11 December 2019

Blue Urea: A fertiliser with reduced environmental impact

Scientists and engineers from the Institute for Sustainable Food and the Energy Institute have created a fertiliser with reduced environmental impact called Blue Urea.

seed and planting concept with Male hand watering young tree over green background

Scientists and engineers have created a fertiliser with reduced environmental impact called Blue Urea.

The world is fast approaching the limit of its ability to feed itself so maximising the efficiency of food production is imperative. As crops grow they use up nutrients from the earth so fertilizers are needed to replenish the soil and maintain agricultural productivity. That’s why, until we can make a step change to increasing organic matter in soils, synthetic nitrogen fertilizers such as urea are a necessity for food production and a vital component in achieving global food security.

The problem is that the production process of urea, (which accounts for more than 70% of worldwide fertilizer usage) emits CO₂, a greenhouse gas that is a major contributor to climate change. Scientists at the University of Sheffield's Institute for Sustainable Food and Energy Institute have found a way to produce urea that reduces CO₂ emissions by up to 21%.

The paper, Blue Urea: A fertiliser with reduced environmental impact by Justin Driver, Rhodri Owen, Terence Makanyire, Janice Lake, James McGregor and Peter Styring is published in ‘Frontiers in Energy Research’ and outlines a number of steps in the production process that when combined lead to a dramatic reduction in the overall CO₂ emitted in the fertilizer’s production.

This was a challenging piece of work due to the complexities of the design. However we got there eventually to produce a very effective fertiliser. There were many delays so we missed the growing season on the farm. Thankfully we were able to use the season long growing facilities in University of Sheffield’s Institute for Sustainable Food which saved the day! The project was funded by BBSRC and Innovate UK and provided us with legacy facilities at scale that we have been able to repurpose in further projects.

Professor Peter Styring

Professor of Chemical Engineering and Chemistry

Tractor spraying pesticide

Saving emissions through decentralising the production process

Urea is normally manufactured in production plants at an enormous scale, with the pelletised urea product then distributed ready for use. The paper demonstrates that the production of Blue Urea can be decentralised and scaled down so significantly that it can be produced at point of use. This means there’s an emissions and cost saving because there is no need to transport the urea long distances between where it is produced and ultimately used. Further cost and energy savings are made because drying and pelletisation, which was required for transportation, is no longer needed. 

Saving emissions through changing the way hydrogen is produced

One of the ingredients of urea is hydrogen. The traditional way of making hydrogen is through a process called steam reformation. The downside of steam reformation is that it requires high temperatures. To achieve those high temperatures we need to combust fossil fuels and when combusted, fossil fuels release CO₂ into the atmosphere. 

There is an alternative way to produce hydrogen that uses renewable energy and does not need fossil fuels as a feedstock for combustion. Electrolysis is a process that can split water into hydrogen and oxygen. If the process is powered by electricity generated from renewable sources such as wind and solar power the process of making hydrogen becomes carbon neutral.

Saving emissions by reusing CO2

Another ingredient for urea is carbon dioxide. This is traditionally produced in the same steam reformation process that is used to create hydrogen. But if hydrogen is produced by electrolysis, the CO₂ has to be sourced from elsewhere. The CO₂ can either be captured and recycled from another emissions source or it can even be extracted from the air. To find out more about the process of capturing and reusing CO₂, take a look at the research being carried out at the University of Sheffield’s Energy Institute. 

Saving emissions by reducing temperatures throughout the production process

The traditional method of producing urea requires high temperatures, and therefore the use of fossil fuels throughout. But to enable production to be decentralised and made on site the authors of this paper have found an alternative method of production that requires ambient temperatures. This again, removes the need for fossil fuel combustion and its associated emissions.

Whilst the paper shows that urea can be made in a way that has reduced environmental impact, the authors acknowledge that the new processes increase the costs of production. This is mainly due to losing the economies of scale achieved in mass production and the energy needed for the electrolysis in hydrogen production. Further research is needed to balance the commercial viability and environmental impact of fertilizers.

Read the research in Frontiers In Energy journal

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