Patent Application
20090211295
The present invention relates to an assembly of heat exchangers, a cryogenic distillation apparatus incorporating the same, and a cryogenic distillation method using the same.
For distilling air, the air is cooled to very low temperatures. To limit the heat exchanges with the external environment, the various columns and heat exchangers in which the various phases of separation/liquefaction of fluids issuing from the gases of air take place are insulated by one or more insulants (perlite, rockwool, etc.), this insulant being contained, for mechanical reasons, in large structures commonly called cold boxes.
The dimensions of these cold boxes depend on the number of columns, of heat exchangers, on the size thereof, on the various piping and other secondary cryogenic elements, and on the insulant distances required between all these cryogenic elements and the external structure containing the insulant.
In many cases, for this air separation apparatus, it is advantageous, for quality and control reasons, to prefabricate these structures containing the “noble” parts, that is, the columns and all or practically all of the secondary cryogenic components and cryogenic piping, and also the heat exchangers, in specialized workshops, the feasibility limit of these “cold box packages” being the configuration for transportation between the place of manufacture and the place of final installation.
The use of two different heat exchanger bodies to cool the air sent to an air separation apparatus is known. FR-A-2 846 077, U.S. Pat. No. 4,555,256, EP-A-0 044 679 and EP-A-0 042 676 describe a first heat exchanger body used to cool and heat the fluids under high pressure and a second heat exchanger body used to cool and heat the fluids under medium pressure.
The present invention is suitable for substantially limiting the dimensions of the external structures containing the insulant, regardless of the type of separation considered and the air treatment capacity of the unit, and, in the case of the cold box packages, for extending the capacity limit of factory-prefabricated separation apparatus.
According to one object of the invention, a heat exchange assembly is provided, comprising at least one first and one second heat exchange body, each body being of the plate heat exchanger type, comprising a plurality of metal plates of substantially similar contour extending along a first dimension or length and a second dimension or width, spaced from and arranged in parallel rows to one another along a third dimension or thickness and sealing means bounding flattened passages with the said plates, forming at least one passage of a first type and at least one passage of a second type, the sealing means allocated to each passage releasing one fluid inlet and one fluid outlet, one inlet of the first body being connected to a first delivery line for fluid to be cooled and one outlet of the first body being connected to a first collecting line for cooled fluid, another inlet of the first body being connected to a first delivery line for fluid to be heated and another outlet of the first body being connected to a first collecting line for heated fluid, one inlet of the second body being connected to a delivery line for fluid to be cooled and one outlet of the second body being connected to a collecting line for cooled fluid, another inlet of the second body being connected to a delivery line for fluid to be heated and another outlet of the second body being connected to a collecting line for heated fluid, characterized in that one side bounded by a width and a thickness of at least one first heat exchange body is located at least partially opposite a side bounded by a width and a thickness of at least one second heat exchange body, the two sides being separated by insulating material.
According to other optional aspects:
The “aligned” heat exchangers are located side by side in the lengthwise direction.
The term “liquid” includes psuedo-liquids, that is, liquids above the critical pressure.
“Liquid injection” means the injection of a cryogenic liquid into the system of columns for the purpose of extracting heat.
According to a further object of the invention, an apparatus for cryogenic separation of a gas mixture is provided, comprising a stripping unit, an assembly according to one of claims 1 to 8 and a system of columns, means for conveying the gas mixture to the stripping unit, means for conveying the stripped gas mixture to the assembly of heat exchangers to be cooled at least in one of the first and second series of heat exchanger bodies to at least one pressure, means for conveying at least some gas mixture cooled in at least one of the first and second heat exchanger bodies to the system of columns, and means for conveying at least one product from the system of columns to each of the first and second heat exchanger bodies.
According to other optional aspects of the invention, the apparatus comprises:
According to a further object of the invention, an apparatus for cryogenic separation of a gas mixture is provided, comprising a stripping unit, an assembly of at least one first heat exchanger and one second heat exchanger and a system of columns, means for conveying the gas mixture to the stripping unit, means for conveying the stripped gas mixture to the assembly of heat exchangers to be cooled at least in one of the first and second heat exchanger bodies to at least one pressure, means for conveying at least some gas mixture cooled in at least one of the first and second heat exchanger bodies to the system of columns, and means for conveying at least one product from the system of columns to each of the first and second heat exchanger bodies, characterized in that the first heat exchanger is located above the second heat exchanger, preferably directly above the second heat exchanger.
