AU2015226629B2

AU2015226629B2 - Process and plant for performing CO shift

Info

Publication number: AU2015226629B2
Application number: AU2015226629A
Authority: AU
Inventors: Daniel Chin
Original assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2014-03-05
Filing date: 2015-03-04
Publication date: 2018-09-06
Anticipated expiration: 2035-03-04
Also published as: WO2015131818A9; AU2015226629A1; WO2015131818A8; WO2015131818A1

Abstract

A process and a plant for converting a carbon monoxide containing crude synthesis gas stream, generated in a multi-stage reformer and/or gasifier plant, by CO shift into a treated syngas stream depleted with regard to carbon monoxide, but enriched with regard to hydrogen and carbon dioxide. To this end, the crude synthesis gas stream is routed to a CO shift reaction section, comprising at least a first shift reactor and possibly also comprising further downstream shift reactors, wherein the first shift reactor comprises at least two subreactors(7a, 7b) which are operated in parallel, wherein the at least two subreactors(7a, 7b) contain different volumes of the shift catalyst.

Description

FIELD OF THE INVENTION

This invention relates to a process for converting a carbon monoxide (CO) containing crude synthesis gas (syngas) stream by reacting the crude syngas with water in the presence of a catalyst according to the so-called CO shift or CO conversion reaction into a syngas stream depleted with regard to CO, but enriched with regard to hydrogen (H₂) and carbon dioxide (CO2). It is among the objects of the invention to provide methods for safely performing such reaction under varying syngas load, especially as a downstream operation of a multi-stage reformer plant or gasifier plant, wherein the different reformer stages or gasifier stages may not all be operated at the same time and/or the flow rate of the crude syngas received from the reformer stages or gasifier stages may vary.

In another aspect, the subject invention relates to a plant suited for performing the CO shift reaction, especially downstream of a multi-stage reformer or gasifier in an integrated reforming plant.

In yet another aspect, the subject invention relates to a method of starting up such plant, especially in situations where the different reformer stages or gasifier stages are started up successively.

BACKGROUND OF THE INVENTION

The CO shift reaction is per se well known in the technical field of chemical

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PCT/CN2015/073621 engineering. General concepts and applications of the CO shift reaction in the context of reforming plants or gasification plants can be found in textbooks like C. Higman and M. van der Burgt, Gasification, Chapter 8.3 “CO Shift”, Gulf Professional Publishing (Elsevier) 2003, or Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition, 1998 Electronic Release, keyword Ammonia, chapter 4.5.1.2 “Carbon Monoxide Shift Conversion”, and keyword “Hydrogen”, chapter 4.1.2.2 “Gasification of Liquid and Gaseous Hydrocarbons”. CO shift is widely applied in reformer plants designed to produce ammonia syngas, since for ammonia synthesis carbon oxides must be completely removed from the raw synthesis gas of the reforming or gasification process.

The CO shift reaction

CO + H₂O = CO₂ + H₂ is strongly exothermic with a standard reaction enthalpy of -41.2 kJ/mol. It can be operated as an additional and separate process from the gasifier or reformer at much lower temperatures in order to modify the H₂/CO ratio of the syngas or maximize the total hydrogen production from the unit. As can be seen from the reaction equation presented above, one mole of hydrogen can be produced from every mole of CO. The reaction itself is equimolar and is therefore largely independent of pressure. The equilibrium for hydrogen production is favored by low temperature. Typical equilibrium concentrations of CO are low; for example, 0.2 vol % at 220 °C and 0.12 vol % at 200 °C for a steam/gas ratio of 0.4.

The CO shift reaction will operate with a variety of catalysts between 200 °C to 500 °C at sufficient reaction rates. The types of catalyst are distinguished by their temperature range of operation and the quality, especially the sulfur

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PCT/CN2015/073621 content, of the syngas to be converted.

Conventional high temperature shift (HT shift) uses an iron oxide-based catalyst promoted typically with chromium and more recently with copper. The operating range of these catalysts is between 300 and 500 °C. Much above 500 °C sintering of the catalyst occurs which leads to catalyst deactivation. HT shift catalyst is tolerant of sulfur up to a practical limit of about 100 vol-ppm, but it is likely to lose mechanical strength, particularly if subjected to changing amounts of sulfur. With regard to reaction engeneering aspects, the reaction is mostly performed in several stages, operated in series, with intermediate heat removal between the individual catalyst beds in which the reaction runs adiabatically, to avoid excessive catalyst temperatures and to have an advantageous equilibrium.

