CPT Unit 2

• Coal is a black or brownish-black sedimentary rock that can be burned for fuel and used to generate electricity
• Coal


  Made up of carbon and hydrocarbons, which contain energy that can be released through combustion
• Coal is a fossil fuel and non-renewable
• Coal formation


  1. Initially, the dead organic materials are decomposed into peat

  2. As time passed, under high pressure and temperature, oxygen, hydrogen, and nitrogen were removed from them, and only carbon content was left to decompose into coal

  3. The process of coal formation from the decomposition of buried plants is known as 'Metamorphism'
• Coal


  • The coal type depends on the plant material deposited, degree of coalification (coal rank), and range of impurities (coal grade)
  • Most coals occur in stratified sedimentary deposits; those deposits may later be subjected to elevated temperatures and pressures caused by igneous intrusions or deformation during orogenesis (i.e., mountain-building processes), resulting in anthracite and even graphite development
• Lignite


  Brown-black coal formed from peat through coalification, an intermediate between peat and sub-bituminous coal, contains low carbon content and calorific value, has high water content and the lowest rank of coal, mainly used for electricity generation
• Sub-bituminous coal


  Black but not shiny, an intermediate rank between lignite and bituminous coal, contains a high calorific value compared to lignite, contains less water and is harder than lignite, making it easier to transport, store, and use, used for electricity generation and can be liquefied and converted into petroleum and gas
• Bituminous Coal


  Dark brown to black, the most abundant form of coal, an intermediate rank between sub-bituminous coal and anthracite, there are two subtypes: thermal coal (slightly higher quality) and metallurgical coal (used in the production of coke, a source of carbon for making steel)
• Anthracite


  Dark black hard coal, the most highly metamorphosed form of coal, contains more fixed carbon than any other form of coal, the least amount of volatile matter and moisture, the highest rank of coal, primarily used for household applications, such as charcoal briquettes
• Parameters affecting coal ranking

  • Carbon content
  • Ash content
  • Moisture content
  • Calorific value
  • Volatile matter
• The ranking depends on the types and amounts of carbon the coal contains and the amount of heat energy the coal can produce. The rank of a coal deposit is determined by the amount of pressure and heat that acted on the plants over time
• Coal power plant for electricity generation

  1. Coal is delivered in bulk and stored

  2. Coal is transported on a conveyor belt into the pulverizer, pulverized into a powder, and blown into a boiler

  3. The boiler heats up the water to produce superheated steam at high pressures

  4. The steam is used to turn the turbine, which, in turn, turns a generator

  5. The electricity from the generator is transmitted into a step-up transformer, the voltage is increased to a high value and transmitted around the country by the national grid

  6. The used steam is cooled by the cooling tower, the condensed steam is reused and pumped back into the boiler

  7. The steam from the cooling tower is waste heat
• Iron and steel-making process

  1. Iron ore (mixture of iron oxides and impurities) is extracted from the ground in open-pit mines or underground mines

  2. The iron ore may undergo sintering or pelletizing, heated with fluxes (limestone) and binders to form pellets or sintered pieces

  3. Coke is formed from coal in coke ovens and is crucial in the iron-making process as it provides the carbon needed to reduce iron oxides

  4. The processed iron ore, coke, and fluxes are fed into a blast furnace

  5. Coke reacts with the oxygen in the air to produce carbon monoxide, which reacts with the iron oxides to produce molten iron and carbon dioxide

  6. The combination of the impurities in the ore and fluxes forms a slag, which floats on top of the molten ore

  7. The molten iron produced in the blast furnace is tapped and transported to a basic oxygen furnace (BOF) or electric arc furnace (EAF) for refining

  8. Oxygen is blown into the molten iron in the BOF process to remove impurities (carbon, silicon, phosphorus, etc.)

  9. Electricity is used to melt scrap steel and reduce impurities in the EAF process

  10. The refined steel undergoes secondary refining (such as ladle refining, argon stirring, and vacuum degassing) to adjust its composition and remove any remaining impurities

  11. Once the desired composition quality is achieved, the molten steel is cast into various shapes, such as slabs, billets, or blooms, using continuous casting

  12. The cast steel products are then formed and finished through processes such as rolling, forging, machining, heat treatment, and surface treatment to produce final steel products ready for use
• Environmental impact of coal usage

  • Climate change (release of carbon dioxide leads to global warming)
  • Air pollution (combustion of coal releases several airborne toxins and pollutants, including mercury, lead, sulfur dioxide, nitrogen oxides, particulates, and other heavy metals)
  • Water pollution (coal sludge is given off during coal washing and may accumulate in groundwater and surface water)
  • Destruction of landscapes and habitats (if a mountain stands in the way of a coal seam within, it will be blasted or leveled, leaving a scarred landscape and disturbing ecosystems and wildlife habitat)
  • Methane occurring in coal deposits can explode if it concentrates in underground mines
  • Injuries, death, and coal dust inhalation leading to diseases
• Impact of coal mining


