In this paper, the research progress of coal slurry flotation process, flotation pre-flotation, flotation reagents and treatment, flotation machine, etc. in recent years is reviewed, and the future development direction of coal slurry flotation technology is prospected.

Coal flotation is a component of coking coal preparation plant, and it is an important task to recover fine coal and purify coal slurry. With the advancement of coal preparation technology, in recent years, the slime flotation technology has made great progress in flotation process, pre-flotation upgrading, flotation reagents and treatment, flotation machine and so on.

1 Improvement of coal slurry flotation process

1.1 Deslimation flotation

Some coal preparation plants have a high content of high-ash fine mud in the flotation feed. High-ash fine mud not only has no value of flotation, but also deteriorates the flotation effect, resulting in high flotation of clean coal, low tail coal ash, and large flotation agent consumption, which makes production management extremely passive. To solve the problem fundamentally, the first task is to remove the fine mud before entering the float. The desilting flotation process is shown in Figure 1.

Figure 1 Deslimation flotation process

There are several types of de-sludge facilities: dewatering by hydrocyclone, de-slipping by simmering concentrator and de-slipping of new de-slipping tank. At present, the new type of desiccant tank is better in use. The principle of hydraulic grading is used to realize the deliming process of flotation feed. The structure is simple, the operation is convenient, the mud removal effect is good, the work efficiency is high, and the underflow of the mud removal tank is fed. The pump is delivered to the flotation operation. The pool has the functions of de-sludge and feed buffer, with less investment and quick effect; in the production, the fine mud content and ash in the flotation feed can be visually adjusted, the hydraulic grading granularity can be flexibly adjusted, and the mud removal amount can be controlled.

1.2 Flotation clean coal secondary selection

Production practice shows that an important way to improve the effect of difficult-to-select coal slime flotation and reduce the flotation of clean coal ash is to carry out secondary flotation of flotation clean coal. The flotation of clean coal in many coal preparation plants in China is relatively high, and the flotation "back ash" is serious, which reduces the overall clean coal yield. For example, the coal slime of the Qianjiaying Coal Preparation Plant of Kailuan Mining Group is difficult to float coal, the flotation effect is poor, and the flotation clean coal ash has been running at a high level. According to the research and analysis, it is found that the high-ash fine mud in the flotation clean coal is the main reason for the high ash content, low yield and poor flotation effect of the coal slurry flotation. Recently, the plant carried out a technical transformation of “flotation of clean coal secondary flotation”, which eliminated most of the high-ash fine mud in the concentrate, and reduced the flotation of the clean coal ash by about 1.5 percentage points, improving the flotation. The effect is to increase the overall clean coal yield. At present, some coal preparation plants in Wuhai area are also undergoing technical transformation of secondary flotation of clean coal.

1.3 Two-stage flotation two-stage dewatering and recovery process

The process is to dewater a section of the flotation concentrate into a sedimentation filter centrifugal dewatering machine. In order to ensure that the fine fraction yield of less than 0.045 mm in the sedimentation filter centrifugal dewatering machine is less than 40%, the sieved part of the coarse coal slurry curved sieve is mixed into the flotation clean coal to ensure the necessary technological conditions of the equipment. . Set the second stage of flotation operation, flotation of the filtrate and centrate of the sedimentation centrifugal dewatering machine. The flotation clean coal of the second stage flotation operation is dehydrated and recovered by the filter press. The clean coal of the sedimentation filter centrifugal dewatering machine and the clean coal of the filter press are incorporated into the final clean coal. At present, the flotation process is applied in many coal preparation plants such as Friendship, Junzheng and Tianchen. It can effectively reduce the ash content of flotation clean coal and avoid the flammable body. loss. The advantage of the sedimentation filter centrifugal dewatering machine not only reduces the load of the filter press, but also reduces the overall moisture of the coking coal.

2 Pre-flotation upgrading technology

2.1 Ultrasonic enhanced flotation technology

The effect of ultrasonic enhanced coal slurry flotation was confirmed in the laboratory. The prepared slurry is subjected to ultrasonic treatment, and the slurry is floated after being cooled to room temperature. When the ultrasonic parameters are: ultrasonic frequency 40 KHz, treatment time 4 min, power 60 w, after treatment of Zhaogezhuang difficult coal slurry, under the same conditions of other flotation conditions, flotation clean coal ash is 1.26% lower than ordinary flotation. The clean coal yield and flotation improvement indicators increased by 17.34% and 13.15%, respectively. Tests have shown that the power, frequency and processing time of the ultrasonic wave have a great influence on the effect of flotation.

However, this technology is limited to laboratory experiments and there are no reports on process applications.

2.2 Modification machine upgrading technology

The linear velocity of the flotation machine impeller has a great influence on the dispersion of the collector . With the increase of the shear strength, the dispersion of diesel oil is gradually improved. After the slurry is treated with different strengths, the conventional flotation test is used. The pulping intensity has an important influence on the yield of clean coal. With the increase of the impeller line speed, the yield of flotation clean coal generally increases. Therefore, high-intensity slurry adjustment before flotation is beneficial to flotation. A typical representative is the M-COL2100 Surface Modifier, which is used in some coal preparation plants in Shanxi and Henan. Recently, the Qianjiaying Coal Preparation Plant adopted the “modification machine” designed by China itself and achieved good results. Using the surface modifier system, the fine coal production rate can be improved compared with the ordinary flotation in the case where the flotation of the clean coal ash is equivalent.

