阅读说明：本技术 处理塑料废热解气的方法 (Method for treating waste pyrolysis gas of plastics ) 是由 安蒂·库尔基耶尔维 汉努·莱赫蒂宁 埃萨·科尔霍宁 米科·马蒂莱宁 马克斯·奈斯特伦 于 2020-06-01 设计创作，主要内容包括：本发明涉及用于处理塑料废热解气的方法,特别是其中避免或至少减轻在该方法中使用的系统的堵塞的方法。(The present invention relates to a process for treating waste pyrolysis gases of plastics, in particular a process in which clogging of the system used in the process is avoided or at least reduced.)

1. A method for processing plastic waste pyrolysis gas, the method comprising:

a) providing a plastic waste pyrolysis gas stream, wherein the temperature of the plastic waste pyrolysis gas stream is 300-,

b) transferring the plastic waste pyrolysis gas stream to a condensing unit (102), wherein the temperature in the condensing unit is lower than the temperature of the plastic waste pyrolysis gas stream of step a), thereby producing a condensed fraction and a gaseous fraction of plastic waste pyrolysis gas,

c) continuously wiping and/or scraping the inner surface of the condensation device, an

d) Separating the gaseous fraction and the condensed fraction to produce a first liquid product stream and a gaseous product stream.

2. The process according to claim 1, wherein the temperature of the condensation device is 100-.

3. The method of claim 1 or 2, comprising collecting the first liquid product stream.

4. A process according to any one of claims 1 to 3, comprising cooling the gaseous product stream of step d) to 10-50 ℃, preferably to 20-40 ℃, thereby producing a second liquid product stream and a gaseous stream.

5. The method of claim 4, comprising collecting the second liquid product stream.

Technical Field

The present invention relates to a process for treating waste pyrolysis gas (pyrolysis gas) of plastics, in particular a process wherein clogging of the system used in the process is avoided.

Background

Large quantities of waste plastics are being produced around the world. For example, municipal solid plastic waste typically includes High Density Polyethylene (HDPE), Low Density Polyethylene (LDPE), polypropylene (PP), Polystyrene (PS), poly (vinyl chloride) (PVC), and poly (ethylene terephthalate) (PET). This is an abundant feedstock that can be used as a platform to replace refinery feedstocks and new plastics and chemicals. However, solid plastic is not a suitable raw material per se, but it needs to be liquefied first. The yield and composition of the product are influenced mainly by the type of plastic and the process conditions (Williams et al energy & Fuels,1999,13, 188-.

The processing of waste plastics is carried out in a chemical recovery system and relies on thermal, pyrolysis reactions to crack long-chain plastic polymers into shorter products, most of which are liquids. Gaseous product mixtures from the pyrolysis of plastics are known to plug and contaminate surfaces, pipes and equipment. This is due in part to the fact that some of the reaction products are heavy waxy components that deposit on surfaces, and that tars, char and more solid coke-type deposits are also common. Waxy components and tars are particularly problematic on the cooled surfaces of the heat exchangers used to condense the reaction mixture, but coke can be deposited anywhere in the equipment. These can lead to two major problems. First, the deposits act as insulators, reducing heat transfer in the heat exchanger. Secondly, the deposits will eventually clog the heat exchanger, preventing any flow of material through it. Thus, if a conventional heat exchanger is used to condense the pyrolysis gas, the plant requirements multiply: while one is operating, the other is in service and cleaning. This is expensive and labor intensive.

This problem has been addressed prior to the use of direct contact condensers. However, spray condensers, for example, suffer from relatively low separation efficiency, and they cannot prevent coke deposition. Furthermore, the liquid circulation used in these condensers requires a liquid hold-up which has two main disadvantages. Firstly, this significantly increases the fire load of the plant, since there is a reservoir of the high-temperature pyrolysis product mixture in the circulation loop. Second, the relatively long residence time (tolerance time) of the reservoir exposes the liquid to additional thermal reactions that can degrade product quality and cause equipment fouling.

Therefore, there is still a need for a further method for treating the pyrolysis gas of plastic waste, wherein the risk of clogging of the system used in the method is reduced.

Disclosure of Invention

The following presents a simplified summary in order to provide a basic understanding of some aspects of various embodiments of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to the more detailed description of exemplary embodiments of the invention.

