Multi-stage comprehensive utilization system and method for cold energy of liquid ammonia in coal-fired power plant

Abstract

The invention relates to a multi-stage comprehensive utilization system and method for liquid ammonia cold energy in a coal-fired power plant, and belongs to the field of ammonia combustion power generation and comprehensive utilization of energy. The system comprises a liquid ammonia pump used for adjusting the proportion of liquid ammonia introduced into a primary cooling unit and a secondary cooling unit from a liquid ammonia storage tank; the primary cooling unit is used for introducing CO2-rich gas and exchanging heat with liquid ammonia; the second-stage cooling unit is used for introducing circulating water and performing heat exchange with liquid ammonia to form low-temperature ammonia gas, and introducing the low-temperature ammonia gas and the cooled circulating water into the third-stage cooling unit; the third-stage cooling unit is used for introducing dead steam and performing heat exchange with the low-temperature ammonia gas to form high-temperature ammonia gas, and meanwhile, the dead steam is cooled and condensed into circulating water; and the power generation unit is used for heating circulating water by blending ammonia gas so as to form water vapor for power generation. According to the invention, cross-temperature gradient deep recovery of cold energy is realized through three-stage cold energy distribution, cross-temperature gradient deep recovery of cold energy is realized, and deep coupling with a water circulation system and a CO2 capture system is realized.

Description

Technical Field

[0001] The present invention belongs to the field of ammonia combustion power generation and comprehensive energy utilization, and specifically relates to a multi-stage comprehensive utilization system and method of liquid ammonia cooling energy in a coal-fired power plant. Background Art

[0002] Coal-fired power plants face a series of energy consumption and efficiency challenges during operation. First, with increasing environmental protection requirements, power plants have added CO2 capture processes. The pre-cooling process consumes a large amount of electricity. The energy consumption of traditional mechanical refrigeration methods accounts for over 30% of the total capture cost, which significantly increases the cost of carbon capture. Second, while the direct air cooling system used for turbine exhaust steam cooling can save water, the plant's electricity utilization rate is as high as 6.5%-8.0%. Especially in the high temperatures of summer, cooling efficiency can drop by 20%-30%, resulting in increased turbine backpressure and seriously affecting the unit's power generation efficiency. Third, during the operation of the circulating water system, a large amount of low-temperature waste heat is not effectively recovered and utilized, resulting in a serious waste of resources.

[0003] Ammonia is a zero-carbon alternative fuel. Its combustion reaction releases energy without producing carbon emissions. Compared to hydrogen, ammonia has the advantages of high energy density, easy liquefaction, and ease of transportation. When blended with ammonia for combustion in coal-fired power plants, it can provide a stable, low-carbon baseload and also play a vital role in peak load regulation. Therefore, green power generation systems fueled by ammonia have attracted considerable attention.

[0004] Currently, liquid ammonia is usually stored at a low temperature of -33°C, and power plants must first gasify it before sending it to boilers for combustion. The latent heat of vaporization of liquid ammonia is about 1370 kJ / kg, and a large amount of cold energy is released during the gasification process. However, traditional methods of utilizing liquid ammonia cold energy are relatively primitive, and most of them only perform simple one-stage heat exchange, resulting in a cold energy utilization rate of less than 60%, causing a large amount of energy waste. At the same time, how to achieve multi-stage and efficient utilization of liquid ammonia cold energy, deeply couple cold energy recovery with CO2 capture, exhaust steam cooling, waste heat recovery and other systems, and realize cascade utilization of energy has become a technical problem that needs to be solved urgently. Summary of the Invention

[0005] The purpose of the present invention is to provide a system and method for the multi-stage comprehensive utilization of liquid ammonia cold energy in coal-fired power plants, so as to solve the problems of low liquid ammonia cold energy utilization rate when coal-fired power plants mix ammonia, and the inability to deeply couple cold energy recovery with the CO2 capture, exhaust steam cooling, waste heat recovery and other systems of the coal-fired power plants.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows: The present invention relates to a multi-stage comprehensive utilization system of liquid ammonia cooling energy in a coal-fired power plant, comprising: Liquid ammonia storage tank, used to store liquid ammonia; Liquid ammonia pump, used to adjust the ratio of liquid ammonia flowing from the liquid ammonia storage tank into the primary cooling unit and the secondary cooling unit; The primary cooling unit is used to introduce the CO2-rich gas generated by the power generation unit and exchange heat with liquid ammonia to form a liquid ammonia and ammonia gas mixture; The secondary cooling unit is used to pass circulating water and exchange heat with liquid ammonia to form low-temperature ammonia gas, and pass the low-temperature ammonia gas and the cooled circulating water into the tertiary cooling unit; The third-stage cooling unit is used to introduce the exhaust steam generated by the power generation unit and exchange heat with the low-temperature ammonia to form high-temperature ammonia, while cooling and condensing the exhaust steam into circulating water; The power generation unit is used to mix and burn the ammonia output from the primary cooling unit and the tertiary cooling unit, heat the circulating water output from the tertiary cooling unit, and then generate water vapor for power generation.

