Cake Characterization

Panfili G, Cinquanta L, Fratianni A and Cubadda R. 2003. Extraction of wheat germ oil by supercritical CO2 oil and defatted cake characterization. J Am Oil Chem Soc 80(2) 157—161. 

In situ local characterization of cake formation is a key step towards a better understanding of filtration processes. Some non-invasive characterization methods have shown their efficiency for cake investigation on flat-sheet membranes but they give only one kind of information. Few studies concern cake characterization in a confined geometry like an inside-out hollow fiber membrane. 

A SAPP with intermediate reactivity is used in combination with fast-acting MCP for the manufacturer of industrial baking powder and for retail and wholesale prepared cake mixes. SAPP imparts a bitter aftertaste which is often characterized as a mild burning sensation, especially when used in a product of low sweetness. SAPP is normally used at an NV of 72. However, it may be used at slightly higher or lower NV to obtain specific effects in certain types of baked goods. 

Rotary Drum Filters The rotaiy drum filter is the most widely used of the continuous filters. There are many design variations, including operation as either a pressure filter or a vacuum filter. The major difference between designs is in the technique for cake discharge, to be discussed later. All the alternatives are characterized by a horizontal-axis drum covered on the cylindrical portion by filter medium over a grid support structure to allow drainage to manifolds. Basic materials of construc tion may be metals or plastics. Sizes (in terms of filter areas) range from 0.37 to 186 m (4 to 2000 ft ). 

When the cake structure is composed of particles that are readily deformed or become rearranged under pressure, the resulting cake is characterized as being compressible. Those that are not readily deformed are referred to as sem-compressible, and those that deform only slightly are considered incompressible. Porosity (defined as the ratio of pore volume to the volume of cake) does not decrease with increasing pressure drop. The porosity of a compressible cake decreases under pressure, and its hydraulic resistance to the flow of the liquid phase increases with an increase in the pressure differential across the filter media. 

As follows from Equation 8, ro characterizes the resistance to liquid flow by a cake having a thickness of 1 m. 

The numerator of Equation 79 characterizes the cake resistance. The denominator contains information on the driving force of the operation. Constant K (sec/m ) characterizes tile intensity at which the filtration rate decreases as a function of increasing filtrate volume. 

Determine the filtration constants a and b, where a is the constant characterizing cake resistance related to 1 of filter area in sec/m, and b characterizes the resistance of the filter medium related to 1 m of filter area in sec./m. ... 

Predictions on the effectiveness of a fluid loss additive formulation can be made on a laboratory scale by characterizing the properties of the filter-cake formed by appropriate experiments. Most of the fluids containing fluid loss additives are thixotropic. Therefore the apparent viscosity will change when a shear stress in a vertical direction is applied, as is very normal in a circulating drilling fluid. For this reason, the results from static filtering experiments are expected to be different in comparison with dynamic experiments. 

Pressure filters or filter presses are commonly of the batch type, and are characterized by smaller floor area, high filtration rates, and lower capital cost. Dryer cakes are produced. The chemical industry uses these filters more widely than mineral processing industries, mainly because of its batch operation. The most common types of pressure filters used are the plate and frame presses. These comprise a series of vertical, alternating parallel frames and plates, with the filter cloth being held against the plate and the formation of cake occurring in the hollow frame. 

Data collected for each run included acid analysis using inductively coupled plasma (ICF) to determine cation concentration and titration to determine H concentration. Filtering characteristics were determined using solid and filtrate yield rates, as well as back pressures during the filtration cycle. The filter cake was characterized by moisture content and composition. Solid samples were analyzed with scanning electron microscopy (SEM) to determine changes in particle shape and size under various process conditions, and X-ray diffraction (XRD) was used to determine the solids composition. 

Ultraviolet spectrophotometry (DuPont 400 SO2 analyzer) was used to monitor the gas phase SO2 concentrations and SO2 removal efficiencies. The pH of scrubbing liquor in each reactor was measured hourly during pilot testing. Solid dewatering properties were characterized by hold tank slurry settling rate and filter cake insoluble solids concentration. Detailed descriptions of the test facilities and analytical procedures were reported earlier(S). 

Equilibrium saturation of the cake, = w /w,, will initially depend on the physical properties of the filter cake. They are characterized by a, e, and K. represents the contact angle (degree of wettability) and K any other grain parameters such as roughness and so on. Furthermore, the physical properties of the wash liquid (density, p, and surface tension, o) and, finally, centrifugal acceleration, b, as process parameter will be of importance ... 

For q - 0 or Tb -> 0, Ucond - 0, and at q - <=° or xb -> <=°, Ucond -> u. That is, to increase the filter capacity, filtration time should be increased. However, such an increase is limited by the maximum allowable pressure drop which at constant operating conditions, establishes a maximum cake thickness. Let s consider the following example for the first case in this analysis. We wish to determine the capacity of a batch filter operating at a constant rate. The rate of filtration is q = 0. 1 X 10 3 m3/m2-s and the auxiliary time is 900 s. The solution to this problem is as follows. The filter capacity is characterized by the average conditional filtration rate, q. Values of ucord calculated are shown plotted in Figure 41. As shown, an increase in the amount of filtrate causes a sharp increase in filter capacity initially, with a limiting value of u attained eventually. 

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