Home  Locomotives, machines Locomotives Researching a GPCS-Accumulator Steam Locomotive
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Researching a GPCS-Accumulator Steam Locomotive |
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Written by Harry Valentine
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The hybrid-accumulator steam locomotive idea described in this
articleis based on input provided by Michael Bahls (Germany) and
RobertEllsworth (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-psiaat
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
belocated 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
to9,000-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 accumulato
rthrough 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 steamline
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.
Harry Valentine,
Transportation Researcher.
harrycv at hotmail.com
http://www.internationalsteam.co.uk/trains/newsteam/modern31.htm |
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