A power plant waste heat recovery system and recovery method

Abstract

The present invention provides a power plant waste heat recovery system and method, which simultaneously recovers a wide range of waste heat from power plants and also implements cascade recycling of waste heat from power plants. The present invention simultaneously recycles all waste heat from thermal power plants, including four types of waste heat: flue gas waste heat, circulating water waste heat, furnace wall waste heat, and slag waste heat. In addition, according to the different characteristics of waste heat, different heat pumps and different heat exchangers are selected to efficiently recover all recoverable waste heat, thereby improving the energy conversion efficiency of the power plant. The present invention designs a cascade recycling of waste heat from power plants, including three recycling methods: a low-pressure steam turbine generator set, a low-boiling-point working fluid generator set, and a heating pipeline. On the one hand, the present invention improves the applicability of the power plant waste heat recovery system, and is applicable to different types of thermal power plants, as well as to the effects of different seasons and environmental temperature factors on various waste heat. On the other hand, by comparing and matching the temperature and pressure set values ​​of the recycling equipment with the measured values, the waste heat is maximized and waste heat is avoided.

Description

Technical Field

[0001] The present 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 burning, gas power generation and heating.

[0003] However, as a fossil fuel, coal poses both energy and environmental risks that cannot be ignored. Currently, desulfurization, denitrification, and dust removal have significantly reduced the significant environmental impact of coal combustion. However, the energy conversion efficiency of coal-fired power plants is currently only 30% to 50%, meaning that a significant amount of heat is still wasted as waste heat in the flue gas, circulating water (for heat exchange with exhaust gas), furnace walls, and slag.

[0004] Flue gas temperatures in thermal power plants typically reach 150°C to 350°C, or even higher. Of the flue gas, 7% to 25% of its sensible heat and 15% of its latent heat are unused and discharged directly into the atmosphere, resulting in significant energy waste and the "white smoke" problem. The power plant's turbine exhaust steam (heat losses account for over 45% of the heat of the steam-water cycle) condenses in the condenser through heat exchange with circulating water (also known as cooling water), releasing heat. This circulating water then becomes another source of waste heat that must be recovered and utilized. To ensure efficient combustion within the furnace and heat exchange between the water-cooled walls and the flames, insulation is typically applied to the exterior of the furnace walls to minimize surface temperature increases. However, due to the extremely high temperatures within the furnace, even though the water in the water-cooled walls absorbs significant heat, the exterior temperature of the furnace walls can still reach over 100°C. Therefore, efficient heat exchange can be considered to absorb heat from the exterior of the furnace walls. This approach reduces heat loss and reduces the use of insulation materials.

[0005] All four types of waste heat are excellent, relatively stable, low-temperature heat sources. Their recovery and utilization can significantly improve the energy efficiency of coal-fired power plants. While waste heat utilization technology for power plants has advanced significantly, it remains inefficient in practical applications. This is primarily due to two key issues: first, the recovery and utilization of only a portion of the higher-temperature waste heat is targeted, and second, the focus of this recovery and utilization is relatively limited.

[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 existing technology, 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 thermal power plants, and combine with heat exchangers and heat pumps and other equipment to carry out cascade recycling according to the characteristics of each waste heat, and use it for power generation and heat supply.

[0008] To solve the above technical problems, the present invention provides a first implementation solution: a power plant waste heat recovery system, 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 equipped with a four-way solenoid valve V1 and a temperature and pressure sensor MS1.

[0010] Compression heat pump No. 1 exchanges heat between the high-temperature flue gas input into compression heat pump No. 1 and 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 compression heat pump No. 1. The high-temperature water 2 delivery pipe is equipped with a four-way solenoid valve V2 and a temperature and pressure sensor MS2.

