A method for generating electricity using a low-temperature hot water system

Abstract

The present invention discloses a method for generating electricity using a low-temperature hot water system, and relates to the field of low-temperature power generation technology. The method for generating electricity using a low-temperature hot water system includes a low-temperature hot water system, which includes an evaporator, an absorber, a generator, a condenser, a refrigerant water circulation pump, a refrigerant water liquid delivery pump, a concentrated solution pump, a solution heat exchanger, a screw power machine, a generator, a cooler, and a high-temperature hot water pump. The method for generating electricity using the low-temperature hot water system uses low-temperature hot water through a second-type absorption heat pump to produce high-temperature hot water (100°C to 130°C) that meets the requirements for efficient and economical operation of a full-flow screw power machine. The high-temperature hot water is used as a working medium to improve the efficiency of hot water power generation after entering the screw power machine power generation system with lower temperature hot water.

Description

Technical Field

[0001] The present invention relates to the technical field of low-temperature power generation, and in particular to a power generation method using a low-temperature hot water system. Background Art

[0002] Hot water with a temperature not higher than 100℃ is usually called low-temperature hot water. In industrial enterprises such as steel mills, there is a large amount of circulating cooling water, which is usually only at a temperature of 60℃ to 80℃. For example, blast furnace slag water, 3200m 3 The blast furnace's slag-flushing water circulates approximately 2,200 t / h. This low-temperature hot water is typically cooled in a cooling tower before being recycled, making it difficult to recycle its heat. While the low-temperature hot water is relatively low in temperature, its volume is large. Cooling it through a cooling tower not only consumes energy for the pumps and fans it runs, but also significantly wastes heat.

[0003] Screw expanders mainly use power sources such as steam, hot water, hot liquid or vapor-liquid two-phase fluid to convert thermal energy into power. They can drive generators to generate electricity, or they can replace electric motors to directly drive mechanical equipment or replace the expansion valve of large refrigerators to recover power.

[0004] Compared to common steam turbines, screw compressors' efficiency can adapt to changes in working fluid parameters and loads, including changes in industrial and mining production, heat and electricity loads, waste heat and residual pressure parameters, and working fluid quality, while maintaining stable, high efficiency and ensuring smooth, safe, and reliable operation. The screw compressor's structural characteristics provide self-decontamination, eliminating the need for specific cleanliness requirements for vapor and liquid working fluids. The working fluid does not require any thermal engineering treatment (such as flash expansion vessels, steam-water separators, superheaters, etc.) before entering the screw compressor, resulting in a relatively simple thermal system.

[0005] There are two main types of screw compressor power generation processes: full-flow system and organic Rankine cycle (ORC) system. The full-flow system has a simpler process structure than the ORC system.

[0006] The second type of absorption heat pump is also called a heating type heat pump. It absorbs heat from a heat source at 60℃~100℃ to produce a relatively small amount of high-temperature hot water with a temperature of 90℃~175℃.

[0007] The Chinese utility model patent "Screw Expansion Power Generator Set" (publication number: CN 201747418U) describes only the optimized design of an independent screw power generator set system. Generally speaking, it is a device that can use low-grade waste heat to generate electricity. This patent points out the optimal operating parameter range for hot water as the working fluid of a full-flow screw power generator, and elaborates on the method of obtaining hot water with optimal operating parameters from low-grade waste heat.

[0008] The Chinese invention patent "A Hot Water Temperature Difference Power Generation System" (publication number: CN 10316652A) describes the use of hot water temperature difference to generate electricity, which is completely different from the idea and equipment system of using a power machine to generate electricity in this patent.

[0009] The invention of a water turbine power generation device that directly uses hot water, as described in the Chinese invention patent "Hot Water Power Generation Device" (publication number: CN 103382858A), is different from the screw motor power generation principle of this patent.

[0010] The Chinese invention patent "A Screw Expansion Power Generation Device" (publication number: CN 106142507A) mainly describes innovations in the manufacturing materials and processes of the screw expansion power generation device body. This patent does not involve content related to equipment manufacturing.

[0011] The Chinese utility model patent "Semi-enclosed screw waste heat power generation system" (publication number: CN 212535796U) describes a specific optimization and improvement of the screw power generation device, and does not involve the innovation point of this patent - how to efficiently and economically complete the low-temperature hot water power generation process.

