On the massive chemical process plant site of Bayer AG in Dormagen, near Dusseldorf, Siemens KWU is preparing to build a gas turbine combined cycle combined heat and power (chp) power plant under contract to RWE Energie AG. Scheduled to go on line during the middle of the year 2000, the new power plant will replace the older M1 lignite-fired power plant, and will generate 580 MWe and up to 490 t/h of process steam (see Table 1).

The new plant will be owned by RWE Energie, which has contracted to supply process heat steam and electricity to the Bayer plant. The plant will generally operate on base load, full output duty, supplying up to 260 MWe to the Bayer plant, and the rest as a very economic power supply to the RWE Energie network. However, the priority product will be the process heat steam. Construction is due to start on-site before the end of October 1998 on receipt of licence permits.

This will be one of the first applications of the recently introduced medium-capacity Siemens V94.2A gas turbines, coupled with a three-cylinder steam turbine. The new V94.2A incorporates similar annular combustors and many other features of the more advanced 260 MWe V94.3A gas turbines, gaining an increase in power output of over 30 MWe over the 160 MWe delivered by the well-proven V94.2 machines. At maximum process heat output, the system will deliver a fuel utilisation factor of 85 per cent. Siemens KWU will also supply the local instrumentation and control systems for the generating plant, and it has also signed a long term maintenance agreement with RWE.

Also for operation during the middle of the year 2000, a new gas turbine combined cycle plus district plant is being supplied by Siemens KWU for Kraftwerke Mainz-Wiesbaden AG (KMW). It will produce some 380 MWe of electricity and 100 MW of district heating, replacing three older 100 MWe coal-fired units. This will be based on a V94.3A gas turbine unit, and again Siemens KWU has concluded the all-important long term maintenance agreement with the plant operator.

These two projects provide evidence that new gas-fired power plants are increasingly penetrating the German electricity supply industry in advance of plans for liberalisation under the new German Energy Law.

The new plant

RWE’s new combined cycle power plant, the GUD Heizkraftwerk Bayer Dormagen, will consist of two plant sections:

  • The gas-fired boiler K10 and existing Frame 5 gas turbine from the present A 787 power plant

  • The newly installed combined cycle chp plant The Frame 5 gas turbine, which will generate some 20 MWe, will be used in combined cycle mode with the K 10 boiler to generate 30 to 40 t/h unfired. In the event of an unplanned outage of the new plant, the gas fired burners can be ignited to yield some 300 t/h of process steam.

    The new plant site is situated on open ground in the north-west of the Bayer chemical plant complex, some 150 m to the south of the existing A 787 power plant, and some 500 m from the western zone of the process plant.

    The equipment will consist of:

  • A supply station for gaseous fuels, and alternative liquid fuels

  • Two V94.2A gas turbines

  • Two unfired exhaust heat recovery steam generators with single stacks – no bypass systems

  • A three casing condensing steam turbine with process heat extraction points

  • Condenser

  • Cell-type wet cooling towers

  • Water steam circuit

  • Redundant steam supply independent of steam turbine operation The water–steam circuit is a three pressure level plus reheat system.

    The present power plant, A 787, will continue to operate in parallel to the new combined cycle plant with the boiler K 10 as an exhaust heat recovery steam generator for the Frame 5 gas turbine.

    In this way, the boiler is maintained in a hot standby state so that in the event of an outage of the combined cycle plan, it can immediately take over as a reserve steam capacity to maintain secure steam availability. In this situation, the burners in boiler K 10 will be ignited.

    The existing power plant can, if required, also be operated at full power in parallel to the combined cycle plant to produce some 580 MWe and up to 490 t/h of process heat steam. The Frame 5 gas turbine will be fed with smoke-laden air extracted from the building air conditioning vents.

    V94.2A gas turbines

    It is immediately obvious from the longitudinal cross section of the V94.2A gas turbine that it looks more like the V94.3A than it looks like the older V94.2 design. The V94.2 design now has over two million operating hours of operating experience behind it.

    The huge off-board silo-type burners have been replaced with annular premix combustion using 24 hybrid burners. In these, the uniformity of the flame temperature results in greatly reduced thermal NOx formation. The compact symmetrical geometry of the annular combustion chamber has been shown to yield major advantages:

  • High uniformity of hot gas flow and temperature fields upstream of the power turbine

  • Reduced combustor chamber surface area, requiring less cooling air and making more compressor discharge air available for low NOx combustion

  • Extremely short hot gas residence time to suppress thermal NOx formation Fewer hot gas path components contribute to increased reliability. Nonetheless, it is still possible for personnel to enter the annular combustion space via two manholes, which greatly reduces inspection outage periods.

    Further improvements and upgrades include:

  • A 16 stage compressor adapted from the “3 series” engines

  • A new four-stage power turbine derived from the Model V94.3A with free standing moving blades only

  • No external cooling of compressor discharge air for blade cooling purposes

  • Cold end drive

  • Axial exhaust gas diffuser with easy access to the turbine rear bearing and last stage blading.

    The power turbine is a four-stage reaction turbine derived from that of the V94.3A but with an adjusted flow rate. It uses the same blading – the first and second row moving blades are of single crystal and directionally solidified type respectively. All four rows of moving blades are free-standing to prevent the gas flow from being disturbed by damping elements. Table 2 compares the two versions. Neither water injection nor selective catalytic reduction are needed while running on natural gas fuel, but standby distillate oil fuel water injection is used.

    Exhaust heat recovery boiler The exhaust heat recovery boiler, for which the successful bidder had not yet been selected at the time of writing, will operate at three pressure levels with reheat producing steam at:
    HP – 110 bar – 550°C
    IP – 31 bar – 300°C
    LP – 6 bar – 200°C
    supplying up to 490 t/h of process steam at three pressure levels:
    HP – 31 bar – 300°C
    IP – 16 bar – 250°C
    LP – 6 bar – 180°C
    Apart from feeding the same steam mains, there is no formal integration of the new steam generation with the existing K 10 steam generator, which was installed in 1972.

    There will be one control room for both the new Siemens combined cycle power plant and the existing K 10 system, which was purchased by RWE Energie from Bayer. There is no automatic dynamic integration between either power plant and the chemical process plant.

    Environmental impact

    Exhaust gases are emitted through a 90 m high chimney. TA – Luft emissions limits as listed in Table 3 will be met well within the design performance of the plant without water injection or SCR.

    Noise emissions reduction provisions have been designed to limit noise levels to critical residential areas close to the site to at least 10 dB(A) less than the legal limit of 35 dB(A).

    The water requirements of the new plant and the waste water handling facilities are dealt with within the existing regulatory allowances of Bayer AG.

    Table 1. Main technical parameters of the Bayer Dormagen combined cycle chp plant
    Table 2. Comparison of V94.2 gas turbine details
    Table 3. Mass concentrations of emissions in exhaust gas after clean-up