Pharos University فاروس Faculty of Engineering جامعه

الهندسة Petrochemical Department كلية البتروكيم�اويات قسم

PE 330 ENERGY CONSERVATIONLECTURE (3)

I)-LIQUID FUELS AND THEIRCHARACTERISTICS

The liquid fuels can be classified as follows :(a) Natural , and Artificial or manufactured fuels .(b) Petroleum and non petroleum fuels.

Advantages of liquid fuels:

(a )They posses higher calorific value per unit mass than solid fuels.(b )They burn without dust, ash, clinkers, etc.

)c( Their firing is easier and also fire can be extinguished easily by stopping liquid fuel supply.

(d )They are easy to transport through pipes.(e )They can be stored indefinitely without any loss.

(f )They are clean in use and economic to handle.(g )Loss of heat in chimney is very low due to greater cleanliness.

(h )They require less excess air for complete combustion.(i )They require less furnace space for combustion.

Disdvantages of liquid fuels:

a( The cost of liquid fuel is relatively much higher as compared to solid fuel.

)b( Costly special storage tanks are required for storing liquid fuels.

)c( There is a greater risk of fire hazards, particularly, in case of highly flammable and volatile liquid fuels.

)d( They give bad odour.)e( For efficient burning of liquid fuels, specially

constructed burners and spraying apparatus are required.

1-Petroleum and its Characteristics Petroleum is a basic naturally occurring brown to black

flammable liquid. Crude oils are principally found in oil reservoirs associated with sedimentary rocks beneath the earth’s surface. Although exactly how crude oils originated is not established, it is generally agreed that crude oils derived from marine animal and plant debris subjected to high temperatures and pressures. It is also suspected that the transformation may have been catalyzed by rock constituents. Regardless of their origins all crude oils are mainly constituted of hydrocarbons mixed with variable amounts of sulfur, nitrogen, and oxygen compounds. Metals in the forms of inorganic salts or organo-metallic compounds are present in the crude mixture in trace amounts.

The ratio of the different constituents in crude oils, however, vary appreciably from one reservoir to another.

Normally, crude oils are not used directly as fuels or as feedstocks for the production of chemicals. This is due to the complex nature of the crude oil mixture and the presence of some impurities that are corrosive or poisonous to processing catalysts.

Crude oils are refined to separate the mixture into simpler fractions that can be used as fuels, lubricants, or as intermediate feedstock to the petrochemical industries

Petroleums are graded according to the following phsio-chemical properties:

)a( Density, Specific Gravity and API Gravity.)b( Salt Content )expressed in milligrams of sodium chloride

per liter oil)(c )Flash point

(d )Ignition point(d )Viscosity

(e )Sulphur contents,(f )Moisture content

)g( Pour Pointh( Calorific valuei( Ash Content )indicates the amount of metallic constituents in

a crude oil).

Classification of Crude Petroleum Crude oils can be arbitrarily classified into three or four

groups depending on the relative ratio of the hydrocarbon classes that predominates in the mixture. The following

describes three types of crudes:A-Paraffinic Base Type Crude Petroleum: This type of petroleum is mainly composed of the

saturated hydrocarbons from CH4 to C35H72 and a little of the napthenes and aromatics. the hydrocarbons from C18 H38 to C35 H72 are sometimes called waxes.

Properties: waxy, less asphaltic, low sulphur, high pour

B-Asphalitc Base Type Crude Petroleum:contain relatively a large amount of polynuclear aromatics,a high asphaltene content, and relatively less paraffins thanparaffinic crudes.Properties: high sulphur, nitrogen, suitable for base oils C-Naphthenic Crude Petroleum: The ratios of naphthenic and aromatic hydrocarbons are

relatively higher than in paraffinic crudes.Properties:less wax, less asphaltic, low pour

Oil products and cuts

II) Manufactured Liquid Fuels and their Characteristics

Manufactured liquid fuels include Gasoline, Diesel oil, Kerosene, Heavy oil, Naptha, Lubricating oils, etc. These are obtained mostly by fractional distillation of crude petroleum or liquefaction of coal.

1-Gasoline and its Characteristics:It contains some undesirable unsaturated straight chain hydrocarbons and

sulphur compounds. It has boiling range of 40-120ºC.The, unsaturated hydrocarbons get oxidized and polymerized, thereby

causing gum and sludge formation on storing. On the other hand, sulphur compounds lead to corrosion of internal combustion engine and at the same time they adversely affect tetraethyl lead, which is generally added to gasoline for better ignition properties.

The sulphur compounds from gasoline are generally removed by treating it with an alkaline solution sodium plumbite. Olefins and colouring matter of gasoline are usually removed by percolating through ‘Fuller’s earth’ which absorbs preferentially only the colours and olefine.

It is used in air-crafts. It is also used as motor fuel, in dry-cleaning and as a solvent.

2-Diesel Fuel and its CharacteristicsThe diesel fuel or gas oil is obtained between 250-320 ºC during

the fractional distillation of crude petroleum. This oil generally contains 85% C. 12% H. Its calorific value is about 11,000 kcal/kg.

