Application of anionic polyacrylamide in coal slime water treatment
1 polyacrylamide or PAM flocculation mechanism, is a kind of linear polymers, non-toxic, non-corrosive, soluble in water, its aqueous solution mixed with coal slurry water after polyacrylamide molecular chain reactive with fine particles of slime water surface adsorption, plays a role of connection between the particles and make the fine grain to form bigger floccules, accelerates the slime settling velocity.
2 preparation of polyacrylamide aqueous solution Xinji coal preparation plant chooses polyacrylamide colloid as preparation raw material, its solid content is 3.75%, molecular weight is about 8 million. According to the preparation of polyacrylamide solution concentration 1‰ to calculate the required amount of water and colloid, first into the mixing cylinder into the water, start the agitator, slowly poured polyacrylamide colloid, so that the mixing evenly; Until the colloid is dissolved, that is, the liquid in the mixing cylinder becomes colorless transparent liquid, and there is no undissolved condensate or block in the liquid, then stop stirring, polyacrylamide solution preparation is completed. During preparation, attention should be paid to avoid excessive stirring to cause degradation of polyacrylamide molecules.
The addition of polyacrylamide aqueous solution is the key link in the treatment of coal slime water, take the appropriate way of adding, will help to improve the flocculation effect. After years of production practice and observation, the plant gradually groped for improvement and formed a set of dosing device; Now take the following way to add: production, open the discharge pipe valve to a certain opening, start the chemical pump, the polyacrylamide solution into the coal slime water. The dosing point is located where there is local mixed flow in the coal slime water, which is helpful to the formation of flocs in the coal slime water. In this factory, dosing points are arranged in water distribution tanks. In order to ensure uniform and stable dosing and timely precipitation of coal slime, at least 2 reagent stirring tanks are used in the production process. Before the injection of one polyacrylamide solution, another solution has been prepared to maintain the continuity of adding reagents. Unstable dosing can easily lead to excessive concentration overflow. During dosing, attention should be paid to the sedimentation of coal sludge water in the concentration tank, and the concentration overflow is stable at 30 ~ 40g L.
4 influence factors of flocculation effect
4.1 Polyacrylamide dosage For the treatment of coal slime water, it is necessary to add an appropriate amount to effectively play its flocculation. It can be determined by experiments according to the treatment technology and properties of slime water selected. Low dosage will lead to slow slime sedimentation rate, enrichment overflow is easy to exceed the standard, can not guarantee the required circulating water index, so that the coal washing product index is difficult to control stably. Although excessive dosage quickens the sedimentation rate of slime, it is easy to cause too high concentration of concentrated bottom flow. Generally, the concentration of concentrated bottom flow is required to be 500g L, which can meet the pressure filtration production. Too much concentration of the bottom flow concentration is sometimes as high as 700g L, and the content of polyacrylamide in the bottom flow increases, which is adverse to the bottom flow transportation and pressure filter production, coal cake is not easy to fall off when the pressure filter unloading coal cake, increase the labor intensity of the operator, reduce the efficiency; At the same time, it also causes waste of medicine and increases production cost. Therefore, the appropriate use of polyacrylamide, not only can improve the flocculation effect, effective treatment of coal slime water, but also to ensure the coal washing product index, improve the efficiency, reduce the cost also plays an important role.
4.2 Coal preparation plants with different concentrations of slime water have different technological requirements for the concentration of slime water entering the concentrator. The plant now produces thermal coal. In order to reduce the pressure of slime water treatment link and improve the production capacity of coal washing, the concentration control of slime water entering the concentrator is required to be higher, that is, the overflow concentration of cyclone is controlled below 70g L. In this way, the flocculation effect can reach a more ideal state and the sedimentation rate of coal slime is faster. Of course, the lower the concentration of coal slime water is, the more favorable it is for flocculation, but it is very difficult to control the cyclone operation. The higher the concentration of slime water is, the more unfavorable it is to flocculation, the slime precipitation rate decreases obviously, the overflow of concentration is difficult to control, the consumption of reagents increases, the precipitated slime is loose, the concentration of concentration bottom flow is lower, and the formation of coal cake by pressure filtration takes longer. When the concentration of slime water reaches 95g L, the consumption of polyacrylamide is twice as high as the normal condition, the overflow of concentration often exceeds the standard, and the coal slime water in the concentration tank is suspended, which seriously affects the coal washing production. Therefore, strictly controlling the concentration of slime water plays a key role in the flocculation effect.
4.3 Temperature of coal slime Water Through the observation of recent years, the temperature change of coal slime water also has a certain influence on the flocculation effect. When the temperature is higher, the flocculation effect of coal slime is better and the sedimentation rate is faster. When the temperature is low, the flocculation effect is relatively poor and the sedimentation rate of coal slime is slow. This kind of phenomenon is more obvious when comparing in summer and winter. In the actual production process, it is very difficult to improve the temperature of coal slime water. In order to ensure that coal slime water is treated in time, the concentration of polyacrylamide aqueous solution can be appropriately increased when the temperature is low, especially in winter.
4.4 Nature of raw coal in washing This plant is a mine type coal preparation plant, and the nature of raw coal in washing is mainly determined by the nature of raw coal in mine production. Due to the change of mining coal seam and underground conditions, the nature of coal produced in different periods will change, so the nature of raw coal washed is not very stable, sometimes the difference is very large, such as the change of ash content and particle size of raw coal, which also has a certain impact on the flocculation effect of coal slime. When the ash content of washed raw coal is low, the coal slime flocculation effect is better, the coal slime precipitation rate is faster, the flocculation is more dense, which is beneficial to the coal slime water treatment, can appropriately reduce the amount of polyacrylamide colloid; When the ash content of washed raw coal is relatively high, the flocculation effect of coal slime becomes worse, and the flocculation rate slows down. At the same time, the flocculation is relatively loose, which is unfavorable to the treatment of coal slime water. Therefore, the dosage of polyacrylamide colloid should be increased. Therefore, grasping the level of washed raw coal ash and adjusting the amount of polyacrylamide colloid play an important role in the flocculation effect of coal slime. When the particle size of washing raw coal becomes small, although the concentration of coal slime water in the concentration tank does not increase, the proportion of fine slime increases. If the amount of polyacrylamide colloid is not increased at this time, the flocculation effect will become worse, and there will be some slime precipitation and some slime suspension in the concentration tank, and the concentration overflow is easy to exceed the standard. At the same time, the concentration of the bottom flow is low, which directly affects the production of pressure filtration. The main reason for this phenomenon is the increase of fine particles in coal slime water, which increases the total specific surface area of each particle. Only by increasing the amount of polyacrylamide, can a large number of fine particles form flocculation.
In the production process of this factory, due to the influence of local conditions, there is a large amount of mud in the coal washing, so that the slime water contains a part of fine mud, and the hardness of the slime water is low, which seriously hinders the coagulation settlement of the slime. It is difficult to achieve the purpose of slime rapid settlement only by the action of polyacrylamide. The plant adopts the auxiliary method of adding halogen tablets (main component magnesium chloride) to cooperate with the use. Its consumption is 0.1 ~ 0.12kg brine sheet for each 1t of coal washed. Add separately with polyacrylamide aqueous solution and dilute with water before adding. The effect of hardness of fine mud and slime water is basically eliminated.
6 conclusion, therefore, to master the configuration of the PAM aqueous solution, and the add operation method and relevant influence factors, aiming at the problems in practical application, adopt corresponding solution, role to play in promoting not only to the coal slime water treatment, and the production of stable system, reduce the production cost, improve the economic benefit is also play an important role
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