According to an optional aspect, the apparatus comprises means for sending a liquid from a column of the system of columns to the second heat exchanger, in which it is vaporized, means for collecting vaporized liquid from the second heat exchanger, and no means for collecting vaporized liquid from the first heat exchanger.
According to a further aspect of the invention, a method is provided for the cryogenic separation of a gas mixture in an apparatus comprising a stripping unit, a heat exchange assembly according to one of claims 1 to 8 and a system of columns, in which the gas mixture is conveyed to the stripping unit, stripped gas mixture is conveyed to at least one first heat exchange body to be cooled therein to at least one pressure, stripped gas mixture is conveyed to at least one second heat exchange body to be cooled therein to at least one pressure, gas mixture cooled in the first heat exchange body is conveyed to the system of columns, gas mixture cooled in the second heat exchange body is conveyed to the system of columns, at least one fluid is conveyed from the system of columns to at least one first heat exchange body, and at least one fluid is conveyed from the system of columns to at least one second heat exchange body, characterized in that the first body (at least one of the first bodies) contains circulating fluids of which at least one is at a pressure above a threshold and the second body (at least one of the second bodies) contains circulating fluids which are only at pressures below this threshold.
At least one first heat exchange body is located above one second heat exchange body. Preferably, all the bodies of the first series are located above all the bodies of the second series.
According to a further aspect of the invention, a method is provided for the cryogenic separation of a gas mixture in an apparatus comprising a stripping unit, a heat exchange assembly according to one of claims 1 to 8 and a system of columns, in which the gas mixture is conveyed to the stripping unit, stripped gas mixture is conveyed to at least one first heat exchange body to be cooled therein to at least one pressure, stripped gas mixture is conveyed to at least one second heat exchange body to be cooled therein to at least one pressure, gas mixture cooled in the first heat exchange body is conveyed to the system of columns, gas mixture cooled in the second heat exchange body is conveyed to the system of columns, at least one fluid is conveyed from the system of columns to at least one first heat exchange body to be heated therein, and at least one fluid is conveyed from the system of columns to at least one second heat exchanger body to be heated therein, characterized in that the first body (at least one of the first bodies) contains only circulating gases and/or at least one circulating liquid which cools and the second body (at least one of the second bodies) contains at least one circulating liquid issuing from the system of columns and which is vaporized therein.
At least one first heat exchange body is located above one second heat exchange body. Preferably, all the bodies of the first series are located above all the bodies of the second series.
According to a further aspect of the invention, a method is provided for the cryogenic separation of a gas mixture in an apparatus comprising a stripping unit, a heat exchange assembly comprising one first heat exchanger and one second heat exchanger and a system of columns, in which the gas mixture is conveyed to the stripping unit, stripped gas mixture is conveyed to at least one first heat exchange body to be cooled therein to at least one pressure, stripped gas mixture is conveyed to at least one second heat exchange body to be cooled therein to at least one pressure, gas mixture cooled in the first heat exchange body is conveyed to the system of columns, gas mixture cooled in the second heat exchange body is conveyed to the system of columns, at least one fluid is conveyed from the system of columns to at least one first heat exchange body and at least one fluid is conveyed from the system of columns to at least one second heat exchange body, the first heat exchanger (at least one of the first bodies) containing circulating fluids of which at least one is at a pressure above a threshold and the second heat exchanger (at least one of the first bodies) contains circulating fluids exclusively at pressures below this threshold, characterized in that the first heat exchanger is located above the second heat exchanger.
According to a further aspect of the invention, a method is provided for the cryogenic separation of a gas mixture in an apparatus comprising a stripping unit, a heat exchange assembly comprising one first and one second heat exchanger and a system of columns, in which the gas mixture is conveyed to the stripping unit, stripped gas mixture is conveyed to at least one first heat exchanger to be cooled therein to at least one pressure, stripped gas mixture is conveyed to at one second heat exchange body to be cooled therein to at least one pressure, gas mixture cooled in the first heat exchanger is conveyed to the system of columns, gas mixture cooled in the second heat exchanger is conveyed to the system of columns, at least one fluid is conveyed from the system of columns to at least one first heat exchanger to be heated therein, and at least one fluid is conveyed from the system of columns to at least one second heat exchanger to be heated therein, the first heat exchanger (at least one of the first heat exchangers) containing only circulating gases (and/or at least one circulating liquid that is cooled) and the second heat exchanger (at least one of the second heat exchangers) containing at least one circulating liquid issuing from the system of columns and which is vaporized therein, characterized in that the first heat exchanger is located above the second heat exchanger.
