Patent Application
20170227284
The present invention relates to a bath condenser-reboiler in which the liquid inside liquid reservoirs provided in at least two evaporation zones is introduced into evaporation passages, and a resulting thermosiphoning effect induced by heat exchange with a gas flowing through a condensation passage is used to evaporate the liquid and condense the gas.
Priority is claimed on Japanese Patent Application No. 2014-169825, filed Aug. 22, 2014, the content of which is incorporated herein by reference.
A bath condenser-reboiler induces indirect heat exchange between liquefied oxygen from the bottom of a low-pressure distillation column (hereafter referred to as “the low-pressure column”) and nitrogen gas from the top of a high-pressure distillation column (hereafter referred to as “the high-pressure column”) in a cryogenic air separation unit by a double column system. As a result of this process, the bath condenser-reboiler generates a rising gas in the low-pressure column through evaporation and gasification of a portion of the liquefied oxygen, and generates a reflux liquid in both columns through condensation and liquefaction of the nitrogen gas.
Common among such bath condenser-reboilers are those that use plate-fin heat exchanger cores. These plate-fin heat exchanger cores have large numbers of heat exchange passages formed from adjacent condensation passages and evaporation passages via parting sheets, and are immersed in a liquid bath, and are formed such that the condensation fluid (nitrogen gas) introduced as a gas undergoes condensation and liquefaction in the condensation passages by indirect heat exchange with the evaporation fluid (liquefied oxygen) in the liquid bath and flows downward through the heat exchanger core, while a portion of the liquefied oxygen introduced into the evaporation passages from the bottom of the heat exchanger core undergoes evaporation and gasification and flows upward trough the heat exchanger core.
The flow into the evaporation passages from bottom and the upward flow occur because evaporation causes the liquid density to be lower than the density inside the liquid bath (a thermosiphoning effect), but because the heat exchanger core is used fully immersed in liquefied oxygen, the liquid head of the liquefied oxygen causes the flow into the heat exchanger core to occur at a lower temperature than the boiling point. The liquid head is expressed as the pressure converted to a liquid height. Accordingly, not only is a certain core height required until boiling begins, but the increase in temperature to the boiling point means the temperature difference with the nitrogen gas of the condensed fluid cannot be ensured, causing the pressure of the nitrogen gas to rise and increasing operating costs.
To resolve this problem caused by the liquid head of the liquefied oxygen, Patent Document 1 discloses a multistage bath condenser in which the evaporation zone is partitioned vertically into multiple zones, and multiple stages of liquid reservoir are provided to hold the liquefied oxygen in each evaporation zone, thereby reducing increases in boiling point and improving efficiency. When the liquid reservoir is provided in multiple stages, means for connecting the liquid reservoirs in each evaporation zone and supplying liquefied oxygen to each liquid reservoir are required. In relation to this point, in Patent Document 1, as illustrated in
Patent Document 1: Published Japanese Translation No. 2003-535301 of PCT
However, in the multistage bath condenser of Patent Document 1, a problem arises in that the reservoir sections on the outside surface of the heat exchanger core and the liquid communication means are complex, resulting in high manufacturing costs.
The present invention has been developed in light of the above problem, and has an object of providing a multistage bath condenser-reboiler that can be produced with a compact size by employing a simple construction for the liquid reservoirs provided in the heat exchanger core and the means by which the liquid reservoirs are connected.
In order to achieve the above object, the inventors of the present invention conceived of incorporating, into the heat exchanger core, means that enable the liquid reservoir sections to communicate and supply liquid to each liquid reservoir section. The present invention is based on this concept, and includes the specific aspects described below.
(1) A multistage bath condenser-reboiler according to the present invention includes: condensation passages which communicate in the vertical direction and through which a gas flows and condenses, evaporation passages which are partitioned into multiple stages through which a liquid flows that undergoes heat exchange with the gas and evaporates, one or more stages of liquid reservoir sections which hold liquid supplied to and discharged from the evaporation passages, and liquid communication passages through which the liquid in the liquid reservoir sections flows from upper liquid reservoir sections to lower liquid reservoir sections, wherein
the multistage bath condenser-reboiler has:
a heat exchanger core composed of (i) a heat exchange section formed by adjacently stacking the condensation passages and the evaporation passages formed from plates and fins, and (ii) a liquid communication section formed from the liquid communication passages provided on at least one side surface in the stacking height direction of the heat exchange section, and
one or more stages of the liquid reservoir sections formed on at least one side surface in the width direction of the heat exchanger core so as to correspond with the number of stages of the evaporation passages.
