Cogeneration or combined heat and power is the utilization of a heat engine for generating both heats as well as electricity simultaneously. In general, thermal power stations, as well as heat engines, do not change the existing energy into electrical energy. Most of the engines waste half of the main energy due to surplus heat. By capturing the surplus heat, combined heat and power utilizes heat that would be wasted in a standard power station, potentially attaining a total efficiency ranges from 80 to 95%. contrasted by at most 40% for the standard power plants. This means that a low fuel to be utilized for producing the equal quantity of required energy. Because there is a high capacity in energy efficiency, CHP is considered to be the main provider to weather change improvement as presenting reasonable as well as consistency benefits on the supply of energy.
Principle of Cogeneration :
Definition of Cogeneration
The term Cogeneration is defined as sequential generation or the combination of two energies forms of useful energy from a single primary energy source used for the generation of electrical energy and well as heat.
● This is an most efficient method of energy utilization in which 40% energy savings when we compared by the separate acquire of electricity from the national grid as well as a gas boiler. Combine Heat and Power plants are normally situated near to the consumer endso the transportations and distribution losses will be reduced thus it improve performance in the electricity transmission and distribution.
● For power consumers where the safety of supply is a significant factor for their power selection manufacture apparatus and gas is plentiful. The cogeneration systems based on gas are preferably suited as captive power plants.
Need of Cogeneration :
In India the maximum percentage of electricity is obtained from steam or thermal power plants. The conventional power plant, efficiency is only 35% and 65% of remaining energy is lost. The large amount of heat is rejected and lost to surrounding water or air due to some restriction of conversion process and thermo- dynamic cycles employed in power generation. Also 10 to 15% of losses are due to the transmission and distribution of electricity in the electrical grid. Hence it is necessary to reduce the loss and reduces the manufacturing price and enhances output. The plant efficiency can be progressed. It helps to conserve utilization of water as well as the cost of water. This is used to reduce an air emission of specific material like mercury, sulphur dioxide, carbon dioxide, otherwise, it would lead to the greenhouse effect. These systems are inexpensive when we contrasted to the usual power station.
Components of Cogeneration unit:
The fundamental components of a combined heat and power system include the following:
1. Prime Mover is an engine used to couple with generator to run.
2. Fuel supply System.
3. The Generator is used to generate electricity from the power distribution system into the building's.
4. Heat Recovery System is used to pick up utilizable heat from L.C. engine or locomotive.
5. Cooling System for dissipating heat which is rejected from the locomotive that cannot be improved.
6. Combustion & Ventilation Air Systems for supplying clean air and to carry waste gases left from the engine.
7. Control System is used for maintaining secure & proficient operation.
8. The Enclosure is used for achieving the protection for the engine as well as machinists, and also for reducing noise.
Opportunities
The small-scale sector occupies a position of prominence in the Indian economy, contributing to more than 50% of the industrial production in value addition terms. In India's present liberalized economy, the survival and growth of small-scale industry largely depends on its ability to innovate, improve operational efficiency and increase productivity
The following Areas/Actions are critical for obtaining best results from cogeneration :
1. Improving technical and operating efficiency of the existing plant
2. Replacing inefficient machinery with new energy efficient equipment.
3. Adopting various means of energy conservation.
4. Optimal design and effective implementation of cogeneration projects.
Potential Cogenerators
Many sectors of industry have very good potential for cogeneration. Industrial units in following sectors can take advantage :
a. Sugar
b. Paper
c. Oil Extraction
d. Rice Milling
e. Chemical Fertilizers
f. Textiles-Cotton & Synthetic
g. Food Processing
h. Rubber Industries
i. Metallurgical Industries
j. Urban Waste Treatment
k. Pharmaceuticals
l. Hotels
m. Distilleries
Cogeneration in a pharmaceutical industry, India
Normally, bulk drug manufacturers have a boiler in their plant to generate low-pressure steam for drying the powders. The boiler used to be very small, as the steam required, ranged from 3 to 1 bar. The problem which kept this industry continuous power, to prevent outages, which would lead to wastage of costly material. Then a large pressure-boiler was selected and utilised the reduction in steam pressure from 43 to 3 bar to generate power for the plant in a straight back-pressure turbine, which at the same time provided the required steam for the various processes. This can saves the diesel costs, the diesel generator being relegated to standby for additional or emergency power in the event of turbine loss.
Textile Industry
● It is currently one of the largest and most important sectors India is 2 in global textile manufacturing and also 2 in silk and cotton production.
● Cogeneration has a wide opportunities in this industry. In this way cogeneration technology can be applied in other industries also.
Types of Cogeneration Power Plants :
Basically, the types of cogeneration power plants are classified based on the operating scheme adapted process and the sequence of energy utilization. Therefore, the types of cogeneration systems are a topping cycle and a bottoming cycle.
Topping Cycle :
● Topping cycle plants primarily produce electricity from a steam turbine. Partly expanded steam is then condensed in a heating condenser at a temperature level that is suitable. e.g. district heating or water desalination.
● In this type of power plant, if the fuel supplied is used first for produce power then, afterward in the production or generation of thermal energy. Which is the byproduct of the cycle and used to satisfy process heat or other thermal requirement.
● This type of cogeneration is the most popular as well as the widely used cogeneration system. A topping cycle power plants are basically classified into four types.
a) Combined Cycle CHP Plant:
A combined cycle CHP plant mainly comprises of a diesel engine otherwise a gas turbine which generates clectrical power or mechanical power tracked through a heat improvement system which is useful in generating steam as well as drives a resultant steam turbine.
b) Steam Turbine CHP Plant :
● The two types of steam turbines most widely used are the backpressure and the extraction.
