Mass flow and particle size monitoring of pulverised fuel vertical spindle mills

Abstract

The first step towards condition based maintenance of the milling plant is the implementation of online condition monitoring of the mill. The following paper presents and analyses methods of monitoring the key performance factors of a vertical spindle mill that is suited for implementation on older power stations, i.e. the quantity (mass flow rate) and quality (particle fineness) of the pulverised fuel produced by the mill. It is shown herein that the mill throughput can be monitored on-line using a simple mill energy balance that successfully predicts the coal throughput within 2.33% as compared to a calibrated coal feeder. A sensitivity analysis reveals that the coal moisture is a critical measurement for this method to be adopted as an on-line mass flow monitoring tool. A laser based particle size analyser tool was tested for use in the power plant environment as an online monitoring solution to measure pulverised fuel fineness. It was revealed that several factors around the set-up and operation of the instrument have an influence on the perceived results. Although the instrument showed good precision and repeatability of results, these factors must be taken into account in order to improve the accuracy of the reported results before the instrument can be commissioned as an on-line monitoring solution.

Wood pellet milling tests in a suspension-fired power plant

“…The isokinetic sampling method could also explain these differences. Archary et al [55] found that sampling coal at the center of vertically oriented burner pipes resulted in a higher concentration of coarse comminuted particles, while the fine particle fraction moved near the pipe wall. Hence, a coarser PSD of the comminuted I2 pellets may lead to an even higher concentration of coarser particles at the inner part of the pipe that is collected by the isokinetic sampling device.…”