Skip to main content
Report, 2007

Användningsområden för biprodukterna vid pressning och omförestring av rapsolja

Bernesson, Sven


Rapeseed contains 40-50% oil that can be extracted by pressing and possibly subsequent extraction. The residue, rapeseed cake, normally contains 10-25% oil, but rapeseed meal subjected to extraction only contains a few percent oil. Rapeseed cake and rapeseed meal can be used as animal feed, fuel, biogas substrate or fertiliser. If the extracted oil is used as a vehicle fuel it is normally transesterified to rapeseed oil methyl ester (RME) and then glycerol is produced as a by-product. Glycerol can be used for animal feed, fuel, biogas substrate or in the chemical industry as a raw material or additive in several products. The main purpose of this work was to evaluate how rapeseed cake and rapeseed meal, together with glycerol from transesterification of rapeseed oil, could be used in different applications, and to calculate their economic values in these uses. Used as a ruminant feed, current rapeseed cultivars can provide the entire dietary protein requirement. Up to 10% of the feed or concentrate mix for pigs, poultry and horses can comprise rapeseed feed. For piglets and horses, the palatability may limit the amount fed. The amount of rapeseed cake fed is restricted by its oil content. Normally, ruminants can manage 5% fat and horses about 2% fat in concentrate, and pigs 5% and poultry 1-1.5% fat in the overall diet. Glycerol can be an energy component of the feed mix. Cattle, sheep and pigs have been successfully fed a mixture containing 5-10% glycerol, and poultry a mixture containing 5%. Glycerol works well as a binding agent in feed pellet manufacture, with an admixture of 2-3% giving a more solid pellet. Glycerol is hygroscopic and absorbs water from the air if too much is added to the feed mixture. This impairs feed storage qualities. Rapeseed cake and rapeseed meal may be incinerated, but produce an ash with a relatively low melting-point, causes sintering and deposits to form in the furnace. The amount of ash is rather high, about 6%. The high nitrogen content (4-6% of dry matter) gives high nitric oxide emissions, often 2-3.6 times the emissions of fuels deficient in nitrogen. The high oil content in rapeseed cake gives it a comparatively high heat of combustion. Glycerol is difficult to incinerate alone, but can be incinerated when mixed with disintegrated solid biofuels such as sawdust or wood shavings. It would probably act as a binding agent in solid biofuel pellets or briquettes. Rapeseed cake and rapeseed meal can be used as an organic fertiliser, with 4-6% nitrogen, 0.4-2% phosphorus and 0.3-1% potassium. Organically bound nitrogen is released slowly. Glycerol has no value as a fertiliser unless it contains potassium residues from the catalyst (about 0.6%) used for transesterification, and possibly also phosphorus residues (about 0.16%) from the phosphoric acid that may be used to neutralise the catalyst. Rapeseed cake, rapeseed meal and glycerol are very suitable for anaerobic digestion. Rapeseed cake and rapeseed meal are nitrogen-rich media that may cause too high a content of ammonium nitrate in the biogas reactor. The oil in rapeseed cake may cause other substrates such as farmyard manure to give a higher gas yield. There are similar observations of methane gas yield increasing when glycerol is digested together with protein-rich media. Glycerol can be used as a carbon source in biogas processes. The plant nutrients in rapeseed cake and rapeseed meal are more easily available after biodigestion. The economic value of rapeseed cake, rapeseed meal and glycerol has been calculated on the basis of the replacement value of barley and soybean meal for feed, forest wood chips for incineration, nitrogen, phosphorus and potassium for fertiliser, or sales of electricity and district heating from a large farm-scale biogas plant. Rapeseed by-products were most valuable when used as feed, followed by use for combustion and biogas with a high gas yield. They were least valuable when used as fertilisers and for biogas with a low gas yield. The world market values of barley, soybean meal and feed fat (rapeseed oil) had a large influence on the value of the by-products and on the gas yield etc. from the biogas plant. The price of forest wood chips and fertilisers had a smaller influence on the results, since these products had a lower initial value. Domestic animals can by far consume all the rapeseed cake and rapeseed meal that can be produced in Sweden. Dairy cows can consume large quantities. Much larger quantities of glycerol can be consumed by domestic animals than can be produced through transesterification of rapeseed oil of Swedish origin. This means that the glycerol from a considerable proportion of imported rapeseed oil could be used for feeding purposes. There is nothing that limits the amount of rapeseed cake, rapeseed meal and glycerol that can be used for combustion or as fertilisers, other than their economic value in these applications. Glycerol may have added value if it can be used successfully as a binding agent in feed pellets, biofuel pellets or briquettes. It is only possible to digest a limited proportion of the potential production of rapeseed cake and rapeseed meal in domestic biogas plants. However, there is no problem with digesting the possible production of domestic glycerol and more in existing biogas plants. Furthermore, the glycerol may have added value because it can increase the methane gas yield from other substrates during co-digestion. Future studies should examine in detail the properties of glycerol as a binding agent in production of feed pellets, biofuel pellets and briquettes. The properties of glycerol as a carbon source for production of biogas when co-digested with other substrates should also be investigated. There is also a need for plant breeding of the rapeseed to decrease the content of anti-nutritional carbohydrates and proportion of husk in the seed. This would allow larger amounts of rapeseed cake and rapeseed meal to be used in animal feed, mainly for monogastric animals


Raps rapsolja RME rapsmjöl rapsexpeller glycerin glycerol foder bränsle förbränning gödselmedel biogas kostnader potential

Published in

Rapport. Miljö, teknik och lantbruk
2007, number: 2007:04
Publisher: Inst f biometri och teknik, SLU

    SLU Authors

    UKÄ Subject classification

    Social Sciences
    Renewable Bioenergy Research
    Agricultural Science
    Economics and Business

    Permanent link to this page (URI)