Introduction
Currently, coal-fired power plants account for more than 80% of carbon dioxide emissions in the electric power industry of the United States and 33% of all the carbon dioxide emissions in the United States. Consequently, reducing carbon dioxide emissions that come from the coal plants is the focus of most proposals that intend to cut on the greenhouse gas emission. The options to do this include capturing and sequestering carbon dioxide that emitted by the coal power plants, replacing the coal power plants with the low or zero carbon dioxide sources of power like the nuclear and wind energy.
Another option is the replacement of coal power with growing use of the natural gas power plants. However, the natural gas power generation process is not a zero carbon dioxide fuel, but the natural gas power fixed with modern technology of generation release less carbon dioxide per megawatt-hour as compared to the coal power plants. The increase in the natural gas reserves, mostly from the formation of shale has further raised the interest in the natural gas power generation as comparatively low carbon dioxide option. This paper will explain how carbon dioxide emitted by power generating plants contributes to pollution. It will then compare the carbon dioxide released by the coal fired power plants to natural gas powered power plants in the United States.
Carbon dioxide (CO2)
Carbon dioxide was identified by a Scottish physician and chemist, Joseph Black in the 1750s. Carbon dioxide is an odourless, colourless gas that is non-flammable and faintly acidic at room temperatures i.e. 20 to 35 oC. Carbon dioxide is a molecule that has a molecular formula of CO2. Carbon dioxide mostly exists in the gaseous form even though it also exists in the liquid and solid forms. It is only in solid form when the temperatures are below negative 78 oC. Carbon dioxide exists in liquid form when it is dissolved in water. It is soluble in water only under pressure and reduction in pressure, the gas escapes in the air in form of bubbles.
Carbon dioxide is mainly found in the air. Human beings use carbon dioxide in different ways with the most popular being its use in the beer and soft drinks which helps in making them fizzy. It is used in some of the fire extinguisher because it is denser than air and as such it can blanket fire due to its heaviness. It puts off fire by preventing oxygen that is required to sustain burning from going to the fire. It is also used in supercritical fluid extraction a technology for decaffeinating coffee. Dry Ice, the solid form of carbon dioxide is used in the theatres to form stage fogs.
The amount of carbon dioxide that is released into the atmosphere due to human activities has been increasing extensively in the past 150 years. Consequently, it has gone above the amounts sequestered in the biomass, in the oceans and in other sinks. There has been a rise of about 90 ppm concentration of carbon dioxide in the atmosphere since the year 1850 and this is mainly attributed to human activities before and after the industrial revolution that began in the year 1850. Currently, the major cause of increase in carbon dioxide concentrations in the air is the burning of fossil fuels, production of cement, forest combustion and land clearing.
Results from Sources Reviewed
Carbon dioxide pollution and global warming
In the recent months, carbon dioxide has been the center stage in environmental arena. In August 2003, United States Administration went on to reverse the decision of previous administration of 1998 that had categorized carbon dioxide to be a pollutant and also made it a subject to Clean Air Act provisions. Due to this reversal, power plants and the automobile manufacturers have been able to evade expensive modifications that were required in the 1998 ruling.
Environment groups in the year 2006 made efforts to push for the legislation that would be helpful in reinstating carbon dioxide to be pollutant. EPA in August 2006 then concluded that because Clean Air Act did not authorize the regulation so as to address climate change, carbon dioxide is therefore not a pollutant. The reasons that were given not to classify carbon dioxide as a pollutant have basis on the fact that CO2 is a natural constituent of the atmosphere and is required by the plants to carry out photosynthesis.
It could not be argued that carbon dioxide is an important constituent of the atmosphere just that it would not argued that Vitamin D is important in the diet of human beings even though excess amounts of it can be very toxic. Ecosystems require that there be a maintained balance between compounds and/or elements so as the system can function without any hitches. When a substance or an element exists in excess and consequently threatens the function ability of the ecosystem, it is toxic and as such it can be considered as a pollutant in spite of the fact that the substance or element is needed in small portions.
Scientists suggest that the ocean warming taking place is part of the causes of the increased carbon dioxide and not vice versa. This has its basis on the fact that there is a lot of carbon dioxide trapped in the oceans and when there is temperature increase, the carbon dioxide is released to the atmosphere because the solubility of gases reduces with the rise in temperature. The carbon dioxide then decreased in the oceans and increases in the atmosphere.
Fossil fuels
Fossil fuel is a major source of carbon dioxide. The carbon dioxide that is found in the fossil fuels had been deposited on the ground in over a million years ago. Because organisms did not completely decay, the carbon dioxide was not released in the atmosphere and was instead stored in the earth. When the fossil fuel is recovered, processed and then burned, the carbon dioxide that would have been naturally released in tens of millions years is all of a sudden released in a few hundred years consequently increasing the amount of carbon dioxide to the environment.
