Use of Feedforward and Decouplers

In many cases the top and bottom composition control loops will show interaction and it is advisable to design and implement decouplers. Depending on the required purity of the products and on the selected control configuration, decoupling is sometimes difficult to achieve. However, for many industrial distillation columns, decoupling considerably improves the performance of the composition control loops Figure 10.

The main source of disturbances usually enters the column with the feed. Whereas the feed composition may vary somewhat, the feed flow varies considerably in many cases. In those situations it might be worthwhile applying feedforward control. If the reflux is controlling the top composition and the steam flow the bottom composition, then feedforward affects both these flows on a column feed change. The principle for the reflux controller is shown in Figure 11, which shows a feedforward controller for feed flow changes. In a similar manner, a feedforward controller for feed composition changes could be implemented. Reflux affects the tray temperature, say via a model GR. If the feed affects the tray temperature via a model GF, then the feedforward controller has the structure GF/GR. One word of caution is necessary: care should be taken to identify properly both models, since a poorly designed feedforward controller may cause poorer control performance than no feedforward controller at all.

Figure 10 Example of dual analyser control using Dl/configuration with decoupling.
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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