June 1999 Geo-Heat Center Quarterly Bulletin

VOL. 20, NO. 2

JUNE 1999

SMALL GEOTHERMAL POWER PROJECTS

ISSN 0276-1084

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GEO-HEAT CENTER QUARTERLY BULLETIN ISSN 0276-1084

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

CONTENTS

PUBLISHED BY

Page

Small Geothermal Power Plants: Design, Performance and Economics Ronald DiPippo

1

Small Geothermal Power Project Examples John W. Lund and Tonya Toni Boyd

9

GEO-HEAT CENTER Oregon Institute of Technology 3201 Campus Drive Klamath Falls, OR 97601 Phone: 541-8851750 Email: [email protected]

Opportunities for Small Geothermal Power Projects Laura Vimmerstedt

27

All articles for the Bulletin are solicited. If you wish to contribute a paper, please contact the editor at the above address.

Geothermal Small Power Generation Opportunites in the Leeward Islands of the Caribbean Sea Gerald W. Huttrer

30

Geothermal Pipeline

34

Progress and Development Update Geothermal progress Monitor

Cover Photos: Top Photograph - Fang, Thailand, 300 kWe ORMAT Energy Converter modular unit, Electric Generation Authority of Thailand (EGAT) (photograph by ORMAT Inc., Sparks, NV--used with permission); and Bottom Photograph - Blue Lagoon at Svartsengi, Iceland combined thermal and electric power plant (16.4 MWe total), The Sudurnes Regional Heating Corporation (photograph by Haukur Snorrason, Reykjavik, Iceland--used with permission).

EDITOR John W. Lund Typesetting/Layout Typesetting/Lay out - Donna Gibson Graphics - Tonya Toni Boyd

WEBSITE http://www.oit.edu/~geoheat FUNDING The Bulletin is provided compliments of the Geo-Heat Center. This material was prepared with the support of the U.S. Department of Energy (DOE Grant No. FG0199-EE35098). However, any any opinions, findings, findings, conclusions, or recommendations expressed herein are those of the author(s) and do not necessarily reflect the view of USDOE.

SUBSCRIPTIONS The Bulletin is mailed mailed free of charge. Please send your name and address to the Geo-Heat Center for addition to the mailing list. If you wish to change your Bulletin Subscription, please complete the form below and return it to the Center.















SMALL GEOTHERMAL POWER PLANTS: DESIGN, PERFORMANCE AND ECONOMICS Ronald DiPippo, Ph.D. Mechanical Engineering Department University of Massachusetts Dartmouth North Dartmouth, Massachusetts 02747 A BRIEF HISTORY OF GEOTHERMAL POWER GENERATION Ninety-five years ago, in the Tuscany village of Larderello, electricity first flowed from geothermal energy when Prince Piero Ginori Conti powered a 3/4-horsepower reciprocating engine engine to drive drive a small generator. generator. The Prince was thereby able to light a few bulbs in his boric acid factory situated amid the boron-rich boron-rich geothermal steam steam field. He upgraded the power system to 20 kW in 1905 [1]. Commercial delivery of geothermally-generated electric power occurred in 1914 when a 250 kW unit at Larderello provided electricity to the nearby cities of Volterra and Pomarance.. Prior to being destroyed in 1944 during World Pomarance War II, Larderello had a total power capacity of 136,800 kW, an annual generation greater than 900 GWh, and an average annual capacity factor of more than 75 percent. The plants were rebuilt after the war and extensive development of the steam field began. Today, there are over 740 MW installed installed at Larderello and the other nearby geothermal fields in the Tuscany region of Italy. Italy. Many of the power plants plants are in the 15-25 MW range, qualifying them as small power plants. New Zealand was the first country to operate a commercial geothermal power plant using a liquid-dominated, hotwater type reservoir (as contrasted with the steam-type at Larderello).. This took place at Wairakei in 1958. The United Larderello) States became the third country to use geothermal energy to generate electricity in 1960 when the Pacific Gas & Electric Company (PG&E) inaugurated an 11 MW Geysers Unit 1. This small plant later earned the designation as a Mechanical Engineering Historical Historical Landmark. The U.S. has become the largest generator of geothermal electricity with an installed capacity of 2850 MW [2,3]. A summary of the state of worldwide installed geothermal electric generating gener ating capacity is given . in Table 1 [4] .

Small power plants have played an important role in the development of geothermal geothermal energy. Since it is not practical practical to transmit high-temperature steam over long distances by pipeline owing to heat losses, most geothermal geotherma l plants are built close to the resource. resource. Given the required minimum spacing of wells to avoid interference (typically 200-300 m) and the usual capacity of a single geothermal well of 4-10 MW (with some rare, spectacular exceptions), geothermal powerplants tend to be in the 20-60 MW range, even those associated with large reservoirs. reservoirs. Much smaller plants, plants, in the the range of 5005003000 kW, are common with binary-type plants. Table 1 Summary of Worldwide Installed Geothermal Power Capacity (as of 1998) Country MW United States 2850 Philippines 1848 Mexico 743 Italy 742 Indonesia 589.5 Japan 530 New Zealand 364 120 Costa Rica El Salvador 105 Nicaragua 70 Iceland 50.6 Kenya 45 28.78 China Turkey 21 Portugal (Azores) 16 Russia 11 Ethiopia 8.5 4 France (Guadeloupe) Argentina 0.7 Australia 0.4 Thailand 0.3 Total 8147.78

No. Units 203 64 26 na 15 18 na 4 5 2 13 3 13 1 5 1 2 1 1 1 1

MW/Unit 14.0 28.9 28.6  39.3 29.4  30 21 35 3.9 15 2.2 21 3.2 11 4.2 4 0.7 0.4 0.3

Plant Types1 DS,1F,2F,B,H 1F,2F,H 1F,2F,H DS,2F,H DS,1F DS,1F,2F 1F,2F,H 1F 1F,2F 1F 1F,2F,H 1F 1F,2F,B 1F 1F,H 1F H 2F B B B

1 DS=Dry Steam, 1F=Single Flash, 2F=Double Flash, B=Binary, H=Hybrid Note: A unit is defined as a turbine-driven generator. Data from Ref. [4] and various other sources. sources.

