Novel bottom-up methodology to build the lifecycle inventory of unit operations: the impact of macroscopic components

The methodology proposed assumed unit operations are composed of macroscopic components, six structural including steel, concrete, insulation (glass wool), aluminum, powering, and electronic, and one functional, catalyst. Unit operations included heat exchangers (shell-and-tube and air-cooled systems), separation units (flash tanks and distillation column), and a methanol reactor. Sets of equations were provided to estimate the lifecycle inventory (LCI), while relying on scaling parameters as reported in techno-economic assessment techniques (i.e., surface area to estimate heat exchangers costs). A Power-to-X case study (system boundary) was selected to demonstrate the methodology functionality to build the equipment LCI to estimate the CO₂ equivalent emissions to produce 1.0 kg of methanol at 25 °C and 1 atm (functional unit).

The case study showed emissions associated to capital goods amounted to 4146 tonnes of CO₂ equivalent, with the methanol reactor having the largest share (67.9%), followed by heat exchangers (23.5%) and separation units (8.6%). Regarding components, steel and concrete comprised the largest contribution for most unit operations (> 53.8% of emissions) excluding the methanol reactor (9.9%). The share of powering and electronics was relevant in the carbon footprint (CF) exercise due to the components intrinsic CF (5.74 and 36.25 kg-CO₂ eq./kg-component, respectively) when compared to other major components (i.e., steel, 0.58 kg-CO₂ eq./kg-component). The component catalyst had a significant impact on the reactor emissions (80.7%) which originated from the need of being renewed every 2.5-year period. For the system boundary, capital goods only amounted to 0.221% of methanol production emissions or 0.0005 kg-CO₂ eq./kg-MeOH.

This study described a novel methodology to estimate the LCI and subsequent CF of capital goods. This new methodology has been used in a specific case study for methanol production using PtX. Ultimately, the authors of this study seek to create the basis of a simple but comprehensive methodology to reduce data gaps associated to lifecycle inventory and assessment of industrial equipment in literature.