june 2007 geo-heat center quarterly bulletin

8/8/2019 June 2007 Geo-Heat Center Quarterly Bulletin

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GEO-HEAT CENTERQUARTERLY BULLETIN

OREGON INSTITUTE OF TECHNOLOGY KLAMATH FALLS, OREGON 97601-8801 (541) 885-1750

VOL. 28 NO. 1 MARCH 2007

ISSN0276-1084

BioFuelsfomGeoThermal


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CONTENTS

Biouels rom Geothermal .................................. 1Te Editor

Geothermal Energy Utilization

in Ethanol Production ........................................ 2

Andrew Chiasson

Greenuels o Oregon:

Geothermal Energy Utilization in

Biodiesel Production .......................................... 6

Andrew Chiasson

Geothermal Power Generation and Biodiesel

Production in Wabuska, Nevada ........................ 9

Claude Sapp

Design o a Geothermal Energy Dryer

or Beans and Grains Drying in Kamojang

Geothermal Field, Indonesia............................. 13

Untung Sumotarto

PUBLISHED BY

GEO-HEA CENEROregon Institute o echnology

3201 Campus DriveKlamath Falls, OR 97601

Phone: (541) 885-1750Email: [email protected]

All articles or the Bulletin are solicited. I youwish to contribute a paper, please contact the editorat the above address.

EDITOR

John W. Lund

Assistant Editor onya oni Boydypesetting/Layout Debi CarrCover Design SmithBates Printing & Design

WEBSITE:

http://geoheat.oit.edu

FUNDING

Te bulletin is provided compliments o the Geo-

Heat Center. Tis material was prepared with thesupport o the U.S. Department o Energy (DOEGrant No. DE-FG02-06ER64214). However, anyopinions, ndings, conclusions, or recommenda-tions expressed herein are those o the authors(s)and do not necessarily refect the view o USDOE.

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Vol. 28 No. 1 March 2007

GEO-HEAT CENTER QUARTERLY BULLETINISSN 0276-1084

A Quarterly Progress and Development Report on the Direct Utilization of Geothermal Resources

Cover -Artwork showing a biorenery using geothermal.Used with permission rom the Idaho National Laboratory

and modied by SmithBates Printing & Design


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GHC BULLETIN, MarCH 2007

BIOFUELS FROM GEOTHERMALThe production o biouels is a popular issue as it is a do-

mestic product that reduces our dependency on imported

ossil uels or the transportation sector o our economy. Two

types o biouels are produced: ethanol and biodiesel, both o

which are used as a blend with conventional uels to power

cars and trucks. The main controversy is the balance be-

tween energy input and energy output, as some reports con-tend that more energy is needed to produce the uel as is

produced rom the uel. The issue appears to be how you

analyze the various energy inputs such as rom ertilizer,

growing the product, transporting it to market and the ener-

gy input in the rening process, as well as the benets o the

byproducts. Many o the steps require the use o ossil uels,

and thus, this is where geothermal energy can contribute, by

replacing some o the energy input.

ETHaNoL ProdUCTIoN

The Model T in 1908 was designed to either run on gaso-

line or ethanol; however, due to cheaper gasoline, it wasnt

until the 1970s oil shock, that ethanol was o interest again.

But, it wasnt until around 2000 that ethanol emerged as a

substitute or methyl tertiary butyl either (MTBE), an oxy-

genate that reduced air pollution, but caused problems when

it leaked into aquiers.

Today, corn is the major product used in ethanol produc-

tion in the United States, with about 20% o the US produc-

tion or 12 billion bushels o corn used annually. This in-

creased demand is great or the armers, as it has doubled the

price o corn in one year to about $4.00 a bushel. This price,

o course, aects cattle eed and then the cost o meat to

consumers. To counter the use o corn, cellulosic ethanol is being investigated that comes rom brous materials like

corn husks and rice hulls, as well as ast-growing reedy crops

that require little ertilizer or tending, such as switch grass

and timber industry wastes.

Ethanol can be blended with gasoline as high as 85% etha-

nol to 15% gasoline, reerred to as E-85, which is presently

oered at about 1,000 gas stations in the United States. Only

about 2.5 percent o the nations cars are fexible uel vehi-

cles that can handle this mixture. Also, the energy content o

ethanol is lower than gasoline, thus, it takes about 1.5 gallons

o ethanol to drive as ar as one gallon o gasoline. Despite

all o these limitations, ethanol production is widely sup-ported by Congress with ew opponents.

BIodIEsEL ProdUCTIoN

The idea o using vegetable oil or uel has been around or

a long time, as Rudolph Diesel, the inventor o the diesel

engine, experimented with uels such as peanut oil around

the 1890s. However, due to the cheap and plentiul availabil-

ity o petroleum distillates, commercial production o biodie-

sel in the United States did not being until the 1990s.

In the United States, the majority o biodiesel is made

rom soybean or canola oils, but is also made rom waste

sources such as used cooking oils or animal ats. In Europe,

biodiesel is mainly produced rom rape seed, which unortu-

nately, due to the high price has cut demand across the EU.

More recently, interest has been in producing biodiesel rom

algae, some o which have over 50% oil content.Since biodiesel is more expensive and has engine compat-

ibility issues, it is mixed at 2% (B2) to 20% (B20) with con-

ventional diesel. The use o biodiesel reduces hydrocarbons

(CO2) and particulate emissions; however increases nitrogen

oxide emissions. At 100% biodiesel, CO2 emissions are re-

duce by over 75%. Biodiesel is non-toxic and biodegrades

our times aster than conventional diesel. Biodiesel does not

fow as well as petroleum diesel in cold weather causing op-

erating issues in colder climates. 100% biodiesel also tends

to reduce uel economy by about 11 percent.

ENErGy EffICIENCyUnortunately, there are not uniorm opinions on the e-

ciency and economics o biouels production. A study by

Cornell and the University o Caliornia Berkeley concluded

that more energy was required to produce ethanol and biodie-

sel than was produced in it use. On the other hand, a study by

NREL in the use o biodiesel with an urban bus concluded

that biodiesel yields 3.2 units o uel product energy or ev-

ery unit o ossil energy consumed in its lie cycle. A study

rom the University o Idaho which analyzed both o these

reports, concluded that the answer was somewhere in be-

tween and that the value o the byproducts, such as animal

eed, needs to be considered. In any event, the use o geo-thermal energy certainly will contribute to the energy bal-

ance and economics in the production o either uels as de-

scribed in the accompanying articles.

The Editor

rEfErENCEs:Is Ethanol the Answer? by Marianne Lavelle and Bret

Schulte, U.S. News & World Report, February 12, 2007, pp.

30-39.

Biodiesel Energy Balance, by Jon Van Gerpen and Dev

Shresthat, University o Idaho,

Lie Cycle Inventory o Biodiesel and Petroleum Diesel orUse in an Urban Bus, by John Sheehan, Vince Camobreco,

James Dueld, Michael, Graboski and Housein Shapouri,

May 1998, National Renewable Energy Laboratory, Golden,

CO

Cornell Ecologists Study Finds that Producing Ethanol and

Biodiesel rom Corn and other Crops is not Worth the Energy

by Susan Lang, Cornell University News Service, http://www.

news.cornell.edu/stories /July 05/ethanol.toocostly.ssl.html.


