Cogeneration and Energy Conservation Interview Questions and Answers:

1. What do you mean by word ‘cogeneration’ ?

Ans. Cogeneration is sequential of energy contained in fuel into two or more usable forms. In one manifestation coal is burnt in the boiler to generate steam. The steam so gener­ated provides heat for manufacturing process in addition to generation of electrical energy. In another manifestation gas is used in gas turbine to generate electricity. The re­maining heat is utilized in generating steam in a heat re­covery boiler. This steam may be used for generation of additional electricity or as process steam for manufactur­ing process.

2. What is topping cycle and why is it suitable for cogeneration ?

Ans. In a topping cycle, the fuel energy is used to generate steam at high temperature and at high pressure and electrical energy is generated in the usual manner. Depending upon the requirement, the process steam at low temperature and pressure is either extracted from the turbine at an intermediate stage (similar to feed water heating) or taken at the turbine exhaust. Generally, the steam required for industrial processes is at low temperature whereas high temperature steam is required for generation of electrical energy, only the topping cycle, therefore, is suitable for cogeneration. Also, the overall efficiency of topping cycle is about 75% while the combined efficiency of two separate systems (for generating electrical energy and steam) is about 55%.

3. What is bottoming cycle ? Why is bottoming cycle of little thermodynamic or economic interest ?

Ans. In a bottoming cycle, the steam produced in a boiler at high temperature and pressure is directly used for manufacturing process and the reject heat is used for generation of electrical energy. The bottoming cycle is of little thermodynamic or economic interest because its combined efficiency is less than that for separate generation of process steam and electricity.

4. Which type of industries are most suitable for cogeneration ?

Ans. Energy intensive industries are suitable for cogeneration. The industries which need both electricity and steam for their manufacturing processes are most suitable for cogeneration. Such industries are paper mills, textile mills, sugar mills and refineries, chemical works, breweries, plastic manufacturing, food processing, laundries and hotels etc.

5. List benefits of cogeneration.

Ans. Benefits of cogeneration are :

  • Fuel economy
  • Lower capital cost
  • Smaller gestation period and
  • Saving to industry from power cuts and power supply interruption.

6. What are the cogeneration technologies ?

Ans. The cogeneration technologies are steam turbine system, gas turbine system, combined cycle system and diesel engine system. In addition fluidized bed combustion, MHD, fuel cells and some other conversion systems are under development.

7. What is energy conservation ?

Ans. Energy conservation refers to the methods of reduction in energy consumption by way of elimination of wastage and promotion of efficiency. The energy consumption can be reduced by adopting various ways of energy conservation which includes efficient use of technologies and avoiding energy wastages. Energy conservation is the key to hold off climate change/global warming, as one unit of electricity saved is equal to 3 or 4 units of electricity generated.