Hydrogen generation process using partial oxidation/steam reforming

Abstract

Partial oxidation/steam reformers ( 222 ) which use heat integrated steam cycles and steam to carbon ratios of at least about 4:1 to enable efficient operation at high pressures suitable for hydrogen purification unit operations such as membrane separation ( 234 ) and pressure swing adsorption.

1 . A process for generating hydrogen at a pressure of at least about 400 kPa absolute comprising supplying as feed to a partial oxidation/steam reforming zone hydrocarbon-containing feedstock, air and steam, wherein free oxygen is provided in a mole ratio to carbon in the feedstock of between about 0.4:1 to 0.6:1 and steam is provided in a mole ratio to carbon in the feedstock in an amount of at least about 4:1; maintaining said zone under partial oxidation/steam reforming conditions including said pressure to partially oxidize a portion of the feedstock to generate heat and to reform a portion of said feedstock to generate hydrogen whereby a reforming effluent stream comprising hydrogen, carbon monoxide and carbon dioxide is provided; and cooling the reforming effluent stream by indirect heat exchange with a stream containing liquid water to provide a steam-containing stream at a temperature of at least about 300° C. which is cycled to the partial oxidation/steam reforming zone wherein at least about 40 percent of the steam in the feed mixture is produced by said indirect heat exchange. 
     
     
         2 . The process of  claim 1  wherein said partial oxidation/steam reforming conditions comprise a temperature of between about 640° and 730° C. and the reforming effluent contains less than about 5 mole percent carbon monoxide (dry basis). 
     
     
         3 . The process of  claim 2  wherein the carbon monoxide content of the reforming effluent is reduced by at least one subsequent unit operation. 
     
     
         4 . The process of  claim 3  wherein said at least one subsequent unit operation comprises pressure swing adsorption. 
     
     
         5 . The process of  claim 4  wherein prior to said pressure swing adsorption, said effluent is subjected to water gas shift conditions including water gas shift temperatures in the presence of water gas shift catalyst sufficient to reduce the concentration of carbon monoxide in the reforming effluent to less than about 2 mole percent (dry basis). 
     
     
         6 . The process of  claim 4  wherein the pressure swing adsorption provides a purge stream and said purge stream is combusted to provide combustion gas which is used to provide heat for reforming. 
     
     
         7 . The process of  claim 6  wherein the combustion gas heats by indirect heat exchange a liquid water containing stream to generate steam for supplying to the reforming zone. 
     
     
         8 . The process of  claim 1  wherein the steam-containing stream is at a temperature of about 450° to 600° C. 
     
     
         9 . The process of  claim 1  wherein the cooled reforming effluent stream is subjected to at least one purification unit operation which unit operation provides a purified hydrogen stream and a reject stream comprising nitrogen, carbon dioxide, carbon monoxide and hydrogen; said reject stream is combusted to provide combustion gas which is used to provide heat for reforming; and at least about 90 percent of the steam supplied to the partial oxidation/steam reforming zone is generated by cooling the reforming effluent stream and by indirect heat exchange with the combustion gas. 
     
     
         10 . A process for generating hydrogen at a pressure of at least about 400 kPa absolute comprising supplying as feed to a partial oxidation/steam reforming zone hydrocarbon-containing feedstock, air and steam, wherein free oxygen is provided in a mole ratio to carbon in the feedstock of between about 0.4:1 to 0.6:1 and steam is provided in a mole ratio to carbon in the feedstock in an amount of at least about 4:1; maintaining said zone under partial oxidation/steam reforming conditions including said pressure to partially oxidize a portion of the feedstock to generate heat and to reform a portion of said feedstock to generate hydrogen whereby a reforming effluent stream comprising hydrogen, carbon monoxide and carbon dioxide is provided; cooling the reforming effluent stream by indirect heat exchange with a stream containing liquid water to provide a steam-containing stream at a temperature of at least about 300° C., which is cycled to the partial oxidation/steam reforming zone wherein at least about 40 percent of the steam in the feed mixture is produced by said indirect heat exchange; and subjecting the cooled reforming effluent stream to at least one purification unit operation. 
     
     
         11 . The process of  claim 10  wherein the purification unit operation provides a purified hydrogen stream and a reject stream comprising nitrogen, carbon dioxide, carbon monoxide and hydrogen, and said reject stream is combusted to provide combustion gas which is used to provide heat for reforming. 
     
     
         12 . The process of  claim 10  wherein the purification unit operation comprises a membrane separation wherein the purified hydrogen stream is the permeate and the reject stream is the retentate. 
     
     
         13 . The process of  claim 10  wherein the purification unit operation comprises a pressure swing adsorption and the reject stream is a purge stream. 
     
     
         14 . The process of  claim 11  wherein the combustion gas heats by indirect heat exchange at least the steam-containing stream from the indirect heat exchange to a temperature in the range of 500° to 750° C. 
     
