Stage inherent

In an effort to obtain higher value products from SRC processes, a hydrocrackiag step was added to convert resid to distillate Hquids. The addition of a hydrocracker to the SRC-I process was called nonintegrated two-stage Hquefaction (NTSL). The NTSL process was essentially two separate processes ia series coal Hquefaction and resid upgrading. NTSL processes were iaefficient owiag to the inherent limitations of the SRC-I process and the high hydrocracker severities required. 

Distillation. Distillation (qv) is by far the most common separation technique because of its inherent advantages. Its phase separation is clean, its equihbrium is closely approached in each stage, and its multistage countercurrent device is relatively easy to build. 

Melt Crystallization. Crystallization (qv) from a melt is inherently more attractive than distillation because the heat of fusion is much lower than that of evaporation. It also benefits from lower operating temperature. In addition, organic crystals are virtually insoluble in each other so that a pure product is possible in a one-stage operation. 

Open-loop systems have inherently long residence times which may be detrimental if the retentate is susceptible to degradation by shear or microbiological contamination. A feed-bleed or closed-loop configuration is a one-stage continuous membrane system. At steady state, the upstream... 

The inherent restrictions are usually the result of definitions and take the form of identities. For example, the concept of the equihbrium stage involves the inherent restrictions that T = and P " = where the superscripts V and L refer to the equihbrium exit streams. 

However, the total number of equilibrium stages N, N/N,n, or the external-reflux ratio can be substituted for one of these three specifications. It should be noted that the feed location is automatically specified as the optimum one this is assumed in the Underwood equations. The assumption of saturated reflux is also inherent in the Fenske and Underwood equations. An important limitation on the Underwood equations is the assumption of constant molar overflow. As discussed by Henley and Seader (op. cit.), this assumption can lead to a prediction of the minimum reflux that is considerably lower than the actual value. No such assumption is inherent in the Fenske equation. An exact calculational technique for minimum reflux is given by Tavana and Hansen [Jnd. E/ig. Chem. Process Des. Dev., 18, 154 (1979)]. A computer program for the FUG method is given by Chang [Hydrocarbon Process., 60(8), 79 (1980)]. The method is best applied to mixtures that form ideal or nearly ideal solutions. 

Understanding the chemistry of the process also provides the greatest opportunity in applying the principles of inherent safety at the chemical synthesis stage. Process chemistry greatly determines the potential impact of the processing facility on people and the environment. It also determines such important safety variables as inventory, ancillary unit operations, by-product disposal, etc. Creative design and selection of process chemistry can result in the use of inherently safer chemicals, a reduction in the inventories of hazardous chemicals and/or a minimization of waste treatment requirements. 

The first step in determining the component values for this compensation method is to determine the inherent dc gain of the power stages. The calculation should be performed with the maximum value of the input voltage, since this is where the system will have its widest exhibited bandwidth. This is done using Equation B.12. 

Exploring inherently safer alternatives may require more resources during the early stages of development than is otherwise the case. 

Process safety is fundamental to the basic practice of chemical engineering thus, the concepts of inherently safer processes should be instilled in chemical engineering students at an early stage. Practicing engineers should be encouraged to adopt the concepts. 

Inherently safer strategies can impact the accident process at any of the three stages. The most effective strategies will prevent initiation of the accident. Inherently safer design can also reduce the potential for propagating an accident, or provide an early termination of the accident sequence before there are major impacts on people, property, or the environment. 

Creative thinking is important not only in new process development, but also in continually reviewing and reevaluating existing processes for opportunities to make the process inherently safer. Many of the tools and techniques discussed in Section 4.2, on Research, are useful in the process development stage as well. It is appropriate to revisit the basic chemistry to study alternate options. 

As the process moves from the process development stage to the design and construction stage the chemistry, unit operations, and type of equipment have been set. The design and construction stage needs to focus primarily on equipment specifications, piping and instrumentation design, installation details, and layout for an inherently safer installation. 

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