RU2710906C1 - Gas-chemical complex for production of polyethylene - Google Patents

Abstract

FIELD: gas chemical industry.SUBSTANCE: invention relates to gas chemical industry. Described is a gas-chemical complex for producing polyethylene, which consists of at least two or more pyrolysis units, each of which includes furnace section, pyrogas compression section and pyro-gas separation section, two or more polyethylene production plants, one or more production units of linear alpha-olefins (LAO), one or more liquid ethane storage tanks, one or more liquid ethylene storage tanks, one or more LAO storage tanks. Ethane raw material and/or crude propane are fed to pyrolysis units, after pyrolysis units gaseous ethylene is directed to polyethylene production plants and/or to LAO production plants. Blows of ethylene-containing gas from storage tanks of liquid ethylene and from plants for production of polyethylene and/or LAO production units are supplied to unit for compression of blow-off gases with subsequent supply to pyrolysis units for integration with pyrogas between furnace section and section of compression of pyrogas or between section of pyrogas compression and section of pyrogas separation depending on pressure of gaseous blowoffs of ethylene-containing gas at outlet of blowing gas compression unit.EFFECT: invention solves the task of developing a gas-chemical complex producing polyethylene, which generates a wide range of polyethylene grades while simultaneously saving olefin feedstock by returning ethylene-containing gas to the process.4 cl, 1 dwg, 1 tbl

Description

The invention provides for the production of a wide range of grades of polyethylene and can be used at enterprises of the gas chemical industry.

In general, polyethylene is the largest tonnage product of the gas chemical industry and is widely used in the national economy, which leads to the need for the production of various grades of polyethylene. Synthesis of polyethylene by low and high pressure methods allows first to obtain polymers of various structures, and then polymer products with a wide range of molecular weight, ductility, strength, dielectric characteristics and other indicators. In addition, the addition to the polymer of more than 100 specific formulations allows you to form the final product with the necessary set of properties. At the same time, difficulties arise during production during the transition of plants from one technological mode of operation to another, which is also associated with a variation in the annual demand for specific grades of polyethylene in the range from several tons to several hundred thousand tons. The formation of a wide range of brands of polyethylene requires the creation of plants with a flexible technological cycle, which allows you to quickly switch from the production of one brand to another, and produce at the same time a large set of them. In parallel with the production of polyethylene of various grades, ethylene can be effectively used in oligomerization processes for the synthesis of linear alpha olefins (LAO), which are then used as comonomers.

Ensuring the variability of the enterprise’s work to produce the required range of polyethylene grades in accordance with the quantitative and qualitative demands of consumers is a serious technical problem associated with the frequent transitions of ethylene polymerization plants and LAO production from one operating mode to another, during which ethylene-containing gas blows are generated (in general in the case, it may also contain other olefins, for example, butene-1), which are discharged to the torch, which leads to large-scale production significant losses of valuable hydrocarbons. In addition, ethylene-containing gas purges include ethylene losses due to the “breathing” of reservoirs for storing liquid ethylene back-up. To a large extent, these problems can be eliminated if blow-offs of ethylene-containing gas are used in technological processes.

A known method of separating hydrocarbons from a polyolefin gaseous purge product, comprising the following stages: separating the polyolefin product, contacting the polyolefin product and purge gas to remove at least a portion of the volatile hydrocarbons to obtain a polymer product in which the concentration of volatile hydrocarbons is reduced, and the gaseous purge product enriched volatile hydrocarbons at a pressure of from about 50 to about 250 kPa (abs), compressing the gaseous purge product to pressure from about 2500 to about 10,000 kPa (abs) in at least two stages, cooling the compressed gaseous purge product, separating the cooled gaseous purge product into a gaseous product comprising at least the first product, and a condensed product including the second product and the third product, and returning at least a portion of at least one of the products to the listed places: the first product in the form of purge gas, the second product in the polymerization reactor, or the third product in the form of gaseous purge product to the stage before compression (patent RU 2589055 C2, IPC C08F 6/00, B01D 53/14, C08J 11/02, C07C 7/00, filed December 17, 2010, published July 10, 2016).