  • Global warming
  • Deforestation and Erosion
  • Negative impacts on agriculture and food security
  • Water resource loss (water is used by thermoelectric generating facilities to make electricity)
  • Air pollution (carbon dioxide, sulfur dioxide)
  • Thermal pollution (power plants and industrial manufacturers using water as a coolant, returning it to the natural environment at a higher temperature, impacting organisms)
• Coal Gasification


  1. It is a thermo-chemical process that converts biomass into a combustible gas called syngas (carbon monoxide, hydrogen, carbon dioxide, methane)

  2. The process proceeds at temperatures ranging from 800°C – 1200°C in a gasifier

  3. The syngas are cleaned to remove impurities (such as sulfur, ammonia, and particulates), involving processes such as desulfurization, ammonia removal, and particulate filtration

  4. Additional cleaning involves the water-gas shift reaction to increase hydrogen content or carbon dioxide removal

  5. Syngas may be used for electricity generation
• Updraft/ countercurrent gasifier


  1. Fuel is loaded into the top of the gasifier

  2. The gasifying agent is introduced at the bottom of the gasifier

  3. The fuel and gasifying agent, which moves counter-currently, reacts

  4. The fuel moves down through the drying zone to remove moisture and the pyrolysis zone to evaporate volatiles and produce char; the char gets reduced and combusted in the oxidation zone

  5. Due to high temperatures (up to 1300°C) in the oxidation zone, ash is mostly removed as a liquid

  6. The product gas has a high methane content
• Downdraft/ co-current gasifier


  1. Solid fuel is introduced from the top of the gasifier

  2. The gasifying agent is introduced from one side of the gasifier, and the product gas is removed from the opposite side

  3. The exit of the product gas and the entry of the gasifying agent are kept almost at the same level

  4. The fuel is dried, pyrolyzed, and gasified before leaving the gasifier

  5. Product gas has high content of carbon monoxide and low hydrogen and methane content
• Cross-draft gasifier


  1. Fuel is fed on the side of the gasifier

  2. A stream of gasifying agents (air, oxygen, or steam) is introduced into the bottom of the gasifier

  3. As the gas flows upward through the bed of solid particles, it creates a fluidized state, causing the particles to behave like a fluid. The bed expands, and the particles become suspended in the gas stream

  4. More carbon is converted due to high-temperature regions in the gasifier
• Fluidized bed gasifiers


  1. Fuel is fed on the side of the gasifier

  2. A stream of gasifying agents (air, oxygen, or steam) is introduced into the bottom of the gasifier

  3. As the gas flows upward through the bed of solid particles, it creates a fluidized state, causing the particles to behave like a fluid. The bed expands, and the particles become suspended in the gas stream

  4. More carbon is converted due to high-temperature regions in the gasifier
• Entrained bed gasifier


  1. Solid fuel and the gasifying agent are fed from the top and flow co-currently to the gasifier

  2. Very fine fuel particles are required for entrained flow gasifiers compared to the fluidized bed gasifiers

  3. Oxygen or air can be used as the gasifying agent, but most commercial plants use oxygen as the gasifying agent

  4. The major part of the ash is removed as slag

  5. High quality product gas is produced
• Fischer-Tropsch Synthesis


  1. The cleaned conditioned syngas is passed over a catalyst bed containing iron or cobalt catalysts

  2. Carbon monoxide and hydrogen in the syngas react over the catalyst to form long-chain hydrocarbons and water

  3. These hydrocarbons range from methane to high molecular weight waxes, which can be further processed into liquid fuels

  4. The Fischer-Tropsch synthesis products are separated into liquid hydrocarbons, water, and light gases. Separation processes may involve distillation, fractionation, and other techniques

  5. The liquid hydrocarbons may undergo further processing to refine them into transportation fuels such as diesel, gasoline, and jet fuel. Hydrocracking, hydrotreating, and other processes may be used to adjust the composition and properties of the fuels
• Hydrogenation of Coal


  1. Coal hydrogenation is a direct coal liquefaction process converting coal to gaseous or liquid hydrocarbon products

  2. Direct liquefaction involves the addition of hydrogen to coal in a solvent slurry at elevated temperature and pressure

  3. Catalysts are normally used to increase the rates of the desirable reactions, which include cracking, hydrogenation, and removal of oxygen, nitrogen, and sulfur

  4. Common types of catalysts used are supported metal-containing catalysts such as cobalt molybdate on alumina and molybdenum oxide or sulfide on alumina-silica support
• Carbon content


  The percentage of carbon in the coal. Coal with a higher carbon content will generally burn hotter and produce more energy.
• Ash content


  The non-combustible mineral material left over after coal is burned. Coal with a lower ash content is typically preferred, as it means there is less waste material.
• Moisture content


  The amount of water present in the coal. Coal with a lower moisture content is generally preferred, as it means there is more potential energy available for combustion.
• Calorific value


  A measure of the amount of energy released when the coal is burned. Coal with a higher calorific value will produce more energy when burned.
• Volatile matter


  The gases and vapors that are released when coal is heated. Coal with a higher volatile matter content will burn more quickly and may produce more pollutants.