Automatic control of the dehydration process
Dehydration is an indispensable process for wet beneficiation . Dehydration has concentrate dehydration, tailings dehydration, washing and dehydration. Concentrate dewatering can accurately control concentrate water and reduce concentrate loss; tailings dewatering is to reduce discharge, reduce energy consumption, and recycle process water; washing ore is used to recover valuable materials in fine mud, improve recovery rate and reduce Energy consumption.
The dehydration process consists of three main stages of concentration, filtration and drying. Concentrate to increase filtration efficiency and dry to further reduce moisture.
This chapter focuses on the dewatering control of concentrates, and explains the example of the concentration control and concentrator control of the concentrator underflow, and the control strategy supply and design reference. The drying process is rarely used in the process of mineral processing in China.
First, concentrate dehydration control system
Concentrate dewatering is accomplished in three stages: concentration, filtration and drying, depending on the water content of the final product. Concentrated dewatering and filtration dewatering are carried out in a concentrator and a filter, respectively.
Concentrate dewatering not only can accurately control concentrate water and reduce energy consumption, but also reduce the labor intensity of workers and improve working conditions.
1. Process requirements and control purposes
A lead-zinc ore beneficiation dehydrated by a vacuum pump system, thickener, of discharge valves, lift pump pulp, dewatering filter, concentrate electronic scales, turn on the water drain tank and other equipment. The connection diagram of the dewatering section equipment is shown in Figure 1. The dewatering operation adopts an intermittent working system, and the driving or parking is determined according to the concentration of the bottom stream of the thickener and the amount of the mineral in the concentration tank.
According to the process requirements, the computer is used for dehydration process control. The control system implements the following detection and control.
Figure 1 Dehydration section equipment connection diagram
(1) Monitoring and control of the concentration of the bottom stream of the concentration tank. When the limit is exceeded, the alarm can be automatically issued to ensure the safe operation of the transmission system of the concentration tank.
(2) Detection of the amount of minerals at the bottom of the concentrator.
(3) Opening and closing control of the discharge valve, fault detection and alarm.
(4) Detection and alarm of the level of the ore tank in the filter.
(5) The opening and closing control of the filter and its auxiliary equipment.
(6) Slurry lifting pump pool overflow detection and alarm.
(7) Weighing, data processing and report output of the concentrate products of the six filters.
2. Control system composition
The microcomputer control system consists of the ZD-065II basic system (including 4KB monitoring, 8KBBASIC, 4KB assembly, 4KB application, etc., the program is solidified in EPPOM), tape drive, terminal, CRT, printer, power supply and so on. The digital input and output are isolated by optocoupler. The system block diagram is shown in Figure 2.
The control system software consists of four functional modules. The functional modules are organically connected by the main program to form a complete dehydration control software.
(1) Input operation module
All control parameters, set values, initialization procedures, etc. are completed in the input operation block.
(2) Interface function module
Analog input signal, digital input: output signal, real-time clock interrupt processing signal, etc., through the parallel interface to complete the input and output control functions. The interface function module consists of 45 function subroutines. Each subroutine is compiled in assembly language and hardened on the interface function block. [next]
(3) Data processing module
Used for data processing after A/D sampling, various condition discrimination and concentrate calculation.
(4) Output control module
Complete single-key Chinese character display, time display, fault display, and test data printout.
The control program is compiled in a combination of assembly language and BASIC language. The functional modules related to the interface are programmed in assembly language, and the subprograms and main programs that are related to the user are programmed in BASIC language. This solves the problem of the speed at which the outside world exchanges information with the host, facilitating human-machine dialogue. The system also has diagnostic and self-diagnostics. The control system software is shown in Figure 3.
3. Dehydration process parameters
In the dehydration control system, the simulated quantity detected has the concentration of the bottom stream of the concentration tank, the amount of the bottom of the thickener, and the weight of the concentrate.