The disadvantages of this invention are:

- the complexity of the hardware design of the system in the form of a standalone installation;

- excessive energy required to condense the third product and its introduction into the gaseous purge product for evaporation;

- limited use of a system operating in a stationary mode for the extraction of ethylene from blowdowns of ethylene-containing gas, which are formed occasionally during the transition of the main equipment from the release of one brand of polyethylene to another.

A known method for the separation of hydrocarbons from a polymerization exhaust gas, comprising the steps of reducing the ethylene flow pressure from a pressure of at least 3.4 MPa to a pressure of not more than 1.4 MP and producing a reduced pressure ethylene stream, cooling the exhaust gas, including the monomer, by heat exchange with a stream reduced pressure ethylene to produce a first condensate comprising at least a portion of the monomer entrained in the first light gas, separating the first condensate and the first light gas, separating the first condensate from the first about light gas, compressing the ethylene stream under reduced pressure to a pressure of at least 2.4 MPa and passing the compressed ethylene stream into the polymerization reactor (patent RU 2569085 C2 IPC C08F 6/00, B01D 19/00, B01J 8/00, F25J 1/02 , F25J 3/06, C08F 10/00, announced July 9, 2010, published November 20, 2015).

The disadvantages of this invention are:

- the complexity of the hardware design of the system in the form of a standalone installation;

- limited use of a system operating in a stationary mode for the extraction of ethylene from blowdowns of ethylene-containing gas, which are formed occasionally during the transition of the main equipment from the release of one brand of polyethylene to another.

When creating the invention, the task was to develop a gas-chemical complex for the production of polyethylene, producing a wide range of grades of polyethylene while saving olefin feedstock by returning to the process of blowing off ethylene-containing gas.

The problem is solved due to the fact that the gas-chemical complex for the production of polyethylene consists of at least two or more pyrolysis units, each of which includes a furnace section, a compression section of the pyrogas and a separation section of the pyrogas, two or more installations of polyethylene production, one or more installations LAO production, one or more storage tanks for liquid ethane, one or more storage tanks for liquid ethylene, one or more storage tanks for LAO, with feed ethane and / or feedstock th propane is fed to pyrolysis plants, after pyrolysis plants ethylene gas is sent to polyethylene production plants and / or LAO production plants, liquid ethylene to liquid ethylene storage tanks, liquid unreacted recycled ethane to liquid ethane storage tanks, gaseous unreacted recycled ethane - for mixing with raw ethane, obtained at the LAO production unit, butene-1 and / or hexene-1 are sent to polyethylene production units as comonomers and / or output to commercial products, while blowing off ethylene-containing gas from liquid ethylene storage tanks and from polyethylene production plants and / or LAO production plants is supplied to the compression gas compression unit with subsequent supply to the pyrolysis units for combining with pyrolysis between the furnace section and the compression section of the pyrogas or between pyrogas compression section and pyrogas separation section depending on the pressure of gaseous blow-offs of ethylene-containing gas at the outlet of the blow-off compression unit waste gases. Such a solution allows almost completely preventing the utilization of ethylene-containing gas purges from polyethylene production units and LAO production units using flare systems, with the exception of emergency situations by returning olefinic hydrocarbons to the process. At the same time, the production scheme of the gas-chemical complex is supplemented with only one node - the unit for compressing the purge gases, providing multi-stage compression of the purge gases, and to reduce the costs of compression and depending on the production need, the compressed purge gas can be removed from the intermediate stages of compression at the pressure necessary to enter the corresponding pipeline or apparatus of the gas chemical complex.

As an alternative, it is also possible to additionally blow off ethylene-containing gas from the blow-off gas compression unit to a polyethylene production unit and / or a LAO production unit.

