Optimum recirculation rate

There is an optimum recirculation rate for each stage. Higher recirculation rates will result in greater productivity (flux), less membrane area, and longer membrane life due to greater flux stability. They also require larger pumps and increased power costs. 

The largest current applications for UF (in terms of installed membrane area) were not envisioned in the early sixties (e.g., UF of electrocoat paint). Further, many of the projected applications have not yet materialized (e.g., fractionation of polymers and proteins). 

In some applications, the product is the retentate, and the objective is to concentrate or purify the retained species (passing unwanted contaminants through the membrane). 

In a few applications, both retentate and filtrate are important. For example, if a valuable product or by-product is a pollutant in a waste stream, recovery and use of the product will often pay for the pollution abatement. The clean permeate may then be reused in the plant in cases where the plant effluent is at elevated temperatures, the hot permeate may be reused in the plant saving additional energy costs. There are only a few applications where UF can be justified for pollution abatement without the recovery of a valuable by-product or energy credit In these cases, the economic incentive is found in the avoidance of a sewer tax or shut down by the Environmental Protection Agency. 

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The special design of the Latham bowl allows for a specific blood cell separation known as SURGE. This technique makes use of the principle of critical velocity. The Latham bowl is filled until the huffy coat, ie, layer of platelets and white cells, moves in front of the bowl optics. At this point the machine starts to recirculate plasma through the bowl at increasing rates. The smallest particles, ie, platelets, ate the first to leave the bowl. Their high number causes the effluent line to turn foggy. The optical density of the fluid in the effluent line is monitored by the line sensor. A special algorithm then determines when to open and close the appropriate valves, as well as the optimum recirculation rate. 

Kinetics of Bound and Free Enzyme. The kinetics of the IME were obtained with the recirculating differential reactor system as described above. The appropriate flow rate, the temperature optimum, and pH optimum as described above were used to most accurately establish the kinetic parameters for this IME emgmie. Substrate solutions from 3 to 150 mM cellobiose in 10 mM sodium acetate were appropriate for this portion of the study. Results were analyzed with the ENZFTT software package (Elsevier Publishers) that permits precise Lineweaver-Burk regressions. 

On 2 July 1909 two representatives of BASF visited Haber s laboratory at Karlsruhe. Their brief was to evaluate Haber s apparatus for the high pressure synthesis of ammonia from its elements. Even under optimum conditions the yield was low, around 5 per cent, but Haber had arranged for unreacted hydrogen and nitrogen to be recirculated. Though exothermic, the reaction was carried out at 600°C in order to increase the rate. The preferred catalyst was osmium or uranium. 

With more dilution water entering the caustic, either the strength of the recirculating stream will be lower or the rate of recirculation of cell product must increase to hold that concentration and reduce the concentration change across the cells. The increased flow rate enhances mixing of the recycle stream in the cells, and there is probably some economic optimum of the circulating rate and solution concentration. Intuitively, that optimum seems to be on tbe side of holding the concentration steady. This is the method usually adopted in practice. 

Figure 5.7 shows the specific mass flow of CO2 required in an extraction cascade to achieve the indicated degree of decaffeination for an extraction period of 12 hours. Data are shown for two pressures at the same temperature. Mass transfer tests of this type enable optimum mass flow rates to be determined for a given efficiency of extraction. It should be noted that the energy consumption of the bean extraction process is directly proportional to the amount of CO2 recirculated. 

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