ࡱ> oqn5@ 0;Jbjbj22 (dXXAJ%  8, ,X 4BPz " """OOOOOOO$QRTHO*""**O O---*p  O-*O-$-.RJM `ra+KO$P0BPKVU,VU<MVUM"/$0-_%S&"""OO$$ -dThe Chena Hot Springs 400kW Geothermal Power Plant: Experience Gained During the First Year of Operation Prepared for the 91Թ Geothermal Energy Utilization Associated with Oil & Gas Development June 12-13th, 2007 in support of presentation by Bernie Karl ABSTRACT In July 2006, Chena Hot Springs Resort installed the first of two 200kW ORC power plant modules designed and built by United Technologies Corporation at their Hartford, Connecticut research facility. The second unit was brought on line the following December. The modules were designed based on the PureCycle 200 product released by UTC in 2004 and designed to operate off industrial waste heat applications. The PureCycle 200 uses components and hardware from the Carrier Refrigeration line in over 90% of the system, which greatly reduces the upfront cost of the equipment since air-conditioning equipment has a cost structure significantly lower than traditional power generation equipment. This is significant because Chena Hot Springs is a moderate temperature geothermal resource with a maximum produced water temperature of only 165F. For this reason, any ORC designed for to generate power from the Chena resource is saddled with an inherently a low thermal efficiency. Low efficiency requires increased power plant equipment size (turbine, condenser, pump and boiler) that can ordinarily become cost prohibitive. One of the main goals for the Chena project was to reduce the equipment cost of these UTC designed PureCycle modules to $1300 per kW. This paper describes the site preparation, installation and operation of the two PureCycle 200 units, and experience gained as the first anniversary of the installation approaches. This paper does not focus on the design of the system, which has already been covered in two previous papers presented at the 2005 (Joost, Biederman, Holdmann) and 2006 (Cogswell) Geothermal Resource Council Annual Meeting. BACKGROUND Despite being an oil exporting state, Alaska is home to some of the highest electric power costs in the United States, particularly in the numerous remote, isolated villages scattered throughout the State. For example, the cost of power at Manley Hot Springs, located northwest of Fairbanks, is currently 86 per kWhr. Residents in rural areas, where average income is below the national poverty level, typically pay 25% or more of their income for utilities, primarily electricity and heating. Chena Hot Springs Resort, located 60 miles Northeast of Fairbanks Alaska, is no exception. Prior to the installation of the geothermal power plant facility, power was generated from a 400kW diesel recip. The cost for generating power in 2006 was 30 per kWhr, and at an average load of 230kW this represented $604,000 in 2005. The fuel cost represented approximately 60% of this expense. Two well-known manufacturers of ORC systems for geothermal applications were approached in 2002 and 2003 about designing a system for Chena Hot Springs. One manufacturer declined the opportunity outright, the second manufacturer was willing to build a one-of system for Chena, however the cost per kW would be very high. In 2004, Chena Hot Springs was able to enter an agreement with UTC to demonstrate their PureCycle technology on the geothermal resource at Chena. UTC was awarded funding from DOE to complete design work on the system, and the power plant modules were designed, assembled, and tested at UTRC in Hartford beginning in late 2004. The first unit (ORC1) underwent 1000 hours of qualification testing before being diassembled and sent to Chena Hot Springs. The second unit (ORC2) was partially assembled but not tested before being sent to Chena. CHENA POWER PLANT DESIGN The PureCycle 200 platform that the Chena plant is based on was designed to produce 200kW of electric power from waste hot gas sources between 500 and 1000F using mass-produced Carrier chiller components. The most critical components include a single-stage centrifugal compressor which runs in reverse as a radial inflow turbine to produce 200kW of power, and heat exchangers originally designed for large chiller applications. Additionally, local and remote monitoring was applied for both operation and data collection. The specific objective of the Chena project for UTC was to demonstrate the feasibility of producing electricity at a cost of less than 