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2 The 125 MW Upper Mahiao Geothermal Power Plant "Largest Geothermal SteadBinary Combined Cycle Plant Starts-Up " by Nessim Forte, Manager, Ormat Inc., Manila Branch ABSTRACT The 125MW UpperMahiao powerplant, the firstgeothermal powerproject to be financed under a Build-Own-Operate-and-Transfer (BOO13 arrangement in the Philippines, expected to complete its start-up testing in August of this year (1996). This plant uses Ormat's environmentally benign technology and is both the largest geothermal steamlbinay combined cycle plant as well as the largest geothermal power plant utilizing air-cooled condensers. The Omat-designed and constructed plant was developed under a fast-track program, with some two years from the April 1994 contract signing through design, engineering, construction and start-up. The plant is owned and operated by a subsidiary of CalEnergy Co., lnc. and supplies power to PNOC-Energy Development Corp. for the National Power Corp. (Napocor) national power grid in the Philippines. Ba c kg ro u n d A fter supplying two smaller projects, Ormat won a BOOT bid from PNOC-EDC for a 125 MW plant for the Upper Mahiao project on the island of Leyte. 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-Import Bank and the Agency for International Development (AID), has been instrumental in the development of its export markets. In 1995, Ormat received the President's "E" Award, from the U.S. Department of Commerce as the only United States exporter of geothermal power equipment. Design Goals Frequently, geothermal power plants are located near residential areas, parks or agricultural areas, requiring environmental considerations. In addition, the project owner's and the power customer's interests must also be considered. Under these circumstances, special atten- tion is paid to: Blending the power plant into the environment. Reducing air emissions and operating noise levels. 3RC BULLETlN AugudSeptember

3 Avoiding the use of scarce water for plant operation. 0 Preserving land surface usage and vegetation. 0 Reducing lead-time for power plant construction. Ensuring equipment reliability and high power plant availability. 0 Improving installation and maintenance. Avoiding depletion of the geothermal resource. These goals were achieved through the use of the Ormat air-cooled Geothermal Combined Cycle technology where-by: 0 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. Air-cooled 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. A combination of the two above lead to: Enhanced reservoir management with all the spent brine reinjected or pressure support and life extension. Easy H2S abatement without vacuum pumps and the possibility to reinject the gases together with the spent geothermal fluid without chemical treatment and waste disposal (a similar system has successfully been used in the Puna Geothermal Power Plant for the last three years). Automatic operation and simplified maintenance. Process Description Figure 1. Processdescription. Note: the Upper Mahiao plant uses the LO-CAT abatement system manufactured by Wheelabrator Clean Air Systems, instead of reinjection shown. nected to three Level I1 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. 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). In addition, the brine energy is recovered in a binary plant using a separate OEC (see Figure 1). Steam Stream 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 follow- ing average conditions: The Geothermal Combined Cycle Unit is comprised of four Level I back pressure steam turbines, each con- Geothermal Steam and NCG Flowrate... 1,019 ffh 300 G RC BULLETlN AugusVSeptember 1996

4 NCC. 20.JLIO 108 u P Figure 2. Heat and mass balance NCG Content Steam Quality /o Steam Pressure... Steam Temperature bar a ( PSIA) 184"C/363"F Brine Flowrate... 1,267 Vh Brine Inlet Temperature Brine Outlet Temperature "C1363" F 164"C/327"F Ambient Air Design Temperature "C/75.6"F (an nu al average) Power Output Total Nominal Output. Total Output at Generator Plant Auxiliaries Consumption... Net Power Output MW 132 MW 13.4 MW MW Equipment Description Level I 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 COz,which may create corrosive conditions. Steam Turbine... GE single cylinder-reaction... 6 Steam Inlet Pressure 10.4 bar a (150.8 PSIA) Steam Outlet Pressure bar a (18.9 PSIA) Steam Quality /o Speed... 3,600 rpm Construction... Horizontal split casing Generator Rated Output... 22,000 kw GRC BULLETIN AugusVSeptember

