown). The descending liquid leaving the packed bed may fall to the next lower chimney tray 140 to be withdrawn, possibly as part of product withdrawal 145. In the example shown in fig. 1, two products may be taken from the top common volume.

The process of vapor ascending and liquid descending also occurs in various segregated volumes within the fractionation column. The example shown in fig. 1 includes a plurality of separation volumes, each comprising a packed bed, a flow distributor above the packed bed, and a chimney tray/liquid draw tray below the packed bed. The example in fig. 1 also includes a column section 160, which corresponds to the column section between the dividing wall 156 and the vessel wall 105 (also referred to as the column wall) of the fractionation column, and a column section 180, which corresponds to the column section between the dividing wall 158 and the vessel wall 105. Note that a top cross-sectional view of the divider walls 156 and 158 is also presented in fig. 1. Column section 160 includes separation volumes 262, 264, 266, and 268. In the example shown in fig. 1, product can be removed at removal location 165 associated with partitioned volume 262 and at removal location 169 associated with partitioned volume 264. Optionally, product may also be removed at locations (not shown) associated with the separation volumes 266 and 268. The column section 180 includes a separation volume 284. Note that packed bed 277 does not correspond to a separation volume, in part because chimney tray 377 receives liquid from packed bed 277 and packed bed 177. Instead, the separation volume 179 qualifies as a separation volume because the packed bed has associated flow distributors and chimney trays, all of which share a common separation wall.

In the example shown in fig. 1, feed inlet volume 174 corresponds to the volume of the column into which feed for separation is introduced via feed inlet 101. Partitioned volumes 171 and 179 can optionally include product withdrawal locations, but in some preferred aspects product withdrawal can be limited to partitioned volumes that are not in direct fluid communication with the volume containing the feed inlet. For example, although a take-off location 352 may be provided in the partitioned volume 171, in the example shown in FIG. 1, this take-off location serves to control the diversion of liquid to each side of the partition wall rather than as an intermediate mixed product. Similarly, take-off location 359 can produce an intermediate product, but in FIG. 1, take-off location 359 is used for flow regulation.

In fig. 1, the partition wall 156 includes at least two wall segments 253 and 257, the wall segments 257 being horizontally offset with respect to the wall segments 253. The offset of wall segment 257 toward the center of the column can provide additional volume for separation volume 266 based on the higher vapor loadings that can be expected in the lower portion of the side-draw product zone of the column. The horizontally offset substantially parallel wall sections may reduce or minimize the amount of waste and increase the column volume utilization compared to diagonal wall sections. Similarly, the partition wall 158 includes at least two wall segments 283 and 287.

As shown in fig. 1, the internal structure within the column may be different on opposite sides of the dividing wall. For example, the packed beds in the separation volume 264 are shown to have a greater depth than the corresponding packed beds associated with the separation volumes 224 on opposite sides of the separation wall 156. Thus, the chimney tray associated with separation volume 264 is at a lower elevation than the corresponding chimney tray associated with separation volume 224 on the opposite side of separation wall 156.

In the example shown in FIG. 1, the dividing walls 156 and 158 have different overall lengths, different top heights 206 and 208 relative to the column height, and different bottom heights 216 and 218 relative to the column height. In various aspects, any convenient dividing wall can have a highest top height and/or a lowest bottom height. It is noted that the top levels 206 and 208 correspond to the liquid split in the example shown in fig. 1, while the bottom levels 216 and 218 correspond to the vapor split.

In fig. 1, side-draw products can be withdrawn from the column at withdrawal locations 165, 169, and 185. Optionally but preferably, the sidedraw product withdrawn at position 185 can have a boiling range between the boiling ranges of the sidedraw product withdrawn at position 165 and the sidedraw product withdrawn at position 169. By having a higher relative volatility in the boiling range between the sidedraw products from locations 165 and 169, the packed bed associated with the separation volume 264 can have a lower equivalent tray count than would otherwise be required for a sidedraw product having an adjacent boiling range.

Control configuration embodiment

Figure 2 shows a similar DWC configuration for producing five different products. However, FIG. 2 provides additional information by indicating the process control structure associated with the operation of the DWC. Note that in fig. 2, the symbol including the letter "T" corresponds to the temperature sensor/controller; symbols including the letter "P" correspond to pressure sensors/controllers, symbols including the letter "L" correspond to level indicators or controllers, symbols including the letter "a" correspond to composition analyzers; the symbol comprising the letter "F" corresponds to a flow sensor/controller; and the symbol comprising the letter "R" corresponds to a ratio (ratio) controller. For temperature, pressure, flow and backflow symbols, the controller is labeled with a "circle in box", while the sensor/indicator is labeled with a circle only.

The top common volume 110 in fig. 1 includes various components and controls for managing pressure and temperature in the column and managing the overhead product stream. A similar height indicator 111 is provided in fig. 2 to indicate the boundary of the top common volume 110.