[0007] Preferably, the power generation unit comprises: The boiler is used to pass ammonia generated in the primary cooling unit and the tertiary cooling unit through the gas channel, and to pass circulating water in the tertiary cooling unit through the liquid channel, and to heat the circulating water by mixing with ammonia to form water vapor, and to pass the water vapor into the steam turbine, and to pass the CO2-rich gas generated during the mixing and mixing process into the primary cooling unit; The steam turbine is driven by water vapor to drive the generator and output the exhaust steam to the tertiary cooling unit; Generator, used to generate electricity.

[0008] Preferably, a circulating water pump and a deaerator are provided on the liquid channel between the boiler and the tertiary cooling unit.

[0009] Preferably, an ammonia buffer tank is provided on the gas passage between the boiler and the primary cooling unit and the tertiary cooling unit.

[0010] Preferably, the first-stage cooling unit is a microchannel heat exchanger, the second-stage cooling unit is a spiral baffle evaporator, and the third-stage cooling unit is an exhaust condensation chamber.

[0011] The present invention also relates to a multi-stage comprehensive utilization method of liquid ammonia cooling energy in a coal-fired power plant, which comprises the following steps: S1. The ratio of liquid ammonia from the liquid ammonia storage tank to the primary cooling unit and the secondary cooling unit is adjusted by the liquid ammonia pump; S2. The CO2-rich gas generated by the power generation unit is passed into a primary cooling unit and heat exchanged with liquid ammonia to form a liquid ammonia-ammonia mixture; S3. Circulating water is introduced into the secondary cooling unit, heat exchanged with liquid ammonia to form low-temperature ammonia gas, and the low-temperature ammonia gas and the cooled circulating water are introduced into the tertiary cooling unit; S4. The exhaust steam generated by the power generation unit is passed into the three-stage cooling tower, where it is heat exchanged with the low-temperature ammonia to form high-temperature ammonia, while the exhaust steam is cooled and condensed into circulating water; S5. The power generation unit burns ammonia output from the primary cooling unit and the tertiary cooling unit, heats the circulating water output from the tertiary cooling unit and generates steam to generate electricity.

