Air Preheater Enhancement – Ince Power Station, UK
As part of the conversion to Orimulsion firing on unit 5 of Ince B Power Station, Howden air heater enhancements contributed to an extra 25 MW output
Ince B consists of two 500MW oil fired units. In 1993 Unit 5 was converted to fire Orimulsion whose composition, in particular the high water content, would lead to an increase in the mass flow and temperature of flue gas leaving the boiler. It was estimated that after conversion, the nominal electrical output from the unit would not be achieved and it would only generate around 450MW.
Two contributory causes were the greater amount of energy being discharged from the stack, and the higher volume flow of gas to the induced draught fan. Following an inspection by Howden, it was determined that it would be possible to:
- increase the heat recovery in the air preheater by increasing the depth of elements and by using more efficient element profile
- to reduce the leakage by upgrading the sealing system.
The 2.78DU hot end elements were replaced with the higher efficiency FNC design resulting in a reduction in gas exit temperature from 168 to 153°C (which equates to an increase in boiler efficiency of 0.65%).
The Howden VN sealing
system was installed in the air preheaters, which reduced leakage to 6.5% from the 12% that had prevailed previously. The lower temperature combined with the reduced air leakage allowed the induced draught fans to handle a greater mass flow of flue gas, which gave the station the ability to fire more fuel. The modifications carried out by the station, which included those on the air preheater, permitted the unit to generate 475MW, 25MW more than originally calculated. After two years operation when the air heater performance was checked, it was found that the air leakage had remained constant. Four years operation showed that the element configuration was suitable for this fuel and that a combination of air-blowing and periodic washing could clean adequately.