introductory

China is the world's largest coal producer and consumer, at present, China's annual production of raw coal contains more than 300 million tonnes of pulverised coal (usually refers to a 0.5mm fine-grained coal), coal washing and processing is generally only recovered +0.5mm coarse-grained coal, and accounted for nearly 15% of raw coal a 25% of fine coal slurry due to the difficulty of processing, the utilisation rate is low, and most of the coal slurry can not be recovered. A large amount of coal slurry occupies the site and pollutes the farmland, meanwhile, the coal dust flies and causes serious environmental pollution. Therefore, economic and effective recovery of this part of fine-grained coal slurry has very important economic benefits and practical significance for coal washing, and very important social benefits and strategic significance for the sustainable development of China's coal industry and environmental protection.

1.Coal sludge dewatering equipment

Dewatering equipment used for coal sludge includes disc vacuum filters, pressurised filters, plate and frame (or chamber)filter pressetc., but the application of this part of the equipment for coal slurry dewatering, the effect is not very satisfactory.

1.1 Difficulty in dewatering vacuum filters

The traditional dewatering equipment for flotation coal is disc vacuum filter, i.e., it causes negative pressure on both sides of the filter net to form pressure difference for solid-liquid separation, but the vacuum pressure difference generated by the vacuum pump can only reach up to o.06MPa, and the pressure difference on the surface of the actual filtered material is even lower, generally less than 0.02MPa, so there are low dewatering efficiency, high moisture of the filter cake, and large energy consumption in the indicator of the vacuum filter. Especially when dealing with fine and sticky materials, filtration and dehydration is more difficult. Specifically manifested in:

(1) Difficulty in dislodging the filter cake, with the help of manual cake poking;

(2) The high concentration of vacuum filter filtrate must be returned to the flotation system, resulting in fine coal sludge circulating in the system, which undoubtedly increases useless work and deteriorates the flotation and filtration effect; (3) The vacuum pump power consumption is large;

(4) Filter cloth replacement is troublesome and costly.

1.2 Deficiencies of pressurised filters

First of all, the expensive price of the pressurised filter makes the medium and small coal processing enterprises deterred, in addition, the actual use of the unsatisfactory, such as the structure, control system complexity, high failure rate, high technical requirements for the operator; and sealing the discharge device of the sealing ring life is short; scraper transporter sticking to the coal is serious; the concentration of the material, the particle size composition of the requirements of the harsh material, the material composition of the particle size of the material is large changes in the product moisture and the filter The processing capacity fluctuates greatly. When the particle size composition of a 200 mesh content greater than 80%, the amount of fine-grained coal slurry through the filter cloth network solenoid into the filtrate is larger, the filter cake is thin when the pressure of the pressurised filter is difficult to maintain, resulting in high moisture.

1.3 Deficiencies of plate and frame (or chamber) filter presses in flotation concentrate dewatering

(1) Plate and frame (or chamber) filter press is the most prominent feature of the dewatered product intermittent centralised unloading, which is the biggest defect for the flotation coal needs continuous dewatering process. At present, the filter press used in the domestic coal plant filter area of 340m2 or more, the largest to 1050m2, a cycle of working time is too long. In addition, the volume of a single piece of filter cake is large and not easy to break. Therefore, if the plate and frame (or chamber) filter press is directly used for flotation coal dewatering, it is difficult to ensure the uniformity of the final coal particle size, moisture and quality.

(2)Large filter pressesThe most suitable feeding concentration is about 500g/L, which is pressed in by pump. The flotation concentrate is a slurry containing a large number of foam, the concentration is usually less than 250g / L, especially the use of bottom-flow discharge and direct flotation coal plant, the concentration is generally less than 200g / L, with the pump pressurised filtration is more difficult. This is because the foam within the slurry will aggravate the use of pumps in the phenomenon of cavitation, so that the efficiency of the pump has decreased significantly; in addition, the low concentration of pressure filtration into the cake takes a long time, the effect is poor, low production efficiency.

(3)The dewatering function of large filter press is single, only relying on the pressure of feed pump to dewater, resulting in long filtering time, high moisture of filter cake, and difficulty of cake shedding.2 Characteristics of fine coal diaphragm fast-opening filter pressFor the deficiencies of vacuum filter and plate and frame (or chamber) filter press, Henan Tangyin Machinery Manufacturing Company and the School of Chemical Engineering of China University of Mining and Technology have jointly developed a flotation coal diaphragm fast-opening filter press, and jointly carried out relevant process experimental research. Jointly carried out the relevant process test research.

Structure of diaphragm quick-opening filter press for flotation concentrate

(1)The outstanding features of flotation coal diaphragm fast-opening filter press are: double-sided filtration, double diaphragm press, its structure sketch is shown in Fig. 1; the beam adopts the form of intermediate without legs, which completely solves the phenomenon of secondary mixing of filter cake and filtrate; the filter plate adopts the ultra-high-molecular-weight polyethylene material, which has the features of light weight, long service life, corrosion-resistant, and no aging; the intake structure adopts the double-row independent type, which has the feature of even moisture of cake, and is conducive to the unloading of cakes and ensures the airway is not blocked; it can be squeezed and dewatered to reduce moisture, and at the same time is conducive to the discharge of cake. The air inlet structure adopts double-row independent type, the moisture of filter cake is even, which is good for unloading cake, and can ensure that the airway is not clogged, and is easy to maintain. The filter plate is equipped with high-strength double-sided diaphragm, which can realise high-pressure strong fluid feeding, strong airflow wind blowing filter cake and diaphragm pressing and squeezing filter cake dewatering, which increases the dewatering function, reduces the moisture of fine coal, improves the effect of filter cake dislodging and produces the filtrate with low concentration that can be directly entered into the circulating water system, which overcomes the shortcomings of the vacuum filter due to the high concentration of the filtrate that has to be returned to flotation, which leads to deterioration of flotation effect.

