Filter press is a solid-liquid separation equipment, mainly for the recovery of coal mud, it will be the end of coal-water separation coal mines, coal preparation plant for briquettes and water, improve coal utilization; conducive to environmental protection, coal washing plant is wash Necessary equipment for closed circuit of water. In the technical transformation of 2007, the Moxinpo Coal Preparation Plant used two XMZ500/1500 type box filter presses to dewater the slime in the tailings. However, between October 2007 and February 2010, two tail coal filter presses failed as many as 325 times, affecting the production time of the Moxinpo Coal Preparation Plant for 361 hours, which directly affected the normal coal washing time of 90 hours, which seriously affected the coal washing. The normal operation of production.

1 problem analysis

1.1 Problems

The design of the tailings filter press of Moxinpo Coal Preparation Plant adopts the filtration pressure provided by the feed pump. The filtration pressure is not only an important factor affecting the filtration speed, but also directly affects the working conditions and separation effect of the filter press. In actual use, it has been found that it is not ideal to increase the filtration pressure and improve the dewatering effect. Because, as the feed pressure of the feed pump increases, the porosity of the filter cake gradually decreases, and the saturation of the filter cake pores gradually decreases; when the saturation of the filter cake approaches the residual saturation, the moisture of the filter cake does not decrease substantially. If the feed pressure is too large, it will aggravate the wear and tear of the equipment components and cause equipment failure. It is of great significance to realize the control of the feed pressure of two tail coal filter presses without changing the concentration of coal slime and ensuring efficient operation of two tail coal filter presses.

1.2 Principle of filter press

The working principle of the tail coal filter press is shown in Figure 1. Under the action of the hydraulic cylinder, all the filter plates 3 are moved between the movable head plate 6 and the fixed tail plate 6 along the main beam to generate a pressing force. A closed filter chamber is formed between adjacent filter plates 3, and the periphery thereof is in a sealed state. The slurry enters the filter chamber from the manhole 1 in the tail plate 6 through a feed pump at a certain pressure, and a pressure difference is formed on the filter medium 2 side by the energy supplied from the feed pump to realize solid-liquid separation. The slime particles are retained in the filter chamber, and the filtrate is discharged through the filter cloth 4 from the water guide hole of the filter plate until the filtrate is no longer discharged, and the filtration dehydration process is completed. After the filtration and dehydration is completed, the slurry is stopped, and the filter plate 3 is pulled apart in turn, and the filter cake 5 is detached by itself, and is transported away by the transportation equipment at the lower part of the filter press, and the entire filter press cycle ends. It can be seen that the solid-liquid separation process is completed by the pressure energy provided by the feed pump. The magnitude of the feed pressure directly affects the dewatering effect and product quality of the slime. Reasonable control of the feed pressure is the key to the whole work.

1.3 Feed pressure control

The feed pressure of the feed pump is the main driving force for the filter press to complete the filter press cycle. In theory, the higher the feed pressure, the faster the filter press speed, but the excessive feed pressure is likely to cause accelerated wear of the equipment. From the analysis of the working process, the filter chamber has not retained enough material at the initial stage of feeding, and the sealing property of the filter chamber is not ideal. The low pressure and large flow rate should be maintained, and the feed pressure is preferably controlled between 0.11 and 0.12 MPa. Otherwise, it will cause the filter press to run out of material, which will adversely affect the subsequent pressure filtration, cake formation and unloading of cake. As the material in the filter chamber increases, the feed pressure can be gradually increased. The final feed pressure of the pressurization stage is 0.4 MPa and can not exceed 0.5 MPa, so as not to cause damage to the filter plate, frame, etc. of the filter press. The wear of the pump.

The control system of the tail coal filter press before the technical transformation is shown in Figure 2. The figure shows that the original design of the Moxinpo Coal Preparation Plant was to feed the tail coal filter press through the slurry pump at the lower part of the mixing tank. In order to avoid the initial pressure being too large, the feed splitting line of the filter press is designed, and a regulating valve is installed on the split line, and the regulating valve is used to control the feed pressure of the filter press. In this way, most of the material discharged from the slurry pump is returned to the mixing tank, which causes inefficient energy consumption, increases the feeding time, prolongs the entire dewatering process cycle of the filter press, and directly affects the processing efficiency and productivity of the filter press. . Meanwhile, since the difference Moxinpo quality coal preparation plant is washed, ash content between 30% to 40%, the loss is large in the washing medium of step (magnetic iron powder), with a substantial loss of residual slime of medium. During the pressure regulation process, the coal slurry containing a large amount of medium will have a great impact on the valve, accelerate the wear of the slurry valve, and cause the instability of the feed pressure.

