A Case Study of How Vertical Spindle Pulverizer Performance is Related to Overall Plant Performance

Pulverizer performance optimization is the first step to a successful combustion optimization program and the inter-relationships of the pulverizers must be considered when attempting to optimize combustion, overall unit performance, operability, reliability, and capacity. Pulverizer capacity seems to be an industry challenge while many units today are undergoing drastic fuel changes. Considering there seems to be a huge disconnect when correlating mill performance with such issues as fuel line distribution, heat rate, NO_x and environmental control equipment performance, it is the intent of this technical paper to provide better understanding of how mechanical optimization & tuning of the pulverizers can yield overall improved plant performance. Low NO_x firing and/or optimization of the burner belt combustion with a limited amount of furnace residence time is absolutely essential to optimizing plant performance. For example, when pulverizer performance is poor, it is also often related to not only high furnace exit gas temperatures, increased slagging and/or high LOI, but also degrading electrostatic precipitator (ESP) performance from the coarse particle ash. Furthermore, reliability of the boiler (ie. tube leaks, fouling, and slagging) can also be impacted negatively by secondary combustion and consequent super heater and re-heater tube metals overheating and/or wall wastage often occurs from non-optimized fuel distribution being delivered from the pulverizers. Whether the reason for improving mill performance is for the aforementioned items and/or perhaps simply to reduce power generation costs with improved fuels flexibility, the purpose of this case study is to review the basics of vertical spindle mill performance improvements. The data used to support this paper is from a compilation of actual field testing & tuning results. Furthermore, Storm Technologies, Inc. (STI) suggests the aforementioned steps as an effective approach to optimization.