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The road to pure plant oil in diesel engines?
Global analysis of alternative construction of the
PPO chain
Evaluation of possible alternative farming systems
This analysis continues to focus on the current practice of growing winter rapeseed. The
crop is treated with KAS, and conventional diesel is used to fuel the agricultural vehicles.
Grey electricity from the grid is also used for decentralised activities such as drying and
small-scale oil production. The straw that remains after harvesting is generally ploughed
back into the soil because there is very little market for this product.
In order to check how sensitive the results of the study are to these system assumptions, the
research team has estimated the net contribution to climate change for a number of
alternative systems, using the following alternatives:
- Using renewable energy carriers. PPO is used for agricultural vehicles and other means
of transport. Green electricity is purchased for drying and small-scale oil production;
- For crop growing, the maximum amount of animal manure is used and minimum
possible fertiliser;
- Straw is not ploughed back into the soil, but used to fuel a decentralised cogeneration
plant.
Using renewable energy carriers
Using PPO in agricultural vehicles and other means of transport, but purchasing green
electricity for other tasks, does not seem to result in a significant reduction in the net
contribution to climate change. This can be explained as follows:
- The system used in this study assumes the use of conventional diesel and grey electricity
as being only 15-20% of the total greenhouse gas emissions in the PPO chain;
- For agricultural activities and transport only 100-150 g of the produced PPO ar
required.
In other words, an important part of using renewable energy carriers would be cancelled out
because there would be less net PPO to be used by the fuels market to replace PPO.
Replacing a maximum amount of fertiliser with animal manure.
Replacing KAS and TSP (TriSuperPhosphate) with animal manure has the potential
advantage that the environmental impact associated with fertiliser production can be saved.
The production of KAS, in particular, provides a significant contribution to the total
greenhouse gas emissions in the PPO chain, due to the N2O emissions that occur during
production.
The amount of fertiliser that animal manure can replace is fairly limited due to the
maximum amount of nitrogen and phosphor that may be ploughed into the soil in the form
of animal manure. Manure also has a lower efficiency as N-fertiliser, which means that more fertiliser/nitrogen would be required. Animal manure also has a higher emission of N2O
per unit of nitrogen.
These three effects ensure that replacing part of the fertiliser would not lead to a reduction in
the net contribution to climate change, but could actually cause a slight increase. This is
further explained in Appendix D.
Using straw as an energy carrier
Straw produced from rapeseed is currently ploughed back into the soil, due to the lack of
sales possibilities. However, current technology means that it would be possible to use the
straw as an energy carrier.
Processing options for rapeseed straw as an energy carrier are, in theory: co-incineration in a
coal-fired power plant, or incineration in a specially built incineration plant31 , such as occurs
in Denmark. The chance that this would take place in the Netherlands is fairly small. Due to
the negative influence of the straw on the quality of the powder coal fly-ash, co-incineration
is not a very attractive option. There are also extra costs involved in making plants suitable
for co-incineration of straw, while it is expected that the management of coal-fired power
plants would offer a lower price for this alternative fuel. The economic profit from residual
flows, such as RWZI sludge (from sewage treatment plants) and B-grade wood are also
looked at carefully by management teams. Incineration in a specially built plant would
probably be too expensive.
In the case of using straw as an energy carrier, part of the environmental impact relating to
the rapeseed crop should be accredited to straw, which means that (conform the LCA
methodology), straw then becomes a valuable by-product.
Based on the current calculation methodology using economic value, it is expected that the
straw-based environmental impact would be limited, because straw as a fuel will have a
market price that will never be higher than a few dozen euro per ton. The value of the oil (€ 600/ton) is so high that, in comparison the turnover for straw will be only marginal.
This picture changes, however, when prices are attributed based on energy content. Straw,
rapeseed cake and oil each represent around 40%, 25% and 35% respectively of the energy
content of the entire plant.
When attributing these amounts based on energy content, and assuming that straw can be
sold as an energy carrier, the crop-related environmental impact of the oil only amounts to
35%. This study assumes a percentage of 70-75%. In other words, the environmental impact
attributed to the oil will then only amount to 50% of the environmental impact calculated by
this study.
Acknowledgements
This publication has been produced by the GAVE programme. GAVE stands for Gaseous
and Liquid Climate-Neutral Energy Carriers, and is a programme that aims to accelerate the
development and introduction of climate-neutral fuels into the Dutch transport sector.
SenterNovem executes the GAVE programme for the Dutch Ministry for Spatial Planning,
Housing and the Environment, in close collaboration with the Ministry of Economic Affairs
and the Ministry of Transport, Public Works and Water Management.
Further information is available from:
Website: http://www.senternovem.nl/gave
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