Optical pyrometric measurements of surface temperatures during black liquor char burning and gasification

Abstract Surface temperatures of single black liquor droplets in high temperature furnace environments were measured using a two-colour optical pyrometer with a quartz optical fibre probe. The experimental conditions were 750–900 °C and in oxidizing and gasifying environments. Surface temperatures were calculated based on measurements at 650 and 1050 nm using an algorithm which accounted for reflection of radiation from the particle surface. The method gave reliable temperatures under combustion conditions during char burning. The droplet temperature during this period reached a maximum which depended upon droplet size and oxygen content. The flame which appeared during the early part of the devolatilization stage apparently contained enough soot particles to obscure the droplets; this resulted in unreliable indicated temperatures. The indicated surface temperature during the latter half of devolatilization was probably closer to the actual surface temperature, but may have been influenced by the combustion of volatile gases near the particle surface. The surface temperature during drying was too low relative to the surrounding furnace temperature to be measured.