TNEB –Tuticorin Thermal Power station is located in South India. It consists of 05 nos. of 210 MW Coal fired boilers. This case study is on Unit #5. The air preheaters are of size: 2 x 27 VIMT 2000, which was commissioned in 1992.

During these years the condition of the sealing system and the condition of the baskets has deteriorated; thereby increasing the fuel consumption and the fan loading.


GEECO was awarded a contract for the spares supply and service supervision.

GEECO has Supplied the following items:-

  • Full set Hot End, Hot Intermediate and Cold End Baskets for one Air Preheater with ‘Basket Bypass Seal’ 

  • Rotor Seals

  • Static Seals

If the gap between the basket and the diaphragm plates/ Shell plates are more and are not closed, will result in bypassing of the gas; thereby not contributing to the heat transfer process. Closing this gap will result in more heat recovery, which will increase the boiler efficiency. GEECO supplied a specially designed ‘Basket Bypass Seal’ to arrest this gap. The dimension of the basket was done such that it will closely fit into the compartments. The GEECO’s special design of baskets will not allow the slip-out of the element sheets; thus avoiding interference during installation.

Further to the supply, GEECO was awarded with the contract for the Service supervision. Investigation by GEECO engineers could pin point the problematic areas and rectify during overhauling. The installation, the repair work and Seal setting was done under GEECO engineer’s supervision.

The operation of the performance since the overhauling is very good and there is significant reduction in fan loading, fuel consumption and increase in unit generation, as indicated below.

Parameters Before O / H After O / H
Generation 214 MW 214 MW
Fuel Consumption 154 T/Hr 134 T/Hr
Total Fan Loading 691 Amps 569 Amps

With increasing power demand and with the deterioratian of the existing plants, ways and means are to be found out to improve the performance and availability of the existing plants. Normally the rotary air preheater typically accounts for approximately 10% to 12% ot a units overall thermal efficiency.

The reported problem with rotary air preheaters is mostly on the deterioratian of thermal performance and the higher air leakage. Mere availability of the air preheater in service mislead that the air preheater is performing good. By retrofitting the state of art through Renovatian and Modernization (R&M), the performance of the air preheater can either be brought to the original condition or with an improvement. Upgrading or enhancing an air preheater is usally one of the most cast effective ways of improving boiler performance.

Renusagar Power Plant in india is having 8 boilers. Out of which 5 boilers are having rotary air preheaters and the balance 3 boilers are having tubular air preheaters. In these boilers , the air preheater high gas inlet temperature resulted in high gas outlet temperature and also the air preheater leakage was on the high side. If the Customer desired to recover this excess heat from the fine gas and also to bring down the leakage.

GEECO engineers did the assessment of the air preheaters, identified the problems and submitted the report with recommendations. Convinced by the recommendations, to start with. the Customer placed an order an GEECO air preheater R&M of Spare boiler.

Based on the long experience in air preheaters, GEECO did the following major changes in the air preheater by incorporating the advanced technology.

  • The height at heating elements was increased to increase the heat recovery. To accommodate this increase in element height, new rotor was supplied. Accordingly housing height was also increased.

  • Supplied all new elements

  • Used more efficient profiles

  • Provided a small depth sacrificing basket at the hot end to reduce the replacement cost in future

  • Double sealing technology to reduce the leakage

  • Upgraded the sealing system to reduce the leakage

  • Machined ‘T’ bars

  • Diaphragm Protection seal

This air preheater R&M job on Spare boiler resulted in the boiler efficiency improvement at 1.5% and the air preheater leakage is reduced from 19.83% to 9.29%. The payback calculated is as low as 9 months.

Retaining the benefits derived by this R&M job, the Customer placed repetitive orders on GEECO for the balance 4 boilers to carry out the same modifications.

After the execution of R&M in all the air preheaters, the customer worked out the efficiency improvement and the leakage reduction. The results are tabulated below :


GEECO assures the air preheater users that it is possible to improve the efficiency and reduce the leakage in most of the air preheaters by implementing the R&M. 

Bharat Aluminium Company Limited at Korba, CPP-II, in Chattisgarh State, India is having 4 x 135 MW boilers. Two numbers of 24 VISMT 1833 size air preheaters were installed in each boiler. Within few years of operation, the boiler struggled to generate its full capacity, due to the deficiency in thermal performance and more leakage in rotary air preheaters. Due to high pressure drop in Primary air side, an additional PA fan was installed.

GEECO was asked to study the problem. On assessing the condition of air preheaters, it was pointed out that the existing air preheater size is insufficient to give the predicted performance.

GEECO recommended that the existing air preheaters can be completely replaced with 2 numbers of 25.5 VIMT 1900(2100) size.

Also it was found that the existing air preheaters space is not sufficient to accommodate this bigger size air preheaters. Hence, it was decided to erect the new air preheater in the 3rd pass (between Economiser and ESP).