It was observed that when the gaseous reaction mixture from the pyrolysis of plastic waste is mixed with the cooled condensed pyrolysis product, the highest boiling fraction of the pyrolysis gases is smoothly condensed from the mixture without clogging.

It has also been observed that clogging of plastic waste pyrolysis products can be avoided by delivering gaseous pyrolysis products to a condensing unit operating at a temperature below the pyrolysis temperature when wiping and/or scraping any solidified material from the inner walls of the condensing unit.

According to the present invention there is provided a novel method for treating waste pyrolysis gas of plastics, the method comprising

a) Providing a plastic waste pyrolysis gas flow, wherein the temperature of the plastic waste pyrolysis gas flow is 300-650 ℃, preferably 450-500 ℃,

b) transferring the plastic waste pyrolysis gas stream to a condensing unit, wherein the temperature in the condensing unit is lower than the temperature of the plastic waste pyrolysis gas stream of step a), thereby producing a condensed fraction and a gaseous fraction of the plastic waste pyrolysis gas,

c) continuously wiping and/or scraping the inner surface of the condensation device, and

d) the gaseous fraction and the condensed fraction are separated to produce a first liquid product stream and a gaseous product stream.

Various exemplary and non-limiting embodiments of the invention are described in the appended dependent claims.

Various exemplary and non-limiting embodiments, methods of operation, and additional objects and advantages thereof, of the present invention will be best understood from the following description of specific exemplary embodiments when read in connection with the accompanying drawings.

The verbs "comprise" and "comprise" are used in this document as disclosure limits and do not exclude nor require the presence of unrecited features. The features recited in the dependent claims may be freely combined with each other, unless explicitly stated otherwise. Furthermore, it should be understood that the use of "a" or "an" throughout this document, i.e., the singular does not exclude the plural.

Drawings

Exemplary and non-limiting embodiments of the invention and their advantages are explained in more detail below with reference to the accompanying drawings, in which

FIG. 1 illustrates an exemplary non-limiting system suitable for processing plastic waste pyrolysis gas according to one embodiment of the invention.

Detailed Description

The present invention relates to the treatment of plastics waste pyrolysis gas to avoid or at least reduce clogging of the systems used in the process.

Fig. 1 illustrates an exemplary system 100 suitable for use with a method according to an embodiment of the invention. According to the embodiment shown in the figures, the plastic waste pyrolysis gas stream (a) is transferred to a condensation device 101. The temperature of the plastic waste pyrolysis gas stream is typically 300-650 ℃, preferably 450-500 ℃. The temperature of the condensing unit is lower than that of the plastic waste pyrolysis gas flow. Exemplary temperatures for the condensing means are 100-300 deg.C, preferably 175-225 deg.C.

According to this embodiment, the condensation device comprises wiping means and/or scraping means 102 adapted to wipe and/or mechanically scrape the inner surface of the condensation device 101. Exemplary suitable condensing units are wiped film condensers and scraped surface heat exchangers. These condensing units are basically jacketed cans with a rotor inside that continuously wipes and scrapes any solidified material on the walls of the condensing unit. This prevents the formation of thick deposits on the condenser walls and thus prevents the clogging of the apparatus.

The condensing unit 101 operates at a temperature lower than the temperature of the plastic waste pyrolysis gas stream. The heaviest fraction of the pyrolysis gas is thus condensed and a gaseous fraction depleted in heavies is produced. The separation of the condensed fraction and the gaseous fraction produces a first liquid product stream (D1) and a gaseous product stream (E1).

The first liquid product stream (D1), the heavy fraction, can be transferred as a heavy product via line 103 to collection means 104. To avoid plugging, line 203 is preferably maintained at a temperature above 100 ℃, more preferably between 150 ℃ and 250 ℃. The desired temperature range may be obtained by isolating the pipeline and/or using one or more heating devices.

According to a preferred embodiment, the gaseous product stream is directed to the second condensing means 106 via line 105. Such condensing means are usually conventional heat exchangers. According to an exemplary embodiment, the temperature of the gaseous fraction in the condensation device 106 is reduced to 10-50 ℃, preferably 20-40 ℃. Cooling produces a condensed liquid and a non-condensable gas. It is expected that there will be no fouling or plugging in line 105 and in the condensing unit 106 since most of the heavy components have been removed. After cooling, the condensed liquid is separated from the non-condensable gases (E2) to produce a second liquid product stream (D2). It can be transferred as a light product in a collection device such as tank 107. The non-condensable gases may be directed for combustion or to one or more additional collection devices. The yield and composition of the light products depend mainly on the nature of the waste plastic, the pyrolysis conditions and the condensation temperature. The non-condensable gases may be directed for combustion or to one or more additional collection devices.

