Power plant waste heat recovery system and recovery method

Abstract

According to the power plant waste heat recovery system and method, the types of recovered power plant waste heat are very comprehensive, and the power plant waste heat is recycled in a stepped mode. All waste heat, including flue gas waste heat, circulating water waste heat, furnace wall waste heat and slag waste heat, of the thermal power plant is recovered at the same time. In addition, different heat pumps and different heat exchangers are selected according to different waste heat characteristics, all recoverable waste heat is efficiently recovered, and the energy conversion efficiency of a power plant is improved. The cascade recycling of the waste heat of the power plant comprises three recycling modes of a low-pressure steam turbine generator set, a low-boiling-point working medium generator set and a heat supply pipeline. According to the method, on one hand, the applicability of the waste heat recovery system of the power plant is improved, the method is suitable for different types of thermal power plants, and is also suitable for the influence of different seasons and environment temperature factors on waste heat, and on the other hand, the waste heat is recycled to the maximum extent according to comparison and matching of the temperature and pressure set value and the measured value of the recycling equipment, and waste of the waste heat is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of waste heat recovery systems, and in particular to a waste heat recovery system and a recovery method for a power plant. Background Art

[0002] For some regions, objective conditions such as resource endowment or other existing conditions determine that their energy utilization pattern is still mainly based on coal-fired power generation and gas-fired power generation and heating.

[0003] However, as a fossil fuel, coal poses a dual crisis of energy and environment that cannot be ignored. At present, the significant impact of coal burning on the environment has been greatly reduced through desulfurization, denitrification, dust removal and other methods. However, the energy conversion efficiency of coal-fired power plants is only 30% to 50%, which means that a large amount of heat is still wasted in the flue gas, circulating water (heat exchange with exhaust gas), furnace walls, and slag in the form of waste heat.

[0004] Usually, the temperature of flue gas in thermal power plants can reach 150℃~350℃, or even higher. 7%~25% of the sensible heat and 15% of the latent heat in the flue gas are directly discharged into the atmosphere without being used, which causes a lot of energy waste and the "white smoke" problem. The exhaust steam of the steam turbine of the power plant (heat loss accounts for more than 45% of the heat of the steam-water cycle) is condensed and releases heat in the condenser with the circulating water (also known as cooling water), making the circulating water another waste heat that must be recycled. Generally, in order to ensure the combustion efficiency in the furnace and the heat exchange efficiency between the water-cooled wall and the flame, an insulation layer is applied to the outside of the furnace wall to avoid the increase of the temperature of the outer surface of the furnace wall. However, due to the extremely high temperature in the furnace, although the water in the water-cooled wall in the furnace absorbs a lot of heat, the temperature of the outer side of the furnace wall can still reach more than 100℃. Therefore, it is possible to consider absorbing the heat outside the furnace wall through efficient heat exchange. This reduces heat loss on the one hand and reduces the use of insulation materials on the other.

[0005] These four types of waste heat are good and relatively stable low-temperature heat sources. Their recycling will greatly improve the energy efficiency of coal-fired power plants. At present, the technology of waste heat utilization in power plants has also been well developed. However, it has not been efficiently reused in practical applications. In summary, there are two main problems. One is that only some of the waste heat with higher temperatures is recycled and utilized, and the other is that the goal orientation of recycling and utilization is relatively single.

[0006] Based on this, the present invention designs a power plant waste heat recovery system and method, aiming to efficiently recover and utilize various types of waste heat. Summary of the invention

[0007] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a power plant waste heat recovery system and recovery method, aiming to solve the problems raised in the technical background, make full use of various types of waste heat generated by the operation of the thermal power plant, and combine with equipment such as heat exchangers and heat pumps to carry out cascade recycling according to the characteristics of each waste heat, and use it for power generation and heating.

[0008] In order to solve the above technical problems, the present invention provides a first implementation scheme: a waste heat recovery system for a power plant, comprising:

[0009] The absorption heat pump drives the high-temperature flue gas in the absorption heat pump to exchange heat with the low-temperature water 1. The heated low-temperature water 1 becomes high-temperature water 1 and is output through the high-temperature water 1 delivery pipe connected to the absorption heat pump. The high-temperature water 1 delivery pipe is provided with a four-way solenoid valve V1 and a temperature and pressure sensor MS1;

[0010] The No. 1 compression heat pump exchanges heat between the high-temperature flue gas input into the No. 1 compression heat pump and the low-temperature water 2. The heated low-temperature water 2 becomes high-temperature water 2 and is output through the high-temperature water 2 delivery pipe connected to the No. 1 compression heat pump. The high-temperature water 2 delivery pipe is provided with a four-way solenoid valve V2 and a temperature and pressure sensor MS2;

[0011] The second compression heat pump exchanges heat with the high-temperature circulating water input into the second compression heat pump and the low-temperature water 3. The heated low-temperature water 3 becomes high-temperature water 3 and is output through the high-temperature water 3 delivery pipe connected to the second compression heat pump. The high-temperature water 3 delivery pipe is provided with a four-way solenoid valve V3 and a temperature and pressure sensor MS3;

[0012] The furnace wall heat exchange coil exchanges heat between the low-temperature water 4 input into the furnace wall heat exchange coil and the furnace wall. The heated low-temperature water 4 becomes high-temperature water 4 and is output through the high-temperature water 4 delivery pipe connected to the furnace wall heat exchange coil. The high-temperature water 4 delivery pipe is provided with a four-way solenoid valve V4 and a temperature and pressure sensor MS4;

