Conceptual stage

Dr. Daniel A. Crowl of Michigan Technological University served as editor for the book. The Subcommittee would also like to acknowledge the contributions of Mr. Robert A. Schulze of CCPS and Mr. Robert Kambach of BASF Corporation for their valuable input during the conceptual stages of this project. 

Clearly, step counting methods can only, at best, give a very approximate idea of the probable cost of a plant. They are useful in the conceptual stage of process design, when comparisons between alternative process routes are being made. 

At the conceptual stage for heat exchanger network synthesis, the calculation of heat transfer coefficients and pressure drops should depend as little as possible on the detailed geometry. However, some assumptions must be made regarding the geometry. 

At the conceptual stage for heat exchanger network synthesis, the calculation of heat transfer coefficient and pressure drop should depend as little as possible on the detailed geometry. Simple models will be developed in which heat transfer coefficient and pressure drop are both related to velocity1. It is thus possible to derive a correlation between the heat transfer coefficient, pressure drop and the surface area by using velocity as a bridge between the two1. 

Feature Conceptual stage Flowsheet stage Line diagram stage (PID)... 

French, M. J. 1985. Engineering Design Conceptual Stage. Berlin Springer-Verlag. 

The depth of the required steps is estimated using the Criticality and Complexity Assessment and may be performed during the early Project Conceptualization stages of a project and reevaluated at Project Initiation. A sample Criticality and Complexity Assessment can be found in Appendix D. 

Unfortunately, this ideal site-targeting CrDDS is only in the conceptual stage. Its construction remains largely unresolved and is still a challenging task in the biomedical and pharmaceutical sciences. 

With the advent of process simulation packages, modeling of pervaporation and vapor permeation processes in a user added subroutine allows these unit processes to be included in overall separation schemes right from the conceptual stage. This enables many different combinations of pervaporation, for example, distillation to be studied and the optimum operating parameters for the preferred configuration to be selected very quickly. Such parameters include membrane feed temperature, which strongly influences the flux rate and, therefore. 

It is at the conceptual stage in the process development where inherent chemical and process safety benefits can be best introduced. It becomes progressively more difficult to achieve such benefits in the later stages of process development. 

From the above description it should be evident that Clean technology involves both chemistry and chemical engineering. If industry is to develop the cleaner processes now being demanded we need to establish multidisciplinary teams at the conceptual stage. 

Process or device development is intimately linked to the availability of materials suitable as active or passive cell components. Design, even in its conceptual stage, is inseparable from what materials are available for electrodes or for containment, what electrolyte compositions may come into consideration, and what separators (if any) are needed. Electrochemical engineering involves not only the cell or cell process but also the often considerable chemical and physical operations (separations, chemical reactors, heat exchangers, control, etc.) that precede and follow the electrochemical step. 

The chemical reactor has a determinant role on both the material balance and the structure of the whole flowsheet. It is important to stress that the downstream levels in the Hierarchical Approach, as the separation system and heat integration, depend entirely on the composition of the reactor exit stream. However, a comprehensive kinetic model of the reaction network is hardly available at an early conceptual stage. To overcome this shortcoming, in a first attempt we may neglect the interaction between the reactor and the rest of the process, and use an analysis based on stoichiometry. A reliable quantitative relationship between the input and the output molar flow rates of components would be sufficient. This information is usually available from laboratory studies on chemistry. Kinetics requires much more effort, which may be justified only after proving that the process is feasible. Note that the detailed description of stoichiometry, taking into account the formation of sub-products and impurities is not a trivial task. The effort is necessary, because otherwise the separation system will be largely underestimated. 

In the case of a heterogeneous reaction the overall process rate must consider the kinetics of both chemical and physical steps. If a very slow step can be identified, this controls in generally the global reaction rate. More often, the analysis should consider several limiting steps, both of physical and chemical nature. Therefore, the computation of the reaction rate in heterogeneous systems requires information that is hardly available at the conceptual stage. 

Snowball effect designates the situation in which small variations of a flowsheet variable, generally a flow rate at the inlet or outlet of a process with recycles, generates large variations of streams around some units inside the process (Fig. 13.7). It is worthy to note that snowball is essentially a steady state effect, and not a dynamic one, because at finite disturbance the amplification remains finite. However, some units cannot tolerate large fluctuations in flows, particularly the distillation columns. Therefore, the designer should avoid snowball effects already at the conceptual stage. 

Drilling rigs and low capacity AC variable speed drives are usually six-phase systems. If these are known to be needed at the conceptual stage of a project then their effects on other equipment... 

---