CHEM 1AB ---------- Lesson 3 - Fuels.pptx

Chemistry for Engineers

1. Fuels

2. Fuel is a combustible substance containing carbon, which on combustion produces a large amount of heat. A combustion reaction takes place when the fuel (solid, liquid, or gaseous form) reacts with the oxygen (𝑂 2 ) present in the air. Fuel + Oxygen  Combustion products + Heat

3. Classification of Fuels Fuels based on occurrence have two types: i . Natural fuels: It is also known as primary fuels since it occurs in nature. e.g. Wood, peat, coal, petroleum, natural gas, crude oil ii. Derived fuels: It is also known as secondary fuels since it were derived from natural fuels e.g. Charcoal, coke, kerosene oil, diesel Fuels based on physical state include solid, liquid, and gaseous fuels.

4. Liquid Fuels Petroleum or crude oil is a naturally occurring brown to black colored viscous oil formed under the crust of the earth, onshore or off shore. Chemically it is a mixture of various hydrocarbons with small amounts of N, O, and S compounds.

5. Gas Fuels Natural gas is a primary gas fuel. It is a mixture of low-molar mass hydrocarbons and other gases trapped with petroleum in the earth’s crust. The calorific value of natural gas varies from 12,000 to 14,000 kcal/m 3 Water gas essentially is a mixture of combustible gases like CO, H2 with little non-combustible gases like CO2 and N2. Its calorific value is 2800 kcal/m 3 Producer gas is a mixture of CO and N2. Its calorific value is 1800 kcal/m 3 .

6. Liquefied petroleum gas is a mixture of propane and butane. The calorific value of LPG is 27,000 kcal/m 3 Biogas is generally produced by the fermentation of bio wastes, sewage wastes, etc., by anaerobic bacteria.

7. Solid Fuels Coal is an important primary solid fuel that has been formed as a result of alteration of vegetable matter under some favorable conditions. Wood → Peat → lignite → sub-bituminous coal → bituminous coal → anthracite

8. Classification of solid fuels and its calorific value

9. Calorific Value 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 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 that evolves when a unit quantity of fuel undergoes complete combustion and the water formed is in a 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 a unit quantity of fuel undergoes combustion and the water formed is in a gaseous state.

10. Dulong’s formula:

11. Example 1 Calculate the gross and net calorific value of coal having the following compositions: 85% carbon, 8% hydrogen, 4% ash, 2% nitrogen, and 1% sulfur. The latent heat of combustion of steam is 587 cal/g.

12. Example 2 Calculate the gross and net calorific valve of a fuel having following composition 82%, C, 8% H, 5% O, 2.5% S, 1.4% N and 2.1% ash

13. Example 3 A coal has the following composition by weight: 𝐶 = 90%, 𝑂 = 3.0%, 𝑆 = 0.5%, 𝑁 = 0.5%, 𝑎𝑛𝑑 𝑎𝑠ℎ = 2.5%. The net calorific value of coal was found to be 8,490.5 𝑘𝑐𝑎𝑙/𝑘𝑔. Calculate the percentage of hydrogen and the higher calorific value of coal.