Method for production of a hydrogen rich gas

Abstract

The present disclosure relates to a process plant and a process for production of a hydrogen rich gas, comprising the steps of (a) directing an amount of a synthesis gas comprising at least 15%, 50% or 80% on dry basis of CO and H.sub.2 in combination, a gas comprising steam, and a recycled intermediate product gas to be combined into a first reactor feed gas, (b) directing said first reactor feed gas to contact a first material catalytically active in water gas shift reaction, producing an intermediate product gas, (c) splitting said intermediate product gas in the recycled intermediate product gas and a remaining intermediate product gas, (d) combining said remaining intermediate product gas with a further amount of synthesis gas forming a second reactor feed gas, (e) directing said second reactor feed gas to contact a second material catalytically active in the water gas shift reaction, producing a product gas, characterized in the H.sub.2O:CO ratio in said first reactor feed gas being from 0.5 to 2.0 and the H.sub.2O:CO ratio in said second reactor feed gas being from 0.5 to 2.0. with the associated benefit of distributing the heat development and thus reducing the maximum temperature in the reactors by limiting the extent of reaction of the reacting mixture, and thereby reducing the amount of steam required for limiting methanation.

Claims

1. A process for production of a hydrogen rich gas, comprising the steps of: (a) combining an amount of a synthesis gas comprising at least 15 mol % on dry basis of CO and H.sub.2 in combination, with the discharge gas of an ejector receiving a gas comprising steam as motive gas, and a recycled intermediate product gas as suction gas, into a first reactor feed gas, (b) directing said first reactor feed gas to contact a first material catalytically active in water gas shift reaction, producing an intermediate product gas, (c) splitting said intermediate product gas in the recycled intermediate product gas and a remaining intermediate product gas, (d) combining said remaining, intermediate product gas with a further amount of synthesis gas forming a second reactor feed gas, (e) directing said second reactor feed gas to contact a second material catalytically active in the water gas shift reaction, producing a product gas, characterized in the H.sub.2O:CO ratio in said first reactor feed gas being from 0.5 to 2.0 and the H.sub.2O:CO ratio in said second reactor teed gas being from 0.5 to 2.0.

2. The process according to claim 1 in which said synthesis gas comprises at least 20 mol % on dry basis.

3. The process according to claim 1 in which the first material catalytically active in the water gas shift reaction comprises an element from Group VIb and a non-noble element from Group VIII.

4. The process according to claim 1 in which the second material catalytically active in the water gas shift reaction is different from the first material catalytically active in the water gas shift reaction.

5. The process according to claim 1 in which the maximum temperature of the first and the second material catalytically active in the water gas shift reaction is below 500 C.

6. The process according to claim 1 in which a final product gas is provided by combination of the product gas and an amount of synthesis gas.

7. The process according to claim 1 which comprises an additional step of directing a gas comprising at least an amount of said product gas as a third reactor feed gas to contact a third material catalytically active in the water gas shift reaction, producing a product gas.

8. The process according to claim 1 in which said synthesis gas comprises at least 200 ppm sulfur.

9. The process according to claim 1 in which at least one of said intermediate product gas, said recycled intermediate product gas, and said remaining intermediate product gas is cooled.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a two stage water gas shift process configuration according to the present disclosure, with sequential synthesis gas addition and recycle driven by an ejector.

(2) FIG. 2 shows a traditional two stage water gas shift process configuration according to the prior art.

(3) FIG. 3 shows a two stage water gas shift process configuration according to the prior art, with sequential synthesis gas addition.

(4) FIG. 4 shows a two stage water gas shift process configuration according to the prior art with recycle driven by a compressor

LIST OF ELEMENTS IN THE DRAWINGS

(5) Feed syngas 102, 202, 302, 402 Main stream 106, 206, 306, 406 Bypass to the second bed 108, 308 Feed bypass stream for adjustment 110, 210, 310, 410 Combined feed stream 114, 214, 314, 414 Bypass syngas stream 108, 308 Steam 120, 220, 320, 420 Recycle stream 122, 422 Intermediate product stream 124, 224, 324, 424 Recycled intermediate product stream 126, 426 Remaining intermediate product stream 128, 428 Cooled intermediate product stream 328 Second reactor feed gas stream 130, 230, 330, 430 Product gas stream 132, 232, 332, 432 Shifted and adjusted product stream 136, 236, 336, 436 First water gas shift reactor 150, 250, 350, 450 Waste heat boiler 152, 252, 352, 452 Ejector 154 Second water gas shift reactor 160, 260, 360, 460 Heat exchanger 162, 262, 362, 458, 462 Compressor 456

