CAE analysis and optimization of energy consumption and ... · PDF fileCAE analysis and optimization of energy consumption and costs of wood drying with use ... on the example of air

04-01-2010

1

CAE analysis and optimization of energy consumption and costs of wood drying with use

of different drying techniques

Željko Gorišek1, Uroš Firšt1, Aleš Straže1

1Department of Wood Science and Technology, Biotechnical Faculty, University of Ljubljana,

22nd – 23rd October 2009 Lisbon, Portugal

Department of Wood Science and TechnologyBiotechnical facultyUniversity of Ljubljana

Cost E53Cost E53 Quality of wood and wood productsEconomic and Technical aspects on quality

control for wood and wood products

Department for Wood Science and TechnologyBiotechnical FacultyUniversity of Ljubljana

WhatWhat to do to do forfor optimal technical, technological optimal technical, technological and economical decisionand economical decision??

ObligatoryObligatory evaluation and detail analyses of evaluation and detail analyses of

�� ttimeime,,

�� energy consumptionenergy consumption,,

�� cost cost ,,

�� woodwood qualityquality..





INTRODUCTION

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INTRODUCTION

The decision is not � simple or

� the same for different cases.

Influencing the large number of variables :� timber species,

� timber dimensions,

� initial and final moisture content,

� type and size of dryers,

� energy availability and its price,

� etc.

The aim of this study

� For different drying techniques set up the CAE simulation of:� Drying kinetics (drying curve, drying schedule, drying rate and time etc.)

� Drying quality (target MC, MC gradient, deffect, ….)

� Energy consumption (total amount, specific energy consumption for kg of water or for m3, kind of energy and their proportion, etc.)

� Costs of drying (influence of MC).

� To make a model for choosing the best combination of drying techniques

� To calculate the optimum MCt at which change of drying techniques would bring the best results.

Verification of the model and the calculation of transition MCton the example of air pre-drying and kiln drying processes.




INTRODUCTION

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METHOD

BASIC DATA

OPTIMIZATIONOPTIMIZATION

du

dCost

du

dCost kilair =

DRYING KINETICS

AND ENERGY

CONSUMPTION

Tipical drying curve u=f(t)Drying schedule ( T, dT, Tv, ur, φ)

Drying time t(u)Drying rate du/dt

Heat and electric energy consumption, Ei(t), ΣEi(t),Specific energy demand,

Energy efficiency

COSTS

Capital costs and amortizationDrying time

Quantity of the wood (yard or kiln)Annual capacity (yard or kiln)

Rate of investment creditCost of maintenance

Cost of labour and transportEnergy costs (heat, electricity)

Insurance and taxes




•Final MC

Wood•Species, (density, vol. shrinkage, FSP, drying coefficient)•Dimensions (thickness)•Drying characteristics (permeability, diffusivity) •Initial MC•Final MC

Environment conditions•Temperature, •Relative humidity –absolute humidity, •equilibrium moisture content

Drying chamber•Dimensions •Kiln charge volume•Construction – thermal isolation•Heat and electricity power installation

Package – lumber stack •Dimensions (height, length, width, •Sticker thickness•Wood volume

Lumber yard •Dimensions (pile spacing,roads, air circulation)•Accessory equipment(stickers, roofs, footingsBASIC DATA

METHOD

Wood� Species, (density, vol.

shrinkage, FSP, drying coefficient)

� Dimensions (thickness)� Drying characteristics

(permeability, diffusivity) � Initial MC� Final MC

Environment conditions� Temperature, � Relative humidity – absolute

humidity, � Equilibrium moisture content

installation

Drying chamber� Dimensions � Kiln charge volume� Construction – thermal

isolation� Heat and electricity power

installation

� Wood volume

Package – lumber stack � Dimensions (height, length,

width), � Sticker thickness� Wood volume

DRYING KINETICS AND ENERGY CONSUMPTION

Air drying� Typical drying curve u(t), � Drying time, � Drying rate - du/dt(u),� Final moisture content uf

