During the most recent decades the utilization of (otherwise) waste materials and biomass as alternative fuels in the cement industry and power plants showed great growth figures. However, the low heat values of alternative fuels require larger handling and storage systems that are more flexible. This article shows, how these materials can be handled.
The utilization of alternative fuels within various industries has been on a path of rapid expansion for the last 20 to 30 years. For instance, cement producers have been pushing for a net negative fuel cost for decades, which only a few plants have truly achieved and the Southeastern U.S. has recently become the hotbed of biomass-based fuel sources for power generation or co-firing. As the world attempts to reduce its dependence on fossil-fuels, what was once considered waste has now become a driver for a rapidly expanding industry which is attempting to combat the global megatrend of climate change and resource scarcity.
The very recent Past
As early as 1986, Kurt E. Peray  suggested that solid fuels in rotary kilns were generally coals: Anthracite, bituminous, lignite and coke, and that “several pre-heater kilns in various parts of the world are being used to dispose of old automobile tires, wood chips and even garbage for introduction into the back end of the kiln”. Alternative fuels have now taken their place in the proverbial front end of the kiln. The times when focusing on alternative fuels purely for financial sake are over. Yes, they still have their place, but a far larger constant has been added to the equation: new emissions regulations.
In 2010, the US Environmental Protection Agency (EPA) finalized the National Emission Standards for Hazardous Air Pollutants (NESHAP) amendments to the standards for Portland cement manufacturing and emissions of mercury, total hydrocarbons (THC), hydrochloric acid (HCl) and particulate matter (PM). In 2013, these new regulations became law. This updated law, together with the New Source Performance Standards (NSPS) regulates NOx, (nitrogen oxides) and SO2 (sulfur dioxide), and required cement plants to be compliant with the new standards.
After a number of lawsuits, modifications and amendments, mostly championed by the Portland Cement Association, all US cement plants should have demonstrated compliance as recently as September 9, 2015. But there’s more. In August 2015, President Obama authorized the new “Clean Power Plan” to regulate CO2 emissions from power plants. With the new emphasis on Greenhouse gasses and their supposed contribution to global warming, can the cement industry be far behind?
Going back to Peray, utilizing coal as a fuel source under stoichiometric conditions in a cement kiln would lead to approximately 18% CO2 in the stack if there were no evolution of CO2 from the raw mix and as much as 28% when considering the CO2 evolving from the raw mix. By their very nature, numerous alternative fuels and raw material additives have reduced chemical constituents that lead to a reduction of overall emissions, reduced fuel costs and the possibility of generating carbon offsets.
Today, wood chips and biomass usage for one of the major world-wide cement producers contributes as much as 24.5% of their fuel input needs . Consequently, the low heat values of alternative fuels now require larger handling and storage systems that are more flexible and permanent fixtures within the plant.