A Thermo-Pneumatic Quasiturbine Locomotive
(with addendum on subway operation)
By: Harry Valentine, Transportation Researcher -
Pneumatic locomotives operating on compressed air were successfully used in coal mines over a period of several decades. The Porter Company (USA) built a model that used an 800-psi accumulator tank, an operating tank set at 280-psi and compound expansion piston engines. These original pneumatic locomotives operated successfully and safely over fairly short distances (up to 60,000-ft) in tunnels, hauling ore cars out of mines. None of these locomotives that were used in both American and in Europe used an air heating system to increase power or raise operating efficiency.
Modern pressure vessel technology allows air to be stored at pressures of up to 45,000-psi (310-Mpa) in reinforced spherical tanks. For pneumatic locomotive operation, spherical tanks of up to 2.75m (external diameter) can hold compressed air at 10,000-psi (68.95-Mpa). Several such tanks may be installed on an articulated locomotive frame, holding up to 40,000-lb (18,000-Kg) of compressed air at 80-degrees F (26-degrees C), air which may be fed into these tanks from larger stationary accumulator tanks holding compressed air up to 20,000-psi (137.9-Mpa). This arrangement would allow for rapid replenishing of locomotive air supply. The stationary tanks may be replenished during off-peak hours, reducing demand for high-priced electric power. Extreme high pressure pumping of air into the stationary tanks would have to be undertaken in stages, with air-over-oil pumping technology being used to achieve pressures of 10,000-psi. Cooling of air under compression would be essential to maximize storage density.
The air-compression technology may operate in a combined cycle with either a building complex or district heating system, allowing for the reject heat obtained for air compression to be put to productive use during winter months. During summer months, the reject heat from air compression may also be used to drive new generation absorption building complex cooling systems. The reject heat from air compression may also contribute to the thermal energy supply being stored in a stationary thermal storage tank, for later transfer into the locomotive thermal storage tank. Both storage tanks could be made from corrosion resistant materials such as silicon-nitride, which could hold a compound such as molten aluminum (melts at 645-degrees C, 170-Btu/lb heat of fusion) or molten lithium carbonate (melts at 723-degrees C, 260-Btu/lb heat of fusion). Heating of the molten metal could be accomplished by using concentrated solar thermal energy, garbage incineration, heat pumping of geothermal energy to a high temperature, biomass combustion, fusion energy or even fission energy (micro-nuclear, using low-radiation pebble-bed technology).
Simultaneous pressurization of the accumulators and heating of the thermal storage material is possible, using cascade heat pumping technology. A low temperature heat pumping circuit using sulfur dioxide could remove heat from the air as it is being compressed. It could reject heat at 260-deg F (125-deg C) with a coefficient of performance (COP) of 6:1 to 9:1, to a higher temperature heat pump circuit using a different working fluid, such as saturated water. The saturated water would be pumped at 80% compressor efficiency from a low pressure of 25-psia (240-deg F) to a high pressure of 250-psia (401 deg F), with a COP of 3.84:1 to 4:1. High temperature heat pumping circuits (COP's of 3:1) on stationary tanks could involve such working fluids as mercury or a mixture of 56% sodium and 44% potassium (circuit material and compressor made from silicon-nitride) to raise the temperature to melt aluminum or lithium carbonate. The high temperature heat pumping could be supplemented with concentrated solar thermal energy during summer months (year round if the locomotives are in arid tropical nations).
To improve thermal efficiency while the locomotive is in operation, the compressed air would need to be heated to a high temperature, prior to expansion in an engine. The locomotive could be a 3-section articulated unit, with a thermal storage tank located at the centre, between the sections carrying the spherical pressure tanks. Cylindrical operating tanks set at 1,000-psi (6,895-Mpa) could be located below the spherical tanks. The operating tanks would feed air to the expander, via the thermal tanks. The on-board thermal tanks could also be made from silicon-nitride and contain molten aluminum or molten lithium carbonate. Heat transfer between stationary and mobile thermal tanks could be accomplished using superheated air as the heat transfer fluid, for reasons of safety.