Prior to entering the feed inlet volume 174, the feed may be analyzed 1574 to characterize the composition of the feed, including the amount of light components that should be excluded from the feed vapor split stream and the amount of heavy components that should be excluded from the feed liquid split stream. The flow of the feed may be controlled and/or monitored by flow controller 1374. Within the feed inlet volume 174, the temperature controller may provide a temperature corresponding to the top feed inlet temperature (at least two theoretical stages below the liquid split). This may correspond to temperature controller 1248, or a separate temperature controller (not shown) may be used. For bottom feed temperatures (at least two theoretical stages above the vapor split), a temperature controller, such as temperature controller 1277, may be used.

At the top of the configuration shown in fig. 2, cooling water may be provided to the condenser 113 by a cooling water supply 1101 and may then exit to a cooling water return 1102. The temperature of the cooling water supplied from the cooling water supply source 1101 can be monitored by the temperature indicator 1201. To manage the temperature at the top of the column, the flow controller 1301 may vary the amount of cooling water delivered to the condenser 113. Temperature indicator 1202 may be used to monitor the temperature of the cooling water after it exits condenser 113.

The overhead pressure may be managed in part using a combination of pressure control steam 1105 and vacuum system 1106. The steam injection into the column may be controlled by the pressure controller 1405 based in part on the input received from the pressure indicator 1403.

Another portion to manage overhead pressure and temperature may be provided based on the amount of overhead product withdrawn. In fig. 1, the overhead product corresponds to product 115. Removal of the product 115 may be managed by a combination of several controllers and indicators. For example, in the configuration shown in fig. 2, analyzer 1515 can be used to characterize the composition of the product withdrawn from the column. Flow controller 1315 may control the amount of product used as product and/or diverted to overflow storage. The remaining withdrawn product may then be returned as an external reflux stream, as managed by flow controller 1317. The amount of external reflux can vary depending on the desired amount of internal reflux required to maintain the energy balance of the product and the controlled temperature in the upper portion of the column. The amount of internal reflux may be calculated based in part on information provided by temperature indicator 1217 and flow controller 1317. Temperature controller 1230 resets the set point for the desired internal reflux flow 1330, thereby stabilizing the fractionation in the packed bed 130 using energy balance.

At the top of the first dividing wall, a reflux splitter 1720 may be included to assist in temperature and pressure management at the liquid split to maintain energy balance on the feed side of the dividing wall. Reflux splitter 1720 may receive a produced stream from a column and return a first portion of the stream over one side of a dividing wall, while returning a second portion of the stream over an opposite side of the dividing wall. The "split" between the first portion and the second portion may be managed by a reflux ratio controller 1721. In the configuration shown in fig. 2, the set point of the ratio controller 1721 may be selected based in part on information received from the flow controller 1371 monitoring the liquid flow portion to the feed side of the dividing wall. The desired set point of the flow controller 1371 may be processed as a constraint variable through a constraint selector (constraint selector) 2000. Information related to the restriction selector 2000 may include, but is not limited to, information from flow controller 1371 and temperature controller 1262, which provide temperature information on the other side of the partition wall.

A second reflux splitter 1740 is also included to help maintain a desired temperature in the feed inlet volume 174 below the liquid split of the dividing wall 158. Feed reflux splitter 1740 can receive a produced stream from a column and return a first portion of that stream above feed inlet volume 174 while returning a second portion of that stream above the opposite side of the dividing wall. The "split" in feed reflux splitter 1740 can be managed by reflux ratio controller 1741. The set point for the feed ratio controller 1741 may be selected based in part on information received from the flow controller 1347 monitoring the flow portion being fed over the feed inlet volume 174. In the configuration shown in fig. 2, the desired set point for the flow controller 1347 may be selected from the temperature controllers 1277. Without being bound to any particular theory, a greater amount of interaction may occur between the internal reflux on the feed side of the wall and the upflow on the feed side of the wall by selecting the reflux split using bottom feed inlet temperature assisted reflux splitter 1740 (as detected by temperature controller 1277). Conversely, if the reflux splitter is controlled based on the top feed inlet temperature (as detected by temperature controller 1248), a more limited amount of interaction occurs between the reflux and upflowing gases prior to temperature sampling. This may result in a more limited feedback response.

In addition to reflux splitter 1720 and feed reflux splitter 1740, other reflux loops may be used to manage the fractionation point temperatures associated with the various product withdrawal locations. For example, for product 2 (reference numeral 165, corresponding to the lightest intermediate product), after analysis of the draw stream by analyzer 1565, a portion of the draw stream may be returned as reflux below the draw location. In the example shown in fig. 2, the backflow of product 2(165) under the withdrawal position may be controlled by flow controller 1364 based in part on temperature information provided by temperature controller 1264 and/or analyzer 1565. Note that analyzer 1565 may provide information regarding product quality. If the composition analyzed by analyzer 1565 does not match the desired composition distribution, the set point of flow controller 1364 may be changed to help adjust the temperature at the location of the fractionation point of product 2. For example, if the composition of product 2 includes too many heavy components, additional reflux may be used to lower the temperature at the cut point location 1264.

