Using alternative fuels to reduce carbon emissions in cement manufacturing

As demand for cement increases, so does the need to reduce its carbon footprint. The Global Cement and Concrete Association (GCCA), which represents 80% of production outside China, has committed to providing society with net zero cement by 2050. Alternative fuels are one way that cement manufacturers can reduce environmental impacts and reduce costs. So, what do plant operators need to consider when replacing fossil fuels with alternative fuels?

After water, cement is the most in-demand material on the planet. It is also one of the most carbon-intensive, with cement manufacturing accounting for at least 8% of global CO2 emissions. This is largely because cement manufacture requires a lot of fuel – approximately 120 kg of coal per tonne of cement. We now know that burning fossil fuels at scale results in emissions of greenhouse gases such as carbon dioxide (CO2) and nitrogen oxide (NOx), which contribute to climate change.

Co-processing – replacing fossil fuels with alternative fuels wherever possible – can therefore help to make cement manufacturing more sustainable. In addition, increasing volatility in the price of fossil fuels means that alternative fuels could become a more reliable energy supply and drive down costs.

 WHAT ARE ALTERNATIVE FUELS?

Alternative fuels is a generic term for fuels derived from different industrial and municipal sources. Examples of solid alternative fuels include:

  • Construction and demolition waste
  • Agricultural by-products such as straw, coffee and rice husks, sugarcane leaves and bagasse, rapeseed stems, and palm nut shells
  • Non-agricultural biomass, including animal fat, dung, meat and bones
  • Household or industrial biological degradable wastes
  • Refuse derived fuels (RDF) such as non-recyclable plastics
  • Old tires.

 WHAT ARE THE BENEFITS OF ALTERNATIVE FUELS?

Alternative fuels offer sustainability benefits as well as a way of achieving a circular economy in cement production. For example, there is an increased net global reduction in CO2 emissions when waste is incorporated in cement kiln systems as opposed to dedicated incinerators. NOx emissions are also reduced when low-grade alternative fuels are burned due to reburn reactions. In addition, replacing conventional fuels with waste-derived alternatives helps to conserve non-renewable resources. Their incineration also reduces reliance on landfill or other, less environmentally friendly, waste disposal methods.

Alternative fuels are still an emerging market in North America and other territories, but they offer significant economic potential. Across Europe and in other countries where landfill is not an option, alternative fuels offer the potential for energy cost reductions compared to conventional fuels, because most are generated from wastes which have only modest processing requirements. The commercial agreements required to fully exploit this potential are still being developed but, according to McKinsey, the ample offtake opportunity provided by the cement industry means that alternative fuels could be supplied for free or even at a negative cost by the producing industries. The total annual net value gain from recirculating energy is expected to be €24 billion by 2050.

HOW EASY IS IT TO INTRODUCE ALTERNATIVE FUELS?

The operating conditions involved in cement manufacturing lend themselves to the use of alternative fuels. For example, clinker production in rotary kiln systems combines high temperatures, an oxidising atmosphere and alkaline environment with long residence times and high thermal inertia. These conditions ensure that the organic component of the fuel is fully destroyed while the inorganic part, including heavy metals, is trapped and combined in the product due to the ash retention in clinker.

Selecting the correct alternative fuel is vital for achieving optimum efficiency as well as product quality. As discussed earlier, alternative fuels come from different sources and so have different characteristics to the fossil fuels they replace. This needs to be taken into consideration to avoid problems such as incomplete combustion or blockages due to residual dust build-up in the kilns. Final product quality can also be affected, where combustion by-products are incorporated into clinker.

Whether the alternative fuels are used as a complete substitute or in combination with fossil fuels, their introduction requires careful planning. Upfront investment may be required regarding adjustment or replacement of the burner, establishment of alternative fuel delivery systems, new fuel storage facilities, and fuel distribution systems.

 SUPPORT WITH ALTERNATIVE FUELS ADOPTION

Alternative fuels are still evolving, which means that feedstocks could change over time. For cement plant operators, it therefore makes sense to adopt plant solutions that can be easily customised to use the most efficient and economical fuel available.

Equipment manufacturers can offer guidance on the best system for your requirements, taking into account operational parameters such as the thermal substitution rate (TSR), which has a significant effect on the overall design of the system and the components used.

The adoption of alternative fuels is an important strategic decision, so be sure to work with a trusted equipment manufacturer that understands your particular technical and logistical requirements and can design custom conveying and storage systems that will optimise your return on investment.

 TAKEAWAY

The cement industry must decarbonize to survive, and alternative fuels offer multiple environmental and commercial advantages. However, their adoption demands careful planning and can require major equipment upgrades to achieve. As cement manufacturers continue the transition to lower carbon production, it is critical that they equip themselves with solutions that not only mitigate the operational challenges of today but are also flexible enough to adapt readily to accommodate the alternative fuels of tomorrow.
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