Low-temperature economizer water inlet manifold coordinated control method
By establishing a coordinated control method for the inlet water header of the low-temperature economizer, the problem of uneven condensate distribution under the traditional control method was solved, and the boiler flue gas temperature was stably reduced and the operating efficiency was improved. This method is applicable to the operation of multiple gas boiler headers.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANGHAI MEISHAN IRON & STEEL CO LTD
- Filing Date
- 2021-10-13
- Publication Date
- 2026-07-31
AI Technical Summary
Traditional control methods cannot effectively match condensate distribution when multiple gas boilers are operating under a main control pipe, resulting in large variations in boiler flue gas temperature and failing to minimize flue gas heat loss.
Establish a baseline condensate flow rate prediction model for multiple low-temperature economizers. Through flue gas temperature regulators and flow distribution adjustment mechanisms, achieve automatic condensate distribution and regulation to ensure the stability and efficiency of flue gas temperature for each boiler.
It has achieved a stable reduction in the flue gas temperature of each boiler, improved boiler operating efficiency and economy, and can cope with the impact of gas pressure fluctuations, ensuring the matching of condensate distribution.
Smart Images
Figure CN115962461B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a control method, specifically a coordinated control method for the inlet water header of a cryogenic economizer, belonging to the field of cryogenic economizer control technology. Background Technology
[0002] Currently, flue gas heat loss accounts for the largest proportion of all heat losses in boiler operation, and flue gas temperature is the main indicator parameter for flue gas heat loss. When the flue gas temperature increases, the flue gas heat loss also increases, and the flue gas temperature in most thermal power plants is higher than the design value. Furthermore, as the boiler ages, the heat exchange performance of equipment such as the air preheater decreases, and the flue gas temperature tends to rise year by year. Properly configuring a low-temperature economizer can utilize waste heat from the flue gas to heat the condensate, further reducing the flue gas temperature, improving boiler operating efficiency, and achieving the goal of energy conservation and emission reduction.
[0003] For main-pipe gas boiler units, a cascaded waste heat recovery method can be adopted to minimize the flue gas temperature of each boiler. The first stage uses gas-to-gas heat exchange, employing a gas heater to heat the gas medium, reducing the boiler flue gas temperature from 170℃ to 145℃. The second stage uses gas-to-water heat exchange, using a low-temperature economizer to heat the cold source medium, further reducing the flue gas temperature from 145℃ to 115℃. The cold source medium here is mainly condensate from various processes, stored in a condensate pool. The condensate is distributed to each economizer via a condensate header for heat exchange.
[0004] In order to reduce the flue gas temperature of each gas boiler to 115℃, traditional control methods such as Figure 1 The diagram illustrates a single-loop control method, where the difference between the setpoint and actual flue gas temperature of a single gas boiler is sent to the flue gas temperature regulator, which calculates the opening command for the condensate feedwater regulating valve. However, during normal operation, gas boilers experience frequent and significant fluctuations in gas pressure, requiring frequent adjustments to the boiler's evaporation rate, resulting in large variations in flue gas temperature. Furthermore, for mainline boiler units, the economizers of each boiler are located at different points on the feedwater mainline, leading to inconsistent responses of the economizer outlet flue gas temperature to condensate flow. This results in ineffective matching of condensate distribution among boilers with their respective boiler conditions. Therefore, the traditional control method performs poorly in multi-gas boiler mainline operation scenarios. To further reduce flue gas temperature in mainline gas boilers, it is necessary to comprehensively consider issues such as frequent and significant gas pressure changes and inconsistent responses of the economizer outlet flue gas temperature to condensate flow. Optimal condensate distribution to each low-temperature economizer is crucial to maximize the reduction of flue gas temperature and minimize flue gas heat loss for each gas boiler. Summary of the Invention
[0005] This invention addresses the problems existing in the prior art by providing a coordinated control method for the inlet water header of a low-temperature economizer. This technical solution establishes a baseline condensate flow rate prediction model for multiple low-temperature economizers, enabling automatic distribution of condensate to each low-temperature economizer, minimizing the exhaust gas temperature of each gas boiler, and improving the automation level of exhaust gas temperature control and the economic efficiency of unit operation.
