Process for vessel decontamination

A process for removal, sufficient to allow human entry into a vessel for repair and maintenance, benzene contamination from a vessel which has been taken out of service and drained, comprising the steps of:

• injecting into the vessel, for a period of time sufficient to reduce benzene contamination by presence of chemical residues to allow safe exposure to humans, steam at a temperature of up to about 375.degree. F.;
• injecting into the vessel, in the presence of the steam, from about 0.06 pounds to about 0.3 pounds per pound of steam of a terpene extractant for the chemical residue in the vessel having a boiling point of up to about the temperature of the steam being injected;
• injecting into the vessel, as an optional component in the presence of the steam up to about 0.2 pounds per pound of steam of a surfactant having an HLB of from about 6 to about 18,
• provided, however, when both the extractant and surfactant are present, they are present in a ratio of from about 0.5 to about 30 pounds of extractant per pound of surfactant;
• allowing steam, extractant and surfactant to condense on internal surfaces within the vessle and invade interstices of scale on the surface to extract and trap benzene contaminants and form a pool of condense liquids and chemical residues;
• and
• removing the condensed liquid and chemical residue from the vessel.

A process for removal, sufficient to allow human entry into a chemical or refining process vessel for repair and maintenance of benzene contamination from a vessel which has been taken out of service and drained, comprising the steps of:

• injecting into the vessel, for a period of time sufficient to reduce contamination by presence of chemical residues to allow safe exposure to humans, steam at a temperature of up to about 375.degree. F.;
• injecting into the vessel, in the presence of the steam, from about 0.1 pounds to about 0.2 pounds per pound of steam of a terpene as an extractant for the benzene from the chemical residue adhering to the interior surfaces of the vessel, such extractant having a boiling point of up to about the temperature of the steam being injected;
• injecting into the vessel, in the presence of the steam from about 0.0003 to about 0.005 pounds per pound of steam of an nonionic, anioic, cationic or amphoteric surfactant or mixtures thereof having an HLB of afrom about 7.5 to about 12,
• provided, however, when both the extractant and surfactant are present, they are present in a ratio of from about 0.5 to about 30 pounds of extractant per pound of surfactant;
• allowing steam, extractant and surfactant to condense on internal surfaces within the vessel and invade interstices of scale on the surface to extract and trap benzene contaminants and form a pool of condensed liquids and chemical residues;
• and removing the condensed liquid and chemical residue from the vessel.

A process for removal, sufficient to allow human entry into a vessel for repair and maintenance, of benzene contamination from a vessel which has been taken out of service and drained, comprising the steps of:

• connecting a circulation loop from the bottom of the vessel to the top of the vessel;
• partially filling the vessel with sufficient water to provided continuous circulation;
• circulating the water through the loop at a rate sufficient to produce uniform flow through the vessel;
• injecting steam into the vessel to heat the water to a temperature of from about 165.degree. F. to about 230.degree. F.;
• injecting into the vessel an effective amount of, as an extractant for the benzene in the vessel, a terpene having a boiling point of up to about the temperature of the steam being injected;
• injecting into the vessel an effective amount, as an emulsifying agent for contaminants, of a surfactant having an HLB of from about 6 to about 18,
• provided, however, the extractant and surfactant are present in a ratio of from about 0.5 to about 30 pounds of extractant per pound of surfactant;
• circulating the heated water, extractant, and surfactant for from about 11/2 to about 7 hours;
• and
• removing the condensed liquid with benzene trapped therein from the vessel.

A process for removal of benzene contamination trapped in scale residue of a process vessel or equipment comprising the steps of:

• contacting the scale on surfaces of the vessel or equipment with an aqueous liquid cleaning mixture or vapors thereof, said mixture containing
• an effective amount of terpene extractant,
• an effective amount of surfactant,
• each having a vapor pressure at treating conditions sufficiently high to disperse such extractant and surfactant through the vessel at such conditions;
• and
• heating the cleaning mixture up to a temperature of from about 165.degree. F. to about 230.degree. F. to disperse such extractant and surfactant through the process equipment to invade interstices of the scale residue, extract the benzene, break down the scale and entrap the benzene and scale residue into the cleaning mixture.

A process for decontaminating process vessels and auxiliary equipment in fluid communication therewith to remove benzene contamination trapped in scale on internal surfaces to permit human entry for repair and maintenance comprising the steps of:

• contacting the benzene contaminated scale and surfaces, at a temperature of from about 160.degree. F. to about 230.degree. F. with an aqueous mixture containing a terpene extractant and a surfactant having an HLB of from about 6 to about 18;
• circulating the mixture through the process vessels in contact with the surfaces to allow invasion of interstices of the scale by the mixture for a time sufficient to break down the scale and entrap the benzene contaminants in the mixture;
• and
• dispersing such extractant and surfactant as vapors through the process vessels to condense on surfaces of the vessels to break down scale and entrap the layers and scale residue in the mixture;
• and
• separating the mixture from the surface to remove the benzene contaminants from the vessels and equipment with the mixture.