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Turning industrial waste heat into avocados

The industrial sector produces large amounts of heat that goes to waste – heat that could be used to dry tons of kelp to store CO2, or grow subtropical crops at higher latitudes.

By Petter Røkke, Research Director; Petter Nekså, Chief Scientist; BragRugstad Knudsen, Research Cientist  

The greenest kilowatt-hour is the one you don't need to generate. That is the short version of major point made by the International Energy Agency (IEA) in its forecasts. 

The IEA's premise is that a whopping 37% of the emissions reductions necessary to reach the two-degree warming target are realised by using existing energy more efficiently. But that message often seems to be forgotten. 

Industrial energy efficiency is overshadowed by other necessary climate measures, like electrification, new renewable electricity and CO2 capture and storage. But if we develop new technology for repurposing industrial waste heat, the potential uses for that energy are limited only by our imaginations. 

We could for example have large drying facilities for kelp, or large-scale cultivation of avocados (in areas where the climate would normally not allow it). 

This is exactly the potential that the Research Council of Norway and 26 industry partners are trying to tap into – namely getting the most out of every kilowatt-hour they consume. 

Research centre HighEFF, where Sintef and NTNU (Norwegian University of Science and Technology) are playing a central role, has ambitious targets: cutting the partner industriesenergy use per produced unit by 20-30%, with associated reductions of 10% in greenhouse gas emissions. 

In the food industry, the Centre has shown that these goals can be reached and even surpassed with a solid marginThese results were achieved with new heat pump solutions and process improvements. But among the participants in the Centre, metal producers are lagging behind. 

This is because production in these facilities has already been made as efficient as possible given current technology. But these industries are sitting on an untapped resource in the form of "low temperature" heat – heat that is between 100°C and 250°C. 

In all industrial processes, some energy gets lost in the form of heat. Metal producers are often good at using this waste heat when it is above 250°C, by making electricity with it, for instance. 

Waste heat under 250°C is more difficult to put to use. Some of it goes to district heating. But this is made complicated by the fact that metal producing infrastructure is usually located away from such heating networks. 

Therefore: if the heat is to be used, we need to start thinking differently. Here are two options: 

  • Low temperature waste heat is ideal to dry humid biomass. In a small country like Norway, waste heat from the metal industry alone would be sufficient to dry 8 million tonnes of kelp every year. 

Drying such large quantity of kelp would bind enough carbon to make up for the emissions of half a million fossil-fuelled cars. For the climate to benefit from such a measure, we would need to find a sustainable way to use the dry kelp – a way that would prevent its carbon from getting released in the atmosphere again. An example of such use would be to make charcoal out of it, and then bury this charcoal in agricultural land to fertilize it. 

Another option is to find uses that displace other CO2-emissions, for example by replacing some fossil-fuels by kelp-based biofuels – or by using kelp as a carbon source in metal production (instead of coal and coke). 

  • Another possible area of use is large-scale greenhouse cultivation of fruit, such as avocados. The world's largest avocado producer, Mexico, is struggling with illegal cultivation, deforestation, and water scarcity. Maybe avocados that are free of those problems (and that don't need to be transported over long distances) could become an important niche product in areas where their cultivation would normally be impossible? 

A huge potential for the EU 

The total of the EU's industrial waste heat is at over 30TWh per year. That's energy worth 60 billion euros going to waste every year – the lion's share of which comes from the iron and steel industry. In cases where the waste heat's temperature too low to generate electricity, or where connection to existing district heating infrastructure is impractical, we will need to start thinking creatively. Putting that heat to use in innovative ways – by growing locally produce that would otherwise have to travel over long distances, for instance – could help us reduce our carbon footprint in more than one way. 


A practical example: Norway 

The industrial waste heat Norway has at its disposal for such uses is made by two industries, which by themselves account for 20% of the country's electricity consumption: 

  • Aluminium production: The lion's share of the available low temperature waste heat is generated here. It could cover the heat needs of large industry clusters. But the plants often lack such neighbours. The heat is also not at the level required to convert it to electricity in a profitable way. 
  • Ferroalloy production: Manganese, chromium and silicon are produced here. Part of the waste heat is sufficiently hot that most plants use it to make electricity. Others supply neighbouring industries with steam. But after all that is done, there is still a lot of waste heat – at a temperature that would be suitable for (for example) drying kelp. 

If Norway is to use all this available energy in an effective way, equipment will be needed to transfer the heat from the metal industry's off-gasses and process material to drying facilities or greenhouses. 

Norway is already known for its long coastline, with the possibilities this gives for hydropower and wind power. The country has lots of freshwater resources and lots of light in the summer. With the right investments, it can become a trailblazer in energy recovery as well.

The article was first published in Dagens Næringsliv on March 25, 2021 and is reproduced here with DN's permission.

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