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New Fire Heater Selecting Between Natural Draft And Forced Draft


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#1 paul88

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Posted 20 May 2016 - 09:42 AM

Dear all,

 

When a Project requires a Fire Heater (with a stack)  with a Design Duty of about 150 Btu/hr, What are the aspects to consider wheather the Fire Heater will be :

  •    Natural Draft  (combustión air is sucked in by natural draft developed in the stack)
  •    Forced Draft  (combustión air is supplied by a Centrifugal Air Blower)  
  •    Induced Draft  (combustión air is sucked in by an Extractor Fan)    

 

Thank you for your kind attention



#2 Bobby Strain

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Posted 20 May 2016 - 06:08 PM

150 btu/hr?

 

Bobby



#3 titim

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Posted 21 May 2016 - 04:46 AM

150 BTU/hr it's too less



#4 paul88

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Posted 23 May 2016 - 08:01 AM

Bobby, Titim,

 

I`m sorry , I meant 150 MMBtu/hr

 

I appreciate your point of view



#5 justnisar

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Posted 08 November 2016 - 11:54 PM

I too am looking for a similar question. how to decide whether a fired heater should be natural/forced/induced draft ?

 

request experts to share their views/experience.



#6 shvet

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Posted 11 November 2016 - 09:01 AM

As I understood there is no precise boundaries between air drafts. Only some guidance:

1. If oil or other durty liquid is used forced or mixed (forced + induced) draft is recommended. It provides better mixing in oil guns and so way less air excess is required.

2. If gas is used for burners and there is only 1-2 burners in furnance plenum forced draft can be a source of an accident. If even one burner is blown out gas can spread around the heater and explode. In case of natural draft explosion is possible only inside of heater shell.

3. In any case if forced draft is used there is a hazard of flue gas leak and personnel poisoning

4. In any case if forced draft is used there is a hazard of leak in radiant section (for example through observation door) and subsequent refractory lining supports or metal structures overheating.

4. Induced draft has more utility consumption than forced since air volumetric flowrate is more

5. Induced or mixed (forced + induced) draft is acceptable if air preheating is used.

6. In all cases forced draft requires less air excess than natural.


Edited by shvet, 11 November 2016 - 09:59 PM.


#7 Saml

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Posted 12 November 2016 - 09:30 AM

Regarding natural draft vs induced/forced, the main disadvantage of natural draft is the stack height you need when you aim for high efficiency.

 

Normally high efficiency means lower stack temperature (lower draft per stack height)  and increased pressure drop in the convection section  due to additional exchangers (higher draft requirement).






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