Hanne Philbert Michelsen

Bio: Hanne Philbert Michelsen is an academic researcher from Technical University of Denmark. The author has contributed to research in topics: Boiler (power generation) & Corrosion. The author has an hindex of 3, co-authored 3 publications receiving 231 citations.

Deposition and High Temperature Corrosion in a 10 MW Straw Fired Boiler

Abstract: Abstract Deposition and corrosion measurements were conducted at a 10 MW wheat straw fired stoker boiler used for combined power and heat production. The plant experiences major problems with deposits on the heat transfer surfaces, and test probes have shown enhanced corrosion due to selective corrosion for metal temperatures above 520°C. Deposition measurements carried out at a position equal to the secondary superheater showed deposits rich in potassium and chlorine and to a lesser extent in silicon, calcium, and sulfur. Potassium and chlorine make up 40–80 wt.% of the deposits. Mechanisms of deposit formation and selective corrosion are discussed based on the results of the practical measurements.

Ash Chemistry Aspects of Straw and Coal-Straw Co-Firing in Utility Boilers

Abstract: Deposits formed in straw-fired grate-boilers showed significant amounts of KCl (40--80% (w/w)) and KCl-coated Ca-Si-rich particles. CFB co-firing of straw and coal caused deposits in the convective pass containing predominantly K{sub 2}SO{sub 4} (50--60% (w/w)) with small amounts of KCl close to the metal surface. In pulverized coal-straw co-fired boilers, deposits almost free of KCl were found. Most of the potassium in these deposits is derived from K-Al-Si-rich fly ash particles and the rest occurs as K{sub 2}SO{sub 4}. The presence of K-Al-Si-rich fly ash particles indicates that solid residue quality and reuse of fly ash in cement and concrete production rather than deposit formation may be of concern when utilizing straw in pulverized fuel boilers. This paper provides a review of Danish experiences with high-temperature ash deposit formation in the following full-scale utility boilers: Slagelse CHP (31 MWth), Haslev CHP (23 MWth) and Rudkoebing CHP (10.7 MWth), all straw-fired grate-boilers; Grenaa CHP (80 MWth), a coal-straw co-fired Circulating Fluidized Bed (CFB) boiler; and the Midtkraft-Studstrup Power Station, Unit 1 (380 MWth), a coal-straw co-fired PF-boiler.

Physical characterisation and chemical composition of densified biomass fuels with regard to their combustion behaviour

Abstract: With respect to the use of densified biomass fuels in fully automatic heating systems for the residential sector a high quality of these fuels is required. Several European countries already have implemented standards for such fuels. In other countries such standards are in preparation or planned. Furthermore, in some countries also standards from associations are existing (e.g. from the Austrian Pellets Association). In addition to these national standards, European standards for solid biomass fuels are under development. For producers of densified biomass fuels, especially for pellet producers, it is therefore very important to produce high-quality fuels keeping the limiting values of the standards addressed. However, in this context it has to be considered that as a high fuel quality as is necessary for the combustion of densified biomass fuels in automatic small-scale furnaces is not necessary if these fuels are used in larger industrial furnaces as they are equipped with more sophisticated flue gas cleaning, combustion and process control systems. Two pellet qualities, one for industrial and one for small-scale consumers seem to be more meaningful. Within the framework of the EU-ALTENER-project “An Integrated European Market for Densified Biomass Fuels (INDEBIF)” a questionnaire survey of European producers of densified biomass fuels was performed. In this connection the possibility was offered to the producers to participate in an analysis programme with their fuels. An overview was obtained of the qualities of densified biomass fuels offered in the European market, covering pellets and briquettes from Austria, Italy, Sweden, Spain, Norway and the Czech Republic. The parameters analysed were the dimensions of the fuels, the bulk and the particle density, the water and the ash content, the gross and the net calorific value, the abrasion, the content of starch (as an indication for the use of biological binding agents), the concentrations of C, H, N, S, Cl, K as well as of the heavy metals Cd, Pb, Zn, Cr, Cu, As and Hg. These parameters have been chosen following the Austrian, German, Swiss and Swedish standards for densified biomass fuels. The results showed that a majority of the participating producers produce fuels of high quality. However, wood pellets of some producers show a high abrasion, one of the most important quality parameters for pellets. An increased amount of fines often causes failures in the feeding systems used in the residential heating sector. In order to decrease abrasion, the addition of small amounts of biological binding agents (e.g. maize or rye) is possible. This kind of additive is most common in Austria. Moreover, some producers obviously use not only chemically untreated raw materials or additives, which increase the content of pollutants. Such fuels cause problems regarding emissions, deposit formation and corrosion. Emission problems are expected due to increased contents of N, Cl, S as well as heavy metals. Increased concentrations of heavy metals additionally contaminate the ash, increased Cl concentrations raise the risk of corrosion. Moreover, an increased content of K has a negative effect on the ash melting behaviour and causes higher aerosol formation, which enhances deposit formation and particulate emissions.

Transformation and Release to the Gas Phase of Cl, K, and S during Combustion of Annual Biomass

Abstract: The transformation of inorganic constituents in annual biomass was experimentally investigated at grate-combustion conditions. A laboratory fixed-bed reactor was applied to obtain quantitative information of the release of Cl, K, and S to the gas phase from six distinctively different annual biomass fuels. Samples of 4.0 g of biomass were combusted at well-controlled conditions at temperatures from 500 to 1150 °C. The elemental release was quantified by analysis of the residual ash and a mass balance on the system. The experimental results revealed that potassium was released to the gas phase in significant amounts at combustion above 700 °C. The potassium release increased with the applied combustion temperature for all biomass fuels; however, the quantity released was largely determined by the ash composition. At 1150 °C, between 50 and 90% of the total potassium was released to the gas phase. The biomass fuels with an appreciable content of silicate showed the lower release of potassium. Between 25 and...