Industrial Users choose Fuel Flexible GT11N2 for burning Blast Furnace Gas in Combined Cycle Power Plants

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1 THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS 345 E. 47th St., New York, N.Y M-133 The Society shall not be responsiblifor statements or opinions advanced in papers or chicussion at meetings of the Society or of its Divisions or Sections, or printed In its publications. Discussion is printed only If the Paler is published in an ASME Journal. Authorization to photocopy. - material for internal. or personal use under circumstance not falling within the fair use *provisions of the Copyright Act is granted by ASME to - libraries and other users registered with the Copyright Clearance Center (CDC) Transactional Reporting Service provided that the base fee of $0.30 per page is paid directly to the CCC. 27 Congress Street Salem MA Requests for special penniesien or bulk reproduction shout! be ackkessed to the ASME Technical Publishing Department Copyright by ASME All Rights Reserved. - Printed in U.S.A Industrial Users choose Fuel Flexible GT11N2 for burning Blast Furnace Gas in Combined Cycle Power Plants W II N G. Gnadig, K. Reyser, W. Fischer, J. Schmidli ABS Power Generation Ltd. Baden, Switerland Introduction Stricter environmental regulations and the need for high-efficiency energy generation have led an increasing number of industrial users to investigate alternatives to burning waste gases from the industrial plants in conventional thermal power plants. Combined cycle power plants using gas turbines capable of burning low-caloric fuels such as blast furnace gas can meet these requirements with thermal efficiencies of more than 45%. In November 1994, the Bao Steel Corporation signed a contract with Kawasaki Heavy Industries and ABB Power Generation for a combined cycle power plant burning blast furnace gas. The Baoshan Project, located near the Chinese city of Shanghai is designed to provide up to 150 MW of electrical power and up to 180 tons/hr of steam to the steel mill, while burning blast furnace gas with a heating value of 80 BTU/SCF (760 Kcal/Nm3). The single-shaft power train consists of a GT11N2- LBTU gas turbine, a fuel gas compressor, a gear-box and a steam turbine located on one side of the 50 Hz generator. The GT11N2 as prime mover of this compact power train is a modern gas turbine rated at 115 MW with natural gas and about 150 MW with blast furnace gas. One specific design feature of this gas turbine is the LBTU combustor located on top of the unit. In order to accommodate the increased fuel flow rates associated with low caloric blast furnace gas, a new LBTU combustor, as well as a new LBTU burner were developed. The other important feature for successfully burning low caloric gases is the extended GT11N2 capability of reduction of air inlet flow through the use of three rows of variable guide vanes in the compressor inlet which allows to operate the GT11N2 at its design pressure ratio. ABB's operating experience is quite extensive, with the first gas turbine unit going into operation on blast furnace gas in 1948 in the Barcaldo facility in Spain. Between 1948 and 1962, twenty-one ABS gas turbines firing Blast Furnace Gas (Table 1) went into commercial operation. The turbine inlet temperature and pressure ratios of Downloaded From: Presented on 11/08/2018 at the ASME Terms ASIA of Use: '97 Congress & Exhibition Singapore - September 30-October 2,1997

2 these units are considerably lower than today's units. The operating experience of these machines exceeds 2 million hours. Two of these 21 units are still in operation with the fleet leader at the Donawitz plant exceeding 250'000 operating hours. Installation Country Start-up Power Output Operating hours Barcaldo Spain '000 92'000 Dudelange Luxenburg '140 Niederrhein I Germany '800 59'500 Stoke on Trent UK ' '990 La Chiers Longwy France '000 Hagen-Haspe Germany '000 79'920 Horde III Germany '890 Pont-A-Mousson France '410 Donawitz Austria ' Huckingen Germany ' Horde I Germany '000 26'400 Knutange France '000 67'700 Rodange Luxenburg '300 48'000 Rheinhausen I Germany '000 57'410 Usinor Denain France ' '000 Rombas France ' '770 Hagondange France '200 25'000 Horde II Germany ' '890 Rheinhausen II Germany '000 85'070 Niederrhein II Germany '000 29'700 Cornigliano Italy '250 88'385 Table I: ABB Gas Turbines operating on Blast Furnace Gas Baoshan Plant Concept The 150 MW single-shaft power train is configured for combined cycle power generation and cogeneration. ABB supplied the GT11N2 gas turbine, the 210 MVA generator and the power train control system PROCONTROL, while ABB's joint venture partner Kawasaki Heavy Industries (KHI) supplied the double-pressure steam turbine, the heat recovery steam generator, the fuel gas compressor and the fuel control system. KHI was also the lead in installing the equipment, and in on-site testing and commissioning. Plant Arrangement The single-shaft arrangement allows for a compact lay-out of the plant. The overall power train length including the exhaust heat recovery boiler is 110 meter. The 2

