RU2576738C9 - Method of natural gas processing and device to this end - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: method includes primary separation of raw natural gas flow with separation of water and gas condensate from it and further treatment of the separated gas from acid components containing hydrogen sulphide and carbon dioxide. Treatment from acid components is performed at two stages: at first hydrogen sulphide removal stage is implemented using adsorbent with hydrogen fractional selectivity and at the next stage carbon dioxide is removed using ultrasound separation. At that gas condensate upon primary separation and ultrasound separation is subjected to stabilization process and in this process gas is returned to hydrogen sulphide removal stage. Hydrogen sulphide upon hydrogen sulphide removal stage is sent to sulphur recovery stage by means of Claus conversion process, the obtained sulphur is subjected to degassing and gas from sulphur degassing is returned to sulphur recovery stage.

EFFECT: improved treatment degree for natural gas from hydrogen sulphide and carbon dioxide at fuller conversion of sulphur compounds.

14 cl, 1 tbl, 1 dwg

Description

The invention relates to the oil and gas industry, in particular to a technology for processing natural gas using a low-temperature separation process for purification from hydrogen sulfide and carbon dioxide.

The problems of developing natural gas reserves in gas and gas condensate fields with a high content of hydrogen sulfide are associated with significant environmental restrictions on emissions of sulfur compounds from gas processing enterprises into the atmosphere.

For example, the gas of the Astrakhan gas condensate field, which has reserves of about 3 trillion m ^{3 of} gas and 1 billion tons of condensate, is characterized by a high content of hydrogen sulfide (up to 25 vol.%), Carbon dioxide (up to 16 vol.%), As well as organosulfur compounds, mercaptans with significant the proportion of heavy hydrocarbons.

At the Astrakhan gas processing plant (GPP), the following technology is used to purify gas from acidic components (hydrogen sulfide and carbon dioxide): 1. Primary separation of the raw natural gas stream with the separation of water and gas condensate from it.

2. Absorption purification of gas separation from acidic components. As absorbents, an aqueous solution of diethanolamine with an initial concentration of 38.3% of the mass is used. A fundamental feature of this technology: H ₂ S and CO ₂ are sorbed together without separation into components and together as ballast are removed from the main stream of natural gas.

3. Extraction of the main volume of sulfur from hydrogen sulfide at the Claus facility through direct oxidation in reaction furnaces. In this case, carbon dioxide is not removed, but as a ballast passes into the tail gas.

4. Post-treatment of tail gases on the catalyst of the Sulfrin installation with additional sulfur recovery from gas.

5. Next, before discharge into the atmosphere, all sulfur compounds present at the outlet of the Sulfrin block are converted to SO ₂ on the block of residual gas afterburning furnaces.

6. To remove hydrogen sulfide absorbed in sulfur obtained in the blocks "Klaus" and "Sulfrin", use the process of degassing liquid sulfur. See: http://www.vipusk.rusoil.net/pages/daykariera/50/en.html.

In this technology, the high content of carbon dioxide in the acidic part of the mixture of gases supplied for oxidation to Klaus blocks adversely affects the process of burning hydrogen sulfide. In addition, due to the reactions of hydrogen sulfide with carbon dioxide, CS ₂ and COS compounds are formed, which are not subjected to further conversion, reduce the sulfur yield and impede the operation of the Sulfrin unit. According to the described technology, recovery of not more than 99.6% of hydrogen sulfide from natural gas is achieved. From an environmental point of view, the achieved degree of purification of natural gas from sulfur compounds is insufficient, and with a further increase in its production, the mass of sulfur emissions becomes environmentally hazardous, since with the existing gas processing capacity a large amount of sulfur compounds is released into the atmosphere during the year. The gas processing technology of the Astrakhan field requires improvement.

The prior art method for purification of raw natural gas, including primary separation with separation from the gas mixture of condensate and water, followed by vortex separation to extract hydrogen sulfide and carbon dioxide from the gas mixture (see patent RU 2216698, IPC: F25J 3/08, publ. 11/20/2003). The method involves the extraction of hydrogen sulfide and carbon dioxide at one general stage of vortex separation, which carries the risk of clogging the purified natural gas with vapors of boiling hydrogen sulfide.

There is a known technology for purifying a stream of raw natural gas from hydrogen sulfide, in which sulfur is separated from the stream using a Klaus plant, sulfur is degassed, and the obtained gas is returned to the hydrogen sulfide extraction stage (see Japan Patent JP 3602268, IPC: B01D 53 / 86; C01B 17/04, publ. 15.12.2004). The resulting natural gas is not purified from CO ₂ , which reduces its quality and complicates subsequent processing.

In addition, a method for separating a mixture of hydrocarbon gases is known from the prior art, including cooling the mixture, expanding the mixture or part thereof, partially condensing the mixture during expansion, separating the mixture or part thereof in a distillation column to obtain products in the liquid and gas phase. The process of expansion of the mixture is carried out by passing the mixture through the nozzle channel, and in the nozzle channel and / or at the entrance to the nozzle channel, the mixture flow is twisted, at the outlet of the nozzle channel or part thereof, the mixture stream is divided into at least two streams, one of which is enriched with components heavier than methane, and the other is depleted in these components. The enriched stream is partially or completely sent to the distillation column, and the gas-phase products obtained in the distillation column are partially or completely sent to the mixture until it is expanded (see RF patent No. 2272973, IPC: F25J 3/02, publ. March 27, 2006). The described method allows to improve the quality of separation of the components of the mixture and significantly increase the purity of the selected phases.

