Rain Technology Seminar Report Pdf Download
Acid Rain Can Be Prevented Without Compromising Industral Ouput Created By: Eric Yezdimer, Tim O'Donnell, Darren Engers, Mike Fevola, and Tom O'Conner.
Sources & Chemistry of Acid Rain
Existing and Future Solutions
Although the combustion of fossil fuels is necessary to provide the power that drives our society and industries, it also presents the issue of acid rain. Acid rain is one of the severest consequences that our society faces due to engaging in heavy industry. Industrial processes relying on fossil fuels for power have led to an increase in acid rain due to greater emissions of gases such as sulfur dioxides (SOx) and nitrogen oxides (NOx). In the atmosphere these gases react with water to form acids which cause a downward shift in the pH of the atmospheric water. This water eventually condenses and falls to the ground as acid rain, where it has profound effects on the environment and its inhabitants.
The technology exists for the prevention of acid rain with respect to industrial emissions, yet there is a strong debate over whether the implementation of such technology is beneficial to the industrial entities. Evidence indicates that employing various techniques to eliminate acid rain can ultimately benefit industry and society.
The main anthropogenic source of SO2 released into the atmosphere is from coal combustion. NOx is a product of combustion reactions such as those in internal combustion engines. The pie graph below (from a recent EPA report) shows the percentage breakdown of emission sources for both SO2 and NOx.
A common misconception about SO2 emissions is that cars and transportion are the primary sources. It is important to note that over 93% of all sulfur dioxide emissions are industral based (with only 3.7% transport based). However, cars and other forms of transportion (trucks, airplanes, boats, etc.) are responsible for large amounts of NOx being released into the atmosphere ( creating smog and ozone pollution ). While some of their effects are similar, the large scale release of these two componds represent two different major enviornmental problems and should not be confused.
After SO2 and NO2 are released into the atmosphere they are not particularuly acidic or soluble in H2O. However they are converted to H2SO4 and HNO3 in the atmosphere (using cloud condensation nuclei as catalases1) which are both acidic and soluble in H2O. The process by which this occurs is :
(1)
(2)
the hydroperoxyl radical then produces more hydroxyl radicals via the reaction :
The sulfuric acid produced in equation (2) is then released from the atmosphere in rain water. A simlar process occurs to produce HNO3 and rid it from the atmosphere. The lifetime of SO2 is only a few days and as a result rainfall containing high amounts of H2SO4 only occurs a few hundred miles from the source of emission. This effect can be seen in a recent pH map of the United States where the lowest pH readings are centered around the NorthEast (the country's industral backbone). Another important fact pertaining to this map is that rainfall is naturally acidic. Carbon dioxide found in the atmosphere is dissolved into the water droplets existing in clouds and effectly lowers the pH of rain to about 5.7 log units. Despite carbon dioxide's role in lowering the pH of rainfall, large increases in the amounts of carbon dioxide found in the atmosphere are not expected to cause a large decrease in the pH of rainfall. ( For instance, a doubling in CO2 concerntrations results in only about a 0.2 unit decrese in pH)1.
The SO2 released be power plants can by reduced by appoximately 90% through the use of a scrubber or more offically known as flue gas desulfuriztion. This is achieved through the use of calcium carbonate.
The final product of this process is a slurry of CaSO4 and CaSO3 which can either be buried in a landfill or recycled back to CaCO3 and reused.
Considerable reductions of SO2 emissions are possible using existing techonologies.
In order to reduce the effects of acid rain, the EPA has recently initiated an Acid Rain Program aimed at "significantly reducing electric utilties emissions of sulfur dioxide and nitrogen oxides". The Clean Air Act's primary goal is reduction of annual SO2 emissions by 10 million tons below 1980 levels (0.9 million tons). Legislation introduced by the EPA calls for a "two-phase tightening of the restrictions placed on fossil fuel-fired power plants." Meeting the new emission restrictions has forced companies to use existing techonoloies to reduce the level of emissions. A large number of emission reducing processes are availiable such as wet and dry flue gas desulfuriztion , dry acid gas scrubbing systems for solid waste incineration , electrostatic precipitators and fabric filters and are currently being empolyed by companies like General Electric.
