M R Shelar Director (Operations), Mahagenco

Mahagenco is the largest amongst state utilities in the country with an installed capacity of 6800 Mw thermal, 2469 Mw hydro and 852 Mw gas power. Thermal generation contributes around 68 per cent of the total generation of Mahagenco. About 13 per cent is contributed by very old units and 50 per cent is from units between 20 to 25 years old.

Very old units

Out of these 34 units, 10 units with capacities below 210 Mw are between 33 years to 42 years-old. These units are facing more forced outages and are difficult to maintain and operate under the norms given by the MERC and commercially incurring heavy financial losses. Hence, Mahagenco has recently decided to close down these units (Total installed capacity 570 Mw) and replacements units are proposed in place of these old units. These replacement units will be commissioned during 2013-14 – Koradi-1 to 4, Bhusawal 1, Parli 1&2 – all of these will be replaced with 660 Mw.

Paras & Nasik 1&2 are also being proposed for replacement.

 Other Old units:

Out of the remaining 24 units, 14 are more than 25 years-old and require major renovation and modernization (R&M) as their boiler components, equipments, breakers and cables have exhausted their life and have not been replaced earlier because of inadequate provision of funds.

Mahagenco has decided to take up a major R&M programme for the following units in phase I in the 11th plan period. Koradi unit no 6- 210 Mw will be replaced with World Bank funding while Nasik unit 3- 210 Mw will be replaced with the help of KFW, both to be completed by end 2013.  Similarly, the following units are also proposed for major R&M in phase II with the help of the World Bank in the 12th plan.

1) Bhusawal unit 2  – 210 MW with World Bank funding

2) Parli unit 3  -  210 MW with World Bank funding

3) Chandrapur unit 1&2  -  210 MW each with World Bank funding

Forced outages on account of boiler tube leakages (BTL) are a major concern for Mahagenco. This is because of the high erosion rate of boiler tubes as ash percentage in coal is relatively very high i.e., 40 per cent. To tackle this problem a committee was formed with a member from BHEL to suggest suitable preventive and remedial action. The committee recommended that boiler components such as economizer, LTHS, super heaters and reheater coils need more frequent replacement.

Mahagenco is implementing a five-year rolling plan to replace these boiler components in a phase-wise manner during annual overhaul of the units. This has helped reduce the boiler tube leakages to below three per cent.  Efforts are being done to reduce this to 1% within the next three years. Recently MahaGenco has encountered BTL soon after overhauling of units due to defective welding of factory welded joints. The matter has been taken up with BHEL. 

Environment issues: Ash emission

Presently the environmental norms have become more stringent. As most of the Mahagenco units are old, their ESP are designed for higher SPM. To meet the present SPM norms of 150mg/Nm3 Mahagenco has taken various steps such as replacing microprocessor based controls, retrofitting of ESP internals of ESP fields and maintenance of ESP fields during overhauls and plans to replace the ESP during major R&M of the units to comply with  new environment norms in 11th and 12th plan.

MahaGenco has also experimented with ESP fitted with bag filters for its Koradi units-5 and 6, but the experience is not encouraging.

Recently Mahagenco has taken up the installation of AFGC system for reducing emission to below 150 mg/nm3 at the following plants.

ESP’s of new units are designed with 70 mg/Nm3 Paras (2 X 250 Mw) and Parli (2 X 250 Mw), Khaperkheda (1 X 500 Mw) and all future projects.

Mahagenco has also decided to put dry fly ash evacuation systems for its new plants i.e., Khaperkheda, Paras and Parli, along with Geho pump for evacuating ash in dense phase. Mahagenco has also been making efforts to maximize fly ash utilization. Present fly ash utilization is around 50 per cent and increased from 2006-07.

Besides short term, long term agreements on BOT basis with cement manufacturers to install dry ash evacuation system and to lift the ash through silos for their use are under finalisation.

Quality of coal

MahaGenco’s coal requirement for its thermal plants is 40 mmtpa. Major coal companies supplying coal to Mahagenco under fuel supply agreements are listed below (with the percentage shares):

Western Coalfields – 61 per cent

Mahanadi Coalfields – 16 per cent

South east coalfields – 16 per cent

Singareni Coal Companies – 6 per cent

Generally E&F grade coal is received by Mahagenco Power Stations and there is a demand/supply gap due to inadequate production of coal. To bridge the gap Mahagenco has to import coal.

For 2010-11 Mahagenco is procuring about 3.35 mmt of coal to bridge the gap as per the directives of ministry of power.

The production from cost-plus mines (Bhatadi, Junad, etc) has started.

This import coal is used in the plant by blending it with indigenous coal so that the average quality shall improve along with loadability of the units.

Mahagenco receives coal with about 40 per cent ash which causes heavy erosion resulting in frequent boiler tube leakages. To overcome this problem Mahagenco has decided to maximize use of washed coal and accordingly placed orders for washed coal of about 10 mmtpa from WCL area, 2 mmtpa from SECL, 3 mmtpa from MCL in order to reduce the ash.  

Mahagenco also faces unloading problems of wagons because of receipt of heavy lumps and shales along with coal when crushers at loading end are under maintenance.

Constraints during the rainy season

Wet coal

Mahagenco receives about 60 per cent coal from WCL. This coal contains excessive mud and gets sticky during the monsoons. Such wet and sticky coal decreases the unloading rate due to choking of various coal chutes in the unloading stream. The issue of wet and sticky coal has been taken up with WCL from time to time. However, WCL has expressed its inability to avoid the supply of wet and sticky coal during the rainy season.

Plant design

Most of the existing CHPs are of old design based on the then coal GCV and have small-sized coal chutes and larger number of transfer points with Y chutes, thereby increasing the potential at various points until the wet coal reaches the coal mill. Considering the above aspect, the CHP at Khaperkheda thermal plant was designed later with minimum transfer points and Y chutes with adequate overload capacity and redundancy in the system.  Coal Handling Plants of Units 6 and 7 of Parli, units 3 and 4 of Paras have single unloading streams and as such without any redundancy and gets stuck-up if any problem occurs in the existing stream.

Problems at the loading end

At most of the sidings loading in rakes is done by pay loaders and therefore mud getting loaded along with coal at the bottom cannot be prevented. On many occasions crushers at the loading end are under maintenance and in such cases the coal company crushes the coal with dozers which generates a lot of fine dust particles, aggravating the choking problems in the plant. These matters are being taken up regularly with coal companies but very little improvement is seen.

Efforts to find solutions

Despite all the above problems Mahagenco is taking all possible measures to improve unloading. To clear the choke-up in the system, additional manpower is deployed at transfer points, chutes and crusher house round the clock. Manual unloading is also carried out by deploying extra manpower and machines like pay loaders. Moreover 48 engineers from MahaGenco are now deputed at various loading points/sidings for monitoring the coal quality before and during loading. We hope all these steps will lead to improvement in the quality of coal loaded on the rakes and the speed of unloading.

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