oil pressing

Oil pressing or expeller pressing means a mechanical method for extracting oil from vegetables, nuts and seeds. by physics pressure, All the courses are without any chemical additive. It is cost efficient, versatile and chemical-free. The most two popular oil extraction methods today are using screw press(oil press machine) and using Chemical solvents, however, in order to squeeze the most oil out from the raw materials, more than one method is used, often, the two methods are used together. Usually press the material firstly by a screw type press machine and then get the rest of oil in the meal by using chemical solvent.

Mechanical extraction is how things were done for centuries. This method usually uses an expeller press to give pressure on vegetables, nuts and seeds to cause the oil to run. Oil pressing ranges in capacity from less than 1 ton to over 50 tons per day, and today the expeller press is universally used for the continuous mechanical extraction of oil regardless of the size of the operation. There are numerous factors play effect on the oil extraction efficiency, such as the vegetable seeds type, seeds cleaning, temperature, and press configuration. Usually the mechanical pressing method provides yields of only 65-70% of the oil, and 80% is considered very good. Most large commercial operations use a mild pressing operation to extract 60 to 70% of the oil, while the remainder is solvent-extracted.

Mechanical Oil Pressing Workshop

Mechanical Extraction VS Solvent Extraction

Mechanical extraction and solvent extraction are the most two popular oil extraction methods in today’s oil making industry. The mechanical extraction way means making use of screw expellers to press oil out from vegetable seed and nuts, the solvent extraction method, however, always use a petroleum by-product, usually Hexane to separate oil out. These two extraction methods are both have advantages and disadvantages, we will show you below.

• The mechanical extraction is a greener and healthier way of making oil for there will be no solvent (chemical) residues in oil. The expeller pressed oil is cleaner more pure oil, higher in natural colors and flavors. The advantages of pure mechanical extraction are lower initial investment costs, higher-value edible oil and meal, less complex operation, versatile to process many kinds of oil seeds, The disadvantages are high power requirements, wear and tear on the equipment that requires maintenance, and lower yield due to residual oil in the meal.
• As compared to the mechanical extraction method, the solvent extraction method makes high oil yield, spends lower production cost and less time and care, it is a much safer alternative to the previous way. You won’t have to spend all day long to watching you expellers working! The solvent extraction method always have disadvantages, Large quantity, can work continuously, high pressure, for example,  the high construction cost of the solvent extraction and refining workshop.

Oil Pressing Process

Generally there are usually two processing systems for oil pressing, one is Pre-pressing (combination with solvent extraction) and the other is Full-pressing (a true mechanical oil extraction process).

Pre-pressing: Pre-pressing means extract oil first by mechanical screw press and then the pre-pressed cake is sent to the solvent extraction plant. This method is usually being used for larger capicity oil mills. Rapeseed/Canola seed and sunflower seed typical vegetable material for pre-pressing. The pre-pressing method can approximately extract oil 65% up to 75% in the seed. If you trying to get more oil out by mechanical method, the electrical energy consumption of the presses will drastically rise, the internal parts of the screw press becomes substantial, the load may exceed mechanical limitations and may lead to capacity reduction and the press cake shows a structure which makes solvent penetration more difficult.  Pre-pressing systems today may have seed processing capacities of 3,000 MTPD and more.

Seeds are firstly fed into the prepress expeller through the feeder opening, and then enter the pressing chamber, where they willl be pressed. 70% of the oil will be extracted; the oil residual in cake is around 15-18%. The solid residue from prepressing is used for solvent extraction process so that the remaining oil can be extracted from it.



Full-Pressing:  Full-pressing refers to extracting the oil only with mechanical pressing method. Full-pressing can be also be called single pressing and usually be applied for smaller capacity oil milling plants. If the seeds have high oil content, double pressing should incorporated for maximum yield. The oil could be extracted as much as possible, the oil residual in cake is around 5-8%.

Due to the nature of the product de-oiling is physically limited by inter-molecular and capillary forces. However, while a typical pre-pressing system shows oil yields of approximately 70% the full-press can reach 90% and beyond. This translates into common residual oil contents in the full-press cakes of 5 to 8%. In order to achieve the extra oil recovery rates, the seed material has to be exposed to higher pressures over longer retention times in the screw presses. The higher pressures are primarily achieved by lower seed moisture leading to considerably higher friction in the presses. The higher pressure limits the capacity of the presses as it determines the maximum diameter of the press cages for mechanical strength reasons. Moreover the desired longer retention time asks for a low shaft speed, which limits the capacity even further. Therefore, full-presses are characterized by a limited capacity of approximately only 1/10 of the capacity of modern pre-presses.

