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Showing posts with label Steam Turbine. Show all posts
Showing posts with label Steam Turbine. Show all posts

Thursday, June 27, 2024

Outage Post-Mortem, and passings

 "If all emotions are common coin, then what is unique to the good man? To welcome with affection that which is sent by fate.

Not to stain or disturb the spirit within him with a mess of false beliefs.

Instead, to preserve it faithfully, by calmly obeying God - saying nothing untrue, doing nothing unjust.

And if the others don't acknowledge it - this life, lived in simplicity, humility, cheerfulness  - he doesn't resent them for it, and isn't deferred from following the road where it leads; to the end of life.

An end to be approached in purity, in serenity, in acceptance, in peaceful unity with what must be." - Marcus Aurelius

Monday, May 13, 2024

Outage addendum 2

 "What the superior man seeks is in himself.  What the small man seeks is in others." - Confucius

Sunday, May 05, 2024

Outage addendum

 "We are so busy doing the urgent that we don't have time to do the important." - Confucius

Friday, April 26, 2024

A few outage pictures - and kiss May goodbye as well...

 "'Misinformation' and 'disinformation are just different words for wrong-think" - Unknown

Thursday, April 04, 2024

Kiss April Goodbye...

 "Strategy without tactics is the slow route to victory.  Tactics without strategy is the noise before defeat." - Sun Tzu

Saturday, April 23, 2022

Hot Steam Turbine Thrust Bearing

 "It is difficult to bring people to goodness with lessons, but it is easy to do by example.:" - Lucius Annaeus Seneca

Wednesday, April 20, 2022

Steam Turbine Valve Maintenance part 2

"What man can you show me who places any value on his time, who reckons the worth of each day, who understands that he is dying daily?

For we are mistaken when we look forward to death; the major portion of death has already passed.  Whatever years are behind us are in death's hands." - Lucius Annaeus Seneca

Sunday, February 13, 2022

Steam Turbine Expansion

"The present moment is the only thing of which anyone can be deprived, at least if this is the only thing he has and he cannot lose what he has not got." - Marcus Aurelius

Wednesday, September 23, 2020

Someone is having a bad day at work...

Have a look at this incident.  I don't like to name facilities, but I am familiar with this one.  It's a General Electric 4x2 power station - Two power blocks, each consisting of 2 gas turbines and boilers creating steam for a single steam turbine.


Saturday, December 27, 2014

Battleships

It's a ways past Pearl Harbor Day, but I have been thinking about that quite a bit.  I am not a great and well-read student of military or Navy history, but I know a little bit about it.  Although I am not a surface ship guy, I think battleships are pretty cool, and so I have read a fair bit about them.

Battleships were at the core of the first modern arms race in the early 20th century.  This battleship arms race began shortly before the outbreak of the first World War (and many historians believe helped to cause it).  But the reign of the battleship ended decisively with the attack on Pearl Harbor.

The idea of a large ship, carrying primarily big guns, goes back to the days of sail.  These were called "ships of the line", because the tactics of the day required bringing a line of several ships broadside to the enemy, and blasting them with the cannons mounted on the sides (a "broadside").

The tactical goal in those days was to "cross the enemy's T", to maneuver so as to have the enemy sailing straight toward the side of your ship.  The front of these vessels were poorly armed, having at most only deck-mounted hand cannons.  Therefore the firepower of a broadside would likely destroy the oncoming enemy ship, with little harm coming to the ship crossing in front of the other ships.

Below, two lines of warships ("Battle ships of the line") firing broadside volleys at one another.

In theory (and in practice), the larger ships with bigger and more cannons would typically sink smaller and less well-armed vessels.  The best defense for a smaller vessel was to rely on speed to escape, or maneuverability to avoid a broadside, if possible.

Below, a sail ship with three rows of cannons

The term "Battleship", while coined during the age of sail, became more common when steam-powered ironclads came onto the scene.  Ironclads were the ship-builder's response to the introduction of incendiary and explosive shells, which of course were highly destructive to wooden vessels.  Additionally, naval cannons were becoming more and more powerful, and later models could blast through several inches of oak, sending wooden shrapnel flying inboard to kill the crew.

