A method for automatic control of salt discharge through online detection of solid-liquid ratio

Abstract

The present invention discloses a method for automatic control of salt discharge through online detection of solid-liquid ratio, which is characterized in that the real-time value of the solid-liquid ratio is obtained online and the regulating valve on the salt discharge pipeline is controlled to adjust the flow rate according to the solid-liquid ratio set value, so as to achieve stable control of the solid-liquid ratio in the tank. The solid-liquid ratio can be measured online, and the solid-liquid ratio is linked with the regulating valve of the salt discharge flow control loop, so that the solid-liquid ratio in the tank remains stable, solving the pain point of the solid-liquid ratio stability in the "five stability" of salt production.

Description

Technical Field

[0001] The invention belongs to the control technology in salt production, and specifically relates to a method for automatic control of salt discharge through online detection of solid-liquid ratio. Background Art

[0002] The solid-liquid ratio in the evaporation tank is an important control and assessment indicator for vacuum salt production. Once the solid-liquid ratio in the tank exceeds the specified range of the process, it is easy to break the system balance and affect the system production capacity and process stability. At present, the solid-liquid ratio is measured by manual sampling. By controlling the salt discharge flow rate, the solid-liquid ratio in the tank is stabilized. This control method has the disadvantages of strong subjectivity, untimely, large randomness, and discontinuity. It is difficult to adjust the process in time according to its changing trend. If the shift output is assessed, the bottom water phenomenon will also occur, which seriously affects the stability of the production system. To this end, the solid-liquid ratio is derived by measuring pressure or differential pressure, and the online detection of the solid-liquid ratio is indirectly realized to overcome the shortcomings of manual sampling detection. Summary of the invention

[0003] In view of the shortcomings of manual sampling and measurement of solid-liquid ratio in the existing technology, a method for automatic control of salt discharge through online detection of solid-liquid ratio is proposed. The solid-liquid ratio can be measured online and linked with the regulating valve to keep the solid-liquid ratio in the tank stable, solving the pain point of solid-liquid ratio stability among the "five stability" of salt production.

[0004] The technical solution adopted by the present invention is: a method for automatically controlling salt discharge through online detection of the solid-liquid ratio, obtaining the real-time value of the solid-liquid ratio online and controlling the regulating valve on the salt discharge pipeline to adjust the flow rate according to the solid-liquid ratio set value, thereby realizing stable control of the solid-liquid ratio in the tank.

[0005] Based on the above scheme, as a preferred method, two pressure collection points are set in the upper and lower directions of the tank or the lower circulation pipe to obtain the differential pressure, and the formula is:

[0006] A=(ΔP / Δh-11858) / 5507.6 (1)

[0007] The solid-liquid ratio is obtained, where A is the solid-liquid ratio, ΔP is the differential pressure, Δh is the height difference between the two pressure collection points, and Δh is a constant.

[0008] On the basis of the above scheme, as a preferred embodiment, the pressure collection points are the upper pressure port and the lower pressure port, and the upper pressure port and the lower pressure port are respectively installed with the upper pressure transmitter and the lower pressure transmitter. The signal data of the upper pressure transmitter and the lower pressure transmitter are transmitted to the DCS system to indirectly obtain the solid-liquid ratio through calculation.

[0009] Based on the above scheme, as a preferred method, according to the formula

[0010] ΔP=ρgΔh=((ρ1v1+ρ2(v0-v1)) / v0)*(gΔh)=(ρ1–ρ2)gΔh*A+ρ2gΔh (2)

[0011] Among them, ΔP is the differential pressure, ρ is the density, Δh is the height difference between the upper and lower pressure ports, v1 / v0=A is the solid-liquid ratio, v0 is the total volume, ρ1 is the density of the mixture of the solid and the liquid that penetrates it, v1 is the volume of the mixture of the solid and the liquid that penetrates it, ρ2 is the density of the liquid mixture, ρ1, ρ2, and g are all constants.

[0012] After the equipment is installed, Δh is fixed, and the solid-liquid ratio of the supersaturated salt solution is linearly related to ΔP. Taking Δh = 1M, we get

[0013] ΔP=(ρ1–ρ2)g*A+ρ2g (3)

[0014] The samples were taken at room temperature and tested immediately.