Similar control schemes may be used to manage the temperature and/or composition profiles at the withdrawal locations for the other intermediate products shown in FIG. 2, corresponding to product 3 (reference number 185) and product 4 (reference number 169). For product 3(185), after analyzing the draw stream by analyzer 1585, a portion of the draw stream may be returned as reflux below the draw location. In the example shown in fig. 2, the reflux of product 3(185) below the withdrawal location may be controlled by flow controller 1378 based in part on temperature information provided by temperature controller 1278 and/or analyzer 1585. Similarly, for product 4(169), after the draw stream is analyzed by analyzer 1569, a portion of the draw stream may be returned as reflux below the draw location. In the example shown in fig. 2, the backflow of product 4(169) under the withdrawal position may be controlled by flow controller 1368 based in part on temperature information provided by temperature controller 1268 and/or analyzer 1569.

The primary heat source for the column is provided by reboiler loop heater 1193 in the bottom region of the column. After the bottoms stream is withdrawn, the composition of the bottoms stream can be analyzed 1595, the temperature can be measured by one or more sensors 1295, and the pressure can be measured by one or more sensors 1495. A portion of the bottoms stream can then be output as a product stream while a second portion is passed through a heater 1193 to be reboiled and then returned to the column. The temperature of the heated return stream can be measured by sensor 1293. The flow of the heated return stream can be controlled by flow controller 1393 based on a set point provided by ratio controller 1760. The reboiler duty cycle may be selected, for example, by a constraint selector 2000. The restriction selector 2000 may provide a set point for boiler control 1891, which may provide a set point for flow controller 1396.

In some aspects, the desired temperature for each product fractionation point, the bottoms temperature, and the overhead temperature can all be separately controlled. In other aspects, a multivariable controller can be used to manage various temperatures within the column. For example, in a conventional distillation column, the duty cycle of heater 1193 is determined based on the desired bottom temperature, such as the set temperature of a controller near temperature controller 1290. However, determining the reboiler duty cycle based solely on the bottoms temperature may result in insufficient heat for fractionation at higher locations in the column. To overcome this difficulty, temperature and flow from various locations in the tower may be input to the restriction selector 2000. The restriction selector 2000 can then monitor various temperatures and flows higher up in the tower. The reboiler duty can then be selected so that all monitored temperatures and flows are sufficient to handle the desired separation. This may require the introduction of additional energy into the column, as higher duty cycles may be required than are required to achieve the desired bottom profile. To the extent that some excess heat may be present in the system due to operating the reboiler at a higher duty cycle, the multivariable controller may also adjust the various reflux splitters and/or product reflux loops to maintain the desired temperatures at various locations. This may allow the energy balance within the column to be maintained so that product production may have the desired composition while also maintaining the desired target temperature within the feed inlet volume.

In the configuration shown in FIG. 2, constraint selector 2000 receives information from different 10 sets of temperature controllers and/or flow controllers. This allows the restriction selector to receive temperature information from various elevations in the distillation column. Based on the received temperature information, the constraint selector 2000 can select the duty cycle of the reboiler heater 1193 to supply sufficient energy to achieve all target temperatures in the column. Optionally, the multivariable controller may also receive information from the feed analyzer 1574 and/or the feed flow controller 1374 to provide feed forward information regarding changes in the input feed. This may allow the multivariable controller to adjust the set points for temperature and/or pressure at various locations based on changes in feed composition and/or feed flow. In the example shown in fig. 2, the column feed corresponds to the bottoms from a previous vessel, such as a previous fractionation column.

Additional embodiments

Embodiment 1. a process for separating a feed into a plurality of products, comprising: feeding a feed comprising i)1 vol% or more of one or more light components, ii)1 vol% or more of one or more heavy components, or iii) a combination of i) and ii) into a feed inlet volume defined in the distillation column by a first dividing wall and a second dividing wall, the feed inlet volume being in fluid communication with the top common volume and with the bottom common volume; maintaining a bottom feed inlet temperature in the feed inlet volume between a first temperature and a second temperature during the passing, the bottom feed inlet temperature measured at a location at least two theoretical stages above the split feed vapor stream, the first temperature and the second temperature being greater than the final boiling point of the one or more light components; maintaining a top feed inlet temperature in the feed inlet volume between a third temperature and a fourth temperature during the passing, the top feed inlet temperature measured at a location at least two theoretical stages below the split flow of feed liquid, the third temperature and the fourth temperature being less than the initial boiling point of the one or more heavy components; withdrawing a first product stream from a first partitioned volume of the distillation column, the first partitioned volume located in a first column zone defined in part by a first partition wall, the first product stream comprising at least a portion of the one or more light components; withdrawing a second product having a lower volatility to normal boiling point than the first product stream from a second divided volume of the distillation column, the second divided volume located in a second column zone bounded in part by a second dividing wall; withdrawing a third product stream from a third partitioned volume of the distillation column having a lower volatility based on normal boiling point than the second product stream, the third partitioned volume being located in the first column zone, the third product stream comprising at least a portion of the one or more heavy components; withdrawing a bottoms product stream from the bottom common volume; and withdrawing an overhead product stream from above the top packed bed of the distillation column, wherein the concentration of the one or more light components at the feed vapor split is less than 0.1 vol% and the concentration of the one or more heavy components at the feed liquid split is less than 0.1 vol%.