Note: Descriptions are shown in the official language in which they were submitted.
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CRYOGENIC AIR SEPARA TION
The present invention relal~s to cryogenic air separation and relates particularly,
but not exclusively, to the operation of expander turbine driven compressors
used in such a process.
A typical cryogenic air separation unit (ASU) comprises a number of
compressors for compressing incoming air, a number of compressors for
compressing nitrogen and a number of expander turbines used for expanding
compressed air or nitrog-en so as to lower the temperature and pressure thereof
prior to its suppty to one or other of the high pressure or low pressure distillation
columns or heat exchangers. It is well known to use some of the energy
released during gas expansion in the expander turbines to drive a compressor
stage, however, in certain arrangements the power available from the expander
turbine is insufficient to meet the requirements of the compressor. Additionally,
in some arrangements, it is not possible to individually load each turbine. Alsoin some arrangements a small flow of nitrogen is required resulting in expensivestandalone compressors
It is an object of the present invention to provide a cryogenic air separation
apparatus which reduces and possibly eliminates both or one of the above
mentioned problem.
Accordingly, the present invention provides a cryogenic air separation apparatuscomprising two or more compression stages and two or more expander turbines
in which said two or more expander turbines are linked in series or parallel to
drive one or more compressor stages.
Preferably, said expander turbines are linked to said compressor via a common
(bull) gear, each expander turbine having an output (driving) gear for driving said
common gear and said one or more compressors having an input gear driven by
said common (bull) gear.
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Conveniently, said common (bull) gear comprises an externally toothed gear and
said compressor input gear is driven from the same external teeth.
Advantageously, the apparatus further includes a motor for driving said common
gear so as to drive said compressor as and when desired.
In a particularly useful arrangement, the apparatus further includes a generatordriven from said common gear as and when desired. Also the apparatus may
include a clutch or fluid coupling to disconnect the motor or generator when
desired .
In certain process conditions the motor may act as a generator.
In certain circumstances, an expander turbine may be driven by gas expanded
from a liquid state or by gas taken at pressure from a condenser column.
Conveniently, the liquid gas comprises liquid product or liquid by-product.
The present invention will now be more particularly described by way of
example only with reference to the accompanying drawings, in which:
Figure 1 is a schematic representation of a cryogenic air separation unit
incorporating features of the present invention, and
Figures 2, 3 and 4 illustrate three alternative arrangements of the present
invention.
Referring briefly to Figure 1, a cryogenic air separation unit (ASU) 10 comprises
a number of compression stages 12, 14, 16 for compressing incoming air A and
a number of expander turbines 18, 20, 22 for expanding compressed air so as
to reduce its temperature to that required in various stages of the cryogenic
distillation process. Further components include a heat exchanger 24 and high
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and low pressure condenser columns-26, 28. The actual operation of the ASU
forms no part of the present application and is therefore not described in detail
herein, however, the following brief explanation is provided for the purpose of
ensuring the readers understanding of Figure 1 attached hereto: Air is
compressed in one or more compression stages 12 and part is passed through
heat exchanger 24 and then direct to the high pressure column 26 so as to
produce 'strip' nitrogen for the low pressure column. Surplus air is compressed
by compression stage 14 and then split with part being directed to expansion
turbine 18 for expansion and cooling therein prior to its introduction into the low
pressure rectification column. Surplus air from compression stage 14 is directedto a compression stage 16, passed through heat exchanger 24 but removed part
way therethrough and passed to expansion turbine 20 prior to being passed to
the high pressure column where it supplements the airflow from compression
stage 12. A supplementary turbine 22 driven by an expanded source of liquid
product or by-product 30 may be provided for reasons which will be explained in
detail late herein. Alternatively, a turbine 17 may be provided for expanding
high pressure nitrogen directly from one or other of the two columns. The
compressors 12, 14, 16 and turbines 18, 20, 22 are provided with respective
driven and driving gears 32, 36 connected in a manner described below.
The operation of the present method of compressor driving is probably best
illustrated by reference to Figures 2 to 4. In Figure 2, it will be seen that the
driving gear 32 of one or other of the compressors 12, 14, 16 (hereinafter
referred to as the compressor 12) is engaged for being driven by a bull or
common gear 34. Two or more of the expander turbines 18, 20, 22 are
connected for driving the bull gear 34 via driving gears 36. One or other of theoutput gears 36 may form the input gear 32 of the compressor 12. In the
Figure 3 arrangement, the third expansion turbine 22 is added to the driving
force and connected for driving the bull gear 34 via output gear 36. A further
additional feature is shown in Figure 4 and comprises an optional
motor/generator combination 38, 40. Such components may be provided either
separately or together and when provided together may be provided as
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individual units or combined together as one motor/generator combination and
may include a clutch or fluid coupling 19 to disconnect the motor/generator
Operation of the present apparatus is simple with two or more turbines 18, 20,
22 driving bull gear 34 which in turn drives compressor 12 and/or compressor
14, 16, 17. The combined output from the turbines being sufficient to drive the
compressor. Supplementary turbines 17 and 22 are added in the Figure 3
embodiment and acts to boost the driving force as and when desired by
allowing expanded product or by-product gas to pass therethrough so as to drive
the turbines 17, 22 and its associated driving gear 36 in a manner which
facilitates the driving of bull gear 34. The provision of the motor/generator
combination, shown in Figure 4, allows the motor to be used to boost the
driving force of the turbines when the driving force is undesirably reduced, such
as, for example when the ASU plant is turned down. When surplus energy is
available, power may be generated by driving generator 40 directly form bull
gear 34. As stated earlier, the bullgear may be connected to the motor
generator 38, 40 by a clutch or fluid coupling which may be used to disconnect
the motor generator when the expander power matches the compressor power
and power balance is achieved.