A desirable engine option for this application would be a relatively compact 3 or 4-stage Quasiturbine system . Exhaust air from a higher-pressure Quasiturbine would be reheated prior to expansion in a larger capacity lower-pressure Quasiturbine. The 3 to 4-stage compound reheat-expansion could raise adiabatic efficiency to over 90%, compared to a radial flow turbine that would have an adiabatic efficiency of 80%. To realize high efficiency, the conventional air turbine would need to operate within 80% of its maximum design operating speed and at maximum air temperature, a power characteristic that would require the use of a multi-speed automatic railway transmission capable of operating at at least 1,000-Hp (746-Kw). By comparison, the Quasiturbine can deliver optimal efficiency over a much wider range of operating speed, requiring the use of a far less complex mechanical transmission. The power output of the Quasiturbine may be varied by using variable timing on the inlet valve, from a minimum valve cut-off of 15% of maximum expansion volume to a maximum of 80%. An electrical transmission system may be impractical, due to the high cost of such a system (accounts for up to 50% the cost of a diesel-electric locomotive). The Quasiturbine system can offer high starting torque at zero RPM, driving directly into an existing geared rail axle propulsion system.
Heat transfer between stationary and mobile thermal tanks may use air being pumped through the heat transfer circuit using a compressor (either a radial-flow turbine or a Quasiturbine) made from silicon-nitride, a material capable of handling extremes of temperature. The multi-pass air lines required to heat the mobile tank would each contain a series of venturies, each causing a successive pressure drop of 0.528 and a successive temperature drop of 0.833 (absolute temperature). After leaving the mobile tank, the heat exchanger air would pass through an air turbine, which would further reduce air temperature while driving a low-pressure air turbo-compressor placed upstream of the main compressor. The air line inside each stationary tank would contain a series of multi-pass tubes, to enhance the transfer of heat. With an adiabatic efficiency of 80%, the compressor would raise the temperature being fed into the mobile thermal tank.
If the compressor has a pressure ratio of 4:1, it would raise absolute air temperature by 48.6%, while a 6:1 pressure ratio would see a 66.85% rise in absolute temperature. If the air leaving the stationary tank is at 1350-degrees R, it would rise to 2170-deg R (1710-deg F) using a 4:1 pressure ratio at 80% adiabatic compressor efficiency. Using a 6:1 pressure ratio, this would increase temperature to 2478-deg R (2018-deg F/1103-deg C) at 80% compressor adiabatic efficiency. Absolute temperatures entering the mobile tanks could be raised an extra 6% - 10%, by using a diffuser downstream of the compressor. This could raise heating temperature to 2166-degrees F (1185-deg C), sufficient to rapidly remelt / reheat the aluminum or lithium carbonate during a thermal recharge.
While the locomotive is in operation, the maximum air mass flow rate passing through the engine could be set between 10,000-lb/hr to 15,000-lb/hr. With a 40,000-lb maximum compressed air capacity (density of 49.98-lb/cu.ft), the usable air supply could last for 2 to 3-hours. With 1,000-psi operating tank pressure and 14.7-psi atmospheric pressure (assume exhaust to atmosphere), the outlet pressure ration would be 68:1, which would translate to an absolute temperature ratio of 3.339 at 100% adiabatic expansion efficiency. With molten aluminum held at 645-degrees C (1193-degrees F), the air could be heated to 1000-deg F prior to expansion. In a single stage expansion, exhaust air would drop to -22.75-deg F, yielding a temperature drop of 1022.75-deg F. Multiplying this by an air specific heat of 0.24-Btu/lb-deg R, an adiabatic efficiency of 90% and a mass flow rate of 10,000-lb/hr, dividing by 2545-Btu/Hp-hr, yields 868-Hp. Increasing air mass flow rate to 15,000-lb/hr raises power to 1302-Hp. This power level allows the locomotive to pull a short commuter train for up to 2-hours at speeds of 60-miles/hour.
