Fuel Gaseous Lecture Notes PDF

Lecture 8 Gaseous Fuels Department of Chemistry Chemistry for Engineers | Gonzaga College of Arts and Sciences University of Southern Mindanao Lecture Outline Natural Gas Composition Occurrence...

Lecture 8 Gaseous Fuels Department of Chemistry Chemistry for Engineers | Gonzaga College of Arts and Sciences University of Southern Mindanao Lecture Outline Natural Gas Composition Occurrence Properties Manufactured Gases Producer Gas Water Gas Hydrogen Wobbe Index Chemistry for Engineers | Gonzaga 2 Natural Gas Natural Gas is obtained from wells dug in the oil-bearing regions. When natural gas occurs along with petroleum in oil wells, it is called wet gas and contains gaseous hydrocarbons from C1 to C4. The wet gas is then suitably treated to remove propane, propene, butane and butene, which is used as liquefied petroleum gas (LPG). When the natural gas is compressed, it is called compressed natural gas (CNG). The primary component present in CNG is methane. Chemistry for Engineers | Gonzaga 3 Natural Gas The natural gas can either be stored in a tank of a vehicle as CNG at 3,000 or 3,600 psi or as liquefied natural gas (LNG) at typically 20-150 psi. A suitable designed natural gas engine may have a higher output compared with a petrol engine because the octane number of natural gas is higher than that of petrol. Chemistry for Engineers | Gonzaga 4 Typical Composition Chemistry for Engineers | Gonzaga 5 Uses of Methane Chemistry for Engineers | Gonzaga 6 Occurrence of Natural Gas 1. Natural gas can exist in the lithosphere: Separately Or with oil 2. Natural gas can occur: Separately Diluted in oil Diluted in water Diluted in rocks (in coal) Chemistry for Engineers | Gonzaga 7 Properties of Natural Gas It has a high calorific value. Depending on its source, its properties are uniform and contains no harmful impurities. Its flame propagation speed is relatively slow, requiring special burners. Its flame is not sooty, which reduces heat loss. However, it is disadvantageous when heat transfer by radiation is needed, e.g. in a boiler, which would require large areas for heat exchange by radiation. Chemistry for Engineers | Gonzaga 8 Properties of Natural Gas It has a high octane rating – good for resisting self-ignition, and it is a good fuel for spark ignition engines but incompatible with diesel. It is also a good fuel for gas turbines. It forms explosive mixtures with air thus requiring safety devices, particularly to allow the starting and stopping the firing systems. However, its density is lower than air, thus are easily dispersed in the atmosphere, reducing the risk of formation of explosive mixtures. Chemistry for Engineers | Gonzaga 9 Properties of Natural Gas The calorific value of natural gas per unit volume is very low. Thus, in its storage and transport, it is compressed or liquefied. Its density is much higher in the liquid phase, so it is more favorable to store and transport as a liquid. However, this would require very low temperatures (about –160°C such that vessels must be cryogenic. To keep the temperature low, some of the liquid is allowed to vaporize, which is indeed results to fuel loss. Chemistry for Engineers | Gonzaga 10 Liquefied Petroleum Gases (LPG) LPGs are hydrocarbons or a mixture of hydrocarbons that are gaseous at normal atmospheric temperature and pressure, but can be stored in the liquid phase at atmospheric temperature at relatively low pressures. As a liquid, they have a higher energy density per unit volume. Main components of LPG: The main sources of LPG are natural gas, crude oil, thermal and catalytic cracking, as well as thermal reforming. Chemistry for Engineers | Gonzaga 11 Bottled Gases BUTANE PROPANE Commercial liquid butane Commercial liquid propane consists mainly of saturated consists mainly of C3 and unsaturated C4 hydrocarbons (propane and hydrocarbons, with less than propylene if obtained from 20% of C3 hydrocarbons and refinery gases), with less than less than 2% of C5 5% of C2 hydrocarbons and hydrocarbons. less than 10% of C4 hydrocarbons. Chemistry for Engineers | Gonzaga 12 Bottled Gases They contain low percentages of sulfur compounds,