Closed centrifugal compressor impellers have been manufactured using several methods through the years. Due to limitations of the materials and machining processes, most of these impellers have been manufactured in what is considered two piece or three piece methods. Despite the vast amount of experience with traditional construction methods, there is a drive to move towards one piece construction, where there are no joints and, in theory, lower probability of preexisting defects. Typically, the impellers that are being offered as one piece are those with relatively large openings where 5-axis milling machines can be utilized. This paper investigates several alternative methods to manufacturing small tip opening impellers as a single piece. The methods discussed include Electrical Discharge Machining (EDM), investment casting, Hot Isostatic Pressed Powder Metal (HIP’d PM), and Direct Metal Laser Sintering (DMLS).
Abstract
sCO2Flex (Horizon 2020 grant agreement #764690) is a project that involves a consortium of several EU public and private partners. Within this program, the consortium addresses the necessities to upgrade existing fossil fuel plants to integrate renewable energy sources increasing the overall efficiency in power generation plus avoiding the use of water. Deliverable of the project is the development and validation of all main components of a sCO2 Brayton cycle capable to provide 25MWe at 100% load ensuring a wide plant flexibility (from 100% to 20% of the electrical load). Moreover, it includes testing of a centrifugal compressor prototype. The present work will describe several new challenges faced by original equipment manufacturer (OEM) during the design of turbomachinery for this application. The first is linked to the operating conditions of the main compressor, which achieves the highest cycle efficiency in a region close to the CO2 critical point. In these conditions, possible co-existence of different phases may occur with sudden change of speed of sound causing uncertainties in performance predictability. To minimize these uncertainties and at the same time fulfil loop flexibility needs, specific design for compressor internals was adopted and will be discussed in this article. The present work will conclude with highlights on the full size 5 MW prototype compressor that was manufactured and tested in OEM test facility in Q2 2021. The test replicated exactly the nominal operating conditions, specifically vicinity of the compressor suction to CO2 critical point. This has enabled a direct validation of compressor performance predictability and at the same time allowed to verify the compressor rotordynamic, mechanics and aerodynamic behavior.
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Citation
Milani, Alberto; Bellobuono, Fulvio; Bigi, Manuele; Dozzini, Matteo; Evangelisti, Silvia; Vannini, Giuseppe (2022). Closed centrifugal compressor impellers have been manufactured using several methods through the years. Due to limitations of the materials and machining processes, most of these impellers have been manufactured in what is considered two piece or three piece methods. Despite the vast amount of experience with traditional construction methods, there is a drive to move towards one piece construction, where there are no joints and, in theory, lower probability of preexisting defects. Typically, the impellers that are being offered as one piece are those with relatively large openings where 5-axis milling machines can be utilized. This paper investigates several alternative methods to manufacturing small tip opening impellers as a single piece. The methods discussed include Electrical Discharge Machining (EDM), investment casting, Hot Isostatic Pressed Powder Metal (HIP’d PM), and Direct Metal Laser Sintering (DMLS).. Turbomachinery Laboratory, Texas A&M Engineering Experiment Station. Available electronically from https : / /hdl .handle .net /1969 .1 /197039.
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