EnSys Energy & Systems, Inc. Refinery Complexity & Fuel Intensity The product quality required to meet consumer fuel specifications is achieved by a combination of process stream fractionation; the removal of sulfur, nitrogen, metals and other contaminants; aromatics reduction; and freezing point and viscosity control. Gasoline products are subject to volatility and octane number specifications; diesel fuel to cetane number and pour point control; jet fuels to aromatics, luminometer number (smoke point) and freezing point specifications; and heavy fuel oils to sulfur content and viscosity limitations. Typically, several refinery streams are combined to produce a final product blended to meet a number of quality specifications. This operation is conducted in the refinery blending area, consisting of storage tanks, pumps, meters and auxiliary equipment. Final Draft B.2. Refining Industry Use of Fuel EnSys Energy & Systems, Inc. Petroleum refineries utilize fuel for all of the following: distilling crude oil and intermediate refinery streams, to provide heat to sustain chemical reactions such as hydrodesulfurization, for fueling boilers that provide steam for process requirements, to drive compressor turbines and for electricity generation, for drying waste sludges, to operate refinery flare stacks, incinerate pollutants and reduce environmental pollutants. to sustain the operations of refinery "offsites" including heating in tanks containing residual fuel, heavy crude or other high boiling streams pumping to move liquid products to and from tankage including shipping via marine, road and rail into and out of the refinery lighting, safety, laboratory, office and other facilities This variety of potential uses establishes a relationship between the complexity of a refinery operation and the quantity of fuel and energy which it consumes. The specific factors which determine the level of refinery fuel usage include the following: Refinery size Refinery complexity Degree of conversion from a heavier crude oil to a lighter product mix Fuel quality specifications and the extent of fuel reformulation Air, water and solid waste pollutant removal, i.e. extent of environmental emissions regulation on the refinery Level of energy efficiency achieved Refinery fuel is consumed primarily in the following major equipment categories: Gas and oil fueled process unit heaters and furnaces Flare gas combustion The majority of refinery fuel is consumed in refinery process units (as distinct from “offsites"). Essentially all refinery processes consume fuel, steam (generated from fuel or from process heat) and electricity (purchased or generated within refinery). The following are among the most important processes from an energy perspective: Utility plant boilers and electricity generators Crude unit atmospheric distillation, vacuum flash and desalter units Catalytic cracking units Catalytic naphtha reformers Propane deasphalters Isomerization and alkylation units Solvent extraction units for fuel gas cleanup and aromatics removal Reduction in GHG emissions associated with petroleum refining may be achieved by reducing the quantity of fuel required to process a barrel of crude oil or by reducing the quantity of carbon entering the refinery. Reducing energy requirements by using more efficient refinery operations reduces the barrels of crude oil or purchased fuels required to produce a given quantity and mix of refinery products. Substituting natural gas and natural gas liquids for crude oil, or substituting lighter for heavier crude oil, reduces Final Draft EnSys Energy & Systems, Inc. the refinery carbon intake, in turn reducing GHG emissions within the refinery works and by producing a higher quality product mix with an overall lower carbon to hydrogen ratio. To illustrate with five examples: If natural gas and associated liquids are substituted for crude oil input, the quantity of carbon entering the refinery complex would be lowered and hence less total carbon dioxide would be emitted to the atmosphere. This substitution may translate into a lower carbon content refinery fuel mix or the production of a higher quality refinery product mix with a lower carbon to hydrogen ratio, or both. The latter is typically achieved by converting natural gas to hydrogen and then hydrogenating refinery streams to reduce the carbon to hydrogen ratio of the products. Increased fuel would be required for the hydrogenation units, but overall the GHG emissions would reduce if the net quantity of carbon entering the refinery is reduced. If a lighter crude oil is run, less carbon will enter the refinery and overall GHG emissions will be reduced. Refinery processing requirement for crude upgrading and quality improvement to achieve a constant product slate will be reduced and hence energy consumption. The overall carbon to hydrogen ratio of the product mix will tend to be lower. Assume that the overall refinery intemal energy consumption is reduced by 5% through a combination of increased feed/product heat exchange and improved heat recovery, operating refinery reactors at lower temperatures and pressures by employing advanced catalysts and by more efficient furnace and burner operation. If the refinery energy requirement is taken at 8% of feed, then 0.4% less crude oil input (in a refinery that generated all its refinery fuel directly from crude oil) would be required to sustain the operation. Substitution alone of refinery still gas for heavy oil furnace fuel does not reduce overall For example, if refinery catalytic cracker conversion and selectivity were changed to convert cracker distillates destined for the refinery fuel pool into still gas, with refinery input unchanged, GHG would not decrease. The carbon atoms would be "moved around" and emerge as GHG from the combustion of the increased catalytic coke Final Draft EnSys Energy & Systems, Inc. make and the higher carbon to hydrogen ratio of the products which accompanies higher catalytic cracker conversion. Consequently the overall GHG emissions would not drop. This is not to be confused with beneficial environmental effects which may be associated with this example, such as reduced sulfur dioxide emissions achieved by treating of the refinery still gas prior to combustion. Commonly employed "carbon rejection" refining schemes also do not tend to reduce GHG emissions. The operation of a coker to produce refinery coke thereby lowering the carbon to hydrogen ratio of the liquid refinery products does not avoid the eventual combustion of the coke within the refinery or downstream. Asphalt production to reject carbon runs up against a limited market for the product. In describing the effects of the preceding examples, the envelope around the refinery was extended beyond internal fuel usage to include the ultimate combustion of all refinery products since they emit GHGs as well as fuel consumed within refinery limits. A key point here is that GHG emissions ex the refinery (fuel) itself and GHG emissions from the refinery's fuels products are intimately interrelated. Altering one tends to alter the other. The following table derived from the EIA PSA 1994, Volume 1, p 118 shows the makeup of the U.S. refinery fuel mix as a percentage of refinery input: % of Refinery Input (FOE Basis) % of Grand Total |