Patent Application
20240410299
This patent application claims the benefit and priority of Chinese Patent Application No. CN202110999876.1 filed with the China National Intellectual Property Administration on Aug. 26, 2021 and entitled “CONDENSATION SYSTEM AND METHOD FOR ELECTRIC POWER PLANT”, the disclosure of which is incorporated by reference herein in its entirety as part of the present application.
The present disclosure relates to the technical field of energy conservation and emission reduction in the circulating cooling system of an electric power plant, in particular to a condensation system and method for an electric power plant.
At present, China has put forward the requirements of carbon emission reduction and zero discharge of waste water in thermal power plants. The carbon emission and waste water discharge of coal-fired power plants mainly come from the following processes:
Firstly, the emission of the flue gas by the boiler causes carbon emission. After desulfurization and denitrification, the main components of flue gas are carbon dioxide, nitrogen and a small amount of water vapor. the emission of these fumes causes the emission of carbon dioxide.
Secondly, the largest volume of waste water discharged by thermal power plants is the circulating cooling wastewater discharged from the steam condensation section. In the condenser the exhausted steam coming from the turbine is condensed into water by cooling water, resulting in a huge pressure drop. The live steam coming from the boiler flows quickly through the turbine under this pressure drop, driving the turbine to rotate at high speed and generate electricity.
The condensation of the exhausted steam in the condenser is reached by heat exchange between the steam and a large amount of cooling water medium. After absorbing the heat of the exhausted steam, the cooling medium water becomes warm and is transferred to cyclic-water-cooling tower. In the cyclic-water-cooling tower, the warm cooling water will fall from the top of the tower to the cooling water pool, and during this process, some of the cooling water will vaporize into the air and thus reducing the temperature of the remaining cooling water. Then the cooled water can be used as cooling water again. In this process, the evaporation of part of the water causes the increase of the ion concentration in the water, and the water become dirtier and dirtier because of entrances of external impurities when the water contact with air, and because of corrosion of the heat exchanger, etc. On the other hand, the periodic increase and decrease of the temperature promotes the growth of bacteria and microorganisms. Therefore, with the increase of the number of cycles, the pollution degree of the cooling water gradually increases. The pollution accelerates the scaling and corrosion of condenser in turn and reduces the heat exchange efficiency seriously. So, after a period of time, part of the circulating water has to be drained and fresh water has to be added in as supplement. The discharge of these polluted wastewater becomes the main source of wastewater discharge of thermal power plants. The amount of the discharged wastewater is very large. At present, in China, the amount of circulating cooling water that needs to be discharged and the amount of fresh water that needs to be replenished per hour for thermal power plants of medium to large scale is generally as high as 50-200 tons/hour. This huge discharge and supplement is a huge burden, both for environmental pollution and precious fresh water resources. Therefore, the Chinese government recently put forward a policy requirement for thermal power enterprises to achieve zero wastewater discharge within a time limit.
In order to solve the above-mentioned problems, the present disclosure provides a novel steam condensation method of using carbon dioxide as cooling medium. According to the method provided by the present disclosure, the problems such as the huge demand for circulation cooling water in the condenser, the needs for complex anti-corrosion and anti-scaling processes, huge amounts of discharged wastewater and high cost to treat the waste water before discharge can be eliminated, and carbon emission of the electric power plant can be reduced to a certain extent when the cooling carbon dioxide is separated from the boiler flue gas.
In order to solve the above-mentioned technical problems, the present disclosure firstly provides a condensation system for an electric power plant. The condensation system comprises a steam turbine 1, a compressor 2, and a condenser 3. The steam turbine 1 comprises a steam turbine outlet, and the steam turbine outlet is used for discharging exhausted steam (low-pressure steam). The compressor 2 comprises a first compressor inlet and a compressor outlet. The condenser 3 comprises an exhausted steam inlet, a cooling medium inlet, a steam condensate outlet, and a cooling medium outlet. The exhausted steam inlet is connected to the steam turbine outlet. The cooling medium inlet is connected to the compressor outlet. The cooling medium inlet is used for inputting liquid carbon dioxide. The cooling medium outlet is connected to the first compressor inlet. The liquid carbon dioxide is used as a cooling medium in the condenser 3, and the cooling medium absorbs heat from the exhausted steam in the condenser 3 to condense the exhausted steam. The gasified carbon dioxide enters the compressor 2 to be compressed into liquid, and then the liquid enters the condenser 3 as cooling medium for recycling.
