Air Preheater Enhancement – Longannet Power Station, UK

Howden modifications to the air heater at the 2400MW Longannet Power Station reduced both fouling and leakage and increased plant availability.

Howden supplied the air preheaters when the station was built around 1970. Over the years the sealing system had deteriorated and was permitting an excessive amount of air to leak to the flue gas stream. In addition, combustion conditions were causing deposits to form in the furnace, which were being transported to the air preheater and lodging in the gaps between the elements.

Howden received a contract to modify the heaters with the aim of reducing both fouling and leakage and of increasing plant availability. The elements were replaced with a CU profile (which had previously been pilot tested) in which the element corrugations spaced the plates further apart than those of the existing elements. Modifications to the rotor allowed the installation of a greater depth of elements than had originally been fitted.

Second, the sootblowers were replaced with fully retractable units, which provided three cleaning options, steam blowing, plus high pressure and low pressure water washing.

Third, the sealing was upgraded to the Howden VN system.

As a result of the work carried out, air leakage has dropped from around 15 to 6%. The element change has increased the boiler efficiency by 0.7%.

Draft fan power has reduced by 80kW. Fouling in the elements has been reduced and water washing has not been necessary (previously it was carried out, off line, approximately twice per year).

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