1. Sources

The present Combustion File is part of the cluster of CFs produced within the literature survey phase of the industrial sponsored research and development project PowerFlam1 and is confidential to the participants registered for that project.

This CF is specifically concerned with the research project:

Abbas, T., Costen, P. Glaser, K., Hassan S. Lockwood, F. Ou, J.-J. (1995): Combined Combustion of Biomass, Municipal Sewage Sludge and Coal in a Pulverised Fuel Plant, which is published within Clean Coal Technology Programme 1992-1994 Vol. II, Combined Combustion of Biomass/Sewage Sludge and Coals: Final Reports, EC-Research Project: APAS-Contract COAL-CT92-0002. Editor – Hein, K.R.G.

2. Background

·         This combustion file is concerned with the provision of combustion related data to the sponsors.

·         In this html file the source of the data is summarised in section 4 below, in order to give the reader a general overview of the way the data was collected.

·         Fuel and related data, prepared for calculation, are presented in individual Microsoft Excel Worksheets, all contained within a Workbook.

·         Please note that in some cases, the worksheet tabs within a workbook are not all visible without scrolling horizontally.

·         This workbook can be down-loaded by the reader and saved to her/his hard disk.

·         To achieve this click on the “xls” icon on the left hand side of the banner above. The file will be retrieved from the server, and with up-to-date versions of the browser, will appear in a separate window, from which it may be saved to the user’s hard disk.

·         The data in these worksheets are protected – thus the reader cannot change the worksheet without knowledge of the protection password.

·         However the reader can copy and paste the data into his/her own project work book as required – at this point the accuracy and integrity of the data becomes the responsibility of the reader. Included in this workbook are copies of the abstract and synopsis for reference purposes.

·         All credits and sources, and where necessary, instructions/advice for data use, are presented in this html file. These are not necessarily reproduced in the Excel Work Sheets.

3. Abstract

An integrated research programme is described in which bench-top, large laboratory-scale and industrial-scale combustion experiments and mathematical modelling have been allied in order to interpret the effect of introducing biomass or sewage sludge derived fuels into existing suspension fired pulverised coal boilers for the generation of power.

A bench top approach was used to establish some of the combustion characteristics of the alternative fuels used, as compared with pulverised coal, as well as an indication of release patterns of the various organics and inorganics.

The large, laboratory-scale combustor, with an output up to 0.5 MW, was used to co-fire two alternative fuels with a number of pulverised bituminous coals in order to investigate how these fuels differed in their handling and feed control characteristics, their comparative stability limits, combustion performance, NO_x emissions and the added burden of heavy metal emissions.

Pine-derived sawdust and sewage sludge were fired with coal for a number of co-firing ratios with a maximum ratio of 30% of the total heat input to the furnace for the former fuel and 100% for the latter. Two different burner injection configurations were also installed to assess the affect of near burner aerodynamics on the combustion behaviour of the fuels. The optimum NO_x emissions were obtained when a fuel with low inherent nitrogen (e.g. sawdust) was fired through an annular injection surrounding an axial coal injection. For sewage sludge, with significantly higher nitrogen content, the obverse configuration produced a reduced NO_x emission, but not to the same extent.

Data obtained from both the bench-top apparatus and the large laboratory-scale furnace were used for the formulation of a mathematical model capable of predicting the co-fired flame performance, individual fuel particle trajectory and NO_x emissions. Initial results have proved encouraging, with the model prediction showing similar trends to the experimental data. Further refinements are being performed in the light of more accurate fuel reactivity data at higher temperatures.

The sewage sludge was also co-fired in the 88 MW burner test facility of Rolls-Royce-International Combustion Limited, Derby, UK to assess of its introduction on the flame performance of a commercial pf burner, as manufactured by the company. At a nominal total firing rate of 10 MW, a co-firing ratio of 30% was established. No adverse effect was observed on the combustion and emissions performance.

The main conclusion of the work suggests that, with appropriate preparation, mixing scheme and injection location, the co-firing of biomass waste and sewage sludge for the production of power is a technically viable proposition, while the emission limits, with the possible, albeit marginal, exception of Cadmium, are not breached by the addition of the waste fuel.

4. Synopsis