[0006] To achieve the above objectives, the technical solution of the present invention is as follows: a coordinated control method for the inlet water header of a low-temperature economizer, characterized in that the method includes the following steps:
[0007] Step 1: Conduct characteristic tests on the three parameters of the feedwater regulating valves involved in the regulation: opening degree, feedwater flow rate, and outlet pressure. The specific process is as follows: Under the premise of meeting safe production requirements, record the corresponding values of feedwater flow rate and outlet pressure at different opening degrees of the feedwater regulating valves, and analyze the safe operating range of each feedwater regulating valve. Conduct characteristic tests on the outlet flue gas temperature of the low-temperature economizers involved in the regulation. The specific process is as follows: Adjust the opening degree of the feedwater regulating valves, record the outlet flue gas temperature of each low-temperature economizer at different condensate flow rates, and analyze the response characteristics of the outlet flue gas temperature of each low-temperature economizer to the condensate flow rate.
[0008] Step 2: The flue gas temperature regulator receives the deviation between the average outlet flue gas temperature of each low-temperature economizer and the setpoint outlet flue gas temperature, as well as the average evaporation rate of the boilers involved in the regulation, and obtains the reference flow rate of condensate required for the low-temperature economizer to reduce the exhaust gas temperature. The condensate will be allocated to the low-temperature economizer with the highest priority. Only after the low-temperature economizer's water supply is met will it be supplied to other users.
[0009] Step 3: Based on the deviation between the actual outlet flue gas temperature of the current low-temperature economizer and the set outlet flue gas temperature, calculate the condensate flow rate required by the current low-temperature economizer to reduce the flue gas temperature.
[0010] Step 4: Establish a flow distribution and adjustment mechanism. Based on the ratio of the condensate demand flow rate to the baseline flow rate, and after manual correction and limitation, generate the required condensate flow rate distribution coefficient for each low-temperature economizer, specifically as follows: Figure 3As shown, the initial current low-temperature economizer flow distribution coefficient is obtained by comparing the condensate demand flow rate with the reference flow rate. A manual correction interface is introduced to allow operators to intervene according to actual needs during operation. The ratio of the demand flow rate to the reference flow rate plus the manual correction value yields a further current low-temperature economizer flow distribution coefficient. The upper and lower limits of the actual flue gas temperature of the current low-temperature economizer are introduced as interlocking conditions for the distribution coefficient. When the actual outlet flue gas temperature reaches the upper limit, the distribution coefficient is decreased; when the actual outlet flue gas temperature reaches the lower limit, the distribution coefficient is increased. After the interlocking conditions are applied, the final current low-temperature economizer flow distribution coefficient is obtained. Step 5: The reference flow rate after distribution coefficient correction is used as the setpoint of the flow regulator, and the actual feedwater flow rate of the current low-temperature economizer is used as the measured value. The flow regulator receives the deviation between the setpoint and the measured value. Under the combined action of proportional, integral, derivative, and feedforward, the adjustment command of the current feedwater regulating valve is calculated. The calculation method is as follows:
[0011] OP(n)=Kp(e(t)+(∫e(t)) / Ti+Td*(e(t) / dt)+FF(n)
[0012] Where: Kp is the proportional action coefficient; Ti is the integral time; Td is the derivative time; FF(n) is the feedforward action; and e(t) is the deviation. This control command also needs to be subject to the upper and lower limits of the safe operating range analyzed in step one, and the command for the water supply regulating valve is obtained after passing through these limits.
[0013] Compared with existing technologies, this invention has the following advantages: 1) This invention achieves automatic adjustment of the flue gas temperature at the outlet of each low-temperature economizer in a coal gas boiler unit through coordinated control of the low-temperature economizer inlet header, effectively reducing the exhaust gas temperature of each boiler and improving the boiler's operating efficiency and economy; 2) This invention proposes a model for predicting the baseline condensate flow rate demand of a single low-temperature economizer. The model calculates the estimated value of the baseline condensate flow rate demand of a single low-temperature economizer by using the average flue gas temperature at the outlet of multiple low-temperature economizers, and incorporates the evaporation rate of the boilers participating in the header operation as feedforward. When the gas pressure fluctuates significantly, it can effectively overcome the disturbance to the boiler exhaust gas temperature caused by fluctuations in boiler evaporation rate with gas pressure, and promptly adjust the required condensate flow rate of the low-temperature economizer to ensure the stability of the boiler exhaust gas temperature; 3) This invention establishes a flow distribution adjustment mechanism. The condensate flow rate demand is calculated by converting the deviation between the actual flue gas temperature at the outlet of a single low-temperature economizer and the expected value. The ratio of the demand flow rate to the baseline flow rate is processed by a manual correction interface and interlocking conditions to form a distribution coefficient. This can effectively overcome the problem that the distribution of condensate in each boiler and the boiler conditions of each boiler cannot be effectively matched due to the inconsistent response of the flue gas temperature at the outlet of each low-temperature economizer to the amount of condensate. Attached Figure Description
[0014] Figure 1Schematic diagram of traditional flue gas temperature control principle;
[0015] Figure 2 Schematic diagram of coordinated control principle of the inlet water header of the low-temperature economizer;
[0016] Figure 3 : Schematic diagram of the distribution coefficient principle of the flow distribution adjustment mechanism;
[0017] Figure 4 Schematic diagram of the inlet header of the low-temperature economizer. Detailed implementation method:
[0018] To enhance understanding of the present invention, the embodiments will be described in detail below with reference to the accompanying drawings.