5/kWh from a 165F geothermal resource with 98% availability. The geothermal application for the PureCycle platform would involve some additional innovation and opportunities for cost reduction beyond that of the original PureCycle 200 platform, including: Changing the working fluid used in the PureCycle ORC plant from R245fa to R134a. This fluid is a better match for low temperature geothermal applications and enables a significant cost reduction, both directly because R134a is a low cost fluid widely used in HVAC equipment and indirectly by allowing lower cost commercially available components to be used in the power plant. Developing low cost heat exchangers specific to geothermal applications based on designs and production capability in place for Carriers large commercial and marine water-cooled chillers. Reducing the plant cost relative to the PureCycle ORC plant by incorporating and qualifying more commercially available components made feasible by the lower operating temperature in geothermal applications. Develop control algorithms and methods for operation with tube and shell heat exchangers rather than the fin-tube technology applied in the PureCycle plant. The geothermal plant modules were designed and qualified at the United Technologies Research Center before installation at Chena Hot Springs. Cycle analysis shows that with the 164F temperature geothermal liquid as the heat source and 40F river water as heat sink, two geothermal power plants can be developed with HFC134a as the working fluid. The first power plant has been operating at the following conditions: Water Design Points Heat source: Tin = 164 F Tout = 130 F Flow rate: 530 gpm Heat sink: Tin = 40 F Tout = 50 F Flow rate: 1614 gpm Refrigerant Design Points Mass flow rate: 26.8 lbm/s Evaporator/turbine inlet pressure: 232 psia Condenser/turbine exit pressure: 63.6 psia Turbine gross power: 250 kW Pump power: 40 kW System output power (net): 210 kW Thermal efficiency: 8.2 % This efficiency was a challenge given the limited thermodynamic availability of the low temperature geothermal heat source. A completely reversible thermodynamic cycle working with the same heat source and heat sink temperature glides would have a thermal efficiency just under 18%. Fortunately, efficiency improvements are far less critical in power generation when the fuel is essentially free. COOLING SUPPLY FOR CONDENSERS (WATER AND AIR) To maximize system performance and take advantage of the excellent cold water resources available locally, the first ORC module was designed to be water cooled at 40F. In order to maximize net power production, a water supply system was designed which would require no pumping load. This was accomplished by employing a low tech siphon to pull water out of a shallow, large diameter well located 2700ft to the east of the power plant. The elevation difference of +33ft between the cold water well and the power plant allows 1500gpm to flow through each condenser at 5psi without a pump. To minimize pressure loss due to friction in the pipeline, the pipeline was oversized with 2400ft of 18in and 300ft of 16in steel pipe. The cold water gains 10F in the condenser before being discharged to Monument Creek, which runs along the northern boundary of the Chena Hot Springs property via an existing drainage ditch. An automated shutdown procedure is in place to avoid the potential for refrigerant discharge into Monument Creek if a leak in the condenser is detected. Due to time constraints, only portions of the pipeline were insulated and buried prior to freezeup in October, 2006. The remaining sections will be completed in 2007. To compensate for freezing temperatures, a supplemental 3in hot water loop was installed piggyback on the cold water line along the entire length. Additionally, the second ORC unit, installed in December 2006, was designed to be cooled either with air or water. This was accomplished through the installation of a separate air cooled condenser which sits next to the power plant building. The air condenser fans draw an additional load of 24kW, however they allow for an increase in net generating capacity at sub zero temperatures, which are common at Chena during the winter months. During the summer, the unit will be switched to use a water cooled condenser identical to the one installed in ORC1. In fact, the air cooled system has worked so effectively, a second air cooled condenser has been ordered and will be installed on