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Posted: 4/13/2011 7:34:40 AM EDT
DO these ever actually occur or are they all just hollywood bullshit, I've seen them used as setpieces often enough in movies and TV shows and I can't help but wonder why there wouldn't be a relief valve. I'd like to think even in the waybgone days of the 1800's they would have had the sense to put a valve that can be opened up by excess pressure on the damn thing.
Link Posted: 4/13/2011 7:50:35 AM EDT
Link Posted: 4/13/2011 7:56:43 AM EDT
They were common back in the days when engineering meant "build it as thick and strong as you can afford," and the operators relied on sight, smell, hearing, and touch, instead of procedures and instrumentation.

They still happen, but it has to be a pretty serious failure cascade.
Link Posted: 4/13/2011 8:07:46 AM EDT
Steam locomotive need water over the side and crownsheets of the firebox.

You lose that layer of water and the steel will become damaged enough that the staybolts won't be able to hold the shape and then they go all Glock-like.

I have a book about the DRGW that has pics of boiler explosions that left the running gear on the tracks and the boiler (with cab) a 1/4 mile away.

I worked as a fireman on a steam train during summer break from college and I always made sure I was acutely aware of my water level.
Link Posted: 4/13/2011 8:08:25 AM EDT
about 15 years ago I had a company service
my boiler they removed the relief valve.

I fired it up and heard Wham Wham Boom
as How water gushed out of it.

I was told i was lucky it did not explode


And They were nice enough to buy me a new Boiler
Link Posted: 4/13/2011 8:09:17 AM EDT
THAT was probably pretty loud!



Link Posted: 4/13/2011 8:10:15 AM EDT
Google "US Navy boiler explosion"

You'll get tons of examples of boiler explosions. some of the more recent: "A boiler explosion in the after fireroom of USS Basilone (DD-824) killed seven sailors and injured another four. 5 February 1973."  USS Basilone (DDE-824, later DD-824), 1949-1982

And even more recently: USS Iwo Jima Oct 1990

Anatomy of a Catastrophic Boiler Accident (LPH-2)
Link Posted: 4/13/2011 8:10:33 AM EDT
Link Posted: 4/13/2011 8:10:59 AM EDT
They can occur, but on modern boilers, multiple fail-safes would have to be bypassed. They have pressure limit switches,mechanical and electronic low water cut off switches and relief valves. The ones I deal with also have several go, no-go switches on the gas train. If certain things don't happen in a certain order, they wont even fire.
Link Posted: 4/13/2011 12:52:33 PM EDT
Don;t think some of you are getting this right, this is how it was explaned to me: Boiler runs low on water and boiler plate is exposed and proceeds to glow red hot. At that point water is introduced to red hot boiler plate and violently flashes off producing a large volume of superheated steam at extremely high pressures. The sudden sharp rise in pressure overwhelms the safeties and blows the boiler.

 We had a steam tractor explode a few years back, killed a couple of people. They said it was low on water and when the tractor went down a small grade,the water ran to one end of the boiler and exposed the boiler plate thus allowing it to get red hot. When the tractor returned to level ground it blew up, because the water ran back over the glowing boiler plate.
Link Posted: 4/13/2011 12:54:14 PM EDT
Originally Posted By SuperJanitor:
They can occur, but on modern boilers, multiple fail-safes would have to be bypassed. They have pressure limit switches,mechanical and electronic low water cut off switches and relief valves. The ones I deal with also have several go, no-go switches on the gas train. If certain things don't happen in a certain order, they wont even fire.


I've encountered boilers dry firing, when I shut the gas off I could see the heat exchanger glowing red hot, I tip toed out and let it cool off on it's own.

