Cogeneration system for recycling waste heat of power plant and working method

Abstract

The invention discloses a combined cooling and power generation system for recovering waste heat of a power plant and a working method, and belongs to the technical field of industrial waste heat recovery. Exhaust steam at the tail end of a steam turbine of the system passes through a steam condenser and a water treatment device and then forms a dynamic heat supply system capable of being adjusted according to required heat with a second water source heat pump. The cooling side of the absorption type refrigerating unit and the first water source heat pump form a stable heat supply system. Supplemental heat sources and constant heat sources, respectively, supply heat demand near the power plant. And the cold supply system is used for supplying cold demands of the power plant and nearby. According to the system, the heat pump device and the absorption type refrigerating unit are combined, dead steam of the steam turbine is successfully recycled for heat supply, meanwhile, residual energy in return water of the heat pump is utilized, and the effect of gradient utilization is achieved. According to the system, the dead steam end can be dynamically adjusted according to the heat using requirement, dead steam is recycled, the utilization of the dead steam amount is controlled, energy is saved and utilized, and the economic benefit and the energy conversion efficiency of the whole cogeneration are improved.

Description

Technical Field

[0001] The invention relates to the technical field of industrial waste heat recovery, and specifically proposes an adjustable cooling and heating cogeneration system suitable for recovering waste heat from a power plant. Background Art

[0002] In recent years, China's energy development has also entered a new era. China's energy has entered a new stage of high-quality development. Cogeneration technology, as an efficient means of energy conservation, can improve the utilization rate of energy. However, as practice has found, there are still some problems that need to be solved. Thermal power plants convert heat into work based on the Rankine cycle to obtain electrical energy, which is accompanied by a large amount of heat loss. The main losses of thermal power plants are the cold source loss of the steam turbine and the heat loss of the boiler flue gas. After a specific efficiency analysis, it was found that the cold source loss of the steam turbine accounts for about 40% of the heat loss of the thermal power plant, and the heat loss of the boiler accounts for about 8% of the heat loss of the thermal power plant. Cold source loss refers to the need to release a large amount of condensation heat during the steam heat medium cycle, which cannot be completely recovered by cogeneration. In addition, although the exhaust steam in thermal power generation cannot be used in the power generation process, it can be used to supply heating and cooling needs from the perspective of energy cascade utilization, so the overall efficiency can be improved. Since the condensing pressure of the condensing unit is low, the corresponding condensate temperature is also low, which is low-grade waste heat and cannot be used directly for heating. Corresponding technical solutions need to be adopted to increase the circulating water temperature to meet the needs of the heating system. The current recovery method has limited impact on the efficiency of the steam turbine while taking into account the recovery of cold end exhaust steam. Therefore, in this era, in view of the cooling and heating needs of power plants and the cascade utilization of energy, the invention of a combined cooling and heating system for recovering waste heat from power plants is of great significance to the field of industrial waste heat recovery. Summary of the invention

[0003] In view of the problems existing in the prior art, the present invention proposes a combined cooling and heat production system for recovering waste heat from power plants. The combined cooling and heat production system for recovering waste heat from power plants is used to solve the problem of exhaust steam recovery for dynamic cooling and heating demands of power plants.

[0004] A combined cooling and power system for recovering waste heat from a power plant. The power plant boiler is connected to the generator via a high-pressure cylinder, a medium-pressure cylinder, and a low-pressure cylinder. The system includes a stable heating system and a dynamic heating system. In the stable heating system, the outlet pipe of the medium-pressure cylinder is connected to the absorption refrigeration unit; the absorption side of the absorption refrigeration unit is connected to the medium-pressure cylinder through a pipe, and the cooling side of the absorption refrigeration unit is connected to the first water source heat pump and the heat demand end through a pipe; The evaporation side of the absorption refrigeration unit is connected to the cold demand end through a pipeline; In the dynamic heating system, the outlet pipeline of the low-pressure cylinder is connected to the condenser, and the outlet pipeline of the condenser is connected to the second water source heat pump and the heat demand end.

