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summary
evaporator is the key component of back-end processing in wet fish meal production process. the fish liquid separates into fish protein water through the separator and the fish protein water turns into concentrated liquid through the separator. fish protein contains a variety of nutrients and is absorbed easily by animals. to add the protein concentrate liquid and to dry fish meal products, fish meal protein increase4-5%. rich nutrition, best quality and increased 20-30% of fish meal flour yield. because the protein is sensitive to heat water and is easy to scale, coke and foam. the first require is low evaporation temperature (above 80 Celsius degrees). so it must work under the condition of vacuum concentration equipment. the second requirement is that the equipment is easy to corrosion resistance and to clean. equipment heating tube is made of stainless steel.

at present our fish liquid evaporator comes in two forms: one is the double effect of falling film type vacuum concentration device; second is second effect of falling film type concentration device combination of steam and vacuum concentration.

concentration process
1.all equipment in the production line is closed design, each equipment is reserved for exhaust gas outlet, and through negative pressure to drain the exhaust gas.

2.the design concept for evaporator equipment is to make full use of the exhaust gas discharged from other major production equipment as a heat source, evaporate the excess water from the protein water, condense the protein water into a high concentration of protein water that is easy to process, and dehydrate it by the dryer.this can not only save energy (using exhaust gas as heating source, reduce the energy consumption of the dryer), but also can increase the efficiency of the dryer;

working principle

fish protein water out of the vertical oil and water separator is pumped into protein bucket by submerged pump and is heated to 85 Celsius degrees with steam(concentration is about of 6.5%). and then into the ii effect evaporator liquid room for circulating enrichment by circulation pump. the protein water in the spray chamber is injected into the the tube. then flow down from the inner wall of the tube in membrane. it is the heated by secondary steam from i effect outside the tube. the explosive evaporation starts in the condition of vacuum negative pressure. the gas-liquid mixture fell to the bottom of vapor liquid storage chamber to keep cycle enrichment. after reaching a certain concentration, the gas-liquid mixture comes into i effect evaporator to continue the next round of cycle concentration through by-pass pipe. the secondary steam produced by concentrated liquid inside i effect evaporator come into the ii effect evaporator to be the heating steam. when the concentration reach 28-34 percent of solid content, protein concentrate water is sent to concentrate cylinder by concentrate pump and mix the press cake then evaporating and drying into the product inside the dryer.

the heating steam of i effect evaporator is from the evaporating water vapor of dryer. it is equipped with backup boiler steam pipe on the intake pipe. the steam temperature is 100 Celsius degrees +2 Celsius degrees. heating steam of ii effect is secondary steam of i effect.according the actual situation, vacuum degree distribution of i effect and ii effect and the heat exchange process is as follows: temperature of fish protein water in ii effect is about 85 Celsius degrees. temperature of secondary steam from i effect is about 60 Celsius degrees. if want to take advantage of this part of steam heat, steam temperature in the ii effect must fall to 42-47 Celsius degrees. the vacuum degree of ii effect evaporator must reach-9.17×104pa. so the fish liquid enter into ii effect to be boiled and evaporated soon. required energy comes from two parts: one part is secondary steam condensation heat releasing of i effect (super cooling degree is 10 Celsius degrees-20 Celsius degrees). the other part is heat of fish liquid( liquid inlet temperature is 85 Celsius degrees, higher than the boiling temperature). heating steam of i effect is waste steam generated by dryer. its temperature is lower than 100 Celsius degrees. i effect evaporation temperature should be 55 to 60 Celsius degrees, therefore the vacuum degree should be 8.7 x 104 pa. as the temperature of fish liquid which enter into the i effect temperature is low(42-47 Celsius degrees), so you have to absorb part of heat to reach the boiling temperature. the vacuum degree of i effect is related to the vacuum degree of ii effect. after ii effect reaches the regulated vacuum degree, water will boil at a certain temperature. the secondary steam from i effect is condensed at the certain temperature. the condensation of water vapor in the sealed container can create vacuum degree corresponding to the condensation temperature. this means that we can the control the vacuum degree of ii effect and i effect at the same time. the key point is sealing of equipment, heat balance and timely eliminating of non-condensing steam. as the evaporating temperature of ii effect is lower than the evaporating temperature of i effect, so the vacuum degree of ii effect is higher than the vacuum degree of i effect.  

vacuum degree of ii effect evaporator is finished by the combined action of hydraulic ejector and water pump. lots of injection water with pressure( the lower water temperature, the better result, generally lower than 25 Celsius degrees) enter into the equipment from the top of ejector. the inner equipment makes full access of soda and water. it was taken away by powerful jet flow to form negative pressure vacuum. when i effect evaporator heat can’t concentrate lots of protein water, we should open the boiler steam in the i effect water vapor inlet pipe to supplement heat.