CEM India - Abstract

Abstract Information :

Mercury (Hg) is part of the Earth's surface (0.00005% = 0.5 g/t) and present in the environment in its natural state. Problematic is the highly toxic nature of Mercury: Even small traces of Mercury can cause severe poisoning when one is exposed over a long period of time. As early as 2008 the anthropogenic Hg- emissions already exceeded 2.000 tons per year. Due to increases worldwide, there are today more laws in place which regulate the release of Mercury.

Continuous measurement and recording of the Hg Emissions at Waste incineration plants, with a daily average limit of 30 µg/Nm3, has been in place in Germany since the end of the 90's. A new annual limit value 10 µg/Nm3 was set beginning of 2019. Since 2011, the USA has mandated strict limits for the Hg-emissions from Power plants and Cement plants which lie well below the 10 µg/m3 limit on a 30 day average. In the current Draft of the LCP BREF(Best available technologies), limit values of anywhere between 1 and 7 µg/m3 are currently being proposed for European Large Combustion plants, depending on the type of fuel being combusted.

All global emission limit values refer to total gaseous mercury (Hgtot). Particle bound mercury is not considered as it is represents just a small amount of the overall mercury present in the flue gas.

All measurement methods for continuous monitoring of total mercury are based on extractive measurement techniques. This is done using a gas sampling system, in some cases a dilution of the sample gas with nitrogen or instrument air within the probe and transportation to the analyzer system via a heated sampling line. For measuring gas transportation either a wear free ejector principle or membrane pump are possible. One crucial part for mercury monitoring is the conversion of the oxidized mercury (Hg+, Hg++) components into elemental mercury (Hg0). This can be done by wet-chemical, "catalytic", or high temperature conversion. It is a necessary step as the analyzers are only able to detect elemental mercury. For cross sensitivity correction some systems subsequently use gold traps which however results in longer measuring cycles. One new approach makes use of the Zeeman principle, which seems to be most promising.

The final analysis of the total gaseous mercury is done using atomic absorption spectroscopy (AAS) or atomic fluorescence spectroscopy (AFS) or differential optical spectroscopy in UV wavelength range.

All analyzers need to provide the possibility to do reference point checks. Internal standards, such as integrated adjustment cell are hereby reliable alternatives to test gas.