Offshore platform compressor cooling system and method thereof

Abstract

The invention relates to an offshore platform compressor cooling system and a method thereof, and the cooling system comprises a first heat exchanger, a second heat exchanger and a third heat exchanger, an inlet of the natural gas compressor is connected with a first outlet of the first heat exchanger; a first inlet of the second heat exchanger is connected with an outlet of the natural gas compressor, and a second inlet of the second heat exchanger is connected with cooling fresh water; and an inlet of the lithium bromide absorption type refrigerating unit is connected with a first outlet of the second heat exchanger, and an outlet of the lithium bromide absorption type refrigerating unit is connected into a second inlet of the first heat exchanger. The system can reduce the consumption of cooling seawater, improve the waste heat utilization rate of the compressor, save the electric power of the compressor and the seawater pump and improve the overall energy efficiency of the system.

Description

Technical Field

[0001] The present invention relates to the technical field of energy - saving utilization of waste heat in offshore oil and gas fields, and specifically relates to a compressor cooling system and method for an offshore platform. Background Art

[0002] After the natural gas is compressed in the process system of the offshore platform, the discharged gas has a high temperature. Usually, a seawater cooling device is used for cooling. After the seawater is heated, it is directly discharged into the sea, which not only causes waste of heat, but also has a significant impact on the marine ecosystem. The discharge of hot water into the sea will change the physical and chemical environment of the sea, affect the growth of phytoplankton and zooplankton, and then affect the balance of the entire marine ecosystem. The exhaust temperature of the compressor can reach nearly 120°C. How to optimize the design of the compressor cooling system, make full use of the waste heat of the compressed natural gas, reduce the consumption of cooling seawater, reduce the waste of low - grade heat sources, and improve the energy efficiency of the compressor is the technical research direction for realizing the green, low - carbon and economic development of the offshore platform.

[0003] Lithium bromide absorption refrigeration is a waste - heat refrigeration technology with good energy - saving and economic benefits in waste - heat refrigeration. Under vacuum conditions, the lithium bromide absorption refrigeration machine uses water as the refrigerant and an aqueous solution of lithium bromide as the absorbent, and utilizes the characteristic that the boiling point of water becomes lower under high - vacuum conditions to refrigerate. Due to its energy - saving, high - efficiency, non - polluting environment, high degree of automation and other characteristics, it has been widely used in central air - conditioning systems.

[0004] However, most of the existing technologies related to the utilization of compressor waste heat focus on the innovation of waste - heat recovery of air compressors, and do not introduce the lithium bromide absorption refrigeration technology into the offshore platform process flow. Summary of the Invention

[0005] In view of the above problems, the purpose of the present invention is to provide a compressor cooling system and method for an offshore platform, which can reduce the amount of cooling seawater used, improve the utilization rate of compressor waste heat, save the power consumption of the compressor and seawater pump, and improve the overall energy efficiency of the system.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions: The compressor cooling system for an offshore platform of the present invention includes: A first heat exchanger, whose first inlet is connected to a natural gas source; A natural gas compressor, whose inlet is connected to the first outlet of the first heat exchanger; A second heat exchanger, whose first inlet is connected to the outlet of the natural gas compressor, and whose second inlet is connected to cooling fresh water; A lithium bromide absorption refrigeration unit, whose inlet is connected to the first outlet of the second heat exchanger, and whose outlet is connected to the second inlet of the first heat exchanger.

[0007] For the compressor cooling system of the offshore platform described above, preferably, the second outlet of the first heat exchanger is connected to cooling fresh water.

[0008] For the compressor cooling system of the offshore platform described above, preferably, it further includes a third heat exchanger. The first inlet of the third heat exchanger is connected to the second outlet of the second heat exchanger. The second inlet of the third heat exchanger is connected to cooling seawater. The first outlet of the third heat exchanger is used for discharging to the sea, and its second outlet is used for outputting cooled natural gas.

[0009] For the compressor cooling system of the offshore platform described above, preferably, the lithium bromide absorption refrigeration unit includes: a generator, a condenser, a throttle valve, an evaporator, an absorber, and a heat exchanger; The outlet of the generator is connected to the inlet of the condenser. The outlet of the condenser is connected to the inlet of the throttle valve. The outlet of the throttle valve is connected to the inlet of the evaporator. The outlet of the evaporator is connected to the inlet of the absorber. The outlet of the absorber is connected to the inlet of the heat exchanger. The outlet of the heat exchanger is connected to the inlet of the generator to form a refrigerant cycle; The first exchange port of the heat exchanger is communicated with the exchange port of the generator. The second exchange port of the heat exchanger is communicated with the exchange port of the absorber to enable the lithium bromide solution to be exchanged between the absorber, the heat exchanger, and the generator.