     
         15 . The process of  claim 14  wherein at least a portion of the air for the feed is admixed with the steam-containing stream prior to the indirect heat exchange with the combustion gas. 
     
     
         16 . The process of  claim 11  wherein the combustion gas heats by indirect heat exchange a liquid water-containing stream to generate steam for supplying to the reforming zone, and at least 90 percent of the steam supplied to the reformer is produced by the indirect heat exchange with the reforming effluent and with the combustion gas. 
     
     
         17 . The process of  claim 11  wherein the steam to carbon ratio is about 4.5:1 to 6.5:1. 
     
     
         18 . The process of  claim 10  wherein the reforming effluent is cooled to a temperature within the range of about 250° to 400° C. by a first indirect heat exchange with a stream comprising liquid water wherein steam is generated and then further cooled in a second indirect heat exchange with a stream comprising liquid water wherein steam is generated. 
     
     
         19 . The process of  claim 11  wherein at least a portion of the hydrocarbon-containing feedstock for the feed is admixed with the steam-containing stream prior to the indirect heat exchange with the combustion gas. 
     
     
         20 . An efficient, integrated process for generating hydrogen from a hydrocarbon-containing feedstock in the essential absence of a shift reaction zone comprising:
 a. passing to a partial oxidation reformer at a pressure of between about 400 and 1500 kPa absolute feed comprising hydrocarbon-containing feedstock, air, and steam wherein the molar ratio of steam to carbon in the hydrocarbon-containing feedstock is at least about 4:1, said reformer being at partial oxidation/steam reforming conditions to provide a reforming effluent stream comprising at least about 40 volume percent (dry basis) hydrogen, nitrogen, steam, carbon monoxide and carbon dioxide;   b. cooling the reforming effluent stream by indirect heat exchange with a stream containing liquid water to provide a steam-containing stream which is cycled to the partial oxidation/steam reforming zone wherein at least about 40 percent of the steam in the feed mixture is produced by said indirect heat exchange;   c. further cooling the cooled reforming effluent stream to pressure swing adsorption conditions, said cooling being sufficient to condense water,   d. during or after the further cooling, separating the condensed water;   e. subjecting the further cooled reforming effluent stream to pressure swing adsorption such that a purified hydrogen stream is produced which (i) is at least about 98 mole percent hydrogen, and (ii) contains less than about 10 ppmv carbon monoxide, and a sorption purge gas is produced at a pressure between about 5 and 100 kPa gauge which comprises less than about 30 volume percent hydrogen (dry basis) and nitrogen, carbon dioxide and carbon monoxide;   f. withdrawing at least a portion of the purified hydrogen stream as hydrogen product;   g. combusting in the substantial absence of added fuel, the sorption purge gas with an oxygen-containing gas in the presence of an oxidation catalyst to provide a combustion gas having a temperature of less than about 800° C.;   h. subjecting the combustion gas to at least one indirect heat exchange with a liquid water-containing stream to generate steam which is cycled to the reformer; and   i. exhausting the cooled combustion gas,   
       wherein the Net Hydrogen Efficiency is at least about 50 percent. 
     
     
         21 . The process of  claim 20  wherein in step (g) at least two indirect heat exchanges occur wherein the combustion gas is in a first heat-exchange with steam and the oxygen-containing stream and in a subsequent heat exchange, the combustion gas is used to vaporize water for steam which is used as feed to the partial oxidation reformer. 
     
     
         22 . The process of  claim 20  wherein the pressure swing absorption comprises four absorbent beds and two pressure equalizations. 
     
     
         23 . The process of  claim 20  wherein the purified hydrogen product comprises at least about 99.9 volume percent hydrogen. 
     
     
         24 . The process of  claim 20  wherein the pressure drop through the oxidation catalyst of step (g) is less than 5 kPa. 
     
     
         25 . A hydrogen generator comprising:
 a) a partial oxidation reformer containing partial oxidation and reforming catalysts and adapted to provide a hydrogen-containing reformate, said reformer having an inlet section and an outlet section,   b) a hydrocarbon-containing feed supply line in fluid communication with the inlet section of the partial oxidation reformer,   c) an oxygen-containing feed supply line in fluid communication with the inlet section of the partial oxidation reformer,   d) an indirect heat exchanger in fluid communication with the outlet section of the partial oxidation reformer said heat exchanger having a hot side through which the hydrogen-containing reformate passes and a cool side in fluid communication with at least a liquid water supply, said heat exchanger adapted to provide a steam-containing stream,   e) a steam line adapted to direct the steam-containing stream from the heat exchanger to the inlet section of the partial oxidation reformer,   f) a cooler adapted to receive cooled reformate from the hot side of the heat exchanger and provide a further cooled reformate and condensed water,   g) means to remove condensed water from the further cooled reformate,   h) a pressure swing adsorber adapted to receive the further cooled reformate from the cooler, which reformate has had condensed water removed, and provide a hydrogen product stream and a purge stream containing hydrogen,   i) a combustor containing oxidation catalyst adapted to receive said purge stream and an oxygen-containing gas and provide a combustion gas, and   j) at least one indirect heat exchanger having a hot side adapted to receive said combustion gas and a cold side in fluid communication with a liquid water line adapted to provide steam, said heat exchanger being in fluid communication with the partial oxidation reformer.   
     
