The present invention relates to a method for production of a hydrogen enriched gas from a synthesis gas. Said method comprises the combined steps of adding steam and recycling product gas, in order to control the gas reactivity.

In the production of hydrogen rich gas, steam is added as a reactant to a synthesis gas comprising CO, which reacts with ¾0 to form ¾ and CO ₂ according to the water gas shift reaction. A side reaction - especially at elevated tempera ^¬ tures - is methanation. To limit methanation, excess steam may be added i.e. by keeping a high steam to carbon monox ^¬ ide ( S : CO) -ratio (i.e. above 2).

The extent of methanation increases at elevated tempera ^¬ tures. Therefore if the temperature profile of the reactor is well controlled the methanation may remain negligible and S:CO-ratio can be lowered, resulting in a lower steam addition, and a related reduction of operational cost.

In US 8,821,833 B2, a water gas shift process in a single reactor with recycle is proposed, with the objective of protecting the high temperature shift iron catalyst against excessive temperatures. In this process the recycle gas is having a temperature of 464 °C which will put very high and expensive demands on the compressor driving the recycle, and the temperature may also be excessive for avoiding me ^¬ thane formation. In addition the use of a compressor will be related to a significant cost of operation. US 4,161,393 discloses a process in multiple reactors with excessive steam addition wherein the downstream reactors receive a portion of the feed gas which has by-passed up ^¬ stream reactors, such that the heat of reaction is distrib- uted over the two reactors .

US 3,595,619 discloses a process operating in two beds in which the S : CO ratio at the inlet to the first bed is 0.5- 4,, and the S : CO ratio at the outlet of the first bed is 5- 15 - and in which further water is added as quench prior to the second bed.

According to the present disclosure it is proposed to dis ^¬ tribute the heat release over the reactors by combining the feed gas with a recycled gas and by directing by-passed feed gas to a downstream reactor, such that only a partial conversion occurs in the first reactor. This secures that both reactors are kept below the critical temperature for methanation, while avoiding excess addition of steam. Bene- ficially the recycle gas may be driven by an ejector, hav ^¬ ing steam as motive gas, to avoid an increase in operation ^¬ al cost.

Definitions :

In the following the term water gas shift process shall be used for a chemical process in which CO and ¾0 reacts to form ¾ and CO2.

In the following the term sour shift shall be used for a water gas shift process taking place in the presence of sulfur compounds employing a catalytically active material which is not deactivated by sulfur compounds. In the following the term concentrations are given on volu ^¬ metric basis. Where the concentration of sulfur is stated, this shall be the volumetric concentration based on the as ^¬ sumption that all sulfur is present as ¾S.

In the following the term synthesis gas or syngas shall be used for a gas in which the combined concentration of CO and ¾ is at least 15%. In the following, where concentrations are stated in % this shall be understood as volumetric (molar) % on a dry basis, unless explicitly stated otherwise.

In the following the module of a synthesis gas is a dimen- sionless number indicating the balance between CO and ¾, and compensating for the presence of CO ₂ shall be defined as M= (H2-CO2) / (CO+CO2) .

In the following references to the periodic table shall be made to the CAS Group definitions. Group VIIIB shall be construed as elements from the periodic table according to the CAS definition, i.e. as the elements of the combined 1990 IUPAC Groups 8, 9 and 10. Similarly Group VI shall be construed as the elements of the combined 1990 IUPAC Group 6.

In the following, where reference is made to a bed or a re ^¬ actor, this may be understood as equivalent, unless other ^¬ wise indicated in the text. In the following, where reference is made to a process stage, such a stage may be implemented in one or more tors or reactor beds . In a broad embodiment, the present disclosure relates to 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 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 re ^¬ cycled intermediate product gas and a remaining in ^¬ termediate 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 ¾0:ΟΌ ratio in said first re ^¬ actor feed gas being from 0.5 to 2.0 and the ¾0:ΟΌ ratio in said second reactor feed gas being from 0.5 to 2.0,

with the associated benefit of distributing the heat devel ^¬ opment and thus reducing the maximum temperature in the re ^¬ actors by limiting the extent of reaction of the reacting mixture, and thereby reducing the amount of steam required for limiting methanation.