[0010] The cooling method of the compressor cooling system of the offshore platform according to the present invention includes the following steps: The high-temperature natural gas discharged after being compressed by the compressor exchanges heat with fresh water in the second heat exchanger to obtain hot water, and the temperature of the natural gas decreases; The obtained hot water enters the lithium bromide absorption refrigeration unit. In the generator, the lithium bromide solution is heated to generate water vapor. The concentration of the lithium bromide aqueous solution in the generator continuously increases and enters the condenser. The water vapor enters the condenser and is cooled by the cooling water in the condenser and then condenses into high-pressure and low-temperature liquid water. The water in the condenser enters the evaporator through the throttle valve, expands rapidly and vaporizes, and absorbs a large amount of heat of the refrigerant water in the evaporator during the vaporization process to produce low-temperature refrigerant water at a set temperature. The low-temperature water vapor enters the absorber and is absorbed by the lithium bromide aqueous solution in the absorber. The solution concentration gradually decreases and is then pumped back to the generator by the circulation pump to complete the entire cycle; The low-temperature refrigerant water produced by the lithium bromide absorption refrigeration unit is used as the cold source of the first heat exchanger. It exchanges heat with the incoming natural gas in the first heat exchanger in front of the compressor to cool the natural gas before the compressor inlet to the set temperature. The refrigerant water whose temperature rises to the set temperature after heat exchange returns to the second heat exchanger again to cool the natural gas after the compressor, and the fresh water is circulated; The natural gas after passing through the second heat exchanger enters the third heat exchanger, is further cooled to a set temperature after heat exchange with seawater, and the seawater is heated and then discharged into the sea.

[0011] Due to the adoption of the above technical solutions, the present invention has the following advantages: Through the innovative design of the waste heat utilization of the compressor and the application of the lithium bromide absorption refrigeration technology, the present invention reduces the consumption of cooling seawater, improves the waste heat utilization rate of the compressor, saves the power consumption of the compressor and the seawater pump, improves the overall energy efficiency of the system, and meets the technical requirements of energy conservation, low carbon and safety of the process system on the offshore platform; For the energy-saving optimization of the compressor system on the offshore platform, the compressor cooling system on the offshore platform shows good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] By reading the following detailed description of the preferred embodiments, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered as limiting the present invention. Throughout the drawings, the same reference numerals are used to denote the same components. In the drawings: Figure 1 is a schematic structural diagram of the compressor cooling system on the offshore platform described in the present invention; Figure 2 is a schematic structural diagram of the lithium bromide absorption refrigeration unit.

[0013] The reference numerals in the drawings are as follows: 1 - natural gas source; 2 - first heat exchanger; 3 - natural gas compressor; 4 - cooling fresh water; 5 - second heat exchanger; 6 - cooling seawater; 7 - third heat exchanger; 8 - cooled natural gas; 9 - low-temperature refrigerant water; 10 - lithium bromide absorption refrigeration unit; 10-1 - generator; 10-2 - condenser; 10-3 - throttle valve; 10-4 - evaporator; 10-5 - absorber; 10-6 - heat exchanger; 10-7 - refrigerant (water); 10-8 - lithium bromide solution; 11 - hot water. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0014] The exemplary embodiments of the present invention will be described in more detail below with reference to the drawings. Although the exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present invention can be more thoroughly understood and the scope of the present invention can be completely conveyed to those skilled in the art.

[0015] The present invention provides a compressor cooling system for an offshore platform. Through innovative design of waste heat utilization of the compressor and application of lithium bromide absorption refrigeration technology, the amount of cooling seawater used is reduced, the waste heat utilization rate of the compressor is increased, the power consumption of the compressor and seawater pump is saved, the overall energy efficiency of the system is improved, meeting the technical requirements of energy conservation, low carbon and safety of the offshore platform process system.