Link Posted: 4/13/2011 2:36:03 PM EDT



Originally Posted By Katana16j:


DO these ever actually occur or are they all just hollywood bullshit, I've seen them used as setpieces often enough in movies and TV shows and I can't help but wonder why there wouldn't be a relief valve. I'd like to think even in the waybgone days of the 1800's they would have had the sense to put a valve that can be opened up by excess pressure on the damn thing.


http://en.wikipedia.org/wiki/SS_Sultana

"The SS Sultana was a Mississippi River steamboat paddlewheeler destroyed in an explosion on April 27, 1865. This resulted in the greatest maritime disaster in United States history. An estimated 1,800 of the 2,400 passengers were killed when three of the ship's four boilers exploded and the Sultana sank near Memphis"



In the case of the Sultana, the captain allegedly ordered the relief valves wired closed to (successfully?) increase pressure:

http://www.rootsweb.ancestry.com/~tnalhn/sultana.htm

"...the captain had wired down the steam relief valve so he
could put on more power and travel faster."

 
Link Posted: 4/13/2011 2:38:46 PM EDT
USS Frank Cable in 2006.  Boiler tubes ruptured before safety valves lifted.  They were in the process of testing safeties for PMs.  I heard somehting about very poor water chemistry, too, but don't recall for sure.  Two sailors killed in about the most cruel, painful way I can think of.  Seven more severly injured.  This was in Guam.  I was on a different ship in Guam at the same time and remember the sirens running over to Polaris Point.

Home heating boilers:  It is not uncommon for homeowners to plug their boiler safety valve because it is dripping.  If it is dripping, lift the valve off of its seat and let it close again.

Posted Via AR15.Com Mobile
Link Posted: 4/13/2011 2:40:38 PM EDT
Steam tractor explosion at the Medina County Fair, five people killed: http://www.farmcollector.com/steam-engines/tragedy-at-medina-county-fairgrounds.aspx
Link Posted: 4/13/2011 2:43:06 PM EDT
[Last Edit: 4/13/2011 2:43:47 PM EDT by fatalerror113]
Had one at a neighboring county fair a few years ago.






ETA::Fuck, I'm getting old, it was in 2001.  http://www.farmcollector.com/steam-engines/tragedy-at-medina-county-fairgrounds.aspx




 
Link Posted: 4/13/2011 2:45:38 PM EDT
When I was in college, there was a separate small (6 room) building just for the campus administrative staff. The building had its own boiler from like 1920 or something. The facility mechanics kept attempting to get the boiler replaced, only to be turned down again and again. They kept saying, "One day that thing's gonna blow."

Well, we came back from the winter holidays to find the brick enclosure where the boiler had been blown to little pieces, and the boiler pretty much missing. (The facility mechanics later admitted - off the record - that they rigged it to blow over the holidays so no one would get hurt.)

No pics. That was 1986.
Link Posted: 4/13/2011 2:51:06 PM EDT
Couple listed here: American Industrial Disasters
Link Posted: 4/13/2011 2:57:18 PM EDT
Link Posted: 4/13/2011 3:09:01 PM EDT
Originally Posted By Katana16j:
DO these ever actually occur or are they all just hollywood bullshit, I've seen them used as setpieces often enough in movies and TV shows and I can't help but wonder why there wouldn't be a relief valve. I'd like to think even in the waybgone days of the 1800's they would have had the sense to put a valve that can be opened up by excess pressure on the damn thing.


Yeah, they have relief valves but over time material wears, and maybe the pressure at which it fails is under the pressure a relief valve would release it.
Link Posted: 4/13/2011 3:14:29 PM EDT
True or not...a buddy of mine that served in the engine room of the USS Horne(guided missile cruiser)..told me that in the event of war..they did away with the safty valves..
Link Posted: 4/13/2011 3:20:13 PM EDT
Originally Posted By clutchsmoke:
Don;t think some of you are getting this right, this is how it was explaned to me: Boiler runs low on water and boiler plate is exposed and proceeds to glow red hot. At that point water is introduced to red hot boiler plate and violently flashes off producing a large volume of superheated steam at extremely high pressures. The sudden sharp rise in pressure overwhelms the safeties and blows the boiler.

 We had a steam tractor explode a few years back, killed a couple of people. They said it was low on water and when the tractor went down a small grade,the water ran to one end of the boiler and exposed the boiler plate thus allowing it to get red hot. When the tractor returned to level ground it blew up, because the water ran back over the glowing boiler plate.


