RU2770777C1 - "mosenergo-turbokon" method for liquishing, storing and gasification of natural gas - Google Patents

Abstract

FIELD: liquefaction technology.

SUBSTANCE: invention relates to the technology of liquefaction, storage and gasification of natural gas and can be applied in the processing of natural gas. The method consists in the fact that natural gas coming from an external network is divided into technological and production flows. The purified production stream is cooled and condensed with a refrigerant stream, throttled and separated in the production stream separator with the gas fraction removed to the vapor collection header and the liquefied part of the production stream is supplied to the operational storage. The process flow is divided into two flows with the supply of these flows to the intermediate and end heat exchangers for cooling the compressed refrigerant. The heated streams are combined, expanded, heated in the refrigerant pre-cooling heat exchanger and fed into the network of the consumer object. The refrigerant after the pre-cooling heat exchanger of the production stream is compressed, cooled, expanded and served as a cooling stream. Part of the liquefied gas from the operational storage is throttled and fed into the heat exchanger for liquefying the vapor supplied from the backup storage. To switch to liquefied natural gas, it is supplied from the backup storage to the gasifier and gasified LNG is supplied to the consumption facility network. Shipment of liquefied gas to consumers is carried out from the operational storage and/or from the backup storage. The reserve storage is replenished with liquefied gas from the operational storage.

EFFECT: reduction of losses and reduction of emissions of greenhouse gases and harmful substances into the atmosphere.

1 cl, 1 dwg

Description

The invention relates to the technology of liquefaction, storage and gasification of natural gas natural gas and can be used in the processing of natural gas used as a fuel in the generation of electricity and heat, in energy technology complexes that provide backup and emergency fuel supply to electric power and heat supply facilities.

From the existing prior art, a boil-off gas treatment method is known, according to which the boil-off gas generated in and discharged from liquefied gas storage tanks is compressed in stages with direct cooling in a compressor to a high pressure and fed to the engine of a floating vehicle with injection of high-pressure natural gas approximately 150 to 400 bar, eg MEGI engine. At the same time, the boil-off gas stream is divided into the first stream and the second stream, where the first stream is fed as fuel to the engine with high-pressure natural gas injection, and the second stream is returned to the storage tank after re-liquefaction in a heat exchanger that heats the second compressed boil-off gas stream. with the flow of boil-off gas discharged from the storage tanks for supply to the compressor (see, for example, RU 2642713C1, published on 01/25/2018).

The disadvantage of this technical solution is the compression of the boil-off gas in compressors, which is accompanied by gas leaks, which during long-term storage will lead to a decrease in the proportion of methane in the tanks for storing liquefied gas.

In the claimed invention, the condensation of liquefied natural gas vapor from the reserve tank is carried out by evaporating the reduced stream of liquefied natural gas (LNG) from the operational tank, while this process takes place in a sealed heat exchanger, in which there are no moving parts and, as a result, there are no leaks through seal units.

From the existing level of technology, a method for liquefying natural gas is known, which consists in the fact that the gas taken off before the gas distribution station (GDS) is dried and divided into production and process streams, the process stream is compressed in the compressor of a turbo-expander unit (TDA), cooled and sent to the TDA expander, where the process stream is cooled and then sent sequentially to heat exchangers for cooling the process and production gas streams, after which it is sent to the outlet, the production stream is cleaned from CO ₂ , part of the gas of the production stream after cleaning is sent to the process stream before it is compressed in the TDA compressor, the rest of the production flow is cooled sequentially in the heat exchanger by the process flow and in the cryogenic heat exchanger by the evaporation gas from the end separator and the process gas flow from the TDA expander, after which the production flow is throttled and the resulting vapor-liquid mixture is sent into the end separator, from which liquefied gas is sent to storage tanks (see, for example, RU 2678236 C1, published on 01/24/2019).

