EP1087195B1

EP1087195B1 - Refrigerator for cryogenic gas separation system

Info

Publication number: EP1087195B1
Application number: EP00120673A
Authority: EP
Inventors: Atsushi Air Water Inc. Miyamoto; Shingo Air Water Inc. Kunitani
Original assignee: Air Water Inc
Current assignee: Air Water Inc
Priority date: 1999-09-24
Filing date: 2000-09-21
Publication date: 2006-11-22
Anticipated expiration: 2020-09-21
Also published as: ES2273642T3; JP3584186B2; EP1087195A3; JP2001091079A; KR20010067201A; KR100647965B1; CN1290845A; DE60031931D1; EP1087195A2; TW477891B; ATE346271T1; CN1158514C; DE60031931T2

Abstract

A cryogenic gas separation system which comprises a refrigerator and utilizes cold produced by the refrigerator as a cold source for separation of a gas. The refrigerator incorporates a rotary valve which comprises a rotary element rotatable about an axis thereof and having a circular cross section perpendicular to the axis, and a housing accommodating the rotary element in a rotatable manner. The rotary element has a plurality of ports provided in an outer peripheral portion thereof, the housing having a plurality of ports provided in a peripheral wall thereof in association with the ports of the rotary element, the rotary valve being operative to be switched between a position where predetermined ones of the ports of the rotary element are aligned with corresponding ones of the ports of the housing for communication therebetween and a position where the predetermined ones of the ports of the rotary element are displaced in non-alignment with the corresponding ones of the ports of the housing for non-communication therebetween by rotation of the rotary element. The valve incorporated in the refrigerator has a smaller size and an extended service, and the cryogenic gas separation system can obtain a sufficient amount of cold with the use of the refrigerator. <IMAGE>

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a cryogenic gas separation system which utilizes cold produced by a refrigerator according to the preamble of claim 1. Such a system is known from FR-A-2751060.