INTRODUCTORY REMARKS The rest of this article will cover the basic geothermal energy conversion systems with regard to their design, thermodynamic performance, performance, and economics. economics. It draws heavily on a recent encyclopedic contribution by the author to the Second Edition of the McGraw-Hill Standard Handbook of

DIRECT-STEAM PLANTS Direct-Steam plants are used at vapor-dominated (or dry steam) reservoirs. Dry, saturated or slightly superheated steam is produced from from wells. The steam carries noncondensable noncondensable gases of variable concentration concentration and composition. Steam from















ing transmission, and a final moisture remover at the entrance to the powerhouse. Figure 1 is a simplified flow diagram for a Direct-Steam plant. A Nomenclature List List at the end of the article identifies identifies the items in this and the ensuing ensuing flow diagrams [5]. [5]. A condensing plant is shown as typical of an installation installati on in the United States. In some countries, back-pressure, back-pressure, exhausting-to-atmoexhausting-to-atmosphere operation is possible in accordance with local environmental standards. standards. Because of noncondensable noncondensable gases (NCG) found in geothermal steam (typically 2-10% by wt. of steam, but sometimes higher), the gas extraction system is a critical plant component. Usually, 2-stage 2-stage steam ejectors with interinterand after-condensers are used, but in some cases vacuum pumps or turbocompressors are required.

Figure 1. Simplified flow diagram for a direct-steam geothermal power plant (5).

A surface-type condenser is shown but direct-contact condensers are often often used. The former is preferred whenever the NCG stream must be treated or processed before release to the atmosphere, e.g., whenever emissions limits for hydrogen sulfide would be exceeded. exceeded. In such cases, an elaborate chemical plant must be installed to remove the hydrogen sulfide. Most units at The Geysers in northern California use Stretford (or similar) systems for this purpose, yielding elemental sulfur as a by-product. Such an elaborate system system would not be economically justified at a very small plant. A water-cooled condenser is shown. Since the steam condensate is not recirculated to a boiler as in a conventional powerplant, it is available available for cooling tower makeup. In fact, an excess of condensate (typically, 10-20% by wt. of the steam) is available and is usually injected back into the reservoir. Long-term production can deplete the reservoir and novel ways are being developed to increase the amount of fluid being returned to the reservoir [6,7]. The use of air-cooled condensers would allow for 100% return but so far have been uneconomic. Mechanical induced-draft cooling towers, either counterflow or crossflow, are mostly used for wet cooling c ooling systems, but natural-draft towers are used at some plants. Recent practice, particularly in Italy, has seen nominal powerplant ratings of 20 or 60 MW per unit, the smaller units being of modular design for rapid installation. installation. Flexible design allows the basic unit to be adapted to a fairly wide range of actual steam conditions. Table 2 lists major the equipment typically used in the four basic types of geothermal powerplants [5,8].

Table 2 Major Equipment Items for Geothermal Powre Plants Type of Energy Conversion System Equipment Steam and/or Brine Supply: Downhole pumps Wellhead valves & controls Silencers Sand/particulate Sand/particu late remover Steam piping Steam cyclone separators Flash vessels Brine piping Brine booster pumps Final moisture separator Heat Exchangers: Evaporators Condensers Turbine-Generator Turbine-Ge nerator & Controls: Steam turbine Organic vaopr turbine Dual-admission Dual-admis sion turbine Control system Plant Pumps:

Dry Steam

Single Flash

Double Flash

Basic Binary

No Yes Yes Yes Yes No No No No Yes

No (Poss.) Yes Yes No Yes Yes No Yes Poss. Yes

No (Poss.) Yes Yes No Yes Yes Yes Yes Poss. Yes

Yes Yes No Yes No No No Yes Poss. No

No Yes (No)

No Yes (No)

No Yes

Yes Yes

Yes No No Yes

Yes No No Yes

Yes No Yes Yes

No Yes No Yes















FLASH-STEAM PLANTS Dry steam reservoirs are rare, the only known major fields being Larderello and and The Geysers. The most common type type of geothermal reservoir reservoir is liquid-dominated. liquid-dominated. For artesian-flowartesian-flowing wells, the produced fluid is a two-phase mixture of liquid and vapor [9]. The quality of the mixture (i.e., the weight percentage of steam) is a function of the reservoir fluid conditions, the well dimensions, and the wellhead pressure which is controlled by a wellhead valve valve or orifice plate. Typical wellhead qualities may range range from 10 to over 50 %. Although some experimental machines have been tested which can receive the total two-phase flow and generate power [10-12], the conventional approach is to separate the phases and use only only the vapor to drive a steam turbine. Since the wellhead pressure is fairly low, typically 0.5-1.0 MPa (75-150 lbf/in2, abs), the liquid and vapor phases differ significantly in density (rf /rg =175-350), allowing effective separation by centrifugal action. Highly efficient cyclone cyclone separators yield steam qualities ranging as high as 99.99 % [13]. The liquid from the separator may be injected, used for its thermal energy via heat exchangers for a variety of directheat applications, or flashed to a lower pressure by means of control valve or orifice plate, thereby generating additional steam for use in a low-pressure turbine. turbine. Plants in which only primary high-pressure steam is used are called Single-Flash plants; plants using both high- and low-pressure flash steam are called Double-Flash plants.

