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Publication Title | Low Heat Power Generation System

Organic Rankine Cycle

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CHEMICAL ENGINEERING TRANSACTIONS VOL. 35, 2013

Guest Editors: Petar Varbanov, Jiří Klemeš, Panos Seferlis, Athanasios I. Papadopoulos, Spyros Voutetakis Copyright © 2013, AIDIC Servizi S.r.l.,

ISBN 978-88-95608-26-6; ISSN 1974-9791

A publication of

The Italian Association of Chemical Engineering www.aidic.it/cet

DOI: 10.3303/CET1335037

Low Heat Power Generation System

Kazuo Matsuda

Chiyoda Corporation, Sustainable Business Development Section, 4-6-2, Minatomirai, Nishi-ku, Yokohama, 220-8765, Japan

kmatsuda@ykh.chiyoda.co.jp

Statistically low-grade heat below about 150 °C, which is the temperature range of waste heat emitted by industry, has so far not usually been recovered and utilized. A large amount of such unused heat is either exhausted to the atmosphere, discarded to cooling water or otherwise lost. When thermal engines such as the Rankine and Kalina cycles are used to generate power from low-grade heat, the second law of thermodynamics binds the conversion efficiency of low temperature heat into work or electricity. The Kalina cycle could achieve higher efficiency in producing acceptable power at the given process conditions than the Rankine cycle because it used a high concentration ammonia-water mixture as a secondary fluid and could be fitted to the falling temperature of a heat source with a finite heat capacity. A low heat power generation (LHPG) system based on the concept of the Kalina cycle has been successfully developed and implemented in Japan.

The overhead vapor from the fractionator was originally cooled down from about 120 °C by many air-fin coolers and further cooled by cooling water coolers but now, instead of the low-grade heat generated by the existing system being discarded to atmosphere or water as waste heat, the LHPG system can utilize such heat as the hot heat source to generate power. The LHPG system has sturdy and reliable performance and, even with a heavily fluctuating heat source, is under stable and safe operation. Introduction

The conversion of the fossil fuel into useful work by combustion and thermal engine is subject to the fundamental laws of thermodynamics, which severely limits the efficiency of such unit’s operation and results in emission of low-grade heat. Many types of low-grade heat remain unused and discarded in industry where a large amount of heat exists in the range of 100 to 150 °C among other heat range. Such low-grade heat is usually exhausted to atmosphere or discarded through coolers by paying cost. However it has a possibility to be transformed to electricity by using a thermal engine such as the Rankine and the Kalina cycles which are binary systems, so called because they use a second fluid that is heated by the hot heat source. Handayani et al. (2012) reported that in organic Rankine cycle (ORC), ammonia and isobutane had the highest thermal efficiency at 90 °C evaporation temperature among other working fluids

Evaporator

Hot Heat Source

Turbine Generator G

Condenser

P Low Heat

Hydraulic Source Working Pump

Evaporator

Hot Heat Source

Separator

Regenerator

Reducing Valve

P Hydraulic Working Pump

Turbine Generator G

Absorber Condenser

Low Heat Source

Figure 1: Rankine cycle

Figure 2: Kalina cycle

Please cite this article as: Matsuda K., 2013, Low heat power generation system, Chemical Engineering Transactions, 35, 223-228 DOI:10.3303/CET1335037

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