A Portable Calibration Gas Generator for H2O, HCl, NH3 and Mercury

Abstract

The calibration of emission measurement systems for water vapor, hydrogen chloride, ammonia and mercury is difficult and span gas is not available for every component. On the principle of the dynamic evaporation of liquids and the continuous addition of carries gas, a portable calibration gas generator was developed. Linearity, accuracy and the reproducibility is comparable with the quality of certified cylinder span gas or even better. Besides a number of advantages over existing calibration methods, the system provides a calibration gas with similar constitution as flue gas especially for water content. Mercury chloride has been investigated up to a concentration of 150 μg/m³. Besides carrier gas flow variation, also time constant and the speciation of mercury under the influence of evaporator temperature has been examined.

Introduction

The calibration of emission measuring systems for H2O, HCl, NH3 and mercury shows a few difficulties: H2O is not available as test gas up to the required concentrations and the handling of HCl needs appropriate experience [1]. The wall adsorption effects of HCl, NH3 and also HF even on heated surfaces of gas feeding components result in time lag, a dragging running behaviour and deviations of the reading, especially at lowconcentrations. Mercury as Hg° is available as test gas. But it is known, that the behaviour of HgCl2 is completely different in terms of adsorption [2]. Moreover Hg° test gas is only suitable to check the photometer
of the Hg-emission measuring system, but not the sample conditioning system. This demand has led to the development of the calibration gas generator HOVACAL.