Heater energy-saving method and system based on multistage waste heat recovery

Abstract

The invention discloses a heater energy-saving method and system based on multi-stage waste heat recovery, and relates to the related field of energy recycling, and the method comprises the steps that exhaust gas of a gas turbine exchanges heat with main circulation feed water through a first-stage heater, and first-stage flue gas after first-stage waste heat recovery treatment is obtained by adjusting the flow of the main circulation feed water; the first-stage flue gas exchanges heat with auxiliary circulating feed water through a second-stage heater, and second-stage flue gas subjected to second-stage waste heat recovery treatment is obtained by adjusting the flow of the auxiliary circulating feed water; and introducing the secondary flue gas into a gas inlet distribution chamber of the denitration reactor, mixing the secondary flue gas with a sprayed ammonia reducing agent, and enabling the mixture to pass through a catalyst layer to generate purified flue gas. The technical problems that an existing heater energy-saving method is low in waste heat recovery efficiency and cannot meet the temperature requirement of follow-up denitration reaction, and consequently the energy utilization efficiency is low are solved, waste heat in exhaust gas of a gas turbine is fully recovered, the flue gas temperature is accurately controlled to meet the temperature requirement of a denitration reactor, and the energy utilization rate is increased. And therefore, the energy utilization efficiency is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of energy recycling, and particularly relates to a heater energy-saving method and system based on multi-stage waste heat recovery. BACKGROUND

[0002] In the process of energy utilization, it is of great significance to improve energy utilization efficiency and reduce energy consumption, which not only helps to reduce energy costs, but also reduces the negative impact on the environment. At present, for the waste heat recovery of gas turbine exhaust, a single-stage heater and circulating feed water heat exchange are mainly used. However, due to only one heat exchange, the waste heat recovery is not sufficient, a large amount of heat is not effectively utilized, resulting in energy waste, and the specific requirements of the denitration reactor on the flue gas temperature cannot be met, affecting the denitration efficiency.

[0003] In the related art at present, the energy-saving method of the heater has the technical problems of low waste heat recovery efficiency, inability to meet the temperature requirements of the subsequent denitration reaction, and low energy utilization efficiency. SUMMARY

[0004] The present application provides a heater energy-saving method and system based on multi-stage waste heat recovery, which uses the gas turbine exhaust into a primary heater, exchanges heat with the main circulating feed water, adjusts the flow of the main circulating feed water, obtains the primary flue gas with reduced temperature, introduces the primary flue gas into a secondary heater, exchanges heat with the auxiliary circulating feed water, adjusts the flow of the auxiliary circulating feed water, obtains the secondary flue gas with further reduced temperature, and passes the secondary flue gas into the inlet distribution chamber of the denitration reactor, mixes with the injected ammonia reducing agent, passes through the catalyst layer, and generates purified flue gas. The technical means solve the technical problems of the existing energy-saving method of the heater, such as low waste heat recovery efficiency, inability to meet the temperature requirements of the subsequent denitration reaction, and low energy utilization efficiency, and achieve the technical effects of fully recovering the waste heat in the gas turbine exhaust, accurately controlling the flue gas temperature to meet the temperature requirements of the denitration reactor, and improving the energy utilization efficiency.

[0005] This application provides an energy-saving method for heaters based on multi-stage waste heat recovery, comprising: exchanging heat between gas turbine exhaust gas and main circulating feedwater through a primary heater; adjusting the flow rate of the main circulating feedwater to obtain primary flue gas after primary waste heat recovery treatment, wherein the temperature of the gas turbine exhaust gas is in a first temperature range, the temperature of the primary flue gas is in a second temperature range, and the lower limit of the first temperature range is greater than the upper limit of the second temperature range; exchanging heat between the primary flue gas and auxiliary circulating feedwater through a secondary heater; adjusting the flow rate of the auxiliary circulating feedwater to obtain secondary flue gas after secondary waste heat recovery treatment, wherein the temperature of the secondary flue gas is in a third temperature range, and the upper limit of the third temperature range is less than the lower limit of the second temperature range; and introducing the secondary flue gas into the inlet distribution chamber of a denitrification reactor, mixing it with injected ammonia reducing agent, and then passing it through a catalyst layer to generate purified flue gas, wherein the median of the third temperature range is equal to the optimal activity temperature of the denitrification catalyst.

[0006] In one possible implementation, the exhaust gas from the gas turbine is heat-exchanged with the main circulating feedwater through a primary heater. By adjusting the flow rate of the main circulating feedwater, primary flue gas after primary waste heat recovery is obtained, and the following processing is performed: the first temperature of the primary flue gas is monitored and obtained in real time; a first temperature difference threshold is preset; when the difference between the first temperature and the upper limit of the second temperature range is less than or equal to the first temperature difference threshold, the flow rate of the main circulating feedwater is increased; when the difference between the first temperature and the lower limit of the second temperature range is less than or equal to the first temperature difference threshold, the flow rate of the main circulating feedwater is decreased.

[0007] In a possible implementation, a first temperature difference threshold is preset. When the difference between the first temperature and the upper limit of the second temperature range is less than or equal to the first temperature difference threshold, the main circulation water flow rate is increased, and the following processing is performed: the current operating frequency of the main circulation water pump is obtained; a target frequency is calculated based on the difference between the first temperature and the upper limit of the second temperature range; an adjustment time is preset, and the main circulation water pump is controlled to linearly increase the current operating frequency to the target frequency within the adjustment time to increase the main circulation water flow rate.

[0008] In a possible implementation, when the difference between the lower limit of the first temperature and the second temperature range is less than or equal to the first temperature difference threshold, the main circulation water flow rate is reduced, and the following processing is performed: obtaining the current flow rate of the main circulation water pump; calculating the target flow rate based on the difference between the lower limit of the first temperature and the second temperature range; calculating the flow rate difference between the current flow rate and the target flow rate; obtaining the number of reduction steps N based on the flow rate difference; and controlling the main circulation water pump to reduce the current flow rate to the target flow rate in N steps based on the number of reduction steps N, thereby reducing the main circulation water flow rate, wherein the number of reduction steps N is positively correlated with the flow rate difference.