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2 GHC BULLETIN, MarCH 2007

The Geo-Heat Center conducted an evaluation o using

geothermal energy in ethanol production, unded and com-

pleted under a grant rom Midwest Research Institute, Na-

tional Renewable Energy Laboratory (NREL) Task Order

No. KLDJ-5-55052-01. Presented here is a summary o theresults o that study.

oVErVIEW of ETHaNoL UsEsaNd ProdUCTIoN

Ethanol is also reerred to as ethyl alcohol or grain alcohol.

According to BBI International (2003), ethanols primary

uses in the U.S. are: as an octane extender or gasoline; as a

clean-air gasoline additive in the orm o an oxygenate; as a

product to oster rural economic development; and as a do-

mestic uel source to aid in the reduction o U.S. dependence

on imported oil. Ethanol blended uels currently represent

more than 12% o U.S. motor gasoline sales, and ethanolblends o up to 10% are approved under the warranties o all

the major automobiles sold in the U.S.

At the time o completion o this report, there are current-

ly about 100 ethanol plants in the U.S., producing over 4.2

billion gallons o ethanol annually (www.bbiethanol.com/).

Over 20 new plants are planned or are under construction,

with an estimated combined annual production o over 1.1

billion gallons o ethanol. As o 2003, approximately 95% o

the U.S. uel ethanol was manuactured rom corn (BBI In-

ternational, 2003).

ETHaNoL ProdUCTIoN ProCEssaNd ENErGy rEQUIrEMENTs

Prior to examining the easibility o utilizing geothermal

energy in ethanol production, it is necessary to detail the

process, along with the associated energy and temperature

requirements at each step. First o all, there are two types o

processes used to produce ethanol: wet-mill process and

dry-mill process. In the wet-mill process, corn is soaked or

steeped and then separated into its component parts, which

are recovered prior to ermentation, and only the starch rac-

tion is processed. In the dry milling process, corn is ground

into four (meal) and processed without separation o com-

ponent parts. Wet-milling plants have much higher up-rontcosts and operating expenses than dry-milling plants, and

thus are not as common. Consequently, this study only deals

with dry-milling process plants.

There are basically eight steps in the dry-milling ethanol

production process as summarized below and shown sche-

matically in Figure 1.

1. Milling: The corn (or barley or wheat) is rst processed

through hammer mills, which grind it into a ne powder

the industry reers to as meal.

GEOTHERMAL ENERGY UTILIZATION IN ETHANOL PRODUCTIONAndrew Chiasson, Geo-Heat Center

2. Cooking and Liqueaction: The meal is then mixed with

water and enzymes, which passes through cookers where

the starch is liqueed. Cooking is generally accomplished

at temperatures o 150-180F (65-80C). The meal is ex-

posed to a high temperature stage o 250-300F (120-150C) or a short period o time to reduce bacterial

growth in the mash.

3. Saccharication : The process o saccharication in-

volves transerring the mash rom the cookers where it is

cooled, and a secondary enzyme (glucoamylase) is added

to convert the liqueed starch to ermentable sugars

(dextrose).

4. Fermentation: Yeast is then added to the mash to erment

the sugars to ethanol and carbon dioxide. Using a con-

tinuous process, the ermenting mash will be allowed to

fow, or cascade, through several ermenters until themash is ully ermented. In a batch ermentation process,

the mash stays in one ermenter or about 48 hours beore

the distillation process is started.

5. Distillation: The ermented mash, now called beer, at

this stage contains about 10% alcohol, as well as non-er-

mentable solids rom the corn and the yeast cells. The

mash is then pumped to the continuous fow, multi-col-

umn distillation system where the alcohol is removed

rom the solids and the water. Ethanol boils at a tempera-

ture o 173F (78.3C) at sea level pressure, allowing the

distillation separation o the ethanol rom water, which

boils at 212F (100C) at sea level. The alcohol will leave

Figure 1. Process schematic o ethanol production using

the dry milling process.


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the top o the nal column at about 95% purity (190

proo), and the residual mash, called stillage, gets trans-

erred rom the base o the column to the co-product pro-

cessing area.

6. Dehydration: The alcohol rom the top o the column is

then passed through a dehydration system where the re-

maining water is removed. At this point, distillation has

diminishing eect, and the remaining water must be re-

moved chemically. Most commercial ethanol plants use a

molecular sieve to capture the remaining water in the

ethanol. The alcohol product at this stage is called anhy-

drous ethanol and is approximately 200 proo.

7. Denaturing: Ethanol to be used or uel is then denatured

with a small amount (2-5%) o a product (usually gaso-

line) to make it unt or human consumption.

8. Co-Products: There are two main co-products created in

the production o ethanol: carbon dioxide and distillers

grain. Carbon dioxide is given o in signicant quanti-

ties during ermentation, and many ethanol plants collect

this carbon dioxide, clean it o any residual alcohol, com-press it, and sell it or use in carbonated beverages or in

the fash reezing o meat. Distillers grain is sold in two

orms: distillers wet grain (DWG) and distillers dried

grain (DDG). Both are high in protein and other nutri-

ents, and are a highly valued livestock eed ingredient.

DWG seems to be preerred by dairy and bee cattle (BBI

International, 2003), but i a cattle eed lot is not within

100 miles o the ethanol plant, storage and transportation

can become problematic. DDG requires a high amount o

input energy to dry the grain to 10-12% moisture. The

main advantage o DDG over DWG is better fowabili-

ty and longer storage lie. Some ethanol plants also cre-ate a syrup that contains some o the letover materials,

and can be sold as a separate product in addition to the

distillers grain, or combined with it to orm so-called

distillers dried grain with solubles (DDGS).

According to BBI International (2003), about 85% o the etha-

nol plants in the U.S. use natural gas as a source o thermal en-

ergy. The remainder use propane, uel oil, or coal. In general,

about 20,000 to 40,000 Btu o energy is required to produce a

gallon o ethanol and associated co-products. The highest energy

requirements are needed when dry distillers grain (DDG) is a

co-product. For comparison, the energy content o ethanol is

about 85,000 Btu/gal.

Geothermal utilization opportunities exist in three

stages o the production process: cooking, distillation,

and dry ing o the distillers grain. In addition, geothermal

energy could be used or space heating.

ECoNoMIC aNaLysIs

For the economic analysis, an ethanol plant producing 10

million gallons o ethanol annually was considered. Ac-

cording to BBI International (2003) a small plant would be

one producing about ve million gallons per year. The rac-

tion o the peak load met by geothermal energy was as-

sumed at 75%, and the remaining 25% was assumed to be

met by natural gas.

The peak heating load o the ctitious plant is estimated

at 26.8 million Btu/hr and the annual heating requirement is

approximately 3.0x1011 Btu (operating 350 days per year).

The annual energy cost o a conventional ethanol plant us-

ing 100% natural gas is estimated at $3.22 million while theannual energy cost o the ctitious ethanol plant using 75%

geothermal energy is estimated at $1.19 million.

Capital costs o the ctitious plant using geothermal en-

ergy included: design and engineering ees, land acquisition

and construction o roads and services to a possibly remote

location, exploratory drilling, and nal well construction.

