Offshore oilfield associated gas dehydration system and method thereof
By introducing lithium bromide absorption refrigeration technology into the associated gas dehydration system of offshore oil fields, a multi-stage heat exchange and gas-liquid separation process is designed, which solves the problems of high energy consumption and large investment in the existing technology, and achieves a low-carbon and safe associated gas dehydration effect.
Patent Information
- Application Number
- CN202510482875.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-17
- Publication Date
- 2025-07-18
AI Technical Summary
The existing offshore oilfield associated gas dehydration technology fails to effectively utilize lithium bromide absorption refrigeration technology, resulting in high energy consumption, large investment, and traditional methods pollute the environment.
The lithium bromide absorption refrigeration technology is used to design the associated gas dehydration system in the offshore oil field. Through associated gas compression, multi-stage heat exchange and gas-liquid separation, combined with the lithium bromide absorption refrigeration unit, efficient dehydration of associated gas is achieved.
It reduces dehydration energy consumption and equipment investment, reduces low-grade energy waste, and achieves green, low-carbon and safe offshore oilfield development.
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Figure CN120329987A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of energy conservation of dehydration systems for offshore oilfields, and specifically relates to a dehydration system and method for associated gas in offshore oilfields. Background Art
[0002] Associated gas refers to the gas generated simultaneously with crude oil during the oil extraction process. Its main component is methane. Direct emission or combustion will cause environmental pollution and increase the greenhouse effect. During the production process of offshore oilfields, a large amount of associated gas is emitted. Therefore, the recovery and comprehensive utilization of associated gas are particularly important. The main uses of associated gas in offshore oilfields are turbine power generation and offshore pipeline transportation. There are certain requirements for the water dew point of associated gas. To ensure safe operation, dehydration treatment of associated gas is required.
[0003] Currently, the commonly used methods for dehydrating associated gas include absorption method, adsorption method, cooling method, etc. The absorption method has good dehydration effect and is suitable for high-pressure gases, but the equipment is complex and the energy consumption is relatively high; the adsorption method has a high dehydration depth and is suitable for gases with low water content, but the adsorbent needs to be regenerated and the equipment investment is large; the cooling method condenses the water vapor in the gas by lowering the temperature, with simple operation and short process, and is suitable for gases with high humidity.
[0004] However, most of the current technologies related to associated gas in offshore oilfields focus on the recovery and utilization of associated gas or innovations in traditional dehydration methods, and do not introduce the lithium bromide absorption refrigeration technology into the dehydration process of associated gas in offshore oilfields. Summary of the Invention
[0005] Aiming at the above problems, the purpose of the present invention is to provide a dehydration system and method for associated gas in offshore oilfields. Through the innovative design of applying the lithium bromide absorption refrigeration technology to the dehydration process of associated gas, it reduces the waste of low-grade energy, saves the electric power of compressors and seawater pumps, reduces the dehydration energy consumption, investment and operation costs, and provides a solution for the green, low-carbon and safe development of offshore oilfields.
[0006] To achieve the above purpose, the present invention adopts the following technical solutions: The dehydration system for associated gas in offshore oilfields described in the present invention includes: An associated gas compressor, whose inlet is connected to the gas source containing associated gas; A primary heat exchanger, whose gas-phase inlet is connected to the outlet of the associated gas compressor, and whose liquid-phase inlet is connected to the cooling fresh water; A secondary heat exchanger, whose gas-phase inlet is connected to the gas-phase outlet of the primary heat exchanger, whose liquid-phase inlet is connected to the cooling seawater, and whose liquid-phase outlet is connected to the sea; A tertiary heat exchanger, whose gas-phase inlet is connected to the gas-phase outlet of the secondary heat exchanger; The lithium bromide absorption refrigeration unit has its inlet connected to the liquid phase outlet of the primary heat exchanger and its outlet connected to the liquid phase inlet of the tertiary heat exchanger; The liquid phase outlet of the tertiary heat exchanger is connected to the liquid phase inlet of the primary heat exchanger.