[0009] In a possible implementation, a first temperature difference threshold is preset, and the following processing is performed: Historical operating data is obtained based on the main circulation feedwater flow rate change log, the first-stage flue gas temperature fluctuation log, the gas turbine load rate log, and the optimal temperature difference threshold log. The optimal temperature difference threshold log is generated by back-calculating the actual temperature difference threshold under stable system conditions using the minimum temperature fluctuation criterion. Based on the historical operating data, a temperature difference threshold prediction model is trained using flow rate change, temperature fluctuation, and load rate as input features and the optimal temperature difference threshold as the output label. A prediction window is preset, and the main circulation feedwater flow rate change data, first-stage flue gas temperature fluctuation data, and gas turbine load rate data within the prediction window are input into the temperature difference threshold prediction model, outputting an adaptive temperature difference threshold. The adaptive temperature difference threshold replaces the first temperature difference threshold for adjusting the main circulation feedwater flow rate.

[0010] In a possible implementation, the following processing is also performed: the gas turbine exhaust gas is heat-exchanged with the main circulating feedwater through a primary heater to generate primary saturated water; the primary saturated water is introduced into a primary evaporator to generate primary steam; the primary steam drives a steam turbine to generate electricity, and then discharges secondary steam; the primary flue gas is heat-exchanged with the auxiliary circulating feedwater through a secondary heater to generate secondary preheated water; the secondary steam and the secondary preheated water are introduced into a secondary evaporator to generate tertiary steam, wherein the pressure of the primary steam is greater than the pressure of the secondary steam, which is greater than the pressure of the tertiary steam; the tertiary steam is injected into the compressor outlet pipe of the gas turbine through a swirl atomizing nozzle to humidify the air.

[0011] In one possible implementation, the tertiary steam is injected into the compressor outlet pipe of the gas turbine through a swirl atomizing nozzle, and the following processes are performed: real-time acquisition of air parameters at the compressor outlet; calculation of injection parameters of the tertiary steam using a PID controller based on the air parameters; and adjustment of the opening degree and pump speed of the swirl atomizing nozzle according to the injection parameters to inject the tertiary steam into the compressor outlet pipe of the gas turbine.

[0012] This application also provides a heater energy-saving system based on multi-stage waste heat recovery, comprising: a primary waste heat recovery module for exchanging heat between gas turbine exhaust gas and main circulating feedwater through a primary heater, and obtaining primary flue gas after primary waste heat recovery treatment by adjusting the flow rate of the main circulating feedwater, wherein the temperature of the gas turbine exhaust gas is in a first temperature range, the temperature of the primary flue gas is in a second temperature range, and the lower limit of the first temperature range is greater than the upper limit of the second temperature range; a secondary waste heat recovery module for exchanging heat between the primary flue gas and auxiliary circulating feedwater through a secondary heater, and obtaining secondary flue gas after secondary waste heat recovery treatment by adjusting the flow rate of the auxiliary circulating feedwater, wherein the temperature of the secondary flue gas is in a third temperature range, and the upper limit of the third temperature range is less than the lower limit of the second temperature range; and a denitrification temperature coordination control module for introducing the secondary flue gas into the inlet distribution chamber of the denitrification reactor, mixing it with injected ammonia reducing agent, and then passing it through the catalyst layer to generate purified flue gas, wherein the median of the third temperature range is equal to the optimal activity temperature of the denitrification catalyst.

[0013] The proposed energy-saving method and system based on multi-stage waste heat recovery heater, as described in this application, firstly, exchanges heat between the gas turbine exhaust gas and the main circulating feedwater through a primary heater. By adjusting the flow rate of the main circulating feedwater, primary flue gas after primary waste heat recovery is obtained. The temperature of the gas turbine exhaust gas is within a first temperature range, and the temperature of the primary flue gas is within a second temperature range, with the lower limit of the first temperature range exceeding the upper limit of the second temperature range. Then, the primary flue gas exchanges heat between the gas turbine exhaust gas and the auxiliary circulating feedwater through a secondary heater. By adjusting the flow rate of the auxiliary circulating feedwater, secondary flue gas after secondary waste heat recovery is obtained. The temperature of the secondary flue gas is within a third temperature range, with the upper limit of the third temperature range less than the lower limit of the second temperature range. Finally, the secondary flue gas is introduced into the inlet distribution chamber of the denitrification reactor, where it mixes with injected ammonia reducing agent and passes through the catalyst layer to generate purified flue gas. The median of the third temperature range is equal to the optimal activity temperature of the denitrification catalyst. This method achieves the technical effect of fully recovering waste heat from the gas turbine exhaust gas and precisely controlling the flue gas temperature to meet the temperature requirements of the denitrification reactor, thereby improving energy utilization efficiency. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments of the present invention will be briefly described below. Flowcharts are used in this application to illustrate the operations performed by the system according to the embodiments of the present application. It should be understood that the preceding or following operations are not necessarily performed precisely in sequence. Instead, various steps can be processed in reverse order or simultaneously as needed. Furthermore, other operations can be added to these processes, or one or more steps can be removed from these processes.

[0015] Figure 1 This is a schematic flowchart of a heater energy-saving method based on multi-stage waste heat recovery provided in an embodiment of this application.

[0016] Figure 2 This is a schematic diagram of the structure of a heater energy-saving system based on multi-stage waste heat recovery provided in an embodiment of this application.

[0017] Figure labeling: 10 for primary waste heat recovery treatment module, 20 for secondary waste heat recovery treatment module, and 30 for denitrification temperature co-control module. Detailed Implementation

[0018] The above description is merely an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below.

