Above is a curve comparing the overhead condenser heat transfer with the RVP attainable. This curve illustrates how much the overhead condenser fouling affects the bottoms RVP. The base case operation reflecting the survey conditions is shown at the lower left of the curve. The minimum simulation RVP attainable is 7.3 with essentially no C₄- in the bottoms. The other data points on the same line indicate how much the gasoline RVP increases as the overhead condenser heat transfer coefficient is reduced. All of the points below the dashed line denoting the survey U of 44 represent feasible operating points. The top curve estimates the effect of higher cooling water temperatures and hence RVP’s in the summer. Almost all of the points are above the existing U dashed line indicating that the operation is unfeasible with the fouled exchangers. All of the runs maintained the same 1.7 LV% C₅+ in the overhead LPG.

The curve clearly shows how much the survey heat transfer coefficient was below design. The curve for the current winter operation indicates that the RVP could be reduced only marginally by removing all of the C₄-. The curve for summer operation shows the large impact that the poor heat transfer coefficient would have in the coming months. Assuming that the exchanger heat transfer coefficient remained constant, the fouled overhead condensers would result in FCCU gasoline RVP’s above 12. This unacceptably high RVP forced a resolution.

 

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