(1) Detection of the concentration of the bottom stream in the concentration tank
Figure 2 Microcomputer control block diagram of dehydration system [next]
Figure 3 Software block diagram of the dehydration control system
   During the concentration process of the slurry in the concentration tank, the change of the concentration of the bottom layer of the slurry makes the input power of the concentrator drive motor have obvious changes, which can indirectly reflect the change of the slurry concentration.
The input power is low, the slurry concentration is low, the filter cake is thin and ventilated during filtration, the dehydration effect is not good, and the filter cloth is wasted. The input power is high, the concentration of the slurry is high, and the concentration is too high, which is easy to block the pipeline and damage the transmission shaft and the transmission gear. Therefore, the concentration of the slurry in the compression zone of the concentrator is used to control the ore discharge valve, the slurry lift pump, and the dewatering filtration.
(2) Detecting the bottom of the concentrator
The amount of concentrate at the bottom of the concentrator is detected by injecting a small amount of water through the valve in the steel pipe to balance the water level in the pipe with the pressure of the slurry in the concentrator. Since the concentrator has a fixed volume, if the internal ore volume changes, the pressure on the bottom will change. In this way, the mineral amount is measured indirectly by a pressure transmitter.
(3) Concentrate weight detection
The dehydrated lead, zinc, sulfur and other concentrate products are weighed by electronic scales. Switched by a pressure sensor. When the concentration of each concentrate reaches the set value, the microcomputer automatically detects the total weight and sends out the unloading concentrate signal. When the concentrate is poured into the concentrate bin, the concentrate is automatically tested for tare weight. Finally, after data processing, the concentrate output of each class is printed periodically.
In the process of analog quantity detection, random sampling, modulus & number conversion were realized for the bottom stream concentration signals of lead, zinc and sulfur, the bottom quantity signal of lead concentrator and the concentrate weight signal of six concentrates. And data processing, and take appropriate anti-interference measures.
(4) Switching input signal detection
The liquid level signal in the filter tank of the dehydration process, the alarm liquid level signal, the super-weight signal of the slurry lift pump box, the position signal of the ore discharge valve, the status signal of the concentrate scale, etc., participate in the dehydration process through microcomputer detection and logic discrimination. control.
The liquid level alarm electrode in the filter tank is damaged, the slurry of the sand pump box overflows, the discharge valve cannot be opened or closed, and an alarm detection is installed in the system. The display automatically displays the measurement result, and the alarm output circuit outputs the alarm signal and the fault location in time. At the same time, the safety measures such as automatically or manually closing the mine valve are adopted to avoid the occurrence of run, run and leak of the concentrate during the dehydration process.
4. Dehydration process control method
The main control of the system includes: start and stop control of the filter, liquid level control of the slurry lifting pump box, opening and closing control of the ore discharging valve, and eight-way alarm control signals issued during the dehydration control process.
(1) Concentrator bottom flow concentration and ore control
When the underflow concentration and the ore amount satisfy the specified value, the ore-mining control is performed. Mining conditions:
Y=A·B·C·D
Where A - concentrator power, upper limit ≥ A > lower limit; [next]
B——concentrate of the concentrator, the upper limit ≥ B> lower limit;
C——the slurry raises the pump tank level, C≤ lower limit value;
D——Filter liquid level, upper limit value>D.
When the conditions are met, the ore discharge valve is opened in turn, the sand pump is started, the slurry is fed into the filter, and the process of dehydration of the concentrate is entered.
(2) Liquid level control and alarm in the filter tank
If the liquid level is too high, it will affect the dehydration effect. The liquid level is too low and is also detrimental to dehydration.
(3) Concentrate scale control
The concentrate scale is controlled when the amount of concentrate after dewatering reaches the set value.
(4) Liquid level control of slurry lifting pump box
When the liquid level of the sand pump box is lower than the lower limit electrode, the discharge valve is opened, the sand pump is started, and the filter is discharged to the filter; when the liquid level of the sand pump box is at the upper limit, the discharge valve must be closed. Above the upper limit, an alarm is displayed to prevent slurry overflow.
