THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS 345 E. 47th St., New York, N.Y

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1 THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS 345 E. 47th St., New York, N.Y GT-177 The Society shall not be responsible for statements or opinions advanced in papers or discussion at meetings of the Society or of its Divisions or Sections, or printed in its publications. Discussion is printed only if the paper is published in an ASME Journal, Papers are available from ASME for 15 months after the meeting. Printed in U.S.A. Copyright 1993 by ASME WOODSDALE - A UNIQUE PEAK GENERATING PLANT Robert P. Carey General Engineering Department The Cincinnati Gas & Electric Company Cincinnati, Ohio Carl C. Cassell Electric Production Department The Cincinnati Gas & Electric Company Cincinnati, Ohio ABSTRACT The Cincinnati Gas & Electric Company (CG&E) has recently completed construction of the first block of units at their Woodsdale Generating Station, near Trenton, Ohio. The first block of six indoor simple cycle combustion turbine-generators are in commercial operation, with additional space allocated for six more units to be constructed as their peak electric load requires. Woodsdale Generating Station, ultimately having a peaking capacity of 960 MW, has several features unique to a peaking plant. The units are fueled with natural gas or propane, with fuel switchover capability. NOx emission control is achieved with water injection, produced by a water treatment system consisting of filtration, reverse osmosis, and demineralizers. The station also includes a central control room, black start unit, office and maintenance facilities, compressed air system, and computer-monitored gas detectors throughout. The plant staffing, operating history, and lessons learned during the first several months of service are presented. PURPOSE OF A PEAKING GENERATING FACILITY Electric utilities install peak generating facilities for various purposes, but the principal reason is to provide electric generation during times of maximum, or peak, load on the electric system, typically during a few hours of the day when the ambient temperature is extreme, either hot or cold. These generating facilities only operate a few hours, typically 500 or fewer, per year. These facilities are inexpensive to construct, relative to a base load generating facility which operates nearly continuously. The base load facilities, typically coal and nuclear fueled steam cycles, are more costly to construct, but are more efficient and use cheaper fuel than peaking facilities. Utilities endeavor to optimize their mix of generating capacity to cover the range of system load conditions year round at the minimum total cost to the customer. The mix of a utility will include base load and peaking units, in the proportion appropriate for each service area. This proportion varies not only with service area, but also with time. In the early 1980's, The Cincinnati Gas & Electric Company (CG&E) determined that their optimum mix of generation capacity required new peak generation units to be ready for operation by 1992, with additional units later in the 1990's. WOODSDALE DESIGN FEATURES The peaking units at Woodsdale are simple cycle combustion turbine-generators, industrial type, 77 MW summer rating each, with water injection for control of NOx emissions. Block I (Units 1-6) were furnished by Asea Brown Boveri (ABB); Block II (Units 7-12) have not yet been purchased. See Table 1. At project inception, CG&E determined the new units would be added to the system capacity to maximize their reliability. This commitment to high reliability led to several design decisions, some of which are unique or unusual in the design of peak generating facilities. New Site CG&E conducted a site selection study of 20 locations to construct the peaking units. Several of those candidate sites were adjacent to existing generating stations operated by CG&E. Some of them required that the new units be dispersed to more than one location because of land availability. CG&E already had peaking units at some of the existing base load stations, operated and maintained by the same staff as the base load units. No matter which of the existing plant sites CG&E could have selected for its new units, there would have been compromises to the commitment to high reliability, at least to some degree. For Presented at the International Gas Turbine and Aeroengine Congress and Exposition Cincinnati, Ohio May 24-27, 1993

