Abstract:
A storage enclosure and an apparatus and method for producing carbon monoxide and/or hydrogen by means of cryogenic separation, including one such enclosure is provided.

Description:
This application is a §371 of International PCT Application PCT/FR2008/050843, filed May 16, 2008. 
     FIELD OF THE INVENTION 
     The present invention relates to a storage enclosure and an apparatus and method for producing carbon monoxide and/or hydrogen by means of cryogenic separation, including one such enclosure. 
     BACKGROUND 
     In a cold box, it is important to have at least one liquid enclosure for controlling the variation in the heat balance of the box. The variations in liquid level thus control the inputs of cold, by liquid injection, by turbine and optionally by cycle. 
     In various units, this enclosure is divided into several pots, and this potentially reduces the operating flexibility. In other units, this enclosure is dedicated, implying the need for additional equipment. 
     SUMMARY OF THE INVENTION 
     The present invention proposes to solve these problems, while having other advantages. 
     This is done by using the same pot to store the refrigeration capacity and, for example, to accommodate a column condenser. It may also be feasible to use another type of existing enclosure, such as a reboiler, a thermosiphon pot, etc. In the example, the condenser is immersed in cryogenic liquid, which overflows around the condenser above a liquid seal inside the pot, the liquid reserve being located in the annular space around this liquid seal. Hence, there is a single unit under pressure. 
     According to one object of the invention, a liquid storage enclosure is provided, suitable for inclusion in a cryogenic separation apparatus comprising a chamber, a heat exchanger placed inside the chamber, a barrier dividing the chamber into two parts, the heat exchanger being located in the first part and the second part being arranged around the first part, the barrier having a lower height than the height of the chamber, at least at certain points, for allowing liquid to pass from the first part to the second part over the barrier, when the enclosure is in service, and being optionally sealingly attached to the base of the chamber, means for sending liquid into the first part of the chamber and means for withdrawing liquid from the second part of the chamber and means for sending a fluid to the heat exchanger and for withdrawing a fluid from the heat exchanger. 
     Optionally:
         the barrier has an essentially cylindrical shape;   the barrier is coaxial with the chamber;   no means are provided for sending liquid issuing from outside the chamber directly to the second part;   means for withdrawing liquid from the second part are not connected to the first part;   the heat exchanger is located toward the bottom of the chamber;   the first part of the chamber, when not in use, only contains the heat exchanger and the fluid transport means connected to this heat exchanger.       

     Thus the second part is only supplied with liquid by the liquid overflow from the first part. 
     According to another object of the invention, a distillation column is provided comprising a liquid storage enclosure as described above, in which the heat exchanger is a bottom reboiler or a top condenser. 
     The distillation column is located outside the chamber. 
     According to another object of the invention, a method is provided for producing carbon monoxide and/or hydrogen by cryogenic separation, comprising an enclosure as described above, said enclosure being included in a separator pot. 
     According to another object of the invention, an apparatus is provided for producing carbon monoxide and/or hydrogen by cryogenic separation, comprising a column as described above, in which the column is a column for separating carbon monoxide and methane or a column for separating carbon monoxide and nitrogen. 
     According to other optional aspects, the apparatus comprises:
         means for sending liquid into the first part issuing from at least two different sources and/or means for withdrawing liquid from the second part to send it subsequently to two different destinations;   a scrub column and means for sending the withdrawn liquid at least to the cooler of the scrub column, for example a scrub column for methane or for carbon monoxide;   a heat exchange line, means for sending the feed fluid from the apparatus to the heat exchange line to be cooled therein, and means for sending the withdrawn liquid at least to the heat exchange line;   a column for separating carbon monoxide and methane or a column for separating carbon monoxide and nitrogen and means for sending the withdrawn liquid at least to a top condenser of the column for separating carbon monoxide and methane or the column for separating carbon monoxide and nitrogen;   a stripping column having a bottom reboiler and means for sending liquid condensed in the bottom reboiler to the first part of the enclosure;   a column for separating carbon monoxide and nitrogen having a bottom reboiler and means for sending liquid condensed in the bottom reboiler to the first part of the enclosure;   a column for separating carbon monoxide and methane having a bottom reboiler and means for sending liquid condensed in the bottom reboiler to the first part of the enclosure;   a heat exchange line and means for sending a liquid from the heat exchange line to the first part of the enclosure.       