No information sources have been found in the prior art that reveal the stage of extraction of hydrogen sulfide and the stage of extraction of carbon dioxide from natural gas using separate sequentially performed operations using supersonic separation to extract CO ₂ .

The closest analogue of the invention is the aforementioned method for purification of raw natural gas, including primary separation and subsequent vortex separation by joint extraction from a gas mixture of hydrogen sulfide and carbon dioxide (RU 2216698, IPC: F25J 3/08, published November 20, 2003).

The invention is aimed at improving the environmental safety of the processes of processing natural gas and gas condensate with a high content of acidic components.

The technical result is to increase the degree of purification of natural gas from hydrogen sulfide and carbon dioxide while providing a more complete conversion of sulfur compounds. In addition, the claimed invention allows to reduce the content of ballast components and harmful impurities in commercial gas processing products while increasing the efficiency of technological processes, in particular the Klaus process.

To solve this problem, a method for purification and processing of natural gas is proposed, including primary separation of the flow of crude natural gas with separation of water and gas condensate from it and subsequent purification of the gas of separation from acidic components containing hydrogen sulfide and carbon dioxide. The claimed solution differs from the prototype in that the extraction of hydrogen sulfide (as well as other sulfur compounds) and the extraction of carbon dioxide is carried out at different stages. That is, the separation gas is purified from hydrogen sulfide and carbon dioxide in succession in two stages: first, a hydrogen sulfide extraction step is carried out using an absorbent with selective hydrogen sulfide selectivity (for example, an absorbent based on polyethylene glycol compounds), and in the next step, carbon dioxide and the residual gas phase are recovered condensate using supersonic separation. The gas condensate after primary separation and the gas condensate obtained after exiting the supersonic separation unit (unit) are subjected to a stabilization process, while the stabilization gas is returned to the hydrogen sulfide extraction stage, and hydrogen sulfide from the hydrogen sulfide extraction stage is sent to the sulfur separation stage by direct oxidation in furnaces with using the Klaus process. The sulfur obtained is subjected to degassing, and the gas from sulfur degassing is returned to the hydrogen sulfide extraction step. After degassing, sulfur is preferably granulated.

The tail gases obtained after the separation of sulfur using the Klaus process are subjected to fine purification from hydrogen sulfide by its adsorption by iron oxides (or adsorbents based on iron oxides) with the direction of the released sulfur also to granulation, and the residual after fine purification of tail gases to afterburning (torch).

The produced water released during the primary separation of raw natural gas, containing salts and solids, is filtered and disposed of.

Gas condensate obtained after the primary separation of crude natural gas and gas condensate obtained after exiting the supersonic separation unit is an unstable product that requires further processing. It is subjected to a stabilization process. As a result of the stabilization process, a fraction of stable gas condensate and a wide fraction of light hydrocarbons (NGL) are isolated.

NGL is either further fractionated to produce liquefied gases and with the release of the residual fraction of stable gas condensate or shipped as a commercial product to the consumer.

It should be noted that the supersonic separation stage is carried out with the removal of products from the installation in the form of pure carbon dioxide and purified (commercial) natural gas containing a mixture of hydrocarbons based on methane (methane more than 85 vol.%, Ethane-propane-butane 12-13 vol. %). Moreover, the above-mentioned commercial natural gas contains an admixture of carbon dioxide in an amount of not more than 3% and nitrogen not more than 0.6%. The finished product, obtained as pure carbon dioxide, contains CO ₂ > 80%, preferably CO ₂ > 85%, most preferably the amount of CO ₂ is more than 95% (by volume).

The proposed technological scheme is based on the concept of separate stepwise extraction of acidic components from natural gas. At the first stage of the extraction of acidic components (after the initial separation), sulfur compounds are extracted from the separation gas using an absorbent with selective hydrogen sulfide selectivity, for example, Selexol.

Advantages of the Selexol type absorbent for the proposed gas purification scheme:

- stability of absorption capacity (up to 10 years);

- good biodegradability;

- non-toxicity and very low corrosivity;

- low heat of absorption (intermediate cooling in the absorber is not required);

- high hygroscopicity and the ability to achieve a low gas dew point in one step;

- low tendency to foaming and low pressure of saturated vapors;

- low absorption of carbon dioxide compared with hydrogen sulfide.

In the second stage, the gas released from the main mass of H ₂ S enters the supersonic separation unit, where the separation of CO ₂ and residual condensate phases occurs. The output produces commercial natural gas containing not more than 3% CO ₂ , and a fraction containing more than 80% CO ₂ , which is also a commercial product.

The invention is illustrated in figure 1, which shows one of the possible options for the installation of purification and processing of natural gas of the claimed method.

To implement the claimed method, an installation for purification and processing of natural gas is used, which includes the following main blocks, interconnected by the flow of gas and / or components (products) extracted from it:

unit 1 of the primary separation of raw natural gas;

block 2 extraction of hydrogen sulfide absorbent with selective selectivity for hydrogen sulfide;

supersonic separation unit 3;

gas condensate stabilization unit 4;

block 5 degassing sulfur;

sulfur recovery unit 6 using the Claus process;

block 7 fractionation of BFLH;

block 8 granulation of sulfur;

block 9 of fine purification of hydrogen sulfide residual gases after the Claus process;

block 10 water purification.

