Rick wrote:



Recips don't require as great a vacuum as a turbine to operate at their
peak efficiency. Plant efficiency without the turbine would drop
considerably as the energy in the recip exhaust would be lost to heating
the sea.



I see you agree with me, the steam would be bypassed to the condensor.
But I'm puzzled by your statement that recips don't need as great a
vaccum for peak efficiency. Isn't thermodynamic efficiency directly
related to the inlet and outlet pressures -or do you mean that most
reciprocating engines run at higher outlet pressures?

Cheers

DSK wrote:

Rick wrote:

One could reasonably assume that the plant was designed to accomodate
the loss of the turbine and the condenser could operate at the vacuum
required to allow full power from the recips.


Sure, but for how long? It's a liner, designed to maneuver with the aid
of tugs. Warships have far greater ability to steam in maneuvers, but at
the cost of efficiency & space. A liner has to make money.


At that time the reliability of the turbine was in question so that the
plant was designed to run without it indefinitely. If I recall, the
bearings proved to be a problem on a sister ship.

Cheers

Rick wrote:

DSK wrote:

Rick wrote:

One could reasonably assume that the plant was designed to accomodate


Sure, but for how long? It's a liner, designed to maneuver with the
aid of tugs.


As long as it takes to fix the problem. The condenser is large enough to
handle the steam flow required to produce full rated power. The
circulator pump moves more water than is required to remove the heat
leaving the turbine. Reduced power operation might have been required,
just as modern plants - even military plants - but there is no time
limit associated with that condition.

Warships have far greater ability to steam in maneuvers, but at the
cost of efficiency & space. A liner has to make money.


I don't believe wasrships have any exclusive claim to maneuverability
... that statement applies equally to a warship or a merchant plant. Our
plants are optimized to operate at a continuous maximum power and steam
flow. Anything less is taking life easy on plant at the cost of a slight
increase in brake specific fuel consumption. There are many factors
involved in how fast we go for how long that have nothing to do with the
engine.

... Plant efficiency without the turbine would drop considerably as
the energy in the recip exhaust would be lost to heating the sea.

Right... and this is why I think it would be difficult to maintain
vacuum if you ran without the turbine for any length of time.


The relationship you imply assumes the condenser was sized to require
the use of the turbine ... that simply is not the case. The turbine
allowed the recovery of waste heat at full power. Their is a subtle
relationship between the efficiency of the recips and the cutoff
settings used when operating with and without the turbine online. If
cutoff is extended, as it might have been when turbine was online, the
recips produced greater power but at less efficiency than when cutoff
was shortened so as to allow maximum expansion in the engine.

Maximum expansion of minimum steam (short cutoff) comes at the cost of
wide temperature variations and condensation and re-evaporation withing
the cylinders which is avoided at high speeds and extended cutoff which
leaves more energy in the steam for the turbine to extract.


Don't you think that if the throttleman overdid the reverse steam, it
could damage the crosshead bearings, or the shaft couplings and/or
line bearings, or maybe fold up the prop? Other ships lost prop blades
and so forth at times. The Olympic class props had the blades bolted
to the hub so that the pitch would be adjustable (the ship had to be
in drydock for them to adjust it).


Don't know why it should. The crosshead bearing only "feel" the side
thrust imposed by piston rod movement relative to the connecting rod and
that is a function of load.

Line bearings don't know or care what direction the shaft rotates.

The torque on the shaft instantly changes from driving the prop to being
driven by the prop the instant the throttle is closed. The inertia of
the rotating shaft is absorbed by impeding the inlet of steam from the
throttle to the cylinder. When the force of the steam exceeds the force
of the piston being driven by the shaft inertia the engine will reverse.
The throttle is not opened wide at the same instant that reverse is
selected ... give the operator a little credit for knowing how to
operate the engine. The time involved is very short though, you do not
have to wait until the shaft stops rotating all by itself.

Ships still shed blades and even break shafts ... even though the props
and shafts are designed to function under torgues and stresses that the
engine would never be able to deliver under any and all concievable
conditions of normal or emergency operation.



Please take it easy on Doug. He's our resident propulsion engineer. His
knowlege is second to none. But seriously, a good accurate post IMO.
Often HP steam was bled to the LP cylinders to start big marine steam
engines? Do you do you do that on your tug?

Cheers

DSK wrote:

I don't think so. There's a volume/temp relationship involved. If you
put steam at a higher pressure & temp into the condenser, at some point
you are going to exceed it's cooling capacity.

Well, in the mode and condition which I described, I KNOW that the
engines can run indefinitely without exceeding the condenser capacity.

... The circulator pump moves more water than is required to remove
the heat leaving the turbine. Reduced power operation might have been
required, just as modern plants - even military plants - but there is
no time limit associated with that condition.


???

What part of steam plant operation and construction elicited the "???" ?
Most condensers and circpumps have a larger capacity than required for
normal operation up to a sea temperature around 85* F. Under some
conditions of sea temperature and load, reduced power operation may be
required to match condenser capacity. Once the balanced is achieved
there is no time limit to operation.

AFAIK there's a time limit, either you regain vacuum and resume steaming
normally, or you don't... and you restrict steam into the engines until
you either have to shut down or you regain vacuum.


Warships have far greater ability to steam in maneuvers, but at the
cost of efficiency & space. A liner has to make money.



I don't believe wasrships have any exclusive claim to maneuverability
... that statement applies equally to a warship or a merchant plant.


