Waste heat recovery method and system under variable-temperature and variable-flow working conditions

Abstract

The invention relates to a waste heat recovery method and system under variable-temperature and variable-flow working conditions, and relates to the field of waste heat recovery. The method comprises the following steps: counting heat extraction points of which the unit heat production is greater than the highest required heat in a plant area, distinguishing the heat extraction points of which the heat extraction amounts cannot be regulated and controlled from the heat extraction points of which the heat extraction amounts can be regulated and controlled, and constructing a main heat system around the heat extraction points of which the heat extraction amounts cannot be regulated and controlled; an auxiliary heating system is constructed around a heat taking point of which the heat taking amount can be regulated and controlled; and finally, the main heating system is selected according to different heat supply periods or the main heating system and the auxiliary heating system are selected to supply heat together. Heat distribution can be flexibly regulated and controlled according to different heat loads, and then long-term stable heat supply is provided according to the heat loads in the centralized heat supply period.

Description

Technical Field

[0001] The present invention relates to the field of waste heat recovery, and in particular to a waste heat recovery method and system under variable temperature and variable flow conditions. Background Art

[0002] In thermal power, steel or petrochemical industries, the waste heat of steam turbine circulating water is usually recovered for power generation or heating. However, in some plant areas, such as some thermal power plants and coking coal plants, when the waste heat of steam turbine is used for heating, there are obvious defects such as unadjustable and uncontrollable heat source of circulating water waste heat due to production restrictions, insufficient in cold seasons, and excessive in non-cold seasons, which cannot meet the requirements of stable, continuous and quality heating.

[0003] At present, a Chinese invention patent application with publication number CN112856544A and publication date May 28, 2021 proposes a method and system for combining exhaust waste heat recovery and heat storage to improve the flexibility of thermal power units. The system includes a waste heat recovery unit, a heat storage unit, a heat network heater, a medium-pressure cylinder, a low-pressure cylinder and connecting pipes; the waste heat recovery unit includes a heat extraction tube bundle, a heating tube bundle and an ejector, and the heat storage unit includes a heat storage tank, a condenser and a heat release heat exchanger, and the cold side outlet of the heat release heat exchanger is connected to the cold side inlet of the heat network heater; the cold side outlet of the heat network heater is connected to the primary network water supply pipeline; an exhaust pipe is arranged on the connecting pipe between the medium-pressure cylinder and the low-pressure cylinder, and the exhaust pipe is divided into two routes, one is connected to the inlet of the heating tube bundle, and the other is connected to the hot side inlet of the heat network heater.

[0004] When in use, the waste heat from boiler exhaust is deeply recovered and utilized, and is directly used as a compensating heat source for the cogeneration unit.

[0005] Regarding the above-mentioned related technologies, since the exhaust heat in the boiler is limited, during the heating period, only the exhaust heat of the boiler is relied upon as a compensating heat source, and the control capability is limited, which cannot meet the stable and continuous heating requirements. Summary of the invention

[0006] In order to improve the waste heat control capability of a heat source unit during centralized heating during the heating period, the present invention provides a waste heat recovery method and system under variable temperature and variable flow conditions.

[0007] In the first aspect, the present invention provides a waste heat recovery method under variable temperature and variable flow conditions, which adopts the following technical solution:

[0008] A waste heat recovery method under variable temperature and variable flow conditions includes obtaining waste heat: obtaining a hot point and obtaining a heat amount;

[0009] Obtaining hotspots: Detecting the production processes in the factory one by one, taking time as the unit and counting the unit heat production of each production process based on production parameters and historical production data, counting the production temperature required for each production process, and calculating the maximum required heat according to the minimum production temperature and maximum heat consumption required for each production process. When the difference between the unit heat production and the maximum required heat at any time in the production process is greater than a first threshold, this production process is set as a hotspot;

[0010] Obtaining heat intake: calculating the difference between the unit heat output of each production process and the maximum required heat to obtain a single-point heat intake, and accumulating the single-point heat intake of each hot spot to obtain a total heat intake;

[0011] Hotspot classification: classify the hotspots according to the regulation conditions of the hotspots, set the hotspots that can be regulated as the main hotspots, and set the hotspots that cannot be regulated as the auxiliary hotspots;

[0012] Heat distribution: heat period distribution and system distribution;

[0013] Heating period allocation: The heating period is divided into the initial heating period, the constant heating period and the final heating period according to the ambient temperature and heat load demand;

[0014] System allocation: the auxiliary heating system is used for heating at the initial stage of heating and at the end of heating, and the main heating system and the auxiliary heating system are used together for heating during the constant heating period.

[0015] By adopting the above technical solution, there will generally be exhaust waste heat in multiple production processes within the factory. When recovering waste heat within the factory, each production process is first statistically analyzed and the production processes with more waste heat are marked in combination with historical production data. If the temperature in the production process is lower than a certain temperature, which will lead to a decrease in production efficiency or an increase in production energy consumption and other factors that affect normal production, the temperature is set as the minimum production temperature. The heat consumed when the equipment in the production process is running at the highest load is counted as the maximum heat consumption. The maximum heat demand of the production process is the heat required for the lowest production temperature plus the maximum heat consumption. Specifically, it is understood that the maximum heat consumption in the production process is the maximum heat demand. After part of the heat in the quantity is consumed, the remaining heat just meets the heat required for the minimum production temperature; the first threshold value can be based on the cost of building the main heat system and the unit price of heat, and the production process with a heating cost less than the construction cost is set as the hot spot, and then the hot spot that cannot adjust the recovery of waste heat during the heating process is set as the main hot spot. Since the heat generated by the main hot spot cannot be adjusted, the main hot spot is used as the main heating when recovering waste heat, and the waste heat recovery strategy is flexibly adjusted in conjunction with the auxiliary hot spot, and the main hot spot is used as the main heating system during the heating period. When the main hot spot cannot meet the heating demand, the recovered heat of the auxiliary hot spot is flexibly adjusted for distribution. In this way, the hot points in the factory are classified, and the main heat system is built around the main hot points, and the auxiliary heat system is built around the auxiliary hot points. Therefore, during the heating period, the main heat system can be used as the main system to achieve long-term heating, and the auxiliary heat system can be used as the auxiliary system to coordinate with the main heat system to actively adjust heat distribution when the heat load is high, and jointly provide heat, thereby improving the waste heat regulation capacity during centralized heating; at the same time, waste heat is recovered from various production processes in the factory, realizing multi-level cascade recycling of discharged waste heat, and further reducing energy waste.

[0016] Optionally, a weight allocation step is further provided after the hot period allocation and before the system allocation;

[0017] Weight allocation: Based on the single-point heat extraction weight of the auxiliary hotspots in the auxiliary heating system, the weight of the auxiliary hotspot with a large single-point heat extraction value is set higher than that of the auxiliary hotspot with a small single-point heat extraction value. When supplying heat, the auxiliary hotspot with a high weight is set to give priority to heating.