It is useful to include a propane dehydrogenation unit in the gas-chemical complex for the production of polyethylene, from which ethylene-containing gas purges are also supplied to the compression gas compression unit to increase the resources of olefin raw materials.

It is advisable to use isothermal tanks of the cryogenic type as storage tanks for liquid ethylene, since due to effective screen-vacuum insulation, ethylene losses are minimized by reducing the amount of ethylene-containing gas purge.

One of the possible options for the implementation of the gas-chemical complex for the production of polyethylene is presented in the figure in the form of a general scheme using the following notation:

1-38 - pipelines;

100 - block pyrolysis units;

101, 102 - installation of pyrolysis;

101/1, 102/1 - section of furnaces;

101/2, 102/2 - section compression pyrogas;

101/3, 102/3 - section separation of the pyrogas

200 - installation for the production of polyethylene (technology using high pressure);

300 - polyethylene production unit (suspension technology);

400 - installation for the production of polyethylene (gas-phase technology);

500 - installation of LAO production;

600 - a reservoir for storing liquid ethylene;

700 - a tank for storing liquid ethane;

800 - LAO storage tank;

900 - block compression of the exhaust gas.

Raw ethane through pipeline 1 together with raw propane fed through pipeline 2 enters the pyrolysis unit 100, being divided between the pyrolysis units 101 and 102 of the pyrolysis unit 100 into pipelines 3 and 4, respectively. Each of the pyrolysis units 101 and 102 includes, respectively: a section of furnaces 101/1 and 102/1, a compression section for pyrogas 101/2 and 102/2, and a separation section for pyrogas 101/3 and 102/3. The pyrogas obtained from a mixture of feed ethane and feed propane in sections of furnaces 101/1 and 102/1 are sent, respectively, via pipelines 5 and 6 to the compression section of pyrogas 101/2 and 102/2, and after compression, through pipelines 7 and 8 to sections for the separation of pyrogas 101/3 and 102/3. After separation of the pyrogas, gaseous unreacted recycle ethane through pipelines 9 and 10 is combined with a mixture of feed ethane and propane before separation for supplying pyrolysis units 101 and 102, and liquid unreacted recycle ethane through pipelines 11 and 12 is discharged into the liquid ethane storage tank 700 so that the lack of raw ethane to send additional ethane through the pipe 13 to the pyrolysis units 101 and 102.

Liquid ethylene extracted from pyrogas from the pyrogas separation sections 101/3 and 102/3 of the pyrolysis units 101 and 102 through pipelines 14 and 15, respectively, is discharged to the liquid ethylene storage tank 600. Liquid ethylene from the liquid ethylene storage tank 600 via pipeline 36 enters shipment as a commercial product, and can also be regasified, followed by piping 35 to combine with ethylene gas discharged from the pyrolysis separation sections 101/3 and 102/3 of the pyrolysis units 101 and 102.

Gaseous ethylene extracted from pyrogas is removed from the pyrogas separation sections 101/3 and 102/3 of the pyrolysis units 101 and 102 through pipelines 16 and 17, respectively, are combined and distributed between polyethylene production units 200, 300, 400 and LAO 500 production unit. Obtained at in an LAO 500 production plant, an oligomer, for example, butene-1, is sent via pipeline 18 to the LAO 800 storage tank for subsequent shipment via pipeline 20 to consumers or through pipeline 19 to polyethylene production plants 300 and 400 as comonomers A polyethylene production. Commodity polyethylene of various grades is diverted from installations for the production of polyethylene 200, 300, 400 through pipelines 21, 22, 23, 24, 25, 26 for subsequent molding and shipment to consumers.