Technically convinced, Customer placed the order for 'Engineering, Manufacturing, Supply and Commissioning of air preheaters', along with the supporting structures, ducts, expansion bellows and dampers. Enormous effort was taken to engineer the structures and ducts to accommodate in the existing limited space. CFD analysis was done to optimize the duct layout. To reduce the boiler downtime, it was planned to erect the air preheaters in the separate bay, while the boiler is running. After the completion of the erection, the boiler was taken for a short shut down and the new air preheaters were connected.


Based on GEECO's long experience, the air preheater was designed by incorporating the latest technology. The special features of newly supplied air preheaters are:

  • Modular design — to reduce erection time.

  • Double sealing — to reduce leakage.

  • Machined T bars — to reduce leakage.

  • Side covered Baskets — to improve the thermal performance.

  • Soft Touch Seal — to reduce the leakage.

  • Peripheral drive with overrunning clutch on electric motor side.

  • Increasing PA angle opening to 72 deg.

The air preheater was totally manufactured at GEECO plant and supplied in various stages to Balco during 2011. Unit #2 was selected for carrying out this replacement. Unit # 2 was commissioned in August 2005. Prior to shut down, the structures, the ducts, expansion bellows and air preheater erection was done in 37 days, after the shut down, the erection activities were done for 25 days. After commissioning the NewAir Preheaters, unit #2 boiler was lighted up in January 2012.


  • Additional PA fan withdrawn

  • MW generation increased

  • Fan loading reduced

  • Now possible to fire with low Calorific value fuel

  • For one APH -12 modules with baskets are erected in record time of 8 hrs.

  • For the entire execution of this replacement, the boiler was shutdown 25 days only.

In most of the underperforming air preheaters like this, it is possible to improve the efficiency and reduce the leakage by replacing the air preheaters either with the equal size or with increased size.

Hindalco industries is the leading manufacturer of Aluminium in India. For their power need at their Renukoot process plant, they have 11 Boilers at Renusagar as Captive power plant. All the rotary Air Preheater: (Size 24.5 VIT 57.5) available in their boilers Were modified by GEECO to reduce the leakage and to improve the thermal performance. The results Were tabulated below.

Realizing the benefits, Hindalco industries discussed to modify their rotary Air Preheater available at their process plant at Renukoot.The size of the Air Preheater available was 23.5VIR1600. GEECO was asked to assess the Air Preheater and suggest the improvements. Based on the assessment and further analysis of their operating conditions, it was recommended by GEECO to increase the size of the Air Preheater from 23.5 VIR 1600 to 24 VIR 1750 by incorporating all the improvements.

To reduce the cost of the R & M, it was recommended to utilize the existing Support Bearing Assembly, Guide Bearing Assembly, Rotor drive Assembly and Soot blower Assembly. The bearings and drive adequacy was checked by GEECO and confirmed. Convinced by the recommendations, Hindalco industries placed an order to GEECO to increase the size of Air Preheater.

Existing supporting columns were not disturbed.

The Air Preheater was designed such as to place the new Air Preheater within the limited accessibility available. The total dismantling & Installation of total Air Preheater was completed within the record time of 23 days.

After the R & M, the performance test was conducted by the Customer to verify the improvement due to R & M. After the test it was calculated by the customer that the bolier efficiency has increased by 1.65% and the leakage has reduced from 11.5% to 6.5%. Based on this improvement the payback was calculated as 12 months.

Tuticorin Thermal Power Station is located in South India operated by Government of Tamilnadu. At this plant, 5 boilers of each 210MW is installed. All boilers are provided with Rotary Air Preheaters.As a part of improving the efficiency of the boiler and reducing the leakage, R&M contract for supply and erection was awarded to GEECO for unit No 3 & 4 separately.

The size of Air Preheater was 27 VIT 72 for unit #3 and 27 VIMT 2000 for unit #4 of 2 Nos. In both boilers, the Air Preheater Leakage was around 15%.

The guarantee for this R&M contract was fixed to reduce the leakage below 6%. Apart from this target, effort was made to increase the boiler efficiency by reducing the fuel consumption.

Some Special Features of this contract:-

  • Increasing the height of Air Preheater from 72 inches to 80 inches for unit #3.

  • Double sealing

  • Modular rotor assembly

  • Supply of machined T-Bars

  • Introduction of sacrificing Baskets

  • Soft touch Radial seals and Axial Seals

GEECO Supplied two Air Preheater of size 27 VIMT 80. The total supply was made with the shortest delivery period.

The situation demanded for shorter erection time. The dismantling of old Air Preheater and the erection of New Air Preheater was completed in a record time.

The performance test was conducted by GEECO in presence of the customer to find out the leakage and the result achieved is given below, which is below the guaranteed value of 6%.

There is a siginificant reduction in fan loading and fuel consumption.

The payback is as low as 6 months.

GEECO confirms to all Rotary Air Preheater users , that it is possible to improve the efficiency and reduce the leakage in most of the Air Preheaters by carrying out such type of R&M.

Leakage Percentage
  Before R & M After R & M
Unit #3 15% 5.65%
Unit #4 12.5% 5.41%