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description of this application will be provided in conjunction with the accompanying drawings. The described embodiments should not be considered as limitations on this application. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] In the following description, references to "some embodiments" describe a subset of all possible embodiments. However, it is understood that "some embodiments" can be the same or different subsets of all possible embodiments and can be combined with each other without conflict. The terms "first" and "second" are used merely to distinguish similar objects and do not represent a specific ordering of objects. The terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or server that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or modules not explicitly listed or inherent to these processes, methods, products, or devices. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing embodiments of this application only.

[0021] This application provides an energy-saving method for heaters based on multi-stage waste heat recovery, such as... Figure 1 As shown, the method includes:

[0022] In step S100, the exhaust gas from the gas turbine is heat-exchanged with the main circulating feedwater through a primary heater. By adjusting the flow rate of the main circulating feedwater, primary flue gas after primary waste heat recovery is obtained. The temperature of the exhaust gas from the gas turbine is in a first temperature range, and the temperature of the primary flue gas is in a second temperature range. The lower limit of the first temperature range is greater than the upper limit of the second temperature range.

[0023] Specifically, gas turbines generate high-temperature exhaust gas during operation, which contains a significant amount of heat energy. The gas turbine exhaust pipe is connected to the hot-side inlet of the first-stage heater, a heat exchanger such as a high-pressure economizer, which transfers the heat from the gas turbine exhaust to the main circulating feedwater. The main circulating feedwater pipe is connected to the cold-side inlet of the first-stage heater. The flow rate of the main circulating feedwater is controlled by regulating valves to ensure efficient heat transfer from the gas turbine exhaust to the feedwater. Temperature sensors are installed at the inlet and outlet of the first-stage heater to monitor the temperature of the gas turbine exhaust and the main circulating feedwater in real time. The feedwater flow rate is adjusted by the control system to ensure that the temperature of the first-stage flue gas remains within the second temperature range.

[0024] For example, the exhaust temperature of the gas turbine is 600℃ (the first temperature range is 550℃-650℃). After heat exchange with the main circulating feedwater through the primary heater, the temperature of the primary flue gas drops to 400℃ (the second temperature range is 350℃-450℃). The initial temperature of the main circulating feedwater is 30℃. After passing through the primary heater, the temperature rises to 150℃, which is then used for subsequent applications such as steam power generation.

[0025] In one possible implementation, the exhaust gas from the gas turbine is heat-exchanged with the main circulating feedwater through a primary heater. By adjusting the flow rate of the main circulating feedwater, primary flue gas after primary waste heat recovery is obtained. Step S100 further includes step S110, which involves real-time monitoring and acquisition of the first temperature of the primary flue gas. Specifically, a temperature sensor is installed at the flue gas outlet of the primary heater, and the value of the temperature sensor is read in real time through a data acquisition system to obtain the first temperature of the primary flue gas.

[0026] Step S120: A first temperature difference threshold is preset. When the difference between the first temperature and the upper limit of the second temperature range is less than or equal to the first temperature difference threshold, the main circulating water flow rate is increased. Specifically, a first temperature difference threshold is set to determine whether the temperature of the primary flue gas is close to the upper limit of the second temperature range, for example, 5°C. The difference between the first temperature and the upper limit of the second temperature range is calculated in real time. When the difference between the first temperature and the upper limit of the second temperature range is less than or equal to the first temperature difference threshold, the main circulating water flow rate is increased by the control system to reduce the temperature of the primary flue gas.

[0027] Step S130: When the difference between the lower limit of the first temperature and the second temperature range is less than or equal to the first temperature difference threshold, the main circulating water flow rate is reduced. Specifically, the difference between the lower limit of the first temperature and the second temperature range is calculated in real time. When the difference between the lower limit of the first temperature and the second temperature range is less than or equal to the first temperature difference threshold, the main circulating water flow rate is reduced by the control system. This implementation method, by monitoring the temperature of the primary flue gas in real time and adjusting the main circulating water flow rate according to the preset temperature difference threshold, can accurately control the temperature of the primary flue gas, keeping it within the second temperature range, thereby helping to ensure the efficient operation of subsequent heat exchange processes and denitrification reactions.

[0028] In one possible implementation, a first temperature difference threshold is preset. When the difference between the first temperature and the upper limit of the second temperature range is less than or equal to the first temperature difference threshold, the main circulating water flow rate is increased. Step S120 further includes step S121, obtaining the current operating frequency of the main circulating water pump. Specifically, a frequency sensor is installed on the motor of the main circulating water pump, or the current operating frequency is read through the control system to obtain the current operating frequency of the main circulating water pump in real time.

[0029] Step S122: Calculate the target frequency based on the difference between the upper limit of the first temperature and the second temperature range. Specifically, calculate the difference between the upper limit of the first temperature and the second temperature range, and calculate the target frequency using a preset formula. The formula for calculating the target frequency can be: f target =f current +k1·△T1, where f target It is the target frequency, f current It is the current operating frequency, k1 is the adjustment coefficient, and ΔT1 is the absolute value of the difference between the upper limit of the first temperature range and the upper limit of the second temperature range.

[0030] Step S123: A preset adjustment time is established. The main circulating water pump is controlled to linearly increase its current operating frequency to the target frequency within the preset adjustment time, thereby increasing the main circulating water flow rate. Specifically, the preset adjustment time is, for example, 30 seconds. The control system linearly increases the operating frequency of the main circulating water pump from the current frequency to the target frequency within the preset adjustment time. This implementation method, through real-time monitoring and calculation of the target frequency, can precisely control the temperature of the primary flue gas, ensuring it remains within the second temperature range. By linearly increasing the frequency, the main circulating water flow rate can be increased smoothly, avoiding system shocks caused by sudden frequency changes, and improving system stability and reliability.

