What are gaseous fuels used in power plants?

Short Answer:

Gaseous fuels are fuels that exist in gaseous form under normal conditions and are widely used in power plants to generate heat energy. The main gaseous fuels used in power plants are natural gas, coal gas, producer gas, water gas, and blast furnace gas. These fuels are burned in gas turbines or boilers to produce heat, which is used to generate electricity.

In simple words, gaseous fuels are clean-burning energy sources that mix easily with air and ignite quickly. They are preferred in modern power plants because they are easy to handle, produce high heat, burn without smoke, and cause less pollution compared to solid and liquid fuels.

Detailed Explanation :

Gaseous Fuels Used in Power Plants

Gaseous fuels are fuels that exist in the gaseous state at normal temperature and pressure. They are composed mainly of hydrogen, carbon monoxide, and hydrocarbons. These fuels are used in thermal and gas turbine power plants for the generation of electricity.

They are obtained from natural sources like petroleum and natural gas fields or manufactured artificially from solid fuels such as coal and coke. The main reason for using gaseous fuels in power plants is their high calorific value, complete combustion, and minimal pollution.

The most commonly used gaseous fuels in power plants are:

  1. Natural Gas
  2. Coal Gas
  3. Producer Gas
  4. Water Gas
  5. Blast Furnace Gas
  1. Natural Gas

Natural gas is one of the most commonly used gaseous fuels in modern power plants. It is obtained directly from underground natural gas reservoirs or from crude oil fields during petroleum extraction.

Composition:
It mainly contains methane (CH₄) along with small quantities of ethane, propane, and butane.

Calorific Value:
About 48,000 to 50,000 kJ/kg.

Uses in Power Plants:
Natural gas is used in combined cycle power plants (CCPPs) and gas turbine plants. It is burned to produce high-temperature gases that directly drive turbines or generate steam for electricity.

Advantages:

  • Very high calorific value.
  • Burns cleanly with almost no smoke or ash.
  • Easy to control and transport through pipelines.
  • Produces less carbon dioxide compared to coal or oil.

Disadvantages:

  • Limited natural reserves.
  • Requires expensive infrastructure for storage and transport.

Example:
Used in large-scale gas-based power plants like the Dabhol Power Plant in Maharashtra, India.

  1. Coal Gas

Coal gas is an artificial gaseous fuel obtained by heating coal in the absence of air (a process called destructive distillation). It was one of the earliest manufactured gaseous fuels used before natural gas became common.

Composition:
It mainly consists of hydrogen (H₂), methane (CH₄), carbon monoxide (CO), and small quantities of carbon dioxide (CO₂) and nitrogen (N₂).

Calorific Value:
About 18,000 to 20,000 kJ/m³.

Uses in Power Plants:
Coal gas is used to fire boilers in small or medium thermal power plants and also as a fuel for gas engines.

Advantages:

  • Can be produced from locally available coal.
  • Easy to ignite and control.
  • Produces a moderate amount of heat.

Disadvantages:

  • Produces toxic carbon monoxide gas.
  • Requires gas purification before use.
  • Less efficient compared to natural gas.
  1. Producer Gas

Producer gas is a low-calorific-value gas produced by passing air and steam over red-hot coal or coke. It is a mixture of combustible and non-combustible gases used in various industrial and power applications.

Composition:
Contains carbon monoxide (CO) and hydrogen (H₂) as the main combustible components, along with nitrogen (N₂) and carbon dioxide (CO₂).

Calorific Value:
About 5,000 to 6,000 kJ/m³, which is relatively low.

Uses in Power Plants:
Producer gas is used as a fuel in gas engines or small boilers for steam generation. It is preferred where coal is easily available but liquid fuels are costly.

Advantages:

  • Inexpensive to produce.
  • Can be generated near the point of use.
  • Reduces dependency on petroleum fuels.

Disadvantages:

  • Low heat value compared to other gaseous fuels.
  • Contains impurities like tar and dust.
  • Requires cleaning before use in turbines.
  1. Water Gas

Water gas is a synthetic gaseous fuel produced by passing steam over red-hot coke or coal. It is sometimes known as blue gas because it burns with a blue flame.

Chemical Reaction:

Composition:
It consists mainly of carbon monoxide (CO) and hydrogen (H₂).

Calorific Value:
About 11,000 to 12,000 kJ/m³.

Uses in Power Plants:
Water gas is used as a fuel in boilers, furnaces, and gas engines for electricity generation. It can also be converted into synthetic natural gas (SNG) for large power plants.

Advantages:

  • Produces a clean, blue flame.
  • Can be produced using cheap raw materials like coke.
  • Burns efficiently when mixed with air.

Disadvantages:

  • Contains poisonous carbon monoxide.
  • Has a lower calorific value than natural gas.
  1. Blast Furnace Gas

Blast furnace gas is a by-product gas obtained from iron and steel manufacturing industries. It is formed during the reduction of iron ore in a blast furnace when hot air reacts with coke.

Composition:
Contains carbon monoxide (CO), carbon dioxide (CO₂), nitrogen (N₂), and small amounts of hydrogen (H₂).

Calorific Value:
About 3,000 to 4,000 kJ/m³, which is quite low compared to other gaseous fuels.

Uses in Power Plants:
Blast furnace gas is often used in captive power plants located within steel plants to generate electricity. It is burned in boilers or gas turbines after cleaning.

Advantages:

  • Utilizes waste gas from steel plants, reducing fuel costs.
  • Environmentally beneficial as it reduces waste emissions.

Disadvantages:

  • Low calorific value, so large volumes are required.
  • Contains impurities that require cleaning before use.

Advantages of Using Gaseous Fuels in Power Plants

  1. High Efficiency:
    • Gaseous fuels burn completely, resulting in high thermal efficiency.
  2. Clean Combustion:
    • Produce very little smoke, soot, or ash.
  3. Easy Control:
    • Flame intensity and temperature can be easily regulated.
  4. Quick Start-Up:
    • Ideal for plants that need fast starting and stopping operations.
  5. Environmentally Friendly:
    • Emit fewer pollutants compared to solid and liquid fuels.

Disadvantages of Gaseous Fuels

  1. Storage Difficulty:
    • Require high-pressure cylinders or tanks for storage.
  2. High Cost:
    • More expensive than coal or solid fuels.
  3. Explosion Risk:
    • Gases are highly flammable and can cause accidents if not handled properly.
  4. Limited Availability:
    • Dependence on natural gas fields or costly gasification systems.
Conclusion

The gaseous fuels used in power plants include natural gas, coal gas, producer gas, water gas, and blast furnace gas. These fuels are either naturally occurring or artificially manufactured and are widely used for generating electricity in thermal and gas turbine plants. They provide several advantages such as clean combustion, high efficiency, and easy control, making them suitable for modern, environmentally friendly power systems. Although gaseous fuels are costlier and require careful handling, their efficient and clean-burning nature makes them an essential energy source for sustainable power generation.