From the existing level of technology, a method for the production of liquefied natural gas is known, in which natural gas is taken from the main pipeline, cleaned of mechanical particles, dried, then separated into production and process streams, of which at least one is compressed and cooled after compression, the production stream is purified from CO ₂ impurities, cooled, passed through a throttle to obtain a vapor-liquid mixture, from which the liquid phase is separated for downloading to the LNG consumer. The process stream is purified from impurities, then it is passed through an expander, purified from impurities and the incoming gas stream is compressed before it is separated into process and production streams, the process stream is passed through an expander equipped with a gas turbine. The torque of the gas turbine is used to compress the incoming gas stream before separating it into process and production streams. The process stream is cleaned from impurities of heavy hydrocarbons by their condensation in the expander nozzle apparatus, which is made of a heat-conducting material, while the liquid phase is supercooled before downloading into the consumer tank (see, for example, RU 2541360 C1, published on February 10, 2015).

The general disadvantages of the above technical solutions in relation to the claimed invention are:

The need to dry both production and process gas flows, which leads to an increase in the size and cost of drying plants, an increase in the consumption of consumables and energy to support the process;

The proposed methods provide only partial liquefaction of the production stream, which leads to a significant increase in the proportion of ethane in liquefied natural gas (LNG). Due to the higher density of ethane relative to methane, an increase in the proportion of ethane will lead to the need for additional adjustment of fuel supply systems designed to supply natural gas to boilers.

From the existing prior art, a method is known for reducing the pressure and liquefying natural gas, according to which natural gas coming from a gas pipeline is heated, expanded in a turboexpander and liquefied in an evaporator with preliminary pressure reduction and purification, after which the liquefied gas is supplied to the storage, while energy , recovered in the process of gas expansion, is used in the form of electrical energy in the node for the production of liquefied gas, and the heat obtained from the liquefaction of natural gas is used to heat the natural gas before its expansion. The process takes place with the participation of a refrigerant, the operation of which is carried out in a closed circuit (see, for example, RU 2680285C2, published on 03/30/2017).

The disadvantages of this technical solution in relation to the claimed invention are:

the production gas stream before liquefaction is expanded in the expander, which leads to a decrease in pressure and temperature of gas condensation. The temperature of the refrigerant must be below the liquefaction temperature of the gas. The lower the temperature of the refrigerant, the higher the energy required to drive the refrigerant compressor. The specified energy costs are provided during expansion of the process gas in the expander, therefore, the lower the condensation pressure of the production stream, the higher the flow rate of the process gas that must be passed through the expander;

the use of a known technical solution for facilities with low inlet gas pressure will require an increase in the share of the process flow in the total flow in comparison with the proposed method and, as a result, a decrease in the performance of the system as a whole.

The task to be solved by the claimed invention is to create a method for liquefying, storing and gasification of natural gas, which ensures the supply of electric and thermal stations with environmentally friendly reserve and emergency fuel, with the implementation in the specified method of technological processes of liquefaction, long-term storage and gasification of natural gas exclusively due to the use of secondary energy resources available at the facility, such as overpressure coming from the external natural gas network, and waste heat from the technological systems of the consumption facility, such as heat from water from the circulating cooling system of power equipment and / or water from the flue gas heat recovery system.

This problem is solved due to the fact that in the method of liquefaction, storage and gasification of natural gas, according to the invention, natural gas coming from an external network is divided into process and production streams;

excess carbon dioxide and moisture are removed from the production stream, the purified and dried production stream is cooled in the pre-cooling heat exchanger of the production stream by transferring heat to the cooling refrigerant stream, then the production stream is condensed in the cryogenic heat exchanger by transferring heat to the cooling refrigerant stream, the liquefied production stream is passed through the throttle and separate the gas fraction in the separator of the production stream with the withdrawal of the specified fraction in the header for collecting vapors and supplying the liquefied part of the production stream to the operational storage;

the process flow is divided into two flows with the supply of these flows to the intermediate and end heat exchangers for cooling the refrigerant compressed in the compressor, the heated flows are combined into a common process flow and subjected to expansion in the expander, the mechanical power of which is transferred to the shaft of the refrigerant compressor, then the process flow is heated in the preheater cooling the refrigerant with its subsequent issuance to the network of the consumer object;

