Refiners match RVP reduction measures to operating problems
Reductions in gasoline vapor pressure specifications have created operational challenges for many refiners. Removal of butanes from gasoline blendstocks has become more critical to meeting product vapor pressure requirements.
Some refiners have made major unit modifications, such as adding alkylation capacity for butane conversion. Others have debottlenecked existing fractionation equipment, thus increasing butane removal.
Three case studies will illustrate vapor pressure reduction solutions. The solutions include: changing unit operating targets, maintaining existing equipment, and debottlenecking minor equipment.
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Analysis of Alky unit DIB exposes design and operating considerations
As refiners strive to increase unit production or accommodate feed composition changes with minimal capital investment, existing equipment design and operations should be evaluated for opportunities to improve efficiency.
In many cases, throughput limitations can be resolved through review and modification of existing equipment design.
A recent examination of an alkylation plant deisobutanizer (DIB) illustrates design and operating considerations that should be addressed when capacity increases and efficiency improvements are desired.
This sulfuric acid alkylation plant had excess feed and reaction zone capacity. The DIB was the limiting factor; specifically, the DIB reboiler duty was at its maximum and the reboiler steam-supply valves were wide open. A new alkylate Rvp specification of 5.0 psia also was constraining operation.
An engineering review suggested minor design modifications and maintenance items which, when implemented, increased alkylate production capacity by more than 25%.
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Deep cut vacuum tower operations can offer significant incentives over existing operations. Defining the exact incentives, capital costs, and payouts requires an engineering study. However, initial project feasibility studies can benefit from simplified analysis. This paper compares deep cut incentives for typical light and heavy crudes, Brent and Arabian Heavy. The resultant yields structures and incentives are compared for the two crudes, and economic calculations presented for various charge rates. Depending on charge rate and degree of improvement, incentives range from 1 to $10 MM/year.
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