Do steam locomotives or tractors have strong mechanical water pumps that replenish water as it runs low?  I ask because it couldn't be a simple system since as much pressure would be imparted on the 'feed' as is going to the pistons.
Link Posted: 4/13/2011 3:28:33 PM EDT
I've been a boiler Engineer since 1975.
I've worked on and operated all kinds of boilers, from high pressure to low pressure.
I've seen safety valves that would not lift when they were suppose to.
I've seen low water safety valves stuck, boiler still running, and no water inside.
I've had high pressure tubes in a water tube boiler firebox blow and rip apart.
I've had the end of a waterwall drum blow. ( We let it gush water for 2 days while trying to cool the boiler down.)
But by far, what is the most dangerous, and still happens way too much, is somebody bypassing the purge cycle for the firebox.
Most all of your explosions today are caused by this.
There is a reason most boilerrooms are built away from the main buildings.
If the boiler blows up, only the engineers will be killed.
Link Posted: 4/13/2011 3:52:23 PM EDT
Originally Posted By MrFuzzybunny:
I've been a boiler Engineer since 1975.
I've worked on and operated all kinds of boilers, from high pressure to low pressure.
I've seen safety valves that would not lift when they were suppose to.
I've seen low water safety valves stuck, boiler still running, and no water inside.
I've had high pressure tubes in a water tube boiler firebox blow and rip apart.
I've had the end of a waterwall drum blow. ( We let it gush water for 2 days while trying to cool the boiler down.)
But by far, what is the most dangerous, and still happens way too much, is somebody bypassing the purge cycle for the firebox.
Most all of your explosions today are caused by this.
There is a reason most boilerrooms are built away from the main buildings.
If the boiler blows up, only the engineers will be killed.


I had a boiler flame out on me on USNS Concord.  The Second and a junior engineer got over to the boiler front to light it back off.  The Junior won the race and started to reset the fuel valves.  He wanted to spray in the fuel to light it off of the hot brick work.  The Second was right behind him, threw him out of the way, and got the fuel valves properly secured just in time.  Then, we lit off right way... with a purge, followed by a torch.  (no automatic igniters on that boiler)

Posted Via AR15.Com Mobile
Link Posted: 4/13/2011 3:59:20 PM EDT
[Last Edit: 4/13/2011 4:15:01 PM EDT by DoubleARon]
http://www.unmuseum.org/crash.htm





In 1912 a steam locomotive being readied for a run
               at the Southern Pacific Roundhouse in San Antonio had its boiler
               rupture for unknown reasons. The resulting explosion leveled most
               of the buildings in the railroad yard and much of the surrounding
               neighborhood. A house and its owner seven blocks away were crushed
               by the front end of the locomotive as it fell from the sky. An
               estimated 40 people were killed and another 50 injured.









ETA: A steam locomotive isn't exactly something you can just turn on and run. Yeah, you can light it and build steam quickly, but it's not going to do the locomotive much good. People got paid to light locomotives and tend the fires while they built steam. In this case, it's possible that whoever was preparing the locomotive fell asleep, and the crown sheet let go when the water level got too low. You could also cause an explosion by letting the water get too low and expose the crown sheet. An inexperienced fireman could add water suddenly, and when it hit the crown sheet, it would flash off into steam, causing the boiler to explode.