This Union ironclad (USS Cairo) appears to have an armored stern wheel for propulsion.  This was a ship used on the Mississippi River during the US Civil War.  Most deep-water ironclads used the newly invented (and less vulnerable) underwater screw.  Note the angled sides, intended to cause incoming shells to deflect rather than penetrate.

Ironclads, and all battleships made up until the introduction of the HMS Dreadnought are considered "Pre-Dreadnought" designs.  The difference between an ironclad and a dreadnought-era battleship is the use of wood underneath the outer iron skin.  Typically 8-12 inches of wood would underlie 4-5 inches of iron or low-quality steel cladding on an ironclad warship.  Ironclads were not particularly fast, nor were they maneuverable.  They used piston steam engines rather than turbines for propulsion.

HMS Dreadnought was such a technological marvel that even decades after she had been scrapped, battleships were called "dreadnoughts".  Pretty impressive!

Below, the ship that started an arms race.


HMS Dreadnought made all warships that had come before obsolete.  She was very fast, because she was the first warship to use steam turbines for propulsion, and thus she could run or fight on her own terms.  Secondly, she was the first battleship to use only large (12 inch diameter) guns.

In the era of HMS Dreadnought, fire control consisted of spotters checking for splashes in the water where shells landed, and then advising the gun crews how to adjust their fire to get closer to the target - and maybe even hit it!  Ships that had a variety of gun sizes would often confuse the spotters, who might see a splash and not know which size of gun battery had fired it, making targeting confusing. On a ship with all large guns, this issue of confusing splashes from large and small guns out on the horizon did not arise.

However even during the heyday of this arms race, a fearful enemy hid just under the surface, and that was the submarine.  Every battleship captain's nightmare was that his gleaming, magnificent, treasury-busting ship-of-the-line would be sunk by a lowly torpedo.  If you look at the photo above, there are a series of poles running alongside the ship.  These would be extended when the ship was not in motion, and torpedo nets would be hung from them.  Not as invulnerable as they seemed, then.

Deploying torpedo nets.


With the launching of HMS Dreadnought, every major ocean-going country in the world immediately set out to build their own series of dreadnoughts, or modern battleships.

France:

Germany:

Japan:

The United States (finally moving to steam turbine propulsion in 1922):

Russia:

So the naval powers of the world, just before the Great War, embarked on the business of bankrupting their treasuries to build fleets of mighty battleships, just as the emerging technologies of air power and submarines were about to render them nearly useless.  And while naval strategists envisioned battles of all big-gun ships, during actual (as opposed to theoretical) wars, most of these ships succumbed to mines, torpedoes, or air attacks.

One of the few battles fought with large-gun capital ships was the Battle of Jutland, in 1916, off the coast of Denmark.  The larger British battle fleet engaged the German battle fleet over the course of two days, with the intent of sinking them or keeping them contained in their home ports.  The British lost twice as many men and tonnage than the Germans did, while causing the Germans to retreat home. Both sides claimed victory, although one could also say that both sides lost.

After the German fleet exploded three of the British Dreadnoughts, David Beatty (commander of the British Battlecruiser fleet)  turned to his flag captain, saying "Chatfield, there seems to be something wrong with our bloody ships today."  He was correct.  British designers and the Navy had traded the weight penalty of thick armor for greater speed and more guns; the British battleships were little more than very expensive floating bombs.

Even though the battleship had proven itself not terribly useful during the Great War, maritime nations continued to build them. There was even a sort of battleship arms control, with each nation allowed to build a certain tonnage of battleships and aircraft carriers.

Below, the German Battleship Bismarck during WW II.  After her rudder was damaged by torpedo bombers, the British battle fleet caught up to her.  She was then sunk by both enemy gunfire and intentional scuttling.

What finally did the battleship in though, was the eye-opening events of December 7,1941.  On that day six aircraft carriers sunk four battleships, damaged four more, and sunk or damaged several cruisers and destroyers, in addition to wreaking havoc on the airfield at Ford Island. 

The attacking aircraft carriers meanwhile were never in any danger from the battleships.  This attack devastated much of the Pacific fleet, and if nothing else, showed the vulnerability of *everything* to a carrier-based air attack.

Below, Pearl Harbor at the beginning of the attack.  Ford Island (center) sits at the center of Pearl Harbor.  In this photo, the battleship West Virginia has just been hit by a torpedo.