[0013] The slag heat exchange equipment exchanges heat between the low-temperature water 5 input into the slag heat exchange equipment and the high-temperature slag. The heated low-temperature water 5 becomes high-temperature water 5 and is output through the high-temperature water 5 delivery pipe connected to the slag heat exchange equipment. The high-temperature water 5 delivery pipe is provided with a four-way solenoid valve V5 and a temperature and pressure sensor MS5;

[0014] It also includes a low-pressure steam turbine generator set, a low-boiling-point working fluid generator set and a heating pipeline, and the low-pressure steam turbine generator set, the low-boiling-point working fluid generator set and the heating pipeline are respectively connected to a four-way solenoid valve V1, a four-way solenoid valve V2, a four-way solenoid valve V3, a four-way solenoid valve V4 and a four-way solenoid valve V5 through pipelines;

[0015] A control cabinet, whose signal inlet end is respectively connected to temperature and pressure sensor MS1, temperature and pressure sensor MS2, temperature and pressure sensor MS3, temperature and pressure sensor MS4 and temperature and pressure sensor MS5, and whose signal outlet end is respectively connected to four-way solenoid valve V1, four-way solenoid valve V2, four-way solenoid valve V3, four-way solenoid valve V4 and four-way solenoid valve V5; the control cabinet compares and matches the temperature and pressure signal measurement values ​​of each high-temperature water received at the signal inlet end with the set value, and then controls the flow direction of each four-way solenoid valve through the output signal to determine whether the four-way solenoid valve outputs the high-temperature water to one of the low-pressure steam turbine generator set, the low-boiling point working fluid generator set, and the heating pipeline.

[0016] Preferably, the control cabinet is respectively set with set values ​​of temperature and pressure required for each high-temperature water to be transported to the low-pressure steam turbine generator set, the low-boiling-point working fluid generator set or the heating pipeline. When the measured values ​​of each temperature and pressure sensor satisfy T≥300°C and the pressure is between 0.5MPa and 2.5MPa, the high-temperature water at the measured temperature and pressure is transported to the low-pressure steam turbine generator set; when the measured values ​​of each temperature and pressure sensor satisfy 160°C≤T<300°C and the pressure<0.5MPa, the high-temperature water at the measured temperature and pressure is transported to the low-boiling-point working fluid generator set; when the measured values ​​of each temperature and pressure sensor do not meet the temperature and pressure set values ​​for transport to the low-boiling-point working fluid generator set, the high-temperature water at the measured temperature and pressure is transported to the heating pipeline.

[0017] Preferably, the No. 1 compression heat pump includes a No. 1 throttle valve, a No. 1 evaporator, a No. 2 evaporator, a No. 1 compressor, a No. 1 condenser and a No. 2 condenser which are connected in series in sequence through pipelines, so that the refrigerant 1 in the No. 1 compression heat pump circulates in the series circuit, the No. 1 evaporator and the No. 2 evaporator are connected in parallel with high-temperature flue gas delivery pipes, the No. 2 condenser is connected with a low-temperature water 2 delivery pipe, the No. 2 condenser is also connected to the No. 1 condenser through a pipeline, and the high-temperature water 2 delivery pipe is connected to the No. 1 condenser.

[0018] Preferably, the No. 1 condenser and the No. 2 condenser are both shell and tube heat exchangers, spiral plate heat exchangers or plate-fin heat exchangers, and the No. 1 evaporator and the No. 2 evaporator are both floating head heat exchangers.

[0019] Preferably, the No. 2 compression heat pump includes a No. 2 throttle valve, a No. 3 condenser, a No. 2 compressor and a No. 3 evaporator which are connected in series in sequence through pipelines, so that the refrigerant 2 in the No. 2 compression heat pump circulates in the series loop, the No. 3 evaporator is connected to a high-temperature circulating water delivery pipe, the No. 3 condenser is connected to a low-temperature water 3 delivery pipe, and the high-temperature water 3 delivery pipe is connected to the No. 3 condenser.

[0020] Preferably, the No. 3 evaporator and the No. 3 condenser are both shell and tube heat exchangers, spiral plate heat exchangers or plate-fin heat exchangers.

[0021] Preferably, the furnace wall heat exchange coil is spirally wound on the outside of the furnace wall, and the water inlet height of the furnace wall heat exchange coil is lower than the water outlet height, so as to enhance the heat exchange effect.

[0022] Preferably, the slag heat exchange equipment includes a conveyor belt, a No. 1 surface plate heat exchanger and a No. 2 surface plate heat exchanger. The conveyor belt is used to transport high-temperature slag. The conveyor belt is arranged between the No. 1 surface plate heat exchanger and the No. 2 surface plate heat exchanger. The No. 1 surface plate heat exchanger and the No. 2 surface plate heat exchanger are respectively connected to a low-temperature water 5 delivery pipe and a high-temperature water 5 delivery pipe.

[0023] Preferably, the water delivery direction of the low-temperature water 5 delivery pipes on the No. 1 surface plate heat exchanger and the No. 2 surface plate heat exchanger is opposite to the transmission direction of the conveyor belt.

[0024] The second implementation scheme provided by the present invention is to provide a recovery method of a waste heat recovery system of a power plant, comprising the following steps:

[0025] The high-temperature flue gas is divided into three streams. The first stream of high-temperature flue gas drives the absorption heat pump, which heats the low-temperature water 1 into high-temperature water 1 and outputs it through the high-temperature water 1 delivery pipe;

[0026] The second high-temperature flue gas exchanges heat with refrigerant 1 through the No. 1 evaporator, and the temperature of refrigerant 1 increases. The third high-temperature flue gas exchanges heat with refrigerant 1 through the No. 2 evaporator, and the temperature of refrigerant 1 further increases. The refrigerant 1 heated by the flue gas twice enters the No. 1 compressor and is compressed and pressurized in the No. 1 compressor. The compressed and pressurized refrigerant 1 then enters the No. 1 condenser to be condensed and release heat, and then enters the No. 2 condenser to be condensed and release heat again. The refrigerant 1 that has released heat and cooled down twice enters the No. 1 throttle valve to reduce the pressure and then starts the next heat pump cycle. The low-temperature water 2 successively absorbs the heat released by the condensation of the refrigerant 1 through the No. 2 condenser and the No. 1 condenser, and is heated to high-temperature water 2.

