User:MPelletier516/sandbox

From Wikipedia, the free encyclopedia
Jump to: navigation, search

Electron beam processing is being researched as a replacement for existing pollution control equipment in active industrial process streams.

Air Pollution Control[edit]

Electron Beam Processing of Pollutants[edit]

Electron beam processing can be used to destroy pollutants, or volatile organic compounds (VOCs), in air streams. Toluene and xylene are the two most abundantly used VOCs, so most research has been focused on these two compounds. This application offers advantages over existing technologies, such as thermal oxidation, catalytic oxidation, condensation, absorption, and adsorption. Companies currently use these methods because the Environmental Protection Agency (EPA) requires that they remove VOCs from industrial exhaust with 95% efficiency. [10] These industries can include petroleum refinery, chemical manufacturing, solvent use, [11] and reagent use. [12] Although existing technologies operate with acceptable efficiencies by EPA regulations, they all have disadvantages:

  • Secondary pollutant creation, i.e. greenhouse gases.
  • Equipment cost
  • Equipment maintenance. [10]

Because of the above disadvantages, researchers have investigated electron beam processing as an air pollution control alternative. This emerging technology is promising because it is a clean process; the breakdown of the pollutants accounts for all of the exhaust. This occurs because the operation of the electron beams only creates free radicals: highly reactive molecules with unpaired electrons. These radicals, specifically the hydroxyl radical, are used to break down the pollutants in the air. [10] Since they also have a very short lifetime, unused radicals will revert back to their original form, i.e. water, oxygen, etc.

Electron beams alone are acceptably efficient by EPA regulations when treating a low concentration (below 100 parts per million) of pollutants. Even stable compounds, such as benzene, are destroyed by electron beams. [11] These compounds, when fully broken down, form either carbon dioxide or carbon monoxide and water.

Hybrid Pollution Abatement System[edit]

The use of electron emitters alone has disadvantages when VOCs are present in high concentrations (well above 100 parts per million). The pollutants are removed with less efficiency, and compounds other than carbon dioxide, carbon monoxide, and water are formed. These other compounds are often equally or more harmful to human and environmental health than the original VOC itself. For example, toluene, if not reacted fully, will form benzene, a known carcinogen.

To address these disadvantages, researchers investigated metallic catalyst use. [13,14] Platinum and palladium can increase destruction efficiency of toluene by over 30%, while manganese increases it by over 20%. [13,14] Experimental data supports that these increases are independent of VOC concentration and catalyst weight percentage. [14]

Platinum, palladium, and manganese are expensive metals, so researchers investigated manganese oxide use. This cheaper catalyst improves the destruction efficiency of toluene by over 30% as well. [12]

Catalyst use has secondary benefits, as it helps to fully break down the VOCs. Carbon dioxide also becomes a more favorable product (by at least 10%) over carbon monoxide. In the case of toluene, polymerization will not occur . [12,14]

Flue Gas Treatment[edit]

Fossil fuel combustion creates many environmentally harmful products, such as sulfur dioxide and nitrogen dioxide. Electron beam processing can be used to destroy these compounds from exhaust streams. With an initial use of ammonia, sulfur dioxide can be removed with up to 98% efficiency and a combination of all oxides of nitrogen by 80%. [15] Electron beam treatment of flue gas is different from the treatment of almost all other VOCs because sulfur dioxide reacts optimally with radiation at 65°C. [15] A VOC removal process would require different parameters for flue gas treatment than for VOC treatment.

The Institute of Nuclear Chemistry and Technology in Warsaw, Poland is home to the majority of the research being performed on flue gas treatment. [15]

Implementation[edit]

The first air pollution abatement system has not yet been implemented. Most research has been performed with high voltage electron accelerators, which are classified as having a voltage that exceeds 300kV. [11] An electron produces x-rays when it collides with a metal. These x-rays are lethal within seconds of exposure, so they require a concrete wall surrounding the accelerator. The equipment is also very large at this scale.

Researchers have also used low voltage electron emitters, which are classified as falling under 300kV, with implementation in mind. [11] Instead of a concrete wall, low voltage electron emitters require lead or stainless steel shielding. Typically, high voltage accelerators are held in a room with concrete walls, whereas the shielding for low voltage emitters typically consists of a box that surrounds the emitters. The emitters themselves are small and easy to move.

Electron emitters alone have a market for treating low concentrations of VOCs and flue gases. The addition of a catalyst extends this market to treating high concentrations of pollutants. The correct combination of emitter use and catalyst is yet to be determined.

Costs[edit]

A pollution abatement system is comprised of the electron emitter, high voltage cables, a control system, x-ray/radiation shielding, and other minor utilities, such as cooling water and gas. These coolants are required because the emitter foil, which acts as the window for electrons to pass through, heats up when a high current is run through it. The water and gas lower the temperature of this foil and increase the life of the emitter.

Electron emitters have a low operational cost. If a system treats 300 cubic feet per minute of polluted air, it is estimated to operate at $5.50 per hour at the current US power rates. [12] These operational costs are significantly lower than those of the existing technologies, and shows that the main costs of a pollution abatement system are the initial acquisition and installation costs.

Electron emitters also have a long lifetime (in the thousands of hours), and are easy to replace. Therefore, minimal maintenance is required on an air pollution abatement system.

Notes[edit]

10. G. R. Parmar and N. N. Rao, “Emerging Control Technologies for Volatile Organic Compounds,” Critical Reviews in Environmental Science and Technology, vol. 39, pp. 41-78, Jan. 2009.
11. J. Kim et al., “Combined Radiolytic and Catalytic Oxidizing Method to Remove Toluene in Gas Phase,” Radiation Physics and Chemistry, vol. 79, pp. 797-802, Jul. 2010.
12. T. Hakoda et al., “An Electron-Beam Irradiation/Catalytic Oxidation System for Purification of Aromatic Hydrocarbons/Air Mixture under Practical Gas-Flow Condition,” Industrial and Engineering Chemistry Research, vol. 49, pp. 5517-5522, Jun. 2010.
13. E. Jeon et al., “Novel Hybrid Technology for VOC Control using an Electron Beam and Catalyst,” Research on Chemical Intermediates, vol. 34, pp. 863-870, Oct. 2008.
14. J. Kim et al., “Combined Radiolytic and Catalytic Oxidizing Method to Remove Toluene in Gas Phase,” Radiation Physics and Chemistry, vol. 79, pp. 797-802, Jul. 2010.
15. A. G. Chmielewski, A. Ostapczuk, and J. Licki, “Electron Beam Technology for Multipollutant Emissions Control from Heavy Fuel Oil-Fired Boiler,” Journal of the Air and Waste Management Association, vol. 60, pp. 932-938, Aug. 2010.