A low-temperature waste heat power generation system based on the principle of heat penetration and concentration difference energy utilization

Abstract

The present invention relates to a low-temperature waste heat power generation system based on the principle of thermal osmosis and the utilization of concentration difference energy, and belongs to the technical field of energy, waste heat and waste pressure recovery and utilization. The system is composed of two mutually coupled cycles: an osmotic side cold water cycle and a concentration difference energy power cycle; the osmotic side cold water cycle includes a hydrophobic membrane assembly, a hydraulic turbine, a cooling tower, a cooler, a cold water booster pump and a cooling water pump; the concentration difference energy power cycle includes a gas-liquid separator, an ejector, an absorption evaporator, a steam turbine, a feed water preheater I, a dilute solution pump, a feed water preheater II, a three-way regulating valve, a waste heat heater, a hydrophobic membrane assembly and a feed water pump. The present invention fully utilizes the thermal osmosis of the solution and the exothermic effect of the concentrated solution absorption and dilution process to efficiently recover the available energy of the low-temperature waste heat to produce high-grade mechanical energy or electrical energy, thereby achieving efficient recovery and utilization of the low-temperature waste heat, thereby maximizing the efficiency of the waste heat power generation system.

Description

Technical Field

[0001] The present invention relates to a low-temperature waste heat power generation system based on the heat penetration principle and concentration difference energy utilization, belonging to the technical field of energy, waste heat and waste pressure recovery and utilization. Background Art

[0002] Low-temperature waste heat below 350°C is a widespread resource, commonly found in industrial processes such as building materials, metallurgy, chemicals, and light industry. Its efficient recovery and utilization is crucial. Utilizing this vast amount of low-temperature waste heat saves approximately 0.4 kg of standard coal and 4 kg of water for every kWh of electricity generated, reducing emissions of environmental pollutants such as 0.997 kg of CO₂, 0.03 kg of SO₂, 0.015 kg of nitrogen oxides, and 0.272 kg of dust. It also alleviates the traffic, transportation, and environmental pressures along power lines caused by the large-scale coal consumption of power plants, and reduces the storage and transportation pressures of boiler ash. Converting the thermal energy of low-temperature waste heat into electricity is an effective way to improve energy efficiency and reduce environmental pollution. Key technologies for converting low-temperature waste heat into power (electricity) include the Organic Rankine Cycle (ORC), the Stirling cycle, thermoelectric power generation using semiconductor thermoelectric materials, the Kalina cycle using ammonia-water mixtures, and thermoacoustic power generation. These waste heat power generation technologies are either inefficient when the waste heat temperature is low (especially between 150-200°C), require high investment, or even face safety and environmental issues. Therefore, the search for new low-temperature waste heat power generation technologies is currently a hot topic of international research and a necessity for the continued development of low-temperature waste heat recovery and utilization technology. In 2014, Elimelech et al. from Yale University first proposed the concept of a thermal osmotic energy conversion system (TOEC). This system utilizes the vapor pressure difference across a membrane to drive water vapor flow across the membrane, recovering the available energy of the transmembrane water through a turbine and outputting mechanical work. The team experimentally demonstrated that a hydrophobic membrane can maintain a very thin air gap between the two liquids, even under a large pressure difference, demonstrating the feasibility of the TOEC. The team then analyzed the impact of system operating and membrane parameters on the system's power generation efficiency, and theoretically calculated that the TOEC system can achieve a power generation efficiency of up to 4.1% (34% Carnot efficiency). This innovative approach provides a new solution for waste heat recovery and the efficient utilization of low-temperature thermal energy, with significant application prospects. But overall, the efficiency of the waste heat power generation system constructed by this innovative exploration is still relatively low, and there is still much room for improvement. Summary of the Invention

[0003] In view of the invention and shortcomings of the above-mentioned prior art, combined with the above analysis, in order to improve the efficiency of the TOEC power generation system and make it have better practical application value. The present invention provides a low-temperature waste heat power generation system based on the principle of heat penetration and concentration difference energy utilization. The present invention makes full use of the heat penetration effect of the solution and the exothermic effect of the concentrated solution absorption and dilution process to efficiently recover the available energy of low-temperature waste heat to produce high-grade mechanical energy or electrical energy, thereby realizing the efficient recovery and utilization of low-temperature waste heat, thereby maximizing the efficiency of the waste heat power generation system, and providing a new idea and method for the utilization of low-temperature waste heat, while having the characteristics of high efficiency, low carbon emissions and high economic benefits.

