"The Goal Of Filter Press Pilot Testing Is To Collect The Data Required To Accurately Size A Full-scale Filter Press System."
Typical data collected includes cake solids, cake density, total processing time, if desired filtrate suspended solids, slurry feed solids, slurry pH, actual chemical conditioning dosages, and maximum operating pressure. Depending on the process requirements the total processing time may be further subdivided into steps such as filtration, cake wash, final squeeze, and cake air blow.
We are two pilot filter presses used for pilot testing. Both are “sidebar” filter presses with a Electro hydraulic System. The filter press consists of a frame, hydraulic system, filter plates with filter cloths. Other equipment needed for a test includes pumps, and mixing tanks with mixers.
There are two basic filter press configurations: recessed chamber and membrane. Both pilot presses are suitable for recessed chamber testing with choice of which press to use based on the amount of sludge available and number of tests required. A recessed chamber test requires the filter press, feed pump(s), and mixing tank with mixer. A membrane test requires all of the equipment needed for recessed chamber test plus a source of compressed gas for membrane squeeze.
The basic test starts with preparing the sludge or slurry as required for the test and preparing the filter press for the test (installing the correct plates and filter cloth). Once the press and sample are ready the pump is turned on and the press is filled. When the press is filled filtrate will be seen and we start timing and taking filtrate samples. The test is continued until both the low flow and maximum pressure conditions have been reached for filtration. For a recessed chamber test the test is ended. For a membrane test it is continued with the optional cake wash, membrane squeeze, and optional air blow down. Once the test is finished the press is opened and the filter cake is removed and cake samples are taken. During the cake release it is important to note how the cake released and the overall surface condition of the filter cloth. Cake release is normally somewhat better on a larger press but if there is poor release on the test unit the release on the larger unit will be fairly poor.
There are numerous filter cloths available on the market. Each cloth “style” has a characteristic weave pattern, particular type of yarn (thread), surface finish, porosity, thread count in each direction, weight, and material of construction. Our preference to use as “open” (higher porosity) a filter cloth as we can since the bulk of the filtration is done by the cake and not the cloth. On most sludges, we prefer relatively open Multifilament fabrics because of their better cake release characteristics. On other applications we will use “tighter” less porous fabrics. Cloth tightness increases in this general order: monofilament, mono/multifilament fabrics, multifilament fabrics, multi/spun fabrics, felts, and special fabrics. The cloth material will determine the maximum tightness for the cloth; nylon cloths can not be made as tight as a polypropylene cloth of the same type.