Experiment8.pdf

Experiment # 8 Objective: Theoretical study cogeneration steam power plant.

Apparatus:

Fig: 8.1 (cogeneration steam power plant)

Theory: What is Cogeneration? Cogeneration is the utilization of 2 forms of energy from 1 source for example hot water/heat and electricity from one gen-set. According to Cogeneration Technologies, the world's first commercial power plant. Thomas Edison's Pearl Street Station built in 1882 - was a cogeneration plant as it made and distributed both electricity and thermal energy, thus the concept has been around for many years, and with the recent interest in greener energy technologies it is currently becoming more popular. It is also called combined heat and power.

Cogeneration power plants: CHP is the use of a heat engine or power station to generate electricity and useful heat at the same time. The terms cogeneration can be also applied to the power systems generating simultaneously electricity, heat, and industrial chemicals. Cogeneration is a more efficient use of fuel because otherwise wasted heat from electricity generation is put to some productive use. Combined heat and power (CHP) plants recover otherwise wasted thermal energy for heating. This is also called combined heat and power district heating. Small CHP plants are an example of decentralized energy. By-product heat at moderate temperatures (100–180 °C, 212–356 °F) can also be used in absorption refrigerators for cooling. The supply of high-temperature heat first drives a gas or steam turbine-powered generator. The resulting low-temperature waste heat is then used for water or space heating. At smaller scales (typically below 1 MW) a gas engine or diesel engine may be used.

Type of CHP: The actual efficiency of a CHP plant depends on how well it supplies the heat it produces. Since the heat is generally carried as hot water, the efficiency is greatest when the power plant is closest to the buildings it's serving. Common CHP plant types are: 1. 2. 3. 4. 5.

Gas turbine Biofuel engine Steam turbine Combined cycle Nuclear power plants

How does CHP work? A conventional power plant makes electricity by a fairly inefficient process. A fossil fuel such as oil, coal, or natural gas is burned in a giant furnace to release heat energy. The heat is used to boil water and make steam, the steam drives a turbine, the turbine drives a generator, and the generator makes electricity. The trouble with this is that energy is wasted in every step of the process-sometimes quite spectacularly. For example, the water that's boiled into steam to drive the steam turbines has to be cooled back down using giant cooling towers in the open air, wasting huge amounts of energymuch of which literally disappears into thin air! Now a fuel-driven power plant has to work by heating and cooling-that's what the laws of physics say-but surely we don't have to waste quite so much energy in the process? Instead of letting heat escape uselessly up cooling towers, why not simply pipe it as hot water to homes and offices instead? That's essentially the idea behind CHP: to capture the heat that would normally be wasted in electricity generation and supply it to local buildings as well. Where a conventional power plant makes electricity and wastes the heat it makes as a byproduct, a CHP power plant makes both electricity and hot water and supplies both to consumers. Cogeneration

(the alternative name for CHP) simply means that the electricity and heat are made at the same time.

How does Micro CHP work? 1. Fuel (coal, natural gas, oil, or biomass) is added at one end. 2. The engine (roughly the same size as a four-cylinder car engine) burns the fuel by ordinary combustion. 3. An electricity generator is connected to and driven by the engine's driveshaft. 4. Something like 15kW of electricity is produced, which can be used for conventional power or as an emergency supply. 5. Exhaust gases from the engine flow through one or more heat exchangers, which remove most of their waste heat. 6. A catalytic converter (similar to the one in a car) removes some of the pollution from the gases. 7. The (relatively clean) exhaust emerges through a tailpipe or chimney. 8. Cold water flowing into the heat exchanger picks up heat from the exhaust gas and exits at a much higher temperature. If it's hot enough, it can be piped directly into radiators or fed into a conventional central-heating boiler for further heating. A unit like this will produce about 40kW of thermal energy (heat).

Fig: 8.2 (Micro CHP)

Advantages and Disadvantages of CHP: The efficiency advantages of CHP speak for themselves, but there are environmental benefits too. Every tone of fossil fuel we avoid burning stops carbon dioxide from entering the atmosphere and reduces, just a little bit, the problem of global warming. Burning fewer fossil fuels also reduces air

pollution and related problems such as water pollution and acid rain. Replacing huge power plants with more CHP plants that are much smaller makes us less dependent on the centralized energy network and, in theory, major system failures and outages (blackouts). Just like conventional power plants, CHP plants can run off virtually any fuel, from oil, gas, and oil to methane gas produced in landfill sites or power made by burning trash in municipal incinerators. CHP has few obvious disadvantages. One problem is that the technology is currently more expensive and complex, so building CHP plants typically requires greater initial investment. Energy savings eventually pay back the investment, but more money still has to be spent upfront to begin with. Maintenance costs can also be greater for CHP. Another problem is that smallerscale CHP plants produce electricity more expensively than larger-scale ones. Much more seriously, fossil-fueled CHP plants reinforce our dependency on the very fuels we should be trying to eliminate (though it is possible to run them on greener fuels such as biomass). And some critics argue that CHP is overhyped and less efficient than alternative technologies such as heat pumps, which could be a far better way to tackle climate change.