[0018] In the auxiliary hotspots, since the single-point heat production of each hotspot is different, the waste heat recovery costs and recovery benefits of different auxiliary hotspots are different. When recovering waste heat, the auxiliary hotspots with larger heat production should be recovered first. By adopting the above technical solution, the waste heat recovery priority of the auxiliary hotspots is set in a weighted manner, and the waste heat of the auxiliary hotspots with high single-point heat production is recovered first, so that more waste heat is recovered at a lower cost, and the waste heat recovery benefit is maximized.

[0019] Optionally, after the hot spot classification and before the heat distribution, a fluctuation distribution step is also included;

[0020] Fluctuation allocation: setting the hot spot whose single-point heat fluctuation value is greater than or equal to the second threshold as a fluctuating hot spot;

[0021] In the weight allocation step, the weight of the fluctuation hotspot is lower than the weight of the auxiliary hotspot;

[0022] In the system allocation step, the fluctuation system and the auxiliary heating system work simultaneously.

[0023] Due to large temperature fluctuations in some production processes, the single-point heat extraction in the hot spot in this production process fluctuates greatly when recovering waste heat. In the subsequent process of recovering waste heat, in order to reduce the adverse effects of excessive temperature on the heat recovery equipment, it is necessary to regulate the single-point heat extraction in the fluctuating hot spot. By adopting the above technical scheme, the fluctuating hot spots in the hot spots are isolated according to the fluctuation value of the single-point heat extraction, and a corresponding fluctuation system is constructed to uniformly regulate the heat in the fluctuating hot spots, thereby reducing the adverse effects on the waste heat recovery equipment when the temperature in the fluctuation system is too high. Since the heat in the fluctuation system fluctuates, the cost of waste heat recovery is higher. Therefore, setting the heat use priority in the fluctuation system is lower, and the fluctuation system cooperates with the auxiliary heating system to supply heat, which can greatly enhance the waste heat regulation ability of the centralized heating system.

[0024] Second aspect: The present invention provides a waste heat recovery system, which adopts the following technical solution:

[0025] A waste heat recovery system, which applies the waste heat recovery method under variable temperature and variable flow conditions as described in the first aspect to a coking coal plant, wherein the waste heat recovery system comprises a main heat system, an auxiliary heat system and a control system;

[0026] The main heat system includes a steam turbine, a main heat station, a water supply pipeline and a return water pipeline. The main heat station is connected to the steam turbine and is used to extract heat from the steam turbine. The main heat station is connected to a heat user through the water supply pipeline and the return water pipeline.

[0027] The auxiliary heat system comprises an ammonia water pump, an ammonia water circulation pipe and a shell heat exchanger, wherein the ammonia water circulation pipe connects the ammonia water pump, the shell heat exchanger and the coke oven gas pipe, the ammonia water pump is used to pump ammonia water to circulate in the ammonia water circulation pipe, the ammonia water circulation pipe is connected to the hot end of the shell heat exchanger, the cold end water inlet of the shell heat exchanger is connected to the return water pipeline, and the cold end water outlet of the shell heat exchanger is connected to the main heat station;

[0028] The main heating system and the auxiliary heating system are both electrically connected to the control system.

[0029] Among them, the technology of recovering waste heat from turbine circulating water after waste heat boiler power generation is mature, but it has the characteristics of being unadjustable, uncontrollable, and unstable in heat. It can be used as the basic heat source for heating residents. By adopting the above technical scheme, the waste heat of turbine circulating water is recovered as the main heat system for heating, and the heat in the coal gas is absorbed through the ammonia circulation pipe, and the heat in the ammonia is transferred to the heating water through the shell heat exchanger to heat the heating water, thereby forming an auxiliary heating system. The heating rate of the auxiliary heating system can be adjusted by adjusting the rate at which the ammonia pump pumps ammonia, thereby realizing a heating system based on the main heating system and an auxiliary heating system as a regulation system. During the centralized heating period, the heat distribution can be flexibly adjusted to improve the waste heat regulation capacity and achieve long-term stable heating; at the same time, the heat in the coal gas can be recovered to further improve the waste heat capacity and save energy consumption.

[0030] Optionally, the auxiliary heat system also includes a secondary system;

[0031] The secondary system includes a transverse tube primary cooler and a first plate heat exchanger. The transverse tube primary cooler is connected to the coke oven gas pipe. The transverse tube primary cooler is used to cool the gas in the coke oven gas pipe and absorb the heat of the gas. The transverse tube primary cooler includes a first stage cooling and a second stage cooling. The hot end of the first plate heat exchanger is connected to the first stage cooling of the transverse tube primary cooler, the cold end water inlet of the first plate heat exchanger is connected to the return water pipeline, and the cold end water outlet of the first plate heat exchanger is connected to the main heat station.

[0032] When cooling coal gas, a horizontal tube pre-cooler is usually used for cooling. The cooling water in the horizontal tube pre-cooler usually also has a certain amount of heat. By adopting the above technical solution, the first plate heat exchanger is used to exchange heat with a section of cooling water in the horizontal tube pre-cooler, and the heat in a section of cooling water is transferred to the heating water to heat the heating water. On the one hand, the heat distribution during heating can be adjusted by adjusting the waste heat recovery amount of the secondary system to further improve the waste heat regulation capability. On the other hand, by constructing a secondary system and recovering different types of waste heat in different ways, step-by-step waste heat recovery is achieved, further improving the waste heat recovery capability.

[0033] Optionally, it also includes a fluctuation system, which includes a two-stage water supply pipe, a two-stage return pipe, a heat pump unit and a heat dissipation device, one end of the two-stage water supply pipe is connected to the two-stage cooling water outlet of the cross-tube pre-cooler, the heat dissipation device is connected to the other end of the two-stage water supply pipe, the other end of the heat dissipation device is connected to the hot end water inlet of the heat pump unit, the cold end water outlet of the heat pump unit is connected to the water supply pipeline, the cold end water inlet of the heat pump unit is connected to the return pipeline, one end of the two-stage return pipe is connected to the hot end water outlet of the heat pump unit, and the two-stage cooling water inlet of the cross-tube pre-cooler is connected to the other end of the two-stage return pipe.

[0034] The second stage cooling circulating water of the horizontal tube primary cooler has a large amount of water, the high temperature point is close to 60 degrees Celsius, the low temperature point is close to the return water temperature of the heating water, the temperature fluctuation range is large, and direct heat exchange is impossible. By adopting the above technical solution, the second stage cooling circulating water of the horizontal tube primary cooler passes through the heat dissipation device and then enters the heat pump unit through the second stage water supply pipe. The heat pump unit uses the second stage cooling circulating water as the low temperature side heat source and heats the heating water. Then the cooled circulating water flows back to the second stage cooling circulating water of the horizontal tube primary cooler through the second stage return pipe. The heat dissipation device will first cool the circulating water in the second stage water supply pipe, and control the circulating water in the second stage water supply pipe at a certain temperature before controlling the circulating water to flow into the heat pump unit. In this way, the heat pump unit can recover the waste heat of the second stage cooling circulating water with large temperature fluctuations, improve the waste heat recovery capacity, and use the heat dissipation device to cool the second stage cooling circulating water before it enters the heat pump unit, so that the second stage cooling circulating water meets the maximum operating temperature requirements of the heat pump unit.

