We have a problem with cardboard recycling. In the United Kingdom they believe that the solution is to use it in a power plant

Every day, millions of cardboard boxes leave our homes heading to the blue container. They are the last link in an accelerated consumption cycle in online commerce. However, this material, so everyday that we don’t even look at it twice, could be on the verge of an unexpected second life: becoming fuel to generate electricity on a large scale.

A residue that enters the energy map. A team of engineers from Nottingham University has shown for the first time that used cardboard can be used as an effective source of biomass in power plants. The investigation, published in the journal Biomass and Bioenergycompares cardboard with a common reference for industrial biomass: eucalyptus.

The engineers didn’t just watch the cardboard burn. They crushed it, studied its shape, broke down its chemistry and analyzed how it reacted to heat and what type of carbon it left behind. They even developed their own method—based on thermogravimetric analysis—to measure exactly how much calcium carbonate each sample contains. This component, common in printed cardboard, gives rigidity to the material but also conditions its behavior when burning. Thanks to this procedure, they can predict which type of cardboard will work well in an industrial boiler and which could cause problems.

The science behind cardboard that burns “better.” The study did not stop at theories. He tested the combustion of cardboard in two types of systems equivalent to those used in power plants:

• Drop Tube Furnace: Simulates the rapid combustion of pulverized biomass.
  Here, the researchers observed that cardboard particles develop chars (the carbonaceous remains that remain after the first combustion phase) highly reactive, with a predominance of fine and porous structures that favor a burnout accelerated.
• Muffle Furnace: Simulates fluidized bed or grate systems. Even with longer residence times, the paperboard maintained its excellent combustion profile.

In addition, the size and shape of the particles were characterized through an analysis with more than one million particles per sample; The tendency of cardboard to form “spongy aggregates” during grinding was observed—a challenge for its industrial handling—and characteristics such as sphericity and aspect ratio were correlated, something that could improve future combustion models. As the academic study explains, this detailed analysis allows predicting combustion efficiency and designing industrial strategies to integrate cardboard into the fuel flow.

The result was very favorable. Thanks to this experiment, the engineers managed to demonstrate that cardboard has less carbon (38%) than eucalyptus (46.7%) and its calorific value is also lower (15.9–16.5 MJ/kg versus 21 MJ/kg). However, its chars are finer, porous and reactive, which accelerates combustion; In addition, it contains much more ash (8.9–10.6%, compared to 0.6% for eucalyptus), a critical aspect for boilers.

What remains to be resolved? Although the technical potential is evident, the study makes it clear that cardboard is not ready to enter the boilers of a power plant tomorrow. There are three fundamental challenges that must be addressed:

• Management and processing problems. When ground, cardboard does not behave like wood: it forms spongy lumps of very low density that make internal transport difficult, complicate the continuous feeding of boilers and can increase the risk of blockages and accumulations. The study warns that it will be essential to adapt the grinding and feeding systems to guarantee a stable and safe flow.
• The behavior of calcium. Cardboard contains very high levels of CaCO₃, especially when printed. This calcium can behave in different ways depending on the temperature and type of boiler. In certain cases it raises the fusion temperature of the ashes – which is positive -; In others it can favor the formation of slag or alter the quality of the fuel. The study recommends analyzing the behavior of cardboard according to the type of plant, because not all technologies tolerate these variations in the same way.
• Large-scale industrial validation. Laboratory tests are promising, but the decisive step is missing: testing the cardboard in real operating conditions. According to the researchers, the industry will have to carry out tests on different technologies in boilers, evaluate emissions, study the accumulation and composition of ash and check their compatibility with existing biomass mixtures. Only then can it be determined whether the cardboard can be safely and stably integrated into the mix of biomass.

An everyday material with an unexpected future. Cardboard protects pizzas, televisions, books and appliances. We recycle it without thinking too much about it. But this research from Nottingham suggests that this everyday waste could become another piece of the energy transition, helping to diversify fuels and take advantage of an abundant and local resource.

Today we see it as garbage. Tomorrow it could help produce electricity. The spark has already been lit: now we need to know if the industry wants – and can – convert it into real energy.

Image | Unsplash and Geograph

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