Using lithium carbonate as thermal storage material could raise air temperature to 1140-deg F, dropping to 19-deg F after expansion (100% adiabatic efficiency). At 90% adiabatic engine efficiency (single pass expansion), the engine would deliver 951-HP using 10,000-lb-air/hr (1427-Hp using 15,000-lb-air/hr). Using the Quasiturbine engine in a multi-stage reheat expansion system would economize on air consumption and increase locomotive operating duration/distance to enable short-distance intercity routes up to 200-kms to be served at moderate rates of speed. Using heat pumping between the thermal tanks to further heat the air may be possible, using a corrosion resistant heat pump circuit and compressor made from silicon-nitride. Possible working fluids would include mercury or a sodium / potassium mixture, enabling COP's of at least 3:1 (this is the minimum COP that will yield a net gain), enabling a net of 1250-Hp at 10,000-lb-air/hr (1875-Hp at 15,000-lb-air/hr). High COP heat pumping could raise compressed air temperatures to 1600 to 1800-deg F prior to expansion, raising engine efficiency levels sufficiently to allow for power to be used to drive the heat pump compressor (240 to 340-Hp for a COP over 3:1; a COP of 1:1 requires 950-Hp at the compressor and yields zero net gain) .
Further improvements in locomotive performance are possible, using "renewable combustion" technology. Certain chemical compounds release heat during bonding and dissociate when heated to a high temperature. Magnesium hydride is one such compound, while potassium oxide is another. During heating, the hydrogen can be dissociated from the magnesium and stored in a separate chamber, or oxygen from potassium. In operation, the heat of formation of the magnesium hydride or potassium oxide could be used to superheat the air prior to expansion in the engine. Some "renewable combustion" combinations (heat of formation) could heat the air to 2000-deg F prior to expansion and raise exhaust temperature to 276-deg F, allowing heat from exhaust air to be re-introduced into the operating tank and into the spherical accumulators, which would be cooling as internal pressure dropped. Recirculating reject heat would further increase the operating range of the thermo-pneumatic locomotive.
Heat from the atmosphere could be heat-pumped into the accumulators to reduce pressure loss during operation. With 2000-deg F air temperature, 1465-Hp would be available at 90% single-pass adiabatic efficiency, using 10,000-lb-air/hr (3-hours in service operation at speeds up to 75-mi/hr or 120-Km/hr) while 2193-Hp would become available over 2-hours using 15,000-lb-air/hr (train speed 90-mi/hr or 1145-Km/hr). Heat exchangers made from silicon-carbide may be used in the high-temperature heating of the compressed air, whether from "renewable combustion" or from combustion of a fuel that would otherwise be unsuitable for use in an internal combustion piston engine (e.g.: low-rank coal-water fuel, corrosive liquid fuels or similar gaseous fuels). These fuels may either destroy engine lubrication or build a sludge and engine deposits that would impair efficient internal combustion engine operation. External combustion engines can yield lower exhaust pollutant emission levels, due to greater scope to manage and refine the combustion process.
In a resource constrained future where oil prices rise to 3 to 4-time present day levels, a thermo-pneumatic Quasiturbine locomotive may be able to operate some types of commuter train services and short-distance intercity passenger train services, both along relatively low-density routes where the cost of railway electrification could not be justified. Alternatively, a thermo-pneumatic Quasiturbine locomotive could operate along rail lines in small nations. Such a locomotive and its energy storage systems would have longer longevity that present competiting technologies, resulting in less need to replace worn or expended parts, at high cost (e.g.: fuel cells cost $3,500/Kw). For a 1,000-Kw hydrogen fuel cell locomotive, the fuel cells alone would cost $3.5-million. In terms of energy efficiency, it would operate at 24%-efficiency from hydro-dam to drive-wheel, or below 12% efficiency from thermal power station fuel supply to drive wheel. A thermo-pneumatic locomotive can be recharged directly from a thermal power station and deliver over 20% efficiency from thermal power station fuel bunker to the drive wheel.
