A Surface Ionization Instrument for On-Line Measurements of Alkali Metal Components in Combustion:  Instrument Description and Applications

Abstract

An instrument for on-line measurements of alkali components in hot flue gas streams is presented. The instrument is based on surface ionization technique and is equipped with a hot sampling line used to extract flue gas for continuous alkali measurements at pressures up to 30 bar. The instrument, its support system and the calibration procedure is described. Field campaigns with the instrument have been performed at fluidized-bed combustion facilities operating under pressurized and atmospheric conditions and using several fuels, including coal, biomass, and demolition waste. The instrument performance has been satisfactory both during pressurized circulating fluidized-bed coal combustion with alkali concentrations downstream of a hot gas filter in the ppb range, and in particle-laden conditions with alkali levels up to about 10 ppm. The measured alkali concentration corresponds to the concentration of alkali components present as vapors and fine-mode particles. In systems with high levels of fluidized-bed material or fly ash, a contribution to the signal from alkali bound to coarse particles is also expected. Under these conditions, the instrument is suggested to be operated in a pulse counting mode where the concentration of coarse particles can be estimated. The instrument is concluded to provide a durable, sensitive, and reliable alkali measurement method with a high time resolution and with a lower detection limit of around 1 ppb, which should be suitable for a large range of applications.

Transmission of Alkali Aerosols through Sampling Systems

“…This principle has been used successfully for the detection of alkali aerosols [30][31][32]. The main component of the SID is a platinum filament heated to a temperature of 1200°C.…”

“…The latter is given as 5.65 eV [30,[33][34][35]. For potassium atoms, the ionization probability is greater than 99 %.…”

“…The SID is constructed similar to the one in [30] and described in detail in [27]. The platinum (purity 99.98 %) used for the filament was purchased from Johnson-Matthey.…”

Mass Spectrometric Methods for Arosol Composition Masurements

“…This technique, known as surface ionisation, is used in some modern instruments such as the SI-PBMS. Its advantage is that it yields large numbers of ions and is very useful for the quantitative study of specific inorganic components of aerosol particles, in particular the alkali elements (Davidsson et al, 2002;Jäglid et al, 1996). This makes the instrument very useful for the study of sea-salt based particles, in particular.…”

Improving Heat Recovery In Biomass-Fired Boilers

“…Most subsequent Vattenfall publications about this approach focused on results obtained with ammonium sulfate. The system, marketed as ChlorOut ® [37], uses the concentration of alkali vapors and fine particles in the flue gases measured by an on-line surface ionization technique [38] to control the addition of ammonium sulfate. The alkali sensor can measure concentrations as low as about 1ppb and as high as about 10ppm.…”