[0035] Optionally, the heat dissipation device is a second plate heat exchanger, the hot end water inlet of the second plate heat exchanger is connected to the second-section water supply pipe, the hot end water outlet of the second plate heat exchanger is connected to the heat pump unit, the cold end water inlet of the second plate heat exchanger is connected to the return pipe, and the cold end water outlet of the second plate heat exchanger is connected to the water supply pipe.

[0036] Since there is still some heat in the second-stage cooling circulating water in the second-stage water supply pipe and the water flow rate of the second-stage cooling circulating water is large, directly dissipating the heat of the second-stage cooling circulating water in the second-stage water supply pipe will result in a large amount of waste heat being wasted. By adopting the above technical solution, the second plate heat exchanger can directly exchange heat between the second-stage cooling circulating water and the heating water in the second-stage water supply pipe, and transport the second-stage cooling circulating water that has undergone heat exchange in the second-stage water supply pipe to the heat pump unit for waste heat recovery. In this way, using the second plate heat exchanger for heat dissipation can not only cool the second-stage cooling circulating water in the second-stage water supply pipe, but also recover the waste heat of the high-temperature second-stage cooling circulating water in the second-stage water supply pipe through the second plate heat exchanger, so that the heat at the high-temperature point in the second-stage cooling circulating water is absorbed by the heating water in the second plate heat exchanger, and the heat at the low-temperature point that cannot be directly absorbed by the heating water is recovered through the heat pump unit, thereby improving the waste heat recovery rate of the second-stage cooling circulating water.

[0037] Optionally, the hot end water inlet of the second plate heat exchanger is connected to the hot end water outlet of the second plate heat exchanger, a first shut-off valve is connected between the hot end water inlet of the second plate heat exchanger and the hot end water outlet of the second plate heat exchanger, a second shut-off valve is connected between the second plate heat exchanger and the second-section water supply pipe, and a third shut-off valve is connected between the second plate heat exchanger and the heat pump unit.

[0038] By adopting the above technical solution, the hot end water inlet and hot end water outlet of the second plate heat exchanger are connected, and the second shut-off valve and the third shut-off valve are closed, so that the second stage cooling circulating water in the second stage water supply pipe can directly enter the heat pump unit without passing through the second plate heat exchanger; the first shut-off valve is closed, and the second shut-off valve and the third shut-off valve are opened so that the second stage cooling circulating water in the second stage water supply pipe must pass through the second plate heat exchanger before entering the heat pump unit. When the temperature of the second stage cooling circulating water is low, the second stage cooling circulating water is controlled not to pass through the second plate heat exchanger, and the heat input reduces the heat loss of the second stage cooling circulating water in the second plate heat exchanger; when the temperature of the second stage cooling circulating water is high, the second stage cooling circulating water must pass through the second plate heat exchanger before entering the heat pump unit, reducing the probability of high-temperature water entering the heat pump unit and affecting the normal operation of the heat pump unit.

[0039] Optionally, the control system includes multiple flow meters, multiple electric control valves and a host computer, and the multiple flow meters and the multiple electric control valves are connected to the return pipe, the first cooling stage and the second cooling stage of the cross-tube pre-cooler, and the multiple flow meters and the multiple electric control valves are electrically connected to the host computer.

[0040] By adopting the above technical solution, the water flow in each pipeline system is detected by connecting the flow meter through the host computer, and the water flow in each pipeline system is controlled by connecting the host computer and the electric control valve, so as to control the waste heat recovery strategy and heat distribution, realize automatic control of waste heat recovery and waste heat regulation, reduce human intervention, and improve the degree of automation and intelligence.

[0041] In summary, the present invention includes at least one of the following beneficial technical effects:

[0042] 1. Through statistical allocation of various hot spots in the plant area, the hot spots that cannot adjust the waste heat recovery are set as the main hot spots, and the hot spots that can adjust the waste heat recovery are set as auxiliary hot spots. The main hot spots are used as the basis for heating, and the auxiliary hot spots are used for regulation, thereby improving the waste heat regulation capacity during centralized heating and meeting the requirements of stable and continuous heating.

[0043] 2. Assign weights to the auxiliary hotspots based on their waste heat recovery. When using the auxiliary hotspots to regulate heating capacity, give priority to using auxiliary hotspots with large weights for supplementary heating. This can provide more supplementary heat when fewer devices are turned on, saving heating costs and enabling faster response when supplementary heat is needed.

[0044] 3. For hot spots with large temperature fluctuations, use heat pump units to recover waste heat. The heat pump unit can recover heat from circulating water with relatively low temperature, and a plate heat exchanger is set before the heat pump unit. The plate heat exchanger can limit the temperature entering the heat pump unit, reducing the impact of high temperature on the heat pump unit. At the same time, it can further recover heat from circulating water with relatively high temperature, further improving the waste heat recovery capacity and waste heat regulation capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a coke oven gas cooling flow chart in the prior art;

[0046] Figure 2 This is a general process flow chart of the waste heat recovery system according to an embodiment of the present invention;

[0047] Figure 3 This is a flow chart of heat extraction from ammonia water according to an embodiment of the present invention;

[0048] Figure 4 Schematic diagram of the cooling water circulation process of the horizontal tube primary cooler according to an embodiment of the present invention.

[0049] Explanation of the reference numerals in the accompanying drawings: 1. Main heat system; 11. Steam turbine; 12. Main heat station; 13. Water supply pipeline; 14. Return pipeline; 2. Auxiliary heat system; 21. Ammonia water pump; 22. Ammonia water circulation pipe; 23. Shell-type heat exchanger; 3. Secondary system; 31. Horizontal tube primary cooler; 32. First stage cooling; 33. Second stage cooling; 34. First plate heat exchanger; 4. Fluctuation system; 41. Second stage water supply pipe; 42. Second stage return pipe; 43. Heat pump unit; 44. Heat dissipation device; 45. Second plate heat exchanger; 46. First shut-off valve; 47. Second shut-off valve; 48. Third shut-off valve; 5. Control system; 51. Flow meter; 52. Electric regulating valve; 53. Host computer; 6. Heat user; 7. Coke oven gas pipe. DETAILED DESCRIPTION

[0050] The following combination Figures 1 to 3 The present invention is described in further detail.

[0051] Embodiment 1: The embodiment of the present invention discloses a waste heat recovery method under variable temperature and variable flow conditions. A waste heat recovery method under variable temperature and variable flow conditions mainly includes: counting the hot spots in the plant area where the unit heat output is greater than the maximum required heat, distinguishing the hot spots where the heat output cannot be regulated from the hot spots where the heat output can be regulated, constructing a main heat system around the hot spots where the heat output cannot be regulated, constructing an auxiliary heat system around the hot spots where the heat output can be regulated, and finally selecting the main heat system or the main heat system and the auxiliary heat system for joint heating according to different heating periods; in this way, the auxiliary heat system that can be regulated can be used for heating when the heat load is small, and the heat distribution can be flexibly regulated and the heat consumption of the main heat system can be reduced; when the heat load is large, the main heat system that cannot be regulated is used as the basic heating and the auxiliary heat system is used for auxiliary heating, and the heat in the auxiliary heat system is flexibly distributed on the basis of the main heat system to provide long-term and stable heating.