[0004] The present invention is achieved through the following technical solutions.

[0005] A low-temperature waste heat power generation system based on the principle of heat penetration and the utilization of concentration difference energy, consisting of two mutually coupled cycles: a cold water cycle on the penetration side and a power cycle on the concentration difference energy side;

[0006] The cold water cycle on the osmosis side includes a hydrophobic membrane assembly 10, a hydraulic turbine 11, a cooling tower 13, a cooler 14, a cold water booster pump 15 and a cooling water pump 16;

[0007] The concentration difference energy cycle includes a gas-liquid separator 1, an ejector 2, an absorption evaporator 3, a steam turbine 4, a feed water preheater I5, a dilute solution pump 6, a feed water preheater II7, a three-way regulating valve 8, a waste heat heater 9, a hydrophobic membrane assembly 10 and a feed water pump 12;

[0008] In the cold water circulation on the permeation side, the permeation side outlet of the hydrophobic membrane assembly 10 is connected to the inlet of the hydraulic turbine 11. The hydraulic turbine 11 is divided into two paths, one of which is connected to the water feed pump 12 in the concentration difference energy circulation, and the other is connected to the liquid water inlet of the cooler 14. The liquid water outlet of the cooler 14 is returned to the permeation side inlet of the hydrophobic membrane assembly 10 through the cold water booster pump 15. The circulating cooling water is cooled by the cooling tower 13 and connected to the cooling circulating water inlet of the cooler 14 through the cooling water pump 16. The cooling circulating water outlet of the cooler 14 is connected to the cooling tower 13 to complete the cold water circulation on the permeation side.

[0009] In the concentration difference energy cycle, the feed water pump 12 is connected to the three-way regulating valve 8. The feed water in the three-way regulating valve 8 is divided into two paths. One path is preheated by the feed water preheater II7 and enters the collection pipe. The other path is preheated by the feed water preheater I5 and enters the collection pipe. The collection pipe is connected to the feed water pipe inlet of the absorption evaporator 3. After absorbing heat in the absorption evaporator 3, the feed water turns into steam and enters the steam turbine 4 to do work. The exhaust steam in the steam turbine 4 enters the ejector 2 as the ejector fluid; the concentrated solution outlet in the hydrophobic membrane assembly 10 passes through the feed water preheater I5 Then it enters the ejector 2 as the working fluid, the outlet of the ejector 2 is connected to the inlet of the gas-liquid separator 1 through a mixing tube, the steam outlet of the gas-liquid separator 1 is connected to the steam distributor at the bottom of the absorption evaporator 3 through a steam pipe, the concentrated solution outlet of the gas-liquid separator 1 is connected to the solution distributor at the top of the absorption evaporator 3 through a pipeline, the liquid well outlet at the bottom of the absorption evaporator 3 enters the feed water preheater II7 and the waste heat heater 9 in turn through the dilute solution pump 6, and then enters the dilute solution outlet of the hydrophobic membrane assembly 10, completing the concentration difference energy cycle.

[0010] The waste heat temperature in the waste heat heater 9 is 150-200°C.

[0011] The hydrophobic membrane in the hydrophobic membrane assembly 10 is a low surface energy polymer such as polytetrafluoroethylene, polyvinylidene fluoride, polypropylene or polyethylene. Due to the microporous structure and surface hydrophobic properties of the hydrophobic membrane, liquid cannot flow across the membrane, while steam can flow across the membrane under the action of the steam pressure difference on both sides, thereby concentrating the dilute solution into a concentrated solution and generating high-pressure water that can be used to recover mechanical work using a hydraulic turbine.

[0012] The concentrated solution is a solution formed by one or a mixture of any of CaCl2, CaBr2, LiCl, LiBr, LiI, LiNO3, NaOH, KCOOH, 1-ethyl-3-methylimidazolium ethyl sulfate, 1-ethyl-3-methylimidazolium tetrafluoroborate, NaOH, [Li(TX-7)]SCN, [EMIM]Ac, and H2SO4.

