Air Preheater Enhancement – Ensted Power Station, Denmark
In 1996 Howden modified air preheaters at Ensted Power Station to accept new gas conditions imposed by the retrofit of an SCR plant. New elements, cleaning lances and sealing systems have resulted in the plant operating successfully.
Unit EV3 at Ensted power station in Denmark consists of a 660MW PF fired boiler burning a range of imported coals that vary in sulphur content from 1.4 to 2.6%. Among measures to comply with new environmental regulations, a selective catalytic reduction (SCR
) was fitted upstream of the air preheater, which therefore had to be modified to take into account the new operating conditions.
Any unused ammonia from the SCR process will produce ammonium bisulphate, which can condense on the air preheater elements at metal temperatures between 150 and 220ºC.
In addition the catalyst has the potential to increase the amount of SO3 in the flue gas, which in combination with fly ash can be a major cause of fouling at the cold end of air preheaters.
The element configuration was changed from three to two-tier. The cold end tier was enamelled to prolong element life when firing high sulphur fuels.
New sootblowers were fitted which combined steam blowing and water cleaning in a single fully retractable lance. This arrangement permitted online high-pressure water washing in addition to regular steam blowing and off-line low-pressure water washing.
The airheater seals were converted to the Howden VN system, which among other things involved upgrading the rotors by increasing the number of seals, and modifying the sector sealing plates. air heater leakage, which in turn reduces the fan flow, allows the FD & ID fans to generate more pressure which will compensate, fully or partly, for the extra draft losses associated with the SCR system.