Integrated process for separating ethanol from fermentation broth for cryogenic applications
阅读说明：本技术 用于低温应用的从发酵液中分离乙醇的集成方法 (Integrated process for separating ethanol from fermentation broth for cryogenic applications ) 是由 穆凯什·库马·夏尔马 戈拉夫·巴贾杰 阿洛克·夏尔马 于 2020-02-17 设计创作，主要内容包括：本发明提供了用于从由不同发酵技术产生的发酵液中回收有机化合物(即乙醇、丙醇、丁醇、丙酮、异丙醇)的方法。本发明特别涉及用于使用集成的蒸气压缩单元(涡轮风扇)、蒸发器(降膜)和发酵液汽提塔(真空蒸馏系统)从发酵液中分离乙醇的集成方法。所述方法通常在低于或为50℃的低温度下进行,以从含有活微生物的发酵液中分离和回收有机化合物(特别是乙醇),以确保发酵液再循环中微生物的活性。另外,还通过将含微生物的发酵液在发酵罐外部的停留时间保持为小于或等于10分钟来进一步确保微生物的活性。(The present invention provides methods for recovering organic compounds (i.e., ethanol, propanol, butanol, acetone, isopropanol) from fermentation broths produced by different fermentation techniques. The invention particularly relates to an integrated process for separating ethanol from a fermentation broth using an integrated vapor compression unit (turbofan), evaporator (falling film) and broth stripper (vacuum distillation system). The process is generally carried out at low temperatures, below or at 50 ℃, to separate and recover organic compounds (in particular ethanol) from the fermentation broth containing the living microorganisms, in order to ensure the activity of the microorganisms in the broth recycling. In addition, the activity of the microorganisms is further ensured by maintaining the residence time of the microorganism-containing fermentation broth outside the fermenter to be less than or equal to 10 minutes.)
1. An integrated process for separating organic compounds from a fermentation broth, the process comprising:
(a) feeding the degassed and preheated fermentation broth to a broth stripper column to produce a vapor;
(b) compressing the vapor obtained from the top of the broth stripper in a turbofan to obtain a compressed vapor at a pressure of 160 to 200 mmHg;
(c) sending demineralized water from the bottom of the broth stripper column to a falling film evaporator to obtain stripping steam, wherein the stripping steam is sent to the broth stripper column;
(d) passing the compressed vapor obtained in step (b) to the falling film evaporator for heat transfer from the compressed vapor to the softened water to produce the stripping vapor, wherein the compressed vapor condenses to obtain a mixture of condensate and remaining vapor;
(e) sending the mixture of the condensate and the remaining vapor obtained in step (d) to a broth stripping condenser to condense the remaining vapor into a condensate; and
(f) collecting the condensate obtained in step (d) and step (e) in a rectifying drum feeder for distillation to obtain 15-25 wt% of the organic compound;
wherein the broth stripper operates at a temperature of 15 ℃ to 50 ℃ with a residence time of 1-10 minutes;
wherein the organic compound is selected from the group consisting of ethanol, propanol, butanol, acetone, and isopropanol.
2. The method of claim 1, wherein the fermentation broth comprises 1-5 wt% of the organic compound.
3. The process of claim 1, wherein a broth recycle comprising less than or equal to 0.15 wt% of the organic compounds is obtained from a side draw of the stripper and recycled from the broth stripper for fermentation.
4. The process of claim 1, wherein the broth stripper is provided with a packed bed section packed with a packed material mass transfer bed for operating the broth stripper under vacuum conditions at a pressure of 45-60 mmHg.
5. The process of claim 1, wherein the broth stripper column is provided with a chimney tray below the packed bed section for removing the broth recycle.
6. The method according to claim 1, wherein the broth stripper column is provided with a tray section at the bottom for supplying the softened water to the falling film evaporator to produce stripping steam.
7. The process of claim 1, wherein for start-up operations, a bottoms product from the broth stripper column is heated in an auxiliary reboiler with low pressure steam to produce stripping steam for start-up.
8. The process of claim 1, wherein for start-up operation, the compressed vapor obtained in step (b) is sent to a start-up condenser to obtain a condensate, which is subsequently sent to the rectifying drum feeder.
9. The process of claim 8, wherein the start-up condenser optionally uses cooling water to provide a vacuum pressure of 45mmHg at a temperature of 42 ℃ to 43 ℃ in the broth stripper.