The installation for purification and processing of natural gas contains interconnected unit 1 for the primary separation of raw natural gas, configured to separate water and gas condensate, unit 2 for the extraction of hydrogen sulfide with absorbent with selective selectivity for hydrogen sulfide, and block 3 for supersonic separation. Moreover, block 3 is installed with the possibility of obtaining carbon dioxide and marketable natural gas based on methane at the outlet of it. In this case, the first input of the hydrogen sulfide extraction unit 2 is connected to the first output of the primary separation unit 1, the second output of which is used for outputting water with mechanical impurities, the third output is connected to the first input of the gas condensate stabilization unit 4, and the input is in communication with the raw natural feed system gas. Moreover, the second and third inputs of the hydrogen sulfide extraction unit 2 are connected respectively to the condensate stabilization unit 4 and to the sulfur degassing unit 5, and the outputs of this block are connected to the sulfur recovery unit 6 using the Klaus process and to the supersonic separation unit 3. The output of block 3 is connected to the second input of the condensate stabilization block 4, with the possibility of obtaining stable condensate at the output. At the same time, the output of the NGL stabilization unit 4 is communicated with the NGL fractionation unit 7, and the sulfur separation unit 6 is connected to the sulfur granulation unit 8 via the Claus process through the degassing unit 5 and through the fine hydrogen purification unit 9, respectively.

Characteristics of the main units of the installation.

Primary separation is the primary process for processing natural gas in the fields. On the primary separation unit 1, the formation mixture of the raw natural gas is separated into separated gas, unstable gas condensate and produced water.

Crude natural gas from a field at a pressure of approximately 7 MPa and with a temperature of approximately 30 ° C is piped to the buffer tank of unit 1, where the primary separation of the liquid phase from the crude gas stream takes place. The separated liquid (condensate, produced water) is throttled from 7.0 MPa to 6.2 MPa and is fed to the upper part of the separation tank equipped with a chipper. Upon impact with the chipper, the liquid is sprayed, which, on the one hand, intensifies the process of its degassing, on the other hand, the gas is saturated with a droplet liquid and an emulsion is formed.

Gas from the buffer tank through the valve - pressure regulator - enters through the nozzles in the upper part of the separation tank. In the sump of the separation tank, there is a separation into three streams:

a) water containing solids and salts is sent through a filter to a water treatment plant after separation of solid particles;

b) hydrocarbon condensate is sent to a stabilization plant or tank farm;

c) the gas from the sump, passing through the swirl necessary for a more accurate gas separation, enters a column equipped with five cap plates, which ensures the removal of micro droplets of liquid entrained in the gas phase.

After the column, the separated natural gas with P = 6.6 MPa and T = 39 ° C, passing through the metering point, is sent for cleaning from acidic components to blocks 2 and 3.

First, the separated gas is sent to the hydrogen sulfide extraction unit 2. The separation of hydrogen sulfide on block 2 is carried out by physical absorption using solutions of absorbents that absorb hydrogen sulfide well and poorly absorb carbon dioxide, for example, polyethylene glycol dimethyl ether or a similar Selexol absorbent containing a mixture of dimethyl ethers of polyethylene glycols (tri-, tetra-penta) are used as absorbent. -, hexa- and heptaethylene glycols). Selexol for absorption is used in concentrated form with a water content of from 0 to 5 mass. %

To reduce the absorption capacity of Selexol, various gas components are located in the following row:

The process of releasing hydrogen sulfide with an absorbent such as Selexol has a high selectivity for hydrogen sulfide, the solubility of which in the absorber is 9-10 times higher than that of carbon dioxide, and therefore its use allows to achieve deep gas purification from sulfur-containing components. To increase the selectivity of the process, the absorbent is pre-saturated with CO ₂ .

The main element of block 2 is a packed absorber. Separation gas at a temperature of 20 ° C and a pressure of 7 MPa enters the lower part of the packed absorber, on top of which a regenerated absorbent Seleskol is supplied, which passes through an air cooler and an irrigation tank to reduce losses of absorbent with purified gas. An absorbent saturated with acidic components and containing a certain amount of hydrocarbons is discharged from the bottom of the absorber.

After the extraction of hydrogen sulfide, natural gas enriched in carbon dioxide is sent to block 3, which includes a supersonic separation unit for the emission of CO ₂ . The sulfur content in it is about 5 mg / m ³ . The main acidic component is carbon dioxide. Block 3, which includes a supersonic separation unit, allows you to split the gas into two streams: a stream depleted in CO ₂ is a commodity natural gas based on methane (admixture of CO ₂ ~ 2 wt.%), And a stream enriched in CO ₂ wherein the content of CO ₂ ≥95 wt. %

Block 3 includes the following basic equipment: heat exchangers, fractionation column, supersonic separation unit, gas-liquid separator, pump, Joule-Thomson valve, mixer, inlet and outlet compressors. To compress gas, it is also possible to use compressor equipment, which is installed on the feed and gas flow of gas.

Block 3 works as follows. After compression and drying, the inlet gas enters the inlet of the heat exchanger with a pressure of 4.6 MPa, where it is cooled to a temperature of 55 ° C. Then the cooled stream is sent to the middle part of the fractionation column. The gas stream from the top of the column is mixed in the mixer with part of the commercial gas that has been compressed and cooled in the heat exchanger. Due to mixing with commercial gas, the gas stream from the top of the column is cooled to a temperature of - 70 ° C and enters the inlet of the gas-liquid separator. The gas phase from the specified separator is directed to the inlet of the supersonic separation unit, in which the natural gas is cooled in a supersonic swirling gas stream. The supersonic flow is realized using the Laval confuser-diffuser nozzle, in which the gas accelerates to speeds exceeding the speed of sound propagation in the gas. In this case, strong cooling of the gas occurs. The liquid (carbon dioxide) released as a result of cooling by centrifugal forces with acceleration reaching 10 ⁶ m / s ^{2 is} discarded to the walls of the outlet bell, and the purified natural gas (mainly methane) leaves through the diffuser. In the diffuser, the kinetic energy acquired by the flow passes into pressure (the outlet pressure is 70-80% of the inlet pressure).