[0005] A first regulating valve is arranged on the pipeline between the power station boiler and the high-pressure cylinder, a second regulating valve is arranged on the pipeline between the power station boiler and the medium-pressure cylinder, and a third regulating valve is arranged on the pipeline between the medium-pressure cylinder and the low-pressure cylinder.

[0006] A method for operating a cooling and power cogeneration system for recovering waste heat from a power plant comprises the following steps: S1. Perform subsequent operations based on the known heat demand of the heat demand end as the starting condition, and obtain the heat demand of the heat demand end based on the actual demand; S2, compare the heat demand of the heat demand end with the heat energy that the system can provide. If the heat demand cannot be provided, exit the system; if the demand can be met, proceed to the next step; S3, comparing the heating capacity of the first water source heat pump with the heat demand at the heat demand end to determine whether the first water source heat pump can bear all the heat demand; S4. If the heating capacity of the first water source heat pump is higher than the heat demand at the heat demand end, the absorption refrigeration unit and the first water source heat pump are turned on successively to form a stable cold and hot supply system; S5. If the heating capacity of the first water source heat pump is lower than the heat demand at the heat demand end, the absorption refrigeration unit and the first water source heat pump are turned on successively to form a stable cold and hot supply system; at the same time, the condenser and the heating system of the second water source heat pump are turned on; S6. Subtract the heating capacity of the first water source heat pump from the heat demand at the heat demand end to obtain the heating capacity that the second water source heat pump needs to provide; then convert the amount of exhaust steam extracted by the low-pressure cylinder to achieve additional heat provided by the additional heat source to complete the process.

[0007] A heat and cold supply system for recovering waste heat from steam turbine units using a heat pump, the components of which include a steam turbine unit, a power plant boiler, a power generation system of the steam turbine unit, including its corresponding condensing equipment, an extraction system for extracting steam from the steam turbine; a water source heat pump heating system; a lithium bromide refrigeration unit cooling system; and various connecting pipeline systems; the water source heat pump heating system includes a water source heat pump unit, and the lithium bromide refrigeration unit cooling system includes a steam-type lithium bromide refrigeration unit. The water source heat pump heating system and the lithium bromide refrigeration unit cooling system are connected by a pipeline connection system to form a stable heat and cold source supply system; the connecting pipeline system includes various air supply pipelines and water pipelines, as well as regulating valves and gate valves on the pipelines, and power unit pumps on the pipelines; Power generation system; including power plant boiler, high-pressure cylinder, medium-pressure cylinder, low-pressure cylinder of steam turbine unit, regulating valve for regulating steam volume, and generator for power generation; fuel is burned in power plant boiler, high-temperature and high-pressure steam is introduced into steam turbine, and steam turbine is connected to generator for power generation; corresponding condensing equipment is composed of condenser and condensate pump. The exhaust of terminal low-pressure cylinder system at the tail of steam turbine enters condenser, steam contacts with cooling medium in condenser, gradually cools and condenses into water; condensate pump extracts condensate and sends it back to boiler for reuse; water is drawn from the water intake pipe branch on the front side of condensate pump to the water source heat pump heating system.

[0008] The steam extraction system is used to extract steam from the steam turbine. The steam extraction pipe is connected to the steam outlet of the intermediate pressure cylinder of the steam turbine, and the end of the pipe is connected to the steam inlet of the absorption lithium bromide refrigeration unit. The corresponding equipment of the water source heat pump system is the water source heat pump unit; the water source heat pump system is generally composed of a water source system and a water source heat pump unit; the water source heat pump unit is composed of an evaporator, a compressor, a condenser, and an expansion valve device; the condensate is drawn to the condenser side of the water source heat pump unit by the water pipe branch of the extraction system shown in the previous article as a water source, and the outlet is divided into two channels, one channel is the domestic water inlet for heat demand, and the other channel is the inlet for other heat demand; the gate valve on the channel is responsible for flow control and timely closing and blocking the fluid; the return water channel at the heat demand end is connected back to the water source heat pump unit with the support of the power unit pump; a water pump is installed on the return water end pipe on the condenser side to connect back to the condensate pump pipe; for the domestic water pipe, water is replenished by the make-up water tank.