10. An integrated system for separating organic compounds from a fermentation broth, wherein the organic compounds are selected from the group consisting of ethanol, propanol, butanol, acetone, isopropanol, the system comprising:
a broth stripper column (C-1) provided with a packed bed section filled with a packed material mass transfer bed, a chimney tray below the packed bed section for removing broth recycle, and a tray section at the bottom for supplying softened water to the falling film evaporator to produce stripping steam;
a turbo fan (K-1) for compressing the vapor obtained from the top of the broth stripper (C-1);
a falling-film evaporator (E-1) for transferring heat from the compressed vapor to demineralized water obtained from the bottom of the broth stripper (C-1) and obtaining a mixture of condensate and residual vapor;
a condenser (E-3) for condensing the residual vapor obtained from the falling-film evaporator (E-1) to obtain a condensate.
A rectifier (V-2) for collecting the condensate obtained from the condenser (E-3);
an auxiliary reboiler (E-2) for heating the bottom product from the broth stripper with low pressure steam during start-up operation; and
a start-up condenser (E-5) for condensing the compressed vapor during a start-up operation.
11. The system of claim 10, wherein the system comprises: a broth recycle pump (P-1) for receiving broth recycle from a side draw of the broth stripper column (C-1); wherein the fermentation broth recycle comprises less than or equal to 0.15 wt% of the organic compound.
12. The system of claim 10, wherein the system comprises a start-up vacuum pump (K-2) at a steam outlet of the rectifier drum feeder (V-2) for maintaining a vacuum.
Technical Field
The present invention relates to an integrated process for separating ethanol from a fermentation broth for low temperature applications, wherein the fermentation broth is produced by different fermentation techniques. The invention particularly relates to an integrated process for separating ethanol from a fermentation broth produced by a gas fermentation process using an integrated vapor compression unit (turbofan), falling film evaporator and fermentation broth stripper (vacuum distillation system). The invention is equally applicable to the separation of other organic compounds from fermentation broths, namely propanol, butanol, acetone and Isopropanol (IPA).
Background
The fermentation broth (broth) from the fermentor contains ethanol, water, microorganisms (live microorganisms)/biomass, and trace amounts of other process chemicals produced by side reactions. Ethanol must be recovered from the fermentation broth containing 1-5 wt% ethanol and the remaining fermentation broth recycled back to the fermentor section during the fermentation process. Since the fermentation broth contains viable microorganisms, the separation of ethanol from the fermentation broth must generally be performed at temperatures below 45 ℃ in order to keep the microorganisms viable and active for the fermentation process in the return fermentor. Furthermore, the survival of microorganisms is strongly dependent on the feed gas. This requires that the residence time of the fermentation broth (containing the microorganisms) outside the fermentation system be minimized to ensure that the microorganisms remain viable and active. Therefore, designing an ethanol separation system at low temperatures and with minimal residence time outside the fermentor is challenging. In addition, in order to compete with other available technologies, it is highly desirable to keep the CAPEX and OPEX of the plant to a minimum while meeting the goal of performing ethanol separation under the required conditions.
Conventional 1G/2G technology for ethanol recovery is not based on the recycle of live microorganisms, so ethanol separation can be performed at distillation column temperatures of about 90 ℃ or higher using a low pressure steam reboiler/direct injection. The overhead vapor is condensed and further sent to a downstream ethanol recovery and dehydration section to obtain high purity ethanol. This type of conventional solution is not suitable for processes in which fermentation processes are carried out using biocatalysts (living microorganisms). Such high temperatures will result in killing of the microorganisms and a reduction in the growth/activity of the microorganisms during the gas/biomass fermentation in the upstream fermentor. In addition, in other processes, such as membrane separation processes for ethanol recovery, cell recycle membranes are used to separate ethanol-water mixtures from fermentation broths containing viable microorganisms at low temperature requirements and to recycle the microorganisms back to the fermentation process. However, the maintenance and service costs of the membrane separation modules are high. In addition, mounting such membranes requires a very large area, especially for low microbial growth rates, depending on the composition of the feed gas. In addition, the reliability of the membrane is poor with respect to changes in operating conditions, feed quality and any ingress of particulate matter in the fermentation broth, resulting in a reduced life cycle of the membrane, which in turn requires frequent replacement during the life of the project.
US 2007/0031954 describes an integrated process comprising a plurality of membranes, which comprises a first membrane separation, followed by a fractional condensation step and another membrane separation for ethanol dehydration. A problem with this approach is the need to remove solids from the fermentation broth prior to the membrane separation process. The solids removal step creates additional capital investment and operating costs, which increase the overall ethanol production cost.
US 13/809269 utilizes the low temperature fermentation broth separation principle achieved together with heat integration for ethanol separation, which is only suitable for ethanol fermentation broths produced by saccharification fermentation, wherein the aim is to separate ethanol and also to prevent enzyme denaturation. However, the technology has a heat integrated system consisting of vacuum distillation, a compressor and a simple heat exchanger. An enzyme-rich stream is withdrawn from the bottom of the column. The method described by said patent application therefore does not ensure a complete protection of the microorganisms during the plant operation under various operating conditions/operating disturbances.
