Patent Publication Number: US-6662595-B2

Title: Process and device for obtaining a compressed product by low temperature separation of air

Description:
The invention relates to a process for obtaining a compressed product by low temperature separation of air in a rectification system which has a pressure column (high pressure column) and a low pressure column, this process comprising the following steps: 
     a. a first flow of compressed and purified feedstock air is cooled in a main heat exchanger system and is fed into the pressure column, 
     b. at least one fraction from the pressure column is expanded and fed into the low pressure column, 
     c. an oxygen-rich fraction from the low pressure column is liquid-pressurized and delivered to the mixing column, 
     d. a heat exchange medium is fed into the lower area of the mixing column and is brought into countercurrent contact with the oxygen-rich fraction, 
     e. a gaseous top product is removed from the upper area of the mixing column and 
     f. a product fraction is removed from the rectification system, liquid-pressurized, vaporized in indirect heat exchange with the gaseous top product of the mixing column and is withdrawn as the compressed product, characterized in that 
     g. indirect heat exchange is carried out for vaporization of the liquid-pressurized product fraction in the main heat exchanger system. 
     The rectification system of the invention can be made as a classical double column system, but also as a three-column or multicolumn system. In addition to the columns for nitrogen-oxygen separation, it can have additional devices for obtaining other air components, especially rare gases. In addition to the rectification system, in the process a mixing column is used in which an oxygen-rich fraction is vaporized from rectification in direct heat exchange with a heat exchange medium. The top gas of the mixing column is used for indirect vaporization of a liquid-pressurized product fraction (so-called internal compression). 
     The oxygen-rich fraction which is used as the feedstock for the mixing column has an oxygen concentration which is higher than that of air and is for example 70 to 99.5% by mole, preferably 90 to 98% by mole. A mixing column is defined as a countercurrent contact column in which a more easily volatile gaseous fraction is sent opposite a more poorly volatile liquid. 
     The process of the invention is suitable for obtaining gaseous compressed oxygen and/or gaseous compressed nitrogen, especially for producing gaseous impure oxygen under pressure. Here impure oxygen is defined as a mixture with an oxygen content of 99.5% by mole or less, especially from 70 to 99.5% by mole. The product pressures are for example 3 to 25 bar, preferably 4 to 16 bar. Of course the compressed product if necessary can be further compressed in the gaseous state. 
     A process of the initially mentioned type is known from DE 19803437 A1. Here liquid oxygen is pumped and vaporized in the top condenser of the mixing column. 
     The object of the invention is to make the initially mentioned process economically more favorable, especially by hardware simplification and/or energy saving. 
     This object is achieved in that indirect heat exchange for vaporization of the liquid-pressurized product fraction is no longer done in a separate condenser-evaporator, but in the main heat exchanger system in which the pressure column air is also cooled. Preferably the product fraction is introduced immediately after pressurization rise (for example, in a pump) into the cold end of the main heat exchanger system, there first heated to the boiling point and then vaporized, both against the condensing or condensed top fraction of the mixing column. 
     In this way a separate condenser-evaporator which is necessary in the process from DE 19803437 A1 can be eliminated, as can a separate heat exchanger for removing the supercooling from the liquid-pressurized product fraction. By integrating the vaporization of the liquid product fraction and the cooling of air moreover the heat exchange process (Q-T diagram) can be improved so that especially small exchange losses are achieved and thus relatively low energy consumption is achieved. 
     The main heat exchanger system in the sense of this invention can, but need not, be implemented by a single heat exchanger block. It can also consist of several blocks connected in parallel or series. With parallel connection the blocks have the same inlet and outlet temperatures. Generally vaporization and at least part of the heating of the liquid-pressurized product flow take place in the same heat exchanger block. 
     The mixing column is operated under a pressure which is enough to vaporize the product fraction below the desired pressure against the condensing top gas of the mixing column, for example below 5 to 17 bar, preferably below 5 to 13 bar. The pressure of the high pressure column in the invention is in the range of for example 5 to 15 bar, preferably 5 to 12 bar, that of the low pressure column for example 1.3 to 6 bar, preferably 1.3 to 4 bar. 
     Preferably the top product of the mixing column downstream of the condensation which takes place in the condenser-evaporator is expanded and recycled into the low pressure column. The top product is introduced therein at a feedpoint, above by at least one theoretical plate (for example, one to ten theoretical plates) the removal point of the oxygen-rich fraction. Between the condenser-evaporator and expansion, the fluid is optionally cooled, for example by indirect heat exchange with the product fraction and/or the oxygen-rich fraction. 