2.3 Pressurized pretreatment flotation

The coal sample is formulated into a certain concentration of coal slurry water for pressure and pressure pretreatment, and the conventional flotation test is carried out after the coal slurry water returns to normal pressure. The test results show that the pretreatment of coal slurry water by pressurized method, the clean coal yield and the flotation improvement index are directly proportional to the pressure, and the clean coal ash content increases slightly with the increase of pressure. The mechanism of action is as follows: the pressure pretreatment increases the amount of nucleation bubbles in the surface diffusion layer of the coal particles, and plays a greater role in the flotation process, thereby effectively improving the flotation effect.

The effectiveness of this technology has been verified by laboratory experiments, but the industry has not yet adopted it.

2.4 Oxidized coal flotation upgrading

In view of the problems of high fine fraction, high ash content and difficult flotation in high ash oxidation coal, the deoxidation of oxidized coal by fatty alcohols (ethanol and butanol) was investigated. The test of the flotation machine showed that after the treatment with the fatty alcohol, the flotation effect of the coal sample was obviously improved. Compared with the blank test, the recovery rate of the combustibles of the coal sample after the butanol treatment was increased by 12.99%, and the clean coal ash was reduced by 16%. 63%. Butanol is more capable of improving the flotation efficiency of oxidized coal than ethanol. However, there are no examples of applications in the industry.

In addition, laboratory research on the treatment of oxidized coal using GD technology has made great progress, which will be the future direction of oxidized coal flotation.

3 Flotation agent treatment

3.1 Flotation agent emulsification

Emulsification of flotation reagents is of great significance. Studies have shown that emulsification of flotation reagents can increase the flotation speed, save the dosage of chemicals, improve the flotation process, and improve the yield of clean coal. There are two representative emulsification equipments available today: jet emulsification systems and labyrinth emulsification systems. The emulsified by the labyrinth emulsification system has a minimum demulsification time of 15'57", and the longest can reach 36'8". By observing the microscope picture and data, it is known that the emulsification fineness is in the range of 2 to 6 μm. Industrial application shows that after using the flotation agent emulsifier, the diesel oil is reduced from about 0.85kg/t (dry coal slime) to about 0.59kg/t (dry coal slime), saving about 30% of diesel oil; the foaming agent is from the original The 0.15kg/t (dry coal slurry) is reduced to about 0.11kg/t (dry coal slurry), saving about 26% of the foaming agent. The overall fuel economy is about 30%. The yield of flotation clean coal increased by 0.48%.

3.2 Flotation agent atomization

Based on the analysis of the advantages and disadvantages of the currently used pulp pretreatment and slurry preparation, the slurry pretreatment concept combining wind-jet atomization flotation agent and slurry falling is proposed, and the atomized drop type is researched and developed. Pulp preprocessor. The atomized drop type slurry pretreatment device has a simple structure and consumes 0.388 kw.h. The laser particle size analyzer measures the droplet diameter of the flotation reagent. The results show that the air-jet atomizer is a flotation agent atomization technology with good dispersion effect. When the wind pressure is 0.08 MPa, the average diameter of the droplets is 7.89 μm in terms of the droplet volume. The production practice proves that when the flotation effect is similar, the use of the atomized drop type slurry pretreatment device saves the flotation agent dosage by more than 24% compared with the slurry preparation device.

4 Flotation of new drugs

4.1 ost accelerator

The ost accelerator is an excellent flotation accelerator developed in recent years. It is miscible with diesel or foaming agent and can be added to the current flotation reagent when used. Laboratory tests and field use indicate that the ost flotation promoter can significantly improve the flotation effect. In general, the yield of clean coal is increased by 5-10% or about 30% of flotation reagents are saved. The accelerator facilitates the adsorption of the collector and the coal particles, and promotes the same volume of the collector to spread a larger area on the coal particles. It is not only suitable for the flotation of easy floating and medium floating coal, but also can significantly improve the flotation effect of difficult coal and oxidized coal. The accelerator is an environmentally friendly product, non-toxic and tasteless, and easy to use. The application of the accelerator can significantly improve the flotation effect, mention the yield of flotation clean coal, and bring better technical and economic benefits to the coal preparation plant.

4.2 Accelerators synthesized from vegetable oils, etc.

Under the action of the catalyst, the fatty acid glycerol vinegar in the vegetable oil (cotton seed oil) undergoes vinegar exchange reaction with the alcoholic substance and undergoes alcoholysis reaction, and the resulting higher fatty acid alcohol ester significantly reduces the liquid-liquid interfacial tension and promotes the hydrocarbon oil in the water. dispersion. The polar functional group of the promoter can also increase the hydrophobicity of the local hydrophilic portion of the coal particles, which is beneficial to reduce the consumption of hydrocarbon oil. The kerosene is added to the coal slurry of the Matou Coal Preparation Plant. When the amount of the collector is equivalent, the yield of clean coal is increased by about 4%, and the ash content of the clean coal is slightly increased. In the case of similar coal ash and fine coal ash, the amount of collector is reduced by 50%. The flotation promoter prepared from cottonseed oil can significantly improve the collection performance of coal (chai) oil.