US8535413B2 discloses a fermentation process for ethanol recovery using an integrated Mechanical Vapor Recompression (MVR) and membrane vapor permeation system, wherein the fermentation is conducted at a temperature in excess of 75-100 ℃. Further, the process discloses recovering ethanol from a fermentation broth feed having an ethanol concentration greater than 5 wt.%. In addition, the process uses steam and carbon dioxide as stripping media in a plant known as a fermentive stripper.
US2013/0175158a1 discloses a method for producing ethanol and an apparatus for producing ethanol suitable for recycling of enzymes. This patent application provides a process for producing ethanol, wherein the process comprises purifying ethanol from an ethanol fermentation broth produced by saccharification and fermentation of a biomass feedstock, and the apparatus for producing ethanol comprises, in addition to a rectification column configured for rectifying ethanol vapor distilled from a vacuum distillation column, a vacuum distillation column for distilling ethanol vapor comprising water vapor and removing an enzyme-containing concentrated waste liquid as a bottoms product
Due to the above limitations of these types of technologies for ethanol production, ethanol separation from fermentation broth cannot be efficiently performed according to conventional methods available in first generation (1G) or second generation (2G) technologies as well as membrane separation methods of ethanol plants. Therefore, it is highly desirable to find alternative technologies/processes/methods that can be used to separate ethanol from this type of fermentation broth and that are also energy efficient. Various approaches have been or are being explored to find solutions to the problem of the requirement for ethanol separation at very low temperatures, with the aim of protecting living microorganisms and minimizing the energy consumption and CAPEX for recovering ethanol from fermentation broth. Furthermore, in such techniques, the microorganisms in the broth solution outside the gas fermenter must be protected based on temperature and residence time limitations. This requires that after separation of the ethanol from the fermentation broth, the microorganisms are recycled back to keep the temperature and residence time within design limits. Although the first generation (1G) or second generation (2G) technologies and membrane separation methods of separating ethanol from a fermentation broth are well known, studies of the prior art do not reveal any integrated process or method that ensures efficient separation of ethanol (and other lower alcohols and lower ketones) from a fermentation broth containing viable microorganisms such that the microorganisms remain in the recycled fermentation broth after ethanol separation.
Disclosure of Invention
Thus, the present invention provides an "integrated process" for the separation of organic compounds (i.e. ethanol, propanol, butanol, acetone, isopropanol), in particular ethanol, from a fermentation broth, wherein the process is carried out at lower system temperatures and residence times, ensuring maximum ethanol recovery at low temperatures, and maintaining the activity of microorganisms in the recycled fermentation broth for further fermentation in the gas fermentation section. The present invention is based on the use of an integrated system comprising a broth stripper (vacuum distillation system), a falling-film evaporator and a vapour compression unit (turbo-fan) overcoming the drawbacks of the prior art and ensuring maximum recovery of ethanol at low temperatures, while ensuring the activity of the microorganisms required for fermentation in the gas fermentation section.
The invention provides an integrated process for the separation of organic compounds from a fermentation broth, said process comprising:
(a) feeding the degassed and preheated fermentation broth to a broth stripper column to produce a vapor;
(b) compressing vapor obtained from the top of the broth stripper in a turbo fan to obtain compressed vapor at a pressure of 160 to 200 mmHg;
(c) sending demineralized water from the bottom of the broth stripper column to a falling film evaporator to obtain stripping steam, wherein the stripping steam is sent to the broth stripper column;
(d) passing the compressed vapor obtained in step (b) to the falling film evaporator for heat transfer from the compressed vapor to the softened water to produce the stripping vapor, wherein the compressed vapor condenses to obtain a mixture of condensate and remaining vapor;
(e) sending the mixture of the condensate and the remaining vapor obtained in step (d) to a broth stripping condenser to condense the remaining vapor into a condensate; and
(f) collecting the condensate obtained in step (d) and step (e) in a rectifying drum feeder for distillation to obtain 15-25 wt% of the organic compound;
wherein the broth stripper operates at a temperature of 15 ℃ to 50 ℃ with a residence time of 1-10 minutes;
wherein the organic compound is selected from the group consisting of ethanol, propanol, butanol, acetone, and isopropanol.
