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Process Plant in Sub-Arctic Location

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gA2002

Mechanical
Sep 6, 2008
8
Good day fellows,

I am currently involve in the engineering of an ore processing plant located in a sub-arctic region where the min/max temperature is -20/20C and the mean ambient year round is -1.7C. With chill factor, the ambient drops to -34C (as it was a couple of days back when I check through Blackberry - Viigo Weather).

I'm scared to think that the process plant might freeze to death in this condition! It make sense to me to enclose all equipment and process facilities inside a building. With that the heating can be more controllable, as I thought. However, my initial calculations on the heating requirement using an air change rate of 2-6 at a potential delta temperature of @ 20C, runs to about 6 MW of heat!
That's enormous and it made me asking for hint from the experienced fellows;
Wat really are the considerations for sub-arctic industrial plant ventillation and process heating?
What is the trick to reduce heat loss from forced air change?
My exposures so far are in the Middle East and in the tropical regions where industrial plant heating is not of epic concern.
Thanks in advance.

 
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Well, to start off, "sub-arctic" to me, means temperatures in the minus 40 degree F range, as opposed to minus 20.
 
The trick to reduce heat requirements for forced air changes is heat recovery. Also, your air change rate should be based on the actual requirements of the space.

A major consideration is what design temperature you need to maintain; above freezing, or comfortable.

Speaking from my designs 6MW (20 million Btu/hr) is large, but not really enormous depending on the application.
 
Do as much heating as you can with process waste heat. Use heat recovery from the building exhaust air.

But if you're every going to need to start the process from a cold-soak condition you're going to need that full 6 MW of heating capacity.
 
Hummm, middle east and tropics experience working on sub-arctic project?.
I'd say that you may need some outside advice if you have not designed any heating system.
that being said, watch out for freezing conditions on your heat exchangers' heat recovery, especially if you have any kind of moisture being exhausted. Then again, do you need humidity control in your process?
You are talking 2-6 ACH of OA? or just ACH recirculation?
why use ACH as basis for calcs? use UADT from skin plus infiltration, plus min. OA load. Must you use 100% OA? Can you reduce OA quantity by improving filtration?
 
Thank you for your responses, they are all warming and thawing away the frost!

TBP: Yes, the minimum ambient temp. can be -34 deg C (-93.2 deg F).

Chris/MintJulep: I did consider the heat losses from the installed equipment and from the ore processing. I based the ACH to the least I can get from recommended values for a mill (general). My concern really is to remove the moisture coming from the slurry.

Recirculation of the air comes as a light bulb! That would save a lot of energy on the steady state and in the temperature ramp up.

cry22: I have based my calculation on a 100% OA change for the 2-6 ACH. But I guess filtration as you mentioned will help drastically in reducing the energy wasted for dehumidification. Can you please educate me of what UADT stands for?

Does anyone knows of an ISO standard i can refer at for recommendations on heating and ventillation?
Any other references you can suggest?

Thanks for the inputs, i can go back to my analysis with tons of heat!
 
UADT would be the steady state heat loss calculation through the wall: U is conductance (1/R thermal resistance) A is the area of the wall, DT is the temperature difference (delta T) between the inside and outside.
 
Ultimately it will be your process which defines what you can do about the ventilation, whether 100%OA and heat recovery or Recirc at a given rate. There should be standards applicable to and adopted by your industry that should provide guidelines at least.

-34degC is -29degF (+ not - 32) The degC and degF scales conveniently cross at -40, which flagged your error.

Don't use chill factor temps with heat loss calcs, it doesn't apply to machines inside buildings, nor buildings outside in the cold and wind.

You should find a mentor who understands HVAC and the norms within your industry, this is looking like a 'where do we start?' thread.
 
Not directly HVAC related, but:

The place will be full of drain and transfer pipes at a low elevation, where it will always be cold, and they will freeze pretty regularly.

At that point, some schmuck has to mechanically remove the ice, with a steam lance and/or a piece of rebar, or whatever can be cobbled up. To get access to all the pipes, he'll have to physically remove any elbows in the pipes. Flexible snakes are useless against ice.

Please, on behalf of said schmucks, specify crosses with plugs, not elbows or tees, everywhere possible.

Similarly for vent pipes, that will get clogged with strange crystals...



Mike Halloran
Pembroke Pines, FL, USA
 
What are you heating the space to? I would guess heating the space to max 5oC might be acceptable to stop freezing, and also consider spot exhaust to exhauut anything that required exshiast (don't ventilated the whole building!)radiant heating, heat tape on pipes, etc.
 
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