[0027] The high-temperature circulating water exchanges heat with refrigerant 2 through the No. 3 evaporator. Refrigerant 2 absorbs the heat of the circulating water and enters the No. 2 compressor to be compressed and pressurized after the temperature rises. The compressed and pressurized refrigerant 2 enters the No. 3 condenser to be condensed and release heat. The refrigerant 2 that has released heat and cooled enters the No. 2 throttle valve to reduce the pressure and then starts the next heat pump cycle. The low-temperature water 3 absorbs the heat released by the condensation of the refrigerant 2 through the No. 3 condenser and is heated to high-temperature water 3.

[0028] The low-temperature water 4 in the furnace wall heat exchange coil located outside the furnace wall absorbs the heat conducted from the furnace wall to the outside of the furnace wall and is heated to high-temperature water 4;

[0029] The low-temperature water 5 flowing in the slag heat exchange equipment conducts heat conduction and radiation heat exchange with the high-temperature slag, absorbs the waste heat of the high-temperature slag, and is heated to high-temperature water 5;

[0030] The control cabinet compares and matches the measured values ​​of the temperature and pressure signals of each high-temperature water received at the signal inlet with the set values, and then controls the flow direction of the four-way solenoid valve on each high-temperature water pipeline through the output signal to determine whether the four-way solenoid valve outputs the high-temperature water to one of the low-pressure steam turbine generator set, the low-boiling point working fluid generator set, and the heating pipeline; when the measured values ​​of the high-temperature water temperature and pressure meet the temperature and pressure set values ​​required for the operation of the low-pressure steam turbine generator set, the control cabinet controls the flow direction of the four-way solenoid valve on the high-temperature water pipeline to deliver the high-temperature water to the low-pressure steam turbine generator set. When the measured values ​​of the high-temperature water temperature and pressure do not reach the temperature and pressure setting values ​​required for the operation of the low-pressure steam turbine generator set, the control cabinet continues to determine whether its temperature and pressure can meet the temperature and pressure setting values ​​required for the operation of the low-boiling-point working fluid generator set. If so, the high-temperature water is sent to the low-boiling-point working fluid generator set by controlling the flow direction of the four-way solenoid valve on the high-temperature water pipeline. If the temperature and pressure setting values ​​required for the operation of the low-boiling-point working fluid generator set are not met, the control cabinet sends the high-temperature water to the heating pipeline by controlling the flow direction of the four-way solenoid valve on the high-temperature water pipeline.

[0031] The power plant waste heat recovery system and recovery method proposed in the present invention have particularly significant technical advantages and innovative effects compared to the prior art, which can be specifically summarized as follows:

[0032] (1) Multi-source waste heat recovery: The waste heat of the power plant is fully recovered, and all waste heat of the thermal power plant is recovered at the same time, including four types of waste heat: flue gas waste heat, high-temperature circulating water waste heat, furnace wall waste heat and slag waste heat. Different heat pumps and different heat exchangers are selected according to the characteristics of different waste heat, and all recoverable waste heat is efficiently recovered, thereby improving the energy conversion efficiency of the power plant. The setting of multi-source waste heat recovery improves the applicability of the system, and can be applied to the recovery of various waste heat possibilities of various power plants (critical, supercritical, ultra-supercritical), and can also adapt to the influence of external factors such as different seasons and different ambient temperatures on various waste heat.

[0033] (2) Multi-directional cascade recycling of waste heat: The recovered waste heat is recycled in cascades according to its temperature and pressure. There are three specific ways of utilization: low-pressure steam turbine generator sets, low-boiling-point working fluid generator sets, and heating pipelines (including heating heat, domestic hot water, and low-temperature industrial hot water supply). Designing a variety of cascade recycling schemes to ensure the scientific recycling of waste heat can avoid the situation where the waste heat is not recycled to the maximum extent and is wasted.

[0034] (3) Realize automatic control: compare and match the thermodynamic conditions of the five types of high-temperature water with the conditions required by the three-way cascade reuse method, and determine the priority output to one of the low-pressure steam turbine generator set, the low-boiling point working fluid generator set and the heating pipeline.

[0035] (4) Achieve the effect of eliminating white smoke: The better the recovery effect of flue gas waste heat, the lower the temperature of the flue gas discharged into the atmosphere, which can avoid the "white smoke" problem and achieve the effect of eliminating white smoke. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a structural schematic diagram of a power plant waste heat recovery system in the present invention.

[0037] Figure 2 This is a control logic flow chart of the control cabinet in the present invention.

