A biomass boiler flue gas temperature control method

Abstract

The application discloses a biomass boiler flue gas temperature control method, which automatically adjusts the water supply flow of a smoke cooler and an air preheater according to the deviation of current boiler load and the deviation of current smoke cooler outlet smoke temperature, quickly responds to the control of the change of boiler load and the change of smoke cooler outlet smoke temperature, replaces the manual control mode of an operator, realizes the automatic control of the exhaust gas temperature of the biomass boiler, and keeps the exhaust gas temperature at the outlet of the smoke cooler stable. The biomass boiler load deviation caused by the change of the boiler load can be quickly adjusted when the boiler load changes, the change of the exhaust gas temperature is ahead of the change of the exhaust gas temperature, the control requirement of the exhaust gas temperature of the boiler is met, and the operation efficiency of the boiler is ensured. The biomass fuel of different types, heat values and moisture contents can be automatically adapted, the real-time change requirement of the boiler load is consistent, the exhaust gas temperature of the boiler is kept stable, the efficiency of the boiler is improved, and fuel consumption is reduced.

Description

Technical Field

[0001] This invention relates to the field of flue gas treatment technology, and in particular to a method for controlling the temperature of flue gas from a biomass boiler. Background Technology

[0002] Against the backdrop of advocating energy conservation and emission reduction, biomass boilers are gaining popularity due to their advantages such as cleanliness, environmental friendliness, abundant fuel, and zero carbon emissions. Controlling boiler flue gas temperature is a crucial aspect of biomass boiler management. Increased flue gas temperature leads to increased heat loss, resulting in excessive consumption of biomass fuel, impacting boiler operating efficiency, and reducing the boiler's lifespan.

[0003] Currently, most biomass boilers use manual control for flue gas temperature. Operators adjust the feeder speed, fuel quantity, and blower speed based on the flue gas temperature measurement at the tail flue outlet to maintain the flue gas temperature. However, these adjustments always lag behind changes in boiler load and combustion, making manual control unsuitable for real-time adjustments. Furthermore, biomass fuels vary greatly in type, calorific value, and moisture content, resulting in significant deviations in calorific value per unit mass. Therefore, the required boiler load, fuel quantity, and combustion air volume cannot be directly derived from the flue gas temperature. Currently, changes in flue gas temperature caused by variations in boiler load, fuel quantity, and combustion air volume are determined by operators based on their experience, which inevitably leads to differences in adjustment skills and operational errors among operators. This makes it impossible to consistently meet demand, potentially causing unstable combustion within the furnace and even boiler shutdowns. Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a method for controlling flue gas temperature in a biomass boiler.

[0005] The present invention provides a method for controlling the flue gas temperature of a biomass boiler. This method is based on a flue gas temperature control system, which includes an economizer, a flue gas cooler, and an air preheater. The flue gas cooler is located within the boiler's flue. The boiler's feedwater system outlet is connected to the hot section inlet of the air preheater, and the hot section outlet of the air preheater is connected to the cold section inlet of the flue gas cooler. The control method includes:

[0006] Based on the deviation between the measured value of the flue gas temperature at the outlet of the flue gas cooler and the set value of the flue gas temperature at the outlet of the flue gas cooler, the water flow rate entering the flue gas cooler and the air preheater is adjusted. If the measured value of the flue gas temperature at the outlet of the flue gas cooler is greater than the set value of the flue gas temperature at the outlet of the flue gas cooler, the water flow rate is increased; if the measured value of the flue gas temperature at the outlet of the flue gas cooler is less than the set value of the flue gas temperature at the outlet of the flue gas cooler, the water flow rate is decreased.

[0007] Based on the deviation between the actual boiler load and the set boiler load, the feedwater flow rate into the flue gas cooler and the air preheater is adjusted. If the actual boiler load is greater than the set boiler load, the feedwater flow rate is increased; if the actual boiler load is less than the set boiler load, the feedwater flow rate is decreased.

[0008] Optionally, the flue gas temperature control system further includes an economizer and a feedwater bypass valve. The boiler feedwater system outlet is connected to the economizer inlet via a feedwater bypass. The feedwater bypass valve is located on the feedwater bypass. The control method includes:

[0009] The flow rate of the water supply bypass is adjusted by regulating the opening degree of the water supply bypass valve, thereby regulating the water supply flow rate entering the flue gas cooler and the air preheater.

[0010] Optionally, the control system includes a flue gas temperature transmitter at the outlet of the flue gas cooler, a flue gas temperature controller at the outlet of the flue gas cooler, and a feedforward controller for the exhaust gas temperature; the control method includes:

[0011] The flue gas cooler outlet temperature controller compares the flue gas cooler outlet temperature measured by the flue gas cooler outlet temperature transmitter with the flue gas cooler outlet temperature setpoint to generate a flue gas cooler outlet temperature deviation signal. When the flue gas cooler outlet temperature measured is greater than the flue gas cooler outlet temperature setpoint, the flue gas cooler outlet temperature deviation is less than 0, and the flue gas cooler outlet temperature controller controls the water supply bypass valve to decrease. When the flue gas cooler outlet temperature measured is less than the flue gas cooler outlet temperature setpoint, the flue gas cooler outlet temperature deviation is greater than 0, and the flue gas cooler outlet temperature controller controls the water supply bypass valve to increase.

[0012] The flue gas feedforward controller generates a flue gas temperature change signal based on the deviation between the actual boiler load and the set boiler load, and inputs it to the flue gas cooler outlet temperature controller. When the actual boiler load is greater than the set boiler load and the flue gas temperature change is less than 0, the flue gas cooler outlet temperature controller controls the feedwater bypass valve to decrease. When the actual boiler load is less than the set boiler load and the flue gas temperature change is greater than 0, the flue gas cooler outlet temperature controller controls the feedwater bypass valve to increase.

