Batch recirculation

Membrane modules can be configured in various ways to produce a plant of the required separation capability. A simple batch recirculation system has already been described in cross-flow filtration. Such an arrangement is most suitable for small-scale batch operation, but larger scale plants will operate as feed and bleed or continuous single pass operation (Figure 16.20). 

Other cell designs, flow cells, can be found in literature [47]. In this design, a flow sonoelectrochemical reactor is the operational unit in a batch recirculation system, see Fig. 4.4. In this, analyzing the performance of the sonoelectrochemical degradation of trichloroacetic acid, influence of the fluid flow, gases evacuation system and, especially, the maintenance of the values of the performance parameters in the scale-up were checked. 

Fig. 4.4 Flow sonoelectrochemical reactor in batch recirculation configuration...

Robinson and Walsh have reviewed earlier cell designs. The performance of a 500 A pilot plant reactor for copper ion removal is described. Simplified expressions were derived for mass transport both in single pass [243] and batch recirculation [244]. For a detailed discussion of the principle and the role of the rotating cylinder electrode reactor in metal ion removal the reader is referred to Refs. [13] and [241] (46 references). 

Idem (1991) Batch recirculation studies and overall pass transport, Hydrometallurgy 26 115 Chem Abstr 114 (1991) 194768x... 

Figure 16.13. MWB (Metallwerk Buchs) batch recirculating crystallizer, with freezing on and melting off insides of thin film heat exchanger tubes adaptable to multistage processing without external solids handling [Miitzenberg and Saxer, 1971).

During 1959 several important advances have increased the efficiency and lowered the costs of electric membrane demineralization development of an improved permselective membrane which has a lower electrical resistance than those formerly used but retains the structural, mechanical, ana chemical stability characteristics for successful demineralization under the high rate of flow necessary for economic operation a practical membrane stack with available membrane area over three times that of stacks formerly used and a continuous-flow, two-stage, single-stack brackish water demineralizer to provide 65 to over 90% demineralization on flows of I to 20 gallons per minute. Formerly batch recirculating—type units were standard for this range of operation. The new units are simpler in construction and more efficient in the use of membrane area. 

The Batch Unit. Previously, if high degrees of demineralization and low flows from a single stack installation were desired, a batch recirculating type of system was utilized (4). The standard batch unit utilized a single Mark I 300-membrane 18 X 20 inch stack. A schematic flow sheet of a recirculating batch unit is shown in Figure 3. 

The allowable current density—normality ratio for electric membrane operation has been approximately doubled by an improved tortuous path spacer with strap turbulence promoters and by operation at higher pressures up to 60 p.s.i. As a result, twice as much water can now be demineralized per square foot of membrane utilized and/or greater demineralization achieved per pass in electric membrane units. One practical result of this development is a new continuous-flow, two-stage single-stack demineralizer which will provide 93% demineralization at a capacity of 5000 gallons per day and 72% demineralization at a capacity of 30,000 gallons per day. These units produce from 67 to 150% more water per unit membrane area than previously used automatic batch-recirculating units and are far simpler in construction and operation. 

It is necessary to consider the mass balances over the electrochemical cell and the reservoir to describe the temporal evolution of COD in the batch recirculation reactor system given in Fig. 1.5. Considering that the volume of the electrochemical reactor Ve (m3) is much smaller than the reservoir volume Vr (m3), we can obtain from the mass balance on COD for the electrochemical cell the following relation ... 

Baseline drift is an obvious objection which can be envisioned to occur when using recirculation. However, it has been reported (17) that the use of batch recirculation did not result in baseline drift when analyzing organic acids using UV detection. In this report 3.5 L of mobile phase was prepared and after about 3 L of column effluent was collected the mobile phase was recycled. It was possible to reuse the mobile phase about five times before fresh mobile phase was prepared. Samples included waste digester and artificial gut liquids , foods (including soy sauce), and wines. 

Classical chemical reaction engineering provides mathematical concepts to describe the ideal (and real) mass balances and reaction kinetics of commonly used reactor types that include discontinuous batch, mixed flow, plug flow, batch recirculation systems and staged or cascade reactor configurations (Levenspiel, 1996). Mixed flow reactors are sometimes referred to as continuously stirred tank reactors (CSTRs). The different reactor types are shown schematically in Fig. 8-1. All these reactor types and configurations are amenable to photochemical reaction engineering. 

Many commercial photochemical reactor systems make use of the batch recirculation mode for the treatment of highly contaminated wastewaters of limited volume. On the other hand, cascades of photoreactor modules (in serial or parallel mode) allow the gradual treatment of contaminated water streams with a very high photon flow Op in total. Hence, there exist powerful photochemical waste-... 