According to other optional aspects:
The heat exchangers occupy a floor area that is generally larger than the set of columns. One solution for limiting this area that prevents the “package” approach is to position the heat exchangers that can be accommodated without disturbing the distillation, typically the gas heat exchangers, above those which cannot be accommodated, typically the heat exchangers with liquid or liquid vaporization. The floor area is greatly reduced.
If the single package approach comprising the columns and heat exchangers cannot be implemented, an independent package of stacked heat exchangers may be advantageous.
This approach can also be followed without this package concept simply in order to reduce the floor area of the units for cryogenic separation of air or of gas such as H2/CO.
The invention is described in greater detail with reference to
The first series of heat exchangers 1 is placed on a stainless steel frame 3 of which the legs rest on the bottom of the cold box package, the second series of heat exchangers being located inside the frame or under the first series, while supporting it. The heat exchanger block formed from the first series of heat exchangers can also be placed on the block formed from the second series, provided that they are even more effectively insulated from one another, because the coldest part of the heat exchangers of the first series is located opposite the hottest part of the second series, one being, in operation, at about the ambient temperature, and the other at a cryogenic temperature. The cold box package is filled with insulating material I.
Two first heat exchange bodies 5 constitute a first series 1 of aligned heat exchanger bodies. The two substantially identical bodies 5 are of the plate heat exchanger type, comprising a plurality of metal plates of substantially similar contour extending along a first dimension or length and a second dimension or width, spaced from and arranged parallel to one another along a third dimension or thickness. Sealing means bound flattened passages with the plates, forming four types of passages, these passages not extending along the whole length of the body. For each type of passage, the sealing means allocated to each passage release one fluid inlet and one fluid outlet at the two ends thereof. A first inlet E1 at the hot end of each first body 5 is connected to a delivery line for medium-pressure air to be cooled D AIRMP and a first outlet S1 at an intermediate position of each first body is connected to a collecting line for cooled medium-pressure air C AIR MP. A second inlet E2 at an intermediate position of each first body 5 is connected to a delivery line for waste nitrogen to be heated DNR and a second outlet S2 at the hot end of each first body 5 is connected to a collecting line for heated waste nitrogen CNR.
Since each body 5 of this series of heat exchangers 1 also performs the function of a subcooler, specifically the coldest part of each body 5, a third inlet E3 at the cold end of each first body 5 is connected to a delivery line for liquid oxygen to be cooled DOL and a third outlet S3 of the first body is connected to a collecting line for cooled liquid oxygen COL and a fourth inlet E4 at the cold end of each first body 5 is connected to a delivery line DLL for nitrogen-rich liquid to be cooled and a fourth outlet S4 of the first body is connected to a collecting line for cooled nitrogen-rich liquid CLL.
It is easily understood that at least one body of the first series can perform a function of a subcooler, thereby making the assembly more compact. In fact, in the case in which the bodies of the first series do not perform this function, the subcooler may consist of at least one separate heat exchanger to be placed preferably between the first and second series. It is also possible for the apparatus to comprise no subcooler.
It will also be understood that the bodies of the first series are not necessarily identical and, in particular, do not all receive the same fluids.
Four second heat exchange bodies 7 constitute a second series 2 of aligned heat exchanger bodies, supported slightly above the bottom of the cold box package by the frame 3. The four substantially identical bodies 7 are each of the plate heat exchanger type, comprising a plurality of metal plates of substantially similar contour extending along a first dimension or length and a second dimension or width, spaced from and arranged parallel to one another along a third dimension or thickness. Sealing means bound flattened passages with the plates, forming five types of passages extending along the whole length of the body. For each type of passage, the sealing means allocated to each passage release one fluid inlet and one fluid outlet at the two ends thereof. One first inlet E1′ at the hot and of each second body 7 is connected to a delivery line for air to be cooled to a first high pressure D1 AIRHP and a first outlet S1′ at the cold end of each second body 7 is connected to a collecting line for cooled high-pressure air C2 AIR HP. A second inlet E2′ at the hot end of each second body 7 is connected to a delivery line for air to be cooled to a second high pressure D2 AIRHP and a second outlet S2′ at the cold end of each second body is connected to a collecting line for cooled high-pressure air C1 AIR HP. A third inlet E3′ of the cold end of each second body 7 is connected to a delivery line for waste nitrogen to be heated DNR′ and the third outlet S3′ at the hot end of each second body 7 is connected to a collecting line for heated waste nitrogen CNR′.
