Coal Burning Power Plants

The production of electricity through the combustion of coal is one of the oldest and cheapest methods to produce electricity. Coal supplies are plentiful and will be available to produce electricity for hundreds of years. While conventional supplies of oil and natural gas are expected to run out in the near future. This has cause a growth in nuclear power. Through out this report one will also learn the disadvantages and advantages to coal burning power plant and how they operate.

Coal has played a major role in electricity production ever since the first power plants were built in the world in the 1880's. The earliest power plant used hand feed wood or coal to heat boiler and produce steam. This steam was used in reciprocation steam engines which turned generators to produce electricity. In the 1920's Pulverized-coal firing was developed which brought advantages that included higher combustion temperatures, improved thermal efficiency, and a lower requirement for excess air for combustion. In the 1940's the cyclone furnace was developed which allowed the combustion of poorer grade coal with less ash production and greater overall efficiency. Improvements in efficiency have continued to occur throughout the years. But overall, electricity production from coal is based on the same methods started over 100 years ago, but the improvements in all areas have brought coal power to be the inexpensive power source used so widely today( Electricity from coal).

Coal Burning Power Plants 3

There are three predominate methods of burning coal to make steam, power turbine, and generate electricity. Most coal power plants either burn pulverized coal blown into a boiler or use cyclone furnaces to burn coal in a vortex of air. The current trend for new coal power plant is to use fluidized bed combustion which has a number of advantages over the other methods (Electricity from coal).

In the Pulverized coal system the coal burning has been pulverized into a fine powder stem, it will burn almost as easily and efficiently as a gas. The feeding rate of coal is according to boiler demand and the amount of air available for drying and transporting the pulverized coal fuel is controlled by computers. Pieces of coal are crushed between balls or cylindrical rollers that move between two tracks or "races". The raw coal is then fed into the pulverizer along with air heated to about 650 degrees F from the boiler. As the coal gets crushed by the rolling action, the hot air dries it and blows the usable fine powder out to be used as fuel. The powdered coal from the pulverizer is directly blown to a burner in the boiler. The burner mixes the powder coal in the air suspension with additional pre-heated combustion air and forces it out of a nozzle. Under operating conditions, there is enough heat in the combustion one to ignite all the incoming fuel (Coal Fired).

Coal Burning Power Plant 4

The Cyclone furnaces were developed after pulverized coal systems and require less processing of the coal fuel. The crushed coal feed is either stored temporarily in bins or transported directly to the cyclone furnace. The furnace is basically a large cylinder jacketed with water pipes that absorb the some of the heated to make steam and protect the burner itself from melting down. A high powered fan blows the heated air and chucks of coal into one end of the cylinder. At the same time additional heated combustion air is injected along the curved surface of the cylinder causing the coal and air mixture to swirl in a centrifugal "cyclone" motion. The whirling of the air and coal enhances the burning properties producing high heat densities and high combustion temperatures. The hot combustion gases leave the other end of the cylinder and enter the boiler to heat the water filled pipes and produce steam. Some slag remains on the walls insulating the burners and directing the heat into the boiler while the rest drains through a trench in the bottom to a collection tank. This ability to collect ash is the biggest advantage to the cyclone furnace burning process. Only 40% of the ash leaves with the exhaust gases compared with 80% for pulverized coal burning. But on the other hand Pulverized coal burning produces less nitrogen oxide pollutants than the Cyclone furnaces (Coal fired).

Both the pulverized coal and cyclone furnaces emphasized maximizing coal and air interaction in the combustion chamber in order to maximize combustion efficiency.

Coal Burning Power Plants 5

The fluidized bed combustors continue this trend, and at the same time attempt to vastly decrease the combustion pollutants of coal. In the Fluidized bed combustion, crushed coal between Ð'ј' and Ð'Ñ*' in size is injected into a bed above a grate-like air distributor. Air is injected upward through the grate lifting and suspending the solid particles. The bed continues to expand allowing a greater air flow rate until an equilibrium position is reached. At this point the particles can move freely, and the bed behaves like fluid. "Bubbles" of air moving upward through the relatively dense "fluid" of particles serve to rapidly mix materials added to the bed and transfer heat rapidly from one part of the bed to another. About half of the heat generated is transferred to in-bed tubes and the hat gases leaving the bed pass through other tubes. Some unburned carbon particles and ash escape with the gases, but they are recaptured in a grit arrestor of cyclone separator and reinject it into the bed to improve combustion efficiency (Coal Fired).

There are several advantages fluidized bed combustion has over other combustion techniques. When limestone is added directly to the fluidized bed it effectively absorbs sulfur dioxide, a major pollutant from sulfur deposits in the coal. Fluidized bed combustors operate at relatively low temperatures resulting in lower emission of nitrogen oxides and less ash fouling of heat transfer surfaces.

Coal Burning Power Plants 6

Coal plants using fluidized beds are more economical to construct as they don't require expensive pulverization equipment or scrubbers to control sulfur dioxide emission, and they are typically much more compact than conventional plant as the fluidized bed is much more efficient in transferring heat than conventional boilers (Electricity from coal).

Now how does coal burning impact our environment? Coal mining causes severe erosion, resulting in the leaching of toxic chemicals into