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Design and Analysis of a Combined Rankine Cycle for Waste Heat Recovery of a Coal Power Plant Using LNG Cryogenic Exergy

Author:
Lee, Ung, Park, Keonhee, Jeong, Yeong Su, Lee, Sangho, Han, Chonghun
Source:
Industrial & Engineering Chemistry Research 2014 v.53 no.23 pp. 9812-9824
ISSN:
1520-5045
Subject:
ambient temperature, carbon dioxide, coal, cold, combustion, energy use and consumption, engineering, evaporation, exergy, heat recovery, liquefaction, liquefied natural gas, power generation, power plants, refrigeration, seawater, steam, wastes
Abstract:
In this study, a combined Rankine cycle was modeled and optimized. This process consists of a coal combustion unit, a steam cycle, a CO₂ capture process, a gas conditioning process, and a CO₂ organic Rankine cycle (ORC). This process is able to extract additional power without consuming additional fossil fuel by integrating the CO₂-ORC with the steam cycle and a liquefied natural gas (LNG) evaporation process. Unlike conventional ORC, the CO₂-ORC utilizes the low grade waste heat only for super heating of working fluid, while the main evaporation process is achieved by seawater. The CO₂ condensation process in the ORC takes place at a temperature lower than the ambient temperature by coupling with the LNG evaporation system as a cold sink. Furthermore, a fraction of liquefied CO₂ is purged for the sequestration. Therefore, CO₂ liquefaction can be achieved without an additional refrigeration cycle. This process not only produces more power with the same fuel consumption but also reduces CO₂ removal energy. The gross power is increased from 42.21 to 90.54 MWₑ compared with the conventional power plant, and total CO₂ removal energy is decreased about 9%. The optimum design and operating conditions were also obtained through parameter sensitivity analysis. The power reduction of the proposed process resulting due to the CO₂ capture process installation was identified as 19.3%. However, the net power generation is about 73% higher than that of the conventional power cycle even without CO₂ capture.
Agid:
5377202