     According to another object of the invention, a method is provided for producing carbon monoxide and/or hydrogen by cryogenic separation in an apparatus comprising an enclosure as described above, said enclosure being included in a separator pot. 
     According to another object of the invention, a method is provided for producing carbon monoxide and/or hydrogen by cryogenic separation in an apparatus comprising a column as described above, in which the column is a column for separating carbon monoxide and methane or a column for separating carbon monoxide and nitrogen. 
     According to other optional features:
         the liquid is sent into the first part issuing from at least two different sources and/or liquid is withdrawn from the second part to send it subsequently to two different destinations;   the apparatus comprises a scrub column and means for sending the withdrawn liquid at least to the cooler of the scrub column;   the apparatus comprises a heat exchange line, means for sending the feed fluid from the apparatus to the heat exchange line to be cooled therein, and means for sending the withdrawn liquid at least to the heat exchange line;   the apparatus comprises a column for separating carbon monoxide and methane or a column for separating carbon monoxide and nitrogen and means for sending the withdrawn liquid at least to a top condenser of the column for separating carbon monoxide and methane or the column for separating carbon monoxide and nitrogen;   the apparatus comprises a stripping column having a bottom reboiler and liquid is sent from the bottom reboiler to the first part of the enclosure;   the apparatus comprises a column for separating carbon monoxide and nitrogen having a bottom reboiler and liquid is sent from the bottom reboiler to the first part of the enclosure;   the apparatus comprises a column for separating carbon monoxide and methane having a bottom reboiler and liquid is sent from the bottom reboiler to the first part of the enclosure;   the apparatus comprises a heat exchange line and liquid is sent from the heat exchange line to the first part of the enclosure;   most of the liquids, or even all the liquids, of the apparatus substantially having the same composition are sent to a single enclosure.       

     This apparatus has many advantages. 
     A single enclosure serves to perform at least two functions: on the one hand, it stores an “independent” refrigerating reserve and, on the other hand, it is required for an element of the method (condenser, heat exchanger thermosiphon, etc.). 
     This enclosure may be supplied by all the streams producing liquid in the cold box. For example, on a methane scrub apparatus, the enclosure is supplied by at least two high pressure streams passing through the reboilers, the high pressure stream circumventing them. It may be supplied by other streams, at various pressures. The joining of all the streams in a single enclosure adds a great flexibility if various operating cases are to be considered, rather than attributing to each high pressure fluid one or more low pressure uses (thermosiphon, condenser, etc.). In addition to flexibility, standardization is also enhanced. If permitted by the pressure of the enclosure, all the liquid requirements can thus pass through this enclosure. 
     The overflow makes it impossible to control the condensation capacity (in the example) by the liquid level. However, it is possible to control the energy exchanged in the condenser by controlling the pressure of the enclosure. 
     In the second part, the liquid reserve serves to control the level by turbine or by liquid injection. This also allows a liquid reserve to operate the apparatus when the turbine is out of order and before starting the liquid injection nitrogen vaporization. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  illustrates an enclosure and a column in accordance with one embodiment of the present invention. 
         FIG. 2  schematically illustrates an apparatus for producing carbon monoxide by cryogenic separation in accordance with one embodiment of the present invention. 
         FIG. 3  schematically illustrates an apparatus for producing carbon monoxide by cryogenic separation in accordance with one embodiment of the present invention. 
         FIG. 4  schematically illustrates an apparatus for producing carbon monoxide by cryogenic separation in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     For a further understanding of the nature and objects for the present invention, reference should be made to the detailed description, taken in conjunction with the accompanying drawing, in which like elements are given the same or analogous reference numbers and wherein: 
     In  FIG. 1 , a column  1  is surmounted by a top condenser  3  supplied with a column head gas. This gas condenses at least partially in the condenser  3  and is returned to the top of the column. The condenser  3  is surrounded by a cylindrical barrier  5  sealingly attached to the base of a cylindrical chamber  21  containing the condenser. The barrier and chamber are substantially concentric with the condenser  3 . The barrier  5  is lower than the chamber  21 . Alternatively or additionally, the barrier may comprise cutouts at the top of the wall allowing the passage of liquid. 