 
Link Posted: 4/13/2011 4:00:10 PM EDT
Yes.  One time I was taking a nap between classes at college and BOOOM.  A boiler exploded in the physical plant.
Link Posted: 4/13/2011 4:02:15 PM EDT
I'm not really sure what a boiler is.  But from what i know it seems ineffiecient way to power something.
Link Posted: 4/13/2011 4:05:30 PM EDT
I met a state boiler inspector who told me that a colleague of his was seriously injured in a boiler explosion.
Link Posted: 4/13/2011 4:06:19 PM EDT
[Last Edit: 4/13/2011 4:11:44 PM EDT by CarbineDad]
1)  ASME Boiler and Pressure Vessel Code

2)  Code Stamps on relief valves and pressure equipment (your water heater and air compressor tanks relief valves probably are code stamped)

3)  Hartford Steam Boiler inspections

4)  Mandatory regulatory inspections
Link Posted: 4/13/2011 4:09:11 PM EDT
They sure do; but it is generally due to safeties being removed or locked out, or faulty equipment.  If everything is working right and the boiler is reasonably maintained, they there is no real danger.
Link Posted: 4/13/2011 4:11:34 PM EDT
Steam is a hateful bitch.
Link Posted: 4/13/2011 4:11:55 PM EDT
Originally Posted By junker46:
I'm not really sure what a boiler is.  But from what i know it seems ineffiecient way to power something.



You should have just stuck with the first part.

Link Posted: 4/13/2011 4:19:17 PM EDT
Originally Posted By MrFuzzybunny:
I've been a boiler Engineer since 1975.
I've worked on and operated all kinds of boilers, from high pressure to low pressure.
I've seen safety valves that would not lift when they were suppose to.
I've seen low water safety valves stuck, boiler still running, and no water inside.
I've had high pressure tubes in a water tube boiler firebox blow and rip apart.
I've had the end of a waterwall drum blow. ( We let it gush water for 2 days while trying to cool the boiler down.)
But by far, what is the most dangerous, and still happens way too much, is somebody bypassing the purge cycle for the firebox.
Most all of your explosions today are caused by this.
There is a reason most boilerrooms are built away from the main buildings.
If the boiler blows up, only the engineers will be killed.


There is nothing to obscure that ARFCOM doesnt have an expert in, thats why I love this place.

I guess I just vastly underestimate the energy involved in these things, I figured in a worst case scenario it would pop a weld and whistle like a teakettle for a while. However there are references showing them leveling whole blocks. Just how much pressure are we talking about that it rivals a modest size bomb?
Link Posted: 4/13/2011 4:24:20 PM EDT
[Last Edit: 4/13/2011 4:27:43 PM EDT by SuperJanitor]
Originally Posted By MrFuzzybunny:
I've been a boiler Engineer since 1975.
I've worked on and operated all kinds of boilers, from high pressure to low pressure.
I've seen safety valves that would not lift when they were suppose to.
I've seen low water safety valves stuck, boiler still running, and no water inside.
I've had high pressure tubes in a water tube boiler firebox blow and rip apart.
I've had the end of a waterwall drum blow. ( We let it gush water for 2 days while trying to cool the boiler down.)
But by far, what is the most dangerous, and still happens way too much, is somebody bypassing the purge cycle for the firebox.
Most all of your explosions today are caused by this.
There is a reason most boilerrooms are built away from the main buildings.
If the boiler blows up, only the engineers will be killed.


We used to have an old Cleaver Brooks boiler that kept tripping the high limit one time. Come to find out, someone had flipped the modulation switch into manual. It always ran in the automatic position and never occured that it would have been changed, so it took a while to figure out what was wrong. The limit tripped out every time. If that would have failed, then hopefully the relief valves would have activated.
Link Posted: 4/13/2011 4:26:18 PM EDT
[Last Edit: 4/13/2011 4:48:21 PM EDT by SuperJanitor]
Originally Posted By junker46:
I'm not really sure what a boiler is.  But from what i know it seems ineffiecient way to power something.


Nuclear power is in effect a boiler. Very efficient.