[0013] The scientific basis of the present invention is that, after years of practice and research as well as solution thermodynamics, it is known that aqueous solutions of some substances with strong absorption characteristics (such as CaCl2, LiCl, LiBr, etc.) have strong absorption characteristics for water vapor, and the absorption process releases a large amount of heat to increase the solution temperature. In some cases, the temperature of the salt solution can be as much as 60-70°C higher than the temperature of saturated water at the same pressure. This shows that such salts with higher concentrations have higher concentration differential energy. By adopting a reasonable method to efficiently utilize this concentration differential energy, useful work can be output to the outside.

[0014] In the cold water circulation on the osmosis side, the waste heat is fully utilized to heat the dilute solution so that the dilute solution has a certain thermal osmotic pressure, and the dilute solution is dehydrated and concentrated with the help of the hydrophobic membrane component 10 to obtain a concentrated solution. The high-pressure water generated by the condensation of the transmembrane water vapor on the osmosis side during the concentration process is then expanded through the hydraulic turbine 11 to perform work and output mechanical energy or electrical energy to the outside.

[0015] In the concentration difference energy cycle, the heat released during the steam dilution process of the concentrated solution in the absorption evaporator 3 is fully utilized to heat the feed water after the hydraulic turbine 11 has done work, so as to generate steam with a certain work capacity, which is then expanded and works through the steam turbine 4 to output mechanical energy or electrical energy to the outside.

[0016] The present invention adopts an ejector 2 and utilizes a concentrated solution with a certain residual pressure as the working fluid to inject the exhaust steam of the steam turbine, thereby reducing the turbine back pressure and increasing the turbine output power, realizing the power exchange between the concentrated solution and the turbine exhaust steam, and at the same time increasing the absorption pressure in the absorption evaporator, so that the absorption process can be carried out at a higher temperature, thereby ensuring that the steam generated by the evaporation coil has a higher work capacity.

[0017] The present invention provides a feed water preheater to efficiently recover the waste heat of the concentrated solution and the dilute solution entering and exiting the absorption evaporator 3, thereby improving the quality of the steam produced by the evaporation coil. The cooled dilute solution can better absorb the waste heat, thereby improving the utilization rate of the waste heat, while minimizing the volume of the absorption evaporator and reducing the cost.

[0018] The working principle of the present invention is:

[0019] In the cold water cycle on the permeation side of this system, the liquid water after the expansion and work of the hydraulic turbine 11 is divided into two paths. One path is used as the feed water for the power cycle of the solution concentration difference, and the other path enters the cooler 14 and is cooled into cold water with a lower temperature by the circulating cooling water delivered by the cooling tower 13. The cold water is delivered to the permeation side of the hydrophobic membrane component 10 by the cold water pressure pump 15 to provide cooling capacity for the transmembrane steam condensation. The two sides of the hydrophobic membrane in the hydrophobic membrane component 10 are respectively the dilute solution with a high temperature after absorbing the waste heat and the cold water. The dilute solution generates water vapor on the membrane surface due to the high heating temperature, while the permeation side has a low temperature and the steam partial pressure on the membrane surface is low, and the dilute solution generates Under the action of the vapor pressure difference on both sides of the membrane, the water vapor passes through the hydrophobic membrane pores to reach the permeation side and is condensed into liquid water by cold water, so that the water flow out of the permeation side of the hydrophobic membrane component 10 increases and the pressure increases. At the same time, the cold water absorbs the heat of condensation of the steam and its temperature increases. The heated high-pressure water coming out of the permeation side of the hydrophobic membrane component 10 is then introduced into the hydraulic turbine 11 for expansion, outputting mechanical work to the outside or driving the excitation generator to generate electricity. A part of the liquid water discharged from the hydraulic turbine 11 is cooled down again by the circulating cooling water in the cooler 14. The circulating cooling water after absorbing heat is cooled down by the cooling tower 13 and then sent to the cooler 14 by the cooling water pump 16 to absorb heat, completing a cycle.

