#Used rotary vacuum filter series#
Then, as the two belts move between a series of rollers, pressure squeezes additional water out of the solids. First, water drains from the solids by gravity. The chemically treated solids are discharged between two moving belts. The belt filter uses a coagulant (polymer) mixed with the influent solids. The plate-and-frame filter consists of a support frame, filter plates covered with porous material, a hydraulic or mechanical mechanism for pressing plates together, and related handling systems for chemical makeup and feed, as well as supernatant and solids collection and transport. The belt filter includes two or more porous belts, rollers, and related handling systems for chemical makeup and feed, as well as supernatant and solids collection and transport. Several types of filter presses are available, but the most commonly used types are belt presses and plate-and-frame presses. Pressure filtration differs from vacuum filtration in that the liquid is forced through the filter media by a positive pressure instead of a vacuum. Next, calculate the pounds of solids per hour:ģ0024lb/hr = 8.13lb/hr/ft2 369.3 ft2 17.6.8 Pressure Filtration Solution: First calculate the filter surface area:Īrea of a cylinder side = 3.14 x Diameter x Length If the sludge concentration is 12%, what is the filter yield in lb/hr/ft2? Assume the sludge weighs 8.34 lb/gal. The vacuum area of the filter is 12 ft wide with a drum diameter of 9.8 ft. Problem: Thickened, thermally conditioned sludge is pumped to a vacuum filter at a rate of 50 gpm. Example 17.27 illustrates how this calculation is made. Probably the most frequent calculation that vacuum filter operators have to make is determining filter yield. Sludge conditioning increases the percentage of solids captured by the filter and improves the dewatering characteristics of the sludge however, conditioned sludge must be filtered as quickly as possible after chemical addition to obtain these desirable results.ġ7.6.7.2 Calculating Vacuum Filter Yield (lb/hr/ft2) Sludge dewatered using vacuum filtration is normally chemically conditioned just prior to filtration. Submergence is usually limited to 1/5 or less of the filter surface at a time. The drum is partially submerged in a vat containing the conditioned sludge. Normally, solids pickup is indirectly related to the drum speed. The drum is equipped with a variable-speed drive to turn the drum from 1/8 to 1 rpm. The filter drum is a maze of pipe work running from a metal screen and wooden skeleton and connecting to a rotating valve port at each end of the drum. The cloth will (with proper care) last several hundred to several thousand hours, depending on the cloth selected, the conditioning chemical, backwash frequency, and cleaning (i.e., acid bath) frequency. The installation of a blanket requires several days. In the belt filter, the cloth is stretched over the drum and through the pulley system. On the drum filter, the cloth is stretched and secured to the surface of the drum. 17.6.7.1.1 Filter Mediaĭrum and belt vacuum filters use natural or synthetic fiber materials. This bar primarily aids in maintaining belt dimensional stability. This type of filter normally has a small-diameter curved bar between the point where the belt leaves the drum and the discharge roll. The media are then returned to the drum and to the vat for another cycle. The media on a belt filter leave the drum surface at the end of the drying zone and pass over a small-diameter discharge roll to aid cake discharge. The coil filter has been used successfully for all types of sludges however, sludges with extremely fine particles or ones that are resistant to flocculation dewater poorly with this system. The coils are then washed and reapplied to the drum. After a dewatering cycle, the two layers of springs leave the drum bed and are separated from each other so the cake is lifted off the lower layer and discharged from the upper layer. The coil type of vacuum filter uses two layers of stainless steel coils arranged in corduroy fashion around the drum. As the drum rotates, each section is thus connected to the appropriate service. This plate rotates in contact with a fixed valve plate with similar parts, which are connected to a vacuum supply, a compressed air supply, and an atmosphere vent. The drum is divided lengthwise into a number of sections that are connected through internal piping to ports in the valve body (plant) at the hub. The rotary drum filter consists of a cylindrical drum rotating partially submerged in a vat or pan of conditioned sludge. The three principal types of rotary vacuum filters are rotary drum, coil, and belt.