[0012] The Chinese invention patent "Gypsum Board Production Line Containing Wet Air Low-Temperature Power Generation System" (publication number: CN202788963U) uses waste heat in the temperature range of 120℃ to 150℃. The waste heat source exchanges heat with water to produce hot water above 90℃. The hot water is then exchanged with a Freon-type organic working fluid to reach a working fluid temperature of about 70℃ to drive the screw machine to generate electricity. The temperature of the remaining heat decreases step by step after each heat exchange. Summary of the Invention

[0013] (1) Technical problems solved

[0014] In view of the shortcomings of the existing technology, the present invention provides a method for generating electricity using a low-temperature hot water system, which solves the technical problems mentioned in the background technology.

[0015] (2) Technical solution

[0016] Using numerical simulation software, the power generation efficiency of full-flow and ORC screw compressor power generation systems with identical boundary conditions was simulated. The purpose of the calculations was to analyze the power generation efficiency of the two systems within the hot water inlet temperature range of 60°C to 175°C. The results showed that the power generation efficiency of the full-flow system was relatively low, at 8-17%, within the hot water inlet temperature range of 60°C to 90°C, while the ORC system's was even lower, at around 5%. Therefore, hot water at 60°C to 90°C is not practical for either power generation system. The power generation efficiency of the full-flow system remained stable at around 21% within the hot water inlet temperature range of 90°C to 175°C, while the power generation efficiency of the ORC system gradually increased from 7% to 27% with hot water temperature, and reached 21% at a hot water temperature of 130°C. In other words, the power generation efficiency of the ORC system surpassed that of the full-flow system within the hot water temperature range of 130°C to 175°C.

[0017] Although low-temperature hot water above 60°C can be directly fed into the screw compressor power generation system, both systems have low power generation efficiency and are essentially of no practical value. However, the second type of lithium bromide absorption heat pump absorbs heat from low-temperature hot water above 60°C to produce high-temperature hot water ranging from 90°C to 175°C. When the heat pump produces hot water at a temperature above 130°C, even if the ORC system exceeds 21% of the power generation efficiency of the full-flow system, due to the heat pump's characteristic of lowering the heating performance coefficient (energy efficiency ratio) with higher hot water production temperatures, the full-flow system's power generation efficiency will not be lower than that of the ORC system, considering the heat pump's energy efficiency characteristics and the screw compressor power generation system as a whole. Furthermore, the ORC system is more complex and expensive than the full-flow system in terms of technology, subsequent operation and maintenance costs. Therefore, the temperature of high-temperature hot water produced by the heat pump should not exceed 130°C.

[0018] Hot water at 90°C to 100°C is considered normal pressure water. To reduce the energy consumption of the high-temperature water pump, the required hot water should be superheated water at a certain pressure, so the hot water temperature cannot be lower than 100°C. Therefore, the temperature range of the high-temperature hot water produced by the heat pump in this solution is 100°C to 130°C, corresponding to an absolute pressure of 1atm to 3atm.

[0019] The low-temperature hot water with a temperature above 60°C is sent to the generator of the heat pump (which exchanges heat with the dilute lithium bromide solution from the absorber inside the heat pump to evaporate the refrigerant water and turn the dilute solution into a concentrated solution in the condenser) and the evaporator after necessary impurity and salt removal. The refrigerant water in the evaporator exchanges heat with the low-temperature hot water and evaporates under a higher pressure. After being absorbed by the concentrated lithium bromide solution in the absorber, the solution becomes dilute. Due to the dual exothermic effects of the phase change of the refrigerant water and the dilution of the solution, the external water exchanged with it can be heated to a high-temperature hot water of 100°C to 130°C that meets the inlet requirements of the screw power machine.

[0020] High-temperature hot water is passed into the screw power machine, allowing the hot water to expand inside the machine body and generate work to drive the generator to generate electricity.

[0021] From the perspectives of reducing cooling energy consumption and improving the overall energy efficiency of the system, the exhaust steam from the screw power unit enters the cooler and is cooled to below 90°C. The hot water below 90°C then enters the absorber again through the water pump.

[0022] The specific plan is as follows:

[0023] A method for generating electricity using a low-temperature hot water system, comprising a low-temperature hot water system comprising an evaporator, an absorber, a generator, a condenser, a refrigerant water circulation pump, a refrigerant water liquid delivery pump, a concentrated solution pump, a solution heat exchanger, a screw power machine, a generator, a cooler, and a high-temperature hot water pump;

[0024] High-temperature hot water, low-temperature hot water, cooling water, refrigerant water, solution;

[0025] The cooling water is used for heat transfer of the condenser and the cooler;

[0026] The low-temperature hot water is used for heat transfer in the evaporator and the generator;

[0027] The output end of the screw power machine is connected to the generator and provides power to the generator;