[0013] Optionally, the method for controlling the flue gas temperature of a biomass boiler includes: the flue gas temperature controller at the outlet of the flue gas cooler adds the deviation of the flue gas temperature at the outlet of the flue gas cooler to the change in the exhaust gas temperature, and the sum of the two forms a total temperature deviation; the flue gas temperature controller at the outlet of the flue gas cooler outputs a control signal based on the total temperature deviation; when the total temperature deviation is greater than 0, the flue gas temperature controller at the outlet of the flue gas cooler controls the feedwater bypass valve to be increased; when the total temperature deviation is less than 0, the flue gas temperature controller at the outlet of the flue gas cooler controls the feedwater bypass valve to be decreased.

[0014] Optionally, the biomass boiler flue gas temperature control method further includes: adjusting the feedwater flow rate of the flue gas cooler based on the deviation between the measured value of the air preheater outlet water temperature and the set value of the air preheater outlet water temperature; when the measured value of the air preheater outlet water temperature is less than the set value of the air preheater outlet temperature, reducing the feedwater flow rate of the flue gas cooler; and when the measured value of the air preheater outlet water temperature is greater than the set value of the air preheater outlet temperature, increasing the feedwater flow rate of the flue gas cooler.

[0015] Optionally, the control system further includes a deaerator and flue gas cooler bypass valve, wherein a flue gas cooler bypass is connected between the outlet of the air preheater hot section and the inlet of the deaerator, and the flue gas cooler bypass valve is located on the flue gas cooler bypass. The control method includes:

[0016] The flow rate of the flue gas cooler bypass is adjusted by regulating the opening degree of the bypass valve of the flue gas cooler, thereby regulating the feed water flow rate of the flue gas cooler.

[0017] Optionally, the control system further includes an air preheater outlet water temperature transmitter and an air preheater outlet water temperature controller, and the control method includes:

[0018] The air preheater outlet water temperature controller compares the measured value of the air preheater outlet water temperature by the air preheater outlet water temperature transmitter with the set value of the air preheater outlet water temperature, and outputs a command to adjust the opening degree of the flue gas cooler bypass valve according to the deviation.

[0019] When the measured value of the air preheater outlet water temperature is less than the set value of the air preheater outlet temperature, the air preheater outlet water temperature controller controls the flue gas cooler bypass valve to increase its opening. When the measured value of the air preheater outlet water temperature is greater than the set value of the air preheater outlet temperature, the air preheater outlet water temperature controller controls the flue gas cooler bypass valve to decrease its opening.

[0020] Optionally, an air preheater bypass is connected between the boiler feedwater system outlet and the flue gas cooler inlet, and the system further includes:

[0021] Based on the deviation between the measured inlet water temperature of the flue gas cooler and the set inlet water temperature of the flue gas cooler, the feedwater flow rate of the air preheater bypass is adjusted. When the measured inlet water temperature of the flue gas cooler is less than the set inlet water temperature of the flue gas cooler, the feedwater flow rate of the air preheater bypass is increased to raise the feedwater temperature at the inlet of the flue gas cooler. When the measured inlet water temperature of the flue gas cooler is greater than the set inlet water temperature of the flue gas cooler, the feedwater flow rate of the air preheater bypass is decreased to lower the feedwater temperature at the inlet of the flue gas cooler.

[0022] Optionally, the control system further includes an air preheater bypass valve, the air preheater bypass valve being located on the air preheater bypass, and the control method includes:

[0023] The flow rate of the air preheater bypass is adjusted by regulating the opening degree of the air preheater bypass valve, thereby regulating the feedwater temperature at the flue gas cooler inlet.

[0024] Optionally, the control system further includes a flue gas cooler inlet water temperature controller and a flue gas cooler inlet water temperature transmitter, and the control method includes:

[0025] The flue gas cooler inlet water temperature controller compares the flue gas cooler inlet water temperature measured by the flue gas cooler inlet water temperature transmitter with the flue gas cooler inlet water temperature setpoint, and adjusts the opening of the air preheater bypass valve according to the deviation.

[0026] When the measured value of the flue gas cooler inlet water temperature is less than the set value of the flue gas cooler inlet water temperature, the flue gas cooler inlet water temperature controller controls the air preheater bypass valve to increase its opening. When the measured value of the flue gas cooler inlet water temperature is greater than the set value of the flue gas cooler inlet water temperature, the flue gas cooler inlet water temperature controller controls the air preheater bypass valve to decrease its opening.

[0027] The biomass boiler flue gas temperature control method provided in this invention replaces manual control by operators, achieving automatic control of the biomass boiler flue gas temperature. By adjusting the feedwater flow into the air preheater and flue gas cooler based on the flue gas cooler outlet temperature and the actual boiler load, the flue gas cooler outlet temperature is kept stable. This ensures that when the boiler load changes, the flue gas temperature is quickly adjusted to compensate for load deviations, anticipating changes in the flue gas temperature and meeting the boiler flue gas temperature control requirements, thus guaranteeing boiler operating efficiency.

[0028] The flue gas temperature control method provided by this invention can automatically adapt to different types of biomass fuels with varying calorific values ​​and moisture content. It will not cause fluctuations in boiler flue gas temperature due to changes in the fuel entering the boiler. It is consistent with the boiler load change requirements in real time, maintains stable boiler flue gas temperature, improves boiler efficiency, and reduces fuel consumption.

[0029] The above and other objects, advantages and features of the present invention will become more apparent to those skilled in the art from the following detailed description of specific embodiments of the invention in conjunction with the accompanying drawings. Attached Figure Description

[0030] The following sections will describe some specific embodiments of the invention in detail by way of example and not limitation, with reference to the accompanying drawings. The same reference numerals in the drawings denote the same or similar parts or portions. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings:

[0031] Figure 1 This is a flue gas flow diagram of the biomass boiler flue gas temperature control method in an embodiment of the present invention.

[0032] Figure 2 This is a water supply flow diagram of the biomass boiler flue gas temperature control method in an embodiment of the present invention.

[0033] Figure 3 This is a flowchart of the flue gas temperature control method for a biomass boiler in an embodiment of the present invention.

