Looking for India's lost generation

23 April 1999

At the Talcher coal fired station a major boiler renovation and modernization project is underway, which aims to restore output to design levels and extend life by 25 years. The project, which includes replacement of existing coal mills with 8.5E9 mill technology, demonstrates upgrades that could be widely applied to India's underperforming older coal stations – with huge potential benefits to the power sector and the national economy.

About 25 GWe of Indian installed capacity, some 30 per cent of the total, consists of ageing coal plants, more than 20 years old. The average load factor of these units in recent times has been running at less than 40 per cent, compared with a world average for coal plants of over 80 per cent. This shortfall in performance is costing the Indian economy tens of billions of dollars, perhaps as much as 3 per cent of GDP.

In the Indian context therefore, renovation and modernization (R&M) represents a major opportunity. Raising the load factors of these older plants to over 75 per cent would be the equivalent of adding ten or more large stations to the grid. But compared with the costs of new plant, R&M is clearly much less expensive – perhaps 15-25 per cent of the cost of new capacity – and the lead times much shorter. R&M also avoids the lengthy and uncertain approval process required for new build, with the potential for U-turns following changes of government and policy.

Declining fuel quality

So what can be done to recover the lost generation at Indian plants? A primary cause of low load factors is a decline in coal quality (due mainly to the switch to open cast mining), with plants having to work with coal of much greater abrasiveness and higher ash content than was envisaged when they were designed. This causes problems for coal milling and handling equipment and results in a rising incidence of tube failures.

The Talcher plant, owned and operated by state-owned utility NTPC (National Thermal Power Corporation) is a good example of an under-performing Indian coal station that has experienced these fuel quality problems. The ambitious refurbishment project now underway at Talcher unit 4 points the way to what might be achieved in India with a concerted effort on R&M. As the utility's first large R&M project of this sort it is significant both for NTPC and for the main contractor, Mitsui Babcock Energy (India) Pvt. Ltd (MBEIPL) and its parent company Mitsui Babcock Energy Ltd (MBEL). MBEL, whose links with India go back over 90 years, sees the country as a key element in its international business strategy.

Comprehensive programme

The first stage of Talcher, consisting of four 62.5 MWe PF-fired units (subsequently derated to 60 MWe due to ageing), was commissioned in the period 1967-69. The boilers for these units, supplied by B&W of the USA, are of the bi-drum type with natural circulation, gas tight enclosure and balanced draft furnace. The turbines were supplied by GE of the USA. Subsequently a second stage, comprising two 110 MWe PF-fired units, was added. For the second stage, commissioned in 1982-83, the boilers and turbines were supplied indigenously by BHEL of India.

The Talcher plant is located in the Angul district of Orissa State, feeding the eastern grid. Originally owned and operated by Orissa State Electricity Board, it was transferred to NTPC in June 1995. Prior to the transfer a number of refurbishment proposals had been put forward to address the problems being faced by the plant due to the declining quality of the fuel being supplied to it from the nearby coal fields. But for a variety of reasons nothing materialised. Problems were compounded by ageing and malfunctioning/non-functioning of various auxiliary systems and pieces of equipment.

NTPC, one of the Indian government's nine "Navratnas" (profit-making government owned companies), is a major utility in world terms, with an installed capacity of no less than 18000 MWe. It immediately put in hand a programme for comprehensive renovation of Talcher, starting with unit 4. Tenders for the boiler work were issued in August 1997 and bids were received by NTPC in October 1997 – a very tight schedule, which had the added challenge of clashing with the local festival season. The contract was awarded to MBEIPL in September 1998.

Poor performance

From the plant log books it was clear that Talcher stage 1 had never reached its rated capacity, running at an average load factor of 25-35 per cent from 1968 to 1994, rising to around 50 per cent in recent years following the transfer to NTPC. The performance of unit 4 was particularly abysmal. An assessment of plant condition showed the following:

  • Substantial deterioration in coal quality. The original plant design envisaged coal with a GCV of 4420 kcal/kg and an ash content of 34 per cent. The GCV of the currently available coal is in the range 3000-3700 kcal/kg with an ash content of 39-43.3 per cent. Therefore the original coal milling plant (of the EL ball and race type) was not able to supply the necessary quantity of coal and was in need of re-sizing and re-engineering.
  • Erosion of boiler bank tubes due to high velocity of flue gas.
  • High back end temperature leading to lower overall boiler efficiency. Flue gas temperature at the exit of the air heater is as high as 165-185°C, against a design value 145-150°C.
  • Soot-blowers not working.
  • Burners eroded.
  • No flame scanners or burner management/furnace safeguard supervisory system. Adequate feedback on fire outs not available in control room, safe operation of boiler not assured, leading to delays in start ups.

    The scope of work

    The scope of the turnkey boiler renovation project awarded to MBEIPL includes complete redesign, replacement/repair, civil works, erection and commissioning. All of this must be completed within 18 months of the issuing of the letter of intent, which was 17 September 1998.

    Major tasks include:

  • Complete redesign and replacement of coal milling plant, PF piping, and burners.
  • Complete redesign and replacement of superheaters, attemperator, interconnecting pipes, boiler bank and economizer tubes.
  • Repair/replacement of furnace in accordance with findings of remnant life assessment.
  • Repair/replacement of rotary airheater components.
  • Complete overhaul of all other components within scope.
  • Installation of new light diesel oil firing system.

    In quantities this amounts to around 1400 t of material to be supplied and installed, dismantling of 800 t of equipment, 40 000 engineering man-hours and 60 000 project man-hours. The end result will be restoration of the boiler to its original rated capacity and assurance of these levels over a sustained period. Guaranteed will be the steam parameters at the superheater outlet: flow of 272 t/h; pressure of 95 kg/cm2; and temperature of 513°C. A boiler efficiency of at least 86.7 per cent will also be guaranteed, as will a back end temperature of less than 125°C.

    Other objectives will be an annual boiler availability of at least 90 per cent and a plant life of at least 25 years from the completion of the R&M project.

    Mill joint venture

    The new coal mill technology to be supplied to Talcher will be of the 8.5 E9 (nine ball) type, with Hi Chrome balls and rings. The order for rings and balls was placed by MBEIPL with Indian steel producer Mukand, with whom MBEIPL has now established a joint venture. All manufacturing for the three new mills will be done in India.

    The Mukand Babcock joint venture was set up in recognition of the need for Indian power plants to upgrade their coal mill technology while at the same time reducing costs by maximising indigenous manufacture. Sourcing ball mills from India is estimated to save 40-50 per cent relative to overseas suppliers. Although, strictly speaking, the joint venture was not completely finalized at the time of the Talcher order, Mukand is working under MBEIPL guidance and the project will demonstrate how the joint venture should work in practice.

    Among the advantages of the 8.5E9 ball mill relative to the old technology used at Talcher are lower power consumption and maintenance costs, high fineness maintained over mill life and a wide range of load ranges, minimum wear rates, and reduced noise and vibration. The 8.5E9 technology is also familiar to NTPC and is widely in use at its newer stations.

    Through the joint venture technology transfer is underway with the prospect of India becoming a key player in the manufacture of state of the art ball mills within the next few years.

    Mitsui Babcock’s passage to India


    Table 1 - Talcher boiler - original design parameters
    The Indian connection

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