A combination of legislation and technology has helped clean up many of the world’s coal-burning plants. Both developed and developing countries have adopted increasingly stringent environmental regulations to govern emissions from coal-fired power plants. In the United States, all coal-fired power plants built after 1978 must be equipped with postcombustion cleanup devices to capture pollutants before they escape into the atmosphere. Cyclones, baghouses, and electrostatic precipitators filter out nearly 99% of the particulates. Flue gas scrubbers use a slurry of crushed limestone and water to absorb sulfur oxides from flue gas. The limestone reacts with the sulfur dioxide to form calcium sulfate, which may be used to produce wallboard. Staged combustion and low-NOx burners are used to burn coal to minimize NOx formation. Another strategy, selective catalytic reduction, reacts ammonia with NOx over a catalyst to produce nonpolluting nitrogen and water vapor.
Conventional coal-fired power plants capture pollutants from the flue gas after it leaves the boiler. Circulating fluidized bed (CFB) combustors capture most of the pollutants before they leave the furnace. Crushed coal particles and limestone circulate inside the CFB combustor, suspended by an upward flow of hot air. Sulfur oxides released during combustion are absorbed by the limestone, forming calcium sulfate, which drops to the bottom of the boiler. The CFB combustor operates at a lower temperature (14001F) compared to pulverized coal (PC) boilers (27001F), which also helps reduce the formation of NO x .
Precombustion coal cleaning is another strategy to reduce sulfur emissions by cleaning the coal before it arrives at the power plant. Sulfur in coal is present as pyrite (FeS2 ), which is physically bound to the coal as tiny mineral inclusions, and as ‘‘organic sulfur,’’ which is chemically bound to the carbon and other atoms in coal. Pyrite is removed in a coal preparation plant, where coal is crushed into particles less than 2 inches in size and is washed in a variety of devices that perform gravity-based separations. Clean coal floats to the surface, whereas pyrite and other mineral impurities sink. Additional cleaning may be performed with flotation cells, which separate coal dust from its impurities based on differences in surface properties. Precombustion removal of organic sulfur can be accomplished only by chemical cleaning. So far, coal combustion emissions and chemical cleaning has proved to be too costly, thus flue gas scrubbers are often required to achieve near-complete removal of sulfur pollutants.
The tightening of environmental regulations is likely to continue throughout the world. In the United States, for example, by December 2008, it is anticipated that coal-fired power plants will have to comply with maximum emission levels for mercury. Emissions of mercury and other trace metals, such as selenium, are under increasing scrutiny of coal combustion emissions because of suspected adverse effects on public health.
Coal is sometimes combusted with waste material as a combined waste reduction/electricity production strategy. The disposal of waste from agriculture and forestry (biomass), municipalities, and hospitals becomes costly when landfill space is limited. Some wastes, particularly biomass feedstock, are combustible, but their low energy density (compared with coal) limits their use as an electricity production fuel. Blending coal with these fuels provides an economical method to produce electric power, reduce waste, and decrease coal plant emissions. Most wood wastes, compared to coal, contain less fuel nitrogen and burn at lower temperatures. These characteristics lead to lower NO x formation. In addition, wood contains minimal sulfur ( o 0.1% by weight) and thus reduces the load on scrubbers and decreases scrubber waste biomass.
Numerous electric utilities have demonstrated that 1–8% of woody drying biomass can be blended with coal with no operational problems. Higher blends may also be used, but require burner and feed intake modifications as well as a separate feed system for the waste fuel. Cofiring in fluidized bed boilers may avoid some of these drawbacks, but the economics of co-firing are not yet sufficiently attractive to make it a widespread practice.
Biodegradable materials are considered those materials that can be destroyed by microorganisms. To prevent the accumulation of non-biodegradable compounds in nature, there are two solutions that are currently under investigation: use roots or microbial strains that can attack thought products were not degradable, biodegradable materials or develop common strains. (more…)
Do we have the resources? Rudolf Diesel developed the diesel engine which ran on biodiesel vegetable oil in the late 1800s. At the time, he speculated that his discovery seemed insignificant, but later could prove to be as important as mankind’s uncovering of future energy uses for petroleum and coal tar. Given the U.S.’ rapid expansion into biofuels, it would appear his vision was correct due to the drawbacks of biofuels. But widespread adoption of biomass-based fuels is not a foregone conclusion. Two questions haunt its progress. First, will it truly reduce U.S. reliance on fossil fuels? And second, is there enough farmland to accommodate widespread production, without jeopardizing food supplies? (more…)
Climate change caused by the enhanced greenhouse effect is one of the most significant global environmental issues. Increased emissions of GHG to the atmosphere, most notably CO2 , are considered the main cause of global climate change. Increasing energy consumption, a reliance on fossil fuels to meet these needs, and deforestation related to land use change are the main sources of increasing atmospheric CO2. (more…)
It is of interest to examine potential sources of greenhouse gases sources or atmospheric CO2 by analysis of the global distribution of carbon in all its forms. Atmospheric carbon, which can be assumed to be essentially all in the form of CO2 (i.e., 700 Gt carbon equals 2570 Gt of CO2) comprises only about 1.6% of total global carbon, excluding lithospheric carbon. Obvious greenhouse gases sources of direct or indirect additions of CO2 to the atmosphere are therefore fossil fuel deposits, since portions of them are combusted each year as fuels, and terrestrial biomass. (more…)
Over the last decade, the number of countries researching the potential of biomass and bioenergy for energy services rose rapidly. This contributed to the biomass as solid and liquid fuels, an interesting and promising option among renewable energy sources available. This includes solid waste and biomass, which comprises of charcoal, firewood, energy crops and forestry and agricultural residues to produce heat and electricity, (more…)
One of the main benefits from future use of biofuels would be the reduction of greenhouse gases compared to the use of fossil fuels. Carbon dioxide, a greenhouse gas that contributes to global warming, is released into the air from combustion. Twenty-four percent of worldwide energy-related carbon emissions in 1997 were from the United States. Carbon and due to rising energy consumption, are expected to increase 1.3 percent per year through 2015. (more…)
Advances in biomass feedstock production are extremely important. These advances have the potential for reducing the final cost of biofuels, power, and products. In addition, advances will allow the production of plants, trees, and residues with characteristics increasingly well suited for feedstocks. For example, genetically engineered plants feedstocks may allow higher yields of usable biomass per acre for fuel and other uses. New methods in erosion control, fertilization, and pre-processing can result in (more…)
Clean Development Mechanism or CDM in short, is an extension of Kyoto Protocol mechanism which objective is for encouraging transfer of technology from industrialized countries to developing countries. At first it is only in technology perspective, then it extend to transfer investments as well. It is expected that developed countries would invest projects to reduce gas emissions in developing countries. As a return, they get credits in Certified Emission Reductions —CER credits— which inline with emission restriction target and compliance with Kyoto Protocol standard to limit gas emission. (more…)
Geothermal energy is energy created by the heat of the Earth. Under the Earth’s crust lies a layer of thick, hot rock with occasional pockets of water. This water sometimes seeps up to the surface in the form of hot springs. Even where the water does not travel naturally to the Earth’s surface, it is sometimes possible to reach it by drilling. This hot water can be used as a virtually free source of renewable energy, either directly as hot water, steam, or heat or as a means of generating power. Geothermal energy as renewable energy is nonpolluting, inexpensive, and in most cases the sources is renewable. (more…)
