A sustainable and innovative system design for carbon dioxide capture and steam condensation in thermal power plants

This doctoral thesis aims to reduce flue gas emissions and reevaluate carbon emissions from coal-fired thermal power plants through innovative methods with environmental and economic value. Within this scope, a novel system has been proposed to mitigate carbon dioxide (CO₂) emissions from thermal power plant flue gases and to develop a zero-waste technology. The performance of the proposed system has been analyzed in comparison with solvent-based carbon capture technologies and membrane systems in the literature, focusing on energy efficiency, environmental impacts, and long-term economic benefits. This innovative system is designed based on CO₂ liquefaction technologies operating under low temperatures and high pressures, integrating these processes into carbon capture and liquefaction systems for thermal power plant flue gases. The system enables the compression and liquefaction of CO₂ present in the flue gas and facilitates its reuse in a closed-loop cycle to create cold ambient conditions. Instead of using a separate cooler system for flue gas cooling, the system utilizes CO₂ cooled to -56.4°C directly within the flue gas. The advantages and disadvantages of this approach have been examined. This method provides a new utilization pathway for captured CO₂. The flue gas temperature (95°C) is reduced to 31°C, which is below the critical temperature for CO₂ liquefaction (31.1°C). The required CO₂ flow rate for flue gas cooling has been calculated as 713.5 kg/s. During the cooling of the flue gas with CO₂ and its reduction to 31°C, the water vapor in the flue gas will condense without requiring an additional condenser. The condensed water will be separated via a water collection, discharge, and storage system integrated into the flue gas cooling and CO₂ capture-liquefaction system. The flow rate of condensed water recovered from the flue gas is 13.28 kg/s, yielding an annual water recovery of 418,798.08 tons. The stored water will be reused for wetting the fly ash captured from the thermal power plant. The fly ash capture rate has been calculated as 9.6 kg/s, corresponding to an annual capture of 302,745.6 tons. Capturing fly ash, which has adverse effects on human health and the environment, not only mitigates these impacts but also provides a significant opportunity for supplying raw materials to certain industrial sectors. Particularly in industries such as cement and building materials, fly ash has a broad range of applications, potentially creating an additional revenue stream for thermal power plants. This contributes to both environmental sustainability and increased economic benefits. The energy requirement of the compressor used in the system has been identified as high (306.6 MW). However, integrating membrane technology and incorporating asurface-cooled boiler into the flue gas cooling chamber (ABG cooling chamber) holds the potential to significantly reduce energy consumption (by 14 MW). This integration enables the production of CO₂ with 100% purity, facilitating the expansion of its reuse areas and economic gains from market supply. These advantages not only offset the system costs but also demonstrate significant profitability, enhancing the economic sustainability of the system as an innovative investment model. As part of this study, the annual CO₂ emissions of 10,596,096 tons from thermal power plant flue gases have been analyzed. It has been calculated that approximately 481 million trees and 1,059,610 hectares of forest area would be required to offset this carbon emission. This area corresponds to 4.56% of Turkey's total forest assets and 1.4% of its total land area. Dedicating such an area solely to balance carbon emissions has been demonstrated to be neither ecologically nor economically sustainable, emphasizing the necessity of carbon capture technologies. In the second part of the thesis, the use of CO₂ captured from thermal power plant flue gases for condensing low-pressure steam (exhaust steam) has been analyzed. Cooling water management in thermal power plants has been categorized into two main methods. In closed-loop systems, cooling water is recirculated back into the system after being cooled in towers or ponds. This method is commonly preferred in regions with limited water resources. In open-loop systems, heated cooling water is discharged directly into its source (sea, lake, or river). Although prevalent in areas with abundant water resources, open-loop systems are limited by environmental regulations due to their thermal pollution and negative effects on ecosystems. Both methods require careful consideration of environmental impacts and sustainability. The role of seawater in the condensing process of low-pressure steam has been examined, revealing an annual requirement of 1,823,231,064 tons of seawater for this purpose. The environmental impacts of cooling water usage in thermal power plants have severe consequences for both water and atmospheric systems. Approximately 5% of the used cooling water is released into the atmosphere as water vapor, intensifying urban heat island effects and contributing to the greenhouse effect due to water vapor being a potent greenhouse gas. The accumulation of water vapor in the atmosphere leads to localized temperature increases, climate imbalances, and an uptick in extreme weather events, causing significant negative effects on ecosystems and human life. The remaining 95% of the cooling water is discharged, heated, into surrounding water sources, such as seas, lakes, and rivers. This results in thermal pollution, adversely impacting not only marine ecosystems but also freshwater ecosystems. The disruption of natural temperature equilibrium in these systems affects species like fish, amphibians, and plankton, reducing their growth and reproductive capacities while decreasing oxygen solubility, leading to the extinction of oxygen-dependent species. Thermal pollution also promotes the spread of invasive species, reducing biodiversity. The use of freshwater resources for cooling water supply, particularly in water-stressed countries like Turkey, exacerbates the challenges of sustainable water use. Strategic freshwater sources, such as lakes and rivers, face increased pressure from this usage, creating environmental, social, and economic issues. This underscores the importance of minimizing freshwater dependency in thermal power plants to ensure environmental sustainability. The proposed system recommends replacing seawater with a closed-loop CO₂ system. This approach allows the continued use of the existing low-pressure steam condensation system, avoiding additional investment costs. By modifying the currentsystem, CO₂ can replace water as the cooling medium in condenser coils. This innovative solution expands the reuse areas of captured CO₂ while amplifying its environmental benefits. System analyses determined the required CO₂ flow rate for low-pressure steam condensation as 7,823.8 kg/s. The closed-loop circulation of CO₂ ensures that it has no adverse impacts on the environment or human health. This approach maintains control over CO₂, supporting environmental sustainability while eliminating health risks. This method not only reduces environmental impacts but also significantly decreases water consumption and thermal pollution. By alleviating the pressure on marine and freshwater sources, it supports ecosystem preservation and the sustainable use of water resources. This approach offers an environmentally friendly paradigm shift in energy production by reducing water dependency in thermal power plants. In conclusion, this thesis presents an innovative and feasible solution for eliminating carbon emissions in thermal power plants. The proposed system establishes a practical model for reducing carbon footprints, lowering energy costs, and conserving natural resources while contributing to environmental sustainability goals. The designed CO₂ capture and liquefaction system has wide applicability, not only in thermal power plants but also in various industrial sectors, such as cement factories, steel production facilities, and petrochemical industries, where CO₂ emissions are generated. Furthermore, the low-pressure steam condensation system provides a viable alternative for condensation requirements in industrial facilities beyond energy plants. This study demonstrates that carbon capture and reuse processes can extend beyond the energy sector to support environmental sustainability, establishing the proposed system as a pioneering technology. This innovative approach offers a valuable contribution to global carbon management and resource efficiency goals. Keywords: Carbon Capture, Thermal Power Plant, Passive Cooling, Environmental Sustainability, Energy Efficiency, CO₂ Utilization for Exhaust Steam Condensation