RU2528460C2 - Liquefying of high-pressure natural gas or low-pressure associated oil gas - Google Patents

Abstract

FIELD: oil-and-gas industry.

SUBSTANCE: invention relates to liquefying of natural or associated oil gas, i.e. propane-butane fraction. Initial flow is cooled, separated to isolate light portion of low-molecular hydrocarbon stock to be liquefied with extraction of liquid propane-butane fraction in power vortex separator. Said vortex separator is composed of three-section vessel accommodating vortex tube to divide the latter into three sections, top, mid and bottom, by horizontal walls. Note here that top section accommodates cold end with vortex tube coil heat exchanger, mid-section accommodating hot end. Bottom section houses hot flow rate regulator and separator of liquid phase from said flow equipped with the valve.

EFFECT: higher yield of pure hydrocarbon stock.

2 dwg

Description

The alleged invention relates to a technology for the preparation and processing of natural or associated petroleum gases into commercial products liquefied gas, representing the propane-butane fraction with a small amount of other hydrocarbons.

The problem of processing natural and associated petroleum gas and producing liquefied gases is very important because it can significantly increase the hydrocarbon resources used in many industries, in particular as domestic and industrial fuels, for example, for the production of motor fuels, as well as petrochemical raw materials for large-scale production of olefins, polyolefins and other chemical products.

However, the production of liquefied gases from natural and associated petroleum gases is a rather difficult task, especially when processing associated petroleum gas that comes out of the wells, even after preliminary treatment, is very contaminated and is a multicomponent mixture containing, in addition to hydrocarbon fractions, non-hydrocarbon components (nitrogen, carbon dioxide, hydrogen sulfide), solids and water.

Natural gases have a more stable composition, as they undergo preliminary training in the fields and gas fractionation at HFCs and are transported as high-pressure gas via gas pipelines with a pressure of 3.0-7.0 MPa, in contrast to associated petroleum gas, which can be classified as low-pressure since its pressure does not exceed 0.2-0.4 MPa.

Currently, the most common technology is the low-temperature throttle method, using vortex chambers for energy separation of low molecular weight hydrocarbons, which are the main ones in natural gases.

Therefore, to obtain liquefied gases, it is proposed to reduce high-pressure main natural gas using vortex apparatuses followed by effective separation of two-phase hydrocarbon mixtures with separation into dry and liquefied gases, which are commercial products.

Obtaining liquefied gases from associated petroleum gas is a more difficult task, since for the efficient operation of vortex energy chambers, in addition to removing unwanted impurities from associated gas, increased pressure is required, therefore it is most advisable to use compression while maintaining the main technological processes used to separate natural gas.

An analogue of the present invention is a method of liquefying natural gas according to the patent RU 2202078, F25J / 00, 2001 - [1], according to which, the liquefaction of natural gas is carried out by the throttle regenerative method, including cooling and purification of the liquefied gas from impurities by freezing in preliminary and regenerative heat exchangers, throttling of the cooled gas, its supply to the condenser-collector, with the separation of the resulting vapor-liquid mixture, while the liquefied gas is cleaned of impurities in one of the two switching heat freezer exchangers, then the gas after the recuperative heat exchanger is divided into two flows, one of which is throttled and fed to the condenser-collector, and the other after throttling is mixed with low-pressure gas exiting the condenser-collector, and a part of the compressed gas stream is sent to the vortex tube , from which a hot stream of low pressure is used to heat the heat exchanger-freezer, and a cold stream supplied for additional cooling of the compressed gas passing through the working heat exchanger-extinct agitator.

This method allows to improve the quality of the liquefied gas by cleaning it from condensing impurities by separating them from the gas stream in the preliminary and recuperative heat exchangers-freezers.

