Soda ash knowledge (one question per day)

Force the fluid in the liquid-solid or gas-solid mixture to pass through the porosity, and the filter medium intercepts the suspended solid particles in it, thereby achieving the separation of the mixture. It is a unit operation belonging to the hydrodynamic process 1. Use a forced discharge mechanism 2. Replace the filter cloth 3. Use the filter liquid level automatic control system 4. Change the properties of the feed (such as increasing the temperature, increasing the particle size, adding surfactant, etc.

The volume of filtrate passing through the unit filter area per unit time becomes the filtration speed. There are many ways to speed up the filtration. For suspensions with fast solid particle settling speed, a filter that feeds the upper part of the filter medium is used to make the filtration direction consistent with the direction of gravity. Coarse particles settle first, which can reduce the clogging of the filter medium and filter residue layer.； Mixing coarse solid particles such as diatomite and expanded perlite into difficult-to-filter suspensions (such as colloids) can loosen the filter residue layer. ； When the viscosity of the filtrate is high, the suspension can be heated to reduce the viscosity. Introduction: Vacuum filter is a device that uses vacuum negative pressure as the driving force to achieve solid-liquid separation. Structurally, the filter sections are arranged along the horizontal length direction, and can continuously complete operations such as filtration, washing, drying, and filter cloth regeneration. The rubber belt filter has the advantages of high filtration efficiency, large production capacity, good washing effect, low filter cake moisture, flexible operation, and low maintenance costs. Rubber belt filters can be widely used for solid-liquid separation in metallurgy, mining, chemical industry, papermaking, food, pharmaceuticals, environmental protection and other fields. They are especially well used in gypsum dehydration (FGD) in flue gas desulfurization. Edit this paragraph Concept of Vacuum Filter Vacuum filter is a solid-liquid separation machine that forms vacuum filtration by negative pressure. It forms negative pressure at the filtrate outlet as the driving force for filtration. Edit this paragraph Purpose Vacuum filters have been widely used in chemical, pharmaceutical, dye, metallurgy, petroleum, textile and other industries. Edit this paragraph The generation filter is a device that uses porous filter media to intercept solid particles in a mixture of liquid and solid particles to achieve solid and liquid separation. Filters are widely used in chemical, petroleum, pharmaceutical, light industry, food, mineral processing, coal and water treatment and other sectors. 　　Filtration technology has been applied in production in ancient China, and paper made from plant fibers was already available in 200 BC. In 105 AD, Cai Lun improved the papermaking method. During the papermaking process, he swung plant fiber pulp on a dense thin bamboo curtain. The water filtered through the gaps in the bamboo curtain, leaving a thin layer of wet pulp on the surface of the bamboo curtain. After drying, it became paper. 　　Most of the earliest filtration was gravity filtration. Later, pressure filtration was used to increase the filtration speed, and then vacuum filtration appeared. The drum vacuum filter invented in the early 20th century realized the continuous filtration operation. Since then, various types of continuous filters have appeared. Edit this paragraph Working Principle The vacuum filter forms a negative pressure at the filtrate outlet as the driving force for filtration. This kind of filter is divided into two types: intermittent operation and continuous operation. The intermittent operating vacuum filter can filter suspensions of various concentrations, and the continuously operating vacuum filter is suitable for filtering thick suspensions containing many solid particles. 　　Intermittent operating filters have been developed because they can realize automated operation, and the filtering area is getting larger and larger. In order to obtain filter residue with low moisture content, mechanically pressed filters have been developed. 　　Use filter media to separate the container into upper and lower chambers to form a simple filter. The suspension is added to the upper chamber and enters the lower chamber through the filter medium under pressure to become filtrate. The solid particles are trapped on the surface of the filter medium to form filter residue (or filter cake). 　　During the filtration process, the filter residue layer accumulated on the surface of the filter medium gradually thickens, and the resistance of liquid passing through the filter residue layer increases accordingly, and the filtration speed decreases. When the filter chamber is full of filter residue or the filtration speed is too low, filtration is stopped, the filter residue is removed, and the filter medium is regenerated to complete a filtration cycle. 　　Liquid must overcome resistance when passing through the filter residue layer and filter media, so there must be a pressure difference on both sides of the filter media, which is the driving force to achieve filtration. Increasing the pressure difference can speed up filtration, but the deformed particles under pressure can easily block the pores of the filter medium when the pressure difference is large, and filtration will slow down instead. 　　There are three methods of suspension filtration: filter residue layer filtration, depth filtration and screen filtration. Residue layer filtration means that after the initial stage of filtration, an initial filter residue layer is formed. After that, the filter residue layer plays a major role in filtration. At this time, both large and small particles are intercepted. ； Depth filtration refers to a filtration in which the filter medium is thicker, the suspension contains fewer solid particles, and the particles are smaller than the pores of the filter medium. During filtration, the particles enter and are adsorbed in the pores. ； Screen filtration is a filtration method in which the trapped solid particles are larger than the pores of the filter medium, and the solid particles are not adsorbed inside the filter medium. For example, a drum filter screen removes coarse impurities in sewage. 　　In the actual filtering process, the three methods often appear at the same time or one after another. The processing capacity of the filter depends on the filtration speed. When the solid particles in the suspension are large and uniform in size, the pores of the filtered residue layer are relatively unobstructed, and the filtrate passes through the filter residue layer at a greater speed. The use of coagulants will aggregate fine particles into larger clumps, which will help increase the filtration speed. 　　For suspensions with fast solid particle settling speed, a filter that feeds the upper part of the filter medium should be used to make the filtering direction consistent with the direction of gravity. Coarse particles will settle first, which can reduce the clogging of the filter medium and filter residue layer. ； Mixing coarse solid particles such as diatomite and expanded perlite into difficult-to-filter suspensions (such as colloids) can loosen the filter residue layer. ； When the viscosity of the filtrate is high, the suspension can be heated to reduce the viscosity. These measures can speed up filtration. Edit this paragraph Classification and characteristics of intermittent vacuum filter: 　　The mechanism of the vacuum filter is basically the same as that of the pressure filter, except that the pressure on one side of the filter medium is lower than the atmospheric pressure and the driving force is smaller. vacuum filter: The structure is simple and the filtration driving force is larger than that of the gravity filter. Vacuum leaf filter: The structure is simple and suitable for filtering general slurry materials, but the operating conditions are poor and the labor intensity is high. 　　Continuous vacuum filter: 　　External filter surface drum vacuum filter: It can operate continuously and automatically, and can effectively carry out filtration, washing and dehydration. The operation site is clean and easy to inspect and repair. The disadvantages are high cost, the range of use is limited by the vapor pressure of hot liquids or volatile liquids, materials with low boiling points or volatile liquids at operating temperatures cannot be filtered, and it is difficult to process slurries with high solid content and large changes in particle properties. The moisture content of the filter cake is around 30%, rarely less than 10%, and is mainly used in the chemical and food industries. 　　Internal filter surface drum vacuum filter: It is suitable for filtering suspensions with uneven solid particle sizes. It does not require a stirring device. The machine cost is low and it can adapt to changes in feed concentration. If it needs to be operated at high temperatures, it is easy to take heat preservation measures. The disadvantage is that the surface of the drum cannot be fully utilized, and the filter cake needs a certain viscosity, otherwise it will easily fall off, resulting in a decrease in vacuum and a change in feed flow. ； It is difficult to replace the filter cloth. 　　Disc vacuum filter: The price is the lowest based on the unit filtering surface, and it occupies a small area, but the filter cake humidity is higher than that of the drum vacuum filter. Since the filter surface is vertical, the thickness of the filter cake is uneven, easy to crack, and difficult to wash. It is difficult to unload the thin layer of filter cake. The filter cloth wears quickly and is easy to clog. It is easy to handle materials with low sedimentation speed and easy to filter. It is not suitable for handling non-viscous materials. Its application range is the same as that of drum vacuum filter. 　　Rotary vacuum filter: The structure is simple and the washing effect is good. The washing liquid and the filtrate are separated. For slurries that are dehydrated quickly, a single filter has a large processing capacity. The disadvantages are that it occupies a large area, the filter cloth wears quickly and is easy to clog. 　　Tipping bucket vacuum filter: It can filter viscous materials and has strong adaptability. It is suitable for separating slurries with a solid content of more than 20%, high density, easy separation and sufficient washing of the filter cake. It is often used in chemical industry, light industry and other industries. 　　Belt vacuum filter: It is divided into three types: fixed chamber type, movable chamber type, and when the filter belt moves intermittently. The belt vacuum filter has a horizontal filtering surface, with materials added above. It has high filtration efficiency and good washing effect. The thickness of the filter cake is adjustable, and the front and back sides of the filter cloth can be washed at the same time. It is flexible in operation and low in maintenance costs. It can be used in the chemical industry, pharmaceutical, and food industries. It has excellent separation performance for slurries that settle quickly, and is even better when the filter cake needs to be washed. Edit this paragraph The new filtration equipment that is developing in the future includes: Mechanical pressing and filtering equipment ； Dynamic filter capable of filtration without filter residue layer ； Large filtration equipment for washing coal wastewater treatment, chemical industry and petroleum industry. 　　In terms of filtration theory research, the measurement of filtration resistance and porosity of the filter residue layer, filtration speed, simulation and amplification of filtration equipment, thin liquid clarification filtration and dynamic filtration mechanisms, and research on filter media are all important topics. The use of electronic computers to control filtration operations is the development direction of filtration equipment.