1.4 slime performance requirements

According to the coal slurry size and muddy degree of Moxinpo Coal Preparation Plant, after a large number of experiments and actual operation of the filter press, it is known that the optimum filtration pressure of the slime in the Moxinpo Coal Preparation Plant should be 0.44~0.5MPa. between. In the original design, the feed pressure provided by the feed pump was 0.8 MPa. Although the design used in the shunt to reduce the pressure, the feed pressure fluctuated greatly and the stability was poor due to the wear of the diverter valve, and the product quality was affected.

1.5 Operating costs

The feed pump motor of the tailings filter press of Moxinpo Coal Preparation Plant adopts 50Hz and 380V three-phase voltage to start the operation directly. After the start-up, the feed pump is in high-speed operation for a long time. In order to control the feed pressure, part of the material output from the feed pump passes through the split pipe and returns to the mixing drum. The amount of coal entering the filter press is much lower than the actual output of the feed pump, resulting in a single feed ratio of the filter press. The material time is long (the coal feeding time is 500g/L, the feeding time is 40min). This not only reduces the efficiency of the filter press. Due to the long-term high-speed operation of the feed pump, the impeller of the pump, the front and rear guard plates and the discharge pump of the feed pump are accelerated and the replacement cycle is shortened (for example, the pump parts are replaced once every 6 months). The material pipe is replaced once every 9 months, which increases the cost of electricity and materials.

2 Technical transformation plan

2.1 Structural transformation of the control system

Through the analysis of the feed pressure system of the tail coal filter press, in order to effectively control the feed pressure of the tail coal filter press, the running time of the feed pump is reduced, and the working efficiency of the filter press is improved. The feed diverter valve and the diverter tube were removed.

2.2 Introducing PMW inverter

In the modified tail coal filter press control system, in order to reduce the running speed of the feed pump, stabilize the feed pressure of the filter press, use the frequency conversion technology to realize the frequency-adjusting speed of the motor to adjust the operating speed characteristics of the motor, and introduce the inverter Feeding system of tail coal filter press. In this way, by controlling the operating frequency of the feed pump motor, the operating speed of the feed pump is adjusted to achieve the purpose of stabilizing the output flow and output pressure of the feed pump. Furthermore, by adjusting the frequency of the frequency converter, it is ensured that the feed pressure of the tail coal filter press is within a reasonable range of 0.4 to 0.5 MPa.

2.3 Realize remote control

In the modified tail coal filter press control system, in order to more convenient operation and observation of the tail coal filter press feeding system inverter, a smart meter (inverter remote controller) is added to control the inverter. The remote controller of the inverter is installed at the site of the tail coal filter press. Through the RS485 network communication protocol, the inverter remote controller controls the start, stop, acceleration, deceleration, forward and reverse of the inverter, and displays the operating frequency of the inverter in real time. Operating status information such as speed. By observing the pressure of the pressure gauge on the inlet pipe of the filter press to adjust the addition and subtraction buttons on the remote controller of the inverter, the feed pressure of the tail coal filter press can be stabilized.

3 technical improvement effect

For the practical application of tail coal filter press, the power cost and material cost are high, the feed pump causes a lot of useless work, the feed time is too long, and the feed pressure stability is poor. Through the analysis of the filtration pressure and the feed pressure, The feasibility plan demonstrates that the structure of the feed control system of the tail coal filter press is modified without affecting the normal operation of the equipment, and the frequency conversion technology and remote control are applied to the filter feed system, which greatly improves the tail. The operation effect of the coal filter press.

After the frequency conversion technology is applied to the feed control system of the tail coal filter press, the tail coal filter press never shows the phenomenon that the feed pressure is unstable, the feed effect is poor, and the filter press cycle is long. The two feed pumps only need a frequency range of 20-35 Hz to ensure that the feed pressure of the tail coal filter press is stable, and the wear of the feed pump fittings and pipes (the pump fittings and pipe replacement cycle is extended by one time) is reduced. The workload of maintenance and overhaul of employees has been greatly reduced, and the annual direct material cost can be saved by more than RMB 40,000. After adopting the frequency conversion technology, all the slime water discharged from the feed pump enters the filter press, saving the feeding time and improving the working efficiency. After the transformation, the feeding time is reduced from 40min before the transformation to 20min, which is equivalent to 1/2 times the processing capacity of the filter press, and the annual electricity saving cost can reach 114,600 yuan.

4 Conclusion

Reasonable control of the feed pressure of the feed pump is a guarantee for efficient operation of the tail coal filter press. Improve the structure of the feed control system and introduce the frequency conversion technology to the tailings filter press feeding system, which not only can reduce the operating cost and create economic benefits, but also improve the reliability of safe operation of the equipment. The successful transformation of the control system of the tail coal filter press in Moxinpo Coal Preparation Plant not only changed the passive situation that restricted production, but also brought direct income of more than 150,000 yuan per year, with significant economic and social benefits.

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