The capital cost o a comparable conventional ethanol plant

is estimated at $21.15 million, while the cost o an ethanol

plant using geothermal energy is estimated at $25.72 mil-

lion. Thus, the incremental cost o the geothermal ethanol

scenario above the conventional is approximately $4.57

million or 21.6%

Annual costs considered include all costs associated with

ethanol production. For this easibility study, relative values

were taken rom BBI International (2003). For both plants,

the greatest annual cost item is that associated with acquir-

ing the eedstock (typically corn) and related chemicals and

enzymes. For the conventional natural gas ethanol plant,

energy costs account or 22.3% o total annual costs, while

only 9.6% o the total annual cost is attributed to energy use

in the 75% geothermal, 25% natural gas ethanol plant sce-

nario. For the geothermal case, an additional well mainte-

nance cost was assumed at $15,000, or 0.1% o the annualcosts.

Annual income was estimated rom relative values rom

BBI International (2003). Income is generated through sale

o ethanol, CO2, and some type o distillers grain. As de-

scribed previously, the distillers grain is sold as animal

eed and can be wet, dry, or mixed with solubles. For the

ethanol plant scenario considered here, gross sales o $18.5

million are realized.

For the scenarios examined here, the conventional natu-

ral gas ethanol plant yields an annual prot beore taxes o

approximately $4.1 million, while the 75% geothermal,

25% natural gas ethanol plant yields an annual prot beore

taxes o approximately $6.1 million. This results in a pre-

tax prot margin o $0.41/gal. or the conventional plant

and $0.61/gal. or the geothermal scenario.

Thirty-year lie-cycle economics were compared using

present value comparison. Given the uncertainty o the cost

o items, a sensitivity analysis was conducted in order to

observe the eects o various cost items on the present

value. The items varied in the sensitivity analysis were:

natural gas costs, energy required per gallon o ethanol,


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raction o energy provided by geothermal, geothermal ini-

tial costs, ethanol market price, eedstock price, and elec-

tricity costs. Results o the sensitivity analysis are shown

in Figure 2. Present values are expressed as a ratio o the

geothermal scenario to the conventional scenario. A dis-

count rate o 8% was assumed.

A review o the data presented in Figure 2 shows that, or

the base case described above, the geothermal case has a

54% greater present value than the conventional case. The

most sensitive item to the present values is the ethanol sell-

ing price. As ethanol selling price is decreased, the ratio o

the present value o the geothermal case to the convention-

al case rises dramatically as operating costs become very

important. As the ethanol selling price is increased by up to

25%, the present value o the geothermal case relative to

the conventional case decreases to about 1.2.

Following the market price or ethanol, the next most

sensitive item on the project economics is the eedstock

price. An increase in eedstock price o 10% increases the

ratio o the present value o the geothermal case to the con-ventional case up to a value o 2.0. A ur ther increase in the

eedstock price up to 25% results in operating costs ex-

ceeding prots (and thus resulting in a negative present

value) or the conventional case, while the geothermal case

remains protable. Lowering the eedstock price has a sim-

ilar eect to lowering the natural gas price and the energy

required per gallon o ethanol, the next most sensitive

items.

The next most sensitive items to the present value ratio,

each having a nearly identical impact, are the natural gas

price and the energy required per gallon o ethanol. Increas-

ing each by 25% increases the ratio o the present value o

the geothermal case to the conventional case to about 2.2.

Decreasing these items by 25% has less o an impact, lower-

ing the ratio o the present value o the geothermal case to

the conventional case increases to about 1.25.

The next most sensitive item to the present value ratio is

the initial geothermal cost, ollowed closely by the raction

o energy provided by geothermal. As the initial geother-

mal cost is decreased by 25% , the ratio o the present value

o the geothermal case to the conventional case increases to

about 1.8. Conversely, as the initial geothermal cost is in-

creased by up to 25%, the ratio o the present value o thegeothermal case to the conventional case decreases to about

1.25. When the raction o energy provided by geothermal

is increased by 25% (i.e. up to 93.75%), the ratio o the

present value o the geothermal case to the conventional

case increases to about 1.76. When the raction o energy

provided by geothermal is decreased by 25% (i.e. down to

56.25%), the ratio o the present value o the geothermal

case to the conventional case decreases to about 1.35. The

project economics are relatively insensitive to the electric-

ity cost.

soME PoTENTIaL BarrIErs ToGEoTHErMaL UTILIZaTIoN INETHaNoL ProdUCTIoN

Although the economics o utilization o geothermal en-

ergy can be quite attractive in ethanol production, some bar-

riers to implementation have been identied. One o these is

geothermal resource location. I the resource is ar rom

ethanol markets and byproducts markets and/or remote rom

transportation inrastructure, economics o an ethanol proj-ect could become prohibitive. Another challenge in the use

o geothermal energy in ethanol production is in the neces-

sary plant design modications. The majority o ethanol

plants use low-temperature steam in their process, but geo-

thermal fuids may be two-phase or single phase liquid, de-

pending on the resource temperatures and pressures.

This will require selection o dierent heat transer equip-

ment and modications to the plant process design (relative

to conventional), and will likely incur more design time and

cost that may become prohibitive.

Finally, there could be some opportunities in ethanolplants or waste heat recovery that can negatively impact the

economics o geothermal energy utilization. This might be

the case where thermal oxidation is the best means o de-

struction o regulated volatile organic emissions and/or

odors that could otherwise be released into the atmosphere.

Thermal oxidation o air pollutants typically requires de-

struction temperatures over 1,000F, resulting in a signi-

cant amount o waste heat available or recovery and use in

the ethanol production process.

Although some barriers do exist in urther development o

geothermal utilization in ethanol production, there are someadvancements being made as well, particularly with regard

to the use o lower temperature resources. New technologies

in ethanol production are evolving through research that has

been aimed at low-temperature, low-energy chemical pro-

cess o extracting ethanol rom many dierent types o or-

ganic materials.

CoNCLUdING sUMMary

A hypothetical ethanol plant using a dry-milling process

was considered or a easibility study, producing 10 million

gallons o ethanol on an annual basis. The energy raction

considered was 75% geothermal and 25% natural gas.

Some specic results o this study are as ollows:

According to BBI International (2003), about 85% o the

ethanol plants in the U.S. use natural gas as a source o

thermal energy. The remainder use propane, uel oil, or

coal. In general, about 25,000 Btu o energy is required to

produce a gallon o ethanol, and the associated dry distill-

ers grain requires an additional 12,700 Btu.

As o 2003, approximately 95% o U.S. uel ethanol was

manuactured rom corn.


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Geothermal utilization opportunities exist in three stages

o the production process: cooking, distillation, and drying

o the distillers grain. In addition, geothermal energy could

be used or space heating.

Cooking is generally accomplished at temperatures o 150-

180F (65-80C). The meal is exposed to a high tempera-

ture stage o 250-300F (120-150C) or a short period o

time to reduce bacterial growth in the mash.

Distillation occurs at temperatures between the boilingpoint o ethanol (173F (78.3C) at sea level pressure) and

the boiling point o water (212F (100C) at sea level).

Grain drying occurs at temperatures exceeding the boiling

point o water

For the base case examined here, the incremental cost o

the 75% geothermal plant above the conventional is ap-

proximately $4.57 million or 21.6%.

The estimated annual energy savings with the 75% geo-

thermal plant is $2.03 million or 63.2%. Energy costs ac-

count or 22.3% o total annual costs or the conventional

plant, while only 9.6% o the total annual cost is att ributed

to energy use in the 75% geothermal plant.

