High temperature corrosion in biomass incineration plants. Final report

The aim of the present project is to study the role of ash deposits in high temperature corrosion of superheater materials in biomass and refuse-fired combined heat and power plants. The project has included the two main activities: A chemical characterisation of ash deposits collected from a major number of biomass and refuse-fired combined heat and power plant boilers; Laboratory exposures and metallurgical examinations of material specimens with ash deposits in well-defined gas environments with HCl and SO_2 in a furnace.

In the first part of the project ash deposits were collected from the radiation chamber, superheater and economizer sections in both waste incineration and straw-fired/wood chip fired power plants. Thirteen plants participated in the investigations giving a total of 52 ash deposit samples. These were analysed using SEM-EDX.

For refuse incineration, predominant elements are sodium, potassium, sulphur, chlorine, magnesium and calcium and in some cases zinc and lead. For straw or wood chip fired power plants, predominant elements are chlorine, sulphur, otassium and magnesium. The laboratory experiments were conducted using the electrically heated furnace rig for gaseous exposures.

Two types of high temperature resistant steels, Sandvik 8LR30 (18Cr 10Ni Ti) and Sanicro 28 (27Cr 31Ni 4Mo) were investigated at 600 deg. C and 800 deg. C flue gas temperature and at a 600 deg. C metal temperature for up to 300 hours. Specimens which were embedded in ash deposits from a straw fired power plant were exposed to HCl (200 ppm) and SO_2 (300 ppm). (EG).