[0020] In the solution concentration difference energy cycle of this system, a part of the feed water discharged from the hydraulic turbine 11 (the flow rate is equal to the flow rate of transmembrane water vapor) is sent to the three-way regulating valve 8 through the feed water pump 12, and is divided into two paths by the three-way regulating valve 8. One path sends the feed water to the feed water preheater I5, and the other path sends it to the feed water preheater II7. The two feed water paths respectively recover the waste heat of the concentrated solution and the dilute solution entering and leaving the absorption evaporator 3. The feed water after absorbing heat is merged and then flows into the tube of the evaporative cooling coil through the feed water pipe. The concentrated solution outside the absorption tube absorbs the heat released in the steam dilution process, and the feed water in the tube absorbs heat and becomes a certain heat. The steam with functional capacity is introduced into the steam turbine 4 to expand and do work, and output work to the outside or drive the excitation generator to output electricity. The turbine exhaust steam after doing work is used as the ejector fluid to exchange work and mix with the working fluid concentrated solution in the ejector 2. At the discharge port of the ejector 2, the turbine exhaust steam is pressurized and then enters the gas-liquid separator 1 together with the concentrated solution. The steam separated by pressure expansion is discharged from the upper part of the gas-liquid separator 1 as the absorbent, and enters the steam distributor at the bottom of the absorption evaporator 3 through the steam pipe. The steam flows upward and is continuously absorbed by the concentrated solution on the outer surface of the evaporation coil. The absorption process releases heat, and the concentrated solution absorbs the steam. After that, it becomes a dilute solution and flows into the 3 liquid wells at the bottom of the absorption evaporator. The dilute solution is pressurized by the dilute solution pump 6 and sent to the feed water preheater II7 to preheat the feed water entering the evaporation coil. After cooling in the feed water preheater II7, the dilute solution enters the waste heat heater 9, absorbs the waste heat with a temperature of 150-200℃, and is heated to a certain temperature so that the water therein has a higher osmotic pressure, and enters the hydrophobic membrane component 10 again. In the hydrophobic membrane component 10, the water in the dilute solution flows across the membrane in the form of steam under the action of the vapor pressure difference on both sides of the membrane into the osmotic side. After the water is removed, the dilute solution becomes a concentrated solution and is discharged from the hydrophobic membrane component 1 0, the concentrated solution then flows into the feed water preheater I5 to preheat the feed water entering the evaporating coil. The concentrated solution with a certain residual pressure after heat exchange is transported to the ejector 2 through the concentrated solution pipe, and is used as the working fluid to inject the turbine exhaust steam from the steam turbine 4 after work. The concentrated solution and the exhaust steam are discharged from the ejector 2 together and enter the gas-liquid separator 1. The concentrated solution coming out of the gas-liquid separator 1 enters the liquid distribution nozzle on the upper part of the absorption evaporator 3, and the nozzle evenly sprays the concentrated solution onto the outer surface of the evaporating coil. The concentrated solution continuously absorbs steam in the process of flowing from top to bottom, and the diluted solution is merged into the liquid well at the bottom of the absorption evaporator 3, completing a cycle.

[0021] The beneficial effects of the present invention are:

[0022] (1) The existing mature waste heat power generation technology has low efficiency and large investment when the waste heat temperature is low (especially within 150-200℃). Even the innovative TOEC power generation technology has problems such as low efficiency. The present invention makes full use of the principle of thermal penetration (material transfer caused by the temperature difference of the membrane) and the utilization of concentration difference energy, which can efficiently convert low-temperature waste heat into useful electrical energy, reduce dependence on high-quality energy, reduce energy consumption and carbon emissions, and does not rely on complex equipment and mechanical systems. Instead, it fully utilizes the unique physical properties of the membrane and solution, has strong modular design and scalability, is easy to industrialize, and has good practical application value.

[0023] (2) The concentration difference energy cycle of the present invention uses water as the working fluid of the power cycle, which has good heat transfer, strong work capacity, and is harmless to the environment. The working fluid is easy to obtain and cheap, and the low-parameter steam turbine is a very mature industrial product, which can ensure that the system has good economy.

