Combustion of solid biomass in large scale power generation has been recognized as a key technology for the transition to a decarbonized electricity sector in the UK by 2050. Much of the near-term forecast capacity is likely to be by the conversion of existing coal-fired pulverized fuel plant (DECC, 2012). In such applications, it will be necessary to ensure that the combustion behaviour of the solid biomass fuels is engineered to match, as far as practical, that of the original plant design. While biomass feedstock characteristics vary considerably, one controllable variable for pulverized fuel is the size of the particles. Useful modelling for adaptation and design of boiler plant can be improved with more detailed measurement of the real behaviour of individual particles of the varying fuels. Typical power plant biomass fuels including pine, eucalyptus and willow with particle sizes ranging from up to 3 mm (Van Loo and Koppejan, 2008) and with differing moisture content and aspect ratios were selected for study. Single particles were supported in a water-cooled cover and then exposed above a flame, simulating biomass combustion in a furnace. Measurements of ignition delay, volatile burning time and char burn-out time were undertaken using high speed image capture. Temperatures of the surrounding environment and near to the particle surface were measured with thermocouples and thermometric imaging. Thermogravimetric measurements on separate samples complement the single particle measurements as a means of verifying the demarcation between the different stages of combustion and providing kinetic data. Analysis of the data identified correlations between the biomass fundamental characteristics, particle size, and the observed combustion profiles. Empirical expressions for the duration of each combustion stage have been derived. These have been validated with basic modelling including the predicted devolatilisation stage calculated by the FG-Biomass model (Chen et al., 1998). (C) 2014 Elsevier Ltd. All rights reserved.

The thermal decomposition of methylarenes labelled with C-13 in the methyl group was investigated. This was conducted using both a direct injection diesel engine and a pyrolysis flow cell connected to a GC-MS. 2-[C-13] methylnaphthalene and 9-[C-13] methylphenanthrene were synthesized by means of the Corey-House coupling reaction and their identity and purity confirmed by mass spectrometry and NMR. GC-MS analysis of the aromatic fraction separated from the extract of the exhaust particulate collected from the engine operated with n-hexadecane doped with the labelled methylnaphthalene showed that the C-13 was not redistributed among the methyl groups of higher PAH. However, with 9-[C-13] methylphenanthrene in the fuel a significant amount was retained in the particulate, even though the principal in-cylinder reaction was dealkylation. Pyrolytic reactions of the C-13-labelled methyl arenes were studied in a micro-pyrolysis-GC-MS-apparatus and confirmed dealkylation as the predominant reaction. The detailed chemical mechanism of the pyrolysis was explained by a scheme involving two alternative radical transfer reactions. (C) 2015 Elsevier Ltd. All rights reserved.

Ash deposition such as slagging and fouling on boiler tube surfaces is an inevitable, though undesirable consequence of burning solid fuels in boilers. The role of fuel characteristics, in affecting the form and severity of the problem, is significant. In recent years, biomass fuels have gained increasing popularity as an environmentally friendly source of energy in power plants all over the world. This study is based on characterising the fusion behaviour of four biomass fuels (pine wood, peanut shells, sunflower stalk and miscanthus) using ash fusion temperature (AFT) tests, simultaneous thermal analysis (STA) of fuel ashes, calculation of empirical indices and predicting ash melting behaviour with the help of thermodynamic equilibrium calculations. The AFT results failed to show any clear trend between fusion temperature and high alkali content of biomass. STA proved useful in predicting the different changes occurring in the ash. Empirical indices predicted high slagging and fouling hazards for nearly all the biomass samples and this was supported by the possible existence of a melt phase at low temperatures as predicted by thermodynamic calculations. (C) 2014 Elsevier Ltd. All rights reserved.