P L A M C Wijewarnasuriya and H S Amarasekera University of Sri Jayewardenepura, Sri Lanka International Forestry and Environment Symposium 2010 Annual Symposium organized by Department of Forestry and Environmental Science, University of Sri Jayewardenepura, Nugegoda, Sri Lanka http://fesympo.sjp.ac.lk/ Full Paper http://staff.sjp.ac.lk/hiran/publications/factors-affecting-seasoning-timber-using-sawdust-operated-kiln

1. FACTORS AFFECTING
SEASONING OF TIMBER USING
SAWDUST OPERATED KILN
P L A M C Wijewarnasuriya
H S Amarasekera
University of Sri Jayewardenepura, Sri
Lanka

2. Introduction
Seasoning is a value addition to timber.
Cost of seasoning is not affordable to small scale saw
millers.
Senadheera (2009) developed a sawdust burner for
seasoning of timber and it has been coupled to a kiln
chamber (50ft3) situated in University of Sri
Jayewardenepura.
In this study , performance and feasibility of that sawdust
operated kiln was investigated with a view to improve its
efficiency.

3. Objectives
To improve the efficiency and to investigate the
performance of sawdust operated kiln
To compare the university kiln with some selected
industrially operating kilns in the country

4. For the first objective
(01) Effect of particle size of sawdust on the efficiency of
the burner
Sawdust was divided into two main groups based on
particle size using a mesh having 1mm wide pores.
Each sawdust group was burnt separately under a same
feeding rate and water was heated. Temperature of water
after a certain time period was measured.

5. Variation of temperature in water Vs time for different
sawdust types
Water – 1000 ml Time – 30 min Feeding rate – 20 g min-1

6. (02) Effect of sawdust feeding rate on the efficiency of the
burner
Water was heated from the heat generated by the most
efficient sawdust type (particle diameter > 1mm) burner
under different sawdust feeding rates.

7. Variation of temperature in water Vs time for different
sawdust feeding rates
Water - 2000 ml Ti me - 30 min Sawdust particle size - > 1 mm

8. (03) Arrangement of heat transferring pipe in the kiln chamber
heat
transferring
pipe Timber
stack

9. (04) Drying of rubber wood using sawdust operated kiln
Dimensions of timber boards – 100 cm * 15 cm * 2.5 cm
Sticker thickness – 25 mm
Sampling – 8 boards were randomly selected

10. Drying rate
Mass of water removed from timber per hour during the kiln
run
Drying rate = MW / T
MW - mass of water removed from timber in each stage
T - time taken
Drying rate = %MC / T
%MC - percentage moisture content reduced in a certain
period of time
T - time taken

11. Drying efficiency
Percentage of water removed in a certain time period in
relation to total water content in timber.
Drying efficiency = ms / mt * 100%
ms - weight of water removed from each stage
mt - total water content in the timber

12. Drying characteristics of rubber wood
Variation of moisture content in rubber wood with the time

13. Time Final MC in wood Drying rate Drying efficiency
hrs % g of water hr-1 % MC hr-1 %
0-8 54.66 1181.25 0.90 14.34
8-16 48.38 1031.25 0.79 12.52
16-24 43.93 900.00 0.56 10.93
24-32 40.16 774.00 0.47 9.40
32-40 36.50 666.00 0.46 8.09
40-48 32.62 600.00 0.49 7.29
48-56 29.42 525.00 0.40 6.37
56-64 26.79 431.25 0.33 5.24
64-72 24.28 412.50 0.31 5.01
72-80 21.88 393.75 0.30 4.78
80-88 20.05 300.00 0.23 3.64
88-96 18.45 262.50 0.20 3.19
96-104 17.20 206.25 0.16 2.50
104-112 16.17 168.75 0.13 2.05
112-120 15.14 150.00 0.13 1.82
120-128 14.23 114.00 0.11 1.38
128-136 13.89 84.00 0.04 1.02
136-144 12.97 54.00 0.11 0.66
0-144 13.00 458.58 0.34 81.3

14. According to Ratnayake (1998); a study has been done
for same volume (25 ft3) of rubber wood using the same
kiln chamber; it has taken only 62 hours for the kiln run
under a dehumidifying system.
Average drying rate was found to be 459 g of water
evaporated per hour for present study while
dehumidifying system has exhibited an average drying
rate of 1290 g of water per hour
When drying rate is expressed as reduction of %MC per
hour, in respect of present study it ranged 0.04 – 0.90
%MC hr-1 and in respect of previous study (Senadheera,
2009) it ranged 0.16 – 0.60 %MC hr1.