Kiln drying� Drying schedule (T, dT, Tv, ur, φ) � Drying time t(u),…, � Drying rate du/dt� Heat and electric energy

consumption, Ei(t), ΣEi(t),� Specific energy demand, � Energy efficiency

Lumber yard � Dimensions (pile spacing,

roads, air circulation)� Accessory equipment

(stickers, roofs, footings etc. )

BASIC DATA� Wood� Environment

conditions� Lumber yard� Package – lumber

stack� Drying chamber

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Artificial drying with predrying (1)

• Final MC• kiln construction• wood volume [m3]

Predrying• drying period,• wood species• initial MC,• thickness,

2. Drying schedule T, dT, Tv, ur, φ•Kinetics: u(t), du/dt(u),…,

•Energy:Ei(t), ΣEi(t),…

Predrying Predrying

u(t), du/dt(u),…,

Results A:Drying kinetics of predrying.

u(t), du/dt(u),…,

NO

Calculation:• Drying kinetics,• Final MC.

Results C:•Drying kinetics of artificial drying w,•Energy consumption.

Data• drying schedule for different wood

species,• climate conditions,• model for air drying of wood,• kiln construction

ComparisonEnergy consumption,

Drying time (1, 2).

Results B:•Drying kinetics of artificial drying with predrying •Energy consumption.

1. Drying scheduleT, dT, Tv, ur, φ•Kinetics:

u(t), du/dt(u),…,•Energy:Ei(t), ΣEi(t),…

Artificial drying (2)•Drying period,•Wood species,•thickness,•initial MC,

•final MC,•kiln construction ,•wood volume [m3].

YES




METHOD

METHOD

KoličinaKalorična vrednost





Režimi (T, Ur, �)Kinetika sušenja (u(t), du/dt, �)Energija




LOG YARD

Razžagovanje hlodovine

CLASIFICATION

Lupljenje hlodovine

STEACKING OF WOOD

Razžagovanje žaganega lesa

SESONING SESONING

KILN DRYINGKILN DRYINGSAW OF TIMBER

KILN DRYINGKILN DRYING

RESAW OF TIMBER

Ostanki skorje in sekancev

Žagovina krajniki

Žagovina, odčelki, žamanje



LOG TRANSPORT

QUALITY DRYED WOOD




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COSTS

OPTIMIZATION

Air drying� Capital costs and

amortization (ground and road preparation),

� Drying time� Quantity of the wood

on the yard� Annual capacity of

the yard� Rate investment

credit� Insurance and taxes

Kiln drying� Capital costs (ground

preparation, technical and thermal characteristics of the kiln and conditioning chamber)

� Cost of maintenance� Cost of labour and

transport� Energy costs (heat,

electricity) � Insurance and taxes

METHOD

METHOD

BASIC DATA

OPTIMIZATIONOPTIMIZATION

du

dCost

du

dCost kilair =

DRYING KINETICS

AND ENERGY

CONSUMPTION

Tipical drying curve u=f(t)Drying schedule ( T, dT, Tv, ur, φ)

Drying time t(u)Drying rate du/dt

Heat and electric energy consumption, Ei(t), ΣEi(t),Specific energy demand,

Energy efficiency

COSTS

Capital costs and amortizationDrying time

Quantity of the wood (yard or kiln)Annual capacity (yard or kiln)

Rate of investment creditCost of maintenance

Cost of labour and transportEnergy costs (heat, electricity)

Insurance and taxes




Influence of MC on air drying costsInfluence of MC on kiln drying costs

� Calculating

transition MCt

� Increase of kiln

capacity

� Energy saving

� Cost saving

•Final MC

Wood•Species, (density, vol. shrinkage, FSP, drying coefficient)•Dimensions (thickness)•Drying characteristics (permeability, diffusivity) •Initial MC•Final MC

Environment conditions•Temperature, •Relative humidity –absolute humidity, •equilibrium moisture content