[0034] Figure label:

[0035] Furnace 1, Flue 2, Economizer 3, Flue gas cooler 4, Air preheater 5, Deaerator 6, Boiler feedwater system 7, Blower 8, Combustion air 9, Air preheater bypass valve 101, Flue gas cooler bypass valve 102, Feedwater bypass valve 103, Deaerator recirculation isolation valve 104, Air preheater outlet water temperature controller 201, Flue gas cooler inlet water temperature controller 202, Flue gas cooler outlet flue gas temperature controller 203, Exhaust gas temperature feedforward controller 204, Air preheater outlet water temperature transmitter 301, Flue gas cooler inlet water temperature transmitter 302, Flue gas cooler outlet flue gas temperature transmitter 303. Detailed Implementation

[0036] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0037] This invention provides a method for controlling flue gas temperature in a biomass boiler. By automatically adjusting the feedwater flow rate of the air preheater and flue gas cooler, the flue gas temperature is controlled, which solves the problem that the flue gas temperature cannot be automatically adjusted according to changes in boiler load and fuel. It also solves the problem that the flue gas temperature adjustment cannot meet the requirements of real-time changes in boiler load and combustion, thus maintaining a stable flue gas temperature and ensuring boiler efficiency.

[0038] The biomass boiler flue gas temperature control method provided in this embodiment of the invention is a control method based on a flue gas temperature control system. For example... Figures 1-3 As shown, the flue gas temperature control system includes an economizer 3, a flue gas cooler 4, and an air preheater 5. The flue gas cooler 4 is located inside the boiler's flue duct 2. The boiler's feedwater system outlet is connected to the hot section inlet of the air preheater 5, and the hot section outlet of the air preheater 5 is connected to the cold section inlet of the flue gas cooler 4. The control method includes:

[0039] Based on the deviation between the measured value of the flue gas temperature at the outlet of the flue gas cooler and the set value of the flue gas temperature at the outlet of the flue gas cooler, the feedwater flow rate into the flue gas cooler 4 and the air preheater 5 is adjusted. If the measured value of the flue gas temperature at the outlet of the flue gas cooler is greater than the set value of the flue gas temperature at the outlet of the flue gas cooler, the feedwater flow rate is increased, thereby reducing the flue gas temperature at the outlet of the flue gas cooler. If the measured value of the flue gas temperature at the outlet of the flue gas cooler is less than the set value of the flue gas temperature at the outlet of the flue gas cooler, the feedwater flow rate is decreased, thereby increasing the flue gas temperature at the outlet of the flue gas cooler.

[0040] Based on the deviation between the actual boiler load and the set boiler load, the feedwater flow rate into the flue gas cooler 4 and the air preheater 5 is adjusted. If the actual boiler load is greater than the set boiler load, the feedwater flow rate is increased to reduce the flue gas temperature at the outlet of the flue gas cooler. If the actual boiler load is less than the set boiler load, the feedwater flow rate is decreased to increase the flue gas temperature at the outlet of the flue gas cooler.

[0041] The biomass boiler flue gas temperature control method provided in this invention automatically adjusts the feedwater flow rate of the flue gas cooler and air preheater based on the deviation of the current boiler load and the deviation of the current flue gas temperature at the flue gas cooler outlet. This provides rapid response control to changes in boiler load and flue gas temperature at the flue gas cooler outlet, replacing manual control by operators and achieving automatic control of the biomass boiler flue gas temperature, thus maintaining a stable flue gas temperature at the flue gas cooler outlet. Furthermore, it ensures rapid adjustment to flue gas temperature changes caused by boiler load deviations when the boiler load changes, anticipating these changes and meeting the boiler flue gas temperature control requirements, thereby guaranteeing boiler operating efficiency.

[0042] The flue gas temperature control method provided by this invention can automatically adapt to different types of biomass fuels with varying calorific values ​​and moisture content. It will not cause fluctuations in boiler flue gas temperature due to changes in the fuel entering the boiler. It is consistent with the boiler load change requirements in real time, maintains stable boiler flue gas temperature, improves boiler efficiency, and reduces fuel consumption.

[0043] The following is based on Figures 1-3 This invention describes a biomass boiler flue gas temperature control system and a flue gas temperature control method based on such a flue gas temperature control system, according to a specific embodiment of the present invention.

[0044] like Figures 1-3 As shown, the flue gas temperature control system includes an economizer 3, a flue gas cooler 4, an air preheater 5, a deaerator 6, an air preheater bypass valve 101, a flue gas cooler bypass valve 102, a feedwater bypass valve 103, a deaerator recirculation isolation valve 104, an air preheater outlet water temperature controller 201, a flue gas cooler inlet water temperature controller 202, a flue gas cooler outlet flue gas temperature controller 203, an exhaust gas temperature feedforward controller 204, an air preheater outlet water temperature transmitter 301, a flue gas cooler inlet water temperature transmitter 302, and a flue gas cooler outlet flue gas temperature transmitter 303.

[0045] Flue 2 is connected to furnace 1. Economizer 3 and flue gas cooler 4 are located inside the flue, while air preheater 5 is located outside the flue. Fuel is burned in furnace 1, and flue gas passes through each heating surface in sequence via flue 2. Finally, after passing through economizer 3 and flue gas cooler 4, the flue gas is controlled to a suitable temperature and then sent to the dust removal system.

[0046] The inlet of the hot section of the air preheater 5 is connected to the boiler feedwater system 7, and the outlet of the hot section of the air preheater 5 is connected to the inlet of the cold section of the flue gas cooler 4. The flue duct 2 is connected to the hot section of the flue gas cooler 4. In some embodiments, the medium inside the air preheater 5 is boiler feedwater, and the medium outside the tubes is cold air. Inside the air preheater 5, the high-temperature boiler feedwater exchanges heat with the cold air, the cold air is preheated, and the boiler feedwater is cooled and its temperature decreases. The flue gas cooler 4 is arranged at the tail end of the flue duct 2. The boiler feedwater with reduced temperature enters the pipes of the flue gas cooler 4. The medium outside the tubes of the flue gas cooler 4 is flue gas. The low-temperature boiler feedwater absorbs heat and reduces the temperature of the flue gas.