Diesel fuels consist of longer hydrocarbons and have low values of ash, sediment, water and sulphur contents.

The suitability of a diesel fuel is determined by its cetane value, and It is used in diesel engines as heating oil and for cracking to get gasoline.

• The hydrocarbon molecules in a diesel fuel should be, as far as possible, the straight-chain ones, with a minimum mixture of aromatic and side-chain hydrocarbon molecules.

3-Kerosene Oil and its CharacteristicsKerosene oil is obtained between 180-250 ºC during

fractional distillation of crude petroleum.It is used as an illuminant, jet engine fuel, tractor fuel, and

for preparing laboratory gas.• With the development of jet engine, kerosene has

become a material of far greater importance than it is used to be.

• When kerosene is used in domestic appliances, it is always vaporized before combustion. By using a fair excess of air it burns with a smokeless blue flame.

4-Heavy Oil and its Characteristics It is a fraction obtained between 320-400ºC during

fractional distillation of crude petroleum. This oil on refractionation gives :

)a( Lubricating oils which are used as lubricants.)b( Petroleum-jelly )Vaseline( which is used as lubricants in

medicines and in cosmetics.)c( Greases which are used as lubricants.)d( Paraffin wax which is used in candles, boot polishes,

wax paper, tarpolin cloth and for electrical insulation purposes.

III)-Manufactured Liquid Fuels (Non Petroluem)and their Characteristics

A- OIL SHALE:Oil shale is a low-permeable rock made of inorganic

material interspersed with a high-molecular weight organic substance called “Kerogen.” Heating the shale rock produces an oily substance with a complex structure.

The composition of oil shales differs greatly from one shale to another. For example, the amount of oil obtained from one ton of eastern U.S. shale deposit is only 10 gallons, compared to 30 gallons from western U.S. shale deposits.

Retorting is a process used to convert the shale to a high molecular weight oily material. In this process, crushed shale is heated to high temperatures to pyrolyze Kerogen. The product oil is a viscous, high molecular weight material )high in nitrogen, oxygen, and sulphur(. Further processing is required to change the oil into a liquid fuel.

B- Tar Sands:Tar sands )oil sands( are large deposits of sand saturated with

bitumen and water. Tar sand deposits are commonly found at or near the earth’s surface entrapped in large sedimentary basins. Large accumulations of tar sand deposits are few. About 98% of all world tar sand is found in Canada.

Tar sand is difficult to handle. During summer, it is soft and sticky, and during the winter it changes to a hard, solid material.

Recovering the bitumen is not easy, and the deposits are either stripmined if they are near the surface, or recovered in situ if they are in deeper beds.

The bitumen could be extracted by using hot water and steam and adding some alkali to disperse it. The produced bitumen is a very thick material having a density of approximately 1.05 g/cm3.

It is then subjected to a cracking process to produce distillate fuels )naptha, kerosine, and gasoline(, and coke. The distillates are hydrotreated to saturate olefinic components.

3-Coal Derived Fuels:Liquid fuels derived from coal range from

highly aromatic coal tars to liquids resembling petroleum.

Coal tar fuels are high boiling fractions of crude tar from pyrolysis in coke ovens and coal retorts.

They are low in sulphur and ash, they contain hydrocarbons, phenols, and heterocyclic nitrogen and oxygen compounds.

They are more aromatic than petroleum fuels they burn with a more luminous flame.

IV) Gaseous FuelsA) Natural Gas:1. Raw natural gas is a combustible gas extracted

primarily from any one of conventional underground sources, namely petroleum crude oil wells, gas wells, and condensate wells.

2. natural gas consists of hydrocarbons with very low boiling point.

3. Methane is the main one with boiling point 119K, ethane with 184 K, propane with 231 K.

Some wells, deliver gas containing levels of hydrogen sulfide, and other sulfur compounds )thiophenes, mercaptants, and organic sulfides( that must be removed before transfer to pipelines.

Pipeline-company contracts typically maximum allowable limits of impurities: H2S and total sulfur compounds seldom exceed 0.023 g/m3.

The majority of pipe line companies limited H2S to less than 0.007 g/m3.

Hydrogen:Hydrogen is used for production of ammonia and

chemicals, in the refining of petroleum, hydrogenation of fats and oils. It is also used as a fuel in industrial cutting and welding operations .

It is produced by steam reforming of natural gas, a by product in thermal cracking of hydrocarbons, and to a small extent by electrolysis of water.

Hydrogen is non polluting form of energy, when electrochemically combined with oxygen in fuel cells, only water, heat and electricity are produced.

Hydrogen can be stored in gaseous, liquid, or solid form.

Acetylene:Acetylene is used in operations requiring high flame

temperature, such as welding and metal cutting.To transport acetylene, it is dissolved in acetone under pressure

and drawn into small containers filled with porous materials.Miscellaneous Fuels:A variety of gases have minor market shares , theses are

reformed gas , oil gases, producer gas, blue water gas, carbureted water gas, coal gas, and blast furnace gas. They are produced by pyrolysis, water gas reaction, or as a by product in iron production .