[0012] Preferably, the specific steps of adjusting the ratio of liquid ammonia from the liquid ammonia storage tank to the primary cooling unit and the secondary cooling unit by the liquid ammonia pump in S1 are: S1.1. Construct the liquid ammonia allocation objective function and constraints. The expression of the objective function is: (1), Where F is the objective function, α and β represent weight coefficients, and α+β=1. Indicates the CO2 capture efficiency, Indicates the recycling water waste heat recovery efficiency; The CO2 capture efficiency is expressed as: (2), in, C in is the concentration of CO2 in the flue gas before entering the primary cooling unit, C out is the concentration of CO2 in the flue gas after passing through the primary cooling unit, which is obtained by fitting. The fitting formula is: , Q 1 is the flow rate of liquid ammonia input to the primary cooling unit, T flue is the temperature of the flue gas before entering the primary cooling unit, f represents the fitting formula; The circulating water waste heat recovery efficiency is expressed as: (2), in, m w is the mass flow rate of circulating water, c w is the specific heat capacity of circulating water, Q 2 is the flow rate of liquid ammonia input to the secondary cooling unit, h v is the latent heat of vaporization of liquid ammonia, T w,in is the temperature of the circulating water before entering the spiral baffle evaporator, T w,out is the temperature of the circulating water after passing through the spiral baffle evaporator, which is obtained by fitting. The fitting formula is: , grepresents the fitting formula; The constraints include liquid ammonia flow constraint, which is expressed as: (3), (4), (5), in, Q total Indicates the total flow of liquid ammonia output from the liquid ammonia storage tank, Q max1 It is the maximum flow rate of liquid ammonia allowed to be input into the primary cooling unit. Q max2 is the maximum flow rate of liquid ammonia allowed to be input into the secondary cooling unit; S1.2. Use the particle swarm optimization algorithm to solve the objective function and obtain the flow rate of liquid ammonia input to the primary cooling unit and the secondary cooling unit. The solution process includes: S1.2.1. Set the maximum number of iterations and fitness change threshold; S1.2.2. Initialize the particle swarm, each particle represents a liquid ammonia distribution scheme X, X = ( Q 1, Q 2), and initialize the velocity V of each particle at the same time, V=( v 1, v 2), calculate the objective function value of each particle F As the fitness of the corresponding particle; S1.2.3. Update the individual optimum and global optimum. Compare the current fitness value of each particle with its historical optimal fitness value, update the individual optimal position, and find the particle position corresponding to the global optimal fitness value. The update formula of the individual optimal position is: (6), (7), in, t Indicates the moment, V i Indicates the number i The speed of the particle, X i Indicates the number i The position of the particle, w is the inertia weight, c 1 and c 2 is the learning factor, r 1 and r 2 is a random number between 0 and 1, pbest i For the number iThe optimal position of the particle, gbest is the particle position corresponding to the global optimal fitness value; S1.2.4. Perform boundary processing on the updated particle positions. Specifically, if the liquid ammonia flow rate input to the primary cooling unit and the secondary cooling unit in the liquid ammonia distribution plan exceeds the range of the constraint conditions, limit the flow rate to the boundary value. S1.2.5. Calculate the fitness change of the particle corresponding to the global optimal fitness value before and after the update, and increase the number of iterations by 1; S1.2.6. Determine whether the number of iterations has reached the set maximum number of iterations and whether the fitness change threshold is less than the set fitness change threshold. If both conditions are not met, return to S1.2.2 and continue the optimization calculation. If either condition is met, output the optimal liquid ammonia distribution plan. S1.3. Based on the optimal liquid ammonia distribution scheme, the ratio of liquid ammonia fed into the primary cooling unit and the secondary cooling unit is adjusted to output liquid ammonia to the primary cooling unit and the secondary cooling unit; S1.4. Monitor the constraints and provide feedback. If the constraints are met, continue to output liquid ammonia according to the ratio in S1.3. If the constraints are not met, return to S1.2 and re-optimize the liquid ammonia distribution plan.

[0013] Preferably, the constraints further include temperature constraints and circulating water system safety constraints; The expression of the CO2 capture temperature constraint is: T CO2,out ≤80℃, in, T CO2,out is the CO2 capture temperature; The expression of the safety constraint of the circulating water system is: T w,out ≥35℃, in, T w,out is the temperature of the circulating water output from the three-stage condensing unit.

[0014] Preferably, the liquid ammonia and ammonia gas mixture formed in S2 and the high-temperature ammonia gas formed in S4 are both introduced into an ammonia buffer tank, and the ammonia gas input into the power generation unit in S5 is output from the ammonia buffer tank.

[0015] Preferably, the high-temperature CO2 generated by the S5 power generation unit is passed into the primary cooling unit; the remaining circulating water of the power generation unit is passed into the secondary cooling unit; and the exhaust steam generated by the power generation unit is passed into the tertiary cooling unit.

[0016] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects: 1. The present invention relates to a multi-stage, comprehensive utilization system for liquid ammonia cooling energy in coal-fired power plants. The system comprises a primary, secondary, and tertiary cooling unit. This multi-stage cooling energy cascade utilizes cooling energy in a cascade, transcending the traditional single-stage heat exchange model. Through three-stage cooling energy distribution, it achieves deep cooling energy recovery across temperature gradients, addressing the low utilization rate of liquid ammonia cooling energy in existing technologies. Furthermore, these three cooling units are deeply coupled with the power generation unit's water circulation system and CO2 capture system, respectively, to achieve plant-wide energy efficiency improvements and environmental synergy.

[0017] 2. The multi-stage comprehensive utilization method of liquid ammonia cooling energy in coal-fired power plants involved in the present invention is based on a particle swarm optimization algorithm and a real-time adaptive adjustment liquid ammonia flow dynamic distribution algorithm. It realizes intelligent distribution of liquid ammonia flow through precise constraint control, breaks through the traditional fixed ratio distribution mode, and further improves the utilization rate of liquid nitrogen gasification cooling energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a structural diagram of the multi-stage comprehensive utilization system of liquid ammonia cooling energy in a coal-fired power plant of the present invention; Figure 2 A flow chart of the liquid ammonia pump of the present invention for adjusting the liquid ammonia delivery ratio; Figure 3 This is a structural diagram of the microchannel heat exchanger of the present invention; Figure 4 This is a schematic diagram of the heat exchange channels with multiple shapes combined according to the present invention.

