The challenge

Sangüesa is a biomass power plant, fuelled by burning straw. This tends to leave a high proportion of unburned residue and ash that settles and mixes at the bottom of the boiler, and some of this mixture is inevitably drawn into the air preheater. This leads to clogging of the air channels through the heater elements, and as a result the plant was experiencing reduced availability. The problem was becoming steadily worse, and we were invited to find a way of remedying the situation.

The solution

We found that the air preheater was fitted with DU heating elements profile in both the hot and cold layers. The DU design offers excellent thermal exchange but can be prone to clogging if used with high-residue fuels.

We carried out a full investigation of the conditions and demands at the plant, including an assessment of the combustion processes, and undertook a modelling exercise using our specially created simulation software. This uses the extensive data we have collected during wind tunnel testing of different element profiles, and combines it with specific information about the operating conditions, including the fuels used and the temperatures, pressures and air flow involved. The software allows us to predict, with great accuracy, the behaviour of the equipment under actual operating conditions.

The results demonstrated that by replacing all of the DU profile elements with our HC Element design the cleanability of the heater was greatly enhanced and fouling reduced. With the new profile configuration the targeted increase in gas outlet temperature and improved pressure drop was reached. Most importantly, it had a marked effect on availability, allowing the plant to stay operating for much longer periods and delivering the outcomes that the operators sought.