Calculation of Drying Costs
Yves Fortin
Fall Meeting of the NEKDA,
3-4 November 2010
Shelburne, New Hampshire
Faculté de foresterie,
de géographie et de
géomatique
Université Laval
Contents
• Introduction
• Energy consumption
• Drying cost components
• Excel spreadsheets
• Case studies
• How to reduce drying costs
• Conclusions
2
Introduction
Why to calculate drying costs?
• to help choosing a new drying installation
• to determine the real cost of drying for an
existing intallation
• to determine custom drying rates
• to determine actions to take to reduce
drying costs
3
Introduction (cont?)
How to determine drying costs?
• Feaseability study (capital investment
decisions): net present value of investment (NPVI: capital
outlays – cash inflows), internal or discounted rate of return
(IRR or DRR) (ref. Engalichev and Eddy 1970)
• Calculation of the various cost components:
calculation of drying costs at a given time, not taking into
account cash inflows and time value of money (Goulet and
Ouimet 1970, McMillen and Wengert 1978, Hukka 2001,
Chanrion et al. 1989)
4
INTRODUCTION (cont’)
The calculation of drying costs involves first the
calculation of energy consumption
5
INTRODUCTION (cont’)
Kiln drying is a very demanding energy process
Balsam fir drying from 100% to 15%: 100 MBF,
2’’x4’’x8’
56 000 kg H2O
→
1.09 kWh/kg H2O
61 040 kWh (208 millions BTU)
1-year bungalow consumption:
100 millions BTU
N.B. 1 kWh= 3 421 BTU
6
Energy consumption Excel spreadsheet
Input data
9 Wood species and lumber dimensions
9 Geometry of kiln and lumber stack
9 Characteristics of equipment
9 Initial and final moisture contents
9 Conditions of exterior climate
9 Drying schedule
9 Drying curve
7
Energy consumption Excel spreadsheet
Sources of energy consumption (at the kiln only)
Heating and
humidification of
incoming air
Q6
Heating and
evaporation of
water from wood
Q5
Heating of
residual water
after drying
Q4
Differential heat
of sorption
Q3
Heat loss through kiln
walls, roofs and floor
Q7
Fan motors
Q8
Heating of kiln
and equipment
Q1
Heating of lumber
Q2
8
Drying cost Excel spreadsheet
Input data
9 Geometry of kiln and lumber stack
9 Characteristics and costs of kiln and storage equipment
9 Initial and final moisture contents
9 Kiln operation capacity and number of kilns
9 Process efficiency
9 Labor salaries
9 Kiln startup factor (1.2 -1.5)
9 Other various costs and rates (stickers, fuel, taxe and interest rates,
etc.)
9
Drying costs Excel spreadsheet
Cost components
• Fixed costs
9
Equipment, buildings and stickers (depreciation)
9
Interest on investment
9Insurances (kilns, equipement, buildings, lumber)
9Administration (office costs attributed to drying)
9Taxes (land, buildings, lumber, yard facilities)
9Interest on lumber inventory and land
9Maintenance of yard and snow removal
10
Drying costs Excel spreadsheet
Cost components
• Variable costs
9
Labor (handling, stacking, kiln, boiler and forklift operators)
9 Energy (heat and electrical)
9 Maintenance of kilns and buildings
9 Forklift maintenance and use
9 Wood residues marketing value
9 Degrades
11
Drying cost Excel spreadsheet
• Global drying capacity
Drying capacity =
∑ (V t )
i i
ca n
Vi = annual volume per species
ti = drying time per species (days)
Ca = apparent coefficient of staking (= 1 for the reference thickness)
n = number of drying days per year
12
Drying cost Excel spreadsheet
• Drying process thermal efficiency
Eff ther =
hvap + hsorp
N
hvap = heat of vaporisation (kJ/kgH2O or BTU/lbH2O)
hsorp = heat of sorption (kJ/kgH2O or BTU/lbH2O)
N = total energy to evaporate one 1 kg or 1 lb of water from
wood) (kJ/kgH2O or BTU/lbH2O)