[0019] Among them, 1-liquid ammonia storage tank; 2-liquid ammonia pump; 3-primary cooling unit; 4-ammonia buffer tank; 5-boiler; 6-steam turbine; 7-generator; 8-secondary cooling unit; 9-tertiary cooling unit; 10-circulating water pump; 11-deaerator; 31-shell; 32-microchannel heat exchange component; 33-air inlet; 34-air outlet; 35-liquid inlet; 36-liquid outlet, 37-heat exchange plate; A-circulating water supply; B-CO2-rich gas; C-CO2 gas outlet; D-exhaust steam inlet; E-circulating return water; F-exhaust steam outlet. DETAILED DESCRIPTION

[0020] In order to further understand the content of the present invention, the present invention is described in detail with reference to the examples. The following examples are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0021] Refer to the attached Figure 1As shown, the present invention relates to a multi-stage comprehensive utilization system of liquid ammonia cooling energy in a coal-fired power plant, including a liquid ammonia storage tank 1, a liquid ammonia pump 2, a primary cooling unit 3, a secondary cooling unit 8, a tertiary cooling unit 9, a buffer tank 4 and a power generation unit. The liquid ammonia storage tank 1 is used to store liquid ammonia, and ammonia is stored in the liquid ammonia storage tank 1 in a liquid form at -33°C. The liquid ammonia pump is used to adjust the ratio of liquid ammonia passed from the liquid ammonia storage tank to the primary cooling unit 3 and the secondary cooling unit 8. The primary cooling unit 3 is used to pass the CO2-rich gas B generated by the power generation unit and exchange heat with the liquid ammonia. The liquid ammonia absorbs the heat in the CO2-rich gas B, and the partial vaporization temperature rises to -10°C, forming a liquid ammonia-ammonia mixture. The CO2-rich gas B is pre-cooled to below 80°C and discharged from the CO2 gas outlet, reducing the subsequent capture energy consumption. The secondary cooling unit 8 circulates the water A and then introduces the circulating water, and exchanges heat with the liquid ammonia. The liquid ammonia is completely vaporized into low-temperature ammonia gas at -10°C, and the circulating water temperature drops to 35°C. The low-temperature ammonia gas and the cooled circulating water are introduced into the tertiary cooling unit 9. The tertiary cooling unit 9 introduces the exhaust steam generated by the power generation unit through the exhaust steam inlet D, and exchanges heat with the low-temperature ammonia gas. The ammonia gas absorbs the heat of the exhaust steam, and the temperature rises to 20°C, thereby forming high-temperature ammonia gas. At the same time, the exhaust steam is cooled and condensed into circulating water. After the exhaust steam is cooled by the tertiary cooling unit 9, part of the heat is recovered by the ammonia gas, reducing the load of the direct cooling tower and reducing the power consumption rate of the plant. The power generation unit is used to mix the ammonia gas output by the primary cooling unit and the tertiary cooling unit, heat the circulating water output by the tertiary cooling unit, and then form water vapor for power generation.

[0022] The liquid ammonia-gas mixture output by the primary cooling unit 3 and the ammonia gas output by the tertiary cooling unit all enter the ammonia buffer tank 4. The power generation unit comprises a boiler 5, a steam turbine 6, and a generator 7. The boiler 5 is used to pass ammonia gas generated by the primary cooling unit 3 and the tertiary cooling unit 9 through a gas channel. Specifically, the gas channel passes ammonia gas from the ammonia buffer tank 4 into the boiler 5. The gas channel then passes ammonia gas into the tertiary cooling unit 9 via a circulating water pump 10 and a deaerator provided in the liquid channel between the boiler 5 and the tertiary cooling unit 9. The circulating water is then heated by co-firing ammonia gas to form steam, which is then passed into the steam turbine. The CO2-rich gas generated during the co-firing process is then passed into the primary cooling unit 3. The steam turbine 6 is driven to rotate by the steam, driving the generator 7 to generate exhaust steam, which is then output through an exhaust steam outlet F and sent to the tertiary cooling unit. The rotating generator is used to generate electricity.

