Gas Throughput

Term from cake filtration. During the demoisturing process under the influence of the gas differential pressure and following the demoisturing of the largest pores a gas throughput through the respectively demoistured pores of the filter cake occurs. With decreasing product moisture the gas throughput increases. It has to be sustained by the gas compressor, in order to maintain the driving pressure for further cake demoisturing. The gas throughput is not the cause but instead the undesired effect of the demoisturing. The gas throughput determines essentially the operational costs of the filter apparatus.

Gas Throughput-Free Filtration

Process developed in Karlsruhe, Germany for cake filtration based on a membrane filter cloth with a high capillary entry pressure as filter medium (BOKELA patent). The process avoids through the structure of this filter medium the gas throughput, normally occurring at the cake demoisturing through the already emptied cake pores. Furthermore particle-free filtrates are produced. The gas throughput-free fitration can be employed for all cake filtration machines due the flexibility and process-tailored fabrication of the filter medium.

Grade Efficiency

Share of percentage of a substance actually separated. The total separation degree for a solid substance out of the suspension includes the separated amount in percentage share of the entirely available solids, while the fractional grade efficiency describes the percentage of the separated share of a solids fraction. The fractional grade efficiency is displayed by the Tromp curve.

Grain Fraction
Particle Fraction
Grain Size
Particle Size
Grain Size Distribution
Particle Size Distribution

The gravity measured on the earth’s surface is derived as the resultant out of the mass attraction and the centrifugal force caused by the earth’s rotation, which in general can be neglected.

Gravity Filtration

The hydrostatic pressure of a liquid column is utilized here as the driving potential for the liquid transport. This can be realized by an over-the-dam height on the surface of a deep bed filter (sand filter for water purification), or by the liquid column in a bulk.

Gravity Thickener

Mostly circular or rectangular basins, in which a feed suspension is separated by gravity. Round thickeners are built with diameters of up to 200 m and are operated continuously. The diluted, often flocculated, suspension is fed centrally. Below the clear liquid zone in the upper thickener section whose outer edge includes the overflow for the clarified liquid, is the interface level where the so-called swarm sedimentation zone begins. This separating zone changes into the compression zone in the lower part of the tank. Here the particles approach each other so closely that they are capable of exerting mechanical forces on each other. The achieved thickening degree depends on the thickness of the compression layer and the compression time. The thickened sludge is conveyed from the bottom of the thickener by a slowly rotating rake to the central sludge outlet. Very high thickening is achieved in so-called deep cone thickeners. Rectangular basins are fed on one side and the liquid flows through horizontally. Flow velocity of the liquid and sedimentation velocity of the particles are perpendicular to each other. The sediment is transported carefully to the sludge outlet by a rake mechanism. The clarified liquid leaves the basin via a weir. Floating sludge can be discharged via a special second weir.


Permeation equation for porous bulk with a similar structure as the Carman & Kozeny-equation:

Δp = pressure difference, ρ = fluid density, v= mean (average) flow velocity, d = characteristic length, hc = cake thickness, ε = porosity, Re Reynolds Number

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