the refrigerant circulating in a closed refrigeration circuit after the pre-cooling heat exchanger of the production stream is subjected to compression in the compressor of the expander-compressor unit and cooled in the refrigerant pre-cooling heat exchanger by transferring heat to the process gas flow, after which the refrigerant is subjected to compression in the refrigerant compressor with sequential cooling in the intermediate and end cooling heat exchangers by separated process gas streams, then the compressed refrigerant is cooled in the pre-cooling heat exchanger of the production stream by transferring heat to the cooling refrigerant stream and expanded in the expander with the generation of mechanical power, which is transferred to the compressor of the expander-compressor unit, while the temperature of the refrigerant decreases relative to the condensation temperature of the production flow, then the refrigerant at a temperature lower than the condensation temperature of the production stream, served as a cooling stream in a cryogenic heat exchanger and then in the pre-cooling heat exchanger of the production stream;

part of the liquefied gas from the operational storage is throttled, followed by the supply of the cooled gas-liquid flow to the heat exchanger for liquefying the vapor supplied from the reserve storage, then the gasified flow is fed to the heat exchanger-recuperator for cooling and partial condensation of the compressed gas; after that, the gas flow is compressed in the auxiliary compressor with intermediate and subsequent cooling of the flow by the coolant from the cooling system of the gas consumption facility; cool and partially condense the gas stream compressed in the auxiliary compressor in the heat exchanger-recuperator by transferring heat to the gas stream from the heat exchanger for liquefying the vapor from the backup storage; after that, the gas-liquid flow is subjected to throttling with the separation of liquid and gas fractions in the auxiliary separator; the liquid fraction is returned from the auxiliary separator to the operational storage, and the gas fraction is diverted to the evaporation collector; the vapor from the operational storage is diverted to the vapor collection manifold, the boil-off gas from the vapor collection manifold is diverted to the pipeline for the issuance of liquefied gas for gasification and then through the gasifier to the network of the consumer object;

to switch to liquefied natural gas supply, it is supplied from the reserve storage by a pump to the gasifier with flow control by returning part of the liquid through the bypass line to the reserve storage, evaporated in the gasifier due to the heat of water supplied from the technological systems of the gas consumption facility and fed to the facility network consumption; shipment of liquefied gas to consumers is carried out from the operational storage and / or from the backup storage; replenishment of the backup storage with liquefied gas is carried out from the operational storage.

The technical result, due to the above set of features, is to provide: liquefaction of natural gas at electric and thermal power plants solely due to excess pressure of network gas, long-term storage of liquefied natural gas without loss and change in the fuel composition corresponding to the composition of the source gas, gasification of liquefied natural gas during the transition for reserve fuel exclusively at the expense of secondary heat sources of the gas consumption facility, as well as reducing emissions of greenhouse gases and harmful substances into the atmosphere when operating on reserve fuel by replacing fuel oil, diesel fuel, coal and other low-economy types of reserve and emergency fuel with liquefied natural gas, which is produced and accumulated during the operation of stations on the main fuel.

In the claimed invention, the production stream is liquefied at a pressure slightly different downward from the pressure in the external network, which makes it possible to obtain an economically justified performance of the LNG energy technology complex at an external network pressure of 0.6-1.2 MPa, typical for large thermal power plants and thermal stations, while providing a component composition of LNG, almost identical to the composition of the original network gas. The latter circumstance makes it possible to burn LNG after gasification without additional adjustment of fuel-consuming devices and automation. The claimed invention contains new technical solutions for integrating the liquefaction system, LNG storage and gasification system into a single energy-technological complex, which allow:

ensure long-term storage of the LNG reserve volume without changing the component composition and losses, which is achieved through the use of LNG from the operational storage as a cooling coolant;

to maintain the operating cryogenic temperature of the metal of the LNG dispensing pipeline for gasification, which makes it possible to promptly transfer gas consumption facilities from supplying with network gas to supplying LNG;

carry out gasification of LNG using waste heat removed with water from the condensers of steam turbines and other power equipment, as well as use the heat of flue gases emitted into the atmosphere, since the available thermal capacity of these sources for large plants is several times higher than the capacity required for gasification of reserve LNG ;

eliminate the consumption of additional fuel for LNG gasification when operating on reserve fuel and at the same time have relatively compact and powerful gasifiers through the use of secondary heat sources.

