Degrees flowsheet

Fig. 13. Flowsheet of medium pressure synthesis, fixed-bed reactor (Lurgi-Ruhrchemie-Sasol) having process conditions for SASOL I of an alkaline, precipitated-iron catalyst, reduction degree 20—25% having a catalyst charge of 32—36 t, at 220—255°C and 2.48 MPa (360 psig) at a fresh feed rate of...

A solvent-extraction flowsheet is broken down into sections such as extraction, scrub, and strip. For each section, one or more component in a process fluid must be moved from one phase to the other phase with a specified degree of completeness. The first design problem is to determine the number of stages for each section to accomplish the required component transfer. With the well-defined stages of the centrifugal contactor, the following extraction factor (E) can be used to estimate the number of stages required ... 

In this flowsheet the presence of the furnace provides an additional control degree of freedom, and there are now two controllers. The first G( (X) controls 7 lmx by manipulating bypass flow Fby. The second Gc2(s) controls Tm by manipulating furnace firing QF. The second controller sees the furnace transfer function GF2(S) which we assume to be a furnace first-order lag and three small lags (see Fig. 7.4b) ... 

Since pure equation-based models involving as many as a few hundred thousand equations arise and require solution, ways are needed to ensure that this activity can occur with some degree of success. Perhaps the oldest of such approaches comes with flowsheeting programs. 

The commercial process simulators contain a range of distillation models with different degrees of sophistication. The design engineer must choose a model that is suitable for the purpose, depending on the problem type, the extent of design information available, and the level of detail required in the solution. In some cases, it may make sense to build different versions of the flowsheet, using different levels of detail in the distillation models so that the simpler model can be used to initialize a more detailed model. 

Material balances can be made for a wide variety of materials, at many scales orsize for the system and-in-various-degrees of-complication. To Qbtain a perspective as to the scope of material balances, examine Figs. 2.3 and 2.4. Figure 2.3 illustrates a world-scale set of mass balances for nitrogen for different systems, while Fig. 2.4 shows a flowsheet for a chemical plant that includes both mass and energy flows. 

In this chapter we first examine how to make sure that a problem is properly and completely specified by extending our earlier treatment in Chap. 2 of the analysis of the degrees of freedom. Then we review how computer codes and, in particular, flowsheeting codes can be employed to solve complex problems. Figure 5.0 shows the relationships among two topics to be discussed in this chapter, and the relationships with topics in previous chapters. 

Figure E5.5a shows a simplified flowsheet. All the units except the separator and lines are adiabatic. The liquid ammonia product is essentially free of Nz, Hz, and A, and assume that the purge gas is free of NH3. Treat the process as four separate units for a degree-of-freedom analysis, and then remove redundant variables and add redundant constraints to obtain the degrees of freedom for the overall process. The fraction conversion in the reactor is 25%.

The accompanying figure represents the schematic flowsheet of a distillation tower used to recover gasoline from the products of catalytic cracker. Is the problem completely specified, that is, is the number of degrees of freedom equal to zero for the purpose of calculating the heat transfer to the cooling water in the condenser ... 

In the late 1960s, Lurgi adopted the CEB for calcination of alumina trihydrate. Design studies have shown that CFBs can be applied for capacities as high as lOOOt/day. A high degree of automation, economy of space, and a simplified process flowsheet are important design criteria. 

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