The purified flow of commercial natural gas exiting the supersonic separation unit is heated in a heat exchanger and sent for compression to the commercial gas compressor. A two-phase stream containing unstable gas condensate, leaving the supersonic separation unit, is heated in a heat exchanger and sent to the input of the compressor for raw gas. In order to ensure a temperature above the crystallization temperature of CO ₂ in the two-phase flow coming from the supersonic separation unit, a hot feed gas is supplied to the supersonic separation unit. To reduce the heating power of the bottom of the column, it is proposed to additionally pump liquid from one part of the column to another using a pump, while the pumped liquid is heated in a heat exchanger. The extracted CO ₂ from the bottom of the column is throttled to a pressure of 0.5 MPA in the Joule-Thomson valve and heated in a heat exchanger.

In block 3, external cooling sources are not used (there are no refrigerators). The thermal power of 1.8 MW, necessary for heating the column, can be summed up by cooling the raw or commercial gas that has undergone compression.

Block 3 provides a reduction in the CO ₂ content in the gas from 60% to 2.7%, while the formation of crystalline CO ₂ in the plant elements is completely eliminated.

A two-phase stream containing unstable gas condensate is directed from the output of block 3 to the input of the gas condensate stabilization block 4. In addition, the flow of unstable gas condensate obtained in the process of primary separation of raw natural gas at block 1 is directed to another input of the indicated block 4.

Block 4 includes one or several parallel working lines that implement the following stages of condensate processing:

a) two-stage degassing of condensate with simultaneous separation from water;

b) electrical desalination of condensate;

c) condensate stabilization.

The target product of the block 4 stabilization of gas condensate are:

- gas stabilization (degassing) of the condensate entering the block 2 extraction of hydrogen sulfide absorbent with selective selectivity for hydrogen sulfide;

- stable condensate supplied to the production of petroleum products.

Unstable gas condensate enters block 4 first into a storage tank, then to the first stage of degassing and sludge in a separator, where the gas phase and condensate are separated from water. The separated condensate passes sequentially through two heat exchangers, where additional gas condensate degassing takes place, as well as water settling.

Desalination is carried out in two stages:

1) process water is supplied to the condensate and thoroughly mixed to dissolve the salts in the condensate;

2) a condensate emulsion is fed to an electric desalting unit to separate condensate and water with dissolved salts.

The supply of process water to the condensate is carried out in two streams. The first stream of water in an amount of up to 3 m ³ / h is injected into the condensate before entering the electric desalting machine. A second stream of water is supplied to the hydrocarbon condensate in front of the heat exchanger. To improve the mixing of condensate with water, a manual mixing valve is installed on the condensate line after injection. After mixing, the condensate emulsion is fed to an electric desalting machine.

The electric desalter is equipped with electrodes, to which a voltage of up to 16000 V is applied through a transformer. When a condensate emulsion enters an alternating electric field between the electrodes, small drops of water are polarized, coarsened and precipitated together with salts dissolved in it.

Dehydrated and desalted condensate rises and is discharged in the upper part of the electric desalting machine. The salt-enriched water, separated from the condensate, is discharged from its lower part. Maintaining a certain water level in the lower part of the apparatus creates an additional electric field in the sludge zone between the surface of the water layer and the electrodes, which contributes to more efficient dehydration of the condensate. Water from the electric demineralizer is discharged to the filtration unit.

Condensate from the top of the desalination unit is fed to the stabilization column. The desalted condensate after the electric desalting unit is divided into two streams. The first stream in an amount of up to 40% of the total quantity is supplied to the 19th plate of the stabilization column as cold irrigation.

The second desalted condensate stream is sent to heat exchangers, where it is heated by a counterflow of stable condensate 130-150 ° C and fed to the eighth plate of the stabilization column as power.

The stabilization column is a vertical apparatus equipped with 19 valve plates. The bottom part of the column is divided by a vertical partition into two compartments. The design of the 15th and 17th plates allows you to output the water evaporated from the condensate to a remote collection. Water from the collector is discharged into the collector of contaminated process water and then to the filtration unit.

In the stabilization column at a pressure of 14.7-16 kgf / cm ² and a cube temperature of 245-260 ° C, light hydrocarbons are evaporated, thereby stabilizing the condensate. The heat required for stripping light hydrocarbons is supplied to the bottom part by a stream of hot condensate circulation through the furnace. The steam flow rising from the cube is in contact with the counter flow of condensate on the trays. As a result of heat and mass transfer, the condensate is freed from light components, which at a temperature of 40-55 ° C in the form of stabilization gases are removed from the upper part of the stabilization column to the collector leading to the input of block 2.

The stabilized condensate contacts the upward steam flow on the plates, is freed from light hydrocarbons and flows into the “cold compartment” of the cube of the stabilization column, from where it is pumped to the coil of the furnace for heating.

The supply of heat to the cube of the column is due to the circulation of condensate through the coils of the furnace.

Stable condensate from the "cold compartment" of the cube column is pumped through a centrifugal pump through a coarse strainer and is fed into the convection chamber of the furnace in four streams.

Stable condensate heated in the convection chamber of the furnace by the exhaust flue gases enters the radiant chamber of the furnace, where it is heated to a temperature of 245-260 ° C due to the thermal radiation of the combustion products and is supplied under the combined plate to the bottom plate of the stabilization column.

The vapor-liquid mixture coming from the furnace under the first plate of the stabilization column is divided into gas and liquid phases.