Drying chamber•Dimensions •Kiln charge volume•Construction – thermal isolation•Heat and electricity power installation

Package – lumber stack •Dimensions (height, length, width, •Sticker thickness•Wood volume

Lumber yard •Dimensions (pile spacing,roads, air circulation)•Accessory equipment(stickers, roofs, footingsBASIC DATA

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20 40 60 80

0,80

0,60

0,40

0,20

Moisture content [%]

Sp

eci

fic

dry

ing

co

st [

eu

r/m

3h

]

MCt

Costs of air drying

Costs of kiln drying

MCt – transition moisture

content

Comparison of

drying costs

between two

different drying

techniques




du

dCost

du

dCost kilair =

METHOD

Species beech wood board ( Fagus silvatica L)Thickness 38 mmInitial MC fresh woodFina MC EMC with environment conditionTime 8 series - every month from December to July Samples 10 samples

Drying rate model

Evaluation of drying process :Drying time and drying rateMoisture content and MC gradientCasehardeningDeffects

))((1 cuuke

a

t

u−−+

=∆∆

AIR DRYINGAIR DRYING




MATERIAL

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0

20

40

60

80

100

0 50 100 150 200 250 300 350

MC

T

j

EMC

MC

T

ϕ

EMC

Drying time [h]

MC

, T

, ϕϕ ϕϕ

, E

MC

Drying time [h]

MC

, T

, ϕϕ ϕϕ

, E

MC

KILN DRYINGKILN DRYINGSpecies beech wood board ( Fagus silvatica L)Thickness 38 mmInitial MC fresh wood (MC i = 78 ±±±± 12%)Fina MC MC f ≈≈≈≈ 8 %Samples 13 samples

Time

Kiln 8,5 m x 7,6 x 5,8 mm (V = 81,65 m 3)

Evaluation of drying process :Drying time and drying rateMoisture content and MC gradientCasehardeningDeffects

=ϑα65

25ln

1 d

MC

MCt

f

i




MATERIAL

-10

-5

0

5

10

15

20

25

nov dec jan feb mar apr maj jun jul avgt [meseci]Ur [%] T [°C]

D e c J a n F e b M a r A p r M a y J u n J u l A u g1 0

2 0

3 0

4 0

5 0

6 0

7 0

8 0

9 0

1 0 0

MC

[%]

t [ m o n t h ]

Air drying curves for 38 mm thick beech wood timber.




TEMPERATURE

EMC

Each curverepresentsaverage valueof 10 boars

RESULTS

AIR DRYING CURVES

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Typical dependence of drying rate from wood moisture content for winter and

spring drying period for 38 mm thick beech wood timber.

10 20 30 40 50 60 70 80 90 1000

1

2

3

4

5

6

7

Dry

ing

rate

du/

dt

[%/d

ay]

Moisture content u [%]

15 20 25 30 35 40 45 50 55 600

1

2

3

4

5

6

7

Dry

ing

rat

e d

u/d

t [%

/day

]

Moisture content u [%]

WINTER SPRING




RESULTS

AIR DRYING RATE ))((1 cuuke

a

t

u−−+

=∆∆

0,00

2,00

4,00

6,00

8,00

0 20 40 60 80 100

JUL

JUN

MAY

APR

MAR

FEB

JAN

DEC

Dry

ing

ra

te [

%/d

ay

]


Influence of drying rate from wood moisture content from December to July.




PeriodInitial

MC (ui)[%]

Final MC(uf)

[%]

Max. drying rate

[%/day]Uc[%]

DEC - APR 68,3 18,8 2,3 47,1

JAN – APR 87,0 17,8 1,4 37,0

FEB - MAY 80,7 17,9 2,1 44,7

MAR – JUN 74,4 18,8 2,4 40,1

APR – JUL 79,8 18,4 6,3 52,3

MAY – JUL 57,3 17,9 5,6 45,9

JUN – AVG 67,2 19,1 3,5 43,7

JUL - SEP 78,7 17,9 7,8 53,6

Drying period, initial and final moisture content, maximal drying rate and moisture content of the

quickest decrease of drying rate for eight air drying processes for 38 mm thick beech wood.