Low temperature shift (LT shift) operates in the temperature range from 200 °C to 270 °C and uses a copper-zinc-aluminum catalyst. It is used in most steam reforming-based ammonia plants to reduce residual CO to about 0.3 mol-%, a requirement for a downstream methanator. The catalyst used is highly sulfur-sensitive, and even with 0.1 vol-ppm H₂S in the inlet gas, will over time become poisoned. Further the catalyst is also sensitive with regard to water condensation. Operation near the dewpoint will cause capillary condensation and consequent damage to the catalyst. With a dewpoint of about 215 °C and a temperature rise of 25 to 30 °C, there is not much margin for error below the upper temperature limit of 270 °C when recrystallization of the copper catalyst begins.

In the traditional plant concept for CO shift in methane steam reforming (SMR) plants, the gas from the secondary reformer, cooled by recovering the waste heat for raising and superheating steam, enters the HT shift reactor filled with an iron-chromium catalyst at 320 to 350 °C. After a temperature increase of

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PCT/CN2015/073621 around 50 to 70 °C (depending on initial CO concentration) and with a residual

CO content of around 3 %, the gas is then cooled to 200 to 210 °C for the LT shift, which is carried out on a copper-zinc-alumina catalyst in a downstream reaction vessel and achieves a carbon monoxide concentration of 0.1 to 0.3 vol-%.

An improved copper-zinc-aluminum catalyst able to operate at higher exit temperatures (300°C) than conventional LT shift has been developed, particularly for use in isothermal reactors. This process is called medium temperature shift (MT shift). Applications in reforming plants have been described, whereas no application in gasification plants is known.

For applications where it is desired to perform CO shift on raw syngas, a cobalt-molybdenum catalyst, variously described as a “sour shift” or “dirty shift” catalyst, can be used. The catalyst is sulfur tolerant since it requires sulfur in the feed gas to maintain it in the active sulfided state. It is generally applied after a water quench of the raw syngas, which typically will provide a gas at about 250 °C saturated with sufficient water to conduct the shift reaction without any further steam addition. For an ammonia application the raw gas shift is typically configured as two or three adiabatic beds with intermediate cooling resulting in a residual CO of about 1.6 or 0.8 mol-%, respectively. An important side-effect of the raw gas shift catalyst is its ability to handle a number of other impurities characteristic of gasification. COS and other organic sulfur compounds are largely converted to H₂S, which eases the task of the downstream acid gas removal (AGR). HCN and any unsaturated hydrocarbons are hydrogenated. Carbonyls are decomposed and deposited as sulfides, which increases the pressure drop over the bed. Selective removal of arsenic in the feed was also described in the prior art.

In applications where a conventional sour shift catalyst with a high activity is

2015226629 03 Aug 2018 used for converting a crude syngas comprising CO in a high concentration (for example, approximately 60 mol-% to 70 mol-% CO on a dry basis) , temperature excursions can appear during the start-up and turndown operation of the CO shift reactor. To cope with this, e.g. in an arrangement where there are several adiabatic 5 reactor stages in series with intermediate heat removal between the stages, a common practice is to split the first shift reactor stage in flow direction into two parallel subreactors, as it is taught for example in European patent specification 0 121 928 B1. In this design, each subreactor comprises a multitude, for example two, catalyst beds with an internal bypass around the first catalyst bed in direction of gas flow.

Typically there is also another main bypass line across both parallel first shift subreactors. This design is shown schematically in figure 1.

In the practical application on site, this setup is often controlled manually by limiting the rawgas flowrate through each catalyst bed by adjusting a manual valve for the 15 respective flow path. The sound application of this method depends on operator experience thus, chances of undesired temperature overshooting in the reactors is relatively high. A further disadvantage is can be seen in the additional investment costs required for the reactor design because of double layers of catalyst bed, supporting means for the latter, and large isolation valves together with extra piping to 20 control the flow in the main and bypass lines.

A reference herein to a patent document or any other matter identified as prior art, is not to be taken as an admission that the document or other matter was known or that the information it contains was part of the common general knowledge as at the 25 priority date of any of the claims.

Where any or all of the terms comprise, comprises, comprised or comprising are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not 30 precluding the presence of one or more other features, integers, steps or components.

2015226629 03 Aug 2018

SUMMARY OF THE INVENTION

The present invention provides a process for converting a crude synthesis gas according to the CO shift reaction into a syngas stream depleted with regard to CO, but enriched with regard to hydrogen (H₂) and carbon dioxide (CO₂), especially as a 5 downstream operation of a multi-stage gasifier or reformer plant, wherein the different gasifier or reformer stages may not all be operated at the same time and/or the flow rate of the crude syngas received from the reformer stages may vary.

