Automatic reactivity characterisation of char particles from pulverised coal combustion using computer vision

Char morphologies produced during pulverised coal combustion may determine coal reactivity which affects the combustion efficiency and the emissions of CO2 in power plants. Commonly, char samples are characterised manually, but this process is subjective and time-consuming. This work proposes methods to automate the char reactivity characterisation using microscopy images and computer vision techniques. These methods are summarised in three contributions: the localisation of char particles based on candidate regions and deep learning methods; the classification of particles into char reactivity groups using morphological and texture features; and the integration in a system of the two previous proposals to characterise char sample reactivity. The proposed system successfully estimate char reactivity in a fast and accurate way

Automated image analysis techniques to characterise pulverised coal particles and predict combustion char morphology

A new automated image analysis system that analyses individual coal particles to predict daughter char morphology is presented. 12 different coals were milled to 75–106 µm, segmented from large mosaic images and the proportions of the different petrographic features were obtained from reflectance histograms via an automated Matlab system. Each sample was then analysed on a particle by particle basis, and daughter char morphologies were automatically predicted using a decision tree-based system built into the program. Predicted morphologies were then compared to ‘real’ char intermediates generated at 1300 °C in a drop-tube furnace (DTF). For the majority of the samples, automated coal particle characterisation and char morphology prediction differed from manually obtained results by a maximum of 9%. This automated system is a step towards eliminating the inherent variability and repeatability issues of manually operated systems in both coal and char analysis. By analysing large numbers of coal particles, the char morphology prediction could potentially be used as a more accurate and reliable method of predicting fuel performance for power generators

OxyCAP UK: Oxyfuel Combustion - academic Programme for the UK

The OxyCAP-UK (Oxyfuel Combustion - Academic Programme for the UK) programme was a £2 M collaboration involving researchers from seven UK universities, supported by E.On and the Engineering and Physical Sciences Research Council. The programme, which ran from November 2009 to July 2014, has successfully completed a broad range of activities related to development of oxyfuel power plants. This paper provides an overview of key findings arising from the programme. It covers development of UK research pilot test facilities for oxyfuel applications; 2-D and 3-D flame imaging systems for monitoring, analysis and diagnostics; fuel characterisation of biomass and coal for oxyfuel combustion applications; ash transformation/deposition in oxyfuel combustion systems; materials and corrosion in oxyfuel combustion systems; and development of advanced simulation based on CFD modelling

Optimising Carbon Type Differentiation Techniques to Reduce Dust Emissions in Blast Furnace Ironmaking

The manufacturing process of iron, using the blast furnace (BF) generates dust as a by-product, which is recycled, however, the generation of the dust in excess is undesirable. A comprehensive review of the dust has determined that each of the raw materials for blast furnace ironmaking contributes to its formation, including several forms of carbon thus addressing the hypothesis ‘The raw materials that feed the blast furnace are expelled into the gas stream and all influence the blast furnace dust.’ The current technique for quantifying coal originating carbon type mostly in the form of coal char, referred to as the nominal term Low Order Carbon (LOC) within BF dust consists of thermogravimetric analysis (TGA) however, this technique does not allow for samples of dust to be analysed in a timely manner, in line with the ever-changing conditions of the blast furnace. In this work, the TGA method has been trialled for use with BF dust, with improvements offered to the heating profile, allowing for faster analysis. Moreover, alternative techniques have been trialled, in combination with various characterisation methods such as X-ray diffraction, Scanning Electron Microscopy, total carbon and Optical Emission Spectroscopy. The ‘Winkler Method’ which was originally designed to quantify charcoal in soil sediment has been successfully adapted and optimised to suit LOC quantification in BF dust, showing a good correlation with the original benchmark technique. This answered the hypothesis, ‘Thermal techniques can be used to differentiate carbon sources in dust generated in blast furnaces that use granulated coal injection.’ The techniques for LOC quantification were applied to dust samples spanning a 9 month period. to determine the process parameters that influence the LOC presence within the dust. It was found that the resolution of sampling is key to identify relationships between process parameters and LOC within the dust. A novel technique to continuously monitor the dust output of the furnace found that the dust output and the LOC within the dust are related, where the increasing dust output leads to increasing concentrations of LOC within the carbon profile of the dust itself. Process parameters including blast pressure, blast volume, and production rate were considered to increase the dust output from the furnace based on the work of the dust probe, thus answering the hypothesis ‘Coal combustion in the raceway can be impacted by process parameters and the evidence can be found in the fingerprint of blast furnace dust.’ A node mapping exercise was used to model an ideal set of process conditions for low dust operations. The foundations to make macro advances in carbon and dust output reduction in blast furnace ironmaking are laid out in this thesis

Reaction kinetics and structural evolution of pyrolysis and gasification chars

Gasification is a versatile technology used to convert coal into synthesis gas for use in cleaner power generation and production of high-value products. This work investigates the pyrolysis and gasification behaviour of a relatively unknown Morupule coal, from Botswana, using a wire-mesh reactor. Morupule coal was pyrolysed in a helium atmosphere and gasified in CO2 at temperatures of 400 – 1050 ºC and heating rates of 1 – 1000 ºC s-1 under pressures of up to 30 bara and holding times of up to 400 s at peak temperature. Elevated pressures induced a suppression of the volatile release during the temperature ramp up. However, ultimate yields at 1000 ºC prove insensitive to pressure. A novel direct gasification approach with in-situ coal pyrolysis, as opposed to decoupling the pyrolysis and gasification experiments, was used to study the intrinsic CO2 gasification kinetics as would be observed in a gasifier. An activation energy of 320 kJ mol-1, higher than published data, is reported. Enhanced gasification rates were obtained at pressures of up to 20 bara, with reduced gasification lag periods previously observed under atmospheric pressure conditions. Morupule coal gasification propagated through the consumption of C-C/C=C bonds, without preference for smaller aromatics. Char morphology was characterised by a developing external surface porosity as gasification proceeded. A distributed activation energy model, assuming a Gaussian distribution, accurately represented the pyrolysis behaviour of Morupule coal. The shrinking core, volumetric and random pore models adequately represented the early-stage atmospheric pressure gasification kinetics. The Langmuir – Hinshelwood rate expression described the high-pressure gasification kinetics fairly well but could not account for the initial gasification lag. In studying the effect of particle size on pyrolysis, larger particles exhibited lower product yields during the heating up period. However, identical yields were obtained under prolonged holding at 1000 ºC at both atmospheric and elevated pressures.Open Acces

A characterisation of combustion and gasification residues from biomass and other fuels.

Imperial Users onl

Transformation of char structure and alkali and alkali earth metallic species during pyrolysis and gasification

This study focused on the formation and transformation of nascent char structure during the pyrolysis in He and the gasification in CO2/O2 of biomass and low-rank coal. The effects of nascent char structure and the concentration of AAEM species on nascent char reactivity were investigated. The results will be useful for the development of low-emission gasification-based technologies for the utilisation of biomass and low-rank coal