Despite the above data, the present invention has the following disadvantages:

- the initial stream of high-pressure natural gas is supplied to the installation in two streams, one is supplied to the freezing heat exchangers, and the other is fed into the main and additional vortex tubes in parallel flows, it follows that the untreated flows are fed into the vortex tubes, and part of the stream is sent to heat exchangers-freezers, and then for the separation of the resulting crystalline hydrates into the condenser-collector, and this is unacceptable, since working on raw gas of the vortex tube will lead to its failure, as a result of clogging and impurities and crystalline hydrates of a nozzle inlet having insignificant dimensions;

- using heat exchanger-freezers, it is possible only to isolate and subsequently remove by heating and separation only crystalline hydrates formed from water-hydrocarbon condensate, but not other mechanical impurities.

The prototype of the alleged invention adopted a method - installation of vortex liquefaction of associated gas according to patent RU 2395763, F25J 1/00, F25B 9/00, 2006 - [2], in which the source gas stream is pre-separated from water, then cooled in a regenerative heat exchanger by 10 -15 ° C with a hot stream of a vortex tube and enters a turbo expander, the output of which is connected to the entrance to the vortex tube.

The hot stream of the vortex tube is connected to the mixing chamber of the ejector, and the cold stream of the vortex tube is connected to the ejector and to the separator-water separator. Two flows are formed in the vortex tube as a result of ene separation of the source, dried and cooled gas: axial - cold flow at a temperature below the condensation temperature of propane-butane fractions and peripheral - hot flow. A cold stream with a temperature of minus 65 ° C consists of a methane gas fraction and small drops of condensed propane-butane fractions. This suspension is separated and separated into methane and propane-butane, which are shipped as finished products.

The invention allows the preparation and processing of associated petroleum gas at a relatively low initial pressure (up to 0.2 MPa) with the possibility of separating and liquefying propane-butane fractions, which are the most popular products for the production of a wide range of industrial uses. However, this invention has some disadvantages:

- the initial flow of associated petroleum gas sequentially passes through 4 apparatuses, including an inlet separator, two regenerative heat exchangers and a turboexpander with an inlet, relatively low pressure (up to 0.2 MPa) and enters the entrance of the vortex tube, which is unacceptable for efficient operation, since the lower boundary the performance of vortex tubes begins at pressures of 1.2-2.0 MPa [3].

- the technological scheme of the installation is difficult, especially in terms of the use of compressor equipment - a turboexpander, a turbocompressor, an electric motor, combined by a common shaft, as well as an ejector and a supercharger. This group of devices requires significant operational and capital costs, as well as difficulties in setting up and maintaining synchronous operation and performing technological parameters of the mode.

To eliminate the above disadvantages, the proposed method provides the following:

- preliminary preparation of natural or associated petroleum gas, including cooling and effective gas separation from heavy water-hydrocarbon fractions and various mechanical impurities (Block A - preparation and purification);

- gas compression (only in the case of associated petroleum gas) and throttle energy liquefaction in a vortex energy separator. When using natural high-pressure main gas, compression is not required (Block B - compression and liquefaction);

- isothermal storage of liquefied gas and the secondary (reverse) condensation of evaporated vapors of liquefied gases, due to the circulation of a certain part of the condensed liquefied gases from evaporated vapors (Block C - isothermal storage and condensation of vapors).

Common to analogues and the proposed method of separation, vortex liquefaction and isothermal storage are:

- preparation of the initial gas stream for separation is carried out using cooling and purification processes;

- compression of the gas stream when it is divided into gas and liquefied components;

- throttle vortex energy gas liquefaction in a high-speed swirling source gas stream in a vortex tube, after its purification ,;

- separation of the resulting two-phase hydrocarbon mixtures.

