Effects of Drying Parameters on Hardwood Lumber Drying Defects and VOC Emissions

EFFECTS OF DRYING PARAMETERS ON HARDWOOD LUMBER DRYING DEFECTS AND VOC EMISSIONS

Sponsoring Institution

National Institute of Food and Agriculture

Project Status

TERMINATED

Funding Source

MCINTIRE-STENNIS

Reporting Frequency

Annual

Accession No.

0192956

Grant No.

(N/A)

Project No.

PEN03899

Proposal No.

(N/A)

Multistate No.

(N/A)

Program Code

(N/A)

Project Start Date

Jul 1, 2002

Project End Date

Jun 30, 2008

Grant Year

(N/A)

Project Director
Blankenhorn, P. R.

Recipient Organization
PENNSYLVANIA STATE UNIVERSITY
208 MUELLER LABORATORY
UNIVERSITY PARK,PA 16802

Performing Department
SCHOOL OF FOREST RESOURCES

Non Technical Summary
Since the original hardwood drying schedules(USDA FS Ag Handbook 188) were published, limited hardwood drying research has been reported on improving the drying rates while maintaining lumber quality or on control of hardwood kiln VOC emissions. The purpose of this project is to investigate the effects of hardwood kiln schedule drying parameters on increasing the drying rate without increasing drying defect development and hardwood kiln drying parameters and procedures on kiln VOC emissions.

Animal Health Component

(N/A)

Research Effort Categories

Basic

50%

Applied

35%

Developmental

15%

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
123	0650	2000	15%
123	0650	2010	15%
123	0650	2020	70%

Knowledge Area
123 - Management and Sustainability of Forest Resources;

Subject Of Investigation
0650 - Wood and wood products;

Field Of Science
2020 - Engineering; 2010 - Physics; 2000 - Chemistry;

Keywords

Goals / Objectives
The objectives of this project are to investigate effects of (1) hardwood kiln schedule drying parameters on increasing the drying rate without increasing drying defect development and (2) hardwood dry kiln drying parameters and procedures on kiln emissions.

Project Methods
The kiln schedule modifications in this project will focus on adjusting the equilibrium moisture content (EMC) conditions in the kiln between the recommended 5 percent moisture content (MC) intervals (USDA FS Ag Handbook 188) to improve the drying rate. The kiln EMC conditions (USDA FS Ag Handbook 188) are related to the dry bulb (DB) and wet bulb (WB) and establish the rate of moisture movement from the wood. At a constant WB depression, the DB temperature (USDA FS Ag Handbook 188) has a large range without major changes in the EMC conditions. At 14 degrees WB depression the EMC changes from 9.6 to 10.0 percent from 100 to 170 F dry bulb. Within 10 to 20 F the EMC values for any given WB depression are within 0.1 percent. This means that for every EMC condition we select during drying we have at least 10 to 20 F DB range and possibly more settings if we go to another slightly higher WB depression value. Modifying hardwood kiln schedules below 30 percent moisture content by adjusting the EMC conditions with the goal of improving the drying rate without increasing the development of drying defects will be the primary objective of this project. Modifying the DB, WB and EMC values below 30 percent MC is at the point where the drying stresses reverse in the wood and the development of new drying defects is minimized. Statistical comparisons will analyze the effects of dry kiln schedule modifications on drying defect development compared to the standard recommended kiln schedule. Another objective of this project will be to obtain quality volatile organic compound (VOC) emission data for hardwoods and determine the feasibility of developing new engineering controls for reducing kiln emissions. Dry kiln VOC emissions will be measured for different hardwood species and drying procedures. Hardwoods are generally dried by air drying, predryers, dehumidification kilns or conventional steam heated kilns. The initial phases of the research will focus on collecting and analyzing the total organic carbon (TOC) in the water discharges from dehumidification kilns for different hardwood species. These results will provide baseline data on emissions for comparion to emissions from conventional dry kilns. This data will be used as a baseline for developing engineering control procedures for dehumidification water discharges. On a laboratory scale, experiments using a conventional drying oven will also be conducted in order to quantify VOC air emissions for various hardwood species. These experiments will provide data on the quantity of emissions based on different drying parameters and for comparison to the TOC data obtained from the dehumidification kilns. The data will also be used to predict emissions from conventional hardwood dry kilns. Drying emissions will be measured at different moisture contents, drying rates and drying temperatures for selected hardwood species. Drying schedule modifications will be investigated as a control measure to lower VOC emissions. The data will be statistically analyzed to determine the usefulness of kiln schedule modifications or drying parameters as engineering control procedures to reduce emissions.

