Objectives for the Separation Process

The main objective of the distillation process is usually the recovery of a valuable component from the feed. In that case there is also often a quality requirement for this valuable component. If the purity of the valuable component is low, then the product has little value. If the concentration meets the specification, then the product value is high.

There may be no distinct quality requirement, in which case the economic value of the product could be a continuous function of the product properties.

Let us assume that both top and bottom product represent an economic value. Then an economic objective for the operation of the process could be defined as:

where cD is the top product value ($ kg-1), cB the bottom product value ($ kg-1), cF the cost of the feed ($ kg-1) and cS the costofthe steam ($ kg-1). The use of cooling water usually involves little cost and fixed costs do not play a role in the optimization of the operation.

If F is fixed and the overall material balance F = B + D is substituted in eqn [1], then the variable part Jd of eqn [1] can be written as:

Figure 3 shows both terms as a function of the steam flow to the column reboiler. When S increases, the yield of the valuable product approaches asymptotically a value which is equal to the amount of top product which is present in the feed: Dlim = F XF lk/XD lk, where the subscript lk refers to the light key component.

'-'optimum

Figure 3 Optimal steam usage in distillation process.

'-'optimum

Figure 3 Optimal steam usage in distillation process.

The maximum value of Jd is found when the tangent to the curve for D parallels the straight line for cSS/(cD — cS), as shown in Figure 3. The optimum point may be located within the operation area. But at different values of the feed, however, some constraint may make the optimum point unreachable, in which case the optimum lies on the constraint.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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