Refinery Complexity Analysis
Developed by Wilbur L. Nelson in 1960 and expanded in 1976, the Nelson Complexity index uses simple numbers to represent the cost of adding complex enhancement systems to a refinery. This relative-cost index is useful to accountants, regulators, investors and others. A baseline rating of 1.0 is assigned to a basic atmospheric distillation unit. Advanced techniques, such as coking and catalytic cracking, are given a Nelson Complexity rating of 6.0. Cost and capacity estimates can then be taken into account to determine whether or not adding new equipment can be a profitable venture.
The Bottom of Barrel index (BoB) is a newer index gaining popularity. BoB is calculated by simple division of a refinery's enhancement capacity to its basic separation capacity. Essentially, this figure quantifies the degree to which a refinery can process heavier crude oil feedstocks. To put this concept in perspective, the 2011 BoB index for the U.S. refining industry as a whole is estimated at 55%, the rest of the world's average at 21%, and the total world average (including the U.S.) at 28%.