The essence of the claimed method is illustrated by the example of the energy technology operation, the scheme of which is shown in Fig. 1 with the following positions:

1 - cleaning and drying unit

2 - pre-cooling heat exchanger of the production flow

3 - cryogenic heat exchanger

4 - product flow separator

5 - vapor collection manifold

6 - operational storage

7 - intermediate heat exchanger

8 - end heat exchanger

9 - expander

10 - refrigerant compressor

11 - refrigerant pre-cooling heat exchanger

12 - compressor of the expander-compressor unit

13 - expander

14 - vapor liquefaction heat exchanger

15 - backup storage

16 - heat exchanger-recuperator

17 - auxiliary compressor

18 - auxiliary separator

19 - gasifier

20 - pump

The method of liquefaction, storage and gasification of natural gas is carried out as follows.

Natural gas from the external network is divided into technological and production streams.

The production stream is fed into the block 1 cleaning and drying. The cleaned and dried product stream is cooled in the pre-cooling heat exchanger 2 of the product stream. The product stream after the pre-cooling heat exchanger 2 is condensed in the cryogenic heat exchanger 3. After that, the liquefied product stream is subjected to throttling, then the gas fraction and the liquefied part of the product stream are separated in the product stream separator 4. The gas fraction of the production stream is diverted to the collector 5 for collecting vapors, and the liquefied part of the production stream is poured into the operational storage 6.

The process stream is divided into two gas streams with separate supply of these streams to the intermediate heat exchanger 7 and the end heat exchanger 8 for cooling the compressed refrigerant. The process gas streams heated in heat exchangers 7 and 8 are combined into a common stream with subsequent expansion of the total process gas stream in expander 9, the mechanical power of which is transferred to the shaft of the refrigerant compressor 10. Next, the process gas flow is heated in the heat exchanger 11 for pre-cooling the refrigerant, followed by the issuance of the process gas to the network of the consumer object.

The refrigerant circulating in a closed refrigeration circuit after the pre-cooling heat exchanger 2 of the production stream is compressed in the compressor 12 of the expander-compressor unit, followed by cooling in the refrigerant pre-cooling heat exchanger 11. Next, the refrigerant is compressed in the refrigerant compressor 10 with cooling in the intermediate and end heat exchangers 7.8. The compressed refrigerant is cooled in the heat exchanger 2 for pre-cooling the production stream, followed by expansion in the expander 13 of the expander-compressor unit, the mechanical power of which is directed to the drive of the compressor 12 of the expander-compressor unit. The refrigerant, which in the process of expansion in the expander 13 has cooled to a temperature below the condensation temperature of the production stream, is fed into the cryogenic heat exchanger 3 and then into the heat exchanger 2 for pre-cooling the production stream.

Part of the liquefied gas from the operational storage 6 is throttled, followed by the supply of the cooled gas-liquid flow to the vapor liquefaction heat exchanger 14, while the liquefied vapor is fed to the specified heat exchanger from the reserve storage 15. In the vapor liquefaction heat exchanger 14, the flow from the operational storage 6 is completely gasified using heat condensation of vapor from the reserve storage 15. After that, the gas flow is fed into the heat exchanger-recuperator 16 for cooling and partial condensation of the compressed gas, after which it is compressed in the auxiliary compressor 17 with intermediate and subsequent cooling by the coolant from the cooling system of the gas consumption object. After the auxiliary compressor 17, the gas stream is cooled and partially condensed in the heat exchanger-recuperator 16, followed by throttling and separation of the liquid and gas fractions in the auxiliary separator 18. The liquid fraction from the auxiliary separator 18 is returned to the operational storage 6, and the gas fraction is diverted to the vapor collection collector 5 Evaporation from operational storage 6 is also diverted to the evaporation collector 5.

The boil-off gas from the vapor collection collector 5 is fed into the pipeline for the issuance of liquefied gas for gasification and then through the gasifier 19 into the network of the consumer object. Thus, the operating temperature of the metal of the specified pipeline is maintained, which reduces the time required to restore the gas supply to the facility when switching from network gas consumption to LNG supply.