     Preferably a second flow of purified feedstock air is compressed to a pressure which is clearly higher than the operating pressure of the pressure column, is cooled in the main heat exchanger system, and then fed into the mixing column as a heat exchange medium. This second air flow at the same time delivers at least some of the heat for heating the liquid-pressurized product fraction downstream of its vaporization. “Clearly higher” is defined here as a pressure difference which is higher than the line losses, especially higher than 1 bar. This pressure difference can be achieved for example by all the air being compressed essentially to the pressure column pressure and then its being branched into two air flows, the second flow being further compressed, for example by a motor-driven compressor. Alternatively, the two air flows can be compressed separately from the atmospheric pressure to the pressures required at the time. The pressure to which the second air flow is compressed is generally 1.1 to 2.0 times the pressure of the liquid product fraction during its vaporization. 
     It is furthermore favorable when the second flow after its cooling in the main heat exchanger system and before it is fed into the mixing column is further cooled in indirect heat exchange with the liquid-pressurized oxygen-rich fraction. Thus the two feedstock fractions of the mixing column are brought to the temperature which is optimum for their feed. 
     For optimization of the Q-T diagram of the main heat exchanger system it is advantageous if the second flow at a first intermediate point below a first intermediate temperature is removed from the main heat exchanger system, the first intermediate temperature being clearly higher than its dew point. The gaseous top product of the mixing column is introduced into the main heat exchanger system at the first intermediate point at which the second flow is removed from the main heat exchanger system. In this way the same passage in the main heat exchanger system can be used both for cooling of the second air flow and also for condensation of the top product of the mixing column. 
     If the compressed product is oxygen, the product fraction is removed from the low pressure column. The product fraction and the oxygen-rich fraction for the mixing column can then be jointly withdrawn from the low pressure column and/or jointly liquid-pressurized; in hardware terms this is especially simple. Alternatively, the product fraction and the oxygen-rich fraction can be removed at different points of the low pressure column. The oxygen-rich fraction is preferably withdrawn at least one theoretical or practical plate above the removal point of the product fraction from the low pressure column. 
     Alternatively or in addition to the compressed oxygen, nitrogen can be obtained as the compressed product. The (additional) product fraction is then removed from the pressure column, if necessary for example liquefied in the top condenser of the pressure column, liquid-pressurized separately from the oxygen-rich fraction and vaporized and heated in the main heat exchanger system. 
     In the lower area a liquid fraction, for example the bottom liquid, is removed from the mixing column, expanded and delivered to the pressure column or to the low pressure column. In the case of feed into the low pressure column, the feed point is preferably above the removal of the oxygen-rich fraction and the return feed of the top fraction from the mixing column, preferably one to twenty theoretical plates above the introduction of the return feed of the top fraction to the mixing column. Before expansion, the liquid fraction from the mixing column is optionally cooled, for example by indirect heat exchange with the product fraction and/or the oxygen-rich fraction. 
     The invention relates moreover to a device for obtaining a compressed product by low-temperature separation of air system which has a pressure column ( 3 ) and a low pressure column ( 4 ) 
     a. with a first feedstock air line for feeding compressed and purified feedstock air via the main heat exchanger system into the pressure column, 
     b. with a liquid transfer line for feed of a fraction from the pressure column into the low pressure column, the liquid transfer line having an expansion means, 
     c. with a means for increasing the pressure of the oxygen-rich fraction from the low pressure column with an outlet which is flow-connected to the mixing column, 
     d. with a supply line for feeding the heat exchange medium into the lower area of the mixing column, 
     e. with a top product line for removing the gaseous top product from the upper area of the mixing column, 
     f. with means for increasing the pressure of a liquid product fraction from the rectification system with an outlet which is flow-connected to the product evaporator which is also connected to the head product line and to the compressed product line 
     wherein 
     g. the product evaporator is formed by the main heat exchanger system. 
     The invention and further details of the invention are explained below using the embodiments shown schematically in the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a first embodiment of the invention with the main heat exchanger system in the form of a single block, 
     FIG. 1A shows a version of FIG. 1 in which the main heat exchanger system is formed by two parallel blocks, 
     FIG. 2 shows another version of FIG. 1, in which only one pump is needed, 
     FIG. 3 shows a fourth embodiment in which in addition to oxygen also nitrogen is internally compressed, 
     FIG. 4 shows a process which combines aspects of FIGS. 2 and 3, 
     FIGS. 5 to  8  show other embodiments which are especially suited for obtaining argon, and 
     FIG. 9 shows the Q-T diagram for the embodiment of FIG.  2 . 
    