[0047] like Figure 2 and Figure 3 As shown, the outlet of boiler feedwater system 7 is connected to the inlet of the hot section of air preheater 5 via a pipeline, and the outlet of boiler feedwater system 7 is also connected to the inlet of economizer 3 via a pipeline. The outlet of the hot section of air preheater 5 is connected to the inlet of the cold section of flue gas cooler 4 via a pipeline, and the outlet of the cold section of flue gas cooler 4 is connected to each of the inlet of economizer 3 and deaerator 6. Specifically, one branch of the outlet of the cold section of flue gas cooler 4 is connected to the inlet of deaerator 6, and another branch is connected to the inlet of economizer 3, with the branch connected to the inlet of economizer 3 located downstream of the branch connected to the inlet of deaerator 6.

[0048] like Figure 2 and Figure 3 As shown, the blower 8 is connected to the cold section inlet of the air preheater 5 and is used to supply cold air to the cold section of the air preheater 5. Inside the air preheater 5, the high-temperature boiler feedwater heats the air supplied by the blower 8, and the outlet of the cold section of the air preheater 5 is combustion air 9. The feedwater at the outlet of the air preheater 5 flows into the flue gas cooler 4, cooling the flue gas inside the flue gas cooler 4 and reducing the exhaust gas temperature at the outlet of the flue gas cooler 4.

[0049] like Figure 2 As shown, the outlet of the boiler feedwater system 7 is connected to the inlet of the flue gas cooler 4 via an air preheater bypass. An air preheater bypass valve 101 is installed on the air preheater bypass. The inlet end of the air preheater bypass is connected to the connecting pipe between the boiler feedwater system 7 and the air preheater 5, and the outlet end of the air preheater bypass is connected to the connecting pipe between the outlet of the air preheater 5 and the inlet of the flue gas cooler 4. The opening and closing of the air preheater bypass valve 101 can regulate the feedwater flow rate in the air preheater bypass, thereby controlling the inlet water temperature of the flue gas cooler 4. When the air preheater bypass valve 101 is opened, the feedwater flow rate in the air preheater bypass increases, the feedwater flow rate entering the air preheater 5 decreases, and the inlet water temperature of the flue gas cooler 4 increases; conversely, when the air preheater bypass valve 101 is closed, the feedwater flow rate in the air preheater bypass decreases, the feedwater flow rate entering the air preheater 5 increases, and the inlet water temperature of the flue gas cooler 4 decreases.

[0050] In some embodiments, the air preheater bypass valve 101 is used to control the inlet water temperature of the flue gas cooler 4 to be no lower than 90°C in order to prevent low-temperature corrosion of the flue gas cooler 4.

[0051] like Figure 2 As shown, a flue gas cooler bypass is connected between the outlet of the hot section of the air preheater and the deaerator 6, and a flue gas cooler bypass valve 102 is installed on the flue gas cooler bypass. The inlet end of the flue gas cooler bypass is connected to the connecting pipeline between the air preheater 5 and the flue gas cooler 4, and the outlet end of the flue gas cooler bypass is connected to the connecting pipeline between the outlet of the flue gas cooler 4 and the deaerator 6. A flue gas cooler bypass valve 102 is installed on the flue gas cooler bypass, and the opening and closing of the flue gas cooler bypass valve 102 can regulate the feedwater flow rate in the flue gas cooler bypass, thereby controlling the feedwater flow rate at the inlet of the flue gas cooler 4. Furthermore, the outlet end of the air preheater bypass is located downstream of the inlet end of the flue gas cooler bypass. When the bypass valve 102 of the flue gas cooler is increased, the bypass flow of the flue gas cooler increases, the water flow into the flue gas cooler 4 decreases, and the outlet flue gas temperature of the flue gas cooler 4 increases; when the bypass valve 102 of the flue gas cooler is decreased, the bypass flow of the flue gas cooler decreases, the water flow into the flue gas cooler 4 increases, and the outlet flue gas temperature of the flue gas cooler 4 decreases.

[0052] The boiler feedwater system 7 is connected to the economizer 3 inlet via a feedwater bypass, and the feedwater bypass valve 103 is located on the feedwater bypass. When the feedwater bypass valve 103 is opened, the feedwater bypass flow increases, the feedwater flow entering the air preheater 5 and the flue gas cooler 4 decreases, and the flue gas temperature rises; when the feedwater bypass valve 103 is closed, the feedwater bypass flow decreases, the feedwater flow entering the air preheater 5 and the flue gas cooler 4 increases, and the flue gas temperature decreases.

[0053] The deaerator recirculation isolation valve 104 is located at the inlet of the deaerator 6. It is used to heat the air and flue gas during boiler startup, so that the temperature of the air and flue gas reaches a reasonable level that allows for switching the main fuel, and to prevent the adsorption and corrosion of the heating surface at the tail of the flue duct 2 by flue gas and dust particles.

[0054] like Figure 3 As shown, the air preheater outlet water temperature transmitter 301 is located at the hot section outlet of air preheater 5 and upstream of the flue gas cooler bypass inlet. It is used to measure the temperature of the boiler feedwater at the outlet of air preheater 5. The air preheater outlet water temperature controller 201 is connected to the air preheater outlet water temperature transmitter 301. The air preheater outlet water temperature transmitter 301 transmits the measured temperature signal to the loop of the air preheater outlet water temperature controller 201. The air preheater outlet water temperature controller 201 outputs a command based on the deviation between the air preheater outlet water temperature setpoint and the measured air preheater outlet water temperature value measured by the air preheater outlet water temperature transmitter 301, thereby adjusting the flue gas cooler bypass valve 102 and thus regulating the feedwater flow rate of flue gas cooler 4.

[0055] Specifically, when the measured value of the air preheater outlet water temperature is less than the set value of the air preheater outlet temperature, it indicates that the air preheater 5 outlet water temperature is too low. In order to control the flue gas temperature, the air preheater outlet water temperature controller 201 controls the flue gas cooler bypass valve 102 to increase the valve opening, thereby reducing the feedwater flow rate into the flue gas cooler 4.

[0056] When the measured value of the air preheater outlet water temperature is greater than the set value of the air preheater outlet temperature, it indicates that the outlet water temperature of the air preheater 5 is too high. In order to control the flue gas temperature, the air preheater outlet water temperature controller 201 controls the flue gas cooler bypass valve 102 to reduce the valve opening, thereby increasing the feedwater flow rate into the flue gas cooler 4.