In a further embodiment the synthesis gas comprises at least 20% and preferably at most 70% CO on dry basis, with the associated benefit of such a synthesis gas being espe ^¬ cially suited for providing a final product gas appropriate for production of carbon based molecules such as methanol and methane.

In a further embodiment the first material catalytically active in the water gas shift reaction comprises an element from Group VIb, preferably Mo and a non-noble element from Group VIII, preferably Co, with the associated benefit of such a composition being effective in water gas shift reaction, and the specific benefit of not being deactivated by presence of sulfur in the reacting mixture.

In a further embodiment 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, with the associated benefit of giving the ability of selecting a material optimal for the conditions in each of said reactors.

In a further embodiment the maximum temperature of the first and the second material catalytically active in the water gas shift reaction is below 500°C, 430°C or 400°C, with the associated benefit of reducing the amount of side reactions, such as methanation. In a further embodiment the recycled intermediate product gas is provided as suction gas and the gas comprising steam as motive gas in an ejector, with the associated benefit of providing the energy for driving the recycle gas from the addition of steam, already required as a reactant, and thus avoiding a compressor with moving parts and an operational cost from energy consumption.

In a further embodiment a final product gas is provided by combination of the product gas and an amount of synthesis gas, with the associated benefit of enabling detailed con ^¬ trol of the composition of the final product gas, since the composition is independent of the reactivity implied by the gas composition, the catalyst and the temperature.

In a further embodiment the process 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, with the associated ben ^¬ efit of such a process comprising a further stage, allowing an increased extent of water gas shift reaction.

In a further embodiment said synthesis gas comprises at least 200 ppm sulfur, with the associated benefit of such a gas not having undergone expensive desulfurization .

In a further embodiment, at least one of said intermediate product gas, said recycled intermediate product gas, and said remaining intermediate product gas is cooled in a heat exchanger or a waste heat boiler, with the associated bene ^¬ fit from cooling the intermediate product that the cooled intermediate product may react further in the water gas shift process without the risk of unintended formation of methane .

A further aspect of the present disclosure relates to a process plant for production of a hydrogen rich gas, comprising a first and a second reactor,

each of said reactors having an inlet and an outlet, and a first reactor recycle line,

said process plant being configured for receiving

a first stream of synthesis gas in a line being in fluid communication with the inlet of the first reactor and a second stream of synthesis gas in a line being in fluid communication with the inlet of the second reactor

and a stream of steam in a line being in fluid communica- tion with the inlet of the first reactor,

where said first reactor is holding a first material cata- lytically active in the water gas shift reaction,

where said second reactor is holding a second material cat- alytically active in the water gas shift reaction,

and where said first reactor recycle line

comprises a means for gas pressurization having an inlet and an outlet

and said process plant is configured for said outlet from the first reactor to be in fluid communication with the in- let of said means for gas pressurization,

and is further configured for said outlet of the means for gas pressurization to be in fluid communication with said first reactor inlet,

and is further configured for said second reactor inlet to be fluid communication with said first reactor outlet, and is further configured for withdrawing a hydrogen rich gas from said outlet of said second reactor, with the associated benefit of such a process plant being configured for carrying out a water gas shift process with low steam consumption and low risk of methanation reaction. In a further embodiment the means for gas pressurization comprises an ejector, having a motive gas inlet, a suction gas inlet and a discharge outlet, in which the motive gas inlet is in fluid communication with said stream of steam, the suction gas inlet is in fluid communication with said first reactor outlet and the discharge outlet is in fluid communication with the inlet of the first reactor, with the associated benefit of such a process plant having low oper ^¬ ational cost, compared to an equivalent process plant em ^¬ ploying a compressor instead of an ejector.

In a further embodiment the process plant further comprises a means for cooling, such as a heat exchanger or a waste heat boiler, having an inlet and an outlet, the inlet of said means for cooling being in fluid communication with the outlet of said first reactor and the outlet of said means for cooling being in fluid communication with the inlet of said second reactor, with the associated benefit of cooling the intermediate product that the cooled intermedi ^¬ ate product may react further in the water gas shift pro- cess without the risk of unintended formation of methane.

