System for generating electricity using cryogenic liquid cold energy

Abstract

The present invention provides a system for generating electricity using cryogenic liquid cold energy, comprising a working fluid expander, a first heat exchanger, a second heat exchanger, a booster pump and a third heat exchanger; the working fluid expander is driven by the working fluid and drives the generator to generate electricity; the first heat exchanger is used for heat exchange between the working fluid and an external heat source, and its inlet is connected to the outlet of the working fluid expander; the second heat exchanger has a first flow channel for the flow of cryogenic liquid and a second flow channel and a third flow channel for the flow of the working fluid respectively, and the first flow channel and the third flow channel both perform heat exchange with the second flow channel; the inlet of the second flow channel is connected to the outlet of the first heat exchanger; the inlet of the booster pump is connected to the outlet of the second flow channel, and its outlet is connected to the inlet of the third flow channel; the third heat exchanger is used for heat exchange between the working fluid and the external heat source, and its inlet is connected to the outlet of the third flow channel, and its outlet is connected to the inlet of the working fluid expander. The present invention can improve the utilization efficiency of cold energy.

Description

Technical Field

[0001] The invention relates to a power generation system, in particular to a system for generating power by utilizing low-temperature liquid cold energy. Background Art

[0002] Cryogenic liquids (LNG, liquid nitrogen, liquid oxygen, etc.) produced by consuming energy all contain a large amount of cold energy. The use of cold energy can also save a lot of energy, reduce carbon emissions, and has huge environmental benefits. For example, the current uses of LNG cold energy include: power generation, liquefied air separation, warehouse freezing, dry ice making, low-temperature crushing, etc., among which the most effective way to use it is cold energy power generation. Through a certain low-temperature thermodynamic cycle, with the help of energy conversion machines (such as expanders), cold energy is converted into mechanical work, and then through the generator, it can generate electricity and output cold capacity.

[0003] In the past, the main methods of power generation using cold energy were: LNG direct expansion method, single-fluid low-temperature Rankine cycle method, cascade low-temperature Rankine cycle method, low-temperature Brighton cycle method and mixed-fluid low-temperature Rankine cycle method. In terms of power generation efficiency, investment and technical complexity, the mixed-fluid low-temperature Rankine cycle method is the most competitive.

[0004] Typical low temperature Rankine cycle power generation system is as follows: Figure 1 As shown, the high-pressure gas-phase mixed working fluid enters the expander 10 to expand and do work to drive the generator 30 to generate electricity. The low-pressure gas-phase mixed working fluid after the expander 10 exchanges heat with the cryogenic liquid in the first heat exchanger 50. The cryogenic liquid releases cold energy and is converted into gas for external supply. The low-pressure gas-phase mixed working fluid is cooled to a low-pressure liquid-phase mixed working fluid, and then pressurized by the booster pump 70 to a high-pressure liquid-phase mixed working fluid, and then passes through the second heat exchanger 90 to absorb heat and heat up to be converted into a high-pressure gas-phase mixed working fluid, and enters the next cycle. The system absorbs heat externally from the process of converting the high-pressure liquid-phase mixed working fluid into the high-pressure gas-phase mixed working fluid, and the system still has room for improvement in the utilization efficiency of cold energy. Summary of the invention

[0005] The purpose of the present invention is to provide a system for generating electricity by utilizing the cold energy of low-temperature liquid, so as to improve the utilization efficiency of cold energy and generate more electricity for the outside world.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions: a system for generating electricity using cryogenic liquid cold energy, comprising a working fluid expander, a first heat exchanger, a second heat exchanger, a booster pump and a third heat exchanger; the working fluid expander is driven by the working fluid and drives the generator to generate electricity; the first heat exchanger is used for heat exchange between the working fluid and an external heat source, and its inlet is connected to the outlet of the working fluid expander; the second heat exchanger has a first flow channel for the flow of cryogenic liquid and a second flow channel and a third flow channel for the flow of the working fluid respectively, and the first flow channel and the third flow channel both exchange heat with the second flow channel; the inlet of the second flow channel is connected to the outlet of the first heat exchanger; the inlet of the booster pump is connected to the outlet of the second flow channel, and its outlet is connected to the inlet of the third flow channel; the third heat exchanger is used for heat exchange between the working fluid and the external heat source, its inlet is connected to the outlet of the third flow channel, and its outlet is connected to the inlet of the working fluid expander.

