Limestone Powder Continuous Pulping Device and Control Method

Abstract

The present invention relates to a device and method for continuously preparing limestone slurry. The device includes a limestone powder silo, an impeller feeder, a weighing screw conveyor, and a limestone slurry tank, which are arranged in sequence from top to bottom. A liquid level gauge is provided on the limestone slurry tank, and a water supply pipe is provided at the top. A flow meter and a regulating valve are provided on the water supply pipe. The device further includes a hot fluidization air pipeline, one end of which is connected to a fluidization blower and the other end is communicated with the feed inlet of the impeller feeder. An electromagnetic valve is provided on the hot fluidization air pipeline. The device also includes a local PLC control cabinet, which is respectively signal-connected to the impeller feeder, the weighing screw conveyor, the liquid level gauge, the flow meter, the regulating valve, and the electromagnetic valve. The local PLC control cabinet is internally provided with a control program for the limestone powder continuous slurry preparation device. The present invention can improve the accuracy of limestone powder feeding measurement, avoid the problem of material blockage during the feeding process, improve the automatic control and rapid response ability of the limestone powder slurry preparation system, and reduce the manual workload.

Description

Technical Field

[0001] The present invention relates to the technical field of limestone-gypsum wet flue gas desulfurization, and particularly relates to a continuous limestone powder pulping device and a control method thereof. Background Art

[0002] The limestone-gypsum wet flue gas desulfurization technology is the most widely used technology in China at present. Limestone powder pulping is a common pulping method in the limestone-gypsum wet flue gas desulfurization system. In the existing limestone powder pulping operations, there are problems such as inaccurate metering of limestone powder, inability to count the actual limestone consumption of the desulfurization system, poor automatic control ability, usually adopting an intermittent operation mode, and consuming a large amount of manual monitoring.

[0003] In a conventional limestone powder pulping system, a vane feeder or a weighing screw conveyor is provided in the feeding pipeline to convey and meter the limestone powder; the feeding amount of the limestone powder and the mass flow rate of SO2 in the flue gas are adjusted in an open loop; the makeup water amount for limestone powder pulping and the density of the limestone slurry are adjusted in a closed loop. This conventional limestone powder pulping system has the following problems: First, when using only a vane feeder for feeding, due to the voids of the limestone powder, there is a problem of inaccurate metering of the limestone powder feeding. And because the pipeline at the inlet of the vane feeder is designed according to the maximum feeding amount, when the vane feeder operates at a low load at the inlet, it is easy to block the material, causing the vane feeder to trip due to overcurrent. Second, when using only a weighing screw conveyor for feeding, the feeding amount at its inlet pipe is greater than the conveying amount of the weighing screw conveyor, resulting in a problem of material blockage. Third, the feeding amount of the limestone powder is only interlocked with the mass flow rate of SO2 in the flue gas. When the liquid level of the limestone slurry tank becomes too high or too low due to changes in the slurry supply amount, manual intervention is required for adjustment. Fourth, the makeup water amount for limestone powder pulping and the density of the limestone slurry are adjusted by a post-feedback closed loop, lacking a feed-forward control of the limestone powder feeding amount, resulting in a problem of lag in the adjustment of the limestone slurry density and causing a large fluctuation range of the limestone slurry density. Fifth, the degree of automatic interlock control is low, requiring manual monitoring, increasing the manual workload, and the control accuracy does not meet the system requirements.

[0004] In a Chinese patent with a publication date of June 2, 2020 and a publication number of CN111217106A, a vane feeder control system is disclosed, which includes a PLC control unit and a frequency converter connected thereto, and also includes a motor connected to the frequency converter and a vane feeder driven by the motor. This patent can very well solve the problem of the stability of material feeding, and can effectively avoid the problem of the production stop caused by the increase in the torque of the vane feeder frequency converter or even overload when the powder is seriously accumulated. However, there is also a problem of blockage of the vane feeder caused by excessive feeding of limestone powder in this patent.