(6) FIG. 1 shows a two stage water gas shift process configuration according to the present disclosure, with sequential synthesis gas addition and recycle driven by an ejector. A feed syngas 102 is first split into a main stream 106, a bypass to the second reactor 108, and a feed bypass stream for adjustment 110. The main stream 106 is heated in heat exchanger 162 and combined with a recycle stream 122. The combined feed stream 114 is directed to the first water gas shift reactor 150 followed by cooling of the intermediate product stream 124 in waste heat boiler 152 e.g. with steam production. An amount of the intermediate product stream is recycled 126 around the first reactor is drawn off by ejector 154 using steam 120 as motive stream. The remaining intermediate product stream 128 is combined with the bypass syngas stream 108 to form the second reactor feed gas stream 130 which is directed to the second water gas shift reactor 160. The product gas stream 132 is cooled in heat exchanger 162 before it optionally is combined with the feed bypass stream for adjustment 110 to form the final shifted and adjusted product stream 136.

(7) The combination of the product gas stream 132 with the feed bypass stream for adjustment 110 is optional and may be omitted e.g. if a high module (i.e. a high amount of H.sub.2 relative to CO) product gas is required, especially if pure hydrogen is produced.

(8) FIG. 2 shows a traditional two stage water gas shift process lay-out according to the prior art. A feed syngas 202 is first split into a main stream 206 and a feed bypass stream 210. The main stream 206 is heated in heat exchanger 262 and combined with a stream of steam 220. The combined feed stream 214 is directed to the first water gas shift reactor 250 followed by cooling of the intermediate product stream 224 in waste heat boiler 252 with steam production. This cooled intermediate product stream is directed to the second water gas shift reactor 260 as a second reactor feed gas stream 230. The product gas stream 232 is cooled in heat exchanger 262 before it is combined with the feed bypass stream for adjustment 210 to form the final shifted and adjusted product stream 236.

(9) FIG. 3 shows a two stage water gas shift process lay-out with sequential synthesis gas addition. A feed syngas 302 is first split into a main stream 306, a bypass to the second bed 308, and a feed bypass stream for adjustment 310. The main stream 306 is heated in heat exchanger 362 and combined with a stream of steam 320. The combined feed stream 314 is directed to the first water gas shift reactor 350 followed by cooling of the intermediate product stream 324 in waste heat boiler 352 with steam production. The cooled intermediate product stream 328 is combined with the bypass syngas stream 308 to form the second reactor feed gas stream 330 which is directed to the second water gas shift reactor 360. The product gas stream 332 is cooled in heat exchanger 362 before it is combined with the feed bypass stream for adjustment 310 to form the final shifted and adjusted product stream 336.

(10) FIG. 4 shows a two stage water gas shift process configuration according to the prior art with recycle driven by a compressor. A feed syngas 402 is first split into a main stream 406, and a feed bypass stream for adjustment 410. The main stream 406 is heated in heat exchanger 462 and combined with a stream of steam 420 and a recycle stream 422. The combined feed stream 414 is directed to the first water gas shift reactor 450 followed by cooling of the intermediate product stream 424 in waste heat boiler 452 with steam production. An amount of the intermediate product stream is recycled 426 around the first reactor by compressor 456. The remaining intermediate product stream 428 is cooled in heat exchanger 458 to form the second reactor feed gas stream 430 which is directed to the second water gas shift reactor 460. The product gas stream 432 is cooled in heat exchanger 462 before it is combined with the feed bypass stream for adjustment 410 to form the final shifted and adjusted product stream 436.

EXAMPLES

(11) In Table 1, a feed synthesis gas is characterized, corresponding to a synthesis gas from a single stage dry feed gasifier operated at 1500 C. and 30 bar. The feed flow rate is assumed to be 200.000 Nm3/h.

