Simulation of the atmospheric distillation Tower at Azzawia refinery
Abstract
The atmospheric distillation tower is the most important unit in any refinery. Its performance is crucial to the economics of operating the refinery. This unit also known as the fractionation column is used to fractionate about 410 m3/hr of crude oil at Azzawia refinery. The crude oil is a blend of Sharara and Hamada oil fields at a composition of 90%, and 10%, respectively. This paper presents a simulation study of this column by using Aspen-Hysys simulation software package which is widely recognized as a reliable simulation tool in the process industries. The study investigates the effect of up to ±10% variations from the actual feed crude oil flow rate on the mass balance of the tower products and the effect of varying the main steam input heat load on the product distribution of the tower. The results obtained showed that, although the feed to the tower is mixed crude, variations of its flow rate between ±10% indicate small changes in the product mass flow rate distribution except for the residue which showed significant variations in its mass flow rate between (±50%). This is due to the nature of the mixed crude having more of the heavy components as indicated by its API gravity of 38.8. Varying steam heat duty on the other hand, either by increasing its quantity or quality, showed significant changes in the naphtha cut. This is explained by the fact that steam reduces the partial pressure of the hydrocarbons and thus lowers the temperature required for vaporization. This result provides for more naphtha that can be stripped off from the residue by just a small increase in the main steam input. The study concludes that the main steam at Azzawia refinery can be used to effectively control the product distribution of the atmospheric tower especially that of naphtha in accordance with market demand.
