Reduction of main steam temperature deviation in a tangentially coal-fired, two pass boiler

This paper describes the main steam temperature deviation and its reduction by changing the injection angles of over-fire air in a 800 MW, tangentially coal-fired, two pass boiler. The CFD simulation showed that the simulated gas temperatures and velocities in the furnace are well matched with the steam temperatures along the steam pathways and the tube metal temperatures of the heaters. The changes in injection angles of over-fire air clearly affect the temperature and flow fields in front of the final superheater, in turn, the main steam temperatures at the final superheater outlet. With the findings of the CFD simulation and the relevant plant data, the field tests to reduce the deviation were performed by changing the yaw and tilt angles of Separate Over-Fire Air (SOFA) and Closed Coupled Over-Fire Air (CCOFA). The field tests showed that, under the optimized injection angles of SOFA and CCOFA, the main steam temperature deviation was reduced from 27 °C to 9 °C and the reheat steam temperature was increased to the desired value.