(12) TABLE-US-00001 TABLE 1 Component Wet molar composition [mole %] CO.sub.2 1 CO 61.9 H.sub.2 32.2 CH.sub.4 0 N.sub.2 + Ar 2.7 H.sub.2S 0.3 H.sub.2O 1.9

(13) Four examples of water gas shift processes on the feed synthesis gas of Table 1 have been evaluated. All examples are based on the feed stream described in Table 1, and with the requirement to produce a product gas with module 3, e.g. with the purpose of producing a synthesis gas which is suitable for production of synthetic natural gas. In Table 2 the examples are characterized by the wet molar compositions and temperatures of selected streams. In Table 3 operational characteristics and costs are summarized.

(14) The catalyst volume, steam consumption, and outlet temperatures has been calculated for four different examples to highlight the benefits of the present disclosure, i.e. using the ejector in combination with a bypass. The design criteria are a module of 3 in the product gas and controlling the outlet temperature of the sour shift beds to avoid excessive methane formation. The four examples are described below.

(15) TABLE-US-00002 TABLE 2 Example 1 Example 2 Stream 114 124 130 132 136 214 224 230 232 236 Temperature [ C.] 242 419 240 347 302 230 460 240 271 233 CO.sub.2 9.9 26.6 20.0 29.6 27.6 0.4 22.6 22.6 25.8 21.5 CO 22.7 6.0 20.3 10.7 14.3 26.0 3.8 3.8 0.7 11.2 H.sub.2 26.0 42.6 39.9 49.4 48.2 13.5 35.7 35.7 38.8 37.7 CH.sub.4 0.02 0.04 0.03 0.09 0.09 0 0.02 0.02 0.02 0.02 H.sub.2O 39.9 23.3 17.8 8.3 7.8 58.7 36.6 36.6 33.4 28.0 Example 3 Example 4 Stream 314 324 330 332 336 414 424 430 432 436 Temperature [ C.] 230 460 240 360 302 238 460 240 294 225 CO.sub.2 0.4 22.6 17.9 29.1 25.2 4.3 25.2 25.2 30.4 25.1 CO 26.0 3.8 16.5 5.3 13.1 28.4 7.4 7.4 2.3 13.0 H.sub.2 13.5 35.7 34.9 46.1 44.2 20.5 41.3 41.3 46.4 43.9 CH.sub.4 0 0.02 0.01 0.04 0.03 0.01 0.05 0.05 0.05 0.04 H.sub.2O 58.8 36.7 29.0 17.8 15.6 45.3 24.4 24.4 19.3 16.2

Example 1

(16) Example 1 according to the present disclosure and FIG. 1 shows a two stage sour shift unit, with recycle via an ejector: Recycle around the first reactor to control outlet temperature to the first reactor, sequential addition of synthesis gas to the second reactor and for adjustment of the module in the final product gas. The feed to the ejector is at 280 C.

Example 2

(17) Example 2 according to FIG. 2 and the prior art shows a two stage sour shift unit, with steam addition to control temperature and sequential addition of synthesis gas for adjustment of the module in the final product gas.

Example 3

(18) Example 3 according to FIG. 3 and the prior art shows a two stage sour shift unit, with steam added to control temperature out of the first reactor, and sequential addition of synthesis gas to the second reactor and for adjustment of the module in the final product gas.

Example 4

(19) Example 4 according to FIG. 4 and the prior art shows a two stage sour shift unit, with recycle using a compressor. The feed to the compressor is at 274 C. The energy consumption from the compressor is not included in the operational cost and an excessive investment is also required for a compressor operating at this temperature.

(20) TABLE-US-00003 TABLE 3 S/CO S/CO Steam Catalyst Index Case Stage 1 Stage 2 consumption volume cost/yr Example 1 1.7 0.9 54% 155% 58% Example 2 2.3 9.6 100% 100% 100% Example 3 2.3 1.8 70% 90% 70% Example 4 1.6 3.3 70% 123% 72%

(21) The key performance metrics and operational costs for the four cases are shown in Table 3. Here it can be seen that the bypass offers both a reduction in catalyst volume and steam consumption in comparison with the 2 stage case of Example 2. The recycle allows for lower steam consumption, however due to the recycle and increased flow rate the catalyst volume increases.

(22) The combination of recycle by ejector and bypass to the second reactor, example 1, allows for even lower steam consumption as well as a lower outlet temperature of the first reactor, and is the only configuration with low S:CO ratio in the feed of both reactors. However, the catalyst volume increases compared with other examples. Therefore the process according to the present disclosure allows for low steam consumption and a low outlet temperature of the first reactor. Furthermore, the operational costs are significantly reduced.