In one aspect, the present invention provides a process for producing a treated 10 synthesis gas, containing carbon oxides and hydrogen, the process comprising the following steps:

(a1) gasifying a carbonaceous feed stream in at least one gasifier stage to produce a crude synthesis gas stream, or (a2) reforming a hydrocarbonaceous feed stream in at least one reformer 15 stage to produce a crude synthesis gas stream, (b) routing the crude synthesis gas stream to a CO shift reaction section, comprising at least a first shift reactor, containing a shift catalyst, and converting the crude synthesis gas stream under CO shift conditions in contact with a CO shift catalyst to a treated synthesis gas stream under CO shift conditions, (c) withdrawing a treated synthesis gas stream from the CO shift reaction section depleted in carbon monoxide (CO) and enriched in hydrogen (H₂) and carbon dioxide (CO₂) with regard to the crude synthesis gas stream, wherein the first shift reactor comprises at least two subreactors which are operated in parallel, wherein the at least two subreactors contain different volumes of 25 the shift catalyst.

Further advantageous aspects of the process according to the invention can be found in claims 2 to 7.

In another aspect, the present invention provides a plant for producing a treated synthesis gas, containing carbon oxides and hydrogen, the plant comprising the following units:

(a) at least one gasifier stage or at least one reformer stage to produce a crude synthesis gas stream,

2015226629 03 Aug 2018 (b) a CO shift reaction section in fluid connection with the at least one gasifier or reformer stage, comprising at least a first shift reactor, containing a shift catalyst, the CO shift reaction section being suited for converting the crude synthesis gas stream under CO shift conditions to a treated synthesis gas stream under CO shift conditions, 5 (c) means for withdrawing a treated synthesis gas stream from the CO shift reaction section, wherein the first shift reactor comprises at least two subreactors which are operated in parallel, wherein the at least two subreactors contain different volumes of the shift catalyst.

Further advantageous aspects of the process according to the invention can be found in claims 9 to 14.

In yet another aspect, the present invention provides a method for starting up a plant 15 for producing a treated synthesis gas, the plant comprising (a) at least three gasifier or reformer stages to produce a crude synthesis gas stream, (b) a CO shift reaction section in fluid connection with the gasifier or reformer stages, comprising at least a first shift reactor, containing a shift catalyst, wherein the first shift reactor comprises at least two subreactors which are operated in parallel and which contain different volumes of the shift catalyst, (c) means for withdrawing a treated synthesis gas stream from the CO shift reaction section, wherein (d) on start-up of the first gasifier or reformer stage, the crude synthesis gas stream is routed to the subreactor containing the smaller volume of the shift catalyst, (e) on start-up of all gasifier or reformer stages, the crude synthesis gas stream is routed to all subreactors.

In still another aspect, the present invention provides a method for shutting down a plant for producing a treated synthesis gas, the plant comprising (a) at least three gasifier or reformer stages to produce a crude synthesis gas stream,

2015226629 03 Aug 2018 (b) a CO shift reaction section in fluid connection with the gasifier or reformer stages, comprising at least a first shift reactor, containing a shift catalyst, wherein the first shift reactor comprises at least two subreactors which are operated in parallel and which contain different volumes of the shift catalyst, (c) means for withdrawing a treated synthesis gas stream from the CO shift reaction section, wherein (d) on shutdown of the first gasifier or reformer stage, the crude synthesis gas stream is routed to the subreactor containing the larger volume of the shift 10 catalyst.

Fluid connection between two regions of the reformer tube is understood to be any kind of connection which enables a fluid, for example the crude synthesis gas stream or the treated synthesis gas stream, to flow from the one to the other of the two 15 regions, regardless of any interposed regions or components.

Adiabatic reactor operation is understood to be a reactor operation wherein except for the convective heat stream introduced with the feed stream no foreign energy is supplied to the reactor and in addition a heat exchange of the reactor with the 20 surroundings is reduced or even completely

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PCT/CN2015/073621 inhibited by constructive measures, for example by mounting thermal insulations.

CO shift conditions are understood to be reaction conditions which effect at least a partial conversion of the crude syngas constituents according to the CO shift reaction equation CO + H₂O = CO₂ + H₂ . These conversion conditions are known in principle to the skilled person from the prior art, for example from the documents discussed above. Necessary adaptations of these conditions to the respective operating requirements, for example to the composition of the feed stream or to the type of catalysts used, will be made on the basis of routine experiments.