[0007] The offshore oilfield associated gas dehydration system preferably further includes a gas-liquid separator. The inlet of the gas-liquid separator is connected to the gas phase outlet of the tertiary heat exchanger. Dry gas is discharged from the gas phase outlet of the gas-liquid separator, and liquid water is discharged from its liquid phase outlet.
[0008] In the offshore oilfield associated gas dehydration system, 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, and 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 communicates with the exchange port of the generator, and the second exchange port of the heat exchanger communicates 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.
[0009] The dehydration method of the offshore oilfield associated gas dehydration system of the present invention includes the following steps: The high-temperature natural gas discharged after the associated gas is compressed by the associated gas compressor exchanges heat with fresh water in the primary heat exchanger to obtain hot water, and the temperature of the associated gas decreases; The obtained hot water enters the lithium bromide absorption refrigeration unit. In the generator of the lithium bromide absorption refrigeration unit, 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. During this process, 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 associated gas after the primary heat exchanger enters the secondary heat exchanger, is further cooled to the set temperature after exchanging heat with seawater, and the seawater is heated and discharged into the sea; The low-temperature refrigerant water produced by the lithium bromide absorption refrigeration unit is used as the cold source of the tertiary heat exchanger, exchanges heat with the associated gas at the outlet of the secondary heat exchanger, cools the associated gas to the set temperature, and the refrigerant water whose temperature rises to the set temperature after heat exchange returns to the primary heat exchanger again to cool the associated gas after the compressor, and the fresh water circulates; A gas-liquid separator is connected to the outlet of the tertiary heat exchanger. The wet gas enters the gas-liquid separator, and under the action of gravity, the liquid and gas are separated to obtain dry gas, completing the dehydration process of the associated gas.
[0010] Due to the adoption of the above technical solutions, the present invention has the following advantages: Through the innovative design of the utilization of the heat of high-temperature associated gas and the application of lithium bromide absorption refrigeration technology, the present invention improves the utilization rate of the waste heat of the compressor, reduces the dehydration energy consumption and equipment investment, and meets the technical requirements of energy conservation, low carbon and safety of the offshore oilfield process system; Aiming at the energy-saving optimization of the dehydration of the associated gas in the offshore oilfield, the dehydration system of the associated gas in the offshore oilfield shows good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS
[0011] 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 to be a limitation of the present invention. Throughout the drawings, the same reference numerals are used to represent the same components. In the drawings: Figure 1 is a schematic structural diagram of the dehydration system of the associated gas in the offshore oilfield described in the present invention; Figure 2 is a schematic structural diagram of the lithium bromide absorption refrigeration unit in the present invention.
[0012] The reference numerals in the drawings are as follows: 1 - Gas source containing associated gas; 2 - Associated gas compressor; 3 - Fresh water for cooling; 4 - Primary heat exchanger; 5 - Seawater for cooling; 6 - Secondary heat exchanger; 7 - Tertiary heat exchanger; 8 - Hot water; 9 - Lithium bromide absorption refrigeration unit; 10 - Low-temperature refrigerant water; 11 - Gas-liquid separator; 12 - Dry gas; 13 - Liquid water. DETAILED DESCRIPTION OF THE EMBODIMENTS
[0013] 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 described 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.
[0014] The present invention provides a dehydration system for associated gas in offshore oilfields. Through the innovative design of applying lithium bromide absorption refrigeration technology to the associated gas dehydration process, it reduces the waste of low-grade energy, saves the electric power of compressors and seawater pumps, reduces the dehydration energy consumption, investment and operating costs, and provides a solution for the green, low-carbon and safe development of offshore oilfields.
