fan or damper control

[Storm_H]

Hope I can get some good input/experience share here.

As a part of an upgrade project for 2 old cement kiln it has (due to cost savings) been considered to install one common ESP filter instead of induvidual filter for each line. A common filter fan will maintain a constant underpressure in front of the filter. One concern is of course how regulation of the draft in one kiln will affect the other, and how to minimize the variations.

Two options has been considered
1) Two indvidual fans control the draft in each kiln
2) Two induvidual dampers control the draft in each kiln, and filter fan fan will have to do all the work (bigger fan)

My intuition tell me option 1 will be the best solution and provide the best induvidual draft control. But I cannot find the arguments.

Anyone here in this forum have some experience or input to share on this matter it would be much appreciated.

Thanks,

 

[GT-EGR]

Comments on Option 1 - until your filter fan reacts to the positive pressure - you’ll have positive pressure duct which should be avoided for this kind of exhaust to leak into the room. You could always put interlocks and stage which fans are in first to avoid this to a degree.

Comments on option 2 - they would need to be open/closed only dampers otherwise the damper and fans will hunt to keep that pressure. It’s also not typically recommended to put dampers in hazardous exhaust airstreams Bc they could possibly fail closed or get stuck in position, especially since this air is not simple environment air.

Why not just use the one exhaust fan, and leave the other connections without anything in between? If you always have that duct negative and the fan is sized for full draft of both kilns, all that will happen is you’ll draw more air from the firing kiln but still air movement will go towards the single fan.

 

[Storm_H]

Thanks a lot for the comment,

Option 1: Underpressure after kiln is expected to be -10 mbar (fan inlet) and -2 mbar before the ESP (maintained by the filter fan by a PIC regulation).

Option 2: Underpressure after kiln is expected to be -10 mbar (damper inlet) and -15 mbar before the ESP (maintained by the filter fan by PIC regulation)

The two kilns might not operate at the same production level, i.e. differenct flue gas amounts. So I need some kind of induvidual control by either a damper or a fan. Maybe my question can be re-phrased to:

What will affect draft less: A pressure change on pressure side of a fan or a pressure change on the outlet of a damper. My thought is fan due to the induced force from the impeller, but I cannot really find the argument when looking at a typical fan curve vs. pressure drop across a damper.

 

[Compositepro]

An air gap between the kiln or oven outlet and the exhaust system is often useful to decouple the two systems.

 

[Drazen]

You cannot use option one, that's basics of air flow logic - if your kilns' draft would be controlled separately, you would have regular scenario that on fan can push against another. Such kind of network is possible only if both branch fan are controlled so that they create equal pressure at connection point - or if they blow into very low-resistance plenum.

 

[Storm_H]

Also my major concern with option 1, that if two different parallel fans one will risk to overrule the other.

I talked to a fan supplier, and they were not that concerned as long as the pressure at filter inlet an outlet was maintained around -2 mbar. They actually suggested option 1 in combination with a louvre damper after each of the 2 fans as the best option. Eventhough providing a pressure loss (=lost money ), having a higher pressure between the fan outlet (if 5 mbar, the fan should be designed for 15 mbar instead of 8 mbar) and the louvre damper will minimize the interaction between the two paralllel fans. I.e. when regulating draft in one kiln it will not affect the the draft in the other kiln much. If only damper regulation draft change in one kiln will impact the other kiln significantly.

Thanks a lot for the comments until now.