[0052] The waste heat recovery method of this embodiment specifically includes the following steps:

[0053] S1 obtains waste heat: including S11 obtaining hot spots and S12 obtaining heat;

[0054] S11 Obtaining the hotspot: inspecting the production processes in the factory one by one, counting the unit heat production of each production process in units of time and based on production parameters and historical production data, counting the production temperature required for each production process, calculating the maximum required heat according to the minimum production temperature and maximum heat consumption required for each production process, and setting this production process as a hotspot when the difference between the unit heat production and the maximum required heat at any time in the production process is greater than a first threshold.

[0055] In this embodiment, the unit heat generation of a single production process within a unit hour is counted in units of hours, and the temperature in the production process that, if lower than a specific temperature, will lead to a decrease in production efficiency or an increase in production energy consumption and other factors that affect normal production is counted and set as the minimum production temperature. The maximum heat consumption refers to the heat consumed per unit time when the equipment in this production process is running at the highest load plus the heat loss carried away by the air. The maximum required heat is the heat required to maintain the minimum production temperature of the production process per unit time plus the maximum heat consumption, so that when the maximum required heat is consumed by this production process, the remaining heat can also maintain the minimum production temperature of the production process during normal production. The single-point heat generation is the difference between the unit heat generation and the maximum required heat. The first threshold is based on the value from The construction cost of the heating system constructed by this production process and the benefit brought by the heating system constructed by this production process are set. Specifically, in this embodiment, the construction cost of the heating system constructed by this production process includes the total investment of site fees, construction fees, maintenance fees and labor fees. The benefit brought by the heating system constructed by this production process is the heat unit price multiplied by the cost recovery period. The first threshold is the quotient of the construction cost divided by the heat unit price and the cost recovery period. The meaning of the first threshold is that a certain amount of heat must be recovered in this production process within a unit hour to ensure that the construction cost can be recovered within the cost recovery period. The difference between the unit heat output and the maximum demand heat is the heat that can be recovered by this production process within a unit time, and the production process whose heat that can be recovered per unit time is greater than the first threshold is set as the hot spot.

[0056] S12 obtains the heat intake: the unit heat output of each production process and the maximum required heat are calculated to obtain the single-point heat intake, and the single-point heat intake of each hot spot is accumulated to obtain the total heat intake.

[0057] In this embodiment, the single-point heat extraction is the difference between the unit heat production of a single production process and the maximum required heat. The specific meaning of the single-point heat extraction is that the remaining heat after the single-point heat extraction is extracted from the production process still does not affect the heat of the normal production of the production process. The total heat extraction is the heat extraction available for the entire plant area.

[0058] S2 hotspot allocation: classifying the hotspots according to the regulation conditions of the hotspots, setting the hotspots that can be regulated as primary hotspots, and setting the hotspots that cannot be regulated as auxiliary hotspots.

[0059] In this embodiment, due to the different heat production conditions of different production processes, some of the production processes cannot be regulated, resulting in their unit heat production and maximum heat demand being fixed values, which in turn causes the unit heat extraction of this production process to be a constant value. However, during the heating period, the ambient temperature changes, resulting in the heat load constantly changing with the ambient temperature, and the unit heat extraction is a constant value, which makes it unable to adapt to the changing heat load. Therefore, the hotspot that cannot be regulated is set as the main hotspot, and heating is provided based on the main hotspot during the heating period. The hotspot that can be regulated is set as the auxiliary hotspot, and heat is flexibly allocated through the auxiliary hotspots during the heating period to meet the changing heat load requirements.

[0060] S3 Fluctuation allocation: setting the hot spot whose single-point heat fluctuation value among the hot spots is greater than or equal to the second threshold as a fluctuation hot spot.

[0061] In this embodiment, also limited by the production process, some production processes need to be flexibly adjusted according to the usage scenario, resulting in continuous changes in the unit heat production and maximum required heat of the hotspot, which in turn leads to large fluctuations in the unit heat extraction value. The heat exchange equipment is limited by material and power, resulting in it only being able to be used for heat exchange within the set temperature range. The second threshold is set according to the use requirements of the heat exchange equipment, and specifically refers to the applicable temperature range of the heat exchange equipment. The hotspot with a fluctuation value greater than or equal to the second threshold is set as the fluctuation point, and waste heat recovery can be performed after subsequent unified temperature control.

[0062] S4 heating implementation: including construction of main heating system in S41, auxiliary heating system in S42 and fluctuating system in S43;

[0063] S41 constructs the main heat system: constructs the main heat station and connects the main hotspot, and connects the main heat station and heat users. Builds the main heat station and connects the main hotspot, and connects the main heat station and heat users.

[0064] In this embodiment, each main hotspot is connected by constructing a pipeline system, and the heat recovered from the main hotspots is uniformly transported to the main thermal station. The main thermal station centrally recovers the waste heat recovered from the main thermal system and transfers it to heating water to supply heat to users for heating.

[0065] S42 constructs an auxiliary heating system: constructs an auxiliary heating station and connects the auxiliary hotspots, and the auxiliary heating station is connected to the main heating station.

[0066] In this embodiment, a pipeline system is constructed to connect the auxiliary hot spots, and the heat recovered from the auxiliary hot spots is concentrated in the auxiliary heat station, which then unifies the temperature of the recovered waste heat and then transports it to the main heat station. On the one hand, it can reduce the fluctuation of recovered heat in the auxiliary heat system, which leads to instability in the heat transferred to the heating water in the main heat station. On the other hand, it can concentrate the heat in the auxiliary heat station and recover it to the main heat station, which then regulates the heat transferred to the heating water, thereby realizing the regulation capability of waste heat recovery for heating water. At the same time, the heat is uniformly distributed and regulated by the main heat station, which can also reduce the complexity of the temperature control strategy.

[0067] S43 constructs a wave system: constructs a wave heat station and connects the wave hotspots, and the wave heat station is connected to the main heat station.

[0068] In this embodiment, a pipeline is constructed to connect the hot spots with large temperature fluctuations. After the temperature in the fluctuation system is uniformly adjusted by the fluctuation heat station, the heat recovered in the fluctuation system is transported to the main heat station. On the one hand, it can reduce the adverse effects of excessive water temperature in the fluctuation system on the normal operation of the main heat station or auxiliary heat station. On the other hand, it can also recover waste heat from production processes with large temperature fluctuations, improve waste heat recovery capacity, and reduce energy waste. S5 Heat supply distribution: including S51 heat period distribution, S52 weight distribution, and S53 system distribution

[0069] S51 Heating period allocation: The heating period is divided into the initial heating period, constant heating period and the final heating period according to the ambient temperature and heat load demand.

