Action to take during power failure-industrial boilers

larryh

System Outline:
Two -500 hp. Fire tube boilers operate at ~ 150 psig; safety valves set at 200 psig.
Steam is supplied to a Chemical Research Facility and used for both heat and process via insulated overhead piping.
Licensed boiler operators are on duty 24/7.
Problem:
This facility recently experienced a 12-hour electric power failure.
Question:
Which of the two following conditions would provide the least possible damage to the boilers?
1. Should the boiler operators close the main steam stop valves and attempt to maintain a water level to cover the fire tubes?
2. Or should they allow the boilers to steam off into the delivery piping and attached heating/process system?
Note: as observed in the past the steaming off is quite rapid with attendant drop in water level. Since we have not had an electric power failure for many years it is not clear how fast or how much water is left in the boiler when equilibrium is achieved.

retiredguy

If this is a normal operating boiler plant the "steaming off" speed should not be a problem if the boilers are equipped with Penberthy Injectors and the operators know how to use them. If you don't have these injectors, then I would instruct the boiler operators (stationary engineers) to close the header valves to control the water level. Once power is restored, a normal cold boiler start-up procedure could be initiated. If the boilers are of an older design they may have a firebox that is refractory lined so the boiler operators may need to blow off enough steam to control the steam pressure or they can let the pressure rise enough to check the operation of the safety valves.

SlamDunk

I have a similar setup and have lost power for similar a duration and did not lose enough water to lock out burners. We have manually ressetable probe type aux. LWCO and primary cutoff. The the auxilliary LWCO never trips.

Ours will trip if water level is less than 9 inches above top row of tubes. In the site glass, the meniscus of the water level should be visible at the bottom of the glass at the same time the aux lwco trips.

pecmsg

1st thought is Why no back up generators?

Jamie Hall

pecmsg said:

1st thought is Why no back up generators?

That would be my first thought, too. At least big enough to maintain boiler water level -- feed water pumps etc.

The second thought is whatever you choose to do, do not let the water level get down to the fire tubes. Keep it above that. If that means a reservoir tank and a diesel powered feed pump, do it. Whatever it takes.

SlamDunk

Speaking for myself, not OP, we have three 750kW generators but they are not worth a dime if won't carry the load because there is NOT a clean break from utility.

We have had two occasions were the generators did not accept the load. Different problems that would have resulted in us back feeding to power lines. Generators are nice but they are not guaranteed to be there when you need them! And, they are smarter than I am. It won't let me kill myself or anyone else.

EBEBRATT-Ed

@larryh

What @retired guy said is correct. Close the header valve to maintain the water level. They may need to open them to releave steam occasionally.

An HRT brick set boiler is different procedure than the scotch marine boilers you have.

Thats why the plant my brother works at has a steam turbine for back up water feed

SlamDunk

Once the burners are off due to a power outage, chances are all field steam consumers will cease demanding steam as well, valves fail closed, so there is no demand- it is the same as closing header valve. You have to flash off 15-18" of water to expose the tubes. With no burners and no demand, it doesnt happen. And if it did, so what? The temperature of steam at 150 psi is 365*f. It will take 12 hrs just to drop to 25psi. Everything is still hot at 266f. I dont see a problem. At least , i havnt experienced one.

pecmsg

All my steam valves Fail Open.

SlamDunk

I guess I have a better system .

EBEBRATT-Ed

@SlamDunk

The danger is with the old brick set HRT boiler and others with a massive brick combustion chamber. You can shut the burner down (power failure) but if you don't have a way of providing feed water and the water level drops you cook the tubes. Those boiler hold a massive amount of heat in the combustion chamber

Shutting down supply valves will help keep water in the boiler but you have to let the steam out or you will pop the safety valve.

At 1 high pressure plant I know of they had electric feed water pumps, steam driven feed water pumps, duplex pumps that could be driven by steam or compressed air and as a last resort city water

SlamDunk

I have scotch marines. I didn't see where op said anything about brick chambers.

But if you isolate a boiler with a hot brick chamber, wouldn't you create a situation that will open the pressure relief valves?

Wait a minute, you said water supply valves. Op said steam valves. I was speaking to steam isolation valves used to isolate boilers.

@EBEBRATT-Ed , i think we may be saying the same thing......long day