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Decrease energy consumption d i ti b d i during timber drying

B.BEDELEAN, D. ŞOVA Transilvania University of Brasov, Romania

23 April, 2009, BLED, SLOVENIA COST ACTION E53 EDG SEMINAR

Introduction In a drying kiln without baffles, about 50% of the flow rate produced by fans passes the material stacks, the rest flows through the four types of passive channels. In order to be sure that the optimal velocity of air is reached in the material stacks, the kiln constructors oversize the air flow rate that is necessary for the drying process.

The additions accomplished by the constructors are situated between 30 – 50 %.

For an addition of 50% it results that on the entire drying process:

• nly half of the fans absorbs electric energy for produce air which is necessary to

drying the material the rest of produced air volume is used only for covering the losses through the passive channels.

50% 50%

100%

From the total air Due to the passive Only half of the total air volume passes

p

50% Losses Through stacks total air volume passive channels air volume passes the stacks

What is the effect of the air additions upon the electric energy consumption? What is the effect of the air additions upon the electric energy consumption? Based on the fans laws it can be observed that an addition of 10 % leads to Based on the fans laws it can be observed that an addition of 10 % leads to an increase of the absorbed power with 33%.

15.0 17.0 19.0 21.0

ată, kW

Puterea totală instalată, kW 670.0 770.0 870.0

trică, kWh/mc

Consumul de energie electrcă, kWh /mc 7.0 9.0 11.0 13.0

terea totală instala

270.0 370.0 470.0 570.0

mul de energie elect

1.0 3.0 5.0 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

Coeficientul de supradimensionare, c Put

70.0 170.0 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

Coeficientul de supradimensionare, c Consum

Once increasing the absorbed power, the electric energy consumption that is necessary for the drying of one cubic meter of material increases proportionally.

In aim to reduce the disadvantage of oversize the air flow upon the electrical g p energy consumption the paper proposes the following solution:

Using a kit of baffles for all passive channels

+

Using a program for adjusting the electric motors power according to passive channels g the optimal air velocity

Air velocity Without baffles With top and lateral baffles Baffles for all passive channels

2 54 3.4 3 00 3.50 4.00 4.50 m/s

Air velocity

Without baffles

The

• bstruction
• f

all passive channels was

1.8 2.54 1.00 1.50 2.00 2.50 3.00 Air velocity, With top and lateral baffles with baffles for all passive channels

p necessary in

• rder

to maximize the air velocity above the

• ptimal

value

0.00 0.50 Without baffles With top and lateral baffles with baffles for all passive h l passive channels

p recommended by the literature.

channels The analysed variants

Material and methods The research was performed on softwood timber (spruce), in a drying kiln with the capacity of 4 mc. The adjusting program of the electric motors power was developed on the basis of the developed on the basis of the criterion that the air velocity has to be framed in the

• ptimal limits of 2 5 – 3 m/s

Current program Proposed program

• ptimal limits of 2.5

3 m/s, according to the literature recommendations.

The obstruction of all passive channels has been accomplished by means of the four types of baffles which are: types of baffles, which are: Top baffles Lateral Vertical b ffl baffles baffles H i t l Horizontal baffles

The measurement of the air velocity was performed at the air exit from the material stacks, by means of a probe and a data logger, made by Ahlborn company.

Almemo data logger 2590 – 4s Ahlborn‐type probe for the measurement of p the air velocity

The data acquisition has been accomplished by use

• f

a computer. co pu e

In order to determine the influence of the proposed solution upon the electric energy In order to determine the influence of the proposed solution upon the electric energy consumption, the next two variants have been submitted to the drying process: The first variant – without baffles + current program

+

Averge motors power: 85 %

+

g p Averge velocity: 1.8 m/s

Without baffles Current program

Heating Stage I Stage II Stage III Stage IV Conditioning Cooling Average The power of the electric motor, % 100 95 85 75 70 85 95 85 Ai l it /

2 1 89 1 76 1 64 1 53 1 76 1 89 1 78

Air velocity, m/s

2 1.89 1.76 1.64 1.53 1.76 1.89 1.78

The second variant – baffles for all passive channels + proposed program

+

Averge power: 65% Averge velocity: 3 m/s

With baffles for all passive channels Proposed program

Heating Stage I Stage II Stage III Stage IV Conditioning Cooling Average The power of the electric motor, % 70 70 70 55 50 70 70 65 Ai l it / 3 2 3 2 3 2 2 66 2 46 3 2 3 2 3 Air velocity, m/s 3.2 3.2 3.2 2.66 2.46 3.2 3.2 3

The running of the process was accomplished according to the drying schedule supplied by the kiln constructor. pp y

The stage of the process Wood moisture content, % Temperature,

0C

Equilibrium moisture content, % Heating

• 50

18 Stage I 40 50 12 Stage II 28 60 10 Stage III 16 65 4,8 Stage IV 10 72 2,9 Conditioning

• 74

7 Co d

• g

7 7 Cooling

• 30
• The parameters monitoring was performed by means of Skype application and the

values registration, by means of a webcam, a clock and a computer.

Parameters monitoring Values registration The reading of the registered values

The measurement of the electric energy consumption was performed by determining The measurement of the electric energy consumption was performed by determining the value of the electric current intensity for each drying stage and the power factor.

3 cos

• =

ϕ U I P

kW

3 cos

• =

ϕ U I P

kW

t P E

• =

kWh

Heme Analyst 2050 The display of the frequency y converter

Results Results

174 172 174 176

• urs

The drying time decreased only with 5% if the proposed solution was applied as compared to the present situation.

165 164 166 168 170 172 rying time, ho

p p

160 162

• Var. I + actual program
• Var. II + proposed program

Dr The analysed variants 228 250 ,

But, the electric energy consumption decreased with 18 % with respect to the current situation

188 100 150 200 ul de energie, Wh/mc

with respect to the current situation.

50

• Var. I + actual program
• Var. II + proposed program

Consum kW The analysed variants

From economically point of view, the proposed solution leads to the decrease of the drying f bi f d i l i h 18 %

The name of variants

cost of one cubic meter of wooden material with 18 %.

First variant Second variant Species spruce Thickness, mm 50 , Annually production, m3 176 Electric energy cost, € / m3 (kWh) 0.076 Electric energy consumption 228 188 Basis Electric energy consumption, kWh / m3 228 188 Total cost of electric energy, € / m3 17.32 14.28 Saving € / m3 ‐ 3 g / Annually saving, € / year ‐ 528 Cost of the baffles kit, € ‐ 234 Amortization (electric energy) ‐ 0.44 years Results ( gy) y (~ 5 months)

It can be observed that the investment that is necessary for the production of the kit of baffles will be reclaimed in five months.

Thank you for your attention!

Also, thanks to for the financial support

bedelean@yahoo.com