Progress 07/01/02 to 06/30/08

Outputs
OUTPUTS: This project investigated the following: (1) effects of hardwood kiln schedule drying parameters on dry kiln emissions; (2) kiln schedule modifications on drying defect development; and, (3) processing and drying defects in small diameter hardwood logs. This project estimated the amount of VOC emissions from red oak, white oak, hard maple, black cherry, red maple, and yellow poplar during kiln drying. Emissions increased for each species at each temperature increase in the kiln schedule. In all 6 species, the highest amounts of VOC emissions (57% to 68% of total), were at MC above 30%. Red oak released the highest estimated amount of VOCs at 0.358 pounds of VOCs per MBF. The average estimated release for the other 5 hardwood species was significantly different with the estimated amount being 0.227 pounds/MBF for white oak, 0.098 pounds/MBF for hard maple, 0.086 pounds/MBF for black cherry, 0.079 pounds/MBF for red maple, and 0.031 pounds/MBF for yellow poplar. The processing and yield of small diameter (11 ins. and lower small end dia) black cherry, sugar maple, and northern red oak logs were investigated. After being sawn and after being kiln dried, every board was examined for end checks, surface checks, shake, twist, bow, cup, crook, and assigned a pre-drying grade. Drying used a conventional kiln drying schedule and two modified milder kiln schedules. Modifications to the conventional kiln schedules maintained comparable EMC conditions for each drying step. As log diameter and log grade increased so did the lumber grade yield. Lumber grade improved in the direction of pith to bark for all species. The boards that graded No. 2 Com and Btr in black cherry ranged from 27% to 32%. Sixteen percent to 35% of sugar maple boards were No. 2 Com and Btr. Approximately 34% of red oak boards processed were No. 2 Com and Btr. The leading reasons for drop in grade after drying for black cherry were surface checking with pith present and shrinkage across the width of the board. Shrinkage across the board's width, shake, and surface checking with pith present were the main causes for red oak boards dropping in grade. Grade sawing in all species had a higher percentage of No. 2 Com and Btr lumber than did live sawing. The higher radial and tangential shrinkage values for small diameter, compared to larger diameter sawlogs, were 43% and 41% for black cherry, 15% and 8% for hard maple, and 17% and 4% for red oak, respectively. Green No. 1 and No. 2 Com black cherry 4/4 inch-thick lumber was dried using selected kiln schedule modifications. The kiln schedule modifications adjusted wet-bulb and dry-bulb temperatures at approximately 3% MC intervals between 30% and 15% MC instead of standard 5% MC intervals. This kiln schedule modification method was used to determine if drying time could be reduced without inducing additional drying defects compared to a conventional kiln schedule. Results of the kiln schedule modifications indicated that drying time for No. 1 and No. 2 Com black cherry lumber may be reduced from approx 20% to 43% between 30% to 15% MC, while still providing usable lumber for hardwood dimension products.(3,157) PARTICIPANTS: P.R. Blankenhorn, C.D. Ray, N. R. Brown, L.R. Stover, B.W. Beakler, and M.S. Scholl TARGET AUDIENCES: Managers and kiln operators in hardwood primary and secondary wood products companies. Additional audience includes US EPA and state air quality regulatory agencies. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
This project investigated the effects of hardwood kiln schedule drying parameters on dry kiln emissions, drying defect development, and drying rate in processing small diameter hardwood logs. Hardwood dry kiln emissions were quantified and the effects of drying parameters on hardwood dry kiln emissions were estimated.

Publications

Ray, C.D., N. Gattani, E. delCastillo, and P.R. Blankenhorn. 2007. Identification of the Relationship between Equilibrium Moisture Content, Dry Bulb Temperature and Humidity Using Regression Analysis. Wood and Fiber Science Vol. 39(2):299-306.
Beakler, B.W., P. R. Blankenhorn, N.R. Brown, M.S. Scholl, and L.R. Stover. 2007. Quantification of the VOCs Released During Kiln Drying Red Oak and White Oak Lumber. Forest Products Journal 57(11):1-6.

