Wet desulphurization slurry supply control method for energy-saving thermal power peak shaving unit

Abstract

The invention discloses a wet desulphurization slurry supply control method for an energy-saving thermal power peak shaving unit. The method comprises the steps of slurry supply amount composition design, dynamic adjustment item calculation rule and slurry composition adaptive adjustment. According to the slurry supply amount composition design, key data such as unit load, SO2 concentration and pH value are collected in real time, and the total slurry supply flow is composed of theoretical slurry supply flow, pH deviation correction slurry supply flow, load change quick response slurry supply flow and SO2 concentration change quick response slurry supply flow. According to the dynamic adjustment item calculation rule, the slurry supply flow and the circulating pump flow are adjusted according to the unit load and SO2 change; the slurry component adapts, adjusts and controls the flow of a slurry supply pump and the start-stop time of a circulating pump, and dynamically adjusts the concentration of limestone slurry. According to the method, unit load and SO2 concentration change can be quickly responded, power consumption of a circulating pump and waste of an absorbent are reduced, the operation economy of a wet desulphurization system is remarkably improved, and the operation requirement of frequent load fluctuation of a thermal power peak regulation unit is met.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection technology and relates to a wet desulfurization slurry supply control method for energy-saving thermal power peak-shaving units. Background Technology

[0002] Limestone-gypsum wet desulfurization technology is currently the mainstream flue gas purification process in coal-fired power plants and is widely used in the power industry. In recent years, with the accelerated transformation of my country's energy structure, the functional positioning of thermal power units has gradually shifted from base load power supply to peak-shaving and flexible power supply, resulting in frequent fluctuations in their operating load. During the dynamic load adjustment process, the boiler combustion system needs to respond to the grid dispatch instructions in real time. However, due to the characteristics of the combustion equipment and system inertia, the oxygen and sulfur content in the flue gas at the boiler tail end also changes rapidly, causing significant fluctuations in the SO2 concentration (converted to baseline oxygen content) in the coal-fired flue gas entering the desulfurization system.

[0003] It is worth noting that changes in unit load not only cause increases or decreases in flue gas volume flow rate, but also lead to synchronous changes in SO2 concentration in flue gas. The two often exhibit the same trend of fluctuation, which significantly increases the difficulty of regulating the wet desulfurization system and places higher demands on the rapid response and stable control of the desulfurization unit.

[0004] Specifically, during rapid load increases in power units, operators often activate standby circulating pumps in advance to address the sharp rise in inlet SO2 concentration, enhancing desulfurization mass transfer capacity and preventing instantaneous SO2 exceedances at the outlet. This reflects that under traditional control methods, the dynamic adjustment capability of the desulfurization system is insufficient to match the desulfurization demands during rapid load increases. Conversely, during load reduction, although additional circulating pumps are not required, the failure of absorbent supply to decrease in tandem with the load reduction leads to excessive limestone slurry supply, resulting in absorbent waste and increased operating costs. To mitigate the risk of instantaneous SO2 exceedances at the outlet due to rapid load fluctuations, operators typically adopt a conservative control strategy, maintaining the outlet SO2 concentration at a low level below emission limits for extended periods. While this approach ensures environmental compliance, it results in continuous high-load operation of the slurry circulating pump, leading to high power consumption and low limestone absorbent utilization, severely restricting the peak-shaving economic efficiency of thermal power units.

[0005] Some new technologies in the industry propose automatic adaptive control schemes for wet desulfurization slurry. For example, patent CN119499841A uses a calculation method of "slurry supply = theoretical value + purity iterative correction + pH deviation correction + SO2 override compensation" to match the dynamic adjustment of slurry supply under load fluctuations. This technology can cope with the risk of SO2 exceeding the standard during load changes through SO2 override compensation, and has a certain peak-shaving adaptability. CN116272323A establishes a "slurry balance model" that calculates theoretical requirements in real time based on pH change curvature and slurry supply, adapting to wide load conditions. It also emphasizes the reset of slurry supply when switching the operation combination of circulating pumps. This technology can adjust the slurry supply through load change rate correlation, adapting to a wide load range of 20%-100%. Existing control methods are mostly based on fixed parameters or single feedback regulation, without setting separate independent adjustment items for "rapid response slurry flow rate to load changes" and "rapid response slurry flow rate to SO2 concentration changes". They are difficult to adapt to working conditions with rapid load changes and SO2 concentration fluctuations. Especially during load increases and decreases, the slurry supply does not match the actual demand, resulting in energy waste or emission risks.