[0028] The inlet of the screw power machine is connected to the outlet of side A of the absorber;

[0029] The outlet of the screw power machine is connected to the inlet of the cooler, the outlet of the cooler is connected to the inlet of the high-temperature hot water pump, and the outlet of the high-temperature hot water pump is connected to the inlet of the A side of the absorber;

[0030] The high-temperature hot water circulates in the screw power machine, the cooler, the high-temperature hot water pump, and the absorber;

[0031] The B-side outlet of the absorber is connected to the B-side inlet of the solution heat exchanger, the B-side outlet of the solution heat exchanger is connected to the B-side inlet of the generator, the B-side outlet of the generator is connected to the inlet of the concentrated solution pump, the outlet of the concentrated solution pump is connected to the A-side inlet of the solution heat exchanger, and the A-side outlet of the solution heat exchanger is connected to the B-side inlet of the absorber;

[0032] The solution circulates in the absorber, the generator, and the solution heat exchanger. When the solution is at the B-side outlet of the absorber and enters the B-side inlet of the generator, it is a dilute solution. When the solution is at the B-side outlet of the generator and enters the B-side inlet of the absorber, it is a concentrated solution.

[0033] The C-side inlet of the absorber is connected to the B-side outlet of the evaporator, the B-side of the evaporator is connected in parallel with the refrigerant water circulation pump, the B-side outlet of the condenser is connected to the inlet of the refrigerant water liquid feeding pump, the outlet of the refrigerant water liquid feeding pump is connected to the B-side of the evaporator, and the C-side outlet of the generator is connected to the inlet of the B-side of the condenser;

[0034] The refrigerant water flows in the evaporator, absorber, generator, and condenser;

[0035] The power generation method comprises the following steps:

[0036] S1: The temperature of the high-temperature hot water is selected between 100°C and 130°C, and the pressure is selected between 1atm and 3atm;

[0037] S2: After necessary impurity and salt removal, low-temperature hot water with a temperature above 60°C is sent to the generator and evaporator respectively. The refrigerant water in the evaporator exchanges heat with the low-temperature hot water and evaporates under a higher pressure. After being absorbed by the concentrated solution in the absorber, the solution becomes dilute. Due to the dual exothermic effect of the refrigerant water phase change and solution dilution, the external water exchanged with it can be heated to high-temperature hot water of 100°C to 130°C that meets the inlet requirements of the screw power machine;

[0038] S3: High-temperature hot water is introduced into the screw power machine, allowing the hot water to expand inside the machine body and generate work to drive the generator to generate electricity;

[0039] S4: The exhaust steam from the screw power machine enters the cooler and is cooled to below 90℃. The hot water below 90℃ enters the absorber again through the water pump.

[0040] Preferably, the solution is a lithium bromide solution.

[0041] Preferably, the dilute lithium bromide solution from the absorber is heat exchanged to evaporate the refrigerant water to the condenser to convert the dilute solution into a concentrated solution.

[0042] Preferably, the heating coefficient of the second type absorption heat pump is 0.4-0.5.

[0043] Preferably, the refrigerant water in the evaporator absorbs heat and evaporates into the absorber. After the refrigerant water vapor enters the absorber, the lithium bromide concentrated solution becomes a dilute solution, accompanied by a double heat release of the refrigerant water phase change and solution dilution.

[0044] Preferably, the unevaporated refrigerant water in the evaporator is again heat-exchanged with low-temperature hot water after passing through a circulation pump.

[0045] Preferably, the lithium bromide concentrated solution in the generator is exchanged with the dilute solution from the absorber in a heat exchanger through a solution pump, and the concentrated solution enters the absorber again, and the dilute solution enters the generator again, completing the lithium bromide absorbent cycle.

[0046] Preferably, the vapor of the refrigerant water enters the condenser and is cooled by external cooling water to become liquid refrigerant water, and then enters the evaporator through a liquid delivery pump to complete the refrigerant water circulation.

[0047] Preferably, the external water absorbs phase change heat and dilution heat in the absorber to become high-temperature hot water of 100°C to 130°C that meets the inlet requirements of the screw power machine. The high-temperature hot water is introduced into the screw power machine to allow the hot water to expand inside the machine body and do work to drive the generator to generate electricity.

[0048] (3) Beneficial effects

[0049] The present invention provides a method for generating electricity using a low-temperature hot water system. It has the following beneficial effects:

[0050] (1) In the power generation method using the low-temperature hot water system, low-temperature hot water is used through a second-type absorption heat pump to produce high-temperature hot water (100°C to 130°C) that meets the requirements for efficient and economical operation of the full-flow screw power machine.