Progress 01/01/07 to 12/31/07

Outputs
OUTPUTS: The objectives of this project examined the effects of hardwood kiln schedule modifications on drying rate, drying defect development, and dry kiln emissions. Drying hardwood lumber introduces a potential environmental burden-the release of volatile organic compounds (VOCs) with the hot, humid kiln exhaust gases. This project was designed to estimate the amount of VOC emissions released from hardwood lumber during drying in conventional, steam-heated dry kilns. Two of the species investigated included Quercus rubra (red oak), and Quercus alba (white oak). VOC emissions were quantified using a small laboratory oven for lumber drying, a heated sampling line and a total hydrocarbon analyzer, as outlined in EPA Medthod 25 A. Species were dried using recommended standard kiln temperature schedule T4. VOC emission data from nine charges of red and white oak were collected. A temporary spike in emissions was observed immediately following each temperature increase (as specified in kiln schedule T4). In both species, the greatest instantaneous concentrations of emissions were observed at higher moisture contents (MC). When drying duration was factored in, red oak showed relatively consistent amounts of emissions per MC interval (10%), while emissions per MC interval (10%) decreased for white oak. Overall, a lower percentage of the total extractive content was removed during white oak drying (0.029 to 0.116 percent on a weight basis). It was speculated that the presence of tyloses could be limiting white oak VOC release. Some of the red oak lumber contained a bacterial infection; the impact of this on emissions remains unclear. On average, red oak released the largest estimated amount of VOCs, ranging from 0.154 to 0.358 pounds per MBF (data range accounts for variance among charges and for the use of two different calculations methods). Average estimated release for white oak was significantly lower, ranging from 0.058 to 0.227 pounds per MBF. The emission data also indicated some influence of temperature and drying time on the emission data. Red oak and white oak released about 68 percent of the VOCs emitted above fiber saturation point. PARTICIPANTS: P.R. Blankenhorn, C.D. Ray, N.R. Brown, L.R. Stover, B.W. Beakler, and M.S. Scholl. TARGET AUDIENCES: Managers and kiln operators in hardwood primary and secondary wood products companies. Additional audience includes US EPA and state air quality regulatory agencies.

Impacts
This project will investigate the effects of hardwood kiln schedule drying parameters on dry kiln emissions and drying defect development and drying rate in processing small diameter hardwood logs. Hardwood dry kiln emissions will be quantified and the effects of drying parameters on hardwood dry kiln emissions will be estimated.

Publications

Ray, C.D., N. Gattani, E. del Castillo, and P.R. Blankenhorn. 2007. Identification of the Relationship Between Equilibrium Moisture Content, Dry Bulb Temperature and Humidity Using Regression Analysis. Wood and Fiber Science Vol. 39(2):299-306.
Beakler, B.W., P.R. Blankenhorn, N.R. Brown, M.S. Scholl, and L.R. Stover. 2007. Quantification of the VOCs Released During Kiln Drying Red Oak and White Oak Lumber. Forest Products Journal. 57(11):1-6.

Progress 01/01/06 to 12/31/06

Outputs
The objectives of this project examined hardwood kiln schedule modifications on drying rate, drying defect development, and dry kiln emissions. In the current phase, the processing and yield of small diameter (11 inches and lower small end diameter) black cherry, sugar maple, and northern red oak logs were investigated. After being sawn every board was examined for end checks, surface checks, shake, twist, bow, cup, crook, and assigned a pre-drying grade. Drying was conducted through the use of a conventional kiln drying schedule and two modified kiln schedules designed to dry the lumber under milder drying conditions. Modifications were made to the conventional kiln schedules but maintained comparable equilibrium moisture content (EMC) conditions for drying steps of the conventional kiln schedules. After drying, each board was again examined for end checks, surface checks, shake, twist, bow, cup, crook, and assigned a post-drying grade. There was a common trend among species between log diameter, log grade, and log quality zone on post-drying lumber grade. As log diameter and log grade increased so did the lumber grade yield. Lumber grade improved in the direction of pith to bark. A higher percentage of boards sawn from the other quality zone graded No. 2 Common and better than did those boards sawn from the inner and core center of the log. Conversely, the core center of the log yielded the highest percentage of boards that graded No. 3 Common or less. The percentage of boards that graded No. 2 Common and better in black cherry ranged from 27% to 32%. Sixteen percent to 35% of sugar maple boards graded No. 2 Common and better. Approximately 34% of red oak boards processed resulted in a grade of No. 2 Common and better. The two leading reasons for drop in grade after drying for black cherry were surface checking with pith present and shrinkage across the width of the board. Black cherry modified kiln schedules #1 and #2 decreased the percentage of total boards that dropped in grade. Modified black cherry kiln schedules #1 and #2 reduced the total percentage of boards that dropped in grade because of shrinkage across the board's width. Shrinkage across the board's width, shake, and surface checking with pith present were the three main causes for red oak boards dropping in grade. Shrinkage across the board's width was most problematic in the outer quality zone of red oak logs. The percentage of total boards that dropped in grade because of shrinkage across a board's width reduced by 4.1% when the modified bacterial infected red oak kiln schedule was utilized versus the control bacterial infected red oak kiln schedule. The percentage of total boards that dropped in grade because of shake decreased by approximately 2% when the modified bacterial infected red oak kiln schedule was used. Twist, cup, and crook increased in black cherry and sugar maple boards as severity of slope of grain increased. Red oak boards experienced an increase in twist, bow, and cup as slope of grain increased in intensity. Grade sawing in all species and kiln charges yielded a higher percentage of No. 2 Common and better lumber than did live sawing.

