6 replies to this topic

[devesh sharma]

The pressure inside firebox is lower than outside; why does flue gas exit without compression?

[pavanayi]

Devesh:
How did the pressure inside the firebox go lower than outside in the first place? Surely an induced draft fan would be there? If the fan is there, that is your compression step!!!

[smalawi]

Hi,

the pressure inside the fire box can be lower (slight vac) even without ID or FD fans. its buoyancy law, light gases go up and if you have a properly sized stack your hot gases being lighter than cold gases outside the fire box will create this slight vacuum as they go up the stack.

cheers,

SM

[Zauberberg]

When observed on a basis of absolute pressure units, you'll see that flue gases always flow from the area of high pressure to the area of low pressure. The key concept is to account for static head of atmospheric air at different elevation levels, observed from a reference line (stack damper or outlet, for example).

See attached file for further clarification.

Attached Files

•  Draft.pdf   95.98KB   62 downloads

[pavanayi]

Apoligies for the half answer posted above. I was going to write about natural draft and density difference (as has been written already), but my typing was interrupted and the half answer got posted .

[Flame]

Dear Devesh,

I am attaching a diagram. Hope i might be able to help you understand.

Attached Files

•  Draft concept.pdf   9.56KB   37 downloads

[fallah]

The pressure inside firebox is lower than outside; why does flue gas exit without compression?

Actually,it is better to say lower pressure inside is created due to flue gas outgoing!