INCREASING HYDROGEN RECOVERY FROM CO + H2 SYNTHESIS GAS

Abstract

The GTLpetrol Process for Maximum H2 Production. The GTLpetrol process uses a proprietary combination of two stage pressure swing adsorption hydrogen purification plus a C02 condensation removal step to give H2 recoveries in the range of 95% to 98% based on H2+CO from synthesis gas generation.

Claims

1. A method, comprising: catalytically shifting carbon monoxide and water to carbon dioxide and hydrogen; removing hydrogen from the carbon dioxide and hydrogen in a first stage pressure swing adsorption (PSA) unit; compressing waste gas from the first PSA unit to an original pressure of the carbon dioxide and hydrogen; drying and cooling the compressed waste gas to at least proximate a freezing point of carbon dioxide to separate the carbon oxide from the compressed waste gas to produce a gas stream; and removing hydrogen from the gas stream using a second PSA unit.

2. The method of claim 1, wherein the hydrogen removed from the carbon dioxide and hydrogen in the first PSA is approximately 88% or greater of the hydrogen.

3. The method of claim 1, wherein the hydrogen removed from the carbon dioxide and hydrogen in the first PSA has less than 50 ppm total impurity.

4. The method of claim 1, wherein the gas stream contain a partial pressure of carbon dioxide of about 6 bar to about 7 bar.

5. The method of claim 1, wherein the hydrogen recovery is at least 95% of total carbon dioxide and hydrogen produced.

Description

DESCRIPTION OF DRAWINGS

[0023] FIG. 1 shows a flowsheet for the hydrogen production process.

[0024] Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

[0025] A CO+H2 synthesis gas stream 11 is produced in a synthesis gas generation system 32 fed with streams of optionally preheated feeds natural gas 34, steam 33, oxygen 35 and a low pressure waste stream 31 at 1.2 bar. The pressure of streams 33, 34 and 35 and the pressure of the product stream 11 can be in the range 25 bar to 100 bar depending on the design of unit 32. In general stream 11 will be the product syngas stream leaving the stream generation unit which is part of the synthesis gas generator 32. It will also contain excess steam, some methane which is unconverted in 32 and a small quantity of nitrogen from the natural gas feed and argon associated with the oxygen feed stream 35. The gas stream 11 passes through a catalyst bed in a catalytic shift converter vessel 1 in which 90% of the CO in the feed stream 11 is converted to H2 by reaction with steam. The exit gas stream is cooled to near ambient temperature in one or more heat exchangers 3 which are used to produce heated boiler feed water or medium pressure steam or a combination of both plus a water cooled heat exchanger 36. Liquid water is separated in 2 leaving as stream 37 and the separated gas stream 16 enters a first multibed pressure swing adsorption unit 4. The first PSA 4 separates 88% of the hydrogen as a product stream 17 with a total impurity level of 20 ppm (molar) leaving a waste gas stream 20 at 1.2 bar pressure. Stream 20 is compressed to approximately the same pressure as stream 11 in a multi-stage centrifugal compressor 5 driven by an electric motor 38. The compressed cooled stream 21 is dried in a desicant dryer 6 with an inlet and outlet regeneration gas 22 and 23. This regeneration stream could be nitrogen from the cryogenic air separation unit providing oxygen to the synthesis gas generation system 32. The dried compressed stream then enters the C02 condensation unit 7. This unit utilises the system described in GTLpetrol US Patent Publication No. 2011/0023539 which is incorporated in its entirety in this description. In unit 7 the compressed and dried PSA 1 waste gas stream is cooled to about −54° C. and the liquid C02 is separated from the gas stream which contains the H2+CO valuable components. The separation can be assisted by using a small liquid C02 stripping column in place of the separator and described in US patent assigned to Air Products. The partial pressure of C02 in the separated gas stream will be 6 bar to 7 bar. The unit 7 includes a C02 refrigeration system which might be part of a C02 compressor, also included in 7, to raise the C02 pressure for delivery into a pipeline at 100 bar to 200 bar pressure. The C02 stream separated and warmed to near ambient temperature is delivered as stream 26. The warmed gas stream 25 is then heated in economiser heat exchanger 8 to a temperature of 2500 C. A steam stream 27 from synthesis gas generation unit 32 is added and the gas plus steam stream 28 enters a second catalytic CO shift reactor 9 where 90% of the CO is converted to H2 and C02 by reaction with steam. The outlet stream 29 is then cooled in the economiser heat exchanger 8 followed by the water cooler 44 to near ambient temperature. Water separator 39 removes the condensed water stream 41 and the exit gas stream 40 enters a second PSA unit 10. This second PSA separates a hydrogen product stream 18 at approximately the same pressure as the H2 product stream from the first PSA. The combined stream of H2 product 19 is about 97% of the molar flow of H2+CO in stream 11.

Example

[0026] The following Table 1 is based on the mass balance given in US Patent Publication No. 2011/0318251 assigned to GTLpetrol which uses a two stage ATR plus parallel GHR reactor system with an integrated gas turbine co-generation power system.

[0027] The first PSA has a H2 recovery of 88%.

[0028] The CO conversion in the first reactor is 90% and in the second reactor is 90%.

[0029] The second PSA has a H2 recovery of 83%. The basis for Table 1 is 100 mols of feed in stream 11.

TABLE-US-00001 TABLE I POINT 11 16 17 20 25 26 40 18 19 31 CO 17.7 1.8 0 1.8 1.8 0 0.2 0 0 0.2 H.sub.2 44.5 60.4 53.2 7.2 7.2 0 8.8 7.3 60.5 1.5 CO.sub.2 3.4 19.3 0 19.3 1.8 17.5 3.4 0 0 3.4 H.sub.2O 33.0 0 0 0 0 0 0 0 0 0 CH.sub.4 1.2 1.2 0 1.2 1.2 0 1.2 0 0 1.2 N.sub.2 + A 0.2 0.2 0 0.2 0.2 0 0.2 0 0 0.2 Pressure bar 77 76 75.6 1.2 77 100 76.5 76 76 1.2 Temp ° C. 32.0 30 30 30 30 30 30 30 30 30 Overall H.sub.2 recovery from CO + H.sub.2 is 97.25%

[0030] A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.