The liquid phase (stable condensate) flows into the second compartment of the column cube and, as it accumulates, is discharged to the consumer.

The gas phase of a stable condensate with a temperature of 245-260 ° C from the cube of the stabilization column passes into the annulus of the heat exchanger, where it is cooled to a temperature of 195-205 ° C by unstable condensate entering the feed part of the column, and is fed into the annulus of the next heat exchanger.

After the heat exchanger, the stable condensate is supplied for cooling to the air cooler and to the water cooler.

Cooled stable condensate with a temperature is supplied for further processing to oil products or to a storage warehouse.

Block 6 processes acid gas, which mainly contains hydrogen sulfide (> 84%), separated from the separation gas stream, on block 2 with an absorbent with selective hydrogen sulfide selectivity. Hydrogen sulfide at block 6 is processed using the Claus process with the release of elemental sulfur. A high concentration of hydrogen sulfide and a low content of CO ₂ in the acid gas supplied to the Claus process, when implementing the inventive method allows to reduce the energy consumption of the processing process.

The Klaus process is the main process for producing sulfur from hydrogen sulfide and is based on the oxidation of hydrogen sulfide to sulfur.

In a modified version, the oxidation is divided into two stages - thermal and catalytic. At the thermal stage, flame hydrogen sulfide is oxidized by air with a stoichiometric amount of oxygen at 900-1350 ° C. In this case, part of the hydrogen sulfide is oxidized to sulfur dioxide:

At the catalytic stage, there is a reaction between hydrogen sulfide and sulfur dioxide in the presence of a catalyst - bauxite or active aluminum trioxide - at 220-250 ° C.

Simultaneously with such a two-stage formation of sulfur, a direct oxidation reaction proceeds:

Since in addition to hydrogen sulfide other components are present in the composition of acid gases, the following side reactions also occur during combustion:

The technology for producing sulfur by the Klaus method implements the above reactions, usually in three stages. The technological design of the process depends on the composition of acid gas - the content of hydrogen sulfide and hydrocarbons in it. The hydrogen sulfide content determines the stability of combustion of acid gas: when its content is above 45% vol., Combustion is stable, and if it is lower, then appropriate measures must be taken to stabilize combustion (heating gas and air, etc.). The high content of carbon dioxide also negatively affects the combustion process of hydrogen sulfide.

In the proposed method, the preliminary extraction of hydrogen sulfide at the stage of absorption separation by an absorbent with selective selectivity for hydrogen sulfide leads to the fact that in the acid gas entering the Claus process, there will be mainly hydrogen sulfide in an amount of 84-94 vol.% With small impurities of CO ₂ and hydrocarbons. In addition, the volume of acid gas is noticeably reduced due to a sharp decrease in the content of CO ₂ in it. Such an acid gas burns well, which significantly improves the economic performance of the Claus process, improves the degree of purification of sulfur compounds from the exhaust gases, and increases the yield of elemental sulfur.

Block 6 for the implementation of the Klaus process consists of two stages of sulfur production - thermal and catalytic. Acid gas is burned at the thermal stage, and the oxygen in the air is supplied to the furnace in the amount necessary for the oxidation of hydrogen sulfide to sulfur:

At the thermal stage of Klaus plants, cylindrical reactors are used, consisting of a combustion chamber and a tubular heat exchanger. In the end part of the combustion chamber there are burners. The main part of hydrogen sulfide and air is fed through tangential channels. In their mixing zone, combustion occurs in a swirling flow. Then, passing a grate of staggered refractory bricks, the combustion products enter the main combustion chamber of a cylindrical shape of a larger diameter.

Then the combustion products are cooled by water, passing through the tube space of the tubular heat exchanger, and enter the condenser, from where the sulfur obtained in the thermal stage is discharged into the storage. The process gas after the thermal stage, containing unreacted hydrogen sulfide, sulfur dioxide, formed simultaneously with sulfur during the flame combustion of hydrogen sulfide, as well as carbon sulfide and carbon disulfide (products of side reactions occurring in the reactor), is again heated to 220-300 ° C and fed to the catalytic the stage where the main reaction occurs in the catalyst bed:

The sulfur output in the Klaus process usually reaches 95-97% of the theoretically possible value. Through the use of a separate scheme for the extraction of hydrogen sulfide and carbon dioxide, it was possible to increase the yield of sulfur to 99-99.5%.

Sulfur obtained at block 6 is transferred further to block 5 degassing of sulfur. Sulfur obtained at Klaus plants contains dissolved hydrogen sulfide in the form of free hydrogen sulfide and chemically bound hydrogen polysulfide, which leads to its release during storage and transportation of liquid sulfur. Such spontaneous release of hydrogen sulfide from liquid sulfur creates dangerous situations in connection with the toxicity and explosiveness of hydrogen sulfide. The sulfur content of H ₂ S is approximately 100-700 ppm. In addition, non-degassed sulfur is more corrosive to apparatus and equipment. Liquid sulfur, obtained at block 6 of the Klaus process, flows by gravity through underground pipelines to the receiving pit of block 5. The volume of the pit is designed to receive sulfur generated during the day at nominal capacity.

The receiving pit is a semi-underground concrete duct, the arch of which is equipped with two explosive safety valves. To maintain the temperature of liquid sulfur, the receiving pit is equipped with a heating coil, to which low-pressure steam is supplied.

Sulfur is pumped from the receiving well by pumps through a steam-heated pipeline to a sulfur degassing pit, where hydrogen sulfide is removed and compounds of the composition H ₂ S _{x are} destroyed in liquid sulfur.