[0011] The second compression heat pump exchanges heat between 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 equipped 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 equipped 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 equipped 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 medium generator set and a heating pipeline, which 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 meet T≥300℃ 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 meet 160℃≤T<300℃ and the pressure is <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 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 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 the low-temperature water 5 delivery pipe and the 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 power plant waste heat recovery system, 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 passes through the No. 1 evaporator to exchange heat with refrigerant 1, and the temperature of refrigerant 1 increases. The third high-temperature flue gas passes through the No. 2 evaporator to exchange heat with refrigerant 1, and the temperature of refrigerant 1 further increases. The refrigerant 1, which has been 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, which has released heat and cooled twice, enters the No. 1 throttle valve to reduce the pressure and start the next heat pump cycle. The low-temperature water 2 passes through the No. 2 condenser and the No. 1 condenser successively to absorb the heat released by the condensation of the refrigerant 1 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, after its temperature rises, enters the No. 2 compressor to be compressed and pressurized. The compressed and pressurized refrigerant 2 enters the No. 3 condenser to be condensed and release heat. The refrigerant 2, which has released heat and cooled, enters the No. 2 throttle valve to reduce its pressure and start the next heat pump cycle. The low-temperature water 3 passes through the No. 3 condenser to absorb the heat released by the condensation of the refrigerant 2 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 undergoes heat conduction and radiation heat exchange with the high-temperature slag, and then 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 temperature and pressure signal measurement values ​​of each high-temperature water received at the signal inlet end 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 measurement 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 send 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 method proposed in this invention have significant technical advantages and innovative effects compared to existing technologies, which can be summarized as follows:

[0032] (1) Multi-source waste heat recovery: The system fully recovers waste heat from power plants and simultaneously recovers all waste heat from thermal power plants, including flue gas waste heat, high-temperature circulating water waste heat, furnace wall waste heat, and slag waste heat. Different heat pumps and heat exchangers are selected according to the characteristics of different waste heats, effectively recovering all recoverable waste heat and improving the energy conversion efficiency of power plants. The multi-source waste heat recovery setting improves the applicability of the system and can be applied to recover a variety of waste heat from various power plants (critical, supercritical, and ultra-supercritical), and can also adapt to the influence of external factors such as different seasons and different ambient temperatures on various waste heats.

[0033] (2) Multi-directional cascade recycling of waste heat: The recovered waste heat is recycled in a cascade according to its temperature and pressure. There are three specific ways to use it: 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 multiple cascade recycling schemes to ensure the scientific recycling of waste heat can avoid the waste of recovered waste heat that is not reused to its maximum extent.

[0034] (3) Realize automatic control: compare and match the thermodynamic conditions of the five types of high-temperature water with the requirements of the three-way cascade reuse method, and determine the priority output to one of the low-pressure steam turbine generator set, low-boiling point working fluid generator set and 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 The figure is a structural diagram of a power plant waste heat recovery system in the present invention.

[0037] Figure 2 This is the 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 easy to understand, 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 making creative efforts shall fall 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 transition 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 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. These four types of waste heat are all good and relatively stable low-temperature heat sources, and their recycling and utilization will greatly improve the energy utilization efficiency of coal-fired power plants. Although the technology for utilizing waste heat from power plants has also been well developed, it has not been efficiently reused in actual applications. There are two main problems. First, only some of the waste heat with higher temperatures is recycled and utilized, and second, the recycling and utilization goals are 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 Figures 1 and 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 equipped with a four-way solenoid valve V1 and a temperature and pressure sensor MS1.

[0045] Compression heat pump No. 1 exchanges heat with low-temperature water 2, which is input into evaporator No. 1 and evaporator No. 2. The heated low-temperature water 2 is converted into high-temperature water 2 and output through the high-temperature water 2 delivery pipe connected to compression heat pump No. 1. The high-temperature water 2 delivery pipe is equipped with a four-way solenoid valve V2 and a temperature and pressure sensor MS2.

[0046] The second compression heat pump exchanges heat with the high-temperature circulating water input to the third evaporator 6 of 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 equipped 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 equipped with a four-way solenoid valve V4 and a temperature and pressure sensor MS4.

