Measuring and calibrating flow rate of primary air for medium speed mills by numerical simulation

The numerical model is built for the primary air duct of the pulverizing system with medium speed mills, and the inner flow fields are simulated by employing the commercial code of FLUENT. The simulated results show that the lengths of the straight ducts before and behind the measuring element are too short to meet the requirement of the flow rate measurement of the primary air due to the compact design in many domestic power plants. The actual flow at the cross section where the measuring element is installed is irregular and disordered and the air velocity obtained by the single measuring element is not the area-weighted average value. The blowing of cool primary air also aggravates the disorder of the flow fields. It is concluded that the flow rate of the primary air can not be measured precisely. The numerical simulation method could be adopted to measure and calibrate the flow rate of the primary air, which can avoid the limitations of the existing method. This solution could improve the precision and reduce the cost of the measurement, which will be a good alternative for the domestic power plants.