The design of the degassing pit is similar to the design of the receiving pit. Sulfur degassing is performed once a day. If there is a normal filling level in the pit, the circulation pumps are switched on, while ammonia is fed into the pump inlet zone. Ammonia contributes to the destruction of sulfates and degassing of sulfur. The degassing gas released from sulfur containing hydrogen sulfide is sent to the inlet of unit 2.

After degassing, sulfur is preferably sent to granulation, then shipped to the consumer. But other options for shipment of finished sulfur are possible both in the form of liquid sulfur, and in the form of lumpy or powder sulfur.

Block 8 granulation of sulfur consists of the following technological units: a granulator, a system for separating water and transporting granular sulfur to a warehouse, a sulfur storage site and a system for collecting and neutralizing water.

Liquid sulfur enters the sulfur distributor in the upper part of the granulator where it is poured into sulfur trays heated by steam, then liquid sulfur enters the granulator through perforated sulfur trays in thin streams. Sulfur droplets form from sulfur streams under the influence of gravity and surface tension of liquid sulfur. When a drop of sulfur separates from a stream of sulfur, a fine granule is formed from the tail of the large granule. Its outer surface cools quickly and forms a crust. The inner part of the droplet cools slowly due to the insulating properties of the crust, cooling and contracting towards the already cooled outer part, forms a low pressure point. The pellet shell is destroyed around this point, forming a small recess or hole. The amount of moisture in this hole is quite small, less than 0.1%. Such a low moisture level in granular sulfur is explained by the surface tension of water acting on the surface of the granule, and the fact that the surface of the hole is small compared to the surface of a spherical granule. Drops fall, passing through the cold zone, and by the time they reach the bottom of the conical granulator, they turn into solid smooth granules.

Process water is supplied countercurrently towards sulfuric droplets. They continue to cool gradually, passing through the lower and colder zones of the granulator, which are a chamber for annealing sulfur drops.

Block 7 fractionation of NGL is standard. (An example is the processing unit for NGL and condensate from the Astrakhan gas field). The target products of BFLH processing are: propane-butane fraction (SPBT), technical butane fraction (BT), the top of the condensate fraction - gas - methane. By-products are sulfur and water.

Block 9 of fine purification from hydrogen sulfide

The purpose of the fine block is to stabilize the cleaning process and increase the depth of purification of the exhaust gas of the Klaus process. For additional gas purification from sulfur compounds to a value of ≥99.99%, the use of the method of chemical adsorption of sulfur compounds by iron oxides or adsorbents based on them is proposed. The oxidation process using iron oxides is taken as a basis.

The novelty of the unit for fine purification from hydrogen sulfide is the use of a catalyst for the oxidation process, which is subject to repeated regeneration.

The principle of operation of block 9 is as follows:

Sour gas from the Klaus process passes through the catalyst bed of the column, then through the separator and filter it will be flared. An inert gas (nitrogen) with a small content of air (oxygen) is passed through the second column. The catalyst regenerates. The reaction comes with a great warming up. The blown sulfur flows through separators and a filter into the storage hopper. The columns operate alternately in the cleaning and regeneration mode. Catalyst regeneration schemes are possible in water or in the presence of hot steam.

Example

An example implementation of the inventive method is shown in relation to the technology for purification and processing of crude (formation) natural gas of the Astrakhan field, which was carried out in a pilot plant, a simplified version of which is schematically shown in FIG. 1. On the primary separation unit 1, the raw natural gas stream coming from the field at a pressure of approximately 7 MPa and with a temperature of approximately 30 ° C is divided into a separated natural gas stream (separation gas) and a liquid phase stream including formation water and unstable gas condensate. Water containing mechanical impurities and salts is separated from the liquid phase on block 1, which, after separation of solid particles through a filter, is sent to the water purification unit at block 10, and unstable gas condensate is sent to the gas condensate stabilization unit at block 4 or to the tank farm.

From block 1, the flow of separation gas with a pressure of 6.6 MPa and at a temperature of 39 ° C through the metering point is sent to clean acid components sequentially to blocks 2 and 3. The separation gas has approximately the following composition (in mol.%):

First, the separation gas stream is sent to block 2 for extraction of hydrogen sulfide with an absorbent with selective selectivity for hydrogen sulfide. The allocation of hydrogen sulfide on block 2 is carried out by physical absorption using solutions of absorbents that absorb hydrogen sulfide well and poorly absorb carbon dioxide. In this example, polyethylene glycol dimethyl ether is used as an absorbent. The main element of block 2 is a packed absorber (absorption column). Separation gas at a temperature of 20 ° C and a pressure of 7 MPa enters the lower part of the packed absorber, on top of which a regenerated absorbent is fed, which passes through an air cooler and an irrigation tank to reduce losses of absorbent with purified gas. An absorbent saturated with acidic components and containing a certain amount of hydrocarbons is discharged from the bottom of the absorber.

After the removal of hydrogen sulfide, a stream of natural gas enriched in carbon dioxide is directed to block 3. The gas entering block 3 has approximately the following composition (mol%):

The content of sulfur compounds in the stream entering block 3 is about 5 mg / m ³ , and the main acidic component is carbon dioxide. Block 3, which includes a supersonic separation unit, allows you to divide the natural gas stream into two streams: a stream depleted in CO ₂ is a commodity natural gas based on methane (admixture of CO ₂ ~ 2 wt.%), And a stream enriched in CO ₂ in which the content of CO ₂ ≥95 wt. % In block 3, the gas stream is cooled to a temperature of -70 ° C and enters the inlet of the gas-liquid separator. The gas phase from the specified separator is directed to the inlet of the supersonic separation unit, in which the natural gas is cooled in a supersonic swirling gas stream. The supersonic flow is realized using the Laval confuser-diffuser nozzle, in which the gas accelerates to speeds exceeding the speed of sound propagation in the gas. In this case, strong cooling of the gas occurs. The liquid (carbon dioxide) released as a result of cooling by centrifugal forces with acceleration reaching 10 ⁶ m / s ² is discarded to the walls of the outlet bell, and the purified natural gas (mainly methane) leaves through the diffuser. The purified flow of commercial natural gas exiting the supersonic separation unit is heated in a heat exchanger and sent for compression to the commercial gas compressor. The extracted CO ₂ goes for implementation. In another embodiment, the use of the resulting carbon dioxide may be that it is pumped back into the formation.