The balance of the plant is also nearly identical to the dry steam plant, the main difference being the much greater amount of liquid liquid that must must be handled. handled. Comparing 55 MW plants, a typical Single-Flash plant produces about 630 kg/s (5x106 lbm/h) of waste liquid, whereas a Direct-Steam plant produces only 20 kg/s (0.16x10 6 lbm/h), a ratio of over 30 to 1. If all of the waste liquid liquid is injected, a Single-Flash Single-Flash plant would return to the reservoir about 85 % of the produced mass; this should be be compared with only 15% for a Direct-Steam plant. The major equipment items for a typical Single-Flash Single-Flash plant are given in Table 2. DOUBLE-FLASH PLANTS About 20-25% more power can be generated from the same geofluid mass flow rate by using Double-Flash technology. The secondary, low-pressure steam steam produced by throttling the separated liquid to a lower pressure is sent either to a separate low-pressure turbine or to an appropriate stage of the main turbine (i.e., a dual-pressure, dual-admission dual-admission turbine). The principles of operation of the Double-Flash plant are similar to those for the Single-Flash Single-Flash plant. The Double-Flash plant plant is, however, more expensive owing to the extra equipment associated with the flash vessel(s), the piping system for the lowpressure steam, additional control valves, and the more elaborate or extra turbine. Figure 3 is a simplified flow diagram for a Double-Flash plant [5]. An equipment list is given in Table 2.

SINGLE-FLASH PLANTS A simplified flow diagram of a Single-Flash plant is shown in Figure 2 [5].

Figure 3. Simplified flow diagram for a double-flash geothermal powerplant [5].

Figure 2. Simplified flow diagram for a single-flash geothermal power plant (5).

The two-phase flow from the well(s) is directed horizontally and tangentially into a vertical cylindrical pressure vessel, the cyclone cyclone separator. The liquid tends to flow circumferentially along the inner wall surface while the vapor moves to the top where it is removed by means of a vertical standpipe. The design shown is called a bottom-outlet bottom-outlet separa-

BINARY PLANTS In a Binary plant, the thermal energy of the geofluid is transferred via a heat exchanger to a secondary working fluid for use in a fairly conventional conventional Rankine Rankine cycle. The geofluid itself does not contact the moving parts of the power plant, thus minimizing, if not eliminating, the adverse effects of erosion. Binary plants may be advantageous advantageous under certain condiconditions such as low geofluid temperatures, say, less than about 150 C (300 F), or geofluids with high dissolved gases or high corrosion or scaling scaling potential. The latter problems are usually usually















plant, from production wells through the heat exchangers to the injection wells. It is an interesting historical note that the first commercial geothermal powerplants at Larderello were, in fact, binarytype plants [15]. The geothermal steam was used to evaporate clean water to run steam turbines because the materials available at that time did not allow the corrosive steam to be used directly in the turbines. A flow diagram for a typical Basic Binary plant is given in Figure 4 [5]. The power cycle cycle consists of of a preheater, an evaporator, a set of control valves, a turbine-generator set, a condenser and a feedpump. Either water or or air may be used for cooling depending depending on site conditions. conditions. If wet cooling is used, an independent source of make-up water must be found since geosteam condensate is not available as it was in the case of Direct- or Flash-Steam Flash-Steam plants. Owing to chemical impurities the waste brine is not generally suitable for cooling tower make-up. There is a wide range of of candidate working fluids for the closed power cycle. cycle. In making the selection, selection, the designer tries to achieve a good thermodynamic match to the particular characteristics of the geofluid, especially the geofluid temperature. Hydrocarbons such such as isobutane, isopentane isopentane and propane are good candidate working fluids as are certain refrigerants. The optimal fluid will will give a high utilization utilization efficiency together with safe and economical operation.

matically in Figure 5 [5]. A 12 MW pilot plant of this type has been designed and is planned for installation at Steamboat Springs in Nevada.

Figure 5. Simplified flow diagram for a Kalina binary geothermal powerplant [5]. COMBINED OR HYBRID PLANTS Since geothermal fluids are found with a wide range of physical and chemical properties (e.g., temperature, pressure, noncondensable gases, dissolved solids, pH, scaling and corrosion potential), a variety of energy conversion systems have been developed developed to suit any particular particular set of conditions. conditions. The basic systems described in the earlier sections can be combined to achieve more effective systems for particular applications. Thus, the following following hybrid or combined plants plants can be designed:

Direct-Steam/Binary Plants [5] Single-Flash/Binary Single-Flash/ Binary Plants [5] Integrated Single- and Double-Flash Plants [20,21] Hybrid Fossil-Geothermal Systems [22-24].

Figure 4. Simplified flow diagram for a basic binary geothermal powerplant [5].

Binary plants are particularly well suited to modular power packages in the the range 1-3 MW per unit. unit. Standardized Standardized,, skid-mounted units can be factory-built, tested, assembled and shipped to a site for rapid field installation. installation. A number of units can then be connected at the site to match the power potential of the resource. Table 2 contains the major equipment items for a Basic Binary plant. If a mixture is selected as the working fluid, (e.g., isobutane and isopentane, or water and ammonia), then the evaporation and condensation processes will occur at variable temperature. This characteristic allows a closer match between

Properly designed combined or hybrid systems achieve a synergistic advantage by having a higher overall efficiency compared with using the two systems or fuels (in the case of the fossil-geothermal plants) in separate state-of-the-a state-of-the-art rt plants. The intricacies of the design of these systems are beyond the scope of this introductory paper and the reader is referred to the references cited above. POWERPLANT PERFORMANCE The modern approach to measuring the performance of energy systems is to use the Second Law of thermodynamics as the basis for assessment. The concept of available work work or energy has been widely used for this purpose [25]. Geothermal powerplants are an excellent illustration of the application of the Second Law (or utilization) efficiency, h u . Since geo-

















volving the secondary working fluid and not the overall operation involving the flow of the geofluid from the production wells, through the plant, and ultimately to the fluid disposal system. The utilization efficiency, h u, measures how well a plant converts the exergy (or available work) of the resource into useful output. For a geothermal plant, it is a found as follows: follows:

where is the net electric power delivered to the grid, is the required total geofluid mass flow rate, and e is the specific energy of the geofluid under under reservoir conditions. conditions. The latter is given by: e = h(P1 - T 1 ) - h(P0 - T 0 ) - T 0[s(P 1 - T 1 ) - s(P 0 - T 0 )].

