ITP Metal Casting: Advanced Melting Technologies: Energy Saving ...

3.3 Melting Process Emissions
Emissions formed as a result of the melting process are a concern in improving melting
technology. Emissions are primarily generated from two sources during the melting process:
• Emissions related to energy supply
• Emissions related to preparing, refining and treating
Energy supply emissions are the result of combustion either at the melting facility or at the plant
generating the electric power used in melting. Preparing, refining and metal treating also result in
emissions that are related to the raw materials brought into the process.
Sixty percent of the metal casting industry’s energy requirements is supplied by natural gas and
27% from electricity. The remainder includes other fuel sources such as coke and breeze. 11
Natural gas is the cleanest burning of all the fossil fuels. Composed primarily of methane, the
main products of the combustion of natural gas are carbon dioxide (CO2) and water vapor.
Emissions of nitrogen oxides (NOx), sulfur dioxide (SO2) and particles from natural gas
combustion are one to three orders of magnitude lower than that for coal and fuel oil, as shown
in Exhibit 7.
Emissions
(pounds per billion Btu of energy input)
Natural Gas Oil Coal
Carbon Dioxide 117,000 164,000 208,000
Carbon Monoxide 40 33 208
Nitrogen Oxides 92 448 457
Sulfur Dioxide 1 1,122 2,591
Particulates 7 94 2,744
Mercury 0 0.007 0.016
Source: EIA - Natural Gas Issues and Trends 1998
Exhibit 7: Fossil fuel emission levels
Melting systems that use electricity do not produce onsite emissions related to the actual heating
of materials. However, significant offsite emissions are produced in the generation and
transmission of electricity. These offsite emissions are directly related to the fuels used to
produce electricity. The major fuels for electric power generation are coal, producing about 51%
of the electricity in the United States; nuclear, producing 20%; and natural gas, producing 6%.
The low efficiency of electricity generation and transmission is also an important factor to
consider in energy and emission analyses. It requires about 10,600 Btu of fuel to produce 1 kWh
(3,412 Btu) of electricity. When coke is used as a fuel and a carbon source in melting furnaces
(e.g., for iron and steel melting), emissions consist mainly of CO2 and CO from incomplete
combustion and to a lesser extent, NOx and SOx.
Emissions related to preparing, refining, and treating are generated in varying amounts
depending on the degree of processing that must be accomplished. These emissions result from
the dirt, moisture, and metallic impurities in the metal charge; erosion and corrosion products
from the metal’s contact with the refractory; and the addition of alloying elements and treatment
chemicals used for removal of impurities and dissolved gases.
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