(2) In the evaporation passages are formed evaporation inlet flow channels which introduce the liquid in the liquid reservoir sections into the partitioned evaporation passages, and evaporation outlet flow channels which discharge a rising vapor-liquid two-phase fluid into the liquid reservoir sections, whereas in the liquid communication passages are formed communicating inlet flow channels which introduce the liquid in the liquid reservoir sections into the liquid communication passages and communicating outlet flow channels from which liquid flows out into the liquid reservoir section beneath.
(3) Further, in the multistage bath condenser-reboiler according to (2) above, the inlet of the communicating inlet flow channel is provided at a position below the position of the outlet of the evaporation outlet flow channel.
(4) Furthermore, in the multistage bath condenser-reboiler according to (2) above, the height position of the inlet of the evaporation inlet flow channel is offset with respect to the height position of the outlet of the communicating outlet flow channel.
(5) Further, in the multistage bath condenser-reboiler according to any of (1) to (4) above, each of the liquid reservoir sections is an enclosed space, and in each liquid reservoir section is provided an evaporation gas extraction port through which the evaporated gas that flows out to the liquid reservoir section is extracted.
(6) Furthermore, in the multistage bath condenser-reboiler according to (5) above, in the liquid reservoir section, in the uppermost liquid reservoir section is provided a liquid inlet port into which liquid is introduced from outside the device, and in the lowermost liquid reservoir section is provided a liquid discharge port from which liquid is discharged externally.
(7) Further, in the multistage bath condenser-reboiler according to any of (1) to (4) above, the liquid reservoir sections are open, and the condenser-reboiler further includes a gas collection vessel that collects the evaporated gas that flows out into the liquid reservoir sections.
(8) Furthermore, in the multistage bath condenser-reboiler according to any of (1) to (7) above, the liquid reservoir sections are provided on both sides in the width direction of the heat exchanger core.
(9) Furthermore, in the multistage bath condenser-reboiler according to any of (1) to (8) above, the liquid communication passages are provided on both side surfaces in the stacking height direction of the heat exchanger core.
In the multistage bath condenser-reboiler according to the present invention, a configuration is employed that includes:
a heat exchanger core composed of (i) a heat exchange section formed by adjacently stacking the evaporation passages and condensation passages formed from plates and fins and (ii) liquid communication sections formed from the liquid communication passages provided on at least one side surface in the stacking height direction of the heat exchanger section, and
one or more stages of liquid reservoir sections formed on at least one side surface in the width direction of the heat exchanger core so as to correspond with the number of stages of the evaporation passages. As a result, the structure is simple compared with a conventional condenser in which the communication means are formed from pipes, enabling a more compact design.
Furthermore, by employing this configuration, the heat exchanger core can be manufactured as an integral unit, thereby reducing manufacturing costs.
Preferred embodiments of the present invention are described below, but, the present invention is not limited to the embodiments below. Various additions, omissions, substitutions and other changes may be made provided that they do not depart from the scope of the present invention.
As illustrated in
a heat exchanger core 5, which is composed of (i) a heat exchange section 3 and (ii) liquid communication sections 4 formed from a first liquid communication passage 35 to a third liquid communication passage 39 provided on both side surfaces of the heat exchange section 3 in the stacking height direction, and
multiple stages of a liquid reservoir section 7 formed on both sides in the width direction of the heat exchanger core 5.
Each part of this structure is described below in detail. In the following description, an example is used in which the multistage bath condenser-reboiler 1 is used as the main condenser in a cryogenic air separation unit that condenses nitrogen gas and evaporates liquid oxygen by inducing heat exchange between the nitrogen gas and the liquid oxygen.
The heat exchange section 3 is a device that causes heat exchange between the liquid oxygen and nitrogen gas flowing therein, thereby condensing the nitrogen gas and evaporating the liquid oxygen, and is composed of condensation passages 17 and evaporation passages 19 stacked adjacent to each other.
In the present embodiment, as illustrated in
As illustrated in
The condensation passages 17 are formed using vertically oriented fins, and as illustrated in
As illustrated in
As illustrated in
Furthermore, as illustrated in
The first liquid communication passage 35 to third liquid communication passage 39 form a liquid communication section 4, and are provided on both sides in the stacking height direction of the heat exchange section 3. As illustrated in
For the sake of simplicity,
The first liquid communication passage 35 is a passage that communicates from the first evaporation zone 9 to the second evaporation zone 11, and the third liquid communication passage 39 is a passage that communicates from the third evaporation zone 13 to the fourth evaporation zone 15, with both of these communication passages formed in the layer C. Furthermore, the second liquid communication passage 37 is a passage that communicates from the second evaporation zone 11 to the third evaporation zone 13, and is formed in the layer D.
