Nelson compexity factors are an indices of factors for the major refining process units that reflects the capital cost of a process unit type (per barrel of capacity) relative to the capital cost of distillation. For example, a unit with a complexity of 2 will cost twice as much to construct as a distillation unit of the same capacity.
The factors are used to estimate an overall capacity weighted complexity index (NCI) for a refinery.
Typical complexity factors for the major process units in a refinery as defined by Nelson:
Unit NCI Factor
Vacuum flash 1.0
Thermal cracking 3.0
Visbreaking 2.0
Coking 5.5
Calcining 108.0
FCC (60% conversion) 5.0
FCC (80% conversion) 6.0
Reforming 5.0
Hydrocracking 6.0
Hydrorefining 3.0
Hydrotreating 1.7
Alkylation 11.0
Aromatics 20.0
Isomerization 3.0
Polymerization 9.0
Lubes 60.0
Asphalt 1.5