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The coal fired power plants are one of the oldest, most common and wide spread generators of electricity. They utilise heat generated by burning coal, that is pulverised in different type of grinding machines selected based on the coal type that is being processed, to produce steam power. For bituminous coal, vertical spindle pulverisers are the preferred and most common equipment for pulverisation. In this thesis, the vertical spindle pulverisers were of interest and their operation is modelled. In order to achieve this goal, a sampling procedure was developed to collect samples from these pulverisers. A standard procedure for sample analyses was followed; and when required, new experimental and sampling tools were developed and manufactured. A multi-component data set of five industrial scale surveys was produced for the pulveriser operating at different coal and air flow conditions. The multi-component data are based on size and ash content as well as density for one test and the feed samples. The selected samples were classified into size-by-size density bins by float/sink density analysis. One of the general outcomes of using multi-component data was confirmation of the mineral matter accumulation in the mill showing its dependency on size. Moreover, the multi-component data were utilised to calculate the flow rates and unknown particle size distributions of the mill interior streams by mass balancing. Hence, the mill interior streams particle size distributions and flow rates, as well as size-by-size ash content distributions were obtained; thus the circulating loads that develop in the pulveriser were calculated. This information was used in constructing the ball feed stream via combining the reject streams with the coal fed to the pulveriser, which is the key stream to compute comminution information and model parameters. The mass balanced streams information were utilised to evaluate the classifications that occur in the pulveriser. The model parameters describing the classification curves that correspond to the two different zones in the pulveriser were found to be closely related to the operational conditions. A 3D multi-component breakage function was developed with the results obtained from compressive breakage tests. It is observed that the coal and mineral matter differ in breakage behaviour. This difference was incorporated into the 3D breakage model in order to be able to predict the breakage of these component particles and their composites. The mass balanced stream information together with the multi-component breakage function was utilised to successfully determine the rate of breakage of particles in the grinding zone. The model parameters describing the rate of breakage of the particles were found to be related to the operational variables. A demonstration of the developed approach was done using a simulator which linked comminution and classification models based on size and density components, to work in closed circuit operation. The classification function used in the overall simulation model was changed to an efficiency curve model based on settling velocities of particles to enable integration of both density and size of particles into the model; rather than employing empirical relations developed based only on particle size. Similarly, parameters for rate of breakage of particles have differed from that of parameters calculated during the computations for open circuit grinding conditions. The results obtained from the simulation studies were satisfactory in describing the existing conditions that occur in the pulveriser at all the sampled conditions. In conclusion, a mathematical model of an industrial scale ball-and-race pulveriser was developed by determining the effect of operational variables on the comminution and classification operations within the pulveriser.

The breakage of a coal in compression tests has been studied with the aim of obtaining an appearance function giving the distribution resulting from the breakage of each particle type, which can be used in the simulation of vertical spindle mills that are commonly used in coal fired power plants. The appearance functions from the compression tests were found to take a linear form on logit axes (log(x/(x m − x))), thus giving a simpler description than is available on other axes. In common with other breakage analysis methods the lines can be identified by the percent passing one tenth of the initial size, the t 10 parameter. An exponential relation between t 10 and specific energy was found for each particle group defined by size and density and the parameters of the exponential relation were related to the particle size and density. It was found for this particular coal that breakage did not preferentially concentrate either coal or mineral matter. The relations developed allow the generation of a three dimensional breakage-appearance function for the breakage of both size and density components which can be used in the simulation of a pulveriser for the coal tested. The paper also demonstrates the type of test work required for the generation of appearance functions for other types of coal.

A new approach to identify multivariable Hammerstein systems is proposed in this paper. By using cardinal cubic spline functions to model the static nonlinearities, the proposed method is effective in modelling processes with hard and/or coupled nonlinearities. With an appropriate transformation, the nonlinear models are parameterized such that the nonlinear identification problem is converted into a linear one. The persistently exciting condition for the transformed input is derived to ensure the estimates are consistent with the true system. A simulation study is performed to demonstrate the effectiveness of the proposed method compared with the existing approaches based on polynomials. (C) 2006 Elsevier Ltd. All rights reserved.

In this paper, a new control design method is proposed for stable processes which can be described using Hammerstein-Wiener models. The internal model control (IMC) framework is extended to accommodate multiple IMC controllers, one for each subsystem. The concept of passive systems is used to construct the IMC controllers which approximate the inverses of the subsystems to achieve dynamic control performance. The Passivity Theorem is used to ensure the closed-loop stability. (c) 2005 Elsevier Ltd. All rights reserved.

When examining a rock mass, joint sets and their orientations can play a significant role with regard to how the rock mass will behave. To identify joint sets present in the rock mass, the orientation of individual fracture planes can be measured on exposed rock faces and the resulting data can be examined for heterogeneity. In this article, the expectation–maximization algorithm is used to fit mixtures of Kent component distributions to the fracture data to aid in the identification of joint sets. An additional uniform component is also included in the model to accommodate the noise present in the data.

The flow split between the products of a hydrocyclone is one of the least understood aspects of hydrocyclone operation. This split is greatly influenced by the air core diameter, so an understanding of the air core behaviour would greatly assist in predicting flow splits. A program of combined theoretical and experimental investigation of the factors that control the air core in a hydrocyclone is being undertaken. Rietema type simplifications of the Navier Stokes equations have been extended to include the prediction of air core diameter. The equations which are indirect in their original form have been converted to give a direct solution for the dimensionless pressure and air core diameter ratio. An experimental program using simplified test units has been undertaken. This has obtained pressure drop, air core diameter and velocity profile data over a considerable range of operating conditions. This data is being used to identify and correct deficiencies in the theoretical analysis, and to investigate the range of validity of the resulting relations. The aim is to produce simple relations that can be used to improve the accuracy of typical simulations of hydrocyclone performance, and also to provide some guidance in the design of hydrocyclones.

This paper presents an evaluation study of the use of newly developed clustering tools for on-stream analysis instrument calibration at Western Mining Corporation's Leinster Nickel Operations. In this application, data corresponding to different ore types are present. This causes unsatisfactory instrument calibration using existing methods. The clustering program is able to identify the distinct regions and superior predictive capabilities from the equipment are demonstrated. The use of an on-line expert system (which utilises the clusters as its knowledge base) to enhance analyser performance and identify instrument and plant anomalies is also discussed.

Airport mean wind and gust speed data is used with past and future simulated data to estimate the maximum gust speed for a 500 year return period. It is demonstrated that the instantaneous speeds lead to the same result as data giving maximums over some time period. The airport mean wind speed was related to the gust speed, and the future simulations related to the past simulations. However, the relation between measured airport data and the simulations is poor. A Weibull distributions fitted to the upper part of the gust data is extrapolated to give the 500 year return period. An alternative approach using techniques similar to some actuarial analyses is also demonstrated.