15. (05) Investigation of drying behaviour of different timber
species
Selected species
Rubber - Hevea brasiliensis
Albizia - Paraserianthes falcataria
Lunumidella - Melia dubia
Mahogany - Swietenia macrophylla
Dimensions of timber boards – 100cm * 15cm * 2.5cm
Sampling – 3 boards for each species was randomly
selected

16. Variation of moisture content in different timbers with the time

17. For second objective
Comparison of kilns
Performance of sawdust operated university kiln (UNI) was
compared with
State Timber Coporation – Kaldemulla (STC)
Rowood Lanka Ltd – Nelundeniya (RWD)
STC kiln: chamber capacity 4096 ft3, operated with two
boilers (furnace oil and wood waste)
RWD kiln: chamber capacity 920 ft3, operated with a boiler
(sawdust)

18. Comparison of kilns was done based on costs and
benefits generated by kilns when seasoning 25mm thick
rubber wood boards under 25mm thick stickers.
In order to dry rubber wood from green conditions upto
13% of moisture content, UNI, STC and RWD kilns
consume 144, 144 and 216 hours respectively.
Costs and benefits were estimated for each kiln for
annual wise assuming that number of operating days per
year is 320.
Therefore, number of possible kiln runs per year for UNI,
STC and RWD kilns are 53, 53 and 35.

19. Estimated costs and benefits for selected kilns
UNI kiln STC kiln RWD kiln
Establishment cost (Rs)
Building 42,123.00 326,305.00 102,400.00
Technology 32,500.00 5,506,000.00 356,000.00
Costs (Rs yr-1)
Annualised cost 8,573.00 723,895.00 46,805.00
Timber 212,000.00 17,367,040.00 2,576,000.00
Labour 180,000.00 1,968,000.00 540,000.00
Maintenance 15,000.00 75,000.00 40,000.00
Electricity 133,290.00 196,705.00 790,326.00
- -
Fuel wood 2,880,000.00
Sawdust 20,670.00 - 106,312.00
- -
Furnace oil 4,032,000.00
6,155.00 36,495.00
CO2 emission 1,078,271.00

20. Benefit (Rs yr-1) UNI kiln STC kiln RWD kiln
Revenue from timber 477,000.00 39,061,440.00 5,796,000.00
Savings due to use of wood waste 383,125.00 2,746,046.00 1,970,490.00
CO2 benefit (neutral emission) 107,748.00 1,657,655.00 554,181.00

21. (01) Cost per unit volume (C1)
C1 = C / V
C- total cost of kiln run V- volume of timber
Kiln Cost (Rs ft-3)
Without CO2 emission With CO2 emission
cost cost
UNI 429.84 434.50
STC 260.98 260.90
RWD 254.31 256.60
Cost efficiency increases : UNI < STC < RWD
However, cost efficiencies of STC and RWD kilns are almost same.

22. Percentage contribution of each cost on total cost of seasoning
Costs (Rs yr-1) % Contribution
UNI STC RWD
Annualised cost 1.5 2.6 1.0
Timber 36.8 61.3 62.4
Labour 31.3 7.0 13.1
Maintenance 2.6 0.3 1.0
Electricity 23.2 0.7 19.1
Fuelwood 0.0 10.2 0.0
Sawdust 3.6 0.0 2.6
Furnace oil 0.0 14.2 0.0
CO2 emission 1.1 3.8 0.9
Total 100.0 100.0 100.0

23. (02) Cost per unit volume per unit time (C2)
C2 = C / (V*T)
C- total cost of kiln run V- volume of timber
T- time taken for the kiln run
Kiln Cost (Rs ft-3 hr-1)
UNI 3.02
STC 1.81
RWD 1.19
Cost efficiency increases : UNI < STC < RWD

24. Comparison of two cost comparisons
Here, two kilns were compared with the kiln which
possesses the least cost of seasoning.
Kiln Comparison
Cost for unit Cost for unit volume and
volume time
UNI 1.7 2.5
STC 1.0 1.5
RWD 1.0 1.0

25. (03) Cost-benefit analysis
Net Present Values were calculated for 15 years based on
following assumptions.
Annual discount rate is 10%.
Annual depreciation rate for buildings is 6%.
Technology life time for UNI, STC and RWD kilns are 5, 15 and 15
years respectively.
Timber supply and sale during the concerned period of time is
consistent.
Kiln Net Present Value
(Rs millions)
UNI 2.68
STC 104.43
RWD 28.84

26. Conclusions
The efficient sawdust feeding rate for the burner is
60 g per minute and sawdust piraticle size should be
more than 1 mm.
Under the existing performance the kiln is suitable
only for fast drying timber species such as rubber
wood and albizia.
The kiln is not suitable to run as an enterprise as it is
not cost efficient.

27. Recommendations
Existing heat transfer technology (hot exhaust gas) should
be changed to steam or hot water. (The maximum
temperature obtained by the kiln chamber was 420C under
the existing heat transfer technology.)
Identified design error regarding the burner should be
corrected. (Total area of combustion chamber should be
utilised for sawdust burning.)
Electricity consumption during kiln operation should be
minimised. (One circulatory fan should be used out of two
fans.)

