Cyclic operation

A familiar type of cyclically operated solenoid electromagnet is the Franz separator, a well-known continuous pe of solenoid separator manufactured by Kriipp-Sol. An enclosed flux return-frame solenoid design for cyclic and continuous use is built by Sala International Inc. 

Although reducing the corrosivity of the external environment wrould reduce cracking, in this case it is judged that cyclic, operational stresses are predominant. Until the source of the stresses is determined and reduced or eliminated, it is doubtful that a permanent solution can be achieved. 

Multiple desiccant beds are used in cyclic operation to dry the gas on a continuous basis. The number and arrangement of the desiccant beds may vary from two towers, adsorbing alternately, to many towers. Three separate functions or cycles must alternately be performed in each dehydrator. They are an adsorbing or gas drying cycle, a heating or regeneration cycle, and a cooling cycle. 

Sorensen (1999) has suggested a cyclic operation policy for batch distillation with repeated filling and dumping of the reflux drum. This configuration achieves the maximum attainable separation and requires minimal control. Furthermore, such a column can be operated very safely. 

For a general CTES undergoing a cyclic operation, the overall energy efficiency j] can be evaluated as... 

The effect of increasing the time horizon length was not investigated in this example, or any of the examples that follow. The results are, therefore, unique in each scenario. The cyclic operation of each process was also not investigated. 

In both solutions presented above, cyclic operation has not been investigated. However, it is very possible that if the operation were cyclic further reuse opportunities could present themselves. 

Disadvantages of the integral control mode are that it responds relatively slowly to an error signal and that it can initially allow a large deviation at the instant the error is produced. This can lead to system instability and cyclic operation. For this reason, the integral control mode is not normally used alone, but is combined with another control mode. 

Although PSA is a batchwise process, by using multiple beds in a sequential manner the overall process is operated in a continuous fashion. Each bed may contain layers of different adsorbent materials selective for specific contaminants in the hydrogen gas stream to be purified. Each bed undergoes a sequence of four basic steps in a PSA cycle adsorption, depressurization, purge at low pressure, and repressurization. This sequence of cyclic operations for each bed is shown schematically for a four-bed PSA process in Figure 8.4 (Yang, 1987 Cassidy, 1980 Miller and Stocker, 1999). 

Tests were carried out at 25°C and at initial pH 6.9. Cultures in the liquid medium were incubated in 50 mL Falcon tubes, continuously shaked at 220 rpm. Each culture contained a fresh Pseudomonas sp. 0X1 colony in 10 mL of medium. The airlift with 10 g of pumice was sterilized at 121°C for 30 min and then housed in a sterile room. One-day culture was transferred to the reactor and, after a batch phase, liquid medium with phenol as the only carbon source was continuously fed. The reactor volume V was fixed at 0.13 L. Aerobic conditions were established sparging technical air. Under these conditions microorganism started to grow immobilized on the solid s support. When immobilized biomass approached steady state, cyclic operation of the airlift was started by alternating aerobic/anaerobic conditions. 

A dynamic model has been developed to simulate the behavior of a Pseudomonas sp. 0X1 biofilm reactor for phenol and azo-dye conversion during the aerobic-anaerobic cyclic operation. Phenol and oxygen were considered as the limiting substrates for growth kinetics. 

Model computations suggest that cyclic operation is able to regenerate during the aerobic stage the reducing potential for dye conversion during the anaerobic stage. 

Some experimental studies (1-7) have demonstrated the possibility of improving the performance of a catalytic reactor through cyclic operation. Eenken et al. (4) reported an improvement of 70% in conversion of ethylene to ethane under periodic operation. In a later article (2), they concluded that periodic operations can be used to eliminate an excessively high local temperature inside the catalytic reactor for a highly exothermic reaction. In our laboratory, Unni et al. (5) showed that under certain conditions of frequency and amplitude associated with the forced concentration cycling of reactants, the rate of oxidation of SC>2 over catalyst can be increased by as much as 30%. Re-... 

Figure 12.4 Some modes of operation of semicontinuous reactors (a) gas-liquid reaction (b) gas-solid (catalyst or reactant) reaction (c) cyclic operation (reaction)-) and regeneration)- -)) for deactivating catalyst...

During remediation, contaminant levels decrease until they achieve an asymptotic level. Once asymptotic conditions are reached for several successive sampling periods, continuing remediation activities generally result in little further decrease in contaminant reduction. However, frequently when active remediation is halted, levels of dissolved contaminants abruptly increase (rebound). This increase is the result of the diffusion into solution of contaminants that were previously adsorbed onto the surface of the aquifer media. Sometimes more efficient cleanup is achieved by operating the remediation system on a cycle of several days on and several days off. Cyclic operation allows the operator to time the remediation to treatment of the higher rebound concentrations. 

The disadvantages of cyclic operation, attributable to the need to remove the cake from batch filters, have been largely overcome by the development of a wide range of continuous vacuum filters as summarised in Table 7.2 which includes data on the selection for a given duty. This is further detailed in Table 7.3 and is based on the work of G. H. Duffield of Stockdale Engineering and E. Davies of ED ACS Ltd. 

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