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A. MILLER
UNIVERSITY OF KANSAS, LAWRENCE, K A N .
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qualitative than quantitative, partly because of thc method i n which the experiments were conducted. Two Russian papers (28, 90) suggest equipment arrangement and method for determining the filterability of clay suspensions and of carbonat,ed sugar juices, respectively.
ECHNICAL papers relating to engineering, and particularly to those areas of engineering in which theory has lagged the practice of the art, are likely to be centered about equipment inventions and improvemcnts and empirical rules of procedure. Most of the publications on filtration are of this general type. I n the past year a particularly large number of' patents relevant t o filters and filtering processes have been issued, the majority of them of the improvement variety. This review is a summary of a major portion of the literature on filtration which is most closely related t o chemical processing appearing in the year prior to October 1949; it includes also part of the material originating in water and sewage treatment plants. As in previous years, it is limited to conventional liquid-solid filtration and excludes gas-solid and gas-liquid separations, centrifugal clarifications, most adsorptive and ion-exrhange percolations, and bio- and trickling filtrations,
EQUIPMENT, M E T H O D S , AND P E R F O R M A N C E
Thp tn c, major manufacturers of filter presses in this country have issued new catalogs (89, 8 1 ) which describe briefly but w ~ l l the features and the operation of plate-and-frame and recessodplate presses. One of fheoe (91) has prepared a chart which classifies all filter pres>es by feed, wash, and filtrate ports, and has summarized graphically the economic optimum combination of size and number of plates; the other (89) has presented up-todate price data for filter presses. A filter press equipped with cake flushing nozzles is the subject of a Russian patent (69). Rey (83) has described a filter involving a granular bed which can be withdrawn, washed, and returned to its place; the filter is reconzmended for clarification of viscose spinning bath. Danil'tsev (93)patented a frameless filter of fabric stretched over R rack, believed to be similar to a design formerly used in this country for paint straining. A number of patents (16, 27, 57, 60) have covered modification to vacuum drum design; these include modification of drainage-pipe arrangements (57, 60)in one care (57) to eliminate blow-back of filtrate-and a takeoff roll t o replace the knife (27). Van Vleck (94) and Cole (21) have prepared descriptive reviews of clarifying filters, the former describing cartridges of both micronic and edge types and the latter discussing cartridge and precoat filters suited to plating-solution conditioning. Schneider (87) invented a portable plaling-solution filter with an integral pump; the whole assembly is adapted to immersion in the bath being filtered. Burley (18), Gunn (43),and Pate ( 7 7 ) obtained patents for different types of cartridge oil-clarifiers. Other inventions included easily replaceable fiber- or cloth-covered cartridge elements (14, 45), a tubular element held rigid by an internal spring (46), and an assembly of filter plates comprising B oneparticle layer of sintered metal on a steel plate base (96). Two short general reviews of filtration equipment currently in use have appeared (70, 7 $ ): the latter describes filters particularly employed in fine-chemical processing. Chilton (20) has evaluated earlier cost data for chemical filters and brought them up to date in a form useful t o the design estimator. A number of specific indiistrial applications have been described, some with performance data. Glenn, Mernan, and Swalm (41) told of the use of filter presses with screen-covered plates for Vinyon-N spinning solution clarification and reported filtration rates of 2 gallons per square foot per hour with a filtrate viscosity of 5 to 10 poises. Bradt (12) discussed the use of filters equipped with sponges, coke or sand beds, terry cloth, or diatamaceous earth precoats to remove oil, emulsified or I I O ~ , from condensate. Other applications of pressure filters mentioned are the Auto-Sluice (Niagara Filter Corporation, Buffalo, N. Y.) precoat leaf filter for improved quality and increased savings in cane sirup processing (%'), and a patented single-disk filter for removing iron stannide crystals from molten iron-tin mixtures (65). Davidsohn ($5) recommended gravity or vacuum beds of wood chips or a filter press used in conjunction with bleaching earth to prepare spent lubricating oil for use as an ink base
T H E O R Y AND DESIGN D A T A
Theoretical contributions have been devoted principally to filter-medium filtration-Le., that type in which no cake develops, but solids accumulate within the medium itself-with not very satisfactory results. Ferrandon (36) has made a classical analysis of the hydrodynamic-s of flow of a perfect fluid through a porous mass which may be considered homogeneous or heterogeneous, isotropic or anisotropic. T h e resulting tensors are said to characterize the permeability and wetted surface of the porous mass. Apart frdhh being difficult to interpret in terms of numerical values fbr the properties of a given system, the results are adequate only in describing the flow through a static, preformed mass, as in filter-cake washing or in the drainage of water through eartbworks. A simpler characterization of the resistance of filter mass (the pulp medium used in beer clarification) to filtrate flow was proposed by van Gastel and van Veldhuizen (do), who applied Poiseuille's or Dqq~y'slaw to determine a permeability factor. On the assumption that all other properties of the pulp remain constant during filtration, the decrease in permeability factor may be taken t o indicate the degree of plugging, and the factor is said t o be useful in determining the suitability of a given freshly formed pulp cake. Hudson (50) made a more realistic approach to the problem of flow through a granular bed in that he attempted to allow for the deposition of floc within the interstices of the bed; his expression is oversimplified, however, and his concept of floc-strength index must bear the test, of many more data over a wide range of variables. Following the earlier analysis of heterogeneous flow through a cake on a vacuum filter, Brownell and Gudz (16) have presented integrated forms of the equations and graphical solutions that permit estimation of the vacuum-pump capacity required for 3 rotary filter. The properties of the particulate solids compressing the cake must be known for use of the charts. I n the realm of experimental work, Samuelson (85) extended his study of viscose filterability to a consideration of the influence of the pulps from which the cellulose was derived, and proposed a n experimental method of evaluating filterability in terms of a clogging constant. Hilinski and Love11 (47) made exploratory attempts t o characterize the filterability of corn mash in terms of several process variables. Tests were conducted with a Biichner funnel and with an Oliver vacuum test leaf. Although they demonstrated that the mash can be filtered, their results are more
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