The road to pure plant oil in diesel engines?

Side tracks, alternative oil sources and alternative applications

Alternative sources

This study primarily focuses on oil produced from rapeseed, but there are also various alternative ‘oil sources’ for producing renewable oils:

• Other crops apart from rapeseed (soya, sunflowers) ;
• Used oils and fats from the catering sector (e.g. cooking oils);
• Oil from animal residues, e.g. residual fats from slaughter houses.

Oil from other crops

Of the other crop alternatives, sunflower oil and soya are relevant for our region. The former is apparently used as transport fuel in France [Aberson, 2004]. Soya is used in the USA [IFEU, 2004].
With respect to storage-related characteristics, rapeseed oil is superior to sunflower oil because it is relatively stable for oxidation and ageing processes, and has a low wax level [Widmann, 2002]. This high stability is also shown by the low iodine number for rapeseed oil. The solidification point of both oil types is slightly lower than for rapeseed oil, which means that the viscosity is comparable or slightly higher than for rapeseed oil. The oil is therefore easier to implement and, for example, gives fewer problems at low temperatures.
As far as the CO2 balance is concerned, sunflower oil would result in approximately 50% lower reduction of greenhouse gas emissions than rapeseed oil [IFEU, 2004]. No information could be found for soya oil.

Used oils and fats

Using oil and fats from the catering sector is, with respect to the environmental impact, an interesting alternative to rapeseed oil. It would mean that the entire crop growth and its related emissions and energy could be avoided.
However, as far as the research team could ascertain, experience with used oils and fats from the catering sector is extremely limited. In the Netherlands the [AD, 2004] reports that around 360,000 tons of used oil and fats are available. To date these have primarily been processed in animal fodder.
In other countries too, direct application in a non-estered form is very limited. As far as is known, used cooking oils (frying fats etc.) are used in Germany and Austria in a number of cogeneration plants, see [Callegari, 2002]. Exactly how it is processed is not clear; this possibly refers to estered fats. Processing the used oils and fats is theoretically possible, as described in [Falk, 2001]. However, this study indicates that some kind of pre-processing would be necessary for estering, and would cost around € 50,00/ton of fat.
An Internet search (keyword search for ‘frittenoel’) shows that there are vehicles running on filtered cooking oil, but that this is confined to a limited group of enthusiasts, who also use the same conversion accessories as those used to modify engines for rapeseed oil.

Processing used oils and fats, according to the following diagram, would have limited environmental impact. The process is comparable to refining rapeseed oil for biodiesel production and application in the foodstuff industry. For refining, the literature consulted [Elsayed et al., 2003] and[FFE], mentioned the following energy usage per ton of raw oil

• 350 - 580 MJ natural gas
• 6 - 10 kWhe

The environmental impact related to this consumption is marginal compared to the environmental impact related to PPO production from rapeseed.
Considering the potentially huge advantages (both economically and environmentally) it is certainly worthwhile studying this route further.

Oil from animal fats

Producing oil from animal fats is, with respect to environmental impact, is a potentially interesting route, due to the fact that there is no need to grow oil-retaining seed crops and thus no associated environmental impact.
The example of the lorry running on chicken fat (Polskamp slaughterhouse in Ermelo) shows that oil from animal fats is a feasible option (see the website:
http://www.zqcentral.com/index/news/show/3276). The BTG study also shows that processing animal fats into a fuel for stationary engines or transport equipment is a clear possibility (see [BTG, 2002]). The Polskamp example apparently indicates that it is economically attractive for the slaughterhouse to process chicken fat into transport fuel: ‘ Per litre of fuel we save around 30%. This saving is the most important point for us.’ Calculating backwards from a diesel price of 80% per litre, the processing costs would need to be at least € 500 net, per ton of oil.
However, there are only a limited amount of fats available. The [BTG, 2002] study apparently shows that in the Netherlands, there is only 28 kton/year of residual fats available from Dutch pig slaughterhouses, which is by far the largest section of the animal slaughter trade.

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