[0038] Description of reference numerals:

[0039] 1. Absorption heat pump; 2. Evaporator No. 1; 3. Evaporator No. 2; 4. Condenser No. 1; 5. Condenser No. 2; 6. Evaporator No. 3; 7. Condenser No. 3; 8. Conveyor belt; 9. Low-pressure steam turbine generator set; 10. Low-boiling-point working fluid generator set; 11. Heating pipeline; 12. Furnace wall; 13. Surface plate heat exchanger No. 1; 14. Surface plate heat exchanger No. 2, 15. Throttle valve No. 1, 16. Compressor No. 1, 17. Throttle valve No. 2, 18. Compressor No. 2. DETAILED DESCRIPTION

[0040] In order to make the above-mentioned purposes, features and advantages of the embodiments of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] The inventors found that due to the characteristics of resource endowment, most regions will not be able to achieve the transformation from coal-fired power generation to renewable energy power generation for a long time in the future. The current energy conversion efficiency of coal-fired power plants is only 30% to 50%, which means that there is still a lot of heat wasted in the flue gas, circulating water (heat exchange with exhaust gas), furnace walls, and slag in the form of waste heat. These four types of waste heat are good and relatively stable low-temperature heat sources, and their recycling will greatly improve the energy efficiency of coal-fired power plants. Although the technology for the utilization of waste heat in power plants has also been well developed, it has not been efficiently reused in actual applications. There are two main problems. One is that only some of the higher temperature waste heat is recycled and utilized, and the other is that the goal orientation of recycling and utilization is relatively single.

[0042] In view of this, the present invention provides a power plant waste heat recovery system and recovery method, which realizes the efficient recovery and utilization of various types of waste heat.

[0043] like Figure 1-2 As shown, the present invention provides a power plant waste heat recovery system, comprising:

[0044] The absorption heat pump 1 drives the high-temperature flue gas in the absorption heat pump 1 to exchange heat with the low-temperature water 1. The heated low-temperature water 1 becomes high-temperature water 1 and is output through the high-temperature water 1 delivery pipe connected to the absorption heat pump 1. The high-temperature water 1 delivery pipe is provided with a four-way solenoid valve V1 and a temperature and pressure sensor MS1;

[0045] The No. 1 compression heat pump exchanges heat with the high-temperature flue gas and low-temperature water 2 input into the No. 1 evaporator 2 and the No. 2 evaporator 3 in the No. 1 compression heat pump, and the heated low-temperature water 2 becomes high-temperature water 2 and is output through the high-temperature water 2 delivery pipe connected to the No. 1 compression heat pump. The high-temperature water 2 delivery pipe is provided with a four-way solenoid valve V2 and a temperature and pressure sensor MS2;

[0046] The No. 2 compression heat pump exchanges heat with the high-temperature circulating water input into the No. 3 evaporator 6 of the No. 2 compression heat pump and the low-temperature water 3. The heated low-temperature water 3 becomes high-temperature water 3 and is output through the high-temperature water 3 delivery pipe connected to the No. 2 compression heat pump. The high-temperature water 3 delivery pipe is provided with a four-way solenoid valve V3 and a temperature and pressure sensor MS3;

[0047] The furnace wall heat exchange coil exchanges heat between the low-temperature water 4 input into the furnace wall heat exchange coil and the furnace wall 12. The heated low-temperature water 4 becomes high-temperature water 4 and is output through the high-temperature water 4 delivery pipe connected to the furnace wall heat exchange coil. The high-temperature water 4 delivery pipe is provided with a four-way solenoid valve V4 and a temperature and pressure sensor MS4.

[0048] The slag heat exchange equipment exchanges heat between the low-temperature water 5 input into the slag heat exchange equipment and the high-temperature slag. The heated low-temperature water 5 becomes high-temperature water 5 and is output through the high-temperature water 5 delivery pipe connected to the slag heat exchange equipment. The high-temperature water 5 delivery pipe is provided with a four-way solenoid valve V5 and a temperature and pressure sensor MS5;

[0049] It also includes a low-pressure steam turbine generator set 9, a low-boiling-point working medium generator set 10 and a heat supply pipeline 11, and the low-pressure steam turbine generator set 9, the low-boiling-point working medium generator set 10 and the heat supply pipeline 11 are respectively connected to a four-way solenoid valve V1, a four-way solenoid valve V2, a four-way solenoid valve V3, a four-way solenoid valve V4 and a four-way solenoid valve V5 through pipelines;

[0050] A control cabinet, whose signal inlet end is respectively connected to temperature and pressure sensor MS1, temperature and pressure sensor MS2, temperature and pressure sensor MS3, temperature and pressure sensor MS4 and temperature and pressure sensor MS5, and whose signal outlet end is respectively connected to four-way solenoid valve V1, four-way solenoid valve V2, four-way solenoid valve V3, four-way solenoid valve V4 and four-way solenoid valve V5; the control cabinet compares and matches the temperature and pressure signal measurement values ​​of each high-temperature water received at the signal inlet end with the set value, and then controls the flow direction of each four-way solenoid valve through the output signal to determine whether the four-way solenoid valve outputs high-temperature water to one of the low-pressure steam turbine generator set 9, the low-boiling point working fluid generator set 10, and the heating pipeline 11.

[0051] Specifically, the control cabinet is set with set values ​​of temperature and pressure required for high-temperature water to be transported to the low-pressure steam turbine generator set 9, the low-boiling-point working fluid generator set 10 or the heating pipeline 11. When the measured values ​​of each temperature and pressure sensor meet T≥300°C and the pressure is between 0.5MPa and 2.5MPa, the high-temperature water at the measured temperature and pressure is transported to the low-pressure steam turbine generator set 9. When the measured values ​​of each temperature and pressure sensor meet 160°C≤T<300°C and the pressure<0.5MPa, the high-temperature water at the measured temperature and pressure is transported to the low-boiling-point working fluid generator set 10. When the measured values ​​of each temperature and pressure sensor do not meet the temperature and pressure set values ​​for transport to the low-boiling-point working fluid generator set 10, the high-temperature water at the measured temperature and pressure is transported to the heating pipeline 11.