[0015] ρ1=1772g / L

[0016] ρ2=1210g / L

[0017] ΔP(Pa)=5507.6A+11858 (4)

[0018] By converting the measured pressure into the differential pressure with a height difference of 1M, the mathematical model for online measurement of the solid-liquid ratio is obtained:

[0019] A=(ΔP-11858) / 5507.6. (5)

[0020] On the basis of the above scheme, as a preferred embodiment, when the deviation between the real-time value of the solid-liquid ratio and the set value of the solid-liquid ratio is less than a preset deviation threshold, in the DCS system, the deviation between the real-time value of the solid-liquid ratio and the set value of the solid-liquid ratio is output through PID calculation as the flow setting value of the inner flow loop, and the deviation between the flow setting value and the real-time value of the flow of the salt discharge pipeline is subjected to PID calculation to adjust the regulating valve, and the adjustment process is: when the real-time value of the solid-liquid ratio is less than the set value of the solid-liquid ratio, the regulating valve is automatically adjusted down to reduce the output flow of the salt discharge pipeline; when the real-time value of the solid-liquid ratio is greater than the set value of the solid-liquid ratio, the regulating valve is automatically adjusted up to increase the output flow of the salt discharge pipeline;

[0021] When the deviation between the real-time value of the solid-liquid ratio and the set value of the solid-liquid ratio is greater than the preset deviation threshold, the cascade switch is disconnected, and the flow on the salt discharge pipeline is controlled by a single loop, and the regulating valve is controlled according to the detection result. The adjustment process is: when the real-time flow value is less than the set flow value, the regulating valve is automatically adjusted to increase the output flow of the salt discharge pipeline; when the real-time flow value is greater than the set flow value, the regulating valve is automatically adjusted to reduce the output flow of the salt discharge pipeline.

[0022] On the basis of the above scheme, as a preference, when the deviation between the real-time value of the solid-liquid ratio and the set value is less than the preset deviation threshold, in the process of automatically controlling the salt discharge according to the solid-liquid ratio, the patency of the salt discharge pipe is judged. If the real-time salt discharge flow rate is lower than the lower limit of the salt discharge flow rate set by the current programmed flushing, it means that the salt discharge pipe is blocked, and the regulating valve on the salt discharge pipe is closed, and the two flushing switch valves on both sides of the regulating valve are automatically opened to clean the salt discharge pipe. After the flushing is completed, if the salt discharge flow rate is higher than the set value of the programmed flushing, the original salt discharge automatic adjustment condition is restored without disturbance. If the detection result of the salt discharge flowmeter is still lower than the set value of the programmed flushing flow rate, the flushing cycle is repeated.

[0023] Based on the above scheme, it is preferably applied to the evaporation and salt removal process.

[0024] On the basis of the above scheme, as a preference, the evaporation tank includes a tank body and a salt leg, a salt discharge pipe, an upper circulation pipe, and a lower circulation pipe installed on the tank body. The upper circulation pipe and the lower circulation pipe are connected by a pump and a heating device, and the upper pressure port and the lower pressure port are arranged on the lower circulation pipe.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] Solve the five stable "solid-liquid ratio" pain points in salt production and realize automatic control of salt discharge through the solid-liquid ratio in the tank.

[0027] The timed manual measurement of solid-liquid ratio is cancelled, and cascade control is established based on the solid-liquid ratio control loop and the salt discharge flow control loop to stabilize production; when the solid-liquid ratio measurement is abnormal, the inner loop flow control can be switched without disturbance. By setting the minimum salt discharge flow, it is judged whether the salt discharge is normal, and the salt discharge pipe line is flushed automatically, which reduces the workload and labor load of operators.

[0028] The solid-liquid ratio in the tank is stable, avoiding large fluctuations in the solid-liquid ratio that lead to liquid level fluctuations and the generation of salt lumps; effectively avoiding blockage of the salt discharge pipe, reducing the frequency of blockage and energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of the evaporation tank of the present invention;

[0030] Figure 2 It is a schematic diagram of the cascade control of the present invention. DETAILED DESCRIPTION

[0031] The present invention will be further described below by taking an evaporator as a specific object as an example, but the scope of the present invention is not limited thereto, and can also be applied to general online measurement of the solid-liquid ratio of a suspension and control of the discharge amount according to the solid-liquid ratio.

