The Government has taken several steps to modernize and improve the efficiency of coal based thermal power plants and to reduce the pollution level of coal based thermal power plants in the vicinity of these plants.
Points to Remember:
Environmental impacts of coal power: air pollution
- Coal plants are the nation’s top source of carbon dioxide (CO2) emissions, the primary cause of global warming.
- Burning coal is also a leading cause of smog, acid rain, and toxic air pollution. Some emissions can be significantly reduced with readily available pollution controls
- Sulfur dioxide (SO2)
- Nitrogen oxides (NOx)
- Particulate matter
- When fossil fuels are burned, nitric oxide and nitrogen dioxide are produced. These pollutants initiate reactions which result in the production of ozone and acid rain. The nitrous oxides (NOx) come from two sources: high-temperature combustion (thermal NOx) and nitrogen bound to the fuel (fuel NOx). For clean-burning fuels like natural gas, fuel NOxgeneration is insignificant.
- In most cases, NOx levels are reduced by lowering flame temperature. This can be accomplished by modifying the burner to create a larger (and therefore lower temperature) flame, injecting water or steam into the flame, recirculating flue gases, or limiting the excess air in the combustion process. In many cases a combination of these approaches is used. In general, reducing the flame temperature will reduce the overall efficiency of the boiler. However, recirculating flue gases and controlling the air-fuel mixture can improve boiler efficiency, so that a combination of techniques may improve total boiler efficiency.
- Natural-gas fired burners with lowered NOx emissions are available for commercial and residential heating applications. One commercial/residential boiler has a burner with inserts above the individual burners; this design reduces NOx emissions by 30%. The boiler also has a “wet base” heat exchanger to capture more of the burner heat and reduce heat loss to flooring.
- NOx production is of special concern in industrial high-temperature processes because thermal NOx production increases with temperature. These processes include metal processing, glass manufacturing, pulp and paper mills and cement kilns. Although natural gas is the cleanest-burning fossil fuel, natural gas can produce NOx emissions as high as 500 ppm or more.
- A burner developed by MIT and and the Gas Research Institute combines staged introduction combustion air, flue gas recirculation and integral reburning to control NOx emissions. These improvements in burner design result in a low-temperature, fuel-rich primary zone, followed by a low-temperature, lean secondary zone; these low temperatures result in lower NOxformation. In addition, any NOx emission present in the recirculated flue gas is reburned, further reducing emissions. A jet pump recirculates a large volume of flue gas to the burner; this reduces NOxemissions and improves heat transfer.
- The low-NOx burner used for commercial and residential space heating is larger in size than conventional burners, although it is designed for ease of installation.
- An electrostatic precipitator (ESP) is a filtration device that removes fine particles, like dust and smoke, from a flowing gas using the force of an induced electrostatic charge minimally impeding the flow of gases through the unit.
- In contrast to wet scrubbers which apply energy directly to the flowing fluid medium, an ESP applies energy only to the particulate matter being collected and therefore is very efficient in its consumption of energy (in the form of electricity)