Stack temperature is the most important parameter to monitor and control since it alone contributes to five different losses of boiler. The first question that should be asked is ‘how do we monitor it’? This parameter changes with load as well as fuel CV and both these factors vary frequently in most boiler systems. Therefore, how to identify when the stack temperature has increased due some system anomalies that can be corrected or controlled?

My suggestion would be to maintain a separate log sheet for this parameter against load and CV. When we notice a significant increase in stack temperature against similar load and CV characteristics, we need to start worrying.

Then again, should we operate LRSB as a corrective measure? This happens to be the common practice in most power and utility boiler systems. Stack temperature may increase if there is fouling in APH. It may increase if we are having low moisture coal in PF Boiler. It may increase if the CAD is passing. It may also increase if the economizer is fouled. It would definitely increase if we are using higher than required air. Would LRSB operation rectify these problems?

Unless we are suffering from slagging and fouling issues, LRSB operation should be done only after elimination of all these possibilities by step by step diagnosis of boiler parameters.