The aftermath:

USS Nevada

USS Arizona

USS West Virginia

USS California (Neosho behind)

...you get the idea...

No number of battleships could have accomplished the destruction that these six aircraft carriers did. Even if the Pearl Harbor battleships had been at sea, they could not even have gotten near enough to the aircraft carriers to harm them without being sunk by torpedo bombers first.  Battleships were immediately placed in secondary roles - such as shore bombardment - in favor of aircraft carriers and submarines.  The urgency of the situation forced military commanders to recognize the military shortcomings of battleships.

In between wars, battleships were gaudy, impressive, and threatening. During an actual shooting war, they were quite a bit less fearsome, spending their time bombarding tropical islands and escorting  more strategically valuable aircraft carriers.

Meanwhile, over the duration of World War II, just 314 far less expensive US submarines sank 1560 enemy ships, an impressive 55% of the total tonnage sunk during the war.

And so, suddenly after one Sunday in Hawaii, the future of US naval warfare shifted sharply toward submarines and aircraft carriers (and the many, many ships required to protect and service aircraft carriers).

Oddly enough, in spite of this painful lesson of history, US battleships gained another lease on life toward the end of the cold war.  Four decommissioned battleships that had been built during WWII were recommissioned, and refitted with guided missiles and also with close-in weapon systems for missile defense. These ships were decomissioned for the second time in the mid 1990s.

Iowa fires a broadside in 1982 for a firepower exhibition.  Exhibition... that kinda says it all.

Now as unimpressed as I am by the usefulness of battleships in actual battles.  I still think they are cool.  Extremely cool.  Just sayin... Check out that armor.  17 inches of steel!

USS Missouri ("Mighty Mo") after her 1980s refit with missiles and modern electronics.  Also, 33-35 knots is pretty darn fast for such a monster!

In closing, I honestly believe that if the navies of the world were to engage in unrestricted warfare, *nothing* would be afloat on the surface within a week.  Only land-based aircraft and a handful of very advanced submarines would remain.

Thursday, November 13, 2014

Steam Turbine Outage

This may or may not be an interesting topic to the random readers that drop by here.  I honestly don't know.  I've been around steam turbines my entire adult life, and have never given the shaft sealing system much thought - until we had a seal failure that ended up with the accumulation of a bit of new knowledge, which I share here.

As you would guess, steam tends to leak out of a steam turbine at the high pressure end, where steam enters the turbine, and air tends to leak in at the exhaust, where the final stage of the turbine is at 1-3 inHg Absolute pressure (25-27 inHg vacuum).  Steam turbines are not sealed like pumps.  Pumps use flexible packing or mechanical seals, that actually come in contact with the shaft.  Steam turbines do not seal this way, due to large swings in operating temperature from cold to running.  Instead turbines are sealed using steam!

I took a quite a few photos while the steam turbine was apart for the seal repair, and thought they were interesting enough to put up.  The steam turbine is a General Electric model A-10.

Most modern steam turbines are what we call "self-sealing".  What that means is that they only need to be supplied with sealing steam during startup and shutdown.  After the turbine reaches a certain load (5-20%), leak-off from the turbine supplies the seal steam, and external sources can be shut down.  If there is any excess leak-off, and the seal steam supply pressure gets above the setpoint, a seal steam dump valve opens, and dumps the excess steam into the main condenser.

The symptoms of a failed steam sealing system are these:  

  • The seal steam dump valve is 100% open, and yet the seal steam header pressure is still too high.
  • Water vapor and condensation coming from the Lube Oil System vents.  
  • Increasing Lube Oil Tank level due to steam ingress and water contamination/condensation.

Note:  Water enters the lube oil system because the turbine shell is very close to the bearing housing.  So as steam leaks out along the shaft of the turbine, it can leak right into the adjacent bearing housing.  The lube oil system is kept under a light vacuum so that air will leak into the bearing housings, rather than oil leaking out.  This will help pull in steam if the steam seal is leaking.

First of all, before any work can begin, the steam turbine must be shut down and allowed to cool.