[0023] Refer to the attached Figure 3The primary cooling unit 3 is a microchannel heat exchanger, which adopts a millimeter or micron channel design to increase the contact area between liquid ammonia and CO2-rich gas, and is used for heat exchange between liquid ammonia and CO2-rich gas; the microchannel heat exchanger includes a shell 31 and a microchannel heat exchange component 32, the shell having an air inlet 33, an air outlet 34, a liquid inlet 35 and a liquid outlet 36, the air inlet 33 is used to pass CO2-rich gas, and the liquid inlet 35 is used to pass liquid ammonia; the microchannel heat exchange component 32 is arranged in the shell 31, and is composed of a plurality of heat exchange plates 37 with millimeter or micron channels stacked, such as Figure 4 As shown, the size range of the channel is 0.1mm-10mm, the material of the heat exchange plate is stainless steel or aluminum alloy, and the shape of the channel is one or more combinations of rectangle, circle or triangle; through the combination of multiple shapes, the turbulent flow of liquid ammonia is enhanced, and the uniformity of gas-liquid two-phase heat exchange in the microfluidic heat exchange channel is enhanced.

[0024] The secondary cooling unit 8 is a spiral baffle evaporator, a common evaporator on the market. It is equipped with a heat exchange tube bundle, allowing the circulating water, acting as a heat source, to fully exchange heat with the liquid ammonia in the liquid ammonia evaporator. The spacing of the spiral baffles ranges from 50mm to 200mm. This spacing controls the flow rate and flow of the circulating water, enhancing the turbulence between the liquid ammonia and the circulating water, and improving heat exchange efficiency. The heat exchange tubes are finned, with a height ranging from 1mm to 5mm and a spacing of 2mm to 10mm.

[0025] The tertiary cooling unit 9 is an exhaust steam condensing chamber with a conventional structure. A heat exchange tube bundle is provided in the exhaust steam condensing chamber. The exhaust steam of the turbine is used as a heat source for further heat exchange with the ammonia gas, so that the exhaust steam is cooled and condensed, thereby improving the vacuum degree of the turbine and further improving the power generation efficiency. The condensed exhaust steam enters the deaerator 11 for deoxygenation treatment and then is recycled.

[0026] The present invention also relates to a multi-stage comprehensive utilization method of liquid ammonia cooling energy in a coal-fired power plant, which comprises the following steps: S1. The ratio of liquid ammonia from the liquid ammonia storage tank 1 to the primary cooling unit 3 and the secondary cooling unit 8 is adjusted by the liquid ammonia pump 2. The specific steps are as shown in the attached Figure 2 As shown, including: S1.1. Construct the liquid ammonia allocation objective function and constraints. The expression of the objective function is: (1), in, F is the objective function, α and β Represent weight coefficients respectively, and α+ β =1, Indicates the CO2 capture efficiency, Indicates the recycling water waste heat recovery efficiency; The CO2 capture efficiency is expressed as: (2), in, C in is the concentration of CO2 in the flue gas before entering the primary cooling unit, C out is the concentration of CO2 in the flue gas after passing through the primary cooling unit, which is obtained by fitting. The fitting formula is: , Q 1 is the flow rate of liquid ammonia input to the primary cooling unit, T flue is the temperature of the flue gas before entering the primary cooling unit, f represents the fitting formula; The circulating water waste heat recovery efficiency is expressed as: (2), in, m w is the mass flow rate of circulating water, c w is the specific heat capacity of circulating water, Q 2 is the flow rate of liquid ammonia input to the secondary cooling unit, h v is the latent heat of vaporization of liquid ammonia, T w,in is the temperature of the circulating water before entering the spiral baffle evaporator, T w,out is the temperature of the circulating water after passing through the spiral baffle evaporator, which is obtained by fitting. The fitting formula is: , g represents the fitting formula; The constraints include liquid ammonia flow constraint, temperature constraint and circulating water system safety constraint; The expression of the liquid ammonia flow constraint is: (3), (4), (5), in, Q total Indicates the total flow of liquid ammonia output from the liquid ammonia storage tank, Q max1 It is the maximum flow rate of liquid ammonia allowed to be input into the primary cooling unit. Q max2 is the maximum flow rate of liquid ammonia allowed to be input into the secondary cooling unit; The expression of the CO2 capture temperature constraint is: T CO2,out ≤80℃, in, T CO2,out is the CO2 capture temperature; The expression of the safety constraint of the circulating water system is: T w,out ≥35℃, in, T w,out is the temperature of the circulating water output from the three-stage condensing unit.