[0019] Example 1: A method for coordinated control of the inlet water header of a low-temperature economizer, the method comprising the following steps:
[0020] Step 1, such as Figure 2 As shown, characteristic tests were conducted on three parameters of the feedwater regulating valve involved in the regulation: opening degree, feedwater flow rate, and outlet pressure. The specific process was as follows: under the premise of meeting safe production requirements, the corresponding values of feedwater flow rate and outlet pressure under different opening degrees of the feedwater regulating valve were recorded, and the safe operating range of each feedwater regulating valve was analyzed. Characteristic tests were also conducted on the outlet flue gas temperature of the low-temperature economizer involved in the regulation. The specific process was as follows: the opening degree of the feedwater regulating valve was adjusted, and the outlet flue gas temperature of each low-temperature economizer under different condensate flow rates was recorded, and the response characteristics of the outlet flue gas temperature of each low-temperature economizer to the condensate flow rate were analyzed.
[0021] Step Two, as follows Figure 2 As shown, the flue gas temperature regulator receives the deviation between the average outlet flue gas temperature of each low-temperature economizer and the setpoint outlet flue gas temperature, as well as the average evaporation rate of the boilers involved in the regulation, to obtain the reference flow rate of condensate required for the low-temperature economizer to reduce the exhaust gas temperature. Condensate is preferentially allocated to the low-temperature economizer, and only after the low-temperature economizer's feedwater needs are met is it supplied to other users; Step 3, as... Figure 3 As shown, based on the deviation between the actual outlet flue gas temperature of the current low-temperature economizer and the set outlet flue gas temperature, the required condensate flow rate for reducing the exhaust gas temperature of the current low-temperature economizer is calculated.
[0022] Step 4, as follows Figure 2 As shown, a flow distribution and adjustment mechanism is established. Based on the ratio of the condensate demand flow rate to the baseline flow rate, and after manual correction and limitation, the required condensate flow rate distribution coefficient for each low-temperature economizer is generated, specifically as follows: Figure 3As shown, the initial current low-temperature economizer flow allocation coefficient is obtained by comparing the condensate demand flow rate with the baseline flow rate. A manual correction interface is introduced, allowing operators to intervene based on actual needs during operation. The ratio of the demand flow rate to the baseline flow rate, plus the manual correction value, yields a further current low-temperature economizer flow allocation coefficient. Upper and lower limits of the actual flue gas temperature of the current low-temperature economizer are introduced as interlocking conditions for the allocation coefficient. When the actual outlet flue gas temperature reaches the upper limit, the allocation coefficient is decreased; when the actual outlet flue gas temperature reaches the lower limit, the allocation coefficient is increased. After these interlocking conditions are applied, the final current low-temperature economizer flow allocation coefficient is obtained. (More specific details are provided in the implementation case.)
[0023] Step 5, as follows Figure 2 As shown, the reference flow rate after correction by the distribution coefficient is used as the setpoint of the flow regulator, and the current actual feedwater flow rate of the low-temperature economizer is used as the measured value. The flow regulator receives the deviation between the setpoint and the measured value, and calculates the current feedwater regulating valve's regulation command under the combined action of proportional, integral, derivative, and feedforward functions. The calculation method is as follows:
[0024] OP(n)=Kp(e(t)+(∫e(t)) / Ti+Td*(e(t) / dt)+FF(n)
[0025] Where: Kp is the proportional gain coefficient; Ti is the integral time; Td is the derivative time; FF(n) is the feedforward effect; e(t) is the bias.
