Recycle flow

Figure 6 shows typical results obtained with the plug-flow quartz reactor containing 0.5 g of Sr(lwt%)/La203 catalyst operated in the continuous flow recycle mode. The inlet CH partial pressure was 20 kPa (20% CH in He) at inlet flowrates of 7.1 and 14.3 cm STP/min. A 20% O2 in He mixture was supplied directly, at a flowrate Fog, in the recycle loop via a needle valve placed after the reactor (Fig. 1). The methane conversion was controlled by adjusting Fog, which was kept at appropriately low levels so that the oxygen conversion...

The following systems represent differing combinations of ideal plug-flow, mixing, dead space, flow recycle and flow by-pass. 

Raw TSS Raw TSS Influent TSS Clarified TSS TSS Removal Float TSS Raw Flow Flow Sludge Flow Recycle Flow Total Flow Addition... 

Test No. Sampling Total Flow Float Flow Clarified Flow Recycle 1... 

Figure 10.7 shows the extended RTN formulated for the benchmark problem. The production process includes diverging and converging material flows, flexible proportions of output goods (task Tj), cyclic material flows (recycling of output from task T3 into state Si), intermediate products which cannot be stored (state nodes S5, S9, S10, S12), and blending of products in task Ti 5. All processing tasks are operated batch-wise with lower and upper bounds on batch sizes. Batch sizes are... 

In the past twenty years many legal provisions have been created to regulate substance flows (recycling management systems, waste management, electrical and automotive recycling). In many instances these laws exphcitly contain threshold values for certain substances or even ban certain substances. They are thus very effective on the use of these substances in production processes. This is also tme for threshold values of chlorinated compounds in industrial waste, the ban on certain heavy metals in the automotive industry and substance-related requirements for waste water from the textile industry (Annexe 38 of Waste Water Ordinance ). 

Chemat, E, Poux, M., Di Martino, J.L. andBerlan, J., A new continuous-flow recycle microwave reactor for homogeneous and heterogeneous chemical reactions, Chem. Eng. Tech., 1996,19(5), 420. 

Switching solvents is a very poor practice because of bed swelling and shrinking from solvent to solvent. Usually, a solvent is selected with a broad solubility range the system is turned on and allowed to equilibrate for 24 hours and then kept in a constant flow recycle mode until needed. When a sample is to be shot, flow is switched out of recycle, the chromatogram run, and then immediately returned to recycle. The pump is left on at all times. 

Internal recycle reactors are designed so that the relative velocity between the catalyst and the fluid phase is increased without increasing the overall feed and outlet flow rates. This facilitates the interphase heat and mass transfer rates. A typical internal flow recycle stirred reactor design proposed by Berty (1974, 1979) is shown in Fig. 18. This type of reactor is ideally suited for laboratory kinetic studies. The reactor, however, works better at higher pressure than at lower pressure. The other types of internal recycle reactors that can be effectively used for gas-liquid-solid reactions are those with a fixed bed of catalyst in a basket placed at the wall or at the center. Brown (1969) showed that imperfect mixing and heat and mass transfer effects are absent above a stirrer speed of about 2,000 rpm. Some important features of internal recycle reactors are listed in Table XII. The information on gas-liquid and liquid-solid mass transfer coefficients in these reactors is rather limited, and more work in this area is necessary. 

Fig. 18. Flow recycle reactor (Berty type). (Berty, 1974 also from Chaudhari el al.. 1986, by courtesy of Marcel Dekker, Inc.)...

Chemical processes more often than not contain recycle, a feature that complicates their analysis. Recycle often occurs, as in the styrene process where unreacted ethylbenzene is recovered and recycled back to the reactor as a physical mass flow. Recycle also occurs in the form of heat exchange (again in the styrene process) and sometimes as information, e.g., a specification that two variable temperatures must equal each other. The sequential-modular solution strategy is based upon knowing all inputs to a module and using these to calculate all outputs. When an input stream to a module is the output of a downstream module (i.e., there is recycle), calculations cannot be performed for the upstream module because one of its inputs is not yet known. This is illustrated in Fig. 4.7 unit 1 cannot be calculated because input stream 4 is the output of unit 2 nor can unit 2 be calculated because input stream 2 is an output of unit 1. This same problem of circular reasoning was encountered in Example 1. This dilemma in the sequential modular solution scheme can be... 

For handling large quantities of granular solids, a cascading rotary dryer is often the equipment of choice. If the material is not naturally free-flowing, recycling of a portion of the final dry product may be used to precondition the feed, either in an external mixer or directly inside the drum. Hanging link chains and/or scrapper chains are also used for sticky feed materials. 

This technique is simple and gives high yields. A high resolution can be obtained with the upward flow, recycling method (Tijssen and Kurstak, 1974). Samples should be partially purified and concentrated by precipitation with 50% (NH4)2S04 and dialyzed against 500 mM of NaCI buffered with 50 mM Tris-HCl, pH 8.0, before gel filtration on Sephadex G-200 or Bio-Gel P-300. 

Fig. 1-3 Typical reactors (a) tubular-flow recycle reactor, (b) multi tube-flow reactor, (c) radial-flow catalytic reactor, (d) stirred-tank reactor with internal cooling, (e) loop reactor, (f) reactor with intercoolers (opposite)...

Y.-S. Hsieh, S.R. Crouch, Flow reversal and flow recycle air-segmented flow injection for simultaneous determination of a binary mixture, Anal. Chim. Acta 304 (1995) 333. 

Figure 27-30,331, shows a ftee-flow recycling apparatus developed by M. Bier and Egan, N.B. in 1979 Electrofocus/78, Haglund, H., Westerfall, J.C. and Ball, J.T. Elsevier, Amsterdam). "The basic idea behind recycling in electrophoresis is that solutes do not have to be completely separated in a single pass... 

Figure 27-30. Preparative free-flow recycling electrophoresis apparatus.

Figure 13.14 Steady-flow recycle cascade of electrolytic cells.

M. Temkin, S. Kiperman, and L. Luk yanova, Flow-recycling method for studies of kinetics of heterogeneous catalytic reactions. Doklady Akademii USSR (Proceedings of the USSR Academy of Sciences), vol. 74, pp. 763-767, 1950. 

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