In a further embodiment the process plant further comprises a third reactor having an inlet and an outlet and compris ^¬ ing a material active in the water gas shift reaction, and a second means for cooling having an inlet and an outlet, the inlet of said second means for cooling being in fluid communication with the outlet of said second reactor and the outlet of said second means for cooling being in fluid communication with the inlet of said third reactor, wherein the hydrogen rich gas from said outlet of said second reac ^¬ tor is an intermediate gas and the outlet of the third re- actor is configured for withdrawal of a further hydrogen enriched product gas with the associated benefit of such a further reaction stage of approaching the equilibrium further, while reducing the risk of exceeding the temperature limit .

In many chemical processes hydrogen is a key reactant. Hy ^¬ drogen may either be required as pure hydrogen, e.g. for hydroprocessing in refineries or in combination with carbon monoxide, e.g. for synthesis of methanol, synthetic natural gas and is part of a synthesis gas provided from gasifica ^¬ tion in the presence of water of a carbonaceous material or a hydrocarbon. Often the amount of carbon monoxide in the synthesis gas is higher than desired. However, the well- known water gas shift reaction is used to partially or ful- ly "shift" the carbon monoxide in the gas to hydrogen, in the presence of an appropriate catalyst by reaction of the carbon monoxide with water. The present disclosure will typically find use in the processes known as sour shift, which typically employ catalysts comprising cobalt and mo- lybdenum, and which have the benefit of operating at moderate temperatures, and without requiring full sulfur removal form the synthesis gas, but which also have a tendency to form methane instead of hydrogen at elevated temperatures, as a side reaction. Temperature control of water gas shift reaction by processes according to the present disclosure may however also be relevant for other water gas shift cat ^¬ alysts. The composition of the synthesis gas is dependent on a num ^¬ ber of aspects, including the gasifier design. Some examples of the composition are given in Higman, C. and van der

Burgt, M. Gasification, Elsevier Inc., 2008. Typically the synthesis gas in oxygen fired gasifiers comprises 25-50% ¾ and 15-75% CO and CO ₂ in combination, but other constitu ^¬ ents e.g. up to 10% CH ₄ may also be present. If the

gasifier operates on atmospheric air, the composition will naturally be dominated by N ₂ , such that other concentra- tions are reduced by an approximate factor 5. In addition synthesis gas may also be provided from other processes, such that the composition may vary from the above, but the combined concentration of CO and H ₂ will be above 15%. As mentioned the formation of methane is a side reaction of the water gas shift reaction especially over so-called sour shift catalysts since sour shift catalysts typically oper ^¬ ate at moderate stoichiometric excess of steam. Methane formation is undesired and various methods have been used to avoid this. The most common measure is to operate the process in two or more adiabatic sections with cooling be ^¬ tween the two sections, or in a boiling water cooled reac ^¬ tor. This may be combined with addition of excess steam to further control the reaction.

However, steam addition beyond what is stoichiometrically required for the reaction, is an excess cost during opera ^¬ tion, and therefore it is desired to reduce the excess ad ^¬ dition of steam. Another way of controlling the reaction temperature has been to by-pass an amount of feed synthesis gas, such that the feed of reactants to the first reactor corresponds to an equilibrium reaction which releases an amount of energy corresponding to an upper temperature limit. Subsequently the cooled product from the first reactor, containing excess steam may be combined with further synthesis gas feed in the second reactor, where it reacts to a second equilibrium, still below the upper temperature lim ^¬ it .

An alternative way of controlling the process is the use of a recycle stream, which has the effect of shifting the equilibrium away from the product, and thus reduces the temperature increase and reduces the residence time. Howev ^¬ er it is also well known that this has the consequence of requiring an increased volume of catalyst, and therefore an increased investment cost, and therefore the combination of several means of reducing the reactivity have been avoided to avoid excessive cost.