    
     For process steps or hardware which agree or correspond to one another in all drawings the same reference numbers or numbers which agree in the last two digits are used. 
     Compressed and purified air  1  is branched in the process shown in FIG. 1 upstream of a main heat exchanger  2  into three component flows  50 ,  60 ,  70 . The air pressure at this point corresponds to the operating pressure of the pressure column  4  plus line losses. 
     The first air flow  50  is cooled in the main heat exchanger  2  against back flows to roughly the dew point temperature and via a line  51  fed into the lower area of a pressure column  3  without pressure-changing measures. 
     Raw oxygen  5  from the bottom of the pressure column  3  is, optionally after supercooling in the supercooling countercurrent heat exchanger  6 —throttled ( 7 ) into the low pressure column  4 . Top nitrogen  8  of the pressure column  3  is routed via the line  9  into a main condenser  10  and liquefied there against vaporizing bottom liquid of the low pressure column  4 . The condensate  11  is delivered at least in part via the line  12  as reflux to the pressure column  3 . Another part can be obtained as liquid nitrogen product  13 . 
     Part  35  of the top nitrogen  8  of the pressure column  3  is routed directly to the main heat exchanger  2  and recovered as gaseous compressed nitrogen product  36 . 
     From an intermediate point of the pressure column  3  nitrogen-rich liquid  14  is removed, supercooled in the supercooling countercurrent heat exchanger  6  and delivered via a butterfly valve  15  of the low pressure column  4  at the top as reflux. 
     At the top of the low pressure column  4  a nitrogen-rich residual gas  16  is withdrawn and heated to roughly ambient temperature in the heat exchangers  6  and  2 . The hot residual gas  17  can be used for example as regeneration gas in a cleaning device which is not shown for the feedstock air  1 . 
     In the bottom of the low pressure column  4  impure oxygen with an oxygen content of 95% by mole is produced. At least part  19  of the bottom liquid  18  of the low pressure column  4  forms the product fraction in the sense of the invention. It is brought by a pump  20  to roughly the product pressure of for example 7.4 bar and routed via a line  21  to the cold end of the main heat exchanger  2 . There, in succession, it is heated to the boiling point, vaporized and heated to roughly ambient temperature in succession. Finally, the product fraction at  22  is withdrawn as gaseous pressurized product below the product pressure of 7.4 bar. Another part  23  of the bottom liquid  18  of the low pressure column  4  can be obtained as liquid oxygen product. 
     Some (for example three theoretical) plates above the bottom of the low pressure column an oxygen-rich fraction  24  with an oxygen content of for example 88% by mole is removed liquid, pressurized in a pump  25  and after heating in  65  delivered via line  26  to the top of a mixing column  27 . The operating pressure of the mixing column is for example 9.6 bar at the bottom. The gaseous top product  28  of the mixing column  27  has an oxygen content of 83% by mole and is fed into the cold part of the main heat exchanger  2 . There it delivers heat for vaporization of the product flow  21  and for its heating to the boiling point. In indirect heat exchange in the main heat exchanger  2  the top product of the mixing column is condensed and supercooled. The liquid flows via the line  29  and the butterfly valve  30  back into the low pressure column  4 . The feed point is roughly three theoretical plates above the point at which the oxygen-rich fraction  24  is removed. 
     The heat exchange medium for the mixing column  27  is formed by the second component flow  60  of feedstock air. It is brought to roughly above the mixing column pressure in a recompressor  61  (in the example driven by means of external energy) with subsequent aftercooling  62  and is routed via the line  63  to the hot end of the main heat exchanger  2 . The second component flow of air is removed again from the main heat exchanger  2  at an intermediate temperature above the cold end. After further cooling in  65  it is introduced into the bottom area of the mixing column as the heat exchange medium  66 . Both the bottom fraction  31 / 32  as well as the intermediate fraction  33 / 34  of the mixing column  27  are supercooled in  65  and then throttled into the low pressure column  4  at the points corresponding to their respective composition. 
     The same passages are used to cool the second component air flow  63  and to condense and cool the top fraction  28  in the main heat exchanger. The cold and the hot sections of these passages are separated from one another by impermeable horizontal walls (in the drawings symbolized by a single horizontal line  67 ). These walls (so-called sidebars) are located at the point of the intermediate temperature at which the top fraction  28  and the second air part  64  are supplied to or taken from the main heat exchanger. 
     To equalize the insulation and exchange losses and optionally to produce liquid products (for example, via a line  13  and/or a line  23 ) cold is produced by work-performing expansion of one or more process flows. In the embodiment of FIG. 1 for this purpose a third part  70 / 73  of the feedstock air at an intermediate temperature is routed out ( 74 ) of the main heat exchanger  2  and expanded in a turbine  75  to 1.4 bar, performing work. To increase the cold output or to reduce the amount of turbine air the air  70  from the work-performing expansion can be recompressed ( 71 ) to a pressure of for example 8 bar. The recompressor  71  in the example is driven by the mechanical energy produced in the turbine  75 , preferably by direct mechanical coupling of the turbine  75  and the recompressor  71 . The compression heat is removed by indirect heat exchange with a coolant in the aftercooler  72 . The air  76 ,  77  which has been expanded to perform work is fed directly into the low pressure column  4 . 
