Refineries skimming

Skimming basin. Oil/water separators ol this design are widely used to treat refinery and petrochemical plant waste waters.1 Similar designs can be found in some oil fields, particularly where large volumes of water must be handled. 

Oil leaks typically require the use of demulsifiers, defoamers, and temporary oil-skimming equipment. Also, heavy chlorination and the use of nonoxidizers effective against SRBs are recommended. Chlorination usually requires the pH to be reduced to 6.5 to 7.0. Add chlorine to provide 1.0 to 2.0 ppm free CI2 for 4 to 6 hours. Also, add 100 to 200 ppm nonionic surfactant 1 to 5 ppm defoamer may be required. All attempts should be made to reduce oil contamination to an absolute minimum. Even in oil refinery cooling systems, where the risk of periodic oil leaks is high, free oil should never exceed 5 ppm. 

Both of the Canadian plants use the technique of hot water extraction to remove the bitumen from the tar sand. In this procedure the tar sand, steam, sodium hydroxide, and hot water are mixed and tumbled at a temperature of around 90°C. Layers of sand pull apart from the bitumen in this process. Additional hot water is added and the bitumen-sand mixture is separated into two fractions by gravity separation in cells in which the bitumen rises to the top and is skimmed off, while the sand settles to the bottom. The upgrading of the bitumen to a synthetic crude is then accomplished by oil refinery procedures including coking, in which carbon is removed by thermal distillation and hydrotreating. 

The chief nonmineral application of froth flotation is to the removal or oil or grease or fibrous materials from waste waters of refineries or food processing plants. Oil droplets, for instance, attach themselves to air bubbles which rise to the surface and are skimmed off Coagulant aids and frothers often are desirable. In one kind of system, the water is saturated with air under pressure and then is pumped into a chamber maintained under a partial vacuum. Bubbles form uniformly throughout the mass and carry out the impurities. The unit illustrated in Figure 20.12 operates at 9 in. mercury vacuum and removes both skimmed and settled... 

Induced Gas Flotation. Mechanically induced gas dotation (IGF) is employed extensively to remove suspended solids, oil, and other organic matter from oil-field and refinery wastewaters. Consequently, these IGF units are particularly suited to the treatment of oil-in-water or reverse emulsions. Such units generally follow gravity oil-water separation units such as FWKOs, gun barrels, and skim tanks in oil-field-produced water-treatment schemes, and also handle the oily water streams generated from all treaters in a specific produced-fiuid treatment plant. 

The dressing operations at the Herculaneum smelter are conducted entirely in kettles. The dross plant uses four 250-ton capacity kettles. The lead bullion is received from the furnaces, and is allowed to cool. This cooling causes the copper, sulfur, and trace amounts of other impurities to precipitate and rise to the surface of the bullion, producing a copper-rich dross. This dross is skimmed off and put through a wet screw classifier and sold as a byproduct to copper smelters. The drossed bullion is transferred to another kettle where it is further cooled and fluxed with sulfur for final decopperizing. This dross is skimmed and recycled to the blast furnace. The decopperized lead bullion is then pumped to the refinery. Maintenance in the dross plant is minimal and is managed on an as needed basis. 

The kettle is drossed periodically by manual skimming and the dross can be recycled to a short rotary furnace for reduction and conversion back to metallic lead. Depending on the alloying components it may be necessary to recycle the lead bullion so produced back to the refinery feed. 

The oil skimmed off on the surface of the API separator is partly reprocessed in the refinery and the rest is incinerated. 

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