Description of Related Art

cryogenic air separation systems utilizing a compact helium (He) refrigerator are disclosed in Japanese Patent Unexamined Publications No. 10-206009 (1998) and No. 10-206010 (1998) and Japanese Patent No. 3007581. For driving such a compact refrigerator typified by a pulse tube refrigerator for these cryogenic air separation systems, a pressure pulsation source is required and, in some cases, a phase controller is required. The pressure pulsation source and the phase controller each have valves for controlling the flow of an operating gas. Referring to Fig. 1, an active buffer pulse tube refrigerator, for example, includes a pressure pulsation source having a compressor 91 and a pair of valves 93, 94, and a phase controller having two buffer tanks 92a, 92b and a pair of valves 95, 96. In Fig. 1, reference numerals 97 and 98 denote a regenerator and a pulse tube, respectively.
The valves 93 to 96 are each opened and closed in a precisely predefined cycle. The open-close cycle is relatively short, which typically provides pressure pulsation of several hertz to several tens hertz. Therefore, a solenoid valve or a compact flat seal rotary valve as shown in section in Fig. 2 is generally employed for the valves 93 to 96. The flat seal rotary valve includes a rotary element 101 having two ports 102, 103 (which communicate with each other via a communication path 104), and a stationary element 105 having three ports 106 to 108 and kept in area contact with the rotary element 101. The rotary element 101 is adapted to be rotated with respect to the stationary element 105 by rotation of a motor 109 so that the ports 102, 103 are selectively connected to the ports 106 to 108 (the port connection is switched between a position where the ports 107, 108 of the stationary element 105 communicate with each other as shown in Fig. 2 and a position where the ports 106, 107 of the stationary element 105 communicate with each other as shown in Fig. 3). Thus, the flat seal rotary valve shown in Fig. 2 is capable of switching the flow path of the operating gas in two ways. Therefore, it is merely necessary to provide such rotary valves one for each of the pressure pulsation source and the phase controller. In Figs. 2 and 3, reference numeral 110 denotes a housing which accommodates the rotary element 101 in a rotatable manner.
For realization of a larger-scale and higher-efficiency refrigerator, a larger volume of the operating gas, a higher operating frequency and a complicated phase controller are required. In consideration of the marketability of such a refrigerator, it is desirable to employ a selector valve having a compact size and a long service life for the refrigerator and to satisfy the aforesaid requirements. However, conventional selector valves typified by the solenoid valve and the flat seal rotary valve shown in Fig. 25 cannot satisfy the aforesaid requirements, making it impossible to realize a larger-scale and higher-efficiency refrigerator.
More specifically, where a solenoid valve is employed as the selector valve, the valve tends to have a complicated construction and an increased size in an attempt to increase the volume of the operating gas, so that high speed operation of the valve is difficult. If the valve is frequently operated at a higher speed, the service life of the valve will drastically be reduced. Where a phase controller is incorporated in the refrigerator, the number of valves should be increased for the complicated construction of the phase controller, so that the overall size of the refrigerator is increased.
Where a flat seal rotary valve is employed as the selector valve, it is necessary to increase the diameters of the rotary element 101 and the stationary element 105 in an attempt to increase the port diameter for passage of a larger volume of the operating gas or to increase the number of ports for the complicated construction of the phase controller. Therefore, the contact areas of the rotary element 101 and the stationary element 105 are increased. Since a pressure exerted on the rotary element 101 is increased correspondingly to the increase in the contact area of the rotary element 101 and the stationary element 105, a motor capable of providing a greater torque should be employed as the motor 109. This increases the overall size of the valve. For this reason, only a smaller-scale refrigerator, having a cryogenic capacity on the order of several watts, has hitherto been developed.
Therefore, in an air separation unit employing a conventional smaller-scale refrigerator, the amount of cold produced is insufficient, so that an expansion turbine or the like should be employed as an auxiliary cold source. This results in a cost increase.
According to one aspect of this invention there is provided a cryogenic gas separation system according to claim 1.
Preferably said recesses of the rotary element provided in an outer peripheral portion of the rotary element are axially independently provided, each being formed in a different location along the axis of the rotary element.
Advantageously refrigerator is a pulse tube refrigerator and the pulse tube refrigerator is a refrigerator having a buffer tank.
A preferred embodiment of the present invention provides a cryogenic gas separation system which may be supplied with a sufficient amount of cold by employing a refrigerator incorporating a compact and longer-life selector valve.
Since in the preferred embodiment the two recesses of the rotary valve incorporated in the refrigerator are axially independently provided, an increase in the diameter of the rotary element is minimised. This allows the rotary valve to have a reduced size and an extended service life. The refrigerator may have a larger scale, a greater capacity and a higher efficiency. For example, the refrigerator can be embodied as a larger-scale refrigerator having a wattage of not smaller than several hundreds watts. Of course, the refrigerator may be embodied as a smaller-scale refrigerator having a wattage of several watts as in the prior art. The larger-scale, greater-capacity and higher-efficiency refrigerator makes it possible to operate the cryogenic gas separation system without the use of any auxiliary means such as an auxiliary cold source, thereby allowing for a cost reduction. The refrigerator to be employed in the cryogenic gas separation system may be of pulse tube type G-M (Gifford-McMahon) type, or Solvay type, but is not limited thereto. The refrigerator may be embodied as any type of refrigerator, as long as the refrigerator is designed so that flow paths of an operating gas are switched by switching a valve. In the present invention, the rotary element has a circular cross-section perpendicular (or normal) to the rotary axis of the element. In other words, the horizontal cross-section of the rotary element is circular when the rotary element is placed vertically upright and the vertical cross-section of the rotary element is circular when the same rotary element is laid horizontally.
The foregoing and other objects, features and effects of the present invention will become more apparent from the following description.
Given by way of example with reference to the accompanying drawings in which:

FIGURE 1 is a diagram illustrating a conventional pulse tube refrigerator,
FIGURE 2 is a diagram illustrating a conventional flat seal rotary valve,
FIGURE 3 is a diagram showing the operation of the flat seal rotary valve of Figure 2,
FIGURE 4 is a diagram illustrating a refrigerator employed in a cryogenic gas separation system in accordance with one embodiment of the present invention,
FIGURE 5 is a view illustrating a rotary element employed for rotary valve in the refrigerator of Figure 4,
FIGURES 6 and 7 are diagrams showing the operation of the rotary valve employing the rotary element of Figure 5, and
FIGURE 8 is a diagram illustrating a cryogenic gas separation system in accordance with the invention.

