The belt filter (sometimes called belt press filter , or belt filter press ) is an industrial machine, used for solid/liquid separation processes , in particular the draining of sludge in the chemical industry, mining and water treatment. Pressed filter belts are also used in the production of apple juice, apple cider and wine making. The filtering process is primarily obtained by passing a pair of filtering cloth and belt through a roller system. This system takes the precipitate or slurry as bait, and separates it into filtrate and solid cake.
Video Belt filter
Apps
The belt filter is mainly used for draining mud and sludge and juice extraction from apples, pears, and other fruits, as well as wine for wine making, etc. Belt filters are used both in municipal and industrial areas in various fields including urban and waste water treatment, metallurgical and mining wastes, steel mills, coal mills, factories, dyeing, tannery, and chemical and paper factories.
The application of the belt filter is limited to mud, pulp or crushed fruit that can be processed. Mud from urban use includes raw, anaerobic, digested and aerobically digested slurries, alum mud, lime softening mud and river water mud. In industry, any mud or sludge is sourced from food processing waste, pulp and paper waste, chemical sludge, pharmaceutical waste, industrial waste, and petrochemical waste. These wastes may include mixed sludges, mineral slurries, dust sediments, selective coal washing sludges, biological slurries, primary mud, and straw, wood or pulp.
Some drying purposes include reducing volume to reduce transportation and storage costs, eliminating liquids prior to final disposal, reducing fuel requirements prior to drying or further incineration, producing sufficient materials for composting, avoiding runoff and collection when used for land applications, and optimizing drying others. process. Belt sieves are specially designed for each of these applications and customized feeds.
Maps Belt filter
Excess/limit
There are many physical separation processes similar to the belt filter press used for dewatering, including centrifugal, vacuum-disc filters, and plate and frame press filters. When compared to other compression filters, the belt filter uses a relatively lower pressure. Although centrifuges have lower moisture content, lower costs and simpler operations in coal tail processing, belt filters tend to make less noise and have faster startup and shutdown times.
Belt filters are simple and reliable, with good availability, low staffing, easy maintenance and long life. The belt strap is most advantageous when mounted in such a way that it is open and can be seen on the floor surface for easy adjustment and monitoring. This of course depends on the lighting and the possible ventilation.
Press filter belts are often used in wastewater treatment, and thus the smell of feed sludge, volatile emissions and chemicals used in the treatment, can be a problem. One method of control is to use chemical odor chemicals such as potassium permanganate. However this only neutralizes the odor and does not affect the gas or chemicals involved. Although all problems can be controlled by attaching filters, the enclosures reduce essential visibility and easy access to the machine for maintenance and repair, leading to costly process automation.
The press filter belt is also known for its high capacity throughput, as it is designed to handle excess capacity. It has a low initial cost and low energy running cost; however, if throughput is less than 4 million gallons per day, the belt filter press may be less cost efficient than liquid transportation, renting processing facilities, or using non-mechanical dewatering methods such as bed drying or reed beds.
Belt filters are less effective when processing multiple feeds. Unless the feed is well mixed from the digester, the use of belt filters will be more expensive when processing the feed with a variety of solid content as this requires more operator attention, increasing staffing costs. Bait with high fat and oil content can decrease the percentage of solids in the cake by blindingly filter the belt and all the feed needs to be filtered to protect the belt so as not to be damaged by sharp objects. Feed types may also affect the washing process. The belt strain needs to be washed frequently which consumes a lot of water and time. Water and time drainage, as well as related costs can be reduced by automating the washing system and using waste.
Design available
The belt filter design is manufactured using the manufacturer's design and performance data, operating installations, trials, similar plant surveys and wastewater solids testing to obtain the desired dry-dried percentage of slurry or slurry for processing.
Belt press filter has 4 main zone: preconditioning zone, gravity drainage zone, linear compression zone (low pressure) and compression zone of roll (high pressure). Pre-decoculated and/or coagulated slurry depends on the feed and process, thickened in the gravity drainage zone. The gravity drainage zone is a flat or sloping belt where a drainage of free water gravity occurs. The gravity drainage area is sized according to the concentration of the feeding solid. Standard sizes may be used for solids concentrations of 1.5 percent or greater, but arrangements with longer drainage areas or extended sizes should be used for 1.5 to 2.5 percent solids for better water drainage prior to compression. For aqueous slurry with a feed solids of less than 1.5 percent, an independent gravity drainage belt can be used. This belt is only used in the area of ​​gravity drainage, not in the pressure zone. The wedge or wedge zone uses two belts, top and bottom, to bait together, but the independent gravity zone has its own separate belt, making the belt filter out the three belt systems. Depending on the condition of the cake required, the belt filter can add wash stage and, infrared, hot gas or even microwave drying stage.