In one embodiment of the present disclosure, the condensation system for an electric power plant further comprises a boiler 4, and a carbon dioxide separation device 5. The steam turbine 1 further comprises a steam turbine inlet. The steam turbine inlet is used for inputting live steam (high-pressure steam) into the steam turbine. The compressor 2 further comprises a second compressor inlet. The boiler 4 comprises a flue gas outlet and a live steam outlet. The live steam outlet is connected to the steam turbine inlet. The flue gas outlet is used for discharging flue gas containing carbon dioxide, and the live steam passes through the steam turbine 1 through the steam turbine inlet and is discharged as exhausted steam (low-pressure steam) through the steam turbine outlet to enter the condenser 3. The carbon dioxide separation device 5 comprises a carbon dioxide separation inlet and a carbon dioxide separation outlet, and the carbon dioxide separation inlet is connected to the flue gas outlet. The carbon dioxide separation outlet discharges gaseous or liquid carbon dioxide. When the carbon dioxide separation outlet discharges carbon dioxide, the carbon dioxide separation outlet is connected to the second compressor inlet. When the carbon dioxide separation outlet discharges gaseous carbon dioxide, the carbon dioxide separation outlet is connected to the second compressor inlet. When the carbon dioxide separation outlet discharges liquid carbon dioxide, the carbon dioxide separation outlet is connected to the condenser medium inlet.
In one embodiment of the present disclosure, boiler water pretreatment equipment 6 is further arranged between the connecting loop of the condenser 3 and the boiler 4, and a liquid carbon dioxide storage tank 7 is further arranged between the compressor outlet and the condenser medium inlet; and a carbon dioxide storage tank 8 is further arranged between the condenser air outlet and the first compressor inlet.
In one embodiment of the present disclosure, the boiler water pretreatment equipment 6 comprises a pretreatment inlet, and a condensate pump 9 is arranged between the condenser water outlet and the pretreatment inlet.
In one embodiment of the present disclosure, the boiler water pretreatment equipment 6 further comprises a pretreatment outlet, the boiler 4 further comprises a feed inlet, and a feed pump 10 is arranged between the pretreatment outlet and the feed inlet.
In one embodiment of the present disclosure, the compressor 2 is a multistage compressor.
The present disclosure further provides a condensation method for an electric power plant, comprising the following steps:
In one embodiment of the present disclosure, before step S1, the condensation method for an electric power plant further comprises the following steps:
In one embodiment of the present disclosure, after step S2, the condensation method for an electric power plant further comprises the step S21 of sending the condensate discharged from the condenser water outlet to the boiler water pretreatment equipment through the condensate pump, and pretreating the condensate by the boiler water pretreatment equipment.
In one embodiment of the present disclosure, after step S21, the condensation method for an electric power plant further comprises the step S22 of sending the condensate treated by the boiler water pretreatment equipment to the boiler through a feed pump.
In the present disclosure, as shown in
Compared with the prior art, the technical scheme of the present disclosure has the following advantages:
Firstly, carbon dioxide is used as a circulating cooling medium of the condenser, instead of using cooling water as a cooling medium of the condenser, so that the consumption of water resources is reduced, zero emission of circulation waste water is realized, the problems of equipment corrosion and scaling caused by the concentration of circulating water are also eliminated. Huge and inefficient cyclic-water-cooling tower equipment and anticorrosion and descaling auxiliary equipment are not needed. The process is simplified, the occupied area of the equipment is greatly reduced, and valuable space is saved for the power plant. Meanwhile, the environmental pollution caused by the cooling and evaporation of circulating water and the high treatment cost before concentrated water emission are eliminated, and the economic benefit and environmental protection benefit are extremely obvious.