[0052] Specifically, a specific structure for realizing heat exchange between high-temperature flue gas and low-temperature water 2 through a No. 1 compression heat pump is provided, wherein the No. 1 compression heat pump includes a No. 1 throttle valve 15, a No. 1 evaporator 2, a No. 2 evaporator 3, a No. 1 compressor 16, a No. 1 condenser 4 and a No. 2 condenser 5 which are sequentially connected in series through pipelines, so that the refrigerant 1 in the No. 1 compression heat pump circulates in the series loop, the No. 1 evaporator 2 and the No. 2 evaporator 3 are connected in parallel with a high-temperature flue gas delivery pipe, the No. 2 condenser 5 is connected with a low-temperature water 2 delivery pipe, the No. 2 condenser 5 is also connected with the No. 1 condenser 4 through a pipeline, and the high-temperature water 2 delivery pipe is connected with the No. 1 condenser 4. In the No. 1 compression heat pump provided here, the high-temperature flue gas is divided into two groups and sent into the No. 1 evaporator 2 and the No. 2 evaporator 3 in parallel, respectively, so that the refrigerant 1 is heated by the high-temperature flue gas twice in succession.

[0053] Specifically, the first condenser 4 and the second condenser 5 are both shell and tube heat exchangers, spiral plate heat exchangers or plate-fin heat exchangers, and the first evaporator 2 and the second evaporator 3 are both floating head heat exchangers.

[0054] Condenser No. 1 4 and Condenser No. 2 5 can use shell and tube heat exchangers, spiral plate heat exchangers or plate-fin heat exchangers, mainly considering their high heat transfer efficiency and compact structure. In addition, the cleanliness of the fluid in the condenser is relatively high, and the heat exchanger does not need to be frequently disassembled and cleaned. Evaporator No. 1 2 and Evaporator No. 2 3 can use floating head heat exchangers, mainly considering that the flue gas cleanliness is not high, and the tube bundle of the floating head heat exchanger can be pulled out for cleaning, and the floating head heat exchanger is suitable for scenes with high temperature, high pressure and large temperature difference.

[0055] Specifically, a specific structure for achieving heat exchange between high-temperature circulating water and low-temperature water 3 through a No. 2 compression heat pump is given, wherein the No. 2 compression heat pump includes a No. 2 throttle valve 17, a No. 3 condenser 7, a No. 2 compressor 18 and a No. 3 evaporator 6 which are connected in series in sequence through pipelines, so that the No. 2 compression heat pump refrigerant 2 circulates in the series loop, the No. 3 evaporator 6 is connected to a high-temperature circulating water delivery pipe, the No. 3 condenser 7 is connected to a low-temperature water 3 delivery pipe, and the high-temperature water 3 delivery pipe is connected to the No. 3 condenser 7.

[0056] Specifically, the third evaporator 6 and the third condenser 7 are both shell and tube heat exchangers, spiral plate heat exchangers or plate-fin heat exchangers.

[0057] The third evaporator 6 and the third condenser 7 can both use shell and tube heat exchangers, spiral plate heat exchangers or plate-fin heat exchangers, mainly considering their high heat transfer efficiency and compact structure. In addition, the fluid cleanliness in the third evaporator 6 and the third condenser 7 is relatively high, and the heat exchanger does not need to be frequently disassembled and cleaned.

[0058] Specifically, the furnace wall heat exchange coil is spirally wound on the outside of the furnace wall 12, and the water inlet height of the furnace wall heat exchange coil is lower than the water outlet height, so as to enhance the heat exchange effect.

[0059] Specifically, the slag heat exchange equipment includes a conveyor belt 8, a No. 1 surface plate heat exchanger 13 and a No. 2 surface plate heat exchanger 14. The conveyor belt 8 is used to transport high-temperature slag. The conveyor belt 8 is arranged between the No. 1 surface plate heat exchanger 13 and the No. 2 surface plate heat exchanger 14. The No. 1 surface plate heat exchanger 13 and the No. 2 surface plate heat exchanger 14 are respectively connected to a low-temperature water 5 delivery pipe and a high-temperature water 5 delivery pipe. The high-temperature slag conducts heat conduction and radiation heat exchange with the low-temperature water 5 flowing in the No. 1 surface plate heat exchanger 13 and the No. 2 surface plate heat exchanger 14.

[0060] In specific use, the conveyor belt 8 is an intermittent conveyor belt. When the high-temperature slag placed on the conveyor belt 8 is conveyed to the No. 1 surface plate heat exchanger 13 and the No. 2 surface plate heat exchanger 14, it stops rotating for 5 minutes to allow this batch of high-temperature slag to conduct heat and radiate heat with the low-temperature water 5 in the No. 1 surface plate heat exchanger 13 and the No. 2 surface plate heat exchanger 14. After staying for 5 minutes, the conveyor belt 8 continues to rotate to transfer the second batch of high-temperature slag to exchange heat with the low-temperature water 5 in the No. 1 surface plate heat exchanger 13 and the No. 2 surface plate heat exchanger 14. A plurality of slag boxes are also connected to the chain plate in 8, each of which is used to hold high-temperature slag. The conveyor belt 8 is driven intermittently. When a new batch of high-temperature slag delivered to the slag box is delivered to the No. 1 surface plate heat exchanger 13 and the No. 2 surface plate heat exchanger 14 via the conveyor belt 8, the conveyor belt 8 stops rotating for 5 minutes, so that this batch of high-temperature slag can conduct heat and radiate heat with the low-temperature water 5 in the No. 1 surface plate heat exchanger 13 and the No. 2 surface plate heat exchanger 14. After staying for 5 minutes, the conveyor belt 8 continues to be driven, and the second batch of high-temperature slag delivered to the slag box continues to be transmitted via the conveyor belt 8.

