Cryogenic refrigeration system

Details Cryogenic refrigeration system Cryogenic refrigeration system

2002-11-07

2003-09-09

Doerrler, William C. (Department: 3744)

Refrigeration

Cryogenic treatment of gas or gas mixture

Liquefaction

C062S335000

Reexamination Certificate

active

06615591

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a cryogenic refrigeration system, and more particularly to a countermeasure against an impurity in the system.
BACKGROUND OF THE INVENTION
A cryogenic refrigeration system employing a combination of a JT refrigerator and a pre-cooling refrigerator is known in the prior art, as disclosed in, for example, Japanese Laid-Open Patent Publication No. 9-229503. A GM refrigerator, or the like, is used as the pre-cooling refrigerator.
The JT refrigerator is a refrigerator that generates coldness of a cryogenic level by subjecting a high pressure helium gas from a compressor to a Joule-Thomson expansion through a JT valve. On the other hand, the GM refrigerator is a refrigerator that generates a coldness by expanding a high pressure helium gas from a compressor through the reciprocating movement of a displacer. The GM refrigerator as a pre-cooling refrigerator pre-cools the helium gas in the JT refrigerator before the Joule-Thomson expansion by using the coldness.
Some cryogenic refrigeration systems including a JT refrigerator and a pre-cooling refrigerator are provided with a heat-collecting heat exchanger that exchanges heat between a high pressure helium and a low pressure helium in the systems. Such a cryogenic refrigeration system performs a heat collecting operation within the system, thereby improving the operating efficiency.
However, if water as an impurity exists in the helium as a refrigerant, the water is frozen in the heat-collecting heat exchanger or in a pipe there around, which may clog the passageway. In view of this, a system as follows has been proposed in the art (see Japanese Laid-Open Patent Publication No. 2001-108320), in which a circuit for eliminating the clog in the passageway is added.
FIG. 9
illustrates such a cryogenic refrigeration system (
100
), including a compressor unit (
101
) and a refrigerator unit (
102
). The compressor unit (
101
) includes a low pressure side compressor (
103
) and a high pressure side compressor (
104
). The refrigerator unit (
102
) includes a GM refrigerator (
112
) having a first heat station (
113
) and a second heat station (
114
), and a JT refrigerator (
111
) having a JT valve (
116
).
In the compressor unit (
101
), a discharge side pipe (
105
) is connected to the discharge side of the high pressure side compressor (
104
), and a suction side pipe (
109
) is connected to the suction side of the low pressure side compressor (
103
). Oil separators (
106
) and an adsorber (
107
) are provided along the discharge side pipe (
105
). The discharge side pipe (
105
) diverges into two high pressure pipes (
108
,
110
). The first high pressure pipe (
108
) is connected to the JT refrigerator (
111
), and the second high pressure pipe (
110
) is connected to the GM refrigerator (
112
). A flow rate control valve (
135
), and a switching valve (
134
) for preventing a refrigerant at room temperature from flowing into the refrigerator unit (
102
) when the operation of the system is shut down, are provided along the first high pressure pipe (
108
). Note that a check valve (
126
) for preventing a refrigerant at room temperature from flowing into the refrigerator unit (
102
) when the operation of the system is shut down is provided also along the suction side pipe (
109
).
A JT circuit (
115
) in the refrigerator unit (
102
) includes a high pressure line (
117
) and a low pressure line (
118
), and the JT valve (
116
) is provided along the high pressure line (
117
). A first pre-cooling section (
119
) in the first heat station (
113
) and a second pre-cooling section (
120
) in the second heat station (
114
) are provided along the high pressure line (
117
). Moreover, first to third heat-collecting heat exchangers (
121
-
123
) for exchanging heat between the high pressure helium gas flowing along the high pressure line (
117
) and the low pressure helium gas flowing along the low pressure line (
118
) are provided in the JT circuit (
115
).
As clog elimination means for eliminating a clog when the passageway of the first heat exchanger (
121
) is clogged, the cryogenic refrigeration system (
100
) includes a supply pipe (
124
) for supplying the discharge gas from the compressors (
103
,
104
) to the outlet side of the high pressure side passageway of the first heat exchanger (
121
), and a collection pipe (
125
) for collecting the discharge gas, which has flowed through the high pressure side passageway of the first heat exchanger (
121
), into the suction side pipe (
109
) of the compressors (
103
,
104
). In order to prevent the refrigerant from flowing into the supply pipe (
124
) and the collection pipe (
125
) during a normal cooling operation, a switching valve (
127
) is provided along the supply pipe (
124
) and a switching valve (
129
) is provided along the collection pipe (
125
). Conversely, in order to allow an appropriate flow of the refrigerant through the supply pipe (
124
) and the collection pipe (
125
) during a clog elimination operation, a switching valve (
128
) is provided along the first high pressure pipe (
108
) and a switching valve (
130
) is provided along the suction side pipe (
109
). Note that an adsorber (
131
), and a switching valve (
132
) for preventing the backflow of water from the adsorber (
131
) during a cooling operation, may be provided along the collection pipe (
125
). Moreover, a flow rate control valve (
133
) may be provided along the collection pipe (
125
).
During a cooling operation, the switching valve (
128
) and the switching valve (
130
) are opened, while the switching valve (
127
) and the switching valve (
129
) are closed, whereby the high pressure helium gas discharged from the compressors (
103
,
104
) is cooled through the first heat exchanger (
121
)→the first pre-cooling section (
119
)→the second heat exchanger (
122
)→the second pre-cooling section (
120
)→the third heat exchanger (
123
). Then, the high pressure helium gas expands through the JT valve (
116
) to be a liquid helium on a cryogenic level, and the liquid helium flows into a helium tank (
136
). A helium gas, which is generated through evaporation in the helium tank (
136
), flows into the suction side pipe (
109
) of the compressors (
103
,
104
) through the low pressure line (
118
), and is compressed through the compressors (
103
,
104
). Then, the circulation as described above is repeated.
During a clog elimination operation, the switching valve (
128
) and the switching valve (
130
) are closed, while the switching valve (
127
) and the switching valve (
129
) are opened, whereby the high pressure helium gas discharged from the compressors (
103
,
104
) is supplied to the outlet side of the high pressure side passageway of the first heat exchanger (
121
) through the supply pipe (
124
), and flows backwards along the high pressure side passageway. Even if water is frozen in the first heat exchanger (
121
), the frozen ice is melted by the high pressure helium gas because a high pressure helium gas has a relatively high temperature. Then, the high pressure helium gas flows along the collection pipe (
125
) together with an impurity in the first heat exchanger (
121
), and flows into the suction side pipe (
109
) of the compressors (
103
,
104
). As described above, a clog of the first heat exchanger (
121
) is eliminated, and an impurity is removed.
However, with the cryogenic refrigeration system (
100
), it is not possible to eliminate a clog occurring in a downstream side portion of the high pressure side passageway of the first heat exchanger (
121
), e.g., the second heat exchanger (
122
) or the third heat exchanger (
123
).
Moreover, the operation of the JT refrigerator (
111
) needs to be shut down temporarily during a clog elimination operation. Then, the liquid helium in the helium tank (
136
) is likely to evaporate, whereby the pressure inside the helium tank (
136
) increases. The conventional cryogenic refrigeration system (
100
) addresses the problem as follows. When the pressure insid

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