The conventional ethanol plant yields an annual prot be-

ore taxes o approximately $4.1 million, while the 75%

geothermal plant yields an annual prot beore taxes o ap-

proximately $6.1 million. This results in a pre-tax prot

margin o $0.41/gal. or the conventional plant and $0.61/

gal. or the geothermal scenario.

The present value o a 30-year lie-cycle o the 75% geo-

thermal plant is 1.54 times greater than the conventional

plant.

A sensitivity analysis o cost items on the present value,

shows that project economics are most sensitive to: ethanol

selling price, eedstock price, natural gas price, energy re-

quired per gallon o ethanol, initial geothermal cost, and

raction o energy provided by geothermal. Project eco-

nomics are relatively insensitive to electricity cost.

Some barriers to urther development o geothermal ener-

gy utilization in ethanol production include: distance o the

geothermal resource rom markets and/or inrastructure;

plant design modications to account or two-phase or sin-

gle-phase liquid geothermal fuids; and other waste heat

recovery opportunities at an ethanol plant.

New technologies in ethanol production are emerging that

require lower temperature and lower energy per gallon, ex-

panding possibilities or low-temperature geothermal en-

ergy utilization.

Figure 2. Sensitivity analysis o various cost items on the present value o a geothermal ethanol plant relative to a

conventional natural gas ethanol plant.

rEfErENCEsBBI International, 2003. Ethanol Plant Development Hand-

book, 4th Ed. BBI International. Cotopaxi, CO.


8/20


INTrodUCTIoN

Greenuels o Oregon is undertaking a new venture in the

Klamath Basin to produce biodiesel using geothermal ener-

gy. The acility is currently under construction, but the pro-

duction process is set up to make use o geothermal energy

in the biodiesel process.

THE GEoTHErMaL rEsoUrCE aNddIsTrIBUTIoN sysTEM

The Greenuels o Oregon biodiesel production acility is

located on the Liskey Ranch (Figure 1), a Known Geother-

mal Resource Area (KGRA) that has seen a long history ogeothermal energy usage since the 1970s. Current uses o

geothermal energy on the Liskey Ranch include space heat-

ing, greenhouse heating, aquaculture pond heating, and now

biodiesel production.

The geothermal resource has been described by Laskin

(1978) and Lund (1994). The area is located near the north-

west edge o the Basin and Range geological province, and

thus the occurrence o geothermal water is controlled by

geologic aults along the ront o the Klamath Hills. These

aults allow groundwater which has circulated to great

depths to rise upward into shallower aquiers where it can be

tapped by water wells. Groundwater temperatures availableor utilization are on the order o 190 to 210F, and wells on

the property can produce geothermal water at several hun-

dreds o gallons per minute.

THE GrEENfUELs of orEGoNGEoTHErMaL sysTEM

Greenuels o Oregon makes extensive use o their geo-

thermal resource or many heating purposes. Uses o geo-

thermal energy include radiant foor space heating o the

biodiesel production building, in addition to use in the pro-

GREENFUELS OF OREGON:GEOTHERMAL ENERGY UTILIZATION IN BIODIESEL PRODUCTIONAndrew Chiasson, Geo-Heat Center

duction o biodiesel itsel. From the biodiesel acility, the

geothermal water is cascaded to greenhouses when various

organic vegetables are grown, and to an aquaculture opera-

tion.

WHaT Is BIodIEsEL?

The Alternative Fuels Data Center o the U.S. Department

o Energy denes biodiesel as a domestically produced, re-

newable uel that can be manuactured rom vegetable oils,

animal ats, or recycled restaurant greases. Biodiesel is sae,

biodegradable, and reduces air pollutants such as particu-

lates, carbon monoxide, hydrocarbons, and air toxins. Blendso 20% biodiesel with 80% petroleum diesel (B20) can gen-

erally be used in unmodied diesel engines; however, users

should consult their OEM (Original Equipment Manuac-

turer) and engine warranty statement. Biodiesel can also be

used in its pure orm (B100), but it may require certain en-

gine modications to avoid maintenance and perormance

problems and may not be suitable or wintertime use.

THE BIodIEsEL ProdUCTIoN ProCEss

The general ormula or making biodiesel is:

alcohol + vegetable oil or at + heat + lye catalyst

biodiesel

The production process to be used by Greenuels o Ore-

gon is shown schematically in Figure 2. The process starts

with some type o eedstock or the organic oil. Greenuels

o Oregon is currently set up or processing canola or soy

beans with equipment shown in Figure 3 and 4.

The next stage o the process is to mix the organic vegeta-

ble oil with methanol and a sodium monoxide catalyst in the

reactor, which is a 600-gallon tank. Heat is also added to the

reactor through geothermal water at approximately 180F


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7GHC BULLETIN, MarCH 2007

Figure 1. Location map o Liskey Ranch.

Figure 2. Schematic drawing o the biodiesel production process at Greenuels o Oregon.


10/20


There is on-going controversy in scientic literature about

the energy balance o biodiesel production. In other words,

there is a recurring question o whether it takes more energy

to produce biodiesel than the energy that the biodiesel uelproduces. The Greenuels o Oregon project in the Klamath

Basin certainly requires a urther examination o this ques-

tion, and this will be the subject o uture bulletin articles.

aCKNoWLEdGEMENTs

The Geo-Heat Center wishes to thank Rick Walsh or pro-

viding the inormation or this article, and Katja Winkler or

providing the photographs o the equipment.

This process is ormally called transesterication and oc-

curs or approximately 30 minutes.

The mixture is then pumped to the decanter where geo-

thermal water is used to wash and separate the nished

biodiesel product rom other materials. Distilled water and

alcohol are recovered by vacuum pumping the decanter and

then recondensing the vapors.

Geothermal gray-water is routed to settling ponds andthen used in the greenhouses. Crude glycerol is a byproduct

o the process. A photograph o the biodiesel production

equipment is shown in Figure 5.

The biodiesel production target or Greenuels o Oregon

is about 1,500 gallons per day, but the actual production will

depend upon eedstock availability. Most o the biodiesel is

planned to be sold locally.

CoNCLUdING sUMMary

Greenuels o Oregon is undertaking a new use o geo-

thermal energy in the Klamath Basin: production o biodie-

sel. In addition, geothermal energy will also be used or

space heating o the building, and the geothermal water will

be cascaded or use in greenhouse and aquaculture pond

heating.

Figure 3. Feedstock grain storage silos.

Figure 4. Photograph o equipment or eedstock grinding.

Figure 5. Photograph o the biodiesel production

equipment.

rEfErENCEsLaskin, S., 1978. Klamath Greenhouses. Geo-Heat UtilizationCenter Quarterly Bulletin, July 1978, Oregon Institute o

Technology, Klamath Falls, Oregon.

Lund, J., 1994. Agriculture & Aquaculture Cascading the

Geothermal Way. Geo-Heat Center Quarterly Bulletin, No-

vember 1994, Oregon Institute o Technology, Klamath Falls,

Oregon.


11/20


INTrodUCTIoN

Wabuska (wuh-BUHS-kuh) is a very small unincorporat-

ed village in Lyon County, Nevada. The population is 150. It

is in the Walker River Basin, on the north end o the Mason

Valley, 10 miles north o Yerington, the Lyon County seat.

