N.J. Miles

Microwave heating applications in environmental engineering -- a review

This paper presents a review of microwave heating applications in environmental engineering. A number of areas are assessed, including contaminated soil remediation, waste processing, minerals processing and activated carbon regeneration. Conclusions are presented, which identify the areas of potential commercial development as contaminated soil vitrification, volatile organic compounds (VOC) treatment and recovery, waste sludge processing, mineral ore grinding and carbon in pulp gold recovery. Reasons are detailed why other areas have not seen investment into and implementation of microwave heating technology. These include difficulties associated with the scaling up of laboratory units to industrial capacities and a lack of fundamental data on material dielectric properties. This has meant that commercialisation of microwave heating processes for environmental engineering applications has so far been slow. In fact, commercialisation is only deemed viable when microwave heating offers additional process-specific advantages over conventional methods of heating.

Methods Employed for Control of Fouling in MF and UF Membranes: A Comprehensive Review

Abstract Membrane‐based processes are very susceptible to flux decline due to concentration polarization and fouling problems and the concept of fouling control via process optimization, membrane surface modification, and cleaning have been the focus of research in wastewater and water treatment. MF and UF membranes are utilized in many areas of industry. The main sector of application includes water and wastewater. There has been emphasis on the various methods used to reduce and, where possible, eliminate fouling. This review is a comprehensive insight into the wide range of techniques used in the control of fouling in both MF and UF membranes. It also addresses the amount of research that has gone into the various techniques used and the results achieved after experimental work.

Effect of the grinding behaviour of coal blends on coal utilisation for combustion

Abstract Grinding of a high volatile bituminous coal was performed in three comminution devices: Raymond Mill (RM), Rolls Crusher (RC) and Ball Mill (BM). The pulverised samples were sieved to obtain four particle size fractions, and temperature-programmed combustion (TPC) was used for the evaluation of their combustion behaviour. In addition, three coals of different hardness and rank were mixed in various proportions in order to compare the combustibility characteristics of the binary coal blends with those of the individual coals. The effect of coal blending on grindability was also studied. It was found that grindability was non-additive especially when coals of very different Hardgrove Grindability Index (HGI) were blended. The combustion studies also suggested that there exists an interaction between individual coals when they are burnt as a blend.

Measurement of boundary fractal dimensions: review of current techniques

Fractal dimensions are extremely useful in quantifying the degree of ruggedness of highly irregular objects. Since the introduction of the concept of fractal dimensions, by Mandelbrot [1], a large number of analysis strategies have been developed to allow the measurement of fractal dimensions. These analysis strategies can be divided into two broad groups, vector and matrix based methods. Vector-based methods include the structured walk algorithms such as the EXACT, FAST, HYBRID and FAENA algorithms. Matrix-based methods, ideally suited to image analysis systems, include Mosaic Amalgamation, Lattice Interception, the Dilation Method, the Blanket Algorithm, Displacement Method and the Distance Transform Method. The EXACT method is ultimately the most accurate vector-based method capable of providing highly detailed Richardson plots, however accuracy is achieved at the cost of analysis speed. The other vector based methods are faster variants of the EXACT method. The Dilation Method based on erosion-dilation logic is probably the most commonly used matrix based method, however, the recently introduced Distance Transform Method is more accurate, produces more data and is substantially quicker.

Upstream swirl-induction for reduction of erosion damage from slurries in pipeline bends

Industries which transport slurries and other particle-laden liquids in pipes expend the equivalent of millions of pounds every year to repair erosion damage caused by solid particle impingement. It is against this background that the perceived relationship between pipeline erosion and imposed swirling flow fields in pipe bends is important. Definitions of flow fields and particle dispersions which minimise erosive wear are sought to facilitate the development of new designs and geometries for slurry handling equipment. Such an approach is pertinent to industries handling valuable or hazardous material in the face of increasing safety, efficiency and economic requirements. Robust erosive wear models must be developed to explore the advantages of swirl flow and subsequent particle dispersion. Collaboration between the universities of Nottingham and Southampton is aimed at the reduction of wear at critical locations in slurry handling pipelines by applying swirl-inducing pipes upstream of pipe bends. This paper details the improved particle distributions, particle impingement conditions and lower flowrates resulting from such swirl flow. These factors are discussed in terms of current erosion models and the predicted reduction in wear rates. Parallel visualisation studies using simulant particle-laden liquids augment computational modelling of the flow patterns.

