Base-case designs

The initial aim of the procedure is to generate a reasonable base case design that can be used for preliminary economic evaluation of the process. This can subsequently be optimized and/or compared with any process alternatives that are identified. The complete process is always considered at each decision level, but additional fine detail is added to the structure of the flowsheet at any stage. Established heuristics and equipment selection procedures are used together with new process synthesis insights to guide each flowsheet decision. 

Base Case Design Design Steady Dynamic Steady... 

PANELIST EPPERLY In our base case design for EDS, we don t make gas as a product. We maximize liquid yield. The options that I talked about involving using combinations of processes for bottoms would look attractive if gas could be sold in parity with the liquid fuel. But there is clearly some uncertainty regarding exactly how all that would work out. So that is the reason that in our base case we make no gas. 

Column 1 As the base case design in Table 5.3 shows, column 1 has 51 stages, and operates with a partial condenser with a duty of 1.371 MW at the top, and a side condenser with a duty of 8.144 MW at stage 2. It has no reboiler however, it receives a side heat stream with a duty of 15.299 MW to the last stage from section 2 of the plant. The temperature profiles of both columns are shown in Figure 5.9. 

Parameter Design 1 (base case) Design 2 (retrofitted)... 

Figure 11.4 shows what happens when the production rate handle (reactor exit temperature) is changed. The starting conditions are the base-case design where reactor exit temperature is 159CC. The reactor temperature controller is tuned at this operating point. Step changes of 8°C at time 5 minutes and 120 minutes are made in the setpoint of the reactor temperature controller (Figure 11.4a). Decreasing the...

Eliminating options is assisted by simple criteria or tests that can identify a large number of options as unviable. Deepening the search can be assisted by more heuristic measures as the aim is usually to establish a viable base-case design rapidly, without necessarily discarding other options. The appropriate criteria to use and the balance between search methods is clearly problem-dependent. 

The user can use the mechanism in the following way. First, he or she develops the base-case design which does not violate any process constraints. Then, the user improves the base-case design in the evolutionary manner by relaxing the decisions that look relatively promising in terms of contribution to the economic potential of the process flowsheet. Suppose we are working on the recycle structure level and we find one design... 

Design Basis. A preliminary design for a multiproduct ioe extraction plant was prepared, based on SCP s proprietary process (Henkel HSaA, op. cit.) and plant design data (Steams Catalytic Corporation, Tolling/Demo SCE Plant, IhlLadelphla, PA, 1984, proprietary data.). Key parameters in the base case design are Feedstock Ibices and herbs (solid)... 

Battery Lfmita Capital Coat, Base Case Design... 

A preliminary process design was pr >ared for a multiproduct plant. The base case design, with two 973 L extractors, could process 770 MJ (1.7 WM lb) of an average ioe feed per year. The hl capacity design would have an annual feed rate of 3060 Mg (6.8 m lb). 

Table 11.2 Base case design (direct sequence) for separation of a ternary mixture...

TABLE IV Mass Flow Rate, Temperature, Pressure, Exergy Flow Rates, Cost Per Exergy Unit, and Cost Flow Rate for Each Stream in the Base-Case Design of the Cogeneration System... 

TABLE VI Sample of a Qualitative Decision Matrix for the First Design Case (Base-Case Design) ... 

Table VI shows a sample of a qualitative decision matrix for the base-case design which summarizes the suggestions from the thermoeconomic evaluation of each component. Decreasing the values of the pressure ratio P2/P1 and the isentropic compressor efficiency tqsc as well as increasing the isentropic turbine efficiency r]st are expected to improve the cost effectiveness of the cogeneration system. Note, that the decrease in the p2 /p 1 value contradicts the corresponding suggestions from the heat-recovery steam generator and the combustion chamber. However, changes snggested by the evaluation of a component should only be considered if they do not contradict...

Compared to the base-case design, the combustion chamber has now a higher relative cost importance than the heat-recoveiy steam generator. To reduce the cost of exergy destruction in the combustion chamber, the value of Ts is increased to 1320 K. 

Throughout Chapters 1 and 3, the role of die process simulators is deemphasized. Rather, emphasis is placed on the steps in process synthesis and the development of the base-case design. Although from time to time these chapters refer to simulation results, a formal discussion of the role of process simulators during process creation is not attempted until Chapter 4 (and the accompanying multimedia CD-ROM). Chapter 3 introduces the steps in process synthesis without discussing many of the key heuristics used in making decisions. A more formal treatment is reserved for Chapter 5. 

As shown in Figure 1.2, in developing a base-case design, the design team checks regularly to confirm that the process remains promising. When this is not the case, the team often returns to one of the steps in process creation or redevelops the base-case design. 

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