Those listed are all similar in nature and in the treatment procedure required although the nature and the level of contamination may vary. Tanks and tankers used for crude oil storage and transportation represent the greatest challenge due to the greater accumulation of solids (typically, these are paraffin waxes, scale and general dirt or sand contained in the crude). Tank cars and tanks used for the transportation and storage of gasoline, for example, typically contain only scale and rust. In the case of crude oil, the soild residue after stripping off all of the hydrocarbons may need additional treatment (e.g., by a second wash or by biological methods such as land-farming or composting) before disposal in a landfill. Residues from gasoline or distillate tanks may be immediately disposable provided that they are hydrocarbon-free.
The procedure used is similar to that for all uses of OIL-XORB ERC. A diluted OIL-XORB ERC solution (1:10 dilution) at 170-200 O F (77-93 O C) is used to pressure-wash the tank walls and floor using pumps and pressure hoses. Operators may require breathing equipment to protect them against hydrocarbon vapors.
The resulting contents of the tank, which includes the material from floor and wall washing, are then pumped into a separate separation tank which permits settling of the solids and mechanical skimming of the hydrocarbon. The presence of OIL-XORB ERC greatly enhances the separation. The separated hydrocarbon can be returned to use (typically by blending with a refinery crude stream) and the solids can be washed and/or treated biologically before final disposal.
The tank cleaning system most commonly encountered commercially is Petrolite's PES41, which costs substantially more per unit volume than OIL-XORB ERC and must be used undiluted. Other products, including Nalco's VISCO 1176 (now called EC 9049A) cost a little more than OIL-XORB ERC but must also be used undiluted. The effective cost of OIL-XORB ERC is much lower and the OIL-XORB ERC product is more effective and presents no environmental problems.