[0005] In a Chinese patent with a publication date of April 24, 2018 and a publication number of CN207266826U, a slurry system for limestone powder pulping is disclosed, which solves problems such as large fineness of the powder ground by the mill in the limestone pulping system, high equipment energy consumption, high failure rate, and long startup time. The slurry system includes a limestone powder silo, a fluidizing fan, a limestone powder feeder, a limestone powder slurry tank, a stirrer for the limestone powder slurry tank, a slurry supply pump, and an absorption tower. The side of the limestone powder silo is connected to the fluidizing fan, the bottom of the limestone powder silo is connected to the limestone powder feeder, the discharge port of the limestone powder feeder is connected to the limestone powder slurry tank, and the slurry in the limestone slurry tank is transported to the absorption tower by the slurry supply pump. In this patent, using conventional control methods, it also has the problems existing in the conventional limestone powder pulping system. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a continuous limestone powder pulping device and a control method in view of the deficiencies existing in the above-mentioned prior art, which can improve the accuracy of limestone powder feeding measurement, avoid the problem of material blockage during the feeding process, improve the automatic control and rapid response ability of the limestone powder pulping system, and reduce the manual workload.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0008] A continuous limestone powder pulping device includes a limestone powder silo, an impeller feeder, a weighing screw conveyor, and a limestone slurry tank, which are arranged in sequence from top to bottom and are connected in series through a limestone powder discharge pipe; a liquid level gauge is provided on the limestone slurry tank, a water replenishing pipe is provided at the top of the limestone slurry tank, and a flow meter and a regulating valve are provided on the water replenishing pipe; the continuous limestone powder pulping device further includes a hot fluidizing air pipeline, one end of the hot fluidizing air pipeline is connected to the fluidizing fan and the other end is communicated with the feed inlet of the impeller feeder, and a solenoid valve is provided on the hot fluidizing air pipeline; the continuous limestone powder pulping device further includes a local PLC control cabinet, and the local PLC control cabinet is respectively signal-connected to the impeller feeder, the weighing screw conveyor, the liquid level gauge, the flow meter, the regulating valve, and the solenoid valve; the control program of the continuous limestone powder pulping device is built in the local PLC control cabinet.

[0009] In the above solution, the continuous limestone powder pulping device further includes a slurry supply return pipe, a slurry supply pump, and a density meter; both ends of the slurry supply return pipe are respectively communicated with the outlet of the slurry supply pump and the top of the limestone slurry tank; the inlet of the slurry supply pump is connected to the bottom of the limestone slurry tank; the density meter is arranged on the slurry supply return pipe, and the density meter is signal-connected to the local PLC control cabinet, and the density meter transmits the measurement signal to the local PLC control cabinet.

[0010] In the above solution, the limestone powder continuous pulping device further includes a DCS control system, and the DCS control system is communicatively connected to the on-site PLC control cabinet for bidirectional data transmission.

[0011] Correspondingly, the present invention also provides a control method for the above limestone powder continuous pulping device, including the following steps:

[0012] S1. Set the feed rate Q

[0013] Calculate the value of Q1 according to the SO2 mass flow rate W transmitted by the DCS to the on-site PLC control cabinet;

[0014] Input the liquid level H of the limestone slurry tank through the level gauge. If H is lower than H1, set Q = Q2. If H is higher than H2, set Q = Q1; The initial value of Q2 is set according to the 100% output of the impeller feeder and can be adjusted through the panel of the on-site PLC control cabinet;

[0015] During operation, after the feed rate Q is set to Q1 or Q2, it remains unchanged. The change of the Q set value is triggered by the following conditions:

[0016] The trigger condition for the feed rate Q to change from Q1 to Q2 is that the liquid level H of the limestone slurry tank is lower than H1;

[0017] The trigger condition for the feed rate Q to change from Q2 to Q1 is that the liquid level H of the limestone slurry tank is higher than H2;

