Yes, Scott you are correct. The reason bleed steam is
used instead of "pure" exhaust steam is that,
stationary plants are generally operate on a
condensing cycle. The exhaust steam ends up below
atomspheric pressure! It has been 30 years since I
took thermo and power plants in college, so I don't
remember all of it. Now the only "steam tables", I can
use are at the buffets!
John D. Mitchell, Jr.
--- "Myers, Scott V." <svmyers@s...> wrote:
> As pointed out below, I assume they have the same
> effect as on any
> stationary power plant. The use of feedwater
> heating increases the
> efficiency of the steam cycle, thus saving fuel. To
> further elaborate, the
> fuel savings is accomplished because the feedwater
> to the boiler has been
> heated, reducing the amount of heat required in the
> boiler itself to finish
> heating the water to the saturation temperature and
> then boil it. In a
> utility power plant, the steam for feedwater heating
> is supplied by
> extractions from the steam turbine. What was the
> source of heat to the
> various types of FWHs used on a locomotive - exhaust
> steam?
>
> Like the use of superheaters for the motive steam
> that also serve to
> increase the cycle efficiency, I had assumed that
> the most modern steam
> locomotives (4-8-4s, 2-10-4s, etc.) tended to use
> both SHs and FWHs. If I
> remember correctly, this type of information is
> listed for all locomotives
> in the book Steam Locomotives of the Burlington
> Route.
>
> > -----Original Message-----
> > From: John D. Mitchell, Jr.
> [SMTP:cbqrr47@y...]
> > Sent: Monday, March 11, 2002 2:59 PM
> > To: BRHSlist@yahoogroups.com
> > Subject: Re: [BRHSlist] Steam engine questions
> >
> > Jonathan
> > You missed it on why the road engines ( in heavy
> > and/or fast service) needed feedwater heaters.
> They
> > saved coal or oil and water. This meant less cost
> for
> > fuel and water, plus fewer servicing stops. The
> > capital costs and maintanace expense had to be
> lower
> > than the savings.
> > John D. Mitchell, Jr.
> > --- jonathanharris@e... wrote:
> > > Thank you, Mike! Your explanation of injectors
> is
> > > very clear and helpful.
> > > Makes me wonder why any railroad would have
> chosen
> > > the "lifting" type.
> > > Maybe it had to do with how different roads ran
> > > their engines, the profiles
> > > of their lines, etc.
> > >
> > > Regarding feedwater heaters: the Burlington's
> three
> > > Coffin-equipped O-3s
> > > (5318, 5325, 5341) all had units that extended
> out
> > > from the smokebox front,
> > > sort of like the giant eyebrow of a cyclops, so
> at
> > > least some of the
> > > mechanism must have been outside the smokebox.
> But
> > > maybe enough of it was
> > > still inside to make it as messy and dirty and
> > > troublesome to maintain as
> > > you describe. An interesting fact about these
> > > engines is that when the
> > > Coffins were removed, sometime between 1935 and
> > > 1952, they were not
> > > replaced with Elesco or Worthington units. The
> > > engines reverted to using
> > > injectors only. So the Coffins really must have
> been
> > > more trouble than they
> > > were worth.
> > >
> > > That got me to wondering about what kinds of
> engines
> > > were equipped with
> > > feedwater heaters and why. A quick perusal of
> the
> > > rosters in Corbin and
> > > Kerka shows that many, though not all, of the
> > > Burlington's mikados had
> > > feedwater heaters. All of the Q's larger engines
> had
> > > them (all 4-8-2s,
> > > 4-6-4s, 2-10-2s, 2-10-4s, and 4-8-4s), but
> almost no
> > > smaller engines --
> > > with the exception of the Pacifics, almost all
> of
> > > which were so equipped,
> > > even the smaller S-1s. What this suggests to me
> is
> > > that the real advantage
> > > of having a FWH was its ability to help
> sustained
> > > steaming, especially on
> > > heavier trains. Hence its use on mainline
> passenger
> > > engines, some of which
> > > produced considerably less tractive effort than
> the
> > > drag-freight 0-3s, some
> > > of which used only injectors.
> > >
> > > In the case of freight engines, the choice of
> > > whether to add a FWH probably
> > > was determined by a combination of the engines'
> > > intended functions and the
> > > terrain where they were assigned. Manifest
> freight
> > > engines, for instance,
> > > would have benefited from feedwater heaters more
> > > than drag freight engines,
> > > as would any and all heavy freight engines
> operating
> > > over uneven terrain.
> > >
> > > Consider the Burlington's USRA O-4 mikados, all
> 15
> > > of which had feedwater
> > > heaters, versus the FW&D's corresponding E4A2s,
> > > which appear to have only
> > > injectors. Presumably the pancake-like
> topography of
> > > central and west Texas
> > > diminished the need for FWHs, while the grades
> of
> > > the Q's western
> > > divisions, where the 0-4s hung out, made such
> > > appliances much more
> > > important. It strikes me as significant that
> > > feedwater heaters seem not to
> > > have been used much on the FW&D, compared to the
> Q
> > > -- or the C&S, where
> > > all engines larger than a 2-8-0 had them.
> > >
> > > Jonathan
> > >
> > >
> > >
> >
> >
> > __________________________________________________
> > Do You Yahoo!?
> > Try FREE Yahoo! Mail - the world's greatest free
> email!
> > http://mail.yahoo.com/
> >
> >
> >
> >
> > Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
> >
>
__________________________________________________
Do You Yahoo!?
Try FREE Yahoo! Mail - the world's greatest free email!
http://mail.yahoo.com/
|