The specific enthalpy, h, and entropy, s, are evaluated at reservoir condition conditions, s, P 1 and T 1, and at the so-called dead state, P 0 and T 0. The latter correspond to the local ambient conditions at the plant plant site. In practice, the design wet-bulb wet-bulb temperature may be used for T 0 (in absolute degrees) when a wet cooling system is used; the design dry-bulb temperature may be used when an air-cooled condenser is used. The major design specifications and actual performance values for selected powerplants of the Direct-Steam, Singleand Double-Flash types are given in Table 3; similar data are

given in Table 4 for selected small Binary powerplants. The specific geofluid consumption, SGC, is given as one measure of performance. One will observe observe a dramatic increase in this parameter (i.e., a decrease in performance) when comparing Binary plants with geothermal steam plants, particularly Direct-Steam plants. plants. It can be seen that Direct-Steam plants plants operate at quite impressive efficiencies based on exergy, typically between 50-70 %. Each utilization efficiency given in Tables 3 and 4 was computed using the appropriate site-specific deadstate temperature. The contemporary use of small modular binary units is exemplified by the the SIGC plant [27,28]. [27,28]. Several small units, units, 2.7 MWn, are clustered together receiving geofluid from several wells through a manifold and generate a total of 33 MW n. The small sacrifice in efficiency of the modular-sized units, istics of the wells are known. The influence of resource temperature and power rating on plant costs for small-size Binary units are summarized in Table 6 [30]. Capital costs (per kW) vary inversely inversely with temperature and rating; annual O&M costs increase with rating but are independent of fluid temperature (over the range studied). These costs are favorable when compared to other renewable energy sources, and are absolutely favorable for remote locations where electricity is usually generated by diesel engines.

Table 3 Design Conditions for Selected Geothermal Steam Plants (after [5]) Plant Location Start-up year Type Rating, MW Output power, MW-net Geofluid flow rate, kg/s Resource temperature, C Turbine: inlet pressure, kPa: primary secondary inlet temperature, C: primary secondary

Valle Secolo, Unit 2 Larderello, Italy 1992 Direct steam 57 52.2 111.1 204

550.3  200-210 

Miravalles, Unit I Guanacaste, Costa Rica 1994 Single flash 55 52 759.5 230

600.0  159 

Beowawe Beowawe, Nevada 1985 Double flash 16.7 16.0 157.5 215

421.4 93.1 146 99















Table 4 Design Conditions for Selected Geothermal Binary Plants (after [5]) Plant Location Start-up year Type No. of units Rating, MW Output power, MW-net Net power/unit, MW Geofluid flow rate, kg/s Resource temperature, C Downwell pumps Working fluid Evaporator(s): No. per unit type heat duty,MWt geofluid temperature, C: inlet outlet Turbine: type inlet temperature, C pressure, kPa: inlet outlet mass flow/turbine, kg/s speed, rpm Condenser(s): No. per unit type heat duty, MWt coolant coolant temperature, C: inlet outlet Plant performance performance:: SGC-net, kg/MWh h , %: gross u net hth, %: gross net

Second Imperial Geothermal Co. Heber, CA 1993 dual-pressure 12 40 32 2.7 999.0 168 yes isopentane, C5H12

2 shell & tube 413.2 (e) 168 71 (e) axial flow na na na na 1,800 2 shell & tube 269.2 water 20.0 28.1 85,049 44.5 35.6 14.0 13.2

ECONOMICS OF GEOTHERMAL POWER The costs associated with building and operating a geothermal powerplant vary widely and depend on such factors

- Resource type (steam or hot water) - Resource temperature

Mammoth-Pacific, Unit I Mammoth, CA 1985 basic 2 10 7 3.5 220.5 169 yes isobutane, C4H10

6 shell & tube 86.75 169 66-88

Amedee Wendel, CA 1988 basic 2 2 1.6 0.8 205.1 103 yes R-114, C2Cl2F4

1 shell & tube 28.72 104 71

radial inflow 138 3,379 variable 92.0 11,050

axial flow 83 993 276 100.8 3,600

11 finned tube 79.72 air variable variable

1 evaporative na water 21.1 na

113,399 32.4 22.7 11.5 8.1

462,669 17.4 13.9 7.0 5.6

rect Steam plants (all at The Geyers) do not include field development costs but cover only only the powerplant. The other figures (all estimated) include both field and plant costs. Table 5 Capital Cost for U.S. Geothermal Plants (after [5])















Table 6 Capital and O&M Costs for Small Binary Geothermal Plants (1993 $) [5] Net Power, kW

100 200 500 1,000

Resource Temperature, C 100 120 140 Capital Cost, $/kW 2,535 2,210 2,015 2,340 2,040 1,860 2,145 1,870 1,705 1,950 1,700 1,550

Total O&M Cost $/year

19,100 24,650 30,405 44,000

SUMMARY AND OUTLOOK Extensive research and development over the last two decades has resulted in an impressive array of commercially available technologies to harness a wide range of geothermal resources. Off-the-shelf power systems systems of the Direct-Steam, Flash-Steam or Binary types can be ordered for use with lowto-high temperature resources of the vapor- or liquid-dominated variety, with any level of noncondensable gas or dissolved solids. If new plants are to be built, however, they must demonstrate an economic advantage over alternative systems. The economics are governed by site-specific and time-specific factors. For example, in the United States in the late 1990s, it has been difficult for any energy source to compete with natural-gas-fired plants, particularly combined steam-and-gas-turbine cycles. The effects of deregulation on the electric industry have also had a negative negative impact on geothermal geothermal plants. No longer endowed with favorable power purchase agreements, geothermal plant must now compete openly with other energy systems. Interestingly, privatization privatization in many other countries, particularly those lacking in indigenous fossil fuels, has actually enhanced the attractiveness of geothermal plants which often turn out to be the lowest cost option among new electric power plants. Since geothermal projects are heavily loaded with upfront costs for exploration, reservoir characterization, characteriza tion, and drilling, all of which carry a measure of risk for investors, research directed at improving the technology in these areas is appropriate. Also, better methods of monitoring monitoring and predicting reservoir behavior, both prior to and during exploitation would allow more systematic and reliable development strategies to

