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Development of alternative fuels in the U.S. cement industry

The use of alternative fuels in the U.S. cement industry is an interesting study in economics, incentives, and the law. Each of these drivers makes alternative fuel use in the United States quite unlike alternative fuel use in any other country. But to understand how alternative fuels fit into the U.S. cement industry it is important to understand how the U.S. cement industry fits into the global cement industry.

Currently, 73 % of all U.S. cement plants use some type of alternative fuel. Forty plants use tire derived fuel, 15 plants use waste oil fuel, 11 plants use solvents as fuel, and 62 plants use some other material. In some cases, plants will use more than one type of alternative fuel [4].
Some examples of the ‘other’ types of fuels used by plants are engineered fuels, refuse derived fuels, agriwaste, ashes, biofuels, biomass, carpet, charcoal, cherry pits, coal pond fines, coke breeze, filter fluff, flexicoke, glycerin, landfill gas, nylon fluff, pecan shells, plastics, rice hulls, sawdust, shingles, spent activated carbon, spent pot liner, textile waste, wind, wood, and even other more unique materials. Many of these fuels provide the fuel producer and the cement plant a unique opportunity. The fuel producer has a ready consumer while the cement plant has a well defined fuel stream.
The Portland Cement Association (PCA) has been reporting alternative and waste fuel usage in the U.S. cement industry since 1977. During that period, the share of alternative and waste fuel usage has increased from minor amounts to 16 % of all fuel use in the cement industry in 2016. That same 16 % corresponds to nearly 50 trillion BTUs (British Thermal Units) (Figure 2). For perspective, that same amount of energy would require two million equivalent short tons of coal. Since 1996 alternative fuel usage in the U.S. has increased in share relative to waste fuel and now accounts for approximately 55 % of their combined total (Figure 3).
The composition of energy consumption in the U.S. cement industry has changed appreciably from 1996 to 2016. Coal and coke, once the dominant share of fuels, has dropped from 74 % to just over 57 %, while natural gas has increased from just over 7 % to nearly 16 % based on BTUs consumed. Waste fuel use increased slightly from 5.5 % to 6.8 % but alternative fuel use more than quadrupled. The alternative fuel use in 1996 represented just 2 % of the energy consumption in cement plants but by 2016, that figure jumped to 8.3 % (Figure 4). The mix of that alternative fuel use also changed.
In 1996 alternative fuels were primarily solvents and those solvents represented nearly 70 % of the BTUs consumed within the alternative fuel mix in U.S. cement plants. That amount was cut in half by 2016. Tire derived fuels increased roughly 5 % from nearly 22 % in 1996 to 26 % in 2016, again on a BTU basis. The use of other alternatives though is especially dramatic. In 1996, other alternative fuels were just under 5 % of the total alternative and waste fuel use heat consumption but by 2016 that single category had increased by nearly a factor of 5. More than 24 % of alternative and waste fuel use in the U.S. cement industry in 2016 was provided by ‘other’ alternative fuels (Figure 5).
These other alternative fuels pose a number of challenges though. Cement producers are keen to have consistent and reliable supplies of alternative fuels. Most importantly, they require a fundamental understanding of the fuel composition and that requires a solid characterization of any proposed fuel. Once that characterization is complete, concerns regarding the supply, storage, and delivery of these fuels can provide additional challenges. The impact that alternative fuels have at the cement plant are not just limited to process and production. They may critically impact a plant’s operating permit.

5 Conclusion

The last twenty years have seen substantial changes in the use of alternative fuels and no doubt those changes will continue. It is likely that coal and coke will continue to decrease as alternative fuels increase. It is also likely that the energy provided by alternative fuels and the spectrum of materials used as alternative fuels will continue to increase.
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