[0070] In this embodiment, the ambient temperature is higher and the heat load is smaller at the beginning and end of the heating period, so the heating periods with smaller heat load and larger heat load are separated, and the heating capacities of the auxiliary heating system and the fluctuation system are counted. When the heat load is less than the average heating capacity of the auxiliary heating system and the fluctuation system, this period is set as the beginning or the end of heating; when the heat load is greater than the average heating capacity of the auxiliary heating system and the fluctuation system, this period is set as a constant heating period. In this way, different heating methods can be used according to different periods to save energy consumption.

[0071] S52 Weight allocation: Based on the single-point heat collection weight of the auxiliary hotspots in the auxiliary heating system, the weight of the auxiliary hotspot with a large single-point heat collection value is set higher than that of the auxiliary hotspot with a small single-point heat collection value, and the weight of the fluctuating hotspot is lower than that of the auxiliary hotspot. When heating, the auxiliary hotspot with a high weight is set to give priority to heating.

[0072] In this embodiment, when constructing the auxiliary heating system, due to the different single-point heating amounts of different production processes, it is necessary to set certain strategies to control the waste heat recovery of different auxiliary hot spots when performing waste heat regulation. Since the auxiliary heating systems are connected and the heat unit price is the same, the auxiliary hot spots with large single-point heating amounts bring higher benefits. Therefore, the auxiliary hot spots with large single-point heating amounts have higher weights, and heating is given priority to the auxiliary hot spots with high weights. However, due to the large temperature fluctuations of the fluctuating hot spots, the waste heat recovery cost of the fluctuating hot spots is greater and the control is more complicated. Therefore, the weight of the fluctuating hot spots is set lower than the weight of the auxiliary hot spots, and the fluctuating hot spots are used for heating when the auxiliary hot spots are insufficient to provide heat, so as to obtain greater benefits.

[0073] S53 system allocation: the auxiliary heating system is used for heating at the initial stage of heating and at the end of heating, the main heating system and the auxiliary heating system are used together for heating during the constant heating period, and the fluctuation system and the auxiliary heating system work simultaneously.

[0074] In this embodiment, during the heating period, since the heat load at the initial and final stages of heating is less than the average heating capacity of the auxiliary heating system and the fluctuation system, the auxiliary heating system and the fluctuation system are used for heating at the initial and final stages of heating, and the weight of the fluctuation hotspot is lower than the weight of the auxiliary hotspot. Therefore, the auxiliary hotspot is used first for heating, and the fluctuation hotspot is used for heating when the auxiliary hotspot is insufficient. This can not only reduce the waste heat waste caused by the inability to control the main heating system, but also meet the flexible waste heat heating control. During the constant heating period, the heat load is greater than the average heating capacity of the auxiliary heating system and the fluctuation system, and the heating demand cannot be met by relying solely on the auxiliary heating system and the fluctuation system. At this time, it is necessary to take the main heating system as the basis and regulate the auxiliary heating system and the fluctuation system to meet the stable heating demand under different temperatures and different heat loads.

[0075] Example 2: This embodiment of the present invention discloses a waste heat recovery system, which applies the waste heat recovery method under variable temperature and variable flow conditions in Example 1 to a coking coal plant. Figures 1 to 3 A waste heat recovery system mainly includes a main heat system 1, an auxiliary heat system 2, a fluctuation system 4 and a control system 5, wherein the main heat system 1 is used to provide basic heating to users, the auxiliary heat system 2 is used to provide auxiliary heating to users first, and the heating capacity is adjusted on the basis of the main heat system 1 to meet the heating needs under different conditions, the fluctuation system 4 is used to recover waste heat from hot spots with large temperature fluctuations in a coking coal plant, and perform auxiliary heating together with the auxiliary heat system 2, the main heat system 1, the auxiliary heat system 2 and the fluctuation system 4 are all electrically connected to the control system 5, and the control system 5 is used to control the main heat system 1, the auxiliary heat system 2 and the fluctuation system 4, and adjust the waste heat distribution strategy.

[0076] Reference Figure 1In the coking plant of a large coal-coke chemical enterprise, in addition to the circulating water of the turbine 11 that can be used for heating, the waste heat from the upper water, middle water, and ammonia circulating water of the raw gas primary cooler can also be recovered for centralized heating of local residents. Coal is distilled at high temperature in the carbonization chamber of the coke oven to generate coke oven gas; the coke oven gas at about 800°C is cooled in multiple stages through the bridge pipe, collecting pipe, and cross-tube primary cooler 31, and the temperature drops to about 22°C before entering the gas purification process; the heat in the gas is dissipated into the circulating ammonia water and cooling circulating water, solving the problem of a single heat source of only using the circulating water of the turbine 11 for heating, and the problem of insufficient heat source in the cold season and the unadjustable and uncontrollable waste heat of the circulating water of the turbine 11.

[0077] Reference Figure 2 The main heat system 1 includes a steam turbine 11, a main heat station 12, a water supply pipeline 13 and a return water pipeline 14. One end of the water supply pipeline 13 and the return water pipeline 14 are connected to the heat user 6, and the other end of the water supply pipeline 13 and the return water pipeline 14 are connected to the main heat station 12. The heating water flows in the water supply pipeline 13 and the return water pipeline 14 to form a water supply circulation system between the main heat station 12 and the heat user 6. The main heat station 12 extracts the heat in the circulating water of the steam turbine 11 and transmits it to The heating water in the water supply circulation system flows out of the turbine 11 with high temperature, flows to the heat user 6 through the water supply pipe 13, and after the heat user 6 is heated, the heating water with low temperature is transported to the main heat station 12 through the return pipe 14 for heating. In this embodiment, the main heat station 12 adopts a mixed water heating unit for heat exchange. The main heat system 1 is relatively conventional in the prior art, so the main heat system 1 in this application can adopt conventional heat exchange methods to exchange heat for the heating water.

[0078] Reference Figure 2 and Figure 3 In this embodiment, the auxiliary heat system 2 is used to recover the waste heat of the circulating ammonia water. According to the circulating ammonia water temperature curve, the temperature of the ammonia water before spraying is relatively stable, between 75-77°C. According to the Technical Specifications for Recycling and Utilization of Waste Heat in the Upper Section of Coking Primary Cooling YB / T4790-2019, the spraying temperature of the circulating ammonia water should not be lower than 65°C. The circulating ammonia water is set to cool down to 68°C after passing through the heat exchanger, leaving a surplus of 3°C; the waste heat that can be recovered is shown in Table 1 below:

[0079] Table 1 Circulating ammonia waste heat table

[0080]

[0081] Specifically: the auxiliary heat system 2 includes an ammonia water pump 21, an ammonia water circulation pipe 22, a shell heat exchanger 23 and a secondary system 3. The ammonia water circulation pipe 22 connects the ammonia water pump 21, the shell heat exchanger 23 and the coke oven gas pipe 7. The ammonia water pump 21 is used to pump ammonia water to circulate in the ammonia water circulation pipe 22. The ammonia water circulation pipe 22 is connected to the hot end of the shell heat exchanger 23. The cold end water inlet of the shell heat exchanger 23 is connected to the return water pipeline 14. The cold end water outlet of the shell heat exchanger 23 is connected to the return water pipeline 14. The main heat station 12 is connected, and the hot end of the shell heat exchanger 23 transfers the heat in the circulating ammonia water to the heating water at the cold end of the shell heat exchanger 23, and recovers the heat in the circulating ammonia water. Since the water quality of the circulating ammonia water is poor, the ammonia content is high, and the corrosiveness is strong, the shell heat exchanger 23 uses a shell and tube water-water heat exchanger made of 316L material, and the circulation rate of the circulating ammonia water is controlled by adjusting the ammonia pump 21 to control the amount of waste heat recovered in the heating water.