There is still resistance to the idea that the increase in carbon dioxide results from burning of the fossil fuel and is responsible for the global warming. The power plants in the United States have little pressure to reduce the emissions of carbon dioxide with notion that “burning fossil fuel benefits the environment” and that “ world is flat”. The European power plants however, were forced to reduce carbon dioxide emissions considerably by the year 2008 and even further between the 2009 and 2012 as it is demanded by the Kyoto Protocol.
Sources of carbon dioxide in the atmosphere
It is with not doubt that the main human activity responsible for largest portion of carbon dioxide is combustion of fossil fuels which include natural gas and coal. The main sources of carbon dioxide emissions in the United States are explained below.
Electricity
In the United States, electricity is a major source of energy that is used in powering homes, businesses and industries. Combustion of coal and natural gases for the generation of electricity constitutes the largest source of carbon dioxide emissions and accounts for more than 40% of the total carbon dioxide emission and 33% of the total green house emissions in the United States in the year 2009. Depending on the type of fossil fuel that is used in the generation of electricity, different amounts of carbon dioxide will be emitted. For the production of a certain amount of electricity, the combustion of coal produces more carbon dioxide than natural gas.
Transportation
The second largest cause of carbon dioxide emissions to the atmosphere comes from the combustion of such fossil fuels like diesel and gasoline that is used in the transportation of people and goods. It accounted for 31% of the total carbon dioxide emissions and about 26% of the total green house gas emissions in the United States in 2010. The category includes sources of transportation such as air travel, highway vehicles, rail and marine transportation.
Industries
Combustion of fossil fuels takes place in most of the industrial processes leading to the emission of carbon dioxide. Some process also emit carbon dioxide through chemical reactions which do not actually involve combustion such as the consumption and production of mineral products like cement, production of metals like steel and iron and also production of some chemicals. In 2010, industrial processes accounted for 14% of the total carbon dioxide emissions and a total of 20% of the green house gas emission in the United States.
Carbon dioxide emission in the atmosphere in the United States went up by almost 12% in the years 1990 to 2010. Because combustion of fossil fuels constitute the biggest portion of the green house gas in the U.S. , changing from fossil fuel combustion has been a dominant factor that is affecting the emission trends in the United States. The aspect of changing from the combustion of fossil fuels for energy is influenced by very many factors that include growth of the population, changes in the prices of energy, economic growth, new technologies, seasonal temperatures and the changing behavior.
Between the years 1990 and 2010, increase in the emissions of carbon dioxide corresponded to the increase in energy consumption by the rising population and economy, even though the economic downturn that started in the year 2008 affected the decrease in the carbon dioxide emissions that were experienced in 2009.
Coal fired power plants
Coal driven power plants are the number one source of carbon dioxide emission in the country and the main cause of global warming. In the year 2011, coal plants emitted an approximate of 1.7 billion tons of carbon dioxide. Every year, a typical coal plant emits about 3.5 million tons of carbon dioxide. Combustion of coal is main cause of the acidic rains, smog and the toxic air pollutions. These emissions would be significantly reduced by use of pollution controls, however most of coal power plants have not been fixed with the required technologies.
Most people think that coal as means of energy has been abandoned and that the American countries have changed to cleaner and safer sources of energy. Contrary to this, coal powered energy plants contribute about half of the electricity in America which is far more than the other sources of power and the use of coal has almost tripled from the year 1960. The use of coal in America will continue to increase if the power industry is successful in its proposition to construct the many power plants. Those who propose these constructions claim that coal is a cheaper means of obtaining electricity energy.
The evolution of technology has the potential to significantly reduce the contribution of coal to the global warming with the ability to capture the carbon dioxide emissions before they can be emitted into the atmosphere. The technology could be a very important achievement in the fight against global warming, however it remains to be known whether the technology will be able to work at the commercial scales and how much it will cost.
Almost every coal power plant in operation today uses the technology of pulverized coal which involves grinding coal, burning the coal to produce steam and then running the steam into turbines so as to generate electricity. There is a newer technology referred to as the integrated gasification combined cycle that first converts the coal into gas and then the gas run into the combustion turbines to produce electricity. The technology uses excess heat produced by the process for the generation of some additional electricity.
This technology is however more expensive than the pulverized coal technology even though it has its environmental advantages. Currently, there is no available commercial control technology that can used in the coal power plants to reduce the carbon dioxide emissions similar to the manner in which the filters and scrubbers capture particulate and sulfur emission respectively. Other than the effect of air pollution, carbon dioxide from coal is causing irreparable damages to the health of people and environment all over the world.
