While the specification concludes with claims distinctly pointing out the subject matter that Applicants regard as their invention, it is believed that the invention will be better understood when taken in connection with the accompanying drawings in which:
With reference to
A feed air stream 10 is compressed at a compression unit 12 that may be a multistage compressor having inter-stage cooling between stages. The compressed and purified air stream is then introduced into a purification unit 14 that is well known in the art. Prepurification unit 14 that can be a temperature swing adsorption unit having beds of alumina or molecular sieve type adsorbent operating out of phase to remove the lower boiling components of the air such as water and carbon dioxide. The resultant compressed and purified stream 16 is cooled to at or near its dew point in main heat exchanger 18 and introduced as a compressed, purified and cooled stream 20 into a distillation column 22.
The introduction of compressed, purified and cooled air stream 20 into distillation column 22 initiates the formation of an ascending vapor phase that becomes evermore rich in nitrogen as it ascends distillation column 22 to produce an oxygen-rich liquid column bottoms 24 and a nitrogen-rich column overhead 26. A first nitrogen-rich vapor stream 26 is condensed within a condenser 28 to return a liquid reflux stream 28 to distillation column 22. The return of liquid reflux stream 29 initiates the formation of a descending liquid phase 29 that becomes evermore rich in oxygen as it descends column 22.
The ascending vapor phase and the descending liquid phase are contacted by mass transfer contact elements 30 and 32 that can be a known structured packing, a random packing or known sieve trays.
An oxygen-rich column bottoms stream 34 is expanded to a lower temperature within an expansion valve 36 and then introduced into a shell 38 of condenser 28 for partial vaporization thereof against the liquefaction of the first nitrogen-rich vapor stream 26. The partially vaporized oxygen-rich liquid column bottoms produces a waste stream 40 that is partially warmed within main heat exchanger 18 and then introduced as a partly warmed waste stream 41 into a turboexpander 42 to produce a refrigerant stream 44 that is fully warmed within main heat exchanger 18 and discharged as a waste stream 46. This action adds refrigeration to air separation plant 1 to maintain it at cryogenic temperatures. Part of the work of expansion can be employed in powering compression unit 12. A second nitrogen-rich vapor stream 48 is fully warmed within main heat exchanger 18 to produce a product nitrogen stream 50.
Thus, the incoming compressed and purified air stream 16 is fully cooled through indirect heat exchange with waste stream 40, the refrigeration stream 44 and the second nitrogen-rich vapor stream 48.
With reference to
With additional reference to
The inlets for the compressed and purified air stream to the lengthwise extending section 62 are provided by inlet headers 66 and 68 and redistribution fins 86 and 88. The redistribution fins 86 and 88 cause the flow to change direction so that the flow is parallel with the width “W” and hence, such inlets can be seen to be principally along the length “L”. The redistribution fins 86 and 88 also distribute the flow across the length “L”. After the flow is redistributed, the flow passes parallel to fins 90 and 92. Upon discharge, the flow passes through redistribution fins 94 and 96, causing the fluid to change direction again and pass to outlet headers 82 and 84. As a result, the cross-sectional flow area is partly defined by the length “L” as opposed to the width “W” as would be the case in a conventional plate-fin heat exchanger in which the flow is parallel to the length “L”. Hence, the outlet for layer 60 is again principally along the length “L” and is provided by redistribution fins 94 and 96 and outlet headers 82 and 84. As can be appreciated such changes in flow produce a pressure drop and therefore, for a particularly long plate-fin heat exchanger intermediate inlets and outlets and redistribution fins could be provided between inlet headers 66 and 68 and outlet headers 82 and 84. Furthermore, although not illustrated, gaps within the end bars associated with layer 60 and the separate lengthwise sections 62 and 64 thereof would be provided, as would be well known in the art, in registry with the inlet headers 66, 68 and the outlet headers 82, 84 to allow flow to enter separate lengthwise section 62 and to be discharged from separate lengthwise section 64.
With principal reference again to
With additional reference to
The inlets and outlets for second layer 98 are provided along the length “L” dimension as inlet headers 126, 128 and 130 for second nitrogen-rich streams 48a and 48b, refrigerant streams 44a and 44b and waste streams 40a and 40b, respectively.
Second nitrogen-rich streams 48a and 48b flow through distribution fins 132, from flow passage 116 to flow passage 122 and along sets of fins 134 and 136. Thereafter, second nitrogen-rich streams 48a and 48b after having been fully warmed pass through distribution fins 138 and are discharged through outlet header 140 as product streams 50a and 50b.
Refrigerant streams 44a and 44b flow into inlet headers 128, distribution fins 142, from flow passage 118 to flow passage 124. Flow passage 118 and flow passage 124 is provided with fins 144 and 146. Since flow passage 124 is wider than flow passage 118, it is provided with intermediate distribution fins 148. The waste streams 46a and 46b are then discharged through distribution fins 150 to outlet headers 152.
The waste streams 40a and 40b pass through distribution fins 154, parallel to fins 156 and then are discharged as partly warmed waste streams 41a and 41b to outlets 158 that are positioned between connected lengthwise section 106 and 108 in a gap 160 provided to accommodate outlets 158. The partly warmed waste streams 41a and 41b flow out of outlet header 162 that can be seen in
Again, although not illustrated, the side bars of second layer 98 would be provided with gaps in registry with the inlet headers 126, 128, 130 and the outlet headers 140, 152 to allow related flows to enter and leave the flow passages formed within second layer 98.
With additional reference again to
Although a plate-fin heat exchanger has been described with reference to one used in connection with a nitrogen generator, the invention should not be taken as having such limited applicability. In this regard, the invention could be applied to a heat exchanger having a first layer for flow of a fluid to exchange heat with two or more other fluids flowing in an alternating layer. The heat exchange may be to warm the fluid flowing in the first layer. Furthermore, in case expansion of flow length is not desired, a heat exchanger in accordance with the present invention could be constructed from only two adjacent sections of two layers. Although second layer 96 is illustrated as being divided into two portions 100 and 102, more portions could be utilized.
While the invention has been described with respect to a preferred embodiment, as will occur to those skilled in the art, numerous changes, additions and omissions may be made without departing from the spirit and scope of the present invention provided for in the appended claims.