     
         26 . The generator of  claim 25  in which the oxidation catalyst in the combustor is adapted to serve as a flame holder. 
     
     
         27 . The generator of  claim 25  in which the pressure swing adsorber has four adsorbent beds. 
     
     
         28 . A process for generating hydrogen comprising contacting at reforming temperature a mixture of hydrocarbon-containing feedstock which also contains sulfur compound, air and steam with an effective amount of at least one catalyst for partially combusting feedstock to generate heat and for reforming said feedstock to generate hydrogen whereby a reforming effluent stream comprising hydrogen, carbon monoxide, carbon dioxide, nitrogen and hydrogen sulfide is provided, wherein:
 a. said contacting is at a pressure greater than about 400 kPa absolute, and   b. steam is provided in a mole ratio to carbon in the feedstock in an amount of at least about 4:1; and   
       cooling the reforming effluent stream to a temperature suitable for hydrogen sulfide sorption said cooling comprising indirect heat exchange with water to generate at least a portion of the steam for the feed to the reformer, and contacting the cooled reforming effluent stream with a hydrogen sulfide sorbent to provide a stream having a reduced hydrogen sulfide concentration. 
     
     
         29 . The process of  claim 28  wherein the cooled reforming effluent stream is subjected to pressure swing adsorption to provide a hydrogen stream having reduced carbon monoxide and carbon dioxide concentrations and a purge stream containing hydrogen, carbon dioxide and carbon monoxide. 
     
     
         30 . The process of  claim 29  wherein the cooled reformer effluent stream contacts the hydrogen sulfide sorbent prior to being subjected to pressure swing adsorption. 
     
     
         31 . The process of  claim 30  wherein the cooled reformer effluent stream is subjected to pressure swing adsorption and hydrogen sulfide is sorbed and contained in the purge stream, and the purge stream is contacted with the hydrogen sulfide sorbent. 
     
     
         32 . The process of  claim 31  wherein the hydrocarbon-containing feedstock contains organosulfides and at least one of carbonyl sulfide and hydrogen sulfide and is contacted with a sorbent for organosulfides prior to reforming to provide a hydrocarbon-containing feedstock comprising at least one of hydrogen sulfide and carbonyl sulfide. 
     
     
         33 . The process of  claim 28  wherein the hydrocarbon-containing feedstock contains organosulfides and at least one of carbonyl sulfide and hydrogen sulfide and is contacted with a sorbent for organosulfides prior to reforming to provide a hydrocarbon-containing feedstock comprising at least one of hydrogen sulfide and carbonyl sulfide. 
     
     
         34 . An autothermal reforming process for generating hydrogen at a pressure of at least about 400 kPa absolute comprising supplying as feed to a partial oxidation/steam reforming zone hydrocarbon-containing feedstock, air and steam, wherein free oxygen is provided in a mole ratio to carbon in the feedstock of between about 0.4:1 to 0.6:1 and steam is provided in a mole ratio to carbon in the feedstock in an amount of at least about 4:1; maintaining said zone under partial oxidation/steam reforming conditions including said pressure to partially oxidize a portion of the feedstock to generate heat and to reform a portion of said feedstock to generate hydrogen whereby a reforming effluent stream comprising hydrogen, carbon monoxide and carbon dioxide is provided; and cooling the reforming effluent stream by indirect heat exchange with a stream containing liquid water to provide a steam-containing stream at a temperature of at least about 300° C. which is cycled to the partial oxidation/steam reforming zone wherein at least about 40 percent of the steam in the feed mixture is produced by said indirect heat exchange and separating a sufficient portion of the reformate and combusting said portion to provide a hot combustion gas to (i) heat at least a portion of the feed by indirect heat exchange with the hot combustion gas to provide an average temperature of the feed to the partial oxidation/steam reforming zone of at least about 450° C. and to provide a cooler combustion gas and (ii) generate the remaining steam to provide said steam to carbon ratio by indirect heat exchange with the cooler combustion gas. 
     
     
         35 . The process of  claim 34  wherein the separation of the reformate is by membrane and the portion combusted is retentate. 
     
     
         36 . The process of  claim 34  wherein the separation of the reformate is by pressure swing adsorption and the portion combusted is purge. 
     
     
         37 . The process of  claim 34  wherein the Net Hydrogen Efficiency is greater than about 50 percent.