Optoelectronic system of on-line measurements of unburned carbon in coal fly ash

Carbon-in-ash level is an important consideration for combustion efficiency as well as ash marketing. The optoelectronic analysing system for on-line determination and monitoring of the unburned carbon content of ash samples is presented. The apparatus operates on the principle (Kubelka-Munk law) that carbon content is proportional to the reflectance of infrared light. Ash samples are collected isokinetically from the flue gas duct and placed in a sample tube with a flat glass bottom. The sample is then exposed to a light. The reflectance intensity is used by the system's computer to determine residual carbon content from correlation curves. The sample is then air purged back to the duct or to the attached sample canister to enable laboratory check analysis. The total cycle time takes between 5 and 10 minutes. Real time results of carbon content with accuracy 0.3-0.7% are reported and can be used for boiler controlling.