Geothermal is now a proven alternative energy source for electric power generation. generation. Because of its economic economic competitiveness in many situations, the operational reliability of the plants, and its environmentally friendly nature, geothermal energy will continue to serve those countries endowed with this natural energy resource. REFERENCES [1] ENEL, 1993. The History of Larderello , Public Relations and Comm. Dept., Rome.

[2] DiPippo, R., 1980. Geothermal Energy as a Source of Electricity: A Worldwide Worldwide Survey of the Design and Operation of Geothermal Power Plants, USDOE/ RA/28320-1, US Gov. Printing Office, Washington. [3] DiPippo, R., 1995. Geothermal Power Powe r Plants in the United States: A Survey and and Update Update for 19901994, Geothermal Resources Council BULLETIN , 24: pp. 141-152. [4] Wright, P. M., 1998. A Look Around the World, Geothermal Resources Council BULLETIN , 27: pp. 154-155. [5] Geothermal Power Systems, R. DiPippo. Sect. 8.2 in Standard Handbook of Powerplant Powerplant Engineering, Engineering, 2nd ed ., ., T. C. Elliott, K. Chen and R C. Swanekamp, eds., pp. 8.27 - 8.60, McGraw-Hill, Inc., New York, 1998. [6] Voge, E.; Koenig, B.; Smith, J. L. B.; Enedy, S.; Beall, J. J.; Adams, M. C. and J. Haizlip, 1994. Initial Findings of the the Geysers Unit 18 Cooperative InjecGeothermal Resources Council tion Project, TRANSACTIONS , 18: pp. 353-357. [7] Cappetti, G. and G. Stefani, 1994. Strategies for Sustaining Production at Larderello, Geothermal Resources Council TRANSACTIONS , 18: pp. 625629.















[12] Austin, A. L. and A. W. Lundberg, 1978. The LLL Geothermal Energy Program: A Status Report on the Development of the Total Flow Concept , Lawrence Livermore Laboratory Rep . UCRL50046-77, Livermore, CA. [13] Lazalde-Crabtree, Lazalde-Crabtree, H., 1984. Design Approach of Steam-Water Separators and Steam Dryers for Geothermal Applications, Geothermal Resources Council BULLETIN , 13: No. 8, pp. 11-20. [14] Frost, J., Introduction to Geothermal Lineshaft Production Pumps, Johnston Pump Co., Pomona, CA. [15] Anon, 1981. Electrical Energy from the Volterra Soffioni, Power, 47: No. 15, p. 531. [16] Demuth, O. J., 1981. Analyses of Mixed Mixed Hydrocarbon Binary Thermodynamic Cycles for Moderate Temperature Geothermal Resources, INEL Rep. EGG-GTH-5753, Idaho Falls, ID. [17] Bliem, C. J., 1983. Preliminary Performance Performance Estimates and Value Analyses for Binary Geothermal Power Plants Using Ammonia-Water Mixtures as Working Fluids, INEL Rep. EGG-GTH-6477, Idaho Falls, ID. [18] Demuth, O. J. and R. J. Kochan, 1981. Analyses of Mixed Hydrocarbon Binary Thermodynamic Cycles for Moderate Moderate Temperature Geothermal Ressources Using Regeneration Techniques, INEL Rep. EGG-GTH-5710, Idaho Falls, ID. [19] Leibowitz, H. M. and D. W. Markus, 1990. Economic Performance of Geothermal Power Plants Using the Kalina Cycle Technique, Geothermal Resources Council TRANSACTIONS , 14 (Part II): pp. 1037042. [20] DiPippo, R., 1987. Ahuachapan Geothermal Power

[23] Khalifa, H.E.; DiPippo, R. and J. Kestin, 1978. Geothermal Preheating Preheating in Fossil-Fired Steam Steam Power Plants, Proc. 13th Intersociety Energy Conversion Engineering Conf. , 2: pp. 1068-1073. [24] Habel, R., 1991. Honey Lake Power Facility, Lassen County, Geothermal Hot Line, 20: No. 1, p. 19. [25] Moran, M.J., 1989. Availability Analysis: A Guide to Efficient Energy Use, Corrected edition, ASME Press, New York. [26] DiPippo, R. and D. F. Marcille, 1984. Exergy Analysis of Geothermal Power Plants, Geothermal Resources Council TRANSACTIONS , 8: pp. 47-52. [27] Ram, H. and Y. Yahalom, 1988. Commercially Successful Large Binary Applications, Geothermal Resources Council BULLETIN , 17: No. 3, pp. 3-7. [28] Anon., 1993. New Geothermal Facility Exceeds Production Expectations, Geothermal Resources Council BULLETIN , 22: pp. 281-282. [29] Schochet, D. N. and and J. J. E. Mock, 1994. How the DeDepartment of Energy Loan Guarantee Program Paved the Way for the the Growth of the Geothermal Industries, Geothermal Resources Council TRANSACTIONS , 18: pp. 61-65. [30] Entingh, D. J.; Easwaran, E. and L. McLarty, 1994. Small Geothermal Electric Systems for Remote Powering, Geothermal Resources Council TRANS ACTIONS , 18: pp. 39-46. NOMENCLATURE FOR PLANT FLOW DIAGRAMS (Figs. 1, 2, 3, 4, 5) BCV - ball check valve CP - condensate pump CSV - con contro troll and sto stop p val valves ves

C - condenser CS - cyclone separator CT - coo coolin ling g tow tower er















SMALL GEOTHERMAL POWER PROJECT EXAMPLES John W. Lund Tonya Toni Boyd Geo-Heat Center WHAT ARE SMALL GEOTHERMAL POWER PROJECTS?