[0015] As Figure 1 shown, the dehydration system for associated gas in offshore oilfields provided by the present invention includes: an associated gas compressor 2, whose inlet is connected to a gas source 1 containing associated gas; a primary heat exchanger 4, whose gas-phase inlet is connected to the outlet of the associated gas compressor 2, and whose liquid-phase inlet is connected to cooling fresh water 3; a secondary heat exchanger 6, whose gas-phase inlet is connected to the gas-phase outlet of the primary heat exchanger 4, and whose liquid-phase inlet is connected to cooling seawater 5, and whose liquid-phase outlet is connected to the sea for discharging to the sea; a tertiary heat exchanger 7, whose gas-phase inlet is connected to the gas-phase outlet of the secondary heat exchanger 6; a lithium bromide absorption refrigeration unit 9, whose inlet is connected to the liquid-phase outlet of the primary heat exchanger 4, and whose outlet is connected to the liquid-phase inlet of the tertiary heat exchanger 7 to make hot water 8 into low-temperature refrigerant water 10; the liquid-phase outlet of the tertiary heat exchanger 7 is connected to the liquid-phase inlet of the primary heat exchanger 4.
[0016] In the above embodiment, preferably, the present invention further includes a gas-liquid separator 11. The inlet of the gas-liquid separator 11 is connected to the gas-phase outlet of the tertiary heat exchanger 7. The gas-phase outlet of the gas-liquid separator 11 discharges dry gas 12, and its liquid-phase outlet discharges liquid water 13.
[0017] In the above embodiment, preferably, as Figure 2 shown, the lithium bromide absorption refrigeration unit 9 includes: a generator 9-1, a condenser 9-2, a throttle valve 9-3, an evaporator 9-4, an absorber 9-5 and a heat exchanger 9-6; the outlet of the generator 9-1 is connected to the inlet of the condenser 9-2, the outlet of the condenser 9-2 is connected to the inlet of the throttle valve 9-3, the outlet of the throttle valve 9-3 is connected to the inlet of the evaporator 9-4, the outlet of the evaporator 9-4 is connected to the inlet of the absorber 9-5, the outlet of the absorber 9-5 is connected to the inlet of the heat exchanger 9-6, and the outlet of the heat exchanger 9-6 is connected to the inlet of the generator 9-1 to enable the refrigerant (water) 9-7 to form a cycle; The first exchange port of the heat exchanger 9-6 is communicated with the exchange port of the generator 9-1, and the second exchange port of the heat exchanger 9-6 is communicated with the exchange port of the absorber 9-5 to enable the lithium bromide solution 9-8 to be exchanged between the absorber 9-5, the heat exchanger 9-6 and the generator 9-1.
[0018] The present invention also provides a dehydration method for the dehydration system of associated gas in offshore oilfields, including the following steps: S1. The high-temperature natural gas discharged after the associated gas is compressed by the associated gas compressor exchanges heat with fresh water in the primary heat exchanger to produce hot water, and the temperature of the associated gas decreases; S2. The produced hot water enters the lithium bromide absorption refrigeration unit. In the lithium bromide absorption refrigeration unit, the lithium bromide solution is heated 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 (about 5°C). During this process, 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; S3. The associated gas after the primary heat exchanger enters the secondary heat exchanger, is further cooled to a set temperature (about 40°C) after exchanging heat with seawater, and the seawater is heated and then discharged into the sea; S4. The low-temperature refrigerant water produced by the lithium bromide absorption refrigeration unit is used as the cold source of the tertiary heat exchanger to exchange heat with the associated gas at the outlet of the secondary heat exchanger, cool the associated gas to a set temperature (about 5°C), and the refrigerant water whose temperature rises to a set temperature (about 12°C) after heat exchange returns to the primary heat exchanger again to cool the associated gas after the compressor and conduct the circulation of fresh water; S5. A gas-liquid separator is connected at the outlet of the tertiary heat exchanger. The wet gas enters the gas-liquid separator, and under the action of gravity, the liquid and gas are separated to obtain dry gas, completing the dehydration process of the associated gas.
