P. Tucker

A strategic environmental assessment method for agricultural policy in the UK

There are a number of significant environmental impacts that arise from agricultural practices that may be influenced by policy. A Strategic Environmental Assessment Method (SEAM) is described which aims to assess the environmental impacts of agricultural policy and aid the development of more sustainable policy formulation. The method addresses the issues of selecting appropriate performance criteria and measurements, and makes use of effect-damage functions and targets to determine the significance of potential impacts in relation to sustainability. A set of profiles is produced, describing the environmental performance of a specific policy. A confidence assessment system (CAS) is also described which provides details about the quality of the assessment and areas of uncertainty. SEAM provides information about impacts in simple format that can be easily used in decision making. It can identify environmental trade-offs and provides a holistic view that is essential when making decisions that affect the environment.

Computer simulation of the Bond Grindability test

Abstract The Bond grindability test is widely used, in the minerals industry, to provide data fundamental to the design of commercial milling installations. The traditional Bond test method is, however, labour intensive and yields only a limited amount of information. Extrapolation of this information, for example to investigate a range of product sizes, can only be achieved through the application of empirical correction factors or through carrying out a separate Bond test at each product size. The work presented in this paper was aimed at alleviating these limitations. A new Bond grindability test method was developed which not only significantly reduces the experimental testwork involved but also implicitly provides the necessary data for as many product sizes that are required. The new method is based on a computer simulation which closely parallels the traditional method. A population balance model of size reduction forms the kernel of the simulator. This model is based on a well-known mathematical representation of the comminution process which has been adapted specifically for the traditional Bond mill. The development of the model is discussed in detail and the simulation methodology outlined. The simulation results are presented and compared with results obtained using the traditional method.

Computer optimisation of a shaking table

Abstract This paper describes work undertaken, under the 3rd. EC Raw Materials Programme in collaboration with Carnon Consolidated Ltd. (CCL) and Beralt Tin and Wolfram SA (BTW), on the development and application of a mathematical model of a shaking table concentrator. The first part of this paper describes the model and the background to its development. Within the model, the major innovation was the introduction of explicit ranking and band width functions for the constituent size/SG fractions, which related their point of discharge from the table (and therefore their recovery) by abundances as well as rank order. This new approach competition between individual size/SG fractions to be modelled directly. This, and other, new features (eg. implicit handling of feed classification, a switch parameter to account for table duty and geometry etc.) gave the model increased robustness and more general validity over a wider spectrum of table applications than could be achieved with previous models. The new model was validated on the table operations at BTW and CCL and also an pilot scale separations at WSL and elsewhere. The second part of the paper describes the application of the model to the optimisation of the primary gravity circuit of the Wheal Jane plant of CCL. The application described here was part of a longer term simulation study, which has already recorded significant benefit at the plant [6]. The application illustrates the role of modelling and simulation in providing quantitative decision support for metallurgical development.

An expert system for shaking table diagnostics

Abstract An expert system, for fault diagnosis of shaking table operations, is presented. The system is designed as one element of an integrated, computer-based method for plant enhancement, for application in the mineral processing industry. The relationship between expert and conventional software techniques is discussed. The system is based on production rules and has been written in the PROLOG language. Diagnostics are at three levels: the first assessing the known table set-up parameters and the deeper levels providing more detailed analysis in identifying the root cause of the problem. The reasoning, at each level, is developed making reference to fragments of PROLOG code abstracted from the computer program. The system is capable of identifying over 120 faults in tabling operation and has been deployed at two commercial productions plants.

A mathematical model of the duplex concentrator

Abstract This paper describes the development of a mathematical model of the Duplex concentrator. The model is formulated in terms of the spatial distribution of material (ie. banding) of each size/ SG component down the length of the Duplex deck. In the model, analytical equations are derived for these distribution profiles for the point in time at which the concentrate is rinsed from the deck. Auxiliary equations are presented to describe how the distribution profiles vary with operating conditions. The physical significance of these relationships is briefly discussed. The model has been based on experimental data collected at South Crofty and at Beralt Tin and Wolfram S.A. (BTW) where a unit has been in production since late 1988. Metallurgical performance data for this unit are summarised. Model validation results are reported and, for completeness, a brief description of the Duplex is also given.