[0018] S2. Adjust the rotation speed of the impeller feeder

[0019] Compare the measured actual feed rate Q output by the weighing screw conveyor s with the set feed rate Q. When the absolute value of the relative deviation Y is within the allowable error (such as 3%), the rotation speed of the impeller feeder remains unchanged; When the absolute value of the relative deviation Y exceeds the allowable error and is a positive deviation, reduce the rotation speed of the impeller feeder; When the absolute value of the relative deviation Y exceeds the allowable error and is a negative deviation, increase the rotation speed of the impeller feeder;

[0020] S3. Adjust the opening of the regulating valve

[0021] Take the measured actual feed rate Q of the weighing screw conveyor s at 60-second intervals. If there is no change between the two, the opening of the regulating valve remains unchanged; If there is a change between the two, recalculate the makeup water volume T, and compare the measured actual makeup water volume T output by the flow meter s with the calculated makeup water volume T. If T s > T, reduce the opening of the regulating valve. If T s < T, increase the opening of the regulating valve;

[0022] S4. Set the automatic control mode of the solenoid valve

[0023] Mode 1: When the feed rate changes and Q ≤ Qmin When it is in this state, the solenoid valve is in the normally open state;

[0024] Method 2: When the feeding amount changes and Q > Q min the solenoid valve automatically opens, closes after a delay of t1, and then opens again after a delay of t2, and this cycle is executed; where the sum of t1 and t2 is a purging period, and t1 < t2, Q min is set to 20% - 30% of the maximum feeding amount Q of the impeller feeder max of; t1, t2, and Q min can be adjusted through the panel of the local PLC control cabinet.

[0025] In the above method, the calculation formula for Q1 is:

[0026] Q1 = W ÷ M SO2 × M CaCO3 × C ÷ A × K1

[0027] In the formula, W is the mass flow rate of SO2; M SO2 is the molar mass of SO2, which is 64; M CaCO3 is the molar mass of CaCO3, which is 100; C is the calcium-sulfur ratio, set between 1.02 - 1.05; A is the purity of limestone, obtained through laboratory analysis; K1 is the correction factor, set between 0.5 - 1.5; the calcium-sulfur ratio C, the purity of limestone A, and the correction factor K1 can be adjusted through the panel of the local PLC control cabinet.

[0028] In the above method, H1 is set to 1 - 2m and can be adjusted through the panel of the local PLC control cabinet; H2 is set to 0.3m - 0.5m less than the overflow level of the limestone slurry tank and can be adjusted through the panel of the local PLC control cabinet.

[0029] In the above method, the sampling time interval of the local PLC control cabinet for the liquid level data of the liquid level gauge is set to 500ms - 5s.

[0030] In the above method, the calculation method of the relative deviation Y:

[0031]

[0032] In the formula, Q s is the measured actual feeding amount output by the weighing screw conveyor, Q is the set feeding amount, Q max is the maximum feeding amount of the impeller feeder, Q max = Q2.

[0033] In the above method, the sampling time interval of the local PLC control cabinet for the weighing data of the weighing screw conveyor is set to 5s - 10s.

[0034] In the above method, the calculation formula for the makeup water volume T is:

[0035] T = Q s ×K2×K3×K4

[0036] Wherein, Q s is the measured feed rate of the weighing screw conveyor; K2 is the water - powder ratio, set between 2.33 - 2.57, and can be adjusted through the panel of the local PLC control cabinet; K3 is the make - up water density adjustment coefficient, set according to the nature of the make - up water. The initial value is set to 1.0 according to process water. When using filtrate water, K3 is set between 1.0 - 1.05. The greater the make - up water density, the higher the K3 value, and it can be adjusted through the panel of the local PLC control cabinet; K4 is the density correction coefficient, and its calculation formula is:

[0037]

[0038] Wherein, P s is the density value measured by the densitometer; P is the set density value; the initial value of the density correction factor K5 is set between 0.8 - 1.2, and it can be adjusted through the panel of the local PLC control cabinet.

