In the processing of trona, the lye refining process such as melting and clarification of trona is first carried out. The traditional method is: the raw material alkali is first melted to make the saponin liquid, and then the sulphate liquid is sent to the Daoer clarification barrel for sedimentation, and after the sedimentation, the clear liquid is sent to evaporate, and the clarified mud (primary mud) is washed into the washing mud bucket. emission. Since the trona mud is composed of silicate, aluminate and carbonate which are extremely fine particles, with the dissolution of the alkali ore, the alkali mud forms a lyosome, floats in the lye, and clarifies the solidification of the mud after sedimentation. The liquid ratio is low (about 30% by volume), and the mud contains a large amount of alkali liquor. Although washed, the alkali content of the sludge is still high; in addition, the clarified alkali liquor has high turbidity and high organic matter content. It is easy to cause the evaporator to foam and bring liquid, which brings inconvenience to the operation and has a great influence on the quality of the product, especially the production of granular soda ash, high content of organic matter, high particle size and whiteness of turbidity. Failure to meet the requirements, causing losses to the enterprise.
In response to the above problems, our institute has improved the filtration method of a mud and clarified liquid, using a new type of high-efficiency filtration equipment such as PE microporous filter, and achieved good results.
The PE microporous filter is first applied to insoluble materials and other impurities in the sewage treatment in sewage treatment. With the continuous development of production technology, this filter has been introduced into other industries with its high clarity, low insoluble content, non-toxic and harmless, and is being used more and more widely.
In the research practice, the structure of microporous filter, the conditions of use are constantly explored and improved, from small-scale development to large-scale production, equipment and microporous tubes are all self-organized to meet the needs of different production conditions. At present, our institute has 11 sets of PE pipe filters produced by Shanghai Weifu Filtration Equipment Co., Ltd., with a total filtration area of ​​1450m?, which is used for filtering primary mud, clarified alkali liquor, lye liquor and caustic soda salting. Liquid, alkali solution for carbonization, and the like.
1. Filter principle and process flow
PE microporous filter is composed of filter tube, filter box, liquid outlet tube, body, etc. PE microporous tube is loaded into the filter. When alkaline mud or lye passes through PE microporous tube, fine mud and some organic particles adhere to it. On the outer wall of the tube, the liquid permeates into the tube through the micropores on the filter tube, and is collected by the filter cartridge and overflowed from the outlet. The microporous tube is sintered from a polymer material, and micropores are formed during the sintering process, and the sintering temperature can be adjusted to obtain a sintered tube of different pore diameters, which is suitable for different filter media.
Brief description of the process: clarify that the mud (refined lye, lye liquor, salting solution, etc.) is pumped into the PE microporous filter, according to the initial low pressure - forming filter cake - stepping pressure - slagging procedure Operation, the initial pressure is controlled below 0.03 MPa. When the slag in the filtrate forms a filter cake on the outer wall of the filter tube, under the pressure of the pump, the particles in the suspension will rapidly “bridge†outside the micropores. "Phenomenon, so that a part of the small particles smaller than the microporous channel is also intercepted, the filtrate penetrates the filter cake into the filter box, flows out from the liquid outlet tube to the storage tank, and is sent to the next process. A schematic diagram of the process flow is shown in Figure 1.
With the formation of the filter cake, the pressurization operation is gradually performed, but the pressure does not exceed 0.2 MPa, and the slagging time is determined according to the filter pressure and the discharge condition, and when the slag is discharged, a compression of 0.4 to 0.6 MPa is introduced from the backflushing valve. The air is subjected to instantaneous back-blowing and slag removal, and then washed by washing water. After washing, the water is discharged into the mud bucket in time. If the caustic soda salt is filtered, the water is sent to the storage tank to be concentrated and sent to evaporate.
The filter tube of the microporous filter is divided into several groups, and the filtration condition can be observed separately. If one of the lye is found to be unqualified, the filter tube is closed to stop working.
2, production application effect
2.1 Filter quality
2.1.1 Hydrazine solution filtration
The choice of PE microporous filter solves the problem of direct filtration of lycopene solution. Most of the trona lakes in Inner Mongolia are distributed in arid deserts. During the process of Chenghu (mine), long-term wind and sand invasion and surface runoff from the lake (mine) are brought into the sediment, and the water insoluble content in the mine is very large. In addition to a part of the mud taken out by the alkali, most of the mud is brought from the lye to the clarification process, and the mud particles are fine and difficult to clarify, especially some alkali ore (such as the ore in the contracted Khan San mining area), and the clarification speed is extremely slow. It is difficult to directly use. After selecting the PE microporous filter, the lycopene solution is directly filtered. The quality of the filtered liquid is high and the effect is good (see Table 1), which can be directly sent to the evaporation system for production. Prior to this, we also selected some filtration equipment, such as mechanical filters, closed filter presses, etc., tried to directly filter the lye liquor, but the filtered lye was high in turbidity and could not be finished. Required, can not be used. After that, the sputum is filtered by the plate and frame filter press. Although the filter cloth is repeatedly selected, the quality of the sputum filter is improved, but the filtration speed is slow. In a short time, the fine mud blocks the filter cloth hole and is Forcing the mud, because the filter plates are not filled with filter cake, each time the mud is discharged, a large part of the lye is drained, and the loss is serious. In addition, the filter mud is stuck between the filter cloths. When the mud is discharged, it needs to be washed repeatedly with water to feed again. The effective operation time is short and the production is uneconomical.
