sprinkler heads in baghouse? 2

[pmover]

fellow engr's,

i encountered this matter yesterday and find it, let's just say pathetic thinking for now unless there are justifications for the design. i am posting this query on behalf of other individuals, but i now understand that another location is subject to the same situation, except that the other location is installing a dry-pipe system.

also, i trust this would be the proper forum to address this matter, even though it does address fire protection issues.

coal-fired boilers with baghouse modules...

the designer installed a wet-pipe sprinkler system and even had sprinkler heads installed inside the baghouse. it is my strong opinion that having sprinkler heads (wet ones at that!)inside the baghouse is potentially a serious problem to equipment and/or personnel. if the system ever activated while boiler is in operation, a potentially serious condition may exist.

is anyone familiar with other installations of similar designs? if so, what are the justifications, codes/stds, etc.?

any stds/codes that can be referenced to justify/not justify the installation of sprinkler heads inside baghouses?

my opinion, this matter needs attention before a bad situation gets worse.

thanks!
-pmover

 

[eboelen]

pmover,

I have been involved with solid fuel combustion for 30 years and I saw people make similar mistakes. As you point out, the activation of the sprinkler system at the wrong time could create a dangerous situation.
Sprinklers in a baghouse are not necessary if the ductwork is laid out properly. I don't know if that is the case with your system but let me describe hereunder the proper way to do it.
The baghouse should always be on the positive side of the ID fan. A three damper system should provide a by-pass around the baghouse in case of shut down of the baghouse for maintenance or in case of a fire. Since the flue gas contains a minimal amount of oxygen, the chances to have a large fire are non-existent. If for some reason a fire is detected, usually by monitoring the temperature in the baghouse and compare it to the inlet temperature or by comparing O2 content before and after the baghouse, the three damper system is immediately activated isolating the baghouse. This isolation removes the oxygen source to the baghouse and the fire is snuffed out. I have seen a few systems that in addition to this, also blanketed the baghouse with CO2 at that time to create a positive pressure in the baghouse and prevent all entry of oxygen.
I hope that this gives you sufficient information to decide what to do about your present system.

 

[pmover]

eboelen,

thanks for the response. what you have stated is sensible, pragmatic, and certainly safer than wet sprinkler heads.

i am hopeful for further responses, particularly with references to codes/stds that justify installing (or otherwise) sprinkler heads in baghouses.

combustion air/flue gas process description is as follows:

outside air -> FD fan -> boiler coal grate & combustion -> baghouses -> ID fan powered by VFD -> discharge dampers - > stack to atmosphere.

i understand that there is bypass capabilities; however, i am not certain as to what equipment (i.e. dampers, louvers, etc) is installed.

i do not have actual flue gas breeching pressure data, but if needed, it can be obtained.

thanks again!
-pmover

 

[eboelen]

pmover,
The first observation is that your system is not put together properly. The baghouse is under negative pressure: every leak in the baghouse, mainly around access hatch and door flanges, causes 21% oxygenated air to be drawn in to the baghouse. This naturally increases the danger for fires compared to the condition I described where the baghouse is under positive pressure.
Creating positive pressure in the baghouse by putting the ID fan before the baghouse also requires that a first type of particulate collection, usually a mechanical cyclone, is present to eliminate the larger pieces and in general to lower the amount of flyash that passes through the ID fan to protect some against excessive wear.
This doesn't mean that you got to condemn your system all together and start from scratch but, to adequately protect your baghouse against fires, I would do the following:
- remove all waterlines and sprinkler heads
- install (if not presently existing) a by-pass over the baghouse with three good closing pneumatic dampers: on the inlet and outlet of the baghouse I would probably go for a good sliding damper, on the by-pass for a butterfly damper. Be aware that environmental regulations may require that this is a zero leak damper, and they are expensive, so you may have to go to another sliding damper.
- install the proper monitoring controls to operate the dampers. The dampers themselves should be operated by local air tanks to allow them to be operated in case of a power failure.
After these changes your system should be pretty well "fire free" but remember, with the negative pressure, pay close attention to all the seals around hatches and doors.
Hope this helped you.

 

[pmover]

eboelen,

again, thanks for the response!

unfortunately, it is an existing system and currently construction of baghouses is nearly completed.

i can only hope no personnel are nearby when sprinkler system is activated.

-pmover

 

[psafety]

pmover,
It sounds like you have a "process-type" working in power generation.

Sprinklers are used quite common in process baghouses in manufacturing operations. I've seen them quite a bit dust collection systems in food processing as well as pulp/paper applications.

Again, it appears the individual(s) are working outside their experience base.

Don Coffman