A method for controlling wet automatic dosing of vacuum salt production using centrifuge current

Abstract

The present invention discloses a method for controlling wet automatic dosing of vacuum salt production using centrifuge current. The main components include a centrifuge current measuring device, a programmable controller (PLC), a frequency converter, a metering pump, and a weight loss scale. The specific control method is as follows: the processing unit calculates the converted salt amount through a program based on the signal of the centrifuge current measuring device, and then first calculates the flow rate of the additive solution that needs to be added based on the current-converted salt amount in combination with the concentration of the agent liquid according to the current formula. The metering pump then makes a preliminary adjustment to the pumping amount based on this flow rate. According to the present invention, the automatic dosing measurement and control process eliminates the need for direct salt weighing equipment, and is simple to operate and maintain. It can not only improve the quality stability of the automatic dosing of vacuum salt production, but also reduce the investment in production line equipment.

Description

Technical Field

[0001] The invention relates to the technical field of vacuum salt production additives, in particular to a method for vacuum salt production wet automatic additives controlled by centrifuge current. Background Art

[0002] Traditional methods of dosing mainly include nuclear scale measurement or belt scale measurement of salt amount and automatic dosing. Therefore, such equipment needs to be installed at the salt production site. The belt scale has a high failure rate due to corrosion from salt dust, and has high maintenance requirements and a large workload. A slight misalignment may lead to large measurement errors, affecting the accuracy of dosing. Due to the risk of radiation, the use and installation of nuclear scales must be inspected by the health, epidemic prevention and public security departments, and special personnel must be arranged for management.

[0003] The present invention is in urgent need of a vacuum salt production wet automatic dosing method that does not require the installation of dynamic weighing equipment such as nuclear scales or belt scales on site. Summary of the Invention

[0004] The present inventors conducted in-depth research on the problems existing in the above-mentioned prior art and unexpectedly found that the current of a centrifuge used for dewatering salt slurry can be used to measure the amount of salt.

[0005] In the current vacuum salt production process, the raw brine collected from the mine is purified and then undergoes an evaporation process (to remove heavy metals and impurities at the same time). The salt slurry from the thickener of the evaporation process is sent to a centrifuge, where water is discharged under the action of centrifugal force, so that the moisture content of the wet salt after dehydration is less than 3%. The wet salt discharged from the centrifuge enters a drying bed for drying, and additives are added before and / or after the drying bed through a metering pump to finally obtain finished salt, which can be packaged and sold out of the factory.

[0006] The centrifuge is a key equipment in vacuum salt production. The salt slurry from the thickener enters the centrifuge and is discharged under the action of centrifugal force, so that the moisture content of the wet salt after dehydration is less than 3%. This method uses the correspondence between the centrifuge current used for salt dehydration in the salt production process and the salt content to measure the salt content for controlling the dosing, eliminating the need to install a belt scale or nuclear scale to detect the salt flow rate. The main components include a centrifuge current measuring device (combined motor protector), a programmable controller (PLC), a frequency converter, a metering pump, and a loss-in-weight scale.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] A method for controlling wet automatic dosing of vacuum salt production by using centrifuge current, the method comprising the following steps:

[0009] (A) Calculate the linear relationship c between current and salt content using the following formula:

[0010] d1=(ba) / c (1)

[0011] Where, c: linear relationship value of current corresponding to salt content (proportional coefficient);

[0012] a: centrifuge no-load current monitoring value (int integer);

[0013] b: centrifuge full load current monitoring value (int integer);

[0014] d1: Full load of salt, unit: Kg.

[0015] The centrifuge current monitoring value, including a, b and A below, is an int integer value obtained by processing by a processor such as a PLC, wherein a 4-20 mA current signal corresponds to 0-27648.

[0016] In one embodiment, the centrifuge's current monitoring value is obtained via a combined motor protector. The motor protector converts the detected current into an analog signal (4-20 mA) and transmits it to a PLC. The resulting integer value, processed by the PLC, is displayed on a monitor (computer). Current measurement is performed using the combined motor protector's transformer component attached to the motor's primary cable. Values a and b can be obtained by monitoring the centrifuge with no load, and b can be obtained by monitoring the centrifuge with full load.

[0017] The full load salt amount d1 is related to the specifications and models of the centrifuge and can be obtained by checking the centrifuge manual.