According to Vimmerstedt (1998 - and this Bulletin), small geothermal power power projects are less than 5 MWe. Others (Entingh, et al., 1994a and b, and Pritchett 1998a) refer to a range of 100 to 1000 kWe as small. In this article, we will use the 5 MWe definition as small. Small power projects, often called village power and sometimes as off-grid power, can serve rural people in developing countries; since, this market may be best served by many small generating units, rather than fewer larger ones. For examples, at 50 watts per household for lighting, lighting, 1 MWe could serve 20,000 households (Cabraal, et al., 1996). Entingh, et al., (1994a) estimates that the demand for electric capacity per person at off-gird sites will range from 0.2 kW in lessdeveloped areas to 1.0 kW or higher in developed areas. are as. Thus, a 100-kWe plant could serve 100 to 500 people, and a 1,000kWe plant would serve 1,000 to 5,000 people. However, one of the main problems with small geothermal power projects is that they are unlikely to obtain financing due to high cost per installed kW and low rate of return; thus, these remote projects often must be subsidized by the government to encourage local economic development. Alternative power at remote locations, which is usually provided by diesel generations, can be much more expensive per kWh than geothermal, as the fuel transportation costs are high. For example at Fang, Thailand, Thailand, a 300-kWe geothermal binary plant supplies power from 6.3 to 8.6 cents/kWh, compared to the alternative of diesel generators at 22 to 25 cents/ kWh (Schochet, 1998). Small geothermal power units are already common, though not always always in remote applications. applications. They are some-

Well spacing must take reservoir characteristics into consideration, and so can not be optimized for power plant size alone. Small units are also found at larger sites where they were used used during during early phases of site development. development. Placing a small plant plant at the site site of a larger anticipated anticipated development supplies electricity during development of the field [and can provide provide a return on investment sooner. Also, if the initial electricity demand at the site is low, then the small-scale plant can be fully utilized until a larger one is justified. When there is a problem in resource development, a smaller plant can utilize resource confirmation holes, or shallow, less expensive wells]. Small systems at large sites have advantages over remote ones in that the financing is often secured for the entire project. The resource is confirmed for that project, operation and maintenance infrastructures are readily available, available, a grid either exists or is constructed for the large project, and sufficient base load is available. A critical distinction between the application of small geothermal plants within a larger site and application in a remote area is the load-following ability of small geothermal systems. systems. Although geothermal

















are unlikely to to be used in small small geothermal plants because dry steam resources are thought to be rare.

The advantages of flash steam systems in small applications include the relative simplicity and low cost of the plant. In contrast to binary plants, they require no secondary working working fluid. However, when the geothermal fluid is flashed to steam, the solids that precipitate can foul equipment, and pose health, safety and disposal problems. If steam contains hydrogen sulfide or other other contaminants, it poses an air quality problem when released directly to the atmosphere. Treating noncondensable gases in the condensing design adds complexity, maintenance, and disposal requirements (Forsha and Nichols, 1997). Flash systems are most often used where higher temperatures (above 300 oF 150oC) are available; although, a lowpressure turbine design for lower-temperature flash plants (230 oF - 110oC) has been proposed (Forsha, 1994) and feasibility of lower-temperature flash plants have been studied (Pritchett, 1998b).

2.

Binary Bina ry po powe werr pla plant ntss can can ac acco comm mmod odat atee a wi wide de ra rang ngee of geothermal reservoir temperatur temperatures, es, 212 to 300 oF (100 to 150 oC). Above 300oF (150oC) flashed- steam plants usually prove less expensive than binary plants.

3.

The de The dema mand nd fo forr el elec ectr tric ic ca capa paci city ty pe perr pe pers rson on at of offfgrid sites will range from 0.2 kWe to 1.0 kWe.

4.

The de The desi sign gn of of the the powe powerr pl plan ants ts and and th thei eirr inte intera racctions with the wells includes provisions for handling fluctuating loads, including low-instantaneous loads ranging ranging from 0 to 25 percent of the installed installed capacity.

5.

Powerr plan Powe plantt de desi sign gnss emph emphas asiz izee a high high de degr gree ee of of computer-based automation, automation, including self starting. starting. Only semi-skilled labor is needed to monitor plant plant operation, on a part-time basis. Complete unattended operation might also be possible, with plant performance monitored monitored and controlled controlled remotely through a satellite link.

6.

The sy The syst stem em re rele leas ases es no gr gree eenh nhou ouse se ga gase sess to th thee atmosphere. There may be very small leakages of the binary-cycle working fluids, but these do not contain chlorine or fluorine and are non-greenhouse gases.

7.

Alll well Al wellss co coul uld d be dr dril ille led d by tru truck ck-m -mou ount nted ed rig rigs, s,















reduce the cost of special features needed to ensure ensure that power is always available. available. Small critical loads such as medical refrigeration or pumps for drinking water could be supported against brief unscheduled outages by a diesel engine or by small amounts of battery storage. COSTS OF SMALL GEOTHERMAL POWER PLANTS

Ultimately, the costs of small geothermal power plants will determine their potential potential market. Reported costs for small plants are rare. Those that do are located located at large fields and are in the $0.05 to $0.07/kWh range, for units in the 1 to 5 MWe range (GRC, 1998). Entingh, Easwaran, and McLarty (1994a and 1994b) developed a model called GT-SMALL for small, binary geothermal systems in the 100 to 1000-kWe 1000-kWe size range. They evaluated reservoir temperatures of 212 - 284 oF (100 - 140oC), production well depth of 656 - 3,281 ft (200 - 1,000 m), and injection well depth of 656 - 1,640 ft (200 - 500 m). Technical costs at the busbar for this evaluation ranged from $0.047 to $0.346/kWh.. An example is shown below for a system cost of $0.346/kWh $0.105/kWh. Technical

