Refinery storage of raw materials (mainly crude oil) and finished products is a complex study and involves concepts of linear programming and Monte Carlo simulation.
However, crude oil storage in refinery can be put in the form of a simplified equation considering various factors such as: Maximum Cargo Capacity (crude parcel size), time duration, Crude Distillation Unit throughput and strategic stockpiling.
Today’s blog entry provides such a simplified equation encompassing the above factors to get a preliminary estimate of crude oil storage in a refinery. The equation can be written as follows:
Vc = Vt + (De + Dd + Du + Ds + Dl)*CDUt + S
Vc = Total Working Capacity of Crude of the Refinery, m3 (bbl)
Vt = Maximum Crude Oil Tanker Cargo or Parcel Size, m3 (bbl)
Note: For large refineries, VLCC tankers with volumetric capacities of 318,000 m3 (2,000,000 bbl) are often the preferred method of receiving crude oil due to the scale of economies.
De = Days of early arrival (normally a term that is considered zero in the above equation)
Dd = Days of Delayed Arrival (typically 3 days are considered)
Du = Days for tanker unloading (typically 1 day)
Ds = Days for settling (typically 1 day)
Dl = Days for leaving, dewatering and crude oil analysis (typically 1 day)
CDUt = CDU daily throughput i.e. plant capacity, m3/SD (BPSD)
S = Strategic Stockpiling Required (if any), m3 (bbl)
Crude oil tankers are planned to enter the port at regular intervals, but may be delayed for bad weather conditions or other reasons. Thus, if tankers are behind schedule, this period must be covered by the crude oil in stock. A maximum of three (3) days should be considered for this period. On the other hand, as the early arrival of a tanker can be controlled by adjusting the cruising speed, it may not be necessary to allow for early arrival in the normal situation.
Individual tank storage capacity and number of storage tanks should be decided on other considerations such as plot plan, pumping capacities to the CDU, limitations of fabrication of large sized storage tanks and HSE studies such as EIA and QRA. A practical maximum tank size could be 130,000 m3 (818,000 bbl) working capacity.