PLATE AND FRA FILTER PRESS PHILIP KRIEGEL T. Shriver & Company, Harrison, N. J
T
HE plate and frame filter press is probably the oldest device for filtration on a large scale now in service in American industry. Although many types of filtering equipment have been designed and perfected since the introduction of the plate and frame filter press, the extent of its applications and the number of units in use have grown steadily year after year. The reason for this growth has been the fact that a large proportion of the filtration problems of industry require the flexibility, high capacity, higher pressures, and rapidity of filtration cycle which are offered by this type of filter. Although vacuum type filters and pressure filters of various kinds have found wide application in many industries, the plate and frame filter press is still most economical and most satisfactory for an extremely wide range of products requiring either clarification or the recovery of solids in suspension. The principle of the plate and frame filter press is fundamentally the same as it was when first designed, but great improvements have been made in the design of types to provide for specific process requirements. One of the outstanding changes has been the increased use of special metals and allpys in construction. Not many years ago practically every filter press mas made of cast iron or wood. Today they are obtainable not only in aluminum, bronze, lead, nickel, and such alloys as stainless steel, Monel metal, Ni-Resist, etc., but they may also be galvanized, plated, rubber-coated, or enameled. They are also made of semihard rubber. Filter presses have been constructed of wood from the beginning, and although the use of rubber and special alloy filters has to some extent replaced wood as a material of construction, there are still many plate and frame filter presses made of various woods to meet special conditions. Another way in which the filter press has been greatly
changed is in the design of special types of plates and frames to meet various specific needs. For example, the tremendous advances made in the use of filter aids have made it necessary to design filter presses capable of producing suitable results in so far as precoating with filter aid prior to the actual filtration is concerned. There has been increasing need for filters capable of operating a t high pressures up to 1000 pounds per square inch and more. This has made necessary the designing of special types of plates and frames which not only have to withstand the higher pressure but provide for adequate drainage surface and sealing. Filtration of volatile and exceptionally thin liquids such as alcohol, wine, solvents, and similar products, which tend to leak in presses of ordinary design, has made necessary the development of leakproof types of filters. There are a great many varieties, each adaptable to specific purposes, including gasketed types, grooved types with return channels to the feed end, gasketed plates and frames with slots inside the joint surface for the filter medium. Many filtering operations require maintenance of a high or low temperature for their successful completion. This has led to the development of filter presses with hollow plates and frames for the circulation of steam, oil, or brine. Along with the development of the filter press has come a corresponding development in the types of filter media. Cotton or woolen cloths are still in extensive use, and filter paper of various types suited to the materials handled is widely employed. However, radical developments in the type of filter paper used, such as the provision of an iron- and calcium-free asbestos type filter paper for filtration of wines, have taken place. A wider range of weaves is nom available than formerly in cotton and woolen filter cloths. Moreover, filter media of new types have been tested and a place has been
(Left) TYPICAL FILTER PLATE FOR OPERATISG PRESSURES TO 1000 POUKDS PER SQUARE INCH WITH GROOVES FOR LEAKAGE CONTROL (Center) SAME PLATE WITH WIRE MESHSCREEN FOR SUPPORTIKG FILTER CLOTHAGAINST HIGHPRESSURE (Right) SOLIDFRAME FOR PLATE
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INDUSTRIAL AND ENGINEERING CHEMISTRY
VOL. 30, NO. 11
(Above) LARGE SIDE FEED,CLOSEDDELIVERY, WASHING FILTER PRESSEQUIPPED WITH HYDRAULIC CLOSINGMECHANISN (BUILTFOR FILTERINC) METALLURGICAL SLIMES) (Above) METALFILTER PLATE WITH RUBBER-GASKET INSIDE JOINT SURFACE AND SLOTFOR CLOTHINSERTION TO ASSURE TIGHTNESS AND LEAKPROOF CLOSURE
(Below) PORTABLE FILTERPRESSWITH RUBBERFILTERPLATES AND FRAMES, RUBBERAND RUBBER-LINED CONNECTIONS, AND RUBBER-LINED DIAPHRAGM PUMP
(Above) RECESSED PLATE (CENTER FEED), OPEN DELIVERY,NOWWASHING FILTER PRESSWITH RATCHETAND GEAR AND PINION CLOSING MECHANISM (BUILTFOR FILTERING GELATIN)
(Below) CORNERFEED (EYED TYPE), CLOSEDDELIVERY. NONWASHING TYPE. ~ _ _ STEAMHEATED, FILTER PRESS WITH ALU: MINUM HOLLOWPLATES AND MONEL METALSCREENS; BOTTOM FEED,TOPDISCHARGE, WITH AIR VENTAT TOP CORNER ~
(Below) CORNERFEED(EYED TYPE), CLOSBD DELIVERY,NONWASHINO FILTERPRESS,WITH DOUBLEFEED,DOUBLECLOSED,VISIBLEITOP DISCHARGE
NOVEMBER, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
found for their use in many industries. Filter cloths made of human hair or glass can greatly reduce the operating costs of many acid filtration problems. The use of filter aids has been mentioned. On a large proportion of clarifying operations and on many cake recovery processes where the rate of filtration is not satisfactory or where the types of solids to be removed do not lend themselves to ordinary filtration, the use of filter aids has increased tremendously. These materials are available in a wide range of types for adaptation to individual filtration problems, It is difficult to determine the type and size of filter press to be recommended for any particular operation until all the factors involved in its selection are known. It is far from uncommon t o find a product filtered in a certain type of press in one plant which in another plant using approximately the same process is not adapted to the same type of press. As a rule, filtrahion tests are required to determine the type and s k e of the filter best adapted to the material, and for this reason there is no feasible way of providing typical costs of installations or of operating costs until these factors are determined for each specific material. The following typical cost data are to be regarded, therefore, as illustrative rather than an indication of the costs which might be expected for the products in question. Actual costs can be determined only by data obtained for the specific material to be filtered.