[0007] Preferably, the first heat exchanger is connected to the working fluid expander through a gas-liquid separator; the gas-liquid separator has an inlet, a gas phase outlet and a liquid phase outlet; the inlet of the gas-liquid separator is connected to the outlet of the working fluid expander, the gas phase outlet is connected to the inlet of the first heat exchanger, and the liquid phase outlet is connected to the inlet of the booster pump.

[0008] Preferably, the outlet of the first flow channel is connected to a gas expander, and the gas expander drives a generator to generate electricity.

[0009] Preferably, the gas expander and the working fluid expander are integrated.

[0010] Preferably, the temperature of the working medium after heat exchange in the first heat exchanger is greater than 0°C and does not exceed 40°C.

[0011] Preferably, the external heat source of the first heat exchanger is natural gas supplementary combustion, air, seawater or waste heat.

[0012] Preferably, the second heat exchanger is a plate type or a coiled tube type heat exchanger.

[0013] Preferably, the external heat source of the third heat exchanger includes natural gas supplementary combustion or waste heat.

[0014] Preferably, the cryogenic liquid is liquefied natural gas, liquid oxygen, liquid nitrogen or liquid ethylene.

[0015] Preferably, the working fluid includes part or all of the following components: methane, ethane, propane, butane, pentane, nitrogen, and acetylene.

[0016] It can be seen from the above technical scheme that the advantages and positive effects of the present invention are: in the system of the present invention, due to the recycling of the cold energy of the low-temperature liquid phase mixed working medium, under the same raw material working conditions, the circulation volume of the working medium will increase, so that more heat can be absorbed from the outside, and more work can be done to the outside to generate electricity, thereby achieving the purpose of improving the efficiency of cold energy utilization. At the same time, the two heatings before and after expansion also increase the absorbed heat, thereby increasing the output work and power generation. In addition, due to the configuration of the pre-expansion heater, space can be left for other cold energy utilization devices such as warehouse freezing, dry ice making, low-temperature crushing, etc., enriching the cold energy utilization methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a system flow chart of the prior art.

[0018] Figure 2 It is a schematic diagram of the system flow of a preferred embodiment of the present invention.

[0019] The description of the reference numerals is as follows: 1. working fluid expander; 3. generator; 4. first heat exchanger; 6. second heat exchanger; 61. first flow channel; 62. second flow channel; 63. third flow channel; 7. booster pump; 8. third heat exchanger. DETAILED DESCRIPTION

[0020] Typical embodiments that embody the features and advantages of the present invention will be described in detail in the following description. It should be understood that the present invention can have various changes in different embodiments without departing from the scope of the present invention, and the descriptions and illustrations therein are essentially used for illustration purposes rather than for limiting the present invention.

[0021] The present invention provides a system for generating electricity using cryogenic liquid cold energy, wherein the cryogenic liquid may be a medium that needs to be gasified before use, such as liquefied natural gas, liquid oxygen, liquid nitrogen or liquid ethylene.

[0022] like Figure 2 As shown, in a preferred embodiment of the present invention, the system mainly includes a working fluid expander 1, a first heat exchanger 4, a second heat exchanger 6, a booster pump 7 and a third heat exchanger 8.

[0023] The working fluid expander 1 is driven by the working fluid and drives the generator 3 to generate electricity; wherein the working fluid is a mixed working fluid, including part or all of the following components: methane, ethane, propane, butane, pentane, nitrogen, and acetylene.

[0024] The first heat exchanger 4 and the third heat exchanger 8 are both used for heat exchange between the working medium and the external heat source, and can be of plate-fin type or shell-and-tube type, etc., and both have an inlet for the working medium to enter and an outlet for the working medium to flow out. The external heat source of the first heat exchanger 4 can be supplementary combustion of natural gas, air, seawater or waste heat, etc., and the external heat source of the third heat exchanger 8 includes but is not limited to supplementary combustion of natural gas, waste heat, etc.

