In contrast with the new-power-plant business, where we have seen a strong tendency towards standardization and modularization, rehabilitation of existing plants is a much more individual task. It is generally characterized by an intensive planning phase with detailed fact finding activities at site and the design and evaluation of different variants and additional options before the actual modernization work starts.

These features are exemplified by two projects we have recently carried out in Ukraine and India. Although both the fossil-fired plants in question use Soviet technology of similar vintage, they differ markedly in size, operation mode and geographical location. Also, the different objectives of the client in each case and the boundary conditions of each project have given the two projects their own special character. For each plant it was necessary to develop tailor-made solutions.

Life extension at Neyveli

The Neyveli plant first appeared on the power map of India in 1965 as the first lignite-fired plant on the subcontinent. Six units of 50 MW and three units of 100 MW were installed with Russian assistance and completed in 1967.

In 1994 Siemens Ltd, India, established a consortium with Bharat Heavy Electricals Limited (BHEL) to undertake power plant improvement projects. This consortium, Powerplant Performance Improvement Ltd, won the tender for renovation, modernization and life extension of Neyveli units 2 to 6 (5 x 50 MW) and Unit 8 (1 x 100 MW). The work was prompted by the fact that the overall plant load factor had dropped significantly below 70 per cent because major components and sub-systems were reaching the end of their lives.

The comprehensive rehabilitation programme started in 1995. Work was carried out on the six units consecutively so that electricity generation at the plant could be kept at the highest possible level. Life extension activities on all units were completed this year.

The major scope of works was:

  • overhaul of steam turbines, including repair of defective parts, reblading of last stage, fixing of new seals;
  • modernization of generator (stator and rotor), including rewinding, new brushes, class “F” insulation;
  • replacement of defective heating surfaces and tube bundles in the boilers;
  • modernization of boiler auxiliaries, including coal mills, air preheaters, feedwater lines and slag removal systems;
  • repair of main steam lines;
  • repair or replacement of balance of plant (BOP) parts, eg, condenser evacuation pumps, feedwater pumps, piping and valves, and feedwater preheaters;
  • modernization of transformers and busducts.

    After completion of these activities the expected plant load factor of the units was raised to 90 per cent and the lifetime of the plant was extended significantly.

    Total renovation at Zmijev VIII

    The 300 MW unit VIII of Zmijev power plant in the Ukraine started operation in 1965. Owing to the necessity of replacing capacity due to closure of the Chernobyl nuclear units, this coal-fired unit was selected, among others, for complete renovation, with the focus on extending service life, improving performance and addressing several other shortcomings. The decline in overall plant performance can be gauged from the fact that unit VIII’s actual maximum load had fallen to 260 MW.

    To carry out the project a consortium of Western European power plant manufacturers, with Siemens as consortium leader, was established in 1995. In the same year work started on putting together the financing arrangements. Extensive discussions about contract structure and relations between partners took place. The project is now backed by the German government through a Hermes export credit guarantee and a credit from the German Kreditanstalt für Wiederaufbau (Reconstruction Loan Corporation).

    In April 1997 the contract for the project was finally signed and the planning process started. A comprehensive rehabilitation plan was worked out with a strong team effort by all consortium parties. Boiler manufacturers Deutsche Babcock and Steinmüller (now Babcock Borsig Power) and EVT (now part of ABB Alstom Power) are playing a major role in the project.

    Actual project execution started in January 1999.

    One main task of the programme is to convert the plant from hard coal to anthracite, which is available in large quantities in the Ukraine at an attractive price. Currently, support firing is necessary even for the local hard coal, due to the low quality of this fuel. Following the modification programme, however, it will be possible to burn anthracite in the load range between 70 and 100 per cent without any support firing – a very challenging task for this low volatile fuel, which is generally more difficult to burn than the local hard coal. The result will be significant lowering in fuel costs.

    The modification of the furnace from open slag tap to advanced slag tap firing (see diagram) will make it possible to realize stable ignition and high burnout even with pulverized anthracite.

    The parallel modernization of the steam turbine will include the overhaul and replacement of HP-, IP- and LP-components. The main upgrade work on the generator will be installation of a new stator. A new control and trip system as well as modernization and replacement work on the existing instrumentation & control will lead to a decisive improvement in availability and reliability and will help ensure operation largely conforms with UCPTE grid operation requirements (eg, control sensitivity range of ± 10 mHz).

    In addition the air preheater and fly-ash removal systems will be renovated. Following the renovation programme, the electrostatic precipitators will reach an efficiency of nearly 99.8 per cent.

    After completion of the basic engineering phase the detailed engineering for the Zmijev project was started recently. Currently, prefabrication of the new components needed and procurement of auxiliary equipment is underway.

    The end result of the Zmijev rehabilitation project will be an economic 325 MW (net) power plant unit with a further 15 to 20 years of useful service life ahead of it, able to help Ukraine overcome its shortfall in power generation. The rehabilitated plant’s independence from imported coal, its reduced fuel costs and its lower emissions will be among the additional benefits.

    Unlocking the potential

    As already mentioned, both plants described here are based on the technology of the former USSR and are more than 30 years old. But despite their long service life these units still had significant rehabilitation potential, as fact-finding missions to the sites testified. Additionally, economic evaluations demonstrated that rehabilitation for these plants is the most profitable solution for the owner when compared with the building of a new plant.

    For some major plant components, the original equipment manufacturer was no longer in existence but it proved possible to renovate these parts. In other cases components have been modified to achieve higher performance by integrating Western technology into the original equipment. These upgrade measures have been developed in close co-operation with the OEM, as, for example, in the case of the Zmijev steam turbine.

    After rehabilitation, both plants will be able to generate power economically for about two more decades.