Determinación directa de contenido de mercurio en carbón

INTRODUCTION

Mercury is one of the most toxic trace contaminant naturally occurring in t he coals. During the coal combustion process at the coal-fired power plants me rcury is released from its bound state into the environment. To manage effectively the stack gas cleaning process, it is necessary to know a comprehensive pattern of mercury content in the fossil fuel, stack gases, and liquid and solid waste (fly ash, bottom ash, boiler slag, FGD products).

Getting this info rmation is a complicated analytical problem, because the mercury content in coals and combustion products ma y vary greatly. In some regions of Russia, China, USA, India, and other countries, ther e exist coal-fields with anomalous high content of mercury (up to 15 ppm). Standard methods of mercury determination in coal usin g atomic absorption spectrometry (ASTM D6414-01 (2006) and ISO 15237:2003) involve preliminary digesti on of the sample that takes from 0.5 to 8 hours depending on the digestion conditions, followed by t he quantitative measurement using Cold Vapor AAS.

Alternative methods for coal anal ysis (ASTM D6722-01(2 006) and EPA 7473) propose a simpler analysis procedure, namely, thermal decomposition of the samp le combined with catalytic conversion, amalgamation and quantitative determination by AAS. The use of an RA-915+/RA-915M analyzer with a PYRO-915+ pyrolytic attachment provides direct determination of mercury in coal without digestion and intermediate amalgamation.

MEASURING METHOD

This method of mercury determination in coal is based on the atomization of mercury contained in the sample in a PYRO-915+ attachment and subsequent mercury dete rmination by flameless AAS in a mercury analyzer RA-915M/RA-915+. The two-section atomizer PYRO-915+ consists of evaporator, in which evaporation of liquid samples and pyrolysis of solid samples are carried out, and of the heated reactor, in which catalytic destruction of the sample matrix compounds proceeds.

After the furnace, the gas flow heated to 700 °C enters directly the analytical cell, which is heated up to 750 °С. The interference from the remaining impurity compounds is eliminated due to the high selectivity of the RA-915M/RA-915+ analyzer with the Zeeman background correction. The analysis procedure has been developed by LUMEX engineers.