Utilizing biomass and waste for power production—a decade of contributing to the understanding, interpretation and analysis of deposits and corrosion products

Through the years, Danish utilities have gained significant knowledge on how to minimize or even avoid ash deposition problems in utility boilers, firing a worldwide suite of high-volatile bituminous coals. In the early 1990s, the Danish Government decided on a 20% reduction in the CO₂-emission before the year 2005, based on the 1988-level. Biomass is considered CO₂-neutral due to its short time of regeneration, compared to fossil fuels. Thus, the Danish power producers are enjoined to burn 1.0 Mtonnes of straw, 0.2 Mtonnes of wood chips and 0.2 Mtonnes of straw/wood chips (free choice) every year beyond year 2005. As a consequence of this, the CHEC Research Centre, Department of Chemical Engineering, Technical University of Denmark, being partly funded by the Danish power utilities, has during the last decade, investigated ash and deposit formation, and corrosion, in utility boilers fired with coal, petcoke, orimulsion, and different types of biomass (straw (barley, rape and wheat), wood (beech, spruce, fibreboard, bark and waste wood), shea nuts, olive stones, etc.). A number of reviews of these full-scale measuring campaigns have been provided in the open literature. Recently, a project on the formation of ash and deposits in waste incinerators has been initiated.This paper summarizes our findings, including recent activities on: (1) deposit formation during coal-wheat straw co-firing in suspension-fired boilers; (2) a pilot-scale study of ash and deposit formation in the Sandia Multi-Fuel Combustor (MFC); (3) a full-scale measuring campaign dealing with the effect of co-firing of biomass on the ash and deposit formation; (4) a full-scale measuring campaign addressing low-temperature corrosion of tubes in the air pre-heater of a straw-fired utility boiler; (5) a lab-scale study of the corrosion of superheater materials in straw-fired utility boilers, and, finally; (6) a fundamental study on ash and deposit formation in municipal solid waste incinerators. The paper provides insight into the experience gained on ash, deposit and corrosion formation in thermal fuel conversion systems fired with solid non-fossil fuels, and focuses attention on how these results fit into our current understanding of this subject. A complete and updated list of references covering our research activities within this area during the last decade is provided. In addition, a brief overview of current and future research activities is provided.