When switching to LNG supply, liquefied gas from the backup storage 15 is fed by the pump 20 to the gasifier 19, while the flow control is carried out by returning part of the liquid through the bypass line to the backup storage 15. The liquefied gas is evaporated in the gasifier 19 due to the heat of the water supplied from the process systems gas consumption facility (equipment cooling systems, flue gas heat recovery systems). The gas flow from the gasifier 19 is fed into the network of the facility, providing the production of electrical and thermal energy.

After the reserve storage 15 is filled with the standard volume of the reserve LNG fuel, it is shipped to consumers, while the shipment can be carried out from the operational 6 and/or from the backup 15 storages. If necessary, the backup storage 15 is replenished with liquefied gas from the operational storage 6.

Claims (1)

A method for liquefying, storing and gasifying natural gas, characterized in that natural gas coming from an external network is divided into process and production streams; excess carbon dioxide and moisture are removed from the production stream, the purified and dried production stream is cooled in the pre-cooling heat exchanger of the production stream by transferring heat to the cooling refrigerant stream, then the production stream is condensed in the cryogenic heat exchanger by transferring heat to the cooling refrigerant stream, the liquefied production stream is passed through the throttle and separate the gas fraction in the separator of the production stream with the withdrawal of the specified fraction in the header for collecting vapors and supplying the liquefied part of the production stream to the operational storage; the process flow is divided into two flows with the supply of these flows to the intermediate and end heat exchangers for cooling the refrigerant compressed in the compressor, the heated flows are combined into a common process flow and subjected to expansion in the expander, the mechanical power of which is transferred to the shaft of the refrigerant compressor, then the process flow is heated in the preheater cooling the refrigerant with its subsequent issuance to the network of the consumer object; the refrigerant circulating in a closed refrigeration circuit after the pre-cooling heat exchanger of the production stream is subjected to compression in the compressor of the expander-compressor unit and cooled in the refrigerant pre-cooling heat exchanger by transferring heat to the process gas flow, after which the refrigerant is subjected to compression in the refrigerant compressor with sequential cooling in the intermediate and end cooling heat exchangers by separated process gas streams, then the compressed refrigerant is cooled in the pre-cooling heat exchanger of the production stream by transferring heat to the cooling refrigerant stream and expanded in the expander with the generation of mechanical power, which is transferred to the compressor of the expander-compressor unit, while the temperature of the refrigerant decreases relative to the condensation temperature of the production flow, then the refrigerant at a temperature lower than the condensation temperature of the production stream, p pass as a cooling stream to a cryogenic heat exchanger and then to a pre-cooling heat exchanger of the production stream; part of the liquefied gas from the operating storage is throttled, followed by the supply of the cooled gas-liquid flow to the vapor liquefaction heat exchanger supplied from the backup storage, then the gasified flow is fed to the heat exchanger-recuperator for cooling and partial condensation of the compressed gas; after that, the gas flow is compressed in the auxiliary compressor with intermediate and subsequent cooling of the flow by the coolant from the cooling system of the gas consumption object; cool and partially condense the gas stream compressed in the auxiliary compressor in the heat exchanger-recuperator by transferring heat to the gas stream from the heat exchanger for liquefying the vapor from the backup storage; after that, the gas-liquid flow is subjected to throttling with the separation of the liquid and gas fractions in the auxiliary separator; the liquid fraction is returned from the auxiliary separator to the operational storage, and the gas fraction is diverted to the evaporation collector; the vapor from the operational storage is diverted to the vapor collection collector, the boil-off gas from the vapor collection collector is diverted to the pipeline for the issuance of liquefied gas for gasification and then through the gasifier to the network of the consumer object; to switch to liquefied natural gas supply, it is supplied from the reserve storage by a pump to the gasifier with flow control by returning part of the liquid through the bypass line to the reserve storage, evaporated in the gasifier due to the heat of water supplied from the technological systems of the gas consumption facility, and fed to the network the object of consumption; shipment of liquefied gas to consumers is carried out from the operational storage and / or from the backup storage; replenishment of the backup storage with liquefied gas is carried out from the operational storage.

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