Incineration4  MSW Combustion
IV.   Problem Solving
  1. Air is more than just oxygen. It is nitrogen, oxygen, water vapor, carbon dioxide, and other trace gases.
  2. Air Composition
    1. Nitrogen - 78.08%
    2. Oxygen - 20.94%
    3. Argon - 0.93%
    4. Carbon Dioxide and other trace gases - 0.04%
    5. Water Vapor - 1 to 4 %
  3. The important point is that air is about 21% oxygen
  4. Type I Problem - calculation of air requirements and flue gas composition
    1. First, determine the amount of oxygen required to combust a known mass of waste (or fuel) into its combustion end products
      1. C + O2 ® CO2
      2. 2H2 + O2 ® 2H2O
      3. S + O2 ® SO2 (SOx)
      4. N2 ® N2 (NOx also)
    2. Convert the amount of oxygen calculated above into the amount of air required knowing that air is approximately 21% oxygen. This is the 0% Excess Air (EA) condition.
      1. 50% EA is 1.5 times the 0% EA
      2. 100% EA is 2 times the 0% EA
    3. Determine the waste (or fuel) feed rate.
    4. Based on the values calculated in the two steps above, calculate the air feed rate for any of the EA conditions.
    5. The flue gas composition is simply the combustion products plus that portion of the feed air that is not changed (i.e. - all non-oxygen components and oxygen in excess of that required for combustion)
  5. Type II Problem - calculation of flue gas temperature
    1. To do this problem, you need to know
      1. The flue gas composition
      2. The energy content of the incoming waste (or fuel)
      3. The energy conversion efficiency
      4. The enthalpy of the flue gases at various temperatures.
    2. Calculate the anticipated energy content of the flue gas. This is the energy content of the incoming waste (or fuel) times the energy conversion efficiency.
    3. Calculate the energy content of the flue gas at various temperatures. This calculation is based on the flue gas composition and the gas enthalpy at a specific temperature.
    4. By interpolation determine at what temperature the calculation from 3 above is equal to the value calculated in 2 above.
  6. Type III Problem - total system analysis
    1. Incorporates concepts from Type I and Type II problems as well as overall system behavior.
    2. Heat (energy) losses are attributed to various process, interactions, and components of system (heating of water, radiant losses, energy recovery, heating of ash, etc.)
    3. Composition of flue gas is a function of not only the design stoichiometry and air supplied. It is also effected by the incomplete combustion of the waste.

 
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