Unlike the first series, the bodies 7 of the second series are connected to a nitrogen gas delivery line and to a liquid oxygen line. A fourth inlet E4′ at the cold end of each second body 7 is connected to a delivery line for nitrogen gas to be heated DN and a fourth outlet S4′ at the hot end of each second body 7 is connected to a collecting line for heated waste nitrogen CN. A fifth inlet E5′ of the cold end of each end of each second body 7 is connected to a delivery line for liquid oxygen to be vaporized DOL and a fifth outlet S5′ at the hot end of each second body 7 is connected to a vaporized oxygen collecting line COG.
It will also be understood that the bodies of the second series are not necessarily identical and, in particular, do not all receive the same fluids.
Two main differences can be identified between the heat exchanger bodies of the first series and those of the second series.
Firstly, any liquid to be vaporized is sent to at least one, and preferably all, of the bodies of the second series. Thus, the bodies of the first series may comprise at least one type of passage for vaporizing liquid oxygen, for example, to several pressures. They may also comprise passages for vaporizing liquid nitrogen.
Secondly, any fluid at a pressure above a given threshold to be cooled or heated is sent to the second series. This second series can obviously also receive fluids at lower pressure but the bodies are intended for use at high pressure. The threshold may be 30 bar abs, 20 bar abs or 15 bar abs.
For the series of heat exchangers 1 and 2, the heat exchanger bodies 5, 7 and their distributing and collecting lines must be insulated with perlite or with rockwool I. Each series may be placed in an individual cold box 4 containing only the heat exchangers and at least some of the delivery and collecting lines, or the two series may be placed in a common cold box containing only the heat exchange bodies and their collecting and delivery lines, or both series may be placed in a common cold box with the system of air separation columns.
As described in EP A 1 230 522, a reboiler-condenser of a double air separation column that is used to vaporize medium-pressure nitrogen against low pressure oxygen may be located outside the columns. In this case, the reboiler-condenser can be placed in the same cold box 4 as the heat exchanger series 1, 2, above the series 1 or between the two series. In this way, all the elements supplied by the same manufacturer (heat exchangers, reboiler-condensers) are located in a single package which can be supplied directly to the site. It can be understood that each element (upper heat exchanger, lower heat exchanger and, optionally, reboiler) can be insulated in an independent cold box or several of these elements may be located in a common cold box.
An assembly as shown in the preceding figures is suitable for incorporation in a cryogenic distillation air separation apparatus according to
The air to be separated is compressed in a main compressor MAC to medium pressure to form the medium-pressure air AIR MP. The pressure of the remainder of the air is first boosted to a first high pressure in a booster compressor S1 to form a high-pressure stream 1 AIR HP and the pressure of the remainder of the air is boosted to a second high pressure in a booster compressor S2 to form the stream 2 AIR HP. The medium-pressure stream AIR MP is sent to the part 1 of the heat exchange assembly located at least some ten metres above the ground, whereas the high-pressure streams 1 AIR HP and 2 AIR HP are sent to the lower part 2 at least one metre above the ground. Part of the medium-pressure air stream may be sent to the lower part 2.
The medium-pressure air is cooled in the body of the first series 1 to an intermediate point, and is then sent to the chamber of the medium-pressure column MP of a double air separation column.
It will be understood that means for extracting heat has not been shown in order to simplify the figure. This may be a medium-pressure air turbine discharging into an air separation column or a nitrogen turbine, supplemented by liquid injection as required.
The high-pressure air is liquefied in the body of the second series and is then sent to one or both columns of the double column.
Liquid oxygen is tapped off from the chamber of the low-pressure column and divided into two streams. One part OL is sent to the coldest part of the bodies of series 1 to be subcooled before being sent to storage S. The remainder is pumped to form a stream OLP which is under at least 20 bar abs or at least 30 bar abs. This stream OLP is vaporized in the bodies of the second series to produce a stream OG.
Medium pressure nitrogen N is tapped off at the top of the medium-pressure column and sent to the second series of bodies in which it is heated to form a product N.
Waste nitrogen tapped off at the top of the low pressure column is divided into two streams, one part NR being sent to the series 1 and the remainder NR′ being sent to the series 2. The two streams are heated and sent to regeneration or to the atmosphere.
A stream of medium-pressure nitrogen-rich liquid LL is subcooled in the series 1 in the coldest part of the bodies and is sent to the top of the low-pressure column to serve as reflux.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0414070 | Dec 2004 | FR | national |
| 0550288 | Feb 2005 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2005/057152 | 12/23/2005 | WO | 00 | 4/22/2008 |