[0016] As Figure 1 shown, the compressor cooling system for an offshore platform provided by the present invention includes: a first heat exchanger 2, whose first inlet is connected to a natural gas source 1; a natural gas compressor 3, whose inlet is connected to the first outlet of the first heat exchanger 2; a second heat exchanger 5, whose first inlet is connected to the outlet of the natural gas compressor 3, and whose second inlet is connected to cooling fresh water 4; a lithium bromide absorption refrigeration unit 10, whose inlet is connected to the first outlet of the second heat exchanger 5, and whose outlet is connected to the second inlet of the first heat exchanger 2, for cooling hot water 11 into low-temperature refrigerant water 9.

[0017] In the above embodiment, preferably, the second outlet of the first heat exchanger 2 is connected to the cooling fresh water 4.

[0018] In the above embodiment, preferably, the present invention further includes a third heat exchanger 7. The first inlet of the third heat exchanger 7 is connected to the second outlet of the second heat exchanger 5, the second inlet of the third heat exchanger 7 is connected to cooling seawater 6, the first outlet of the third heat exchanger 7 is used for discharging to the sea, and its second outlet is used for outputting cooled natural gas 8.

[0019] In the above embodiment, preferably, as Figure 2 shown, the lithium bromide absorption refrigeration unit includes: a generator 10-1, a condenser 10-2, a throttle valve 10-3, an evaporator 10-4, an absorber 10-5 and a heat exchanger 10-6; The outlet of the generator 10-1 is connected to the inlet of the condenser 10-2, the outlet of the condenser 10-2 is connected to the inlet of the throttle valve 10-3, the outlet of the throttle valve 10-3 is connected to the inlet of the evaporator 10-4, the outlet of the evaporator 10-4 is connected to the inlet of the absorber 10-5, the outlet of the absorber 10-5 is connected to the inlet of the heat exchanger 10-6, and the outlet of the heat exchanger 10-6 is connected to the inlet of the generator 10-1, so that the refrigerant (water) 10-7 forms a cycle; The first exchange port of the heat exchanger 10-6 is communicated with the exchange port of the generator 10-1, and the second exchange port of the heat exchanger 10-6 is communicated with the exchange port of the absorber 10-5, so that the lithium bromide solution 10-8 is exchanged between the absorber 10-5, the heat exchanger 10-6 and the generator 10-1.

[0020] The present invention also provides a cooling method for a compressor cooling system of an offshore platform, including the following steps: S1. The high-temperature natural gas discharged after being compressed by the compressor exchanges heat with fresh water in the second heat exchanger to produce hot water, and the temperature of the natural gas decreases. S2. The produced hot water enters the lithium bromide absorption refrigeration unit. In the generator, the lithium bromide solution is heated to generate water vapor. The concentration of the lithium bromide aqueous solution in the generator continuously increases and enters the condenser. The water vapor enters the condenser and is cooled by the cooling water in the condenser and then condenses into high-pressure and low-temperature liquid water. The water in the condenser enters the evaporator through a throttle valve, expands rapidly and vaporizes, and absorbs a large amount of heat of the refrigerant water in the evaporator during the vaporization process to produce low-temperature refrigerant water at a set temperature (about 5°C). The low-temperature water vapor enters the absorber and is absorbed by the lithium bromide aqueous solution in the absorber. The solution concentration gradually decreases and then is pumped back to the generator by a circulating pump to complete the whole cycle. S3. The low-temperature refrigerant water produced by the lithium bromide absorption refrigeration unit is used as the cold source of the first heat exchanger. It exchanges heat with the incoming natural gas in the first heat exchanger before the compressor, cools the natural gas before the compressor inlet to the set temperature (about 20°C), and the refrigerant water whose temperature rises to the set temperature (about 12°C) after heat exchange returns to the second heat exchanger to cool the natural gas after the compressor, and the fresh water circulates. S4. The natural gas after passing through the second heat exchanger enters the third heat exchanger, is further cooled to the set temperature (about 40°C) after exchanging heat with seawater, and the seawater is heated and then discharged to the sea.

