RU2840008C9 - Liquefied natural gas production plant - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention relates to the gas industry, in particular to the gases and their mixtures liquefaction plants, and can be used to produce the liquefied natural gas (LNG) in the gas distribution station (GDS) conditions. Liquefied natural gas production plant is connected to a natural gas supply source and includes the following units connected by natural gas supply and discharge pipelines: unit of inlet devices with gas measurement, booster-compressor, high and low pressure drying units, high pressure cleaning unit, twisted double-flow heat exchangers: preliminary cooling heat exchanger, external cold source heat exchanger, end heat exchanger and pre-cooling heat exchanger of natural gas of the turboexpander unit, turboexpander unit with an electric generator, as well as ejector, loading unit, high and low pressure separators. Diode bridges are connected in electric generator of turbine expander plant with possibility of obtaining DC voltage. Turboexpander unit electric generator is electrically connected to the regeneration gas electric heaters in the low pressure drying, high pressure drying, high pressure cleaning units, and is also electrically connected, with the possibility of outputting power of industrial voltage and frequency after conversion, with units of the plant that consume electric power in order to ensure zero power consumption from external power supply sources for the production of LNG at the gas distribution station.

EFFECT: ensuring energy saving, increasing efficiency and reliability in the production of LNG at gas distribution stations.

1 cl, 1 dwg

Description

The invention relates to the gas industry, in particular to installations for liquefying gases and their mixtures, and can find application in organizing the process of liquefying natural gas and producing liquefied natural gas (LNG) in a gas distribution station (GDS).

The production and use of LNG as an energy resource is one of the most promising areas of global energy. LNG technologies are increasingly replacing Russia's traditional pipeline supply segment. Liquefied gas produced in small-scale plants can be effectively used to supply households, businesses, and industrial thermal power plants, as well as as a motor fuel. Furthermore, LNG can be used as a backup fuel during peak loads and to maintain distribution networks during gas distribution station maintenance.

LNG production plants, devices, and systems are widely known. One of the simplest technical solutions is a natural gas liquefaction system based on a high-pressure throttle-ejector cycle using an external cold source. The external cold source is typically a freon refrigeration unit, capable of cooling natural gas to -40 to -55°C.

The need to use external cold sources increases LNG production, simultaneously increasing the energy consumption of the liquefaction process, which significantly reduces the energy efficiency of this process. Also, in existing installations and devices, the preparation of natural gas for liquefaction still requires a relatively high level of electricity from external power sources. To improve the energy efficiency of the natural gas liquefaction process, a booster compressor is incorporated into the design of existing liquefaction installations, operating on the energy differential of the compressed gas from the main gas pipeline. For example, the "Liquefied Natural Gas Production Installation" is known, Russian Patent No. 2783611, Class F25J 1/00, published in 2008. November 15, 2022, which comprises a booster compressor, pre- and post-cooling heat exchangers, a drying unit, a cleaning unit, control valves, production and process ejectors, and separators for the preliminary and final separation of the vapor-liquid mixture into vapor and liquid phases, all connected by natural gas supply and outlet pipelines. This well-known gas compression system with a booster compressor allows for partial elimination of the need for external power generation, but does not completely eliminate this requirement.

Also, to generate electricity for the units of a natural gas liquefaction plant at a gas distribution station (GDS), the design of known plants can include a turboexpander unit for recovering the energy obtained during the expansion of natural gas due to the pressure difference at the GDS inlet and outlet. The closest in technical essence to the proposed invention is the natural gas liquefaction plant "Liquefaction of Natural Gas (LNG) in a Gas Distribution Station (GDS)", Russian Federation Patent No. 2673642, Class F25J 1/00, published November 28, 2018. This known technical solution is aimed at increasing the efficiency of the natural gas liquefaction process through the use of a turboexpander unit. The known installation includes a gas purification unit, a turboexpander unit with an electric generator, a main-cycle compressor, a natural gas liquefaction unit with an integrated expander and flash cycle, a tank farm for an LNG storage facility, a commercial LNG distribution unit, and a flare unit. While energy savings are claimed, the known installation utilizes electrically driven compressors that consume electricity from external power sources. All energy extracted through the use of a turboexpander unit requires additional conversion to industrial frequency before use in the units of the known installation. This complicates the design of the electric generator, reducing its reliability and the overall reliability of the known installation. Furthermore, a multi-flow heat exchanger is used for the liquefaction process, which also negatively impacts the reliability and efficiency of the known installation.

The objective of the invention is to ensure energy conservation, increase efficiency and reliability in the production of LNG at gas distribution stations.