2 example, locating them at existing plants would have restricted their accessibility for maintenance due to low available acreage. Locating them at existing plants would have also resulted in sharing of staff personnel, tools, and support facilities, such as office space, maintenance shop space, and materials management operations. CG&E decided to construct the new units at one new site. Each of the 20 candidate sites was evaluated against 17 criteria, with each site being scored for each criterion. The scores were then weighted in accordance with the importance of each criterion, and totaled for each site. The Woodsdale location was selected as the preferred site. See Figure 1. The Woodsdale site was close to existing electric transmission lines, natural gas transmission pipelines, liquid petroleum products transmission pipeline, and underground water supply. The Woodsdale site was purchased and laid out to accommodate 12 units, for an ultimate plant size of 960 MW. Since the site was to be developed from a greenfield condition, CG&E made the commitment to provide the support facilities adequate for achieving high reliability. The staff is provided with a complete service facility, including offices, training room, lunch room, storeroom, laboratory, and maintenance shops for electrical and mechanical work. An existing rail siding on adjacent property was extended to Woodsdale for transporting the turbines, generators, transformers, and propane storage tanks. Indoors In support of the reliability commitment, CG&E elected to make Woodsdale an indoor plant. The turbine-generators and the maintenance laydown space are within the turbine hall, and coverage is provided by a traveling bridge crane. Work on the units can be accomplished without regard to temperature, precipitation, wind, or darkness. Rolling doors are furnished to provide truck access between all units and to the laydown space. The supporting facilities are connected to the turbine hall, eliminating the need for staff to go outdoors for most functions. Control of noise indoors at Woodsdale is achieved by furnishing each unit with an acoustic enclosure and acoustic treatment of the turbine hall siding. The unit enclosures also function as carbon dioxide containment for the fire detection and suppression system. The turbine hall is protected by sprinkler systems between the units. The enclosures and siding are designed to not exceed an 85 dba noise level indoors with all units operating. The turbine hall also contributes to the design criteria for outdoor noise level of 55 dba at a distance of 400 ft. (122m). Other measures taken to achieve this outdoor noise level include inlet silencers, exhaust silencers, and slow-speed cooling fans. Dual Fueled-Gas and Propane The experience of many operators of combustion turbine units indicates higher reliability with gaseous fuels than liquid fuels. CG&E determined to enhance Woodsdale's reliability by providing each unit with two gaseous fuels: natural gas and propane. The natural gas is piped to Woodsdale through pressure control stations direct from a transmission pipeline, without the need for gas compressors. Because of CG&E's experience with propane to augment their natural gas system through propane-air plants, and because CG&E had a propane terminal and storage cavern, propane was selected as the second gaseous fuel. It is transported and stored in liquid phase. In addition to the offsite cavern storage, additional storage was provided at Woodsdale in mounded steel tanks. The liquid propane is forwarded to each unit, where it is vaporized and superheated. The heating is accomplished by a propane-fired packaged boiler at each unit, with circulating water transferring the heat from the boilers to the vaporizers and superheaters. See Table 2. The gaseous propane and natural gas are piped to a 3-way valve at each unit, which enables the operator to select either fuel at any unit load. See Figure 2. To enhance safety, CG&E installed detection systems throughout the fuel system for both gas and propane. The detectors are continuously monitored by the plant distributed control system, which provides graphic displays and alarms in the central control room. Central Control Room A central control room is provided at Woodsdale. Each unit may be operated locally, or remotely at the control room through a distributed control system (DCS). The backbone of the DCS is the micro-processor-based Westinghouse WDPF, consisting of seven distributed processing units (DPU), six station interface units (SIU), one universal programmable controller interface (UPCI), two operator stations, one engineer station, and a DEC Microvax connected by a redundant data highway. The DPU's control and monitor the natural gas, propane, compressed air, and plant electrical systems. The SIU's communicate with the ABB Egatrol 5 controllers over an RS-232 link; information flows in both directions. The black start unit, water treatment system, and remote well water supply system communicate to the WDPF by RS-232 to the UPCI. The DEC Microvax gathers and stores selected plant historical data for trending and logging functions. The operator stations consist of a keyboard and two CRT's capable of approximately 150 graphics on the touchscreens. The propane system also has a hard-wired safety system to shut down any portions of the propane system if certain parameters exceed the pre-set safe range. The control room also contains an electric system mimic board with indicator lights to display breaker position, driven by the 2

