Knowledge of flotation coal

There are many types of coal, coal float is one of them, here are some of the knowledge about the introduction of floating coal is divided into several parts about:

1 characteristics of coal slurry flotation process; 2 current status of flotation process parameter control technology; 3 foreign flotation control technology status; 4 coal preparation plant flotation control system; 5 domestic flotation control technology status; 6 China flotation control technology The problem faced; 7 the development direction of coal slurry flotation process parameter control.

1 Characteristics of the process of coal slime flotation.

Flotation is one of the most effective methods for processing fine-grained coal (<0.5 mm). But the flotation process is done in solid-liquid-gas three-phase, which is an extremely complex physical and chemical process. Therefore, there are many factors affecting the effect of the flotation process, and there are coupling phenomena between the factors, making their mechanism of action more complicated. In addition, the flotation process has nonlinear characteristics. There is a strong nonlinear relationship between the amount of chemical added and the flotation of clean coal ash, the concentration of floating liquid and the ash content of the product. In addition, the flotation process is still a large time-delay system. It takes about ten minutes for the material to complete the whole process. The adjustment of the process parameters often lags behind the disturbance changes. These characteristics of the slime flotation process bring about the establishment of a dynamic model of the flotation process and the difficulty of implementing a control strategy based on a mathematical model.

2 Current status of flotation process parameter control technology.

In recent years, due to the large-scale flotation equipment , the improvement of process detection sensors and the development of computer technology, the automation of slime flotation has also been greatly developed.

3 Status of foreign flotation control technology.

Due to the leading position of foreign sensors and computer technology, the control of foreign coal flotation flotation process is earlier than domestic and the level is higher. In this field, the countries with leading technology levels are mainly Australia, the United States and Germany. These countries have begun to shift from fixed value control to the use of online ash control device optimization control, control strategy is also transferred from PID control to fuzzy logic control, the following examples reflect the advanced level of foreign coal flotation control.

In 1984, an online analyzer (ASHSCAN) capable of measuring coal ash and solids content was developed by the Julius Kruttschnitt Mineral Research Center (JKMRC) and the Utah Development Co., Ltd. of the University of Queensland, Australia, and applied to Peak in January 1985. In the automatic control of the coarse flotation unit of Downs Coal Preparation Plant, the principle of the control system is shown in Figure 1. It is based on the ash and solid content of flotation feed, clean coal and tail coal flow measured online by ASHSCAN, and adjusts the set values ​​of the three loops of dosing amount, flotation machine level and vacuum filter speed respectively. The coal slurry liquid detection sensor is installed in the third chamber of the flotation machine, and the tail gas is controlled by the PI regulator to stabilize the liquid level. The use of this control system not only makes the clean coal ash and solid content more stable, but also improves the flotation efficiency by more than 10%.

4 Coal preparation plant flotation control system.

In 1990, American Process Technology Co., Ltd. (PTI) developed an online ash analyzer capable of detecting coal ash with a particle size of less than 10 mm. The accuracy of the flotation clean coal and tail coal ash was 0.5%. And 0.75%. In 1992, the online monitoring system developed with this ash meter was applied to the coking coal flotation control of the West Virginia Coal Preparation Plant. By detecting the ash and material flow online, the ash and mass balance of the product can be calculated. Control provides basic data. The coal particle loss of the froth flotation system is minimized by detecting changes in tailings ash in real time. The performance test shows that after applying this online monitoring system to flotation control, the foam product is relatively pure, the tail coal ash is higher, and the total clean coal yield of the whole plant is increased by 11.5%. From March to April 1993, PTI installed a set of such flotation control systems at the Alabama Thermal Coal Preparation Plant. The control strategy used was based on fuzzy logic technology. After the technical system was put into production, the manual and automatic control comparison tests were carried out on the high ash and low ash coal slime respectively. The results showed that the yield increased by 7.8% when using automatic control.

Hans Jensen et al. also used the Amdel Coal Slurry Analysis System (CSA) to control the flotation process. It changed the flotation agent addition and flotation based on the flotation of the clean coal ash and tail coal ash. The liquid level of the machine is adjusted using fuzzy logic control. The application results show that the control system can stabilize the clean coal ash and increase the yield of clean coal; and it can minimize the consumption of chemicals.

In addition, the German RGI company's ash analyzer, the Polish G-4 and MPOF online ash analyzer and the FLOTASTER system have also been applied in flotation control, and achieved good results.

5 Status of domestic flotation control technology.

The automatic control of the process parameters of coal slime flotation in China started late, and it is about 10 years behind compared with foreign countries. Since there is no coal slurry meter, China still stays at the level of fixed value control.

In 1982, Huainan Mining College and Huainan Mining Bureau Wangfenggang Coal Preparation Plant were combined to use the PID regulator designed by single-board machine to realize the automatic control of flotation feed concentration and dosing amount for the first time in China. Reduce the consumption of flotation reagents and improve the yield of clean coal. After years of promotion and application and improvement, many coal preparation plants have also equipped this control system and become the basic mode of automatic control of slime flotation in China.

In 1988 and 1989, the Tangshan Branch of the Coal Science Research Institute successively researched and successfully tested the FC-I and FC-II flotation process parameters. This control system uses a single-chip controller as a controller to solve the small-flow flotation reagent. Automatic metering and decentralized multi-point adding technology, the dosage will not only automatically track the dry coal slurry volume, but also automatically track the concentration of the floating coal slurry, so that the flotation agent addition amount is more reasonable and the precision is greatly improved.

