Conceptual process design

FT conditions for their HSOD membrane. A conceptual process design indicated that application of SOD membranes in the FT reaction could be economically viable [54]. 

This work was carried out at the Helsinki University of Technology in the Laboratory of Chemical Engineering and Plant Design from April 1993 to July 1998. The thesis discusses inherent safety in the conceptual process design. 

Another widely used safety analysis method in process industry is the Hazard and Operability Analysis, better known as Hazop (Kletz, 1992). The conventional Hazop is developed to identify probable process disturbances when complete process and instrumentation diagrams are available. Therefore it is not very applicable to conceptual process design. Kletz has also mentioned a Hazop of a flowsheet, which can be used in preliminary process design, but it is not widely used. More usable method in preliminary process design is PIIS (Edwards and Lawrence, 1993), which has been developed to select safe process routes. 

Table 6. The characteristics of inherent safety in conceptual process design. 

In the Chapter 7 the selected inherent safety parameters for conceptual process design were presented. From these parameters an inherent safety index is formed in this Chapter. There is a straight link between inherent safety principles and the inherent safety index as discussed earlier (see Figure 5). 

Chemical process design, as it is commonly known, typically starts with a general problem statement with respect to the chemical product that needs to be produced, its specifications that need to be matched, and the chemicals (raw materials) that may be used to produce it. Based on this information, a series of decisions and calculations are made at various stages of the design process to obtain first a conceptual process design, which is then further developed to obtain a final design, satisfying at the same time, a set of economic and process constraints. The important point to note here is that the identity of the chemical product and its desired qualities are known at the start but the process (flowsheet/operations) and its details are unknown. 

Douglas, J., 1988 Conceptual process design, McGraw-Hill. 

The next section will reflect on common conceptual process design practices for overall flowsheet development. The remainder of this chapter reviews recent developments in process synthesis methods for reaction and separation systems that systematically guide the design decision-making process toward novel and improved designs. 

Various industrial applications of the step-by-step design approach have been reported (see, e.g., Ref. 8). A number of these and other confidential projects have shown the value of the coordinated approach to conceptual process design. 

Ferrandon, M.S., et a1. (2008), The Hybrid Cu-CI Thermochemical Cycle. I. Conceptual Process Design and H2A Cost Analysis. II. Limiting the Formation of CuCl During Hydrolysis , NHA Annual Hydrogen Conference, Sacramento Convention Center, CA, 30 March-3 April. 

The preliminary conceptual process design and the corresponding flow sheet have shown an efficiency of 39-41% (LHV). These values depend on assumptions regarding the operability of the electrolyser and the crystalliser, which separates components in the spent anolyte and catholyte. 

The test results with the ultrasonic nozzle were obtained with an estimated steam to copper (S/Cu) ratio of 23 and the humidified Ar was injected co-currently with the CuCl2 solution. Several variables remain to be investigated, i.e. lower S/Cu ratios, counter-current instead of co-current operation, and subatmospheric pressures. LeChatelier s Principle predicts that reducing the pressure in the hydrolysis reactor should reduce the S/Cu ratio. The effect of a reduced pressure was quantified by the results of a sensitivity study using Aspen. Aspen predicts that a S/Cu ratio of 17 is needed for essentially complete conversion at 375°C and atmospheric pressure while a S/Cu ratio of 13 is required at 0.5 bar. The conceptual process design specifies that the hydrolysis reactor be run at 0.25 bar. The pressure drop in the reactor is achieved by adding a low temperature steam ejector after the condenser at the exit of the hydrolysis reactor in the conceptual design. 

Douglas, J. M., and Stephanopolous, G. (1995). Hierarchical approaches in conceptual process design framework and computer-aided implementation, In Foundations of Computer-Aided Process Design (L. T. Biegler and M. F. Doherty, eds.), pp. 183—197, AIChF Symposium Series, 91(304), New York. 

The determination of feasible products is very important for conceptual process design and for the evaluation of competing process variants. In this chapter, methods have been discussed to identify feasible products as singular points of residue curve maps (RCM). RCM-analysis is a tool which is well established for nonreactive and reactive distillation processes. Here, it is shown how RCM can also be used for reactive membrane separation processes. 

By this approach, the solution of the ecological problems results fundamentally from the conceptual process design. Two directions can be envisaged ... 

We may define the objectives of conceptual process design as follows ... 

Figu re 2.1 Classical hierarchical approach of conceptual process design [2]. 

Level 1 Chemistry and Thermodynamics. This level deals with the analysis of the fundamental knowledge needed for performing the conceptual process design. A detailed description of chemistry is essential for designing the chemical reactor, as well as for handling safety and environmental issues. Here, the constraints set by chemical equilibrium or by chemical kinetics are identified. The nonideal behavior of key mixtures is analyzed in view of separation, namely by distillation. 

This introductory case study presents the key features of a conceptual process design by using the systematic methods presented in the previous chapters. The selected process is the manufacture of cyclohexanone, a key intermediate in the production of e-caprolactam and adipic acid, which are basic materials for nylon-type polymers. 

The sponsor s R D Group has prepared a conceptual process design showing 50 pieces of equipment and estimated a total installed cost of around 12 million dollars. 

Although much (perhaps most) conceptual process design is in fact done by the evolutionary modification of whole or partial existing flowsheets, it is sometimes necessary to generate a flowsheet from scratch. 

However sophomoric the AIDES computer implementation, the hierarchical process synthesis procedure itself offers three important lessons which have had a significant industrial impact—lessons that can be used even manually by conceptual process designers. 

Consider the following industrial example of a process for the production of methyl acetate, first synthesized in the conventional conceptual process design manner, then modified using evolutionary approaches, and finally resynthesized using the lessons from the hierarchical process synthesis procedure experience. For simplicity here, only identity, amount, and composition differences are resolved (that is, temperature and pressure changers will be ignored). 

The classic flowsheet for the production of acetates was unsuitable for adoption for methyl acetate. However, the flowsheet generated by the conventional conceptual process design approach using literature schemes and standard patterns seems especially complicated for such simple chemistry involving so few components. This first flowsheet is a candidate for evolutionary modification. 

Conceptual process design is an underdefined problem. Only a very small fraction of the information needed to define a design problem is available from the problem statement. The design decisions of the process designer provide this missing information. For example, the designer makes design decisions about what kind of process units to use, how to interconnect those units, and so on. From this perspective, the conceptual... 

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