Secondly, compared with a system and a method using water as a cooling medium, the system and the method using the liquid carbon dioxide as a cooling medium have the following advantages. In the first aspect, the condensation of the exhausted steam (low-pressure steam) is reached by vaporization of the liquid carbon dioxide. The heat transfer processes of both sides of cold and hot fluids in the heat exchanger (condenser) belong to the heat transfer process with phase change, and the convective heat transfer coefficient of the heat transfer process with phase change is much higher than that of the convective heat transfer process without phase change, which occurs in the cooling process with water used as the cooling medium. Therefore, the total heat transfer coefficient in the heat transfer process by using liquid carbon dioxide as cooling medium can be about 10 times bigger than the heat transfer coefficient in the heat transfer process by using water as cooling medium. Accordingly, the heat transfer rate will be increased about ten times. he working efficiency will be greatly improved. Or, under similar working efficiency, the volume of the condenser will be reduced by about ten times. This will greatly reduce the floor area of the condenser and save space for the power plant, and reduce the equipment cost. In the second aspect, the latent heat released by vaporization of the liquid carbon dioxide is much higher than the sensible heat released by the temperature rise of the cooling water. The latent heat of vaporization of the liquid carbon dioxide is about 572.7-577.8 kJ/kg according to pressure condition at temperature range of −78.5° C. to −56.6° C., and the specific heat capacity at constant pressure is 0.838 KJ/kg° C. under 0° C. Assuming that carbon dioxide is vaporized and heated to 10° C., the heat absorption per kilogram of carbon dioxide is about 580 kJ/kg. If water is used as a refrigerant, assuming that the water temperature rises by 15° C., the heat absorption per kilogram of water is 63 KJ/kg. Therefore, the consumption of the cooling medium can be reduced by about 9.2 times when carbon dioxide is used as a coolant compared with that when water is used as a coolant. The reduction of cooling medium consumption and the increase of heat transfer temperature difference will greatly improve the heat transfer efficiency. In the third aspect, using carbon dioxide instead of water as refrigerant can improve the power generation efficiency of power plants. When use carbon dioxide as the cooling medium, the temperature of gasification of liquid carbon dioxide is between −50° C. and −70° C., and the back pressure of the condenser is lower through the low cold-side temperature, so that the steam expansion work power of the steam turbine is increased, then the electric power generation economy and profit of power plant can be greatly improved. In the fourth aspect, the used carbon dioxide can come from the flue gas of the electric power plant and does not need to be purchased at cost, and waste is changed into wealth, so that the outsourcing cost is saved. Therefore, using carbon dioxide instead of water as the cooling medium can simultaneously achieve the technical effects of improving heat exchange efficiency, improving power generation efficiency, reducing costs, saving water resources, reducing environmental pollution, etc.
Thirdly, the cost is reduced. The compressor is electrified by an auxiliary power supply of the electric power plant, and the cost of the compression of carbon dioxide is low. Meanwhile, the using of circulating cooling water is cancelled, thereby the huge cost of cyclic-water-cooling tower and circulation system caused by the circulation of cooling water, as well as the high costs of circulating water, high-pollution drainage water treatment, equipment corrosion maintenance, scaling and efficiency reduction, cleaning and maintenance of the heat exchanger are eliminated together. Therefore, the method proposed by the present disclosure can reduce the operating cost of the electric power plant.
For the purpose that the content of the present disclosure is clearly understood more easily, the following further illustrates the present disclosure according to the specific embodiments of the present disclosure and in combination with the attached figures.
Reference signs in
The present disclosure is further described in conjunction with the attached figures and specific embodiments so that those skilled in the art can better understand and implement the present disclosure, but the embodiments are not intended to be limitation of the present disclosure.
