Case study process flowsheet

Fig, 2. Ammonia process case study. Reprinted with permission from Comp. Chem. Eng., 11, 143-152, Y.-D. Lang and L. T. Biegler, A Unified Algorithm for flowsheet optimization, Copyright 1987, Pergamon Press PLC. 

The case studies cover key applications in chemical process industries, from petrochemistry to polymers and biofuels. The selection of processes was confronted with the problem of availability of sufficient design and technology data. The development of the flowsheet and its integration is based on employing a systems viewpoint and systematic process synthesis techniques, amply explained over three chapters. In consequence, the solution contains elements of originality, but in each case this is compared to schemes and economic indices reported in the literature. 

Figure 2.13 illustrates the variation of the economic potential during flowsheet synthesis at different stages as a function of the dominant variable, reactor conversion. EPmin is necessary to ensure the economic viability of the process. At the input/output level EP2 sets the upper limit of the reactor conversion. On the other hand, the lower bound is set at the reactor/separation/recycle level by EP3, which accounts for the cost of reactor and recycles, and eventually of the separations. In this way, the range of optimal conversion can be determined. This problem may be handled conveniently by means of standard optimization capabilities of simulation packages, as demonstrated by the case study of a HDA plant [3]. 

The case study of cyclohexanone manufacturing by phenol hydrogenation illustrates the basic principles of the conceptual development of a process flowsheet. For more complexity we consider a two-step process. Firstly, phenol is submitted to hydrogenation, in which both cyclohexanone and cyclohexanol... 

However, the two flowsheets presented here are simulated based on the general process design principles to closely resemble the actual processes. The two case studies should help the reader in understanding the difference in strategy in purifying intracellular and extracellular protein products. 

Figure 1.9 shows different kinds of flowsheets which mark the start and the end of the part of the overall design process which is covered by the case study. At the beginning, the chemical process is described by an abstract flowsheet which decomposes the process into basic steps without considering the equipment to be used (upper part of Fig. 1.9). The process consists of three steps reaction of caprolactam and water, separation of input substances which are fed back into the reaction, and compounding, which manipulates the polymer produced in the reaction step such that the end product meets the requirements. The lower part of Fig. 1.9 shows a process flowsheet which consists of chemical devices and therefore describes the chemical plant to be built - still at a fairly high level of abstraction. The process flowsheet serves as input for detail engineering, which is beyond the scope of the case study.

Finally, the process simulators have the ability to optimize a process flowsheet by adjusting the continuous variables such as the purge/recycle ratio and the reflux ratio. Chapter 18 presents a general discussion of optimization methods, followed by two case studies. 

The case study is a diesel hydrotreating process and the flowsheet is shown in Figure 9.14. The combined feed is preheated by reaction effluent via E-lOO and furnace and then goes to the reactor. After transferring heat to the combined feed, the reaction effluent is cooled in the air cooler and then goes to the high-pressure... 

This case study involves the production process of p-galactosidase (p-gal), an intracellular enzyme produced by Escherichia coli. The case study has been presented by Carvalho et al. [17]. P-Gal allows people to d est milk or milk products, having a critical role in the production of lactose-free milk products. The flowsheet for the p-gal production process is shown in Fig. 11.9. 

With the feasible path approach the optimization algorithm automatically performs case studies by variing input data. There are several drawbacks the process equations (32c) have to be solved every time the performance index is evaluated. Efficient gradient-based optimization techniques can only be used with great difficulties because derivatives can only be evaluated by perturbing the entire flowsheet with respect to the decision variables. This is very time consuming. Second, process units are often described by discrete and discontinuous relations or by functions that may be nondifferentiable at certain points. To overcome these problems quadratic module models can be... 

Figure 9.8 shows the flowsheet of an algae-based biorefinery case study. The mass balance was determined using spreadsheet calculations, and the conversion and yield factors of the various process units are presented in Table 9.8. The production of lOOOkgh" of dry algae biomass is used as basis. The composition of algae biomass is shown in Table 9.9. 

As mentioned throughout the discussion of preliminary process synthesis and the creation of the process flow diagram, the process simulator usually plays an important role, even if a simulation model is not prepared for the entire flowsheet. When parts of a simulation model exist, it is common for the design team to assemble a more comprehensive model, one that enables the team to examine the effect of parametric changes on the entire process. In other cases, when the process simulators have not been used for design, a simulation model is often created for comparison with the pilot-plant data and for parametric studies. 

Hydrodealkylation of toluene is a process where toluene is converted into benzene by reaction with hydrogen, forming Diphenyl as a byproduct. This is a well known process, which has been studied in numerous publications. The reference design and flowsheet considered in this paper are taken from Seider et al. (1999), where further details can be found. The necessary steady state simulations have been performed with a commercial process simulator, from where the results have been transferred to a software developed for this work to calculate the indicator values. The steady state simulation results are also transferred to ICAS (ICAS Documentation, 2002) to determine the environmental impact factors, the sustainability metrics and the safety factors. Table 1 shows the most important indicator-values from the base case design. A detailed calculation results document can be obtained from the corresponding author. 

---