the first ORC unit for next winter. HOT WATER SUPPLY AND REINJECTION SYSTEM All available geothermal waters in the vicinity of Chena Hot Springs have been sampled and analyzed for their basic brine chemistry, stable isotopes, total organic carbon and dissolved inorganic carbon as part of the DOE funded GRED III project. Quartz and Na-K-Ca geothermometers predict temperatures as high as 278 and 263 oF respectively as the base temperature of a deeper resource at Chena. These temperatures are expected to be accessed at depths of 1500 to 2500ft, according to the model developed through the Chena GRED III project. The Chena thermal spring waters are quite dilute for thermal waters, having a total dissolved content of only 300 to 388 mg/l, with a pH near 9. This has made selecting materials for the power plant heat exchangers somewhat easier than usual for a geothermal fluid, however there are still concerns about the sulfur content and reactions with the copper alloy as well as oxidation in the evaporator units. This causes some minor scaling and ultimately it may be necessary to inject a surfactant into the hot water supply, as is common in many other geothermal installations. This issue is still being researched. Development as part of the current power generation project has focused on the shallow geothermal system, and extensive testing of the resource has determined the upflow zones lies approximately 1500ft to the west of the natural hot springs area. Test wells with the highest artesian pressures and temperatures (168.9F) were drilled in this area during 2006. Prior to 2006, drilling had focused on the area immediately surrounding the hot springs, and to the east of the springs. It has now been established from clear rollovers in the temperature depths curves that this is part of the outflow plume, and not the source of the upflow. The main geothermal production well was drilled to a depth of 713 ft in May and June, 2006. Three productivity values for the well were calculated based on separate flow tests, and the overall productivity of the well is approximately 15.6gpm/psi. From this value, we were able to estimate a drawdown of 148ft in the well at the production rate of 1000gpm, which is required for power plant operation. This allowed us to select a pump and determine what depth the pump should be set at to prevent cavitation. A 40hp submersible Franklin Electric motor with a Flowserve Model 10EHL single stage submersible turbine pump was selected, with a VFD controller. A backup pump, capable of supplying 400gpm, will be installed in 2007 in a nearby well in case of primary pump failure. Actual drawdown in the production well was measured to be 90ft after the pump was installed. Installation of 3000ft of 8in insulated HDPE was completed at the end of July to supply water from the primary production well to the power plant. The line was laid in a shallow ditch along 90% of the route, and will eventually be buried. The pipeline follows an existing unimproved road along the south boundary of the Chena Hot Springs Resort Property. 1.8F is lost in the pipeline between the production well and the power plant. Developing a successful injection strategy is integral to the success of any large scale geothermal project. Chena has been working on characterizing its wells for nearly 2-1/2 years, largely in anticipation of minimizing the stresses placed on the reservoir due to this power generation project. Initial injection well candidates were chosen primarily due to their distance from the proposed production area. However, additional testing has shown that while these wells are both unequivocally linked to the geothermal system/ reservoir, both have low injectivity indexes which make them poor candidates for injection of any substantial volume of fluid under the low wellhead pressures planned. Currently, Chena is using a single injection well located near the power plant building. This well has a total depth of 702ft, and injection testing conducted in December 2005 indicated a very high injectivity index which has subsequently been verified through actual injection of spent fluid. The well was cemented in July, 2006 and has been used successfully for injection ever since the first unit began operating. The geothermal field is still being monitored, and changes to the injection strategy over the long term is expected to minimize cooling of the resource. INSTALLATION AND STARTUP OF ORC2 The second ORC power