Calculate Drying Costs

8/11/2019 Calculate Drying Costs

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Dr. Jim Reeb, Ph.D.

Associate ProfessorForest Engineering, Resources and Management

54-574-6537 Ext [email protected]

Compare Costs of DifferentFuels for Drying Lumber

PICMET 11International Conference

July 31-August 4, 2011Portland, Oregon, USA


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What the heck is a British Thermal Unit (Btu) andwhy do we care?

One Btu is the amount of energy needed to raise thetemperature of one pound of water one degree Fahrenheit,and at sea level it takes 1,000 British thermal units of energyto evaporate 1 pound of water.

Different sources of energy, such as natural gas, electricity,

propane and wood can be compared using their heatcontent. In the US, the most common measure of heatcontent is the British Thermal Unit (Btu).


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Calculating Energy Use

Wood

Btu

Gas OilElectricity

Conversion values:

Unit of wood is 200 cu. ft.

= 1900 lbs. sawdust= 2600 lbs. bark

(Dry lb. is = 8,500 Btus

ranges from about 7,600-9,600 Btus/lb)

Therm of gas is = 100,000 Btu

Gallon of heating oil is = 140,000 Btus

~

~

~

~KWH of electricity is = 3,415 Btus


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Source: Understanding Wood by Bruce Hoadley

Water and Wood


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RELATIVE ENERGY80% to 15%

0 10 20 30 40 50 60 70 80 and higher

Moisture Content, % (lb HOH/lb BD AIR)

1500

1200

900

600

300

0

1000 Btu/lb2300 kJ/kg

Energy to evaporatefree water

Energy to evaporatebound water


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I!"RTANT T" #N"$ "$ T"

CALCULATE ENERGY U&E

ust 'e a'le to (eter)ine t*e total energy

use o+ all sources ust 'e a'le to (eter)ine *o, )uc* ,ater

,as re)o-e( +ro) t*e ,oo(


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.UEL VALUE& ."R$""/ GA& "IL AN/

ELECTRICITY ."R

/RYING

$/unit $/MMBTU*

Wood

5040 4.033.22

$/therm

Natural gas 0.5

0.6

6.43

7.71

$/barrel

No. 6 Heavy oil 75.00 14.43

$/KWH

Electricity .05

.06

14.64

17.57

*The assumed combustion efficiencies of thethree fuels are 61.2%, 77.8%, 82.5% and

100%, respectively. The wood fuel is at 45%MC (wet basis).

30 2.42

1.05 13.50

.07 20.50

100.00 19.24


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Energy +or /rying Lu)'er

Natural Gas Easy to use

Clean burning

Lower capital cost

Higher fuel cost

>80% efficiency

Wood Must handle

More emissions

Higher initial cost

Lower fuel cost

60-70% efficiency Availability


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Approximately, for every 1% increase in moisture content, starting at bonedry, there is a 1% decrease in heating value.

Example: if a piece of firewood has a heating value of 8,500 Btus perpound at 0% moisture content (bone dry) then it will have an approximateheating value of only 1,700 Btus per pound at 80% moisture content.

----------------------------------------------------------------------------------------------------Species effect high density woods have higher heating value than lowdensity woods.

Dry wood cell wall material weighs ~95 lbs/cu ft

Dry wood weighs ~12 - 85 lbs/cu ft

Negative Effect of Moisture on Heating Value of Wood

Lignum vitae (Guaiacum sanctum) sp gravity 1.37 = 85 lbs/cu ftBalsawood (Ochroma pyramidale) sp gravity 0.19 = 12 lbs/cu ft

Extremes:

~~


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Energy .ro) urning $oo(

WoodMoisture

Content (%) HHV

1

(Btus/lb)

0 8750

20 700050 4375

80 17501High heating value approximate values, for exampleat oven-dry, HHV ranges from about 7600-9600 Btus/lb


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Energy Use for Drying Lumber

MC (%) Energy Use

Initial FinalBtus/lb of Water1

Evaporated MMBtus/MBF

Doug-fir 45 15 2,000-3,000 1.2-1.8

S. pine 100 12 1,600-2,200 3.0-4.0

Red oak 80 6 3,000+ 6.4+

1Note: 1,000 Btus is theoretical value of energy to evaporate 1 lb HOH.


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$oo(2Relate( Energy Use

eat $oo(

eat $ater in $oo(

eat o+ $etting 3energy to 'rea4 c*e)ical 'oun(s E-a6orate $ater +ro) $oo( &ur+ace

ay'e 50% or a 'it )ore is use( to actually (ry t*e,oo(7 $*at is t*e rest o+ t*e energy (oing


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$*ere t*e

"t*er Energy

Goes

Kiln

Re-heating Make Up Air

Loss Through

Walls

Flash Tank

LossHeating Kiln Parts


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Use A'out 50% .or E++iciency ecause 50% $as

Use( +or /rying an( 50% +or "t*er

Energy 9 $ater E-a6orate( 3l':s ;


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ini)iBe Energy Use

Air (ry 'e+ore 4iln (ry

#ee6 rain an( sno,o++ t*e lu)'er

Re(uce +an s6ee( /ry to *ig*er C

ig*er te)6erature Vent less

A-oi( stea) s6ray

Maintain traps

Fix steam leaks

Insulate pipes

Minimize timebetween charges


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&te6s to A66roi)ate Cost o+ /rying Lu)'er