[0006] In summary, existing wet desulfurization slurry supply control methods are ill-suited to the rapid load changes characteristic of thermal power units under deep peak-shaving conditions, and cannot achieve the optimal balance between economic efficiency and environmental protection in desulfurization systems. Therefore, developing an energy-saving control method that can respond in real time to changes in load and SO2 concentration and dynamically optimize the slurry supply strategy is of urgent practical significance for improving the economic efficiency and environmental coordination of peak-shaving operation of thermal power units. Summary of the Invention

[0007] The technical problem to be solved by this invention is that the existing wet desulfurization slurry supply control of thermal power peak-shaving units cannot respond quickly to changes in unit load and SO2 concentration, resulting in high power consumption of circulating pumps, unreasonable absorbent supply, and poor operating economy.

[0008] To achieve the above objectives, this invention proposes a wet desulfurization slurry supply control method for energy-saving thermal power peak-shaving units. The method includes the following steps: (1) slurry supply composition design; (2) dynamic adjustment item calculation rules; and (3) slurry composition adaptation adjustment.

[0009] The slurry supply design employs a composite calculation method of "basic item + dynamic adjustment item," specifically: Slurry supply flow rate = Theoretical slurry supply flow rate + pH deviation correction slurry supply flow rate + Load change rapid response slurry supply flow rate + SO2 concentration change rapid response slurry supply flow rate. The theoretical slurry supply flow rate is the basic slurry supply rate calculated based on the desulfurization system design parameters (such as inlet SO2 concentration, flue gas volume, and desulfurization efficiency requirements) to meet desulfurization needs under stable operating conditions. The pH deviation correction slurry supply flow rate is calculated based on the deviation between the actual pH value of the desulfurization tower slurry and the set pH value (5.0-5.6), used to correct the slurry's acidity / alkalinity deviation and ensure desulfurization reaction efficiency. The load change rapid response slurry supply flow rate is a dynamic adjustment item for unit load fluctuations, calculated based on the load change rate, SO2 deviation coefficient, and load factor to proactively adapt to the slurry supply demand caused by load changes. The SO2 concentration change rapid response slurry supply flow rate is a dynamic adjustment item for inlet SO2 concentration fluctuations, calculated based on the SO2 concentration change rate, load deviation coefficient, and SO2 concentration factor to match the slurry supply demand caused by SO2 concentration changes in real time.

[0010] The dynamic adjustment calculation rules include two modes: constant circulating pump operation combination and switching circulating pump operation combination. When the circulating pump operation combination remains constant, if the unit load change rate > 0, the rapid response slurry supply flow rate for load changes = unit load change rate × SO2 deviation coefficient × load increase factor; when the unit load change rate < 0, the rapid response slurry supply flow rate for load changes = unit load change rate × SO2 deviation coefficient × load decrease factor; if the SO2 concentration change rate > 0, the rapid response slurry supply flow rate for SO2 concentration changes = SO2 concentration change rate × load deviation coefficient × SO2 concentration increase factor; if the SO2 concentration change rate < 0, the rapid response slurry supply flow rate for SO2 concentration changes = SO2 concentration change rate × load deviation coefficient × SO2 concentration decrease factor. Wherein, the SO2 deviation coefficient is the ratio of the actual SO2 concentration to the design value, the load deviation coefficient is the ratio of the actual load to the rated load, and the load increase factor, load decrease factor, SO2 concentration increase factor, and SO2 concentration decrease factor are determined by fitting historical operating data from the field. When the circulating pump operation combination is switched, in order to ensure the stability of system control, the slurry supply flow rate for rapid response to load changes and the slurry supply flow rate for rapid response to SO2 concentration changes are set to zero.

