**4. Techno-Economic and Environmental Assessment Methodology**

This section of the paper is dedicated to present the overall techno-economic and environmental plant performance indicators. All evaluated decarbonized energy-intensive industrial concepts were mathematically modeled and simulated using ChemCAD software. The most important simulation data (as mass and energy balances, fuel conversion yields, overall plant decarbonization rate, etc.) were benchmarked against industrial data for model validation; e.g., for the gasification [18] and combustion [19] power plant concepts, for the integrated steel plants [3], for the cement production plants [4], for the alkanolamines-based carbon capture processes [26] and for the calcium looping-based carbon capture [27] and its integration into various energy systems [28]. No significant differences between simulation results and literature data were noticed/registered.

After validation of the simulation results, the most relevant techno-economic and environmental plant performance indexes were calculated using the following equations:

*Gross*/*net* power conversion efficiencies show the energy conversion rates for the gasification and combustion power plants:

$$
\eta\_{\text{gross/net}} = \frac{\text{Gross / net electricity output [MW\_c]}}{\text{Thermal energy of used fuel (coal) [MW\_{th}]}} \times 100\tag{5}
$$

Ancillary power consumption was calculated considering all electricity consumptions of various plant sub-systems:

$$\text{Antillarg power consumption} = \sum \text{Plant units power consumption} \tag{6}$$

Plant decarbonization rate (noted as CO2 Capture Rate—*CCR*) takes into account the percentage of feedstock carbon that was captured:

$$\text{CCR} = \frac{\text{Sequenceed carbon molar flow} \, [kmole/h]}{\text{Carbon molar flow of coal} \, [kmole/h]} \times 100\tag{7}$$

Specific emission of CO2 (*SECO*2) quantifies the vented CO2 quantity when 1 MW of power or 1 ton of steel/cement is produced:

$$SE\_{CO\_2} = \frac{Emitted \, CO\_2 \, mass \, flow \, [kg/h]}{Net \, power \, output \, [MW\_t] \, / \, Stel \, or \, element \, output \, [t]} \times 100\tag{8}$$

Specific consumption of primary energy for CO2 avoided (*SPECCA*) takes into accounts both non-carbon capture and carbon capture power plant concepts using the following equation:

$$\begin{array}{c} \text{SPECCA} = \\ = \frac{\text{Hant rate}\_{\text{Capture}} \left[ \frac{\text{Ml}\_{\text{H}} \text{H} \text{V}}{\text{M} \text{Wb}\_{\text{P}}} \right] - \text{Hant rate}\_{\text{No capture}} \left[ \frac{\text{Ml}\_{\text{H}} \text{H} \text{V}}{\text{M} \text{Wb}\_{\text{P}}} \right]}{\text{Specific emissivity}\_{\text{No capture}} \text{No capture} \left[ \frac{\text{kg CoO}\_{2}}{\text{MWb}\_{\text{P}}} \right] - \text{Specific emissivity}\_{\text{Capte}} \left[ \frac{\text{kg CoO}\_{2}}{\text{MWb}\_{\text{P}}} \right]} \end{array} \tag{9}$$

Specific capital investment (*SCI*) calculates the capital investment required for production of 1 kW of net power or 1 ton of steel/cement:

$$\text{SCI} = \frac{\text{Capital investment [MEuro]}}{\text{Net power output [kW\_t] / Stole or element output [t]}} \cdot 100\tag{10}$$

Levelized costs of decarbonized power, steel, and cement were calculated according to the International Energy Agency-Greenhouse Gas R&D Program methodology [29] using the net present value method. This method was translated into in-house developed calculation routines.

*CO*<sup>2</sup> *avoided cost* was calculated considering the levelized cost of electricity (or steel/cement) and *specific CO*<sup>2</sup> *emissions* in both plant conditions with and without carbon capture:

$$\text{CO}\_2\text{avoided }\cos t = \frac{\text{LCOE}\_{\text{Capture}} - \text{LCOE}\_{\text{No capita}}}{\text{Specific CO}\_2 \text{ emissions}\_{\text{No capture}} - \text{Specific CO}\_2 \text{ emissions}\_{\text{Capture}}} \tag{11}$$

The above-mentioned performance indicators, as well as others (e.g., fuel and raw material consumptions, ancillary energy consumptions, etc.) were calculated for the evaluated fossil-intensive industrial applications. Regarding environmental impact indicators, several Life Cycle Assessment (LCA) studies were performed by the authors for gasification [30], combustion [31], and iron and steel [32] but due length constraints only the carbon footprint was presented in details. The LCA results are presented in detail for one illustrative case (i.e., super-critical combustion power plant).
