Highly valuable attributes such as high efficiency and competitive capital costs are the underlying factors for the prominence of carbon dioxide (CO2) cycles not only in theoretical fields but also in commercial applications. As a result, we are witnessing an increasing number of research projects and support for activities related to these cycles. Recently, there has been a new initiative to develop an even more promising working fluid by mixing CO2 with certain dopants. One of them seems to be the CO2-SO2 mixture. Given the promising potential of this specific mixture, which seems to be exceptionally well-suited for application in transcritical cycles, this paper provides an overview of the early results of the transient analysis of transcritical Rankine cycle using this mixture in waste heat recovery applications (WHR).

The primary focus of this paper is to utilize the CO2-SO2 mixture in a 70-30 ratio for the double recuperated recompression Rankine cycle. In doing so, this study not only examines the unique characteristics of this mixture but also explores its potential applications for WHR under fluctuating operational conditions. The paper describes the modeling methodology implemented in Aspen Plus software and illustrates the key plant components transient operating conditions. By conducting the analysis of this working fluid, the paper aims to evaluate its effectiveness in harnessing waste heat, thereby contributing to the advancement of more sustainable and efficient energy solutions.

Decarbonization of power generation, transportation, and energy-intensive industries (i.e., steel and iron, cement, aluminum, glass, food and beverage, paper, etc.) is necessary to reduce CO₂ emissions considering the continually growing world population and related increasing energy consumption. CO₂ emissions from energy-intensive industries can be reduced through several different approaches (i.e., direct - alternative fuel or energy source and Carbon capture systems; indirect - utilization of waste heat for the plant’s own consumption), where waste heat recovery represents a low-cost, zero-emissions power generation option with near-term deployment opportunities. In this paper, the steelmaking process is investigated as a potential source of waste heat to reduce the plant’s own consumption. The steelmaking process has three sources of waste heat in three different steps where the waste heat can be utilized. The exhaust gas stream is only approximately 10 % of the available waste heat. However, the temperatures are between 473 and 1573 K based on the process step and type of furnace (i.e., Blast furnace, Basic oxygen furnace, Electric arc furnace). Due to the large temperature range, potential retrofitting, and limited footprint, a sCO₂ waste heat recovery system can be an ideal candidate for utilizing waste heat streams in the steelmaking processes. The paper is focused on the optimization of potential waste heat recovery systems based on sCO₂ power cycle for a steel plant with several electric arc furnaces (EAF). Several different sCO₂ cycle layouts (i.e., Simple, Recuperated, Intercooling, Re-compression, Reheating, Split expansion cycle) have been investigated to meet the requirements. Results show higher performance of the sCO₂ cycle and potential retrofitting into the current steel plants. The sCO₂ power cycles can reach cycle efficiencies above 40 % and provide approximately 800 kWel from the waste heat stream. Part of the work is cost analysis which provided additional parameter/decision value for cycle layout selection.

In the face of mounting global interest in reducing
greenhouse gas emissions and achieving carbon neutrality, there
is an urgent need to develop and implement diverse measures. In
particular, it is imperative to explore the potential of utilising
waste heat from industrial processes and power generation, as
this has the potential to significantly enhance energy efficiency
and reduce greenhouse gas emissions while also capturing
otherwise wasted energy.
Concurrently, supercritical CO2 power generation is
regarded as a prospective technology for fossil, nuclear, solar,
thermal energy storage and waste heat recovery applications,
attributable to its elevated thermodynamic efficiency,
miniaturised plant configuration, and environmental stability.
sCO2 power cycles function above the critical point of CO2
(31.1°C, 7.38 MPa) and deliver higher energy density and heat
transfer performance in comparison to conventional power
cycles. It is particularly effective for power generation systems
using medium-temperature waste heat and has the advantage of
being applicable to various industrial environments. KEPCO
(Korea Electric Power Corporation) has been promoting research
and development of sCO2 power cycles as a promising future
technology since 2014. Following a series of feasibility studies,
KEPCO aimed to construct an MW-scale sCO2 power
generation system that recovers waste heat at low temperatures
and has the capacity to reduce risks in the early stages of
development. Additionally, the system was designed to achieve
a high probability of demonstration success and initial
marketability. In 2016, with the support of KEPCO, we initiated
a strategic project to achieve a net output of 2MW by recovering
waste heat from engines. A suitable onshore power generation
engine to output MW-scale sCO2 power output was selected as
well as a partial heating sCO2 cycle to recover waste heat from
the engine exhaust. A design feasibility study was also
conducted. This paper provides an overview of the development
of KEPCO's 2MW sCO2 power generation system designed to
recover waste heat. This paper also describes the cycle analysis
results and the specifications and fabrication of major equipment
(turbine, compressor, heat exchanger, etc.).