Patent Publication Number: US-6339939-B1

Title: Process for the conversion of a flow containing hydrocarbons by partial oxidation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a division of application Ser. No. 09/134,671, filed Aug. 14, 1998, now U.S. Pat. No. 6,110,980. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a process and to a plant for the conversion of a flow containing hydrocarbons by partial oxidation. 
     BACKGROUND OF THE INVENTION 
     In this type of process, a flow containing hydrocarbons, typically natural gas, is converted into synthesis gas after partial oxidation with oxygen or oxygen-enriched air. 
     This conversion can be carried out by a reforming process, for example of the ATR (Autothermal Reforming) type, which mates it possible to produce a synthesis gas. Following catalytic conversion, the synthesis gas is converted into liquid hydrocarbons (kerosene, diesel, naphtha). 
     This type of process is described in U.S. Pat. No. 5,628,931, WO 93 15999, GB 2249555, GB 2183672, EP 214 432 A. 
     SUMMARY OF THE INVENTION 
     The present invention also relates to a process and to a plant for the separation of air by cryogenic distillation and, in particular, to those processes and plants which make it possible to produce oxygen. 
     According to one subject of the invention, a process is provided for the conversion of a flow containing hydrocarbons by partial oxidation with oxygen, 
     characterized in that the oxygen needed for the conversion is separated by cryogenic distillation from air in a single column installed on a boat. 
     According to other aspects of the invention, 
     the flow containing hydrocarbons is methane, natural gas or LPG, 
     the oxygen is drawn off from the single column in liquid form, pressurized and vaporized, 
     the conversion is carried out by a reforming process producing a synthesis gas, which reforming is followed by catalytic conversion of the synthesis gas into liquid hydrocarbons, 
     the nitrogen needed for the process is produced by adsorption or permeation. 
     According to another subject of the invention, a plant is provided for the conversion of a flow containing hydrocarbons, comprising a partial-oxidation unit fed with oxygen, 
     characterized in that it comprises air separation apparatus including a single column ( 8 ) installed on a boat. 
     Oxygen is generally produced by the distillation of air in a double column. When this column is placed on an unstable support, such as the deck of a boat, the quality of the distillation is degraded because the plates or packing contained in the column cannot function correctly. 
     “Nitrogen for Inerting” Tank and Bulk Carrier, November 1973 and “Distillation Problems on a Floating Plant” CEP, November 1982, describe solutions for improving distillation on a boat. 
     The object of this invention is to provide an air separation process which is compatible with the working conditions on a boat. 
     According to another subject of the invention, a process is provided for the separation of air by cryogenic distillation in a single column, in which 
     i) air to be distilled is sent into a single column where it is separated into a nitrogen-enriched vapour and an oxygen-enriched liquid, 
     ii) the base of the column is heated by means of a boiler, 
     characterized in that at least some of the oxygen-enriched liquid is drawn off, pressurized and vaporized by heat exchange with a pressurized flow. 
     According to other aspects of the invention, the fluid used to heat the boiler is nitrogen or at least some of the air to be distilled, 
     the air sent to the boiler comes from a turbine, optionally coupled to a booster, 
     the pressurized flow is air at a boosted pressure or compressed nitrogen, 
     vapour is drawn off from the head of the column and at least some of it is compressed, 
     at least some of the compressed nitrogen is recycled to the column, 
     oxygen-enriched liquid is produced, 
     at least some of the air intended for the column is cooled to an intermediate temperature in a heat exchanger, before being expanded, optionally to the column pressure, in a turbine. 
     According to another subject of the invention, a plant is provided for the separation of air by cryogenic distillation, comprising, 
     a single column, 
     means for feeding the single column with air, 
     a boiler at the base of the single column, 
     means for sending a heating fluid to the boiler, 
     characterized in that it comprises 
     means for drawing off an oxygen-enriched liquid from the base of the single column, 
     means for pressurizing at least some of the liquid, 
     means for vaporizing at least some of the pressurized liquid by heat exchange with a pressurized flow. 
     According to other aspects of the invention, 
     the boiler is heated with nitrogen or at least some of the air to be distilled, 
     the boiler is connected to a turbine, 
     the pressured flow is air at a boosted pressure or compressed nitrogen, 
     means are provided for compressing a nitrogen-enriched flow drawn off from the head of the column, 
     the single column contains plates or structured packing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other aspects of the invention will now be described with reference to FIGS. 1 to  4 , which are diagrams of processes according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIG. 1, an air flow is compressed by the compressor  1  to 4.5 bar and purified in the unit  2  to remove water and CO 2 . 
     A first fraction of the air has its pressure raised to  6  bar by the booster  4 , is partially cooled in the exchanger  6  and is expanded in the turbine  5  to 1.4 bar. The fraction is then supercooled in the exchanger  10  before being sent to the column  8  installed on a boat  31 . 
     A second air fraction has its pressure raised to 70 bar in the booster  3  and condensed at least partially in the exchanger  6 . 
     The rest of the air passes fully through the exchanger  6 , condenses at least partially in the base boiler  7  and is sent to the head of the column  8 , after having been supercooled and expanded in a valve. 
     A flow containing oxygen with a purity of at least 95% in liquid form is drawn off from the base of the column  8 , pumped to 36 bar (in  9 ) and vaporized in the exchanger  6  by heat exchange with air at a boosted pressure of 70 bar. 
     Nitrogen-enriched vapour is drawn off from the head of the column  8  and heated in the exchangers  10  and  6 . 
     FIG. 2 shows the booster turbines  4 ,  5 , but the booster  3  is replaced by a nitrogen cycle. 
     Nitrogen-enriched vapour is heated to ambient temperature and compressed to 70 bar by a compressor  30 . At least some of the compressed nitrogen is recycled to the column after having been cooled in the exchangers  6  and  10 . 
     The process may be simplified (FIG. 3) to use a single air compressor. All of the air is compressed by the compressor  4  to about 28 bar and then cooled in the exchanger  6  to an intermediate temperature, at which some of the air is drawn off, expanded and sent into the boiler  7  where it condenses at least partially before being expanded in a valve and sent to the head of the column  8 . The rest of the air continues to cool and is liquefied in the exchanger  6 , is supercooled in the exchanger  10  and is sent to the column, after having been mixed with the other part of the air. 
     FIG. 4 shows a process diagram according to the invention, in which the air  103  is distilled in an air separation unit  104  such as those illustrated in FIGS. 1 to  3 . 
     Vaporized liquid oxygen  105  is sent to a partial-oxidation unit  102 , also supplied with natural gas  101 . The synthesis gas  107  produced in this way undergoes a catalytic conversion step  109  (of the FISCHER-TROPSCH type), in order to produce liquid hydrocarbons (kerosene, diesel and/or naphtha).