     In FIG. 1 the main heat exchanger system in the sense of the invention is formed by a single block  2  which was called the main heat exchanger above. In contrast, in the process which is shown in FIG. 1A, the main heat exchanger system is formed by two separate blocks  102 ,  102   b.  In  102   a,  the main heat exchanger in the narrower sense, the gaseous product flows  35 ,  16  are heated against the first and third air flow  50 ,  73 . In the oxygen heat exchanger  102   b  solely the liquid product flow is heated and vaporized, in countercurrent to the top fraction  28  of the mixing column  27  and to the second air flow  63 . 
     The procedure from FIG. 1A is more favorable in terms of hardware because only the oxygen heat exchanger  102   b  need be designed for the high pressure of the second component flow  63  of air. This approach-is recommended for smaller plants. Complete integration of the two heat exchange processes as shown in FIG. 1 is more favorable in terms of energy and is thus more advantageous for larger plants. 
     The process from FIG. 2 differs from the process shown in FIG. 1 by saving one pump ( 25  in FIG.  1 ). This is done by withdrawing ( 218 ,  218   a ) the product fraction  21  and the oxygen-rich fraction  224 / 226  jointly from the bottom of the low pressure column  4  and pressurizing them in a pump  220 . The high pressure liquid  218   b  is then divided into a product flow  21  and feedstock liquid  224  for the mixing column  27 . (The apparatus which are shown in the drawings as individual pumps are generally made as a pair of pumps for redundancy purposes). 
     FIG. 3 likewise agrees for the most part with FIG.  1 . In this process, however, the gaseous compressed nitrogen product  336  is obtained at a higher pressure which is clearly above the operating pressure of the pressure column  3 . The line  335  is connected to the outlet and not the inlet (see  35  in FIG. 1) of the main condenser  10 . The liquid nitrogen  335  is brought to the required product pressure (for example, 6 to 25 bar) in another pump  337  and heated and vaporized in the main heat exchanger  2 . To do this of course the other flows must be adapted accordingly, especially the amount of high pressure air  63  compared to FIG. 1 must be increased. Thus, with the process as claimed in the invention nitrogen can be produced under high pressure more economically without an additional gas compressor. 
     Compressed nitrogen production  335 ,  337  as shown in FIG. 3 is combined in FIG. 4 with the joint compression  218   a,    220  of the oxygen-rich fraction and product fraction. In one version of the process from FIG. 4 the internal nitrogen compression  335 / 337  is carried out without internal oxygen compression, i.e. the pump  220  is used only to deliver liquid to the top of the mixing column and not to produce a gaseous oxygen product. 
     The process of the invention is suited not only for obtaining impure oxygen, but also allows product purities of 98% by mole or more (for example 98 to 99.9%, preferably 98 to 99.5%) in the oxygen product  22 . In this-case argon production can be connected, as shown in FIG.  5 . Here a conventional raw argon column  538  is connected to an intermediate point of the low pressure column ( 539 ,  540 ). The argon transition  539 / 540  is between the feed points of the two liquids  30 ,  34  from the mixing column  27 . The top condenser  541  of the raw argon column can be operated, as usual, with raw oxygen  5  downstream of the supercooling  6  (not shown). The raw argon product  542  is preferably further purified, for example in a pure argon column which is likewise not shown. 
     To increase the argon yield, it is possible to eliminate direct introduction of air into the low pressure column  4  ( 77  in FIG. 5) by expanding the third component flow  73  of the feedstock air in the turbine  75  to roughly the operating pressure of the pressure column  3 , as shown in FIG.  6 . The turbine exhaust gas  676  is then supplied ( 677 ) to the pressure column  3 , in the example jointly with the direct air (first component flow  51  of air). 
     If the cold output achieved in FIG. 6 is not enough, the pressure ratio on the turbine  75  must be increased. As shown in FIG. 7, this can be done without using an additional machine by using the externally driven recompressor for the mixing column air  763  in addition for increasing the pressure in the turbine air  770 . The turbine  75  expands in the example to the low pressure column pressure, thus especially high liquid production is possible. 
     In FIG. 8 pure nitrogen  843 - 844 - 845  is also obtained in the low pressure column  4 . To do this, part  814  of the liquid nitrogen  11  from the main condenser  10  is supercooled in  6  and delivered via a butterfly valve  815  as reflux to the low pressure column  4 . (The intermediate discharge point  14  shown in the other embodiments on the pressure column can be omitted here). Impure nitrogen (nitrogen-rich residual gas)  816  is removed from the intermediate point of the low pressure column underneath the pure nitrogen section  846 . 
     The liquid nitrogen product  813  is withdrawn from the low pressure column  4  in FIG.  8 . Moreover, the methods for obtaining compressed nitrogen of FIG. 1 ( 35 - 36 ) and FIG. 3 ( 335 - 337 - 338 - 336 ) are implemented at the same time. Thus gaseous nitrogen ( 845 ,  36 ,  336 ) can be made available under a total of three different pressures without an additional gas compressor having to be used. 
     The special measures of FIGS. 6 to  8  can also be used fundamentally without argon recovery (raw argon column  538 ). 
     The following numerical examples in Tables 1 and 2 relate to the embodiment from FIG.  2 . They relate to two design cases with different purity of the oxygen product. 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 O 2 content 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 Amount 
                 Pressure 
                 Temperature 
                 in % 
               