(5) Alarm control system
During the dehydration process, lead, zinc, sulfur concentrator power over-limit signal, sand pump box overweight signal, filter internal electrode fault signal, mine valve fault signal, concentrate scale full load signal, etc. are pre-stored in the memory correspondingly The fixed value is compared, the sound and light alarm is output through the switch quantity, and the fault is processed in time to ensure the normal operation of the dehydration process.
5. Main features of the control system
The control system mainly has the following characteristics:
(1) The system uses reliable isolation technology in the input) output to solve the problem of field of view interference.
(2) A modular structure is adopted in software design. It adopts assembly language and BASIC language cross programming, which is more flexible and convenient.
(3) After adopting the system, the lead filtration efficiency of the plant is increased by 3.1 times, zinc is increased by 1.6 times, the water content of lead concentrate is reduced by 2~10%, and the water content of 11% zinc concentrate is reduced by 0.5~7.5%, reaching 13%. Better efficiency.
Second, the concentrator underflow discharge concentration automatic control system
In the production, the concentration of the bottom stream of the thickener fluctuates greatly, and it is difficult for the artificial control to be accurately controlled, which directly affects the beneficiation process index. The automatic control system of the bottom flow ore concentration of the concentrator is used to realize the automatic detection of the concentration of the slurry in the bottom of the concentrator. Through the automatic adjustment of the flow rate of the underflow discharge, the automatic control of the underflow slurry in a given range is achieved, and the stable production process is achieved. Improve the purpose of production efficiency.
1. Control plan
According to the requirements of the system control index, a manual manual adjustment method is adopted to install a concentration meter and an electric control valve on the pipeline at the outlet of the sand pump, and the opening degree of the electric control valve is automatically adjusted through the detection of the concentration of the underflow slurry. In order to change the underflow discharge flow, the slurry concentration is stabilized in a given range.
2. System configuration and control principle
The system configuration consists of concentration detection, discharge flow regulation and actuators. The system configuration is shown in Figure 2.
The underflow concentration detection was performed by an FD-3 type gamma ray concentration meter installed on the outlet pipe of the sand pump.
The discharge adjustment is carried out by a ZSX-BS type 152.4 mm (6 inch) hose valve installed on the outlet pipe of the sand pump, a FC servo amplifier, an AC servo motor and a position transmitter DKZ-510 linear actuator. In addition to adjusting the degree of valve switching, the DFD-09 electric power operator is also used to realize the conversion between manual and automatic operation.
Figure 4 System configuration
1. Φ30m concentration tank; 2. Φ102mm sand pump; 3. Φ152.4mm slurry pipeline;
4.FD-3 type concentration meter probe; 5. Concentration meter host; 6.A/DV/A converter;
7.TP-801 single board machine; 8.Tp-801P printer; 9.FC servo amplifier;
10.DFD-09 electric operator; 11.DKZ-510 electric actuator; 12. Φ152.4mm
Hose valve; 13. concentration indicator; 14. valve position indicator [next]
The system control principle is as follows: Firstly, the concentration value of the underflow slurry is measured by a concentration meter, and a current signal reflecting the magnitude of the concentration value is output. This signal is indicated by the ammeter on the one hand, and input to the computer for processing by A/D conversion on the other hand. The measured concentration value is compared with the given concentration value in the computer, and if the concentration value is greater than the given range, the adjustment signal output by the computer after D/A conversion is correspondingly increased, and the valve opening adjustment is performed; otherwise, the adjustment signal is correspondingly Reduce and adjust the valve. The degree of opening (closing) valve depends on the amount of increase (decrease) of the adjustment signal. When the concentration value is within the given range, the adjustment signal does not change, so that the valve position is not adjusted and maintains the original state. This achieves automatic adjustment of the hose valve. The block diagram is shown in Figure 5.
Figure 5 Â Control program flow box
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