Following the shutdown, the steam turbine has to be continuously rolled at low speed (typically 4-10 RPM) for about 3 days.  Steam turbines operate at very high steam pressures and temperatures, and as a result, the turbine shell is very thick at the high pressure end.  The shell is also insulated for thermal efficiency as well as for safety.  For these reasons it takes several days before the turbine is cool enough to stop turning.

The purpose of rolling the turbine is to prevent warping the rotor.  If the rotor is allowed to stop, it will develop a bow.  Once a bow develops, it may sometimes work itself out when the steam turbine is returned to service; the rotor, reheated by steam, becomes ductile again and the bow mostly disappears.  Other times, with severe bowing, the machine cannot even be started due to increased vibration caused by the off-center mass of the rotor.  The damaged rotor will require machining and the addition of balance weights to compensate for the bowing, if not complete replacement.  Needles to say, it's preferable to keep the steam turbine on the turning gear until it cools down.

Interestingly, a steam turbine rotor does not sag if it cannot be rolled during cooldown.  Instead it humps up in the middle, because of the temperature differential between the top and bottom of the turbine shell.  It is not unusual to have a 200 degree temperature differential between the top of the shell and the bottom.  As heat rises inside the shell, the bottom part of a motionless rotor will contract more quickly than the top, which then bows the rotor upwards.

Onward now to the bits and pieces of a smallish high pressure steam turbine outage...

Below, a worker uses a sledge hammer to remove a nut from a through-bolt on the high pressure turbine shell.

Just above the worker's hard hat, is a black bundle of tubes.  This bundle is the power supply for an inductive heater.  The inductive heater fits down inside the through-bolt (which is hollow), and heats it up.  As the bolt heats up, it stretches out, making it much easier to remove the nut.  The same thing takes place during installation, except when the bolt cools, it shrinks, which draw the upper and lower half of the turbine shell very tightly together.  Note the insulating blanket on top of the shell.  Workers didn't want their feet to get burned while removing auxiliary piping.

Below: The top of the High Pressure turbine shell.  The far end (burnt off paint) is the high pressure steam inlet.

Below, two workers removing the high pressure inlet steam seals.

Below: Another image of the high pressure turbine.  At the bottom left corner on the rotor, are holes for balance weights.  Next is the steam sealing section, then a series of discs with tiny blades at the end.  These discs are the 10 stages of the high pressure steam turbine.  The generator is the big thing to the right.  Notice how thick the steam turbine shell is - This is why it takes three days to cool the steam turbine down from 1050 degrees F.

This is a close-up of the high pressure steam sealing section, with the packing (or labyrinth seals) removed.  High pressure (up to 1800 psi) steam enters the turbine just to the left of the disk on the right hand side, and then flows off to the right. At 1800 PSI, steam would tend to leak out along the shaft and be a hazard for everyone around, as well as causing a loss of efficiency.  To prevent this, steam turbines use labyrinth seals.

Below: Side view of a labyrinth seal.  These segments slide into the grooves in the sealing section of the shell, sitting very close to, but not rubbing on the rotor.  The purpose is to make the steam pass through a "labyrinth", or a series of very tight passages, losing a little pressure with each ridge.  At the left end of the seal in the photo above, a small fan draws off the tiny amount of leak-off steam and condenses it for re-use.  Clever!

Below, labyrinth seals (or packing) installed in the grooves on the high pressure turbine.  Interestingly these are held in place by springs that are merely short flat pieces of steel These springs press against the inside of the packing gland and the outside of the labyrinth seal.  Several of these springs were found to be broken during this outage.

The picture below shows a part of the steam turbine that is contained within the lube oil system.  At the right is a journal bearing.  This supports the aft end of the high pressure turbine (which is just off the picture to the right).  You can see a wire coming off this journal bearing, which is used to transmit the temperature of the bearing metal.  To the left of the bearing is a flat metal flange on the shaft.  This is used to determine rotor expansion.  The shaft expands quite a bit as the steam turbine goes from a cold condition to the normal operating temperature of 1050 degrees F.  The coil of blue wire connects the rotor expansion position sensor to the monitoring system. The big gear is for rolling the rotor when the steam turbine is not in operation.  The big round flange with all the holes in it is the coupling which connects the generator to the turbine.



