Dissertation

Utilisation of high carbon pulverised fuel ash

Mahmud, Maythem Naji

2011

Overview

Coal combustion by-products generated from coal-fired power plant and cause enormous problems for disposal unless a way can be found to utilize these by-products through resource recovery programs. The implementation of air act regulations to reduce NOx emission have resulted millions of tonnes of pulverised fuel ash (PFA) accumulated with high percentage of unburned carbon made it un-saleable for the cement industry. Moreover, alternative fuels such as biomass and import coals were suggested to reduce gas emissions but on the other hand PFA marketability was reduced. The main objective of this study was thus to utilise high carbon PFA into value added products. Through this work, the relationships beside the factors that could influence the carbon content in the PFA and reduce it in terms of producing raw material useful for different applications were explored. These factors were extensively investigated through thermogravimetric analyses, surface area measurements, microscopy and optical studies, and particle size distribution analyses. Five high unburned carbon PFAs were selected as feedstocks for PFA beneficiation, cement tests, and carbon activation. In order to beneficiate a high carbon PFA, incipient fluidisation was selected as the preferred route being a dry separation method which does not expose the carbon to potential contaminants that may alter its reactivity or physical properties. Enriched PFAs (i.e. depleted carbon) were separated and then cement tests were conducted in different mixture ratios (PFA/cement) throughout different time scales. These tests were demonstrated by using samples derived from biomass co-firing and import coals. The PFA/cement mixtures achieved good strength and workability via standard values. Unburned carbon (i.e. enriched carbon) streams were activated using steam at temperature 850 C and time from 60-300 minutes. For all unburned carbons investigated in this project, the surface areas of their activated counterparts increased to reach maximum level after three hours and four hours compared with other works. But this increase dropped back according to the reduction of the pore widening. Consequently, the surface area exhibited a high level of low carbon burn-out for the carbon sourced from biomass co-firing (1435 m2/g and 38 wt.%, respectively). This was revealed due to the carbon gasification and pore widening level. In addition, optical studies showed that the carbon types changed in a different manner during the activation.

• Publisher: ProQuest Dissertations & Theses
• Subject: Civil engineering