Flow measurement of five seal air pipes at a coal mill using the heater method at a coal fired power plant and numerical analysis of one of the pipes with curvature

Abstract

High efficiency coal fired power plants are expected to operate at a certain rate due to low generated electricity costs. In coal fired power plants, coal mills are important machinery that pulverize the coal and supplies the coal powder to the boiler. To protect the bearings from coal dust, seal air is added. The seal air is supplied from one air compressor to each position of several coal mills at a target power station. An imbalance in its flowrate can lead to coal mill failures, thereby affecting the operation of coal fired power plants. In order to diagnose any problems with the operation of a coal mill immediately after maintenance, the heater method was used to measure the seal air at five locations from the outside of the supply pipes. The heater method is possible to measure the flow rate of compressed air and steam in the pipes from the outside of the pipes without any modification of the pipes, and has previously been applied to the measurement of cooling air flow in gas turbines. In the present case, three pipes out of five measuring points have curvature, so that a numerical analysis was carried out to verify whether the heater method is valid. Due to the effects of the corona disaster and other work, the measurement schedule at the power station was restricted and the installation, measurement and removal of instruments at five locations was carried out in a period of five days. As a result, it was confirmed that the seal air flowrate at each of the coal mill locations was normal value and that there were no problems with operation.