Thermoeconomic and environmental assessment of a crude oil distillation unit of a Nigerian refinery

The renovation of refineries should be aimed at achieving the highest possible technical efficiencies at a considerable investment cost and not only at replacing damaged components to attain full capacity utilisation. This study examined a crude distillation unit (CDU) of a Nigerian refinery plant comprising the atmospheric distillation unit (ADU), vacuum distillation unit (VDU), preflash unit (PFU), splitter unit (SPU), stabiliser unit (SBU) and heat exchanger network (HEN) to determine critical areas of inefficiencies as the plant managements plan renovation. Using real plant data, the CDU was simulated with Aspen Hysys® and the thermoeconomic and environmental analyses were carried out. The results show that the energy and exergy efficiencies of the CDU were 9.0 and 4.0% respectively. The specific CO2 emission was 3.67 kg CO2/bbl. The highly inefficient subunits accounting for 77.4 and 90.0% of the overall energy and exergy losses respectively and 60.3% of the emission released were the PFU, ADU and HEN. The highly inefficient components are the furnaces which accounted for 51.6% of the overall exergy losses. The environmental and economic analysis also indicated that these components are the most potent for improvement. The columns of the PFU and ADU should be revamped to reduce their energy demands and the HEN should be modified to minimise effluent losses.