[0039] The beneficial effects of the present invention are as follows:

[0040] 1. For the limestone powder continuous pulping device of the present invention, an impeller feeder and a weighing screw conveyor are connected in series in the limestone powder down - feeding pipe. The two form a closed - loop control circuit for limestone powder feeding. The impeller feeder is responsible for adjusting the limestone powder feeding rate, and the weighing screw conveyor is responsible for weighing the limestone powder, combining the advantages of both, realizing the separation of feeding adjustment and weighing, and improving the metering accuracy of limestone powder feeding.

[0041] 2. For the limestone powder continuous pulping device of the present invention, a hot fluidizing air pipeline is connected to the feed inlet of the impeller feeder. When the impeller feeder operates at low load, hot fluidizing air is blown in through the solenoid valve to prevent blockage of the powder down - feeding pipe above the impeller feeder, reduce the powder feeding amount, and avoid over - current tripping of the impeller feeder caused by blockage.

[0042] 3. For the limestone powder continuous pulping device of the present invention, a make - up water pipe is provided for the limestone slurry tank. The make - up water amount can be double - adjusted through the forward feedback of the limestone powder feeding rate and the backward feedback of the limestone slurry density, shortening the reaction time of limestone density adjustment and preventing fluctuations in the limestone slurry density caused by adjustment lag.

[0043] 4. The present invention sets the limestone powder feeding rate through two parameters of the limestone slurry tank liquid level and the SO2 mass flow rate, preventing fluctuations in the limestone tank liquid level, improving the automatic operation ability of the system, and eliminating the need for manual intervention.

[0044] 5. The present invention can operate continuously at low load of the desulfurization system, reducing the workload of manual monitoring. Brief Description of the Drawings

[0045] The present invention will be further described below in conjunction with the drawings and embodiments. In the drawings:

[0046] Figure 1 is a schematic structural diagram of the limestone powder continuous pulping device of the present invention;

[0047] Figure 2 is a control flow chart of the limestone powder continuous pulping device of the present invention.

[0048] In the figure: 1, limestone powder bin; 2, limestone slurry tank; 3, limestone powder feeding pipe; 4, impeller feeder; 5, weighing screw conveyor; 6, top electric slide gate; 7, bottom electric slide gate; 8, upper flexible pipe; 9, lower flexible pipe; 10, liquid level gauge; 11, water supply pipe; 12, flow meter; 13, regulating valve; 14, density meter; 15, slurry supply pump; 16, slurry supply return pipe; 17, solenoid valve; 18, hot fluidization air pipeline; 19, local PLC control cabinet; 20, DCS control system. Detailed Embodiments

[0049] In order to have a clearer understanding of the technical features, objectives and effects of the present invention, the detailed embodiments of the present invention will now be described in detail with reference to the drawings.

[0050] As Figure 1 shown, a limestone powder continuous pulping device provided by an embodiment of the present invention includes a limestone powder bin 1, an impeller feeder 4, a weighing screw conveyor 5 and a limestone slurry tank 2 arranged in sequence from top to bottom, and the four are connected in series through a limestone powder feeding pipe 3. A liquid level gauge 10 is provided on the limestone slurry tank 2, a water supply pipe 11 is provided at the top of the limestone slurry tank 2, and a flow meter 12 and a regulating valve 13 are provided on the water supply pipe 11. The limestone powder continuous pulping device further includes a hot fluidization air pipeline 18, one end of the hot fluidization air pipeline 18 is connected to a fluidization blower and the other end is communicated with the feed inlet of the impeller feeder 4, and a solenoid valve 17 is provided on the hot fluidization air pipeline 18. The limestone powder continuous pulping device further includes a slurry supply return pipe 16, a slurry supply pump 15 and a density meter 14; both ends of the slurry supply return pipe 16 are respectively communicated with the outlet of the slurry supply pump 15 and the top of the limestone slurry tank 2, the inlet of the slurry supply pump 15 is connected to the bottom of the limestone slurry tank 2 (or arranged on the limestone slurry tank 2) to provide slurry for the density meter 14; the density meter 14 is arranged on the slurry supply return pipe 16.

