Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
59Z
The invention relates to a refrigeration process, wherein
a refrigerant circulates in a closed cycle, which comprises ~ ~
supplying the refrigerant at a relatively low pressure to the ~ -
; low pressure side of a compressor, compressing the refrigerant
to a relatively high pressure, passing the refrigerant to a
cooler and cooling the refrigerant, passing the refrigerant to
a process system in which refrigeration is needed, expanding
the refrigerant to a relatively lo~ pressure so that refrigera-
tion i8 provided and returning the expanded gaseous refrigerant
to the low pressure side of the compressor, thus completing the
cycle.
A refrigeration process of this kind is known and an embodi- -
ment of such a process is described, for example, in Applicant's
British patent specifica~tion No. 895,094, published on 2nd May,
1962, wherein the refrigeration obtained is used for the lique-
faction of a gas, in particular natural gas or methane.
The compressors used in processes of this kind are
preferably so-called turbo-compressors. When a turbo-compressor
is used it is required to use a so-called recycle system for
starting and stopping of the compressor and during operation of
bhe compressor at low throughput. The use of such a recycle
system is well known and comprises branching.~fpart of the
refrigerant leaving the cooler and returning it through a
recycle line to the low pressure side of the compressor, wherein
the recycle flow passing through the recycle line is controlled
by a recycle valve.
i, ,
';
,
:`
,.~,. .
, .
,
3 ~ 59Z
' . .
A valve, normally a check valve, is arranged downstream
of the location where the recycle stream is branched off. As ' ;
the compressor slows down to stop, the recycle valve gradually
opens and the check valve closes automatio~ly to prevent flow -
reversal. While the compressor is stopped the contents of the ~ -
entire recycle loop is released through the recycle valve
: until the recycle loop and the low pressure system at the low
pressure side of the compressor are at the same pressure.
If the said low pressure system is an enclosed space of
limited capacity this equalization through the recycle valve -
can cause the pressure in the low pressure system to rise to the -
extent that gas is discharged from the relief valves which protect
the low p~essure system from over-pressure. This discharge of
refrigerant through the relief valves is an economic loss of
valuable refrigerant and a source of operating inconvenience if
refrigerant stocks are low.
. .1 .
It is therefore desirable to design a recycle system in
such a way that the contents of the recycle loop are as small `
as possible.
.ii ~ .~-
If the refrigerant which is compressed condenses partly
in the cooler, it is moreover necessary to separate the condensed
liquid before the recycle stream passes through the control
. . .
~- valve. Otherwise satisfactory control of the recycle flow will
`~ not be possible.
It is an object of the invention to provide a refrigeration
process of the above-mentioned kind with an improved recycling
,~ .
' ~' ` .,
.
:.~ .
. . .
:
.~ ~
. ~, . . . . . .
., . :
~ 4 ~ ~J44S9z
process, having the advantage that loss of refrigerant is reduced
as much as possible and furthermore that a satisfactory control
of the recycle flow is possible even in the case that partial
condensation of the refrigerant occurs in the cooler.
It is another object Or the invention to provide an in-
stallation for carrying out the said refrigeration process.
; The refrigeration process according to the invention comprises:
a. supplying a refrigerant at a relatively low pressure to
the low pressure side of a compressor;
b. in the compressor compressing the refrigerant to a relatively
high pressure;
c. passing the refrigerant from the high pressure side of the
compressor to a cooler and cooling the refrigerant;
d. passing the refrigerant from the cooler to a gas/liquid
separator;
e. passing refrigerant from the gas/liquid separator through
a one-way valve to a process system in which refrigeration is
needed.
~20 f. in the process system expanding the refrigerant to a
relatively low pressure so that refrigeration is provided;
g. returning the expanded gaseous refrigerant to the low
pressure side of the compressor;
h. in which process, when recycling is necessary, gaseous re-
~25 frigerant is passed from the gas/liquid separator through a
recycle valve to the low pressure side of the compressor in
order to obtain recycling.
.; ~ .
.
. . .
, . . . .
- 5- ~45~Z `~
; In the process according to the invention, it is possible
to use a refrigerant which is a mixture of substances, a so-called
"mixed refrigerant". Ex mples of such mixed refrigerants are
described in the said British patent specification No. 895,094,
which discloses the use of a mixture of ethane, propane and butane
in one cycle and the use of a mixture of methane and ethane
in another cycle.
Alternatively, it is possible to use a refrigerant which
i8 substantially a single substance, such as, for example,
propane.
The invention will be described with reference to the
drawings, wherein:
Figure 1 shows a first embodiment of the process according
to the invention, wherein the refrigerant used is a mixture of
substances.
Figure 2 shows a second embodiment of the process according
to the invention, wherein the refrigerant used is single substance.
