I was thinking about how a steam locomotive could be converted to use solar thermal energy to replace or supplement other fuels to provide the heat and found the following two articles that seem to indicate all of the major technical issues have been solved for decades. Imagine if we spent a fraction of what we are spending on war to develop a transit system based on these ideas!
Researching a GPCS-Accumulator Steam Locomotive
The hybrid-accumulator steam locomotive idea described in this article is based on input provided by Michael Bahls (Germany) and Robert Ellsworth (USA).
A GPCS-accumulator locomotive would combine the advantages of a fireless steam locomotive with features of a conventional steam locomotive. It would borrow technology from both, combining the high-pressure (1000-psia) accumulator of a fireless locomotive with a GPCS (gas producer combustion system) firebox. Water in the locomotive’s accumulator (filled to 75% to 80% capacity) would be heated by injecting pressurised superheated steam into the water through a perforated pipe located near the bottom of the accumulator, a practice pioneered on classical fireless steam locomotives. Water would be heated to the operating temperature and pressure levels (1000-psia at 544-deg F). GPCS-accumulator locomotives would have their water supply replenished and be thermally recharged at industrial sites where high-pressure steam is available and where other types of fireless steam locomotives are recharged.
To maximise power output and operating duration, the locomotive would need to be built to the operating railway’s maximum right-of-way clearance dimensions. Several world railway systems allow railcars are built to a length of 85-ft (between couplers) and a width of 10’6″, on 60-ft truck/bogie centres. On such a railway right-of-way, the locomotive accumulator may be built to an inside diameter of 7-ft and interior length of 65-ft (10’6″ exterior diameter and 70-ft exterior length), yielding a volume of 2500-cu.ft and holding 90,000-lb of saturated water at 1,000-psia at 80% capacity. The front end of the locomotive could be extend by using a tapered section (containing the driving cab) with the coupler mounted on an extended bogie/truck. The non-tapered end would house the GPCS firebox and be semi-permanently coupled to a fuel tender unit. The locomotive would measure 95-ft to 100-ft from front-end coupler to tender. A driving cab could also be located either on the tender, allowing bi-directional operation.
Prior to the GPCS-accumulator locomotive entering or re-entering service, the accumulator would be filled to 75% volume with hot, pressurised saturated water. It would be further heated with superheated steam to a volume of 80%, a temperature of 544-deg F and 1,000-psia pressure. This would provide one-third of the locomotive’s required total thermal energy, which could be supplied from such sources as concentrated solar energy or heat-pumped geothermal energy. While in operation, the locomotive would be able to combust various forms of low cost, clean burning, low heat content (5,000 to 9,000-Btu/lb) biomass, including bio-fuel pellets, poultry litter (eg: Thetford Power Station, UK) or even bagasse carried in a semi-permanently coupled tender unit. Automatic fuel feed (stoking) using an auger screw mechanism would transfer fuel into the GPCS firebox, located on the locomotive section. Combustion ash could be transferred by a smaller auger into a holding pan located under the tender. During service lay-overs, the ash pan would be emptied (biomass ash is a fertilizer).
When the locomotive is in service, steam leaving the accumulator through the steam dome would be superheated to 1200-deg F in the GPCS firebox, then flow into a heat exchange pipe located inside the accumulator at its lower level. Saturated water at 1,000-psia and 544-deg F has an enthalpy of 542.6-Btu/lb in the liquid state. For this liquid to flash into steam, it would need to draw 650.4-Btu/lb from the remaining saturated liquid. The steam in the steam line would replenish this heat by making 4 to 5 successive passes through the firebox (for re-superheating) and lower level of the accumulator. This heat exchange steam line would allow 650-Btu/lb to be added to the saturated water, maintaining optimal accumulator temperature and pressure levels. The 6th re-superheat would occur prior to the steam being expanded in the steam engine, with a possible 7th re-superheat being used for compound expansion . A variety of positive-displacement single and compound expansion steam engine designs may be located close to the GPCS firebox, directly driving the axles.