You have two seperate systems. The reactor makes steam in a closed loop. The super heated steam from that goes to a heat exchanger which in turn boils water in the secondary loop. That steam powers turbins that in turn spin generators.
Link Posted: 4/13/2011 4:27:06 PM EDT
Our firm recently settled a very important death case. In April 2006, Steve Thrasher was employed at the Rock Tenn paper mill in Demopolis, Ala. He was sent to check the operation of one of the mill steam boilers. The subject boiler, roughly 30 feet square and 60 feet tall, was built and installed in the mid-1950s and had been in continuous operation for over 50 years. Although the ASME boiler code specifies that tubing of steam power boilers should be inspected regularly, portions of the subject boiler tubing were encased in a concrete-like material known as a refractory and were never inspected during the life of the boiler. The boiler inspection company hired to perform the annual inspections is recognized as a leader in boiler technology but it never utilized its own ultrasound or x-ray inspection technology on the boiler. Rather, the company simply relied on visual inspections of the portions of the boiler that were readily accessible. As a result, dangerously thin sections of steam tubing encased within the refractory were never discovered.

Unfortunately, as Steve Thrasher walked by the boiler one of the internal tubes failed and violently ruptured. The force of the tube failure blew a hole in the steel outer casing of the boiler and spewed superheated steam directly onto Steve. Somehow Steve managed to walk to the mill control room and was first transported to the local emergency room and then to the burn trauma unit at South Alabama in Mobile. Despite world class burn care, Steve Thrasher died from his burns. After extensive case preparation which included multiple depositions of experts in metallurgy, boiler operation, inspection techniques and burn care, this case settled a week before we were set to select a jury. The amount and terms of the settlement agreement are confidential. Mike Andrews handled this case for the family. He and his staff did a tremendous job in working this case up.


This was a friend of mine, there was another explosion back in the 50's that killed several and injured a few others.
Link Posted: 4/13/2011 4:28:49 PM EDT
OP, see MKT's "Crash at Crush".
Link Posted: 4/13/2011 4:29:34 PM EDT
Originally Posted By junker46:
I'm not really sure what a boiler is.  But from what i know it seems ineffiecient way to power something.


Between the OP and this guy I think this thread wins the "WAAAAYYYYY over some member's heads" award.
Link Posted: 4/13/2011 4:36:31 PM EDT
Link Posted: 4/13/2011 4:41:11 PM EDT
[Last Edit: 4/13/2011 4:51:02 PM EDT by R2point0]
Originally Posted By Katana16j:
Originally Posted By MrFuzzybunny:
I've been a boiler Engineer since 1975.
I've worked on and operated all kinds of boilers, from high pressure to low pressure.
I've seen safety valves that would not lift when they were suppose to.
I've seen low water safety valves stuck, boiler still running, and no water inside.
I've had high pressure tubes in a water tube boiler firebox blow and rip apart.
I've had the end of a waterwall drum blow. ( We let it gush water for 2 days while trying to cool the boiler down.)
But by far, what is the most dangerous, and still happens way too much, is somebody bypassing the purge cycle for the firebox.
Most all of your explosions today are caused by this.
There is a reason most boilerrooms are built away from the main buildings.
If the boiler blows up, only the engineers will be killed.


There is nothing to obscure that ARFCOM doesnt have an expert in, thats why I love this place.

I guess I just vastly underestimate the energy involved in these things, I figured in a worst case scenario it would pop a weld and whistle like a teakettle for a while. However there are references showing them leveling whole blocks. Just how much pressure are we talking about that it rivals a modest size bomb?


It's not the pressure - it's the energy.  In order to get a boiler to working temperature, you need to pump a LOT of energy into the working fluid and components.  Likewise when bringing it down for maintenance, it needs a good while to lose that energy.  Everything is fine as long as there are no sudden changes.  But if something does change rapidly, bad things happen.  The ideal gas law states that, for a given temperature, pressure and temperature are inversely proportionate.  The higher the pressure, the smaller the volume the gas (steam) takes up.  Now, punch a hole in the boiler.  When mechanical containment is lost, the pressure drops VERY rapidly toward atmospheric - which means that the steam expands equally rapidly.  I.e. it explodes.