The use of grey level measurement in predicting coal flotation performance

Abstract It has long been accepted that the texture of a froth is generally a good qualitative indicator as to the performance of the flotation process. During investigation into quantifying froth textures by image analysis, it was observed that the grey level of a coal froth can provide significant information. The grey level showed correlations with flotation performance (e.g. ash content and froth mass flows rates) for both a single flotation cell and a bank of four pilot-scale cells. However, the two systems showed distinct differences in the texture of the froth surfaces. Testwork demonstrated that the effect of varying background illumination had a negligible effect on the results.

Smoothing and interpolation of float/sink data for coals

Abstract Washability data for a coal generally consists of triplets of values of three inter-related variables:- relative density, mass and ash content. Although the M-curve incorporates details of only mass and ash content, it can be used in combination with the relationship between ash content and relative density to smooth the experimental data and to interpolate as required. The method of representation and the curve fitting procedures are described and details are given of the initial proving of the technique. Practical experience in the use of the technique is reported together with an analysis of seventy-three sets of data. Examples are given to illustrate good and poor overall fitting.

Automated maceral analysis using fluorescence microscopy and image analysis

Abstract This paper describes the feasibility of using fluorescence microscopy in conjunction with normal white light microscopy and image analysis in order to carry out fully automated maceral analysis. A short review of current image systems shows a lack of success in distinguishing the liptinite species from the resin media used to form the coal block. Fluorescent lighting is commonly used during manual analysis and in this paper fluorescence is shown to provide a means of performing automated maceral analysis which includes an accurate determination of the liptinite content. The work presented indicates that the system can be used with a wide range of coals from around the world. A realistic assessment of repeatability and reproducibility is also made.

Experimental Investigation on the Separation of Bentonite using Ceramic Membranes: Effect of Turbulence Promoters

Abstract The static turbulence promoters presented in this work are designed to enhance filtration within tubular ceramic membranes of 0.5 micron pore size. Permeate flux enhancement still remains a topical problem during tangential crossflow filtration. The decline in flux with time is due to the usual phenomena of concentration polarization and membrane fouling, operating parameters including the system pressures, feed composition, membrane type and configuration, and the hydrodynamics within the membrane module. Solute accumulates on the membrane surface and forms a high concentration gel layer, thus increasing the effective membrane thickness and reduces its hydraulic permeability. Turbulence promoters of varying pitch lengths have been incorporated into the work to ultimately reduce the deposition of bentonite particles on the membrane surface during microfiltration. Yeast suspensions have previously been used as feed suspensions in order to compare the effectiveness of the turbulence promoters with an organic foulant. The objective of this work was to investigate the influence of static promoter geometry on flux sustainability enhancement during bentonite suspension filtration. All experiments have been conducted on a tubular ceramic membrane and the experimental membrane rig as shown in this paper. The effects of feed concentration, feed temperature, system pressures, and crossflow rates on the membrane flux sustainability were investigated. It was found that the promoters greatly improved flux sustainability and membrane efficiency over time and in some cases, a loss of 3% in membrane efficiency was realized with turbulence promoters at higher feed temperatures. The use of the turbulence promoter caused a large scouring of the membrane surface and membrane cleaning was significantly improved compared to the experiments without the promoters.

AN AUTOMATED IMAGE ANALYSIS SYSTEM FOR MAJOR MACERAL GROUP ANALYSIS IN COALS

Abstract An image analysis system has been developed capable of performing major maceral group analysis, based on morphological features as well as grey scale shading. The technique can be used to carry out the analysis without significant input from the operator. The main advantage of the system lies in its ability to distinguish liptinite from resin. Previous grey scale methods have been unable to do this, especially with lower rank coals. The method is described, together with the settings of the appropriate parameters. The repeatability of the method is tested and found to be comparable with manual point counting. Five coals from different parts of the world, with different petrologies, were analysed by point counting and by image analysis and there is good agreement between the results.