Performance comparison of sCO2 and steam cycles for waste heat recovery based on annual semi-transient modeling under complex industrial constraints

Abstract

The increasing demand for energy efficiency is compelling industries to seek ways to save energy. Waste heat recovery plays a crucial role by optimizing fuel usage through combined heat and power generation. In recent decades, sCO2 technologies have emerged as potential contenders to traditional steam cycles. However, there is a noticeable gap in literature regarding case studies on integrating off-design behaviors of components in complex industrial environments. To address this gap, this study focuses on a specific scenario involving a waste incinerator already linked to a steam generator within a cogeneration setup, alongside a flue gas cleaning unit. The conventional steam bottoming cycle is innovatively replaced with an sCO2 cycle, and a comparison between the performance of the existing steam technology and a numerical sCO2 model is conducted. This comparison involves modeling the off-design behaviors of each component run hourly over a one-year period. Results show that the sCO2 setup increases the electric power generation by 25% with the global efficiency around 43%, compared to the initial 37.3%. These outcomes answer a need in literature by showing that, even in off-design, the higher exergy efficiency of the sCO2 setup is more advantageous. Unlike steam evaporation at constant temperature, sCO2 is less constrained by temperature limitations in the heater and allows for higher turbine inlet temperatures. Additionally, an economic assessment reveals a levelized cost of electricity between 8.5 and 16.7 $/MWhe. However, further advancements in component modeling and enhanced energy recovery from cooler/exhaust gases are identified as areas for future research.

Keywords

• sCO2 cycles
• Waste heat recovery
• Semi-transient
• Cogenerative application
• Exergy efficiency
• Economic assessment