Investigation of carbon capture technologies for Sävenäs waste-to-energy plant
Abstract: Carbon capture technologies have the potential to decarbonize the emissions to air from the heat and power sector and contribute to the necessary greenhouse gas emission mitigation in order to meet the Paris Agreement requirements. The energy requirement and ability to retrofit carbon capture units are crucial to convert existing power plants into more environmental benign processes to meet the Swedish national goal of greenhouse gas neutrality at 2045. This report investigates the viability of carbon capture technologies at waste-to-energy (WTE) plants with a techno-economic analysis of the Sävenäs WTE plant in Gothenburg. Flue gas characteristics at WTE plants, with a carbon dioxide (CO2) concentration of ~10%, facilitates absorption techniques for post-combustion capturing which offers a high level of readiness and large-scale operations compared to other capture technologies. To assess the feasibility of the carbon capture options, multicriteria aspects were considered covering energy requirement, environmental impact as well as economic advantages and disadvantages associated with CO2 emission abatement and loss of income due to energy withdrawal. Mass and energy balance calculations were executed based on steady-state assumptions and conservation of mass and energy in order to develop process models for carbon capture and thus expose process integration possibilities and the energy recovery potential. The balance calculations were performed for Monoethanolamine (MEA) and Chilled Ammonia Process (CAP) as they were the most promising absorption technologies at the time of this master thesis project. The calculations show that the energy efficiency at Sävenäs WTE plant is reduced by 32% using MEA solution on a yearly average. However, extensive energy recovery would be achieved by integrating a heat-pump to the treatment process combined with district heating integration. With this integration the energy efficiency was reduce only by 12%. Energy penalty associated with CAP was found to reduce the efficiency by 21%. Energy recovery solutions are primarily derived from district heating integration which result in a net energy efficiency reduction by 10%. Due to its location in Sweden the demand of heat produced at Sävenäs WTE plant is at its highest between October and March. The CO2 emission abatement and cost analysis showed that a carbon capture facility is preferable operating during summertime when most of the about 1.5 TWh heat distributed per year from Sävenäs WTE plant won’t have to be replaced with other less environmental benign and energy efficient sources. If captured biogenic CO2 is considered a negative emission, then the WTE plant would achieve carbon neutrality even by operating only six months per year due to the high fraction of biogenic content in the fuel mixture. The process model for CAP revealed extensive water utilization to avoid ammonia slip and thus additional energy requirements associated with cooling. The flue gas treatment characteristics at Sävenäs WTE plant corresponds well with the specifications for CAP but nonetheless the location of the WTE plant does not offer a natural source of cooling water with a preferable temperature of 5ºC. Hence, MEA was found to be the most viable option for Sävenäs WTE plant with a high technological readiness and seasonal operation already proven feasible at large pilot-scale plants.
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