**1. Introduction**

Global warming and climate change are fundamental issues nowadays. In order to significantly reduce global warming for long-term sustainable development, the greenhouse gas emissions (especially the fossil ones) need to be significantly cut and decoupled from economic growth [1]. Along this line, the industrial and transport sectors are facing important modifications and restructuring with the aim of reducing the fossil energy sources as required for the development of an economy with a low carbon footprint. Among industrial applications with significant greenhouse gas emissions, the heat, and power generation, iron and cement production, and various fossil-based chemical systems are the biggest contributors. To illustrate the major importance of these industrial sectors and to consider the global greenhouse gas emissions one can mention that the coal-based power generation is responsible

by more than 10 Gt CO2 from the 33.1 Gt CO2 emitted globally in 2018 [2], production of iron and steel counts for about 6% of global CO2 emissions [3], and the cement production counts for 5% of global CO2 emissions [4]. Accordingly, the fossil-intensive industrial processes need significant changes in forthcoming years to efficiently contribute to the global effort of reducing carbon emissions.

As possible technical and scientific options to cut the fossil carbon emissions, a broad range of measures can be applied, ranging from promoting renewable ene.g., increasing the energy conversion, and utilization yields too large scale deployment of carbon capture, utilization and storage (CCUS) technologies [5]. These technologies are seen as important options for the medium time horizon to allow a smoothly transition from the current fossil-based economy to a future low carbon one. For the integration of the CO2 capture process into various energy-intensive applications, several conceptual options are already available and widely evaluated in the literature, e.g., pre-, post- and oxy-fuel combustion methods [6]. Once captured, CO2 can be used as raw material for various processes (e.g., production of various chemicals and fuels), stored in appropriate geological formations (e.g., saline aquifers) or used for increasing the oil/gas recovery yields [7].

This work is assessing some key fossil fuel-intensive industrial applications in view of energy and cost-effective process decarbonization. The selected industrial applications are power generation, iron and steel production, cement production, as well as producing chemicals which can also be used as decarbonized energy carriers (e.g., hydrogen). The chemical absorption (scrubbing) method [8] and the innovative chemical/calcium looping cycles based on reactive adsorption systems [9] were evaluated as decarbonization technologies. Apart from the carbon footprint reduction, the overall energy conversion yields, as well as other techno-economic and environmental performance indicators, represent important elements in the present evaluations. Similar non-carbon capture plants are also assessed to quantify the various penalties imposed by decarbonization (e.g., ene.g., raw materials, and utility consumptions, overall energy efficiency, main economic factors). The decarbonized plant concepts have a 90% CO2 capture rate, a value which is in line with assessment methodology of CO2 capture technologies presented in relevant literature sources, e.g., International Energy Agency Greenhouse Gas Programme (IEAGHG) reports for decarbonization of iron and steel production [3] or cement production [4]. In addition to technical and environmental indicators, the economic impact of process decarbonization is also presented considering key performance indexes.

The selected industrial applications were subject to various technical investigations ranging from the conceptual design of decarbonized plants and evaluation of CO2 capture unit mass and energy integration analysis, usage of computer-aided tools for process design, and integration to the evaluation of main plant performance indexes based on industrial and simulation results. The key novelty aspect of the presented work is to provide an integrated in-depth techno-economic and environmental evaluation methodology of decarbonized industrial processes.