5 Laboratory test results of inhibitors

Aiming at the problem of high coal ash content in coal slurry flotation flotation, the effects of flotation process and inhibitors on flotation of clean coal ash were studied in the laboratory. Firstly, the coal slurry is flotation, the primary flotation coal is subjected to secondary flotation, and the inhibitor (carboxymethyl cellulose) is added during the secondary flotation process, so that the primary coal ash can be floated once. From 12.10% to 9.87%, the flotation of clean coal ash is significantly reduced, improving the flotation effect.

Use hexametaphosphate sodium phosphate can also be used as depressants. The test determined that the inhibitor dosage was 1 kg/t (into the floating coal slurry). In the application of the production of flotation system, the clean coal ash was reduced from 14.36% before the use of the inhibitor to 10.56%, and the yield of the flotation concentrate was only decreased by 7.8%.

However, the inhibitors are still largely unused in the industrial coal preparation industry.

6 Progress of conventional flotation machines and centrifugal flotation

6.1 Technical progress of conventional flotation machines

After improvement, China has developed XJM-(K)S series mechanical agitating flotation machine. At present, this type of flotation machine is widely used in coal preparation plants in China. The pseudo-bottom suction of the surrounding stream of the slurry through the way to adapt to the amount of feed and the change in floatability; the double-layered umbrella impeller and the combination of the core of the mixing mechanism generated by the "W" type slurry flow state In theory, it conforms to the flotation process; the jet pre-mineralizer replaces the conventional slurry preparation operation, which simplifies the flotation process. At present, the flotation machine has a single tank volume of 40 m3.

On the basis of summarizing the advantages and disadvantages of the 2nd generation, the jet flotation machine was improved. The improved FJC flotation machine of the jet flotation machine is shown in Fig. 2.

Figure 2 Improved FJC flotation machine

Mainly for the modification of the aeration mixing device, the immersion aeration stirring mechanism is adopted, which can improve the reliability of the whole flotation machine. The improved FJC flotation machine eliminates the umbrella disperser, shortening the length of the hose, reducing pipe wear and increasing the life of the equipment. The power consumption is reduced, the inflation uniformity is improved, and the impact force of the slurry on the false bottom is enhanced, which is favorable for reflection to the periphery in the "W" shape, and the stirring region in the groove is enlarged. The cross section of the tank is changed from a trapezoid to a rectangle, which is advantageous for the enlargement of the equipment. At present, the flotation machine has a single tank volume of 48 m3.

In addition, a large breakthrough has been made in the enlargement and high efficiency of the flotation column.

6.2 Flotation technology in centrifugal force field

Flotation in a centrifugal field is an advanced technology. The flotation speed in the centrifugal force field is faster, which can improve the entrainment phenomenon of high-ash fine mud in the clean coal and enhance the flotation effect of the fine coal slurry; the centrifugal flotation equipment has small volume, small floor space and saves production cost. However, the centrifugal force field is more suitable for the flotation of fine particles, and the centrifugal strength cannot be too large, so as to avoid the loss of coarse coal.

At present, centrifugal flotation equipment mainly has the following three categories: circular centrifugal flotation machine, flotation cyclone and ASH, and their structural schematics are shown in 3. For various reasons, centrifugal flotation technology is developing very slowly in China. In the future, in the development of new centrifugal flotation equipment, it is necessary to fully absorb the previous experience and lessons, especially in consideration of various unfavorable factors, to develop a reliable and practical centrifugal flotation equipment.

Figure 3 Schematic diagram of centrifugal flotation equipment

7 Conclusion and outlook

The effect of coal flotation flotation is affected by many factors. The research on flotation technology should consider the interaction effects of various factors. First of all, we must focus on coal quality research. Different coal quality adopt different flotation methods, and secondly, we should create the best flotation conditions to achieve the best sorting effect. For slime with high ash and fine mud content, it is best to use deliming flotation or secondary selection process. It is a potential technology for the use of inhibitors, the research and treatment of highly selective flotation reagents, and the pretreatment of pulp before flotation. The research should be strengthened. Such as high-efficiency, environmentally friendly, and can replace the new type of flotation agent for petroleum is the future research direction; the agent should be reliably atomized to improve its use, in addition to the existing nozzle air pressure atomization, by means of the car The principle of the engine to atomize the flotation agent is a good method. The selection and use of inhibitors should be further explored, but it should be noted that the use of inhibitors does not clarify the side effects of slime water. Strengthen research on GM flotation technology of oxidized coal, and strive to enter industrial production as soon as possible. With the large-scale coal preparation plant in China, the large-scale, automation and adaptability of flotation equipment is an urgent problem to be solved. Centrifugal flotation technology has its unique advantages, so strengthening the research on centrifugal flotation theory and equipment is a promising task.

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