[0048] The slag heat exchanger exchanges heat between the low-temperature water 5 input into the slag heat exchanger 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 exchanger. The high-temperature water 5 delivery pipe is equipped 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. 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 the four-way solenoid valve V1, the four-way solenoid valve V2, the four-way solenoid valve V3, the four-way solenoid valve V4 and the four-way solenoid valve V5 through pipelines;

[0050] The control cabinet has its signal input end connected to the temperature and pressure sensor MS1, the temperature and pressure sensor MS2, the temperature and pressure sensor MS3, the temperature and pressure sensor MS4 and the temperature and pressure sensor MS5, and its signal output end connected to the four-way solenoid valve V1, the four-way solenoid valve V2, the four-way solenoid valve V3, the four-way solenoid valve V4 and the four-way solenoid valve V5, respectively; the control cabinet compares and matches the temperature and pressure signal measurement values ​​of each high-temperature water received at the signal input 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.

[0051] Specifically, the control cabinet is set with set values ​​for the 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℃ 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℃≤T<300℃ and the pressure is less than 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 achieving 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 this series circuit. The No. 1 evaporator 2 and the No. 2 evaporator 3 are connected in parallel with a high-temperature flue gas delivery pipe, and the No. 2 condenser 5 is connected to 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. In the No. 1 compression heat pump provided here, the high-temperature flue gas is divided into two groups and fed into the No. 1 evaporator 2 and the No. 2 evaporator 3 in parallel, respectively, so that the refrigerant 1 is heated twice in succession by the high-temperature flue gas.

[0053] Specifically, the No. 1 condenser 4 and the No. 2 condenser 5 are both shell and tube heat exchangers, spiral plate heat exchangers or plate-fin heat exchangers, and the No. 1 evaporator 2 and the No. 2 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, primarily due to their high heat transfer efficiency and compact structure. Furthermore, the fluid cleanliness in the condensers is high, eliminating the need for frequent disassembly and cleaning of the heat exchangers. Floating-head heat exchangers can be used for Evaporator No. 1 (2) and Evaporator No. 2 (3), primarily due to the low cleanliness of the flue gas. The tube bundles of floating-head heat exchangers can be removed for cleaning, and floating-head heat exchangers are suitable for high-temperature, high-pressure, and large temperature differential scenarios.

[0055] Specifically, a specific structure for realizing 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] Both evaporator #3 (6) and condenser #3 (7) can be equipped with shell-and-tube, spiral plate, or plate-fin heat exchangers, primarily due to their high heat transfer efficiency and compact structure. Furthermore, the fluids in evaporator #3 (6) and condenser #3 (7) are highly clean, eliminating the need for frequent disassembly and cleaning of the heat exchangers.

[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 first surface plate heat exchanger 13, and a second surface plate heat exchanger 14. The conveyor belt 8 is used to transport high-temperature slag and is located between the first and second surface plate heat exchangers 13, 14. The first and second surface plate heat exchangers 13, 14 are connected to low-temperature and high-temperature water delivery pipes 5, respectively. The high-temperature slag exchanges heat with the low-temperature water 5 flowing through the first and second surface plate heat exchangers 13, 14 through heat conduction and radiation.

[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, so that this batch of high-temperature slag and the low-temperature water 5 in the No. 1 surface plate heat exchanger 13 and the No. 2 surface plate heat exchanger 14 are heat-conducted and radiated. After staying for 5 minutes, the conveyor belt 8 continues to rotate to transfer the second batch of high-temperature slag to the No. 1 surface plate heat exchanger 13 and the No. 2 surface plate heat exchanger 14 for heat exchange. The conveyor belt There are also multiple slag boxes connected to the chain plate in 8, each slag box is used to hold high-temperature slag, and the conveyor belt 8 is driven intermittently. When a new batch of high-temperature slag is conveyed to the slag box by the conveyor belt 8 and 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, so that this batch of high-temperature slag can conduct heat conduction and radiation heat exchange 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, it continues to be transmitted, and the second batch of high-temperature slag conveyed to the slag box continues to be transported by the conveyor belt 8.