In the layers C and D which constitute the liquid communication section 4, parts that do not function as passages (dummy passages) are formed, and these dummy passages are indicated by crosshatching in
At the top of the first and third liquid communication passages 35 and 39 are formed a first communicating inlet flow channel 35a and a third communicating inlet flow channel 39a respectively, each formed from horizontally oriented fins into which liquid oxygen is introduced from the liquid reservoir sections 7 of the first and third evaporation zones 9 and 13 respectively. At the bottom of the first and third liquid communication passages 35 and 39 are formed a first communicating outlet flow channel 35b and a third communicating outlet flow channel 39b respectively, each formed from horizontally oriented fins that guide liquid oxygen to the liquid reservoir sections 7 of the second and fourth evaporation zones 11 and 15 respectively.
In a similar manner, a second communicating inlet flow channel 37a is formed at the top of the second liquid communication passage 37, and a second communicating outlet flow channel 37b is formed at the bottom of the second liquid communication passage 37.
In this manner, because a liquid communication section composed of the first liquid communication passage 35 to third liquid communication passage 39 can be formed by providing plates 31 and fins on the side surfaces of the heat exchange section 3, the structure can be made more simple and compact than conventional condensers in which communication means passages are composed of piping.
Furthermore, by using the configuration described above, the liquid communication sections 4 and the heat exchange section 3 can be manufactured integrally as a plate fin type heat exchanger core 5. Specifically, the heat exchanger core 5 can be produced by assembling the plates 25, the fins 27 and the side bars 29 of the heat exchange section 3 and the liquid communication sections 4 that constitute the heat exchanger core 5 (as illustrated in
Furthermore, because the communication channel sections 4 of the first liquid communication passage 35 to third liquid communication passage 39 are provided on the outside surfaces of the heat exchange section 3 rather than the inside surfaces, heat exchange with the fluid in the condensation passages 17 can be avoided.
In the example illustrated in
The entire throughput flow of liquid oxygen is supplied to the liquid reservoir section 7 of the first evaporation zone 9, and because a substantially equivalent amount is evaporated in each evaporation zone, the flow rate through the communication passages decreases in order from the first liquid communication passage 35 to the second liquid communication passage 37 and then the third liquid communication passage 39. Accordingly, the size of the opening of the inlet (communicating inlet flow channel) of each communication passage is changed to provide the same fluid resistance, thereby realizing a uniform liquid head in each liquid reservoir.
A liquid reservoir section 7 is provided in each evaporation zone on at least one side surface of the heat exchanger core 5 in the width direction. In the present example, as illustrated in
A liquid inlet port 41 through which a liquid (liquid oxygen) can be introduced from outside the device is provided on the liquid reservoir section 7 of the first evaporation zone 9, and a liquid discharge port 43 through which a liquid (liquid oxygen) can be discharged externally is provided on the liquid reservoir section 7 of the fourth evaporation zone 15 (see
Furthermore, the liquid reservoir sections 7 also function as collectors of oxygen gas, and an evaporation gas extraction port 7a is provided in each liquid reservoir section 7 for the purpose of extracting the evaporated gas (oxygen gas) that flows out to the reservoir section (see
A method for performing heat exchange between nitrogen gas and liquid oxygen using the multistage bath condenser-reboiler 1 of the configuration described above is described below, together with a description of the operation of the multistage bath condenser-reboiler 1.
Liquid oxygen is introduced from outside the device via the liquid inlet port 41 and accumulates in the liquid reservoir section 7 of the first evaporation zone 9. On the other hand, nitrogen gas is introduced into the condensation passages 17 via the nitrogen gas header 21.
Head pressure causes the liquid oxygen accumulated in the liquid reservoir section 7 to flow into the evaporation passage 19 from the evaporation inlet flow channel 19a, and the liquid surface levels inside the liquid reservoir section 7 and the evaporation passage 19 reach the same height.
When nitrogen gas passes through the condensation passages 17 in this state, heat exchange occurs between the nitrogen gas and the liquid oxygen in the evaporation passage 19, a portion of the liquid oxygen undergoes evaporation and gasification to become oxygen gas, and the liquid oxygen in the evaporation passage 19 becomes a gas-liquid mixture (vapor-liquid two-phase fluid). Due to the difference in density from the liquid oxygen inside the liquid reservoir section 7, a rising flow is generated in the evaporation passage 19 and is discharged from the evaporation outlet flow channel 19b as a vapor-liquid two-phase fluid. The discharged evaporated oxygen gas is extracted from the evaporation gas extraction port 7a of the liquid reservoir section 7, and the liquid oxygen that did not evaporate returns to the liquid reservoir section 7, forming a circulating flow between the liquid reservoir section 7 and the evaporation passage 19 (a thermosiphoning effect).
When the liquid surface level in the liquid reservoir section 7 reaches or exceeds the height of the first communicating inlet flow channel 35a, the liquid oxygen flows from the first communicating inlet flow channel 35a into the first communication passage 35, is discharged from the first communicating outlet flow channel 35b, and accumulates in the liquid reservoir section 7 of the second evaporation zone.