The elevation is 4300 eet. The town is on Highway 95A, and

a Union Pacic rail line crosses the highway at Wabuska.

The history o Wabuska (the Washoe Indian term or white

grass) started in the 1870s when the settlement served as a

coach and reight stop or travelers and shipments o sup-

plies going to the booming mining towns o Nevada, includ-

ing Aurora, Goldeld, and Bodie, Caliornia. By 1881 the

town was a stop on the newly constructed Carson and Colo-

rado railroad. Southern Pacic Rail purchased the rail line

around 1900, and soon ater copper was discovered in theMason Valley, increasing reight and passenger trac

through Wabuska until the decline o mining throughout Ne-

vada in the 1920s.

While Nevada mining operations drove the development

o Wabuska in the late 19th and early 20th centuries, Wa-

buska today is in a predominantly agricultural area. Current

local industry includes hay and alala, cattle and sheep, and

dairy. The only notable current non-agricultural business

and industry in Wabuska includes a plastics abricator (AES

GEOTHERMAL POwER GENERATION AND BIODIESEL PRODUCTIONIN wABUSkA, NEvADAClaude Sapp, Inniuel Biodiesel, Dayton, NV

Industries), Lindas Old Wabuska Bar, Homestretch Geo-

thermal and Inniuel Biodiesel.

There are hot springs in and near Wabuska, and the 20thcentury saw a ew businesses that sought to utilize the hot

water. Probably in response to the oil shock o the 70s, in

1981 TADs Enterprises built a 400,000 gallons per year

ethanol plant in Wabuska, hoping to rail in corn as the eed-

stock. The plant was operational or a ew years, and had an

old geothermal well that supplied heat or the ethanol pro-

cess. The owners commissioned a easibility study per-

ormed by the Geo-Heat Center (GHC), to assess the nan-

cial impact o expanded use o the geothermal resource,

looking or improvements that would lead to cost savings,

including electrical power generation.

Subsequent to the GHC study, Wabuska became home to

the rst geothermal power production unit in Nevada. In

1984, Wabuska I went online, an Ormat binary power pro-

duction unit. This was ollowed by Wabuska II in 1987, an-

other Ormat unit. While the ethanol plant was decommis-

sioned by the mid 1980s and then mothballed or decades,

geothermal power production continues today, and has been

operational in Wabuska almost continuously since going on-

line. Homestretch Geothermal currently operates the geo-

thermal acility.


12/20


GEoLoGy aNd HydroLoGy

The Wabuska geothermal area is located at the margin o Ma-

son Valley, where both the valley margin and the thermal springs

coincide with a northeast-striking zone o aults reerred to asthe Wabuska lineament (Stewart, 1988). Some aults are associ-

ated with the lineament cut Pleistocene units (Sawyer and Saw-

yer, 1999). Production is apparently rom Quaternary gravels

and sands; geothermal fuid may circulate along aults related to

the Wabuska lineament as well as an unconormity above Meso-

zoic metasedimentary rocks possibly present at depth (Nevada

Bureau o Mines and Geology, 2006).

Table 1. Water Chemistry

mg/L mg/L

Al 0.08 K 19.83

As 0.05 Na 300.67

B 0.02 Cl 63.40

Ba 1.09 F 9.47

Ca 42.17 SO4 447.00

Cu 0.02 pH 7.39

Fe 0.02 TDS 1107.67

Mg 0.28 Hardness 106.33

Constituents with concentrations in excess o water quality

criteria are arsenic (As), boron (B), copper (Cu), fuoride

(F), sulate (SO4) and TDS (Nevada Division o Environ-

mental Protection Fact Sheet 2003 2005).LoCaTIoN aNd dEsCrIPTIoN

Homestretch Geothermal operates the acility at 15 Julian

Lane in Wabuska, NV (39 09' 40" N, 119 11' 00" W, T15N

R25E S15SW and S16SE).

Homestretch Geothermal owns 500 acres ee simple along

with the geothermal rights and 8500 acre eet o water rights.

The majority o the land is undeveloped, but expansion plans

include the development and sale o an industrial park served

by geothermal utilities on the property.

GEoTHErMaL WELLs& dIsCHarGE WaTEr

The resource consists o two wells reerred to as Produc-

tion Well #1 (PW#1) and Production Well #2 (PW#2), each

less than 500 eet deep. PW#1 was dr illed in 1959 and was

rst used as the water and heat supply or a large hydro-

ponic vegetable business. In 1984, Tads Enterprises who

then owned the property and resource built the rst geo-

thermal power plant to ever sell power in Nevada. Theyutilized the fow rom PW#1 or the brine to power the bi-

nary Rankine cycle generator and then used the discharge

brine to provide the cooling water.

The original temperature o the resource was 220F. The

fow rate o the well was 750 gpm. The original well is still

producing 750 gpm at 218F 48 years later, and the well has

produced water continuously at least 97% o the entire past

20 years. Flow has not diminished at all. The water level in

the well while pumping is regularly monitored and only

fuctuates minimally rom season to season but remains

constant year to year. In May 2003, Homestretch Geother-

mal had the well televised while it was down or a pump

change-out. The televising revealed that the original casing

is still in excellent condition even though it is 48 years

old.

Production Well #2 was drilled in 1986 by TADs Enter-

prises and a second power generation unit was built and put

on line that year. PW#2 also started with a temperature o

220F. It also, 20 years later, continues to produce water at

218F. It originally was set up to pump 800 gpm. In May o

2003 Homestretch Geothermal also had PW#2 televised

and the casing was in perect condition. Every aspect o the

well design showed to be excellent. Another fow test wasconducted by Homestretch Geothermal and the well pro-

duced 2,200 gpm or 48 hours with very little draw down

on the well and no apparent aect on PW#1. The well cur-

rently produces 2,800 gpm with virtually no change in

temperature, fow or draw down.

Currently, PW#1 is o-line, and has not been pumped or

two years. PW#2 is fowing 2,800gpm at 218F, and is run-

ning the two original power production units, and a third

unit that was added by Homestretch Geothermal. Plans or

expanded production include drilling a third well in 2007

and putting our more power production units online.

One unique act about Wabuska is that geothermal water

is not reinjected ater passing through power generation. It

is the only geothermal site in Nevada that is not required by

the State to reinject, so the water simply passes through

ponds to cool o. Water exits the geothermal units at 180F,

and is pumped to two 400 x 125 cooling ponds. Each pond

has 110 spray nozzles three eet above the pond surace that

the hot water sprays through to air cool and settle in the

pond. Water exits the ponds, and then drains onto property

to leech back into the soil.

Figure 1. 2MW geothermal power plant that provides

electricity or the biodiesel plant.


13/20


Figure 2. Spray pond.

PoWEr ProdUCTIoN & oPEraTIoNs

Homestretch Geothermal purchased the two power pro-

duction units TADs installed in the 1980s, and in 2002

added a third power production unit that is producing powertoday. There are our more power production units staged on

property that are ofine. Once drilling o the third well on

property is complete, these last our units will be brought

online. Each o the seven units is rated at 800kW.

