The International Steam Pages
A Multi-Section Modern Fireless Steam Locomotive
A modernised fireless steam locomotive could be a low cost and proven rail traction technology that could still provide a variety of services in the modern era. It is a concept that can operate quite cheaply in under-developed tropical countries. Ongoing research into this concept has so far revealed that when production of fireless steam locomotives ended, much potential was still left unexplored and undeveloped. During a future time when oil supplies may decline and oil prices escalate, fireless steam railway traction could become a viable option in many types of railway services. Such locomotives could be recharged from a wide variety of competitively priced renewable thermal energy sources, including biomass, solar energy and geothermal energy.
Earlier generations of fireless locomotives delivered low power levels and offered a limited operating range, characteristics that relegated them to duties in railway shunting yards or on short industrial branch lines. During the heyday of fireless steam power, the state of the art in metallurgy and metal manufacturing limited the size of available accumulators (pressure vessels). Modern metal manufacturing technology can now produce much larger accumulators (out of stainless steel) which can operate at much higher pressures and temperatures. Available thermal energy storage technology systems typically involve low long-term costs, providing many times the life expectancy of electrical energy storage systems such as batteries. Saturated water and various types of molten metals have been shown to be low-cost thermal storage media. Various multi-section fireless locomotive concepts using such thermal storage are described below.
1) A Multi-Accumulator Fireless Steam Locomotive:
Saturated water has a long proven record as a reliable, low-cost thermal energy storage medium. It the basis of energy storage in classical fireless steam locomotive operation. In a previous research paper on heat pumping a fireless steam locomotive, it was revealed that saturated water could be used as a high-temperature "refrigerant". This research was based on calculations pertaining to the enthalphy and entropy of saturated water at varying pressure and temperature levels. A heat-pumped two-accumulator fireless steam locomotive could operate at a higher level of thermal efficiency while delivering a constant level of power output over most of its duty cycle. Its operating range, efficiency and power output levels can be increased by introducing a third accumulator, in an accompanying tender unit.
The tender section of such a locomotive would comprise a high-pressure accumulator (2000 to 2500 cu.ft) that would release no steam or high-pressure saturated water while in operation. It would be filled to 85% of its volume with 60,000-lbs of saturated water at 2000-psia, storing 672.1-Btu/lb thermal energy (at 635.8-deg F) that would be heat pumped into the main accumulator. This would allow the main accumulator on the locomotive section to operate at constant temperature (544-deg F) and pressure (1,000-psia) levels over an extended duration. To enable heat pumping, an (low-pressure) evaporator would be immersed in the hot saturated water in the tender, while a (high-pressure) condenser would be housed near the bottom of the operating accumulator. The main accumulator would hold 48,000-lbs of saturated water with an enthalpy of 542.6-Btu/lb in the liquid state. It would need to continually receive 650.4-Btu/lb in heat energy from the high-pressure accumulator while the locomotive is in operation, in order to maintain constant temperature and pressure levels. Variable rate heat pumping could transfer over 12,000,000-Btu's of energy into the main accumulator. By adding 774-Btu/lb of energy to steam prior to expansion, over 15,000-lb of steam from the main accumulator may be expanded in the steam engine for propulsion.
The steam engine could operate at 280-psia, a pressure level that could be maintained by using compound valve throttling in the steam line and inside the main accumulator. This throttling of steam would return heat to the main accumulator. The low pressure working steam could be re-superheated inside the main accumulator, with thermal energy from both the main and the high-pressure accumulator, prior to expansion at 600-deg F and 1316-Btu/lb in the steam engine. As temperature and pressure in the high-pressure accumulator drops, heat pumping of thermal energy at a high level of COP could maintain optimal temperature levels in the main operating accumulator. Heat pumping could enable superheated steam at 600-deg F to be expanded in the steam engine for an extended operating duration.
During recharging, the accumulators may be reheated in series or independently of each other. In series reheating, the tender accumulator would be heated by using an internal heat exchanger through which superheated steam would flow. During the early recharging stage, the cooled steam leaving the tender could initially be used to replenish the main accumulator's partially depleted volume. During the latter stage of recharging, this steam would be re-superheated from an external source prior to entering the main accumulator, raising the saturated water supply to its operating temperature and pressure levels. When independently reheated, water from the tender accumulator would be circulated through an external heater. Alternately, the tender accumulator could also be reheated through an internal heat exchanger, allowing heat from an external heat exchanger to be transferred into the tender.