[0051] The limestone powder continuous pulping device further includes a local PLC control cabinet 19 and a DCS control system 20. The local PLC control cabinet 19 is respectively connected to the impeller feeder 4, the weighing screw conveyor 5, the liquid level gauge 10, the flow meter 12, the regulating valve 13, the solenoid valve 17, and the density meter 14 through cables. Among them, the weighing screw conveyor 5, the liquid level gauge 10, the flow meter 12, and the density meter 14 transmit measurement signals to the local PLC control cabinet 19; the local PLC control cabinet 19 transmits control signals to the impeller feeder 4, the regulating valve 13, and the solenoid valve 17. The control program of the limestone powder continuous pulping device is pre-installed in the local PLC control cabinet 19, and various parameters are adjusted through the panel of the local PLC control cabinet 19. The limestone powder continuous pulping device further includes a DCS control system 20, and the DCS control system 20 is communicatively connected to the local PLC control cabinet 19 for bidirectional data transmission.

[0052] For further optimization, a top electric plug valve 6 is provided at the connection between the limestone powder feeding pipe 3 and the limestone powder silo 1. The impeller feeder 4 is arranged below the top electric plug valve 6. A hot fluidizing air pipeline 18 is connected between the impeller feeder 4 and the top electric plug valve 6. The weighing screw conveyor 5 is arranged below the impeller feeder 4; a bottom electric plug valve 7 is provided at the connection between the limestone powder feeding pipe 3 and the limestone slurry tank 2. By setting the electric plug valve, on the one hand, it is convenient to set automatic control during remote operation, and on the other hand, when the pulping system stops, the plug valve is closed to prevent the water vapor in the limestone slurry tank from entering the feeding pipe.

[0053] For further optimization, an upper flexible pipe 8 is provided at the feeding port of the weighing screw conveyor 5, and a lower flexible pipe 9 is provided at the discharging port of the weighing screw conveyor 5. Using a hard connection at the inlet and outlet of the weighing screw conveyor 5 will affect its measurement accuracy. In the present invention, the flexible connection is used. Firstly, it is convenient for on-site installation, and secondly, it does not affect the measurement accuracy of the weighing screw conveyor 5.

[0054] For further optimization, the weighing screw conveyor 5 is installed on the top of the limestone slurry tank 2 through a rigid support.

[0055] For further optimization, the flow meter 12 is installed before the regulating valve 13.

[0056] For further optimization, a stirrer is provided in the limestone slurry tank 2.

[0057] For further optimization, the impeller feeder 4 is a variable-frequency electric impeller feeder.

[0058] For further optimization, the weighing screw conveyor 5 is a fixed-frequency electric weighing screw conveyor.

[0059] For further optimization, the liquid level gauge 10 is a diaphragm pressure transmitter type liquid level gauge.

[0060] For further optimization, the density meter 14 is a mass flow density meter.

[0061] For further optimization, the flowmeter 12 is an electromagnetic flowmeter.

[0062] For further optimization, the regulating valve 13 is an electric ceramic regulating ball valve.

[0063] For further optimization, the solenoid valve 17 is a two-position five-way double-electric-control solenoid valve.

[0064] Correspondingly, the present invention also provides a control method for the above limestone powder continuous pulping device, including the following steps:

[0065] S1. Set the feed rate Q

[0066] Calculate the value of Q1 according to the SO2 mass flow rate W transmitted by the DCS control system 20 to the local PLC control cabinet 19. The calculation formula of Q1 is:

[0067] Q1 = W ÷ M SO2 × M CaCO3 × C ÷ A × K1

[0068] In the formula, W is the SO2 mass flow rate; M SO2 is the molar mass of SO2, which is 64; M CaCO3 is the molar mass of CaCO3, which is 100; C is the calcium-sulfur ratio, taking 1.03; A is the limestone purity, obtained through laboratory analysis; K1 is the correction coefficient, set between 0.5 - 1.5; the calcium-sulfur ratio C, the limestone purity A, and the correction coefficient K1 can be adjusted through the panel of the local PLC control cabinet 19.

