Oxygen production in cryogenic air separation units is related to a significant carbon footprint and its supply in the medicinal sphere became critical during the recent COVID-19 crisis. An improved unit design was proposed, utilizing a part of waste heat produced during air pre-cooling and intercooling via absorption coolers, to reduce power consumption. Variable ambient air humidity impact on compressed air dryers’ regeneration was also considered. A steady-state process simulation of a model 500 t h⁻¹ inlet cryogenic air separation unit was performed in Aspen Plus^® V11. Comparison of a model without and with absorption coolers yielded an achievable reduction in power consumption for air compression and air dryer regeneration by 6 to 9% (23 to 33 GWh year⁻¹) and a favorable simple payback period of 4 to 10 years, both depending on air pressure loss in additional heat exchangers to be installed. The resulting specific oxygen production decrease amounted to EUR 2–4.2 t⁻¹. Emissions of major gaseous pollutants from power production were both calculated by an in-house developed thermal power plant model and adopted from literature. A power consumption cut was translated into the following annual greenhouse gas emission reduction: CO₂ 16 to 30 kilotons, CO 0.3 to 2.3 tons, SO_x 4.7 to 187 tons and NO_x 11 to 56 tons, depending on applied fossil fuel-based emission factors. Considering a more renewable energy sources-containing energy mix, annual greenhouse gas emissions decreased by 50 to over 80%, varying for individual pollutants.

Repowering of industrial combined heat and power units allows reducing industrial greenhouse gases emissions. An existing industrial unit served as model in the gas turbines-based repowering study, aiming at fuel consumption and carbon dioxide emissions reduction. Following unit's model setup and verification, two conservative repowering options (hot windbox and separate gas turbine + heat recovery steam generator) were assessed from economic, energetic, and environmental point of view, including seasonal impact. Hot windbox option leads to annual power production increase by 14.3% (72.8 GWh/year), accompanied by carbon dioxide emissions reduction by 3.9 % (29.5 ktons/year) compared to the base case. The second option delivered more significant power production increase (+261.9 to +298.6 GWh/year) with CO2 emissions, either slightly higher (+1.5 %) or modestly lower (-4.0%), than in base case depending on heat recovery efficiency from gas turbine exhaust. Both options show feasible economics with simple payback period as low as four years under favorable combination of fuel and electricity prices and CO2 costs. External CO2 emissions change due to the change in unit's power production further reduces the total CO2 emissions, strongly depending on the applied power production emission factor.

Trigeneration provides an effective means of power, heat, and cold production on site. Proper design and well-managed operation of such units can bring in substantial savings in consumed primary energy as well as in the amount of greenhouse gases released to the atmosphere, compared to separate production of all three media. The studied sub-MW-sized trigeneration unit comprises an internal combustion engine combined with an absorption chiller and a heat management system, delivering all three media to a nearby industrial facility. A mathematical model is developed based on available design and process data, a profit function is set up, and the subsequent sensitivity analysis of economic parameters is realized. The lowered efficiency of summer operation is analyzed, and a suitable solution is proposed, with an estimated total investment cost of EUR 114,000 and an anticipated simple payback period less than 2 years.