Current total power production rom the three units aver-

ages 1.2MW, throughout the year. Peak production in the

winter is about 1.4MW, and in the warmer summer months

electrical generation dips to about 1.1MW. The plant service

requirement is 290kW, so a net o approximately 910kW is

sold back to Sierra Pacic Power Company and put back on

the grid, connected via a 24.9kV line. The current electricity

is purchased under the terms o a 30 year power purchase

agreement (PPA) that was entered into with Sierra Pacic in

1985, with purchase rates in the range o $0.06/kWh. An-

other PPA is being negotiated or the planned capacity in-

crease and additional electrical generation expected to come

online this year.

Operation and maintenance is perormed by a sta o two

persons. The units operate mostly unattended and automati-

cally, with an estimated 98% runtime. Should the units ail

or shutdown, the service panel identies the problem to be

xed, and an emergency diesel generator provides startup

power or the acility ater problems have been xed. Rou-tine maintenance costs average approximately $60,000 per

year excluding salary. In 2006, routine and emergency main-

tenance included replacing a well pump, cleaning condens-

ers, cleaning out heat exchanger tubing, rebuilding the tur-

bine in unit #1, and replacing two iso-pentane pumps. The

only extended downtime the plant has ever experienced was

between 1996 and 1998. The plant was shutdown in 1996 due

to the unavailability o Freon 114, the working fuid in the

power units. The units were converted to iso-pentane in

1998, and resumed regular operations.

BIodIEsEL PLaNT

In 2006, Homestretch Geothermal and Inniuel Biodie-

sel entered into an agreement to orm Inniuel Wabuska, a

company that would retrot the decommissioned ethanol

plant on property in order to produce biodiesel. The goal was

to produce a liquid renewable uel using renewable energy

or the heat and electricity used in biodiesel production, and

in so doing, build the worlds rst geothermal biodiesel

plant.

The biodiesel acility is a 3,600 sq. t. building housing

two reactor processors (7,000 and 4,000 gallons), and eight

7,600 gallon wash tanks in two banks o our. Though cur-

rent production is under 1.0 million gpy, capacity o the plant

is between 4-5 million gpy o biodiesel. Additional storage

tanks are outside, the whole system is stainless steel, and all

is connected by stainless steel piping and approximately 200

connected HP o motors and pumps.

The raw material needed or biodiesel is vegetable oil and

alcohol. Current production is rom used vegetable oil col-

lected rom local restaurants, with additional oil comingrom a grease collector in Caliornia. The alcohol used is

methanol, and this is the only petroleum product directly

used in the process. In order to be more green Inniuel

has entered into discussion with a company that recycles

medical waste, their byproduct being methanol. I this meth-

anol rom a recycled product is used in Wabuska, Inniuel

may run the only liquid uel plant in the world that does not

use petroleum products. To urther eciency, Inniuel is

planning to use the two distillation towers rom the old etha-

nol acility to recover unused methanol rom the biodiesel

production process. Distillation is an energy intensive pro-

cess, but geothermal makes it much more economic to pur-

sue.

Inniuel has also partnered with the University o Ne-

vada Reno (UNR) and Desert Research Institute (DRI) to

investigate the easibility o growing oil crops in Nevada as

an alternative to the predominant dirt crops, hay and alala.

Figure 3. Grain silo, methanol recovery towers, tank arm.


14/20


Nevada armers have been receptive to the idea, accepting

crops like crambe, fax, and sunfower as rotation crops that

improve the soil and use less water than hay or alala. As

Wabuska is in a ripe agricultural valley and there is muchland proximate to the geothermal and biodiesel plants to cul-

tivate, Inniuel can experiment with oil crops in partner-

ship with UNR and DRI.

Algae is also being investigated as an oil crop. In the

1980s the Department o Energys Renewable Fuels Lab did

research on algae to determine i it was easible to extract oil

rom algae to produce biodiesel. Their ndings generally

supported the concept. One point to consider was that they

were proposing to grow algae in the western deserts where

land and sunlight are abundant, but where temperatures

could drop at night providing a less than ideal environment

or algae to grow. The lack o a system to regulate tempera-ture was considered a hurdle, but the geothermal at Wabuska

gives Inniuel, UNR, and DRI the means to keep a constant

and ideal temperature or algae research and production. The

researchers at UNR are perecting an oil extraction process

or the algae that is based on heating the oil out o the algae,

eliminating the need or mechanical or chemical extraction.

The extraction process is ecient at 200F, a perect tem-

perature or the resource at Wabuska. While there is also a

grain storage silo and a hammer mill at the Wabuska acility

or mechanical oil extraction, the oil extraction process us-

ing heat alone is an example o how we are searching or

every way to make use o the geothermal resource onsite.

CoNCLUsIoN

Though Wabuska is a sleepy little village where there are

more sheep than persons, exciting things are being done

there with geothermal water. It has a long history o direct

and indirect geothermal use, and is notable as being the site

o the rst geothermal electricity production in the State o

Nevada. In the past, geothermal was used in numerous busi-

nesses in Wabuska, rom growing hot house tomatoes to dis-

tilling ethanol. Recently we have added to the history, pro-

ducing biodiesel using geothermal or the heat and electricity

needed in the biodiesel plant. The uture looks promising.

As our academic research partners are looking or ways to

expand renewable energy production in Nevada, Wabuskamay turn into an important eld research center. Hopeully,

others may benet rom our experience as well.

Figure 4. Biodiesel processors and wash tanks are in the

building to the let.

rEfErENCEsSawyer, J.E., and Sawyer, T.L., compilers, 1999, Fault number

1665, Unnamed aults west o Desert Mountains, in Quater-

nary ault and old database o the United States: U.S. Geo-

logical Survey website, http://earthquakes.usgs.gov/regional/

qaults, accessed 2/27/07.

Stewart, J.H., 1988, Tectonics o the Walker Lane belt, west-

ern Great Basin: Mesozoic and Cenozoic deormation in a

zone o shear, in Ernst, W.G., Metamorphism and crustal evo-

lution o the western United States, Rubey volume VII: Pren-

tice Hall, Englewood Clis, N.J., p. 683-713.

Nevada Bureau o Mines and Geology (NBMG), 2006, Wa-

buska Hot Springs (TADs Enterprises): Nevada Bureau o

Mines and Geology website http://www.nbmg.unr.edu/geo-

thermal/site.php?sid=Wabuska Hot Springs, accessed

2/27/07.

Figure 5. Algae research ponds.


15/20


DESIGN OF A GEOTHERMAL ENERGY DRYER FOR BEANS AND GRAINS DRYING INkAMOJANG GEOTHERMAL FIELD, INDONESIAUntung Sumotarto, Agency or the Assessment and Application o Technology-BPPT, Indonesia

aBsTraCT

Indonesia is a country rich in geothermal energy. O ap-

proximately 20,000 MWe energy potential, only about 850

MW has been utilized or electricity purposes. There are notmany direct utilization activities or various purposes that

have been implemented. This paper discusses a design o a

geothermal dryer or beans and grains drying that will be

implemented in Kamojang geothermal eld, West Java, In-

donesia. Geothermal fuid waste rom a Kamojang well o

approximately 160C will be used to supply the equipment.

The heat will be extracted to produce a room drying tem-

perature, or which coee bean will be used as an experi-

mental grain to be dried. A tube-bank heat exchanger has

been designed, consisting o 1-meter-staggered pipes o 2-

inches (50.1-mm) outer diameter. An air blower rom one

side produces air fow o varying velocities to fow heated airinto a drying room on the other side. With a geothermal fuid

fow containing a heat transer rate o 1000 W and various

air fow velocities o 4 to 9 m/s, the HE design could produce

an output drying temperature o 45.48 to 40.64C and drying

energy (heat) produced in the drying room o about 41.0 to

68.0 kW/m length o the heat exchanger. Depending on the

beans humidity, the drying time has to be set accordingly.