[0069] Input the liquid level H of the limestone slurry tank 2 through the level gauge 10. If H is lower than H1, set Q = Q2; if H is higher than H2, set Q = Q1. H1 is set to 2m and can be adjusted through the panel of the local PLC control cabinet 19; H2 is set to the overflow liquid level of the limestone slurry tank 2 - 0.3m and can be adjusted through the panel of the local PLC control cabinet 19. The initial value of Q2 is set according to the 100% output of the impeller feeder 4 and can be adjusted through the panel of the local PLC control cabinet 19.

[0070] During operation, after the feed rate Q is set to Q1 or Q2, it remains unchanged. The change of the Q set value is triggered by the following conditions:

[0071] The trigger condition for the feed rate Q to change from Q1 to Q2 is: the liquid level H of the limestone slurry tank 2 is lower than H1;

[0072] The trigger condition for the feed rate Q to change from Q2 to Q1 is: the liquid level H of the limestone slurry tank 2 is higher than H2.

[0073] Preferably, the sampling time interval of the local PLC control cabinet 19 for the liquid level data of the liquid level gauge 10 is set to 500 ms - 5 s.

[0074] S2. Adjust the rotation speed of the impeller feeder 4

[0075] Compare the measured feed rate Q output by the weighing screw conveyor 5 s with the set feed rate Q. When the absolute value of the relative deviation Y is within the allowable range of 3%, the rotation speed of the impeller feeder 4 remains unchanged; when the absolute value of the relative deviation Y exceeds 3% and is a positive deviation, reduce the rotation speed of the impeller feeder 4; when the absolute value of the relative deviation Y exceeds 3% and is a negative deviation, increase the rotation speed of the impeller feeder 4.

[0076] Calculation method of relative deviation Y:

[0077]

[0078] In the formula, Q s is the measured feed rate output by the weighing screw conveyor 5, Q is the set feed rate, Q max is the maximum feed rate of the impeller feeder 4, Q max = Q2.

[0079] Preferably, the sampling time interval of the local PLC control cabinet 19 for the weighing data of the weighing screw conveyor 5 is set to 5 s - 10 s.

[0080] S3. Adjust the opening of the regulating valve 13

[0081] Take the measured feed rate Q of the weighing screw conveyor 5 s at 60 - second interval values. If there is no change between the two, the opening of the regulating valve 13 remains unchanged; if there is a change between the two, recalculate the makeup water volume T, and compare the measured makeup water volume T output by the flow meter 12 s with the calculated makeup water volume T. If T s > T, reduce the opening of the regulating valve 13; if T s < T, increase the opening of the regulating valve 13.

[0082] The calculation formula for the makeup water volume T is:

[0083] T = Q s × K2 × K3 × K4

[0084] In the formula, Q s$Q_0$ is the measured feed rate of the weighing screw conveyor 5; $K_2$ is the water-powder ratio, which is set between 2.33 - 2.57 and can be adjusted through the panel of the local PLC control cabinet 19; $K_3$ is the make-up water density adjustment coefficient, which is set according to the nature of the make-up water. The initial value is set to 1.0 for process water. When using filtrate water, $K_3$ is set between 1.0 - 1.05. The greater the make-up water density, the higher the value of $K_3$, and it can be adjusted through the panel of the local PLC control cabinet 19; $K_4$ is the density correction coefficient, and its calculation formula is:

[0085]

[0086] In the formula, $P$ s is the density value measured by the densitometer 14; $P_0$ is the set density value, and $P_0$ is set to 1200; the initial value of the density correction factor $K_5$ is set between 0.8 - 1.2 and can be adjusted through the panel of the local PLC control cabinet 19.

