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McDonalds Lime Ltd, situated in Otorohanga, New Zealand, operate two dry process rotary lime kilns producing burnt and hydrated lime for a range of industries including agriculture, roading, water treatment, gold mining and steel making. The following Technology in Industry Fellowship (TIF) funded Masters Project is structured around investigating the combustion characteristics of Kiln Two at McDonald’s Lime Ltd using Computational Fluid Dynamics (CFD). Numerical results obtained using the commercial CFD code FLUENT were first validated against experimental data from the International Flame Research Foundation’s (IFRF) Furnace No.1. The validation study focussed on comparing the finite rate and mixture fraction/PDF approaches to combustion chemistry, as well as different methods for defining coal particle size distributions. Numerical modelling of Kiln Two at McDonald’s Lime Ltd began with full three-dimensional simulations, however due to their complexity and large computational times, two-dimensional axisymmetric models were primarily used for investigations. Comparisons were made between the two approaches. Investigations into the original pulverised coal fired system focussed on how the kiln aerodynamics and heat transfer properties were affected by changes to the coal and air inlet properties. The performance of a recently installed waste oil firing system was also investigated, with results showing that firing the kiln with a 25% thermal substitution of oil is the most efficient mode of operation. As the investigations focussed on the combustion characteristics the effects of the reacting limestone bed were ignored in all simulations. CFD modelling of the combustion characteristics within a large scale rotary kiln proved to be an extremely complex task. The work presented in this thesis has however provided some promising results which will ultimately assist McDonalds Lime Ltd in reducing their operating costs and environmental impact. Futhermore, the project has laid the foundation for further investigations.

Degree: PhD Department: Engineering / 1997, South African’s major power utility, recognised the need to improve the understanding of fly ash formation and slag deposition of South African coals. This requirement is due to the predicted quality changes of power station feedstocks and the limited research into the slagging propensity of South African coals. This research seeks to develop an analytical technique and a fly ash formation model for predicting the slagging propensity of coals. The research will establish if the models based on Carboniferous coals can be applied to South African Permian coals. A water-cooled suction pyrometer with a custom designed slag probe was used to obtain samples of fly ash and slag from within a 200 MWe pulverised fuel boiler. Simultaneously, samples of pulverised fuel feedstock were collected. The mineral attributes in the pulverised fuel and the phases in fly ash and slag deposit were quantified by CCSEM. The analytical procedure, CCSEM, has been developed with a novel procedure for identifying minerals and C-bearing phases. The new fly ash formation model assumes that the mineral attributes of the combusting pulverised fuel particle controls the size and elemental signature of the resultant fly ash particle(s). The new model has shown that the inherent mineral attributes controls the physical and chemical characteristics of the initial fly ash phases. Thereafter, conditions (stoichiometric, temperature and turbulence) within the combustion chamber promote the physical and/or chemical interaction of the initial fly ash particles. Slag deposits are enriched in Ca- and Fe-bearing alumino-silicates. The new slagging propensity index is based on either predicting or measuring the proportion of Ca- and Fe-bearing alumino-silicates. iv The numerous fly ash formation models, based on Carboniferous coals are not necessarily valid for South African coals. It is not the integrity of the actual fly ash formation mechanisms that is questioned, but rather the experimental scale on which the models are based. This research has produced an analytical technique and a fly ash formation model to predict the slagging propensity of coals. This forms a platform for further research into the role that organically bound cations, combustion conditions and boiler configuration has on the formation of Ca- and Fe-bearing alumino-silicates.