Belt filters are very versatile and are made in accordance with mud, slurry or mashed fruit for processing. For feed or processing processes that produce unpleasant odors, volatile emissions, pathogens and harmful gases such as hydrogen sulfide, the belt filters may include smoke hoods or even fully enclosed in gas-proof housing. Due to the reduced visibility and increased corrosion associated with enclosures, the belt filter process can also be performed automatically. Large filtration areas, additional rollers, and variable belt speeds can be found in advanced belt press filter designs.
Process characteristics
Belt press filters are designed for solid capacity, based on weight or volume, rather than waste water flow. The solids concentration should be determined on the basis of the primary solid concentration in the feed and further solids that may precipitate during the treatment. The concentration of solids for a process will vary, so the design must have the capacity to handle various concentrations of feeding solids.
The feedback to the belt press filter depends on the type of solid, the desired product and the filter design. For most types of sludge, the dry matter dryness concentration typically ranges from 1-10%. The dried concentration of dried dirt (or dried cake) produced is usually falling in the range of 12-50%. The resultant concentration of the dilute solids solids on the cake with higher moisture content while the higher concentration of feeding solids resulted in better solids filtration rates and the drier end product.
The input to the belt press filter is generally measured as the loading rate of dry solids (dry solid mass per time per width of the belt). Again, the loading of the solid input depends on the type of sludge and the filter medium, so there is a large variation in the dry solids compaction rate of the operating belt press filter. Typically, the lower level of loading of the solids falls within the range of 40-230 kg/h/m width of the belt and the high level of the solid charge rate falls within the range of 300-910 kg/h/m width belt. While loading is important to measure production levels, it is also important to consider the thickness of the cake formed in the gravitational drainage section. The thickness of the cake affects the permeability of filtration media and filtration rate. Tests for certain types of mud should be performed to determine optimal cake thickness. In some cases where filtrate recovery is important, it may be necessary to introduce a cake washing step.
The main purpose of the belt press filter is to dry the sludge process and much of this dewatering takes place in the gravity drainage zone. The gravity drainage zone can reach 5 to 10 percent increase in solids concentration. The level of dewatering in the gravity drainage zone is highly dependent on the type of solids, filter media and sludge conditioning. The drainage achieved in the gravity drainage zone is affected if the precipitate is not well dispersed in the belt or insufficient residence time. Sludge conditioning is the addition of chemicals to promote the flocculation of particles to form thickened mud and to promote dewatering. Drying can be promoted by addition of surfactant and flocculation achieved by the addition of high molecular weight polymers. Flocculation is enhanced by optimal polymer dose, polymer dilution and mixing. The feed slurry pH should also be monitored and controlled because low pH decreases flocculation. It is important to find the optimal value for each conditioning parameter because too much polymer or mixing can adversely affect flocculation and greatly increase operating costs. The effects of sludge conditioning are most apparent in gravity drainage zones that can be easily replicated on a laboratory scale where optimal conditioning strategies can be determined. For the belt filter press to be industrially feasible it must be economically efficient and thus the maximum throughput desired. Without adequate conditioning, gravitational drainage is generally a limiting process step, but with optimal dilution, the restriction process steps can be transferred to the compression zone.
In the compression zone of a filter belt press, the filter cake is compressed between two belts and through the rollers to press pressure on the cake. There is an optimal number of rollers on which the drier product is not necessarily the result. The dried product is obtained from a reduction in belt speed rather than an increase in press time.
The overall performance of the belt press filters is enhanced when parameter variations such as mud type, feed solidity and conditioning con- centrations are minimized.
The efficiency of a belt press filter is often assessed based on the dry matter content of the product cake, solid recovery and forward mud migration on the belt. Solid recovery is the percentage of dry solids obtained from the feed slurry. Solid recovery depends on the filter medium to be selected for good permeability to promote dewatering but with a fairly small pore diameter so that solids recovery is not greatly reduced. It is important that the belt press filter has an effective, so blinding belt wash section does not reduce the belt permeability. Solid recovery is directly related to the quality of the filtrate and thus the filter media and process settings must meet the desired cake and filtrate qualities. The dry matter content is a measure of the drying rate. Dewatering rates increase as belt speed decreases. Lowering belt speed reduces process capacity. The following correlations connect the mass flow rate of the input to the belt speed:
Where Q 0 = mass flow rate (kg/s), m 0 = mass loading (kg/m 2 ), s b = speed belt (m/s) and L sludge0 = initial width of sludge across belt (m). Thus to maintain industrial-scale economic throughput at lower belt speeds, mass loading and sludge width across the belt must be increased. It has been found that increasing the loading load slightly decreases the dry solids concentration of the cake while significantly increasing the potency of overflow belts. The lateral migration of the sludge on the belt is a measure of how the sludge spreads across the width of the belt. Increased migration of lateral mud means that the mud exits from the edge of the belt and overflows into the filtrate. Therefore, an increase in lateral sludge migration negatively affects the quality of the filtrate and the recovery of dry solids.