[0031] In one possible implementation, when the difference between the lower limit of the first temperature and the second temperature range is less than or equal to the first temperature difference threshold, the main circulating water flow rate is reduced. Step S130 further includes step S131, obtaining the current flow rate of the main circulating water pump. Specifically, a flow sensor is installed at the outlet of the main circulating water pump, or the current flow rate is read through the control system to obtain the current flow rate of the main circulating water pump in real time.

[0032] Step S132: Calculate the target flow rate based on the difference between the lower limits of the first temperature and the second temperature range. Specifically, calculate the difference between the lower limits of the first temperature and the second temperature range, and calculate the target flow rate using a preset formula. The formula for calculating the target flow rate can be: Q target =Q current -k2·△T2, where Q target It is the target traffic, Q current ΔT2 is the current flow rate, k2 is the adjustment coefficient, and ΔT2 is the absolute value of the difference between the lower limits of the first and second temperature ranges.

[0033] Step S133: Calculate the flow difference between the current flow rate and the target flow rate. Based on the flow difference, obtain the number of reduction steps N. Based on the number of reduction steps N, control the main circulation feedwater pump to reduce the current flow rate to the target flow rate in N stages, thereby reducing the main circulation feedwater flow rate. The number of reduction steps N is positively correlated with the flow difference. Specifically, calculate the flow difference between the current flow rate and the target flow rate, determine the number of reduction steps N based on the flow difference, and N is positively correlated with the flow difference. The control system gradually reduces the current flow rate to the target flow rate in N stages, with each reduction being the same flow rate. For example, the flow difference is 100 m³ / s. 3 / h, assuming the flow rate change per stage is 20m³ / h 3 / h, then: N=100÷20=5, the control system will gradually reduce the current flow rate to the target flow rate in 5 steps, each time reducing it by 20m. 3 / h. This implementation method, by gradually reducing the flow rate in multiple stages, can smoothly reduce the main circulation water flow rate, avoid system shocks caused by sudden flow changes, and improve the stability and reliability of the system.

[0034] In one possible implementation, a first temperature difference threshold is preset. Step S120 may further include step S124, which involves obtaining historical operating data based on the main circulation feedwater flow rate change log, the first-stage flue gas temperature fluctuation log, the gas turbine load rate log, and the optimal temperature difference threshold log. The optimal temperature difference threshold log is generated by back-calculating the actual temperature difference threshold under stable system conditions using the minimum temperature fluctuation criterion. Specifically, the main circulation feedwater flow rate change log, the first-stage flue gas temperature fluctuation log, and the gas turbine load rate log are extracted from the system's historical operating records. The optimal temperature difference threshold log is generated by back-calculating the actual temperature difference threshold under stable system conditions using the minimum temperature fluctuation criterion. Specifically, during stable system operation, parameters such as the main circulation feedwater flow rate, the first-stage flue gas temperature, and the gas turbine load rate will fluctuate within a certain range. At this time, the system will have an actual temperature difference threshold, allowing the first-stage flue gas temperature to stabilize within a second temperature range. This actual temperature difference threshold is naturally formed during stable system operation, reflecting the optimal temperature difference control range under current operating conditions. To ensure system stability and efficient operation, an optimal temperature difference threshold needs to be found to minimize the temperature fluctuation of the first-stage flue gas. The minimum temperature fluctuation criterion is an optimization objective that requires the temperature change of the first-stage flue gas to be as small as possible during system operation, thereby ensuring system stability and heat exchange efficiency. Logs of main circulation feedwater flow rate changes, first-stage flue gas temperature fluctuations, and gas turbine load rates are collected under stable operating conditions. The actual temperature difference thresholds under these operating conditions are also recorded. For each actual temperature difference threshold under each operating condition, the corresponding temperature fluctuation is calculated (e.g., average value, standard deviation). The temperature difference threshold with the smallest temperature fluctuation is selected as the optimal temperature difference threshold, and these optimal temperature difference thresholds are recorded to form an optimal temperature difference threshold log.

[0035] Step S125: Based on the historical operating data, using flow rate changes, temperature fluctuations, and load rate as input features, and the optimal temperature difference threshold as the output label, train a temperature difference threshold prediction model. Specifically, use historical operating data as the training dataset, with flow rate changes, temperature fluctuations, and load rate as input features, and the optimal temperature difference threshold as the output label. Use machine learning algorithms (such as linear regression, decision trees, neural networks, etc.) to train the temperature difference threshold prediction model, and evaluate the model's performance through methods such as cross-validation to ensure the model's accuracy and generalization ability.

[0036] Step S126: A prediction window is preset. The main circulation feedwater flow rate change data, first-stage flue gas temperature fluctuation data, and gas turbine load rate data within the prediction window are input into the temperature difference threshold prediction model, and the model outputs an adaptive temperature difference threshold. Specifically, the prediction window is preset, for example, 1 hour. The main circulation feedwater flow rate change data, first-stage flue gas temperature fluctuation data, and gas turbine load rate data within the prediction window are collected and input into the temperature difference threshold prediction model. The model outputs an adaptive temperature difference threshold.

[0037] Step S127: The adaptive temperature difference threshold replaces the first temperature difference threshold to adjust the main circulation water flow rate. Specifically, the adaptive temperature difference threshold is updated in the control system, replacing the preset first temperature difference threshold. The control system adjusts the main circulation water flow rate in real time based on the adaptive temperature difference threshold. This implementation predicts the adaptive temperature difference threshold using a machine learning model, allowing the system to dynamically adjust the temperature difference threshold according to actual operating conditions, improving control flexibility and adaptability. The adaptive temperature difference threshold better adapts to dynamic changes in system operation, reduces temperature fluctuations, and improves system stability and reliability.

[0038] In step S200, the primary flue gas is passed through a secondary heater and heat exchanged with auxiliary circulating water. By adjusting the flow rate of the auxiliary circulating water, secondary flue gas after secondary waste heat recovery is obtained. The temperature of the secondary flue gas is in a third temperature range, and the upper limit of the third temperature range is less than the lower limit of the second temperature range.