Another analogy, though not exact, is dry firing a bow.  Pulling the string back loads the limbs up with energy.  When they are released, the energy has to go somewhere - either smoothly into the arrow or all at once into the string.
Link Posted: 4/13/2011 4:46:59 PM EDT
[Last Edit: 4/13/2011 5:31:00 PM EDT by timco]
OK. Lets break this down. I will do an overview of 99% of the residential boilers (houses) and commercial (large apartment buildings)

Steam. All cast iron, natural draft. The Empire State building runs on 5lbs of steam. I run my 5 story apartment buildings on maybe 1/2lb of steam. If several vents or traps are bad, it could take 2lbs of steam to do the job. Google a Hartford Loop. This is the safety mechanism piped into the returns of any steam boiler so if the wet return ruptures, the boiler's water does not just dump out. It is the connecting point and the 'loop' you see which is also part of the equalizer.

Steamers are cast iron boilers. no tubes, just cast iron sections. They have 2 low water cut offs by code, and both can be a float or one can be a probe. One has to be a manual reset. They kill the gas. All steamers also have two pressuretrols, one controls boiler pressure and one is a high-limit manual reset. They also have a relief valve equal to the boiler's BTUs and that valve is set for 15lbs.

Hot water gives you infinite designs, copper, stainless steel, cast iron, and so on. These are 30lbs max. Typically they are set to 12lbs. In tall structures (the tallest I maintain is 14 stories) they run at 80lbs to get the water to the top floor.




FIXED pics..
Link Posted: 4/13/2011 4:47:19 PM EDT
[Last Edit: 4/13/2011 4:48:49 PM EDT by ElectricSheep556]
Water tube rupture is probably the most common cause of boiler accidents. There's no real way to monitor the water tubes beyond regular inspection. Accidents caused by light off explosions, low water level, and overpressure are far less common than they used to be due to the technology available to us. For example, there are now sensors which monitor the flame of the burner, and if it is the wrong color, or if the burner goes out, it cuts off the fuel. Likewise, if the water level is low, the fuel is cut off. Its all a little more complicated than that, but for people that "don't really know anything about boilers," that's sufficient.

 
Link Posted: 4/13/2011 4:50:11 PM EDT
Link Posted: 4/13/2011 4:52:30 PM EDT
[Last Edit: 4/13/2011 4:55:55 PM EDT by ElectricSheep556]





Originally Posted By MrFuzzybunny:



I've been a boiler Engineer since 1975.


I've worked on and operated all kinds of boilers, from high pressure to low pressure.


I've seen safety valves that would not lift when they were suppose to.


I've seen low water safety valves stuck, boiler still running, and no water inside.


I've had high pressure tubes in a water tube boiler firebox blow and rip apart.


I've had the end of a waterwall drum blow. ( We let it gush water for 2 days while trying to cool the boiler down.)


But by far, what is the most dangerous, and still happens way too much, is somebody bypassing the purge cycle for the firebox.


Most all of your explosions today are caused by this.


There is a reason most boilerrooms are built away from the main buildings.


If the boiler blows up, only the engineers will be killed.



...why would anyone do that? I mean, its so obviously dumb, and I see no upside at all, unless the BMS and the redundancy/ies were completely broken.





 
Link Posted: 4/13/2011 4:54:50 PM EDT
Originally Posted By junker46:
I'm not really sure what a boiler is.  But from what i know it seems ineffiecient way to power something.


Actually very efficient and cost effective, especially on natural gas. That's why they are used everywhere.

Link Posted: 4/13/2011 4:54:59 PM EDT
Originally Posted By ElectricSheep556:

Originally Posted By MrFuzzybunny:
I've been a boiler Engineer since 1975.
I've worked on and operated all kinds of boilers, from high pressure to low pressure.
I've seen safety valves that would not lift when they were suppose to.
I've seen low water safety valves stuck, boiler still running, and no water inside.
I've had high pressure tubes in a water tube boiler firebox blow and rip apart.
I've had the end of a waterwall drum blow. ( We let it gush water for 2 days while trying to cool the boiler down.)
But by far, what is the most dangerous, and still happens way too much, is somebody bypassing the purge cycle for the firebox.
Most all of your explosions today are caused by this.
There is a reason most boilerrooms are built away from the main buildings.
If the boiler blows up, only the engineers will be killed.

