Application 2 Implementing Key Indicators to Controllers

Many opportunities for energy improvement can be achieved from changing the plant conditions by adjusting the set point of key variables. In some cases, these opportunities for energy improvement may be possible by incorporating these key variables into an APC if the investment for such an APC is justified by the value to be captured. 

There are many energy-saving opportunities that can be incorporated into APC applications  

One example of a single variable control strategy is applied to a stripper in a hydrocracking unit. The main purpose of the stripper is to remove H2S and noncondensable components from the bottom product. One of the key indicators identified is the water dew point at the top of the stripper column. As a matter of fact, the dew point is a function of column overhead vapor composition and the amount of water. There was no monitoring capability available for the dew point temperature. If the column top temperature is lower than the dew point, the hydrogen sulfide will dissolve in the condensed water and cause corrosion to the column overhead system. 

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