               
                   
                 No. 
                 in Nm 3 /h 
                 in bar 
                 in K 
                 by mole 
               
               
                   
               
               
                 total air 
                  1 
                 183117 
                  5.40 
                 290.0 
                 20.95% 
               
               
                 1. 1st component 
                  51 
                 113445 
                  5.32 
                 101.9 
                 20.95% 
               
               
                 flow before feed 
               
               
                 into the pressure 
               
               
                 column 
               
               
                 2. 2nd component 
                  63 
                  53540 
                  9.60 
                 290.0 
                 20.95% 
               
               
                 flow upstream 
               
               
                 of the main heat 
               
               
                 exchanger system 
               
               
                 2. component 
                  66 
                  53540 
                  9.52 
                 107.6 
                 20.95% 
               
               
                 flow upstream of 
               
               
                 mixing column 
               
               
                 3. 3rd component 
                  74 
                  15971 
                  7.68 
                 142.8 
                 20.95% 
               
               
                 flow upstream 
               
               
                 of turbine 
               
               
                 3. 3rd component 
                  76 
                  15971 
                  1.40 
                  92.8 
                 20.95% 
               
               
                 flow downstream 
               
               
                 of turbine 
               
               
                 bottom liquid 
                  31 
                  32774 
                  9.51 
                 107.4 
                 37.79% 
               
               
                 of mixing column 
               
               
                 intermediate 
                  33 
                  53304 
                  9.51 
                 111.0 
                 61.84% 
               
               
                 liquid of mixing 
               
               
                 column 
               
               
                 oxygen upstream 
                 218a 
                  77569 
                  1.40 
                  92.6 
                 95.00% 
               