[0057] In this embodiment, the air preheater outlet water temperature controller 201 is a PID controller. The air preheater outlet water temperature setpoint is used as the setpoint SP, and the measured air preheater outlet water temperature is used as the feedback value PV. Based on the deviation between the setpoint SP and the feedback value PV, the PID controller outputs a 0-100% command to the flue gas cooler bypass valve 102, guiding the opening degree of the flue gas cooler bypass valve 102 and adjusting the feedwater flow rate of the flue gas cooler 4.

[0058] The flue gas cooler inlet water temperature transmitter 302 is located at the cold section inlet of the flue gas cooler 4, downstream of the air preheater bypass outlet, and is used to measure the feedwater temperature at the inlet of the flue gas cooler 4. The flue gas cooler inlet water temperature controller 202 is connected to the flue gas cooler inlet water temperature transmitter 302. The flue gas cooler inlet water temperature transmitter 302 transmits the measured temperature signal to the flue gas cooler inlet water temperature controller 202 circuit. The flue gas cooler inlet water temperature controller 202 outputs a command based on the deviation between the flue gas cooler inlet water temperature setpoint and the flue gas cooler inlet water temperature measured by the flue gas cooler inlet water temperature transmitter 302, and adjusts the air preheater bypass valve 101, thereby adjusting the inlet water temperature of the flue gas cooler 4.

[0059] Specifically, when the measured value of the inlet water temperature of the flue gas cooler is less than the set value of the inlet water temperature of the flue gas cooler, it indicates that the inlet temperature of the flue gas cooler 4 is too low. The flue gas cooler inlet water temperature controller 202 controls the air preheater bypass valve 101 to increase the valve opening, increase the feed water flow of the air preheater bypass, thereby reducing the feed water flow of the air preheater 5 and increasing the feed water temperature at the inlet of the flue gas cooler 4.

[0060] When the measured value of the inlet water temperature of the flue gas cooler is greater than the set value of the inlet water temperature of the flue gas cooler, it indicates that the inlet temperature of the flue gas cooler 4 is too high. The flue gas cooler inlet water temperature controller 202 controls the air preheater bypass valve 101 to reduce the valve opening and reduce the feed water flow of the air preheater bypass, thereby increasing the feed water flow of the air preheater 5 and reducing the feed water temperature at the inlet of the flue gas cooler 4.

[0061] In this embodiment, the flue gas cooler inlet water temperature controller 202 is a PID controller. The setpoint for the flue gas cooler inlet water temperature is used as the setpoint SP, and the measured value of the flue gas cooler inlet water temperature is used as the feedback value PV. The flue gas cooler inlet water temperature transmitter 302 sends the feedback value PV into the loop and compares it with the setpoint SP to form a flue gas cooler inlet feedwater temperature deviation signal. This deviation signal is sent to the flue gas cooler inlet water temperature controller 202 to act on the air preheater bypass valve 101, guiding the opening degree of the air preheater bypass valve 101, thereby regulating the flue gas cooler inlet feedwater temperature.

[0062] A flue gas temperature transmitter 303 is installed at the flue gas outlet of the flue gas cooler 4 to measure the flue gas temperature at the outlet. A flue gas temperature controller 203 is connected to the flue gas temperature transmitter 303, and the transmitter transmits the measured flue gas temperature value to the controller 203. The controller 203 outputs a signal based on the deviation between the measured flue gas temperature value and the setpoint, thereby controlling the feedwater flow to the air preheater 5 and the flue gas cooler 4 to control the exhaust gas temperature at the outlet of the flue gas cooler 4.

[0063] In this embodiment, the flue gas temperature controller 203 at the outlet of the flue gas cooler is a PID controller. The setpoint for the flue gas temperature at the outlet of the flue gas cooler is used as the setpoint SP, and the measured value of the flue gas temperature at the outlet of the flue gas cooler is used as the feedback value PV. The flue gas temperature transmitter 303 at the outlet of the flue gas cooler sends the actual feedback value PV into the loop and compares it with the setpoint SP to form a flue gas temperature deviation signal at the outlet of the flue gas cooler.

[0064] When the measured flue gas temperature at the outlet of the flue gas cooler is greater than the set value, it indicates that the outlet flue gas temperature is too high and the exhaust gas temperature needs to be reduced. When the flue gas temperature deviation at the outlet of the flue gas cooler is less than 0, the feedwater flow rate into the air preheater 5 and the flue gas cooler 4 should be increased, and the flue gas temperature controller 203 should control the feedwater bypass valve 103 to decrease, thereby reducing the exhaust gas temperature at the outlet of the flue gas cooler. When the measured flue gas temperature at the outlet of the flue gas cooler is less than the set value, it indicates that the outlet flue gas temperature is too low and the exhaust gas temperature needs to be increased. When the flue gas temperature deviation at the outlet of the flue gas cooler is greater than 0, the feedwater flow rate into the air preheater 5 and the flue gas cooler 4 should be decreased, and the flue gas temperature controller 203 should control the feedwater bypass valve 103 to increase, thereby increasing the exhaust gas temperature at the outlet of the flue gas cooler.

[0065] To accommodate rapid changes in boiler load, the flue gas temperature at the flue gas cooler outlet needs to be adjusted quickly. This invention introduces a faster-responding flue gas temperature feedforward controller 204, which can respond more quickly to changes in boiler load and better control the flue gas temperature. The flue gas temperature feedforward controller 204 outputs a signal indicating the change in flue gas temperature at the flue gas cooler outlet based on the deviation between the boiler load setpoint and the actual boiler load.

[0066] In this embodiment, the flue gas temperature feedforward controller 204 is a PD controller. The input value of the PD controller is the deviation between the boiler load setpoint SP and the actual boiler load PV, and the output value is the flue gas temperature change signal at the outlet of the flue gas cooler. It can be understood that this flue gas temperature change value is the theoretical change value, that is, the flue gas temperature change value that the boiler load deviation will theoretically lead to.

