The International Steam Pages


Idling Firetube Steam

Locomotives in the Modern Era

There are occasions in railway operation where a locomotive may be parked in a siding (idle) while it is out of service. Extended periods of idle time (such as a weekend) were a problem for steam locomotives of earlier generation. The firetube boilers on such locomotives would cool to near ambient within five to seven hours of the flame in the firebox having being extinguished. Deficiencies in boiler insulation during an earlier generation of railway traction resulted in rapid heat loss. Reheating a cold firetube boiler in a steam locomotive could typically have taken up to seven hours during the heyday of steam power, a task undertaken solely by using the flame in the firebox. 

The time required to restart a cold steam locomotive was reduced toward the end of the steam era. Perforated pipes were installed at the bottom of the firetube boilers of a few of the last active steam locomotives. Such pipes were normally used to re-energise fireless steam locomotives. The firetube boiler of a locomotive that was so equipped could be re-heated within less that two hours after injecting superheated steam from an external supply into the perforated pipe. The flame in the combustion chamber could be re-lit as the boiler approached its operating pressure and temperature. Adding heat directly to cold water inside a cold boiler without a flame in the firebox does create thermal stresses. The combination of a flame in the firebox and steam injection into the boiler would greatly reduce such stresses.

Modern insulation material installed around the boilers of modernised steam locomotives greatly extends the duration over which usable heat is retained. The 2-10-0 locomotive that was modified by DLM of Switzerland can remain out of service for 12-hours and be ready to re-enter service within 30-minutes of its flame (in the firebox) being relit. DLM has also developed an external recirculating heater system that removes water from a cooled boiler and pumps it through an external (watertube) heater before the heated water is returned into the boiler. Some locomotives can be ready for service within under 1-hour after being re-heated using this method.

Steam locomotives that operate in the modern era would need to have the same availability for service as electric locomotives and diesel locomotives. An idling steam locomotive would need to be ready for service within a few minutes of the operator having entered into the cab in the modern era. The operator then ought to be able to shunt the locomotive to where it may be coupled to a waiting train that could be ready to leave within a few minutes. New technology can be installed on modern/modernised steam locomotives and in terminals that can ensure their almost immediate availability for service. Some of this technology is proven and is being used to maintain the temperature in diesel engines (after they have been shut off) during cold weather.

Onboard Heating:

Companies like Espar and Webasto manufacture engine heating systems that circulate a heated fluid through engines that are off and out of service. The heaters use a small amount of fuel to heat the fluid and a small amount of power from a battery to drive the pump that circulates the heated fluid through an engine. Similiar technology can be adapted for use on modern steam locomotives to maintain the temperature and pressure inside boilers that are already warm or hot. DLM's external heater system for cold firetube boilers could be adapted and modified for onboard operation.

The water pump of this heater could be powered either by onboard batteries or by an external electric wire. The water heater could be coil monotube boiler that feeds into a perforated pipe that would be located at the bottom of the firetube boiler. The fuel that is used to heat the monotube boiler may be gaseous (an external supply of natural gas), combustible liquid fuel (in a small onboard tank) or a solid (onboard supply of sawdust or biomass fuel pellets). Biomass fuel pellets are used as home heating fuel in (automated) pellet stoves. Pellet stoves feature gasifier combustors and auger feed mechanisms that supply fuel to the combustor and that remove ash into ashpans. The pellet fuel is ignited by a glowplug. 

Automated (computer) controlled pellet stove technology can be adapted for use on the firetube boiler of a modern/modernised steam locomotives. A pressure gauge and/or a temperature gauge could be preset to activate the pellet stove heating system and shut it off during extended (weekend) layovers where the locomotive is idle. A boiler that is treated with Porta water treatment could be kept warm for several months at a time. Onboard heater systems would work well to maintain heat and pressure on Porta treated boilers during extended periods of idling. An operator could be assigned to such a locomotive at almost any time and would shut off the automated boiler heating system and relight the flame in the combustion chamber after entering the driving cab. Modern technology can allow that flame to be relit from a distance (remote starter technology) so that the locomotive would be ready for service the moment the operator enters the driving cab.

External Heating:

The temperature and pressure inside firetube boilers (treated by Porta water treatment) of steam locomotives and inside accumulators of fireless (steam) locomotives could be maintained within a narrow range over extended idle periods (weekends). A single small stationary boiler may be all that would be needed to supply superheated steam through a network of underground insulated pipes in a locomotive terminal. The steam from such a boiler could maintain heat and pressure in the boilers/accumulators/thermal storage systems of a fleet of modern/modernised steam locomotives. Steam would be supplied to a heater pipe (via a quick-connect mechanism) that would pass through the boiler/accumulator/thermal storage system of each locomotive.

The heater pipe in each locomotive would diverge into a diffuser (increasing area along its length) inside the boiler/accumulator/thermal storage system. The diffuser would divide into multiple heater pipes that would make at least 3-passes inside the boiler/accumulator/ thermal storage system before connecting into a choke valve and exit pipe. The superheated steam could transform into saturated steam as it releases heat through the multiple heater pipes. 

Saturated steam that then passes through the choke valve would undergo a reduction in temperature and in pressure before leaving the locomotive as saturated liquid via an exit pipe. Heat removed from the steam would be conducted through the valve material and into the saturated water in which it is immersed or into thermal storage material that surrounds it. Cooled saturated water would leave each locomotive and enter a piping system (via a quick connect) that would returned it to the stationary boiler where it would be reheated and then recirculated through the system. 

The steam that enters the heater pipes in each locomotive could pass through a valve that is regulated by the locomotive pressure gauge or temperature gauge. The gauge could send a signal to the control valve as to whether to open or to close. Such a control system would ensure that the locomotive boilers/accumulators/thermal storage systems do not overheat during prolonged layovers at terminals that provide external heating. Steam locomotives that layover at such terminals would have a very high rate of availability for service. The flame in its combustion chamber could even be lit by remote activation prior to it having to enter service.

Harry Valentine
Transportation Researcher
November 2006
E-mail: harrycv@hotmail.com


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Rob Dickinson

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