               
                 of the pump 
               
               
                 oxygen down- 
                 218b 
                  77569 
                 11.00 
                  93.3 
                 95.00% 
               
               
                 stream of the 
               
               
                 pump 
               
               
                 oxygen-rich 
                 226 
                  77569 
                 10.89 
                 116.9 
                 95.00% 
               
               
                 fraction upstream 
               
               
                 of the mixing 
               
               
                 column 
               
               
                 oxygen product 
                  22 
                  38000 
                  7.38 
                 287.3 
                 95.00% 
               
               
                 compressed nitro- 
                  36 
                    1 
                  5.16 
                 287.3 
                  0.95% 
               
               
                 gen product 
               
               
                 residual gas 
                  17 
                  22001 
                  1.24 
                 287.3 
                  1.54% 
               
               
                 liquid nitro- 
                  13 
                    1 
                  1.39 
                  80.3 
                  2.28% 
               
               
                 gen product 
               
               
                 liquid nitro- 
                  23 
                    1 
                  1.35 
                  91.0 
                 95.00% 
               
               
                 gen product 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 O 2 content 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 Amount 
                 Pressure 
                 Temperature 
                 in % 
               
               
                   
                 No. 
                 in Nm 3 /h 
                 in bar 
                 in K 
                 by mole 
               
               
                   
               
               
                 total air 
                  1 
                 202839 
                  5.40 
                 290.0 
                 20.95% 
               
               
                 1. 1st component 
                  51 
                 128022 
                  5.32 
                 108.8 
                 20.95% 
               
               
                 flow before feed 
               
               
                 into the pressure 
               
               
                 column 
               
               
                 2. 2nd component 
                  63 
                  58713 
                 18.30 
                 290.0 
                 20.95% 
               
               
                 flow upstream 
               
               
                 of the main heat 
               
               
                 exchanger system 
               
               
                 2. component 
                  66 
                  58713 
                 18.22 
                 118.2 
                 20.95% 
               
               
                 flow upstream of 
               
               
                 mixing column 
               
               
                 3. 3rd component 
                  74 
                  15943 
                  8.80 
                 179.8 
                 20.95% 
               
               
                 flow upstream 
               
               
                 of turbine 
               
               
                 3. 3rd component 
                  76 
                  15943 
                  1.39 
                 113.7 
                 20.95% 
               
               
                 flow downstream 
               
               
                 of turbine 
               
               
                 bottom liquid 
                  31 
                  39656 
                 18.01 
                 118.0 
                 33.00% 
               
               
                 of mixing column 
               
               
                 intermediate 
                  33 
                  57370 
                 18.01 
                 123.0 
                 61.09% 
               
               
                 liquid of mixing 
               
               
                 column 
               
               
                 oxygen upstream 
                 218a 
                  84828 
                  1.40 
                  92.8 
                 90.50% 
               
               
                 of the pump 
               
               
                 oxygen down- 
                 218b 
                  84828 
                 19.00 
                  94.2 
                 90.50% 
               
               
                 stream of the 
               
               
                 pump 
               
               
                 oxygen-rich 
                 226 
                  84828 
                 18.89 
                 130.0 
                 90.50% 
               
               
                 fraction upstream 
               
               
                 of the mixing 
               
               
                 column 
               
               
                 oxygen product 
                  22 
                  38000 
                 14.88 
                 287.0 
                 99.35% 
               
               
                 compressed nitro- 
                  36 
                    1 
                  5.16 
                 287.0 
                  2.40% 
               
               
                 gen product 
               
               
                 residual gas 
                  17 
                  22001 
                  1.24 
                 287.0 
                  2.86% 
               
               
                 liquid nitro- 
                  13 
                    1 
                  1.39 
                  80.5 
                  5.71% 
               
               
                 gen product 
               
               
                 liquid nitro- 
                  23 
                    1 
                  1.35 
                  91.0 
                 90.50% 
               
               
                 gen product 
               
               
                   
               
            
           
         
       
     
     FIG. 9 shows the heat exchange diagram (Q-T diagram) for the main heat exchanger system  2  of the process as shown in FIG. 2 (Table 1). 
     The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples. 
     The entire disclosure of all applications, patents and publications, cited above and below, and of corresponding German Application No. 101 39 727.5, filed Aug. 13, 2001 is hereby incorporated by reference. 
     From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.