The process described in steps (a) to (f) of the present invention is equally applicable to the separation of propanol, butanol, acetone, Isopropanol (IPA) from a fermentation broth
Furthermore, the present invention provides an integrated system for separating an organic compound from a fermentation broth, wherein the organic compound is selected from the group consisting of ethanol, propanol, butanol, acetone, isopropanol, the system comprising:
a broth stripper column (C-1) provided with a packed bed section filled with a packed material mass transfer bed, a chimney tray below the packed bed section for removing broth recycle, and a tray section at the bottom for supplying softened water to the falling film evaporator to produce stripping steam;
a turbo fan (K-1) for compressing the vapor obtained from the top of the broth stripper (C-1);
a falling-film evaporator (E-1) for transferring heat from the compressed vapor to demineralized water obtained from the bottom of the broth stripper (C-1) and obtaining a mixture of condensate and residual vapor;
a condenser (E-3) for condensing the remaining vapour obtained from the falling-film evaporator to obtain a condensate.
A rectifier (V-2) for collecting the condensate obtained from the condenser (E-3);
an auxiliary reboiler (E-2) for heating the bottom product from the broth stripper with low pressure steam during start-up operation; and
a start-up condenser (E-5) for condensing the compressed vapor during a start-up operation.
Object of the Invention
The main object of the present invention is to efficiently recover organic compounds (i.e. ethanol, propanol, butanol, acetone, isopropanol), in particular ethanol, from a fermentation broth containing living microorganisms while protecting the microorganisms from temperature variations and residence time limitations.
Another object is to provide a low temperature separation and recovery of ethanol from a fermentation broth containing viable microorganisms at temperatures typically below or at 50 ℃, preferably below 45 ℃.
It is another object of the present invention to ensure the activity of the microorganisms by maintaining the residence time of the microorganism-containing fermentation broth outside the fermenter to be less than 10 minutes.
It is yet another object of the present invention to provide an integrated process that is efficiently performed with fermentation broths containing as low as 1 wt.% ethanol.
It is another object of the present invention to provide an integrated process for ethanol separation comprising a turbo-fan, an evaporator and a broth stripper for energy optimization and reduction of OPEX (operating costs) of the plant.
Brief Description of Drawings
FIG. 1 is a schematic of configuration-1 for ethanol recovery from a fermentation broth according to the present invention.
FIG. 2 is a schematic of configuration-2 for ethanol recovery from fermentation broth according to the present invention (for operation in hot countries).
FIG. 3 is a schematic of configuration-3 for ethanol recovery from fermentation broth according to the present invention (for operation in hot countries).
FIG. 4 is a schematic diagram of a fermentation broth separation process based on a typical 1G/2G ethanol plant
FIG. 5 shows a schematic of a membrane separation process for recovering ethanol from a fermentation broth.
Detailed Description
The present invention relates to an integrated process for recovering ethanol from fermentation broths produced by different fermentation technologies. The invention particularly relates to an integrated process for separating ethanol from a fermentation broth produced by a gas fermentation process using an integrated system of a broth stripper (vacuum distillation system), a turbofan and a falling film evaporator.
The invention is also applicable to the separation of propanol, butanol, acetone, Isopropanol (IPA) from a fermentation broth solution. Furthermore, the present invention can be used globally for the separation of ethanol, acetone, Isopropanol (IPA), propanol, butanol (at low temperatures) in a variety of fermentation technologies directed to the production of ethanol, acetone, Isopropanol (IPA) from waste sources such as municipal waste (MSW), industrial waste gases, refinery waste gases, biomass and coke gasification, steel plant waste gases, and the like. More specifically, the present invention protects microorganisms under operating temperature and residence time limitations outside the fermentation process, providing energy savings compared to other available conventional distillation schemes and membrane separation methods. In addition to gas fermentation techniques, the process is also applicable to fermentation techniques where temperature and residence time are limited. The system can be used for fermentation broths containing organic compounds (i.e. ethanol, propanol, butanol, acetone, isopropanol) at concentrations as low as 1% by weight, in particular ethanol.
According to the present invention, a fermentation broth stream containing ethanol (referred to as a fermentation broth solution or broth) is obtained from a gas fermentation apparatus having living microorganisms. The fermentation broth thus obtained contains about 1-5 wt.% ethanol, depending on the mass of the feed gas, while the remainder is mainly water and other impurities and viable microorganisms. According to the present invention, ethanol is recovered from the fermentation broth at low temperatures (i.e. typically below or at 50 ℃ to protect viable microorganisms) and the ethanol thus recovered is further purified in a downstream distillation and dehydration section to achieve fuel grade high purity ethanol. According to the present invention, the separation of ethanol from fermentation broth is efficiently achieved using an integrated vapor compression unit (turbo fan), evaporator/reboiler and stripper (vacuum distillation system). Distillation of ethanol is performed under vacuum by column operation to achieve low temperature separation to ensure microbial activity in the recycled fermentation broth. A vapor compression unit (turbofan) is used to achieve integration of the vacuum column overhead vapor heat to produce stripping steam in the falling film evaporator reboiler. The combination not only saves energy, but also realizes the purpose of separating ethanol from fermentation liquor containing living microorganisms at low temperature.