[0027] S1.2. Use the particle swarm optimization algorithm to solve the objective function and obtain the flow rate of liquid ammonia input to the primary cooling unit and the secondary cooling unit. The solution process includes: S1.2.1. Set the maximum number of iterations and fitness change threshold; S1.2.2. Initialize the particle swarm, each particle represents a liquid ammonia distribution scheme X, X = ( Q 1, Q 2), and initialize the velocity V of each particle at the same time, V=( v 1, v 2), calculate the objective function value of each particle F As the fitness of the corresponding particle; S1.2.3. Update the individual optimum and global optimum. Compare the current fitness value of each particle with its historical optimal fitness value, update the individual optimal position, and find the particle position corresponding to the global optimal fitness value. The update formula of the individual optimal position is: (6), (7), in, t Indicates the moment, V i Indicates the number i The speed of the particle, X i Indicates the number i The position of the particle, w is the inertia weight, c 1 and c 2 is the learning factor, r 1 and r 2 is a random number between 0 and 1, pbest i For the number i The optimal position of the particle, gbestis the particle position corresponding to the global optimal fitness value; S1.2.4. Perform boundary processing on the updated particle positions. Specifically, if the liquid ammonia flow rate input to the primary cooling unit and the secondary cooling unit in the liquid ammonia distribution plan exceeds the range of the constraint conditions, limit the flow rate to the boundary value. S1.2.5. Calculate the fitness change of the particle corresponding to the global optimal fitness value before and after the update, and increase the number of iterations by 1; S1.2.6. Determine whether the number of iterations has reached the set maximum number of iterations and whether the fitness change threshold is less than the set fitness change threshold. If both conditions are not met, return to S1.2.2 and continue the optimization calculation. If either condition is met, output the optimal liquid ammonia distribution plan. S1.3. Based on the optimal liquid ammonia distribution scheme, the ratio of liquid ammonia fed into the primary cooling unit and the secondary cooling unit is adjusted to output liquid ammonia to the primary cooling unit and the secondary cooling unit; S1.4. Monitor the constraints and provide feedback. If the constraints are met, continue to output liquid ammonia according to the ratio in S1.3. If the constraints are not met, return to S1.2 to re-optimize the liquid ammonia distribution plan, and the number of iterations for a single optimization of the liquid ammonia distribution plan is k No more than 100 times, that is, when k =100, force the optimization to end.

[0028] S2. The CO2-rich gas generated by the power generation unit is passed into the primary cooling unit 3, heat exchanged with liquid ammonia to form a liquid ammonia-ammonia mixture, and the formed liquid ammonia-ammonia mixture is passed into the ammonia buffer tank 4; S3. Circulating water is introduced into the secondary cooling unit 8, heat exchanged with liquid ammonia to form low-temperature ammonia gas, and the low-temperature ammonia gas and the cooled circulating water are introduced into the tertiary cooling unit 9; S4. The exhaust steam generated by the power generation unit is passed into the three-stage cooling tower 9, and the low-temperature ammonia is heat exchanged to form high-temperature ammonia. At the same time, the exhaust steam is cooled and condensed into circulating water, and the high-temperature ammonia formed is passed into the ammonia buffer tank; S5. The ammonia buffer tank 4 outputs ammonia to the power generation unit. The power generation unit then blends the ammonia to heat the circulating water output from the tertiary cooling unit, generating steam to generate electricity. Specifically, the ammonia in the ammonia buffer tank 4 is passed into the boiler 5 and blended with the coal in the boiler 5. The circulating water from the tertiary cooling unit 9 is then introduced into the boiler 5 via a circulating water pump 10 and a deaerator 11 provided in the liquid passage between the boiler 5 and the tertiary cooling unit 9. The blended ammonia is then used to heat the circulating water to generate steam, which is then passed into the steam turbine 6. The blended combustion process generates CO2-rich gas, which is then passed into the primary cooling unit 3. The steam drives the steam turbine 6 to rotate, driving the generator 7. Excess steam forms exhaust steam, which is then output from the exhaust steam outlet F to the tertiary cooling unit 9. The rotating generator 7 generates electricity.