● Steam turbine CHP plant is used to generate electrical power and process vapor through burning coal for generating high force vapor, which is afterward agreed by a steam turbine for generating the required power, and then the exhaust vapor is used as low force procedure steam to heat up water intended for a variety of purposes.
● The power generation efficiency of the demand for electricity is greater than one MW up to a few hundreds of MW. Due to the system inertia, their operation is not suitable for sites with intermittent energy demand.
c) Internal Combustion Engine:
● An internal Combustion Engine CHP plant includes a cover of exhaust jacket cooling system water is flowing through a heat recovery system and exhaust gas at high temperature for producing vapor otherwise hot water for gap heating.
● These cogeneration systems have high power generation efficiencies in comparison with other prime movers.
● The heat recovery can be quite efficient for smaller systems, these systems are more popular with smaller energy consuming facilities.
● The initial machines investment cost is low, but operating and maintenance costs are high due to high fuel wear and tear respectively.
● technology, significant reduction in installation cons and better environmental performance,
● Biofuel engine CHP plants use an adapted reciprocating gas engine or diesel engine, depending upon which biofuel is being used, and are otherwise very similar in design to a Gas engine CHP plant.
● The advantage of using a biofuel is one of reduced hydrocarbon fuel consumption and thus reduced carbon emissions.
● These plants are generally manufactured as fully packaged units that can be installed within a plant room or external plant compound with simple connections to the site's electrical distribution and heating systems.
● Another variant is the wood gasifier CHP plant whereby a wood pellet or wood chip biofuel is gasified in a zero oxygen high temperature environment, the resulting gas is then used to power the gas engine.
d) Gas Turbine :
● Gas turbine cogeneration has probably experienced the most rapid development in the recent years due to the greater availability of natural gas, rapid progress in the technology, significant reduction in installation cons and better environmental performance.
● In this gas turbine CHP plant, a normal gas turbine in used to drive a generator for electricity generation.
● The turbine exhaust is supplied using a heat recovery boiler for generating process heat and steam.
● The highest electricity generation efficiency can be reached now a days by combination of gas turbine with steam cycle. This means that Rankine cycle is heated by exhaust gas of turbine. If the heat output is less than that required by the set, it is possible to have supplementary natural gas firing by mixing additional fuel to the oxygen-rich exhaust Sasha boost the thermal output more efficiently, Steam generated from the exhaust gas of the gas turbine is passed through a hack pressure or extraction-condensing steam turbine to generate additional power. The exhaust or the extracted team from the steam turbine provides the required thermal energy.
Bottoming Cycle System :
Bottoming cycle plants produce high temperature heat for industrial processes, then a waste heat recovery boiler feeds an electrical plant. In this plant the main fuel is utilized for generating thermal energy at a high-temperature. The heat discarded in this method is then utilized for generating power using a recovery boiler and a turbine generator. These days, this type of plants is extensively used in the process of manufacturing that needs heat at high-temperatures in boilers, as well as refuses heat at very high temperature. Although they are used in industries like cement, steel, ceramic, petrochemical, gas, etc. Bottoming cycle plants are not frequent & not applicable for topping cycle plants.
Parameters for Cogeneration :
1. Heat-to-Power Ratio:
● The heat-to-power ratio of a facility should match with the characteristics of the cogeneration system to be installed and heat-to-power ratios of the different cogeneration systems.
● It is defined as the ratio of thermal energy to electricity required by the energy consuming facility. It expressed in different units such as, kJ/kWh,1b./hr/kW,etc., here it is presented on the basis of the same energy unit (kW). In large cogeneration plant use additional boost firing of the exhaust gases in order to modify the heat : power ratio of the system to match site loads.2. Quality of heat Energy:
The heat quality temperature and pressure required also determines the type of cogeneration system. Heat energy for a cement plant requiring at about 1450°C, a bottoming cycle cogeneration system can meet both high quality thermal or heat energy and electricity demands of the plant.
3. Availability of Fuels :
The easily available of cheap fuels or waste heat products are most dependent factor for cogeneration The fuels used at a site is one of the major factors in the technical consideration because it determines the competitiveness of the cogeneration system.
4. A grid-dependency:
A grid-dependentor known as a "stand-alone" system has access to the grid to buy or sell electricity and meet all the energy demands of the site. The technical configuration of the cogeneration system designed as a grid dependent system would be different from that of a stand-alone system
5. Retrofittings
Most of the cogeneration plant is installed as a retrofitting so as to improve existing energy conversion systems, such as boilers, can still be used.
Advantages of Cogeneration :
1. Cogeneration helps to improve the efficiency of the plant.
3. It reduces cost of production and improve productivity.
4. Cogeneration system helps to save water consumption and water costs.
5. Cogeneration system is more economical as compared to conventional power plant.
7. Large cost saving, thus additional competitiveness for industrial and commercial user and affordable heat for domestic user.
8. Improve local and general security of supply to reduce the risk for consumer to run out of electricity and/or heating
9. It reduces fuel need reduce import dependancy.
10. Provide an opportunity to increase the generation plant diversity and competition.
11. An opportunity to move towards more decentralization forms of electricity generation with a plant design to meet need of local consumer, providing with high efficiency, avoiding transmission losses and increasing flexibility in system use.