[0009] The cooling system of lithium bromide refrigeration unit includes steam type lithium bromide refrigeration unit; steam type lithium bromide refrigeration unit is generally composed of evaporator, absorber, condenser, regenerator, heat exchanger, solution pump, refrigerant pump, etc.; the steam extraction pipe shown in the above text is connected from the exhaust end of the intermediate pressure cylinder of the steam turbine, and the end of the pipe receives the heat source and is connected to the steam inlet of the absorption type lithium bromide refrigeration unit; the water supply pipe on the evaporator side leads to the cold demand end, and the return pipe is connected from the cold demand end back to the absorption type lithium bromide unit, and a pump and a valve are connected to the pipe; the cooling water generated from the condenser is led by a pipe to the water source heat pump heating system shown in the above text 1; the water source heat pump heating system is generally composed of a water source system and a water source heat pump unit; the outlet of the water source heat pump outlet channel is divided into two channels: one channel is the inlet of domestic water for heat demand, and the other channel is the inlet of other heat demand; the return water end is connected from the heat demand end back to the water source heat pump, and the return water end pipe is installed with a valve and a pump; for the domestic water pipe, water is replenished by the water replenishment tank.

[0010] Beneficial effect: The beneficial effect of the present invention is that it uses a combination of a traditional compression heat pump and a lithium bromide absorption refrigeration unit as an adjustable exhaust steam recovery heating device; and it can realize dynamic adjustment according to the heat load of the heat user, and can realize feedback according to the requirements of the demand side; the specific implementation method is that under the refrigeration demand, the steam-type lithium bromide refrigeration unit is turned on to provide cooling, and the return water end is used as the water source of the water source heat pump to extract heat from it as a stable heat source for heating, forming a stable cold and heat supply system, which can provide a fixed heat supply. When the heat demand is not large, the connection system can provide all the heat; this method recovers the heat at the return water end. The heat of low-temperature water, in previous schemes, this part of residual heat energy is often ignored. This scheme recovers the heat energy therein, achieves the effect of cascade utilization, and forms a stable cold and heat supply system at the same time; when the heating demand is greater, the exhaust steam discharged from the low-pressure cylinder of the steam turbine is converted into a water source to provide it to the water source heat pump as a supplementary heat source. This supplementary heat source is time-varying and can be changed at any time according to the change of heat demand. It can effectively recover the exhaust steam of the steam turbine, recover the residual energy therein, reduce the cold end loss, and can be used in conjunction with the above-mentioned cold and heat supply system as an adjustable heating system; and the amount of exhaust steam recovery can be dynamically adjusted as needed. This control strategy can solve the problem of conventional recovery schemes dealing with insufficient heat. At the same time, for changes in heat demand, the supplementary scheme can be directly fed back to the heating end according to the instantaneous demand end, without causing energy waste and excessive utilization. At the same time, before implementing the strategy, the feasibility and adaptability of the scheme can be intuitively fed back through simple judgments, simplifying the implementation of the strategy.

[0011] The system includes a power plant power generation device, a condenser, a water source heat pump, and a steam-type lithium bromide refrigeration unit. The exhaust steam at the end of the turbine passes through the condenser and then the water treatment device to form a dynamic heating system that can be adjusted according to the required heat with the water source heat pump. The steam extraction in the middle section of the turbine and the steam-type lithium bromide refrigeration unit form a system that can stably supply cooling. The cooling side of the steam-type lithium bromide refrigeration unit and another water source heat pump form another system that can stably supply heat. The above two heating systems can respectively supplement the heat source and the constant heat source to supply the heat demand near the power plant, and the cooling system is used to supply the cooling demand of the power plant and the vicinity. The innovation of this system is that by using the combination of a heat pump device and an absorption refrigeration unit, the exhaust steam of the steam turbine is successfully recovered for heat supply, and the residual energy in the return water of the heat pump is also utilized to achieve the effect of cascade utilization; this system can dynamically adjust the exhaust steam end according to the demand for heat near the power plant, recover the exhaust steam and control the utilization of the exhaust steam amount, so as to achieve energy conservation and utilization, and improve the economic benefits and energy conversion efficiency of the entire cogeneration of heat and power. Solve problems in the field of waste heat recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a structural diagram of a combined cooling and power system for recovering waste heat from power plants.

