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2 Geothermal Resources Council TRANSACTONS, Vol. 20, SeptemberlOctober 996 THE 25 MW UPPER MAHAO GEOTHERMAL POWER PLANT "Laqest Geothermal SteamlBina y Combined Cycle Plant Starts-Up " by Nessim Forte, Manager, Ormat nc., Manila Branch ABSTRACT The 25 MW Upper Mahiao power plant, the first geothermal power project to be financed under a B uild~~erate-and-transfer (BOOT) arrangement in the Philippines, expected to complete its start-up testing in August of this year (996). This plant uses Onnat's environmentally benign technology and is both the largest geothermal steam/bin~ combined cycle plant as well as the largest geothermal power plant utilizing air cooled condensers. The Ormat designed and constructed plant was developed under a fast track program, with some two years from the April 99Q contract signing through design, engineering, construction and start- UP- The plant is owned and operated by a subsidiary of CalEnergy Co., nc. and supplies power to PNOC-Energy Development Corporation for the National Power Corporation (Napocor) national power grid in the Philippines. Background After supplying two smaller projects, Ormat won a BOOT bid from PNOC-EE for a 25 MW plant for the Upper Mahiao project on the island of Lqte. CalEnergy became the owner and operator of the plant, which Ormat developed as the EPC contractor and power plant equipment supplier. Ormat's successful export of its environmentally friendly technology provided hundreds of jobs for its 80 suppliers across the United States. The company's support by United States government agencies, such as the Export-mport Bank and the Agency for nternational Development (AD) has been instrumental in the development of its export markets. n 995, Ormat received the President's "E" Award, from the United States Department of Commerce as the only United States expoker of geothermal power equipment. Design Goals Frequently geothermal power plants are located near residential areas, parks or agricultural areas, requiring environmental considerations. n addition, the project owner's and the power customer's interests must also be considered. Under these circumstances, special attention is paid to: Blending the power plant into the environment. Reduction of air emissions and operating noise levels. 0 Avoiding the use of scarce water for plant operation. Preservation of land surface usage and vegetation. Short lead-time for power plant construction. High equipment reliability and high power plant availability. Ease of installation and maintenance. * Avoiding depletion of the geothermal resource. These goals were achieved through the use of the k a t air-cooled Geothermal Combined Cycle technology whereby: Geothermal fluid is maintained at above atmospheric pressure without the use of vacuum pumps or ejectors, thus saving power, maintenance expenses and handling of noncondensibles. Aircooled condensers are used, which result in lower plant profile, no water consumption, no use of chemicals, no blowdown disposal treatment and no cooling tower plumes. Combination of the two above lead to: Enhanced reservoir management with all the spent brine reinjected or pressure support and life extension. Easy HzS abatement without vacuum pumps and even the possibility to reinject the gases together with the spent geothermal fluid without chemical treatment and waste disposal (a similar system has successfdly been used in the Puna Geothermal Power Plant for the last three years). 743

3 Automatic operation and simplified maintenance. Process Description General The power plant is based on the Geothermal Combined Cycle Unit (GCCU) which is a combination of a back pressure turbine followed downstream by Ormat Energy Converters (OECs) operating on an Organic Rankine Cycle (ORC). n addition, the brine energy is recovered in a binary plant using a separate OEC (see Figure ). Steam Stream The Geothermal Combined Cycle Unit is comprised of four Level back pressure steam turbines, each connected to three Level X OEC units downstream in which the expanded steam is used to vaporize the motive fluid with the steam condensate used to preheat the motive fluid. The noncondensible gases are separated from the steam in the steam condenser/motive fluid vaporizer at above atmospheric pressure. Brine Stream The energy of the brine stream is utilized in a binary plant comprised of a single OEC unit. Heat and Mass Balance (Figure 2) Geothermal steam and brine exiting from separators are supplied at the power plant perimeter at the following average conditions: Geothermal Steam and NCG Flowrate...,09 t/h NCG Content... 2% Steam Quality % Steam Pressu bar a (56.6 PSA) Steam Temperature... Brine mowrate... Brine nlet Temperatu re... Brine Outlet Temperature... Ambient Air Design Temperature... Power Output 84"C/363"F,267 t/h 84"C/363"F 64"C/327"F..24.2"C / 75.6"F (annual average) Total Nominal Output MW Total Output at Generator Terminals MW. Figure, Process description. Note: the Upper Mahiao plant uses the LO-CAT abatement system manufactured by Wheelabrator Clean Air Systems, instead of reinjection shown. Plant Auxiliaries Consumption. Net Power Output... Equipment Description eve 3.4 MW 8.6 MW The turbine is a multi-stage reaction-type steam turbine. The turbine housing, shaft assembly and nozzle rings are designed to Ormat specification for operation with geothermal steam containing H2S and C& which, may create corrosive conditions. Steam Turbine Type... GE single cylinder-reaction No. of Stages... 6 Steam nlet Pressure. 0.4 bar a (50.8 PSA) Steam Outlet Pressure..3 bar a (8.9 PSA) Steam Quality % Speed... 3,600 rpm Construction... Horizontal split casing Generator Rated Output... 22,OOO kw 744