[0087] S4. Set the automatic control mode of the solenoid valve 17

[0088] Mode 1: When the feed rate changes and $Q\leq Q_1$ min , the solenoid valve 17 is in the normally open state;

[0089] Mode 2: When the feed rate changes and $Q > Q_1$ min , the solenoid valve 17 automatically opens, closes after a delay of $t_1$, and then opens again after a delay of $t_2$, and this is executed in a loop; where the sum of $t_1$ and $t_2$ is a purge cycle, and $t_1 < t_2$. $Q_1$ min is set to 20% - 30% of the maximum feed rate $Q_{max}$ of the impeller feeder 4. $t_1$, $t_2$ and $Q_1$ max can be adjusted through the panel of the local PLC control cabinet 19. min

[0090] Furthermore, the protection trigger conditions of the limestone powder continuous pulping device are as follows: the material level in the limestone powder silo 1 is less than the set value (such as 2 - 5 m), or the liquid level $H$ in the limestone slurry tank 2 is greater than the overflow level, or the device malfunctions. After the protection condition is triggered, the following operations are performed: 1) Close the regulating valve 13; 2) Stop the impeller feeder 4 and delay for 10 seconds; 3) Stop the weighing screw conveyor 5.

[0091] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. For the same or similar parts among the embodiments, reference can be made to each other.

[0092] The embodiments of the present invention have been described above in conjunction with the accompanying drawings. However, the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative rather than restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms without departing from the spirit of the present invention and the scope protected by the claims. All of these are within the protection scope of the present invention.

Claims

1. Control method for a continuous limestone powder pulping device. The continuous limestone powder pulping device includes a limestone powder bin, an impeller feeder, a weighing screw conveyor, and a limestone slurry tank that are arranged in sequence from top to bottom and are connected in series through a limestone powder feeding pipe. A liquid level gauge is provided on the limestone slurry tank, a water replenishing pipe is provided at the top of the limestone slurry tank, and a flow meter and a regulating valve are provided on the water replenishing pipe. The continuous limestone powder pulping device also includes a hot fluidizing air pipeline. One end of the hot fluidizing air pipeline is connected to a fluidizing air blower, and the other end is communicated with the feeding port of the impeller feeder. An electromagnetic valve is provided on the hot fluidizing air pipeline. It is characterized in that the continuous limestone powder pulping device further includes a local PLC control cabinet, and the local PLC control cabinet is respectively signal-connected to the impeller feeder, the weighing screw conveyor, the liquid level gauge, the flow meter, the regulating valve, and the electromagnetic valve. The local PLC control cabinet is built-in with a control program for the continuous limestone powder pulping device. The control method includes the following steps: S1. Set the feeding amount Q Calculate the Q1 value according to the SO2 mass flow rate W transmitted from the DCS to the local PLC control cabinet. The calculation formula of Q1 is: Q1 = W ÷ M SO2 × M CaCO3 × C ÷ A × K1 Wherein, W is the mass flow rate of SO2; M SO2 is the molar mass of SO2, which is 64; M CaCO3 is the molar mass of CaCO3, which is 100; C is the calcium-sulfur ratio, set between 1.02 and 1.05; A is the purity of limestone, obtained through laboratory analysis; K1 is a correction factor, set between 0.5 and 1.5; the calcium-sulfur ratio C, the purity of limestone A, and the correction factor K1 can be adjusted through the panel of the on-site PLC control cabinet; Input the liquid level H of the limestone slurry tank through the liquid level gauge. If H is lower than H1, set Q = Q2. If H is higher than H2, set Q = Q1. H1 is set to 1 - 2m and can be adjusted through the panel of the local PLC control cabinet. H2 is set to the overflow liquid level of the limestone slurry tank minus 0.3m - 0.5m and can be adjusted through the panel of the local PLC control cabinet. The initial value of Q2 is set according to 100% output of the impeller feeder and can be adjusted through the panel of the local PLC control cabinet. During operation, after the feeding amount Q is set to Q1 or Q2, it remains unchanged. The change of the Q set value is triggered by the following conditions: The trigger condition for the feeding amount Q to change from Q1 to Q2 is that the liquid level H of the limestone slurry tank is lower than H1. The trigger condition for the feeding amount Q to change from Q2 to Q1 is that the liquid level H of the limestone slurry tank is higher than H2. S2. Adjust the rotation speed of the impeller feeder Compare the measured feed rate Q output by the weighing screw conveyor s with the set feed rate Q. When the absolute value of the relative deviation Y is within the allowable error range, the rotational speed of the impeller feeder remains unchanged; when the absolute value of the relative deviation Y exceeds the allowable error and is a positive deviation, the rotational speed of the impeller feeder is reduced; when the absolute value of the relative deviation Y exceeds the allowable error and is a negative deviation, the rotational speed of the impeller feeder is increased; S3. Adjust the opening degree of the regulating valve Obtain the measured feed rate Q of the weighing screw conveyor s At the 60-second interval value, if there is no change between the two, the opening of the regulating valve remains unchanged; if there is a change between the two, recalculate the makeup water volume T and compare the measured makeup water volume T output by the flowmeter s With the calculated makeup water volume T, if T s > T, reduce the opening of the regulating valve, if T s < T, increase the opening of the regulating valve; S4. Set the automatic control mode of the electromagnetic valve Method 1: When the feed rate changes and Q ≤ Q min , the solenoid valve is placed in the normally open state; Method 2: When the feeding rate changes and Q > Q min , the solenoid valve automatically opens, closes after a delay of t1, and then opens again after a delay of t2, and this cycle is executed; Among them, the sum of t1 and t2 is a purging cycle, and t1 < t2, Q min is set to 20%-30% of the maximum feeding amount Q of the impeller feeder max ; t1, t2, and Q min can be adjusted through the panel of the local PLC control cabinet.