[0067] When the actual boiler load is greater than the set boiler load, it indicates that the boiler load is too high. If no adjustment is made, the flue gas outlet temperature will increase. Therefore, the flue gas temperature needs to be reduced. The flue gas temperature change value output by the flue gas temperature feedforward controller 204 is less than 0. When the actual boiler load is less than the set boiler load, it indicates that the boiler load is too low. If no adjustment is made, the flue gas outlet temperature will decrease. Therefore, the flue gas temperature needs to be increased. The flue gas temperature change value output by the flue gas temperature feedforward controller 204 is greater than 0.

[0068] Optionally, the output range of the flue gas temperature feedforward controller 204 is -3℃ to 10℃.

[0069] In this embodiment of the invention, the flue gas cooler outlet temperature transmitter 303 transmits the measured flue gas cooler outlet temperature value to the loop for comparison with the set value of the flue gas cooler outlet temperature, forming a flue gas cooler outlet temperature deviation signal. The flue gas cooler outlet temperature controller 203 simultaneously processes the flue gas cooler outlet temperature deviation signal and the exhaust gas temperature change value signal, adds the flue gas cooler outlet temperature deviation to the exhaust gas temperature change value output by the exhaust gas temperature feedforward controller 204 to form a total temperature deviation, and outputs a control signal based on the total temperature deviation to control the opening degree of the feedwater bypass valve 103.

[0070] Specifically, when the total temperature deviation is greater than 0, the flue gas temperature controller 203 at the outlet of the flue gas cooler outputs an increase signal to control the water supply bypass valve 103 to increase, thereby reducing the water supply flow of the air preheater 5 and the flue gas cooler 4 and increasing the exhaust gas temperature at the outlet of the flue gas cooler 4.

[0071] When the total temperature deviation is less than 0, the flue gas temperature controller 203 at the outlet of the flue gas cooler outputs a reduction signal to control the water supply bypass valve 103 to reduce the flow rate of the air preheater 5 and the flue gas cooler 4, thereby reducing the exhaust gas temperature at the outlet of the flue gas cooler 4.

[0072] The flue gas cooler outlet temperature controller 203 can quickly respond to changes in boiler load and flue gas cooler outlet temperature based on the sum of the deviations in current boiler load and flue gas cooler outlet temperature. On one hand, when the boiler load remains stable, if the flue gas cooler outlet temperature changes, it will directly affect the change in the "total temperature deviation." The flue gas cooler outlet temperature controller 203 controls the opening of the feedwater bypass valve 103 based on the total temperature deviation. On the other hand, when the flue gas cooler outlet temperature is stable, if the boiler load changes, the output value of the exhaust gas temperature feedforward controller 204 will also change directly, directly affecting the change in the "total temperature deviation." The flue gas cooler outlet temperature controller 203 controls the opening of the feedwater bypass valve 103 based on the total temperature deviation to ensure that the change in the opening of the feedwater bypass valve 103 precedes the change in exhaust gas temperature.

[0073] For example, when the boiler load changes, the change is not yet reflected in the change of flue gas temperature, i.e. the flue gas temperature deviation signal at the outlet of the flue gas cooler is 0. However, due to the change in the output value of the flue gas temperature feedforward controller 204, the total temperature difference deviation obtained by the flue gas temperature controller 203 at the outlet of the flue gas cooler changes. Thus, the opening of the feedwater bypass valve 103 can be adjusted before the flue gas temperature at the outlet of the flue gas cooler changes, so as to prevent the flue gas temperature at the outlet of the flue gas cooler from changing due to the boiler load.

[0074] The biomass boiler flue gas temperature control method provided in this invention replaces manual control by operators, achieving automatic control of the biomass boiler flue gas temperature. By adjusting the feedwater bypass valve, the feedwater flow into the air preheater and flue gas cooler is controlled, keeping the flue gas temperature at the cooler outlet stable. Simultaneously, by introducing a new flue gas temperature feedforward controller, it ensures rapid adjustment to flue gas temperature changes caused by boiler load deviations when the boiler load changes. This ensures that changes in the feedwater bypass valve opening precede changes in flue gas temperature, meeting the boiler flue gas temperature control requirements and guaranteeing boiler operating efficiency.

[0075] The flue gas temperature control method provided by this invention can automatically adapt to different types of biomass fuels with varying calorific values ​​and moisture content. It will not cause fluctuations in boiler flue gas temperature due to changes in the fuel entering the boiler. It is consistent with the boiler load change requirements in real time, maintains stable boiler flue gas temperature, improves boiler efficiency, and reduces fuel consumption.

[0076] In this invention, the boiler feedwater is heated and supplied to the air preheater. The feedwater at the outlet of the air preheater flows into the flue gas cooler to cool the flue gas inside the cooler, thereby reducing the exhaust gas temperature at the outlet of the cooler and increasing the feedwater temperature flowing into the economizer. This reduces both the exhaust gas temperature and the low-temperature corrosion of the air preheater and the cooler, ensuring boiler efficiency.

[0077] The following is based on Figures 1-3This invention describes the detailed working process and control method of the biomass boiler flue gas temperature control system provided in the embodiments of the present invention.

[0078] During the initial startup phase, the boiler auxiliary steam source is activated to heat the feedwater in deaerator 6. The heated feedwater then enters the boiler feedwater system 7. Once the outlet water temperature of deaerator 6 reaches 105℃, the flue gas cooler bypass valve 102 is opened. The feedwater from boiler feedwater system 7 first flows to air preheater 5, and then returns to deaerator 6 via the flue gas cooler bypass to the deaerator recirculation pipeline. The feedwater circulates between deaerator 6 and air preheater 5 until the outlet water temperature of air preheater 5 reaches 90℃.

[0079] Close the flue gas cooler bypass valve 102 and open the air preheater bypass valve 101. The feedwater from the boiler feedwater system 7 outlet enters the flue gas cooler 4 through the air preheater 5 and the air preheater bypass, heating the heat exchange surfaces of the flue gas cooler 4. After passing through the flue gas cooler 4, the feedwater returns to the deaerator 6.