[0039] Specifically, after being treated by the primary heater, the temperature of the primary flue gas has decreased but it still contains a certain amount of heat. This flue gas undergoes heat exchange with the auxiliary circulating feedwater through a secondary heater (such as a low-pressure economizer) to further recover heat. The outlet of the primary heater is connected to the hot-side inlet of the secondary heater, and the auxiliary circulating feedwater pipeline is connected to the cold-side inlet of the secondary heater. The flow rate of the auxiliary circulating feedwater is controlled by a regulating valve, allowing the heat from the primary flue gas to be further transferred to the auxiliary circulating feedwater. Temperature sensors are installed at the inlet and outlet of the secondary heater to monitor the temperature of the primary flue gas and the auxiliary circulating feedwater in real time. The feedwater flow rate is adjusted by the control system to ensure that the temperature of the secondary flue gas is within the third temperature range. The control mechanism in step S200 is similar to that in step S100, both controlling the flue gas temperature by monitoring the flue gas temperature in real time and adjusting the feedwater flow rate according to a preset temperature difference threshold. Through multi-stage waste heat recovery, the heat in the gas turbine exhaust is recovered to the maximum extent, improving the energy utilization efficiency of the system.

[0040] For example, the primary flue gas temperature is 400℃ (the second temperature range is 350℃-450℃). After heat exchange with the auxiliary circulating feedwater through the secondary heater, the secondary flue gas temperature drops to 250℃ (the third temperature range is 200℃-300℃). The initial temperature of the auxiliary circulating feedwater is 20℃. After passing through the secondary heater, the temperature rises to 100℃, which is used for preheating boiler feedwater and other purposes.

[0041] In step S300, the secondary flue gas is introduced into the inlet distribution chamber of the denitrification reactor, mixed with the injected ammonia reducing agent, and then passed through the catalyst layer to generate purified flue gas. The median value of the third temperature range is equal to the optimal activity temperature of the denitrification catalyst.

[0042] Specifically, the flue gas, after being treated by the secondary heater, has a lower temperature but still contains some heat. The outlet of the secondary heater is connected to the inlet distribution chamber of the denitrification reactor, a catalyst-containing reactor used to convert nitrogen oxides (NOx) in the flue gas into harmless nitrogen (N2) and water (H2O). An ammonia reducing agent (such as ammonia or urea solution) is injected into the inlet distribution chamber of the denitrification reactor via an injection system, mixing with the secondary flue gas. A catalyst layer is installed inside the denitrification reactor to ensure sufficient reaction as the flue gas passes through it. By controlling the temperature of the secondary flue gas within the optimal activity range of the catalyst, no additional heat energy is required to maintain the catalyst's activity.

[0043] For example, the secondary flue gas temperature is 250℃ (the third temperature range is 200℃-300℃), and the optimal activity temperature of the catalyst is 250℃. By precisely controlling the flue gas temperature, the high efficiency of the denitrification reaction is ensured. The injected ammonia reducing agent reacts with NOx in the flue gas to produce harmless nitrogen and water, and the purified flue gas can be safely emitted.

[0044] In one possible implementation, the method may further include: exchanging heat between the gas turbine exhaust gas and the main circulating feedwater through a primary heater to heat the main circulating feedwater and generate primary saturated water; introducing the primary saturated water into a primary evaporator to generate primary steam; using the primary steam to drive a steam turbine to generate electricity, and then discharging secondary steam; exchanging heat between the primary flue gas and the auxiliary circulating feedwater through a secondary heater to heat the auxiliary circulating feedwater and generate secondary preheated water; introducing the secondary steam and the secondary preheated water into a secondary evaporator to generate tertiary steam, wherein the pressure of the primary steam is greater than the pressure of the secondary steam, which is greater than the pressure of the tertiary steam; and injecting the tertiary steam into the compressor outlet pipe of the gas turbine through a swirl atomizing nozzle to humidify the air.

[0045] Specifically, the high-temperature exhaust gas generated by the gas turbine exchanges heat with the main circulating feedwater through a primary heater (such as a high-pressure economizer), heating the feedwater to generate primary saturated water. This primary saturated water is water heated to saturation by the primary heater. It then enters the primary evaporator, where it is depressurized to generate primary steam. This primary steam is used to drive the turbine to generate electricity, and the steam discharged after power generation is called secondary steam.

[0046] After being treated by the primary heater, the temperature of the primary flue gas has decreased, but it still contains some heat. This flue gas undergoes heat exchange with the auxiliary circulating feedwater through a secondary heater (such as a low-pressure economizer), heating the auxiliary circulating feedwater to generate secondary preheated water. Secondary steam and secondary preheated water enter the secondary evaporator, where the waste heat of the secondary steam is used to heat the secondary preheated water. Further heat exchange generates tertiary steam, which has a lower pressure than the secondary steam. The tertiary steam is injected into the compressor outlet pipe of the gas turbine through a swirl atomizing nozzle to humidify the air and improve combustion efficiency.

[0047] For example, if the gas turbine exhaust temperature is 600℃, the first-stage heater heats the main circulating feedwater to 150℃, generating high-pressure saturated water (first-stage saturated water). This first-stage saturated water enters the first-stage evaporator, where it directly generates first-stage steam at a pressure of 10MPa through pressure reduction and other means. The first-stage steam drives the turbine to generate electricity, and then discharges second-stage steam at a pressure of 5MPa. The first-stage flue gas temperature drops to 400℃, and the second-stage heater heats the auxiliary circulating feedwater to 100℃, generating second-stage preheated water. The second-stage steam and second-stage preheated water enter the second-stage evaporator, where heat exchange generates tertiary steam at a pressure of 2MPa. The tertiary steam is injected into the gas turbine compressor outlet pipe through a swirl atomizing nozzle to humidify the air.