[0082] Reference Figure 2 and Figure 4 In this embodiment, the secondary system 3 is used to recover the waste heat of the circulating water at the upper end of the horizontal tube primary cooler 31, and three horizontal tube primary coolers 31 are arranged in the cold drum electric capture area in the coking coal plant. During normal production, two are in use and one is in reserve. In this embodiment, the cooling section of the horizontal tube primary cooler 31 is divided into a first cooling section 32, a second cooling section 33, and a lower section. The lower section is cooled by refrigerated water, the second cooling section 33 is cooled by circulating water, and the first cooling section 32 is cooled by circulating water or heating water.

[0083] In this embodiment, according to the data provided by the heat source unit, the average temperature difference of the first stage cooling 32 water inlet and outlet is 9.3℃, the average flow rate is 110m3 / h, and the average heat supply is 1189kW. In the heating season, the first stage cooling 32 water operates independently to provide heating for the factory area and nearby areas. According to the heat supply, the heating area is estimated to be about 10,000 square meters; according to the gas cooling capacity and the first stage cooling 32 heat exchange area, the chemical industry has put forward data: the total flow of the first stage cooling 32 water is 400m3 / h, and the inlet and outlet temperatures of the cooling water can be controlled at 71 / 61℃. The first stage cooling 32 water provides a total heat of 4.65MW. Combined with the factory's heating season operation data and calculation data, the heat supply is shown in Table 2 below.

[0084] Table 2 Horizontal tube primary cooler first stage cooling heat supply table

[0085]

[0086] Specifically, in this embodiment, the secondary system 3 includes a transverse tube primary cooler 31 and a first plate heat exchanger 34. The transverse tube primary cooler 31 is connected to the coke oven gas pipe 7. The transverse tube primary cooler 31 is used to recover the heat of the gas in the coke oven gas pipe 7. The transverse tube primary cooler 31 includes a first cooling stage 32 and a second cooling stage 33. The hot end of the first plate heat exchanger 34 is connected to the first cooling stage 32 of the transverse tube primary cooler 31. The cold end water inlet of the first plate heat exchanger 34 is connected to the return water pipeline 14. The cold end water outlet of the first plate heat exchanger 34 is connected to the main heat station 12. The first plate heat exchanger 34 transfers the waste heat of the circulating water in the first cooling stage 32 to the heating water at the cold end of the first plate heat exchanger 34 through the hot end of the first plate heat exchanger 34, and The heating water at the cold end of the first plate heat exchanger 34 is transported to the main heat station 12, and the main heat station 12 jointly distributes the waste heat. In specific implementation, a branch pipeline can be set on the outlet pipe of the existing cross-tube primary cooler 31 and the first cooling 32 to connect to the first plate heat exchanger 34. The interface of the first plate heat exchanger 34 is provided with a flow regulating valve to control the water intake. The circulating water of the first cooling 32 of the cross-tube primary cooler 31 after heat exchange is connected to the existing heating water tank and pumped to the original circulating water pipeline by a water pump. According to the water quality test report of the cooling circulating water at one end provided by the heat source unit, it is basically equivalent to heating water, and may be mixed with a small amount of coal tar. Therefore, the first plate heat exchanger 34 selects a 4MW small temperature difference plate heat exchanger made of 316L for waste heat recovery.

[0087] Since the total heat recovered in the secondary system 3 is less than the total heat recovered in the auxiliary heating system 2, when setting the heating priority, the auxiliary heating system 2 should be used for heating first, and the secondary system 3 should be used for heating when the auxiliary heating system 2 is insufficient.

[0088] Reference Figure 2 and Figure 4 In this embodiment, the fluctuation system 4 is used to recover the waste heat of the second stage cooling 33 circulating water of the cross tube primary cooler 31. According to the report provided by the heat source unit, the average temperature of the second stage cooling 33 circulating water of the cross tube primary cooler 31 is 44.8 (the high temperature point is nearly 60°C, and the fluctuation range is large), the average flow rate is 1692m3 / h, and the average heat supply is 49.5MW. According to parameters such as the gas cooling amount, the chemical industry proposes data; the total flow rate of the circulating water of the second stage cooling 33 is ~2000m3 / h, the inlet and outlet water temperatures of the circulating water of the second stage cooling 33 are 45 / 28°C, and the total heat provided by the second stage cooling 33 circulating water is 39.5MW. Since the circulating water temperature of the second stage cooling 33 is close to the return water temperature of the heating water under normal circumstances, it is impossible to directly exchange heat. After multiple discussions, the high temperature centrifugal water source heat pump unit 43 is finally selected for heat exchange, and the circulating water of the second stage cooling 33 is used as the heat source on the low temperature side of the heat pump. The heat pump parameters are shown in Table 3 below:

[0089] Table 3 Heat pump parameters

[0090]

[0091] The heat pump evaporator inlet and outlet temperatures are 45 / 37.9℃, the flow rate is 1099m3 / h, and the heat used is 9.08MW. Combined with the operation data and calculation data of the heat source unit plant, the heat supply is shown in Table 4 below:

[0092] Table 4 Horizontal tube primary cooler second stage cooling heat supply table

[0093]

[0094] Reference Figure 2 and Figure 4 The wave system 4 specifically includes a two-stage water supply pipe 41, a two-stage water return pipe 42, a heat pump unit 43 and a heat sink 44. One end of the two-stage water supply pipe 41 is connected to the water outlet of the two-stage cooling 33 of the cross-tube primary cooler 31, and the heat sink 44 is connected to the other end of the two-stage water supply pipe 41. The other end of the heat sink 44 is connected to the hot end water inlet of the heat pump unit 43. The cold end water outlet of the heat pump unit 43 is connected to the water supply pipeline 13, and the cold end water inlet of the heat pump unit 43 is connected to the return pipe 14. One end of the two-stage return pipe 42 is connected to the hot end water outlet of the heat pump unit 43, and the water inlet of the two-stage cooling 33 of the cross-tube primary cooler 31 is connected to the other end of the two-stage return pipe 42. The two-stage water supply pipe 41 cools the circulating water of the two-stage cooling 33 through the heat sink 44 It is transported to the heat pump unit 43. Considering that the maximum water temperature on the heat source side of the water source heat pump cannot exceed 45°C, and the water temperature of the second-stage cooling 33 circulating water varies greatly due to production, the maximum temperature of the second-stage cooling 33 circulating water is nearly 60°C. Therefore, it is necessary to install a heat dissipation device 44 before the second-stage cooling 33 circulating water enters the heat pump to cool the second-stage cooling 33 circulating water to meet the heat pump operation conditions. The heat dissipation device 44 controls the water temperature entering the heat pump unit 43 from the second-stage water supply pipe 41 to be below the operating temperature of the heat pump unit 43. Then the heat pump unit 43 transfers the temperature of the second-stage cooling 33 circulating water to the heating water, completing the waste heat recovery of the second-stage cooling 33 circulating water. The second-stage cooling 33 circulating water after heat exchange by the heat pump unit 43 is recycled from the second-stage return water pipe 42, thereby realizing the waste heat recovery of the second-stage cooling 33 circulating water whose temperature is consistent with the return water temperature of the heating water.