The difference of the proposed method from analogue and prototype is:

- the ability to carry out the separation at this installation, as a high-pressure main natural gas, and low-pressure associated petroleum gas;

- in the proposed method, the initial gas stream after cooling is fed to efficient separation in a multistage centrifugal separator, in which the light gas fraction is separated from the water-hydrocarbon condensate, including oil residues (for the case of associated petroleum gas) and various impurities emitted with a heavy phase;

- in the analogue, part of the source gas enters the vortex tubes in parallel flows, and the main part of the gas enters the regenerative heat exchangers - freezers, and in the prototype the initial gas stream after drying in the separator, enters two consecutive regenerative heat exchangers for cooling, and then into the turboexpander and vortex tube ;

- in the proposed method, compression is used to compress the light separated gas phase after centrifugal separation of the initial gas stream (only when using associated petroleum gas) when entering the vortex energy separator.

In the prototype, compression is used to compress the hot gas stream separated from the liquid to supply it to the mixing chamber of the ejector to supply methane to the external gas pipeline.

- the presence of isothermal storage of liquefied gas with secondary condensation of the vaporized vapor of the liquefied gas.

In the prototype, this stage of the process is missing.

The technical result of the claimed invention is to increase the efficiency of processing natural or associated petroleum gas by sequentially liquefying and separation phase separation and simultaneous purification from unwanted impurities.

This can significantly increase the resources of pure hydrocarbon raw materials used in many industries, when the feed contains many undesirable impurities.

The essence of the alleged invention of a centrifugal separation method, vortex liquefaction and isothermal storage is as follows: a method of liquefying a high-pressure natural or low-pressure associated petroleum gas, comprising natural gas or associated petroleum gas coming from a gas pipeline, which is a mixture consisting of multicomponent hydrocarbon gases and impurities, including purification of liquefied gases from impurities by cooling, condensation and separation of the resulting two-phase mixture into gas components w and the condensed liquid phase comprising water and hydrocarbon condensate and impurities. In this case, the gas phase is subjected to vortex energy separation in a three-stream vortex tube into dry gas and liquefied gases, and the water-hydrocarbon condensate is sent for separation with the release of aqueous, hydrocarbon and impurities. The initial stream of high-pressure natural gas or low-pressure associated petroleum gas, after cooling, condensation and separation in the first multistage centrifugal separator, the condensed liquid phase is taken out for processing.

The gas phase, in the case of using low-pressure associated petroleum gas, after separation is subjected to compression of the separated gas phase, representing a low molecular weight fraction of hydrocarbons. Then, the separated gas phase of high-pressure natural or low-pressure associated petroleum gas is subjected to vortex energy separation, liquefaction, and gas-dynamic separation in a vortex tube placed vertically in a three-section, consisting of the upper, middle, and lower sections of the tank - a vortex energy separator separated by horizontal partitions in the upper partitions the initial gas stream is cooled in a heat exchanger - a coil, washed by the condensate of a cold stream, which then flows into the middle projection of cooling hot end of the vortex tube, located in the middle section, where the portion of the liquefied gas is supplied from the middle section for cooling the feed gas stream in an indirect heat exchanger. The main part of the liquefied gas, after cooling the vaporized vapor in an isothermal storage, in a regenerative heat exchanger, a throttling valve and a coil heat exchanger, enters the isothermal storage. The vaporized liquefied gas vapors are subjected to secondary condensation on the surface of the cooled coil heat exchanger located in the upper part of the isothermal storage, the condensed vapors flow to the lower part of the vault, and the non-condensed vapors in the form of a two-phase mixture are sent to the second separator for secondary separation into gas and liquid after cooling. Moreover, the gas is subjected to secondary vortex energy separation in a vortex energy separator, and the liquid is sent to an isothermal storage, in the lower section of the separator tank, the hot gas stream is separated from the liquid phase, which is sent to an isothermal storage. The gas stream is diverted from the gas space of the lower section of the vortex energy separator, separated by a partition, as a commodity methane fraction, and from the lower part of the section is a separated phase, which is poured into an isothermal container, from which the liquefied gas fraction is taken as a commodity product.