13
Drying cost Excel spreadsheet
• Annual heat consumption
Cc =
Db (M i − M f )VN
100 R
(kJ or BTU)
Db = Green basic density of wood
Mi = initial moisture content (%)
Mf = final moisture content (%)
R = boiler efficiency
14
Drying cost Excel spreadsheet
• Calculation approaches
9 group of species: gives an average drying cost only
9 one species and one size at the time:
- can be done on the individual drying capacity basis
- can be done on the global drying capacity basis by taking
into account individual drying times and volumes and
applying a correction factor to the cost components which
are affected by the global capacity approach (existing
installations)
15
Case study No 1: SPF medium size mill
9 75 millions MBF yearly production
9 2x4 commodities, 50% white spruce, 50% balsam fir
9 Fir IMC: 115%; Spruce IMC: 60%; Target MC: 15%
9 Drying time: 150 hrs for fir; 65 hrs for spruce
9 Global drying capacity: 969 MBF (670 M bm for fir; 299 for spruce)
9 3 track-loaded kilns of 223 MBF for fir; 2 kilns of 150 MBF for spruce (individual
capacity approach)
9 4 track-loaded kilns of 248 MBF each for the global capacity approach
9 Cross-shaft fan arrangement
9 Steam heated kilns (bark and sawdust residues)
9 Conventional drying schedule
9 Exterior air conditions: 41oF (5oC) and 70% RH
9 Electricity cost: 0.135$/kWh
9 5-7% downgrading for each grade
16
Case study: white spruce individual capacity
Energy consumption and kiln efficiency sheet
Q
Qii
kJ
%
kJ
%
Heat +
Heat
+ Electricity
Electricity
10
5.0
10 931
931 187
187
5.0
1
1
2
2
kJ
kJ
%
kJ/m³
%
kJ/m³app
app
Heat
Heat only
only
kWh/kg
kWh/kgH
H22O
O
10
10 931
931 187
187
7
7 027
027 762
762
5.2
5.2
3.4
3.4
28
28 707
707
18
18 456
456
0.06
0.06
0.04
0.04
0.5
0.5
2.5
2.5
59.1
59.1
25.8
25.8
3.6
3.6
2
2 564
564
13
13 663
663
323 661
661
323
141
141 249
249
19
806
19 806
0.01
0.01
0.03
0.03
56.8
56.8
24.8
24.8
3.5
3.5
976
976 505
505
5
5 202
202 651
651
123 245
245 581
581
123
53
53 785
785 634
634
7
541
796
7 541 796
3.8
3.8
100
100
------208
208 711
711 117
117
100
100
548
548 105
105
1.23
1.23
3
3
4
4
7
7 027
027 762
762
976 505
505
976
5
202
5 202 651
651
3.2
3.2
0.5
0.5
2.4
2.4
5
5
6
6
7
7
123
123 245
245 581
581
53
53 785
785 634
634
7
541
796
7 541 796
8
8
Total
Total
8
8 169
169 882
882
216
216 880
880 999
999
0.72
0.72
0.32
0.32
0.04
0.04
Corrected
Corrected heat
heat consumption
consumption (energy
(energy recovered
recovered from
from fans)
fans)
530
530 941
941
Apparent
Apparent efficiency
efficiency
0.58
0.58
Boiler
heat
Boiler heat consumption
consumption
3
3
MJ/m
MJ/m app
app
707.9
707.9
BTU/MBF
BTU/MBF
1
1 583
583 597
597
17
Case study: white spruce individual capacity
Cost sheet
Cost component
Depreciation
Interest on investment
Insurances
Administration
Taxes
Interest on inventory and land
Yard maintenance and snow
removal
Labor
Electrical energy
Forklift maintenance and fuel
Building and equipment
maintenance
Wood residues marketing value
Drying degrades
Total
Total annual
drying cost $
198 479
70 019
32 262
42 426
5 375
18 959
$/m³
$/MBF
2.34
0.83
0.38
0.50
0.06
0.22
5.52
1.95
0.90
1.18
0.15
0.53
Percentage
15.89
5.61
2.58
3.48
0.42
1.55
15 000
0.18
0.42
1.18
195 000
126 831
41 750
2.30
1.49
0.49
5.42
3.53
1.16
15.31
8.70
3.28
29 925
0.35
0.83
3.45
325 017
148 068
3.83
1.75
9.04
4.12
22.30
12.14
1 249 110
14.72
34.74
100
18
Case study: white spruce global capacity
Cost sheet
Cost component
Depreciation
Interest on investment
Insurances
Administration
Taxes
Interest on inventory and land
Yard maintenance and snow
removal
Labor
Electrical energy
Forklift maintenance and fuel
Building and equipment
maintenance
