Raw Material• Crude Oil is the raw material for any refinery.• In Pakistan ratio of imported Crude & local crude is 85% & 15% respectively.
Refinery Processes• Because of wide differences in crude oils , we find number of different Refinery Processes methods• The most important method of separating petroleum products is Distillation .
Distillation• In this process, the crude oil is heated to above 400 OC to vapourize. The resulting vapours are then carried to a fractional column, having different temperature zones i-e. fractional column is divided into several compartments, each compartment has a specific range of temperature. As the petroleum vapours ascent the column, cont….
several fractionscondense & separate inthese compartments. More than 500hydrocarbons areseparated from crude oil.The lighter moleculescomes off at the top ofthe distillationcolumn, the heavier atthe bottom.
Number of BoilingFraction Carbon Range (oC) Atomsnatural gas < 20 C1 to C4petroleum ether 20 - 60 C5 to C6gasoline 40 - 200 C5 to C12kerosene 150 - 260 C12 to C13fuel oils > 260 C14 to C19lubricants > 400 C20 and aboveasphalt or Residue polycycliccoke
Cracking• Cracking is a process in which heavy-molecular weight hydrocarbons are broken up into light hydrocarbon molecules by the application of heat and pressure, with or without the use of catalysts, to derive a variety of fuel products. Cracking is one of the principal ways in which crude oil is converted into useful fuels such as motor gasoline, jet fuel, and home heating oil.
Example C16H34 C8H18+C8H16• Molecule with 16 carbon atoms cannot be used as gasoline but molecule with 8 carbon atom can.
Coking• The coking process is very similar to an extreme case of cracking where one of the end products is coke• Heavy residual products which accumulate at the base of the fractionation tower have become more of a problem for petroleum refneries.• This is primarily due to the decrease in demand for heavy residual fuels.
Dewaxing• Petroleum dewaxing is used to extract high molecular weight components, often referred to as waxes, from a petroleum stream. These impurities cause petroleum products to gel or solidify at higher temperatures.
• Gases such as propane are useful as dewaxing agents. When propane is injected into the fluid stream it becomes a gas; this effect, called auto refrigeration, causes the fluid to cool rapidly. The waxy materials will turn from liquid to solid and can be filtered out or skimmed from the top of the tank.
HYDROFINISHING UNIT• In this final processing stage, the lube base oils are stabilized and their colour is further improved by hydrogenation under severe operating conditions in the presence of a catalyst.• The hydrofinished lube oils are dispatched to refinery storage tanks for distribution to Oil Marketing/Lube Oil Blending Companies.
•Environmental Pollution in Petroleum Refineries
Air Pollutants from Refining Operations Major air pollutant that may be emittedfrom refining operations are• Sulphur Compounds• Hydrocarbons• Nitrogen oxides• Particulates• etc
Sulphur Compounds• The main source of sulphur dioxide emissions are from combustion operations such as fired heaters , boilers & catalytic cracking.
Hydrocarbons• The emissions of hydrocarbons result mainly from evaporation of light oils during storage & handling of crude & petroleum products & from leaks.
Nitrogen oxides• Combustion of fuel in fired heaters & boilers & in internal combustion engines , electric generators are the main source of Nitrogen oxides emissions.
Particulates• The major sources include sludge burner, emergency flares , and boilers , furnaces , emergency operations and incomplete combustion.
Water Pollution fromRefining Operations• Water is used in petroleum refineries for variety of puposes.Since water does not enter into the final product , it can be expected that 80-90% of the water supplied to the refinery comes out as waste water.
Characteristics Of wastewater fromPetroleum Refineries in PakistanS.No. Effluent characteristics Value1 Flow,1/kg oil 1.52 pH 6.8-7.23 Suspended solids, mg/l 200-4004 BOD , mg/l 100-3005 COD , mg/l ---6 BOD/COD ---7 BOD load, g/unit product 0.3