Note: Descriptions are shown in the official language in which they were submitted.
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ARRANGEMENT AND METHOD FOR TREATMENT OF COMPRESSED
GAS
Technical Field of the Invention
The invention relates to an arrangement for pre-processing compressed gas.
for separation in an air-gas or other gas-gas separation unit, such as and
preferably
by membrane filtering. The arrangement includes a heat recovery arrangement
for
use with a compressor for gas, and to a method of recovering heat from
compressor
cooling fluid for regulating the temperature of the compressed gas before
entering
the gas separation unit.
Background of the Invention
In the pre-processing of air or other gas for a membrane based air-gas or
other gas-gas separation unit, it is important that air fed to the separation
unit
satisfies defined criteria. The dew point of the air must be such as to avoid
condensation. The air must be filtered at an acceptable temperature to avoid
aerosol
and particle carry over. The air must be at a suitable operating temperature
for
efficient membrane separation. This is especially important and the
temperature
must be regulated before entering the separation unit to achieve best possible
operation of the separation unit. The invention is concerned with heat
recovery from
the compressor cooling fluid for the continuous temperature regulation of the
supply
of air to satisfy these criteria.
Disclosure of the Invention
The invention provides an arrangement for use with a liquid cooled and/or
lubricated compressor for compressing gas, and incorporating provision to add
liquid for cooling purposes to the gas prior to entry of the gas into the
compressor,
in which downstream of the compressor there is a liqiuid/gas separator to
separate
the liquid from the gas and in which there is means to recover heat from the
liquid,
and in which there is at least one filter in the gas streain downstreain of
the
liquid/gas separator, and there is a heater in the gas stream downstream of
the filter
in which the gas is heated using heat recovered from the liquid, whereby to
regulate
the temperature of the pressurised gas prior to gas entry into the-separator
unit.
It is preferred that there is a heat exchanger in the gas stream between the
liquid/gas separator and the at least one filter, and in that heat exchanger
cooling
medium from an external source is used to cool the gas stream.
It is also preferred that there is a refrigerant dryer group arranged to cool
the gas
after the liquid has been separated from the gas, and before the gas is passed
through the at least one filter.
The at least one filter may be a coalescing particle filter, or a carbon
filter
for removal of vapour from the cooling liquid.
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The at least one filter may include two stage filtration, the first filter
stage
comprising a coalescing particle filter, and the second filter stage
comprising a
carbon filter for removal of vapour from the cooling liquid.
The invention includes the arrangement described above, in combination
with a membrane gas separator unit arranged to receive gas from the heater
using
the heat recovered from the liquid prior to the liquid passing through the
filter.
The invention includes the arrangement described above, in combination
with a compressor for compressing the gas. The compressor may be a screw
compressor, and the screw compressor may be cooled or cooled and lubricated by
oil or other suitable cooling liquid.
The invention also includes a method of recovering heat from a coinpressed
gas from a liquid cooled and/or lubricated coinpressor, and comprising the
steps of
adding liquid for cooling purposes to a gas or directly into the compressor
prior to
the gas entering into the compressor, separating liquid from the gas after the
gas has
left the compressor, recovering heat from the liquid, passing the gas through
at least
one filter, and, downstream of the filter, using heat recovered from the
liquid before
the gas passed through the filter to heat the gas, whereby the regulate the
teinperature of the pressurised gas.
Advantages of the Invention
Performance of the separation process is dependent upon a relatively narrow
range of operating parameters, particularly feed air temperature and pressure.
It is
for this reason that efficient conditioning of feed air supplied to the
separator is
iinportant. The specific embodiment of the invention described above includes
efficient use of heat supplied to the air, arranges for filters for the
compressed air to
operate at near optimum conditions, and allows the separation meinbranes to
function at near optimuin air pressure, teinperature and dryness. Use of heat
withdrawn from the gas stream to reduce the gas temperature before the
filters, to
preheat the gas streain after the filters makes efficient use of the energy
applied to
the system. The temperature regulation of the gas before entering the
separation unit
may in several prior art cases some from an external heating source. It is in
some
cases possible that additional heating from an external source.inay be
required. The
need is however reduced and in many cases eliminated by the invention.
The invention is especially suited for building a module based system
(compressor, arrangement for conditioning of compressed gas, separation unit)
where the conditioning module does not require an external heating source.
Brief Description of the Drawing
A specific embodiment of an arrangement to pre-process air for a ineinbrane
nitrogen- separator will now be described by way of example with reference to
the
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accompanying-process flow drawing, which shows a compressor section and a
nitrogen separator section.
Description of the Specific Embodiment .
