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Abstract: This paper focuses on the role of coal particle size distribution on pressure drop and gas flow distribution through packed coal beds. This fundamental knowledge is helpful in better understanding the operational behaviour of fixed bed dry bottom gasifiers. The Sasol synfuels plants in South Africa use 80 such gasifiers to convert more than 26 million tons of coal per annum to synthesis gas, and ensuring stable operation is of primary importance to ensure high synthesis gas production rates and gasifier availability. Pressure drop measurements on laboratory scale equipment were conducted to investigate the effect of particle size distribution on packed bed pressure drop. The well-known Ergun equation for pressure drop does not accommodate the effect of size distribution on pressure drop. A novel approach was followed to model pressure drop through simulated coal bed structures using Computational Fluid Dynamics (CFD). The coal bed structures were simulated by assuming that the coal particles are represented by randomised convex polyhedra in three-dimensional space. The computational space was divided into polyhedra using statistical Voronoi tessellation technique, which have been shown to be versatile in modelling problems in many fields, e.g. filtration, molecular physics, metallurgy, geology, forestry and astrophysics. This approach of flow modelling through packed coal beds is able to accommodate size distribution effects on pressure drop and gas flow distribution. The modelling work shows large deviations from plug flow with broad size distributions. The lowest bed pressure drop with the closest approximation to plug flow is obtained with the narrowest particle size distribution. Low gas flow rates are also beneficial for reducing excessive channel flow. Combustion profiles for different particle size distributions were studied using a pilot scale combustor. The combustion profiles provide confirmation of the CFD modelling results, namely that narrow particle size distributions and low gas flow rates reduce channel burning. Excessive channel burning was observed for broad particle size distributions, and is enhanced by high gas flow rates. The experimental and modelling work which was conducted, clearly indicate that narrow coal particle size distributions are desirable for optimum gas flow distribution and lowest packed bed pressure drop. [Copyright &y& Elsevier]

Abstract: In 2001 Sasol investigated the possibility to convert a Sasol-Lurgi MK III fixed bed dry bottom coal gasifier at the former Sasolburg coal-to-liquids plant to a slagging gasification process and selected the Lurgi Multi Purpose Gasification (MPG) process for this purpose. At the time the MPG process was considered as a possible technology option suitable for the gasification of feedstocks which are difficult to manage, for example solid–liquid mixtures which are unsuitable for conventional solids or liquids processes and furthermore tars with a large variety of properties and high solids content have been gasified successfully. The most obvious differences between the feedstocks previously gasified, compared to the Sasol dusty tar, were found to be the viscosity and melting point of the dusty tar. The viscosity of the Sasol dusty tar mixture (as received) was higher than a factor of 10 of the previously used feedstocks. Another important feedstock property is the ash melting point of the feed within the gasifier. Ash particles fed with the tar melt in the high temperature zone of the flame. Molten ash particles, which hit the gasifier wall, will solidify and stick to the wall, if the wall temperature is below the melting point of the ash. The melting point of the dusty tar ash is 1380°C and a fluxing agent has to be added to the dusty in order to reduce the melting temperature below 1250°C to limit excessive wear of the refractory lining. Two approaches were evaluated in order to lower the viscosity, i.e. milling of the dusty tar and addition of low viscosity feedstocks to the dusty tar. It was concluded from this study that the viscosity of dusty tar can be decreased with the addition of specific waste solvent streams. The ash fusion temperatures of dusty tar can be lowered with the addition of a fluxing agent. The addition of spent Fe-catalyst as fluxing agent was also investigated, but was found to be not as effective as limestone. In some cases the addition of Fe can cause the acid/base ratio to change in such a way that the ash fusion temperature increases. In conclusion it can be highlighted that the ash flow temperature and viscosity of the Sasol dusty tar stream, and possibly other carbonaceous sources as well, can be decreased to acceptable values for slagging gasification applications. The results clearly show in both oxidizing and reducing atmospheres the Fe-catalyst was transformed into the slag melt as either Fe2O3 under oxidizing conditions and FeO under reducing conditions. The slag showed no sign of metallic Fe and was very homogeneous under oxidizing and reducing conditions. Spent Fe-catalyst can be discarded in a safe and environmentally acceptable way during high temperature gasification. [Copyright &y& Elsevier]

Limited data exist on the incidence of hip fractures in South Africa (SA). We report gender and ethnic specific incidence rates of hip fractures in SA. In a multicentre prospective study, conducted in geographically defined municipalities of three provinces in SA, a structured questionnaire was administered to all subjects aged 40 years and over, presenting with a new atraumatic hip fracture, from 1 April 2017 to 31 March 2018. Gender and ethnic specific incidence rates (IR) of hip fractures were calculated using population statistics from Statistics SA. Of the 2767 subjects enrolled, 1914 (69·2%) were women and 853 (30·8%) were men. The majority of subjects were from the White population (40·9%) followed by those from the African (26·4%), Coloured (18·7%) and Indian (13·9%) populations. Men with hip fractures were significantly younger than women in the total group (69 [IQR 59–79] versus 77 years [IQR 68–84], p < 0·001) and in each ethnic group. White subjects were significantly older (p < 0·0001) and Africans significantly younger (p < 0·0001) than the other ethnic groups. In women, the highest IR was noted in the White population (176·0 per 100,000), followed by that in the Indian (147·7 per 100,000), Coloured (73·2 per 100,000) and African populations (43·6 per 100,000). A similar pattern was seen in men albeit at lower rates, with the highest rate in White men at 76·5 per 100,000. In the total study population and the African population, the IR was higher in men compared to women in subjects under 60 years. In the White population, the IR was higher in men compared to women in the 40–44 years age group. While in the Coloured and Indian populations the IR was higher in men compared to women in the 40–49 years and 45–54 years age groups, respectively. There was an increase in the relative risk ratios with age in the total study population, and in all ethnic groups in both women and men. Hip fractures occur in all ethnic groups in South Africa with higher IRs in the White and Indian populations compared to the Coloured and African populations. Consistent with the published literature, the overall hip fracture IR was higher in women than in men, except in the younger age groups, and increased with age. South African Medical Research Council and the University of KwaZulu-Natal Competitive Research Grant. • This study is the first to examine the incidence of hip fractures in all ethnic groups in South Africa. • The incidence rate was higher in women compared to men, except in subjects under 60 years of age. • Men were significantly younger than women at the time of the hip fracture. • The incidence rate was highest in the White population, followed by the Indian, Coloured and African populations. • The relative risk of hip fractures increased with age in all ethnic groups. [ABSTRACT FROM AUTHOR]