STOICH

• Liquid hydrocarbon fuels are commonly derived from crude oil through distillation and cracking processes.
• Liquid fuels can also be obtained from biomass, coal tar, sand and oil shale.
• Most liquid fuels are mixture of hydrocarbons for which compositions are usually given in terms of mass fractions.
• Advantages of Liquid fuels

  1. Require less space for storage
  2. higher calorific value
  3. they have nearly constant calorific value
  4. easy control of consumption
  5. staff economy
  6. absence of danger from spontaneous combustion
  7. easy handling and transportation
  8. cleanliness
  9. no ash problem
  10. non-deterioration of the oil in storage
• Disadvantages of liquid fuels

  1. Higher cost
  2. greater risk of fire
  3. costly containers are required for storage and transport
• Specific Gravity - ratio of the density of the fuel to the density of water
• Specific Gravity - an indication of the composition
• For most liquid fuels, a lower specific gravity suggest a higher percentage of light hydrocarbon and faster burning fuel.
• Viscocity of a fluid - measure of its internal resistance to flow
• Viscosity - most important characteristic in the storage and use of fuel oil
• Viscosity - influences the degree of preheat required fro handling, storage and satisfactory atomization
• if the oil is too viscous, it may become difficult to pump, hard to light the burner, and tough to operate
• If the oil is too thin, it will be easy to handle but may not have enough heat value or energy content
• Flash point of a fuel - lowest temperature at which the fuel can be heated so that the vapour gives off flashes momentarily when an open flame is passed over it
• flash point for furnace oil is 66 degree celcius
• Pour Point of a fuel - lowest temperature at which it will pour or flow when cooled under prescribe conditions
• Pour point - very rough indication of the lowest temperature at which fuel oil is readily pumpable
• Specific Heat - amount of energy needed to raise the temperature of 1 kg of oil by 1 degree celcius
• Specific heat - determines how much steam or electrical energy it takes to heat oil to a desired temperature
• Light oils have a low specific heat, whereas heavier oils have a higher specific heat.
• Sulfur content - amount of sulfur in the fuel oil depends mainly on the source of the crude oil and to a lesser extent on the refining process
• the normal sulfur content for the residual fuel oil (furnace oil) is in the order of 2-4%
• the main disadvantage of sulfur is the risk of corrosion by sulfuric acid formed during and after combustion, and condensing in cool parts of the chimney or stack, air preheater and economister
• Carbon Residue - indicates the tendency of oil to deposit a carbonaceous solid residue on a hot surface, such as a burner or injection nozzle, when its vaporisable constituents evaporate
• residual oil contain carbon residue ranging from 1 percent or more
• 2 main classes of liquid fuels

  1. light oil or spirits
  2. heavy oil
• Light oil or spirits - suitable for use with internal combustion engines and jet engines
• light oils or spirits includes

  1. the lighter, more volatile fractions obtained by distilling or cracking natural petroleum oils and related natural deposits
  2. the light fractions obtained by the hydrogenation of coal, coal tar or heacy oil residues
  3. the light fractions obtained by the synthesis of hydrocarbons by the Fischer Tropsch Process
  4. alcohols, particularly methyl and ethyl alcohol, obtained by the synthesis of fermentation process
  5. benzole, obtained by the distillation of coal tar or by extraction from coal gas
  6. Alcogas or gasohol, mixture of methyl or ethyl alcohol and gasoline
• light oils or spirits - only the most volatile and cleanest products, gasoline or petrol (natural and synthetic), benzole and alcohol are suitable for sphark ignition engine
• light oils and spirit - the next higher fractions of petroleum oil, shale oil and synthetic oil, generally included in the class of oils known as paraffin, kerosene or naptha are suitable for jet engine
• Heavy Oils - include the heaviest grades of natural petroleum oils and lubricating oils from which the more valuable lubricating oil and factions have been removed by distillation
• Mazut - residue after atmospheric distillation of crude oil
• gudron - residue after vacuum distillation of crude oil
• The heavy heating oil has high viscocity, which requires heating up to temperatures pf 65-90 degree celcius for transportation and atomization
• Crude oil is a naturally occuring, unrefined petroleum product composed of hydrocarbon deposits and other organic materials.
• typical crude oil is a mixture of alkanes (propane, butane), aromatics (benzene, toluene) and cycloalkane (napthalene) of organic compounds containing C, H, O, N, and S elements
• a type of fossil fuel, crude oil can be refined to produce usable products such as gasoline, diesel, and various other forms of petrochemicals
• crude oil - a non-renewable resource, which means that it can't be replaced naturally at the rate we consume it and is, therefore, a limited resource
• Three Stages of refining

  1. separation
  2. conversion
  3. treating
• separation - the first step, molecules are separated through fractional distillation at normal atmospheric pressure, according to their molecular weight