According to a main feature, the present invention provides an integrated process for the separation of organic compounds from a fermentation broth, said process comprising:
(a) feeding the degassed and preheated fermentation broth to a broth stripper column to produce a vapor;
(b) compressing vapor obtained from the top of the broth stripper in a turbo fan to obtain compressed vapor at a pressure of 160 to 200 mmHg;
(c) sending demineralized water from the bottom of the broth stripper column to a falling film evaporator to obtain stripping steam, wherein the stripping steam is sent to the broth stripper column;
(d) passing the compressed vapor obtained in step (b) to the falling film evaporator for heat transfer from the compressed vapor to the softened water to produce the stripping vapor, wherein the compressed vapor condenses to obtain a mixture of condensate and remaining vapor;
(e) sending the mixture of the condensate and the remaining vapor obtained in step (d) to a broth stripping condenser to condense the remaining vapor into a condensate; and
(f) collecting the condensate obtained in step (d) and step (e) in a rectifying drum feeder for distillation to obtain 15-25 wt% of the organic compound;
wherein the fermentation liquor stripping tower is operated at the temperature of less than or equal to 50 ℃, and the retention time is less than or equal to 10 minutes;
wherein the organic compound is selected from the group consisting of ethanol, propanol, butanol, acetone, and isopropanol.
In a preferred embodiment, the residence time is from 1 minute to 10 minutes, more preferably from 5 minutes to 10 minutes, and the temperature in the broth stripper is from 15 ℃ to 50 ℃, more preferably from 30 ℃ to 45 ℃.
In one embodiment, the fermentation broth further comprises living microorganisms, wherein the fermentation broth is produced in a different fermentation technology, in particular gas fermentation. In addition, the fermentation broth comprises an enzyme. Thus, the ethanol separation process is operated at low temperatures with short residence times to ensure that the microorganisms remain active in the process and are further recycled to the fermentation unit.
In a preferred feature, the present invention provides an integrated process for separating ethanol from a fermentation broth, the process comprising:
(a) feeding the degassed and preheated fermentation broth to a fermentation broth stripper to produce a vapor;
(b) compressing vapor obtained from an overhead of the fermentation broth stripper in a turbo fan to obtain compressed vapor at a pressure of 160mmHg to 200 mmHg;
(c) feeding demineralized water from the bottom of the broth stripper column to a falling-film evaporator to obtain stripping steam, wherein the stripping steam is fed to the broth stripper column;
(d) passing the compressed vapor obtained in step (b) to a falling film evaporator to transfer heat from the compressed vapor to demineralized water to produce stripping vapor, wherein the compressed vapor is condensed to obtain a mixture of condensate and remaining vapor;
(e) sending the mixture of the condensate and the remaining vapor obtained in step (d) to a broth stripping condenser to condense the remaining vapor into a condensate; and
(f) collecting the condensate obtained in step (d) and step (e) in a rectifying drum feeder to be distilled to obtain 15 to 25 wt.% ethanol;
wherein the fermentation liquor stripping tower is operated at the temperature of less than or equal to 50 ℃ for the retention time of less than or equal to 10 minutes.
The process described in steps (a) to (f) of the present invention is equally applicable to the separation of propanol, butanol, acetone and Isopropanol (IPA) from a fermentation broth.
In one embodiment, the invention provides that the fermentation broth fed to the broth stripper column comprises 1 to 5 wt% of organic compounds, in particular ethanol.
In another embodiment, the present invention provides a broth recycle comprising less than or equal to 0.15 wt% of organic compounds, preferably ethanol, obtained from a side draw of a broth stripper and recycled from the broth stripper for fermentation. The broth cycle preferably comprises 0.05 wt.% to 0.15 wt.% ethanol, more preferably the broth cycle comprises 0.08 wt.% to 0.1 wt.% ethanol.
In a preferred embodiment, the broth stripper is provided with a packed bed section packed with a packed material mass transfer bed to operate the broth stripper at a temperature <45 ℃ at a pressure of 45mm Hg to 60mm Hg, preferably 56mm Hg, under vacuum conditions. Furthermore, the broth stripper column is provided with a chimney tray below the packed bed section for removal of broth recycle, and is also provided with an additional tray section at the bottom to provide demineralised water to the falling film evaporator to produce stripping steam.
