An innovative compressed air dryer system, offering complete
flexibility for OEM railway applications and above all for the modernisation
and refurbishment of older locomotive rolling stock.
Along with electricity or diesel, the provision of compressed
air on board a locomotive is the second most important source of
energy. For example, for the operation of doors, for raising and
lowering the pantograph and even in some passenger locomotives,
adding to the comfort of the journey in the form of air suspension.
As consumers, we take the existence of electrical power and diesel
for granted, likewise the expensive energy potential of compressed
air source. Compressed air, however, rarely meets the requirements
of the user following the compression process.
Due to the location of a compressed air system, hidden away in
the depths of the locomotive chassis, the saying “out of sight,
out of mind” could be regarded as being very apt. Only on
failure of one of the many components driven by compressed air is
anything undertaken. Strange when one thinks that the very safety
of the locomotive is dependent upon the reliability of the compressed
air supply. Consequently, the brakes cannot be applied properly
without this, and a locomotive can only move off, where sufficient
compressed air is available in the braking system.
This safe, reliable energy source is contaminated with water, dirt
particles, wear particles and used lubricating oil. This aggressive
acidic sludge, referred to as condensate, leads to corrosion and
wear in valves and pneumatically driven servos throughout the entire
system. In the worst case it can result in a locomotive being taken
out of service, with all of the consequential costs.
The Quality of the Air Drawn into the Compressor
Compression of compressed air to pressures in excess of 6 bar,
which are typical in locomotive applications, results in the formation
of large amounts of water as the air cools back down to atmospheric
temperatures.
Most compressed air systems in locomotives are fitted with condensate
or water removal systems, called drains directly after the compressor.
These merely separate the bulk liquid produced. The higher the temperature
of the compressed air, the greater the danger that water will at
some point condense out further along the compressed air line or
in the main receiver tank. A danger which is especially apparent
in terms of the cooling effect of the chill factors experienced
during operation in the undercarriage of the locomotive, in addition
to this there is the fall in temperature experienced on a train
standing idle overnight.
The worldwide operation of railway technology necessitates a system
for the reliable removal of this water problem. With ambient temperatures
of 40°C or more and with a relative humidity of 80%, which is
not uncommon in some parts of the world, the air downstream of the
compressor will be 100% saturated. Where water vapour at these temperatures
cannot be removed, every subsequent fall in temperature will cause
water to further condense out in the compressed air system.
These facts can be clearly expressed where a calculation of the
theoretical water loading present in a compressed air system, on
a locomotive, under operating conditions is performed.
Based upon Northern European climatic conditions and the operating
parameters of a diesel driven locomotive of the type operated by
DB Cargo in Germany, a water loading of 18 litres per hour during
operation is to be expected.
Operating Parameters BR 294/295
Compressor Delivery: 144 m3/h
Operating Pressure: Minimum 8 bar
Operating Temperature: 60°C
The humidity of the air when fully saturated at 60°C is 129,54
g/m3. Under these conditions a water loading of 18kg/h (18 litres)
is experienced.
All of these problems can be effectively handled by the installation
of an air dryer. With an extensive range of high efficiency compressed
air treatment products, domnick hunter has achieved a leading world-wide
reputation and in recent years has literally put this extensive
knowledge down “on the rails”.
An air dryer for railway applications must be in a position to
reduce the dewpoint (the temperature under which condensate occurs)
to such an extent, that the locomotive remains in service under
the most varied of climatic conditions, being suitable for operation
from the Australian Savanne to the Siberian Stepps.
By installing the innovative technology of an air dryer system from
domnick hunter, constant dewpoints of -40°C at ambient temperatures
of +60°C to -30°C, with the additional guarantee of oil
and particle removal are achievable.
Nothing grasps the imagination more than modern high-speed locomotives
cutting journey times by half and transporting their guests safely
in comfort to their final destination. These locomotives are very
often fitted with air dryer technology from the outset. The story
is different, however, where shunting stock is concerned. “Work
horse” locomotives carrying out the heaviest of transportation
tasks daily, or rolling stock desperate for modernisation and refurbishment.
These locomotives are equipped with either one or two chamber dryers,
which are often unable to function effectively enough to prevent
freezing of the braking system in winter, or alternatively these
locomotives have no dryers whatsoever. It is especially in this
area of application where suitable solutions are being sought, which
are capable of being integrated into the existing locomotive chassis,
where the space envelope available, has until now not made any provision
for the installation of a traditional air dryer.
The development of the domnick hunter railway dryer has in recent
years concentrated on perfecting the resistance to vibration of
the adsorption beds, reliable controls and the most modern valve
technology, to meet the special requirements of the railway customer.
The air treatment package has been specifically developed for locomotives,
(photo 4) where a reduction in size and weight compared with traditional
systems is paramount.
The solution to these problems is an extruded aluminium profile
housing, containing two drying chambers, which reduces the overall
weight in comparison with existing systems by up to 60%. The added
feature of internal and external corrosion protection ensures that
climatic conditions can be overcome effectively in comparison with
traditional dryers.
Traditional one and two chamber railway dryers consist mainly of
steel vessels, filled with adsorption material, which alternatively
carry out the task of moisture adsorption and regeneration. Very
often insufficient pre-filtration prior to the dryer, for the protection
of the adsorption material, causes premature contamination and failure,
leading to inferior dewpoints.
It pays to protect the adsorption bed from oil, water and dirt
particle contamination. Not only is the lifetime of the adsorption
material greatly improved, but dewpoint requirements can also be
met.
The dryer modules of the domnick hunter dryer are filled with
adsorption material using the “snow storm” filling technique,
which allows maximum packing density to be achieved. In order to
maintain tension on the adsorption bed, and prevent fluidisation
as a result of vibration, the bed is held in place by springs. This
rigid construction prevents channeling as the air is forced through
the bed in an even manner. The dryer construction is such that often
not more than half of the adsorption material required by a traditional
dryer is needed to achieve complete moisture removal.
By combining the proven advantages of adsorption air dryer with
modern design, domnick hunter has developed an extremely compact
and reliable system . The modular construction offers complete flexibility
for the installation in or under the locomotive, mounted vertically
or horizontally to meet the specific requirements of railway applications.
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| Photos published with the kind
permission of DB Cargo, Chemnitz, Germany. |
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