3 dimensions of the machine hall show a width of 26 meter and a length of 52 meter (figure 1). The train consists of the gas turbine, the fuel gas compressor, the reduction gear, the steam turbine and the generator; all components are connected with fixed couplings. COCOMP Figure 1: GT11N2-LBTU in single-shaft arrangement The table-mounted design allows for easy accessibility of all heavy equipment items during maintenance without disassembly of piping, including the blast furnace gas pipe connection below the blast furnace gas compressor. This lay-out also allows the installation of the condenser below the steam turbine. One single overhead crane is located at a height of 26.4 meter; this crane can be positioned at any point of the power train for removal of upper equipment casings or entire components, thus facilitating maintenance work. Performance The blast furnace gas (BFG) used for the Baoshan facility has a low caloric heating value of kcal/nm 3 (2'000-2'600 kj/kg). Natural gas has a heating value of 48'000 kj/kg which is about a factor 18 higher than BFG. For a given heat input, the gas turbine burning BFG will therefore require a higher fuel flow rate: While the natural gas fired Gill N2 requires a fuel flow of approximately 8 kg/sec, the same unit firing BFG will require a fuel flow of 144 kg/sec. This large difference can only be accommodated, because the GT11N2 compressor utilizes three rows of variable guide vanes, allowing for adequate reduction of the air inlet flow. 3

4 The power output of the Gill i'42 with BFG at the GT coupling is 144 MW. The gas compressor consumes approximately 52 MW for increasing the pressure of the BFG from 1.02 bar to about 16 bar required for injection into the gas turbine combustor. With the hot gases from the turbine exhaust, steam is generated in the heat recovery steam generator for expansion in the steam turbine. This raises the total power output of the single-shaft power train to approximately 150 MW. In a different operating mode, with reduced power output, the power train can produce up to 180 tons/hour of steam to the industrial complex (figure 2). Without water or steam injection, NOx emission levels are expected to be less than 35 ppmv (corn to 15% 02). Figure 2: BFG fired CC Power Plant-System Diagram Operating and Control Concept The operation of the gas turbine burning blast furnace gas requires modifications to a standard application. Start-up of the gas turbine power train commences with steam from an outside source being used for warming up and accelerating the steam turbine. After air purging the heat recovery steam generator, the steam flow to the turbine is increased to the point that the speed of the power train reaches approximately 800 rpm; at this point the speed required for ignition of the gas turbine is reached and diesel fuel is injected into the gas turbine combustor. The power train is synchronized to grid frequency while operating on diesel and then loaded up to about 20 MW generator output. At this point the fuel compressor will provide blast furnace gas at conditions at which the gas valve to the combustor can be opened. Within a small load range, up to approximately 30 MW, the gas turbine will bum blast furnace gas and diesel fuel simultaneously, then diesel will be switched off and the power train will be loaded up to baseload power with blast furnace gas. 4

5 The blast furnace gas flow to the gas turbine is controlled by the combination of the pressure control valve and the stator blade angle of the fuel gas compressor. The control system of the gas turbine itself is a standard EGATROL system, operating with a combination of speed, load and temperature control. The unit will be operated at baseload with only 2 starts per year. Power Train Description The single-shaft power train used for the Baoshan project is based on the ABS gas turbine GT11N2, a two-casing SULZER fuel gas compressor with intercooler, a RENK gear-box and a KHI steam turbine located on one side of the ABB.VVY21 generator. The GT11N2 was originally developed as a gas turbine for the 60 cycle market, capable of burning natural gas and diesel fuels. In 1993, the first unit went into operation in the E.W. Brown Power Station, located in Kentucky, U.S. Since then, 15 units of this type have been sold to various customers in simple and combined cycle applications. Fgure 3 GT11N2-LBTU Thermal Block

