RU2738531C1 - Integrated cooling unit of natural gas - Google Patents

Abstract

FIELD: oil, gas and coke-chemical industries.

SUBSTANCE: invention relates to cooling of natural gas and can be used in complexes combining gas processing and gas-chemical plants. Integrated natural gas refrigeration unit is connected to natural gas pipeline at booster compressor station outlet by auxiliary input pipeline, along which part of high-pressure warm natural gas flow is supplied to integrated plant and divided into two flows. First flow is supplied via the first pipeline to the expander inlet for expansion and cooling. Outlet of the expander is connected to the first input of the recuperative heat exchanger by the second pipeline. Second flow through the third pipeline is directed to the second input of the recuperative heat exchanger for cooling by the flow of expanded and cooled natural gas. First flow is supplied via the first outlet of the recuperative heat exchanger to the booster compressor station along the fourth pipeline. Second flow is fed through the second outlet of the recuperative heat exchanger to the gas supplied to the main gas line and/or to the gas supplied to the liquefied natural gas production.

EFFECT: invention reduces power consumption.

5 cl, 1 dwg

Description

The invention relates to a natural gas cooling unit and can be used as part of complexes that combine gas processing and gas chemical enterprises.

Before being fed into the main gas pipeline, natural gas is cooled in air coolers (hereinafter AVO) to 20-40 ° C due to its heating when compressed at booster compressor stations (hereinafter BCS), which causes a decrease in gas density, an increase in its speed and an indirect increase in the drop pressure on transportation. However, due to the low heat transfer coefficient in the air-natural gas system, the air cooling unit requires a large heat transfer surface. In addition, due to seasonal changes in air temperature, AVOs do not provide the required temperature of natural gas at the entrance to the main gas pipeline in the summer, which increases energy consumption for gas pumping and compressor capacity.

Known installation for cooling natural gas, containing tubular heat-exchange sections with transported natural gas, placed in a housing located on vertical racks, made in the form of a cylinder filled with a liquid coolant and covered by a casing, while vertically oriented heat exchanger tubes are built into the housing for the passage of cooling air liquid heat carrier, an exhaust fan equipped with a frequency converter is installed above the casing, the casing diameter is chosen equal to the blades diameter, the inner surface of the casing is equipped with ultrasonic emitters (utility model patent RU 184773 U1, IPC F28D 15/02, declared 06/15/2018, published 11/08 .2018). The disadvantages of this utility model are:

- use of an additional liquid heat carrier;

- seasonal limitations of natural gas cooling temperature;

- loss of cooling efficiency due to the presence of an intermediate refrigerant.

A known method for cooling a hydrocarbon stream, which includes at least the following steps:

(a) supplying a refrigerant stream;

(b) passing the refrigerant stream through at least three heat exchange stages at different pressure levels;

(c) passing the hydrocarbon stream through at least two heat exchange stages of step (b);

(d) expanding and vaporizing a portion of the refrigerant stream in each heat exchange step of step (c) to a different pressure to obtain a first vaporized refrigerant stream at a first vaporization pressure, and at least two other vaporized refrigerant streams at a pressure below the first pressure evaporation;

(e) compressing the first vaporized refrigerant stream in the highest pressure compressor stage to obtain at least a portion of the refrigerant stream at the refrigerant pressure of step (a);

(f) compressing other evaporated refrigerant streams in at least two parallel reduced pressure compressor stages to produce two or more partially compressed refrigerant streams;

(g) passing all partially compressed refrigerant streams through the high pressure compressor stage of stage (e) (patent for invention RU 2499962 A, IPC F25J 1/02, filed 02.12.2008, published 27.11.2013). The disadvantages of this invention are:

- use of an additional refrigerant;

- the technical complexity of the method (three heat exchangers, three stages of compression).

A known method for cooling a hydrocarbon stream, for example, natural gas, includes the following stages:

(a) heat exchange of the hydrocarbon stream with the first refrigerant stream;

(b) compressing the at least partially vaporized refrigerant stream using one or more compressors;

(c) cooling the compressed refrigerant stream with the environment after one or more compressions;

(d) dynamically expanding the cooled compressed refrigerant stream from step (c) to form an expanded refrigerant stream;

(e) additional cooling of the expanded refrigerant stream to obtain at least partially condensed refrigerant stream (patent for invention RU 2467268 C2, IPC F25J 1/02, filed on January 23, 2008, published on November 20, 2012). The disadvantages of this invention are:

- use of two streams of refrigerant;

- the complexity of the refrigeration process control in two interconnected refrigerant circuits;

- use of multi-flow heat exchangers of complex design.