[0051] (2) In the power generation method using a low-temperature hot water system, high-temperature hot water and low-temperature hot water are used as working fluids to enter the screw power generation system to improve the hot water power generation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 Schematic diagram of the system of the present invention.

[0053] In the figure: 1. Evaporator; 2. Absorber; 3. Generator; 4. Condenser; 5. Refrigerant water circulation pump; 6. Refrigerant water liquid delivery pump; 7. Concentrated solution pump; 8. Solution heat exchanger; 9. Screw power machine; 10. Generator; 11. Cooler; 12. High-temperature hot water pump. DETAILED DESCRIPTION

[0054] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0055] Based on the actual situation, the factory conducts load statistical calculations on the cooling circulating water conditions where a low-temperature hot water power generation system is required, and selects the heat pump and screw expander generator sets based on the calculation results.

[0056] The low-temperature hot water with a temperature above 60°C is sent to the evaporator 1 and generator 3 of the heat pump after necessary impurity and salt removal for heat exchange and then returned to the original system for use.

[0057] The refrigerant water in evaporator 1 absorbs heat and evaporates into absorber 2. After the refrigerant water vapor enters absorber 2, the lithium bromide concentrated solution becomes a dilute solution, accompanied by double heat release of refrigerant water phase change and solution dilution.

[0058] The unevaporated refrigerant water in the evaporator 1 passes through the circulation pump 5 and exchanges heat with the low-temperature hot water again.

[0059] After the dilute lithium bromide solution in the generator 3 absorbs heat, the refrigerant water evaporates and enters the condenser 4. At the same time, the dilute lithium bromide solution in the generator 3 becomes a concentrated solution.

[0060] The concentrated lithium bromide solution in the generator 3 is pumped by the solution pump 7 and then heat-exchanged with the dilute solution from the absorber 2 in the heat exchanger 8. The concentrated solution then enters the absorber 2 again, and the dilute solution then enters the generator 3 again, completing the lithium bromide absorbent cycle.

[0061] The refrigerant water vapor enters the condenser 4 and is cooled by the external cooling water into liquid refrigerant water, and then enters the evaporator 1 through the liquid pump 6, completing the refrigerant water cycle.

[0062] After absorbing phase change heat and dilution heat in the absorber 2, the external water becomes high-temperature hot water of 100°C to 130°C that meets the inlet requirements of the screw power machine 9. The high-temperature hot water is passed into the screw power machine 9 to allow the hot water to expand inside the machine body and do work to drive the generator 10 to generate electricity.

[0063] The exhaust steam from the screw power machine 9 enters the cooler 11 and is cooled to hot water below 90°C. It then enters the absorber 2 again through the water pump 12 for heat exchange, completing the high-temperature hot water cycle.

[0064] The high-temperature hot water circulation system needs to be equipped with a water replenishment device to make up for the losses during its circulation operation.

[0065] In this scheme, the low-temperature hot water inlet and outlet temperatures of the heat pump system are calculated as 80℃ / 60℃, and the high-temperature hot water inlet and outlet temperatures of the screw power machine are calculated as 130℃ / 90℃. The heating coefficient of the heat pump system is about 0.45, so 1000t / h of low-temperature hot water can be matched with a 900kW screw expander generator set.

[0066] It should be noted that, in the description of the invention, the terms "up", "down", "left", "right", "front", "back", etc. indicating directions or positional relationships are based on the description of the structure of the present invention as shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, it cannot be understood as a limitation on the present invention.

[0067] The "first" and "second" in this technical solution are only used to distinguish the same or similar structures, or corresponding structures with similar functions, and are not an arrangement of the importance of these structures, nor do they have any ranking, size comparison, or other meanings.

[0068] In addition, unless otherwise expressly specified or limited, the terms "installed" and "connected" should be understood broadly. For example, a connection can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be internal communication between two structures. Those skilled in the art can understand the specific meanings of the above terms in the present invention based on the overall principles of the present invention and the specific context of this solution.