The heat exchange steam line inside the accumulator would heat the water in a similar manner as do the firetubes inside a conventional firetube boiler. However, the steam line would be totally immune to any build-up of creosote, clinker or carbon deposits that foul the insides of fire-tubes, greatly reducing locomotive combustion system cleaning and maintenance requirements. The absence of cold water flowing on to a hot and dry crown sheet (of a firetube boiler) is eliminated in a steam-heated accumulator, enhancing “boiler” safety. Baffles would be needed inside the large accumulator to keep the heat exchange steam line covered with water. They would also reduce interior fluid wave action and splashing caused by the locomotive accelerating or deccelerating, or by changes in gradient and by lateral swaying (yaw). By using a multi-pass steam line to heat fluid in the accumulator, the (fluidized bed) GPCS firebox and smokebox could be built as a single combined unit. This layout would offer improved energy efficiency while reducing overall combustion system maintenance and cleaning requirements.
The heated accumulator in the locomotive can allow up to 65,000-lb of the saturated water to be used for propulsion, with the remainder covering the heat-exchange steam line. The total energy available for propulsion would be some 40,000-Hp-hr. If the steam engine is an oil-free ceramic unit (from the German company Spilling) capable of receiving steam at over 1200-deg F (enthalpy of 1633-Btu/lb) and operating at a thermal efficiency level of 20%, some 8,000-Hp-hr would be available to the drive wheel. This power level could allow the locomotive to pull a 7-coach double-decker express passenger train at speeds of near 50-miles per hour for up to 5-hrs at 1,500-Hp, operating intercity routes of up to 250-miles. A thermal efficiency level of 25% would allow an operating duration of 6-hours at 1,500-Hp. At the present day, a variety of positive displacement steam engine designs could be built from ceramic materials and operate without oil.
For operation on railways using the UK right-of-way dimensions, overall width would be restricted to 9′ 3″ by 65-ft length. The accumulator capacity would be reduced to a maximum capacity of 1400-cu.ft (6-ft inside diameter by 50-ft inside length), carry 52,000-lb saturated water at 1,000-psia, of which 39,000-lb could be used for propulsion. On this restricted railway gauge, the driving cab may be located on the tender (train operated with the tender leading), or ahead of the accumulator in a tapered end section of the locomotive. In service, the smaller locomotive operating at 20%-efficiency would be able to provide 1,500-Hp for a 3-hour duration, able to pull light trains along non-electrified lines for distances ranging from 120-miles to 200-miles. If engine efficiency were raised to 25%, the locomotive could deliver 2500-Hp for 2-hours and pull a fast passenger train distances between 140 and 200-miles.
Ted Pritchard of Australia ( http://www.pritchardpower.com ) has designed and built highly efficient Vee-2 compound expansion uniflow piston steam engines that have delivered up to 19% thermal efficiency in mobile operation. This engine design is quite capable of directly driving powered axles through flexible quill-drives, similar to a concept used on the Henschel V-8 steam locomotive. Two designs of rotary uniflow steam engines are also possible, one from the Quasiturbine group of Montreal (Dr. Gilles Saint-Hilaire: http://quasiturbine.promci.qc.ca ) and one from the Western Railway Group of Boise, Idaho (Tom Blasingame). The latter rotary engine design can operate without mechanical valves, yet offer equivalent minimum inlet valve cut-offs as low as 12.5%, with an equivalent maximum of near 50%. It has very low starting torque and would need to operate in tandem with a piston engine to start the train and enable low-speed operation. If the Quasiturbine was operated as a uni-directional engine, then it does not need any valves … just inlet and exhaust ports. … For a steam-powered Quasiturbine to be bi-directional, it may have to use some kind of valve system to direct steam alternatively either at the inlets (forward) or the outlets (reverse direction) ports. Two-Quasiturbines operating at 45-degrees out of phase with each other, would have enough zero-RPM torque to start a train.
A horizontally opposed steam piston engine design that can operate as an underfloor engine, is being designed/evaluated by John Davies and the S-Team in South Africa. In the Ukraine, engineer Viktor Gorondyanskiy has designed a unique multi-piston/ compound-expansion. steam engine that can theoretically operate at 35% thermal efficiency, using inlet steam at 1300-deg F (650-deg C). Using a direct mechanical drive system would reduce overall locomotive capital cost (electrical running gear can account for over 60% of locomotive capital cost). Oil-free, self-lubricating jacket heated ceramic steam expanders (engines) would be designed to operate using 250 to 300-psia pressure superheated steam at 1300-deg F. Steam pressure would be reduced from 1,000-psia accumulator pressure entering the steam line, to 297-psia using 2-expansion valves, each causing a pressure drop of 54.5% (1000-psia x 0.545 x 0.545 = 297-psia). Since steam engines give their highest energy efficiency levels when operating at part load and at minimal inlet valve cut-off ratios, large overall engine displacements would be optimal.
