Laser-based technique for continuously monitoring metal emissions from thermal waste treatment units

摘要

The authors describe the development of an advanced continuous emissions monitor for measuring metals contained in the effluent from thermal waste treatment units. The monitor is based on a measurement technique known as LAser-Spark-Spectroscopy (LASS), in which a focused pulsed laser is used to rapidly heat material contained in the focal region, producing a plasma (or laser ''spark'') that contains excited-state atoms and ions. Spectrally resolved measurements of optical emission from the plasma are used to identify and quantify the elements that are present. The LASS technique can measure atomic species embedded in solid or liquid aerosols, in addition to vapor-phase species. Thus, the technique is particularly well-suited for measuring metals in thermal-waste-treatment effluent, in which a large percentage of the metals are found in aerosol form. Experimental results presented here demonstrate that the LASS technique can be used to measure the eleven metals regulated under the Clean Air Act at levels typically permitted in the effluent from thermal waste treatment facilities. Measured detectability limits for these metals range from less than 0.1 (mu)g/scm for beryllium to 250 (mu)g/scm for lead. Also discussed are design considerations for a rugged, fieldable monitoring probe.