2. The control method of the limestone powder continuous pulping device according to claim 1, characterized in that, The continuous limestone powder pulping device further includes a slurry supply return pipe, a slurry supply pump, and a density meter. Both ends of the slurry supply return pipe are respectively communicated with the outlet of the slurry supply pump and the top of the limestone slurry tank. The inlet of the slurry supply pump is connected to the bottom of the limestone slurry tank. The density meter is arranged on the slurry supply return pipe, and the density meter is signal-connected to the local PLC control cabinet. The density meter transmits the measurement signal to the local PLC control cabinet.

3. The control method of the limestone powder continuous pulping device according to claim 1, characterized in that, The continuous limestone powder pulping device further includes a DCS control system, and the DCS control system is communicatively connected with the local PLC control cabinet for two-way data transmission.

4. The control method of the limestone powder continuous pulping device according to claim 1, characterized in that The sampling time interval of the local PLC control cabinet for the liquid level data of the liquid level gauge is set to 500ms - 5s.

5. The control method of the limestone powder continuous pulping device according to claim 1, characterized in that, Calculation method of relative deviation Y: Where Q s is the measured actual feed rate output by the weighing screw conveyor, Q is the set feed rate, Q max is the maximum feed rate of the impeller feeder, Q max = Q2.

6. The control method of the limestone powder continuous pulping device according to claim 1, characterized in that, The sampling time interval of the local PLC control cabinet for the weighing data of the weighing screw conveyor is set to 5s - 10s.

7. The control method of the limestone powder continuous pulping device according to claim 1, characterized in that Calculation formula of the water replenishing amount T: T = Q s × K2 × K3 × K4 where Q s is the measured feed rate of the weighing screw conveyor; K2 is the water-to-powder ratio, set between 2.33 and 2.57, and can be adjusted through the panel of the local PLC control cabinet; K3 is the makeup water density adjustment coefficient, set according to the nature of the makeup water. The initial value is set to 1.0 for process water. When using filtrate water, K3 is set between 1.0 and 1.

05. The greater the makeup water density, the higher the K3 value, and it can be adjusted through the panel of the local PLC control cabinet; K4 is the density correction coefficient, and its calculation formula is: Wherein, P s is the density value measured by the densitometer; P is the set density value; the initial value of the density correction factor K5 is set between 0.8 and 1.2 and can be adjusted through the panel of the local PLC control cabinet.

Images