Contractor killed in Robertson County, Texas power plant boiler explosion !!!! 3

[MJCronin]

Luminant, the owner of the 1,600-megawatt coal-fired power plant in Robertson County, issued a statement saying that the incident occurred around 8 a.m. during the commissioning of a new auxiliary boiler. One Contractor dead no other injuries

https://www.kbtx.com/2023/05/31/explosion-reported-franklin-power-plant/

MJCronin
Sr. Process Engineer

 

[TugboatEng]

I heard a classmate of mine got in a bit of trouble when he tried to light a burner off the hot refractory of a boiler (no purge). It ballooned the casing.

 

[FacEngrPE]

This boiler is large enough to be in the scope of NFPA 85: Boiler and Combustion Systems Hazards Code. These boilers have an operating control system and a flame safety supervisor, which both rely on software and require tuning. The damage viable in the video is the sort of damage I would expect if the boiler purge time is set too short, and an attempt to relight was made with an explosive mixture still in the boiler. An alternate theory it that firing very lean or very rich can create explosive conditions.

screenshot from MJ's link.
When I was involved with power boilers boiler purge time was one thing I was really careful with.
A published ASME PROCEEDINGS PAPER will be relevant to this sort of event (assuming my guesses are close)"Root Cause Analysis of an Industrial Boiler Explosion (and How Hazard Analysis Could Have Prevented It)", the summary explains the scenario.

This incident occurred during commissioning (according to the mj's link), which is a time when extra care is needed as the performance of the safety systems is not yet proven.

 

[TugboatEng]

I had not seen the video when I decided to share my anecdote above. I didn't realize this was actually a casing explosion. In my above story, I believe the person unintentionally tripped the boiler and was trying to relight it before steam pressure fell and alerted others on the ship of a problem. These are large d-type water tube boilers with a big furnace that holds a lot of combustible vapor.

Onto the automation of the purge cycle, typically during the purge the force draft fan is set to high speed and the registers are opened to allow maximum airflow through the furnace. I haven't worked on any boilers made after the 1970s. What kind of feedback is there to ensure that there is airflow through the furnace? A failed limit switch on a damper may indicate a successful purge of the furnace which would be quite dangerous. I don't know many boilers that have stack flow measurements that could confirm a completed purge.

 

[ProSafPlant1]

An excellent book on the subject

 

[FacEngrPE]

thread794-495768he Flame safety system

The boiler management system makes the purge happen. The flame safety system monitors for completion of purge, and sets the allowed to fire permissive.

Commissioning is supposed to set the boiler controls to match the design intent, and verify correct operation of all components.

Proof of flow may be as simple as a forced draft fan damper position limit switch. That is not enough if the FD fan has a damper and VFD, then airflow must be measured with some sort of flow station, with some rules to minimize the risk of common mode failures between operating controls and the safety supervisor. Add in low nox burners and flue gas recirculation, initial tuning gets more complicated.

Even when a stack gas analyzer is present, I would not would not permit it's use for proof of purge. Stack gas analyzers are not designed for use in safety applications.

This event is very likely to have been a repeat of Tug's scenario, except for marine boilers the applicable rules are in the Coast Guard regulations (which copies NFPA 85).

 

[davefitz]

Most boiler explosions I am familiar with were associated with the flame scanner contacts being jumpered. This is espescially true of boilers that explode during startup operations. The first thing the shift supervisor does after the boom is he gets up off the floorand runs down and removes the alligator clips.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick