SELECTION AND OPERAT ION OF VARIABLE SPEED BOILER FEED PUMPS IN A TRIPLE PRESSURE COMBINED CYCLE PLANT

摘要

This paper discusses various issues that pertain to the proper selection and operation of variable speed boiler feed pumps in a combined cycle plant equipped with a triple pressure boiler. There are numerous selection criteria to be met in order to achieve the best operational efficiency with variable speed pumps. In addition, it is imperative that all cases of operation be analyzed to ensure proper pump selection. The triple pressure Heat Recovery Steam Generator (HRSG) is typically found in the combined cycle plant. Unlike its fossil fired predecessor, it requires a high component flow through each section of the HRSG. By far the most difficult choice when selecting the boiler feed pump for the boiler arrangement is how to balance the pressure and flow requirements of each section of the boiler with the pressure requirements that result from varying loads on the plant. The primary benefit of the variable speed pump is economy of operation at reduced load, yet this is also the very issue that makes selection difficult. Each pressure component of the HRSG has varying requirements that are non-linear with plant demand. A secondary but less tangible benefit from variable speed operation is improved life of system components, with the most significant benefit relating to the main feedwater control valve.