[0018] (B) Calculate the instantaneous salt content according to the following formula:

[0019] d=(Aa) / c (2)

[0020] Where, d: instantaneous salt content, unit Kg;

[0021] A: Current centrifuge current monitoring value (int integer);

[0022] The values of a and c are as defined above;

[0023] (C) Calculate the amount of the additive according to the following formula:

[0024] The amount of auxiliary agent (unit L) = instantaneous salt amount d (Kg) * set content / 0.592991 / content concentration / 10000 (3);

[0025] The set content is the mass content of the additive in the salt, which is calculated here according to the corresponding ppm value, for example, 23ppm is calculated as 23, and the content concentration is calculated according to the corresponding mass percentage concentration, for example, 5% by mass is calculated as 5. The coefficients 0.592991 and 10000 are empirical values, which are empirical coefficients obtained through experiments.

[0026] (D) According to the calculated amount of additive, set the metering pump parameters to achieve the amount of additive added.

[0027] When the amount of the auxiliary agent and the instantaneous salt value are obtained, the parameters of the metering pump can be set according to the parameters of the selected metering pump, so that the auxiliary agent is added to the salt at the set content. The auxiliary agent here is, for example, one or more selected from a loosening agent (such as potassium ferrocyanide) and an iodine agent. The auxiliary agent can be added before and / or after the drying bed. For example, the loosening agent is generally added before the drying bed, and the iodine is generally added after the drying bed, but it can also be added before the drying bed. The method of the present invention is preferably used for adding before the drying bed.

[0028] According to one embodiment, the metering pump parameter is the metering pump frequency, which is obtained according to the following formula:

[0029] Metering pump frequency AD value = amount of additive * 100000 / metering pump coefficient / metering pump range (4).

[0030] The metering pump frequency is measured in Hertz. The metering pump range is adjusted on-site using a dial. For example, if the metering pump range is 80%, it is calculated as 80. The PLC calculates the metering pump frequency AD value and then sends a signal to the metering pump (inverter) to determine the corresponding metering pump frequency. The metering pump frequency AD value ranges from 0-27648, corresponding to a frequency of 0-50 Hz. For example, for 30 Hz, the AD value required is 27648*30 / 50=16589, and for 10 Hz, the AD value required is 27648*10 / 50=5530.

[0031] Among them, the metering pump coefficient = the ratio of the measured flow rate to the theoretical flow rate. For example, when the metering pump is running at a rated frequency of 50HZ, the theoretical flow rate of the metering pump is 90L / H (check the metering pump manual), and the actual flow measured by the instrument is 101.07L / H. Then the metering pump coefficient = the ratio of the measured flow rate to the theoretical flow rate = 101.07 / 90 = 1.123.

[0032] In the present application, a processing unit such as a PLC calculates the converted salt amount d1=(b a ) / c according to the signal of the centrifuge motor current measuring device through a program, where a is the centrifuge no-load current conversion value (obtained by computer program monitoring when the centrifuge is no-load), b is the full-load current conversion value (obtained by computer program monitoring when the centrifuge is fully loaded), and c is the linear relationship between the current and the salt amount (the full-load salt amount d1 can be found in the centrifuge manual and the c value can be deduced). Then, according to the current formula, the flow rate of the added solution required to add the salt amount converted from the current is first calculated in combination with the concentration of the liquid configuration, and the metering pump makes a preliminary adjustment to the metering pump output according to this flow rate. In the addition system, the liquid loss-in-weight scale calculates the current addition flow rate of the current liquid additive in real time, and the error of the current addition amount can be obtained by combining the mathematical target flow rate calculated by the formula by the previous system. The system automatically adjusts the operating frequency of the metering pump according to this error (for example, by increasing or decreasing the set content value) to continuously reduce the addition error, thereby forming a complete closed-loop control loop so that the process of adding the solution to the system operates normally within a controllable adjustment function.

[0033] The current fluctuation of the centrifuge cannot be predicted under many working conditions due to the workload. Therefore, during the normal salt production process, we continuously collect the current data of a single centrifuge during operation to find the current fluctuation curve. The peak and trough values are filtered out through a function algorithm to obtain the data A of the stable current change during the operation process.

[0034] During the salt production process, the centrifuge current fluctuates within its curve. The system collects this data and generates a linear equation using the no-load current as the zero point and the full-load current as the full-scale value. The system then calculates the instantaneous salt production from the centrifuge current fluctuations as d = (Aa) / c (c: proportionality factor, A: current centrifuge current monitoring value, a: no-load current monitoring value).