Resource Te Temperature System Net Capacity Number of Wells Capacity Factor Plant Life Rate of Return on Investment

248oF (120oC) 300 kWe 2 0.8 30 years 12%/yr

EXAMPLES OF SMALL GEOTHERMAL POWER PLANTS

The generating potential of a geothermal resource can be estimated from the temperature and flow rate as shown in Figure 1 (Nichols, 1986). 1986). This figure gives the net power power output which accounts for the parasitic loads such as due to the condenser and feed pump power requirements. Single modular units can handle flow rates up to 1000 gpm (63 l/s), with multiple units required to accommodate greater flow rates and produce proportionately larger output output power. The output power from two-phase water-steam or steam alone is much greater than the curves curves shown for liquid liquid in Figure Figure 1. Temperatures o o above 350 F (175 C) can also be accommodated with high efficiencies by making minor modifications to the modular units. However, it should be pointed out that the conversion efficiency is quite low at the lower lower temperature and therefore, the cost of power becomes becomes higher. Reservoir temperature temperature is the physical factor to which overall project costs are most sensitive. A schematic of the binary cycle (Rankine cycle) is shown in Figure 2 (Nichols, 1986).















1.

Ameede Am deee Geo eotthe herm rmal al Ve Vent ntur uree bin inar ary y pl plan antt (Fig. 3),

located in northern California near Susanville was placed in operation in 1988. The plant consists of two units of one MWe each with a total net output of 1.5 MWe. The resource temperature is 219oF (104oC), and well depth of 850 ft (260 m) with a maximum flow rate of 3,200 gpm (205 l/s). The plant uses R114 working fluid and cooling ponds for makeup water. The units were designed by Barber-Nichols Barber-Nichols Engineering Company of of Arvada, Colorado. They have an availability is 90% and the system is remotely rem otely monitored by telephone line. Geothermal fluids from two wells are used to operate the plant, and surface discharge is used to dispose of the spent fluid. This is possible because the geothermal fluids have a very low salinity and a composition the same as area hot spring water. Figure 4. Wineagel Developers 750-kWe binary plant.

The plant is completely completely automated. The entire plant, including the well pump, is controlled by either module. By pushing one one button on the the module control control panel, the plant will start, synchronize to the power line and continue continue operation. operation. If the power line line goes down, the module and the downhole pump immediately shut down, since no power is available for its operation. When the power line line is re-energized, the modules restart the downhole pump, then bring themselves on line. The two, identical power plant mod-















Figure 5. Schematic of one of the Wineagle modular units (Nichols, 1986).

the Iso-Pentane working fluid does not mix with water; thus, water leakage is not a problem as it was with Freon 114. Gene Culver (1987) of the Geo-















Figure 7. OESI/AMOR II binary plant near Empire, Nevada.

The resource was acquired by Empire L.P. in 1996. The cooler production wells were then shut-in and additional geothermal fluid supplied at 306 oF (152oC) from a new well. A three-cell cooling tower tower was also added which resulted in the net output increasing to 3.85 MWe in 1998 . The power plant is, thus, operating above design capacity, and produced almost 18 GWh in 1997. The onion/garlic dehydration plant is still operating at full capacity using the same re-

Figure 8. Cove Fort Geothermal No. 1 - 4.8-MWe 4.8-MW e combined power plant. 6.

Soda La Lake Ge Geothermal Po Power Pl Plan antt No No. 1, Fallon,

Nevada, commenced generating generating power in 1988. This is a 3.6-MWe binary power plant comprising three ORMAT OECs modular units units (Fig. 9). The power plant operates on a liquid dominated resource at 370 oF (188oC). The power plant was was designed and built built on a turnkey basis by ORMAT, is owned by Constellation Developments, Inc. (CDI) and ORMAT Energy Systems, Inc. (OESI), and is operated by OESI, with































The power plant initially operated for 6,400 hours, and then was shutdown due to failure of the downhole pumps. The cable failed after after 15 days of operation and the seals after seven months of operation. The wells were then operated without pumps and experienced severe scaling. scaling. The downhole pumps pumps were replaced and the plant recommissioned in August of 1998. It is currently operating satisfactorily. This is the only completely stand-alone, off-grid geothermal power project in operation. The town of Nagque, which is a political, cultural, economic and traffic center of the North Tibet Plateau, has a population of about 20,000. Prior to 1993, there were 10 diesel generators with a total nominal capacity capacit y of 1.68 MWe supply supply electricity to the area. area. This capacity capacity could only satisfy the lighting needs of the local organizations and some inhabitants, lasting only 4 to 5 hours every night due to high production cost. The

10.

Tu Chang binary po power plant , Taiwan, connected

to the grid in 1987. This is a 300 kWe, water cooled ORMAT OEC that uses a liquid dominated resource at 266oF (130oC) (Fig. 12). The project is owned and operated by the Industrial Technology Research Institute and the power is sold to the Taiwan Power Company. It has a CO2 recovery system, as the noncondensable gases are two percent by weight. The project, including the 1,640-foot (500-m) deep well, cost $2 million and the power is sold at four cents/ kWh.















giving approximately 2.2 MWe available for the Bay of Plenty Power Power Board (BOP) (BOP) grid. The monitoring system allows unattended operation that ensures that unscheduled outages can be quickly reported. The plant performance is also monitored by the manufacturers in Israel, who provide weekly reports directly to the BOP offices in Whakatane. Whakatane. Tilson, et al., (1990) reported no deposition in the heat exchangers and, with little maintenance required, load factors for the first six months of operation were over 90%, with 96.6% availability. The unit average output was about 1,800 MWh per month for the initial operation. The OECs utilize separated geothermal water which previously ran into the Ta Tarawera rawera River. The installation of the OECs, thereby, contributes to environmental conservation by reducing pollution. Figure 14.

