The Role of Oxygen-Enriched Air in Sustainable Hydrogen Production and Combustion Performance in Fired Heaters
Authors: Elyamani M. A. 
Published: October 2024

Producing hydrogen presents challenges, including the optimal utilization of its byproduct, oxygen. This research explores how oxygen can be utilized to support hydrogen production and reduce its cost. Specifically, it focuses on using oxygen in the combustion system of fired heaters/furnaces. By using pure oxygen in hydrogen-fueled heaters, water produced from combustion can be fully recovered and recycled for hydrogen production. This sustainable system produces no CO2 and uses minimal water. Incase using hydrocarbon fuel as natural gas, water recovery and CO2 capturing will be reached easily.

The required gas in combustion air is Oxygen. The source of Oxygen is combustion air in fired heater and this air contain around 21% Oxygen and 79% Nitrogen. Firing requires only oxygen for combustion however, N2 is an inert gas that does not participate on combustion reaction and Nitrogen carries a lot of energy to the ambient environment after combustion as Nitrogen enter the fired heater with ambient temperature and leave the heater with flow gases at stack temperatures. Any chance to increase Oxygen content in combustion air will reduce the amount of Nitrogen and lead to save this waste energy and improve the efficiency.

Below Figure 01 and figure 02 shows that the differences in Methane combustion with air and pure Oxygen.

Above figures shows that about 20% of methane HHV is lost by N2.

In addition, Lower nitrogen concentration leads to higher concentrations of CO2 and H2O that are good radiation emitters so, the total gas emissivity increase. Using oxygen instead of air has great results (process wise) in Claus process or sulfuric acid production.

Oxygen concentration in combustion air can be increased by adding pure oxygen to combustion air, using Oxygen enriched air or using pure oxygen for combustion.

Oxygen-Enriched Air mean air with higher amount of Oxygen more than normal percent 21%.

Figure 1 When methane combustion takes place in air (21% O2, 79% N2), a significant portion of the methane's heat content is lost through the stack. Figure 2 Combustion in pure oxygen converts 79% of the methane's energy content into useable heat.

There are many sources of Oxygen as follow: Air separation units.Air separation units: These facilities use various methods, such as cryogenic distillation to separate oxygen from other components in the air, producing high-purity oxygen for use in industries, hospitals, and other applications.Oxygen enriched air generator.Oxygen-enriched air generator: These generators are designed to enrich the air with oxygen by removing nitrogen and other gases, resulting in a higher concentration of oxygen in the output gas mixture. This can be useful in various industries, such as healthcare, where patients may require supplemental oxygen. Or can be added in industries if needed.The waste gas of Nitrogen Plant.The waste gas of Nitrogen Plant: Nitrogen plants produce nitrogen gas as the primary product, but they also generate waste gas streams that contain residual oxygen. This oxygen can be recovered and purified for use in various applications. This waste gas contains around 30 to 35 % Oxygen content.The future source from green hydrogen production (hydrogen is produced via electrolysis)Green hydrogen is produced via electrolysis, which involves splitting water molecules into hydrogen and oxygen using electricity. The oxygen produced during this process can be captured and utilized as a source of oxygen.Ammonia productionAmmonia is one of the effective tools for hydrogen transportation and utilization. oxygen is a byproduct of nitrogen production for ammonia synthesis, as it is separated during the cryogenic distillation of air. This nitrogen, along with green hydrogen, is then used to produce ammonia through the Haber-Bosch process.Pressure swing adsorption (PSA):This method uses a molecular sieve to selectively adsorb nitrogen from compressed air, allowing oxygen to pass through. PSA is less efficient than cryogenic distillation but can be more cost-effective for smaller-scale operations.Membrane separation for oxygen production:It is a process that uses a selectively permeable membrane to separate oxygen from other components in air, such as nitrogen and argon. This process is also known as air separation or membrane oxygenation.