[0035] During the bedside dosing process, the system first calculates the required flow rate of the added solution based on the current formula and the concentration of the solution. The metering pump then makes preliminary adjustments to the pump output based on this flow rate. In the addition system, the liquid loss-in-weight scale calculates the current addition flow rate of the liquid additive in real time. Combined with the mathematical target flow rate calculated by the previous system from the formula, the error in the current addition amount can be determined. The system automatically adjusts the operating frequency of the metering pump based on this error, continuously reducing the addition error. This forms a complete closed-loop control circuit, allowing the system's solution addition process to operate normally within a controllable adjustment function.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. The relationship between centrifuge current and salt content is used to replace the salt weighing equipment. Compared with the direct use of salt weighing equipment, the workload of complicated use and maintenance is reduced. At the same time, it also avoids the problem of inaccurate dosing caused by inaccurate salt content due to inadequate use and maintenance, and can improve the dosing accuracy and stability.

[0038] 2. The present invention reduces the investment in weighing equipment, lowering the equipment investment and subsequent use and maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Added control flow diagram for additives. DETAILED DESCRIPTION

[0040] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0041] In the drawings, the same reference numerals all refer to the same components.

[0042] In addition, if a detailed description of a known technology is not necessary to illustrate the features of the present invention, it will be omitted. It should be noted that the words "front", "rear", "left", "right", "upper", and "lower" used in the following description refer to directions in the drawings, and the words "inner" and "outer" refer to directions toward or away from the geometric center of a particular component, respectively.

[0043] like Figure 1 As shown, the centrifuge current measured by a centrifuge current measuring device (such as a combined motor protector) is input into the additive addition control system PLC. The PLC controls the metering pump frequency via a frequency converter. The metering pump adds the additive to the loss-in-weight scale at the set frequency and then adds it to the salt before the drying bed. The loss-in-weight scale calculates the current addition flow rate of the liquid additive in real time. Combined with the mathematical target flow rate (addition amount) calculated by the previous system based on the recipe, the current addition amount error is determined. The PLC system automatically adjusts the frequency converter frequency and the metering pump output based on this error, continuously reducing the addition error until the actual additive flow rate matches the calculated target flow rate.

[0044] Taking the addition of loosening agent (potassium ferrocyanide) as an example, the control method of using centrifuge current to control the addition of the agent is explained.

[0045] The current of the centrifuge is detected by the motor protector, and the additives are added at the centrifuge discharge port.

[0046] The method comprises the following steps:

[0047] (A) Calculate the linear relationship between current and salt content, c:

[0048] d1=(ba) / c (1)

[0049] Where, c: linear relationship value of current corresponding to salt content (proportional coefficient);

[0050] a: centrifuge no-load current monitoring value (int integer); A: current centrifuge current monitoring value (int integer, range 0-27648, corresponding to 4-20mA current signal);

[0051] b: full load current monitoring value (int integer);

[0052] d1: Full load of salt.

[0053] a: Centrifuge no-load current monitoring value, by monitoring the centrifuge no-load operation a = 8264 (int integer), when the centrifuge is fully loaded with wet salt measurement d1 is 50000 kg, monitoring b = 98686 (int integer); c = d1 /

[0054] (ba)=50000 / (98686-8264)≈0.55296.

[0055] (B) Calculate the instantaneous salt content d = (Aa) / c,

[0056] A: The current centrifuge current monitoring value is 17997, c = 0.55296, a = 8264, and d = (Aa) / c = (17997-8264) / 0.55296 ≈ 17602 kg is calculated.

[0057] (C) Calculate the amount of the additive according to the following formula:

[0058] During monitoring, the instantaneous salt amount is 17602 kg, and the amount of auxiliary agent = instantaneous salt amount * set content (23 ppm) / 0.592991 / content concentration (content concentration is a percentage value of 5) / 10000. Therefore, the amount of auxiliary agent calculated by PLC = 13.65437 L, where 0.592991 and 10000 are empirical coefficients.

[0059] (D) According to the calculated amount of additive, set the metering pump parameters to achieve the amount of additive added.

[0060] The PLC calculates the metering pump frequency AD value = additive amount (in L) * 100,000 / metering pump coefficient / metering pump range = 13.65437 * 100,000 / 1.123 / 80 ≈ 15,199. When the metering pump is operating at its rated frequency of 50 Hz, the theoretical flow rate is 90 L / H (see the metering pump manual), while the metering instrument measures 101.07 L / H. The metering pump coefficient = the ratio of measured flow rate to theoretical flow rate = 101.07 / 90 = 1.123. The metering pump range is 80%, so 80 is used. The PLC calculates the metering pump frequency AD value and then sends a signal to the metering pump (inverter) to control the metering pump's operating frequency. The metering pump frequency AD value range of 0-27,648 corresponds to a frequency of 0-50 Hz.

