Abstract: Based on debugging and testing data, the issues of low main steam temperature and low reheat steam temperature existing in the tangentially-fired boilers after low NOx combustion reform are analyzed, which concludes that the boiler heat distribution moving towards the water walls after the reform is the main cause for the excessively low main steam and reheat steam temperatures. Moreover, the heat distribution shifting is caused by the new separated over-fire air(SOFA) that increases the oxygen content of burn-out zone, leading to a significant rise of burning rate. Meanwhile the secondary air flow redistribution caused by SOFA makes the burning rate in the primary combustion zone shift from smooth change to rapid change with oxygen content. After the reformation of low NOx combustion technology, the primary combustion zone and the burn-out zone both lie in the rapidly changing range of the burning rate with oxygen content. In this range, the change of oxygen content will have significant effect on boiler heat distribution, and consequently, some key parameters including the steam temperature and pressure and the water level in the drum fluctuates widely.

Key words: tangentially-fired boiler, low NOx combustion technology, heat distribution, burning rate, steam temperature