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The road to pure plant oil in diesel engines?

Sensitivity analysis for environmental statistics

This chapter includes a global sensitivity analysis for the indicative well-to-wheel analysis carried out in the previous chapter and for the estimated environmental impact per unit of PPO.

Two approaches were taken:
• Comparing the results of other studies;
• Global calculations of several alternatives to the PPO chain.

Comparing the results of other studies

Comparisons with other studies are difficult. Firstly, because these studies use varying basis data and assumptions, e.g. for the environmental impact relating to fertiliser and electricity production. Secondly, this current study for the Netherlands assumes the use of natural gas for underfiring in industrial processes, and Dutch crop details. In order countries, underfiring may often use oil, while crop results and use of fertilisers can vary from the situation in the Netherlands.
Comparing the results based on the use of energy carriers and additives is often both possible and useful. However, it is clear that many other studies use/advise a nitrogen fertiliser that is less than half that indicated in the various ATO reports. This has considerable consequences for the total contribution of the PPO chain to climate change.

Comparing N2O emissions

Estimating emissions from laughing gas seems to be an important point. This study assumes the following emission factors:

• For production of calcium ammonium nitrate fertiliser (KAS) conform [Wood, 2004] an average emission factor of 1.5%29 is assumed, as determined for the European fertiliser industry;
• For N2O emissions through converting nitrogen from soil-derived KAS, an emission factor of 1% is assumed, conform [Kroeze, 1994]. This RIVM report determines the Dutch emission factor for N2O from fertiliser using the internationally recognised IPSS methodology.

Based on these (net) emission factors and fertilisation of 170-195 kg N/ha, the total N2O emission (field + plant) amounts to 3.1-5.7 kg/ton of PPO. In addition to this, the CO2 emission amounts to around 240-650 kg/ton of PPO, due to the transport emissions and the use of natural gas and electricity for frying, oil production and eventual refining of the oil.
This brings the total contribution to climate change to 1,460 – 2,650 kg CO2-eq/ton PPO. In comparison: the use of 35 GJ diesel30 would contribute to climate change by around 2,960 kg CO2-eq, including diesel precombustion.

On the other hand, the Sheffield study, for example, which served as the basis for [Broek, 2003], used other emission factors:

• For production of ammonium nitrate fertiliser (KAS) this study assumed an emission factor of 1.5%, which is similar to that used in this current study;
• For N2O emission through converting nitrogen from soil-derived KAS, an emission factor of 0.36% was assumed – an IPCC emission factor that has now been changed to 1.25%.

For these emission factors the N2O emission would only be 1.9-4.2 kg/ton of PPO, and the total contribution to climate change would be 1,100-2,200 kg CO2-eq/ton PPO.

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