Block 3 provides a reduction in the content of CO ₂ in the natural gas stream from 60% to 2.7%.

The unstable gas condensate from the outlet of the primary separation unit 1 and the gas condensate obtained at the outlet of the supersonic separation unit 3 are subjected to the stabilization process at unit 4, while the stabilization gas is returned to the stage of extraction of hydrogen sulfide to block 2, and the hydrogen sulfide from the stage of extraction of hydrogen sulfide is directed to block 6 to the stage of sulfur evolution by direct oxidation in furnaces using the Claus process.

In the proposed method, the preliminary extraction of hydrogen sulfide on block 2 with an absorbent with selective selectivity for hydrogen sulfide leads to the fact that in the acid gas supplied to the Claus process, there will be mainly hydrogen sulfide in the amount of 84-94 vol.% With small impurities of CO ₂ and hydrocarbons. In addition, the volume of acid gas is noticeably reduced due to a sharp decrease in the content of CO ₂ in it. Such an acid gas burns well, which significantly improves the economic performance of the Claus process, improves the degree of purification of sulfur compounds from the exhaust gases, and increases the yield of elemental sulfur. In accordance with the above example, the gas entering block 6 for the Claus process has approximately the following composition (in mol.%):

Block 6 for the implementation of the Klaus process consists of two stages of sulfur production - thermal and catalytic. Acid gas is burned at the thermal stage, and the oxygen in the air is supplied to the furnace in the amount necessary for the oxidation of hydrogen sulfide to sulfur:

At the thermal stage of Klaus plants, cylindrical reactors are used, consisting of a combustion chamber and a tubular heat exchanger. The combustion products are cooled by water, passing through the tube space of the tubular heat exchanger, and enter the condenser, from where the sulfur obtained in the thermal stage is discharged into the storage. The process gas after the thermal stage, containing unreacted hydrogen sulfide, sulfur dioxide, formed simultaneously with sulfur during the flame combustion of hydrogen sulfide, as well as carbon sulfide and carbon disulfide (products of side reactions occurring in the reactor), is again heated to 220-300 ° C and fed to the catalytic the stage where the main reaction occurs in the catalyst bed:

The sulfur output in the Klaus process usually reaches 95-97% of the theoretically possible value. Through the use of a separate scheme for the extraction of hydrogen sulfide and carbon dioxide, it was possible to increase the yield of sulfur to 99-99.5%.

Sulfur obtained at block 6 is transferred further to block 5 degassing of sulfur. Sulfur obtained at Klaus plants contains dissolved hydrogen sulfide in the form of free hydrogen sulfide and chemically bound hydrogen polysulfide, which leads to its release during storage and transportation of liquid sulfur. The spontaneous release of hydrogen sulfide from liquid sulfur creates dangerous situations in connection with the toxicity and explosion hazard of hydrogen sulfide. Therefore, the sulfur obtained at block 6 is degassed at block 5, and the gas from sulfur degassing is again returned to block 2 at the stage of hydrogen sulfide extraction. After degassing, sulfur is preferably sent to block 8 for granulation.

The tail gases obtained in block 6 after the sulfur separation by the Claus process are subjected to fine purification from hydrogen sulfide in block 9 by adsorption of hydrogen sulfide by iron oxides (or adsorbents based on iron oxides) with the direction of the released sulfur also to granulation to block 8, and tail gases after fine cleaning unit 9 is sent to the afterburner (torch).

On said block 4, gas condensate is stabilized to obtain stable gas condensate at the outlet as a finished product. In this case, the output of the stabilization unit 4 for BFLH can either be communicated with the BFLU fractionation unit 7 or the BFLU stream is withdrawn from the installation as a finished product.

The proposed approach to the purification and processing of raw natural gas introduces innovations not only in the sequence of operations of the method for purifying the natural gas stream from acidic components, but also the processes of primary gas processing themselves change the quality and quantity indicators for the better.

Table 1 shows the indicators of the processing process according to the new technological scheme shown in FIG. 1. The calculations were performed for a pilot plant with a gas flow rate of separation of 30,000 nm ³ / hour.

The proposed method allows to achieve a degree of conversion of sulfur compounds, close to 99.9%. For additional purification of gas from sulfur to a value of ≥99.99%, an additional block of fine purification is used using the method of chemical adsorption by iron oxides or adsorbents based on them.

From an environmental point of view, the effectiveness of the new technological scheme is not in doubt. The degree of purification from acid gases increases significantly. Significantly reduced emissions of sulfur-containing compounds in the atmosphere (torch).

From the economic side, new opportunities appear to reduce costs and increase profits due to a new marketable product - pure carbon dioxide (CO2 concentration _of more than 85% makes it possible to obtain, for example, food products).