2.1.2 Primary mud filtration
In the past, the mud, that is, the clarified mud, was sent directly to the washing mud bucket for washing. In order to maintain the water balance of the production system, the amount of water added during the washing of the mud was not too great, so the alkali content of the sludge after washing was still high, generally More than 8%, after filtration through the microporous filter, the solid-liquid ratio of the secondary mud (drained after filtration) is increased, the amount of mud is reduced, and the alkali content of the mud after washing the mud washing bucket is not more than 3%, which reduces the washing. The mud load reduces the alkali content of the sludge, which saves raw material consumption and reduces production costs. Our soda ash production capacity is 50 kt / a, the average daily discharge of mud about 250m?, the sludge contains about 20% of alkali, after filtration, the alkali can be recovered 25t per day (100% Na2CO3) ), 7500 tons of alkali can be recovered throughout the year.
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2.1.3 Clarification solution filtration
Continuous clarification of the lye of the barrel clarification, the turbidity is generally above 50ppm, the color is light due to the presence of organic matter in the lye, the soda ash produced by the lye, the whiteness is poor, especially for the production of granular soda ash. It affects the formation of particle size. If it is not properly operated, it will easily cause excessive fine crystals in the evaporation, causing abnormal phenomena such as leakage in the centrifuge and "cracking of the evaporator". After the microporous filtration, the turbidity of the lye can be The control is about 20ppm, the color is clear and transparent, which is convenient for evaporation operation and guarantees the quality of the product. The quality control before and after filtration of the clarified liquid is shown in Table 3.
2.1.4 Filtration of caustic soda
In the process of caustic soda production, the salting out process is the key process to control the quality of caustic soda. In production, the quality of the raw material trona varies greatly. There are two layers of alkali, autumn sun alkali, summer sun alkali, etc., the total alkali content is from 15% by weight to 30%, and the salt nitrate content is from 1% to 10%. Different, especially when the NaCl content is high, it is difficult to separate by evaporation, mainly relying on cold precipitation filtration. We pass the cold-dissolved NaOH solution through a microporous filter, and filter out the fine crystal nuclei which are not easy to settle in the cold precipitation clear liquid, further improve The quality of the salting out solution ensures the purity of the caustic soda.
The quality of the caustic soda before and after filtration is shown in Table 4.
2.2 Filtering capacity
See Table 5 for the filter capacity test data of different media of 100m? filter.
It can be seen from the table that the greater the viscosity of the material, the higher the suspended solid content, the smaller the filtration capacity, and the more frequent the discharge.
3. Introduction to filters and supporting equipment
3.1 Filter PE In the microporous filter, one end of the PE tube is connected to the filter box by the wire nozzle, and the other end is closed and vertically in the filter. The filtrate enters the tube through the micropores on the PE tube under pressure and is collected in the filter box. Outflow through the pipe, the liquid outlet pipe is equipped with a sight glass and a valve to observe and control the liquid discharge condition. The filter is equipped with an air back-blowing pipe. The function of the back-blowing is to blow out the liquid in the filter box and the filter tube, and blow off the outer wall of the filter tube. The adsorption layer and the filter are also equipped with a pressure gauge, and the slag discharge time is controlled according to the pressure rise and fall and the liquid discharge amount.
The PE tube in the filter is made of a polymer polymer sintered at a certain temperature, and has the characteristics of acid resistance, alkali resistance, pressure resistance, etc., and the sintering temperature is adjusted to obtain different microporous PE tubes. The raw materials and different molds can be completed in the drying box.
3.2 Auxiliary equipment PE microporous filter equipment is relatively simple, only need to be equipped with feed pump, air compressor can run.
4. Economic and social benefits
4.1 Economic Benefits Our hospital* selected the 100m? PE pipe filter of Shanghai Weifu Filtration Equipment Co., Ltd., and later used to filter the alkali solution for carbonization, filtered the mud and made 6 new filters of 150m? 410,000 yuan (including supporting equipment, civil engineering, etc.), the investment per m? filtration area is 455.6 yuan, the filter capacity of the filter is 0.00698m?/m?.h (primary filtration capacity), daily filtration liquid The quantity is 0.1256m?/m? (effective production time is 18h/day), and the 6 filter clear liquids are 113.04m?/day, which is converted into the standard clear liquid output of 248.78m? (standard) / day (including total The base is 100g/L is 1 standard), the soda ash is 25 tons/day, and 7500 tons/year. The cost of lye solution in our lye preparation workshop is 22.73 yuan/standard, and the cost of lye after microfiltration is 9.09. The yuan/standard side can save more than 1 million yuan per year (only lye), and it can recover all the investment in less than half a year.
If the lye recovered by filtration is used to produce granular soda ash, the cost of solid caustic soda is low, and the production cost of the whole process is about 500 yuan/ton, and the economic benefit of more than 4 million yuan can be obtained throughout the year.
4.2 Social Benefits After the unit is put into production, the operation is stable and the filtering effect is good. The problem of difficult lye refining is solved, and a new technical approach has been opened up in the direct recycling of clarified mud. The recovery of the lye in the clarified mud not only reduces the production cost, but also saves the raw material alkali and prolongs the service life of the alkali lake. In the refining process of caustic soda liquid, good results have also been achieved, which has brought the quality of caustic soda to a new level and has a good application and promotion value. In addition, the equipment can also be used in chemical plants. "Recycling of waste residue wastewater in the treatment.
5. Problems exist After the PE microporous tube is used for a certain period of time, the microporous tube will be clogged. Although it is soaked with dilute acid and rinsed for regeneration, the service life is generally one and a half years, and the filter box inside the device needs to be raised once. It is more troublesome. The next step is to conduct research and experiment on the material of the PE pipe to minimize the number of regenerations and prolong the service life, so that the equipment is more perfect.
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