[0061] The high-temperature slag and the low-temperature water 5 are fully heat-exchanged through two parallel surface plate heat exchangers 13 and 14, and the low-temperature water 5 is heated to high-temperature water 5.

[0062] Specifically, the water delivery direction of the low-temperature water 5 delivery pipes on the No. 1 surface plate heat exchanger 13 and the No. 2 surface plate heat exchanger 14 is opposite to the transmission direction of the conveyor belt 8, which is beneficial to increase the heat transfer contact area and increase the heat exchange time, thereby enhancing the heat exchange effect.

[0063] A recovery method of a waste heat recovery system of a power plant comprises the following steps:

[0064] The high-temperature flue gas is divided into three streams, the first stream of high-temperature flue gas drives the absorption heat pump 1, and the absorption heat pump 1 heats the low-temperature water 1 into high-temperature water 1, and outputs the high-temperature water 1 through the high-temperature water 1 delivery pipe;

[0065] The second high-temperature flue gas exchanges heat with the refrigerant 1 through the No. 1 evaporator 2, and the temperature of the refrigerant 1 increases. The third high-temperature flue gas exchanges heat with the refrigerant 1 through the No. 2 evaporator 3, and the temperature of the refrigerant 1 further increases. The refrigerant 1 heated by the high-temperature flue gas twice enters the No. 1 compressor 16, and is compressed and pressurized in the No. 1 compressor 16. The compressed and pressurized refrigerant 1 then enters the No. 1 condenser 4 to be condensed and release heat, and then enters the No. 2 condenser 5 to be condensed and release heat again. The refrigerant 1 that has released heat and cooled down twice enters the No. 1 throttle valve 15 to reduce the pressure and start the next heat pump cycle. The low-temperature water 2 successively absorbs the heat released by the condensation of the refrigerant 1 through the No. 2 condenser 5 and the No. 1 condenser 4, and is heated to high-temperature water 2.

[0066] The high-temperature circulating water exchanges heat with the refrigerant 2 through the No. 3 evaporator 6. The refrigerant 2 absorbs the heat of the circulating water and enters the No. 2 compressor 18 to be compressed and pressurized after the temperature rises. The compressed and pressurized refrigerant 2 enters the No. 3 condenser 7 to be condensed and release heat. The refrigerant 2 that releases heat and cools down enters the No. 2 throttle valve 17 in the No. 2 compression heat pump to reduce the pressure, and then enters to start the next heat pump cycle. The low-temperature water 3 absorbs the heat released by the condensation of the refrigerant 2 through the No. 3 condenser 7 and is heated to high-temperature water 3.

[0067] The low-temperature water 4 in the furnace wall heat exchange coil located outside the furnace wall 12 absorbs the heat conducted from the furnace wall 12 to the outside of the furnace wall 12 and is heated to high-temperature water 4;

[0068] The low-temperature water 5 flowing in the first surface plate heat exchanger 13 and the second surface plate heat exchanger 14 conducts heat conduction and radiation heat exchange with the high-temperature slag, and then absorbs the residual heat of the high-temperature slag to be heated into high-temperature water 5;

[0069] The control cabinet compares and matches the temperature and pressure signal measurement values ​​of each high-temperature water received at the signal inlet with the set values, and then controls the flow direction of the four-way solenoid valve on each high-temperature water pipeline through the output signal to determine whether the four-way solenoid valve outputs high-temperature water to one of the low-pressure steam turbine generator set 9, the low-boiling point working fluid generator set 10, and the heating pipeline 11; when the measured values ​​of the high-temperature water temperature and pressure meet the temperature and pressure set values ​​required for the operation of the low-pressure steam turbine generator set 9, the high-temperature water is delivered to the low-pressure steam turbine generator set 9 by controlling the flow direction of the four-way solenoid valve on the high-temperature water pipeline. When the measured values ​​of the high-temperature water temperature and pressure do not reach the temperature and pressure set values ​​required for the operation of the low-pressure steam turbine generator set 9, the control cabinet continues to determine whether its temperature and pressure can meet the temperature and pressure set values ​​required for the operation of the low-boiling-point working fluid generator set 10. If so, the high-temperature water is sent to the low-boiling-point working fluid generator set 10 by controlling the flow direction of the four-way solenoid valve on the high-temperature water pipeline. If the temperature and pressure set values ​​required for the operation of the low-boiling-point working fluid generator set 10 are not met, the control cabinet sends the high-temperature water to the heating pipeline 11 by controlling the flow direction of the four-way solenoid valve on the high-temperature water pipeline.

[0070] The present invention designs a power plant waste heat recovery system and method, which aims to make full use of all kinds of waste heat generated by the operation of thermal power plants, and use them for power generation and heating according to the characteristics of each waste heat, combined with heat exchangers and heat pumps and other equipment. Thereby, the energy conversion efficiency of power plants is improved, and 50%-70% of the energy in thermal power plants is avoided from being wasted.

[0071] In this embodiment, water (low temperature water 1, low temperature water 2, low temperature water 3, low temperature water 4, low temperature water 5) is used to exchange heat with high temperature flue gas, high temperature circulating water, furnace wall and slag respectively. If other working fluids are used, the above four types of waste heat can also be recovered. It should be emphasized that if other working fluids are used, the set values ​​of temperature and pressure in the control cabinet will be different depending on the type of working fluid, which is also within the protection scope of the present invention.

