Main content area

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

Lee, Ung, Park, Keonhee, Jeong, Yeong Su, Lee, Sangho, Han, Chonghun
Industrial & Engineering Chemistry Research 2014 v.53 no.23 pp. 9812-9824
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
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.