In the embodiment according to figure 1, mixed refrigerant,
for example a gaseou9 mixture of ethane, propane and butane at
low pressure is supplied through line 23 to the low pressure
side of the compressor 11. In compressor 11 the refrigerant is
- compressed to a relatively high pressure. The gaseous refrigerant
leaves the high pressure side of the compressor 11 and is
passed through line 12 to a cooler 13. In the cooler 13 the
^25 refrigerant is cooled so that it condenses partially. The
partially condensed refrigerant is passed from cooler 13 through
line 14 to a gas/liquid separator 15. Refrigerant leaves the
, :
,~ .
.
- lf~4~S9Z
separator 15 through the bottom line 16. In all operating
modes other than total recycle at least part of the refrigerant
in gaseous condition passes through the bottom line 16 taking
with it all the refrigerant in liquid condition.
The refrigerant is led via bottom line 16, one way valve 17
and line 18 to a receiver 19. In the receiver 19, the liquid
refrigerant accumulates. Liquid refrigerant is passed from
receiver 19 through line 20 to a process system 22 in which
refrigeration is needed. Gaseous refrigerant is passed from
receiver 19 through line 21 to the process system 22 as well.
The said liquid and gaseous refrigerant are expanded to a
relatively low pressure to provide refrigeration. The resultant
gaseous refrigerant which is at a relatively low pressure is
passed through line 27 and line 23 to the low pressure side of
the compressor 1, thus completing the cycle. When recycling
is necessary, recycle gas is withdrawn from the top of gaslliquid
separator 15 and is passed through line 24, recycle valve 25, line
26 to line 23 and through line 23 to the low pressure side of
the compressor 11. In this wa~ recycle valve 25 controls a ~ ;
cooled liquid-free gas stream.
The particular advantage of the recycle arrangement as des-
cribed is that right up to the onset of total recycle there is -~
no liquid accumulation in the recycle loop. If total recycle
is maintained partial condensation in cooler 13 can only continue
until the gas circulating in loop 12, 13, 14, 15, 24, 25, 26, 23
is at its dew point in line 14.
:;
.,
- 1~4~S9~
The arrangement as described has the advantage that only
a relatively small quantity of gaseous and liquid refrigerant is -
contained in elements 12, 13, 14, 15, 16 and 24 which lead~ -
to only small losses of refrigerant inventory when the recycle
loop equalizes on compressor shut-down. In other words, since
the total refriæerant inventory contained upstream of non-return
valve 17 is much smaller than in the conventional systems in ~--
which the special arrangement of the said gas/liquid separator
15 .~ 8 not present, refrigerant losses are much reduced as compared
with the said conventional systems.
In the related embodiment as shown in figure 2, the refrigerant
consists hasically of only a single substance, for example ~-
propane. ;
The refrigerant is supplied through line 47 to the low pressure
side of compressor 30. In compressor 30 the refrigerant is
compressed to a relatively high pressure. The gaseous refrigerant
leaves the high pressure side o~ the compressor 30 and is passed
through line 31 to a cooler 32. In the cooler 32 the refrigerant
is desuperheated, possibly partially condensed and passed
through line 33 to gas/liquid separator 34.
Refrigerant leaves the separator 34 through its bottom line ~
35. In all operating modes other than total recycle at least ~ -
part of the gas passes through the bottom line 35 taking with i~
all the liquid. The refrigerant is then passed through one
` 25 way valve 36 throughline 37 to cooler 38. In cooler 38 the re-
frigerant is substantially condensed and passed via line 39
to receiver 40. Liquid refrigerant is passed from receiver 40
through line 41 to the process system 42 in which refrigeration
is needed. Then the liquid refrigerant is expanded to a relatively
~- .
''' ' ~ ~" .
- 8 - 1~44592
low pressure so that its evaporation provides the necessary
rerrigeration. Fro~ process system 42, the gaseous refrigerant
which is at relatively low pressure is passed through lines 43
and 47 to the low pressure side of the compressor 30, thus
completing the cycle. When recycling ~s necessary, recycle
gas is withdrawn from the top of gaslliquid separator 34 and is
passed through line 44, recycle valve 45 and line 46 to line
47 and through line 47 to the low pressure side o~ the compressor
30. In this way recycle valve 45 controls a cooled liquid-free
gas stream.
In this case build-up of liquid refrigerant in the recycle
: loop during total recycle and its accumulation in separator 34
is prevented by the fact that the pressure in cooler 38 and receiver
40 drops when there is no load on cooler 38. Hence, generally,
if condensate i8 collected in separator 34, it will drain through
one way valve 36 because the higher temperature in flowing
system 32, 33, 34, 44 creates a higher vapour pressure than can
exist in the static 9y9tem communicating with receiver 40.
,
~.. . - . . . .
.
:; - , - .
. .