[0025] The second heat exchanger 6 is a multi-channel heat exchanger having a first flow channel 61 for the flow of low-temperature liquid and a second flow channel 62 and a third flow channel 63 for the flow of working fluid, wherein the first flow channel 61 and the third flow channel 63 both exchange heat with the second flow channel 62. The second heat exchanger 6 can be a plate type or a coiled tube type heat exchanger.

[0026] The outlet of the working fluid expander 1 is connected to the inlet of the first heat exchanger 4, the outlet of the first heat exchanger 4 is connected to the inlet of the second flow channel 62, the outlet of the second flow channel 62 is connected to the inlet of the booster pump 7, the outlet of the booster pump 7 is connected to the inlet of the third flow channel 63, the outlet of the third flow channel 63 is connected to the inlet of the third heat exchanger 8, and the outlet of the third heat exchanger 8 is connected to the inlet of the working fluid expander 1.

[0027] The working medium flows through the working medium expander 1, the first heat exchanger 4, the second flow channel 62 of the second heat exchanger 6, the booster pump 7, the third flow channel 63 of the second heat exchanger 6, the third heat exchanger 8 in sequence and then returns to the working medium expander 1, forming a cycle.

[0028] The working principle of the system is roughly as follows: high-pressure and high-temperature gas-phase working fluid enters the working fluid expander 1 to expand and work to become low-pressure and low-temperature gas-phase working fluid, absorbs heat from an external heat source in the first heat exchanger 4 to become low-pressure and normal-temperature gas-phase working fluid, and then is condensed into a low-pressure liquid-phase working fluid in the second heat exchanger 6, while the temperature is also reduced, and then passes through a booster pump 7 to increase the pressure to a high-pressure liquid-phase working fluid, and then returns to the second heat exchanger 6 to absorb heat and increase the temperature, and then absorbs heat from an external heat source in the third heat exchanger 8, and the high-pressure and high-temperature gas-phase working fluid finally formed enters the working fluid expander 1. The working fluid expander 1 drives the generator 3 to work and generate electricity.

[0029] In this system, the temperature of the gas phase working medium before the inlet of the first heat exchanger 4 is below zero, and becomes a normal temperature working medium after absorbing heat and heating in the first heat exchanger 4. Preferably, the temperature of the working medium at the outlet of the first heat exchanger 4 is greater than 0°C and does not exceed 40°C. The normal temperature working medium exchanges heat with the low temperature liquid flowing through the first flow channel 61 and the low temperature and high pressure liquid phase working medium flowing through the third flow channel 63 in the second flow channel 62 of the second heat exchanger 6. The normal temperature gas phase working medium is condensed into a liquid phase, and the low temperature liquid absorbs the heat of the gas phase working medium and heats up and vaporizes. The low temperature and high pressure liquid phase working medium absorbs heat and increases in temperature to become a gas-liquid mixed phase. Since the gas phase working medium is at normal temperature before entering the second heat exchanger 6, the gas after the low temperature liquid absorbs heat and vaporizes can also reach normal temperature, meeting the external transmission requirements, and the gas can be directly supplied to the outside without reheating. In addition, compared with the prior art, the temperature difference before and after the low-temperature liquid is vaporized is increased, and more cooling capacity can be provided under the same raw material conditions. At the same time, the low-temperature and high-pressure liquid phase working fluid also provides cooling capacity to the gas phase working fluid in the second heat exchanger 6, so that a larger flow rate of gas phase working fluid can be condensed, thereby increasing the circulation amount of the working fluid in the system.

[0030] Preferably, the first heat exchanger 4 is connected to the working medium expander 1 through a gas-liquid separator (not shown in the figure); wherein the gas-liquid separator has an inlet, a gas phase outlet and a liquid phase outlet; the inlet of the gas-liquid separator is connected to the outlet of the working medium expander 1, the gas phase outlet is connected to the inlet of the first heat exchanger 4, and the liquid phase outlet is connected to the inlet of the booster pump 7. The gas phase working medium separated by the gas-liquid separator enters the first heat exchanger 4 for heat exchange, and the liquid phase working medium is mixed with the low-pressure liquid phase working medium before the booster pump 7 and enters the booster pump 7 for pressure increase.

