Wednesday, March 12, 2008

Fires Lighted, 1A Boiler

(It might not hurt to occasionally refer to the diagram here.)

So we now have fires lit in 1A boiler. Naval boilers, when not steaming, are always laid up in a manner that helps prevent corrosion. The most common short-term layup is a "steam blanket", where steam that is supplied from either a steaming boiler or, in port, from a steam supply line from the pier, is piped to the top of the boiler to keep air out. If we have a steam blanket, that means the water in the boiler is somewhat warmed. You secure the steam blanket, obviously, just before light-off.

Initially, not much happens. The boiler slowly heats, as you can only run one burner with the electric forced air blower. If you put in more fuel than the light-off blower can supply air for, you will emit black smoke and that is bad form. Once you get to about 50psi on the steam pressure gauge, you can open the outlet for the boiler and start to feed steam to the steam pipes to warm them up.

Gradual warming up of the steam lines is critical. The steam lines at light off are at room temperature. At operating pressure and temperature, the main steam line has a steam pressure of 1,175# at 950degF. You must heat the lines evenly and slowly in order to prevent uneven expansion, which in turn, leads to leaks around the gaskets that connect valves to the pipes and sections of the steam pipes to each other. At this point, the main steam valves are all closed (they are large gate valves). Each main steam valve has a small bypass line to equalize the pressure on either side of the valve before opening it; the bypass valves are opened, in sequence, to heat the steam lines. You pressurize and start to heat each section before you start on the next one. Then you open the main steam valves and begin feeding steam, now at 100# or more, through the plant.

Now stuff starts to happen. You can start rolling the main forced draft blowers, which are powered by steam turbines, and you can secure the electric blower. The main forced draft blowers can put out a lot more volume of air, so you can start a second burner. Once you have one burner going, when you start more, you just open them up, as they will light off from the burner in use. You also start the steam-driven main feed pump, as it can supply feedwater at higher pressures than the main feed booster pump, which is what you were using.

Both the man forced-draft blowers and and the main feed pumps exhaust their working steam into the auxiliary exhaust system, as do all steam auxiliary systems. The aux exhaust (which are not liquid, this is steam at 5-25# or so) feed to the deaerating feed tank (DFT), which both deaerates the feedwater and supplies feedwater to the main feed booster pump. The aux exhaust also dump into the condensers for the ship's service turbogenerators (SSTGs) and the main engines. But you cannot do that until you have enough steam pressure to roll the SSTGs, as the aux steam will unevenly heat the turbines of the SSTGs, and that is a bad thing.

The problem is that the DFT cannot handle the steam load that is being dumped into the aux exhaust, so the aux exhaust system overpressurizes and lifts the relief valve, which vents out the stack just below the smoke vents. A steady cloud of steam vapor comes out the vents, and that is water that has to be made up from the feedwater tanks. This is a tricky time, you have to get pressure built fast enough so you have enough steam pressure to at least one SSTG rolling so you can cut in aux exhaust to its condenser. This is where the EOOW doing the light-off of the plant has to pray that the Chief Engineer doesn't go topside and sees the steam blowing out the vents, as regardless of whether the light-off is going well or not, you can bet the CHENG will have something caustic to say about the feedwater being used up.

Once you can roll a SSTG and get aux exhaust cut into the SSTG's condenser, the steam system becomes closed and you aren't using that much feedwater. But until you do, from the time you blow the relief valve, you use a lot of feedwater. It is considered to be bad form to have to call the Culligan truck to top your feedwater tanks off once you start the light-off. It happens to everyone sooner or later, but if you make a habit of it, your ship will get a bad reputation as being unable to do a light-off unassisted, which means the Captain will hear about it at various social parties, if not officially from the Squadron or Group Commanders, which means you will hear about it from the Captain and the conversation will not be pleasant.

Once you have one SSTG rolling, then you can crank up the blowers and build steam pressure faster. When the 150# aux steam lines in the Engineroom are up to pressure, the machinist's mates can start the evaporators so the evaps can begin making distilled water from the surrounding water in port, so you can refill the feedwater tanks. This water has to go to feedwater; you don't cut the evaps to the potable water tanks in port unless it is an emergency, for the water then must be heavily treated to be safe. You are about where you can start feeding steam though the "hotel" system to feed the heating systems, the water heaters and the galleys, and you can secure the steam lines from the pier.

Now you are up to main steam pressure. You bring one SSTG up to speed and it feeds to the main electrical switchboard. You call the Quarterdeck and have the word passed over the ship's PA system (the "1MC"): "Place all electronic equipment in standby while the ship shifts from shore power to ships' power." You wait about five minutes, then order the EM on watch to switch to ship's power. Using a synchroscope that is built into the switchboard's panel, the EM matches the phases of shore power and the output of the SSTG, controlling the SSTG to run at a slightly higher frequency. When the needle of the sychroscope is between 11 and 12 o'clock, the EM parallels the SSTG to shore power and then immediately trips the breaker to shore power.

You wait a few minutes to see if everything is stable. If it is, you call the Quarterdeck and ask them to pass the word "the ship is now on ship's power."

You are now "auxiliary steaming." The only services the ship is receiving from the pier are fresh water in, sewage out, and telephones.

6 comments:

physioprof said...

Beautiful! I don't know how much traffic you're getting for this stuff, but you can count me as one fascinated reader!

The Earth Bound Misfit said...

Not a lot, but this is a new blog. And it's pretty specialized.

W Ton said...

Question here. I'm not a snipe, just an engineer with a naval history fixation. I've seen diagrams and procedures for WWII-era plants that have auxiliary condensers. The SSTGs could be aligned to the auxiliary condensers or to the main condensers. You seem to describe a system only with main condensers. It seems to me that those aux condensers would solve the open-loop problem. The aux exhaust could be fed to the aux condensers without involving the SSTGs at all. Am I missing something?

Comrade Misfit said...

The diagram only shows the main condenser, but yes, the SSTGs had their own condensers. That is why it was so important to get at least one SSTG rolling so that aux exhaust could be cut into the SSTG's condenser.

On the 1200# plants, the SSTG's exhaust went into their own condensers, not to the main condenser. They were not switchable.

W Ton said...

I get it. And because they were not switchable, the SSTGs could not be isolated from the aux condensers, hence the aux condensers could not be used at all until you could roll an SSTG. Thanks.

W Ton said...

If you are interested, you can look at the Fletcher/Sumner/Gearing class auxiliary exhaust layout on page 124 at the address below. Scroll down.

http://www.hnsa.org/doc/destroyer/steam/sec08.htm

The diagram showing the SSTG exhaust to either condenser is most clear for engine room #2 on the left. I imagine you did not even have a valve between your SSTG and its condenser.