Air Quality 2007

PP029 - Development and Testing of an Oxidised mercury Calibration Gas Source for CEMs and Instrumetnal Reference methods

Authors: Dr Matthew A Dexter, Dr Isabelle Atheaux, Dr Warren T Corns and Dr Peter B Stockwell (PSA)

The Clean Air Mercury Rule has provided the legislation for the regulation and control of mercury emissions from coal fired utilities in the United States.  The rule requires periodic testing with elemental mercury and mercury(II) chloride calibration gases to ensure the integrity of the CEMs.  These calibration gases are also required by the current draft Instrumental Reference Method.  It is therefore essential to develop suitable calibration sources which are traceable to national standards (NIST or other standards bodies) for use in CEM and IRM testing.

Since the introduction of its first mercury continuous emissions monitor P S Analytical has provided a calibration source, the Cavkit, which allows an automatically adjustable set concentration of mercury to be introduced at various stages in the sampling and measurement cycle.  This has been successfully used to check calibration and to test the integrity of CEM systems.  The system has been evaluated by NIST. 

A mercury(II) chloride calibration gas source has been developed for use in CEM and IRM testing.  The HgCl2 generator can be located at the analyser or the sample probe to minimise sample transport issues.  Development of the HgCl2 calibration gas generator and early experiences of this in the field will be described.

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Air Quality 2005

PP018 - Mercury Speciation in Flue Gas using Dry Based Conditioning with Atomic Fluorescence Spectrometry

Authors: Dr Warren T Corns, Dr Peter B Stockwell and Dr Matthew A Dexter (PSA)

Gas-phase mercury in power plant stack emissions is present as elemental and oxidised mercury.  Current legislative developments are increasing the demand for robust, low maintenance mercury continuous emission monitors (CEM’s).  Existing wet chemical methods for the speciation of mercury in flue gas and wet preconditioning systems involve the use of large quantities of reagents and require considerable operator skill and attention.

The flue gas matrix presents particular challenges.  Firstly, representative sampling from the stack, including separation from the reactive flyash without this affecting the mercury speciation or level in the flue gas is necessary.  Secondly, the composition of the flue gas contains significant levels of a range of acid gases (e.g. sulfur dioxide, nitrogen oxides, hydrogen chloride), which can interfere with the determination of mercury.

A dry based mercury speciation module will be described in detail and typical data from bench, pilot and full scale facilities will be presented.  Mercury is measured in two streams, total gas-phase mercury (HgT) and Hg0, thus speciation by difference can be achieved.  A high temperature catalytic process is used to convert Hg2+ to Hg0 for measurement of total Hg and an adsorbent specifically for oxidised mercury is used to produce a stream corresponding to elemental Hg.  A peltier cooler is used to remove water from the matrix, prior to determination of mercury in the two sample streams by amalgamation atomic fluorescence spectroscopy (AFS).  The system has been designed to produce an interference free measurement without the need for dilution.  

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PP017 - Evaluation of Spike and Recovery Tests to Establish the Accuracy of Hg Speciation Measurements in the Presence of Fly Ash

Authors: Dr Warren T Corns, Dr Peter B Stockwell and Dr Matthew A Dexter (PSA), Dr David Fitzgerald and Stuart Bowden (Mitsui Babcock Tech)

Accurate measurement of mercury speciation in flue gas from coal fired power utilities and waste incinerators is necessary to model the fate and transportation of mercury in the atmosphere and to evaluate the effectiveness of mercury control technologies.  There a numerous measurement and sampling issues that have to be addressed to ensure accurate results are obtained.  Sampling in the presence of reactive flyash is problematic using conventional filtering techniques since captured flyash may collect mercury or change the speciation.  To overcome this problem inertial filters have been designed and these have been used in the field successfully for several years. The accuracy of mercury speciation measurements using this approach was evaluated using dynamic spiking of elemental mercury at the tip of the probe into the flue gas stream.  To perform these experiments a calibration system based on dilution of saturated mercury vapour was used. A carrier gas containing a known concentration of CO was utilised so that the exact spike dilution rate could be confirmed by measurement of CO at the analyser exhaust. This approach was found to be more accurate than using conventional venturi flowmeter readings thus allowing a quantitative spike recovery calculation.  All measurements were performed using a dry speciation module coupled to amalgamation - AFS. This paper will present typical spike and recovery data from plant and pilot test facilities. The concept and implementation of applying correction factors based on mercury speciation spike recovery data will be critically discussed.

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