No, but warships are designed & built with far less regard to cost and
far greater regard to increased capacity. No merchant ship is ever going
to give up the tonnage & space for such a power plant. For example, a
Fletcher class destroyer's hull was about half filled by it's boiler &
engine rooms.

The Fletcher is smaller than most merchant steamships so of course the
plant takes up a larger proportion of the hull volume ... hardly a
reflection on plant capacity or maneuvering traits.

Right. But you're assuming that the condenser was enough oversized to
accept all the additional energy from the steam normally extracted by
the turbine.

Not at all, read my posts.

Suppose you took a somewhat more modern plant and installed a pipe from
the crossover into the LP exhaust trunk, shunting exhaust from the HP or
IP turbine directly into the condenser. That would be a similar
situation... and I'm thinking it would be difficult or impossible to
keep vacuum. But after reflection (as I said in my last post), I'm also
thinking it wouldn't matter so much with the Olympics because they would
only have to do this for a short time.

We carry just such a pipe. It is made precisely for use in case a LP
turbine casualty occurs and allows HP turbine exhaust to go directly to
the condenser. No big deal, just reduce power to maintain the vacuum
required for the auxilliaries and carry on for as long as it takes.

Just exactly the same way Titanic would operate if the turbine was
unavailable.


Wouldn't stopping the engine against the force from the prop potentially
create greater loads than normal forward operation?

Don't know why it should, steam is compressible.

True, but they care a *lot* about compression on the shaft, which is
going to produce axial forces. If you're trying to stop the prop against
the force of water going by, it seems to me you could generate at least
as much compression as if you are trying to accelerate the ship.

Run that by again ... "compression" of the shaft? I would love to see
the figures on that one ...

But there's more than just shaft inertia involved here... there's the
inertia of the whole ship driving the prop.

Not to seem too cynical but I have to ask if that is the source of the
shaft compression that is going to effect the line bearings ...

I dunno about "all concievable conditions"... that sounds really
expensive! And remember, back in 1912 engineering metallurgy had not
advanced as far.

Yes, it is and always has been expensive. All conceivable conditions are
often met and/or exceeded on ships over their life of steaming around
the world essentially non stop for a quarter century or longer.

Rick

Nav wrote:
... It was Doug who said there was no bypass valve.

I didn't say anything of the kind, you clown.

Go back and re-read my posts. I said that a turbine will not be stopped
by opening a bypass valve, which is what you claimed was the summ &
total of how to reverse the Titanic's engines.


... He
seemd to think it was stopped by just closing a valve -but where he
thinks the steam from the main engines would go is anybodys guess.

Do tell.


While the inlet was subatmospheric,

In other words, under a vacuum... as I said.


.... the steam would still be passed to
the condensor whose pressures were even lower. I think it's also pretty
sloppy to call the inlet prssure to a turbine a vacuum. Don't you guys
traditionally use mmHg for near vacuum pressures?

It was you who is quoting a psia figure and confusing it with psi.

DSK

Nav wrote:
I still say the inlet pressure was 9psi!

You can say whatever you like.

...Care to admit I was right?

Why? You're not. Like I said... go and ask somebody else, or look it up
yourself. I've given you plenty of references if you can't possibly
believe my answers.

DSK

An apology would be in order, but isn't really expected.



Nav wrote:
Yes it is -from you! I said the inlet pressure it was 9 psi to correct
your statement that the inlet was at vacuum. You then said I was wrong
and it was 11psi.

No, I did not, Navsprit... or is it Navjax?



You are busted.

For what, proving that you're blabbing about things you don't
understand... again?

DSK

Nav wrote:

I think it's also pretty
sloppy to call the inlet prssure to a turbine a vacuum. Don't you guys
traditionally use mmHg for near vacuum pressures?

We sometimes us inHg and sometimes we use psia, depends on the
shipbuilder and machinery supplier. It is reasonable to assume a metric
ship displays mmHg ... makes no matter as far as operation is concerned.

It is hardly "sloppy" to call inlet pressure the condenser a vacuum. It
is engine exhasut and as long as it is less than atmospheric it is a
vacuum.

Condenser pressure is engine exhaust pressure for engineering purposes.
We determine condensate depression and other operational factors by
calculating condenser vacuum based on exhaust temperature.

Rick

Nav wrote:
At that time the reliability of the turbine was in question so that the
plant was designed to run without it indefinitely.

Oh really? Perhaps you can produce a reference to that?

Doesn't matter, steam turbines had been in service for some years
before. It wasn't an issue of reliability *at all*. The issue was cost.
The Royal Navy subsidized the construction of the Mauretania and the
Lusitania, both of which were in service several years before the
Olympic & Titanic were designed. Another smaller issue Harlan & Wolff's
relative inexperience with an all-turbine plant of that size.


... If I recall, the
bearings proved to be a problem on a sister ship.

Care to produce a cite on that? Or did you just pull that out of thin
air, like almost everything else you've said so far in this thread and
many others?

Next you'll be claiming that you know more about the Constit... oops, I
mean the Titanic's steam plant than anybody else!

The real question: why am I bothering to attempt a discussion with such
a loony-tunes?

DSK

Rick wrote:
We determine condensate depression and other operational factors by
calculating condenser vacuum based on exhaust temperature.

Here's a good homework question for Navvie/Navjax/Navsprit:

Define "condensate depression" and explain it's significance in steam
plant operations.

DSK