How important an evaporator in a fishmeal plant

 

 

Let us consider fish meal consists of protein, moisture, oil and ash(mineral) only.

Solids: fat-free dry matter including protein and ash

 

Above we can find the mass ballance in a fishmeal plant for reference, the actual data will vary according to different raw material. But the diagram is sufficient to ilustrate the general trend.

From above figure we can see:

From 1000kg raw material, after pressing and decanting, we get 350kg presscake containing 55% moisture and 40% solids. After evaporation, we get 92kg syrup(stickwater concentrate) containing 25% protein(considering no ash), 65% moisture and 10% oil.

So in the complete line of wet pressed fishmeal plant, 1000kg raw material we finally get 212kg fish meal(with stickwater concentrate). We consider ash content in the final products as 20%,

 

212kgX20%=42.4kg

 

42.4kg is the ash in 1000kg material. Consider there is no ash in the stickwater concentrate, all ash is from presscake with decanting sludge.

 

Now we are going to calculate the fishmeal yield in a fish meal plant with and without evaporator. We will know how important is the evaporator in a fishmeal plant.

 

1. Without:

 

We get

Solids: 350kgX40%=140kg

Ash: 42.4kg

Protein: 140kg-42.4kg=97.6kg

Oil: 350kgX5%=17.5kg

 

Considering moiture content in the fish meal as 10%, so the fish meal yield will be:

 

Fish meal: (140kg solids+17.5kg oil)/90%=175kg

Protein: 97.6/175=55.8%

Oil: 17.5/175=10%

Ash: 42.4/175=24.2%

 

2. With:

 

We get

Solids: 140kg+(92kgX25%)* =163kg    (*) means protein in stickwater concentrate

Ash: 42.4kg

Protein: 163kg-42.4kg=120.6kg

Oil: 17.5kg+92kgX10%=26.7kg

The final fish meal product is:

 

Fish meal: 212kg

Protein: 120.6/212=56.8%

Oil: 26.7/212=12.6%

Ash: 20%

 

The yield difference:

212kg-175kg=37kg

37kg/175kg x 100%=21.14%

 

So, from above, we can get the result:

A fishmeal plant with an evaporator will increase the yield by 21.14% and protein content by 1%.

(Very good news, and we have more good news)

 

 

 

 

An evaporator can also save lots of energy.

 

We have to know some rules:

1. In a double falling film evaporator, one needs 0.5kg steam to evaporate 1kg water at least.

2. In an indirect steam heating disc dryer disc steam dryer, 1kg steam only can evaporate 0.833kg water in maximum.

 

From the Mass balance figure we can know, after evaporation, there will be 442kg cake totally to dry in the dryer. It will consume (442kg cake-212kg fish meal)/0.833=276kg steam, so there will be 442kg-212kg=230kg second hand steam to evaporator and this steam can evaporate 460kg(maximum) water in the stickwater. We get only 450kg stickwater to treat. It means the waste vapor from the dryer can be sufficient to be the energy resource to complete the evaporation mission. Practically, the waste vapor from cooker will also support.

 

So, we use the second hand steam from the fishmeal plant thus save energy.

 

Let’s come to the conlusion in short:

With an evaporator in fishmeal plant:

1.      More yield

2.      Higher protein content

3.      More energy saving

4.      Less pollution*

(*) Stickwater and waster vapor from fishmeal plant will cause terrible pollution)