[0061] The high-temperature slag and the low-temperature water 5 are fully exchanged with each other through the 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 for a power plant waste heat recovery system 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, which heats the low-temperature water 1 into high-temperature water 1 and outputs it through the high-temperature water 1 delivery pipe;

[0065] The second high-temperature flue gas passes through the No. 1 evaporator 2 and exchanges 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 and exchanges heat with the refrigerant 1, and the temperature of the refrigerant 1 further increases. The refrigerant 1, which has been heated twice by the high-temperature flue gas, 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, which 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 in succession to continuously absorb the heat released by the condensation of the refrigerant 1 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, after its temperature rises, enters the No. 2 compressor 18 to be compressed and pressurized. 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 in the No. 2 compression heat pump to reduce its pressure and then enter 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 undergoes heat conduction and radiation heat exchange with the high-temperature slag, and then absorbs the waste 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 end 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 measurement 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 sent 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 setting 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 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.

[0070] This invention proposes a power plant waste heat recovery system and method. This system aims to fully utilize all types of waste heat generated by thermal power plants. Based on the characteristics of each waste heat, the system, combined with heat exchangers and heat pumps, can be used for power generation and heating. This improves the power plant's energy conversion efficiency and avoids the 50%-70% energy waste in thermal power plants.

[0071] In this embodiment, water (low-temperature water 1, low-temperature water 2, low-temperature water 3, low-temperature water 4, and low-temperature water 5) is used to exchange heat with high-temperature flue gas, high-temperature circulating water, furnace walls, and slag. Using other working fluids can also recover these four types of waste heat. It should be emphasized that using other working fluids will result in different temperature and pressure settings in the control cabinet, which is within the scope of this invention.

[0072] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims and their equivalents, the present invention is intended to include such 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 is converted into high-temperature water 1 and outputted 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; Compression heat pump No. 1 exchanges heat between the high-temperature flue gas input into compression heat pump No. 1 and 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 compression heat pump No.

1. The high-temperature water 2 delivery pipe is equipped with a four-way solenoid valve V2 and a temperature and pressure sensor MS2. The second compression heat pump exchanges heat between 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 equipped 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 is converted into high-temperature water 4 and 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 equipped with a four-way solenoid valve V5 and a temperature and pressure sensor MS5. The system further comprises a low-pressure steam turbine generator set (9), a low-boiling-point working medium generator set (10) and a heat supply pipeline (11), wherein 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; 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 values, 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 medium 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 medium 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 medium generator set (10), the high-temperature water at the measured temperature and pressure is delivered to the heating pipeline (11).

3. The 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. The 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. The 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 recovery method of 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 high-temperature flue gas drives an absorption heat pump (1), and the absorption heat pump (1) heats low-temperature water 1 into high-temperature water 1, and outputs the high-temperature water 1 through a high-temperature water 1 delivery pipe; The second high-temperature flue gas passes through the No. 1 evaporator (2) and exchanges 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) and exchanges 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 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 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) after the temperature is increased to be compressed and pressurized. 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 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 high-temperature water 4; The low-temperature water 5 flowing in the slag heat exchange equipment undergoes heat conduction and radiation heat exchange with the high-temperature slag, and then 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 medium 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 send 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 send 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 reach the temperature and pressure setting values ​​required for the operation of the low-pressure steam turbine generator set (9), the control cabinet continues to judge whether the temperature and pressure can meet the temperature and pressure setting values ​​required for the operation of the low-boiling-point working medium generator set (10). If they can meet the requirements, the high-temperature water is sent to the low-boiling-point working medium 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 medium 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.

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