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Hindawi Publishing Corporation International Journal of Rotating Machinery Volume 2009, Article ID 718107, 12 pages doi:10.1155/2009/718107

Research Article

An Advanced Microturbine System with Water-Lubricated Bearings

Susumu Nakano,1 Tadaharu Kishibe,1 Tomoaki Inoue,2 and Hiroyuki Shiraiwa3

1 Energy and Environmental Systems Laboratory, Hitachi Ltd., Hitachi, Ibaraki 319-1221, Japan

2 Mechanical Engineering Research Laboratory, Hitachi Ltd., Hitachinaka, Ibaraki 312-0034, Japan 3 Engineering Division, Hitachi Engineering & Services Co., Hitachi, Ibaraki 317-0073, Japan

Correspondence should be addressed to Susumu Nakano, susumu.nakano.re@hitachi.com Received 12 May 2009; Revised 16 September 2009; Accepted 24 September 2009 Recommended by Kazuhiko Kawaike

A prototype of the next-generation, high-performance microturbine system was developed for laboratory evaluation. Its unique feature is its utilization of water. Water is the lubricant for the bearings in this first reported application of water-lubricated bearings in gas turbines. Bearing losses and limitations under usage conditions were found from component tests done on the bearings and load tests done on the prototype microturbine. The rotor system using the water-lubricated bearings achieved stable rotating conditions at a rated rotational speed of 51,000 rpm. An electrical output of 135 kW with an efficiency of more than 33% was obtained. Water was also utilized to improve electrical output and efficiency through water atomizing inlet air cooling (WAC) and a humid air turbine (HAT). The operation test results for the WAC and HAT revealed the WAC and HAT operations had significant effects on both electrical output and electrical efficiency.

Copyright © 2009 Susumu Nakano et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

1. Introduction

In the USA, electricity deregulation began at the end of the 1990s. With deregulation, distributed power generation apparatuses such as microturbines were expected to play an important role. Though a booming market for micro- turbines was anticipated early in the 2000s, this has not realized, partially due to complicated reasons related to regulatory barriers and partially due to reasons of their low efficiencies and high costs. Gas engines have often competed against microturbines. Comparing microturbines with reciprocating gas engines reveals that the former has lower NOx emissions, lower maintenance costs, less noise, and less vibration than gas engines do. Some effort has been put into improving their efficiencies (Parente et al. [1], Williamson and Luker [2], Tsuchiya et al. [3]). The lower maintenance costs of microturbines will be of great advantage in the near future. Microturbines have an electrical efficiency of 33% to 35% and half the maintenance costs of

gas engines which should make them sufficiently competitive with gas engines (Tsuchiya and Okamoto [4]).

A prototype for the next-generation microturbine system that will be able to satisfy the demand for high electrical efficiency and low maintenance costs has been developed for laboratory evaluation (Nakano et al. [5]). The final target of the present study was to develop a 150kW machine with an electrical output efficiency of 35%, which was expected to be more competitive with gas engines. The use of water-lubricated bearings contributes to electrical output efficiency because both bearing losses and auxiliary power consumption can be reduced. Water is the lubricant for the bearings in this first reported application in gas turbines (Nakano et al. [6]). The simplified Humid Air Turbine (HAT) cycle (Hatamiya et al. [7]) was applied to achieve the target. Some calculated results and component tests on water-lubricated bearings are presented in this paper, including load tests done on the prototype microturbine with its water-lubricated bearings. The load tests were carried out with and without WAC and HAT.

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