Fuels PDF

FUELS  is a combustible substance that reacts with air FUELS resulting to combustion releasing heat that can converted to other form of energy to be used for transportation, domestic and industrial purposes. A combustion reaction takes place wh...

FUELS  is a combustible substance that reacts with air FUELS resulting to combustion releasing heat that can converted to other form of energy to be used for transportation, domestic and industrial purposes. A combustion reaction takes place when the fuel (solid, liquid, or gaseous form) reacts with the oxygen (solid, liquid, or gaseous form) present in air. Fossil Fuels – are non renewable energy resources which are stored up to millions of years ago by photosynthesis. Generally, fuels contains carbon as main constituent. The combustion reaction takes place when the carbon and hydrogen of the fuel (solid, liquid, or gaseous form) reacts with the oxygen 𝑂2 present in air. A complete combustion is observed when all the combustible components of the fuel are converted; all carbon is converted to carbon dioxide, all hydrogen is converted to water, all sulfur is converted to sulfur dioxide. Units of Heat Calorie (cal): The amount of heat required to raise the temperature of one gram (1 g) of water through one degree centigrade (1°C). e.g. 14.5 to 15.5°C 1 𝑐𝑎𝑙 = 4.18 𝐽𝑜𝑢𝑙𝑒 = 4.18 𝑥 107𝑒𝑟𝑔𝑠 Kilocalorie (kcal): The amount of heat required to raise the temperature of one kilogram (1 kg) of water through one degree centigrade (1°C). e.g. e.g. 14.5 to 15.5°C 1 𝑘𝑐𝑎𝑙 = 1000 𝑐𝑎𝑙 British thermal unit (BTU): The amount of heat required to raise the temperature of one pound of water through one degree Fahrenheit (1°F). e.g. e.g. 60 to 61°F 1 𝐵𝑇𝑈 = 252 𝑐𝑎𝑙 = 0.252 𝑘𝑐𝑎𝑙 1 𝑘𝑐𝑎𝑙 = 3.968 𝐵𝑇𝑈 Centigrade heat unit (CHU): The amount of heat required to raise the temperature of one pound of water through one degree centigrade (1°C). e.g. 14.5 to 15.5°C Relation between different heat units: 1 𝑘𝑐𝑎𝑙 = 1000 𝑐𝑎𝑙 = 3.968 𝐵𝑇𝑈 = 2.2 𝐶𝐻𝑈 Units of Calorific Value For solid and liquid fuels: calorie per gram (𝑐𝑎𝑙/𝑔) or kilocalorie per kilogram (𝑘𝑐𝑎𝑙/𝑘𝑔) or British thermal unit per pound (𝐵𝑇𝑈/𝑙𝑏). For gaseous fuels: kilocalorie per cubic meter (𝑘𝑐𝑎𝑙/𝑚3) or British thermal unit per cubic feet (𝐵𝑇𝑈/𝑓𝑡3) The CALORIFIC VALUE OR HEATING VALUE of a fuel is defined as the total amount of heat evolved by the combustion of a unit quantity (in mass or in volume) of fuel at a reference temperature. Higher calorific value (HCV): It is also known as gross calorific value (GCV) or higher heating value (HHV). It is the amount of heat evolved when a unit quantity of fuel undergoes complete combustion and the water formed is in liquid state Lower calorific value (LCV): It is also known as net calorific value (NCV) or lower heating value (LHV). It is the amount of heat evolved when unit quantity of fuel undergoes combustion and the water formed is in gaseous state. Calorimeter A calorimeter is defines as an apparatus/equipment used for calorimetry, the process of measuring heat transfer associated by chemical reactions, physical changes, or phase changes (1) Bomb calorimeter: It is used to determine the calorific value of solid fuel and non-volatile liquid fuel. It consists of a cylindrical stainless steel vessel called bomb and is capable of withstanding high pressure. Calorimeter  It is used to determine the calorific value of gaseous (2) Boy’s gas calorimeter: fuel and volatile liquid fuel. Classification of Fuels Combustion Analysis Is a chemical reaction in which one of the reactants is oxygen from air and the other is fuel, whether it is gaseous, liquid or solid. It is created by the evolution of light and heat COMPLETE COMBUSTION THEORETICAL OXYGEN It is the oxygen required for COMPLETE COMBUSTION. Method 1: The individual balanced equation for the oxidation of each combustible is written. It is the sum of all oxygen used in complete combustion. Example: Determine the theoretical oxygen required for the combustion of one mole of refinery gases containing 6% 𝐻2𝑆, 5% 𝐻2, 57 𝐶3𝐻8, 2% 𝐶𝑂2, 𝑎𝑛𝑑 30% 𝐶4𝐻10. Method 2. Elements of the fuel are broken down into equivalent atoms of carbon, sulfur, hydrogen and oxygen present. Each atom C needs 1 mole O2 for full combustion; each atom sulfur needs 1 mole O2; each atom H requires 1⁄4 mole O2. The total moles of O2 in the fuel are subtracted from the specifications of O2 to give theoretical O2 out of the air. Before the volume of O2 is extracted from the air, the fuel first uses the fuel along with it. As a result: Example: Determine the theoretical oxygen required for the combustion of one mole of refinery gases containing 6% 𝐻2𝑆, 5% 𝐻2, 57 𝐶3𝐻8, 2% 𝐶𝑂2, 𝑎𝑛𝑑 30% 𝐶4𝐻10.  Theoretical air is air that contains the exact amount of theoretical 𝑂2. Air for combustion calculations is assumed to be 21% 𝑂2 and 79% 𝑁2 by Theoretical Air for Combustion volume. 𝑁 in air is non-combustible and acts as a diluent to the 𝑂2 in the 2 air. There are two methods of determining the theoretical oxygen: Example: A furnace is fired with petroleum oil containing 80%C, 13% H, 3%S, 1% N, 3% O. Determine the moles theoretical air required for the combustion of one kg of oil.  The theoretical air is not sufficient for complete combustion. The 𝐶𝑂 𝑎𝑛𝑑 𝐻2 formation in the flue gas and presence of unburned combustibles indicates an Percent Excess Air incomplete or partial combustion. In order to complete the combustion reaction, excess air supply or excess 𝑂2 is needed and calculated as follows: INCOMPLETE COMBUSTION Incomplete combustion of fuel represents a loss of heat since this should have been given off for additional power use had the fuel been completely burnt. Indicators of incomplete combustion are the presence CO, H2 and soot in the exhaust gas well as unburned combustible in the refuse.