The technical result of the invention is the development of a simple, reliable installation, entirely based on domestic components, ensuring zero consumption of electricity from external power sources for the production of liquefied natural gas in gas distribution stations.

The stated objective and the required technical result are achieved due to the fact that the liquefied natural gas production unit is connected to a natural gas supply source and comprises the following units, connected by natural gas supply and outlet pipelines: a block of inlet devices with gas metering, a booster compressor, high-pressure and low-pressure drying units, a high-pressure cleaning unit, coiled two-flow heat exchangers: a pre-cooling heat exchanger, a heat exchanger of an external cold source, an end heat exchanger and a heat exchanger for pre-cooling natural gas of a turboexpander unit, a turboexpander unit with an electric generator, as well as an ejector, an unloading unit, high-pressure and low-pressure separators. The main pipeline with the natural gas flow from the natural gas supply source is connected to the inlet of the block of inlet devices with gas metering, at the outlet of which the main pipeline with the natural gas flow is divided into two pipelines: a production flow pipeline and a process flow pipeline. The process flow pipeline is connected to the inlet of the low-pressure drying unit and is then connected in series with the possibility of successive passage through the natural gas pre-cooling heat exchanger of the turboexpander unit, the turboexpander unit, the heat exchanger of the external cold source and again through the natural gas pre-cooling heat exchanger of the turboexpander unit, to one of the outlets of which a pipeline for the removal of unliquefied gas from the process flow is connected with the possibility of directing the unliquefied gas flow into the low-pressure network. The product flow pipeline is connected to the inlet of the booster compressor and is then connected in series with the possibility of successive passage through the high-pressure drying unit, the high-pressure cleaning unit, the pre-cooling heat exchanger, the heat exchanger of the external cold source, the end heat exchanger, the ejector, the high and low pressure separators, the unloading unit for supplying liquefied natural gas to the consumer. The vapor phase pipeline from one of the outlets of the high-pressure separator is connected to the inlet of the end heat exchanger and then connected in series with the possibility of successive passage through the pre-cooling heat exchanger with the possibility of heating the vapor phase from the heat of the product gas stream. The vapor phase pipeline from one of the outlets of the low-pressure separator is connected to the inlet of the ejector suction chamber with the possibility of connecting with the product gas stream. The first and second pipelines for removing unliquefied gas from the product stream are connected to the outlets of the booster compressor and the pre-cooling heat exchanger, respectively, with the possibility of directing the unliquefied gas stream into the low-pressure network. Diode bridges with the possibility of obtaining direct current voltage are connected in the electric generator of the turboexpander unit, wherein the electric generator of the turboexpander unit is electrically connected to the electric heaters of the regeneration gas in the low-pressure drying unit, in the high-pressure drying unit, in the high-pressure cleaning unit with the possibility of generating electric power with a voltage and frequency higher than the industrial ones. The turboexpander unit's electric generator is electrically connected, with the ability to produce electric power of industrial voltage and frequency after conversion, to the units of the unit that consume electric power, with the ability to ensure zero consumption of electric power from external power sources for the production of liquefied natural gas.

The liquefaction unit's design is simple and reliable, using entirely domestically produced components. The process of producing LNG at a gas distribution station using this unit is efficient and completely energy-independent, as the simultaneous use of a booster compressor operating on the differential pressure of compressed gas from the main gas pipeline and a turboexpander unit with an integrated electric generator eliminates the need for external refrigeration sources and external power supplies for the LNG production process at the gas distribution station. The inclusion of diode bridges in the turboexpander unit's electric generator allows for the supply of electricity with a voltage and frequency higher than industrial standards to the liquefaction unit, reducing power conversion losses and thereby enabling the most efficient use of the generated electricity. The use of double-flow, twisted-coil heat exchangers in the liquefaction unit simplifies the design and improves its reliability.

The present invention and its advantages will be better understood by reference to the following detailed description and the accompanying drawing (Fig. 1). The drawing shows a diagram of one embodiment of this invention. The drawing does not exclude from the scope of the invention other embodiments that result from normal and intended modifications of this specific embodiment. Various required auxiliary devices, such as valves, flow mixers, and sensors, have been omitted from the drawing for the sake of simplicity.

