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The road to pure plant oil in diesel engines?
Distribution, from processing to
end-user
Technology
PPO refuelling and storage
PPO should be stored in an oxygen-free dark environment, and well protected against water
leakage. The transport equipment and storage tanks used for storage and distribution should
be made of synthetic material or stainless steel, due to the high acidity of PPO.
For large-scale distribution systems, the stocking of distribution locations will generally
occur in the same way as for fossil diesel [IEA, 1996]. This means that the distribution occurs
from a central point and that refuelling stations are regularly restocked from tanker lorries.
In theory, PPO can be mixed at refuelling stations with fossil diesel – in any ratio. However,
a mixture of PPO and diesel is not desired by the market because it can give problems for
vehicles that have not been modified (see Chapter 7).
Solaroilsystems will use an alternative distribution system in the Netherlands. The oil will be
transported to the customers in tankers containing 15,000-20,000 litres, which will be
coupled at each location to a modified diesel pump. The fuel will be sold to hauliers, utility
companies owning fleets of vehicles, shipping and other large-scale diesel users
[Solaroilsystems, 2003].
It is currently not yet possible to refuel your car with PPO at commercial refuelling stations
in the Netherlands, because PPO does not meet European criteria for motor fuels, and the
government is also not prepared to grant duty exemption. However, this is the case in
Germany, where PPO is offered separately at refuelling stations. In the Netherlands PPO can
only be tanked at several oil presses, where a permit has been granted. In order to refuel
vehicles on private property using PPO, refuelling installations (1,000 litres) can be
purchased in the Netherlands for around € 750, excluding VAT19 . For larger installations,
the costs per litre are lower. A modified refuelling nozzle is required when refuelling the
vehicle with PPO, due to the higher viscosity.
Stability
With regard to the stability concerning oxidation of PPO, the literature and the experts
consulted gave opposing indications. The following section gives first a brief theoretical
description, followed by a summary of practical experience gained.
A quality reduction can occur through bacteriological deterioration (it is actually a liquid
that deteriorates easily), water intake and oxidation. The last two mechanisms produce free
fatty acids, which can cause corrosion of the injector pumps and injectors during direct
injection into diesel engines. In addition, quality change also leads to changes in the
combustion-technical characteristics, which in turn has consequences for the performance
and emissions of modern engines. These are regulated with considerable accuracy within a
small margin and are fine-tuned according to the expected characteristics of the fuel.
In general, the iodine number of a fuel provides an indication of its stability for oxidation.
Oils with a low iodine number are less sensitive to oxidation than oils with a high iodine
number. Considering the high iodine number in PPO it is a relatively unstable plant oil, but
it is more stable than biodiesel. There is very little information available about the problems
that this can cause. PPO is in any case less stable than traditional diesel (because PPO can
damage copper pipes), but it is more stable than biodiesel. Apparently adding an
antioxidant may help prevent the oil being degraded through oxidation.
In practice, some parts of the aforementioned description agree with the practical experience
gained, however in some cases, the experience has been more negative.
According to [Thuneke, 2004], the stability of PPO should not be a problem. When taking the
regulations for storage into account, PPO can be stored for 6-12 months without the oil
deteriorating.
Under the framework of the ‘100 Tractors project’ it has been clearly determined that there is
considerable degradation of PPO when stored for a long time [Hassel, 2004]. Oil that
originally met the ‘RK Qualitätsstandard 05/2000’ appeared, after long-term storage , to
have deteriorated such that it no longer met this standard. Based on their practical
experience the authors of this report therefore conclude that it is necessary to refine the oil in
order to guarantee a high-value fuel .
One standard for fuel quality
Rapeseed oil does not meet the current European standard (EN 590) for diesel, therefore it
may not be sold as a fuel on the Dutch market (i.e. at a refuelling station). The government
has granted an exemption for a trial project in the north of the Netherlands, where 3.5
million litres of PPO may be produced until the year 2010. However, a product
standardisation is necessary for large-scale market introduction.
There is no such standard for raw rapeseed oil, such as for other biofuels (e.g. biodiesel). The
reason for this is the limited use, to date. Because reliable use of the fuel and optimum
engine tuning (emissions) are very important, a German working group (representing
manufacturers, research organisations, engine manufacturers and the relevant governmen
ministries) have recommended a single standard for cold pressed rapeseed oil. The fact that
this took place in Germany is due to the number of activities relating to PPO use in vehicles
and vehicle modifications in this country.
The RK standard (Qualitätsstandard für Rapsöl als Kraftstoff) that has been developed
specially for PPO describes a number of important parameters that specify the product.
Despite the fact that the standard is still not final, because further experiments are still being
carried out, it is seen as a guideline by engine manufacturers, rapeseed producers and
processors. The proposal is shown in Table 6.1. At the time of writing, Germany is working
on a DIN standard21 (DIN UA 632.2) where the RK standard serves as starting point.
Standardisation in the Netherlands is not yet relevant due to the small market for PPO, in
contrast to that in Germany. According to Mr Aberson of Solaroilsystems, production in the
Netherlands will also follow this German standard.
The characteristic criteria are determined by nature, and vary only slightly. The variable
characteristics, such as phosphor content, ash content, and water content, are influenced by
the way in which it is grown, harvested and pressed. The variation in these characteristics is much larger. German scientists indicate that the RK standard forms a good basis for a
German or European norm (Remmele, 2002].
Practical tests in Germany show that in many cases PPO does not meet the RK standard,
particularly the variable characteristics are in excess of the maximum value. The reasons for
this are the low seed quality, lack of refining steps and quality assurance throughout the
chain. Deficient storage conditions also play a role [BLT Wieselburg, 203]. A Japanese study
showed that not carrying out a number of purifications steps reduces the quality of the fuel
and can even cause problems through the build-up of uncombusted particles [Togashi,
1998].
Energy usage
Energy usage from distributing PPO is estimated at 1% of the energy content. In other
words, distribution will use around 10 litres of diesel per ton of oil. For small-scale
distribution this may be slightly higher [IEA, 1996]. On the other hand, if PPO is sold
directly from the oil press or the local rapeseed supplier, there is no real energy
consumption, or this is extremely limited.
The environment
Emissions of hydrocarbons during storage and refuelling are negligible due to the low
vapour pressure of PPO. The following emissions are estimated for distribution (based on
diesel consumption and emission data from [MV5, 2000]). It is assumed that distribution will
be by road (in lorries).
Costs
The costs of distributing PPO are in the same ballpark as for other biofuels and fossil fuels.
Various GAVE studies have estimated this at € 0.10/litre, or around € 110/ton of oil.
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