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:

Cenni, R., Janisch, B., Spliethoff, H. and Hein, K.R.G. (2001): Legislative and environmental issues on the use of ash from coal and municipal sewage sludge co-firing as construction material, which is published within Journal Waste Management, Vol. 21, pp. 17-31

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

For the economy of any co-firing process, it is important that the common waste management options of ash remain practical. Ash from bituminous coal combustion is typically handed to the construction industry. This paper describes the current European legislation on use of ash for construction purposes. Also, it presents an experimental study on the suitability of fly ash from combustion of mixtures of bituminous coal and municipal sewage sludge as additives to cement and concrete, and for use in open-air construction works, based on the ash chemical composition and the characteristics of the extract of the ash. Currently, two European standards forbid the use of ash from co-firing as additive to cement or concrete. This study shows that ash derived from coal and sewage sludge co-firing contains generally less unburned carbon, alkali, magnesium oxide, chlorine, and sulfate than coal ash. Only the concentration of free lime in mixed ash is higher than in coal, even though, at least up to 25% of the thermal input, still below the requirements of the standards. This ash also meets the requirements for the use of fly ash in open-air construction works – concentration and mobility of few elements – although this management option is forbidden to ash from co-firing. The leaching of Cd, Cr, Cu, Ni, Pb and Zn was investigated with three leaching tests. The concentration of these metals in the extracts was below the detection limit in most cases. The concentration of Cu and Zn in the extract from fly ash was found to increase with increasing share of sewage sludge in the fuel mixture. However, the concentration of these two metals in the extract is not regulated. This study indicates that excluding a priori the use of ash from co-firing as a suitable additive for construction material could cause an unnecessary burden on the environment, since probably ash would have to be disposed of in landfill. However, allowing this requires the modification of current European standards to include limitations on all elements and compounds, absent in coal but which might be present in other fuels, that are deleterious for the quality of construction materials.

4. Synopsis