While in operation, the total stored energy level of over 8,000-Hp-hr (12,000,000-Btu from the tender accumulator; 15,500-lb steam from the main accumulator at 1316-Btu/lb at 600-deg F) could be available to be converted into traction, at efficiency levels of 10% to 15%. The multi-section fireless steam locomotive could haul short commuter trains for distances of 25 to 40-miles, using 800-Hp for over 1-hr at moderate speeds (25 to 40-mi/hr) on tracks in under-developed nations, operating along lower-density branch lines or even in commuter service operations. The locomotive's overall operating range and power level would depend on the volume storage capacity in both accumulators. This restriction favours railway systems allowing generous exterior railcar right-of-way clearance dimensions, in turn favouring much larger water-based fireless steam locomotives that can operate at higher power levels of extended distances.
2) Heat-of-Fusion Accumulator Tender
A previous research paper described the possible use of corrosion-resistant ceramic materials such as silicon-carbide and silicon carbide, in a heat-of-fusion thermal storage system. Materials such as Aluminium (aluminum in the USA), Lithium Carbonate or Aluminium-Copper mixtures can be used as heat-of-fusion thermal energy storage materials. Despite these ceramics being used in applications requiring tensile strength, such as for turbine blades in jet engines and cylinder liners in internal combustion engines, in steam locomotive operation the ceramic material will need to be used in applications where the are subjected to minimal tensile stresses. Ceramic materials can withstand compressive stresses of over 10,000-psi, allowing pressurized steam to surround 36-inch diameter by 2-inch thick silicon-carbide (SC-1000) storage cylinders. Heat-of-fusion material would be contained in ceramic cylinders (with tapered and rounded ends) which would be housed horizontally inside stainless steel cylinders. Steam at 300-psia would circulated inside these stainless steel cylinders, being superheated by heat from within the ceramic cylinders prior to being expanded in the steam engine. Compressive (hoop) stress below 3,000-psi would occur on these ceramic cylinders, from steam at 300-psia.
Thermal energy from a metal compound such as lithium carbonate which melts at 723-deg C (1334-deg F), would release a latent heat-of-fusion of 260-Btu/lb at constant temperature. Pure aluminum melts at 645-deg C (1193-deg F) with 170-Btu/lb, while an aluminum-copper mixture would melt below 400-deg C (752-deg F). Heat from thermal storage tender would be transferred into the main accumulator through a heat exchanger recirculating steam, to maintain optimal temperature and pressure levels. Heat from the thermal storage tender would also be used to superheat steam prior to expansion in the steam engine. With over 170-Btu/lb being available from 150,000-lb of storage material, some 25,500,000-Btu's could be used to maintain heat levels in the main accumulator as well as to superheat the steam prior to expansion at 300-psia at 600 to 800-deg F. If saturated water is maintained in the main accumulator at 1,000-psia and 544-deg F (542-Btu/lb), heat from the tender could allow for up to 32,000-lb water to be superheated to 700-deg F (1368.9-Btu/lb).
The quality of steam entering the steam engine could raise efficiency levels to well excess of 20% (single expansion ceramic uniflow engine with minimum inlet valve cut-off ratios as low as 10%; reciprocating or rotary design). The infrared spectrum of solar thermal energy used to reheat the metal inside the ceramic cylinders, using special collector lenses and special fibre-optic cables. Superheated steam may also be used for reheating of both the main accumulator as well as the thermal storage tanks (flowing low pressure steam at 900-deg C or 1650-deg F). It could process some 30,000-lb of steam from a main accumulator holding some 60,000-lb saturated water at 80% volume. With stored energy levels of over 16,000-Hp-hr and energy efficiencies between 15% and 20%, this type of fireless steam locomotive could pull short trains for up to 4-hours at 800-Hp, travelling at low speeds (25 to 40-mi/hr) along rural lines, branch lines, industrial lines, short line operations, commuter passenger services or even inter city services in developing nations.
Research in the world of chemistry has developed a variety of new compounds over the past several years. Such developments have included super-ceramic materials and high-temperature superconductivity materials. One possible future compound may be a low-cost material that melts at 400-deg C or 750-deg F and with a heat of fusion near 400-Btu/lb. A tender storing 100,000-lb of such material could deliver 40,000,000-Btu of high grade heat to steam leaving the main accumulator, allowing 45,000-lb of steam to be processed from a total of 75,000-lb of saturated water stored at 1,000-psia and 544-deg F. Superheated steam at 280-psia and 700-deg F (1370-Btu/lb) could be expanded at near 20%-efficiency, allowing a fireless locomotive to deliver 1,000-Hp while pulling a short train at speeds of over 50-mi/hr for up to 4-hours or more duration.
Fireless steam locomotives have the potential to be developed to provide useful services in several types of non-electrified railway operation in a future oil-constrained environment. They can be developed to operate commuter as well as intercity services in smaller countries.