[0024] (3) The present invention adopts equipment with mature production and manufacturing technology, which is conducive to industrialization and has good BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a structural schematic diagram of the low-temperature waste heat power generation system based on the heat penetration principle and concentration difference energy utilization of the present invention.

[0026] In the figure: 1-gas-liquid separator, 2-ejector, 3-absorption evaporator, 4-steam turbine, 5-feed water preheater I, 6-dilute solution pump, 7-feed water preheater II, 8-three-way regulating valve, 9-waste heat heater, 10-hydrophobic membrane assembly, 11-hydraulic turbine, 12-feed water pump, 13-cooling tower, 14-cooler, 15-cold water booster pump, 16-cooling water pump. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0028] Example 1

[0029] like Figure 1 As shown, the low-temperature waste heat power generation system based on the heat penetration principle and the utilization of concentration difference energy is composed of two mutually coupled cycles: the permeation side cold water cycle and the concentration difference energy power cycle;

[0030] The cold water cycle on the osmosis side includes a hydrophobic membrane assembly 10, a hydraulic turbine 11, a cooling tower 13, a cooler 14, a cold water booster pump 15 and a cooling water pump 16;

[0031] The concentration difference energy cycle includes a gas-liquid separator 1, an ejector 2, an absorption evaporator 3, a steam turbine 4, a feed water preheater I5, a dilute solution pump 6, a feed water preheater II7, a three-way regulating valve 8, a waste heat heater 9, a hydrophobic membrane assembly 10 and a feed water pump 12;

[0032] In the cold water circulation on the permeation side, the permeation side outlet of the hydrophobic membrane assembly 10 is connected to the inlet of the hydraulic turbine 11. The hydraulic turbine 11 is divided into two paths, one of which is connected to the water feed pump 12 in the concentration difference energy circulation, and the other is connected to the liquid water inlet of the cooler 14. The liquid water outlet of the cooler 14 is returned to the permeation side inlet of the hydrophobic membrane assembly 10 through the cold water booster pump 15. The circulating cooling water is cooled by the cooling tower 13 and connected to the cooling circulating water inlet of the cooler 14 through the cooling water pump 16. The cooling circulating water outlet of the cooler 14 is connected to the cooling tower 13 to complete the cold water circulation on the permeation side.

[0033] In the concentration difference energy cycle, the feed water pump 12 is connected to the three-way regulating valve 8. The feed water in the three-way regulating valve 8 is divided into two paths. One path is preheated by the feed water preheater II7 and enters the collection pipe. The other path is preheated by the feed water preheater I5 and enters the collection pipe. The collection pipe is connected to the feed water pipe inlet of the absorption evaporator 3. After absorbing heat in the absorption evaporator 3, the feed water turns into steam and enters the steam turbine 4 to do work. The exhaust steam in the steam turbine 4 enters the ejector 2 as the ejector fluid; the concentrated solution outlet in the hydrophobic membrane assembly 10 passes through the feed water preheater I5 Then it enters the ejector 2 as the working fluid, the outlet of the ejector 2 is connected to the inlet of the gas-liquid separator 1 through a mixing tube, the steam outlet of the gas-liquid separator 1 is connected to the steam distributor at the bottom of the absorption evaporator 3 through a steam pipe, the concentrated solution outlet of the gas-liquid separator 1 is connected to the solution distributor at the top of the absorption evaporator 3 through a pipeline, the liquid well outlet at the bottom of the absorption evaporator 3 enters the feed water preheater II7 and the waste heat heater 9 in turn through the dilute solution pump 6, and then enters the dilute solution outlet of the hydrophobic membrane assembly 10, completing the concentration difference energy cycle.

[0034] The waste heat temperature in the waste heat heater 9 is 150-200°C.

[0035] The hydrophobic membrane in the hydrophobic membrane assembly 10 is made of polytetrafluoroethylene. Due to the microporous structure and surface hydrophobic properties of the hydrophobic membrane, liquid cannot flow across the membrane, but steam can flow across the membrane under the action of the steam pressure difference on both sides, thereby concentrating the dilute solution into a concentrated solution and generating high-pressure water that can be used to recover mechanical work using a hydraulic turbine.