5 Voltage... Power Factor kv,3 phase, 60 Hz Ormat Energy Converter ORC Level I! and Binary Plant Turbines Organic Vapor Turbine Type... Speed... Construction (lagging) Impulse 1,800 rpm Horizontal (overhang) vertical split casing No. of Stages... Generator Rated Capacity... Terminal Voltage... Efficiency... Vaporizer Two 4,500 kw for GCCU OEC Level I1 5,500 kw for binary plant OEC 13,8 kv,3 phase, 60 Hz 96% of full load Tube in shell Total Heat Transfer Area... 4,630 m (48,837 sq. ft.) (per Level I1 OEC) Stainless 3,400 tubes 31 6L Binary OEC Parameters Condensers OD 19 mm (3/4 in.) 930 m 10,010 sq. ft.) and 1,485 tubes of SA 21 4 Air-Cooled No. of Bays... 9 per unit for Level II OEC 7 for binary plant OEC Fans of 26.3 HP for Level II OEC 21 of 12.7 HP forthe binary OEC Motive Fluid, N-Pentane Motive Fluid Mass Flow per OEC Level II ,000 kg/h (974,444 Ib./h) per OEC Binary Plant ,880 kg/h (495,775 Ib./h) Motive Fluid Pump Consumption OEC Level I... OEC Binary Plant... OEC Power and Control System 220 kw 340 kw Each OEC control system is controlled by a Program- mable Controller (PLC) using Ormat ORBUILDER soft- ware, which controls the automatic operation of the OEC as an Independent 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. The system controls and monitors the start-up procedure, normal operation, normal and emergency shutoff, protection, alarms and other func- tions. The Central Station Control System is based on programmable controllers using the Ormat ORBUIL- DER software and an operator-controlled console which includes PCs, monitors, and all switches, push buttons, indicating lights, metering instruments. Project Execution As the EPC contractor, Ormat assumed the full re- sponsibility 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 TIC, the construction subcontractor. Project Schedule Ormat was awarded an engineering-procurement- construction (EPC) contract on 8 April Earthwork began in late September 1994, with the first concrete pour in April GRC BULLETIN Augustheptember 1996

6 Construction The fast-track 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 6,500 cubic yards of concrete. Wire installations totaling roughly 500,000 linear feet, of which approximately 210,000 linear feet were instrument cables and 16,000 feet of fiber optics. Figure 3. Equipment being off-loaded for landing by barge. The on-site installation of the 12 Ormat Energy Converters (OECs) was started in May 1996, and the last GCCU was tested on 27 June The power plant started to supply power to the Napocor Grid in August 1996, as part of its commissioning regime, and full operation will begin as soon as the full transmission line is completed by Napocor. 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 1995 to February 1996 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 Ormoc Bay Island of Leyte, 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 for 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 91 air shipments completed since August 1995 (Figure 4). More than 20,000 linear feet of pipe 2-inches or more was installed. Of that, 7,500 linear feet was stainless steel piping. Training and Start-up During the months of February and March of 1996, 22 of the plant's CE Cebu Operations and Maintenance personnel successfully completed a course organized by Ormat on 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 125 MW Upper Mahaio Geothermal Steam/Bi- nary Combined Cycle Power Plant was financed by CE Cebu and constructed on schedule under a fast-track program, and has demonstrated its operational readi- ness (Figure 5). Figure 4. Trucking equipment to project site. GRC BULLETIN AugusVSeptember

7 The plant ushers in a new phase of dedicated geothermal power plant technology. A technology that has the capability to reduce (a) the environmental impacts, (b) the operational complexity and (c) the operating and maintenance expenses of utility-size geothermal power plants. With (a) turbine train components that do not en- counter low-pressure wet geothermal steam; (b) no vac- uum 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) 100 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. Figure MW Upper Mahaio power plant completed. 304 GRC BULLETlN AugusffSeptember 1996