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Refractory issues related to the use of hydrogen as an alternative fuel sidered when directly introducing hydrogen into the current industrial gas streams include product quality, process efficien- cy, and pollutant emissions (NOx). Both computer simulations (computational fluid dynamics, CFD) and actual experiments were performed using “off-the-shelf” industrial burner systems in a semi-industrial burner rig, with the effects of hydrogen contents of up to 50% by volume considered regarding process efficiency, heat transfer, and pollutant emissions. Three differ- ent burner systems were considered: a modular nonpremixed jet burner, a forced-draught burner, and a flameless oxidation burner (firing rates for all burners in the range of 100 kW and air excess ratios of 1.05). Increased NOx emissions were noted in the burner testing due to increased local combustion temperatures, but these emissions could be controlled to some degree by adjusting the settings of the individual burners (especially for the flameless oxidation burner). Changes in flame length (decreased with increasing hydrogen content) and shape were also seen in CFD modeling of the burners. Additionally, modeling showed that higher hydrogen concentrations in the fuel impacts the energy balance of the furnace, which could lead to insufficient heat released inside the furnace. To evaluate changes in furnace efficiency and heat balance, a heat transfer impact factor (HTIF) was developed (Equation 1),7 where Q ̇ Load is the heat flux into the furnace load (product), Q ̇ Load,Reference is the reference case heat flux into the furnace load (product), Q ̇ Wall is the heat flux into the furnace wall, and Q ̇ Wall,Reference is the reference case heat flux into the furnace wall. HTIF=Q ̇ Load/Q ̇ Load,Reference =Q ̇ Wall/Q ̇ Wall,Reference) (1) Using this factor, heat flux within a hypothetical furnace was evaluated using CFD simulations to estimate the heat flux into the product being processed or directly into the furnace walls for various hydrogen concentration levels. An analysis for 20% by volume of hydrogen in natural gas showed reductions of 5–13% in HTIF compared to pure natural gas firing. This finding indicates that more heat is going into the refractory walls of the furnace than into the product when firing hydro- gen, thus raising the operating temperatures of the refractory, which accelerate corrosion and wear and require more energy input into the process. A similar computer simulation analysis was carried out for a regenerative glass melting furnace (for pure natural gas, 10% hydrogen substitution, and 50% hydrogen substitution).7 Flue gas temperatures were seen to decrease with the introduction of hydrogen, while maximum furnace temperatures within the model tended to increase with hydrogen concentration. This situation resulted in reduced heat transfer to the glass melt and increased heat transfer to the furnace walls, as seen in the earlier simulation described above. Additionally, dras- tic increases in NOx emissions were noted. Finally, questions regarding whether hydrogen will chemically interact with the metal and glass products being processed were raised, as well as a need was identified to determine the possible interactions of the hydrogen with the refractory lining materials of the furnace, which could lead to reduced furnace lifetimes and increased maintenance requirements. A more recent area where hydrogen was considered as an alternative fuel is in industrial boilers.10 To reduce carbon monoxide and carbon dioxide emissions, along with plant fuel costs, users of industrial boilers are considering alternative fuel sources that they have available to them, such as residual hydrogen left over from reforming and refining processes. Such hydrogen (which is often flared or released) can be injected into a fuel gas stream to supplement normal fuels. However, as noted by users and previously highlighted, the use of this hydrogen can lead to higher flame speeds and firing temperatures, requiring changes in burner construction materi- als and burner types to facilitate the incorporation of hydrogen into the fuel stream. Additionally, it was noted that some steels used in traditional burner construction could undergo hydrogen embrittlement and attack at elevated temperatures, which can lead to premature failure of the burner. Due to the burner modifications noted above, impact is also seen in burner emissions and performance.10 The high flame propagation speed of hydrogen causes the combustion process to occur more rapidly than for natural gas, leading to local- ized heating near the flame and increased NOx emission rates. (Field and test facility data have shown that standard low-NOx burners firing hydrogen typically exhibit an increase in NOx emission rates by up to a factor of 3.) These phenomena are confirmed in earlier efforts by the petroleum industry to use hydrogen in the firing of process heaters, where a stainless 28 www.ceramics.org | American Ceramic Society Bulletin, Vol. 101, No. 2 The H2@Scale initiative at DOE The H2@Scale initiative at the United States Department of Energy was created to “bring together stakeholders to advance affordable hydrogen production, transport, storage, and utilization to enable decarbonization and revenue opportunities across multiple sectors.”8 Under this initiative, in October 2021, the DOE announced nearly $8 million in cooperative projects at U.S. national labo- ratories to support DOE’s Hydrogen Shot goal to drive down the cost of clean hydrogen by 80% within the decade.9 Projects funded under this initiative will be carried out under coopera- tive research and development agreements (CRADAs) and will leverage the Advanced Research on Intergraded Energy Systems (ARIES) platform to enable the integration of hydrogen technologies in future energy systems, including energy stor- age and a specific focus on safety and risk mitigation. A list of funded projects can be found at: https://www.energy.gov/eere/articles/doe-announces-nearly- 8-million-national-laboratory-h2scale-projects-help-reach Additional information on the H2@Scale initiative and the Hydrogen Shot goal can be found at: https://www.energy.gov/eere/fuelcells/h2scale https://www.energy.gov/eere/fuelcells/hydrogen-shot nPDF Image | hydrogen as an alternative fuel
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