In FIG. 1 shows a schematic flow chart for implementing the proposed method. In FIG. Figure 2 shows a schematic design of a vortex energy separator (enlarged) for liquefying natural and associated petroleum gas.

On the technological scheme (Fig. 1) are presented: block A - preparation and purification of the source gas for separation; block B - compression and liquefaction; block C - isothermal storage of liquefied gas and secondary vapor condensation, as well as flows: I - the initial flow of natural or associated petroleum gas; II - water-hydrocarbon condensate and impurities; III - light gaseous fractions; entering the vortex energy separator; IV - compressible light gaseous fractions (when working on associated petroleum gas); V is the liquefied gas leaving the vortex energy separator; VI - hot gas stream leaving the vortex energy separator; VII - vapor, vaporized liquefied gas, leaving the isothermal storage; VIII - liquefied gas vapors after the refrigerator entering the pump inlet; IX - cooled vapors entering the separator; X - separated liquefied gas entering the isothermal storage; XI - separated from the hot stream of the vortex energy separator, liquefied gas entering the isothermal storage; XII - part of the separated liquefied gas entering the recuperative heat exchanger to cool the initial gas stream; XIII - liquefied gas after a recuperative heat exchanger entering the vortex energy separator; XIV is the separated gas leaving the vapor separator and entering the stream III; XV - shipment of commercial liquefied gas from an isothermal storage facility; XVI - methane fraction exiting the vortex energy separator into the main gas pipeline.

The technological diagram also presents apparatuses, equipment and main valves (devices for implementing the proposed method, other valves, valves, sensors are excluded from the scheme for simplification), including: 1 - recuperative heat exchanger; 2 - the first multistage centrifugal separator; 3 - compressor; 4 - vertical capacity of the vortex energy separator; 5 - upper horizontal partition; 6 - lower horizontal partition; 7 - three-flow vortex tube placed coaxially in the tank 4; 8 - the cold end of the vortex tube, placed above the upper horizontal partition; 9 - a tubular heat exchanger for cooling the initial gas stream at the entrance to the vortex tube 7; 10 - the hot end of the vortex tube 7, located in the lower horizontal partition; 11 - valve control device flow of hot gas flow and selection of the separated liquid from the gas; 12 - a handle with a rod and a screw device for moving the valve to change the annular gap between the conical end of the hot end and the valve 11; 13 - horizontal partition with peripheral holes located in the lower section of the tank - to separate the gas space and the liquid collector; 14 - drain pipe mounted on the upper horizontal partition; 15 - isothermal storage; 16 - a screen in the form of a coil, located in the upper space of the isothermal storage; 17 - regenerative heat exchanger for cooling the vapor; 18 - pump; 19 - a second separator; 20 ... 27 - shut-off and control valves.

Moreover, the valves are located: 20 - on the line of the initial flow of natural (associated petroleum) gas (stream 1); 21 - on the line for the selection of water-hydrocarbon condensate and impurities (stream II); 22 - on the line of exit of the light gas fraction from the centrifugal separator and the entrance to the vortex energy separator (stream XIII); 23 - on the line of exit of the light gas fraction from the centrifugal separator and the inlet to the compressor 3 (stream III); 24 - selection of methane fraction in the fuel network; 25 - on the sampling line of the separated liquid phase from the vortex energy separator 4 into the recuperative heat exchanger 1 (stream XII); 26 - on the line for introducing liquefied gas from a vortex energy separator into an isothermal storage (stream V); 27 - on the line for the selection of commercial liquefied gas (stream XV).

The initial stream of natural (or associated petroleum) gas I comes from the main gas pipeline (or from a field separator) for cooling to a recuperative heat exchanger 1, and then it is tangentially introduced into a multi-stage centrifugal separator 2 to separate light gas fractions from water-hydrocarbon condensate and impurities, which are removed from the bottom of the separator by flow II (with valve 21 open) for further separation (not shown in the diagram).

