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Title: Implementing Strategies for Drying and Pressing Wood Without Emissions Controls

Abstract

Drying and pressing wood for the manufacture of lumber, particleboard, oriented strand board (OSB), veneer and medium density fiberboard (MDF) release volatile organic compounds (VOCs) into the atmosphere. These emissions require control equipment that are capital-intensive and consume significant quantities of natural gas and electricity. The objective of our work was to understand the mechanisms through which volatile organic compounds are generated and released and to develop simple control strategies. Of the several strategies developed, two have been implemented for OSB manufacture over the course of this study. First, it was found that increasing final wood moisture by about 2-4 percentage points reduced the dryer emissions of hazardous air pollutants by over 70%. As wood dries, the escaping water evaporatively cools the wood. This cooling tapers off wood when the wood is nearly dry and the wood temperature rises. Thermal breakdown of the wood tissue occurs and VOCs are released. Raising the final wood moisture by only a few percentage points minimizes the temperature rise and reduces emissions. Evaporative cooling also impacts has implications for VOC release from wood fines. Flaking wood for OSB manufacture inevitable generates fines. Fines dry out rapidly because of their high surface area and evaporativemore » cooling is lost more rapidly than for flakes. As a result, fines emit a disproportionate quantity of VOCs. Fines can be reduced in two ways: through screening of the green furnish and through reducing their generation during flaking. The second approach is preferable because it also increased wood yield. A procedure to do this by matching the sharpness angle of the flaker knife to the ambient temperature was also developed. Other findings of practical interests are as follows: Dielectric heating of wood under low-headspace conditions removes terpenes and other extractives from softwood; The monoterpene content in trees depend upon temperature and seasonal effects; Method 25A emissions from lumber drying can be modeled from a knowledge of the airflow through the kiln; A heat transfer model shows that VOCs released during hot-pressing mainly originate from the surface of the board; and Boiler ash can be used to adsorb formaldehyde from air streams.« less

Authors:
;
Publication Date:
Research Org.:
Georgia Tech
Sponsoring Org.:
USDOE
OSTI Identifier:
913620
Report Number(s):
ID13439 final
TRN: US200802%%900
DOE Contract Number:
FC36-96ID13439
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
03 NATURAL GAS; 09 BIOMASS FUELS; 36 MATERIALS SCIENCE; AMBIENT TEMPERATURE; CONTROL EQUIPMENT; DIELECTRIC MATERIALS; DRYING; ELECTRICITY; EVAPORATIVE COOLING; FORMALDEHYDE; HEAT TRANSFER; HOT PRESSING; NATURAL GAS; ORGANIC COMPOUNDS; PRESSING; SURFACE AREA; VOLATILE MATTER; WOOD

Citation Formats

Sujit Banerjee, and Terrance Conners. Implementing Strategies for Drying and Pressing Wood Without Emissions Controls. United States: N. p., 2007. Web. doi:10.2172/913620.
Sujit Banerjee, & Terrance Conners. Implementing Strategies for Drying and Pressing Wood Without Emissions Controls. United States. doi:10.2172/913620.
Sujit Banerjee, and Terrance Conners. Fri . "Implementing Strategies for Drying and Pressing Wood Without Emissions Controls". United States. doi:10.2172/913620. https://www.osti.gov/servlets/purl/913620.
@article{osti_913620,
title = {Implementing Strategies for Drying and Pressing Wood Without Emissions Controls},
author = {Sujit Banerjee and Terrance Conners},
abstractNote = {Drying and pressing wood for the manufacture of lumber, particleboard, oriented strand board (OSB), veneer and medium density fiberboard (MDF) release volatile organic compounds (VOCs) into the atmosphere. These emissions require control equipment that are capital-intensive and consume significant quantities of natural gas and electricity. The objective of our work was to understand the mechanisms through which volatile organic compounds are generated and released and to develop simple control strategies. Of the several strategies developed, two have been implemented for OSB manufacture over the course of this study. First, it was found that increasing final wood moisture by about 2-4 percentage points reduced the dryer emissions of hazardous air pollutants by over 70%. As wood dries, the escaping water evaporatively cools the wood. This cooling tapers off wood when the wood is nearly dry and the wood temperature rises. Thermal breakdown of the wood tissue occurs and VOCs are released. Raising the final wood moisture by only a few percentage points minimizes the temperature rise and reduces emissions. Evaporative cooling also impacts has implications for VOC release from wood fines. Flaking wood for OSB manufacture inevitable generates fines. Fines dry out rapidly because of their high surface area and evaporative cooling is lost more rapidly than for flakes. As a result, fines emit a disproportionate quantity of VOCs. Fines can be reduced in two ways: through screening of the green furnish and through reducing their generation during flaking. The second approach is preferable because it also increased wood yield. A procedure to do this by matching the sharpness angle of the flaker knife to the ambient temperature was also developed. Other findings of practical interests are as follows: Dielectric heating of wood under low-headspace conditions removes terpenes and other extractives from softwood; The monoterpene content in trees depend upon temperature and seasonal effects; Method 25A emissions from lumber drying can be modeled from a knowledge of the airflow through the kiln; A heat transfer model shows that VOCs released during hot-pressing mainly originate from the surface of the board; and Boiler ash can be used to adsorb formaldehyde from air streams.},
doi = {10.2172/913620},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Sep 07 00:00:00 EDT 2007},
month = {Fri Sep 07 00:00:00 EDT 2007}
}

Technical Report:

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  • Pilot-scale shoe press and roll press experiments have been conducted to compare impulse drying and double felted pressing. Both ceramic coated and Beloit Type C press rolls have been evaluated. The experiments show that impulse drying can provide significantly higher outgoing solids than double felled pressing at the same impulse. For example, at an impulse of 0.234 MPa seconds (34 psi seconds), sheets at an ingoing solids of 52% were impulse dried (using the Beloit Type C press roll) to 68% solids while optimized double felled pressing could only yield press dryness of, at most, 60%.
  • Pilot-scale shoe press and roll press experiments have been conducted to compare impulse drying and double felted pressing. Both ceramic coated and Beloit Type C press rolls have been evaluated. The experiments show that impulse drying can provide significantly higher outgoing solids than double felled pressing at the same impulse. For example, at an impulse of 0.234 MPa seconds (34 psi seconds), sheets at an ingoing solids of 52% were impulse dried (using the Beloit Type C press roll) to 68% solids while optimized double felled pressing could only yield press dryness of, at most, 60%.
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