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Process-based control of HAPs emissions from drying wood flakes.
Sujit Banerjee1, Krishna Pendyala, Mike Buchanan
1Institute of Paper Science and Technology, School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 500 Tenth Street NW, Atlanta, Georgia 30332, USA. sb@gatech.edu
Environmental Science & Technology
|May 2, 2006
Summary
Reducing hazardous air pollutant (HAP) emissions from wood flake drying involves screening out fine particles and lowering dryer temperatures. This strategy can significantly decrease HAPs, potentially eliminating the need for control devices.
Area of Science:
- Environmental Engineering
- Chemical Engineering
- Forest Products
Background:
- Industrial wood flake drying releases hazardous air pollutants (HAPs) like methanol and formaldehyde.
- Fine wood particles (<500 microm) are susceptible to thermal degradation, leading to disproportionately high HAP emissions.
Purpose of the Study:
- To investigate the relationship between wood particle size, thermal degradation, and HAP generation during industrial drying.
- To propose mitigation strategies for reducing HAP emissions from wood drying processes.
Main Methods:
- Theoretical modeling of particle thermal degradation.
- Full-scale industrial practice observations of wood charring.
- Laboratory measurement of activation energy for wood tissue breakdown.
- Field measurements under nonisothermal conditions.
Main Results:
- Particles smaller than 500 microm showed visible charring in industrial practice.
- Laboratory activation energy for methanol and formaldehyde release was ~17 kcal/mol.
- Field measurements indicated higher apparent activation energy due to fines fraction heating.
Conclusions:
- Screening out fines (<500 microm) and reducing dryer inlet temperature can substantially decrease HAP emissions.
- These mitigation strategies may allow for downsizing or elimination of emission control devices.
- The study provides a semiquantitative method for estimating HAP reductions.