Light fractions of gas III emerging from the top of the separator 2, through valve 22, enter the vortex energy separator 4 (during the processing of associated petroleum gas, this gas stream IV enters, through valve 23, into the compressor 3, and then into the vortex energy separator 4.

The vortex energy separator 4 is a three-section capacity in which the vortex tube 7 is vertically placed in such a way that it is divided into three sections by horizontal partitions 5, 6 and 13: the upper, middle and lower, while the upper end has a cold end 8 with a coil heat exchanger 9 of the vortex tube 7, in the middle - the hot end 10, and in the bottom - the regulating device for the flow of hot flow and a separation device for separation from the liquid phase stream, containing the valve 11.

In the lower section of the tank there is a horizontal partition 13, dividing the space of the section into the upper gas space and the lower one, for collecting the separated liquid phase from the hot stream, for which the septum has peripheral openings for draining the liquid from the upper space to the lower one.

The input gas stream is introduced into the vortex energy separator 4 by means of a heat exchanger — a coil 9 with the cold end of the vortex tube 8 located in the upper section of the tank, which allows cooling the incoming gas stream IV, which exits the liquid phase of the cold stream. A part of the condensate of the cold stream from the upper section flows down the drain pipe 14 into the middle section, cooling the hot end of the vortex tube, which improves the efficiency of the separation process of separating from the hot stream the liquid phase that accumulates in the middle section of the energy separator 4.

The regulation of the flow rate of the hot stream and the selection of the separated liquid phase accumulating in the lower section of the energy separator is carried out by a regulating device 12 with a helical gear and an adjustment knob.

The liquefied gas phase is discharged (stream V) from the vortex energy separator 4, which, after the regenerative heat exchanger 17, which cools the vapor and passes through the throttling valve 26 and the coil screen 16, is discharged into the isothermal tank 15. In this case, a part of the liquefied gas from the middle section (from the stream XI) is taken by valve 25 and flow XII enters the cooling of the original gas stream (stream I) in the regenerative heat exchanger 1. The main part of the liquefied gas from the middle section of the vortex energy separator 4 (stream V), passing regenerative heat exchanger 17, in which the liquefied gas, giving off cold during the evaporation of vapors (stream VII), leaving the top of the isothermal storage 15, is condensed in the heat exchanger and fed to the centrifugal separator 19 by a pump 18. The condensed liquid after the heat exchanger 17 (stream V) is throttled by a valve 26 and sent to the coil screen 16, after which the liquid is drained into the isothermal storage 15.

Evaporated vapors of liquefied gas from the isothermal tank are discharged through a coil-screen 16, located in the upper part of the isothermal storage, which, having passed through the regenerative heat exchanger 17, are cooled, condensed and pumped out by pump 16 to flow separator 19, in which the liquid part of the vapor is separated from the gaseous part, and then the liquid phase XI merges into an isothermal tank, and the gaseous phase enters the input of the vortex energy separator 4 (stream XIV).

The selection of the product liquefied gas XV is carried out from the isothermal storage 15 through the valve 27.

Thus, the proposed method of centrifugal separation of isothermal storage allows you to process natural high-pressure main natural gas, as well as low-pressure associated petroleum gas coming from oil fields at the stage of floor separation or from field compressor stations. Gas preparation for separation is carried out by the method of multistage centrifugal separation, as a result of which heavy impurities are cleaned and moisture is dried.

Further separation of the light gas fraction of the feed stream is carried out by deep cooling of the gas to minus 50 ° C in a vortex energy separator, resulting in the production of dry methane and commercial liquefied propane-butane fraction, which is discharged into an isothermal storage, for subsequent shipment to the consumer.

The ground isothermal storage of isothermal gas is a common, for example, a vertical tank coated with thermal insulation. Liquefied gas is stored at a temperature of minus 40 ... 50 ° C under a slight overpressure close to atmospheric, and is equal to: 50 ... 250 mm. water Art. (1.03 ... 1.05 kgf / cm ² ).