28. References
Gjerdrum, P. (2000). Cost efficient timber drying, Proceedings of 2nd
Workshop on Quality Drying of Hardwoods, Sopron, Hungary.
Perry, R.H. and Chilton, C.H. (1973). Chemical Engineer’s Hand Book,
4th edition. pp 245.
Ratnayake R.S.S. (1998). Development of drying schedules for rubber
and pine timbers for the dehumidification kiln drying, M.Sc. thesis,
Department of forestry and environmental science, University of Sri
Jayewardenepura, Sri Lanka.
Senadheera, D.K.L.K. (2009). Development of sawdust burner for kiln
seasoning of timber, B.Sc. dissertation, Department of forestry and
environmental science, University of Sri Jayewardenepura, Sri Lanka.

30. Moisture content in moisture content test pieces (MCTP)
MC = (m1 – m0) / m0 * 100%
m1 –average initial weight of MCTP
m0 – average oven dry weight of MCTP
Estimated oven dry weight of sample boards
MO = M1 / ( MC / 100 + 1)
M1 – initial weight of the sample board
Current moisture content of sample boards
MP = ( M2/M0 ) – 1) * 100%
M2 - current weight of the sample board

31. PV - present value of investment for technology (Rs)
r - annual discount rate (yr-1)
t - life time of machinery (yrs)
Annualised cost = PV x r
[1 – (1 + r)-t]
PV - present value of investment for technology (Rs)
r - annual discount rate (yr-1)
t - life time of machinery (yrs)
Cost of Timber = PG x N x VT
VT - timber volume per kiln run (capacity for timber in kiln chamber) (ft3)
N - number of kiln runs per year
PG - unit price of green timber (Rs. ft-3)
Cost of labour = NL x S
NL - number of labourers
S - monthly salary (Rs. month-1)

32. Cost of energy = AE x N x PE
AE - amount of energy source per kiln run (kg or ℓ or kWh)
N - number of kiln runs
PE - unit price of energy (Rs kg-1 or Rs ℓ-1 or Rs kWh-1)
Cost for CO2 emission = Af x N x Df x F x VC
1000
Af - amount of furnace oil per kiln run (ℓ)
N - number of kiln runs per year
Df - density of furnace oil (kg ℓ-1)
F - factor for carbon dioxide emission per unit mass of furnace oil (kg kg-1)
VC - annual value of carbon dioxide emission (Rs Mt-1)

33. Revenue from seasoned timber = 0.9 x VT x N x PS
RT - annual revenue from timber (Rs)
VT - timber volume per kiln run (capacity for timber in kiln chamber) (ft3)
N - number of kiln runs per year
PS - unit price of seasoned timber (Rs. ft-3)
Cost saving due to use of wood waste = [ MW x HW x CO ] – CW
HO
CO - unit cost of furnace oil (Rs ℓ-1)
CW - annual cost of wood waste (Rs)
HO - calorific value of furnace oil (MJ ℓ-1)
HW - calorific value of wood waste (MJ kg-1)
MW - annual requirement of wood waste (kg)

34. Benefit due to neutral CO2 emission = MW x HW x Df x F x VC
1000 x HO
Df - density of furnace oil (kg ℓ-1)
F - factor for carbon dioxide emission per unit mass of furnace oil (kg kg-1)
HO - calorific value of furnace oil (MJ ℓ-1)
HW - calorific value of wood waste (MJ kg-1)
MW - annual requirement of wood waste (kg)
VC - annual value of carbon dioxide emission (Rs Mt-1)
Building resale value = BV – (BV x DR x LT)
BV - present value of the building (Rs)
DR - depreciation rate for buildings (yr-1)
LT - time period (yrs)

35. The density of furnace oil is 1.005 kg ℓ-1 and burning of 1 kg of
furnace oil emits 3.15 kg of CO2 (
http://numero57.net/2008/03/20/carbon-dioxide-emissions-per-bar
as at 10/08/2010). The annual cost of CO2 emission is US $
20 Mt-1 (Source: New south Wales Environmental Protection
Authority, 1998) calculated in 1998. 1 US $ is Rs 111.58 (
www.cbsl.gov.lk as at 10/08/2010). CO2 emission cost was
converted for year 2010 according to following formula.
Value in 1998 GDP deflactor for 1998
=
Value in 2010 GDP deflactor for 2010
GDP deflators for year 1998 and year 2010 are 85.51 and
109.77 respectively. Therefore, estimated CO2 emission
value for year 2010 is US $ 26.44.

36. However, 60% of electricity generation in Sri Lanka is based on
fossil fuels mainly oil (
http://www.energy.gov.lk/pdf/Sri%20Lanka%20Energy%20Balance%
as at 12/08/2010).
Therefore, electricity consumption (60%) is responsible for
emission of CO-2. Therefore, there is a cost of CO-2 emission due
to use of electricity for all three kilns.
In order to generate 1 kWh; fossil oil releases 0.24 kg of CO2 (
http://www.engineeringtoolbox.com/co2-emission-fuels-d_1085.html a
).