[0026] The adjustment command also needs to be subject to the upper and lower limits of the safe operating range obtained in step one, and the command of the water supply regulating valve is obtained after the limit value.
[0027] Specific embodiment: A coordinated control method for the inlet water header of a low-temperature economizer, the control method is as follows: Taking Meigang #2, #3, #5 and #6 boilers as examples, such as... Figure 4 As shown, each boiler is equipped with a low-temperature economizer and a feedwater regulating valve. The low-temperature economizers operate in parallel, and condensate from the condensate pool is transported to each low-temperature economizer through the inlet header for heat exchange.
[0028] Step 1: Conduct characteristic tests on parameters such as opening degree, feedwater flow rate, and outlet pressure of feedwater regulating valves #2, #3, #5, and #6. Open the feedwater regulating valves from their fully closed adjustment value and record the feedwater flow rate and outlet pressure values. Analyze the safe operating ranges of feedwater regulating valves #2, #3, #5, and #6 to be 20%-80%, 20%-80%, 25%-90%, and 25%-90%, respectively. Next, conduct characteristic tests on the outlet flue gas temperature of the low-temperature economizers #2, #3, #5, and #6. Adjust the opening degree of the feedwater regulating valves and record the outlet flue gas temperature of each low-temperature economizer under different condensate flow rates. Analyze the response characteristics of the outlet flue gas temperature of the low-temperature economizers #2, #3, #5, and #6 to condensate flow rates. The outlet flue gas temperatures of the low-temperature economizers #2 and #3 respond more rapidly to changes in desuperheating water flow rate, while the outlet flue gas temperatures of the low-temperature economizers #5 and #6 respond more slowly to changes in desuperheating water flow rate.
[0029] Step 2: Take the average flue gas temperature at the outlet of the #2, #3, #5, and #6 low-temperature economizers. The setpoint for the outlet flue gas temperature is manually set according to actual needs. The deviation between the average outlet flue gas temperature and the setpoint, as well as the average evaporation rate of boilers #2, #3, #5, and #6, are fed forward to the flue gas temperature regulator. According to the formula: OP(n)=Kp(e(t)+(∫e(t)) / Ti+Td*(e(t) / dt)+FF(n), the reference condensate flow rate required for the low-temperature economizer to reduce the flue gas temperature is calculated, where the proportionality coefficient Kp=1.3, the integral time Ti=95, and the derivative time Td=13.
[0030] Step 3: Based on the deviation between the actual outlet flue gas temperature of the #2 low-temperature economizer and the setpoint in Step 2, calculate the condensate flow rate required to reduce the flue gas temperature of the current low-temperature economizer. Similarly, obtain the condensate flow rate required to reduce the flue gas temperature of the #3, #5, and #6 low-temperature economizers respectively.
[0031] Step 4: Establish a flow distribution and adjustment mechanism. Based on the ratio of the condensate demand flow rate to the baseline flow rate, and after manual correction and limitation, generate the required condensate flow rate distribution coefficient for each low-temperature economizer. Specifically, obtain the initial flow distribution coefficient for the #2 low-temperature economizer by using the ratio of the condensate demand flow rate of the #2 low-temperature economizer to the baseline flow rate in Step 2. Introduce a manual correction interface for operators to intervene according to actual needs during operation. Considering that the outlet flue gas temperature of the #2 low-temperature economizer responds relatively quickly to changes in the desuperheating water flow rate as analyzed in Step 1, the flow distribution coefficient of the #2 low-temperature economizer can be gradually reduced through manual correction when adjusting the condensate flow rate of the #2 feedwater regulating valve until the outlet flue gas temperature of the #2 low-temperature economizer can be stably maintained at the set value. Conversely, when the outlet flue gas temperature of the low-temperature economizer responds relatively slowly to changes in the desuperheating water flow rate, the distribution coefficient needs to be gradually increased through manual correction. The manually corrected flow distribution coefficient for the #2 cryogenic economizer also needs to incorporate signals indicating that the actual flue gas temperature at the #2 economizer outlet reaches its upper and lower limits as interlocking conditions. When the actual flue gas temperature at the #2 economizer outlet reaches its upper limit, the interlocking factor decreases; when the actual flue gas temperature at the #2 economizer outlet reaches its lower limit, the interlocking factor increases. After these interlocking conditions are applied, the final flow distribution coefficient for the #2 cryogenic economizer is obtained. Similarly, the flow distribution coefficients for the #3, #5, and #6 cryogenic economizers are calculated.