The liquefied natural gas production unit is connected to a natural gas supply source, mounted on a gas distribution station and connected to a main pipeline. The unit comprises the following units connected by natural gas supply and discharge pipelines: a unit 1 of inlet devices with gas metering, a booster compressor 2, a high-pressure drying unit 3, a low-pressure drying unit 8, a high-pressure cleaning unit 4, a turboexpander unit 10, an electric generator 15 of the turboexpander unit 10, a pre-cooling heat exchanger 5, a heat exchanger 6 of an external cold source, an end heat exchanger 7 and a heat exchanger 9 for pre-cooling natural gas of the turboexpander unit 10, an ejector 11, a high-pressure separator 12, a low-pressure separator 13, and an LNG unloading unit 14. The unit includes a process flow non-liquefied gas removal pipeline and first and second non-liquefied gas removal pipelines for the product flow. To simplify the design and improve operational reliability, all heat exchangers in the unit are double-wound, coiled-coil units.

In one specific implementation, but not limited to, the unit is mounted on a gas distribution station (GDS), uses a natural gas main pipeline as the natural gas supply source, and operates as follows. Natural gas enters the liquefaction unit and is directed to Block 1 of inlet devices with gas metering, where the flow rate of the incoming natural gas is measured and its component composition is determined. At the outlet of Block 1, the natural gas pipeline is divided into two pipelines: a production pipeline and a process pipeline.

The natural gas production pipeline is connected to the inlet of booster compressor 2. Booster compressor 2, which operates using the energy differential of compressed gas from the main gas pipeline, compresses the natural gas. The compressed natural gas flow, at a pressure of no more than 25 MPa, is then fed from booster compressor 2 through the production pipeline to the inlet of high-pressure drying unit 3, where moisture is absorbed from the natural gas to a concentration corresponding to a water dew point no higher than minus 60°C. The compressed natural gas flow then enters high-pressure cleaning unit 4, where carbon dioxide ( _CO2 ) is removed from the natural gas. CO2, when the temperature drops below the solubility limit for a given concentration, can crystallize during methane liquefaction, thereby disrupting the unit's operation. High-pressure cleaning unit 4 also removes other acidic components from the compressed natural gas flow. The prepared (dried and purified) compressed natural gas of the production stream passes sequentially through three heat exchangers: pre-cooling heat exchanger 5, external cold source heat exchanger 6, and final heat exchanger 7, where it is pre-cooled. It is then directed to ejector 11, where its pressure is reduced. After ejector 11, the natural gas of the production stream with a pressure of 1.3 MPa enters high-pressure separator 12. In high-pressure separator 12, the two-phase mixture of natural gas is separated into liquid and vapor phases. The vapor phase pipeline from one of the outlets of high-pressure separator 12 is connected to one of the inlets of final heat exchanger 7, and is then connected in series to one of the inlets of pre-cooling heat exchanger 5. Passing heat exchangers 5 and 7, the vapor phase is heated due to heat removal from the production stream. The heated gas is discharged into a low-pressure network (0.3-1.2 MPa). The liquid phase formed in the high-pressure separator 12 passes through a throttle (not shown in the drawing), where, when the pressure drops to 0.3 MPa, a two-phase flow is formed, which, in turn, is directed to the low-pressure separator 13, which is a cryogenic tank for storing LNG. After the low-pressure separator 13, through the LNG unloading unit 14, the liquid phase with the required parameters: temperature minus 141.1°C, pressure 0.3 MPa, is directed to the outlet for supplying liquefied natural gas to the consumer. The vapor phase pipeline from one of the outlets of the low-pressure separator 13 is connected to the inlet of the suction chamber of the ejector 11, in which, after increasing the pressure, it is mixed with the product stream leaving the end heat exchanger 7.

The pipeline of the process flow of natural gas is connected to the inlet of the low-pressure drying unit 8, where the natural gas is dried to a dew point temperature of no higher than minus 70°C. To obtain an additional source of cold, the unit is provided with a turboexpander unit 10 with a pre-cooling heat exchanger 9. At the outlet of the low-pressure drying unit 8, the pipeline of the process flow is connected to the inlet of the natural gas pre-cooling heat exchanger 9 of the turboexpander unit 10, where the gas is pre-cooled, and is directed to the turboexpander unit 10. In the turboexpander unit 10, the process of expansion of natural gas occurs with a simultaneous decrease in its pressure and temperature. Further, the pipeline of the process flow is connected in series through the heat exchanger 6 of the external cold source and the heat exchanger 9 of the natural gas pre-cooling heat exchanger of the turboexpander unit 10. Passing the heat exchanger 6 of the external cold source, the process flow gas additionally cools the product gas stream. Next, in the natural gas pre-cooling heat exchanger 9 of the turboexpander unit 10, it is further heated and sent via the process flow's unliquefied gas outlet pipeline to the low-pressure network for delivery to the consumer of natural gas with the required parameters. The first and second unliquefied gas outlet pipelines of the product flow are connected to one of the outlets of the booster compressor 2 and the pre-cooling heat exchanger 5, respectively, through which the unliquefied gas stream is sent to the low-pressure network for delivery to the consumer of natural gas with the required parameters. Diode bridges (not shown in the drawing) are connected in the electric generator 15 of the turboexpander unit 10 to generate DC voltage. The electric generator 15 of the turboexpander unit 10 is electrically connected (shown by dashed lines in the drawing) to the regeneration gas electric heaters (not shown in the drawing) installed in the low-pressure drying unit 8, in the high-pressure drying unit 3, and in the high-pressure cleaning unit 4. To power the regeneration gas electric heaters, electric power with a voltage and frequency higher than the industrial ones is supplied from the electric generator 15, thereby reducing the electric power conversion losses. In addition, the electric generator 15 of the turboexpander unit 10 is electrically connected with the possibility of outputting electric power of industrial voltage and frequency after conversion to all units of the unit consuming such electric power: electric power is supplied to the unit 1 of input devices with gas metering, to the LNG unloading unit 14, and is used to power flow meters, pumps, and actuators (not shown in the drawing).