     The barrier divides the chamber into two parts A and B, the first part A being located between the condenser and the barrier  5  and the second part B being located between the barrier  5  and the wall of the chamber  21 . 
     Lines  15 ,  17 ,  19  feed the first part A and a line  7  is attached to the second part B, then being divided into lines  9 ,  11 . 
     When in service, the condenser is fed with liquid from at least one of the lines  15 ,  17 ,  19 . This liquid is partially vaporized and the vapor  25  thus formed is withdrawn from the chamber  21 . When the liquid level reaches the top of barrier  5 , the liquid collected overflows and falls into the second part B. 
     In  FIG. 2 , the enclosure shown operates as described above and has the same structure as the one described for  FIG. 1 . The method in  FIG. 2  is a methane scrubbing method comprising a methane scrub column K 01 , a stripping column K 02 , a column for separating carbon monoxide and methane K 03  and a column for separating carbon monoxide and nitrogen K 04 . The streams supplying the columns and produced by the columns are not shown for the sake of simplification. Conventional apparatus which are suitable for operating according to the invention are shown in “Herstellung von Kohlenmonoxyd and Wasserstoff aus Erdgas” by Linde Berichte 33/1973, Ullmann&#39;s Encyclopedia of Industrial Chemistry, 5 th  edition, page 270, “Progress in H2/CO Low Temperature Separation” by Berninger, Linde Berichte, 44/1988, pages 20-21, Tieftemperaturtechnik, 2 nd  edition, pages 417-418, Research Disclosure 42654 of October 1999, DE-A-3741906, FR-A-2015667, US2002/134243, U.S. Pat. Nos. 6,269,657, 6,094,938, 6,082,134, 6,073,461, 6,062,042, 5,592,831, 5,295,356, 5,133,793 and 4,888,035. 
     It can be easily understood that the method could comprise fewer columns or more columns. In particular, the column for separating carbon monoxide and nitrogen is not an essential element of the invention. 
     In short, the column K 01  is fed with a feed stream, a fluid from the column depleted of hydrogen is sent to the stripping column K 02 , the liquid from the bottom of the stripping column is sent to the CO/CH 4  separating column K 03  and the column K 04  is fed with a fluid from the column K 03 , for producing pure carbon monoxide at the top of the column K 04 . 
     The enclosure C is fed with a liquid  21  from at least two different sources but substantially having the same composition. This liquid is rich in carbon monoxide. The liquid  15  sent to the first part of the chamber issues from the reboiler Q 6  of the stripping column K 02 . The liquid  17  sent to the first part of the chamber issues from the reboiler Q 7  of a column for separating carbon monoxide and methane. 
     The liquid  19  sent to the first part of the chamber issues from the heat exchanger  49 . 
     The liquid which has overflowed the barrier is divided into three parts. Part X is sent to a heat exchanger for cooling the scrub column K 01 . Part Y is sent to a pot  41  and then to the main heat exchange line where the mixture fed to the apparatus is cooled. Part  7  is sent to the top condenser of the CO/nitrogen separating column K 04 . Part X evaporates in the cooling heat exchanger to form a stream  39 . It is mixed with the vaporized streams  25 ,  37  from the condensers of the column K 03  and the column K 04  respectively. The mixed stream  43  joins the top gas of the separator pot  41  and is cooled in the heat exchanger  51 . 
     This stream  43  is compressed by a compressor C 1 . A compressed part  45  is sent to the heat exchanger  49  and is then divided, the part  31  feeding the column K 04  and the remainder constituting the stream  19 . 
     The rest of the stream  43  is compressed in the compressor C 2  to partly form the stream  47  which, cooled in the heat exchanger  51 , becomes the stream  15  sent to the enclosure C. The compressor C 3  compresses the rest of the stream to form the stream  49  which is divided into two. Part of the stream is mixed with the stream  49  and the remainder becomes the stream  17 . 