[0036] The concentrated solution is a CaCl2 solution with a concentration of 30-45 wt%, and the dilute solution is a CaCl2 solution with a concentration of 10-15 wt%.

[0037] The above describes the specific embodiments of the present invention in detail with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in this field without departing from the scope of the present invention.

Claims

1. A low-temperature waste heat power generation system based on the principle of heat penetration and concentration difference energy utilization, characterized by: It consists of two mutually coupled cycles: the cold water cycle on the osmotic side and the concentration difference energy cycle; The cold water cycle on the permeation side includes a hydrophobic membrane assembly (10), a hydraulic turbine (11), a cooling tower (13), a cooler (14), a cold water booster pump (15) and a cooling water pump (16); The concentration difference energy cycle includes a gas-liquid separator (1), an ejector (2), an absorption evaporator (3), a steam turbine (4), a feed water preheater I (5), a dilute solution pump (6), a feed water preheater II (7), a three-way regulating valve (8), a waste heat heater (9), a hydrophobic membrane assembly (10) and a feed water pump (12); The permeate side outlet of the hydrophobic membrane assembly (10) in the permeate side cold water circulation is connected to the inlet of the hydraulic turbine (11). The hydraulic turbine (11) is divided into two paths, one path is connected to the water feed pump (12) in the concentration difference energy circulation, and the other path is connected to the liquid water inlet of the cooler (14). The liquid water outlet of the cooler (14) returns to the permeate side inlet of the hydrophobic membrane assembly (10) through the cold water booster pump (15). The circulating cooling water is cooled by the cooling tower (13) and then connected to the cooling circulating water inlet of the cooler (14) through the cooling water pump (16). The cooling circulating water outlet of the cooler (14) is connected to the cooling tower (13), completing the permeate side cold water circulation; In the concentration difference energy cycle, the feed water pump (12) is connected to the three-way regulating valve (8). The feed water in the three-way regulating valve (8) is divided into two paths. One path is preheated by the feed water preheater II (7) and then enters the collection pipe. The other path is preheated by the feed water preheater I (5) and then enters the collection pipe. The collection pipe is connected to the feed water pipe inlet of the absorption evaporator (3). After absorbing heat in the absorption evaporator (3), the feed water becomes steam and enters the steam turbine (4) to do work. The exhaust steam in the steam turbine (4) enters the ejector (2) as the ejector fluid. The concentrated solution outlet of the hydrophobic membrane assembly (10) passes through the feed water preheater I (5) and then enters the collection pipe. The liquid enters the ejector (2) as a working fluid, the outlet of the ejector (2) is connected to the inlet of the gas-liquid separator (1) through a mixing tube, the steam outlet of the gas-liquid separator (1) is connected to the steam distributor at the bottom of the absorption evaporator (3) through a steam pipe, the concentrated solution outlet of the gas-liquid separator (1) is connected to the solution distributor at the top of the absorption evaporator (3) through a pipeline, the outlet of the liquid well at the bottom of the absorption evaporator (3) enters the feed water preheater II (7) and the waste heat heater (9) in sequence through the dilute solution pump (6), and then enters the dilute solution outlet of the hydrophobic membrane assembly (10), completing the concentration difference energy cycle.

2. The low-temperature waste heat power generation system based on the heat penetration principle and concentration difference energy utilization according to claim 1 is characterized in that: The waste heat temperature in the waste heat heater (9) is 150-200°C.

3. The low-temperature waste heat power generation system based on the heat penetration principle and concentration difference energy utilization according to claim 1 is characterized in that: The hydrophobic membrane in the hydrophobic membrane assembly (10) is a polymer with low surface energy, such as polytetrafluoroethylene, polyvinylidene fluoride, polypropylene or polyethylene.

4. The low-temperature waste heat power generation system based on the heat penetration principle and concentration difference energy utilization according to claim 1 is characterized in that: The concentrated solution is a solution formed by one or a mixture of any of CaCl2, CaBr2, LiCl, LiBr, LiI, LiNO3, NaOH, KCOOH, 1-ethyl-3-methylimidazolium ethyl sulfate, 1-ethyl-3-methylimidazolium tetrafluoroborate, NaOH, [Li(TX-7)]SCN, [EMIM]Ac, and H2SO4.

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