In 1990, the Mineral Processing Laboratory of the Graduate School of China University of Mining and Technology in Beijing was developed and put into use in the flotation automatic control system of the Bayi Coal Preparation Plant. The test parameters were limited to the feed concentration, coal slurry flow rate and chemical dosage. The main function of the flotation automatic control system is to calculate the amount of dry coal in the feed according to the automatically detected feed concentration and flow rate, control the amount of flotation agent added according to the amount of dry coal in the feed, and maintain the float by adjusting the additional water. The appropriate slurry concentration is selected and the control device used is the STD bus industrial control machine.

In 1991, the Beijing Coal Chemistry Institute of the Coal Science Research Institute designed the flotation process process parameter control system for the Zhuzhou Coal Preparation Plant. It has four main functions, which can reasonably control the size and stability of the feed flow; The concentration and stability of the concentration; according to the change of dry coal slurry, control the dosage of each dosing point of the flotation machine; maintain the stability and suitable height of the flotation liquid level. The PID control is used to realize the fixed value control, and the flotation process and process parameters are stabilized by comprehensively controlling the parameters of the floating concentration, flow rate, flotation machine liquid level and dosage.

All of these control systems in China use fixed value control for the control of flotation process parameters. The control algorithm used is PID adjustment. The fixed value control of the flotation process can reduce the consumption of flotation reagents and improve the recovery rate of clean coal to a certain extent, but the set value of the floating concentration, the set value of the flow rate, and the consumption and ratio of the dry coal slurry per ton It is determined that there is no reasonable theoretical derivation method, which can only be determined by experience and experiment. At the same time, the coal control quality of each coal preparation plant is different from that of the flotation agent used. How to change these settings in time to obtain the best flotation effect according to changes in coal quality and environmental changes is a subject worthy of study. At present, there are few reports on this aspect.

6 China's flotation control technology is facing problems.

China's coal slurry flotation process parameter control process has been carried out for more than ten years, and the coal preparation plant that has obtained the title of “Modern Coal Preparation Plant” has automatic flotation control. However, compared with foreign countries, the level of flotation technology and flotation automatic control in China's coal preparation plants is still relatively low. Although many coal preparation plants have realized flotation automation, their use is not satisfactory, the reliability is poor, and the service life is short. There are only a few of the actual real use in the country. What is the reason?

First of all, China's existing flotation control system is relatively backward in terms of control devices, detection components and actuators, and needs to be updated and improved. In the dosing device, the existing slime flotation control system mostly uses solenoid valves and gear pumps. Practice has proved that the effect and reliability are extremely poor, but for the calculation and control of micro-flow medicaments, precision metering pumps have appeared in the chemical industry. The use effect is good, and it has been applied in Zhuzhou Coal Preparation Plant and Huaibei Coal Preparation Plant. For the control of coal slurry level, there are very few applications in China, because there is no basis for the adjustment of the liquid level. In addition, the electric actuator used for lifting the tailgate in the field, whether manual or automatic, is difficult to operate normally. There is a need to develop new actuators. The flotation process parameter control system developed in the past has been made to be less reliable due to the limitations of the hardware and software technical conditions at that time. The flotation control system of the coal preparation plant should be continuously improved with the emergence and development of new technologies and new instruments mentioned above.

Compared with foreign countries, it can be seen from the comparison of examples that the reasons for the backwardness of coal slurry flotation control technology in China are mainly reflected in the sensor (mainly coal slurry meter) and control strategy. Although China's research on isotope ash has been very deep, from the 1970s to the present, there are more than 50 domestic ash meters, but most of them are off-line, and the measured coal samples are limited to raw coal or final clean coal. There is no report on the coal slurry ash analyzer successfully designed by our country for use in the field. This is also the main obstacle to the development of China's slime flotation control technology. But in this regard, foreign countries are quite mature.

7 Development direction of process parameter control of slime flotation.

After the technical characteristics of the computer structure and testing instruments meet the requirements, the technical level of the control system mainly depends on the control strategy. The development of the coal flotation flotation control strategy in China has gone through two stages, namely the classical control strategy and the model-based Modern control strategies, but their theoretical basis is the mathematical model that requires precise control of the object.

There are many process parameters affecting the flotation index, and many process variables are very difficult to detect. The best combination of various process parameters is the difficulty of flotation operation, and also the key to obtaining higher recovery rate. So far, a mathematical model that can fully and accurately reflect the flotation process has not been established. The control system designed by the model-based modern control strategy often fails to achieve the desired effect or even be used. Therefore, it is imperative to introduce artificial intelligence into flotation control.

In foreign countries, fuzzy logic has been used in the field of flotation control to realize artificial intelligence, but it is impossible to obtain deeper technical information. In China, artificial intelligence-based computer control has been applied in many fields, but it has not appeared in the process control of the coal preparation industry. At the same time, the Tianzhuang Coal Preparation Plant introduced the first and only Amdel coal slurry ash analyzer from Australia in 1995, but it is currently only used for testing, and has not achieved control over the quality and yield of flotation clean coal products. . Therefore, it is urgent to use this supporting flotation process parameter control system, which has broad application prospects and theoretical research value.

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