Article Number 200103, March 2001

MODELLING OF TOXIC HEAVY METAL MERCURY PARTITIONING FROM PULVERISED FUEL COMBUSTION
D. DAJNAK and F.C. LOCKWOOD

Department of Mechanical Engineering - Thermofluid Section
Imperial College of Science, Technology and Medicine
Exhibition Road - South Kensington
London SW7 2BX, UK

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ABSTRACT:

The principal anthropogenic source of mercury in the atmosphere is from the coal-fired generation of electricity in utility boilers. Because of mercury's combined qualities of potential toxicity, environmental persistence and potential for bioaccumulation, this metal is a particularly insidious and difficult pollutant to manage. There is great concern over the emission of the toxic heavy metal mercury in the atmosphere and as a result there is an impetus to investigate the reduction of ongoing inputs of mercury into the environment.

A mathematical tool has been developed as a means of predicting the mercury content of the ash residue of coal combustion, or waste co-utilisation, in pulverised fuel fired systems. The treatment is novel in its use of a more general modelling methodology, particularly in regard to simulating the behaviour of mercury within the gas phase and its partitioning in the solid fuel combustion processes. Gaseous mercury escaping to the atmosphere and mercury chlorination between Hg and HCl released from the fuel are also encompassed by the methodology.

The model has initially been validated for thermodynamic behaviour against combustion data from a large laboratory scale pulverised fuel combustor fired with coal. The vaporization of elemental mercury from coal combustion has been successfully modelled. The subsequent speciation, nucleation, condensation and adsorption of elemental mercury and its species have been predicted. There is an urgent need of furnace data to validate both the speciation of mercury in the gas phase and its partitioning amongst the captured and emitted particulate phase. A comprehensive parametric investigation encompassing coal and waste fuel types, operating conditions and the evaluation of appropriate mercury sorbents, will accompany further developments of the model.

Key Words: Modelling, mercury, coal combustion, toxic emissions.