Once liquid oxygen has accumulated in the liquid reservoir section 7 of the second evaporation zone 11, then in a similar manner to the first evaporation zone 9, the liquid oxygen flows from the evaporation inlet flow channel 19a into the evaporation passage 19 and is discharged from the evaporation outlet flow channel 19b as a vapor-liquid two-phase fluid, and when the liquid surface level in the liquid reservoir section 7 reaches or exceeds the height of the second communicating inlet flow channel 37a, the liquid oxygen flows into the second communication flow channel 37 and enters the liquid reservoir section 7 of the lower-stage third evaporation zone 13 via the second communicating outlet flow channel 37b.
The flow of liquid oxygen from the third evaporation zone 13 into the fourth evaporation zone 15 occurs in a similar manner. The liquid oxygen that accumulates in the liquid reservoir section 7 of the fourth evaporation zone 15 is extracted via the liquid discharge port 43 so that the liquid surface level remains constant.
On the other hand, the nitrogen gas undergoes heat exchange with the liquid oxygen in the adjacent evaporation passages 19 while passing through the condensation passages 17, condenses (is liquefied) and flows down from the bottom end of the condensation passages 17, and is extracted via the liquid nitrogen header 23 and the liquid nitrogen extraction pipe.
As is apparent from this description of the operation of the device, because a vapor-liquid two-phase fluid is discharged from the evaporation outlet flow channel 19b to the liquid reservoir section 7, it is preferable that the liquid surface level of the liquid reservoir section 7 is below the evaporation outlet flow channel 19b so as not to impede this discharge. Accordingly, the heights of the communicating inlet flow channels (the first communicating inlet flow channel 35a, the second communicating inlet flow channel 37a and the third communicating inlet flow channel 39a) in each evaporation zone are preferably set lower than the evaporation outlet flow channels 19b.
In the liquid reservoir sections 7, in the vicinity of the evaporation inlet flow channels 19a, the liquid oxygen flows from the liquid reservoir section 7 toward the inward direction of the heat exchanger core 5, whereas in the vicinity of the communicating outlet flow channels (the first communicating outlet flow channel 35b, the second communicating outlet flow channel 37b and the third communicating outlet flow channel 39b), the liquid oxygen flows from the heat exchanger core 5 toward the liquid reservoir section 7. Accordingly, if the evaporation inlet flow channel 19a and the communicating outlet flow channels are near each other, there is a possibility that the opposing flows may interfere with each other, causing stagnation in the flow, and therefore the evaporation inlet flow channel 19a and the communicating outlet flow channels are preferably placed as far apart as possible. For example, the height position of the evaporation inlet flow channel 19a may be displaced relative to the height position of the communicating outlet flow channels.
It is particularly preferable that the height position of the evaporation inlet flow channel 19a is lower than the height position of the communicating outlet flow channels. By employing such a configuration, the liquid oxygen can still flow into the evaporation inlet flow channel 19a in situations such as at startup when little liquid oxygen has accumulated in the liquid reservoir section 7,
In the low-pressure column 55, as a result of distillation of the oxygen-enriched liquid in the bottom of the high-pressure column as the main raw material, low-pressure nitrogen gas is produced at the top of the column and liquid oxygen is produced at the bottom of the column, and this liquid oxygen is supplied to the multistage bath condenser-reboiler 1, undergoes evaporation and gasification, and is returned to the bottom of the low-pressure column as a rising gas.
In the above description, as illustrated in
In the above description, an example was described in which the liquid reservoir sections 7 have the roles of storing liquid oxygen and of collecting oxygen gas, but the liquid reservoir section 7 need not necessarily have the role of collecting oxygen gas. Examples of such configurations are shown in
Components in
As illustrated in FIG.13, the open-type multistage bath condenser-reboiler 60 is placed in a gas collection vessel 61 that covers the multistage bath condenser-reboiler 60 in its entirety, so that the evaporated gas (oxygen gas) that flows out to the liquid reservoir sections collects in the gas collection vessel 61.
Furthermore, in the case of the devices shown in
The cryogenic air separation unit 63 is a modification of the cryogenic air separation unit 51 illustrated in
In the embodiment 1 and the embodiment 2 described above, an example was described in which, because four stages of evaporation zones were provided, a first liquid communication passage 35 through to a third liquid communication passage 39 were formed, but the number, shape and other attributes of the liquid communication passages may be changed as required in accordance with the number of evaporation zones.
A multistage bath condenser-reboiler can be obtained in which the liquid reservoirs provided in the condensation evaporator core and the means by which the liquid reservoirs communicate have a simple construction, enabling a compact design.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-169825 | Aug 2014 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2015/073553 | 8/21/2015 | WO | 00 |
