Principle, calibration, and application of the in situ alkali chloride monitor

Abstract

The extended use of biomass for heat and power production has caused increased operational problems with fouling and high-temperature corrosion in boilers. These problems are mainly related to the presence of alkali chlorides (KCl and NaCl) at high concentrations in the flue gas. The in situ alkali chloride monitor (IACM) was developed by Vattenfall Research and Development AB for measuring the alkali chloride concentration in hot flue gases (less than or approximately 650 degrees C). The measurement technique is based on molecular differential absorption spectroscopy in the UV range. Simultaneous measurement of SO(2) concentration is also possible. The measuring range is 1-50 ppm for the sum of KCl and NaCl concentrations and 4-750 ppm for SO(2). This paper describes the principle of the IACM as well as its calibration. Furthermore, an example of its application in an industrial boiler is given.

Development of an alkali chloride vapour-generating apparatus for calibration of ultraviolet absorption measurements

“…Uncertainties due to salt losses, non-uniform temperature profile, and pressure build-up in the previous calibration 023112- 8 Leffler et al…”

“…The differences are significantly higher than the uncertainties estimated for the cell vapour pressures as described above and are probably related to the original calibration procedure on which the absorption evaluation is based. 8 In the evaluation, the measured spectrum is fitted to a calibration spectrum measured during continuous evaporation of a certain mass of KCl transported through a calibration cell placed in a furnace. 8 Possible sources of error are salt losses during transport to the cell, a non-uniform temperature profile in the furnace, and pressure build-up in the calibration cell.…”

“…8 In the evaluation, the measured spectrum is fitted to a calibration spectrum measured during continuous evaporation of a certain mass of KCl transported through a calibration cell placed in a furnace. 8 Possible sources of error are salt losses during transport to the cell, a non-uniform temperature profile in the furnace, and pressure build-up in the calibration cell. During operation of this previous calibration equipment it has been noticed that absorption spectra on occasion show traces of previously measured compounds, which indicates that salt vapour can stick to the walls of the tube, which transports a gas-mixture of N 2 and vaporized KCl to the measuring chamber.…”

“…For example, there might be insufficient data for relevant species such as an absorption cross section for potassium hydroxide as reported by Sorvajärvi et al 5 New techniques developed for flue gas measurements, such as the LIDAR concept for KCl detection, 6 also require calibration for a) Electronic mail: tomas.leffler@forbrf.lth.se accurate quantitative measurements. Moreover, extension of instruments based on broadband absorption such as the in situ alkali chloride monitor (IACM) 7,8 to incorporate additional alkali species also call for the possibility to measure well-defined reference spectra. There is thus a demand for development of a suitable calibration cell to produce spectra of different alkali compounds under well-controlled conditions that can subsequently be used to carry out reliable quantitative determination of concentrations.…”

“…Grosch et al 9 have developed a high-temperature open flow cell for reactive gases at temperatures up to 530 • C. This flow cell allows for highresolution spectroscopic measurements in the ultraviolet (UV) and infrared (IR) spectral regions (190-20 000 nm). Vattenfall Research and Development AB has developed and patented an in situ alkali chloride monitor (IACM) 7 based on UV absorption and designed a calibration cell 8 for this instrument. This calibration cell operates at atmospheric pressure where solid potassium chloride is vaporized at 781 • C and the KCl vapour is subsequently diluted with N 2 and transported to a measuring chamber.…”