Typical Cost Data for Recovery of Filter Cake The product filtered was a slurry containing 1000 pounds of chromium hydroxide [Cr(OH)s.2H20]. The following filtration data were obtained by experiments in a laboratory filter press: Most practical cake thickness, in. Max. operating pressure, lb./sq. in. Vol. filtrate per cu. ft. of cake, gal. Av. rate of filtration gal./sq. ft./hr. Vol. wash water per’cu. ft. cake, gal. Time for filtration, hr. :min. Time for washing, hr.: min. Time for cleaning filter press, hr. Total operating cycle, hr. Weight wet press cake, Ib./cu. ft. Weight dry press cake, lb./cu. ft.
1
3:45 2:15 1
7 82.8 38.3
~ _ _ _ _ _ ~
This cost does not include drying.
Sweet cider, pretreated with an enzyme, was to be filtered a t a rate of 2400 gallons per day. Filtration data (obtained by experiments on a laboratory filter press) were as follows: Most practical cake thickness, in. Max. operating pressure, Ib./sq. in. Filter aid for recoat, oz./sq. f t . filtering area Filter aid for gatch % by weight Weight of filter aid: lb./cu. f t . Av. rate of filtration, gal./sq. ft./hr. Time for filtration, hr. Time for cleaning filter press, hr.
‘
1 60 2 0.2 21 10.4 4 0.5
-
Total operating cycle, hr.
4.5
Loss of cider in operation, %
3/8
By means of these data we find that if one batch of cider is to be produced per 8-hour day with an operating cycle of 4.5 hours, a filter with a capacity of 600 gallons per hour will meet all requirements. This demands a filtering area of (600/10.4) or 57.6 square feet. For cider, semihard rubber is the most suitable material of construction. A 24-inchsquare, 12-chamber, rubber filter press with frames 1 inch thick has a filtering area of 58 square feet and a holding capacity of 2.41 cubic feet. The filter aid per batch of 2400 gallons (20,500 pounds) is 48 pounds, with a weight of 21 pounds per cubic foot, so that a holding capacity of 2.28 cubic feet is all that is required per batch. The pump used to feed this filter press should have a capacity of at least 10 gallons per minute a t 25 pounds per square inch and 5 to 10 gallons a t 60 pounds. A one-horsepower motor is ample: First ..-. costs: ... .
Owning costs, including interest, o eration, .and repairs (20% annually on first cost) per bat& (on basis of batch of 2400 gal. per day for season of 60 days) Operating costs per batch: Filter cloth (60-day life assumed) Filter aid (Drecoat), 7 Ib. a t 56 Filter aid (batch), 41 Ib. a t 56 Power for pump and agitator at 36 per kw-hr. Labor, 1.5 man-hr. a t 506
First costs: 36-in., 40-chamber, open-delivery washing filter press, cast-iron 1-in. frames $1750.00 P u m and motor 200.00 Instakhioii and piping 150.00
Total operatin oost per batch Total oost per %atch Cost per pound Cr(OHh.2HsO
Typical Cost Data for a Clarifying Operation
24-in., 12-chamber, closed-delivery nonwaahing filter press, semihard rubber, 1-in. frames $520.00 Pump a n d motor 120.00 Installation and piping 80.00
60
43.75 0.47 22.5
By means of these data we find that 1000 pounds of chromium hydroxide will require a filter press having (1000/38.3) or 26.1 cubic feet of cake capacity. Cast iron is suitable as a material of construction. A 36-inch-square1 40-chamber1 cast-iron filter press with frames 1 inch thick has approximately the required capacity (26.0 cubic feet). The pump used to feed this filter press should have a capacity of a t least 15 gallons per minute at 25 pounds per square inch pressure, and 5 to 10 gallons per minute a t 60 pounds pressure. A 1-horsepower motor should be satisfactory, but under any circumstances a 2-horsepower motor will be ample.
Owning costs, including interest depreciation, a n d repairs (20% annually on first cost) per batch on basis of one batch per day, 250 days per year Operating costs: Filter cloth (30-day life aasumed) per batch Power for ump and agitator a t 3$ per kw-hr. (per batch) Labor per gatch for cleaning and operation, 4 man-hr. a t 606
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2100.00 1.68 1.61 0.36 2.00 3.97 5.65 0.00565
Total operating cost per batch Loss of 3/8% on 2400 gal. or 9 gal. a t 126 per gal. Total owning and operating cost per batch Cost per gal.
720.00 2.40 0.16 0.35 2.05 0.24 0.75
3.55 1.08 7.03 0.00292
Advantages of Plate and Frame Filter Press 1. First cost is low. 2. The filtering area per unit of floor space required is greater. 3. As a rule, production rates in terms of hours of service in actual filtration are higher. 4. There are no accessories or complicated mechanical devices which require adjustment by trained mechanics. 5. Unskilled labor is quickly and satisfactorily trained to handle Btration. 6. Thorough and rapid washing of filter cake is possible. 7. Depending on the character of the solids involved, filter cake may be obtained from very dry to fairly dry condition. 8. The only power requirements are those for the operation of the pump or other device used in supplying the material to the filter press. Rmcplrvmn November 22, 1937.