[0019] Example 1: A conventional dehydration system for 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. After the natural gas is pressurized by a compressor, the pressure rises to 2500 KPaG and the temperature rises to 143 °C. The useful power of the 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 required to be 8584 m³ / day, and the useful power of the seawater is 92 kW. Then, conventional refrigeration (such as expansion refrigeration) is used to further reduce the temperature to 10 °C, and the refrigeration power is 1325 kW. The low-temperature natural gas enters the gas-liquid separator for gas-liquid separation and then is exported. After adopting a new offshore oilfield associated gas dehydration system, the high CO₂-containing natural gas in the same state is pressurized by a compressor to 2500 KPaG and the temperature rises to 143 °C. The useful power of the compressor is 3810 kW. After compression, the natural gas is cooled to 80 °C through a primary heat exchanger. Then, the natural gas passes through a conventional open seawater cooler (secondary heat exchanger) to further reduce the temperature of the natural gas to 40 °C. The open cooling system requires a seawater lift pump displacement of 3381 m³ / day, and the useful power of the seawater is 36 kW. Then, it exchanges heat with the low-temperature water of the lithium bromide unit (tertiary heat exchanger) to reduce the temperature to 10 °C and then enters the gas-liquid separator for gas-liquid separation and is exported. The power of the lithium bromide absorption refrigeration unit is about 40 kW. Compared with the conventional natural gas dehydration system, the total power of the new offshore oilfield associated gas dehydration system is reduced by about 1340 kW. The annual power saving is about 10.72 million kW·h.
[0020] 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 for 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 associated gas dehydration system for an offshore oilfield, characterized in that, Including: An associated gas compressor, whose inlet is connected to a gas source containing associated gas; A primary heat exchanger, whose gas-phase inlet is connected to the outlet of the associated gas compressor, and whose liquid-phase inlet is connected to fresh water for cooling; A secondary heat exchanger, whose gas-phase inlet is connected to the gas-phase outlet of the primary heat exchanger, whose liquid-phase inlet is connected to seawater for cooling, and whose liquid-phase outlet is connected to the sea; A tertiary heat exchanger, whose gas-phase inlet is connected to the gas-phase outlet of the secondary heat exchanger; A lithium bromide absorption refrigeration unit, whose inlet is connected to the liquid-phase outlet of the primary heat exchanger, and whose outlet is connected to the liquid-phase inlet of the tertiary heat exchanger; The liquid-phase outlet of the tertiary heat exchanger is connected to the liquid-phase inlet of the primary heat exchanger.
2. The dehydration system for associated gas in an offshore oilfield according to claim 1, wherein, It also includes a gas-liquid separator. The inlet of the gas-liquid separator is connected to the gas-phase outlet of the tertiary heat exchanger. The gas-phase outlet of the gas-liquid separator discharges dry gas, and its liquid-phase outlet discharges liquid water.
3. The dehydration system for associated gas in an offshore oilfield according to claim 1, wherein 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, and 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 communicates with the exchange port of the generator, and the second exchange port of the heat exchanger communicates 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.
4. A dehydration method for the dehydration system of associated gas in an offshore oilfield according to any one of claims 1 to 3, characterized in that, Including the following steps: The high-temperature natural gas discharged after the associated gas is compressed by the associated gas compressor exchanges heat with fresh water in the primary heat exchanger to obtain hot water, and the temperature of the associated gas decreases; The obtained hot water enters the lithium bromide absorption refrigeration unit. In the lithium bromide absorption refrigeration unit, the lithium bromide solution is heated 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. During this process, 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 associated gas after the primary heat exchanger enters the secondary heat exchanger, is further cooled to the set temperature after exchanging heat with seawater, and the seawater is heated and discharged into the sea; The low-temperature refrigerant water produced by the lithium bromide absorption refrigeration unit is used as the cold source of the tertiary heat exchanger to exchange heat with the associated gas at the outlet of the secondary heat exchanger, cool the associated gas to the set temperature, and the refrigerant water whose temperature rises to the set temperature after heat exchange returns to the primary heat exchanger again to cool the associated gas after the compressor and conduct the circulation of fresh water; A gas-liquid separator is connected to the outlet of the three-stage heat exchanger. The wet gas enters the gas-liquid separator, and under the action of gravity, the liquid and gas are separated to obtain dry gas, completing the dehydration process of associated gas.