When using the new technological scheme, the acid gas flow to the Claus plant is reduced by 33%, the reaction time of the combustion of hydrogen sulfide at such higher concentrations in acid gas is reduced by 35-50%. The required capacity of the hydrogen sulfide extraction unit and the fine purification unit is also 33% less. As an advantage, the lower operating costs of these plants should also be taken into account.

The new technology undoubtedly has great environmental and economic advantages over the existing one at the Astrakhan gas processing plant.

Table 1 Name Separated gas
(gas separation) Sour gas entering the Klaus process Gas entering the 3S separation Commodity gas (purified natural gas) Gas afterburning / Torch Consumption of ¹ gas, nm ³ / h 30000 10300 19700 16272 ~ 1800 Pressure, MPa 6.8-7.0 6.8-7.0 4,5 4,5 - Composition,% mol CH ₄ 53.14 ≤2.2 70.71 ≥85 0,0 C ₂ -C ₄ 4.42 ≤2.4 5.48 ≤12.42 0,0 C ₊₅ 3.91 ≤0.214 5.84 0,0 0,0 N ₂ 0.37 - 0.56 0.58 - H ₂ s 25.97 93,032 ≤5 mg / m ³ ≤5.5 mg / m ³ ≤0.01% CO ₂ 12.09 ≤2.0 17.4 ≤2.0 - Mercaptans 0.05 ~ 0,077 ≤10 ^-5 ≤10 ^-5 0,0 CO 0.05 ≤0.077 ≤0.001 ≤0.001 - ¹ flow rate is indicated in cubic meters under normal conditions (nm ³ / h).

Claims (14)

1. A method of processing raw natural gas, including primary separation of the flow of raw natural gas with the separation of water and gas condensate from it and subsequent purification of the gas separation from acidic components containing hydrogen sulfide and carbon dioxide, characterized in that the cleaning of acidic components is carried out in series in two stage: first carry out the stage of extraction of hydrogen sulfide using an absorbent with selective selectivity for hydrogen sulfide, and in the next step, carbon dioxide and residual phases are extracted the gas condensate using supersonic separation, and the gas condensate after the primary separation, as well as after supersonic separation is subjected to a stabilization process, while the stabilization gas is returned to the stage of extraction of hydrogen sulfide, hydrogen sulfide from the stage of extraction of hydrogen sulfide is sent to the stage of sulfur extraction using the Claus process obtained sulfur is degassed, and the gas from sulfur degassing is returned to the hydrogen sulfide recovery step. 2. The method according to p. 1, characterized in that after degassing, sulfur is granulated. 3. The method according to p. 1, characterized in that the tail gases obtained after the separation of sulfur using the Claus process, are subjected to fine purification from hydrogen sulfide by adsorption by iron oxides or adsorbents based on them. 4. The method according to p. 1, characterized in that the water released during the primary separation of crude natural gas containing salts and solids is subjected to filtration and disposal. 5. The method according to p. 1, characterized in that as a result of the stabilization process, a stable gas condensate fraction and a wide fraction of light hydrocarbons (NGL) are isolated. 6. The method according to p. 5, characterized in that the BFLH is subjected to fractionation to produce liquefied gases and with the additional allocation of a fraction of stable gas condensate. 7. The method according to p. 1, characterized in that the supersonic separation step is carried out to obtain a product based on carbon dioxide and a product based on methane in the form of purified natural gas. 8. The method according to p. 7, characterized in that the purified natural gas is obtained when the methane content in an amount of more than 85 vol.% And when the content of carbon dioxide impurities in an amount of not more than 3 vol.%. 9. The method according to p. 7, characterized in that the carbon dioxide-based product is obtained when the content of CO ₂ more than 80 vol.%, Preferably CO ₂ more than 85 vol.%, Most preferably the content of CO ₂ is more than 95 vol.%. 10. The method according to p. 1, characterized in that the absorbent containing polyethylene glycol dimethyl ether is used as an absorbent with selective hydrogen sulfide selectivity. 11. Raw natural gas processing unit, characterized in that it contains interconnected unit 1 for the primary separation of raw natural gas, unit 2 for the extraction of hydrogen sulfide with an absorbent with selective selectivity for hydrogen sulfide, and block 3 for supersonic separation, installed with the possibility of obtaining carbon dioxide and purified natural gas, while the first input of the H ₂ S extraction unit 2 is connected to the first output of the primary separation unit 1, the second output of which is used for outputting water with mechanical and impurities, the third output is connected to the first input of the gas condensate stabilization unit 4, and the input is connected to the raw natural gas supply system, the second and third inputs of the H ₂ S extraction unit 2 are connected respectively to the condensate stabilization unit 4 and sulfur degassing unit 5, and the outputs of this block are connected to the sulfur recovery unit 6 using the Klaus process and to the supersonic separation unit 3, the output of this unit 3 is connected to the second input of the condensate stabilization unit 4, with the possibility of obtaining stable condensate at the output, In this case, the output of the NGL stabilization unit 4 is communicated with the NGL fractionation unit 7, and the sulfur separation unit 6 is connected to the sulfur granulation unit 8 through the Claus process through the sulfur degassing unit 5 and through the fine gas purification unit 9 from hydrogen sulfide. 12. Installation according to claim 11, characterized in that the hydrogen sulfide extraction unit 2 is made in the form of a container containing an absorbent with selective selectivity for hydrogen sulfide. 13. Installation according to claim 11, characterized in that the hydrogen sulfide extraction unit 2 is made in the form of an absorption column containing an absorbent with selective hydrogen sulfide selectivity. 14. Installation according to any one of paragraphs. 12 or 13, characterized in that, as an absorbent with selective hydrogen sulfide selectivity, block 2 contains an absorbent containing polyethylene glycol dimethyl ether.