     In  FIG. 3 , the enclosure shown operates as described above and has the same structure as the one described for  FIG. 1 . The method in  FIG. 3  may be a method for methane scrubbing comprising at least one stripping column, a column for separating carbon monoxide and methane and a column for separating carbon monoxide and nitrogen. 
     It can be easily understood that the method could comprise fewer columns or more columns. 
     For example, in the case of a methane scrubbing process, the apparatus comprises a methane scrub column. 
     The enclosure C is fed with liquid issuing from at least two different sources but substantially having the same composition. This liquid may, for example, be a liquid rich in carbon monoxide, rich in nitrogen or a mixture mainly containing hydrogen and carbon monoxide. The liquid  15  sent to the first part of the chamber issues from the reboiler Q 6  of a stripping column. The liquid  17  sent to the first part of the chamber issues from the reboiler Q 7  of a column for separating carbon monoxide and methane. 
     The liquid  19  sent to the first part of the chamber issues from the reboiler Q 8  of a column for separating carbon monoxide and nitrogen, if any. 
     The liquid  7  which overflows the barrier is divided into three parts  9 ,  11 ,  12 . Part  9  is sent to a heat exchanger for cooling a scrubbing column, if any. Part  11  is sent to the main heat exchange line where the mixture feeding the apparatus is cooled. Part  12  is sent to the top condenser of a column other than column  1 , for example a column for separating carbon monoxide and nitrogen, like the column K 04  in  FIG. 2 . 
     Each of these parts  9 ,  11 ,  12  is vaporized and is mixed with the vaporized liquid  25  issuing from the condenser  3 . The mixed stream forms a cycle gas which is compressed in a multistage compressor, called compressor C 1 , C 1 ′ and C 2  connected in series. Compressor C 1  compresses the gas to form a stream  45  which becomes the stream  19  downstream of the reboiler Q 8 . There may be a compressor C 1 ′ which forms a stream  47  which is partly sent ( 147 ) to the reboiler Q 6  and partly ( 149 ) to the reboiler Q 8 . The compressor C 2  produces a stream  49  which feeds the reboilers Q 6 , Q 7 , the remainder forming the stream  20  also sent to the condenser  13 . 
     The method in  FIG. 4  shows a method for producing carbon monoxide and hydrogen by partial condensation. 
     The apparatus comprises a separator pot  405 , a stripping column  411  and a column for separating carbon monoxide and nitrogen  1 . The column  1  comprises a storage enclosure according to the invention. 
     A stream of synthesis gas  401  containing nitrogen but substantially without methane is cooled in the heat exchange line  403 . Part of the synthesis gas is used to reboil the stripping column  411  using the reboiler  405 . The partially condensed synthesis gas leaves the heat exchange line  403  and is sent to the separator pot  405 . The top gas  407  is heated in the heat exchange line and serves as a hydrogen-rich product. The liquid  409  is sent to the top of the stripping column  411 . The top gas  410  from the stripping column  411  leaves the apparatus after heating in the heat exchange line  403 . The bottom liquid  415  of the stripping column  411  is sent to an intermediate point of the heat exchange line  403  where it cools and is divided into two. One part  419  is sent to the separation column  1  after expansion. The remainder  417  is heated in the heat exchange line and is sent to the separating column  1  at a lower level. The bottom liquid  449  from the separating column  1  is sent to the top condenser thereof where it is partially vaporized. The vaporized liquid rich in carbon monoxide  425  is sent to the heat exchange line  403  to be heated and then to the compressor C 1 . The carbon monoxide is cooled with water. A part  453  serves as a product after a compression step in the compressor C 2 . The remainder  451  is cooled in the heat exchange line. A part  431  is expanded in the turbine T to supply the refrigerating capacity for the separation and recycled to the compressor C 1 . The remainder  433  is divided into two. A part  435  is sent at an intermediate temperature of the heat exchange line  403  at the bottom of the column  1  and to the top condenser (stream  437 ) after cooling in the heat exchanger  451  against a stream of liquid injection of liquid nitrogen  441 . The remainder  453  is sent to the condenser at the temperature of the cold end of the heat exchange line  403 . 
     The cycle gas compressed in the compressor C 1  may be a gas rich in carbon monoxide, a nitrogen-rich gas or a gas mixture of hydrogen and carbon monoxide. 
     It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.