[0048] This approach maximizes the recovery of heat from gas turbine exhaust through multi-stage waste heat recovery. The primary heater heats the main circulating feedwater to generate high-pressure saturated water, which directly produces primary steam for power generation. The secondary heater heats the auxiliary circulating feedwater to generate secondary preheated water, which, together with the secondary steam, generates tertiary steam for air humidification. This multi-stage waste heat recovery and utilization method ensures full utilization of thermal energy in the system, reduces heat waste, and improves the overall energy efficiency of the system.

[0049] In one possible implementation, the tertiary steam is injected into the compressor outlet pipe of the gas turbine through a swirl atomizing nozzle, further comprising: acquiring the air parameters at the compressor outlet in real time; calculating the injection parameters of the tertiary steam based on the air parameters using a PID controller; and adjusting the opening degree and pump speed of the swirl atomizing nozzle according to the injection parameters to inject the tertiary steam into the compressor outlet pipe of the gas turbine.

[0050] Specifically, temperature, humidity, and pressure sensors are installed at the compressor outlet. A data acquisition system reads the values ​​from these sensors in real time to obtain the air parameters at the compressor outlet. A target value, such as target humidity or target temperature, is set for the PID controller. Based on the real-time air parameters, the PID controller calculates the required flow rate and pressure of the tertiary steam to be injected. The PID controller outputs a control signal based on the calculation results. A regulating valve and a frequency converter are installed on the inlet pipe of the swirl atomizing nozzle. Based on the output signal from the PID controller, the opening of the regulating valve and the frequency of the frequency converter are adjusted to control the opening of the swirl atomizing nozzle and the pump speed. Through a feedback mechanism, the control parameters are adjusted in real time to ensure that the injected tertiary steam quantity meets system requirements. This implementation method, by monitoring the air parameters at the compressor outlet in real time and using the PID controller to calculate the injection parameters, enables the system to precisely control the injection quantity of tertiary steam, ensuring the stability and effectiveness of the humidification process. By precisely controlling the humidification process, the air humidity and temperature at the compressor outlet are ensured to be within the optimal range, thereby improving the combustion efficiency of the gas turbine and reducing fuel consumption.

[0051] This application's embodiment employs a technique where gas turbine exhaust enters a primary heater, exchanges heat with the main circulating feedwater, and the main circulating feedwater flow rate is adjusted to obtain primary flue gas with a lower temperature. The primary flue gas is then introduced into a secondary heater, exchanges heat with auxiliary circulating feedwater, and the auxiliary circulating feedwater flow rate is adjusted to obtain secondary flue gas with a further lower temperature. This secondary flue gas is then fed into the inlet distribution chamber of the denitrification reactor, mixed with injected ammonia reducing agent, and passes through a catalyst layer to generate purified flue gas. This technique solves the technical problems of low waste heat recovery efficiency and inability to meet the temperature requirements of subsequent denitrification reactions in existing heater energy-saving methods, resulting in low energy utilization efficiency. It achieves the technical effect of fully recovering waste heat from gas turbine exhaust and precisely controlling the flue gas temperature to meet the temperature requirements of the denitrification reactor, thereby improving energy utilization efficiency.

[0052] In the above text, refer to Figure 1 A heater energy-saving method based on multi-stage waste heat recovery according to embodiments of the present invention is described in detail. Next, reference will be made to... Figure 2 A heater energy-saving system based on multi-stage waste heat recovery according to an embodiment of the present invention is described.

[0053] The heater energy-saving system based on multi-stage waste heat recovery according to embodiments of the present invention addresses the technical problems of low waste heat recovery efficiency and inability to meet the temperature requirements of subsequent denitrification reactions in existing heater energy-saving methods, resulting in low energy utilization efficiency. It achieves the technical effect of fully recovering waste heat from gas turbine exhaust and precisely controlling the flue gas temperature to meet the temperature requirements of the denitrification reactor, thereby improving energy utilization efficiency. The heater energy-saving system based on multi-stage waste heat recovery includes: a primary waste heat recovery processing module 10, a secondary waste heat recovery processing module 20, and a denitrification temperature collaborative control module 30.

[0054] The primary waste heat recovery module 10 is used to exchange heat between the gas turbine exhaust gas and the main circulating feedwater through a primary heater. By adjusting the flow rate of the main circulating feedwater, primary flue gas after primary waste heat recovery treatment is obtained. The temperature of the gas turbine exhaust gas is in a first temperature range, and the temperature of the primary flue gas is in a second temperature range. The lower limit of the first temperature range is greater than the upper limit of the second temperature range. The secondary waste heat recovery module 20 is used to exchange heat between the primary flue gas and the auxiliary circulating feedwater through a secondary heater. By adjusting the flow rate of the auxiliary circulating feedwater, secondary flue gas after secondary waste heat recovery treatment is obtained. The temperature of the secondary flue gas is in a third temperature range. The upper limit of the third temperature range is less than the lower limit of the second temperature range. The denitrification temperature coordination control module 30 is used to introduce the secondary flue gas into the inlet distribution chamber of the denitrification reactor. After mixing with the injected ammonia reducing agent, the gas passes through the catalyst layer to generate purified flue gas. The median of the third temperature range is equal to the optimal activity temperature of the denitrification catalyst.

[0055] The specific configuration of the primary waste heat recovery module 10 will be described in detail below. As mentioned above, the exhaust gas from the gas turbine is heat-exchanged with the main circulating feedwater through a primary heater. By adjusting the flow rate of the main circulating feedwater, the primary flue gas after primary waste heat recovery treatment is obtained. The primary waste heat recovery module 10 may further include: a temperature monitoring unit for real-time monitoring and acquisition of the first temperature of the primary flue gas; and a main circulating feedwater flow rate adjustment unit for presetting a first temperature difference threshold. When the difference between the first temperature and the upper limit of the second temperature range is less than or equal to the first temperature difference threshold, the main circulating feedwater flow rate is increased; when the difference between the first temperature and the lower limit of the second temperature range is less than or equal to the first temperature difference threshold, the main circulating feedwater flow rate is decreased.