Wood residues marketing value
Drying degrades
Total
Total annual
drying cost $
184 387
64 078
29 991
43 892
4 094
18 615
$/m³
$/MBF
2.10
0.73
0.34
0.50
0.05
0.21
4.96
1.72
0.81
1.18
0.11
0.50
Percentage
15.21
5.29
2.47
3.62
0.34
1.54
13 905
0.16
0.37
1.15
195 000
108 695
56 200
2.22
1.24
0.64
5.24
2.92
1.51
16.09
8.97
4.64
27 300
312 535
153 185
0.31
3.56
1.75
0.73
8.40
4.12
3.20
25.79
12.64
1 211 876
13.81
32.58
100
19
Case study: balsam fir individual capacity
Energy consumption and kiln efficiency sheet
Q
Qii
1
1
2
2
kJ
%
kJ
%
Heat
Heat +
+ Electricity
Electricity
15
2.5
15 946
946 661
661
2.5
kJ
kJ
%
kJ/m³
%
kJ/m³app
app
Heat
Heat only
only
kWh/kg
kWh/kgH
H22O
O
15
15 946
946 661
661
9
9 730
730 394
394
2.6
2.6
1.6
1.6
27
27 919
919
17
17 036
036
0.03
0.03
0.02
0.02
1
1 422
422 907
907
7 586
7
586 422
422
0.2
0.2
1.3
1.3
0.00
0.00
0.01
0.01
59.6
59.6
26.5
26.5
3.7
3.7
379
379 288
288 029
029
168 624
168
624 253
253
23
763
483
23 763 483
62.6
62.6
27.8
27.8
3.9
3.9
2
2 491
491
13 282
13
282
664 043
043
664
295 221
221
295
41
604
41 604
4.7
4.7
100
100
------606
606 362
362 148
148
100
100
1
1 061
061 596
596
1.16
1.16
3
3
4
4
9
9 730
730 394
394
1 422
422 907
907
1
7 586
586 422
422
7
1.5
1.5
0.2
0.2
1.2
1.2
5
5
6
6
7
7
379
379 288
288 029
029
168 624
168
624 253
253
23
763
483
23 763 483
8
8
Total
Total
29
29 609
609 619
619
635
635 971
971 767
767
0.72
0.72
0.32
0.32
0.05
0.05
Corrected
Corrected heat
heat consumption
consumption (energy
(energy recovered
recovered from
from fans)
fans)
1
1 020
020 125
125
Apparent
Apparent efficiency
efficiency
0.61
0.61
Boiler
heat
Boiler heat consumption
consumption
3
MJ/m
MJ/m3app
app
1 360.2
360.2
1
BTU/MBF
BTU/MBF
3 042
3
042 647
647
20
Case study: balsam fir separate capacity
Cost sheet
Cost component
Depreciation
Interest on investment
Insurances
Administration
Taxes
Interest on inventory and land
Yard maintenance and snow
removal
Labor
Electrical energy
Forklift maintenance and fuel
Building and equipment
maintenance
Wood residues marketing value
Drying degrades
Total
Total annual
drying cost $
385 410
132 765
62 245
42 268
9 500
41 284
$/m³
$/MBF
Percentage
4.56
1.57
0.74
0.50
0.11
0.49
10.76
3.71
1.74
1.18
0.27
1.15
19.31
6.65
3.12
2.12
0.48
2.07
15 000
0.18
0.42
0.75
217 500
263 954
41 750
2.57
3.12
0.49
6.07
7.37
1.17
10.90
13.23
2.09
56 400
580 249
147 514
0.67
6.86
1.75
1.57
16.20
4.12
4.31
29.07
7.39
1 995 838
23.61
55.72
100
21
Case study No 2: White pine mill
9 14.8 millions MBF yearly production ; boards 4/4
9 IMC: 120%; Target MC: 7%
9 Drying time: 240 hrs
9 Drying capacity: 425 MBF
9 4 package-loaded kilns
9 Steam heated kilns (dry residues: 60$/dry metric tonne)
9 Conventional drying schedule
9 Exterior air conditions: 41oF (5oC) and 70% RH
9 Electricity cost: 0.135$/kWh
9 Storage shed for dry lumber
9 Top loading plates
9 7-10% downgrading for each grade
22
Case study: white pine global capacity
Energy consumption and kiln efficiency sheet
Q
Qii
kJ
%
kJ
%
Heat
Heat +
+ Electricity
Electricity
11
2.2
11 162
162 850
850
2.2
1
1
2
2
3
3
4
4
6
6 197
197 180
180
2 921
921 826
826
2
2 414
414 420
420
2
1.2
1.2
0.6
0.6
0.5
0.5
5
5
6
6
7
7
294
294 379
379 506
506
130 276
130
276 285
285
22 259
259 545
545
22
58.2
58.2
25.7
25.7
4.4
4.4
8
8
Total
Total
36
36 592
592 941
941
506 204
506
204 552
552
7.2
7.2
100
100
kJ
kJ
%
kJ/m³
%
kJ/m³app
app
Heat
Heat only
only
kWh/kg
kWh/kgH
H22O
O
11
11 162
162 850
850
6 197
197 180
180
6
2.4
2.4
1.3
1.3
44
44 602
602
24 761
761
24
0.03
0.03
0.02
0.02
2
2 921
921 826
826
2 414
2
414 420
420
0.6
0.6
0.5
0.5
11
11 674
674
9 647
9
647
0.01
0.01
0.01
0.01
294
294 379
379 506
506
130 276