[0080] The pressure in the boiler drum is gradually increased to 1.8 MPa. Straw fuel is added to the furnace 11. After the straw fuel is added, the deaerator recirculation isolation valve 104 is closed. The feedwater from the outlet of the flue gas cooler 4 no longer enters the deaerator 6, but instead enters the boiler drum through the economizer 3.

[0081] As the boiler load increases, the flue gas temperature controller 203 at the outlet of the flue gas cooler gradually adjusts the feedwater bypass valve 103 to reduce the flow rate of the loop water entering the air preheater 5 and the flue gas cooler 4. At the same time, the flue gas temperature controller 202 at the inlet of the flue gas cooler adjusts the opening of the air preheater bypass valve 101 to control the inlet water temperature of the flue gas cooler 4 until the inlet water temperature of the flue gas cooler 4 meets the condition that the heating surface of the flue gas cooler 4 does not experience low-temperature corrosion, and also ensures that the flue gas temperature at the outlet of the flue gas cooler is maintained within the set range (127℃~140℃).

[0082] The air preheater outlet water temperature controller 201 automatically controls the opening of the flue gas cooler bypass valve 102 based on the deviation between the set air preheater outlet water temperature (85℃~90℃) and the measured air preheater outlet water temperature. When the actual temperature feedback is lower than the set value, the opening of the flue gas cooler bypass valve 102 is increased, that is, when the actual air preheater outlet water temperature drops below 85℃, the flue gas cooler bypass valve 102 gradually opens; when the actual temperature feedback is higher than the set value, the opening of the flue gas cooler bypass valve 102 is decreased, that is, when the actual air preheater outlet water temperature is higher than 90℃, the flue gas cooler bypass valve 102 gradually closes.

[0083] The flue gas cooler inlet water temperature controller 202 automatically controls the opening of the air preheater bypass valve 101 based on the set value (90℃~95℃) and the measured value of the flue gas cooler inlet water temperature. When the actual temperature is lower than the set value, the opening of the air preheater bypass valve 101 is increased, that is, when the actual inlet water temperature of the flue gas cooler drops below 90℃, the air preheater bypass valve 101 gradually opens; when the actual temperature is higher than the set value, the opening of the air preheater bypass valve 101 is decreased, that is, when the actual inlet water temperature of the flue gas cooler is higher than 95℃, the air preheater bypass valve 101 gradually closes.

[0084] The flue gas cooler outlet temperature controller 203 automatically controls the opening of the feedwater bypass valve 103 based on the set value (127℃~140℃) and the measured value of the flue gas cooler outlet temperature. When the actual exhaust gas temperature is higher than the feedback value, the opening of the feedwater bypass valve 103 is reduced. That is, if the flue gas cooler outlet temperature exceeds the preset flue gas temperature, the opening of the feedwater bypass valve 103 is gradually reduced, increasing the feedwater flow rate into the air preheater 5 and the flue gas cooler 4, thereby lowering the flue gas cooler outlet temperature. When the actual exhaust gas temperature is lower than the feedback value, the opening of the feedwater bypass valve 103 is increased. That is, if the flue gas cooler outlet temperature is lower than the preset flue gas temperature, the opening of the feedwater bypass valve 103 is gradually increased, decreasing the feedwater flow rate into the air preheater 5 and the flue gas cooler 4, thereby increasing the flue gas cooler outlet temperature.

[0085] The flue gas temperature controller 203 continuously controls the flow rate of feedwater entering the air preheater 5 and the flue gas cooler 4 by adjusting the opening of the feedwater bypass valve 103. When using biomass fuels of different types, calorific values, and moisture content, the flue gas temperature controller 203 outputs an accurate valve opening degree required by the boiler load and fuel quantity based on the "total temperature deviation," maintaining a stable boiler flue gas emission temperature and ensuring that the measured flue gas temperature at the boiler's flue gas cooler outlet matches the set value. Simultaneously, it maintains the inlet water temperature of the flue gas cooler at no less than 90℃, ultimately achieving the purpose of automatically adjusting the flue gas temperature at the flue gas cooler outlet.

[0086] This invention solves the problem of flue gas temperature control in biomass boilers failing to automatically adjust to changes in boiler load and fuel. It also addresses the issues of slow flue gas temperature adjustment and inability to follow the setpoint. Furthermore, it reduces low-temperature corrosion on the tail-end heating surfaces, prevents slagging and ash accumulation in the air preheater and flue gas cooler, minimizes flue gas losses, and ensures boiler efficiency. This invention is of great significance for rationally controlling the flue gas temperature of biomass boilers, reducing excessive biomass fuel consumption, developing and utilizing biomass energy, reducing carbon dioxide emissions, and achieving the "dual carbon target."

