Bulk heating cleans paraffinic bottoms from crude tanks

It is often challenging to remove from service crude oil tanks that have been in use for many years. Bulk heating, as opposed to localized heating, has been used to successfully liquefy heavy paraffinic or asphaltic bases in crude oil tanks. The process provides economical product recovery, while minimizing waste production and reducing human exposure to hazardous working conditions. Statia Terminals Point Tupper Inc., Point Tupper, N.S., used bulk heating to remove 2 ft of weathered, paraffinic tank bottoms from six 450,000 bbl tanks that held Cabinda crude from West Africa. Immersion tube heaters were installed through the tank manholes and a diluent was added. Two 10-million BTU/hr propane burners supplied heat, and tank mixers operated continuously to aid in heat transfer. The tank contents were heated to 135 F and the temperature was held constant for 3 days. The resulting hot liquid was a pumpable and recoverable product. About 10 days were required to clean each tank. The paper describes the heating and cleaning operation as well as the economics of the Statia project.