1. IUFRO 2003 Conference : Drying Energy Efficiency Through Partial Air-Drying: a Case Study
Radu Pantea1; Mouloud Amazouz1; François Léger2; Jonathan Gaudreault3
Introduction
The lumber drying is the most energy consuming operation of a lumber mill. One way to reduce the energy consumption is to introduce the air-drying practice as an integrated part of the overall drying operations. The goal of the operation is to reduce the initial moisture content of the lumber without completely drying it.
Table 3
Necessary working days in order to produce the equivalent of 195 loads of lumber
Sawing
Drying
Planing
247
393 per kiln drier
213
The drying operation is the bottleneck.
Accounting Management
Objective
The objective of this work is to find if the air-drying process of the softwood lumber (balsam fir) should be considered as a part of the overall drying operations.
Break-even analysis for different scenarios of natural gas prices
Table 4
Scenario analysis
Accounting variable
Gas price [$CDN/m³]
Air-drying rate [%/day]
Inventory-insurance cost [yearly%]
Pessimist
0.24
0.83 8
Realist
0.32
1.11 10
Optimist
0.40
1.67 12
0.00
500.00
1.00
2.00
3.00
4.00
5.00
6.00
Air-drying time [weeks]
Dollars [$ CDN]
Break-even point
0.24 $CDN/m³
0.32 $CDN/m³
Case study
Average drying rate: 1.67 [%/day]
Air-drying operation: 6 [week]
Inventory & Insurance rate: 8 [%]
Average initial MC: [%]
Gas savings [$CDN]
Gas price 0.40 [$CDN/m³]
Gas savings [$CDN]
Gas price 0.24 [$CDN/m³]
Gas price 0.32 [$CDN/m³]
Air-drying cost [$CDN]
0.40 $CDN/m³
Methods
Identified the main factors influencing the decision-making process of accepting or not the air-drying operation.
Gathered and explored data describing the main factors: Meteorological conditions, Operations management and Accounting Management.
Used break-even analysis for determining the air-drying time at which total revenues are equal to total costs.
Presented pessimist, realist and optimist scenarios for gas price ($CDN/m³), air-drying rate (%MC/Day) and inventory-insurance cost (yearly%).
The gas price represents the accounting variable with the most important influence on the air-drying operation performance.
When:
Gas price   Air-drying time   Operation flexibility 
Air-drying   Air-drying time   Operation flexibility 
Inventory-insurance   Air-drying time   Operation flexibility 
Break-even analysis for different scenarios of air-drying rate
Results
Meteorological Conditions
Table 1
0.00
2.00
4.00
6.00
8.00
10.00
12.00
Air-drying time [weeks]
Dollars [$ CDN]
Break-even point
Drying rate 1.11 [%/day]
Case study
Natural gas price: 0.32 $CDN/m³
Air-drying operation: 6 [week]
Inventory & Insurance rate: 8 [%]
Average initial MC: [%]
Gas savings [$CDN]
Drying rate 0.83 [%/day]
Drying rate1.67 [%/day]
Air-drying cost [$CDN]
Drying rate 1.67 [%/day]
Conclusions
The break-even technique represents a useful decision-making tool when it’s time to introduce air-drying as a part of the overall drying operations.
The air-drying operations are a different way of managing the lumber inventory.
The air-drying operations have a positive effect on energy and greenhouse gas emissions reductions.
The scenario analysis helped to find the most important accounting variable concerning the air-drying operations performance.
The analysis should be repeated when changes in the economical and meteorological environment are observed allowing the management personnel to verify if the air-drying operation is still in a positive performance situation.
The balsam fir sorting strategy combined with air-drying practice can become a competitive tool for a lumber mill.
Meteorological conditions
Average values
T [°C]
19.00
Rain [mm]
100.20
Relative humidity [%]
68.20
EMC [%]
12.13
Wind velocity [m/s]
3.67
Temperature and the EMC values are favourable for air-drying conditions.
Wind velocities are favourable for MC uniformity among the lumber in the load.
Operations Management
Break-even analysis for different scenarios of inventory-insurance cost
Table 2
Summary operations data for a 2x4 dimension of balsam fir
Lumber sorting strategy (based on initial weight)
Low
Medium
High
Lumber Initial MC [%]
71.62
106.93
141.67
Estimated drying energy consumption [GJ]
468.77
651.35
804.51
Estimated GHG emissions [CO2 t/load]
23.37
32.47
40.11
0.00
2.00
4.00
6.00
8.00
10.00
12.00
Air-drying time [weeks]
Dollars [$ CDN]
Case study
Natural gas price 0.32 $CDN
Air-drying operation: 9 [week]
Air-drying rate: 1.11 [%/day]
Average initial MC: [%]
Gas savings [$CDN]
Air-drying cost [$CDN]
Inventory-insurance rate 8 [%]
Inventory-insurance rate 10 [%]
Inventory-insurance rate 12 [%]
Break-even point
Acknowledgements
The authors wish to thank the Leduc lumber mill personnel, for their support in data gathering process, as well as for the insightful discussions concerning different particularities of the lumber transformation process.
The High lumber chosen for air-drying due to its high initial MC.
The energy and GHG emissions are reduced with almost 50 per cent when the lumber dries from High to Low state.
1. CETC-Varennes, Natural Resources Canada, 1615 Lionel-Boulet Blvd, PO Box 4800 Varennes, Quebec J3X 1S6, Canada.
2. Forintek Canada Corp., 319 rue Franquet, Sainte-Foy, Québec (QC) G1P 4R4, Canada.
3. Pavillon Adrien-Pouliot, Université Laval, Québec (QC) G1K 7P4, Canada.