Waste Heat and Water Recovery System Optimization for Flue Gas in Thermal Power Plants

Syed Shamsi,Assmelash Negash,Gyu Cho,Young Kim

doi:10.3390/su11071881

Syed Shamsi, Assmelash Negash + Show 2 more

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https://doi.org/10.3390/su11071881

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Abstract

Fossil-fueled power plants present a problem of significant water consumption, carbon dioxide emissions, and environmental pollution. Several techniques have been developed to utilize flue gas, which can help solve these problems. Among these, the ones focusing on energy extraction beyond the dew point of the moisture present within the flue gas are quite attractive. In this study, a novel waste heat and water recovery system (WHWRS) composed of an organic Rankine cycle (ORC) and cooling cycles using singular working fluid accompanied by phase change was proposed and optimized for maximum power output. Furthermore, WHWRS configurations were analyzed for fixed water yield and fixed ambient temperature, covering possible trade-off scenarios between power loss and the number of stages as per desired yields of water recovery at ambient temperatures in a practical range. For a 600 MW power plant with 16% water vapor volume in flue gas at 150 °C, the WHWRS can produce 4–6 MWe while recovering 50% water by cooling the flue gas to 40 °C at an ambient temperature of 20 °C. Pragmatic results and design flexibility, while utilizing single working fluid, makes this proposed system a desirable candidate for practical application.

Highlights

Power plants that utilize fossil fuels, such as coal, pose fuel consumption problems, resulting in higher CO2 emissions, significant water consumption and hazardous gas emissions
The characteristics of the system were analyzed for constant water recovery yield and thereafter for constant ambient temperature conditions, providing power output behaviors and the effect that the range of ambient temperature and water recovery yield had on the capital cost in terms of system stages
Other than the water being used for the primary purposes of cooling and condensing hazardous gases, water recovery itself reduces the incidence of white plumes and smog around the power plant, since the high humidity flue gas prevents pollutant diffusion, which promotes secondary air pollutant transformation, and contributes to smog

Summary

Introduction

Power plants that utilize fossil fuels, such as coal, pose fuel consumption problems, resulting in higher CO2 emissions, significant water consumption and hazardous gas emissions. Utilization of waste heat recovery from the flue gas of power plants leads to its condensation and can be a simultaneous solution for the problems mentioned above. Many studies are being conducted to find ways to utilize flue gas to reduce carbon footprints; these include employing it in the synthesis of methane and ammonia [1], as well as investigations focusing on waste heat recovery and utilization. Some studies focus on the reuse of exhaust gases for co-generation [2] and the use of this energy for pre-drying in coal power plants, which increases the thermal efficiency of the system by approximately 2% [3]. Investigations are being conducted to utilize the harvested power by using smart and efficient grid and electrical distribution systems which can reduce the power loss at the consumer end [10,11]

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