[0095] Reference Figure 2In this embodiment, the heat dissipation device 44 is a second plate heat exchanger 45, the hot end water inlet of the second plate heat exchanger 45 is connected to the second-stage water supply pipe 41, the hot end water outlet of the second plate heat exchanger 45 is connected to the heat pump unit 43, and the hot end water inlet of the second plate heat exchanger 45 is communicated with the hot end water outlet of the second plate heat exchanger 45, and a first shut-off valve 46 is connected between the hot end water inlet of the second plate heat exchanger 45 and the hot end water outlet of the second plate heat exchanger 45, a second shut-off valve 47 is connected between the second plate heat exchanger 45 and the second-stage water supply pipe 41, a third shut-off valve 48 is connected between the second plate heat exchanger 45 and the heat pump unit 43, the cold end water inlet of the second plate heat exchanger 45 is connected to the return water pipeline 14, and the cold end water outlet of the second plate heat exchanger 45 is connected to the water supply pipe 14. The heat dissipation device 44 is connected with the second stage cooling 33 circulating water by the second plate heat exchanger 45. The heat dissipation device 44 is set as a small temperature difference plate heat exchanger. The heating water can be used to recover the waste heat of the high temperature section in the second stage cooling 33 circulating water and cool the second stage cooling 33 circulating water, which will further improve the waste heat recovery rate. The hot end water inlet and the hot end water outlet of the second plate heat exchanger 45 are connected, and the second shut-off valve 47 and the third shut-off valve 48 are closed. The second stage cooling 33 circulating water in the second stage water supply pipe 41 can directly enter the heat pump unit 43 without passing through the second plate heat exchanger 45; the first shut-off valve 46 is closed, and the second shut-off valve 47 and the third shut-off valve 48 are opened, so that the second stage cooling 33 circulating water in the second stage water supply pipe 41 must pass through the second plate heat exchanger 45 before entering the heat pump unit 43, which can reduce the heat loss caused by the second stage cooling 33 circulating water circulating in the second plate heat exchanger 45 when the temperature of the second stage cooling 33 circulating water is low.

[0096] Reference Figure 2 The control system 5 includes multiple flow meters 51, multiple electric regulating valves 52 and a host computer 53. The multiple flow meters 51 and multiple electric regulating valves 52 are connected to the return water pipeline 14, the first stage cooling 32 and the second stage cooling 33 of the cross-tube primary cooler 31. The multiple flow meters 51 and multiple electric regulating valves 52 are electrically connected to the host computer 53. Specifically, a set of automatic master station is added in the wave system 4 area, and Siemens series PLC is selected and configured in the power distribution room of the wave system 4; all equipment control signals and instrument measurement points in the wave system 4 area enter the control system 5. Communicate with the RIO remote station configured in the cabinet near the ammonia pump 21 of this solution to form a ring network, and the communication protocol is MODBUSTCP; add a set of 5KVAUPS; add two host computers 53, which are arranged in the main control room of the main heat station 12.

[0097] The implementation principle of a waste heat recovery system in an embodiment of the present invention is as follows: after the implementation of this application, there will be 4 heat sources for heating, which are the main heat station 12, the shell heat exchanger 23, the first plate heat exchanger 34 and the second plate heat exchanger 45; before heating, the heating company confirms the heat source usage plan according to weather changes and the heating load demand, and should implement it according to the following principles (mainly related to the heat source price and waste heat load): give priority to using the auxiliary heating system 2 and the secondary system 3 for heating, then use the circulating water waste heat source of the steam turbine 11 main heat station 12, and finally use the fluctuation system 4 heat source for peak heating to ensure stable heating quality; at the initial stage of heating, when the weather temperature is high and the existing auxiliary heating system 2 and the secondary system 3 can meet the heat load demand, start the ammonia pump 21 and the shell heat exchanger 23, the cross tube primary cooler 31 and the first plate The heat exchanger 34 supplies heat to the outside, and the heat pump unit 43 and the second plate heat exchanger 45 are started to assist in heating when necessary; when the weather turns cold and the above heat sources cannot meet the heat load, the heating company should apply in advance to use the circulating water waste heat of the steam turbine 11; when the circulating water waste heat is put into the heating system, the steam turbine 11 and the main heat station 12 are used as the basic heating system, and the auxiliary heating system 2 and the secondary system 3 are used as supplementary heat sources. The system automatically controls the heating amount according to the heat load, and starts the fluctuation system 4 to recover the secondary cooling 33 waste heat for peak heating when necessary; at the end of the heating period, the weather turns warmer, when the circulating water waste heat of the steam turbine 11 exceeds the heat load, the heating company should promptly apply for the circulating water waste heat cut-out operation, and use the auxiliary heating system 2 and the secondary system 3 heat sources for heating in the future, and use the fluctuation system 4 heat source for auxiliary heating when necessary to ensure the heating quality.

[0098] In summary, the present application realizes efficient recovery of waste heat by setting up 4 kinds of exhaust waste heat sources, among which the waste heat of circulating water of a steam turbine 11 is the basic heat source, and the other three are adjustable heat sources to realize the adjustability and controllability of the heating heat source; the waste heat of three kinds of waste heat, such as ammonia circulating water, primary cooler first stage cooling water 32, and second stage cooling water 33, is recovered by using a network return water, thereby improving the recovery efficiency and optimizing the multi-heat source recovery process flow, thereby realizing efficient recovery and utilization of multiple heat sources without affecting the normal production of the heat source unit; the free waste heat of the second stage cooling water 33 of the horizontal tube primary cooler 31 is recovered, which can realize a greater degree of cascade recovery and utilization. Specifically, because the second stage cooling However, the water volume and water temperature of 33 vary greatly. First, a small temperature difference plate exchange unit is used to recover the waste heat of the high-temperature section of the middle water and cool the middle water to meet the purpose of the maximum operating temperature requirement of the heat pump. Then, a customized non-standard high-temperature centrifugal heat pump unit 43 is used to perform secondary recovery of the waste heat of the middle water after cooling. The COP value can reach more than 11. If the heat load increases in the later stage, the heat source water recovered by the high-temperature heat pump unit 43 can be used again by a conventional heat pump unit 43 to perform tertiary extraction of the waste heat of the middle water to meet the new heat load demand, thereby realizing multi-stage cascade recovery and utilization of the exhausted waste heat, and further improving the waste heat recovery capacity and waste heat regulation capacity.

