Emergency Shutdown 2

[aida2011]

Dear all

I was assigned by my superior to do an emergency shutdown procedure in the event of water not visible in the level gauge glass of a boiler.

Water not visible could be the glass is full or empty, so, if anybody has the experience doing such an emergency procedure, could you please share or advise?

Thanks

Aida

 

[pmover]

generally, no water observed in boiler sight glass leads to an immediate burner shutdown and depressurize the boiler by isolating the boiler from the system and manually opening the boiler safety valves. once the boiler cools down, conduct an external inspection of the pressure parts.

what kind of boiler? stationery or marine? drum, firetube, etc.

provide more details leads to a better response.

 

[aida2011]

Dear Mr. pmover

Thanks for your response.

The boiler is a water tube boiler, 40 t/h, with 35 bar of pressure. The boiler uses transparent gauge glasses. The question raised was in the event of no interface in the gauge glass, and the gauge glass could be full or could be empty, would you proceed to shut down the burner right away, or test the gauge glass first to confirm the level of the water?

Thanks

Aida

 

[mk3223]

Should the boiler have a redundant level indication/alarm or shutdown system for the safety operation? To depend on only a level glass gauge for the boiler operation may not be reliable and could be misleading.

________________________________________________

Just sharing the idea, but take it at your own risk.

 

[MJCronin]

You state "in the event of water not visible in the level gauge glass of a boiler"....

So, you are telling me that some random operator MAY notice that there is no water in the boiler, and this condition may have been occuring for some time ???

True boiler safety depends on safety features that ensure water in the boiler at all times. Explosions will occur if you depend on some boiler operator doing his job.

In more regulated Western countries, boilers are required to have redundant "low water cut-off" valves. These devices cut the fuel supply to the boiler. It is so important to maintain water in the boiler that most codes require that these devices must be made redundant.

http://www.nationalboard.org/index.aspx?pageID=164&ID=220

MJCronin
Sr. Process Engineer

 

[crshears]

The question raised was in the event of no interface in the gauge glass, and the gauge glass could be full or could be empty, would you proceed to shut down the burner right away, or test the gauge glass first to confirm the level of the water?

The answer is, it depends...

Expanding on what MJCronin said, in the more regulated western countries, boilers having a water level under normal conditions, in other words non-flash boilers, are commonly "guarded," meaning equipped with either a single or duplicate low drum water level float, the electrical contacts of which are wired to trip the boiler out of service without human intervention.

These low level trip floats are sometimes equipped with a manually operated "defeating" pushbutton that the plant operator can hold depressed with one hand while blowing down the float connections to ensure they are clear, as well as a pilot bulb, annunciating horn, or equivalent that clearly indicates when the trip contacts have operated. By this means every effort can be taken to confirm the trip floats are operating correctly.

If a boiler is equipped with one or two of these, and their correct operation is confirmed once per watch/shift [which they should be], tripping a boiler out of service due to no visible meniscus in the gauge glass would be very bad form; since gauge glasses are also commonly blown down once per watch by a plant operator, the first step would be to carefully and completely perform the entire gauge glass blowdown procedure once again before proceeding further.

In some plants it is common practice, when a boiler is being removed from service to, instead of simply manually shutting down all burners/pulling fires, to have a plant operator intentionally trip the boiler out of service by simulating a low drum water level; this is done by closing the lower pipe connection to a/the water level trip float, then opening its drain valve, not forgetting to return these valves to their normal positions once the boiler trips.

Hope this helps.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[KoachCSR]

I am assuming your boiler is controlled via a Distributed Control System (DCS).

My recommended guidelines for your procedure are as follows:

As you note, a level absent in the gauge glass means it's either full or empty. The first thing you should do is check the level indication in DCS - not knowing your boiler, I can only assume your DCS utilizes more than one transmitter to confirm boiler level.

If the DCS level is acceptable, check the gauge glass valve positions and perform a blowdown of the gauge glass.

If the DCS level is indicating high, visually check your steam drum level control valve - if open, manually isolate it. Use bottom blowdown valves to carefully lower the water level. Note: if water has been carried over into the steam line - trip the burner(s). Investigate the source of the problem and make repairs as required.

If the DCS level is indicating low, shut down the boiler immediately, but allow the FD fan to continue running. Isolate the feedwater to prevent flow into the boiler. The boiler must be cooled before feedwater is re-admitted - cooling time is dependent on the severity of pressure part overheating. If the boiler was firing for two minutes or less just below low water cutout level (if equipped with this safety feature), allow at least two hours of cooling followed by a slow introduction of feedwater. Conservative decision making should be employed (the longer the boiler is fired on low level, the more cooling time is required). Investigate the source of the problem and make necessary repairs. Note: be cautious when restarting the boiler and check for pressure part leaks.

 

[MJCronin]

aida2011 .....

crshears and KoachCSR give wise advice .....

As stated above:

"If the DCS level is indicating low, shut down the boiler immediately, but allow the FD fan to continue running. Isolate the feedwater to prevent flow into the boiler. The boiler must be cooled before feedwater is re-admitted -"

Here is an excellent report outlining WHAT CAN HAPPEN WHEN THE INCOMPETENT RUN BOILER OPERATIONS !!!

The spectacular 2007 Dana Corporation boiler failure report should be made mandatory reading for all process plant personnel. This is what happens when a low level is suddenly discovered and feedwater is introduced into a hot boiler.

http://www.ipemaritimes.com/bxpl.pdf

Tell us more about your existing safety features and procedures, aida2011

MJCronin
Sr. Process Engineer

 

[georgeverghese]

Writing this emergency procedure is all well and good, but what would happen on a day when you have extra maintenance support duties in the plant, and no one looked at this LG ? Your supervisor should also be held responsible to ensure adequate manning at ALL times, and not look for ways to pin blame on Operations staff.

 

[crshears]

Thanks for the acknowledgement, MJ.

I am assuming your boiler is controlled via a Distributed Control System (DCS). - KoachCSR

If I may be so bold, depending on where you are in the world, use of a DCS may not be the best option to pursue, since finding personnel with the skill set needed to maintain the equipment or correct issues with it may be a challenge; there may also be difficulties obtaining replacement parts. It may make better sense in such cases to use simpler, old-school, more robust and more easily repairable safety and control systems.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]