When creating the claimed invention, the task was set to develop an integrated unit for chilling natural gas, providing a decrease in energy consumption due to the supply of natural gas at a low temperature in the summer to the main gas pipeline, and the rest of the time - for the production of liquefied natural gas.

The task is solved due to the fact that an integrated natural gas chilling unit, including a recuperative heat exchanger, an expander and a pipeline system, is connected to the natural gas pipeline at the outlet of the booster compressor station with an auxiliary inlet pipeline, through which part of the stream of high-pressure warm natural gas is supplied to the integrated unit and is divided into two streams: the first flow through the first pipeline is directed to the expander inlet for expansion and cooling, while the expander outlet by the second pipeline is connected to the first inlet of the recuperative heat exchanger, the second flow through the third pipeline is directed to the second inlet of the recuperative heat exchanger for cooling by the expanded and cooled stream natural gas, the first flow through the first outlet of the recuperative heat exchanger enters the booster compressor station through the fourth pipeline, the second flow through the second outlet of the recuperative heat exchanger is directed are mixed with gas entering the main gas pipeline through the fifth pipeline and / or with gas supplied to the production of liquefied natural gas through the sixth pipeline.

The main advantage of the developed integrated natural gas cooling unit is that its operation does not require additional refrigerants: natural gas itself is used. The unit is bifunctional, since in the summer, when the AVO BCS cannot provide the required degree of natural gas cooling for its economical transportation through the main gas pipeline, it cools down the transported natural gas, and the rest of the time, with the efficient operation of the ABO BCS, it can additionally cool down the flow entering liquefied natural gas production.

Estimated part of the warm high-pressure natural gas Y supplied to the integrated unit through the inlet auxiliary pipeline, the balance amount of partially heated cold low-pressure natural gas X supplied to the booster compressor station, and the flow rate of cooled natural gas Z discharged into the main gas pipeline in summer time can be calculated based on the system of modified heat balance equations for 100 kg of natural gas produced at the gas processing plant and supplied to the booster compressor station:

where t _ABO is the natural gas temperature after the AVO BCS, ° С;

t _Зпг - temperature of cooled natural gas, ° C;

t _mg is the temperature of natural gas, which must be maintained at the entrance to the main gas pipeline, ° С;

t _vd - temperature of natural gas at the expander outlet, ° С;

t _WRT - temperature of partially heated cold natural gas of low pressure at the outlet of the recuperative heat exchanger, ° С.

A similar approach to determining the material flows of the installation can be used for natural gas supplied to the production of liquefied natural gas.

It is advisable to install a compressor on the expander shaft, then the first flow of natural gas after the recuperative heat exchanger enters the compressor inlet for compression and subsequent cooling using the AVO, and then through the auxiliary outlet pipeline to the booster compressor station to the second stage of natural gas compression, which allows to reduce the power of the first stage ...

It is possible to operate the unit when an electric power generator is installed on the expander shaft, which makes it possible to additionally produce electricity for industrial needs, while the first low-pressure natural gas flow enters the first compression stage of the booster compressor station after the recuperative heat exchanger.

Alternatively, a Joule-Thomson butterfly valve can be used instead of an expander for an integrated chill-down unit.

It is useful to use the integrated unit in the summer - for cooling the gas entering the main gas pipeline, and in the winter - for cooling the gas supplied to the liquefied natural gas production.

The figure shows a schematic diagram of one of the embodiments of an integrated natural gas chilling unit using the following designations:

1-12 - pipelines;

100 - DCS;

200 - integrated gas cooling unit;

201 - expander;

202 - recuperative heat exchanger;

203 - compressor;

204 - AVO;

205, 206 - valve;

300 - main gas pipeline.