[0013] Figure 2 It is a flow chart of a combined cooling and power system for recovering waste heat from a power plant.

[0014] In the figure: 1. Power station boiler, 2. First regulating valve, 3. High-pressure cylinder, 4. Second regulating valve, 5. Medium-pressure cylinder, 6. Third regulating valve, 7. Low-pressure cylinder, 8. Generator, 9. Condenser, 10. Condensate pump, 11. Absorption refrigeration unit, 12. Cold demand end, 13. First water source heat pump, 14. Hot demand end, 15. Second water source heat pump, 16. Make-up water tank. DETAILED DESCRIPTION

[0015] Figure 1 The figure shows that a power plant is equipped with a power generation steam turbine unit, and the unit is currently undergoing a waste steam recovery modification.

[0016] Under the condition of normal operation of the power plant, the waste heat recovery system in the cogeneration scenario includes a steam turbine, a corresponding condensing system, an extraction system for extracting steam from the steam turbine, a water source heat pump heating system, a lithium bromide refrigeration unit cooling system, a water source heat pump heating system, and various connecting pipeline systems.

[0017] The power station boiler 1 burns fuel to generate high-temperature steam. The steam flow is adjusted by the first regulating valve 2. The steam flows to the high-pressure cylinder 3, the medium-pressure cylinder 5, and the low-pressure cylinder 7. The steam volume is controlled by the first regulating valve 2, the second regulating valve 4, and the third regulating valve 6. The steam is then connected to the generator 8 through a pipeline to generate electricity.

[0018] The steam turbine has multiple stages of steam extraction. According to the available pressure level, generally the fourth to fifth level pressure, that is, the pressure of the intermediate pressure cylinder, is used to extract steam in the intermediate pressure cylinder 5. The required steam volume is calculated according to the user's cooling demand in summer, and a hole is drilled in the above-mentioned steam extraction pipeline or a new pipeline is connected to the absorption refrigeration unit 11.

[0019] The absorption refrigeration unit 11 adopts a steam-type lithium bromide refrigeration unit; the steam-type lithium bromide refrigeration unit is generally composed of an evaporator, an absorber, a condenser, a generator, a regenerator, a heat exchanger, a solution circulation pump, a refrigerant pump, etc.; the above pipeline is connected to the generator of the absorption refrigeration unit 11, and the steam in the pipeline heats the dilute lithium bromide solution in the generator to produce water vapor and a concentrated lithium bromide solution. The concentrated lithium bromide solution enters the absorber, and the water vapor passes through the condenser part of the refrigeration unit, where it condenses and releases heat to be converted into high-pressure and low-temperature liquid water. High-pressure and low-temperature liquid water reaches the evaporator through the throttle valve, expands and heats up in the evaporator and vaporizes. During the vaporization process, it absorbs the heat of the chilled water in the evaporator and cools the chilled water. In this process, low-temperature water vapor enters the absorber, diluting the concentration of the lithium bromide aqueous solution, and is then sent back to the generator by the circulating pump to complete the cycle. The chilled water after cooling in the above-mentioned evaporator is connected to the cold demand side with a cold pipe, and there is a valve on the pipe to control the start and stop. The return pipe of the cold user is connected back to the evaporator side of the absorption refrigeration unit 11, and the return pipe is equipped with a pump and a valve.