[0032] Evaporation tank, reference Figure 1 It specifically includes a tank body 1 and a salt leg installed on the tank body, an upper circulation pipe 2, a lower circulation pipe 4, and a salt discharge pipeline 8. The upper circulation pipe and the lower circulation pipe are connected by a pump 3 and a heating device 12. The upper pressure port and the lower pressure port are arranged on the lower circulation pipe or the tank body. The upper pressure port and the lower pressure port are respectively installed with an upper pressure transmitter 7 and a lower pressure transmitter 5. The upper pressure transmitter 7 and the two pressure transmitters transmit signal data to the DCS system 6 for calculation to obtain the solid-liquid ratio, and the salt discharge cascade control is performed according to the solid-liquid ratio.

[0033] Among them, the salt discharge pipeline is provided with two flushing switch valves 10 (pneumatic O-type switch ball valve), a regulating valve 9 (pneumatic V-type regulating ball valve) and a flow meter 11. The two flushing switch valves 10 are located on both sides of the regulating valve 9. The flushing switch valve located between the tank body and the regulating valve is a backwashing switch valve, and the flushing switch valve located behind the regulating valve is a salt discharge pipeline flushing valve.

[0034] The upper pressure port and the lower pressure port correspond to the upper and lower pressure collection points. During operation, the upper pressure transmitter and the lower pressure transmitter transmit data to the DCS system to obtain the solid-liquid ratio.

[0035] Solid-liquid ratio formula:

[0036] A=(ΔP / Δh-11858) / 5507.6 (1)

[0037] Among them, A is the solid-liquid ratio, ΔP is the differential pressure, and Δh is the height difference between the pressure collection points. After the equipment is installed, Δh is a constant.

[0038] Acquisition process:

[0039] According to the formula

[0040] ΔP=ρgΔh=((ρ1v1+ρ2(v0-v1)) / v0)*(gΔh)=(ρ1–ρ2)gΔh*A+ρ2gΔh (2)

[0041] Among them, ΔP is the differential pressure, ρ is the density, Δh is the height difference between the upper and lower pressure ports, v1 / v0=A is the solid-liquid ratio, v0 is the total volume, ρ1 is the density of the mixture of the solid and the liquid that penetrates it, v1 is the volume of the mixture of the solid and the liquid that penetrates it, ρ2 is the density of the liquid mixture, ρ1, ρ2, and g are all constants.

[0042] After the equipment is installed, Δh is fixed, and the solid-liquid ratio of the supersaturated salt solution is linearly related to ΔP. Taking Δh = 1M, we get

[0043] ΔP=(ρ1–ρ2)g*A+ρ2g (3)

[0044] The samples were taken at room temperature and tested immediately.

[0045] ρ1=1772g / L

[0046] ρ2=1210g / L

[0047] ΔP(Pa)=5507.6A+11858 (4)

[0048] By converting the measured pressure into the differential pressure with a height difference of 1M, the mathematical model for online measurement of the solid-liquid ratio is obtained:

[0049] A=(ΔP-11858) / 5507.6. (5)

[0050] The above-mentioned DCS system can obtain the real-time value of the solid-liquid ratio online, and control the regulating valve on the salt discharge pipeline to adjust the solid-liquid ratio in the tank according to the real-time value and the set value of the solid-liquid ratio.

