- Cogeneration Definition: Cogeneration, or combined heat and power (CHP), is defined as a system that produces both electricity and heat from a single fuel source.
- High Efficiency: Cogeneration plants are highly efficient, with efficiency rates of 80-90%, compared to the 35% efficiency of conventional power plants.
- Environmental Benefits: Cogeneration reduces emissions of pollutants and greenhouse gases, helping to combat climate change.
- Economic Advantages: These systems lower production costs, improve productivity, and save on water consumption and costs.
- Types of Cogeneration Plants: There are two main types of cogeneration plants—topping cycle and bottoming cycle—each with different methods for generating electricity and heat.
Cogeneration, also known as ombined heat and power (CHP), works on the concept of producing two different forms of energy from one fuel source. These forms are typically thermal energy (heat) and either electrical or mechanical energy.
Cogeneration is an optimal, reliable, clean, and efficient way to use fuel. The fuel can be natural gas, oil, diesel, propane, wood, or coal. The basic principle is simple: fuel generates electricity, which then produces heat. This heat is used to boil water for steam, space heating, or even cooling buildings.
In a conventional power plant, the fuel is burnt in a boiler, which in turn produces high pressure steam. This high pressure steam is used to drive a tribune, which is in turn is connected to an alternator and hence drive an alternator to produce electric energy.
The exhaust steam in a conventional power plant is sent to a condenser, where it cools down, turns back into water, and returns to the boiler to produce more electricity. These plants are only 35% efficient. In a cogeneration plant, low-pressure steam from the turbine is not condensed into water but is used for heating or cooling buildings and factories, utilizing its high thermal energy.
Cogeneration plants are highly efficient, achieving around 80-90% efficiency. In India, the potential power generation from cogeneration plants exceeds 20,000 MW. The first commercial cogeneration plant was built by Thomas Edison in New York in 1882.
As shown in above diagram, in traditional power plant, when we gave fuel as input we get electrical energy and losses as output but in case of cogeneration with fuel as input, the output is electrical energy, heat or thermal energy and losses.
In a conventional power plant, only 45% of the energy input is used, and 55% is wasted. In contrast, cogeneration uses 80% of the energy, wasting only 20%. This makes cogeneration more efficient, optimizing fuel use, and more economical.
Need for Cogeneration
- Cogeneration helps to improve the efficiency of the plant.
- Cogeneration reduce air emissions of particulate matter, nitrous oxides, sulphur dioxide, mercury and carbon dioxide which would otherwise leads to greenhouse effect.
- It reduces cost of production and improve productivity.
- Cogeneration system helps to save water consumption and water costs.
- Cogeneration system is more economical as compared to conventional power plant.
Types of Cogeneration Power Plants
In a typical Combined heat and power plant system there is a steam or gas turbine which take steam and drives an alternator. A waste heat exchanger is also installed in cogeneration plant, which recovers the excess heat or exhaust gas from the electric generator to in turn generate steam or hot water.
There are basically two types of cogeneration power plants, such as-
- Topping cycle power plant
- Bottoming cycle power plant
Topping Cycle Power Plant
In this type of Combine Heat and Power plant electricity is generated first and then waste or exhaust steam is used to heating water or building. There are basically four types of topping cycles.
- Combined-cycle topping CHP plant- In this type of plant the fuel is firstly burnt in a steam boiler. The steam so produced in a boiler is used to drive turbine and hence synchronous generator which in turn produces electrical energy. The exhaust from this turbine can be either used to provide usable heat, or can be send to a heat recovery system to generate steam, which maybe further used to drive a secondary steam turbine.
- Steam-turbine topping CHP Plant- In this the fuel is burned to produce steam, which generates power. The exhaust steam is then used as low-pressure process steam to heat water for various purposes.
- Water turbine topping CHP Plant- In this type of CHP plant a jacket of cooling water is run through a heat recovery system to generate steam or hot water for space heating.
- Gas turbine topping CHP plant- In This topping plant a natural gas fired turbine is used to drives a synchronous generator to produce electricity. The exhaust gas is sent to a heat recovery boiler where it is used to convert water into steam, or to make usable heat for heating purposes.
Bottoming Cycle Power Plant
As its name indicate bottoming cycle is exactly opposite of topping cycle. In this type of CHP plant the excess heat from a manufacturing process is used to generate steam, and this steam is used for generating electrical energy. In this type of cycle no extra fuel is required to produce electricity, as fuel is already burnt in production process.
Configuration of Cogeneration Plant
- Gas turbine Combine heat power plants which uses the waste heat in the flue gas emerging out of gas turbines.
- Steam turbine Combine heat power plants that use the heating system as the jet steam condenser for the steam turbine.
- Molten-carbonate fuel cells have a hot exhaust, very suitable for heating.
- Combined cycle power plants adapted for Combine Heat and Power.