[0029] The present invention has been described in detail above with reference to the embodiments. However, the contents described are only preferred embodiments of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A multi-stage comprehensive utilization system of liquid ammonia cooling energy in a coal-fired power plant, characterized by: It includes: Liquid ammonia storage tank, used to store liquid ammonia; Liquid ammonia pump, used to adjust the ratio of liquid ammonia flowing from the liquid ammonia storage tank into the primary cooling unit and the secondary cooling unit; The primary cooling unit is used to introduce the CO2-rich gas generated by the power generation unit and exchange heat with liquid ammonia to form a liquid ammonia and ammonia gas mixture; The secondary cooling unit is used to pass circulating water and exchange heat with liquid ammonia to form low-temperature ammonia gas, and pass the low-temperature ammonia gas and the cooled circulating water into the tertiary cooling unit; The third-stage cooling unit is used to introduce the exhaust steam generated by the power generation unit and exchange heat with the low-temperature ammonia to form high-temperature ammonia, while cooling and condensing the exhaust steam into circulating water; The power generation unit is used to mix and burn the ammonia output from the primary cooling unit and the tertiary cooling unit, heat the circulating water output from the tertiary cooling unit, and then generate water vapor for power generation.

2. The multi-stage comprehensive utilization system of liquid ammonia cooling energy in a coal-fired power plant according to claim 1, characterized in that: The power generation unit comprises: The boiler is used to pass ammonia generated in the primary cooling unit and the tertiary cooling unit through the gas channel, and to pass circulating water in the tertiary cooling unit through the liquid channel, and to heat the circulating water by mixing with ammonia to form water vapor, and to pass the water vapor into the steam turbine, and to pass the CO2-rich gas generated during the mixing and mixing process into the primary cooling unit; The steam turbine is driven by water vapor to drive the generator and output the exhaust steam to the tertiary cooling unit; Generator, used to generate electricity.

3. The multi-stage comprehensive utilization system of liquid ammonia cooling energy in a coal-fired power plant according to claim 2, characterized in that: A circulating water pump and a deaerator are provided on the liquid channel between the boiler and the three-stage cooling unit.

4. The multi-stage comprehensive utilization system of liquid ammonia cooling energy in a coal-fired power plant according to claim 2, characterized in that: An ammonia buffer tank is provided on the gas passage between the boiler and the primary cooling unit and the tertiary cooling unit.

5. The multi-stage comprehensive utilization system of liquid ammonia cooling energy in a coal-fired power plant according to claim 1, characterized in that: The first-stage cooling unit is a microchannel heat exchanger, the second-stage cooling unit is a spiral baffle evaporator, and the third-stage cooling unit is an exhaust condensation chamber.

6. A multi-stage comprehensive utilization method of liquid ammonia cooling energy in a coal-fired power plant, characterized by: It includes the following steps: S1. The ratio of liquid ammonia from the liquid ammonia storage tank to the primary cooling unit and the secondary cooling unit is adjusted by the liquid ammonia pump; S2. The CO2-rich gas generated by the power generation unit is passed into a primary cooling unit and heat exchanged with liquid ammonia to form a liquid ammonia-ammonia mixture; S3. Circulating water is introduced into the secondary cooling unit, heat exchanged with liquid ammonia to form low-temperature ammonia gas, and the low-temperature ammonia gas and the cooled circulating water are introduced into the tertiary cooling unit; S4. The exhaust steam generated by the power generation unit is passed into the three-stage cooling tower, where it is heat exchanged with the low-temperature ammonia to form high-temperature ammonia, while the exhaust steam is cooled and condensed into circulating water; S5. The power generation unit burns ammonia output from the primary cooling unit and the tertiary cooling unit, heats the circulating water output from the tertiary cooling unit and generates steam to generate electricity.

7. The multi-stage comprehensive utilization method of liquid ammonia cooling energy in a coal-fired power plant according to claim 6, characterized in that: The specific steps of adjusting the ratio of liquid ammonia from the liquid ammonia storage tank to the primary cooling unit and the secondary cooling unit by the liquid ammonia pump in S1 are as follows: S1.

