Produktion av kvävegödsel baserad på förnybar energi - En översikt av teknik, miljöeffekter och ekonomi för några alternativ

Mineral nitrogen fertilizer is one of the main reasons for the high yields in modern, industrial agriculture. There is currently no production of mineral nitrogen fertilizer in Sweden – the entire demand is met by imports from abroad. Global production is at present based on fossil resources, which are used both as raw materials for the production and as energy to fuel the process. We are thus dependent on foreign fossil resources – as fuel and fertilizer – for our agricultural production. However, nitrogen fertilizers could be produced using renewable resources, which could pave the way for a more sustainable production of food and bioenergy.
This report aims to describe and compare different production process options for the production of nitrogen fertilizers based on renewable energy sources. The report presents estimated production costs based on techno-economic modelling, environmental impact of renewable fertilizer based on life cycle assessments, and an overview of potential risks and benefits of renewable fertilizers. The report can be read as a feasibility study, which can be used to provide information for actors who are interested in supporting the development of renewable fertilizers.
The results show that the cost of producing nitrogen fertilizer depends on the choice of production process technology and that some technologies benefit from economies of scale. Among the studied options, the production cost for renewable nitrogen fertilizer was lowest when produced through thermochemical gasification of biomass. The cost for this option was estimated to 11-14 SEK/kg N, which can be compared with the current price of about 10 SEK/kg N. However, gasification of biomass is not yet a commercially available technology but rather a future possibility.
The report also shows that there are options that could be realized in the near future. For these options the needed technologies for nitrogen fertilizer based on renewable energy is commercially available. It is "only" a matter of putting together the various elements that is needed. These options are expected to be about 2-3 times more expensive than conventionally produced nitrogen fertilizers. One of the most promising alternatives is to make urea of biogas, which is estimated to cost approx. 20 SEK/kg N. Another option is to produce ammonium nitrate from wind power, which is estimated to cost approx. 24 SEK/kg N.
The different technology options – different renewable energy sources – each have their pros and cons. When comparing processes based on wind powered electrolysis and reforming of biogas, production costs are similar. Biogas has however a lower investment cost and a lower proportion of fixed costs. Biogas is also a less intermittent energy source, which is a clear advantage over wind that becomes heavily dependent on a hydrogen storage system or the regional energy system to equalize variations in electricity production. Being dependent on the regional energy system means greater risk for cost variation. Reliance on the regional energy system can also be important for the climate impact assessment, depending on how electric power is generated in the region.
Regarding the choice of the final nitrogen fertilizer product, we can conclude that ammonia is the cheapest to produce. However, there is no infrastructure or experience of handling anhydrous ammonia in Sweden, indicating that distribution, storage, handling and use would all require extra investment costs. There are however large risks connected to the handling of anhydrous ammonia as it is dangerous for the environment and to human health in case of leakage. In the comparison between ammonium nitrate and urea, we can see that the estimated production costs are quite similar, with a slight advantage for urea. Urea does however need a source of carbon dioxide, making it an unsuitable option in combination with wind power. Ammonium nitrate is also associated with large risks in storage and distribution, as it is highly explosive.
One of the purposes of producing nitrogen fertilizer based on renewable energy is to reduce the greenhouse gas emissions that are associated with agricultural production. In this report, a summary is made of results from previous life cycle assessment studies. Emissions of greenhouse gases for the production of nitrogen fertilizer based on renewable energy was found to vary between 0.1 to 1.5 kg CO2-eq / kg N, compared with production based on fossil energy that varies between 2.2 to 14.2 kg CO2-eq / kg N. Thus, the nitrogen fertilizers based on renewable energy would yield significant climate benefits compared to conventional, fossil alternatives.
Using renewable energy for fertilizer production is thus an opportunity to utilize renewable resources in a new way to mitigate climate change, while at the same time reducing the dependency of agricultural production on fossil energy market volatility. We conclude that in the short term biogas-to-urea seems like a very promising option that should be studied further. In the longer term, biomass gasification becomes more interesting, given that the technology of gasification proves itself successful in commercial applications. Although there are actors showing interest in renewable fertilizers, there is yet no market for such products. Articulating a demand pull for renewable fertilizers, as well as formulating policy instruments for a technology push are important aspects that need to be investigated further.