[0056] The system includes a preset first temperature difference threshold. When the difference between the first temperature and the upper limit of the second temperature range is less than or equal to the first temperature difference threshold, the main circulation water flow rate is increased. The main circulation water flow rate adjustment unit may further include: a water pump frequency acquisition subunit for acquiring the current operating frequency of the main circulation water pump; a target frequency calculation subunit for calculating the target frequency based on the difference between the first temperature and the upper limit of the second temperature range; and a frequency boosting subunit for preset adjustment time, controlling the main circulation water pump to linearly boost the current operating frequency to the target frequency within the adjustment time to increase the main circulation water flow rate.

[0057] Wherein, when the difference between the lower limit of the first temperature and the second temperature range is less than or equal to the first temperature difference threshold, the main circulation water flow rate is reduced. The main circulation water flow rate adjustment unit may further include: a water pump flow rate acquisition subunit for acquiring the current flow rate of the main circulation water pump; a target flow rate calculation subunit for calculating the target flow rate based on the difference between the lower limit of the first temperature and the second temperature range; and a stepped flow reduction subunit for calculating the flow rate difference between the current flow rate and the target flow rate, acquiring the number of step reductions N based on the flow rate difference, and controlling the main circulation water pump to reduce the current flow rate to the target flow rate in N steps based on the number of step reductions N, thereby reducing the main circulation water flow rate, wherein the number of step reductions N is positively correlated with the flow rate difference.

[0058] The main circulation feedwater flow regulation unit, which presets a first temperature difference threshold, may further include: a historical operating data acquisition subunit for acquiring historical operating data based on the main circulation feedwater flow change log, the first-stage flue gas temperature fluctuation log, the gas turbine load rate log, and the optimal temperature difference threshold log, wherein the optimal temperature difference threshold log is generated by back-calculating the actual temperature difference threshold under stable system conditions using the minimum temperature fluctuation criterion; a temperature difference threshold prediction model training subunit for training a temperature difference threshold prediction model based on the historical operating data, using flow change, temperature fluctuation, and load rate as input features, and the optimal temperature difference threshold as the output label; an adaptive temperature difference threshold output subunit for presetting a prediction window, inputting the main circulation feedwater flow change data, the first-stage flue gas temperature fluctuation data, and the gas turbine load rate data within the prediction window into the temperature difference threshold prediction model, and outputting an adaptive temperature difference threshold; and an adaptive substitution subunit for replacing the first temperature difference threshold with the adaptive temperature difference threshold to regulate the main circulation feedwater flow.

[0059] The method may further include: a primary saturated water generation module for exchanging heat between the gas turbine exhaust gas and the main circulating feedwater through a primary heater to heat the main circulating feedwater and generate primary saturated water; a turbine power generation drive module for introducing the primary saturated water into a primary evaporator to generate primary steam, which then drives the turbine to generate electricity and discharges secondary steam; a secondary preheating water generation module for exchanging heat between the primary flue gas and the auxiliary circulating feedwater through a secondary heater to heat the auxiliary circulating feedwater and generate secondary preheating water; a tertiary steam generation module for introducing the secondary steam and the secondary preheating water into a secondary evaporator to generate tertiary steam, wherein the pressure of the primary steam is greater than the pressure of the secondary steam, which is greater than the pressure of the tertiary steam; and an air humidification module for injecting the tertiary steam into the compressor outlet pipe of the gas turbine through a swirl atomizing nozzle to humidify the air.

[0060] The specific configuration of the air humidification module will be described in detail below. As mentioned above, the three-stage steam is injected into the compressor outlet pipe of the gas turbine through a swirling atomizing nozzle. The air humidification module may further include: an air parameter acquisition unit for acquiring the air parameters at the compressor outlet in real time; an injection parameter calculation unit for calculating the injection parameters of the three-stage steam based on the air parameters using a PID controller; and a steam injection unit for adjusting the opening degree and pump speed of the swirling atomizing nozzle according to the injection parameters, thereby injecting the three-stage steam into the compressor outlet pipe of the gas turbine.

[0061] The heater energy-saving system based on multi-stage waste heat recovery provided in the embodiments of the present invention can execute the heater energy-saving method based on multi-stage waste heat recovery provided in any embodiment of the present invention, and has the corresponding functional modules and beneficial effects of the method.

[0062] Although this application makes various references to certain modules in the system according to the embodiments of this application, any number of different modules can be used and run on user terminals and / or servers. The various units and modules included are only divided according to functional logic, but are not limited to the above division, as long as the corresponding functions can be achieved; in addition, the specific names of each functional unit are only for easy distinction between each other and are not used to limit the scope of protection of this invention.

[0063] The specific embodiments described above do not constitute a limitation on the scope of protection of this application. Those skilled in the art should understand that various modifications, combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the scope of protection of this application. In some cases, the actions or steps described in this application can be performed in a different order than that shown in the embodiments and still achieve the desired results. Furthermore, the processes depicted in the accompanying drawings do not necessarily require a specific or sequential order to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

Claims

1. A heater energy-saving method based on multi-stage waste heat recovery, characterized in that, The method includes: The exhaust gas from the gas turbine is heat-exchanged with the main circulating feedwater through a primary heater. By adjusting the flow rate of the main circulating feedwater, the primary flue gas after primary waste heat recovery treatment is obtained. The temperature of the gas turbine exhaust gas is in a first temperature range, and the temperature of the primary flue gas is in a second temperature range. The lower limit of the first temperature range is greater than the upper limit of the second temperature range. The primary flue gas is passed through a secondary heater and heat exchanged with auxiliary circulating water. By adjusting the flow rate of the auxiliary circulating water, secondary flue gas after secondary waste heat recovery is obtained. The temperature of the secondary flue gas is in a third temperature range, and the upper limit of the third temperature range is less than the lower limit of the second temperature range. The secondary flue gas is introduced into the inlet distribution chamber of the denitrification reactor, mixed with the injected ammonia reducing agent, and then passes through the catalyst layer to generate purified flue gas. The median value of the third temperature range is equal to the optimal activity temperature of the denitrification catalyst.