Now according to the present invention a two stage process with effective control of side reactions has been identi- fied. In this two stage process, excess steam is added to the feed of a first reactor, in combination with recycle of the product from the first stage and sequential addition of synthesis gas with the result of good temperature control may be even better controlled and reduced consumption of steam. Surprisingly it has been identified that this pro ^¬ cess configuration has an overall lower cost, since the re ^¬ duced operational cost due to the reduced steam consumption more than outweighs the increased investment in catalyst. In a preferred embodiment the means for pressurizing the recycle stream is an ejector with the added steam as motive gas, which avoids the otherwise significant operational and investment cost of a compressor.

Brief description of the drawings

Figure 1 shows a two stage water gas shift process configu ^¬ ration according to the present disclosure, with sequential synthesis gas addition and recycle driven by an ejector.

Figure 2 shows a traditional two stage water gas shift pro- cess configuration according to the prior art.

Figure 3 shows a two stage water gas shift process configu ^¬ ration according to the prior art, with sequential synthe ^¬ sis gas addition.

Figure 4 shows a two stage water gas shift process configu ^¬ ration according to the prior art with recycle driven by a compressor List of elements in the drawings:

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

Figure 1 shows a two stage water gas shift process configu ^¬ ration 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 ejec ^¬ tor 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. 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 ¾ relative to CO) product gas is required, especially if pure hydrogen is produced.

Figure 2 shows a traditional two stage water gas shift pro ^¬ cess 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 by ^¬ pass stream for adjustment 210 to form the final shifted and adjusted product stream 236.

Figure 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 sec- ond 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 by ^¬ pass stream for adjustment 310 to form the final shifted and adjusted product stream 336.

Figure 4 shows a two stage water gas shift process configu ^¬ ration 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 in- termediate 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 compres ^¬ sor 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

In Table 1, a feed synthesis gas is characterized, corre ^¬ sponding 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. Table 1 :

Wet molar composition

Component

[mole %]

C0 ₂ 1

CO 61.9

H ₂ 32.2

CH ₄ 0

N ₂ + Ar 2.7

H ₂ S 0.3

H ₂ 0 1 .9

Four examples of water gas shift processes on the feed syn ^¬ thesis 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 composi- tions and temperatures of selected streams. In Table 3 op ^¬ erational characteristics and costs are summarized.

The catalyst volume, steam consumption, and outlet tempera ^¬ tures has been calculated for four different examples to highlight the benefits of the present disclosure, i.e. us ^¬ ing the ejector in combination with a bypass. The design criteria are a module of 3 in the product gas and control ^¬ ling the outlet temperature of the sour shift beds to avoid excessive methane formation. The four examples are de- scribed below. 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

C0 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 1 1.2

H ₂ 26.0 42.6 39.9 49.4 48.2 13.5 35.7 35.7 38.8 37.7

CH ₄ 0.02 0.04 0.03 0.09 0.09 0 0.02 0.02 0.02 0.02

H ₂ 0 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

C0 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 ₂ 13.5 35.7 34.9 46.1 44.2 20.5 41.3 41.3 46.4 43.9

CH ₄ 0 0.02 0.01 0.04 0.03 0.01 0.05 0.05 0.05 0.04

H ₂ 0 58.8 36.7 29.0 17.8 15.6 45.3 24.4 24.4 19.3 16.2

Example 1

Example 1 according to the present disclosure and Figure 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 ejec- tor is at 280 °C.

Example 2

Example 2 according to Figure 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

Example 3 according to Figure 3 and the prior art shows a two stage sour shift unit, with steam added to control tem ^¬ perature 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

Example 4 according to Figure 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 opera ^¬ tional cost and an excessive investment is also required for a compressor operating at this temperature.

Table 3:

S/CO S/CO Steam conCatalyst Index

Case

Stage 1 Stage 2 sumption 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%

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 cat ^¬ alyst volume increases. 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 pro ^¬ cess according to the present disclosure allows for low steam consumption and a low outlet temperature of the first reactor. Furthermore, the operational costs are signifi ^¬ cantly reduced.