Ammonia Heater

[gwapa]

Dear all
We design a fish defrost room for 10000 kg per day
The room should be at 5 ºC and 85% RH
The fish come from a freezer at -20ºC and we desing to defrost in 24 h
To compensate the room load (light,wall motors etc) we install 6 DX evaporator (amonia).
Now (as always happen) the customer wants to defrost 60000 kg in the same 24 h.
He (the costumer) guess to use hot has the keep the room at 5ºC
It is more or less to use hot gas defrost but all the time . At the week end we have to switch over to normal cooling evaporator due to we will not have frosted fish
I know we have to figure out the amout of heat involved in the system (heat rejected and heat getting in) and I also be aware of the instruments , control involved and the oil settled down.
But I would like to ask you all if you are face a problem like this and what could you advice me .
Thanks a lot
Gwapa

[RANGER1]

Gwapa,
Have worked on a similar application where it was on hot gas defrost all the time, with the
fans running all the time.

Have to be carefull of high levels in accumulators, due to the condensed hot gas.
If this is a potential problem use seperate condensate collector & pump back to main liquid reciever.

[gwapa]

Thanks Ranger1
You know the cold load due to the 60 tm of frosted fish is huge. I have to be sure that the system have enought heat to defrost those.Otherwise the presure in the receiver will go down .Also we think we will have to turn off condenser
How was your system capacity?
cheer

[Segei]

For this type of application you need continuous load. If you don't have a load, you won't be able to keep required head pressure even without condensers.

[RANGER1]

Thanks Ranger1
You know the cold load due to the 60 tm of frosted fish is huge. I have to be sure that the system have enought heat to defrost those.Otherwise the presure in the receiver will go down .Also we think we will have to turn off condenser
How was your system capacity?
cheer

gwapa,
The system we installed was only probably 10-15% of full load. We also had thermosyphon oil coolers, blasts, cold store etc.
You may be able to run a pretty low head pressure to achieve your result if the rest of the plant can cope with that.
The system we have is basically a reverse cool room & only gradually raised product to above zero so it did'nt spoil.
With fish I would imagine it to be the same!

Can fresh air be somehow utilized, filtered, mixed?

I have also seen a plant with a heat sink on a coolstore with 2 evaporators only on it.
It is like an ice tank with coil in it & water circulating pump. This generates a load for HG defrost.
Maybe there is something you could do to benefit this plant in some way!

[Sandro Baptista]

Gwapa

Can you quantify your service refrigeration needs and how much they can work per day?
Can you describe the plant you have?

[Magoo]

Concider using microwave defrost modules. Used for defosting frozen beef and fish blocks pre production.

[Magoo]

An idea from left field, what about using a plate freezer concept, but fead with hot gas Don't know how, but just a thought

[Sandro Baptista]

Also if you have a lot of water available free (from a pit, for example) you could use it continuously. Of course that water after pass by the product would be lost, back to the ground. In this way you would have a heat source of about +10ºC...+20ºC. Many cod fish producers uses that technique here on Portugal...they receive the cod fish freeze and then the put it on water tanks.

[gwapa]

The fish Plant is located at sea coast at the Caribbean . There are a lot of warm tropical sea water (24 ºC). The Sweet water is low. Use saltwater is very complicate. The atmospheric air is warm . But to defrost 60 Tm of fish in 24 h you need a lot of heat and also blow the air through to frosted fish . Additional the production people require the temperature in the room be 5º C and 85 % RH. So the fan could be of the very high capacity and you will raise the room temperature.
At the first glance I though use hot gas, but the system does not have enough heat rejection to do that .
May be he most simple thing is to install fancoils with a closed water circuit to keep the room at 5ºC
Do you agree ?
Gwapa

[Sandro Baptista]

The fish Plant is located at sea coast at the Caribbean . There are a lot of warm tropical sea water (24 ºC). The Sweet water is low. Use saltwater is very complicate. The atmospheric air is warm . But to defrost 60 Tm of fish in 24 h you need a lot of heat and also blow the air through to frosted fish . Additional the production people require the temperature in the room be 5º C and 85 % RH. So the fan could be of the very high capacity and you will raise the room temperature.
At the first glance I though use hot gas, but the system does not have enough heat rejection to do that .
May be he most simple thing is to install fancoils with a closed water circuit to keep the room at 5ºC
Do you agree ?
Gwapa

"Additional the production people require the temperature in the room be 5º C and 85 % RH. So the fan could be of the very high capacity and you will raise the room temperature." If you have a lot contact heat exchanger surface between the product and the air I don't think so.

"May be he most simple thing is to install fancoils with a closed water circuit to keep the room at 5ºC"
If you don't want to use sea water directly (why?) you can use a titatium or cooper nickel heat exchanger to exchange between the sea water and a dry cooler, with sweet water, and this sweet water will warm up the air that passes through the product.

[gwapa]

Sandro
Thanks for your advice
You know the sea water should be very well filtered and those create a lot of maintenance.
But I will think about your idea it look very interesting
Thanks a lot
GWAPA