High flow rates

Thickening Pressure Filters. The most important disadvantage of conventional cake filtration is the declining rate due to the increased pressure drop caused by the growth of the cake on the filter medium. A high flow rate of Hquid through the medium can be maintained if Httle or no cake is allowed to form on the medium. This leads to thickening of the slurry on the upstream part of the medium filters based on this principle are sometimes called filter thickeners. 

Viscosity. Sedimentation rate increases with decreased viscosity, )J., and viscosity is dependent on temperature. Often mineral oils, which are highly viscous at room temperature, have a viscosity that is reduced by a factor of 10 at 70—80°C. Tar, soHd at room temperature, is a low viscosity Hquid at 150—200°C and can be clarified of inorganic soHds at high flow rates. Even the viscosity of water changes significantly when the temperature changes between 10 and 35°C (10). 

The pump may have formed a vortex at high flow rates or low liquid level. Does the vessel have a vortex breaker Does the incoming flow cause the surface to swirl or be agitated ... 

Axial-flow fans are designed to handle veiy high flow rates and low pressure. The disc-type fans are similar to those of a household fan. They are usually for general circulation or exhaust work without ducts. 

At high-flow rates through perforated plates such as those that occur in distillation columns, Calderbank and Rennie [Trans. In.stn. Chem. Engrs., 40, T3 (1962)] Porter et al. [ibid., 45, T265 (1967)] Rennie and Evans [Br. Chem. Eng, 7, 498 (1962)] and Valentin (op. cit.. Chap. 3) have investigated and discussed the effect of the flow conditions through the iTuutiple orifices on the froths and foams that occur above perforated plates. 

Filtrate is collected in the underdrain system, which may be as simple as a network of perforated pipes covered by graded gravel or a complex structure with slotted nozzles or conduits that will retain the finest sand media while maintaining high flow rates. This latter design allows the use of both air and liquid for the backwashing and cleaning operations. 

Circumstances that may induce cavitation include vibration, excessively high flow rates, insufficient supply of fluid to the suction side of pumps, and operation of valves in a partially open or closed position. 

The filter elements should remove particles of five microns, must be water-resistant, have a high flow rate capability with low pressure drop, possess high dirt-retention capacity, and be rupture-resistant. The clean pressure drop should not exceed five psig at 100 °F (38 °C). The elements must have a minimum collapse differential pressure of 50 psig. Pleated-paper elements are preferred—provided they meet these requirements. Usually, the pleated-paper element will yield the five psig clean drop when used in a filter that was sized to use depth-type elements. This result is due to the greater surface area of the pleated element, more than twice the area of a conventional stacked disc-type or other depth-type elements. 

The Cv Concept. From a quantitative standpoint, steam loss can be estimated through the application of the C, concept. A familiar term in control valve technology, C, expresses the flow capability of a fluid-controlling device—in this case, a steam trap. A large C,. means a high flow rate a low C, means a low flow rate. 

Slurry is pumped and fills the ehambers at a high flow rate and low pressure whieh gradually builds-up as the eake gets thieker. The drip trays whieh are positioned below the filterpress for the eolleetion of drippings elosed. 

---