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Oil Recovery plants process anchovies and menhaden, among other fish. At the docks the fish are pumped into a storage “raw box” and then metered to a live steam cooker. The cooked fish are pressed in screw presses (double pressing has been used successfully).
The press liquor, which has about 10% solids, goes to a centrifuge to separate oil. After the oil is removed the press liquor, which is called “stick water”, goes to a steam evaporator. The concentrated stick water is called “solubles” and is sold (at 50% moisture) as an animal feed ingredient.
The press cake is made into fish meal in a dryer without recycling capability. Extensive (triple) cooling is required for the meal coming out of this dryer. Either an antioxidant must be added or it must be shifted from pile to pile because the high protein is prone to spontaneous combustion. It is sold as fish meal, a very valuable ingredient for animal feedstuffs, especially chicken feed.
Oil recovery from menhaden can be 7 to 15% oil. Menhaden is known as the fish the pilgrims planted with their corn seeds; they did this with it because the fish was too oily to eat.
Fish meal is produced as a by-product in the second type of fish processing plant. The facility works with waste materials such as scrap fish from shrimp boats, crab shells, or trim materials and viscera from a larger fish processing plant. The raw fish (whole or pieces) are coarse ground at the start of the process. Small plants run the ground material directly to a rotating drum dryer, while the larger plants will first run the fish through a screw press, followed by a dryer. The fish meal comes out of the dryer at around 10% moisture.
Dryers used to produce this fish meal require the capability to recycle the fish meal; commonly they are small 10,000 #/hr systems. The rotating drum dryer is ideally suited for preparing fish meal because it very efficiently removes the moisture. The key design feature for making whole fish meal is that partially dried material is extracted from the triple pass dryer and mixed with the incoming material. This recirculation assures both that the product will not be overheated and burned and that the dryer will not plug with sticky substances.
Fish meal has 60% protein or more, with only 5% fat, so it is a valuable ingredient for animal feedstuffs. The final product is fine ground (not pelleted) before being loaded out to a feed mill. At the feedmill, typically 5% is blended into chicken feed.