Principle of the hottest filtration and analysis o

2022-07-15
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Filtration principle and filter medium analysis

the lithium battery industry is in a period of demand explosion. I. the original filter pointed the pointer to the 300 (150) J reticle theory

(I) basic concept filtration is the operation of separating the suspension with a certain porous medium. During operation, under the action of external force, the liquid in the suspension flows out through the pores of the medium, and the solid particles are intercepted, so as to realize separation. Generally, the suspension to be filtered is called filter slurry; The porous medium used is called filter medium; The liquid passing through the medium channel is called filtrate; The retained solids are called filter cake or filter residue

the driving force of filtration operation is the pressure difference between the upstream and downstream sides of the filter medium. There are several methods to generate the pressure difference:

① use the pressure head of the filter slurry itself

② pressurize the filter slurry surface

③ vacuumize at the downstream side of the filter medium

④ use inertial centrifugal force

the filtration operation can be divided into two categories according to the action principle:

① the number of holes in the sieve filtration medium is smaller than the diameter of solid particles, and the solid particles are removed from the suspension by sieve analysis

at the initial stage of filtration, fine particles flow out and the filtrate is turbid. With the formation and thickening of cake layer, the filtrate becomes clear gradually. As the screen holes are gradually blocked, the filtration speed tends to decrease. In the filtration process, when the filter cake layer is formed, the screening analysis function is generated by the cake layer. The filter medium loses the screening analysis function and only plays the role of supporting the cake layer, which is called cake layer filtration

② adsorption filtration (deep bed filtration): the number of holes in the filter medium is greater than the diameter of solid particles, and the solid particles are adsorbed on the surface of the medium after entering the pores of the filter medium

in actual production, sieve analysis and adsorption act at the same time, and the adsorption filter medium intercepts large particles; The cake layer of sieve analysis filter medium can adsorb small particles

II. Filter media and filter aids

1 Filter media? The main function of the filter medium is to support the filter cake. It must have porous structure, sufficient mechanical strength, as little flow resistance as possible, and corrosion resistance

commonly used filter media include the following types:

① fabric media, such as industrial filter cloth, metal wire, etc

② granular media, such as perlite powder, cellulose, diatomite, etc

③ solid paperboard, such as decolorized wood paperboard, synthetic fiberboard, etc

④ filter membrane, composed of cellulose and other polymers. Granular medium is used as filter aid precoated on the surface of fabric medium for coarse filtration; Solid paperboard media are mostly used for semi fine filtration and fine filtration; Filter membrane medium is used for fine filtration and ultra fine filtration

2, filter aid precoats some hard particles on the surface of the filter medium or adds them to the filter slurry to form a relatively hard and loose filter cake so that the filtrate can pass smoothly. This kind of particles is called filter aid. Requirements for filter aid: the filter aid is a hard, loose structure powdery or fibrous solid. The energetic filter aid should be well suspended in the feed liquid, with appropriate particle size and free of substances soluble in the filtrate

commonly used filter aids include diatomite, cellulose, etc

the purpose of using the filter aid is to prevent the filter medium channel from blocking or reduce the filter resistance of the filter cake

there are pre coating and pre mixing methods for adding filter aids

diatomite and cellulose are the main filter aids used in wine production. Diatomite is the fossil of aquatic plant diatom, which is composed of the remains of paleontological sedimentary diatom. Its main component is SiO2 (accounting for%). It is gray white powder, and the particle size is generally μ m. Minimum 2 μ m. Max μ m. Specific gravity is 0 7.

its main characteristics are:

① the main component is SiO2, with good chemical stability. Insoluble in any strong acid except hydrofluoric acid, soluble in caustic soda. It can be applied to filter slurries with different concentrations and temperatures

② when used as a filter aid, higher filtration speed and ideal clarity can be obtained. Diatomite has numerous pores and multiple pores, and its porosity is%, which provides a large space for intercepting solid particles. In addition, the framework is hard, and the formed filter cake is basically incompressible. It can basically maintain a loose and porous state under the change of pressure, and the filtration resistance is small, which can obtain a high filtration speed and ideal clarity

III. filtering speed

1 Filtration speed and filtration rate the volume of filtrate passing through unit filtration area in unit time is called filtration speed, i.e.:? U=v/atm3/m2, where: a - filtering area, m2;? T -- filtering time, s;? V - volume of filtrate flowing out in time t, m3 volume of filtrate obtained in unit time is called filtration rate, which indicates the production capacity of filtration equipment.? Filtration rate? Q=V/t=u.A? It is expressed in m3/h and l/min

2. Factors affecting filtration speed

① the greater the viscosity of the filter slurry, the greater the filtration resistance, and the smaller the filtration speed

② filter cake thickness the greater the filter cake thickness, the greater the resistance and the smaller the filtration speed. When the thickness reaches a certain degree, the filtration will be terminated

③ the nature of the filter cake is that the particles of the incompressible filter cake are hard, the flow passage through which the filtrate passes will not be reduced due to the increase of pressure, the resistance remains basically unchanged, or the resistance increases slowly with the continuous filtration time, and the filtration speed increases proportionally with the increase of pressure; Small particles will block the channel under high pressure, so the pressure at the initial stage of filtration should not be too large to avoid premature blockage of the channel

the main business of Siping coal Shenma Group is sluggish, and the way of filtering operation is

1 Constant pressure filtration

the filtration operation is carried out under a constant pressure difference, which is called constant pressure filtration. Constant pressure filtration is the most commonly used filtration method. During the filtration process, with the continuous thickening of the cake layer, the resistance increases greatly. Due to the constant pressure difference, the filtration speed will gradually decrease

2. Constant speed filtering

the filtering operation is carried out at a constant speed, which is called constant speed filtering. With the continuous filtration time, the cake thickness increases, the resistance increases, and the filtration pressure difference increases linearly with the continuous filtration time. The pressure resistance of the filter equipment is limited, and the pressure should not be too high. For the compressible filter cake, the excessive increase of pressure can not increase the speed, on the contrary, it will cause the end of filtration

3. Constant speed first and then constant pressure filtration

this filtration method starts with constant speed filtration at a lower speed to avoid channel blockage caused by premature pressure rise. When the pressure rises to a given value, constant pressure filtration is adopted. The constant rate is maintained at the initial stage of filtration with a constant pump. As time goes on, the pump outlet pressure increases. If this pressure rises to the set value that can automatically open the branch valve, the branch opens, part of the filter slurry returns to the pump inlet, the filter slurry entering the filter press decreases, and the pressure at the filter press inlet remains constant, so the constant pressure filtration begins. More than 50 national and industrial standards for the fluorochemical industry were developed and revised under the auspices of DFD (end)

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