This investigation commenced with the sampling of high carbon PFA being produced as a byproduct arising from the operation of a carbon-separation process-plant at Didcot A power station.The sampling exercise took place over a number of days and the set of samples collected were then analyzed to evaluate their properties and variability in to judge the potential suitability of this material as a solid fuel additive for com. brick manufacture - with particular reference to use at the Desford brickworks of Hanson Building Products Ltd.The investigation was complicated by the difficulties experienced due to the inconsistent running of Didcot A power station during the latter part of the overall sampling period, within which, the collection of samples was divided into two sep. phases.During the first period, the power station was operating continuously and the analyzed properties of the material collected showed a good level of consistency.However, during the second collection period, the station's operation was interrupted by irregular shut-down's and the test results of the samples obtained were found to be detrimentally affected.This was particularly noticeable in relation to their carbon contents that were found to fluctuate considerably.This was of concern as consistency would be a key requirement for its use.A complimentary study was also carried out on a stockpile of the PFA located in the power station storage area.The same testing/evaluation procedures used earlier were applied again, using bulk samples obtained by vertically trenching across the stockpile.The results from the Individual trenches showed an agreeable level of consistency.This 'evening-out' of properties (particularly carbon content) is considered to be a result of the stockpile emplacement procedure, which follows a layer-upon-layer 'build-up' pattern, thereby creating a stable layered structure in which individual 'days-make' material overlays earlier material.The evidence of the testing results obtained, suggest that if this stockpile were to be subsequently recovered/removed by vertical (downward) excavation, it would result in even further effective homogenizing, thereby yielding a 'product' of high consistency and likely to be well within the boundary of specification required by Desford brickworks for use as a solid-fuel additive for brick making.The concluding part of the report addresses the planned full-scale factory trial of the Didcot high carbon byproduct at Hanson's Desford brickworks, to be held in the Spring of 2009.The purpose of this study was an evaluation of the influence of this PFA on the ceramic properties of the bricks being produced at this factory and in particular its suitability to be used as a replacement for the coal fines currently added as a fuel additive (sourced from Rossington coal-mine).This empirical evaluation was carried out in two phases.The first involved an assessment of the overall ceramic behavior of the Desford brick-body when containing increasing levels of both the Rossington coal-fines and Didcot high carbon PFA in parallel on an equal heat-value input.As the calorific value of the Rossington material is approx. three times that of the Dicot PFA, the resp. levels of weight/weight addition were proportioned accordingly.Overall, similar patterns in ceramic behavior were recorded for both exptl. products.However, the set containing the PFA was observed to exhibit more pronounced property changes than that containing the coal fines.The difference can be attributed to the three-fold addition of the PFA required to achieve equivalent heat-input.The results confirmed the ability of the Didcot high carbon PFA to be used in the same role currently provided by the Rossington coal fines.In the concluding part of this laboratory evaluation, clay bodies containing the two alternative carbonaceous materials were used in an experiment reproducing the forming method employed at the Desford brickworks (extrusion wire-cut).Both materials were introduced on a like-for-like c/v basis (necessitating three times the weight of PFA to match the Rossington material).After making and drying, bar-samples of the extruded products were divided and two representative batches were sent the Desford brickworks to be fired through the tunnel kiln with standard bricks under two different firing environments.A third batch was fired in Staffordshire University's ceramics laboratory in an elec. kiln following a similar firing profile to that operating at the brickworks.Subsequent ceramic testing revealed the product containing the Rossington material to be marginally superior in ceramic properties.However, the difference in magnitude between this and the PFA products suggests that the performance of the mix-design containing 15% weight/weight of high carbon PFA would comfortably meet market requirements.Moreover, in addition to offering an alternative carbonaceous additive, the results achieved confirmed that a product of this sort can not only be successfully fired in a com. kiln, but also possesses a number of supplementary advantages to be considered when comparing it with the current use of coal fines.These are noted at the conclusion of the report.
