27th meeting of the Coal Research Forum and the Environmental and Coal Characterisation Divisions

The meeting was held in the Department of Chemical Engineering at Imperial College in South Kensington, London, on 20 April 2016. It was a packed day of presentations, allowing little time to visit the nearby museums. The morning session discussed the timely subject of the control of mercury and trace elements. David Graham of Uniper Technologies (formerly E.ON Technologies) began the day’s proceedings with an overview of mercury monitoring options and techniques. Measuring mercury in the flue gas exiting the stack is required to be carried out periodically (at least once a year) under the EU Industrial Emissions Directive (in force from 1 January 2016). But continuous monitoring will be needed in the future (possibly by 2021) under the new BREF (best available technique reference) document for large combustion plants that is currently being compiled. Dr Lesly Sloss from the IEA Clean Coal Centre provided an overview of current and imminent legislation on trace element emissions. Canada was the first country to legislate mercury emissions, with an emissions cap implemented for each province. She pointed out that artisanal mining is a large source for mercury emissions but since it is illegal it is difficult to obtain accurate emission data. It has been estimated that some 15 million people could be involved in artisanal mining. Mercury is mostly removed from coal-fired power plants as a co-benefit in the pollution control devices, the amount ranging from negligible to over 90%, depending on the pollution control system, type of coal and other factors. Mercury emissions are expected to increase in Asia, whilst decreasing in Europe. However, mercury emissions are thought to have peaked in China last year – their new coal-fired power plants have pollution control equipment installed that can easily meet the 30 µg/m3 emission limit set by the government. Mercury emissions are expected to rise in India. India is considering introducing a mercury emission limit of 30 µg/m3, but this would be difficult for their coal-fired power plants to meet since they do not have flue gas desulphurisation systems installed.

Dr Kevin Hughes from Sheffield University described his experimental and modelling work on gas-phase mercury oxidation. The oxidation of mercury in the gas-phase is dominated by chlorine. The reaction kinetics determined were slower than other values published in the literature. Janos Szuhanszki, another speaker from Sheffield University, described his work using inductively coupled plasma (ICP) spectroscopy for on online measurement of trace metal emissions at the 250 kW test facility. The test facility is a down fired combustor and uses a low NOx burner. Oxyfuel conditions can also be generated. The gas sample is transported over a 40 m heated line to the ICP spectrometer, located in a self-contained unit, for analysis. Experiments have been carried out on both coal and biomass to measure online emissions and elements that can cause slagging, fouling and corrosion.

The annual general meeting of the Coal Research Forum was then held, including the election for vacancies on the Executive Committee and progress reports from the various Divisional chairmen.

The theme of the afternoon session was the analysis and characterisation of coal and biomass for utilisation. Dr Will Quick from Uniper Technologies began by describing coal and biomass characterisation for a power generator. Uniper runs an accredited fuel characterisation laboratory. He emphasised the importance of proper sampling and preparation, which are critical steps in the analysis process. Tests for biomass include evaluating the durability of biomass pellets – that they will not disintegrate into dust. Uniper has its own fuel evaluation tool, derived from the Black & Vetch/EPRI Coal Quality Impact Model.

Analytical techniques for optimising recoveries in coal production was the theme of Dr Paul O’Meara’s talk. His presentation was based on a webinar that is available from the PANalytical company’s website. He described cross belt analysis of coal that can eliminate sampling difficulties – techniques such as neuron activation analysers. Other techniques covered included X-ray diffraction, computed tomography and X-ray fluorescence. A new method has been developed that avoids the time consuming ashing process step required in X-ray fluorescence.

The session finished with four post-graduates describing their current coal and biomass characterisation research. Stephen Chilton discussed the limitations of X-ray fluorescence analysis for biomass fuels, low grade coal and agglomerates. He concluded that results need to be used with caution – validation is still required as results from different machines and laboratories vary. There are no calibration standards for biomass yet. Dane Sexton from Cardiff University is using X-ray photoelectron spectroscopy to characterise coal, for example, functional groups and elements, at a depth of 5-10 nm. Patrick Mason at the University of Leeds is measuring the thermal conductivity of biomass. Thermal conductivity varies depending on whether it is measured across or parallel to the grain. Most of the published information on thermal conductivity is for large pieces of bulk wood, whereas biomass pellets are small. The last talk by Joseph Perkins from Nottingham University compared the use of air and oil immersion microscopy for mineral analysis of fuels.

Prof John Patrick concluded the interesting meeting, pointing out the links between the morning and afternoon sessions.