Matt Colie wrote:
Max,

The use is possibly interesting if you understand it.

These and many other engines and turbines were used for a very simple
reason:
It is cheaper to make high pressure steam than low. This is a curious
aspect of steam, the transition for liquid to gas take fewer BTUs per
pound as pressure increases.


Right because the change of state (liquid to gas) takes a
huge amount of energy in itself, so that is sort of a
built-in "overhead" cost of generating steam. Once you
generated that much heat to get steam in the first place,
you might as well make a little more heat and get a lot more
steam, proportionately. It's also more effective to transfer
heat from fluid to solid when the fluid is under pressure,
so the higher steam pressure makes the transfer of heat from
the metal of the boiler to the water more efficient too.


So- why not make high pressure steam and then let the pressure down
before you send it off to heat buildings?

Or use "waste heat" steam generated from some other process?

- Good Idea -
If you try to simply reduct the pressure you end up with velocity
problems. But, if you use the steam in something and then exhaust it at
the desired presure and temperature, you just got the steam qaulity you
wanted and some mechanical work done for the price of the steam.

The reason engines like this were contracted well into the 20th century
is also simple:
Turbines Want Superheated Steam.
Superheat is when something is heated to greater than the saturated
temperature at that pressure (15psi heated to 250F 212).
This requires an extras part in the boiler (steam generator) called a
superheater (-duh) and makes the operation of the plant much more critical.
Reciprocating engines find little value in superheat.


It's also difficult to add superheaters to small boilers,
waste heat boilers, trash furnace boilers, etc etc.

If the engine runs a generator (like this one did) it can offset the
elecric load required for any large facility. One place I worked years
ago had two of these side by side. Was very much like the pictured
unit. The other had a directly conected air compressor.


As the price of fuel goes up & up, it will be interesting to
see if more of these type plants go back into operation.

DSK