In another embodiment, the separation process of the present invention provides for starting up the bottoms from the fermentation liquor stripper in an auxiliary reboiler heated with low pressure steam (pressure about 5 bar) to produce stripping steam for start-up operations.
In yet another embodiment, the present invention also provides that during start-up operation of the process, the vapor obtained in step (a) (of the above process) is sent to a start-up condenser to obtain a condensate, which is subsequently sent to a rectifying drum feeder.
The startup operation facilitates the start of the method to achieve minimum flow requirements for the turbofan. Once the method begins to run and the turbofan begins to operate, the start-up related equipment will shut down and the method will conserve the energy of the system through an efficient heat transfer process to operate in an energy efficient mode based on the heat generated within the system. In hot countries, the cooling water temperature is higher, so that the cooling of the overhead vapor is reduced. Thus, for operation in hot countries, in a preferred embodiment, the startup condenser optionally uses chilled water to provide a vacuum pressure of 45mmHg at a temperature of 42 ℃ to 43 ℃ in the broth stripper. Thus, in order to operate the process in hot countries, the present invention provides a three stage turbofan operation to separate organic compounds, in particular ethanol (fig. 2).
In a preferred embodiment of the process for operation in hot countries, the present invention provides a two-stage turbofan operation for ethanol separation, wherein the broth stripper condenser is optionally provided with a continuous chiller operation to provide a vacuum pressure of 45mmHg at a temperature of 42 ℃ to 43 ℃ in the broth stripper, thereby eliminating the need for an additional start-up condenser in the separation process.
The present invention also provides an integrated system for separating organic compounds from a fermentation broth, wherein the organic compounds are selected from the group consisting of ethanol, propanol, butanol, acetone, isopropanol, the system comprising:
a broth stripper column (C-1) provided with a packed bed section filled with a packed material mass transfer bed, a chimney tray below the packed bed section for removing broth recirculation and a tray section at the bottom for providing demineralised water to the falling film evaporator for producing stripping steam;
a turbo fan (K-1) for compressing the vapor obtained from the top of the fermentation broth stripper column (C-1);
a falling-film evaporator (E-1) for heat transfer from the compressed vapor to demineralized water obtained from the bottom of the broth stripper (C-1) and obtaining a mixture of condensate and residual vapor;
a condenser (E-3) for condensing the residual vapor obtained from the falling-film evaporator (E-1) to obtain a condensate;
a rectifying drum feeder (V-2) for collecting the condensate obtained from the condenser (E-3);
a co-reboiler (E-2) for heating the bottom product from the broth stripper column (C-1) with low pressure steam during start-up operation; and
a start-up condenser (E-5), said start-up condenser (E-5) being used for condensing the compressed vapour during a start-up operation.
In a preferred feature, an integrated system is employed to separate the ethanol.
In another embodiment, the system includes a broth circulation pump (P-1) for receiving a broth circulation from a side draw of a broth stripper column (C-1); wherein the fermentation broth recycle comprises less than or equal to 0.15 wt% of organic compounds, preferably ethanol.
In another embodiment, the system includes a start-up vacuum pump (K-2) at the vapor outlet of the fairing barrel feeder (V-2) for maintaining a vacuum.
The present invention operates based on three different configurations depending on the cooling water supply temperature in hot and cold countries. All 3 configurations are feasible in cold countries, while
configuration 1 (fig. 1): integrated vacuum tower, FFE with turbofan configuration (three stage turbofan)
In this configuration (FIG. 1), the degassed fermentation broth received from the upstream fermentor (stream #1) is preheated in (feed/bottom exchanger) and enters the vacuum column (C-1) operating under vacuum. The column is operated with heat integration of the overhead vapor with a falling film evaporator reboiler (E-1) to reuse the heat of the overhead vapor and thus reduce any external energy input required for stripping ethanol from the fermentation broth.
By operating under vacuum conditions at about 56mmHg head pressure, the low temperature in the column is maintained and a packed bed is used to ensure low Delta P in the column. The overhead vapor comprises 20 wt% to 22 wt% ethanol (stream #2) and is compressed with a turbofan (K-1) to achieve a pressure sufficient to transfer heat to a Falling Film Evaporator (FFE) reboiler (E-1) (i.e., the bottoms temperature and FFE temperature approach defines the turbofan exit pressure). Chimney trays were installed below the packed bed to remove the broth recycle (stream #3), and the bottom portion of the column included a column section where the process water (stream #5) entered and reached the FFE to produce vapor. The FFE (E-1) tube side outlet vapor enters the bottom tray portion of the column and is used as the stripping medium for ethanol separation. As the FFE shell outlet vapor + condensate was further cooled in the trim condenser (trimcondensor) (E-3) and collected in the rectifying drum feeder (V-2) for processing in the downstream distillation section (stream #4), the remaining uncondensed vapor was further sent to the vacuum scrubber system. Vacuum is maintained throughout the system by operating a vacuum scrubber and vacuum pump installed at the vapor outlet of the downstream feed buffer tank (V-2) of the unit.