INTrodUCTIoN

Indonesia is a country having many volcanoes and rich in

geothermal energy. There are at least 177 volcanic centers

that are spread over volcanic belts o 7000 km along the In-donesian islands. From that many centers, there is at least

20,000 MWe-equivalent rom geothermal energy resources

contained in the volcanic areas. Islands in which geothermal

energy can be ound are Sumatera, Java, Nusa Tenggara, Su-

lawesi, and Maluku.

By now, only about 850 MW o that much energy potency

has been utilized or electricity power generation. The rest

has not been utilized optimally. Among the elds that have

been developed are Kamojang, Darajat, Gunung Salak,

Patuha, Wayang Windu, Dieng, Lahendong, and Sibayak.

Electricity has been produced rom those major elds. Un-

ortunately, there is only limited direct utilization o geo-

thermal energy in those elds as well as in other undevel-

oped ones.

Meanwhile, in the geothermal elds that have been devel-

oped and utilized such as Kamojang, Dieng, Darajat, Gu-

nung Salak, etc, there have been production geothermal

wells that already have depleted pressure, temperature, and

production rate thus unable to supply the existing electric

power plants. Such wells have been modied to re-injection

or monitoring wells. There are also waste geothermal fuids

rom electric power plants that are usually re-injected into

the reservoir to maintain the lie o the geothermal reservoir.

The heat contained in the fuids can still be extracted to sup-

ply equipment or engines or producing resh water steam, tosupply heating or drying equipment or sterilization o grow-

ing media, drying agricultural and husbandry products and

other direct utilizations.

The existence o geothermal energy resources that is com-

monly ound in mountainous and inland regions has its own

benet. In Indonesian mountainous and inland regions there

are ound agricultural, plantation, and orestry areas in

which their products require processes such as drying, pres-

ervation, heating, sterilization, pasteurization, etc. The agri-

cultural and plantation product processing requiring heat are

or examples: rice, coee, and tea drying, potato seeding,

mushroom cultivation, milk pasteurization, etc.

To initiate direct utilization o geothermal energy, the

Agency or the Assessment and Applied Technology (BPPT),

has been doing research in that eld since 1999-2000. The

rst eort was a research in geothermal energy utilization

or sterilization o mushroom growing media in Kamojang

geothermal eld. The research was a success and is now

planned to continue to commercial scale. The research pres-

ently continues to design a geothermal dryer or beans and

grains. This paper discusses such design to see the technical

easibility i the equipment will be built (Sumotarto et al.,

2000)(Sumotarto, 2001).

METHodoLoGy & dEsIGNof EQUIPMENT

Traditionally, grains and beans drying in Indonesia have

been done by heating the products under sunshine (solar

drying). The products will be infuenced by seasonal and

weather changes, thus making the drying process un-con-

tinuous. This will result in cracking, racturing, and imper-

ect drying products.

To improve the process, drying has to be done continu-

ously, requiring continuous heat supply. This can be reached

by using continuous energy resource supply such as geother-mal fuid fows.

EquipmEnt DEsign

The dryer used in this research will be made o a fuid-air

heat exchanger to produce hot air that will be blown into a

drying room lled with trays o grains or beans. Figures 1

4 show the design o the equipment. The waste geothermal

fuid is fowed into a bank o steel pipes, and air is blown

outside the pipes to extract heat rom geothermal fuids in-

side the tubes or the drying process.


16/20


The equipment does not use a drying belt to save energy

or moving the belt. Instead, the beans and grains are placed

on trays in the drying room. The only moving part is an air

blower that can be designed to move by geothermal energy

(pressure), while its heat content is used or the heat ex-

changer. The air blower is placed on one side o the heat ex-

changer while the drying room is on the other side.

The drying duration depends on the original humidity o

the products. By doing several drying experiments, an ideal

drying time can be ound or which the product is perectly

dried. The dryer is designed as simple to assist the technical

easibility o geothermal energy direct utilization. I the dry-

ing is proven to be easible, then the technology and design

can be improved while the scale can be increased to meet a

commercial project.

HEaT & ENErGy EQUaTIoNs

The energy balance equations governing the heat exchang-

er can be modeled in two parts. The rst part is heat transer

rom the geothermal fuids inside the tubes to the outer side

o the tubes, and the second part govern the heat transer

process outside the tubes into the drying room. Figure 3

shows the rst part o energy (heat) transer and, gure 4

shows the second part.

Calculation o energy transer in this part is perormed

when the equipment is in operation with steady state energy

Figure 1. 3D view o the geothermal dryer design or drying grains and beans.

Figure 2. Longitudinal cross section o the geothermal dryer


17/20


Figure 3. Heat transer across the heat exchanger pipes.

transer (heat fow). The calculation is based on phenomena

where energy (heat) fows across a cylindrical pipe (Figure

3). Outside the heat exchanger the air is assumed to fow

convectional into the drying room. There is assumed no oth-

er mode o heat fows i.e. radiation, because o the high speed

o convection air current.

part i:

For simple calculation, this part can be modeled as one-

dimensional radial heat fow. I there is no energy generation

in the equipment, heat transer equation governing the sys-

tem is

According to Fouriers Law, energy (heat) fow rate by

conduction through solid cylindrical surace can be ex-

pressed as

where A=2rL= area o the surace normal to the direction

o heat transer. The heat transer rate qr , not heat transer

fux qr, is a constant value in radial direction.

Equation (1) can be integrated twice to nd a general solu-

tion

With boundary conditions: T(r1) = Ts,1 and T(r2) = Ts,2

(Figure 4), C1 and C2 can be ound as

Substituting C1 and C2 back to Equation (1) results in a

general equation o temperature or the system as ollows

Note: Temperature distribution or a system associated

with radial conduction heat fow through a cylindrical sur-

ace is in the orm o logarithmic, not linear such as on a fat

wall o similar condition.

Further, substitution o Equation (4) into Equation (2) re-

sults in a general equation o heat rate as ollows

where

The heat fow rom the center o the tube to the inside wall

o the tube and rom the outer side o the tube into the open

air is a convection fow. For the whole system rom T,1 -> Ts,1

-> Ts,2 -> T,2, the heat fow rate equation (5) can be ormu-

lated as

which can also be expressed in heat rate equations or each

portion o the entire fow as

Those three equations (6.a, 6.b, and 6.c) can be used to

calculate Ts,1 andTs,2 because qr= qr,1 = qr,2 = qr,3 .

part ii:

As heat leaves the outer side o the pipes the governing

equations can be modeled as an air convection fow through

a bank o tubes (Figure 4). The tube rows in this heat ex-

changer are staggered in the direction ofuid velocity (V).

The conguration is characterized by the tube diameter (D)


18/20


and by the transverse pitch (ST) andlongitudinal pitch (SL)

measured between tube centers. Flow conditions within the

bank are dominated by boundary layer separation eects

and by wake interactions, which in turn infuence convec-

tion heat transer. Incropera et.al (1985), describes such phe-

nomena with the ollowing equations.