Diagram of TG2 3.5-MWe binary unit at Kawerau, New Zealand.















14.

Ko ko ko no no e Ka Ka nk nk o H ot ot el el co co nd nd en ens in in g f la la sh sh un un it it ,

Kokonoe, Kyushu, Japan, was installed in 1998. This is the most recent installation of a small-scale geothermal power plant in Japan (Esaki, 1998). The condensing unit with a geared turbine (about 8,000 rpm) is installed on the premises of this resort hotel, and when the hotel load is below the unit capacity, which it is most of the time, they sell power to Kyushu Electric Power Company. Company. The installed capacity capacity is 2,000 kWe, with major parastic loads of 356 kWe (hot well pump, vacuum pump for gas extraction, cooling tower fan and auxiliary cooling water pump) or about 17% of the gross output giving a net output of 1,644 kWe. The reason for the high parasitic parasiti c load is that a vacuum pump (164 kWe), not a set of steam jet ejectors, is employed for gas extraction to reduce noise during the operation because the plant is located adjacent to a campsite of the hotel.

the isle of Basse Terre, some som e 1,600 feet (500 m) south of the center of Bouillante and some 9 miles (15 km) from the Soufriere volcano. The operation of the power-plant is mainly automatic and the electric output will meet 6% of the Guadeloupe electric power demand at a cost lower than that obtained with diesel generators. Numerous modernization modernization and and improvements were undertaken in 1995 and 1996 (Correia, et al., 1998). Three automated controllers monitor plant activity and manage all operation. operation. The plant, located within a residential district, was designed so as not to produce noise greater than the ambient noise of the city. Geothermal wells on the island produced temperatures of 446 to 482 oF ( 230 to 250 oC) at depths of 2,000 to 8,200 ft. (600 to 2,500 m) with a steam to water mixture of 20 to 80% (Jaud and Lamethe, 1985). A study was made of the various means to produce































was installed and put in continuous operation in both wells. In 1997, the output was 42.3 GWh, the availability factor was 99.5% and the load factor 96.5%. The actual installed geothermal power production meets 20% of San Miguel Islands electricity demand, which represents 50% of the Azorean total demand. The CGRG plant is presently being expanded (Phase

20.

Back pressure turbine , Bjarnarflag, Namafjall, Ice-

land, was installed in 1969. Based on exploration in northern Iceland, a field temperature of 482 to 500 oF (250 to 260 oC) was utilized to provide power to the area through the Laxa Power Works, to gain experience in geothermal power generation, and to reduce the use of imported and expensive fuel in their diesel plants (Fig. 19). 19). In order to minimize minimize the construc-















Reykjavik (Lienau, 1996). 1996). The thermal output output is 125 MWt and the electric output is 16.4 MWe, with part of the load going the Keflavik airport and a U.S. military base. The heating plant was built built by the National Energy Authority in 1974 and in 1976-77, a preliminary power plant plant of 3 MWe was commissioned. commissioned. In 1978, the first 1-MWe turbogenerator was commissioned. Both of these units units no longer longer are in opera-

posed into the Blue Lagoon a popular outdoor bathing facility. The flash steam turbine uses 320 oF (160oC) fluid, and the reject fluid at 217oF (103oC) is used in the binary units and finally rejected at 77 oF (25 oC) to the heat exchange column (Figure 20). 22.

Inttegrat In ateed ge geot oth herma mall pow poweer pl plan antt , Aluto Langano,

Ethiopia, was synchronized to the Ethiopian national















25.

Latera power plants , Latera, Italy, are reported as

under construction. construction. They consist of a 3.5-MWe 3.5-MWe flash plant and a 2-MWe binary plant (GRC database). 26.

Bi na na ry ry g eo eot he herm al al p ow ow er er pl an ants , Los Azufres,

Michoacan, Mexico, were commissioned in 1993. Two 1.5-MW ORMAT OEC unit are installed in two separate locations in the Los Azufres geothermal field















field. All are Ansaldo-Makrotek units units using wells U1 through U-7 (GRC data base and Gerardo Hiriart, CFE). Their net output output ranges from 3.7 to 4.8 4.8 MWe and they produce between 33 and 42 GWh/year (Quijano-Leon (Quijano-Leo n and Guterrez Negrin, Negrin, 1995). The resource temperatures vary from 608 to 644 oF ( 320 to 340oC) with inlet temperature of 338 oF (170oC) and pressure of 116 psi (8 bar). Well depths range from 5,250 to 7,300 feet (1,600 to 2,225 m). The estimated

weighting 30 tons, was then moved by Pertamina of Indonesia to the Sibayak geothermal site in North Sumatra, where it was installed as the first geothermal power plant on that island. These units were noncondensing, skid mounted steam turbine and generator with switch gear and control system all mounted in one package. The skid mounted package has a stainless steel outer covering for protection from corrosion due to the H S gas in the steam (Geothermal















ing troubles were experienced with scaling from heavy metal sulphides, silica and silicon compounds, and thus the plant was modified with the addition of a high pressure cyclone separator (362 psi - 25 bar), a steam scrubbing system and various other auxiliary equipment. The plant was finally shut down down in 1988, as strong opposition against its operation was encountered among the inhabitants and local organizations of the island (Fytikas, et al, 1995).

34.

E x pe pe ri ri me me n t al al bi bi na na ry ry po pow er er pl pl an an t , Paratunka,

Kamchatka, Russia, commissioned in 1967 (Moskvickeva and Popov, 1970). This was one of the first geothermal binary power units installed in the world, rated at 680 kWe and used 178 oF (81oC) water (Fig. 28). It was dismantled dismantled by 1985.





























































































































June 1999 Geo-Heat Center Quarterly Bulletin

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