Page 530 - Materials Chemistry, Second Edition

CAT3525_C15.qxd 1/27/2005 12:40 PM Page 501
Incineration of Hazardous Wastes 501
baghouses. The removal of acid gases is accomplished using technologies identical to those for
MSW incinerators (see Chapter 9). For example, wet scrubbers and packed-tower absorbers are
highly effective for the condensation and removal of HCl and SO .
x
Most hazardous waste incinerator facilities employ one of three possible schemes for overall air
pollution control:

● Venturi scrubber (for particulates) followed by a packed tower absorber (for gases)
● Ionizing wet scrubber (for particulates) combined with a packed tower absorber (for
gases)
● Dry scrubber (for particulates) followed by a baghouse or an electrostatic precipitator
(for particulates).

EXAMPLE 15.4
A hazardous waste incinerator is operating for the destruction of a mixed nonchlorinated solvent
waste. The flue gas is passed through a lime (CaO) slurry in a dry scrubber where acid gases are
partially neutralized and the gases cooled. The gases then pass through a baghouse for particulate
removal and are released via the flue.
The flue gas contains 410 kg/h of SO and 325 kg/h of HCl. The dry scrubber lime feed rate is
2
1.2 stoichiometric rate, and it is 75% efficient in removing SO and 88% efficient in HCl
2
removal.
1. Calculate the lime feed rate in kg/h.
2. Determine how many kg/h of SO and HCl will remain in the flue gas following the dry
2
scrubbing process.
Assume that CO in the flue gas does not react with the lime.
2
CaO SO → CaSO 3
2
CaO 2HCl → CaCl H O
2
2
(MWs: CaO 56; SO 64; HCl 36.5)
2
SOLUTION
410 kg/h per 64 kg/mol 6.4 mol/h SO in flue gas
2
325 lb/h per 36.5 kg/mol 6.71 mol/h HCl in flue gas
SO requires 6.4 mol/h CaO 1.2 7.68 mol/h
2
HCl requires 6.71 mol/h CaO 1.2 8.05 mol/h
Total CaO required 15.73 mol/h

1. Total lime usage 15.7 mol/h 56 kg/mol 879.2 kg/h
2. 0.25 410 kg/h 103 kg/h SO in flue gas
2
0.12 245 kg/h 29 kg/h HCl in flue gas
Note. Further treatment of this flue gas to remove additional acid gases is warranted.

REFERENCES

Brunner, C.D., Hazardous Waste Incineration, McGraw-Hill, Inc., New York, NY, 1993.
Brunner, C.D., Incineration Systems: Selection and Design, Incinerator Consultants, Inc., Reston, VA, 1988.