[0061] The additive was added at the metering pump frequency described above, and the resulting salt product was sampled multiple times for testing and analysis of the potassium ferrocyanide content. The results were consistent with the set content of 23 ppm. In actual control, when the test value is inconsistent with the control value, the amount of additive added can be adjusted by adjusting the set content value. If the test value is low, the set content value is increased; if the test value is high, the set content value is decreased, thereby achieving consistency between the actual test value and the control value.

[0062] In this application, the PLC control system first calculates the flow rate of the liquid required to add the salt amount converted from the centrifuge current based on the current formula and the liquid concentration. The metering pump then makes a preliminary adjustment to the metering pump output based on this flow rate through the frequency converter. In the addition system, the loss-in-weight scale calculates the current addition flow rate of the current liquid additive in real time. Combined with the mathematical target flow rate calculated by the previous system based on the formula, the error of the current addition amount can be obtained. The PLC system automatically adjusts the frequency converter frequency and the output of the metering pump based on this error, so that the addition error is continuously reduced until the actual flow rate of the additive detected is consistent with the calculated target flow rate.

[0063] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for wet automatic dosing of vacuum salt production using centrifuge current control, the method comprising the following steps: (A) The linear relationship c between current and salt content is calculated using the following formula: d1=(ba) / c Wherein, c: linear relationship value of current corresponding to salt content; a: centrifuge no-load current monitoring value, int integer; b: centrifuge full load current monitoring value, int integer; d1: Full load of salt, unit Kg; (B) Calculate the instantaneous salt content according to the following formula: d=(Aa) / c Where, d: instantaneous salt content, unit Kg; A: Current centrifuge current monitoring value, int integer; The values of a and c are as defined above; (C) Calculate the amount of additives according to the following formula: Amount of additive = instantaneous salt amount d*set content / 0.592991 / content concentration / 10000 The unit of the amount of the additive is L. The set content is the mass content of the additive in the salt, which is calculated here as the corresponding ppm value, and the content concentration is calculated as the corresponding mass percentage concentration; (D) According to the calculated amount of additives, set the metering pump parameters to achieve the amount of additives added.

2. The method for wet automatic dosing of vacuum salt production using centrifuge current control according to claim 1 is characterized in that: The metering pump frequency is obtained according to the following formula: Metering pump frequency AD value = amount of additive * 100000 / metering pump coefficient / metering pump range; The unit of metering pump frequency is Hertz. The PLC calculates the AD value of the metering pump frequency and then sends a signal to the metering pump to determine the corresponding metering pump frequency.

3. The method for wet automatic dosing of vacuum salt production using centrifuge current control according to claim 2, characterized in that: Metering pump coefficient = ratio of measured flow rate to theoretical flow rate.

4. The method for vacuum salt production wet automatic dosing using centrifuge current control according to any one of claims 1 to 3, characterized in that: The centrifuge current monitoring values, including a, b, and A, are int integer values obtained through PLC processing, where the 4-20mA current signal corresponds to 0-27648.

5. The method for wet automatic dosing of vacuum salt production using centrifuge current control according to claim 4 is characterized in that: The current monitoring value of the centrifuge is obtained through the combined motor protector. The motor protector converts the detected current into an analog signal and outputs it to the PLC. The int integer obtained after PLC processing is displayed through the monitor. The current measurement is the combined motor protector mutual inductor component set on the primary cable of the motor.

6. The method for vacuum salt production wet automatic dosing using centrifuge current control according to any one of claims 1 to 3, characterized in that: The loss-in-weight scale calculates the current addition flow of the current liquid additive in real time, and combines it with the addition amount calculated by the system from the formula to obtain the error of the current addition amount. The PLC system automatically adjusts the inverter frequency and the output of the metering pump based on this error, so that the addition error is continuously reduced until the actual flow rate of the additive detected is consistent with the calculated target flow rate.

7. The method for wet automatic dosing of vacuum salt production using centrifuge current control according to claim 5, characterized in that: The loss-in-weight scale calculates the current addition flow of the current liquid additive in real time, and combines it with the addition amount calculated by the system from the formula to obtain the error of the current addition amount. The PLC system automatically adjusts the inverter frequency and the output of the metering pump based on this error, so that the addition error is continuously reduced until the actual flow rate of the additive detected is consistent with the calculated target flow rate.

8. The method for vacuum salt production wet automatic dosing using centrifuge current control according to any one of claims 1 to 3, characterized in that: The auxiliary agent is one or more selected from loosening agents and iodine agents.

9. The method for wet automatic dosing of vacuum salt production using centrifuge current control according to claim 8, characterized in that: Loosening agent and iodine are added before the drying bed.

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