The operating range and power level could be extended, by re-using a portion of the exhaust steam. The Swedish Ranotor company ( http://www.ranotor.se ) designs and builds heat exchangers that can condense the steam, however, effective condensing only works on lower-powered steam locomotives. The maximum possible size of the heat-exchangers that can be fitted to a railway vehicle, restricts how much thermal energy can be managed and in turn imposes power restrictions on locomotive output. Prior to being pumped at high-pressure into the accumulator, the water would pass through several (4 to 6) coiled monotube boilers that would heat the 1,000-psia water to 540-deg F, adding 3,000,000 to 4,500,000-Btu/hr (5500 to 8200-lb/hr) to the accumulator. This could add up to 1-hour of extra operating duration and operating range to the locomotive.
The GPCS-accumulator locomotive may be operated on intercity journeys up to 250-miles, along non-electrified routes. It is an alternative form of rail traction intended for operation during an era where oil becomes scarce and oil prices escalate to levels that make alternative fuels economically more viable. Most of the componentry to build a GPCS-accumulator locomotive already exists.
Modernising the Fireless Steam Accumulator Locomotive
The accumulator locomotive was traditionally a fireless steam locomotive used for shunting duties. All designs used a steam accumulator that was essentially a thermos bottle laying on its side. To be energised, the accumulator had to be at least 3/4 full of water. Heating of this water was done by an external steam source. While some designs used a coiled heat exchanger line, most later designs injected superheated directly into the accumulator tank, using a perforated pipe near the tank bottom. This design enabled rapid energy re-charges (15 to 30-minutes) to be undertaken every few hours. A cross-section layout of a fireless cooker is at http://www.rr-fallenflags.org/porter/page44.jpg .
The last fireless locomotives were 0-4-0′s built in Germany during the early 1960′s, by the Henschel group, based on research undertaken during the 1930′s by Prof. Gilli. These locomotives were small in size and were designed to operate on accumulator pressures of 1,000-psig. Some models used onboard, natural gas fired heaters and a coiled monotube boiler. This arrangement used an external an external supply of natural gas to heat the boiler and water pumped at high-pressure from an external source.The fireless Henschel locomotives were smaller that American built Heisler fireless steam locomotives, which operated on lower accumulator pressures (200-psig). Nevertheless, a fully recharged American Heisler 0-4-0 fireless locomotive of pre-WW2 vintage could lumber along for distance of almost 95-miles on its own, or tow a train of 10-loaded freight cars for distances of up to 20-miles. Porter fireless locomotives operated on a tank pressure of 150-psig (see http://www.rr-fallenflags.org/porter/porter-pd.html ). Using the performance date obtained from early fireless locomotive designs, extrapolations were undertaken to increase the operating range and power output of a modern accumulator fireless locomotive, using larger tanks storing higher pressures.
Modern manufacturing techniques can enable long, high-pressure accumulator tanks to be built out of alloy steels, at very competitive prices. A modern fireless design based on traditional concepts, could use multiple high-pressure tanks, each with its own perforated recharging pipe at tank bottom. Each tank could also be supplied with its own onboard coiled monotube boiler. Monotube boilers have been built that operate at over 1,000-psig, with 200-Hp thermal capability and up to 85% heat transfer efficiency from combustion to steam generation. Theoretically, such boilers would only be used for energy recharging where no external supply of high-pressure superheated steam is available. Performance improvements and extended operating range would result from increased thermal storage capacity and improved piston efficiency. Most thermal recharges would be done using stationary, high-pressure water-tube boilers (up to 2,000-psig) fired by gasified renewable (local) bio-fuels, or solar thermal energy stored at high temperature. A multi-tank accumulator fireless locomotive could be fully recharged within 15-30-minutes.