[0072] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A waste heat recovery system for a power plant, characterized in that: include: The absorption heat pump (1) drives the high-temperature flue gas in the absorption heat pump (1) to exchange heat with the low-temperature water 1, and the heated low-temperature water 1 becomes high-temperature water 1 and is output through a high-temperature water 1 delivery pipe connected to the absorption heat pump (1). The high-temperature water 1 delivery pipe is provided with a four-way solenoid valve V1 and a temperature and pressure sensor MS1; The No. 1 compression heat pump exchanges heat between the high-temperature flue gas input into the No. 1 compression heat pump and the low-temperature water 2. The heated low-temperature water 2 becomes high-temperature water 2 and is output through the high-temperature water 2 delivery pipe connected to the No. 1 compression heat pump. The high-temperature water 2 delivery pipe is provided with a four-way solenoid valve V2 and a temperature and pressure sensor MS2; The second compression heat pump exchanges heat with the high-temperature circulating water input into the second compression heat pump and the low-temperature water 3. The heated low-temperature water 3 becomes high-temperature water 3 and is output through the high-temperature water 3 delivery pipe connected to the second compression heat pump. The high-temperature water 3 delivery pipe is provided with a four-way solenoid valve V3 and a temperature and pressure sensor MS3; The furnace wall heat exchange coil exchanges heat between the low-temperature water 4 input into the furnace wall heat exchange coil and the furnace wall (12), and the heated low-temperature water 4 becomes high-temperature water 4 and is output through the high-temperature water 4 delivery pipe connected to the furnace wall heat exchange coil. The high-temperature water 4 delivery pipe is provided with a four-way solenoid valve V4 and a temperature and pressure sensor MS4; The slag heat exchange equipment exchanges heat between the low-temperature water 5 input into the slag heat exchange equipment and the high-temperature slag. The heated low-temperature water 5 becomes high-temperature water 5 and is output through the high-temperature water 5 delivery pipe connected to the slag heat exchange equipment. The high-temperature water 5 delivery pipe is provided with a four-way solenoid valve V5 and a temperature and pressure sensor MS5; It also includes a low-pressure steam turbine generator set (9), a low-boiling-point working fluid generator set (10) and a heat supply pipeline (11), wherein the low-pressure steam turbine generator set (9), the low-boiling-point working fluid generator set (10) and the heat supply pipeline (11) are respectively connected to a four-way solenoid valve V1, a four-way solenoid valve V2, a four-way solenoid valve V3, a four-way solenoid valve V4 and a four-way solenoid valve V5 through pipelines; A control cabinet, whose signal inlet end is respectively connected to temperature and pressure sensors MS1, MS2, MS3, MS4 and MS5, and whose signal outlet end is respectively connected to four-way solenoid valves V1, V2, V3, V4 and V5; the control cabinet compares and matches the temperature and pressure signal measurement values ​​of each high-temperature water received at the signal inlet end with the set value, and then controls the flow direction of each four-way solenoid valve through the output signal to determine whether the four-way solenoid valve outputs the high-temperature water to one of the low-pressure steam turbine generator set (9), the low-boiling point working fluid generator set (10) and the heating pipeline (11).

2. A power plant waste heat recovery system according to claim 1, characterized in that: The control cabinet is respectively set with set values ​​of temperature and pressure required for each high-temperature water to be delivered to the low-pressure steam turbine generator set (9), the low-boiling-point working fluid generator set (10) or the heating pipeline (11). When the measured values ​​of each temperature and pressure sensor meet T≥300°C and the pressure is between 0.5MPa and 2.5MPa, the high-temperature water at the measured temperature and pressure is delivered to the low-pressure steam turbine generator set (9). When the measured values ​​of each temperature and pressure sensor meet 160°C≤T<300°C and the pressure is less than 0.5MPa, the high-temperature water at the measured temperature and pressure is delivered to the low-boiling-point working fluid generator set (10). When the measured values ​​of each temperature and pressure sensor do not meet the temperature and pressure set values ​​for delivery to the low-boiling-point working fluid generator set (10), the high-temperature water at the measured temperature and pressure is delivered to the heating pipeline (11).

3. A power plant waste heat recovery system according to claim 1, characterized in that: The No. 1 compression heat pump comprises a No. 1 throttle valve (15), a No. 1 evaporator (2), a No. 2 evaporator (3), a No. 1 compressor (16), a No. 1 condenser (4) and a No. 2 condenser (5) which are sequentially connected in series through pipelines, so that the refrigerant 1 in the No. 1 compression heat pump circulates in the series circuit, the No. 1 evaporator (2) and the No. 2 evaporator (3) are connected in parallel with high-temperature flue gas delivery pipes, the No. 2 condenser (5) is connected with a low-temperature water 2 delivery pipe, the No. 2 condenser (5) is also connected to the No. 1 condenser (4) through a pipeline, and the high-temperature water 2 delivery pipe is connected to the No. 1 condenser (4).

4. A power plant waste heat recovery system according to claim 3, characterized in that: The first condenser (4) and the second condenser (5) are both shell and tube heat exchangers, spiral plate heat exchangers or plate-fin heat exchangers, and the first evaporator (2) and the second evaporator (3) are both floating head heat exchangers.

5. A power plant waste heat recovery system according to claim 4, characterized in that: The No. 2 compression heat pump comprises a No. 2 throttle valve (17), a No. 3 condenser (7), a No. 2 compressor (18) and a No. 3 evaporator (6) which are sequentially connected in series through pipelines, so that the refrigerant 2 in the No. 2 compression heat pump circulates in the series circuit, the No. 3 evaporator (6) is connected to a high-temperature circulating water delivery pipe, the No. 3 condenser (7) is connected to a low-temperature water 3 delivery pipe, and the high-temperature water 3 delivery pipe is connected to the No. 3 condenser (7).

