High-temperature corrosion in a multifuel circulating fluidized bed (CFB) boiler co-firing refuse derived fuel (RDF) and hard coal

In this work samples of corrosion products collected from waterwalls made of P235GH and 16Mo3 steel are investigated. The samples originated from a full-scale circulating fluidized bed (CFB) boiler co-firing refuse derived fuel (RDF) with hard coal. The samples were analyzed using SEM-EDS technique to determine the composition and distribution of corrosion products. Two types of corrosion spots were distinguished: these rich in chlorine and potassium (up to 46.6% and 26.3%, respectively) and these rich in chlorine and sodium (up to 47.7% and 34.8%, respectively). Moreover, laboratory corrosion tests were performed to determine the corrosion characteristics at 510 and 410 °C and to investigate the influence of fuel additives on corrosion rates. High contents of chlorine (5.07%) and sodium (5.58% of Na₂O) in RDF ash together with high potassium content (4.34% K₂O) in coal ash resulted in high corrosion rate. To mitigate this unwanted effect, additives such as halloysite, kaolin and sulfur were tested and halloysite was proven to be the most effective. The oxide scales formed on the steel within deposits varied in terms of thickness, structure and porosity. It was found that the porosity and adhesion of the oxide layer play a key role in the corrosion process.