[0051] Adjustment process:

[0052] When the deviation between the real-time value of the solid-liquid ratio and the set value of the solid-liquid ratio is less than the preset deviation threshold, in the DCS system, the deviation between the real-time value of the solid-liquid ratio and the set value of the solid-liquid ratio is output as the flow set value of the inner flow loop through PID calculation, and the deviation between the flow set value and the real-time value of the flow of the salt discharge pipeline is PID calculated to adjust the regulating valve. The adjustment process is: when the real-time value of the solid-liquid ratio is less than the set value of the solid-liquid ratio, the regulating valve is automatically adjusted down to reduce the output flow of the salt discharge pipeline; when the real-time value of the solid-liquid ratio is greater than the set value of the solid-liquid ratio, the regulating valve is automatically adjusted up to increase the output flow of the salt discharge pipeline;

[0053] When the deviation between the real-time value of the solid-liquid ratio and the set value of the solid-liquid ratio is greater than the preset deviation threshold, the cascade switch is disconnected, and the flow on the salt discharge pipeline is controlled by a single loop, and the regulating valve is controlled according to the detection result. The adjustment process is: when the real-time flow value is less than the set flow value, the regulating valve is automatically adjusted to increase the output flow of the salt discharge pipeline; when the real-time flow value is greater than the set flow value, the regulating valve is automatically adjusted to reduce the output flow of the salt discharge pipeline.

[0054] When the deviation between the real-time value of the solid-liquid ratio and the set value is less than the preset deviation threshold, the salt discharge pipe is judged for its unobstructed condition during the automatic control of salt discharge according to the solid-liquid ratio. If the real-time salt discharge flow rate is lower than the lower limit of the salt discharge flow rate set by the current programmed flushing, it indicates that the salt discharge pipe is blocked. Close the regulating valve on the salt discharge pipe, and automatically open the two flushing switch valves on both sides of the regulating valve to clean the salt discharge pipe. After the flushing is completed, if the salt discharge flow rate is higher than the set value of the programmed flushing, restore the original automatic salt discharge adjustment condition without disturbance. If the detection result of the salt discharge flowmeter is still lower than the set value of the programmed flushing flow rate, the flushing cycle is repeated.

[0055] Specific control process such as Figure 2 As shown, in Figure 2 In the process, the real-time value EXPV of the solid-liquid ratio output by DY204 of the outer loop and the external given value, that is, the solid-liquid ratio set value EXSV, produce a deviation DV1. When DV1 is within the deviation threshold, DV1 outputs EXMV as the external given value of the inner loop after PID operation. At the same time, the INPV measured by the FI2220 flowmeter is used as the real-time value of the inner loop and forms a deviation DV2 with EXMV. DV2 acts on FCV2220 after INMV after PID operation of FIC2220. The flow control of the inner loop ultimately affects the solid-liquid ratio control of the outer loop, thereby stabilizing the solid-liquid ratio in the tank. During program operation, it also detects and judges whether the salt discharge pipe is blocked in real time. When the salt discharge flow rate is lower than the set lower limit flow rate, it means that the salt discharge pipe is blocked, close the regulating valve, open the flushing switch valve for flushing, and set the valve position tracking, and the cascade control can be switched without disturbance after the flushing is completed.

[0056] The flow rate fluctuates greatly during actual production. In order to avoid frequent triggering of flushing, it is necessary to perform a delayed stabilization judgment. That is, the flushing of the salt discharge pipeline can only be triggered when the flow rate value is higher than the setting of the program-controlled flushing within a certain period of time.

