A common misconception we hear from oil millers is that after the pressing process, oil extraction ends with a perfectly clean oil product. In reality, the oil leaving the press tends to contain solid contaminants, consisting of small pieces of seed husks and hulls to dust and other impurities and a certain level of phospholipids. In fact, if you don’t see many solids in your oil stream, you likely aren’t squeezing hard enough! While a certain amount of solid contaminants or “foots” are expected, these particles need to be filtered out to varying degrees depending upon the oil’s intended use.
There are a few ways to remove the fines from the oil, and the decision to choose between one clarification method over another depends on the processor’s market and need. Let’s look at different oil clarification methods and discuss how to select the best one for your product.
Clear and Clean
Oil from a screw press will contain 10 percent to 15 percent solids in a typical processing environment, depending on numerous factors. The most common way to remove this material is with gravity; the oil is pumped to a large screening tank and given 45 and 60 minutes of residence time to allow gravitational forces to pull the solids to the tank’s bottom. The tank’s rotating paddles scrape the settled foots off the bottom, lift them to the top, drag them across a wedge wire screen to allow any free oil to drain off, and then dump them into a recycle stream to return them to the press. These recovered solids can contain over 50% oil by weight and should be recycled to the presses to recover as much of the oil as possible. The product oil is continuously pumped off the top layer of the screening tank from an overflow chamber to storage or further processing.
Even after the screening step, however, most oils will still contain approximately 5-6 percent solids. This oil is then sent to a filtration system consisting of a pressurized tank containing stainless steel leaf devices holding wire mesh of varying granularity. This process usually gets the oil down to 0.1 percent solids or less, making it suitable for animal feed rations or for further refining, bleaching, and deodorizing (RBD) if intended for human consumption.
Another approach to removing solids from oilseed is to apply centrifugal force. The oil can be rotated at up to 4,500 RPM in a decanter or large centrifuge to provide a very rapid and slightly less effective separation of the solids from the oil.
The decision to use the gravity method or the centrifuge and decanter method for oil clarification is a choice that must take into account several variables, including budgets, operating practice, and physical infrastructure.
The Right Choice for You
The benefits of each approach depend primarily on the individual processor’s goals and existing environment. Centrifuges and decanters take up far less floor space in the processing plant than screening tanks and filtration systems, but their maintenance costs are far higher. Conversely, screening tanks and pressure lead filters require substantial floor space, but the maintenance cost is nearly zero.
Both types of filtration systems require electricity; however, the energy consumed by the screening tank and leaf filter are 60-75% less than the energy consumed by a centrifuge and decanter. The trade-off is that a decanter and centrifuge system can clean the oil much more quickly than a screening tank and leaf filter.
How do you ensure you are using the right system? One critical factor is the intended use of the oil you are processing. Oil slated for human consumption needs to be among the cleanest, while other uses, such as animal feed, have lower standards. Monetary considerations like cost-per-liter and expected profit margins also weigh on the decision, along with available skill sets of in-house maintenance staff, since their expertise determines the tasks that can be handled routinely versus what will require outside help.
Another factor is the ease of use for the operators that run the filtration system. Centrifuges and decanters are simple systems and easy to operate. However, a challenge with the centrifuge and decanter systems is the possibility of clogging. An operator needs to consider both the flow rate and the number of solids they need to separate, or they will risk clogging the system. To ensure smooth operation, processors must appropriately size the machine and remember to factor the solids into the equation.
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Working with an Experienced Partner
No matter which clarification solution is best suited for your operation, it is essential to seek an experienced partner to guide you through the selection process. Choosing an inappropriate clarification system for your oilseed process could be costly and inefficient for years to come, diminishing profits and hampering your competitive position in an increasingly challenging industry.
Additionally, an experienced engineering team, like our oilseed processing consultants at Anderson, can ensure your clarification system integrates well with your overall processing environment. One of the keys to an efficient operation is the smooth transfer of materials from one stage to another.
The good news is that there is an ideal solution for your plant, one that can lower costs, streamline operations, and produce a better-quality product. The biggest challenge is to determine which is right for you.
For information on how Anderson can help you align your processing infrastructure with your business goals, contact us today.