Destruction and Removal Efficiency (DRE):

Destruction and removal efficiency is defined as

DRE = (W_in - W_out)/W_in ´ 100

Where W_in = mass feed rate of a particular POHC

W_in = mass emission rate of a particular POHC

Example 3.9: A mixture described below is being incinerated at 2000 °F with 50% excess air and a residence time of 2.1 seconds. The flow rate from the incinerator is measured at 12500 dscfm (dry standard cubic feet per minute). The O₂ concentration in the flue gas is 7.0%. Calculate DRE for all organic compounds; concentration of particulates leaving the system, gr/dscf; and the removal efficiency for HCl. The following data apply:

Compound	Inlet mass flow rate (lb/h)	Outlet mass flow rate/(lb/h)	M
Benzene	2015	0.537	78.11
Chlorobenzene	1150	0.109	112.5
Ethylbenzene	2230	0.757	106.17
Toluene	637	0.022	92.10
Xylene	3040	1.25	106.17

Hydrochloric acid gas is leaving at a rate of 10.7 lb/h. Particulate matter in exit gases is 23.4 gr/dscf. Molecular weight of HCl is 36.45.

Solution Basis 1 h of operation.

C Destruction and removal efficiency (DRE):

DRE = (W_in - W_out)/W_in

And is tabulated for different components

	Benzene	Chlorobenzene	Ethylbenzene	Toluene	Xylene
DRE	99.9733	99.9905	99.9661	99.9965	99.9589

C Chlorobenzene reacted = 1150 - 0.11 = 1149.89 lb

= 1149.89/112.5 = 10.22 moles

From the stoichiometry, one mole of chlorobenzene can produce one mole of HCl.

C HCl produced = 10.22 moles = 10.22(36.45) = 372.56 lb

The incinerated stream goes to the absorber where HCl is absorbed.

Mass of HCl in the stream leaving the absorber is = 10.7 lb

C HCl removal efficiency = (372.56 - 10.7)/372.56 = 97.128%

C Concentration of particulate matter leaving the system

= 23.4(7000)/(12500(60)) = 0.2184 gr/dscf