[0057] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein, on the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. A method for automatic control of salt discharge by online detection of solid-liquid ratio, characterized in that: The real-time value of the solid-liquid ratio is obtained online and the regulating valve on the salt discharge pipeline is controlled to adjust the flow rate according to the solid-liquid ratio setting value to achieve stable control of the solid-liquid ratio in the tank. When the deviation between the real-time value of the solid-liquid ratio and the set value of the solid-liquid ratio is less than the preset deviation threshold, in the DCS system, the deviation between the real-time value of the solid-liquid ratio and the set value of the solid-liquid ratio is output through PID calculation as the flow set value of the inner flow loop, and the deviation between the flow set value and the real-time value of the flow of the salt discharge pipeline is PID calculated to adjust the regulating valve. The adjustment process is: when the real-time value of the solid-liquid ratio is less than the set value of the solid-liquid ratio, the regulating valve is automatically adjusted down to reduce the output flow of the salt discharge pipeline; when the real-time value of the solid-liquid ratio is greater than the set value of the solid-liquid ratio, the regulating valve is automatically adjusted up to increase the output flow of the salt discharge pipeline. When the deviation between the real-time value of the solid-liquid ratio and the set value is less than the preset deviation threshold, the salt discharge pipe is judged for its unobstructed condition during the process of automatically controlling the salt discharge according to the solid-liquid ratio. If the real-time flow rate of the salt discharge is lower than the lower limit flow rate of the salt discharge set by the current program-controlled flushing, it indicates that the salt discharge pipe is blocked. The regulating valve on the salt discharge pipe is closed, and the two flushing switch valves on both sides of the regulating valve are automatically opened to clean the salt discharge pipe. After the flushing is completed, if the salt discharge flow rate is higher than the set value of the program-controlled flushing, the original salt discharge automatic adjustment condition is restored without disturbance. If the detection result of the salt discharge flowmeter is still lower than the set value of the program-controlled flushing flow rate, the flushing cycle is performed. When the deviation between the real-time value of the solid-liquid ratio and the set value of the solid-liquid ratio is greater than the preset deviation threshold, the cascade switch is disconnected, and single-loop control is performed through the flow on the salt discharge pipeline. The regulating valve is controlled according to the detection results. The adjustment process is: when the real-time value of the flow is less than the set value of the flow, the regulating valve is automatically adjusted to increase the output flow of the salt discharge pipeline. When the real-time value of the flow is greater than the set value of the flow, the regulating valve is automatically adjusted to reduce the output flow of the salt discharge pipeline.

2. The method for automatic control of salt discharge by online detection of solid-liquid ratio according to claim 1, characterized in that: The differential pressure is obtained by setting two pressure collection points in the upper and lower directions of the tank or the lower circulation pipe, and the formula is: A=(ΔP / Δh-11858) / 5507.6 (1) The real-time value of the solid-liquid ratio is obtained, where A is the solid-liquid ratio, ΔP is the differential pressure, Δh is the height difference between the two pressure collection points, and Δh is a constant.

3. The method for automatic control of salt discharge by online detection of solid-liquid ratio according to claim 2, characterized in that: The pressure collection points are the upper pressure port and the lower pressure port. The upper pressure port and the lower pressure port are respectively installed with the upper pressure transmitter and the lower pressure transmitter. The signal data of the upper pressure transmitter and the lower pressure transmitter are transmitted to the DCS system to indirectly obtain the solid-liquid ratio through calculation.

4. The method for automatic control of salt removal by online detection of solid-liquid ratio according to claim 3, characterized in that: According to the formula ΔP = ρgΔh= ((ρ1v1 +ρ2(v0-v1)) / v0) * (gΔh)=(ρ1–ρ2) gΔh*A+ρ2 gΔh (2) Among them, ΔP is the differential pressure, ρ is the density, Δh is the height difference between the upper and lower pressure ports, v1 / v0=A is the solid-liquid ratio, v0 is the total volume, ρ1 is the density of the mixture of the solid and the liquid that penetrates it, v1 is the volume of the mixture of the solid and the liquid that penetrates it, and ρ2 is the density of the liquid mixture. ρ1, ρ2, and g are all constants. After the equipment is installed, Δh is fixed, and the solid-liquid ratio of the supersaturated salt solution is linearly related to ΔP. Taking Δh = 1M, we get ΔP=(ρ1–ρ2) g*A+ρ2 g (3) The samples were taken at room temperature and tested immediately. ρ1=1772g / L ρ2=1210g / L ΔP(Pa)=5507.6A+11858 (4) By converting the measured pressure into the differential pressure with a height difference of 1M, the mathematical model for online measurement of the solid-liquid ratio is obtained: A=(ΔP-11858) / 5507.6 (5).

5. The method for automatic control of salt discharge by online detection of solid-liquid ratio according to claim 1, characterized in that: Applied in the evaporation and salt removal process.

6. The method for automatic control of salt discharge by online detection of solid-liquid ratio according to claim 5, characterized in that: The evaporator includes a tank body and salt legs, a salt discharge pipe, an upper circulation pipe and a lower circulation pipe installed on the tank body. The upper circulation pipe and the lower circulation pipe are connected by a pump and a heating device. The upper pressure port and the lower pressure port are arranged on the lower circulation pipe.

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