The average convection heat transer coecient (h) can

be calculated using the ollowing equation

The heated air temperature produced rom the heat ex-changer can be calculated using a log-mean temperature di-

erence

where TiandToare temperatures o the fuid as it enters (Ti)

and leaves (To) the bank, respectively andTs is the tempera-

ture o the tube outside surace. The outlet temperature To,

which is needed to determine Tlm may be estimated rom

Finally, the heat transer rate per unit length o the tubes

may be computed rom

sIMULaTIoN aNd rEsULTs

Using the equations described in the above section, it can be

determined the relation between the air fow velocity (V) pro-

duced by the air blower and the drying temperature (To). De-

pending on the drying temperatures that are specic to each

product, the air fow velocity (V) can be adjusted accordingly.

The calculation and simulation are conducted as ollows:

1. Write a computer program or the calculation according

to the equations described in previous sections.

2. Prepare parameters and constants needed in the calcula-

tion such as geothermal fuid temperature inside the tube,

drying temperature required, heat transer coecients,

etc. Table 1 shows parameter and constants needed or

the calculation.

Figure 4. Heat exchanger pipes lay-out.

The amount o heat transer can be calculated by, rst cal-

culating the air-side Nusselt number as:

C and m are constants that depend on tube conguration

(tabulated in table 1 (Howell and Buckius, 1987)).

TheReynolds number (Re D,max) or the oregoing correla-

tions is based on the maximum fuid velocity (Vmax) occurring

within the tube bank. For the staggered conguration, the

maximum velocity may occur at either the transverse plane

or the diagonal plane. I the rows are placed such that


19/20

GHC BULLETIN, MarCH 2007 17

3. Usingtheproperdataandcalculationprocedure,itcan

becalculatedtheparameterneededorthedryingpro-

cess.

4. Tablesandguresshowingvariousrelationscanbemade

accordingtothecalculationresults.

velocitiesromtheairblowerobetween4to9m/s,thedry-

ingtemperaturewouldvarybetween45.48to40.64C,which

willproduceadryingheattranserrateo41.0to68.0kW

permeterlengthotheHE.

CONCLUSIONS

Fromthedesignothegeothermaldryingequipmentand

equationsmodelneededorthedesigntherecanbecalcu-

lated various parameters needed or the drying process.

From thecalculation andsimulationperormedin this re-

searchitcanbeconcludedtheollowing:

Table 1. Parameters used in the simulation and calculation

o the geothermal drying equipment or grains and beans.

Table 2. Relationship between geothermal heat fow rate

(qr[W]) inside the HE tubes and inside and outside pipe

surace temperature (Ts1,T

s2[C]) and air temperature (T

2[C])

or a constant geothermal fuid temperature (T1

[C]) o 160

[C].

Usingtheabovesimulationprocedureitisoundthatata

geothermalfuidtemperatureo160C,therecanbecalcu-

latedvarious heat transer rate anddrying temperatureat

variousairfowvelocityproducedromtheairblower.Ta-

bles2,3and4showtheresultsothecalculationsandthe

relationsbetweenairfowvelocitytoheattranserrateand

dryingtemperature.

Table2showsthatatvariousgeothermalfuidfowswith

heat transer rate (qr)obetween1000to6000W,theoutside

suracetemperatureotheheatexchangerpipeswouldreach

ashighas159.93to159.60C.Further,Table3showsthatat

theabovevariousheattranserrate,theoutput temperature

(To)otheHEwouldreach45.48to45.44C,romwhichwe

canhaveenoughtemperatureordryingpurposes.Itcanbe

seenherethatvaryinggeothermalheattranserratedoesnot

resultinsignicantrangeooutsidetemperatureotheHE

pipesandoutputtemperatureotheHEinthedryingroom.

Thereore,itisenoughtopickonevalueothegeothermal

heattranserratetobeusedorsensitivityanalysisothe

othergoverningparametersi.e.air fow rate (V)romthe

blower.

Further,bypickingaxedheat transer rateo 1000W,

whichresultsinoutsidesuracetemperatureotheHEpipes

o159.93C,itcanbeseeninTable4thatorvariousairfow

Table 3. Output (drying) temperature (To[C]) and heattranser rate per length o HE (q

rate[kW/m]) at various

outside surace temperature o the HE (Ts2

[C]).

Table 4. Output (drying) temperature (To[C]) and heat

transer rate per length o the HE (qrate

[kW/m]) at various

air fow rate (V[m/s]) rom the air blower or a constant

geothermal heat fow rate (qr[W]) o 1000 [W] and a constant

surace temperature o the HE pipes (Ts[C]) o 159.93 [C].


20/20

GEO-HEAT CENTEROregon Institute of Technology

Klamath Falls, OR 97601-8801

Thedryingequipmentdesignedinthisresearchusesaheat

exchangerthatcanbemodeledasstaggeredpipesbankin

whichreshairromtheatmosphereisfowedthroughthe

heatexchangerusinganairblowerintoadryingroomlled

withtraysoproductstobedried.

Theequationsgoverningtheheatexchangerdesigncanbe

modeledintotwoparts.Therstpartisheattranserrom

geothermalfuidsinsidethepipestotheoutersideothe

pipewhereheatistranserredthroughconvectionandcon-

ductionmodes.Thesecondpartisheattranserromthe

outersideothepipeintothedryingroomwhereheatis

mainlytranserredby(orced)convectionmode.

Dependingontheproductbeingdried,thedryingtempera-

turecanbesettondaproperairfowvelocityromtheair

blower. In this experiment, calculation is perormed to

computevariousheattranserrateandairfowvelocityor

varyingdryingtemperatureusingaxedgeothermalfu-

idstemperatureo160C.

Calculationo the experiment using a xed geothermal

fuidfowwithaheattranserrateo1000Wwithvarious

airfowvelocitieso4to9m/sresultsinanoutputdrying

temperature o 45.48 to 40.64 C, a temperature range

enough or drying purposes, with drying energy (heat)

producedinthedryingroomoabout41.50to68.90kW/m

lengthotheheatexchanger.

Fromthesimulationsperormedintheexperimentsshows

thatthemostimportantparameterstogovernthedrying

temperatureare,amongothers,geothermalfuidtempera-

ture,geothermalfuidfowratewhichdeterminesgeother-

malheattranserrate,andairfowvelocityromtheblow-

er.

Thisresearchhas tobeollowedupwithmoredetailex-

perimentsandcalculationsinordertondacompleteand

thoroughdesignotheequipmentthatcanworkoptimally.

rEFErENCESHowell,J.R.&Buckius,R.O.:FundamentalsoEngineering

Thermodynamics,McGraw-HillBookCo.,1987,697p.

Incropera,F.P.&DeWitt,D.P.:Fundamentals oHeat and

MassTranser,2ndEd.,JohnWiley&Sons,1985,802p.

Sumotarto,U.,Surana,T.,andLasman,F.,(2000)Utilization

oGeothermalEnergyorMushroomGrowing,Presentedat

the4thINAGAAnnualConerence,Jakarta,25-26January

2000.

Sumotarto,U.:ProblemsinDirectUtilizationoGeothermal

EnergyinKamojangGeothermalField,Indonesia.Presented

attheINAGAAnnualConerence,Yogyakarta,2001.

june 2007 geo-heat center quarterly bulletin

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