[0099] The above are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A waste heat recovery method under variable temperature and variable flow conditions, characterized in that: include Obtaining waste heat: including obtaining heat extraction point and obtaining heat extraction amount; Obtaining hotspots: Detecting the production processes in the factory one by one, taking time as the unit and counting the unit heat production of each production process based on production parameters and historical production data, counting the production temperature required for each production process, and calculating the maximum required heat according to the minimum production temperature and maximum heat consumption required for each production process. When the difference between the unit heat production and the maximum required heat at any time in the production process is greater than a first threshold, this production process is set as a hotspot; Obtaining heat intake: calculating the difference between the unit heat output of each production process and the maximum required heat to obtain a single-point heat intake, and accumulating the single-point heat intake of each hot spot to obtain a total heat intake; Hotspot classification: classify the hotspots according to the regulation conditions of the hotspots, set the hotspots that can be regulated as the main hotspots, and set the hotspots that cannot be regulated as the auxiliary hotspots; Heat distribution: heat period distribution and system distribution; Heating period allocation: The heating period is divided into the initial heating period, the constant heating period and the final heating period according to the ambient temperature and heat load demand; System allocation: the auxiliary heating system is used for heating at the initial stage of heating and at the end of heating, and the main heating system and the auxiliary heating system are used together for heating during the constant heating period.

2. The waste heat recovery method under variable temperature and variable flow conditions according to claim 1, characterized in that: A weight allocation step is also provided after the hot period allocation and before the system allocation; Weight allocation: Based on the single-point heat extraction weight of the auxiliary hotspots in the auxiliary heating system, the weight of the auxiliary hotspot with a large single-point heat extraction value is set higher than that of the auxiliary hotspot with a small single-point heat extraction value. When supplying heat, the auxiliary hotspot with a high weight is set to give priority to heating.

3. The waste heat recovery method under variable temperature and variable flow conditions according to claim 2 is characterized in that: After the hot spot classification and before the heat distribution, a fluctuation distribution step is also included; Fluctuation allocation: setting the hot spot whose single-point heat fluctuation value is greater than or equal to the second threshold as a fluctuating hot spot; In the weight allocation step, the weight of the fluctuation hotspot is lower than the weight of the auxiliary hotspot; In the system allocation step, the fluctuation system and the auxiliary heating system work simultaneously.

4. A waste heat recovery system, characterized in that: The waste heat recovery method under variable temperature and variable flow conditions as described in any one of claims 1 to 3 is applied in a coking coal plant, wherein the waste heat recovery system comprises: a main heat system (1), an auxiliary heat system (2) and a control system (5); The main heat system (1) comprises a steam turbine (11), a main heat station (12), a water supply pipeline (13) and a water return pipeline (14); the main heat station (12) is connected to the steam turbine (11); the main heat station (12) is used to extract heat from the steam turbine (11); the main heat station (12) is connected to a heat user via the water supply pipeline (13) and the water return pipeline (14); The auxiliary heat system (2) comprises an ammonia water pump (21), an ammonia water circulation pipe (22) and a shell-type heat exchanger (23); the ammonia water circulation pipe (22) connects the ammonia water pump (21), the shell-type heat exchanger (23) and a coke oven gas pipe; the ammonia water pump (21) is used to pump ammonia water to circulate in the ammonia water circulation pipe (22); the ammonia water circulation pipe (22) is connected to the hot end of the shell-type heat exchanger (23); the cold end water inlet of the shell-type heat exchanger (23) is connected to the return water pipeline (14); and the cold end water outlet of the shell-type heat exchanger (23) is connected to the main heat station (12); The main heating system (1) and the auxiliary heating system (2) are both electrically connected to the control system (5).

5. A waste heat recovery system according to claim 4, characterized in that: The auxiliary heating system (2) also includes a secondary system (3); The secondary system (3) comprises a transverse tube primary cooler (31) and a first plate heat exchanger (34); the transverse tube primary cooler (31) is connected to a coke oven gas pipe and is used to cool the gas in the coke oven gas pipe and absorb the heat of the gas; the transverse tube primary cooler (31) comprises a first cooling stage (32) and a second cooling stage (33); the hot end of the first plate heat exchanger (34) is connected to the first cooling stage (32) of the transverse tube primary cooler (31); the cold end water inlet of the first plate heat exchanger (34) is connected to the return water pipeline (14); and the cold end water outlet of the first plate heat exchanger (34) is connected to the main heat station (12).

6. A waste heat recovery system according to claim 5, characterized in that: The invention also comprises a wave system (4), wherein the wave system (4) comprises a two-stage water supply pipe (41), a two-stage water return pipe (42), a heat pump unit (43) and a heat dissipation device (44), wherein one end of the two-stage water supply pipe (41) is connected to the water outlet of the two-stage cooling (33) of the horizontal tube primary cooler (31), the heat dissipation device (44) is connected to the other end of the two-stage water supply pipe (41), and the other end of the heat dissipation device (44) is connected to the heat pump unit (43). The hot end water inlet of the heat pump unit (43) is connected, the cold end water outlet of the heat pump unit (43) is connected to the water supply pipeline (13), the cold end water inlet of the heat pump unit (43) is connected to the return water pipeline (14), one end of the two-stage return water pipe (42) is connected to the hot end water outlet of the heat pump unit (43), and the second-stage cooling (33) water inlet of the horizontal tube primary cooler (31) is connected to the other end of the two-stage return water pipe (42).

7. A waste heat recovery system according to claim 6, characterized in that: The heat dissipation device (44) is a second plate heat exchanger (45); a hot end water inlet of the second plate heat exchanger (45) is connected to the second-section water supply pipe (41); a hot end water outlet of the second plate heat exchanger (45) is connected to the heat pump unit (43); a cold end water inlet of the second plate heat exchanger (45) is connected to the return water pipeline (14); and a cold end water outlet of the second plate heat exchanger (45) is connected to the water supply pipeline (13).

8. A waste heat recovery system according to claim 7, characterized in that: The hot end water inlet of the second plate heat exchanger (45) is in communication with the hot end water outlet of the second plate heat exchanger (45); a first shutoff valve (46) is connected between the hot end water inlet of the second plate heat exchanger (45) and the hot end water outlet of the second plate heat exchanger (45); a second shutoff valve (47) is connected between the second plate heat exchanger (45) and the second-section water supply pipe (41); and a third shutoff valve (48) is connected between the second plate heat exchanger (45) and the heat pump unit (43).

9. The waste heat recovery system according to claim 5, characterized in that: The control system (5) comprises a plurality of flow meters (51), a plurality of electrically adjustable valves (52) and a host computer (53); the plurality of flow meters (51) and the plurality of electrically adjustable valves (52) are connected to the return water pipeline (14), the first cooling stage (32) and the second cooling stage (33) of the cross-tube primary cooler (31); and the plurality of flow meters (51) and the plurality of electrically adjustable valves (52) are electrically connected to the host computer (53).

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