[0021] Example 1: The high CO₂-containing natural gas with a pressure of 900 KPaG, a temperature of 40°C, and a gas volume of 2,000,000 m³ / day on an offshore platform is pressurized by a compressor, and the pressure rises to 2500 KPaG and the temperature rises to 143°C. The useful power of the natural gas compressor is 3810 kW. To reduce the temperature of the pressurized natural gas to 40°C through a conventional open seawater cooler, the displacement of the seawater lift pump is 8584 m³ / day, and the useful power of the seawater is 92 kW. After adopting the new offshore platform compressor cooling system, the high CO₂-containing natural gas in the same state is pressurized by the compressor, the pressure rises to 2500 KPaG, the temperature rises to 127.7°C, the useful power of the compressor is 3700 kW, the temperature of the natural gas is reduced to 40°C, the displacement of the seawater lift pump is 3990 m³ / day, the useful power of the seawater is 43 kW, and the power of the lithium bromide unit is about 20 kW. Compared with the conventional open cooling system, the power is reduced by about 140 kW after adopting the new offshore platform compressor cooling system. The annual power saving is about 1.11 million kW·h.

[0022] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An offshore platform compressor cooling system, characterized in that, Comprising: A first heat exchanger, whose first inlet is connected to a natural gas source; A natural gas compressor, whose inlet is connected to the first outlet of the first heat exchanger; A second heat exchanger, whose first inlet is connected to the outlet of the natural gas compressor, and whose second inlet is connected to cooling fresh water; A lithium bromide absorption refrigeration unit, whose inlet is connected to the first outlet of the second heat exchanger, and whose outlet is connected to the second inlet of the first heat exchanger.

2. The compressor cooling system for an offshore platform according to claim 1, wherein The second outlet of the first heat exchanger is connected to cooling fresh water.

3. The compressor cooling system for an offshore platform according to claim 1, characterized in that, It further comprises a third heat exchanger. The first inlet of the third heat exchanger is connected to the second outlet of the second heat exchanger. The second inlet of the third heat exchanger is connected to cooling seawater. The first outlet of the third heat exchanger is used for discharging to the sea, and its second outlet is used for outputting cooled natural gas.

4. The compressor cooling system for an offshore platform according to claim 1, characterized in that, The lithium bromide absorption refrigeration unit comprises: a generator, a condenser, a throttle valve, an evaporator, an absorber and a heat exchanger; The outlet of the generator is connected to the inlet of the condenser, the outlet of the condenser is connected to the inlet of the throttle valve, the outlet of the throttle valve is connected to the inlet of the evaporator, the outlet of the evaporator is connected to the inlet of the absorber, the outlet of the absorber is connected to the inlet of the heat exchanger, and the outlet of the heat exchanger is connected to the inlet of the generator, so that the refrigerant forms a cycle; The first exchange port of the heat exchanger is communicated with the exchange port of the generator, and the second exchange port of the heat exchanger is communicated with the exchange port of the absorber, so that the lithium bromide solution is exchanged between the absorber, the heat exchanger and the generator.

5. A cooling method for a compressor cooling system of an offshore platform according to any one of claims 1 to 4, characterized in that, Comprising the following steps: The high-temperature natural gas discharged after being compressed by the compressor exchanges heat with fresh water in the second heat exchanger to obtain hot water, and the temperature of the natural gas decreases; The obtained hot water enters the lithium bromide absorption refrigeration unit, heats the lithium bromide solution in the generator to generate water vapor, the concentration of the lithium bromide aqueous solution in the generator continuously increases, and enters the condenser. The water vapor enters the condenser and is cooled by the cooling water in the condenser and then condenses into high-pressure and low-temperature liquid water. The water in the condenser enters the evaporator through the throttle valve, expands rapidly and vaporizes, and absorbs a large amount of heat of the refrigerant water in the evaporator during the vaporization process to produce low-temperature refrigerant water at a set temperature. The low-temperature water vapor enters the absorber and is absorbed by the lithium bromide aqueous solution in the absorber, and the solution concentration gradually decreases, and then is pumped back to the generator by the circulation pump to complete the whole cycle; The low-temperature refrigerant water produced by the lithium bromide absorption refrigeration unit is used as the cold source of the first heat exchanger, exchanges heat with the incoming natural gas in the first heat exchanger in front of the compressor, cools the natural gas in front of the compressor inlet to the set temperature, and the refrigerant water whose temperature rises to the set temperature after heat exchange returns to the second heat exchanger again to cool the natural gas after the compressor, and the fresh water circulates; The natural gas after passing through the second heat exchanger enters the third heat exchanger, is further cooled to the set temperature after exchanging heat with seawater, and the seawater is heated and discharged to the sea.

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