2. The heater energy-saving method based on multi-stage waste heat recovery as described in claim 1, characterized in that, The exhaust gas from the gas turbine is passed through a primary heater and exchanged with the main circulating feedwater. By adjusting the flow rate of the main circulating feedwater, the primary flue gas after primary waste heat recovery treatment is obtained, including: The first temperature of the primary flue gas is obtained through real-time monitoring; A first temperature difference threshold is preset. When the difference between the first temperature and the upper limit of the second temperature range is less than or equal to the first temperature difference threshold, the main circulation water flow rate is increased. When the difference between the first temperature and the lower limit of the second temperature range is less than or equal to the first temperature difference threshold, the main circulation water flow rate is reduced.

3. The heater energy-saving method based on multi-stage waste heat recovery as described in claim 2, characterized in that, A first temperature difference threshold is preset. When the difference between the first temperature and the upper limit of the second temperature range is less than or equal to the first temperature difference threshold, the main circulation water flow rate is increased, including: Obtain the current operating frequency of the main circulating water pump; The target frequency is calculated based on the difference between the upper limit of the first temperature and the second temperature range; A preset adjustment time is set, and the main circulation water pump is controlled to linearly increase the current operating frequency to the target frequency within the adjustment time to increase the main circulation water flow.

4. The heater energy-saving method based on multi-stage waste heat recovery as described in claim 2, characterized in that, When the difference between the first temperature and the lower limit of the second temperature range is less than or equal to the first temperature difference threshold, the main circulation water flow rate is reduced, including: Get the current flow rate of the main circulating water pump; The target flow rate is calculated based on the difference between the lower limits of the first temperature and the second temperature range; Calculate the flow difference between the current flow rate and the target flow rate, obtain the number of reduction steps N based on the flow difference, and control the main circulation water pump to reduce the current flow rate to the target flow rate in N steps based on the number of reduction steps N, so as to reduce the main circulation water flow rate. The number of reduction steps N is positively correlated with the flow difference.

5. The heater energy-saving method based on multi-stage waste heat recovery as described in claim 2, characterized in that, The preset first temperature difference threshold also includes: Historical operating data is obtained based on the main circulation feedwater flow change log, the first-stage flue gas temperature fluctuation log, the gas turbine load rate log, and the optimal temperature difference threshold log. The optimal temperature difference threshold log is generated by back-calculation based on the actual temperature difference threshold under the stable state of the system using the criterion of minimum temperature fluctuation. Based on the historical operating data, a temperature difference threshold prediction model is trained with flow rate changes, temperature fluctuations, and load rate as input features and the optimal temperature difference threshold as the output label. A preset prediction window is used to input the main circulation feedwater flow rate change data, primary flue gas temperature fluctuation data, and gas turbine load rate data within the prediction window into the temperature difference threshold prediction model, and an adaptive temperature difference threshold is output. The adaptive temperature difference threshold is used to replace the first temperature difference threshold to adjust the main circulation water flow rate.

6. The heater energy-saving method based on multi-stage waste heat recovery as described in claim 1, characterized in that, The method further includes: The exhaust gas from the gas turbine is heated by exchanging heat with the main circulating feedwater through a primary heater to generate primary saturated water. The first-stage saturated water is introduced into the first-stage evaporator to generate first-stage steam. The first-stage steam drives a steam turbine to generate electricity, and then discharges second-stage steam. The primary flue gas is passed through a secondary heater to exchange heat with the auxiliary circulating feedwater, which heats the auxiliary circulating feedwater to generate secondary preheated water. The secondary steam and the secondary preheated water are introduced into the secondary evaporator to generate tertiary steam, wherein the pressure of the primary steam is greater than the pressure of the secondary steam, which is greater than the pressure of the tertiary steam; The third-stage steam is injected into the compressor outlet pipe of the gas turbine through a swirling atomizing nozzle to humidify the air.

7. The heater energy-saving method based on multi-stage waste heat recovery as described in claim 6, characterized in that, The third-stage steam is injected into the compressor outlet pipe of the gas turbine through a swirling atomizing nozzle, including: Real-time acquisition of air parameters at the compressor outlet; Based on the air parameters, the injection parameters of the three-stage steam are calculated using a PID controller; Adjust the opening of the swirling atomizing nozzle and the pump speed according to the injection parameters to inject the three-stage steam into the compressor outlet pipe of the gas turbine.

8. A heater energy-saving system based on multi-stage waste heat recovery, characterized in that, The system is used to implement the heater energy-saving method based on multi-stage waste heat recovery as described in any one of claims 1-7, and the system comprises: The primary waste heat recovery module is used to exchange heat between the gas turbine exhaust and the main circulating feedwater through a primary heater. By adjusting the flow rate of the main circulating feedwater, the primary flue gas after primary waste heat recovery is obtained. The temperature of the gas turbine exhaust is in a first temperature range, and the temperature of the primary flue gas is in a second temperature range. The lower limit of the first temperature range is greater than the upper limit of the second temperature range. The secondary waste heat recovery module is used to exchange heat between the primary flue gas and the auxiliary circulating water through the secondary heater. By adjusting the flow rate of the auxiliary circulating water, the secondary flue gas after secondary waste heat recovery is obtained. The temperature of the secondary flue gas is in a third temperature range, and the upper limit of the third temperature range is less than the lower limit of the second temperature range. The denitrification temperature co-control module is used to introduce the secondary flue gas into the inlet distribution chamber of the denitrification reactor, mix it with the injected ammonia reducing agent, and then pass it through the catalyst layer to generate purified flue gas. The median value of the third temperature range is equal to the optimal activity temperature of the denitrification catalyst.

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