Plate and frame filter presses are dewatering machines which utilize pressure (6080 psi, typically) to remove the liquid from a liquid-solid slurry. They are particularly suited for low solids (<2% solids), or solids composed of fines (-200 mesh), however they will essentially dewater many combinations of particle size distribution and percent solid slurries. The diagram at left, shows the basic operation of a plate and frame filter press. The feed enters the press at the bottom of the plate, using a pump suitable for pumping up to 80-90 psi. Then, T hen, the feed travels the path of least resistance r esistance (up bewteen the filter plates), which has filter f ilter media inserted between the plates, and the void between the plates is filled with the slurry, as the liquid passes through the filter media, and travels up to the outlet port at the top of the plate. This liquid is referred to as the "filtrate", and is discharged from the press. The solids remain in the void between the plates, until the plates discharge the filtered solids.
Filter press, Plate & Frame Filter Press, Sludge Dewatering, Precious Metal Recovery, Recessed Plate Filter Press • • •
Efficiency
The Hoffland Environmental, Inc. Filter Press is one of the most efficient means of liquid/solid separation through pressure filtration; either for solution filtration or sludge volume reduction. It provides a simple, reliable method of high compaction pressure to compress and dewater solids into cakes of 25 - 60% total concentration producing clearer filtrate solutions than systems which remove only free water.
Sludge Dewatering Slurries of waste water, such as metal hydroxides, alum sludges, etc., are pumped into the chambers of the filter press. The filtrate passes through the filter cloth and the solids are retained. The solids collect on the cloth forming an excellent filter or if one were to intentionally pre-coat the cloth. As additional solids are pumped into the chamber, the solids continue to collect until the entire chamber is full of dewatered solids. The press must then be cleaned and recycled.
Filtration
Fluids such as wine, beer, etc., may be clarified by pumping through a filter media like diatomaceous earth or cellulose filter aid. In the case of filtration, the retained solids are not important. It is the clarity of the filtrate that justifies the use of the filter press. The filter press produces a recoverable solid such as dye stuff, or precious metals, or may be used with the intent of reducing the volume of the waste. Reducing the volume of waste is very for hazardous materials. A liquid slurry of hazardous metal hydroxide waste may be reduced from 40 drums of 1% solids to one drum of 40% solids. When processing hazardous waste, the filter press may economically justify itself in less than one month.
Typical Applications • • • • • • • • •
Process Filtration and Plate Washing Pharmaceuticals and Chemicals Clarification of Processed Fluids Municipal Sludge Dewatering Reduction of Waste Solids Precious Metal Recovery Biological Filtration Food Processing Saline Filtration
Operation Dewatering is accomplished by pumping sludge into chamber (A) surrounded by filter cloths (B). As pumping pressure is increased, the filtrate is forced through the accumulated filter cake (C) and cloth, leaving the chambers full of solid filter cake. The chambers in HEI filter press are formed by two recessed plates held together under hydraulic pressure. The hydraulic ram (D) moves the follower (E) against the stack of filter plates (F) closing the press. The ram continues to apply pressure of sufficient force to counteract the high internal compaction pressures. The head stock (G) and tail stock (H) are held in place by specially engineered side rail supports bars (I).
The filtrate passes through the filter cloth and is directed b y channels in the plates and drain ports (J) to the head stock for discharge. The filtrate typically contains less than 15 ppm suspended solids. The filter cake is easily removed by simply reversing the hydraulic ram, thus opening the press. The lightweight filter press plates may then be moved apart permitting the compacted cake to fall from the chamber.
Construction
The HEI Filter Press is constructed of heavy duty steel or stainless steel designed to withstand up to 225 psig pumping pressure. All structural steel is sand blasted, primed and painted with corrosion resistant epoxy paint. Internal components are constructed of high molecular weight heat stabilized chemical resistant plastic. Areas subject to wear such as the top of the side rails are covered with corrosion resistant wear plates. Hoffland Environmental, Inc. has a custom manufacturing policy which will tailor a Filter Press for your specific application.
Benefits
HEI Filter Presses are equipped with lightweight, corrosion-resistant polypropylene filter plates (gasketed, non-gasketed, and membrane) and can be engineered with an automatic plate spreader for easy and safe removal of compacted solids. A self-compensating hydraulic system automatically prevents decreases in closure pressure due to thermal exposure/contraction of the chambers between the polypropylene filter plates.
Sizing Your HEI Filter Press
The HEI Filter Press will compact sludge to a dry cake having a density that is not only dependent upon the ultimate compaction pressure, but also the specific characteristics of each sludge. The chart below gives the average dry weight of three common sludges. Use the accompanying equation to calculate the size of your filter press. First determine the quantity of sludge to be processed per cycle (minimum of 8 hours per cycle is recommended). Then insert the solids content (ppm must be divided by 1,000,000 or percent divided by 100), weight per gallon of the liquid in pounds, and pounds dry weight per cubic foot (from the chart). Co mplete the equation to calculate the capacity of the filter press. The cycle time is dependent upon both the sludge dewatering characteristics and the solids content. High solids content dramatically shortens the compaction cycle. Please contact your HEI representative for recommendations on sludge thickening equipment.
Sludge Type
Percent of Cake Dry Weight Average Pounds Dry Weight Per Solids Cubic Foot 115 - 25 15
Biological Sludge Metal Hydroxide 25 - 40 Sludge Lime Treated Sludge 30 - 60
25 35