Filtration rate: The volume of filtrate passing through unit filtration area per unit time becomes the filtration speed. The volume of filtrate obtained per unit time is usually called the filtration rate. The volume of filtrate passing through the unit filtration area per unit time becomes the filtration speed. There are many ways to speed up the filtration speed. For suspensions with fast solid particle settling speed, a filter with feeding materials on the upper part of the filter medium is used to make the filtration direction consistent with the direction of gravity. Coarse particles settle first, which can reduce the clogging of the filter medium and filter residue layer. ； Mixing coarse solid particles such as diatomite and expanded perlite into difficult-to-filter suspensions (such as colloids) can loosen the filter residue layer. ； When the viscosity of the filtrate is high, the suspension can be heated to reduce the viscosity.

The filtration speed refers to the filtrate flow rate per square meter of filtration area per unit time. Expressed by the formula: v=V/Ft, m3/m2 sec where v——filtration speed, m3/m2 sec; V——filtrate area, m3; F——filtration area, m2; t——filtration time, seconds. The vacuum filter creates negative pressure at the filtrate outlet as the driving force for filtration. For suspensions with fast solid particle settling speed, a filter that feeds the upper part of the filter medium should be used to make the filtering direction consistent with the direction of gravity. Coarse particles will settle first, which can reduce the clogging of the filter medium and filter residue layer. ； Mixing coarse solid particles such as diatomite and expanded perlite into difficult-to-filter suspensions (such as colloids) can loosen the filter residue layer. ； When the viscosity of the filtrate is high, the suspension can be heated to reduce the viscosity. These measures can speed up filtration.

The moderator on the third floor said it in great detail. I think because continuous production is required, the regeneration of filter cloth in actual production should also be considered a key factor in increasing the filtration speed.