[0011] The aforementioned slurry composition adaptation adjustment refers to the process where, when the unit load increases, the increased inlet SO2 concentration leads to a decrease in the slurry pH value. Therefore, it is necessary to increase the mass ratio of limestone powder in the limestone slurry to enhance the alkalinity of the slurry and ensure desulfurization efficiency. When the load decreases, the mass ratio of limestone powder is restored to reduce material consumption. Detailed Implementation

[0013] This invention relates to a method for controlling the slurry supply in wet desulfurization of thermal power peak-shaving units, the method comprising the following steps: 1. Data Acquisition and Preprocessing Real-time data collection of unit operation data, including unit load and load change rate, SO2 concentration and concentration change rate at the desulfurization inlet, pH value of desulfurization tower slurry, oxygen content in flue gas, SO2 concentration at the desulfurization outlet, and operating status of slurry circulation pumps, is used to convert the collected SO2 concentration into a concentration value under a 6% O2 benchmark as a basis for evaluating the desulfurization effect.

[0014] 2. Calculation and adjustment of slurry flow rate Theoretical slurry supply flow rate calculation: Based on the inlet SO2 concentration, flue gas volume and designed desulfurization efficiency under the 6% O2 benchmark, the theoretical slurry supply flow rate is calculated using the material balance formula.

[0015] pH deviation correction slurry flow rate calculation: If the actual pH value of the slurry is lower than the set value, increase the pH deviation correction slurry flow rate; if it is higher than the set value, reduce this flow rate to ensure that the pH value is stable in the range of 5.0-5.6.

[0016] Dynamic adjustment calculation: Based on the unit load change rate, SO2 concentration change rate and current circulating pump operating combination status, the rapid response slurry flow rate for load change and the rapid response slurry flow rate for SO2 concentration change are calculated according to the formula set in this invention.

[0017] Total slurry supply flow output: The above four flow rates are superimposed to obtain the final slurry supply flow rate, and the limestone slurry supply system is controlled to output according to this flow rate.

[0018] 3. Optimization of circulating pump operation combination When the unit increases load, it responds quickly to the adjustment of slurry flow rate according to the load change. If the outlet SO2 concentration can be stably controlled below the emission limit, the start-up time of the standby circulating pump is delayed. When the unit decreases load, if the slurry supply has been reduced and the outlet SO2 concentration is still below the limit, the redundant circulating pump is shut down in advance to reduce power consumption.

Claims

1. A method for controlling the slurry supply in wet desulfurization of an energy-saving thermal power peak-shaving unit, characterized in that, The slurry supply flow rate adopts a composite calculation method of "theoretical slurry supply flow rate + pH deviation correction slurry supply flow rate + load change rapid response slurry supply flow rate + SO2 concentration change rapid response slurry supply flow rate". Specifically, it includes: 1) Theoretical slurry supply flow rate is calculated based on the SO2 concentration at the desulfurization inlet, flue gas volume and design desulfurization efficiency under a 6% O2 benchmark; 2) pH deviation correction slurry supply flow rate is adjusted based on the deviation between the actual pH value of the desulfurization tower slurry and the set value (5.0-5.6); 3) Load change rapid response slurry supply flow rate is calculated based on the unit load change rate, SO2 deviation coefficient (actual SO2 value / design value) and load factor. This flow rate is 0 when the circulating pump operation combination is switched; 4) SO2 concentration change rapid response slurry supply flow rate is calculated based on the SO2 concentration change rate, load deviation coefficient and SO2 concentration factor. This flow rate is 0 when the circulating pump operation combination is switched.

2. The method according to claim 1, characterized in that, The baseline value for flue gas oxygen content is set at 6% O2. The SO2 concentration corresponding to the actual flue gas oxygen content under different loads is converted to the concentration value under the 6% O2 baseline, which serves as the basis for horizontal comparison of desulfurization effect.

3. The method according to claim 1, characterized in that, When the unit load increases, the mass ratio of limestone powder in the limestone slurry is increased to enhance the alkalinity of the slurry and ensure desulfurization efficiency; when the load decreases, the mass ratio of limestone powder is restored to reduce material consumption.

4. The method according to claim 1, characterized in that, When the unit load increases, if the outlet SO2 concentration can stably meet the standard, the start-up time of the standby slurry circulation pump is delayed; when the unit load decreases, if the outlet SO2 concentration is lower than the limit, the redundant circulation pump is shut down in advance.