Incineration2- MSW Combustion
II.   Design - typically turn key approach; design, construct, turn over the key
  1. Three T’s temperature, turbulence, time (Fig 9-31 pg. )
  2. Refuse receipt and storage
    1. Scales
    2. Sufficient length of road to entrance to avoid backup
    3. Tipping area enclosed to prevent nuisance conditions
    4. Tipping area large enough to permit more the 1 truck to maneuver
    5. Storage for 2-3 days (also seasonal variations) so that continuous incinerator operation is possible
  3. Refuse feeding
    1. Batch feeding bad, variation in furnace T due to air leakage lead to incomplete combustion
    2. Small plants use rams to push into furnace
    3. Large plants use traveling bridge cranes to transfer from pit to charging hopper (1.5-8 cy bucket)
    4. Charging hopper with steep slope fuel fed into furnace by ram, grate, or screw
  4. Grate system - most crucial
    1. Transport refuse through furnace, promote combustion by adequate agitation and mixing with air, excessive turbulence leads to excessive carryover of particulates
    2. 75-100 tons/sf/hr or 250-300,000 BTU/sf/hr
    3. Types = traveling grate ( no longer used), rocking grate, reciprocating grate, rotary kiln, other proprietary grates (Fig 13-4)
  5. Underfire Air - combustion achieved by injection of combustion air below grates, provided by fans, also cools grates = 40 to 100% of total air, too low air inhibit combustion leads to high grate T, slagging which blocks grate and air - clinkers
  6. Overfire Air - injection above grate, complete combustion of flue gases and part, promotes turbulence, supplied by forced air blower or induced draft or both. Particularly important for temperature control where energy recovery not provided. Above air injection line parallel to grate plane, also first pass of secondary combustion chamber
  7. Furnace volume - primary (above grates ) and secondary combustion chamber (few seconds sufficient to retain gases in high T zone for max. fuel volatilization. to ensure complete combustion)
  8. Supplementary Fuel - T control, if heat content of fuel insufficient
  9. Refractory Lined furnace - no heat recovery, greater excess air requirements to control terms, conductive heating ( heat transfer by progressive heating of adjacent elements - pot on a stove - 100-200% EA required
  10. Waterwall units, in furnace (mass fired) - most common, primary combustion chamber fabricated from closely spaced steel tube with waster recirculation, 50-100% EA required for cooling (radiation chamber - heat transfer between 2 bodies not in dirrect physical contact and at diff T, water and burning fuel)
  11. Boilers - heat recovery, water converted to steam, water flows countercurrent to gas flow
    1. Economizers - heat boiler feedwater by extracting gases as they leave convective section
    2. Convection tube - heat transfer from hot gases moving past tubes) boiler tubes perpendicular to flow of gas as exits incinerator, sat. steam produced
    3. Super heater - tubular section upstream of convective section hot inc. gases superheat steam generated at convective tube

 
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