Protein Rendering

Background/Challenge : A leading supplier of ingredients for agriculture and animal/livestock nutrition needed to cost-efficiently increase its yield of premium products and capture the high-quality protein meal market. The supplier wanted to avoid the conventional practice of using vibrating or high-frequency screens, which are susceptible to blinding and costly maintenance. As the company researched its expansion it was led to Sturtevant’s unique approach of AIR CLASSIFICATION , a technology that would allow them to separate the fines, converting the normal protein meal into a high-value, low-ash grade meal. At the same time, the coarse fraction would still contain enough protein that it could be sold as regular protein feed.

The supplier consulted with Sturtevant, a company with more than 95 years of classifying experience in countless applications – among them a number of installations in South East Asia within large protein meal production operations. Sturtevant’s specialized air classifier technology is specifically designed to separate protein meals. Sturtevant was chosen for its proprietary equipment, air classifier experience and engineering skills, as well as its ability to test product specifications in their own lab.



Rendered animal protein meals are produced through a series of steps that include pressing, cooking, defatting, milling and screening. This process creates animal protein meals that are sold for livestock. Specialized air classification technology separates the finer powder meal from the coarse meal. The resulting air classified fines fraction contains higher protein/lower ash which can be sold for premium value domestic animal pet food products (dogs & cats) or for aquaculture feed products (fish). At the same time, the air classified coarse fraction can still be sold as the regular protein/regular ash feed meal product for livestock animals.


Air classification has been proven to reduce the ash content and increase the protein content in every species of animal meals tested.
Below are several examples of the air classifier’s performance with various animal protein meals. Typical results include reduction of ash content as low as 5- to 7-percent and an increase of protein levels by 3- to 5-percent, which is suitable for the ultra-premium pet food grade market.



The Sturtevant Whirlwind Air Classifier uses an internal fan to fluidize the Protein Meal and mechanical selector blades to separate the animal feed meal into a fines fraction and a coarse fraction. This process is much more selective and versatile than cyclones or screens and the air classifier also does not clog like fine screens do. By changing the quantity of selector blades, a wide range of low ash, high protein products can be made with the machine. Once the best selector blade setting is determined, operators can simply dial-in a speed adjustment using a variable speed drive to fine-tune the desired product specifications or to compensate for any unexpected changes in the composition of the raw materials (ash, protein, fat, moisture). In all cases, there is a controllable relationship between protein/ash levels and output yields of the fines fraction (lower ash/higher protein) and the coarse fraction (regular ash/regular protein).

Below is an example of this relationship, using poultry meal :

Below is another example of this relationship, using fish meal:


The Whirlwind Air Classifier has only one motor that controls the entire machine. The motor rotates a feed distribution plate that scatters the meal into an open area. The same motor rotates an internal fan creating updraft airflow that accelerates finer/lighter protein particles, separating them from coarser/heavier ash particles. The same motor also rotates a series of selector blades that reject some of the undesirable near size ash particles. By using only one motor, the energy consumption is very low (approximately 3- 5 HP per TPH of feed capacity). Below is a chart that outlines the various models with their relative motor HP and rate feed capacities.
The Whirlwind Air Classifier features an internal fan and air recycle design that does not require auxiliary equipment (baghouses, cyclones, or ductwork) to capture the lower ash and higher protein fine product. The fluidized meal is also resistant to major clogging because the machine has minimal dead zones where high fat and sticky material can settle. This makes the air classifier both low in maintenance and reliable for continuous use.



Air classification technology produces a high-value, low-ash protein meal product from low quality feed meals. At the same time, the coarse fraction still contains enough protein that it can be sold as a regular livestock grade feed product.

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