Decentralized oil mill
The decentralized oil mill is a production facility for the production of vegetable oil . In this facility, oil seeds or fruits are pressed into vegetable oil and the by-product press cake . The decentralized oil mill differs from the central oil mill mainly in the lower processing capacity (0.5 to 25 t oil seeds per day), the processing method ( cold pressing , production of native oil) and - related to this - the lower oil yield with a higher residual fat content in the press cake . In addition, decentralized oil mills usually work in an agricultural environment.
The products to be pressed are processed according to the cold pressing principle . With this method, only two processing steps are used, namely pressing and subsequent filtering. In addition to the actual processing (pressing), the oil seeds / fruits are usually stored and cleaned and the oil is stored in the oil mill.
The image of a decentralized oil mill is shaped by the following components:
- Storage warehouse for the processed products
- Cleaning, if necessary drying of the products
- Intermediate storage before processing
- Compression of the products using a perforated cylinder screw press or a strainer rod screw press
- Store the lees before cleaning the oil and press cake
- Oil cleaning by filtering or sedimentation
- Security filter ( police filter )
- Final storage of the pure oil
The oilseeds are stored in dry, ventilated and pest-proof oilseed storage facilities in halls or as outdoor storage. The processed products are removed, for example, via screw conveyors. Drying and cleaning of the oilseeds play a special role in the decentralized oil mill, since errors in storage reduce the quality of the natural oil considerably and cannot - as with central oil mills - be compensated for by subsequent refining. Because of the lower number of raw material batches in decentralized oil mills, quality reductions in individual batches are more significant. In rapeseed, the residual moisture should be less than 9 percent. Contamination, for example from weed seeds (foreign material) or poorly cleaned transport vehicles, must be avoided or removed.
For the production of oil, the oil seeds and fruits are pressed. The vegetable oil contained in it emerges through openings in the oil press , the solids (press cake) with residual fat content are removed at the end of the press. Common designs in decentralized oil mills are cylinder-hole screw presses and strainer-bar screw presses. Similar to the meat grinder, the product to be processed is transported by a screw (spindle) in a cylinder. The material to be pressed is fed to the screw via a funnel-shaped opening. Cylinder screw presses are more likely to be used in the small output range (up to approx. 70 kg of seeds / hour), the strainer rod screw press more in the larger output range.
After pressing, the oil is still very heavily contaminated with pressed sediments. That is why it is temporarily stored in the lees oil tank until it is filtered. An agitator is usually used here, which keeps the sediments in suspension before the oil cleaning takes place. The oil is cleaned by filtering and / or sedimentation.
In the filtering chamber come filter press , the cake-forming filtration and bag filter are used. Candle filters are mainly used as downstream safety or police filters . This ensures that the oil no longer contains any impurities before the product leaves the oil mill.
In sedimentation , which is used in smaller oil production plants, instead of an external energy supply (e.g. to drive a pressure pump), the earth's gravity field is used to remove the sediments from the sediment oil. The pressed oil is put into a container in which it remains for up to several weeks, while the heavier sediments slowly sink to the ground due to gravity. After the sedimentation, the cleaned oil is slowly removed from the container so that the lowered particles remain in the sedimentation container. The oil is then passed through a safety filter and stored in the pure oil tank. Newer sedimentation processes run continuously. The trub oil to be cleaned flows through a system of pipes through containers connected one after the other.
The pure oil storage should be as cool and dark as possible. In this respect, it makes sense to install the warehouse in halls or underground. Tanks made of stainless steel are often used as the material for storing pure oil. The storage tanks should be as easy to clean as possible and protected against the entry of condensation water.
Proper storage of the press cake is crucial to maintain its quality. During production, the press cake develops a high temperature and still has a high proportion of water vapor. In order to reduce the water content, cooling and ventilation are important for long-term storage.
Raw materials and products used
Many different oil fruits and plants are processed in decentralized oil mills. The following types of use are important:
- Vegetable oils as food (edible oil, basic material for many other foods)
- Vegetable oils as energy sources and renewable raw materials ( biofuel , heat generation, bio-based plastics , raw material for the cosmetics industry)
- Press cake as a by-product in oil extraction (high-quality protein and fat-rich feed, fuel and substrate for biogas production).
There are many regional and traditional specialties for the edible oil sector, most of which are marketed regionally or directly. The decentralized oil mills that have emerged in Germany in recent years mainly process rapeseed.
Many decentralized oil mills have been built in Germany since the 1990s. According to the Straubing Technology and Promotion Center, around 79 decentralized oil mills were known in 1999, compared with at least 219 plants in spring 2004. In 2008 around 600 systems were in operation. The growth of these decentralized oil mills is mainly due to the generation of renewable energy sources, especially biofuels. Rapeseed is important as a starting product for biodiesel and rapeseed oil fuel .
For the agriculture sector, in which a large number of decentralized mills are directly integrated, in the so-called industrial nations these have contributed to creating a second mainstay , a further sales market.
The political framework conditions contribute significantly to whether decentralized oil mills have a long-term economic perspective. The balancing of these points with the points listed below is the subject of intense political disputes internationally.
Ecological and social aspects
Ecological aspects are also associated with the use of vegetable oil as a biofuel. Theoretically, the use of vegetable oil only causes as many climate-damaging CO 2 emissions as was bound when the plant grew. In practice, it must be taken into account that the cultivation, processing and transport of oil products using conventional methods removes some of the emissions from the CO 2 cycle. In contrast to central processing, decentralized oil mills usually process oilseeds produced locally. Environmentally harmful transport routes are saved.
- FNR, Handbook Production of Rapeseed Oil Fuel in Decentralized Oil Extraction Plants (pdf) (5.41 MB)
- KTBL - Document 427, Decentralized Oilseed Processing
- Eder, Barbara / Eder, Franz “Vegetable oil as fuel”, ISBN 978-3-936896-05-3 .
- Technologie und Förderzentrum Straubing (TFZ): Production - Oil extraction.
- Technologie- und Förderzentrum Straubing (TFZ): Oil cleaning in decentralized oil mills ( Memento of the original from August 4, 2008 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.
- BLT Wieselburg: Announcements of the Renewable Raw Materials Working Group, No. 34, December 2004 ( Memento of the original dated February 11, 2006 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.