Figure 4 illustrates a pulse tube refrigerator 121 to be employed in the cryogenic gas separation system in accordance with one embodiment of the present invention. The pulse tube refrigerator according to this embodiment has substantially the same construction as the pulse tube refrigerator shown in Figure 1, except that rotary valves D as shown in Figures 5, 6 and 7 are respectively employed instead of the pair of valves 93, 94 and the pair of valves 95, 96. Since the other components of the pulse tube refrigerator of Figure 4 are the same as those of the pulse tube refrigerator of Figure 1, like components are denoted by like reference numerals.
In the rotary valves D the rotary element 1 has recesses 32 and 33 respectively formed in an outer peripheral portion thereof on opposite sides thereof (on the left-hand side and the right-hand side thereof in Figure 5. The housing 2 has three ports 34 to 36 formed in a circumferential wall thereof on one side thereof (on the left-hand side in Fig. 6), the ports 34, 35 being adapted to be brought into communication with the recess 32, the ports 35, 36 being adapted to be brought into communication with the recess 33. When the rotary element 1 is rotated into the position as shown in Fig. 6, the ports 34, 35 communicate with the recess 32 to permit an operating gas to flow therethrough. At this time, the ports 35, 36 do not communicate with the recess 33, so that the operating gas is prevented from flowing therethrough. When the rotary element 1 is rotated from this position into a position as shown in Fig. 7, the ports 35, 36 are brought into communication with the recess 33 to permit the operating gas to flow therethrough. At this time, the ports 34, 35 do not communicate with the recess 32, so that the operating gas is prevented from flowing therethrough. Although two rotary valves D are employed in this embodiment, the arrangement of the rotary valves is not limited thereto. For example, only one rotary valve D may be employed instead of the pair of valves 93, 94 or the pair of valves 95,96 Since the rotary element 1 of the rotary valve D has a small diameter and hence a small cross-section, the influence of a pressure load exerted on the rotary element 1 can be minimised. Where a seal (not shown) is provided between the rotary element 1 and the housing 2, torque generated by friction of the seal can be reduced, because the circumferential speed of the outer diameter of the rotary element 1 is reduced. The reduction in the pressure load and the torque generated by the friction of the seal reduces the power required for the rotation of the motor provided to drive the valve. As a result, a compact and high-speed motor can be employed as the motor. Further, the reduction in the circumferential speed of the rotary element 1 makes it possible to extend the service life of the seal (which is provided between the rotary element 1 and the housing 2) and to increase the rotational speed of the rotary element 1.
Since loads axially and radially exerted on the rotary element 1 of the preferred embodiment are received by bearings, the load exerted on the motor is reduced, whereby the power required for the rotation of the motor can be minimised. The pressure load exerted on the rotary element 1 is further reduced by the bearings which support the rotary element 1. This allows for size reduction of the rotary element 1 and the motor, so that the overall sizes of the rotary valves D can be minimised.
A cryogenic gas separation system as shown in Figure 8 is constructed such that the pulse tube refrigerator 121 shown in Figure 4 is incorporated in an air separation unit (nitrogen gas production unit of a single column type), and the pulse tube refrigerator 121 is used for cooling of feed air. More specifically, the feed air which is compressed up to a predetermined pressure at an increased temperature by a feed air compressor 122 is cooled close to an ordinary temperature (about 25°C) by a water-cooled heat exchanger 123.
After H₂O and CO₂ are almost completely removed from the feed air by an H₂O/CO₂ removal unit 124 or the like, the resulting feed air is supplied into a cold box 125. In the cold box 125, the feed air flows through a main heat exchanger 126 and is cooled to a liquefying temperature thereof, and then flows through a cold extracting portion 127 of the pulse tube refrigerator 121 so that the amount of liquefied feed air is increased. The resulting feed air is supplied to a lower portion of a rectification column 128. The cooling capacity of the pulse tube refrigerator 121 is equivalent to the sum of the amount of heat introduced from ambient temperature to the cold box 125, the heat transfer loss of the main heat exchanger 126, and the liquefaction energy required for extraction of a liquefied product.
A gaseous air portion of the feed air supplied into the lower portion of the rectification column 128 flows upward through the rectification column 128. A liquid air portion of the feed air is accumulated in the bottom of the rectification column 128 and then is supplied as a coolant into a condenser 129 located above the rectification column 128. In the condenser 129, the coolant liquefies N₂ gas in an upper portion of the rectification column 128 and then is returned as a reflux liquid into the upper portion of the rectification column 128. The feed air is rectified by the reflux liquid and the ascending gas, and the N₂ gas is separated from the air and extracted from the upper portion of the rectification column 128. After cold is recovered by the main heat exchanger 126, a product N₂ gas is taken out. In Fig. 8, reference numerals 130 and 131 denote an expansion valve and an exhaust gas outlet path, respectively.
In the air separation system, the pulse tube refrigerator 121 shown in Fig. 4 is used for the cooling of the feed air (all or part of the feed air output from the main heat exchanger 126 is cooled by the pulse tube refrigerator 121), but as objects to be cooled are not limited thereto. For example, the product nitrogen gas, the exhaust gas, the gas within the rectification column 128, the liquefied air or the like may be cooled by the pulse tube refrigerator 121. Alternatively, the pulse tube refrigerator 121 may cool and liquefy the feed air at an inlet of the main heat exchanger 126 or the product nitrogen gas or the exhaust gas at outlets of the main heat exchanger 126, and the liquefied gas may be supplied to a cryogenic portion of the cold box 125. Where the amount of cold produced by the pulse tube refrigerator 121 is insufficient, liquid nitrogen, liquid oxygen or the like may be supplied into the cold box to make up for any insufficient cold supply.
In the cryogenic gas separation system shown in Fig. 8, the air separation unit is embodied as a nitrogen gas production unit of a single column type, but also may be embodied as a common nitrogen gas production unit of a dual column type. The cryogenic gas separation system shown in Fig. 8 is constructed such that the pulse tube refrigerator 121 shown in Fig. 4 is incorporated in the air separation unit, but may be utilised for separation of various gas mixtures as long as the gas mixture separation is achieved through a cryogenic gas separation process.

