Experimental Study on Online Measurement of Unburned Carbon in Pulverized Fuel Boilers by Thermal Oxidation of Ash

Abstract

The unburned carbon (UC) in the ash in Indian power plants is presently measured offline by manually collecting the samples and analyzing it by loss on ignition or thermogravimetric analysis methods. The manual collection and offline analysis of samples take 6-8 h. By this time, the existing operating conditions of the boiler may be different from the conditions when the samples were collected. The combustion optimization and corrective maintenance activities can be performed immediately by plant operation and maintenance team if the UC values are available online along with furnace flame intensity and the percentage of CO in flue gases at economizer outlet. The presence of high amounts of the UC in ash decreases the boiler efficiency and reduces the utilization of ash in cement industries. In this paper, 20 ash samples were collected from five Indian thermal power plants of range 150-500 MW. An experimental setup has been developed for the measurement of the UC using the percentages of CO2 and CO obtained by thermal oxidation of ash. The experimental results were compared with the laboratory results. The maximum deviation between experimental and laboratory results was within the range of ± 0.30. The percentages of the UC is more accurate when CO2 and CO both are considered in comparison to the present existing online measurement based on CO2 only.

Keywords

• Carbon loss
• unburned carbon
• pulverized fuel boiler
• bottom ash
• fly ash