The Cost Savings of Steam Today.

NW Mailing List nw-mailing-list at nwhs.org
Sat Jan 12 10:37:22 EST 2008


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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>

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