Calculate t*e a)ount o+ ,ater e-a6orate(

Use esti)ate o+


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Energy Drying Costs - Example

100,000 bf of western red cedar Avg SGgrn = 0.31

MC1 = 80% MC2 = 15% m1 = 0.80 lbs HOH/lb BDairm2 = 0.15 lbs HOH/lb BDair

Estimate: 1 ft3 = 14 bf

Drying Cost = lb HOH evaporated X 2,000 Btu/lb HOH evaporated X Energy Cost $/MM Btu

Weight of HOH evaporated (lbs) = SG X 62.4 lbs X 1 ft3 X (0.80 0.15) X 100,000 bf =ft3 14 bf

= 89,811 lbs of HOH evaporated

Btu needed = 89,811 lbs HOH X 2,000 Btu/lb HOH X Energy Cost $ = 179.62 MM Btus1,000,000,000 Btu

Continued on Next Slide


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Drying costs = 89,811 lbs HOH X 2,000 BTU X Energy Cost $ =lb HOH MM BTU

= 179.62 MM BTU X $/MM BTU

Energy Drying Costs (continued)

If dry 100,000,000 bf per year, what would the annual cost be?

Cost to dry 100 mmbf$/MM BTU MM Btu Annual Cost

Wood 4.03 X 179.62 = ~$ 724 $ 724,000

Natural gas 13.50 X 179.62 = ~$2,425 $2,425,000Oil 19.24 X 179.62 = ~$3,456 $3,455,000Electricity 20.50 X 179.62 = ~$3,682 $3,682,000

Other considerations:Initial cost of wood boiler is greaterWood has to be handled and stored on site operating costs are greaterWood is usually available so might actually be free or low cost (have to ignore opportunity costs if you thinkits free!)

Depreciation, upkeep, etc. are costs not accounted for in this example upkeep is greater for a wood-firedboiler.

Dry a 100 mbf of western red cedar from 80% to 15% MC


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&UARYFRE/UCING TE C"&T ". /RYING LUER

Nee( to realiBe i)6ortance o+ 4no,ing t*etrue (rying cost +or lu)'er

Nee( to ea)ine )eans o+ re(ucing (ryingcosts

Nee( to re(uce energy consu)6tion

electricity natural gas oil an( *ogge( +uel


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/RYING C"&T ."R &".T$""/ LUER

&ur-ey o+ Lu)'er /rying !artici6ants311 6artici6ants (i(n:t 4no, t*eir (rying cost

0

2

4

6

8

10

0 10 20 30 40 50 60 70 80

Drying Cost, $/MBF

Dr. Jim Wilson, Oregon State University, CORRIM


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/RYING C"&T& INCLU/E

Energy Use Ca6ital

aintenance an(

Re6air Insurance

La'or

!er)its En-iron)ental

"-er*ea(

Lu)'er /egra(e


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.ACT"R& A..ECTING TE C"&T ". /RYING

Kiln

Lumber

Kiln Schedule

Operator


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/ETERINING /RYING C"&TEa)6leF /rying cost o+


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/RYING C"&T ".


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/RYING C"&T ".


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0

2

4

6

8

10

0 10 20 30 40 50 60 70 80

Drying Cost, $/MBF

/RYING C"&T ."R &".T$""/ LUER&ur-ey o+ Lu)'er /rying !artici6ants

311 6artici6ants (i(n:t 4no, t*eir (rying cost

Calculated dryingcost of $30.53


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N"TE& "N /RYING CALCULATI"N&

T*e stea) cost ,as (eter)ine( 'ase( on a cost o+ 1J 6er 10006oun(s ,*ic* re+lects t*e true cost +or o6erating a ne, 'oilerD I+ +ully

(e6reciate( ol(er 'oiler is use( to su66ly stea) an( t*e cost ,oul(

'e 5 to 10 6er 1000 6oun(s o+ stea)D

Calculate( 'y assu)ing 6roKect +inance( ,it* 'orro,e( +un(s at t*erate o+ 8D5%D

Cost ignores (egra(e -alue an( ta s*iel( ,*ic* ,oul( 'e eHual tot*e 6ro(uct o+ ta rate 3@5% an( t*e su) o+ t*e annual (e6reciation

an( interest c*argesD


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TE A"UNT ". /EGRA/E $ILL A..ECT TE/RYING C"&T

30

35

40

45

50

0 2 4 6

Degrade (% of throughput)

D

ryingCost($

perMBF)

Based on a 2x4 hem-fir price of $326/MBF


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&UARYFRE/UCING TE C"&T ". /RYING LUER

Nee( to realiBe i)6ortance o+ 4no,ing t*etrue (rying cost +or lu)'er

Nee( to ea)ine )eans o+ re(ucing (ryingcosts

Nee( to re(uce energy consu)6tion

electricity natural gas oil an( *ogge( +uel


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Fuel Cost Calculator &Estimator of Lumber

Drying Costs

http://extension.oregonstate.edu/lincoln/forestry/wood-industry


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References:

Dry Kiln Operators Manualhttp://www.treesearch.fs.fed.us/pubs/7164

U.S. Energy Information Administrationhttp://www.eia.doe.gov/

Wood Handbook: Wood As An Engineering Materialhttp://www.treesearch.fs.fed.us/pubs/5734

Documents

Calculate Drying Costs