Impacts
This project will investigate the effects of hardwood kiln schedule drying parameters on dry kiln emissions and drying defect development and drying rate in processing small diameter hardwood logs. Hardwood dry kiln emissions will be quantified and the effects of drying parameters on hardwood dry kiln emissions will be investigated.

Publications

Scholl, M. S., Blankenhorn, P. R., Stover, L. R., and Ray, C. D. 2005. Reduction of Kily Drying Time for Black Cherry Lumber. Forest Products Journal 55(12) 77-82.

Progress 01/01/05 to 12/31/05

Outputs
The effects of hardwood kiln schedule modifications on drying rate, drying defect development, and dry kiln emissions will be investigated. Very limited information has been available on dry kiln schedule modifications on drying defect development or on the quantity of volatile organic compounds (VOCs) released while kiln drying hardwood lumber. In the current phase of this project, Green No. 1 and No. 2 Common black cherry 4/4 inch thick lumber was dried using carefully selected kiln schedule modifications. The lumber was inspected for end checks, surface checks, shake, twist, bow, cup, and crook prior to kiln drying. Once inside the kiln, the lumber was dried using a conventional kiln schedule or one of three modified kiln schedules. The kiln schedule modifications included adjusting wet-bulb (WB) and dry-bulb (DB) temperatures at approximately 3 percent moisture content (MC) intervals between 30 percent-15 percent MC instead of standard 5 percent MC intervals. The modification to the conventional kiln schedule reflected the same equilibrium moisture content as at the end of the standard 5 percent MC intervals. This kiln schedule modification method was used to determine if drying time could be reduced without inducing a large amount of additional drying defects compared to the conventional kiln schedule. After drying, the lumber again underwent a close inspection for drying induced defects. Pre-drying and post-drying defects were recorded for each modified kiln schedule for use in comparison with similar data for a conventional kiln schedule. Results of the kiln schedule modifications indicated that the drying time for No. 1 and No. 2 Common black cherry lumber may be reduced from approximately 20 percent to 43 percent between 30 percent to 15 percent MC, while still providing usable lumber for hardwood dimension products. Using the modified kiln schedules, No. 1 Common black cherry lumber tended to have more twist and bow, while No. 2 Common black cherry lumber had a tendency to have more twist and shake than similar grade black cherry lumber dried with a conventional kiln schedule.

Impacts
This project will investigate the effects of hardwood kiln schedule drying parameters on dry kiln emissions and drying defect development. Results from this project will determine the usefulness of kiln schedule modifications on drying defect development and drying rate. Hardwood dry kiln emissions will be quantified and the effects of drying parameters on hardwood dry kiln emissions will be investigated.

Publications

Beakler, B.W., Blankenhorn, P. R., Stover, L. R., and Ray, C. D. 2005. Total Organic Compounds Released for Dehumidification Drying of Air-Dried Hardwood Lumber. Forest Products Journal 55(2):57-61.
Gattani, N., delCastillo, E., Ray, C.D., and Blankenhorn, P. R. 2005. Times Series Analysis and Control of a Dry Kiln. Wood and Fiber Science 37(3):472-483.
Ray, C. D., Gattani, N., delCastillo, E., and Blankenhorn, P. R. 2005. Time Series Techniques for Dynamic Real-time Control of Wood-Drying Processes. Forest Products Journal 55(10):1-8.