6 The choice for the GT11N2 was based on the units rugged design with the external SILO combustor and the three rows of variable guide vanes (Figure 3). The size of 150 MW in is a block of power well-suited for such an application, as is the 3600 rpm shaft speed for compressor drive. The main focus on adapting the GT11N2 for low caloric blast furnace gas was in the development of a new LBTU combustor and a single burner capable of firing the large volume flows associated with LBTU gas. The 16-stage compressor of the GT11N2 is equipped with threes rows of variable guide vanes, thus allowing for an effective reduction of air inlet flow from 375 kg/s to 260 kg/sec without the need for air extraction or air bleeding. The hot gas casing, leading the combustion gases from the combustor to the turbine inlet, has a separate cooling shell for effective cooling of the inner casing. The 4- stage turbine is moderately loaded, with the first two stages utilizing air cooled blades and vanes. Both compressor and turbine section are arranged on a common rotor with only two journal bearings. As on all ABB turbines, the rotor is welded together from forged disks, resulting in an extremely rugged and maintenance-free design. The size of the SILO combustor was increased to match the higher fuel flow required for firing LBTU gases. The design of the LBTU combustor required a different cooling concept, since the air flow has been reduced by approximately 1/3 of the air flow available during natural gas and diesel oil operation. All cooling air from the inlet to the combustor annulus is used for cooling the inner liner. Instead of tiles in the upper combustor zone, cooling segments are used with a much lower cooling air consumption. Only minor modifications were needed to adapt an already existing LBTU diffusion burner for this application. The burner design is based on the proven design of the similar burners installed in the 21 units operating on blast furnace gas. The swirler of the LBTU burner has a diameter of approximately 1.5 meter. The lower caloric heating value of the BFG results in a fuel flow which is 18 times greater than for natural gas operation. The BFG is therefore brought into the swirler through separate flanges located at the side of the actual burner. Figure 4 shows a bottom view of the burner, with the swirler vanes seperating the channels for BFG and air. The diesel oil for start-up is injected during start-up and for stabilization at gas turbine part load conditions below 20 MW. Between 20 MW to 30 MW, the units is operated in co-firing mode with diesel oil and BFG, and above 30 MW, the gas turbine is operated exclusively with BFG in diffusion mode. The GT11N2-LBTU is capable of firing BFG with a heating value as low as 74 BTU/SCF (700 Kcal/Nm3), thus not requiring enrichment of the blast furnace gas with coke ofen gas or other fuels. 6

7 Figure 4*, Bottom view of BFG burner Part of the gas turbine shaft power is used for driving the 51.5 MW gas compressor from SULZER. This compressor is separated into a high pressure and low pressure casing with intercoolers located beneath the compressor. The compressor is operated at 3600 rpm, the same speed as the gas turbine. The 100 MW gear-box by RENK with a gear ratio of 1.2 reduces the speed down to 3000 rpm. The 60 MW steam turbine is a two-pressure design from KHI which is connected to the gear-box on one side, while driving the ABB VVY21 Generator on the other side. This generator is rated at 210 MVA and utilizes the well established TEWAC (lotal Enclosed Water-to-Aircooled) design. Operating Experience In order to verify the low BTU burner design, a series of tests have been carried out in co-operation with KHI at the Kawasaki Steel Works in Japan. Due to today's higher firing temperatures in gas turbines, ABB's original design technology for low BTU applications from the early 1950's had to be modified. After first sucessfully testing at ABB's combustion facilities in Baden, Switzerland, a one-fifth scale model burner was designed and tested extensively in Mizushima, Japan. These tests were carried out at atmospheric pressure and the results are summarized by Liu and Schmidli. The results from these tests confirmed that the ABB LBTU combustor can bum BFG without any supplementary fuel down to

8 heating values of 2'000 kj/kg. In addition, very low NOx emissions in the single-digit range were measured, indicating that the GT11N2-LBTU will reach the predicted NOx levels of less than 35 ppmv (corr. to 15% 02) at operating conditions. Conclusion The Gill N2 gas turbine is well-suited for low caloric gases. The main design changes were required on the combustor and burner. Experiments with a scaled burner and the first operating experience of the Baoshan unit are very good and confirm that the predicted performance and emissions can be reached. The high thermal efficiency of such plants with more than 45% make them an attractive solution for industrial users burning waste gases. In addition, the GT11N2-LBTU is well suited for syngas applications from oxygen-blown gasification processes, if the syngas is diluted with inert gas or steam, thus meeting lower heating value requirements of the LBTU burner. References Pfenninger, H.: "Experience with Gas Turbines Fired with Blast-Furnace Gas", Brown-Boveri Review (1) Mukherjee, D.: "Experience with unconventional Gas Turbine Fuels" 1996 Liu, Y. and Schmidli, J.: "Experiments with a Gas Turbine Model Combustor Firing Blast-Furnace Gas", ASME 96-GT-52