Fish oil

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1. GENERAL DESCRIPTION:


1. General Flowsheet of fish production
(BAT in Slaughterhouses and Animal By-product Industries, June 2005)

The fish-meal and fish-oil production process may be summarised as follows, with the figure below illustrating the raw material, intermediate material and final product process order.


Material flow in fish-meal and fish-oil production.jpg


The following figure shows a simplified schematic diagram of the production process in a large fish-meal factory, where fish-oil is a sub-product. This overview shows only the most important mass flows:


Schematic diagram of the production process in a large Danish fish-meal factory.jpg


2. Description of techniques, methods and equipment
(BAT in Slaughterhouses and Animal By-product Industries, June 2005)

In principle, the fish-meal process is the removal of oil and water from the raw material and the separation of the material into 3 fractions, i.e. oil, meal and water. The water fraction is disposed of, normally to sea. The process is characterised by the continuous processing of very large quantities of raw material. Production normally takes place 24 hours a day, using large quantities of energy and seawater and with a minimum of manual labour. Fish-oil production comprises of the following steps:


a) Raw material: Whole marine fish caught in the sea, or parts of fish from the filleting industry.

b) Unloading:If the fish are specifically caught for fish-meal and fish-oil processing, they are unloaded from the fishing vessels and weighed. During unloading, fish samples of 300 - 500 kg, i.e. 70 – 100 spot samples, are taken and analysed to determine the quality of the raw material. Freshness is extremely important to the final product quality. The parameter used to measure freshness is the total volatile nitrogen (TVN). This is the nitrogen created by the degradation of protein in the raw material. Ideally, the raw material should be fresh and dry. It often contains melt water from ice used to conserve the fish.

c) Raw material buffer silo:The raw material is stored in a silo, which has enough capacity for 16 – 24 hours. The unloading capacity is greater than the production capacity because the plants cannot control the delivery times of the vessels, so production takes place 24 hours a day. Unloading tends to take place during the day. The buffer silos have to be empty when offloading starts the next day, to maintain a fresh throughput.

d) Cooker:Fish are 70 - 75 % water. They are indirect-steam cooked for 20 minutes in their own water at 90-100 °C. The protein coagulates and it is this which forms the press cake.

e) Press:The cooked fish are pressed for 15 minutes, in a screw press to produce a liquid phase, known as press water and a solid phase known as press cake. The press water contains some dry matter and solid matter, known as fines. The press cake is 50 % dry matter.

f) Decanter: The press water is separated further, in a decanter, to produce decanter water and another solid phase, known as grax.

g) Centrifuge:The decanter water is separated further in a centrifuge to produce fish-oil and a liquid containing dissolved dry matter and small amounts of suspended solids, known as stickwater. Approximately 20 % of the fish-meal is in the stickwater.

h) Oil finishing/purification:The fish-oil from the centrifuge is washed with hot water in another centrifuge, then settled and stored. If necessary it may be passed through a carbon filter-press to remove traces of dioxins. The spent carbon is incinerated in a hazardous waste incinerator.

i) Storage: Fish-meal and fish-oil can be stored for at least one year in storage houses and in tanks.


3. Temperature ranges and other parameters (table)
(BAT in Slaughterhouses and Animal By-product Industries, June 2005)


Temperature ranges-fish oil.jpg


4. Benchmark data (from BAT or from other sources)
(BAT in Slaughterhouses and Animal By-product Industries, June 2005)


Benchmark data-fish oil.jpg


2. NEW TECHNOLOGIES:


a) Changes in the process: No information is available.

b) Changes in the energy distribution system: No information is available.

c) Changes in the heat supply system: No information is available.


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