Utilities flow-sheet presentation

The solution to the problem is obtained by solving mass and energy balances to yield the quantity and state (i.e., composition, temperature, pressure) of all the streams and the utility requirements. Additional parameters for the process equipment, sufficient so that stream specifications are met and the cost of the equipment can be estimated, are calculated. The cost of equipment, raw materials, and utilities is estimated and an economic analysis is carried out. Methods of cost estimation and economic analysis are presented later in this text. This entire procedure may be repeated many times to examine modifications of the process flow sheet or to find optimal values of key process variables. Computer software can greatly simplify these repetitive calculations for the engineer. But even without the need for repetition, the software may simplify the calculations and provide detail and accuracy that would have been impossible otherwise. 

Several alternative methods for presenting material balances in graphic form will be mentioned. Figure 3-4 shows a method where all the stream components and weights are placed at the proper location on the flow diagram. There is only a section of the entire process shown here. This method has utility for very simple process flow sheets, but it can be seen that a rather cumbersome method of presentation results when the number of stream components is large. 

Operating Cost and Economic Analysis. This section begins with a presentation of the annual costs of operating the proposed plant, that is, the cost sheet, as discussed in Section 17.2 and shown in Table 17.1. In addition to the total production cost on the cost sheet, it should provide an estimate of the cost per unit weight of the product (e.g., per lb, kg, ton, or tonne). Note that when cash flows are computed for different production rates from year to year, a separate cost sheet is required for each unique production rate. Note also that, in addition to appearing on the cost sheet, the utilities for each equipment unit and their costs should be sununarized in a separate table. 

Steady-state flow reactors, with a constant supply of reactants and continuous removal of products, can be operated as both a continuous stirred-tank bioreactor (CSTB) and as a plug flow bioreactor (PFB). It is possible to have different configurations of the membrane bioreactor where the biocatalyst is immobilized in the fractionated membrane support (Katoh and Yoshida, 2010). In Fig. 1.6 the scheme of a CSMB in which the biocatalyst is immobilized on the surface of the membrane beads is presented. The biocatalyst immobilized in the porous structure of a fractioned membrane can also be operated in CSMB. For example, two configurations are shown in Fig. 1.7 (a) for flat-sheet and (b) for spherical porous structures, respectively. Such structures could also be adopted for PFB, where a bed of membrane support with the immobilized biocatalyst could be utilized, in either a fixed or fluid configuration. 

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