To facilitate efficient performance of the membrane nitrogen separator,
compressed air must be cooled down to remove liquid, the dew point temperature
must be reduced in order to avoid liquid condensation, the air must be
filtered at an
acceptable teinperature to .avoid aerosol and particle carry over, and finally
the air
temperature must be increased to the operating temperature for membrane
separation.
According to this example, air for the compressor section is drawn in
through an inlet filter 9 to a single stage oil cooled/lubricated screw
compressor 10.
The coinpressed air with entrained oil passes to an oil/air separator 11,
having a
safety valve 12. The air passes on through a coinpressed air aftercooler 14
(also
known as a'combicooler'). The aftercooler 14 comprises an integrated water
cooled
heat exchanger which also functions as a temperature control unit for the
compressed air.
The air then passes through a combined water separator/refrigerant
cooler/dryer 15. This reduces the dew point to approximately 15degC below
inlet
temperature, so that condensation will not occur further downstream. The dryer
15
is equipped with a dedicated cooling inedium recycling unit with evaporator,
coinpressor and condenser.
It should be noted that the dryer 15 is not essential. However, if the dryer
is
dispensed with, the air from the compressor 10 will be at its saturation point
after
leaving the cooler 14. In this circumstance the temperature of the air must be
increased to avoid condensation further downstream. A problem may arise in
that
the increased temperature might be beyond the limitations of the polymer
membranes preferably used in the nitrogen separator section.
Air from the dryer 15 passes through a check valve 16 and a ball valve 16a.
The cooled air is now at a suitable temperature, pressure and dryness to pass
through a coalescing particle filter 17 (for retention of oil aerosol carry
over) and a
carbon filter 18 (for removal of oil vapour). Elimination of the dryer 15
might also
lead to inefficiencies in the filters 17 and 18 due to the higher operating
temperatures.
After emerging from the carbon filter 18, the air passes through a feed air
heater 19 to preheat the air for processing in the nitrogen separator section.
The
feed air heater 19 increases the compressed air temperature to 45 - 50degC. A
control valve 21 regulates the air leaving the compressor section, and this
air can be
directed through a valve 22 to a duplex system (not shown) or through a valve
23 to
the nitrogen separator section.
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Oil from the oil/air separator 11 is led to a cooling heat exchange circuit.
Cooling water from inlet 24 feeds the compressed air aftercooler 14 and an oil
air/water heat exchanger 27 before leaving the compressor section by outlet
25. Oil
from the oil/air separator 11 passes through a three way thermostatic valve 26
to
enter the heat exchanger 27 or to return via inlet filter 9a to the compressor
10.
Following the invention, oil from the oil/air separator unit 11 can pass to an
energy recovery unit 29 which is supplied with cooling water from a second
three
way thermostatic valve 28. Water heated in the energy recovery unit 29 is
carried
past the filters 18 and 19, and is used to raise the temperature of the air in
the feed
air heater 19. Thus the filters 18 and 19 can operate at close to optimum
temperatures, and the air can be preheated beyond those filters to enter the
nitrogen
separator section at a higher temperature which is suitable for operation of
the
separation membranes.
Drains 32, 33 and 34 lead from the refrigerant air dryer 15, the coalescing
particle filter 17 and the carbon filter 18 respectively to an external drain
valve 35.
Conditioned air from valve 23 is led to the nitrogen separator section. This
coinprises a ineinbrane module bank 41, having a plurality of membrane air gas
separators. Each separator consists of a bundle of hollow fibres contained in
a metal
housing. The housing has three external connections 42, 43 and 44. One
connection
is located at each end of the housing leading to the entrance 42 and exit 43
to and
from the bore sides of the fibres respectively, and one side connection 44
leads to
the shell side of the fibres. Each fibre consists of a composite layer of
polymers.
One relatively thick layer acts as a support, and the other layer (a thin
film)
functions as the separation controlling layer. At this stage it is important
that the
operation temperature does not exceed the maximuin allowable teinperature of
the
polymer.
Separation is effected by the selective penneation of the gases in air through
the thin film of the composite polymer membranes. Nitrogen perineates at a
slower
rate than the other gases, and so nitrogen in the conditioned air entering at
connection 42 passes along the bores and exits at the other end of the
separator 43,
while oxygen and other gases pass through the membranes, and are led through
the
separator's side connection 44 and so via a vent line to atmosphere.
The nitrogen separator section exit connection 43 is fitted with a product
flow indicator 45, a flow control valve 46 and =a pressure control valve 47.
Quality
monitoring analysers are fitted in a quality monitoring group 48 forming no
part of
this invention.
Nitrogen produced in the membrane separator 41 is led to a product outlet
49, or, during start-up when the quality is fluctuating, can be led to a vent
50 which
also allows the other gases to escape to atmosphere.