(2) In order to overcome the drawbacks of traditional tailings filter press with large model, long single-cycle time, intermittent centralised cake unloading leading to uneven total fine coal quality, etc., while taking into account the optimal economic volume of the material tank and air bag. In the initial design, try to choose a small-size model with a filtration area of 100m2 and the number of chambers less than 50 to achieve the comprehensive effect of fast filtration speed, i.e., fast manning speed, fast plate opening speed, fast cake unloading speed, and short auxiliary time.

(3) Although the above design has achieved very good results, with the continuous progress of the whole coal washing technology, some inadequacies have been gradually exposed, and there are two prominent problems: first, the model specification is small, which is uneconomical to be used in large-scale coal processing plants; second, although the filtration speed has been accelerated, but ultimately can not completely get rid of the effect of intermittent centralised cake unloading. For this reason, the researchers designed a diaphragm quick-opening filter press suitable for large coal processing plants. In addition to retaining the characteristics of the original model, such as double-sided pressing, the new model adopts a set of compression mechanism in its structure, and a new type of alternating manpower at both ends.

(4) Working principle of the new model. The two pressing plates are connected to the cylinder and piston rod of the main cylinder respectively, and the other side is a big flat surface of the same size as the filter plate, so that when any one of the pressing plates is fixed, the other one can be moved in the opposite direction under the push of the main cylinder. The pressing plate is controlled by the inserting cylinder, which controls the movement of the pressing plate by pulling up or down the inserting plate. Inlets can be mounted on top of the thrust plate and the hold down plate. The chain drive mechanism is the pulling mechanism of the pressing plate and transition plate, which can be rotated in both forward and reverse directions. The left filter plate is connected with the transition plate 2 and compression plate 18 respectively, and the right filter plate 10 is connected with the transition plate 9 and compression plate 16 respectively through the cable chain 8 and other spacing blocks. When the inserting plate cylinder 6 inserts the inserting plate 15 and restricts the compression plate 16 to be immovable, the compression plate 18 will be pushed by the main cylinder to tighten the left filter plate, and the left filter plate group will start to be loaded with materials. At the end of feeding at the left end, insert plate 15 is withdrawn, and the chain mechanism pulls the two compression plates to the right, pulling open the left 1/3 filter plate to discharge the cake; at the same time, close the right end filter plate group, insert insert plate 5, and restrict the compression plate 18 from moving, then the compression plate 16 is pushed by the piston rod of the main cylinder, pressing the right end filter plate group, and the right end filter plate group will begin to be fed. At the same time of feeding, the chain drive mechanism of the transition plate 2 rotates forward and backward once, and pulls 1/3 of the filter plate respectively, that is to say, pulls the remaining 2/3 of the filter plate to unload the cake. At this time, the right end of the filter plate group is basically complete with the adult material, pull out the insert plate 5. Similarly, the chain mechanism to pull the compression plate back the same time, pulling 1/3 of the filter plate, the filter plate 9, respectively, positive and negative rotation to pull the rest of the 2/3 of the filter plate to remove the cake. In this way, the machine at both ends of the filter plate group alternating material, not into the material time interval is very short, not unloading the cake time interval is also very short, to achieve a quasi-continuous feeding, quasi-continuous unloading the effect of the cake. In addition, compared with filter presses with the same filtration area, this model occupies a small area and is very suitable for large coal processing plants.

Filter Press Dewatering Process

Large diaphragm quick-opening filter pressThe outstanding feature is to change the traditional slurry pump feeding method, using compressed air feeding. Significant difference with the pump feeding is that from the beginning can instantly reach high pressure into the material, its filter dewatering process flow shown. Adopting self-flow and air pressure feeding, it can better deal with the unfavourable factors such as low concentration of flotation concentrate, large amount of foam, easy to produce cavitation, etc., which not only solves the difficulty of pumping the foam slurry, but also maximises the feeding pressure in a relatively short period of time to improve the filtration speed. The dewatering process adopts Pc programme automatic control, reliable operation, reasonable configuration and flexible adjustment.

Application effect of diaphragm quick-opening filter press for flotation concentrate

According to the natural incoming coal conditions of on-site production, the filter press feed was taken to do a small sieve test, and the cake moisture and filter press time of vacuum filter and flotation fine coal diaphragm quick-opening filter press were measured at the same time under the same conditions, and a small sieve test was done on the filter cake. The flotation fine coal diaphragm quick-opening filter press has good adaptability to the composition of the material size. Different material size composition has a large impact on product moisture. In the test, the equivalent diameter of filter press material particles 74 micron content of 51.60%, at this time, the moisture of the vacuum filter cake is 28.90%, flotation coal diaphragm fast-opening filter press cake moisture is 22.20%, the feed filtration time is only 2.5min. The results show that, in the same conditions of the feed, the cake moisture of the filter press is 6-9 percentage points lower than that of the vacuum filter. Moisture decreased by 6-9 percentage points, the cake shedding rate increased by 30% a 40%, while energy saving 60% ~ 70%, obviously, the dewatering effect is ideal.

reach a verdict

(1)Diaphragm quick-opening filter pressesHigh dewatering efficiency for flotation coal. Under the same feeding condition, not only the moisture of filter cake is low, but also save time and energy.

(2) Flotation coal diaphragm fast-opening filter press dewatering process indicators are advanced, power consumption is small, maintenance is small, stable and reliable operation, is an effective and economic flotation coal dewatering equipment.