For the start-up of the turbo fan (K-1), the auxiliary reboiler (E-2) is provided with LP steam to achieve the minimum flow requirement of the turbo fan (K-1). The system vacuum was initially maintained using a start-up vacuum pump (K-2) and the resulting vapor condensed using an OVHD start-up cooling water condenser (E-5). After obtaining the minimum flow of the overhead vapor, the turbo fan (K-1) is started and stabilized, and then the re-boilerduty required for the column is obtained from the overhead vapor through the FFE reboiler (E-1).
By this means, low temperature fermentation broth separation and heat integration is achieved without adversely affecting the growth of viable microorganisms that are the core of the fermentation process. The piping from the gas fermentor to the distillation section and back to the fermentor is minimized while maintaining the minimum volume required in the degasser, vacuum distillation column, etc. to minimize the total residence time of the fermentation broth outside the fermentor.
Configuration 2 (fig. 2): integrated vacuum tower, FFE with turbofan configuration (three stage turbofan + start up chiller)
This scheme (fig. 2) further allows the broth separation column to be operated at about 42 ℃ to 43 ℃ and a higher vacuum of 45 mmHg. The turbofan (K-1) with three stage configuration is sufficient to meet the boost requirement of the tower with heat integration. However, during start-up, a higher vacuum of 45mmHg would require a start-up condenser (E-5) with chilled water to operate. For low temperatures in the condenser chiller unit, a three stage turbofan configuration is required. This configuration is suitable for hot countries where the cooling water temperature is high and limits the condensation of steam. In addition, this configuration provides a significant operating margin that exceeds the design limits of the microorganism operating temperature (typically <45 ℃).
Configuration 3 (fig. 3): integrated vacuum tower, FFE with turbofan configuration (2 stage turbofan + continuously operating chiller)
The vacuum configuration with three stages of turbo fans (as mentioned in configuration 2) allows the installation of a trim condenser with cooling water of about 33 ℃ (i.e. reaching the dew point with cooling water without chilled water). Meanwhile, the turbofan with 2 stages (configuration 3) has a low dew point and requires chilled water (i.e., continuous chiller operation). This configuration (fig. 3) allows the column to operate at 45mmHg and less power in the turbofan and does not require a stage. However, there is a net increase in power demand due to chiller operation, but also a greater margin for column bottom temperature, resulting in column operation of about 42 ℃ to 43 ℃.
According to the invention, the process for separating ethanol from a fermentation broth at low temperatures (typically <45 ℃) uses the following main components:
a) an integrated turbofan (K1) having a falling film evaporator (E-1) and a vacuum distillation system (C-1);
b) a vacuum distillation column (C-1) with a packed material mass transfer bed;
c) a side cut of the broth recycle stream from the vacuum distillation column (C-1) with the broth recycle pump (P-1);
d) starting a vacuum pump (K-2) and a tower top condenser (E-5);
e) starting an auxiliary reboiler (E-2); and
f) a rectifying barrel type feeder (V-2).
According to the invention, the integrated turbofan (K1), falling film evaporator (E-1) and vacuum distillation system/broth stripper (C-1) are designed such that a broth cycle with <0.1 wt.% ethanol is obtained in the process, ensuring adherence to the operating temperature limits (typically <45 ℃) and residence time (<10 minutes) of the broth containing live microorganisms.
According to the present invention, a process for separating ethanol from a fermentation broth at low temperature operation discloses the following features:
a) the broth feed Ex fermentor was fed to the broth stripper (C1) operation at a pressure of 56mmHg for temperatures typically <45 ℃ (
b) Compressing the overhead vapor from the broth stripper (C1) with a turbo-fan (K1) to a pressure and temperature sufficient to transfer energy/heat to the downstream falling film evaporator (E-1)
c) Cryogenic process for efficient heat transfer from overhead vapor to bottoms water stream using falling film evaporator reboiler (E-1)
d) Using a packed bed column instead of trays/grid trays in a broth stripper column (C1) to achieve low delta P ensures operation within temperature limits at the broth collection tray and at the bottom of the column
e) Installing a chimney tray below the packed bed section of the broth stripper column (C1) to collect the circulating broth comprising live microorganisms and recycling the collected broth back to the upstream fermentor in the fermentation section
f) Minimizing piping and distance between the fermentation section and the fermentation broth separation section to minimize circulation and residence time of the fermentation broth outside the fermentation zone
g) Installing a small tray section below the chimney tray to generate stripping steam by FFE (E-1)
h) For start-up operation, an auxiliary reboiler (E-2) with Low Pressure (LP) steam is installed to achieve minimum flow requirements for turbofan (K-1).