As thermal insulation, vacuum-powder thermal insulation or polyurethane foam (expanded polymer) can be used.

In order to reduce losses of liquefied gas in an isothermal storage, secondary condensation of evaporated vapors of the liquefied fraction is provided, using refrigeration cycles, due to cold cold flow of the vortex tube, regenerative heat transfer, throttling valve and separation of the resulting gas-liquid mixture.

The given set of distinctive features is not known at this level of technological development and does not follow from well-known rules for designing such universal plants with processing of almost any natural and associated petroleum gas with various inlet pressures in the range from 0.2 to 70 MPa, which meets the criterion of "inventive step" ".

Given the versatility of the technology allows you to process almost any low molecular weight hydrocarbon natural gas according to this method, according to the above claims, together with the foregoing features, is new to produce liquefied gases, and therefore meets the criterion of "novelty."

The constructive implementation of the claimed invention with the indicated combination of features and a detailed description of the structural elements of the apparatus does not present any structural, technical and technological difficulties, from which the criterion “industrial applicability” follows.

Information sources

1. Patent RU 220078, F25J 1/00, 2001.

2. Patent RU 2395763, F25J 1/00, F25B 9/00. 2006 - prototype.

3. Kisin V.A., Tyurina L.A. Deep preparation of associated petroleum gas for processing into commercial products. Scientific and technical journal. Science and technology in the gas industry. 2008., No. 1 (33), pp. 4-10.

Claims (1)

A method of liquefying high-pressure natural or low-pressure associated petroleum gas, including natural or associated petroleum gas coming from a gas pipeline, which is a mixture consisting of multicomponent hydrocarbon gases and impurities, including purification of liquefied gases from impurities by cooling, condensation and separation of the resulting two-phase mixture into gas components and a condensed liquid phase, including water-hydrocarbon condensate and impurities, while the gas phase is subjected to vortex energy chemical separation in a three-stream vortex tube into dry gas and liquefied gases, and the water-hydrocarbon condensate is directed to separation with the release of water-carbon condensate and impurities, characterized in that from the initial stream of high-pressure natural gas or low-pressure associated petroleum gas, after cooling, condensation and separation in the first multistage centrifugal separator, the condensed liquid phase is taken out for processing, and the gas phase, in the case of using low-pressure associated petroleum gas , after separation, the separated gas phase representing the low molecular weight hydrocarbon fraction is subjected to compression, then the separated gas phase of the high-pressure natural or low-pressure associated petroleum gas is subjected to vortex energy separation, liquefaction and gas-dynamic separation in a vortex tube arranged vertically in a three-section upper and lower middle section section of the tank - vortex energy separator, divided by horizontal partitions, in the upper section of one gas stream is cooled in a heat exchanger — a coil washed by a cold stream condensate, which then flows into the middle section, from which part of the liquefied gas from the middle section is fed to cool the initial gas stream in the recuperative heat exchanger, and the main part of the liquefied gas, after cooling the evaporated vapors in an isothermal the storage, in the regenerative heat exchanger, the throttling valve and the coil heat exchanger, enters the isothermal storage, the vaporized liquefied gas vapors are subjected to second of condensation on the surface of the cooled coil heat exchanger located in the upper part of the isothermal storage, the condensed vapors flow to the lower part of the storage, and the non-condensed vapors in the form of a two-phase mixture after cooling are sent to the second separator for secondary separation into gas and liquid, and the gas is subjected to a second vortex energy separation in a vortex energy separator, and the liquid is sent to an isothermal storage, in the lower section of the separator tank, the hot stream is separated gas from the liquid phase, which is sent to an isothermal storage, the gas stream is removed from the gas space of the lower section of the vortex energy separator, separated by a partition, as a commodity methane fraction, and from the lower part of the section is a separated phase, which is drained into an isothermal container, from which the liquefied fraction of gases as a commercial product.

Images