Thus, the design of the natural gas liquefaction plant with a gas-driven booster compressor 2 and a turboexpander unit 10 with a connected electric generator 15 eliminates the need for external refrigeration sources and eliminates the need for external power supplies, making the LNG production process at the gas distribution station completely energy-independent. The inclusion of diode bridges in the turboexpander unit's electric generator allows the liquefaction plant to operate with electricity at a voltage and frequency higher than industrial standards, reducing energy conversion losses and efficiently utilizing the recovered electricity. The use of coiled, dual-flow heat exchangers 5, 6, 7, and 9 in the liquefaction plant simplifies the plant's design and improves its operational reliability.

Claims (1)

A liquefied natural gas production plant connected to a natural gas supply source, comprising the following units connected by natural gas supply and outlet pipelines: a unit of inlet devices with gas metering, a booster compressor, high and low pressure drying units, a high pressure cleaning unit, coiled two-flow heat exchangers: a pre-cooling heat exchanger, an external cold source heat exchanger, an end heat exchanger and a pre-cooling heat exchanger of the natural gas of a turboexpander unit, a turboexpander unit with an electric generator, as well as an ejector, an unloading unit, high and low pressure separators, in which the main pipeline with a flow of natural gas from the natural gas supply source is connected to the inlet of the unit of inlet devices with gas metering, at the outlet of which the main pipeline with a flow of natural gas is divided into two pipelines: a production flow pipeline and a process flow pipeline, wherein the process flow pipeline is connected to the inlet of the low pressure drying unit and is then connected in series with the possibility of sequentially passing through a heat exchanger for pre-cooling natural gas of a turboexpander unit, a turboexpander unit, a heat exchanger of an external cold source and again through the heat exchanger for pre-cooling natural gas of a turboexpander unit, to one of the outputs of which a pipeline for removing unliquefied gas of the process flow is connected with the possibility of directing the unliquefied gas flow into the low-pressure network, and the pipeline of the production flow is connected to the inlet of the booster compressor and is then connected in series with the possibility of successive passage through a high-pressure drying unit, a high-pressure cleaning unit, a pre-cooling heat exchanger, a heat exchanger of an external cold source, an end heat exchanger, an ejector, high and low pressure separators, an unloading unit for supplying liquefied natural gas to the consumer, wherein the pipeline of the vapor phase from one of the outputs of the high-pressure separator is connected to the inlet of the end heat exchanger and is then connected in series with the possibility of successive passage through the pre-cooling heat exchanger with the possibility of heating the vapor phase from the heat of the production gas flow, also, the pipeline of the vapor phase from one of the outlets of the low-pressure separator it is connected to the inlet of the suction chamber of the ejector with the possibility of connecting with the production gas flow, in addition, the first and second pipelines for removing unliquefied gas from the production flow are connected to the outlets of the booster-compressor and the preliminary cooling heat exchanger, respectively, with the possibility of directing the unliquefied gas flow into the low-pressure network, and in the electric generator of the turboexpander unit, diode bridges are connected with the possibility of obtaining a direct current voltage, wherein the electric generator of the turboexpander unit is electrically connected with the electric heaters of the regeneration gas in the low-pressure drying unit, in the high-pressure drying unit, in the high-pressure cleaning unit with the possibility of generating electric power with a voltage and frequency higher than the industrial ones, in addition, the electric generator of the turboexpander unit is electrically connected, with the possibility of generating electric power of industrial voltage and frequency after conversion, with the units of the unit consuming electric power, with the possibility of ensuring zero consumption of electric power from external power supply sources for the production of liquefied natural gas.