3 DCS. Generator output meters and various emergency trip push buttons, as well as annunciator panels, are on the mimic board. The central fire detection panel and a closed circuit television (CCTV) panel are in the control room. The CCTV was installed to allow the operators to view inside the turbine hall and outside the plant. There are no windows between the control room and turbine hall, as a safety measure. The sequence-of-events recorder furnished by ABB is installed in the control room. Water Treatment System Control of NOx emissions is achieved at Woodsdale by water injection into the combustor to moderate the flame temperature. Since this water passes through the turbine and exhausts up the stack, high purity is imperative. The water source is an aquifer about one mile from the plant, and the water is withdrawn by deepwell pumps. It is piped to the raw water storage tank at the plant, which is the water supply to the purification system. Raw water is also piped to a separate tank reserved for the fire protection system. A standpipe arrangement in the process raw water tank reserves a portion of its capacity as a second supply of fire protection water. The water treatment system has a capacity of 1,362 GPM and consists of greensand filters, with manganese for removal of iron, cartridge filters, decarbonator, reverse osmosis, and mixed bed demineralizer. The effectiveness of the water treatment system is represented by the following data: iron & manganese sodium & potassium silica conductivity Raw Final 0.28 ppm < 50 ppb 4.86 ppm < 50 ppb 0.01 ppm < 7 ppb 700gmho/cm < 0.1gmho/cm The system includes all necessary auxiliary equipment, such as, regeneration pumps, booster pumps, chemical feed systems, sump pumps, and waste neutralization system. The waste stream from the reverse osmosis system is piped to the Great Miami River, and the other wastes are neutralized and pumped to the county sewer system. The water treatment system is monitored and controlled with a programmable logic controller, with a CRT operator interface. Monitoring may also be accomplished in the control room through the DCS. The purified water is piped to storage tanks, from which the injection pumps at each unit are fed. Black Start Unit CG&E has included a black start unit at Woodsdale. It is a combustion turbine-generator rated at 3.8 MW, natural gas fired. Upon loss of system voltage, the black start unit starts automatically from a diesel engine cranking unit. The cranking unit brings the turbine to firing speed. The turbine-generator will generate sufficient power to carry certain station loads and start a main unit. Once power is established at Woodsdale, it can feed to other plants as needed for startup in a system black out situation. WOODSDALE STAFFING Providing a dedicated staff for a stand-alone peaking station presented a new challenge and opportunity for CG&E. They needed operators available at all times, but it was hard to justify an operations staff for a station that would run only 5% of the time. After many different proposed organizations, CG&E decided on a "lean and mean" group of twenty-three individuals to form the Woodsdale staff. Operations and Maintenance were combined into one group, with individuals in that department performing maintenance work when they were not busy with operations duties. The Instrument & Controls/Technical Services group handles duties normally assigned to three different groups at steam stations: power plant controls, laboratory chemistry, environmental reporting, and performance monitoring. In addition to the eleven people in Operations/Maintenance and eight in I&C/Tech Services, Woodsdale has two materials management personnel, one clerk, and the station manager. All twenty-three positions were filled from existing CG&E power stations. Candidates were selected on the basis of interviews, and testing and seniority for union jobs. The entire staff was transferred to Woodsdale by April 1991, over a year before the first unit was finished. During this year, they went through extensive classroom and hands-on training. In addition, the station personnel were involved in all start-up activities along with ABB. The idea of having the ultimate customer participate so thoroughly in start-up activities was a new concept to ABB, but afterwards all agreed it was very beneficial to all parties. WOODSDALE OPERATION The Woodsdale combustion turbines have a very brief, but promising operating history. In the first four months of commercial operation, the average unit ran 11 times for 54 hours. The unseasonably cool summer temperatures in the Midwest in 1992 contributed to the low usage of Woodsdale. Successful start percentage was 84% through November. To date, no major problems have surfaced, but it is still too early in the operating life of these units to reach any conclusions from this early success. LESSONS LEARNED Woodsdale has already benefitted from several of the unique aspects of the project. At no time during start-up, operations, or maintenance activities was weather a concern, once the building was completed. There is normally no need to walk to individual units during operations, since nearly all functions are performed 3

4 in the central control room. Having a new site with a devoted staff has encouraged teamwork, pride, and enthusiasm for success. TABLE 1 - COMBUSTION TURBINE UNIT DATA - UNITS 1-6 Manufacturer Model Capacity - Summer - Winter Fuels Elevation Heat Rate - gas - Propane NO Limits - gas - propane NO Control Water Injection Rate Starting System Asea Brown Boveri (ABB) 11N, Simple Cycle 77MW 94MW Natural Gas, Propane 654 ft. (199 m) 12,930 BTU/KWH (13,642 KJ/KWH) 13,170 BTU/KWH (13,895 KJ/KWH) 42 ppmv 65 ppmv Water Injection 150 GPM (568 L/min) at 94 MW Generator, via Static Frequency Converter TABLE 2 - PROPANE SYSTEM DATA Liquid Propane Storage Tanks (6) Propane Forwarding Pumps (7) Propane Varpoizers (6) Propane Superheaters (6) Hot Water Boilers (6) Hot Water Circulating Pumps (6) 90,000 gal each (340,687 L) 11 ft. OD x 134 ft. long (3.35 m x 40.8 m) ASME Sec VIII Div. 1 Byron Jackson 19-Stage Vertical 75 hp, 250 GPM, 340 PSIG (55.9 kw, 946 L/min, 2344 kpag) Applied Engineering Co. Bayonet Type Tubes Vertical 250GPM, 20 F in, 155 F out (946 L/min, -6.7 C, 68.3 C) Two-Pass Shell and Tube 200 F out (93.3 C) Cleaver Brooks Four-Pass Horiz. Fire Tube Propane Vapor Fueled 500 hp, 16.7 MBTU/H (4.9 MW) 30 PSIG Pressure, 250 F out (207 kpag, 121 C) Bell and Gossett 1200 GPM, 60 PSIG (4,542 L/min, 414 kpag)

5 Figure 1 - WOODSDALE GENERATING STATION NATURAL GAS PIPELINE PIPEUNE TAP STATION FIRST STAGE REGULATOR SECOND STAGE REGULATOR LIQUID PROPANE PIPELINE EACH UNIT _10,- IDENTICAL LTO UNIT STORAGE CAVERNS 7 MILLION GAL CAPACITY (6) TANKS 90,000 GAL EACH Figure 2 - FUEL SYSTEMS DIAGRAM 5