Gasification of high ash coal and chars from South African coals

This study seeks to explore the behaviour of several different South African bituminous coals currently used as feed in local power stations and to establish their technical performance and structural changes in a fluidised bed gasifier. It is anticipated that this would also assist in optimising gasifier operations for the gasification of fine high ash coals for power generation. The research was conducted by correlating the gasification performance of the selected coals and their derived chars against a range of chemical, physical and optical characteristics including mineral and maceral (and specifically inertinite) contents after testing in a pilot scale fluidised bed gasifier. Of specific interest were the changes in chemical microstructures during the transformation of the various coal macerals to their relevant chars following gasification. Raman spectroscopy and XRD analyses were used to examine the chemical carbon structures and the minerals associated in the coal. The relationship between the organic components and their gasified products (macerals-to-char) and the inorganic components to their gasified products (mineralsto- ash) including their physical structure and behaviour was determined by petrographic analysis. A higher loss of coal reactivity was obtained from vitrinites-rich coals due to a higher degree of structural transformation of carbon in the coal. Inertinite-rich coals experienced a lower loss of coal reactivity and lower degree of structural transformation even with longer residence time. The structural transformation of the macerals is due to realignment of the carbon molecules leading to substantial swelling (enhanced plasticity) in some macerals. Further modification was found to be due to proximity to melted minerals. Furthermore, the gasification performance of low grade coals can be optimised by varying the oxygen content used for coal gasification

A process investigation of the biosolubilisation of low rank coal in slurry system

Includes bibliographical references (leaves 127-136).The coal biosolubilisation processes may be used to convert low rank coal to either a clean, cost-effective energy source or to value-added products. This can lead to increased utilisation of low-rank coal. Low-rank coal is currently under-utilised because of its low calorific value, high moisture and sulphur content. Most research on coal biosolubilisation has centred on pre-treated coal. Little work is reported on naive coal. Low yields of solubilised coal products are currently reported in the literature. This may be due to further degradation of the soluble processes or to limitation of solubilisation step. These products have potential as starting materials for biotransformation to value-added products. However, to date, small volumes of solubilised coal products are available to assess their potential for further biotransformation owing to current biosolubilisation of low-rank coal being widely carried out as a small scale Petri dishes or Erlenmeyer flask of volume. This dissertation presents the results of the investigation of biosolubilisation of low-rank coal in slurry systems using Trichoderma alroviride. Its main objectives were to investigate key operating variables influencing untreated low rank coal biosolubilisation and degradation of soluble products, and to study different reactor configurations for coal biosolubilisatio

Chemical looping combustion (CLC) of municipal solid waste (MSW)

Chemical Looping Combustion (CLC) has been found to be a better alternative in converting Municipal Solid Waste (MSW) to energy and has the potential to reduce the generation of dioxins due to the inhibition of the de-novo synthesis of dioxins. This study comprehensively reviews the experimental studies of CLC of MSW, the oxygen carriers, reactor types, performance evaluation, and ash interaction studies. Modeling and simulation studies of CLC of MSW were also critically presented. Plastic waste is MSW’s most studied non-biomass component in MSW under CLC conditions. This is because CLC has been shown to reduce the emission of dioxins and furans, which are normally emitted during the conventional combustion of plastics. From the several oxygen carriers tested with MSW’s CLC, alkaline earth metals (AEM) modified iron ore was the most effective for reducing dioxin emissions, improving combustion efficiency and carbon conversion. Also, oxygen carriers with supports were more reactive than single carriers and CaSO4/Fe2O3 and CaSO4 in silica sol had the highest oxygen transport ability. Though XRD analysis and thermodynamic calculations of the reacted oxygen carriers yielded diverse results due to software computation constraints, modified iron ore produced less HCl and heavy metal chlorides compared to iron ore and ilmenite. However, alkali silicates, a significant cause of fouling, were observed instead. The best reactor configuration for the CLC of MSW is the fluidized bed reactor, because it is easy to obtain high and homogeneous solid–gas mass transfer. Future research should focus on the development of improved oxygen carriers that can sustain reactivity after several cycles, as well as the system’s techno-economic feasibility

Experimental Evaluation Using Plastic Waste, Paper Waste, and Coal as Fuel in\ua0a\ua0Chemical Looping Combustion Batch Reactor

A comparative study of chemical looping combustion (CLC) with paper, plastic, and coal as fuel was carried out. Experiments were performed in a laboratory fluidized-bed reactor by alternating between reduction and oxidation cycles. The results obtained indicated that a higher temperature leads to an increase in the CO yield and carbon conversion for all fuels. Paper had the highest fractional conversion of CO to CO followed by polyvinyl chloride (PVC) and coal. This was due to the higher fraction of volatiles in paper compared to PVC and coal. Scanning electron microscopy (SEM) analysis of the oxygen carrier particle after each of the solid fuel experiment was carried out. For the used ilmenite, there was a slight difference in the morphology for the three different fuels

Experimental Evaluation Using Plastic Waste, Paper Waste, and Coal as Fuel in a Chemical Looping Combustion Batch Reactor

A comparative study of chemical looping combustion (CLC) with paper, plastic, and coal as fuel was carried out. Experiments were performed in a laboratory fluidized-bed reactor by alternating between reduction and oxidation cycles. The results obtained indicated that a higher temperature leads to an increase in the CO yield and carbon conversion for all fuels. Paper had the highest fractional conversion of CO to CO followed by polyvinyl chloride (PVC) and coal. This was due to the higher fraction of volatiles in paper compared to PVC and coal. Scanning electron microscopy (SEM) analysis of the oxygen carrier particle after each of the solid fuel experiment was carried out. For the used ilmenite, there was a slight difference in the morphology for the three different fuels