Catalysts which are active for CO shift, especially sour gas shift, are in principle known to the skilled person and are commercially available from the trade for a variety of different applications. The expert will select a suited CO shift catalyst with regard to the reaction temperature (HT / MT / LT shift) to be employed, and for special applications like sour / dirty gas CO shift.

By means for withdrawing a treated synthesis gas stream from the CO shift reaction section, any devices that are suited for this purpose are understood, especially piping or tubing systems, possibly in combination with conveyors like blowers or pumps.

Gasifier stages or reformer stages are to be understood as defined regions or spaces where a gasification or reforming reaction takes place. The term “stage” is not be understood as implying any specific interconnection with other stages, e. g. whether the stages are connected in series or in parallel.

The invention is based on the fact that the CO shift reaction is strongly exothermic as outlined above. Thus, varying the flow rate of the crude syngas

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PCT/CN2015/073621 to the CO shift reactor with regard to a given catalyst inventory, i.e., varying the space velocity of the crude syngas, may lead to high temperature fluctuations. Especially in situations where the flow rate is too low in relation to the catalyst volume, the reaction equilibrium will be established, and the heat of rection liberated, in a small portion of the catalyst bed. This will lead to temperature overshooting and hot spot formation in this catalyst bed portion, and eventually to premature catalyst deactivation due to thermal ageing or sintering of the catalyst in this location. This effect is in principle relevant for any reactor design, but especially serious in the case of adiabatic fixed-bed reactors which are widely employed in CO shift due to their simple and inexpensive design. As a means of mitigating this effect, a reactor design as shown in Fig. 1 and described in the prior art is used, where the first shift reactor is divided into e.g. two parallel subreactors, each comprising e.g. two catalyst beds, wherein the flow rate to each subreactor may be regulated by means of valves, and the first catalyst beds, seen in flow direction, may be bypassed. The sound application of this method depends on operator experience; thus, chances of undesired temperature overshooting in the reactors is relatively high. A further disadvantage can be seen in the additional investment costs required for the reactor design because of double layers of catalyst bed, supporting means for the latter, and large isolation valves together with extra piping to control the flow in the main and bypass lines.

It has been found in the context of the present invention that it is advantageous to design the first shift reactor, either designed as stand-alone reactor or being the first, most upstream reactor stage in a series of consecutive CO shift reactor stages, for example downstream of a multi-stage reformer or gasifier unit, so as to comprise at least two subreactors which are operated in parallel, wherein the at least two subreactors contain different volumes of the shift catalyst. This allows for a greater flexibility when changes of flow rate of the crude syngas occur, for example during start-ups or shutdowns of the crude

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PCT/CN2015/073621 syngas preparation section, i.e. the successive gasifier or reformer stages. Larger crude syngas flows may be sent to the subreactor containing the larger volume portion of the CO shift catalyst, while smaller crude syngas flows may be sent to the subreactor containing the smaller volume portion of the CO shift catalyst. The advantage is that in both scenarios, the deviation from the design value for the optimum space velocity is smaller compared to a situation where either large or small flow rates of crude syngas are routed to the same catalyst volume, for example in an arrangement where two subreactors are symmetrically filled with the same amount of catalyst. This leads to less temperature overshooting and thus to less thermal stress on the catalyst and reactor materials.

With regard to the process according to the invention, it has been found advantageous that in case the crude synthesis gas stream is produced by gasifying a carbonaceous feed stream in at least one gasifier, and the crude synthesis gas stream comprises at least 50 mol-%, preferably 60 to 70 mol-% CO and acidic gas components, the crude synthesis gas stream is routed to a CO sour shift reaction section, containing a sour shift catalyst. Especially in these situations, the heat liberated per unit volume of catalyst is high, as is the tendency for temperature overshooting upon fluctuations of the crude syngas flow rate. This tendency is even more pronounced if the reaction is carried out in adiabatic reactors.

Preferably, the first shift reactor consists of two subreactors which are operated in parallel, wherein the catalyst volumes in the two subreactors are present in a ratio of one third in the one subreactor to two thirds in the second subreactor. Such an arrangement has the advantage of being simple from a constructional point of view, while, at the same time, being capable of dealing with a wide range of different crude syngas flow rates, as they are observed on start-up or

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PCT/CN2015/073621 shutdown of a syngas production plant comprising a multitude of gasifier stages and/or reforming stages which are operated in series and/or in parallel.