* * * * *
Voici un extrait de Reuter New of August 28, 2003 intitle :
Fuel Cell Locomotive Could Free Subways from Grid
NEW YORK - The hundreds of thousands of subway passengers trapped for
hours on the New York City subways during the largest North American
blackout earlier this month take note: one day subways could run independent
of the electricity grid.
The Denver-based Fuelcell Propulsion Institute plans to convert a
120-ton diesel locomotive into a fuel cell-driven train, a project that
could one day make fuel cells a reality for subways.
"Subway systems running on the grid is obviously a precarious
proposition," said Arnold Miller, spokesman for the five-year project. "Fuel
cell subways would not be dependent on the grid." (...)
Complete story at :
This article has been at the origin of the present paper by M. Harry Valentine.
Further subway operation considerations follows as this :
Operating a fuel-cell locomotive on the subways is not good during the
summer months, when the weather is hot and humid. The fuel cell locomotives
have an exhaust that will release humidity into the subway tunnels .......
and make the subways very uncomfortable for subway users.
Hydrogen leaks in subway could also be a major concern as it is for coal miners.
The subway does use a lot of expensive electricity
(purchased at industrial rates) during the rush hours.
It is cheaper to buy the electricity between 12:00AM and 6:00AM to
recharge the trains.
Many years ago, compressed air (800-psi / 55-bar) locomotives were used in
coal mines. There was an intermediate tank (280-psi / 19-bar) that supplied
air to compound cylinders. Recharge was done from tanks of compressed air,
located outside the coal mine. The American Porter company manufactured
compressed air locomotives.
At the present day, air tanks can hold 4,000-psi (275-bar). These tanks are
used to transport compressed natural gas and also hydrogen gas, on the
railways. The same tanks can be used on a modern compressed air locomotive.
The high pressure air would feed into an intermediate tank, that could then
feed air into compound-expansion Quasiturbine engines. For operation in
subways, the air can be dried during the summer months, so that dry air is
released in the subway tunnels.
For recharge, stationary high-pressure air tanks would be located on the
subway system. This will allow for fast recharge (10-minutes) of compressed
air locomotives operating in subways. Much of the air can be compressed
between 12:00AM and 6:00AM, when electricity prices are low. Atmospheric air
is much safer to use in tunnels. There has never been any tank explosions on
compressed air locomotives. In the event of a collision, hydrogen could burn
in the subways and cause serious problems. If a disaster happens, a
compressed air locomotive will not cause any fires. If the the high-pressure
tank leaks, it will releace atmospheric air into the subway system ..... and
this air is very safe for people to breathe in.
Hydrogen to operate fuel-cell locomotives in subway transit systems will
come from electricity. Electrolysis has an efficiency of 67%, cooling the
hydrogen fo for storage is 89%-efficient (overall 59.63%-efficiency from
electrical supply to the fuel tank. The PEM fuel cell operates at
55%-efficiency at part-load, while the electric traction motors will operate
at 85%-efficiency (part-load) ...... for a total overall energy efficiency
of 27.78%-efficiency from the electrical supply to the drive-wheel. If the
fuel-cell locomotive is receiving electric power from a thermal power
station (40%-efficiency), the overall direct energy efficiency is 11.12% (In
1949 in France, on Chemin-de-Fer Nord, Engineer Andre Chapelon designed
steam locomotives that returned 12%-efficiency, burning coal).
The fuel cell will reject 45% of the energy as heat, while the electric
motors will reject 15% energy as heat. When combined with the intense
humidity the fuel-cell locomotive will release in the subway tunnels, a very
large tunnel air-conditioning system will be needed during the hot, humid
summer months, to keep the subway system cool and dry for commuters.
Storage batteries will return 50% of the recharge energy. A battery-electric
locomotive will release battery acid gases and extra heat into the subway
tunnels. A flywheel-electric locomotive has been used in mines. In a transit
subway system, there is the danger that the flywheel could explode and
injure transit users.