Below, the bearings at the other end of the high pressure steam turbine.  In the center is a journal bearing, with thrust bearings to either side.  The journal bearing supports the shaft, and keeps it from moving in a radial (side to side or up and down) direction.  The purpose of the thrust bearing is to keep the shaft from moving axially (left to right) .  The shiny flanges with no holes in them are a part of the rotor called thrust collars.  The shiny things just inside them are the thrust bearings.  This section of the steam turbine is continuously supplied with oil to cool and lubricate the components.

One of the pads from the old thrust bearing... not in very good shape at all.

These looked in pretty bad shape as well.  Obviously there had been some heating and breakdown of the oil into carbon deposits.



Replacement labyrinth seals installed on the high pressure turbine lower half.  Note the serpentine path that leak-off steam must travel.

High pressure steam turbine back together and being fitted with brand new insulating blankets.

One of the things you run into while starting a cold steam turbine is rotor growth.  The rotor does not contain as much material as the turbine shell, and it is completely surrounded by steam (although the steam temperature is kept as low as possible during start up).  At the same time, the turbine shell is also cold, but only has steam warming the inside of a *very* thick piece of steel.  As a result, the rotor heats up much more quickly than the turbine shell, and it therefore expands much more rapidly.

Because one end of the rotor is held in place by the thrust bearing, the other end of the rotor grows as steam heats it.  It's quite possible to have rubs if the expansion of the rotor gets too far ahead of the shell.  That's why you will find rotor expansion proximitors (Below). These little pucks monitor exactly how much the rotor has expanded.


This is one of the few outages I have had time to take pictures and learn a few things, because on scheduled outages, I usually have assignments that keep me too busy for that.  Was fun to learn, fun to share.

NOTE: There is a continuation to this post with some further useful information HERE.

Sunday, August 18, 2013

The steam cycle

I have been meaning to do a post on the steam cycle, otherwise known as the Rankine Cycle. It's pretty simple to describe the four-step process. The complicated part is designing, maintaining, and operating the machinery that makes it happen continuously, year after year.

The water/steam cycle is the most practical and commonly used means of converting heat energy into electrical energy.  The process works like this:  Fuel is burned for heat.  The heat vaporizes a liquid (typically very pure water), which is then expanded through a steam turbine.  Lastly it is condensed at very low pressure to extract all possible thermal energy and also to re-use the pure water. 

Saturday, May 25, 2013

Early Steam Turbines

Today those of us who work with steam turbines for a living are familiar with axial-flow turbines, where steam flows through a series of rotating and stationary blades in a direction along the shaft.  Below is a cutaway of a small five stage turbine. 

Thursday, April 11, 2013

Very Basic Steam Turbine

Steam Turbines come in an infinite number of sizes and designs.  It's amazing how many ways a machine can be designed to extract energy from expanding steam.

The oldest known design dates from the Greeks about 10 yrs A. D., and is known as Hero's Aeolipile (How you pronounce that, I am not sure).  Here is a drawing of one from antiquity:




Apparently a few of these were made from bronze, and were simply curiousities.  Heat from the fire below boils water in the bronze reservior.  Steam from the boiling water is carried up in pipes to a hollow ball at the top.  The pipes that carry the steam up to the ball support it, but also allow the ball to rotate freely on the axis.  The steam is then allowed to escape from the ball via two nozzles, spinning the ball.

A couple of interesting things to note about this design: 
  1. This design would not be useful as anything other than a curiousity because it has no output shaft.
  2. The very first steam turbine design is a reaction turbine.
Item #1 probably prevented the steam age from happening for 1800 years.

Item #2 is interesting because although Issac Newton didn't explain the Third Law of Motion until 1687, the process was understood long before then!  Newton's third law is usually paraphrased as "For every action there is an equal and opposite reaction", thus the term "reaction" turbine.

Reaction turbines achieve movement (and actual work) by squirting steam through nozzles, like our Aeolipile above.  The steam squirts out, and the reaction force causes the ball to spin in the opposite direction from the steam jet.

The other type of turbine is called an impulse turbine.  In this design, steam is directed at a set of blades on a shaft and bounced off of them.  This provides an "impulse" to move.  Below is a simple diagram showing the difference between the two basic designs.


In other posts I will decribe a little of the evolution of piston steam engines, steam turbines, and show some intersting modern designs and cutaways.