The coal industry does not pay for the damages it causes but the world is. It cannot be doubted that the world has technically renewable energy that is accessible to meet the current demands of energy. The world really needs to replace the dirty energy sources such as coal. Regrettably, the governments all over the world have continued to allow the industry to spend many billions of dollars in the construction coal fired power plant and also plan for more in the future. The governments have been seduced by a delusion of clean coal where the industry has come up with technological fixes which claim to make combustion of coal safe to the environment. If these coal power plants are built, carbon dioxide emission from coal is expected to increase by 60% by the year 2030. Any international agreements meant to tackle the climate changes will be undermined as an effect.
Natural gas power plants
Natural gas is a form fossil fuel that is formed when the layers of buried animals and plants are exposed to pressure and intense heat in thousands of years. Energy that the animals and plants had originally gotten from the sun gets stored in form of carbon a natural gas. The natural gas is the combusted so as to generate electricity and this enables the energy stored to be converted into power that can be used. Natural gas is a resource that is nonrenewable and cannot also be replenished on the time frame of humans.
The power production process of natural gas starts with extraction on the natural gas, goes to treatment and transportation to power plants and then ends at the combustion stage which takes place in boilers and turbines where electricity is generated. To start with, wells are actually drilled into the earth so as to get the natural gas. Pipelines are used for the transportation of the natural gas to the power plants from the gas plants. The power plants utilize several method to transform the natural gas to electricity. A more common approach is whereby the gas is burned in the combustion turbine but also the gas can be burned in a boiler to produce steam that is used to drive steam turbines that generate electricity.
Synthesis
Another common technology that has gained popularity is where the natural gas is burned in combustion turbines and the hot combustion exhaust is used to make steam that drives the steam turbines. This technology referred to as combined cycle has been able to achieve high efficiencies through use of same fuel source in about two times.
At the natural gas power plants, burning of the natural gas causes emission of carbon dioxide and nitrogen oxides even though they are in lower quantities as compared to combustion of coal. Methane is the major component of the natural gas and as such, greenhouse gases are emitted to the atmosphere if the natural gas is not completely burned. This methane can also be emitted into the atmosphere due to losses and leaks at the time of transportation.
Conclusion
The average rates of emission from the natural gas-powered plants in the United States are 1136 lbs per ever MWh of carbon dioxide. As compared to the average emissions into the air that come from the coal-powered generation plants, the natural gas powered plants produce half the carbon dioxide produced from coal. However, the process of extraction, transport and treatment of natural gas to power plants causes some additional emissions.
The emissions caused by natural gas are about 40% below the emission by coal. This is clear indication that substituting the natural gas for coal in the economy can help in reducing emission from power plants. This has been evidenced by United Kingdom where the use of natural gas has been growing significantly in the last 30 years. The total use of fossil energy in the United Kingdom has been very stable over the period while the carbon dioxide emissions have decreased by almost 20%.
In the United States, the use of natural gas could offer the economy an energy path which would be helpful in both underpinning growth and delivering reduction in emissions. More importantly, natural gas is affordable given the low particulate and sulfur emissions as it does not need heavy policy interventions. They outcomes may be delivered especially in the
United States due to retirement of the old coal plants combined with the economic pressures of having an indigenous, abundant and even cleaner source of energy supply.
Natural gas however is very much associated to with high rates of leakage of methane which then offsets the advantage of carbon dioxide emissions. The combustion of coal also causes at least some sulfur emissions which consequently acts as a coolant in stratosphere offsetting part of the global warming that is connected to carbon dioxide emissions caused by coal driven power plants.
Even though there are massive global plans to replace coal with the natural gas in the next 30 years, this will still not get far to the 2050s, before the limit for carbon in the atmosphere is exceeded. Natural gas can gain some more valuable years even though it will later need an alternative. This then indicates that there is future requirement for the CCS (Carbon capture and storage) and also a greater push on the nuclear power and renewable energy. However these technologies have their own issues that are related to public acceptance, costs, technical suitability and capacity for the grid management.
This comes down to the question of balancing targets on emissions, costs and meeting the ever growing energy demands. In the short term, the natural gas can be able to balance these factors than coal can. The targets on emission can be met on lower costs and also satisfying the demand for energy and as the use of natural gas rises in comparison to coal, the benefit of lower carbon dioxide emissions into the atmosphere is achieved. As head to a world that really needs deep cuts on emissions, natural gas power plants that have CCS can offer low emission source of energy that can be able to compete the renewable and nuclear sources.
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