[0020] The water outlet on the condenser side of the absorption refrigeration unit 11 is connected to the evaporator side of the first water source heat pump 13; a conventional water source heat pump should be composed of components including an evaporator, a compressor, a condenser, and an expansion valve; the above-mentioned outlet water as the water source evaporates the low-temperature and low-pressure liquid refrigerant therein on the evaporator side, causing the refrigerant to evaporate into a low-temperature and low-pressure gas. The gaseous refrigerant is compressed by the compressor to increase its temperature and pressure and is converted into a high-temperature and high-pressure gas. The high-temperature and high-pressure gaseous refrigerant reaches the condenser and condenses, releasing heat to the circulating water therein, thereby heating the refrigerant. After cooling and condensing into a high-pressure liquid state, the high-pressure liquid refrigerant flows through the expansion valve, and after cooling and reducing the pressure, it becomes the initial state of low temperature and low pressure and returns to the evaporator to start a new cycle; the circulating hot water heated by the above condenser is divided into two pipes at the outlet, which are respectively connected to the domestic water pipes with heat demand, and the second channel is other heat demand pipes; the return pipe of the heat demand end 14 is connected to the condenser side of the water source heat pump, and the return pipe on the evaporator side of the first water source heat pump 13 is connected to the return pipe on the condenser side of the absorption refrigeration unit 11. Each pipe is equipped with a valve to control the start and stop, and the return pipe is powered by a pump. The condensed water returns to the boiler feed water to maintain water balance.

[0021] The connection system between the absorption refrigeration unit 11 and the first water source heat pump 13; After the absorption refrigeration refrigeration unit 11 uses the turbine steam to cool the user's cooling needs, there is still usable energy on the original return water side that can be extracted. The innovation of this patent is to further extract the remaining energy in this part of the low-temperature water after refrigeration using a water source heat pump to generate heat to supply the heat demand end, further achieving the effect of cascade utilization of energy. At the same time, the system can be used as a stable and constant source of cold and heat supply, effectively solving the problem of simultaneous supply of cold and heat.

[0022] When the second water source heat pump 15 in the heating system is running, water is taken from the pipeline discharged from the condenser 9 to the cooling tower to the evaporator side of the second water source heat pump 15, and the outlet water is used to evaporate the liquid refrigerant in it. Hot water is produced on the condenser side after heating by the water source heat pump, and is divided into two pipelines at the hot water outlet, namely the domestic water pipeline with heat demand and the other pipeline with heat demand; the return water pipeline at the heat demand end is connected back to the condenser side of the water source heat pump, and the return water on the evaporator side of the second water source heat pump 15 is connected back to the condensate pump 10 to return to the boiler feed water.

[0023] The connection system between the steam turbine and the above-mentioned heating system forms a dynamic heating system. The connection system between the above-mentioned absorption refrigeration unit 11 and the first water source heat pump 13 serves as a constant heat source supply system, which undertakes the supply of part of the heat load, and this system can serve as a supplementary heat source supply system to undertake the supply of other heat loads of heat demand. At the same time, the advantage of this heating system is that it can be adjusted according to comprehensive angles such as heat load, economy, and energy utilization, and feedback can be given to the operation end based on the demand end, thereby avoiding energy waste and ineffective utilization of steam. At the same time, the dynamic heating system and the stable cold and heat supply system connected to the above-mentioned absorption refrigeration unit 11 and the first water source heat pump 13 can be used in combination to supply cold and heat needs under different conditions, effectively reducing energy loss and unnecessary losses.

[0024] according to Figure 2 Describe the specific working process of the system: Taking the modification of the control strategy in a certain power plant as an example, the intermediate exhaust pressure is used to drive the above-mentioned absorption refrigeration unit 11; for the intermediate pressure of the turbine, it is generally above 0.4Mpa, which can drive the refrigeration unit. The low-pressure cylinder exhaust is used to provide water supply for the first water source heat pump 13; based on the equipment selection of this scheme, the steam-type absorption refrigeration unit of the following specifications is taken as the absorption refrigeration unit 11 of this scheme. Assuming that the steam consumption of the product is 3 tons / hour, the size can be compared with the exhaust volume of the intermediate pressure cylinder of the turbine to know whether the product can be used. Similarly, for the products of the first water source heat pump 13 and the second water source heat pump 15, it is only necessary to compare the sum of the heating capacity of the first water source heat pump and the heating capacity of the second water source heat pump 15 with the heat demand. If the heat demand is higher than the total heating capacity, the water source heat pump can be operated.

[0025] Step 1: The known heat demand of the heat user needs to be known as the starting condition for subsequent operations. The heat demand of the heat user is obtained based on the actual demand.