The effectiveness of these processes can be easily seen by the almost 50% reduction of the total national amount of sulfer dioxide released from the 1980 emission level (about 40% below the EPA allowable emissions for 1995).
Despite the large decrease in SO2 emissions by 1995, the annual heat input from utilities remained constant (even increasing in some states) as can be shown by examining figures2 2 and 3. This shows that current techonolgies are able to cause significant reduction of sulfur dioxide emissions without having an addverse effect on industral output.
figure 2 
The EPA has devised an Allowance Trading Plan to help ease the cost of installing clean air systems. Each year the allowable amount of emissions are are divided into credits and given to companies where the emissions of each company is not to exceed thier number of credits. Companies are allowed to sell their credits as they chose. By selling there credits to a larger company, smaller companies are able to afford the costs of installation. The volume of allowance trading shows that more and more companies are taking advantage of the EPA's system and are updating their plants. Since the second phase of the EPA's plan will increase the number of units involed from about 450 to 2000, this is a positive indicator that the future goals (for the year 2000) will be able to be met.
There have been some companies that have taken advantage of the cleaning of the waste produced by coal-powered electric plants. The Tennessee Valley Authority's Cumberland Power plant is one such example. During the production of power, the sulfur gases produced are sent through electrostatic precipitators, which remove the fly ash, and then continue through the flue gas desulfurization scrubbers where the gas is sprayed with a scubber slurry that absorbs the SO2. This SO2 laden acidic liquid is then neutralized by the addition of crushed limestone which results in calcium sulfite. With a heavy blast of air, the material is oxidized and forms calcium sulfate- more commonly known as "gypsum." This Plant produced over a million tons of gypsum annually.
In the past, this product was shipped off to a disposal site where it was buried at a cost to the company and could possibly harm the environment. At the Cumberland Plant, they have signed several contracts with other companies, SYNMAT and Temple Inland, for the purchase of the high quality gypsum. These companies would then use the gypsum to produce wallboard, cement additives, and for use in loosening soil for agricultural purposes. The wallboard plant was built next to the power plant to minimize hauling distances (reduce pollution from transport vehicles). Not only does this process make more jobs available, but it also reduces environmental pollutants while generating another source of income for the company. Still other companies such as ReUse use the collected sulfer to make soil feritzlers. This will pay for the extra costs involved with the installation of the advanced technologies.
New techonologies are being developed to create more efficeint filtering systems. Companies are developing methods using activated coke/carbon to help reduce toxic gas emissions (claims a 98% sulfur removal rate). Other researchers3 report that vast improvements in the reaction rate of calcuim with SO2 are possible by reducing the diameter of the calcium particles used in scubbers (thus increase their effectivness).
NOx gasses have had recent solutions discovered. Ballard Power systems has designed a fuel cell that runs on external fuel. This process converts hydrogen and oxygen into water and produces electricity. (diagram) The only drawback to implementing this system is the cost. The fuel cells cost roughly ten times the amount of the internal combustion engine, running the price from near $3000 to $30,000. The fuel cells are hoped to be in cars within the next decade.
2 1995 EPA report on Acid Rain Emissons.
3 Masayoshi Sadakata, Takashi Shinbo, Azuchi Harano, Hiroshi Yamamoto and Hi Jun Kim. J.Chem.Eng.Jpn. V27 1994. p550-552. 4 EPA's Acid Rain Progrom Web Site (link include above).
5 General Electric Environmental Systems Web Site (link include above).
6 Reuse Web Site (link include above).
Source: http://udel.edu/chem/C465/senior/fall97/acid_rain/senior.html
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