Research undertaken in Australia by Ted Pritchard (Pritchard Steam http://prsteam.inventdata.com.au) into modernised uniflow (inlet valve, exhaust ports) steam engines, has shown that in actual service, the efficiency levels of a properly designed uniflow engine could be double that of single-expansion piston engines. The modernised steam piston engine is insulated using modern technology along its outer (third) layer. It is also jacket-heated outside the cylinder walls to yield higher performance levels. Modern valve control in the form of precise inlet valve cut-off operation, further enhances efficiency. Earlier fireless locomotives used only throttle valve control for speed/power control. Pritchard-type uniflow steam engines could be mounted directly on the trucks (bogies) of modern fireless accumulator locomotives. An alternative engine that can operate on the uniflow principle is the Quasiturbine rotary engine, which can also be mounted in the axle trucks/bogies (http://quasiturbine.promci.qc.ca/QTIndex.htm).
High-pressure accumulator tanks enable higher levels of energy to be stored. A lower-pressure downstream tank can allow high-pressure energy storage to be combined with lower-pressure pistons. This approach is analogous the electronic “chopper” control used in DC circuitry. Small bursts of power are sent to capacitors for temporary storage, while inductors regulate reduce levels of power flow. A similar system can be used in a steam storage system. In a steam “chopper” system, a valve from the high pressure accumulators would rapidly open (fully) and shut in response to pressure sensitive valves in the cylinder-feed accumulator tanks (the steam “capacitor”). The cylinder-feed accumulator could operate at pressures up to 300-psig, while main storage tank pressures would hold pressure levels of up to 2,000-psig.
A modern steam accumulator locomotive could be built to the same dimensions of the 3-level automobile carriers used on North American railway systems. These cars are nearly 100-feet (30-m) between couplers, 9-feet 6-inches (2.85-m) wide and with a height of 19-feet 8-inches (6-m) above the head of the rail. To carry the locomotive weight, a wheel/axle arrangement similar to that of the American Penn Central GG1 locomotives’ 4-6-6-4 layout may need to be used, on a longer bogie/truck-centre spacing. The energy storage capability could be up to 20-times that of a 1960′s era Henschel fireless, with at least 50% higher engine brake thermal efficiency than traditional piston designs. Lumbering on its own at 40-Km/hr, the modern accumulator fireless locomotive could have a range of up to 350-miles. A design built to the exterior dimensions of a passenger rail coach (10’6″ or 3.2-m wide, 14’6″ or 4.4-m high and 85′ or 26-m between couplers) could still store over 10-times the thermal energy of a Henschel fireless loco. The main operating niche of such a locomotive type would be in developing countries, where few paved roads exist and where right-of way clearances would allow passage to large locomotives.
The condition of rail lines in some developing nations are such that intercity trains rarely travel at speeds above 30-miles per hour (50-Km/hr) and often slower. This type of operations allows for use of low-powered locomotives that develop less than 1000-Hp (745-Kw). Stops and lay-overs are frequent, operating characteristics that would favour a large accumulator fireless steam locomotive. Recharging of accumulator tanks could occur at rest stops or at terminals, every 25 to 50-miles. A large steam accumulator locomotive could pull a passenger, freight or mixed train over a 50-mile journey segments, distances that are not uncommon in developing countries. Certain rainy regions in Asia, Central Africa (Congo area), Central and South America would be potential candidates for modernised and improved traditional accumulator locomotive operations. These are regions where rainfall is frequent and water for locomotive operation would be available.
Such locomotives would require very low levels of maintenance and are easily repairable. Fuel supplies for the stationary water-tube boilers would be predominantly locally supplied. A small number of wayside water-tube boilers could supply energy to a relatively large fleet of accumulator locomotives, provided that they do not all need to re-charged at the same time in the same location (an extremely rare occurrence). The cost of such a fleet of locomotives would be comparatively low, while their availability levels would be quite high (due to modern thermal insulation around the accumulator tanks) and the speed over which fireless accumulator steam locomotives could be re-charged (rarely more that 30-minutes using the perforated pipe with a baffle above it). One person locomotive operation would prevail, while added manpower (stationary engineers) would be needed to staff the stationary water-tube boilers.