[0026] Step 2: Compare the heat energy that the whole system can provide, and exit the system if it cannot provide the heat demand. Determine whether the energy provided by the first water source heat pump 13 can provide the heat demand around the power plant. Step 3: If the heat demand can be fully provided, further compare the heating capacity of the first water source heat pump 11 with the heat demand to determine whether the first water source heat pump 11 can bear all the heat demand.

[0027] Step 4: If the heating capacity of the first water source heat pump 11 is higher than the heat demand, the absorption refrigeration unit 11 and the first water source heat pump 13 are turned on in sequence to form a stable cold and hot supply system.

[0028] Step 5: If the heating capacity of the first water source heat pump 11 is lower than the heat demand, that is, the system is not sufficient to fully meet the heat demand, then turn on the absorption refrigeration unit 11 and the first water source heat pump 13, and at the same time turn on the condenser 9 and the heating system of the second water source heat pump 15. Step six: obtain the still required heat through the difference between the heat supply of the first water source heat pump 13 and the total heat demand, and convert it into the amount of exhausted steam to be extracted; by controlling the extraction of corresponding exhausted steam, an additional heat source is provided to supplement the still required heat, thereby completing the process.

[0029] In the description of the present invention, it should be understood that the terms "one end", "the other end", "upper", "top", "bottom", "inner", "outer" and the like indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention. .

[0030] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A combined cooling and power generation system for recovering waste heat from a power plant, wherein a power plant boiler (1) is connected to a generator (8) via a high-pressure cylinder (3), a medium-pressure cylinder (5), and a low-pressure cylinder (7); characterized in that: It includes stable heating system and dynamic heating system; In the stable heat supply system, the outlet pipe of the medium-pressure cylinder (7) is connected to the absorption refrigeration unit 11; the absorption side of the absorption refrigeration unit (11) is connected to the medium-pressure cylinder (7) through a pipe, and the cooling side of the absorption refrigeration unit (11) is connected to the first water source heat pump (13) and the heat demand end (14) through a pipe; The evaporation side of the absorption refrigeration unit (11) is connected to the cold demand end (13) via a pipeline; In the dynamic heating system, the outlet pipeline of the low-pressure cylinder (7) is connected to the condenser (9), and the outlet pipeline of the condenser (9) is connected to the second water source heat pump (15) and the heat demand end (4).

2. A cooling and power cogeneration system for recovering waste heat from a power plant according to claim 1, characterized in that: A first regulating valve (2) is provided on the pipeline between the power station boiler (1) and the high-pressure cylinder (3), a second regulating valve (4) is provided on the pipeline between the power station boiler (1) and the medium-pressure cylinder (5), and a third regulating valve (6) is provided on the pipeline between the medium-pressure cylinder (5) and the low-pressure cylinder (7).

3. The working method of a combined cooling and power system for recovering waste heat from a power plant according to claim 2, characterized in that: The following steps are involved: S1, using the known heat demand of the heat demand end (14) as the starting condition for subsequent operations, and obtaining the heat demand of the heat demand end (14) according to the actual demand; S2, comparing the heat demand of the heat demand end (14) with the heat energy that can be provided by the system. If the heat demand cannot be provided, exit the system; if the demand can be met, proceed to the next step; S3, comparing the heating capacity of the first water source heat pump (13) with the heat demand of the heat demand end (14), and determining whether the first water source heat pump (13) can bear all the heat demand; S4, if the heating capacity of the first water source heat pump (13) is higher than the heat demand of the heat demand end (14), the absorption refrigeration unit (11) and the first water source heat pump (13) are turned on successively to establish a stable cold and heat supply system; S5. If the heating capacity of the first water source heat pump (13) is lower than the heat demand of the heat demand end (14), the absorption refrigeration unit (11) and the first water source heat pump (13) are turned on successively to establish a stable cold and hot supply system; at the same time, the condenser (9) and the heating system of the second water source heat pump (15) are turned on; S6. The heating capacity of the first water source heat pump (13) is subtracted from the heat demand at the heat demand end (14) to obtain the heating capacity that the second water source heat pump (15) needs to provide; the amount of exhaust steam extracted from the low-pressure cylinder (7) is then converted to achieve the process of providing additional heat with an additional heat source.

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