Building rammed earth structures provides a sustainable alternative to concrete. As a building material, rammed earth exhibits very varied physical and material properties depending on the proportion of constituting soil types. When very sandy soil is used in rammed earth production, the properties are different from when a clayey soil is used. This variability can be seen as a very great advantage in the use of rammed earth as a building material. Builders are able to adjust specific properties by changing mix proportions to obtain a desirable balance in the characteristics of the resulting rammed earth structure. This research work looks at selected mechanical and physical properties of different mixes of rammed earth. It describes typical range of values in density, thermal conductivity, ultrasonic pulse velocity, water ingress and compressive strength. It examines how these factors interrelate in the same soil mixes. Samples were prepared by blending various soil types in specific proportions to ensure that each definition of soil grade is as specific as possible. Unstabilised rammed earth was tested as was cement stabilised rammed earth. Rammed earth was tested at various levels of stabilisation and it was discovered that higher rates of stabilisation was not always beneficial to every material property. The research also looked into the potential disposal of waste materials in rammed earth. As rammed earth is a monolithic material that largely remains undisturbed throughout its life span, it was suggested that waste materials could be stored in an inert form inside of rammed earth rather than dumping it in otherwise agricultural landmass. Pulverised Fuel Ash and Palm Kernel Shells were identified as wastes to be disposed in rammed earth. Pulverised Fuel Ash, a by-product of industrial furnace is found in abundance in developed countries that burn carbonaceous materials in power plants. Disposals have been seen as a problem as only a small proportion of high loss on ignition (LOI) Pulverised Fuel Ash has found application. Palm Kernel Shell is a by-product of the oil palm industry and is currently a menace in many developing countries that need to dispose large quantities of the shell in landfills. At an early stage of the research, experimental trial runs quickly showed that these supposedly waste materials had a positive effect on some of the material properties of the rammed earth walls they were made into. This research effort evolved to look into exploiting these materials to improve the physical and material property of rammed earth and to suggest their effect on stabilised and unstabilised rammed earth. The extent to which these materials could be useful and the level at which diminishing returns set in was also investigated. It was discovered that soil mixes that would otherwise not be considered suitable for use in rammed earth wall production can now be utilised as their characteristics can be improved on simply by adding Pulverised Fuel Ash or Palm Kernel shell in the right proportion. Incorporating Pulverised Fuel Ash in rammed earth resulted in increased compressive strength. Palm Kernel shell improved thermal properties without compromising compressive strength.

Preplaced aggregate concrete (PAC) is produced by grouting high workability cement based grouts among the voids of compacted coarse aggregate mass. Because of its low shrinkage, PAC has been used for many repair jobs like; tunnel lines, dams and bridge piers. Moreover, it has been used for underwater construction. Grout has a major effect on the properties of produced PAC and well defined grout controls the properties of resulted PAC. The effect of types and amount of powder materials, admixtures, sand and water content on the properties of fresh and hardened grout for the production of PAC have been investigated. Tests on hardened grout and PAC properties have also been carried out to investigate the most important effects. A correlation between hardened properties of grout and PAC has also been analyzed. Grout rheology using four different gradation sands at two different cement-sand and at different w/c ratios ratios has been identified experimentally; no added chemical admixtures or mineral additives had first employed, then superplasticizer (SP) was added at 2% and 1%, and finally a combination of 1% SP and pulverized fuel ash (Pfa) at 20% of the cement weight was employed for all mixes. Grout tests have included two point workability tests by the Viskomat NT, flow time funnel test, Colcrete flow meter test, and water bleeding test. After that, eighteen grout mixes with high workability were produced using three different sands at three w/c ratios and two c/s ratios with 1% SP and Pfa at 20% of the cement weight were designed. Eighteen hardened grout and PAC then produced and their compressive strength and sorptivity were tested. Grout rheology can be defined by the rheology of cement paste employed and the internal distance between sand particles. The effect of sand surface texture on grout rheology is important at very low internal distances. Fresh grout yield stress is the most important property which gives the same degree of sensitivity for all grouts regardless the material type and content used in the mix. There are strong relations between compressive strength of grout and PAC, but less correlation between them in sorptivity test because of the effect high quantity of coarse aggregate of PAC. Sorptivity of PAC is low comparing with different kinds of concrete suggesting its advantage for underwater construction.