This research focuses on the co-firing of low-quality coal with refuse derived fuel (RDF) as a means to reduce the volume of waste dumped in landfill sites. The co-combustion behaviour and kinetics of various RDF/coal blends at different weight ratios, along with their physicochemical characteristics were investigated. The physicochemical analysis revealed that the run-of-mine and discard coal have relatively low calorific values of 21.7 MJ/kg and 16.7 MJ/kg, respectively. The RDF samples, plastic blend (31.2 MJ/kg) and paper blend (22.4 MJ/kg), were found to have higher energy contents. The thermogravimetric analysis was performed in an atmosphere of air, over a temperature range of 25-850 C, and the results showed that the RDF samples had lower ignition, devolatilisation, and burnout temperatures compared to the coals. The ignition temperatures for the blended fuel occurs in the lower temperature region when RDF is added to the blend, likewise the peak temperatures and burnout temperature shifted to a lower temperature zone. The activation energies (E a ) were determined using the Coats-Redfern method. The E a for the run-of-mine (ROM) coal of 104.4 kJ/mol, was found to reduce to 31.4 kJ/mol for the 75% PB þ 25% ROM coal blend and 35 kJ/mol for the 75% PL þ 25% ROM coal blend, respectively. The discard coal which had an E a of 109.9 kJ/mol was reduced to 30.9 kJ/mol for the 75% PB þ 25% discard blend, and 33.5 kJ/mol for the 75% PL þ 25% discard coal blend. It was determined that the most favourable blend for co-combustion was 70% discard coal þ 30% PL RDF due to the similarity of the combustion profile to that of 100% coal and the simultaneous reduction in apparent activation energy.
Summary Chemical reactions between reservoir minerals and cement filtrate and leachate have been investigated experimentally under simulated reservoir temperature and pressure. Results indicate that individual filtrate/mineral and leachate/mineral reactions are markedly different, with cement leachate appearing much more aggressive than cement filtrate. In all experiments dissolution and precipitation reactions were rapid, on a scale of days, with the formation of a range of low density high volume calcium aluminium silicate hydrate minerals. A very large increase in solid volume was observed in a number of filtrate and leachate reactions with single mineral separates. Clearly, porosity occlusion associated with these reactions could lead to impaired permeability. In contrast, however, an observed decrease in cohesiveness in quartz sandstone used in core flood experiments implies that permeability enhancement is possible, through primary mineral dissolution. The significance of these results with regard to cement fluid reactivity under real reservoir conditions needs to be investigated further. Introduction In the near-wellbore environment injected portland cement reacts with both wall-rock and pore water, and there is a potential for significant formation damage. Cementing operations produce two distinct generations of aggressive alkaline fluids which can permeate into and react with the formation adjacent to the cement rock interface:invasion filtrates are forced from the liquid cement into wall-rock porosity during cement pumping and setting shut-in; andcement leachates evolve and diffuse/advect away from the wellbore as the set cement equilibrates with aqueous formation pore fluids. Potential formation damage mechanisms due to cementing operations include the following.- Fines migration from the cement slurry into the formation.- Precipitation of solids from the cement derived fluids within the formation.- Differential dissolution of reservoir minerals leading to fines migration.- Precipitation of expansive secondary minerals following reservoir mineral dissolution.
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