[0031] In a preferred embodiment, the outlet of the first flow channel 61 of the second heat exchanger 6 is connected to a gas expander, and the gas vaporized from the cryogenic liquid drives the gas expander to work, drives the generator to generate electricity, and utilizes the gas to do work to increase the power generation. The gas expander and the working fluid expander 1 are preferably an integrated machine.

[0032] According to the above introduction, the present invention has at least the following advantages: In the system of the present invention, due to the recycling of the cold energy of the low-temperature liquid phase mixed working medium, under the same raw material working conditions, the circulation volume of the working medium will increase, so that more heat can be absorbed from the outside, more work can be done to the outside to generate electricity, thereby achieving the purpose of improving the efficiency of cold energy utilization. At the same time, the two heatings before and after expansion also increase the absorbed heat, thereby increasing the output work and power generation. In addition, due to the configuration of the pre-expansion heater, space can be left for other cold energy utilization devices such as warehouse freezing, dry ice making, low-temperature crushing, etc., enriching the cold energy utilization methods.

[0033] Although the present invention has been described with reference to several typical embodiments, it should be understood that the terms used are illustrative and exemplary, rather than restrictive. Since the present invention can be embodied in a variety of forms without departing from the spirit or essence of the invention, it should be understood that the above embodiments are not limited to any of the foregoing details, but should be interpreted broadly within the spirit and scope defined by the appended claims, so all changes and modifications falling within the scope of the claims or their equivalents should be covered by the appended claims.

Claims

1. A system for generating electricity using cryogenic liquid cold energy, characterized in that: include: The working fluid expander is driven by the working fluid and drives the generator to generate electricity; A first heat exchanger is used for heat exchange between the working fluid and an external heat source, wherein the inlet of the first heat exchanger is connected to the outlet of the working fluid expander, and the temperature of the working fluid after heat exchange by the first heat exchanger is greater than 0°C and does not exceed 40°C; The second heat exchanger has a first flow channel for low-temperature liquid to flow, and a second flow channel and a third flow channel for working fluid to flow, respectively, the first flow channel and the third flow channel both perform heat exchange with the second flow channel; the inlet of the second flow channel is connected to the outlet of the first heat exchanger; a booster pump, the inlet of which is connected to the outlet of the second flow channel, and the outlet of which is connected to the inlet of the third flow channel; A third heat exchanger is used for heat exchange between the working fluid and an external heat source, wherein the inlet of the third heat exchanger is connected to the outlet of the third flow channel, and the outlet of the third heat exchanger is connected to the inlet of the working fluid expander; the first heat exchanger is connected to the working fluid expander through a gas-liquid separator; The gas-liquid separator has an inlet, a gas phase outlet and a liquid phase outlet; the inlet of the gas-liquid separator is connected to the outlet of the working fluid expander, the gas phase outlet is connected to the inlet of the first heat exchanger, and the liquid phase outlet is connected to the inlet of the booster pump.

2. The system according to claim 1, characterized in that The outlet of the first flow channel is connected to a gas expander, and the gas expander drives the generator to generate electricity.

3. The system according to claim 2, characterized in that The gas expander and the working fluid expander are integrated.

4. The system according to claim 1, characterized in that The external heat source of the first heat exchanger is natural gas supplementary combustion, air, seawater or waste heat.

5. The system according to claim 1, characterized in that The second heat exchanger is a plate type or a coiled tube type heat exchanger.

6. The system according to any one of claims 1 to 5, characterized in that: The external heat source of the third heat exchanger includes natural gas supplementary combustion or waste heat.

7. The system according to any one of claims 1 to 5, characterized in that: The cryogenic liquid is liquefied natural gas, liquid oxygen, liquid nitrogen or liquid ethylene.

8. The system according to any one of claims 1 to 5, characterized in that: The working fluid includes part or all of the following components: methane, ethane, propane, butane, pentane, nitrogen, and acetylene.

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