1.1 Background of the Study
Distillation is a unit operation that has been around for a long time and continues to be the primary method of separation in processing plants, in spite of its inherently low thermodynamic efficiency. The pre-eminence of distillation for the separation of fluid mixtures is not accidental, but fundamental, and therefore unlikely to be displaced(kister, 1992)
From a kinetic standpoint (kister, 1992) mass transfer per unit volume in distillation is limited only by the diffusional resistances on either side of the vapour-liquid interface in turbulent phases, with no inert present. In almost every other separation process, there are inert solvents or solid matrices, and these lower mass fluxes. Distillation has the potential for high mass transfer rates.
From a thermodynamic viewpoint, a typical thermodynamic efficiency of a distillation system is about 10 per cent (kister, 1992). This can be enhanced if inter-condensers and inter-reboilers are used.
In fact, it has been shown that conceptually, a distillation system can be devised, which requires only the minimum work of separation (kister, 1992).
Although, a thermodynamic efficiency of 10 per cent appears low, not many other processes are more efficient(Haselden, 1981)
Distillation in general provides the cheapest and best method for separating a liquid mixture from its components.
Distillation has evolved from simple laboratory procedure to prime separation in the crude oil refining processes.
The world crude oil refining capacity is approximately 82 million barrels per day equivalent to about 4,200 million tonnes (Mt) per annum. This capacity is currently provided by a total of 720 refineries.(Oche, November, 2014)
Nigeria has a total number of four (4) crude oil refineries located in Port-Harcourt, Warri and Kaduna, with a total refining capacity of 445,000BPD. Port-Harcourt has two refineries, one with a capacity of 60000BPD and the other 150000BPD, Warri refinery has a capacity of 125000BPD and Kaduna refinery-110000BPD. Despite the large amount of crude oil deposit, Nigeria continues to experience perpetual shortages of products due to poor configurations and inefficient operations of the refineries, resulting in frequent breakdowns occasioned by poor or lack of turn around maintenance.(Oche, November, 2014).