Cutting Oxygen Production-Related Greenhouse Gas Emissions by Improved Compression Heat Management in a Cryogenic Air Separation Unit

Abstract

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, SOx 4.7 to 187 tons and NOx 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.

Energy and Environmental Assessment of Steam Management Optimization in an Ethylene Plant

“…Emission factors from electricity production are known to vary significantly depending on the energy mix and other conditions considered in their evaluation [83,84]. As discussed in our recent study [85], the emission factor of CO 2 can vary between close to zero values for an almost exclusively renewable energy-based mix up to 700 to 900 kg/MWh for coaland oil-fired power plants. Adopting a value of 700 kg/MWh [86] instead of that from Table 5 (136 kg/MWh) substantially changes the resulting global CO 2 balance of increased steam import into SC: global increase in CO 2 emissions of 5600 t/year changes to the reduction of approximately 900 t/year.…”

“…Li et al (2019) [95] studied the environmental performance of a high-temperature heat pump-assisted gas separation plant located in China within a more complex frame of energy, exergy, economic and environmental optimization of the given plant, yielding achievable savings in CO 2 , NO x , and SO 2 emissions. Finally, the authors themselves applied the balances of CO 2 , NO x, and SO x emissions based on fuel composition and field emissions data in their earlier studies on refinery processes [38] or oxygen production plant [85] optimization. It can be concluded that, while all mentioned approaches are viable, using available field data ensures the validity of the environmental assessment results both generally and in a particular on-site application.…”

Structure Activity Relationships for Reversible O2 Chemisorption by the Solid Phases of Co(salen) and Co(3F-salen)

“…The discovery of an energy-efficient material for the swing absorption of O 2 remains highly sought for a wide range of applications from O 2 supplies to COPD patients, to aircraft and submarine emergency O 2 supplies, and for separation from H 2 in water electrolysis to name just a few. The typical energy consumption in units for the cryogenic separation of O 2 from air exceeds 200 kWh of electricity per ton of produced oxygen − and is thus associated with significant environmental impact. , Despite the eight intervening decades since Calvin and co-worker’s impressive studies using 42 variations on the Co­(salen) scaffold, and which were deemed highly important for the U.S. National Defense, no advance has been made. At that time, however, no SAR insight through crystallographic characterization was possible.…”

Repowering Industrial Combined Heat and Power Units: a Contribution to Cleaner Energy Production

“…As to obtain yet more data for model verification, a model for condensing power production only was set-up and presented elsewhere [110]. Specific steam production for condensing power production of over 4.5 t MWh -1 and net electric efficiency of 30.6% are within the range of performance parameters of subcritical sub-100 MW scale thermal power plants listed in reference literature [68,80].…”