Design process constraints

The first concern in designing process capable products is to guarantee the proper functioning of the product, and therefore to satisfy technical constraints. Dimensional... 

Material, traffic and people are involved, and the constraints on internal layouts will be different to those for site layouts but will not affect the design process. The constraints will include organization of the factory work tasks, which may involve trade practices and the type of organization adopted for the control of the process equipment. This is discussed in Section 7.2. 

According to Cano-Ruiz and McRae, process design as a part of process development starts with problem framing. At this stage, the concept definition, scope of analysis, design objectives, constraints, evaluation and interruption criteria have to be determined. They argued that framing decisions are often made implicitly, whereas the critical importance... 

The constraints, particularly the external constraints, should be identified early in the design process. 

For a first pass through the design, it is usually adequate, if process constraints permit, to set distillation pressure to as low a pressure above ambient as allows cooling water or air-cooling to be used in the condenser. If a total condenser is to be used, and a liquid top product taken, the pressure should be fixed such that ... 

Donna Haraway observes that bodies are portrayed not in terms of their essential properties but as strategic systems or information-processing devices. People, she says, are described in terms of design, boundary constraints, rates of flows, system logic.. .. Persons can be reasonably thought of in terms of disassembly and reassembly . 

Parameter estimation is also an important activity in process design, evaluation, and control. Because data taken from chemical processes do not satisfy process constraints, error-in-variable methods provide both parameter estimates and reconciled data estimates that are consistent with respect to the model. These problems represent a special class of optimization problem because the structure of least squares can be exploited in the development of optimization methods. A review of this subject can be found in the work of Biegler et al. (1986). 

The estimation of model parameters is an important activity in the design, evaluation, optimization, and control of a process. As discussed in previous chapters, process data do not satisfy process constraints exactly and they need to be rectified. The reconciled data are then used for estimating parameters in process models involving, in general, nonlinear differential and algebraic equations (Tjoa and Biegler, 1992). 

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. 

Fig. 8. CDK4 selective library design process of Honma et al. (64). (A) Align sequences of 390 kinases. Dark circles denote residues with <40% conservation or subject to replacement in CDK1/2/6. (B) Darker residues in ATP binding site pinpoint the least conserved residues highlighted in (A). (C) Map lead structure onto difference residues. Arrows denote direction and distance to said amino acids. (D) Design library according to these constraints. Resulting compounds show up to 180-fold selectivity for CDK4 with respect to CDK2. Adapted from ref. 64.

These tools may assist the scientist in two ways. First, the design process can be optimized with the nse of more complex constraints than could otherwise be handled. Second, in some cases the need for time-consuming and costly physical or chemical property measurements can be eliminated with the use of estimation techniques for properties of interest. 

Physico-chemical properties and evaluation of potential safety liabilities are important aspects of the library design process. Predicted properties like hERG liability (45), compound aqueous solubility, etc. (46-48) have been extensively studied and included in various library design strategies (49, 50) as a part of multiple constraints optimisation. We have therefore further extended the ProSAR concept to take the library property profile into account in the design process. Several in-house calculated properties are considered these include a compound novelty check (that checks in in-house and external compound databases to see if the compound is novel), predicted aqueous solubility... 

A student design project can only provide an approximation to industrial design work. However, it should be possible to consider the nature of the design process and various aspects realistically. Student design projects are restricted only by time. In industry the same constraint applies with the additional consideration of economics. 

If design, production, or process constraints (e.g., due to numerous openings or heat transfer from the outer barrel to the insert) do not allow the use of inserts, the housing can be designed as a solid part. 

In the RSR approach the chemical reactor is the key unit, designed and simulated in terms of productivity, stability and flexibility. From the systemic viewpoint the key issue is the quality and dynamics of flows entering the reactor and less how they have been produced. Obviously, these flows include fresh reactants and recycle streams. The dynamics of flows must respect the overall material balance at steady state, as well as the process constraints. For this reason, the chemical-reactor analysis should be based on a kinetic model. 

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