The Cost Savings of Steam Today.

[NW Mailing List]

 Guys:  No matter what, physics still dictate the overall thermal efficiency
of the diesel cycle and thee steam locomotive cycle.  The thermal efficiency
is a function of the temperature difference achieved when expanding the gas
in a cylinder from te beginning of the cycle to the end.  In this case,
burning inside the gas to be expanded in the cylinder (diesel and about
5000F) and burning outside the gas to be expanded (steam locomotive and a
steam inlet temperature  of about 800F after transferring to steam in a
boiler) gives the advantage to the diesel for thermal efficiency FOREVER. 

 

The conversion efficiency of each type ultimately matters: i. e. steam
requires burning coal which burns at a high temeperture (roughly 4000F),
heat gets transferred to water in the boiler with a lot of losses, losses in
heat and pressure in flowing the steam through the piping, parasitic losses
when taping steam off to run electrical turbines, feed water heaters and so
on.  Diesels have similar conversion issues.

 

Turbines can be very efficient, but the meaning of this is that the flow of
gas through the turbine blading AT DESIGN CONDITIONS can transfer most of
the energy in the gas ( heat energy, kinetic energy and pressure energy) to
the blades as mechanical work very, very well.  However, "part throttle"
operation means that the flow is not at the design conditions ( the vectors
of the flow of the gas are not at the optimum direction) and the transfer of
energy is much, much less efficient.   ( think of the turbine blades as
little wings that are forced to take different angles of attack from the
on-coming gas flow; at part throttle, little wings don't work very well at
all at the wrong flow angle- they can stall!)  Turbine can be as much as
98-99% efficient with repect to capturing the energy in the flow.  Off
design, the efficiency can drop significantly to levels as low as 30%.  But
what about the rest of the system needed to make steam for the turbine?  How
efficient is that?  

 

Could steam be used today again in a profitable and efficient way?
Probably not, the conversion cycle is not very efficient and the
opportunities to make improvements in it are not good ones.

 

Coal fired turbines?  Tried for years, but burning raw coal in the gas
stream has always caused serious slag issues in the combustors.  The slag
either erodes away turbine blades or coats the blades and ruins the wing
shape.  This is a virtually intractable problem.  The coal needs to be
refined to get rid of the slag products--- which leads one right back to
refining petroleum to make diesel fuel or converting coal to an oil in
another refining type cycle (the Nazis did it but it is an expensive and
inefficient process).  And turbines lead right back to the off-design issues
at part throttle.  

 

While a cycle or an energy conversion process can be proposed, the devil IS
in the details.  Developing a process to work reliably, economically and
environmentally acceptably take a whole bunch of time and money.  Then you
have to get the entire world to adopt this way of doing business.

 

Ed and Harry are right to voice skepticism at this early stage.  Adopting
new technology and getting it into place is a very, very difficult process.
The internet was invented in about 1970- 37 years ago- and only part of the
human race has access to this today.

 

Gary Rolih  

Cincinnati

 

 

 

 

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