Claims

A cryogenic gas separation system which comprises a refrigerator and utilises cold produced by the refrigerator as a cold source for separation of a gas, the refrigerator incorporating a rotary valve for controlling the flow of an operating gas, the rotary valve comprising a rotary element (1) rotatable about an axis thereof and having a circular cross-section perpendicular to the axis, and a hollow housing (2) accommodating the rotary element in a rotatable manner and having three ports (34,35,36), the rotary element (1) being switchable between a first position and a second position by rotation, characterized in that the rotary element having two separate recesses (32, 33) provided in an outer peripheral portion thereof, on opposite sides thereof, the three ports (34-36) being provided on one side of the housing and at axially spaced positions in a peripheral wall thereof in association with the recesses of the rotary element, there being a first pair of said three ports (34, 35) which includes a central one (35) of the three ports adapted to be brought into communication with a first said recess (32) and a second pair of said three ports (35, 36) which also includes the central one (35) of the three ports adapted to be brought into communication with the second said recess (33), the rotary valve being operative to be switched between the first position where the first recess (32) of the rotary element is aligned with the first pair of ports (34, 35) of the housing for communication therebetween, and the second recess (33) is displaced in non-alignment with the second pair of ports (35, 36) for non-communication therebetween, and the second position where the second recess (33) of the rotary element is aligned with the second pair of ports (35, 36) of the housing for communication therebetween, and the first recess (32) is displaced in non-alignment with the first pair of ports (34, 35) for non-communication therebetween.
A cryogenic gas separation system as set forth in Claim 1 wherein said recesses (32, 33) of the rotary element provided in an outer peripheral portion of the rotary element (1) are axially independently provided, each being formed in a different location along the axis of the rotary element.
A cryogenic gas separation system as set forth in Claim 1 or 2 wherein refrigerator is a pulse tube refrigerator and the pulse tube refrigerator is a refrigerator having buffer tank (92A or 92B).