2 Nov 2009 blind terror

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2 Nov 2009 blind terror

Postby redearsau on Wed Nov 04, 2009 12:19 am

hahaha, great expression Alan.
Ears back, fists, and the turn of hips to take 'bloody big steps' (as recommended in the 'fine manual').
I've seen that 'oh shit' face myself - and made it a few times.. working in heavy industry
If that turbine is running without much load and a jammed control actuator, its may run rather fast.
Looking forward to see whats next, and hoping this time they are quick enough.
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Re: 2 Nov 2009 blind terror

Postby Bruce Bergman on Wed Nov 04, 2009 10:51 pm

Well, if they'd have had time and knowledge, they could have switched in a dummy load or channeled the output straight to a dozen emergency propellers to act as a load sink - aim them in opposite directions and they cancel each other out and use energy...

But even with the knowledge, they had no time.

They need to get the pressure in the tea-kettle down NOW, because the Inlay plugged off all the safeties - using the throttle control ram to knock the throttle valve open will release the pressure. With any luck they can clear the room and slam the door shut before that turbine overspeeds and grenades. Having a semi-controlled steam leak is Bad enough, but...

If they let the converter rupture and release all pressure instantly, that would be Real Bad. One gallon of superheated water held under pressure flashes to 300 gallons of steam, and I'll take a guess the system holds several hundred thousand gallons. Letting loose a few million gallons of instant steam in the bowels of a ship would crack the whole thing like an egg.

"Hi, I'm your Electrician, and I'm a trained professional. If you see me running like crazy for the exit door screaming "EVACUATE THE BUILDING!" do NOT ask dumb questions - Just try to keep up."

Go look up some of the wonderful disasters that ruptured steam boilers produce, one of the reasons they got away from the steam locomotive. Well, that and overall efficiency, and the many hours of maintenance for every hour of operation, but you get the picture.

Steam locos do make thermodynamic sense if you own the forest or the coal mine (or have a nice waste stream that can be burned) and get your fuel free or cheap. But if you have to buy the oil or natural gas to burn, it goes a lot farther in an internal combustion engine than a steam boiler.

--<< Bruce >>--
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Re: 2 Nov 2009 blind terror

Postby redearsau on Thu Nov 05, 2009 2:48 am

As Bruce says, the beauty of steam is that you can release a LOT of energy in short time from a boiler, many times its constant power rating.. but thats also the danger of it. Electricity works in about the same way during faults. I figure if the turbine over ran while still online ( the jump start) it may, or may not be disconnected by a breaker tripping out. An out of control turbine is pretty dangerous, but disconnecting it so it runs wild and overspeeds is grenade like. Of course once it blows up there will be space for the steam to expand into. Where I have worked there are similar explosions in blocked pumps, the friction of the impeller spinning in water makes it hotter and hotter, and depending on the plumbing pressure can rise until the castings crack and turn into huge shrapnel and steam explosion. Thats why when we find a steaming pump we bravely run away screaming on the radio to have the Ops warn anyone on site and shut it off.

OK, I admit it, I'm an electrician. I once had the job of powering up a flash fire (flour dust) damaged high power switchboard (415V 2000A full load motor control center) with an Operator and the site General Manager 'observing'. The carbonised surfaces of the control board started conducting fine feathery burning arcs that wandered like beautiful will-o-whisps over the metalwork toward the supply busbars and disaster (read explosing- everyone frys). It looked like an aerial view of grassfires. The GM (general manager) was between myself and the switch, so he got *slightly* shouldered / bumped on my way past. After swinging the main switch to OFF, I turned round saying "well, that was ...... close" and found the room empty. The GM and Op where outside but still way too close inside the blast zone for a high ka fault.

Arc flash from shorts in high power switchboards basically shotgun and barbeque anyone with the debris and fireball that results.
Theres info on arc flashes over here http://www.littelfuse.com/data/en/Technical_Articles/Arc_Flash_Whitepaper_8-18-03.pdf
Which explains why electrician wear funny suits and use a rope to operate high power oil circuit breakers, while hiding behind a wall.
Oil circuit breakers can not only explode if they don't switch properly, but also throw burning boiling oil around.

On another site I got to try to rebuild a powerhouse that had an 18 tonne per hour boiler split a superheater tube due to mis-operation. It was running completely manually, all the safetys bypassed except pressure relief (third world country). The guy watching the (water) drum level made a cardboard bed on the catwalk and had a lil nap (this boiler is as big as a two story flat). When he woke up the water was low, so the Ops panic flooded the boiler with cold water (bad) and werent quick enough turning it off. Water entered the red hot superheater tubes, they cracked, and it blew the burning fire back out the manual stoke holes on to the operators (Fuel feed systems and bed fluidisation all out of service and bypassed). Two operators died and half the factory was on fire. The local fire brigade did so much damage that the factory now insists the brigade NOT be called in event of fire. That place was scary, open top rotating knife chopper pits two feet from the top of stairs, narrow catwalks high above concrete floors, without railings and covered in product oil. But thats the third world for you, it pays to be vewy vewy careful working in places where there isnt great medical help (eg: learn how to reshape and butterfly stitch your own fingertips).

So yeah, I've seen that 'oh shit' face myself, made it a few times, and taken some 'bloody long steps' on occasion. This part of the series brings back some wonderful and scary memories. Thanks :) .
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Re: 2 Nov 2009 blind terror

Postby deathbringer on Thu Nov 05, 2009 10:48 am

...oh great, now i'm gonna be bricking it every time i'm in the room with an autoclave. Though i suppose they only have high-pressure steam, no spinny bits or high voltages.
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Re: 2 Nov 2009 blind terror

Postby redearsau on Thu Nov 05, 2009 2:31 pm

Autoclaves are nice big pressure cookers.. :) thankfully with only a little steam that condses to give up its heat, and the condesate (water) running back to the heater to turn into steam and rise again to kill the bugs on the 'thing to sterilize' . h2o changing state from steam to water releases a lot of heat energy.

Happily autoclaves are usually designed to have less water in them, sothey dont need as much energy to operate and get up to temperature quicker.
Boilers hold most of their water under high pressure so it doesnt steam .. (unless the boiler fails) like a radiator on a car operates above the boiling point of unpressurized water. (modern cars do this to run more efficiently and make less emissions). The boiler heats its steam further past boiling in superheaters, which are exposed to the hottest part of the fire gasses / heat exchanger / heatsource. Superheated steam is a LOT hotter than the autoclave 134C, and often runs over 400 C.
Superheaters http://en.wikipedia.org/wiki/Superheat
Superheated steam http://www.spiraxsarco.com/resources/steam-engineering-tutorials/steam-engineering-principles-and-heat-transfer/superheated-steam.asp
Autoclave 134C http://en.wikipedia.org/wiki/Autoclave
Superheat steam avoids having liquid water present, it erodes piping (particularly at corners) and impacts turbine blades to cause pitting and then risk of cracking (thus grenading)..
Autoclaves usually have backup safetys, but can still fail. Just like an old fashion household water heater can... ( dont monkey with the nice safety valve just because it leaks annoyingly)
Now I'm rethinking putting a 14 litre Hot water unit in my camper .. might go instant heat instead - less stored energy.
Heres the inevitable YouTube of an electric water heat deliberatly blowing up http://www.youtube.com/watch?v=GF_Wrm-Ns0I
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