Claims

1. A method for generating electricity using a low-temperature hot water system, comprising: The low-temperature hot water system includes an evaporator, an absorber, a generator, a condenser, a refrigerant water circulation pump, a refrigerant water liquid delivery pump, a concentrated solution pump, a solution heat exchanger, a screw power machine, a generator, a cooler, and a high-temperature hot water pump; High-temperature hot water, low-temperature hot water, cooling water, refrigerant water, solution; The cooling water is used for heat transfer of the condenser and the cooler; The low-temperature hot water is used for heat transfer in the evaporator and the generator; The output end of the screw power machine is connected to the generator and provides power to the generator; The inlet of the screw power machine is connected to the outlet of side A of the absorber; The outlet of the screw power machine is connected to the inlet of the cooler, the outlet of the cooler is connected to the inlet of the high-temperature hot water pump, and the outlet of the high-temperature hot water pump is connected to the inlet of the A side of the absorber; The high-temperature hot water circulates in the screw power machine, the cooler, the high-temperature hot water pump, and the absorber; The B-side outlet of the absorber is connected to the B-side inlet of the solution heat exchanger, the B-side outlet of the solution heat exchanger is connected to the B-side inlet of the generator, the B-side outlet of the generator is connected to the inlet of the concentrated solution pump, the outlet of the concentrated solution pump is connected to the A-side inlet of the solution heat exchanger, and the A-side outlet of the solution heat exchanger is connected to the B-side inlet of the absorber; The solution circulates in the absorber, the generator, and the solution heat exchanger. When the solution is at the B-side outlet of the absorber and enters the B-side inlet of the generator, it is a dilute solution. When the solution is at the B-side outlet of the generator and enters the B-side inlet of the absorber, it is a concentrated solution. The C-side inlet of the absorber is connected to the B-side outlet of the evaporator, the B-side of the evaporator is connected in parallel with the refrigerant water circulation pump, the B-side outlet of the condenser is connected to the inlet of the refrigerant water liquid feeding pump, the outlet of the refrigerant water liquid feeding pump is connected to the B-side of the evaporator, and the C-side outlet of the generator is connected to the inlet of the B-side of the condenser; The refrigerant water flows in the evaporator, absorber, generator, and condenser; The power generation method comprises the following steps: S1: The temperature of the high-temperature hot water is selected between 100°C and 130°C, and the pressure is selected between 1atm and 3atm; S2: After necessary impurity and salt removal, low-temperature hot water with a temperature above 60°C is sent to the generator and evaporator respectively. The refrigerant water in the evaporator exchanges heat with the low-temperature hot water and evaporates under a higher pressure. After being absorbed by the concentrated solution in the absorber, the solution becomes dilute. Due to the dual exothermic effect of the refrigerant water phase change and solution dilution, the external water exchanged with it can be heated to high-temperature hot water of 100°C to 130°C that meets the inlet requirements of the screw power machine; S3: High-temperature hot water is introduced into the screw power machine, allowing the hot water to expand inside the machine body and generate work to drive the generator to generate electricity; S4: The exhaust steam from the screw power machine enters the cooler and is cooled to below 90℃. The hot water below 90℃ enters the absorber again through the water pump.

2. The method for generating electricity using a low-temperature hot water system according to claim 1, characterized in that: The solution is a lithium bromide solution.

3. The method for generating electricity using a low-temperature hot water system according to claim 2, characterized in that: The dilute lithium bromide solution from the absorber exchanges heat and evaporates the refrigerant water into the condenser, and the dilute solution becomes a concentrated solution.

4. The method for generating electricity using a low-temperature hot water system according to claim 2, characterized in that: The refrigerant water in the evaporator absorbs heat and evaporates into the absorber. After the refrigerant water vapor enters the absorber, the lithium bromide concentrated solution becomes a dilute solution, accompanied by double heat release of the refrigerant water phase change and solution dilution.

5. The method for generating electricity using a low-temperature hot water system according to claim 1, characterized in that: The refrigerant water that has not evaporated in the evaporator is passed through the circulation pump and then exchanges heat with the low-temperature hot water again.

6. The method for generating electricity using a low-temperature hot water system according to claim 2, characterized in that: The lithium bromide concentrated solution in the generator is pumped through a solution pump and then heat-exchanged with the dilute solution from the absorber in a heat exchanger. The concentrated solution then enters the absorber again, and the dilute solution then enters the generator again, completing the lithium bromide absorbent cycle.

7. The method for generating electricity using a low-temperature hot water system according to claim 1, characterized in that: The refrigerant water vapor enters the condenser and is cooled by external cooling water to become liquid refrigerant water, and then enters the evaporator through the liquid delivery pump, completing the refrigerant water cycle.

8. The method for generating electricity using a low-temperature hot water system according to claim 1, characterized in that: The external water absorbs phase change heat and dilution heat in the absorber and becomes high-temperature hot water of 100°C to 130°C that meets the inlet requirements of the screw power machine. The high-temperature hot water is passed into the screw power machine to expand inside the machine body and do work to drive the generator to generate electricity.

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