The heating media used in the drying and conditioning of green waste is flue gas from the fluid bed combustor, supplemented by 400# steam. The dryer equipment includes an Selective Catalytic Reduction (SCR) system for reducing NOX in the flue gas. The dryer operates at 1 bar (14.7 psig) internal pressure and sends evaporated steam and volatile organic compounds (VOCs) from the feed to heat exchangers that cool and deliver these gases to a pressurized condenser. The condenser removes most of the water for treatment and sends the remaining VOC’s to the combustor.

VOC’s

The green wood and other green waste will evolve volatile organic compounds (VOCs) when subject to the high temperatures in the feed dryer. The source and nature of the feedstock will not only change seasonally but also daily; therefore, a representative sample is chosen for simplicity reasons - an article entitled “Assessment of air emissions from industrial kiln drying of Pinus radiata wood,” by A.G. MacDonnald et al details what VOCs to expect from the abovementioned type of wood. The paper provides a lengthy list of compounds; Table below lists the VOCs that make up 95.6 percent of the total mass.

The VOCs are condensed in Heat Exchanger and collected in Pressure Vessel. For the purposes of sizing, all of the VOCs are assumed to be condensed. The stream of the VOCs to be collected at the outlet of the Heat Exchanger.

Volatile organic compounds evolved in drying process

Compound Name

Mass Percent

b-Pinene

39.0%

Ethanol

20.0%

a-Pinene

15.7%

Methanol

7.6%

Acetic Acid

3.5%

a-Terpineol

2.7%

Acetaldehyde

2.3%

Formic acid

2.1%

b-phellandrene

1.3%

Acrolein + Acetone

1.3%

Total Mass Percent

95.6%