1. Construct the liquid ammonia allocation objective function and constraints. The expression of the objective function is: （1）， Where F is the objective function, α and β represent weight coefficients, and α+β=1. Indicates the CO2 capture efficiency, Indicates the recycling water waste heat recovery efficiency; The CO2 capture efficiency is expressed as: （2）， in, C in is the concentration of CO2 in the flue gas before entering the primary cooling unit, C out is the concentration of CO2 in the flue gas after passing through the primary cooling unit, which is obtained by fitting. The fitting formula is: , Q 1 is the flow rate of liquid ammonia input to the primary cooling unit, T flue is the temperature of the flue gas before entering the primary cooling unit, f represents the fitting formula; The circulating water waste heat recovery efficiency is expressed as: （2）， in, m w is the mass flow rate of circulating water, c w is the specific heat capacity of circulating water, Q 2 is the flow rate of liquid ammonia input to the secondary cooling unit, h v is the latent heat of vaporization of liquid ammonia, T w,in is the temperature of the circulating water before entering the spiral baffle evaporator, T w,out is the temperature of the circulating water after passing through the spiral baffle evaporator, which is obtained by fitting. The fitting formula is: , g represents the fitting formula; The constraints include liquid ammonia flow constraint, which is expressed as: （3）， （4）， （5）， in, Q total Indicates the total flow of liquid ammonia output from the liquid ammonia storage tank, Q max1 It is the maximum flow rate of liquid ammonia allowed to be input into the primary cooling unit. Q max2 is the maximum flow rate of liquid ammonia allowed to be input into the secondary cooling unit; S1.

2. Use the particle swarm optimization algorithm to solve the objective function and obtain the flow rate of liquid ammonia input to the primary cooling unit and the secondary cooling unit. The solution process includes: S1.2.

1. Set the maximum number of iterations and fitness change threshold; S1.2.

2. Initialize the particle swarm, each particle represents a liquid ammonia distribution scheme X, X = ( Q 1, Q 2), and initialize the velocity V of each particle at the same time, V=( v 1, v 2), calculate the objective function value of each particle F As the fitness of the corresponding particle; S1.2.

3. Update the individual optimum and global optimum. Compare the current fitness value of each particle with its historical optimal fitness value, update the individual optimal position, and find the particle position corresponding to the global optimal fitness value. The update formula of the individual optimal position is: （6）， （7）， in, t Indicates the moment, V i Indicates the number i The speed of the particle, X i Indicates the number i The position of the particle, w is the inertia weight, c 1 and c 2 is the learning factor, r 1 and r 2 is a random number between 0 and 1, pbest i For the number i The optimal position of the particle, gbest is the particle position corresponding to the global optimal fitness value; S1.2.

4. Perform boundary processing on the updated particle positions. Specifically, if the liquid ammonia flow rate input to the primary cooling unit and the secondary cooling unit in the liquid ammonia distribution plan exceeds the range of the constraint conditions, limit the flow rate to the boundary value. S1.2.

5. Calculate the fitness change of the particle corresponding to the global optimal fitness value before and after the update, and increase the number of iterations by 1; S1.2.

6. Determine whether the number of iterations has reached the set maximum number of iterations and whether the fitness change threshold is less than the set fitness change threshold. If both conditions are not met, return to S1.2.2 and continue the optimization calculation. If either condition is met, output the optimal liquid ammonia distribution plan. S1.

3. Based on the optimal liquid ammonia distribution scheme, the ratio of liquid ammonia fed into the primary cooling unit and the secondary cooling unit is adjusted to output liquid ammonia to the primary cooling unit and the secondary cooling unit; S1.

4. Monitor the constraints and provide feedback. If the constraints are met, continue to output liquid ammonia according to the ratio in S1.

3. If the constraints are not met, return to S1.2 and re-optimize the liquid ammonia distribution plan.

8. The multi-stage comprehensive utilization method of liquid ammonia cooling energy in a coal-fired power plant according to claim 7, characterized in that: The constraints also include temperature constraints and circulating water system safety constraints; The expression of the CO2 capture temperature constraint is: T CO2,out ≤80℃， in, T CO2,out is the CO2 capture temperature; The expression of the safety constraint of the circulating water system is: T w,out ≥35℃， in, T w,out is the temperature of the circulating water output from the three-stage condensing unit.

9. The multi-stage comprehensive utilization method of liquid ammonia cooling energy in a coal-fired power plant according to claim 6, characterized in that: The liquid ammonia and ammonia gas mixture formed in S2 and the high-temperature ammonia gas formed in S4 are both introduced into the ammonia buffer tank, and the ammonia gas input into the power generation unit in S5 is output from the ammonia buffer tank.

10. The multi-stage comprehensive utilization method of liquid ammonia cooling energy in a coal-fired power plant according to claim 6, characterized in that: The high-temperature CO2 generated by the S5 power generation unit is passed into the primary cooling unit; the remaining circulating water of the power generation unit is passed into the secondary cooling unit; and the exhaust steam generated by the power generation unit is passed into the tertiary cooling unit.

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