In operation, air-pressure motors can operate from 36% to 91% adiabatic
efficiency. Example, if the air motor is a turbine (80%-adiabatic
efficiency) designed to operate at 12,000-RPM, it will operate at that high
efficiency provided the rotational speed remains above 75% of maximum (over
9,000-RPM). A multi-speed transmission will need to be used (they do exist
in the heavy on-road and off-road truck industry, with appropriate gear
ratio's). A Quasiturbine, being a positive displacement engine, could also
return a high level of adiabatic efficiency over a much wider RPM range
(you'd need to consult Dr. Gilles Saint-Hilaire re this).
The only way to realise any kind of efficiency from using compressed air for
propulsion, is to operate it on a combined-cycle-efficiency basis. One major
advantage of compressed air technology, is the long life expectancy of the
concept. Electric batteries can only withstand 1,000-deep drain
discharge/recharge cycles. Fuel cells operated at maximum output also have
reduce life expectancy. The hydrogen storage tanks have low
life-expectancies as well. There are major replacement-parts costs involved
with battery and with fuel-cell operation.
For transit subway operation, the only safe locomotive that can be used
(other that straight electric power) is a compressed air locomotive.
Transportation Researcher, email@example.com
Autres commentaires de QT :
In case of stoppage of the train in the subway, pneumatic technology would be safer
to make people to walk on the tracks without risk of liquid fuel leak,
toxic battery vapor, hydrogen vapor or high voltage lines around them.
De plus, la détente adiabatique de l'air dans les moteurs Quasiturbine
produit du froid qui tend à compenser la chaleur produite par
le freinage des rames de métro, et aide à la climatisation en été !
L'efficacité d'un circuit pneumatique est excellente à basse pression,
et se dégrade avec l'augmentation de la pression d'opération.
La raison des hautes pressions est uniquement d'augmenter
l'autonomie et de réduire la taille des réservoirs et des moteurs.
Or, comme ces trains ont des autonomies restreintes,
qu'ils peuvent transporter des réservoirs volumineux,
qu'ils peuvent faire le plein d'air comprimé à plusieurs stations,
et que la Quasiturbine a une très hautes densité spécifique de puissance,
l'efficacité du système pneumatique peut-être bien supérieure
à la plupart des autres techniques de stockage,
compte-tenu de son excellente réversibilité à pression intermédiaire.
Comme il y a toujours de courtes périodes entre la compression de l'air et sa consommation,
les réservoirs d'air peuvent être thermiquement isolés
et l'air stockée avec sa chaleur latente de compression adiabatique.
De cette façon, il faut moins d'air dans les réservoirs pour atteindre les pressions désirées,
et comme ce sont les pressions qui comptent
on gagne considérablement sur l'efficacité du système,
puisque la chaleur de compression sert à la poussée
dans la Quasiturbine au moment de la détente, et son refroidissement adiabatique
donne alors de l'air à la température ambiante à la sortie du moteur
(on pert évidemment l'effet climatisation, mais non celui de l'assèchement).
Puisque la Quasiturbine pneumatique est un moteur réversible
capable d'agir en compresseur, l'énergie de freinage peut-être récupérée,
augmentant ainsi l'efficacité du train,
et réduisant la production de chaleur dans le métro !
Extended subways are not linked at a single grid power location.
Backup generators would not be an easy setup to maintain a relayable
temporary overall service.
* * * * *
Stirling-Hydraulic Quasiturbine Locomotive
See : http://quasiturbine.promci.qc.ca/QTPneumatique.html
Quasiturbine Pneumatic and Fuel cell :
A perfect Match (using liquid nitrogen) !
See : http://quasiturbine.promci.qc.ca/QTPileCombustible.html
Quasiturbine Pneumatique Inc.
Casier 2804, 3535 Ave Papineau, Montréal Québec H2K 4J9 CANADA (514) 527-8484 Fax (514) 527-9530