Progress 01/01/04 to 12/31/04

Outputs
The effects of hardwood kiln schedule modifications on drying rate, drying defect development, and dry kiln emissions will be investigated. Very limited information has been available on the quantity of volatile organic compounds (VOCs) and total organic compounds (TOC) emissions while kiln drying hardwood lumber. One phase of this project investigated the quantity of TOC in the effluent of a commercial dehumidification kiln used to finish drying mixed charges of air dried hardwood lumber. Kiln effluent containing the TOC for each charge was determined both before and after an activated charcoal filter. The total estimated amount of TOC for each kiln charge was compared among kiln charges. The effluent, after passing through activated charcoal, was analyzed to determine the effectiveness of the activated charcoal in removing TOC and in reducing the pH of the effluent from mixed hardwood kiln charges. The results indicated that a mixed charge of red and white oak lumber, dried from an initial moisture content of 21 percent, released the highest estimated total amount of TOC (1.37 lbs) of the 6 mixed hardwood kiln charges in this study. The study also revealed that activated charcoal was effective in reducing TOC from the effluent of the kiln charges. In general, the pH increased after charcoal filtration and the total amount of TOC decreased.

Impacts
This project will investigate the effects of hardwood kiln schedule drying parameters on dry kiln emissions and drying defect development. Results from this project will determine the usefulness of kiln schedule modifications on drying defect development, drying rate, and reduction in hardwood dry kiln emissions. Successful development of hardwood kiln schedule modifications to control emissions and drying defect development will support the continued economic viability of the hardwood lumber industry.

Publications

No publications reported this period

Progress 01/01/03 to 12/31/03

Outputs
The effects of hardwood kiln schedule drying parameters and procedures on drying rate, drying defect development, and dry kiln emissions will be investigated in this project. Modified standard kiln schedules for 1 and 2 Common black cherry using additional dry bulb and wet bulb settings at moisture contents below 30% have been investigated. Results of the kiln schedule modifications indicated that the kiln residence time for 1 and 2 Common black cherry may be reduced from 12 to 37% between 35 to 15% moisture content, while still providing usable lumber for hardwood dimension products. Using the modified kiln schedules, 1 Common black cherry lumber tended to have more twist and bow, while 2 Common black cherry lumber had a tendency to have more twist and shake than similar grade black cherry lumber dried with a standard kiln schedule. Determining a kiln schedule that will result in a decrease in the kiln residency time, while producing an acceptable amount of drying defects will allow for increased dry kiln productivity. Graduate Students-2.

Impacts
This project will investigate the effects of hardwood kiln schedule drying parameters on dry kiln emissions and drying defect development. Results from this project will determine the usefulness of kiln schedule modifications on drying defect development, drying rate, and reduction in hardwood dry kiln emissions. Successful development of hardwood kiln schedule modifications will help improve the economic viability of the hardwood lumber industry.

Publications

Scholl, M.S. 2003. Reduction of Kiln Residency Time for 4/4 Black Cherry Lumber. M. S. Thesis, The Pennsylvania State University, University Park, PA. 63 pp.

Progress 01/01/02 to 12/31/02

Outputs
The objectives of this project are to investigate the effects of hardwood kiln schedule drying parameters on the drying rate without increasing drying defect development and hardwood dry kiln drying parameters and procedures on dry kiln emissions. A unique approach of modifying hardwood dry kiln schedules is being investigated in this project in the first phase of research. The equilibrium moisture content (EMC) conditions and the dry bulb and wet bulb settings in the middle of the recommended standard 5% moisture content intervals will be changed to improve the drying rate. The kiln EMC conditions are interrelated with the dry bulb and wet bulb and as such establish the rate of moisture movement from the wood into the kiln atmosphere. This project is investigating changing the standard kiln schedule during the intermediate and final stages of the drying schedule and will use black cherry lumber for the experiments. Some data have been collected and is currently being analyzed. Graduate Students=2

Impacts
The project will investigate effects of hardwood kiln schedule drying parameters on dry kiln emissions and drying defect development. Results from this project will determine the usefulness of kiln schedule modifications on drying defect development, drying rate, and reduction in kiln emissions. These results will help improve the economic viability of hardwood lumber industry.

Publications

No publications reported this period