RESULTS

AIR DRYING RATE

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Drying schedule (temperature T, relative humidityϕϕϕϕ, equilibrium

moisture content EMC) and drying curve for 38 mm thick beech wood

timber.




RESULTS

0

20

40

60

80

100

0 50 100 150 200 250 300 350

MC

T

ϕ

EMC

Drying time [h]

MC

, T

, ϕϕ ϕϕ

, E

MC

KILN DRYING SCHEDULE

Increase of drying costs during air drying for eight series (DEC – JUL),

for 38 mm thick beech wood timber.

0 10 20 30 40 50 60 70 80

DEC JAN FEB MAR APR MAY JUN JUL

Co

sts

[ EU

R/m

3 h

]





RESULTS

AIR DRYING - COSTS

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Costs of air drying






Sp

eci

fic

dry

ing

co

st [

eu

r/m

3h

]

20 40 60 80

0,80

0,60

0,40

0,20

MCt

RESULTS

0,0

10,0

20,0

30,0

40,0

50,0

DEC JAN FEB MAR APR MAY JUN JUL

Mo

istu

reco

nte

nt

[%]

Calculated optimal transition moisture contents (MCt) from air to kiln drying for eight drying periods for 38 mm thick

beech wood timber.

TRANSITION MOISTURE CONTENT MCt

Costs of air drying






Sp

eci

fic

dry

ing

co

st [

eu

r/m

3h

]

20 40 60 80

0,80

0,60

0,40

0,20

MCt

RESULTS

Reduction of kiln drying time with use of air predrying from green condition to transition MC for eight drying

periods for 38 mm thick beech wood timber.

Air dryingKiln

drying

MCiMCf

29,2

29,2

34,8

40,9

48,1

37

48,1

49,7

0 10 20 30 40 50 60 70 80

DEC

JAN

FEB

MAR

APR

MAY

JUN

JUL

Reduction of kiln drying time [%]

DRYING TIME

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Costs of air drying






Sp

eci

fic

dry

ing

co

st [

eu

r/m

3h

]

20 40 60 80

0,80

0,60

0,40

0,20

MCt

RESULTS

Energy saving during kiln drying with use of air predrying from green condition to transition MC for eight drying


Air dryingKiln

drying

MCiMCf

48

48,8

56

62,3

71,4

57,2

71,4

72,1

0 20 40 60 80

DEC

JAN

FEB

MAR

APR

MAY

JUN

JUL

Energy saving [%]

ENERGY CONSUMPTION

Costs of air drying






Sp

eci

fic

dry

ing

co

st [

eu

r/m

3h

]

20 40 60 80

0,80

0,60

0,40

0,20

MCt

RESULTS

Reduction of costs for kiln drying with use of air predrying from green condition to transition MC for eight drying


Air drying

Kilndrying

MCiMCf

SAVING15,8

8,7

18,2

21,4

34,9

27

32,5

33,2

0 20 40 60 80

DEC

JAN

FEB

MAR

APR

MAY

JUN

JUL

Reduction of costs[%]

COSTS

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CONCLUSIONS

With analyzing and comparing the costs of more drying processes we are able to predict the wood moisture content at which alteration from air to kiln drying would get the best results.

With this method we can predict:� the potentional energy savings, � the lowering of kiln drying time and consequently rising

of available kiln drying capacities� the costs saving.

The model can be used for optimising the combination of anydrying techniques.




Thank you for your attention !

CAE analysis and optimization of energy consumption and costs of wood drying with use of different drying techniques

• Željko Gorišek1, Uroš Firšt1, Aleš Straže1

•


Department of Wood Science and TechnologyBiotechnical facultyUniversity of Ljubljana

Documents

CAE analysis and optimization of energy consumption and ... · PDF fileCAE analysis and optimization of energy consumption and costs of wood drying with use ... on the example of air