4 r-- i i.. L-- --A L M.90.7 U d.23 P lm.4 ofc-4 ; ; OLC-42 ; lb Y 04.0 W) : : 9 q 2o.m Y Y 04.0 UlSlCNl Ni3 DKf BULB CCNCRAOR lcrylnus :.M UW Figure 2. Heat and mass balance. Voltage... Power Factor... Ormat Energy Converter ORC f eve/ and Binary Plant 0 Turbines Organic Vapor Turbine 3.8 kv. phase, 60 Hz 0.85 (lagging) Type... mpulse Speed...,800 rpm Construction... Horizontal (overhang) vertical split casing No. of Stages... Two 0 Generator Rated Capacity kw for GCCU OEC Level 5,500 kw for binary plant OEC Tedal Voltage. 3,8 kv,3 phase, 60 Hz Effiaen... 96% of full load Vaporizer Tube in shell Total Heat Transfer Area ,630 m (48,837 sq. ft.) (per Level OEC) Stainless 3,400 tubes 36L. OD 9 mm (3/4 in.) Binary OEC Parameters. 930 m2(0,00 sq. ft.) and,485 tubes of SA 24 0 Condensers Air-Cooled No. of Bays... Fans... 9 per unit for Level OEC 7 for binary plant OEC 27 of 26.3 HP for Level OEC 2 of 2.7 HP for the binary OEC 0 Motive Fluid, N-Pentane Motive Fluid Mass Flow per OEC Level ,000 kg/h (974,444 lb./h) per OEC Binary Plant ,880 kg/h (495,775 lb./h) Motive Fluid Pump Consumption OEC Level... OEC Binary Plant kw 340 kw OEC Power and Control System Each OEC Control system is controlled by a Programmable Controller (PLC) using Ormat ORBULDER software 745

5 which controls the automatic operation of the OEC as an ndependent part of the station. The OEC control and protection system contains the following items: Programmable controller, central processing unit with analog and digital input and output modules and communication control unit. Synchronizer, check synchronizer, voltage regulator and VAR controller,..... Balance of Plant The power plant consist of the Geothermal Combined Cycle Units, plus the following main systems: Power plant geothermal fluid systems. Auxiliary systems. Electrical Systems. Main station control and auxiliaries building. Station Control System The central station control system governs the power plant operation under operating conditions. The system controls and monitors the start-up procedure, normal operation, normal and emergency shutoff, protection, alarms and other functions. The Central Station Control System is based on programmable controllers using the Ormat ORBULDER software and an operator controlled console which includes PCs, monitors, and all; switches, push buttons, indicating lights, metering instruments, etc. Project Execution As the EPC contractor, Ormat assumed the full responsibility for the engineering and procurement of its supply and the materials and services from the other vendors, as well as the logistics of transportation for TC, the construction subcontract or. Figure 3. Equipment being off loaded for landing by barge. Transportation The Upper Mahiao shipping and logistics operations involved 345 (40 ft.) containers and 5,000 tons of bulk freight, which was shipped over the period from February 995 to February 996 in 20 Ocean shipments. The majority of the cargo (80 percent) was moved in five special heavy lift chartered vessels from Houston Port directly to Orma Bay, sland of byte, in the Philippines. This bay is too shallow for direct discharge to land, via the port, so the vessels anchored in the open sea for discharge to LCTs which brought up along side the vessel being discharged. Using the Ocean vessel's on-board crane, the freight was directly discharged to the awaiting LTCs. The unloading went very smoothly, even when the sea did not remain calm or the off loading (Figure 3). The balance of the shipments were made from Oakland, California, direct to the Port of Manila and then barged to Ormoc Port or to Tacloban Port. The Upper Mahiao shipment operation also involved more than 9 air shipments completed since August 995 (Figure 4). Project Schedule Ormat was awarded an engineering-procurement-construdion (EPC) contract on 8 April 994. Earthwork began in late September 994, with the first concrete pour in April 995. The on-site installation of the 2 Ormat Energy Converters (OECs) was started in May 996, and the last GCCU was tested on 27 June 996. The power plant started to supply power to the Napocor Grid in August 996, as part of its commissioning regime and full operation will begin as soon as the full transmission line is completed by Napocor. Figure 4. Trucking equipment to project site. 746

6 Figure MW Upper Mahaio power plant completed. Construction The fast tract project entailed the efforts of up to 800 men on-site, with much of the work accomplished in difficult rainy conditions. Some of the salient statistics include: A total of some cubic yards of concrete. Wire installations totaling roughly 500,000 linear feet, of which approximately 20,000 linear feet were instrument cables and 6,000 feet of fiber optics. More than 20,000 linear feet of pipe of more than 2-inch was installed. Of that, 7,500 linear feet was stainless steel piping. Training and Start-up During the months of February and March of 996, twenty-two of the plant's CE Cebu Operations and Maintenance personnel successfully completed a course organized by Ormat in the operation and maintenance of the plant's various systems. The start-up effort of the power plant was executed by Ormat personnel assisted by CE Cebu operators. This course was divided into a five-week classroom training session, and an eight-week "hands-on" training period conducted by the commissioning team. Conclusions The 25 MW Upper Mahaio Geothermal Steam/Binary Combined Cycle Power Plant was financed by CE Cebu and constructed on schedule under a fast tract program, and has demonstrated its operational readiness (Figire 5). The plant ushers in a new phase of dedicated geothermal power plant technology. A technology that has the capability to reduce (a) the environmental the operational complexity and (c) the operating and maintenance expenses of utility size geothermal power plants. With (a) turbine train components that do not encounter low-pressure wet geothermal steam; (b) no vacuum pumps or ejectors; (c) full use of the energy from the steam and brine; (d) the benefits of dry air-cooling: the cost-effectiveness and reliability; (e) 00 percent spent brine reinjection, and (f) a simplified abatement system having the potential of H2S reinjection, the power plant is indeed the product of advanced geothermal technology design, engineering, manufacturing and project execution. ' 747