plant module was installed in November and December, 2006 as scheduled. It was brought online on December 16th, 2006. The installation of the second unit was completed almost entirely by the crew of Chena Power, with UTRC and UTC Power representatives onsite for only a few days for final hookup of control wiring, systems check, and initial startup. The second unit is essentially identical to the first one, however a muffler was fabricated by Chena Power and installed at the turbine outlet to reduce the noise level. This has been very effective and ORC#1 may be retrofitted with a similar muffler in the future. As discussed previously, the second ORC unit is a dual air and water cooled system. This allows maximization of system performance by taking advantage of the cold ambient air in winter, and the cool groundwater in the summer months. The second unit has been operating consistently since installation, however due to problems with the cold water supply ORC #1 has been shut down temporarily. Both units are expected to be running in tandem in early 2007. Modification to existing electric infrastructure and hookup to UPS system One of the major project challenges has been upgrading an aging diesel generator plant and marginal power distribution infrastructure to permit installation of the geothermal power plant modules. Modifications to the exiting electric infrastructure began almost a year prior to the installation of the first ORC module. One specific challenge was how to allow the geothermal modules, which generate power via induction generators and thus requires grid support to provide a stable input voltage and frequency for startup, to operate as stand alone generation. This was accomplished through the installation of a 3MW UPS system. The 480V inverter which is part of the UPS system can provide voltage and frequency to the induction generator as it extracts current. This type of system, with batteries for startup and load balancing, allows for the grid-independent operation required by Chena Power. An additional benefit of the UPS system was that it allows seamless power production from multiple sources (primarily the ORC units and the paralleled diesel generators) to smoothly and continually provide power to the site, via the inverters which are part of the UPS system. BUDGET AND TIMELINE The project has been completed on schedule and close to the original budget of $1,899,065. At the end of 2006, project expenses totaled $2,007,770, or 5% above the original estimate. The project was funded in part through a $246,288 grant from the Alaska Energy Authority. An additional loan was obtained through the AIDEA Power Project Loan Fund in the amount of $650,000. The rest of the project included cash and in-kind contributions from Chena Power and its sister corporations Chena Hot Springs Resort and K&K Recycling. REFERENCES Brasz, J.J., Holdmann, Gwen, Power Production from a Moderate -Temperature Geothermal Resource, paper presented at the GRC annual meeting, Reno, Nevada, September 25-28, 2005. Cogswell, F, An ORC power plant operating on a low-temperature (165 F) geothermal source, paper presented at the GRC annual meeting San Diego, California, 2006 www.yourownpower.com http://www.utcfuelcells.com/utcpower/products/purecycle/purecycle.shtm  Carrier Refrigeration is a division of United Technologies Corporation     PAGE  PAGE 3 56jkl   3 w S ^ v -9˝xxxtttpixtethN hhh~^h~ hh~^hPqjhxq0JUhxqhP!hhWJ5hh~^5 h]+6]h]+h]+6H*]h]+h6]h]+h]+6]h]+h]+h5CJ$aJ$h]+h]+5CJ$aJ$h]+hP!5CJ$aJ$h]+h;-5CJ$aJ$'6kl   deBCgdlgdwgd>//55566778888=::::;;<|<~<<<<!=#=0>O>0?D?@9AEEh+$h%J5;h+$h%JH* h<h%J h<5h<h%Jh+$hwH* h+$hwhw h+$h%Jh+$h%J5H@9A:A}B~BDDEEEHHHH_ItIIIIJgd>$ & F7$8$H$^`a$gdn|$ & F 7$8$H$a$gdl$ & F 7$8$H$a$gdn|gd gd%Jgd%Jgd<EEHHHH,HmHHHHII^I_IsItIIIӶ}l]O@3]hlhn|B*CJphhlhlB*CJaJphhlB*CJ\aJphhlhn|B*CJaJph hlhlB*CJ\aJph hl6B*CJ\]aJph&hlhl6B*CJ\]aJph&hlhn|6B*CJ\]aJphh B*CJaJph hn|hn|6B*CJaJphhn|B*CJaJph hn|5hn|hn|5hn| h+$h%Jh<h%J5IIIIJJJ J J JJJJJJJJJJJ%J&J'J(J)J+J,J9J:J;JſſſŴſ۰hD;h]+0JmHnHu hl0Jjhl0JUjhk~Uhk~hljhl0JU hhzxhn|hn|B*CJaJphJJ J J J JJJJJJJJ)J*J+J,J-J.J/J0J1J2J3J4J5J6J7J &`#$gdmDb7J8J9J:J;Jgd>&1h:p+&/ =!"#$%D@D NormalCJ_HaJmH nHsH tHZ@Z zx Heading 1$<@&5CJ KH OJQJ\^JaJ N@N ~^ Heading 5 <@&56CJ\]aJDA@D Default Paragraph FontRiR  Table Normal4 l4a (k(No List8B@8 ~^ Body Text 7$8$H$fOf ~^Default 7$8$H$1B*CJOJQJ^J_HaJmH nHphsH tH4>@4 Title B*^Jph4 @"4 Footer  !.)@1.  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