Prepared natural gas from the gas processing plant through pipeline 1 under a pressure of 2.5 MPa at a temperature of 20 ° C is supplied to the BCS 100, where its two-stage compression is provided (at the first stage up to 6.0 MPa, at the second stage up to 9.5 MPa), and in the form of a commercial fuel gas under a pressure of 9.5 MPa at a temperature of 40 ° C through pipeline 12 is sent to the main gas pipeline 300 for further supply to consumers. At the same time, it is envisaged to supply one part of natural gas through pipeline 10 for the production of liquefied natural gas and the other through an auxiliary inlet pipeline 2 to the integrated gas cooling unit 200. Part of the commercial fuel gas in the form of warm high-pressure natural gas supplied through pipeline 2 to the integrated unit cooldown gas 200 is divided into two streams. The first stream under a pressure of 9.5 MPa with a temperature of 40 ° C is directed to the inlet of expander 201 for expansion to a pressure of 3.1 MPa and cooling to a temperature of minus 30 ° C. The outlet of the expander 201 is connected by pipeline 3 to the first inlet of the recuperative heat exchanger 202. The second flow is directed through the pipeline 7 to the second inlet of the recuperative heat exchanger 202 for cooling with the expanded and cooled gas of the pipeline 3, and then is discharged through the second outlet of the recuperative heat exchanger 202 at a pressure of 9.5 MPa s temperature of 20 ° C and is directed for mixing with gas entering the main gas pipeline 300 through pipeline 8, and / or with gas entering the production of liquefied natural gas through pipeline 9. To switch the gas supply from the recuperative heat exchanger 202 to pipelines 8 and 9 use valves 205 and 206, respectively. Through the first outlet of the recuperative heat exchanger 202 through pipeline 4, the first flow under a pressure of 3.1 MPa with a temperature of 21 ° C enters first the inlet of the compressor 203 for compression to a pressure of 6 MPa with heating to a temperature of 72 ° C, and then through pipeline 5 to AVO 204 , from where, through the auxiliary outlet pipeline 6, the gas cooled to 40 ° C returns to the second compression stage of the BCS 100. It is possible to operate the integrated unit without turning on the compressor 203 (for example, when generating electricity), then the gas after the recuperative heat exchanger 202 is supplied through the pipeline 11 to the first compression stage DKS 100.

Example 1. In the summer, when the temperature of natural gas at the entrance to the main gas pipeline is ensured t _mg = 30 ° C with the temperature of natural gas after the AVO BCS t _ABO = 40 ° C according to the diagram shown in the figure, the temperatures of natural gas flows will be:

t _ABO = 40 ° C;

t _zpg = 20 ° C;

t _mg = 30 ° C;

t _vd = minus 30 ° C;

t _WRT = 21 ° C.

When performing the calculation according to the system of equations (1) for 100 kg / h of commercial fuel gas in the form of compressed natural gas directed from the booster compressor station 100 through pipeline 12 to the main gas pipeline 300, the internal flows of the natural gas chilling unit are: X = 24 kg / h, Y = 74 kg / h, Z = 50 kg / h. At a fuel gas flow rate other than 100 kg / h, the X, Y, Z values change proportionally. The use of the claimed invention in the summer allows to reduce energy consumption for compensation of head losses to overcome friction forces by 15% or to increase the distance of gas transportation by 5% while maintaining head losses through the main gas pipeline.

Example 2. In winter, when the temperature of natural gas supplied to the production of liquefied natural gas is ensured, 20 ° C with the temperature of natural gas after the ABO BCS t _ABO = 30 ° C according to the system of equations (1) and the heat balance of the recuperative heat exchanger, the balance amount of partially heated up to 21 ° C cold low pressure natural gas X entering the compressor after the recuperative heat exchanger is 24.4 kg / h. The use of the claimed invention will reduce energy consumption for natural gas liquefaction by 1-2%.

Thus, the claimed invention provides a reduction in energy consumption due to the supply of natural gas at a low temperature in the summer - to the main gas pipeline, and the rest of the time - for the production of liquefied natural gas.

Claims (5)

1. An integrated natural gas chilling unit, including a recuperative heat exchanger, an expander and a pipeline system, characterized in that the unit is connected to the natural gas pipeline at the outlet of the booster compressor station with an auxiliary inlet pipeline, through which part of the stream of high pressure warm natural gas is supplied to the integrated unit and divided into two streams: the first flow through the first pipeline is directed to the inlet of the expander for expansion and cooling, while the outlet of the expander by the second pipeline is connected to the first inlet of the recuperative heat exchanger, the second flow through the third pipeline is directed to the second inlet of the recuperative heat exchanger for cooling by the expanded and cooled natural gas, the first flow through the first outlet of the recuperative heat exchanger enters the booster compressor station through the fourth pipeline, the second flow through the second outlet of the recuperative heat exchanger is directed to mixing with gas entering the main gas pipeline via the fifth pipeline and / or with gas supplied to the production of liquefied natural gas via the sixth pipeline. 2. Installation according to claim 1, characterized in that a compressor is installed on the expander shaft, while the first natural gas stream after the recuperative heat exchanger enters the compressor inlet for compression and subsequent cooling using an air cooler, and then through an auxiliary outlet pipeline to booster compressor station. 3. Installation according to claim 1, characterized in that an electric power generator is installed on the expander shaft. 4. Installation according to claim 1, characterized in that the installation uses a Joule-Thomson throttle valve. 5. Installation according to claim 1, characterized in that the installation is used in the summer to cool the gas entering the natural gas main pipeline, and in the winter to cool the gas supplied to the production of liquefied natural gas.

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