A detailed evaluation of the combustion air system in a kraft recovery boiler

Procedures and specialized measurement tools have been developed for evaluating and optimizing the combustion air systems of recovery boilers. Measurements include the combustion air supply distribution on all walls at each level, velocity profiles under cold flow conditions, and temperature profiles in the boiler under operating conditions. We have recently introduced a novel velocity probe which, for the first time, permits the determination of boiler velocity profiles during fossil fuel and liquor firing. In this report, measurements on a recovery boiler are used to illustrate how a combustion air system can be evaluated. This boiler offered a unique opportunity to gather velocity data between the tertiary air levels and bullnose, due to the presence of a network of port openings at this level. Unbalanced air distribution in the operating boiler resulted in a high velocity chimney pushed toward the front left corner of the boiler. Differences in flow behaviour under cold flow and operating conditions underline the importance of collecting hot-flow data. Non-uniformities in the boiler were very significant and increased the propensity for carryover and plugging. Detailed suggestions for air system adjustments were made which should reduce the carryover and plugging tendency, even with liquor firing rates increased by 7-8 %.