Improvements to Existing Overfire Air Systems for IED Compliance

摘要

Utilities have been responding to the IED requirements to reduce NOx emissions below 200 mg/Nm~3, and are under increasing pressure from the pending BREF requirements to make further reductions. Many power plants have already installed low-NOx burners (LNB) and/or implemented deeper combustion staging by the addition of conventional overfire air (OFA), or close-coupled overfire air (CCOFA) and separated overfire air (SOFA) systems. This combination of controls is rarely able to meet the IED NOx limits, and tends to result in an increase in products of incomplete combustion. Utilities are then faced with the prospect of having to install costly post-combustion control systems, such as SCR. However, the application of rotating opposed-fired air (ROFA) systems have demonstrated the ability to significantly reduce NOx emissions below what was achieved with combinations of LNB, CCOFA and/or SOFA, or standard OFA for wall-fired units. This paper will present the results of two projects in which ROFA was installed on units with existing CCOFA and SOFA, and achieved further NOx reductions approaching 40%.