[0032] Step 5: The reference flow rate, corrected by the flow distribution coefficient of the #2 low-temperature economizer, is used as the setpoint for the flow regulator of the #2 feedwater regulating valve, and the actual feedwater flow rate of the #2 low-temperature economizer is used as the measured value. The #2 feedwater regulating valve flow regulator receives the deviation between the setpoint and the measured value, calculates the regulation command for the #2 feedwater regulating valve, and the regulation command must also be subject to the upper and lower limits of the safe operating range analyzed in Step 1. After exceeding these limits, the command for the #2 feedwater regulating valve is obtained. Similarly, the commands for the #3, #5, and #6 feedwater regulating valves are calculated.
[0033] It should be noted that the above embodiments are not intended to limit the scope of protection of the present invention. Equivalent transformations or substitutions made based on the above technical solutions all fall within the scope of protection of the claims of the present invention.
Claims
1. A low-temperature economizer water inlet manifold coordination control method, characterized in that, The method includes the following steps: Step 1: Conduct characteristic tests on the three parameters of the feedwater regulating valves involved in the regulation: opening degree, feedwater flow rate, and outlet pressure. The specific process is as follows: Under the premise of meeting safe production requirements, record the corresponding values of feedwater flow rate and outlet pressure at different opening degrees of the feedwater regulating valves, and analyze the safe operating range of each feedwater regulating valve. Conduct characteristic tests on the outlet flue gas temperature of the low-temperature economizers involved in the regulation. The specific process is as follows: Adjust the opening degree of the feedwater regulating valves, record the outlet flue gas temperature of each low-temperature economizer at different condensate flow rates, and analyze the response characteristics of the outlet flue gas temperature of each low-temperature economizer to the condensate flow rate. Step 2: The flue gas temperature regulator receives the deviation between the average outlet flue gas temperature of each low-temperature economizer and the setpoint outlet flue gas temperature, as well as the average evaporation rate of the boilers involved in the regulation, and obtains the reference flow rate of condensate required for the low-temperature economizer to reduce the exhaust gas temperature. The condensate will be allocated to the low-temperature economizer with the highest priority. Only after the low-temperature economizer's water supply is met will it be supplied to other users. Step 3: Based on the deviation between the actual outlet flue gas temperature of the current low-temperature economizer and the set outlet flue gas temperature, calculate the condensate flow rate required by the current low-temperature economizer to reduce the flue gas temperature. Step 4: Establish a flow allocation and adjustment mechanism; Step 5: Use the baseline flow rate, after adjustment by the distribution coefficient, as the setpoint for the flow regulator; Step four, establishing a flow distribution adjustment mechanism, is as follows: Based on the ratio of condensate demand flow rate to the baseline flow rate, after manual correction and restriction, the required condensate flow rate distribution coefficient for each low-temperature economizer is generated. Specifically: the preliminary current low-temperature economizer flow rate distribution coefficient is obtained through the ratio of condensate demand flow rate to the baseline flow rate. A manual correction interface is introduced, allowing operators to intervene according to actual needs during operation. The ratio of demand flow rate to baseline flow rate plus the manual correction value yields a further current low-temperature economizer flow rate distribution coefficient. The upper and lower limits of the actual flue gas temperature of the current low-temperature economizer are introduced as the locking conditions for the distribution coefficient. When the actual outlet flue gas temperature reaches the upper limit, the distribution coefficient is locked down; when the actual outlet flue gas temperature reaches the lower limit, the distribution coefficient is locked up. After the locking conditions are restricted, the final current low-temperature economizer flow rate distribution coefficient is obtained. Step 5: Use the reference flow rate corrected by the distribution coefficient as the setpoint of the flow regulator, and the current actual feedwater flow rate of the low-temperature economizer as the measured value. The flow regulator receives the deviation between the setpoint and the measured value, and calculates the current feedwater regulating valve's regulation command under the combined action of proportional, integral, derivative, and feedforward functions. The calculation method is as follows: OP(n)=Kp(e(t)+(∫e(t)) / Ti +Td*(e(t) / dt)+FF(n) Where: Kp is the proportional gain; Ti is the integral time; Td is the derivative time; FF(n) is the feedforward action; e(t) is the bias. The adjustment command also needs to be subject to the upper and lower limits of the safe operating range obtained in step one, and the command of the water supply regulating valve is obtained after the limit value.