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Refractory issues related to the use of hydrogen as an alternative fuel lined vessels that would be affected include preheating and calcination tow- ers, clinker production kilns, and cooling sections. Additionally, examples of the use of hydrogen in aluminum production were not found, but hydrogen may be a suitable alternative to natural gas used in secondary aluminum production furnac- es, which accounts for more than 80% of U.S. aluminum production.4 Issues con- cerning mechanical abuse, thermal shock, and metal penetration/reaction already exist in many aluminum reverberatory furnaces, and these issues are expected to be compounded by changes in furnace atmosphere and temperature profiles if hydrogen is introduced. Conclusions Significant resources and attention are being devoted to the use of hydrogen as an alternative fuel source to fossil fuels. By doing so, significant reductions in carbon dioxide emissions are possible, but modifi- cations to burner technology and furnace operating procedures will be necessary. Although much effort has been documented regarding burner design and implementation, less information is available regarding the effects of hydrogen firing on processes and process vessels. In addition, almost no informa- tion is available regarding the effects on refractory ceramic materials when hydrogen is used as a part or all of the fuel stream. Many of the issues associated with the firing of hydrogen in place of traditional fuels such as natural gas result from the properties of the gas itself. Hydrogen is a light molecule with a high heating value on a mass basis but low heating value on a volume basis. This fact leads to higher volumetric flow rates (higher fuel pres- sures) being required compared to other common fuels. Additionally, hydrogen exhibits high flame speeds and relatively high adiabatic flame temperatures com- pared to other fuels, leading to higher radiation of heat transfer from the flame and reduced combustion product volume flow rates. This process has been shown in many cases to result in higher tem- peratures, longer heating resident times, increased NOx levels, and different heat distributions within furnaces, causing more extreme conditions for burner and correspondingly furnace components. Examples of hydrogen being used in industrial processes date back over a decade and often involve mixing hydro- gen with other traditional fuel sources such as natural gas. Many of these efforts rely on hydrogen from tail gases, vented from chemical processes, or recovered from other processes, while more recent efforts use “blue” or “green” hydrogen production. Regardless of the source, sev- eral common issues are prevalent when hydrogen is used as an alternative fuel. As mentioned above, with increased hydrogen use, the volume and tem- perature of the furnace flue gas can be decreased, therefore reducing the internal furnace pressure. This reduced pressure leads to reduced residence time of hot gases in the furnace and ineffi- cient heat exchange/transfer, along with excess heat in the furnace convection zone or increased overall furnace tem- peratures requiring changes to furnace operating parameters. Additionally, increased local combustion temperatures and changes in flame length, speed, and shape can occur, affecting the energy balance of the furnace. Also noted in all cases where hydrogen was used was a significant to extreme increase in NOx emissions and increased presence of water in the furnace. With the decrease in flue gas temperature and the increase in water content within the furnace, there may also be concern about aque- ous condensation and dissolution of NOx to form an acid compound. These issues can all have deleterious effects on refractory ceramic lining mate- rial performance. Such effects can include accelerated wear, chemical attack, and overheating. For example, it was shown that reactions occur between reducing gas (such as hydrogen) and stable oxides like silica, alumina, and zirconia that make up many refractory ceramic lining mate- rials.21 This reaction produces gaseous suboxides and water vapor that can be carried downstream to interact with fur- nace components and the product being processed. Additionally, such reduction of these oxides was shown to accelerate refractory corrosion and deceased refrac- tory strength.22 Thus, alternative refractory selection may be necessary, or the use of novel lining strategies or configurations may be required to maintain current fur- nace lifetimes and maintenance schedules. Acknowledgments This document was authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the U.S. Department of Energy (DOE). The U.S. government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. government retains a nonexclusive, paid-up, irrevo- cable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for U.S. government purposes. DOE will provide public access to these results of federally sponsored research in accor- dance with the DOE Public Access Plan (http://energy.gov/downloads/doe- public-access-plan). About the author James G. Hemrick is senior R&D staff in the Materials Science & Technology Division at Oak Ridge National Laboratory. Contact Hemrick at hemrickjg@ornl.gov. References 1Friedlingstein P., et al., “Global carbon budget 2019,” Earth System Science Data 11:4 1783–1838. https://essd.copernicus.org/ articles/11/1783/2019/ (2019). 2Bartlett J. and Krupnick A., “Decarbonized hydrogen in the US power and industrial sec- tors: Identifying and incentivizing opportuni- ties to lower emissions,” Resources for the Future, Report 20–25, December (2020). 3Baukal C., Johnson B., Haag M., Theis G., Henneke M., Varner V., and Wendel K., “High hydrogen fuels in fired heaters,” American Flame Research Committee Symposium, Houston, Texas, Oct. 10–12, 2021. 4“Fuels,” C. Baukal (ed), The John Zink Hamworthy Combustion Handbook, Vol. 1: Fundamentals, CRC Press, Boca Raton, Fla., (2013). 5Hsu C.K., Lee C.L., Wang C.H., and Jou C.J., “Reduction of energy consumption and pollution emissions for industrial furnace using hydrogen-rich tail gas,” International Journal of Hydrogen Energy, 39:18, 9675-9680, (2014). 30 www.ceramics.org | American Ceramic Society Bulletin, Vol. 101, No. 2PDF Image | hydrogen as an alternative fuel
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