Blow-offs of ethylene-containing gas from 200, 300, 400 polyethylene production units, LAO 500 production units, and from liquid ethylene storage tank 600 via pipelines 27, 28, 29, 30, and 31, respectively, go to the unit for compressing blow-off gases 900. During the start-up period , if it is not possible to supply ethylene to the polyethylene production units 200, 300, 400 and the LAO 500 production unit, the compressed purge gas is condensed and returned in the liquid state to the liquid ethylene storage tank 600 via line 32. Compressed purge gas with blast gas compression unit 900 is discharged through a pipeline 33 and depending on the requirements for raw materials of polyethylene production plants 200, 300, 400 and a LAO 500 production plant, it is distributed as follows: depending on the pressure of the compressed blast gas, it is supplied through pipelines 37 and 38 for combining with pyrogas pipelines 5 and 6, respectively, or through pipelines 39 and 40 for combining with compressed pyrogas in pipelines 7 and 8, respectively, and / or through pipe 34 are sent for combining with gaseous thylene pyrolysis units 101 and 102 before the units for the production of polyethylene 200, 300, 400 and the unit for the production of LAO 500.

Mathematical modeling of the gas-chemical complex for the production of polyethylene is carried out, the scheme of which is shown in the figure. According to calculations, with the release of several different grades of polyethylene and LAO, an average of 13130 tons of ethylene-containing gas is blown off during the year, discharged through pipelines 27, 28, 29 and 30, respectively, to a compression unit for blow-off gases 900 and containing from 76.040 mol%. up to 99.900 mol% olefinic hydrocarbons (table 1). After combining them with blow-offs of ethylene-containing gas from the liquid ethylene storage tank 600, coming in through the pipeline 31 in the amount of 75,000 t / year, and subsequent compression in the blow-off gas compression unit 900, a combined flow of blow-off gas discharged through the pipe 33 in the amount of 88130 t / a year with a purity of ethylene content of 99.320 mol%. Thus, over the year, 87,178.2 tons of ethylene can be returned to the production cycle instead of burning in flare systems.

Thus, the claimed invention solves the task of developing a gas-chemical complex for the production of polyethylene, producing a wide range of grades of polyethylene while saving olefin raw materials by returning to the process of blowing off ethylene-containing gas.

Claims (4)

1. Gas-chemical complex for the production of polyethylene, consisting of at least two or more pyrolysis units, each of which includes a section for furnaces, a section for compressing pyrogas and a section for separating pyrogas, two or more units for producing polyethylene, one or more units for producing linear alpha olefins (LAO), one or more storage tanks for liquid ethane, one or more storage tanks for liquid ethylene, one or more storage tanks for LAO, wherein feed ethane and / or feed propane are supplied and pyrolysis plants, after pyrolysis plants, ethylene gas is sent to polyethylene production plants and / or LAO production plants, liquid ethylene to liquid ethylene storage tanks, liquid unreacted recycle ethane to liquid ethane storage tanks, gaseous unreacted recycle ethane to be mixed with raw ethane obtained at the LAO production plant butene-1 and / or hexene-1 are sent to polyethylene production plants as comonomers and / or are withdrawn as commodity items products, ethylene-containing gas purges from liquid ethylene storage tanks and from polyethylene production plants and / or LAO production plants are supplied to the compressed gas compression unit with subsequent supply to the pyrolysis units for combining with the pyrolysis between the furnace section and the pyrogas compression section or between the pyrogas compression section and the separation section of the pyrogas depending on the pressure of the gaseous purges of ethylene-containing gas at the outlet of the compression gas compression unit. 2. The complex according to claim 1, in which additionally blowing off the ethylene-containing gas from the compression unit of the blowing gases is directed to polyethylene production units and / or LAO production units. 3. The complex according to claim 1, in which the gas-chemical complex for the production of polyethylene further includes a propane dehydrogenation unit, from which the blow-off of ethylene-containing gas is supplied to the blow-off gas compression unit. 4. The complex according to claim 1, in which isothermal tanks of the cryogenic type are used as storage tanks for liquid ethylene.

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