i) Vacuum system is installed to create and maintain vacuum conditions during start-up and continuous operation
j) In the case of cooling water temperature limitation in hot countries, the tower and chiller system are operated for startup in configuration 2 (FIG. 2) and continuous operation in configuration 3 (FIG. 3), for overhead vapor
The process protects live microorganisms (biocatalysts) and meets the maximum temperature limit (typically <45 ℃) and residence time criteria (<10 minutes) required for the technology to separate ethanol from fermentation broth.
FIG. 4 shows a schematic of a conventional process for ethanol separation if used for gas fermentation broth separation. This type of solution is adopted in the conventional first and second generation technologies mainly used for the production of ethanol from molasses, rice hulls, wheat straw, etc. Since conventional 1G/2G technology is not based on recovery of live microorganisms, ethanol separation can be performed using a low pressure steam reboiler/direct injection at the bottom of the distillation column at temperatures of about 90 ℃ or higher. The overhead vapor (enriched in 20 wt% to 22 wt% ethanol) is condensed and further sent to a downstream ethanol recovery and dehydration section to yield high purity ethanol. This type of convection scheme cannot be used in processes where biocatalysts (living microorganisms) are used in the fermentation process. Such high temperatures will result in the killing of microorganisms and reduce the growth/activity of microorganisms during gas/biomass fermentation in the upstream fermentor.
Also, FIG. 5 shows a schematic of a membrane separation process for recovering ethanol from a fermentation broth. In such systems, cell-cycling membranes are used to separate ethanol-water mixtures from fermentation broths containing live microorganisms and to recycle the microorganisms back to the fermentation process with low temperature requirements. However, the maintenance and servicing costs of the membrane separation module are high. Furthermore, the installation of such membranes requires a very large area, in particular a low growth rate of microorganisms depending on the feed gas composition. Furthermore, the reliability of the membrane is poor in terms of changes in operating conditions, feed quality and any ingress of particulate matter in the fermentation broth, and the low life cycle of the membrane requires frequent replacement during the life of the project.
The disclosed process for separating organic compounds (i.e., ethanol, propanol, butanol, acetone, isopropanol) from a fermentation broth, preferably ethanol, provides the following technical advantages:
cryogenic separation and recovery of ethanol from a fermentation broth comprising live microorganisms, typically less than or equal to 50 DEG C
Ensuring the activity of the microorganisms by keeping the residence time of the microorganisms comprising the fermentation broth outside the fermentor <10 minutes
Application of an integrated turbofan, evaporator and vacuum distillation system to achieve energy optimization and reduce OPEX (operating cost)
No external steam input is required except for the start-up operation
A power reduction of about 40% to 50% can be achieved compared to conventional solutions
A cooling water reduction of about 60% to 70% can be achieved compared to conventional solutions
Besides the mentioned gas fermentation techniques, the process is also applicable to other fermentation techniques with temperature and residence time limitations
The process can be used for fermentation broth ethanol concentrations as low as 1 wt. -%
Having described the basic aspects of the invention, the following non-limiting examples illustrate specific embodiments thereof.
Table 1: ethanol
The expected major benefits of the integrated process for ethanol separation disclosed in the present invention are summarized in table 4 according to configuration-1 (fig. 1), relative to a typical conventional process as depicted in fig. 4.
Table 2: conventional methods for ethanol separation and comparison of the invention set forth in the examples
Conventional processes require a reboiler with LP steam on a continuous basis. Thus, as shown in table 2 above, in the case of the conventional process, the energy required to recover 20 to 22 wt% ethanol from a fermentation feed having 2 to 3 wt% ethanol is equivalent to 10 to 12 tons/hour of LP steam, whereas in the proposed invention, steam is not required for continuous operation of the broth stripper. In conventional processes, in order to condense the broth stripper overhead vapor at 56mmHg, a chilled water system is required due to the low dew point of the vapor produced under operating conditions, which in turn requires 1.4MW to 1.6MW of power and 1500m3Hour to 1700m3Cooling water per hour to circulate the chilled water system. In contrast, the proposed ethanol separation process only requires 0.7MW to 0.8MW of power for turbofan operation and 500m3Hour to 600m3Cooling water for the trim condenser per hour.
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