[0087] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for controlling flue gas temperature in a biomass boiler, characterized in that, The flue gas temperature control method is a control method based on a flue gas temperature control system. The flue gas temperature control system includes an economizer, a flue gas cooler, and an air preheater. The flue gas cooler is located inside the boiler's flue. The boiler's feedwater system outlet is connected to the hot section inlet of the air preheater, and the hot section outlet of the air preheater is connected to the cold section inlet of the flue gas cooler. The control method includes: Based on the deviation between the measured value of the flue gas temperature at the outlet of the flue gas cooler and the set value of the flue gas temperature at the outlet of the flue gas cooler, the water flow rate entering the flue gas cooler and the air preheater is adjusted. If the measured value of the flue gas temperature at the outlet of the flue gas cooler is greater than the set value of the flue gas temperature at the outlet of the flue gas cooler, the water flow rate is increased; if the measured value of the flue gas temperature at the outlet of the flue gas cooler is less than the set value of the flue gas temperature at the outlet of the flue gas cooler, the water flow rate is decreased. Based on the deviation between the actual boiler load and the set boiler load, the feedwater flow rate into the flue gas cooler and the air preheater is adjusted. If the actual boiler load is greater than the set boiler load, the feedwater flow rate is increased; if the actual boiler load is less than the set boiler load, the feedwater flow rate is decreased. The flue gas temperature control system further includes an economizer and a feedwater bypass valve. The boiler feedwater system outlet is connected to the economizer inlet via a feedwater bypass. The feedwater bypass valve is located on the feedwater bypass. The control method includes: The flow rate of the water supply bypass is adjusted by regulating the opening degree of the water supply bypass valve, thereby regulating the water supply flow rate entering the flue gas cooler and the air preheater; The control system includes a flue gas temperature transmitter at the outlet of the flue gas cooler, a flue gas temperature controller at the outlet of the flue gas cooler, and a feedforward controller for the exhaust gas temperature. The control method includes: The flue gas cooler outlet temperature controller compares the flue gas cooler outlet temperature measured by the flue gas cooler outlet temperature transmitter with the flue gas cooler outlet temperature setpoint to generate a flue gas cooler outlet temperature deviation signal. When the flue gas cooler outlet temperature measured is greater than the flue gas cooler outlet temperature setpoint, the flue gas cooler outlet temperature deviation is less than 0, and the flue gas cooler outlet temperature controller controls the water supply bypass valve to decrease. When the flue gas cooler outlet temperature measured is less than the flue gas cooler outlet temperature setpoint, the flue gas cooler outlet temperature deviation is greater than 0, and the flue gas cooler outlet temperature controller controls the water supply bypass valve to increase. The flue gas temperature feedforward controller generates a flue gas temperature change signal based on the deviation between the actual boiler load and the set boiler load, and inputs it to the flue gas cooler outlet temperature controller. When the actual boiler load is greater than the set boiler load and the flue gas temperature change is less than 0, the flue gas cooler outlet temperature controller controls the feedwater bypass valve to decrease. When the actual boiler load is less than the set boiler load and the flue gas temperature change is greater than 0, the flue gas cooler outlet temperature controller controls the feedwater bypass valve to increase.

2. The method for controlling flue gas temperature in a biomass boiler according to claim 1, characterized in that, Also includes: The flue gas cooler outlet temperature controller adds the flue gas temperature deviation at the flue gas cooler outlet to the change in exhaust gas temperature, and the sum of the two forms the total temperature deviation. The flue gas cooler outlet temperature controller outputs a control signal based on the total temperature deviation. When the total temperature deviation is greater than 0, the flue gas cooler outlet temperature controller controls the water supply bypass valve to increase its opening. When the total temperature deviation is less than 0, the flue gas cooler outlet temperature controller controls the water supply bypass valve to decrease its opening.

3. The method for controlling flue gas temperature in a biomass boiler according to claim 1 or 2, characterized in that, Also includes: The feedwater flow rate of the flue gas cooler is adjusted according to the deviation between the measured value of the air preheater outlet water temperature and the set value of the air preheater outlet water temperature. When the measured value of the air preheater outlet water temperature is less than the set value of the air preheater outlet temperature, the feedwater flow rate of the flue gas cooler is reduced. When the measured value of the air preheater outlet water temperature is greater than the set value of the air preheater outlet temperature, the feedwater flow rate of the flue gas cooler is increased.

4. The method for controlling flue gas temperature in a biomass boiler according to claim 3, characterized in that, The control system further includes bypass valves for the deaerator and the flue gas cooler. A flue gas cooler bypass is connected between the outlet of the hot section of the air preheater and the inlet of the deaerator. The flue gas cooler bypass valve is located on the flue gas cooler bypass. The control method includes: The flow rate of the flue gas cooler bypass is adjusted by regulating the opening degree of the bypass valve of the flue gas cooler, thereby regulating the feed water flow rate of the flue gas cooler. The control system further includes an air preheater outlet water temperature transmitter and an air preheater outlet water temperature controller, and the control method includes: The air preheater outlet water temperature controller compares the measured value of the air preheater outlet water temperature by the air preheater outlet water temperature transmitter with the set value of the air preheater outlet water temperature, and outputs a command to adjust the opening degree of the flue gas cooler bypass valve according to the deviation. When the measured value of the air preheater outlet water temperature is less than the set value of the air preheater outlet temperature, the air preheater outlet water temperature controller controls the flue gas cooler bypass valve to increase its opening. When the measured value of the air preheater outlet water temperature is greater than the set value of the air preheater outlet temperature, the air preheater outlet water temperature controller controls the flue gas cooler bypass valve to decrease its opening.

5. The method for controlling flue gas temperature in a biomass boiler according to claim 1, 2, or 4, characterized in that, An air preheater bypass is connected between the boiler feedwater system outlet and the flue gas cooler inlet, and the system further includes: Based on the deviation between the measured value of the flue gas cooler inlet water temperature and the set value of the flue gas cooler inlet water temperature, the feedwater flow rate of the air preheater bypass is adjusted. When the measured value of the flue gas cooler inlet water temperature is less than the set value of the flue gas cooler inlet water temperature, the feedwater flow rate of the air preheater bypass is increased to increase the feedwater temperature at the flue gas cooler inlet. When the measured value of the flue gas cooler inlet water temperature is greater than the set value of the flue gas cooler inlet water temperature, the feedwater flow rate of the air preheater bypass is decreased to reduce the feedwater temperature at the flue gas cooler inlet. The control system further includes an air preheater bypass valve, which is located on the air preheater bypass. The control method includes: The flow rate of the air preheater bypass is adjusted by regulating the opening degree of the air preheater bypass valve, thereby regulating the feedwater temperature at the inlet of the flue gas cooler. The control system further includes a flue gas cooler inlet water temperature controller and a flue gas cooler inlet water temperature transmitter, and the control method includes: The flue gas cooler inlet water temperature controller compares the flue gas cooler inlet water temperature measured by the flue gas cooler inlet water temperature transmitter with the flue gas cooler inlet water temperature setpoint, and adjusts the opening of the air preheater bypass valve according to the deviation. When the measured value of the flue gas cooler inlet water temperature is less than the set value of the flue gas cooler inlet water temperature, the flue gas cooler inlet water temperature controller controls the air preheater bypass valve to increase its opening. When the measured value of the flue gas cooler inlet water temperature is greater than the set value of the flue gas cooler inlet water temperature, the flue gas cooler inlet water temperature controller controls the air preheater bypass valve to decrease its opening.

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