Generally, the minimum design cake thickness is 3-5 mm. This ensures that the cake is thick enough to be removed and easily removed from the belt.
Design heuristics
In order to increase the cost and decrease the humidity the most commonly used drying products are thickening, deep bed thickening, belt compression and membrane filter presses. In general centrifugal and other competing technologies do not show significant cost advantages compared to belt press filters, for the same cake drought. Flocculant costs are often the main operating costs of the drainage equipment. Belt press filters generally have the lowest flocculant consumption for each process listed outside the membrane and centrifugal filter pressure.
Increasing the concentration of the feed solids increases the solid filtration rate, minimizing the water content of the cake and producing more homogeneous cakes which are all desirable results. If the increase in feed solids concentration is impractical, the addition of flocculants in the pre-treatment step has similar results. The optimal rate of flocculant dose can be found by monitoring the viscosity of slurry.
The desired homogeneous cake as if the pulp is too dilute filter cake will contain higher water content as a result of stratification. The minimum feed concentration that produces homogeneous cake is determined by observing the slurry sample. If there is rapid precipitation the filter cake formed will not be homogeneous and the filtration rate decreases.
The minimum cake salt thickness for the horizontal belt press filter is in the region of 5 mm.
Belt selection is very important for the function of belt press filter and various material and weaving available. The filter cloth for the belt press filter should be as open as possible while maintaining the desired filtrate clarity or, if precoat is used, to prevent loss of precoate. The lighter fabric produces a clearer and less obstructing filtrate but its durability and lifespan are significantly shorter than heavier fabrics. Belt seamless and seam available. Disguised belts are faster used on stitches and cause wear on the doctor's roller and blade. Type-zipper and chip-type stitching belts are also available with zipper types that have longer life spans as they provide less discontinuity. The smoothest belt has the longest life span but is more expensive. It should also be ensured that the belt press is compatible with a seamless belt.
An increase in the temperature of the feed slurry decreases the viscosity of the liquid phase. This is useful because it increases the filtration rate and decreases the water content of the cake. The same advantage can be obtained by other drying methods such as passing dry vapor through deliquored cakes to raise the remaining moisture temperature, or other drying methods can be utilized.
The thickness of the cake may have to be controlled or restricted when washing the required cake or the final cake moisture is an important parameter. When the washing time of the cake is a factor that dominates the maximum filtration rate will occur when the minimum cake thickness for the discharge is reached. The time taken for washing increases with the square of the thickness ratio of the cake. For example, if the thickness of the cake doubled, washing time will increase roughly by a factor of 4.
The required post-care system
Completely clean filtrate can not be obtained by using the belt press filter except in rare circumstances. Thus further treatment may be required for the filtrate before being reused or disposed of as waste. If the filter downstream of the clarifier or thickener filtrate (and washing water) can be recycled back to the clarifier to reduce the required filtrate clarity and enable the use of more durable fabrics. If recycling or reuse is not an option, filtrate must be disposed of in accordance with the laws and licensing requirements. Further treatment of clarified water (screening or chemical treatment) may be required before disposal.
The filter cake usually has a sufficiently high solids concentration to allow all types of disposal methods without further treatment including recycling to process, landfill/composting and incineration. The polymer content of the filter cake from the belt press filter is more in line with the above mentioned disposal method than the cake which is conditioned with iron chloride and lime which can occur with other draining processes.
Recent developments
Significant developments in the belt press filter technology include: fabric development, using three belts and a V-folding belt. The development of multiple woven fabrics that incorporate different thread types to combine specific advantages of each. Woven woven double wire meshes are also available which have better life span and durability than conventional wire belts.
The belt press belt using three belts can reach independent speed and have different belt types for pressure and gravity zones. This allows the filter system to accommodate the higher hydraulic loading that occurs with sludge feeding (feed solids concentration below 1.5%). The three-belt system is more efficient with higher production levels and cake solids at the expense of mechanical complexity.
The V-fold belt is similar to a belt filter press with the main difference being that only a single belt, folded along the center line used. Technology has not been widely proven. A final dry-weight solid content of 9-13% is usually achievable; this is smaller than competing technology. Currently this technology is suitable for small scale applications (up to about 3000 L of slurry per hour because the maximum belt size is 0.75 m). The V-fold belt has a small footprint, low energy consumption and water wash and low capital and operating costs. They do their own tracking and can process sludge from various compositions, reducing operator involvement.
See also
- List of wastewater treatment technologies
References
Source of the article : Wikipedia
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