In sunny tropical countries where adequate water for steam locomotive operation is available, solar thermal energy could be used to assist in replenishing locomotive energy supply. Large solar heliostats would collect intense solar thermal energy. Insulated fibre- optic lines made from processes aluminium-oxide (purified & clear industrial sapphire) would transmit the intense solar thermal energy into very large, stationary, ceramic-lined and insulated thermal energy storage tanks. Thermal energy would be stored in the high heats of fusion from various metal-oxides. A low-cost material thermal storage material, lithium-nitrate, occurs quite naturally across Southern Africa. The addition of steam converts it to lithium-hydroxide, which has a latent heat of fusion of 185-Btu/lb at 460-degrees C. Superior thermal storage materials include a new generation of metallic oxide polymers (super-molecules) such as aluminium-oxide polymers, having latent heats of fusion up to 500-Btu/lb, near 500-degrees Celsius.
To prevent tank and water-tube corrosion, tank interiors and water-tube exteriors would have to be lined with a corrosion resistant material like carbon fibre or a high-temperature fluoro-plastic. Such tanks can be used onboard accumulator fireless locomotives to improve performance and efficiency, by superheating steam prior to entry into and expansion in the engine. A wide variety of thermal energy storage materials have life expectancies of several million alternating deep-drain and full-recharge cycles, with no loss of energy storage capacity. The high cost of replacement electrical batteries may be deferred indefinitely, by using such thermal storage technology. By comparison, electric batteries become spent after several hundred cycles of deep-cycle draining and recharging, requiring costly replacement. A battery-electric system only returns some 50% of the energy put into it, dissipating the rest as heat mainly during the charging cycle.
A modernised traditional fireless accumulator locomotive could be economical to operate in terms of fuel supply and efficiency. It would also be well suited to operating conditions that presently exist on several “short-line” rail systems or railways in many developing countries. Such locomotives would also be able to operate commuter service (rapid energy recharge at the end of line) and tourist train excursion service. They may even have application in commuter service along non-electrified rail lines in some developed nations. In arid/dry regions of the world, fireless locomotives would need to use a water replenishing technology such as multiple expansion valves and condensing radiators on the exhaust steam. Condensing effectiveness may be improved by using an onboard sealed “cold-tank” containing either ice or dry ice.
A variant of the fireless steam locomotive was the compressed air locomotive, built by the same locomotive manufacturers (Porter, Baldwin, Whistler, Henschel) as conventional and fireless steam traction. The two concepts can be combined into one, for short-distance operation only, in extremely dry climates. The pressurised, saturated water would be used as a thermal storage medium, instead of driving the wheels directly and exhausting steam to the atmosphere. Externally energised onboard water-pumps and monotube boilers would allow for energy re-charging, much in the same manner as the extensively modified locomotives that came from DLM. Compressed air (5,000-psi) stored in tanks in a separate car, would be heated in tubes passing through the water tanks, prior to expansion in a traction engine (such as a quasiturbine). Heat may also be stored in a molten metallic oxide polymer in a lined (to combat corrosion) and insulated tank, with coated (corrosion resistance) tubes passing through the thermal storage tank.
The energy in such thermal storage tanks may also be used to energise a closed-cycle Brayton turbine, using atmospheric air at varying pressure levels as the working fluid. The Escher-Wyss division of Sulzer built a 2,000-Kw closed-cycle regenerative turbines operating on variable pressure atmospheric air, delivering its optimal efficiency (15% in hot weather to 32% in cool weather) between 20% to 80% of maximum power output. In California,USA, the Power Now company has been testing a 7-Kw closed cycle turbine (http://www.companydr.com/vanaar/PowerNow/FAQs.htm) using variable pressure air. This type of “steamless” variant of the fireless locomotive would have to store its thermal energy supply in the latent heat of fusion of a metallic-oxide polymer. It could operate in short-line/branch-line operation on several types of railway systems. In passenger service, it could pull tourist/excursion trains, operate in low-frequency suburban commuter and pull short, light intercity trains up to 300-km (at 100-km/hr). It could also pull light intermodal trains (highway trailers on rail axles) of up to 50-cars, on intercity journeys of up to 300-km.
Harry Valentine, Transportation Researcher, email@example.com