Recirculation rate

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. 

For catalytic investigations, the rotating basket or fixed basket with internal recirciilation are the standard devices nowadays, usually more convenient and less expensive than equipment with external recirculation. In the fixed basket type, an internal recirculation rate of 10 to 15 or so times the feed rate effectively eliminates external diffusional resistance, and temperature gradients. A unit holding 50 cm (3.05 in ) of catalyst can operate up to 800 K (1440 R) and 50 bar (725 psi). 

This method may also be used for the thermal design of horizontal thermosiphon rehoilers. The recirculation rate and pressure profile of the thermosiphon loop can be calculated by the methods of Fair [Pet Refiner, 39(2), I05-I23 (I960)]. 

Forced-Recirculation Reboilers In forced-recirculation reboilers, a pump is used to ensure circiilation of the liquid past the heattransfer surface. Force-recirculation reboilers may be designed so that boiling occurs inside vertical tubes, inside horizontal tubes, or on the shell side. For forced boihng inside vertical tubes. Fair s method (loc. cit.) may be employed, making only the minor modification that the recirculation rate is fixed and does not need to be balanced against the pressure available in the downcomer. Excess pressure required to circiilate the two-phase fluid through the tubes and back into the column is supphed by the pump, which must develop a positive pressure increase in the hquid. 

Experience in air separation plant operations and other ciyogenic processing plants has shown that local freeze-out of impurities such as carbon dioxide can occur at concentrations well below the solubihty limit. For this reason, the carbon dioxide content of the feed gas sub-jec t to the minimum operating temperature is usually kept below 50 ppm. The amine process and the molecular sieve adsorption process are the most widely used methods for carbon dioxide removal. The amine process involves adsorption of the impurity by a lean aqueous organic amine solution. With sufficient amine recirculation rate, the carbon dioxide in the treated gas can be reduced to less than 25 ppm. Oxygen is removed by a catalytic reaction with hydrogen to form water. 

The older internal recycle reactors of Berty et al (1969), and Berty (1974) are shown on Figures 2.4.3 a, b. The reactor of Romer and Luft (1974) uses no mechanical moving parts. The recirculation is generated by the feed gas as it expands through a nozzle. A major disadvantage of using a jet is that feed rate and recirculation rate are not independent. Due to the low efficiency of jet pumps, recycle rates are quite low. 

Adding a recirculating loop to the transport reactor, a well-mixed condition is achieved provided the recirculation rate is large with... 

Mist type flow usually does not occur in an economic design, even though the recirculation rates may be high. 

Free caustic alkalinity usually is not recommended for jet-type electrode, as foaming conditions may develop rapidly because of the high recirculation rate. Where high alkalinity is present and FW contamination from colloidal or organic matter takes place, the foaming that develops quickly causes the boiler to be shut down. 

The variation of removal efficiencies of benzene according to the inlet loading rate and the liquid recirculation rate is shown in Fig. 3. As shown in the figure, the removal efficiency of benzene decreases with increasing the inlet loading rate and decreasing the liquid recirculation rate. At an inlet loading rate less than 40 g/m -hr, benzene removal efficiency shows a little variation as the liquid recirculation rate increases. However, the removal efficiency... 

As an indicator of conditions, the process treats 5 g s-1 of chlorine, which for the purposes of the simulation was assumed to be steady arisings, although in practice there was significant variation as a function of time and specific plant operations. There was a recirculation vessel in addition to the column sump and the combined inventory was approximately 5 m3, approximately half of which was discharged and replaced at the blow-down and make-up period. The recirculation rate to the scrubber... 

Table 26.1 shows the effects of the two main design variables. Specifically, the results of the batch simulations for the same system as described above are given for different in-loop reactor (catalyst) volumes, recirculation rates. As would be expected increasing the catalyst volume decreases the hypochlorite concentration at all points and times through the process. Increasing the recirculation rate also appears to have a... 

An alternative method of reducing the resistance to filtration is to recirculate the slurry and thereby maintain a high velocity of flow parallel to the surface of the filter medium. Typical recirculation rates may be 10-20 times the filtration rate. By this means the cake is prevented from forming during the early stages of filtration. This can be particularly beneficial when the slurry is flocculated and exhibits shear-thinning non-Newtonian properties. This method of operation is discussed by Mackley and Sherman(21) and by Holdich, Cumming and Ismail(22). 

Higher tangential veloceties (or recirculation rates) should decrease the boundary layer thickness (6) and increase the mass transfer coefficient (k) in Equation 3 resulting in higher slopes of the flux vs concentration curve (Figure 11) without changing the gel-concentration. 

Figure 37. UF flux as a function of recirculation rate for UF of HSA in a spiral...

Figure 52. Operating costs v. recirculation rate for a crossflow UF plant...

The increased energy costs of the future are expected to shift the design point of Figure 52 to the left-to lower recirculation rates. 

Direct-oxidation processes can conveniently remove H2S from the process gas to levels of 100 ppm. At significantly greater cost, levels of perhaps 10 ppm can be achieved. The systems are characterized by relatively low sulfur-carrying capacities and, therefore, high liquor recirculation rates. They are not generally applicable to gas streams with high partial pressures of carbon dioxide the carbon dioxide also dissolves in the solution, causing a pinch in the column and a reduction of sulfur purification capability. 

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