130
276 285
285
22 259
259 545
545
22
62.7
62.7
27.7
27.7
4.7
4.7
1
1 176
176 211
211
520
520 527
527
88
88 939
939
0.72
0.72
0.32
0.32
0.05
0.05
100
100
1
1 876
876 362
362
1.15
1.15
------469
469 611
611 611
611
Corrected
Corrected heat
heat consumption
consumption (energy
(energy recovered
recovered from
from fans)
fans)
1 759
759 394
394
1
Apparent
Apparent efficiency
efficiency
0.63
0.63
Boiler heat
heat consumption
consumption
Boiler
3
3
MJ/m
MJ/m app
app
2
2 345.9
345.9
BTU/MBF
BTU/MBF
5
5 247
247 608
608
23
Case study: white pine global capacity
Cost sheet
Cost component
Depreciation
Interest on investment
Insurances
Administration
Taxes
Interest on inventory and land
Yard maintenance and snow
removal
Labor
Electrical energy
Forklift maintenance and fuel
Building and equipment
maintenance
Wood residues marketing value
Drying degrades
Total
Total annual
drying cost $
345 260
117 588
65 957
104 475
30 375
116 667
$/m³
$/MBF
Percentage
9.91
3.38
1.89
3.00
0.87
3.35
23.40
7.97
4.47
7.08
2.06
7.91
17.99
6.13
3.44
5.44
1.58
6.08
15 000
0.43
1.02
0.78
240 000
238 280
41 750
6.89
6.84
1.20
16.26
16.15
2.83
12.50
12.41
2.18
48 759
332 501
222 880
1.40
9.55
6.40
3.30
22.53
15.10
4.34
17.32
11.61
1 919 492
55.12
130.08
100
24
How to reduce drying costs
• Air predrying
• Reduction of drying time (computer optimisation techniques)
• Increase the quality of drying (reduction of degrade losses)
• Install heat recovery systems
• Install variable frequency motor drives
• Improve the kiln maintenance
• Improve the air circulation in the kiln
• Improve the efficiency of the heating system
25
Conclusions
9 The calculation of energy consumption and drying costs
are two preconditions for the optimisation of the drying
process.
9 Investment costs, labor cost, energy cost, and degrade
cost are the main cost components to which actions
can be taken to reduce drying costs, although all other
costs are important to consider.
9 The reduction of drying cost should not, however, be at
the expense of drying quality.
26
Conclusions (cont’)
9 An increase of drying cost can even be justified with an
increase value of the dried products (e.g. value-added
products).
9 For new installations, the calculation of drying costs must be
made in combination with a financial feasibility study (more
thorough analysis).
27
References
• Chanrion, P., M. Fouquet and D. Aléon. 1989. Le séchage des résineux. Cahier
131, CTBA, Paris
• Chanrion, P. and A. Davesne. 1991. Le séchage des feuillus. Cahier L049, CTBA, Paris.
• Engalichev, N. and Eddy, W. 1970. Economic analysis of low temperature kilns in
processing softwood lumber for markets. Extension Bulletin No. 178, Univ. of New
Hampshire.
• Garrahan, P. and D. Canne. 1988. Analyse des niveaux de déclassement causés par le
séchage des sciages de dimensions spécifiées d'épinette-pin-sapin. Rapport interne,
Forintek Canada Corp., Ottawa.
• Goulet, M. and M. Ouimet. 1970. Établissement du prix de revient du séchage des bois. Note
technique no 5, Département d'exploitation et utilisation des bois, Université Laval.
• Hukka, A. 2001. Drying cost and quality with different types of drying kilns. Proceedings of
the 3rd Cost E, 2001.
• McMillen, J.M. and E. M. Wengert. 1978. Drying eastern hardwood lumber. Agric.
Handbook No. 528, FPL, USDA Dept. of Agriculture.
• Shottafer, J.E. and C.E. Shuler. 1974. Estimating heat consumption in kiln drying lumber.
Life Sciences and Agriculture Experiment Station. Tech. Bulletin 73, Univ. of Maine.
28
Calculation of Drying Costs
Yves Fortin
Thanks for your attention
Faculté de foresterie,
de géographie et de
géomatique
Université Laval