6. A power plant waste heat recovery system according to claim 5, characterized in that: The third evaporator (6) and the third condenser (7) are both shell and tube heat exchangers, spiral plate heat exchangers or plate-fin heat exchangers.

7. A power plant waste heat recovery system according to claim 1, characterized in that: The furnace wall heat exchange coil is spirally wound on the outside of the furnace wall (12), and the water inlet height of the furnace wall heat exchange coil is lower than the water outlet height to enhance the heat exchange effect.

8. A power plant waste heat recovery system according to claim 1, characterized in that: The slag heat exchange equipment comprises a conveyor belt (8), a No. 1 surface plate heat exchanger (13) and a No. 2 surface plate heat exchanger (14); the conveyor belt (8) is used to transport high-temperature slag; the conveyor belt (8) is arranged between the No. 1 surface plate heat exchanger (13) and the No. 2 surface plate heat exchanger (14); the No. 1 surface plate heat exchanger (13) and the No. 2 surface plate heat exchanger (14) are respectively connected to a low-temperature water 5 delivery pipe and a high-temperature water 5 delivery pipe.

9. A power plant waste heat recovery system according to claim 8, characterized in that: The water delivery direction of the low-temperature water 5 delivery pipes on the No. 1 surface plate heat exchanger (13) and the No. 2 surface plate heat exchanger (14) is opposite to the transmission direction of the conveyor belt (8).

10. The method for recovering waste heat from a power plant waste heat recovery system according to claim 6, characterized in that: The steps include: The high-temperature flue gas is divided into three streams, the first stream of the high-temperature flue gas drives the absorption heat pump (1), and the absorption heat pump (1) heats the low-temperature water 1 into high-temperature water 1, and outputs the high-temperature water 1 through the high-temperature water 1 delivery pipe; The second high-temperature flue gas passes through the No. 1 evaporator (2) to exchange heat with the refrigerant 1, and the temperature of the refrigerant 1 increases. The third high-temperature flue gas passes through the No. 2 evaporator (3) to exchange heat with the refrigerant 1, and the temperature of the refrigerant 1 further increases. The refrigerant 1 heated by the flue gas twice enters the No. 1 compressor (16) and is compressed and pressurized in the No. 1 compressor (16). The compressed and pressurized refrigerant 1 then enters the No. 1 condenser (4) to be condensed and release heat, and then enters the No. 2 condenser (5) to be condensed and release heat again. The refrigerant 1 that has released heat and cooled twice enters the No. 1 throttle valve (15) to reduce the pressure and start the next heat pump cycle. The low-temperature water 2 passes through the No. 2 condenser (5) and the No. 1 condenser (4) successively to continuously absorb the heat released by the condensation of the refrigerant 1 and is heated to high-temperature water 2. The high-temperature circulating water exchanges heat with the refrigerant 2 through the No. 3 evaporator (6). The refrigerant 2 absorbs the heat of the circulating water and enters the No. 2 compressor (18) to be compressed and pressurized after the temperature rises. The compressed and pressurized refrigerant 2 enters the No. 3 condenser (7) to be condensed and release heat. The refrigerant 2 that has released heat and cooled enters the No. 2 throttle valve (17) to reduce the pressure and start the next heat pump cycle. The low-temperature water 3 absorbs the heat released by the condensation of the refrigerant 2 through the No. 3 condenser (7) and is heated to become the high-temperature water 3. The low-temperature water 4 in the furnace wall heat exchange coil located outside the furnace wall (12) absorbs the heat conducted from the furnace wall (12) to the outside of the furnace wall (12), and is heated to become high-temperature water 4; The low-temperature water 5 flowing in the slag heat exchange equipment conducts heat conduction and radiation heat exchange with the high-temperature slag, absorbs the waste heat of the high-temperature slag, and is heated to high-temperature water 5; The control cabinet compares and matches the temperature and pressure signal measurement values ​​of each high-temperature water received at the signal inlet with the set values, and then controls the flow direction of the four-way solenoid valve on each high-temperature water pipeline through the output signal to determine whether the four-way solenoid valve outputs the high-temperature water to one of the low-pressure steam turbine generator set (9), the low-boiling point working fluid generator set (10), and the heating pipeline (11); when the temperature and pressure measurement values ​​of the high-temperature water meet the temperature and pressure set values ​​required for the operation of the low-pressure steam turbine generator set (9), the control cabinet controls the flow direction of the four-way solenoid valve on the high-temperature water pipeline to deliver the high-temperature water to the low-pressure steam turbine generator set (9); when the high-pressure steam turbine generator set (9) meets the temperature and pressure set values ​​required for the operation of the low-pressure steam turbine generator set (9), the control cabinet controls the flow direction of the four-way solenoid valve on the high-temperature water pipeline to deliver the high-temperature water to the low-pressure steam turbine generator set (9); When the measured values ​​of the temperature and pressure of the warm water do not meet the temperature and pressure setting values ​​required for the operation of the low-pressure steam turbine generator set (9), the control cabinet continues to determine whether the temperature and pressure can meet the temperature and pressure setting values ​​required for the operation of the low-boiling-point working fluid generator set (10). If so, the high-temperature water is sent to the low-boiling-point working fluid generator set (10) by controlling the flow direction of the four-way solenoid valve on the high-temperature water pipeline. If the temperature and pressure setting values ​​required for the operation of the low-boiling-point working fluid generator set (10) are not met, the control cabinet sends the high-temperature water to the heating pipeline (11) by controlling the flow direction of the four-way solenoid valve on the high-temperature water pipeline.

Images