Cycles batch operation

Clearly, the time chart shown in Fig. 4.14 indicates that individual items of equipment have a poor utilization i.e., they are in use for only a small fraction of the batch cycle time. To improve the equipment utilization, overlap batches as shown in the time-event chart in Fig. 4.15. Here, more than one batch, at difierent processing stages, resides in the process at any given time. Clearly, it is not possible to recycle directly from the separators to the reactor, since the reactor is fed at a time different from that at which the separation is carried out. A storage tank is needed to hold the recycle material. This material is then used to provide part of the feed for the next batch. The final flowsheet for batch operation is shown in Fig. 4.16. Equipment utilization might be improved further by various methods which are considered in Chap. 8 when economic tradeoffs are discussed. 

Process and Operating Conditions The major parameters that must be fixed or identified are the solvent to be used, the temperature, the terminal stream compositions and quantities, leaching cycle (batch or continuous), contact method, and specific extractor choice. 

Although the continuous-countercurrent type of operation has found limited application in the removal of gaseous pollutants from process streams (Tor example, the removal of carbon dioxide and sulfur compounds such as hydrogen sulfide and carbonyl sulfide), by far the most common type of operation presently in use is the fixed-bed adsorber. The relatively high cost of continuously transporting solid particles as required in steady-state operations makes fixed-bed adsorption an attractive, economical alternative. If intermittent or batch operation is practical, a simple one-bed system, cycling alternately between the adsorption and regeneration phases, 1 suffice. 

A semi-batch reactor has the same disadvantages as the batch reactor. However, it has the advantages of good temperature control and the capability of minimizing unwanted side reactions by maintaining a low concentration of one of the reactants. Semi-batch reactors are also of value when parallel reactions of different orders occur, where it may be more profitable to use semi-batch rather than batch operations. In many applications semi-batch reactors involve a substantial increase in the volume of reaction mixture during a processing cycle (i.e., emulsion polymerization). 

Often pilot plant or research data for developing a process are obtained on a batch operation. Later, a continuous process will usually prove that smaller equipment can be used and that the operation. vill be more economical. Normally batch mixing requires 10%-25% more power than continuous [29] for stable conditions how ev-er, the reaction time for continuous flow is always longer than the reaction time for batch flow, but the practical result may show batch time cycle is increased by filling,... 

A semibatch reactor is a variation of a batch reactor in which one reactant may be added intermittently or continuously to another contained as a batch in a vessel, or a product may be removed intermittently or continuously from the vessel as reaction proceeds. The reaction may be single-phase or multiphase. As in a batch reactor, the operation is inherently unsteady-state and usually characterized by a cycle of operation, although in a more complex manner. 

Ridelhoover and Seagrave [57] studied the behaviour of these same reactions in a semi-batch reactor. Here, feed is pumped into the reactor while chemical reaction is occurring. After the reactor is filled, the reaction mixture is assumed to remain at constant volume for a period of time the reactor is then emptied to a specified level and the cycle of operation is repeated. In some respects, this can be regarded as providing mixing effects similcir to those obtained with a recycle reactor. Circumstances could be chosen so that the operational procedure could be characterised by two independent parameters the rate coefficients were specified separately. It was found that, with certain combinations of operational variables, it was possible to obtain yields of B higher than those expected from the ideal reactor types. It was necessary to use numerical procedures to solve the equations derived from material balances. 

Smooth scale-ups from R D laboratory or bench scale to pilot scale and then to commercial size batch-operated, multi-purpose chemical plants are often not easy to achieve for a variety of reasons, often resulting from compromises due to the need to use existing equipment. The consequences of this lack of scalability can be a reduction in product quality and yield, increased by-product formation, longer cycle times, and, in some cases, an inability to reproduce key product properties such as color, size, or crystal structure. These consequences invariably result in an increased use of mass and energy and a production of greater waste per unit mass of product. 

Toluene and olefinic stock from storage are pumped (at 80°F) separately through individual driers and filters into the alkylation reactor. The streams combine just before they enter the reactor. The reactor is batch operated 4 hr/cycle it is equipped with a single impeller agitator and a feed hopper for solid aluminum chloride which is charged manually from small drams. The alkylation... 

In semi-batch operation, when the initial charge of A has been consumed, the flow of B is interrupted, the products discharged, and the cycle begun again with a fresh charge of A. If required, however, the advantages of semi-batch operation may be retained but the reactor system designed for continuous flow of both reactants. In... 

The batch reactor is perhaps the most natural of all chemical reactors. Most events in the natural world are time-varying batch events. They start from some initial conditions and proceed to change dynamically with time over some batch time. The whole cycle of animal and plant life is a batch operation. The conception, gestation, birth, growth, and death of an animal occur in a batch cycle. Our first exposure to a chemical reaction is probably in a high school chemistry class in which the reaction takes place batchwise in a test tube or flask. 

One important issue of the fed-batch operation is the variable volume of material in the reactor and its effect on heat transfer area. If jacket cooling is used, the heat transfer area covered by the liquid in the reactor will be proportional to the volume of the liquid at any point in time. However, if the reaction liquid is circulated through an external heat exchanger, the full heat transfer area is available throughout the batch cycle. 

During saccharification, pretreated corn stover is sent to several 950,000-gal (3600-m3) vessels, with an associated capital cost of 650,000 per vessel. Cellulase is then added at 10 or 20 FPU/g of cellulose, and the reaction proceeds. The number of required vessels is calculated based on the total volume required to process 430,000 kg/h of pretreated corn stover over the reaction cycle, which is 5 d for batch operation and 15 d for semibatch operation. The total volume for the semibatch processes is slightly higher than the batch processes owing to inert solids that build up during the 15-d processing time. 

Seven of the most promising resins were tested for regenerability and stability using a modified extraction procedure combining acid and hot water washes. Two (XUS 40285 and XFS-40422) showed both good stable capacities for succinic acid over 10 cycles and >95% recovery in a batch operation. 

Recent advances on the Ca-Br cycle were presented in an ANL paper. The original concept for this cycle involved solid phase reactions in a semi-continuous batch operation. The ANL paper reported on experiments that used a direct sparging reactor in the hydrolysis reaction to allow continuous production of HBr which is then electrolytically decomposed to produce hydrogen. The sparging steam was introduced into the molten bath of CaBr2 which yielded HBr in a stable and continuous operation. 

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