Oil Press Machine

Oil press machine (oil expeller press) is the soul equipment of the pressing process, it can be divided into small oil press and big oil press according to its capacity, it can also be put into screw oil press and hydraulic oil press as to its working principle. In comparison with the hydraulic oil press, the screw type expeller press has a great deal advantages, For example, better adaptability, flexible production, high quality of the oil, light color, pure flavor, simple technology, and few supporting equipments etc. Here we will talk about the screw type oil expeller.

Small Oil Press	Big Oil Press	Integrated Oil Press

How Does the Screw Expeller Press Work?

An expeller press is a screw-type machine that presses oil seeds through a caged barrel-like cavity. Raw materials enter one side of the press and waste products exit the other side. The machine uses friction and continuous pressure from the screw drives to move and compress the seed material. The oil seeps through small openings that do not allow seed fiber solids to pass through. Afterward, the pressed seeds are formed into a hardened cake, which is removed from the machine. Pressure involved in expeller pressing creates heat in the range of 140–210 °F (60–99 °C). Pressure involved in expeller pressing creates heat in the range of 140-210º F (60-99º C).

Main Parts of Oil Press Machine

The typical oil press features three important parts: the cage, screw, and cage bars.

Cage: This assembly houses the screw and cage bars. As seeds pass through this section, oil seeps out into the oil reservoir below. Some solids pass through as well and are pumped out with the crude oil.

Screw: This conveys the seeds through the press cage and against the cage bars. The action of the seeds being conveyed against the cage bars squeezes the oil out of the meal. When the meal reaches the end, the cake falls out and is conveyed to the next process. A motor is used to drive this screw.

Cage Bars: These bars are spaced very closely together and form a ring around the screw. When the cage is closed, these encircle the screw. As mentioned above, these work with the screw to help shear and press the oil out of the seeds.

Small Oil Pressing Plant

The small oil pressing plant is a mini capacity oil extraction line which is fully adopted mechanical driven. It connects a series single oil processing equipment together to realize continuous oil extraction with easier operation and higher rate of oil yield for a greater efficiency. The small plant is able to process a great number of vegetable seeds and nuts, such as peanuts/groundnuts, canola/ rapeseeds, sunflower seeds, soybeans etc.

Merits for Small Oil Pressing Plant

• Small investment, fewer land space, but with the complete function of oil processing plant.
• Easy to operate, install and commissioning.
• Wide application for a great number of vegetable plant seeds.
• Labor saving and can make worker more safty under the higher temperature working situation.

Main Equipment Included

Screw Oil Press
	Screw oil press is the key equipment in the small oil pressing unit. It is a mechanical method for extracting oil from raw materials. Different models screw expellers will be used according to different capacity and oilseeds you are going to process.

Cooker
	Cooker or you can say oilseed roasting machine is always being used to warm up the oilseeds before pressing. Every crop material has its most suitable crushing temperature, so adjust the temperature and water content before pressing by a cooker will obviously increase the oil output.

Filter Press
	Filter press is being used to purify the crude vegetable oils after pressing, the filtering machine utilizes a fine-mesh filtering cloth, which is particularly useful in bio-diesel oil refinement.

Extrusion – Better Way to Improve Press Efficiency and Oil Yield

There are other ways to expand oil processing as well. Extrusion may be able to increase press efficiency and yields by allowing oil cells to rupture, making the oil easier to access and remove. In the case of soybeans, this process is able to extract up to 66% of the available oil out of the seed. Other seeds can be processed in this manner as well. Oil pressing is just the beginning, and with the proper equipment and guidance, you will be able to process efficiently and chemical-free.

What Can Be Done with the Meal After Mecanical Oil Extraction?

Mechanical oil extraction not only produces crude oil but also oil meals( oil cakes) at the same time. Oil meal made by the mechanical pressing method is more valuable as a livestock feed for it contains approximately 5 to 10 percent or more of the original oil content of the seeds. Oilseed meal is often used as a protein supplement for cattle. Therefore, cake with a higher protein content often commands a higher price. But protein is not the only thing that matters. Canola meal (which has a lower percentage of protein than soybean meal) has been found to be good for milk production in cows. Some cake is not suitable for livestock feed. Mustard seed meal, for example, has high concentrations of glucosinolates, which prevent absorption of some nutrients. However, this meal has been shown to have excellent herbicidal and pesticidal properties when used as a soil amendment and has the potential to be a high-value by-product.