Continuous Monitoring of Toxic Metals in Gas Flows Using Direct-Current Plasma Excited Atomic Absorption Spectroscopy

Abstract

A measurement apparatus employing direct current (dc) plasma excited atomic absorption spectroscopy was developed and demonstrated for continuous measurement of toxic metals in process gases. Process gas is continuously sampled along a heated sample line. Metal compounds contained in the gas are thermally decomposed by mixing the gas with a plasma jet produced with a dc nitrogen plasma torch. Transmission of monochromatic light is measured through the gas jet, and absorbance caused by metal atoms is distinguished from the background by means of the Zeeman effect. The metal concentration in the sample gas is calculated from the measured absorbance with the known dilution and decomposition factors taken into account. The detection limits of the current prototype are 0.04 mg/m3 for cadmium and 0.4 mg/m3 for lead. The measurement accuracy is better than 20%, and the maximum measurement rate is about 100 values per minute. The instrument was designed to withstand wet, corrosive, and particulate-laden flue gases at temperatures up to 1100 °C. The instrument can also be used, after minor modification, for measurements at pressurized conditions. The performance of the instrument was demonstrated in connection with a real fluidized bed combustor.

On-Line Detection of Vapor-Phase Copper Species by Plasma-Excited Atomic Absorption Spectroscopy

“…The experimental arrangement was the same as reported previously 4 except that a conventional Cu hollow cathode lamp from Hamamatsu was used as a reference light source and the magnetic eld across the gas jet was varied between zero and 0.88 T. In direct current plasma torches, copper is a typical material of the plasm a nozzle due to its high therm al conductivity. In this work we also used the copper plasma nozzle in the beginning.…”

“…In a previous paper a new on-line toxic metal analyzer developed by two of the authors was introduced. 4 So far, the analyzer has been used for detection of cadmium and lead in combustion processes. 5 In the present work we have studied the applicability of the analyzer to the detection of Cu species in industrial process gases.…”

Continuous Monitoring of Alkali Metals in Gas Flows Using Direct-Current Plasma Excited Atomic Spectroscopy

“…The signals transferred by individual bers are combined and coupled to the monochrom ator slit using a short piece of f 1 mm ber. (A better coupling ef ciency can be achieved using an arranged ber; 13 however, the signal level is not critical in the present application.) The monochromator is a Czerny-Turner type grating instrument (Lomo MDR-23) with 0.6 m focal length and 1200 grooves/mm.…”

“…The principle of the PEARLS m ethod was reported in 1996 assuming chemical equilibrium in the hot gas jet. 12 Since then, a modi cation of the method dedicated to the measurem ent of heavy metals was developed, 13 which is based on a hollow cathode lamp and Zeeman background correction. 14 In the case of the alkali metals, the measurement is based on the use of a broadband light source, which allows a m ore rugged and simple construction, also capable of operation at elevated pressures.…”

Frequency-doubled diode laser for ultraviolet absorption spectroscopy at 325 nm

“…17 Copper atoms were produced in three different environments: a hollow cathode lamp, a butane burner, and a direct current plasma jet of an on-line heavy metal analyzer. 18 The hollow cathode lamp ͑Hamamatsu L2783-29He-Cu͒ was a see-through-type discharge lamp. In the diffusion flame of the small butane burner and in the direct current plasma jet copper atoms were produced by feeding copper chloride powder into the sample region.…”