Referring to
The embodiment provides a condensation method for an electric power plant utilizing the system. The condensation method for an electric power plant comprises the following steps:
Compared with using water as the cooling medium, the method of using liquid carbon dioxide as the cooling medium has many advantages. Firstly, carbon dioxide comes from waste gas of the electric power plant and does not need to be purchased at cost, and waste is changed into wealth. Secondly, the consumption of water resources is reduced, the environment is protected. Thirdly, exhausted steam is condensed by vaporization of the liquid carbon dioxide. The heat transfer processes on both sides of cold and hot fluids in the heat exchanger (condenser) are convective heat transfer process with phase change. The heat transfer process with water as the cooling medium is the convective heat transfer process without phase change. The convective heat transfer coefficient of the heat transfer process with phase change is much higher than that of the convective heat transfer process without phase change. Therefore, the total heat transfer coefficient in the process of carbon dioxide heat transfer process is about 10 times higher than the heat transfer coefficient of the water convective heat transfer process. In another word, the heat transfer efficiency will be improved about 10 times higher in the heat transfer process by using liquid carbon dioxide as cooling medium than the heat transfer efficiency in the heat transfer process by using water as cooling medium. Fourthly, the latent heat released by the vaporization of the liquid carbon dioxide is much higher than the sensible heat released by the temperature rise of the cooling water. Under normal pressure, the latent heat of vaporization of the liquid carbon dioxide is 577.8 KJ/kg, and the specific heat capacity at constant pressure is 0.838 KJ/kg·° C. at zero. Assuming that carbon dioxide is vaporized and heated to 10° C., the heat absorption per kilogram of carbon dioxide is 580 kJ. If water is used as a refrigerant, assuming that the water temperature rises by 15° C., the heat absorption per kilogram of water is 63 kJ. Therefore, the consumption of the cooling medium can be reduced by about 10 times when carbon dioxide is used as a coolant compared with that when water is used as a coolant, the consumption of the cooling medium is reduced, the size of pipeline equipment and the space volume of the condenser can be correspondingly reduced. Fifthly, the thermal economy of the electric power plant can be improved. The temperature of the carbon dioxide as the cooling medium is 50° C. to 70° C. lower than that of water, so that the back pressure of the condenser can reach a lower limit, the steam expansion work power of the steam turbine is increased, the power generation efficiency is improved, and the electric power generation economy and profit of power plant can be greatly improved.
The liquid carbon dioxide cooling medium in the embodiment is obtained through flue gas separation and compression of a boiler. The continuously referring to
Further, boiler water pretreatment equipment 6 is further arranged between the connecting loop of the condenser 3 and the boiler 4, and a liquid carbon dioxide storage tank 7 is further arranged between the compressor 2 outlet and the condenser cooling medium inlet. A carbon dioxide storage tank 8 is further arranged between the condenser cooling medium outlet and the first compressor inlet. The boiler water pretreatment equipment 6 comprises a pretreatment inlet, and a condensate pump 9 is arranged between the condenser water outlet and the pretreatment inlet. The boiler water pretreatment equipment 6 further comprises a pretreatment outlet, the boiler 4 further comprises a feed inlet, and a feed pump 10 is arranged between the pretreatment outlet and the feed inlet. The compressor 2 is preferably a multistage compressor, and the gaseous carbon dioxide can be better compressed.
Through the arrangement, a cyclic-water-cooling tower is not required, and a series problem such as equipment corrosion, scaling of a heat exchanger, drainage water treatment can be eliminated. Other problems, such as needs for anti-corrosion and anti-scaling equipments, big floor space and air pollution caused by water evaporation can be eliminated too.
Further, the embodiment further provides a technological method utilizing the system, comprising the following steps:
In the embodiment, if the carbon dioxide discharged from the separation outlet in the step S2 is gas, a part of separated carbon dioxide is firstly taken as a by-product, and the other part of separated carbon dioxide is introduced into the compressor from the second compressor inlet to be compressed to obtain the liquid carbon dioxide, and the liquid carbon dioxide is introduced into the condenser 3 through the condenser medium inlet.
Obviously, the embodiments are merely illustrative of the present disclosure as examples and are not intended to be limitation of embodiments of the present disclosure. For those of ordinary skill in the art, other variations or modifications in different forms may be made on the basis of the above description. All embodiments need not be exhaustive or otherwise impossible to be exhaustive herein. Obvious changes or variations which belong to the technical scheme of the present disclosure are still within the scope of protection of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202110999876.1 | Aug 2021 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2022/094316 | 5/23/2022 | WO |
