The Cost Savings of Steam Today.

[NW Mailing List]

Gary,

Have you read the paper?  With the massive cost difference between Coal and
Diesel fuel, the steam locomotive can have lower thermal efficiency and
still be cheaper.  The number I quoted in the email i originally sent was
based on steam locomotives having about 10% thermal efficiency compared to
diesels running at 25-30% thermal efficiency depending on type.  Steam
locomotives in service in other countries have exceeded the thermal
efficiency I used for the locomotives in my comparison.

John Rhodes.

On Jan 11, 2008 6:26 PM, NW Mailing List <nw-mailing-list at nwhs.org> wrote:


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>  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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