Fig. 8.1 Types of ideal chemical reactors (Levenspiel, 1996). The batch recirculation reactor system consists of a vessel of total volume V and a reactor of a specified volume Vr, CSTR continuously stirred tank reactor.

Levenspid earlier presented, in 1972, a qualitative discussion about the product distribution related to photochemical reactions comparing batch and batch recirculation photochemical reactors. The essentials of this discussion can be transferred to photo-initiated AOPs (at least to the H2O2-UV process), which at low concentrations of a pollutant M ([M] <100 mg L ) usually follow an overall first order reaction kinetics (Bolton et al, 1996). 

On the other hand, the treatment of M in a batch recirculation reactor system will generate a completely different concentration profile (Fig. 8-2, situation B). Small fractions of fluid are continuously removed from the batch tank and pumped through the photoreactor module (PR). Here, the same amount of OH... 

Fig. 8.2 Comparison of the concentrationtime profiles in a batch (A) and a batch recirculation photoreactor (PR) system (B) (adopted from Levenspiel 972, p. 174/175). In...

Fig. 5.5 Experimental setup of batch recirculating electrodeposition (Reproduced from Ref. [164], with kind permission of The Electrochemical Society)...

Commence batch recirculation through a 150-pm-aperture stainless steel screen. Maintain until batch is filled. 

A large amount of N2O was formed from the initial stage over LaM03 (M = Co, Mn, Fe, Cr, Ni) at 573 K. The time course of the NO+CO reaction (performed in a batch recirculation system) reflects this situation. These results support a two-step reaction pathway in which N2O is an intermediate for nitrogen formation, deal et al. (1994) confirm the role of N2O as intermediate in this reaction over perovskite oxides. They used steady-state isotopic transient kinetic analysis to study the mechanism of NO + CO reaction over LaCo03. They concluded that N2O was an intermediate in the formation of N2 at T < 873 K. They also concluded that at high temperature CO2 desorption became the rate-limiting step of the overall reaction. This is likely due to the rapid formation and slow decomposition of very stable carbonates on the perovskite surface as reported by Milt et al. (1996). 

Batch, recirculating batch, extractive semibatch, semicontinuous flow, continuously stirred tank (CSTR) and continuous packed bed reactors have alt been succesfully tested as enzyme reactors for SCFs (Figure 4.9-1). References to helpful descriptions for designing small-scale reactors for enzymatic studies are collected in Table 4.9-1. 

Sopajaree, K., Qasim, S. A., Basak, S., and Rajeshwar, K., 1999a, Integrated flow-reactor membrane filtration system for heterogeneous photocatalysis. Part I. Experiments and modeling of a batch - recirculated photoreactor, J. App. Electrochem., 29(5) 533-539. 

The two major types of heated-air grain dryers are bin dryers and portable dryers. Bin dryers are available in batch, recirculating, and continuous categories, whereas portable dryers are available commonly in recirculating and nonrecirculating types. 

Fig. 3.17. Batch recirculating oven passes gases through the loads many times, saving fuel. The circulating gases have burner poc, and thus help uniformity.

Sopajaree K, Qasim S A, Basak S and Rajeshwar K (1999a), An integrated flow reactor-membrane filtration system for heterogeneous photocatalysis. Part I Experiments and modelling of a batch-recirculated photoreactor , / Appl Electrochem, 29,533-539. 

The previous systems for the recovery of metal ions have been primarily concerned with solutions containing only one metal ion. With mixed metal ion solutions there are thermodynamic and kinetic limitations which can effect the selectivity of the system and the final metal deposit. With some mixed metal ion solutions the difference in equilibrium potentials for the reactions can indicate that selective electrodeposition is probable, e.g. with solutions of zinc or cadmium and copper in dilute sulphuric acid solutions as used in fluidised bed electrolysis. Another example is the use of a flow-by carbon felt electrode in the extraction of Cu, Pb and Hg in a batch recirculating reactor [27]. The felt was of fibre diameter 1.1 x 10 m, with a porosity of 0.91 and a specific area of 2200 m By fixing the... 

THE PROBLEM A batch recirculating system is used to recover metal from an aqueous electrolyte under limiting current conditions. Compare the conversions achieved after 2 x 10" seconds with a simple batch reactor, a recirculating plug-flow reactor and a recirculating stirred-tank reactor, assuming that the total electrolyte volume remains the same. The data in Table 4.3 can be used. 

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