...why would anyone do that? I mean, its so obviously dumb, and I see no upside at all.
 


A purge cycle? Must be a high-efficiency boiler as all others are natural draft and thus always pruging while between heat calls. Please elaborate? I am curious.
Link Posted: 4/13/2011 4:58:49 PM EDT



Originally Posted By timco:

A purge cycle? Must be a high-efficiency boiler as all others are natural draft and thus always pruging while between heat calls. Please elaborate? I am curious.


In the petrochemical and refining industries they're almost always induced draft, as far as I know.



 
Link Posted: 4/13/2011 5:01:24 PM EDT
Link Posted: 4/13/2011 5:01:40 PM EDT
Originally Posted By clutchsmoke:
Originally Posted By SuperJanitor:
They can occur, but on modern boilers, multiple fail-safes would have to be bypassed. They have pressure limit switches,mechanical and electronic low water cut off switches and relief valves. The ones I deal with also have several go, no-go switches on the gas train. If certain things don't happen in a certain order, they wont even fire.


I've encountered boilers dry firing, when I shut the gas off I could see the heat exchanger glowing red hot, I tip toed out and let it cool off on it's own.



 I worked on a low pressure hot water boiler that was gas fired with a 2" gas inlet.The installers had wired it wrong and that thing would open the 2" gas valve BEFORE a pilot was proved..............
Link Posted: 4/13/2011 5:01:43 PM EDT
Originally Posted By ElectricSheep556:

Originally Posted By timco:
A purge cycle? Must be a high-efficiency boiler as all others are natural draft and thus always pruging while between heat calls. Please elaborate? I am curious.

In the petrochemical and refining industries they're almost always induced draft, as far as I know.
 


Prepurge and postpurge are utilized regardless of wether it's induced draft, forced draft, etc. Thats apples and oranges.
Link Posted: 4/13/2011 5:04:09 PM EDT



Originally Posted By beachcommando:

Prepurge and postpurge are utilized regardless of wether it's induced draft, forced draft, etc. Thats apples and oranges.



I have no experience with natural draft boilers but he said that they don't require steam purges, so I was replying to that.



 
Link Posted: 4/13/2011 5:05:03 PM EDT
Originally Posted By ElectricSheep556:
Water tube rupture is probably the most common cause of boiler accidents. There's no real way to monitor the water tubes beyond regular inspection. Accidents caused by light off explosions, low water level, and overpressure are far less common than they used to be due to the technology available to us. For example, there are now sensors which monitor the flame of the burner, and if it is the wrong color, or if the burner goes out, it cuts off the fuel. Likewise, if the water level is low, the fuel is cut off. Its all a little more complicated than that, but for people that "don't really know anything about boilers," that's sufficient.  


Yep. I like to think of it in terms of a rocket launch. When Houston is doing their go, no-go sequence for a rocket launch, they are sequencing things in a certain order that have to be right before ignition. The same thing is going on with your modern boilers. You have gas pressure sensors, they either give a go or a no-go, if that's ok then we need to be sure that the water is at the proper level, if that is ok then we start our ignition sequence. First we pre-purge (we make sure that there are no combustable gasses in the fire box, we do this by applying positive pressure to the fire box for a prescribed ammount of time), the we do an ignition trial (we send a small ammount of fuel in and by either a hot surface ignitor (HSI) or a high voltage spark, we test for ignition) If the infared sensor detects a flame, we turn on the main fuel and run our cycle. Once we get to operating temp, something called modulation happens. This is where air flow and fuel are slowly regulated to maintain the proper temp for the desired pressure.

Another neat thing about more modern boilers (usually the hydronic variety) is staging. As heat is needed, stages fire. Basically, there are multiple sets of burners in each boiler unit and they come on as demand dictates. The building I work in was constructed in three different phases over a period of 20 years. I have both hot water and steam heat in the same building. I have 2 steam and 2 hydronic plants. It's crazy, especially for a building that houses less than 400 students. More government logic I guess.
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