Example 1

This procedure is performed with Aspen plus software simulation. The main part of the pygas was modeled using pseudo-components and the light ends (light ends) were modeled using real components. The pseudo-components were estimated using experimentally measured distillation curves and densities from crude plastic pyrolysis oil. The density used was 809.8kg/m³And the True Boiling Point (TBP) distillation curve is shown in table 1.

TABLE 1

Recovery quality (%)	Temperature (. degree.C.)
		2	36.0
5	68.6
		10	97.4
30	171.9
		50	236.0
70	316.0
		90	430.4
95	474.3
		100	582.4

The amount and composition of the light fraction is estimated from the literature (Williams et al, energy & Fuels,1999,13, 188-196; Williams et al, Recouresses, convention and Recycling,2007,51, 754-769). The mass ratio of the light fraction to the pseudo component was 0.27, and the composition of the light fraction was shown in table 2.

TABLE 2

The thermodynamic model used in the simulation was Braun K-10 and assumed an ideal separation stage in the condensing unit.

A plastics waste pyrolysis gas stream having a pressure of 95kpa (a), a temperature of 500 ℃ and an average molar weight of 69.2g/mol and a mass flow rate of 20kg/h leaves the reactor. It is passed into a wiped film condenser, which is cooled by cooling oil. The scraper keeps the heat exchange surface clean and the gas partially condenses. The product was collected from the bottom of the vessel. The product temperature from the heat exchanger was adjusted to 200 ℃ by adjusting the cooling oil temperature. The heat transfer coefficient of the wall of the metal heat exchanger is 176kW/m²℃。

The simulation results are shown in table 3.

TABLE 3

Example 2

This process was simulated using Aspen plus software. The main portion of the pygas is modeled using pseudo-components, and the light fraction is modeled using real components. Using experimental measurementsAnd density estimation from crude plastic pyrolysis oil. The density used was 809.8kg/m³And the True Boiling Point (TBP) distillation curve is shown in table 4.

TABLE 4

Recovery quality (%)	Temperature (C degree)
		2	36.0
5	68.6
		10	97.4
30	171.9
		50	236.0
70	316.0
		90	430.4
95	474.3
		100	582.4

The amount and composition of the light fraction is estimated from the literature (Williams et al, energy & Fuels,1999,13, 188-196; Williams et al, Recouresses, convention and Recycling,2007,51, 754-769). The mass ratio of the light fraction to the pseudo component was 0.27, and the composition of the light fraction was shown in table 5.

TABLE 5

Components	wt-％
		Methane	36.3
Ethylene	2.2
		Ethane (III)	28.9
Propylene (PA)	4.7
		Propane	19.9
Butene (butylene)	1.5
		Butane	6.7

The thermodynamic model used in the simulation was Braun K-10 and assumed an ideal separation stage in the condensing unit.

A plastics waste pyrolysis gas stream having a pressure of 95kpa (a), a temperature of 500 ℃ and an average molar weight of 69.2g/mol and a mass flow rate of 20kg/h leaves the reactor. It was passed into a wiped film condenser where cooling oil was cooled and wiped off. This results in partial condensation and collection of liquid product from the bottom of the vessel. As the condensation products adhering to the heat exchange surfaces are not continuously scraped off, deposits accumulate on the walls as a result.

The temperature of the product from the heat exchanger was adjusted to the original 200 ℃ by the cooling oil temperature. However, as the deposits accumulate, heat transfer decreases and less condensation occurs. This reduces the amount of condensed products. The scale formation rate is assumed to be 1mm/h, and the heat transfer coefficients of the metal heat exchanger wall and the scale formation layer are 176kW/m respectively²DEG C and 0.083kW/m ℃.

The simulation results are shown in table 6.

TABLE 6

As can be seen from table 3, the performance of the heat exchanger remains unchanged over time when scraping is used to keep the heat exchange surfaces clean. On the other hand, it can be observed from table 6 that fouling has a significant impact on the performance of the heat exchanger if the fouling layer is not treated.

The specific embodiments provided in the description given above should not be construed as limiting the scope and/or applicability of the appended claims.