Furthermore, with regard to the process according to the invention, it is especially advantageous if the crude synthesis gas stream is produced in three gasifier stages and/or reforming stages. In combination with a design in which two subreactors are operated in parallel, wherein the catalyst volumes in the two subreactors are present in a ratio of one third in the one subreactor to two thirds in the second subreactor, all crude syngas flow rates that occur during start-up or shutdown of the gasifier and/or reforming stages can be processed in the CO shift unit under optimum space velocity conditions: In case one gasifier and/or reforming stage is in operation, the complete crude syngas flow will exclusively be routed to the subreactor comprising one third of the total CO shift catalyst. In case two gasifier and/or reforming stages are in operation, the complete crude syngas flow will exclusively be routed to the subreactor comprising two thirds of the total CO shift catalyst. In case all three gasifier and/or reforming stages are in operation, the complete crude syngas flow will be routed to both subreactors, wherein the ratio of total crude syngas flow rate to total catalyst volume is in agreement with the optimum design value for the space velocity.

It is particularly preferred that the process according to the invention is carried out in adiabatic reactors, especially with regard to the fact that that at least the two subreactors in the first shift reactor are adiabatic reactors. Adiabatic reactors are advantageous due to their simple construction; however, due to the fact that they comprise thermal insulations to reduce the heat loss from the reactor interior to the environment, they are rather sensitive with regard to temperature overshooting. Thus, they work especially well in combination with a process as outlined in claims 1 to 5.

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PCT/CN2015/073621

With regard to the plant according to the invention, it has been found advantageous that in case the crude synthesis gas stream is produced by gasifying a carbonaceous feed stream in at least one gasifier, and the crude synthesis gas stream comprises at least 50 mol-%, preferably 60 to 70 mol-% CO and acidic gas components, the CO shift reaction section contains a sour shift catalyst. Especially in these situations, the heat liberated per unit volume of catalyst is high, as is the tendency for temperature overshooting upon fluctuations of the crude syngas flow rate. This tendency is even more pronounced if the reaction is carried out in adiabatic reactors.

In a further preferred embodiment of the plant according to the invention, the first shift reactor consists of two subreactors which are operated in parallel, wherein the catalyst volumes in the two subreactors are present in a ratio of one third in the one subreactor to two thirds in the second subreactor. This embodiment has specific advantages when employed in a flow sheet where the crude synthesis gas stream is produced in a multitude of gasifier stages and/or reforming stages which are operated in series and/or in parallel.

In another preferred embodiment of the plant according to the invention, the crude synthesis gas stream is produced in a multitude of gasifier stages and/or reforming stages which are operated in series and/or in parallel. This embodiment has specific advantages when employed in a flow sheet comprising a first shift reactor, consisting of two subreactors which are operated in parallel, wherein the catalyst volumes in the two subreactors are present in a ratio of one third in the one subreactor to two thirds in the second subreactor. Especially in an integrated synthesis gas plant where the crude synthesis gas stream is produced in three gasifier stages and/or reforming stages, this embodiment allows different options and scenarios of distributing the crude syngas flow to the two CO shift subreactors, e. g. during start-up or shutdown of the crude synthesis gas production, as will be explained in the

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PCT/CN2015/073621 exemplary embodiment below.

It is particularly preferred that the plant according to the invention comprises adiabatic reactors, especially with regard to the fact that that at least the two subreactors in the first shift reactor are adiabatic reactors. Adiabatic reactors are advantageous due to their simple construction; however, due to the fact that they comprise thermal insulations to reduce the heat loss from the reactor interior to the environment, they are rather sensitive with regard to temperature overshooting. Thus, they work especially well in combination with a plant as outlined in claims 7 to 12.

With regard to the method of starting up or shutting down a plant according to the invention, the plant comprising (a) at least three gasifier or reformer stages to produce a crude synthesis gas stream, (b) a CO shift reaction section in fluid connection with the gasifier or reformer stages, comprising at least a first shift reactor, containing a shift catalyst, wherein the first shift reactor comprises at least two subreactors which are operated in parallel and wherein the catalyst volumes in the two subreactors are present in a ratio of one third in the one subreactor to two thirds in the second subreactor, (c) means for withdrawing a treated synthesis gas stream from the CO shift reaction section, it has been found advantageous that

d) on start-up of the first gasifier or reformer stage, the crude synthesis gas stream is routed to the subreactor containing the smaller volume of the shift catalyst, (e) on start-up of all gasifier or reformer stages, the crude synthesis gas stream is routed to all subreactors.

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In addition, it has been found advantageous that (d) on shutdown of the first gasifier or reformer stage, the crude synthesis gas stream is routed to the subreactor containing two thirds of the total volume of the shift catalyst.

This start-up and shutdown philosophy is consistent with the observation that larger crude syngas flows may preferably be sent to the subreactor containing the larger volume portion of the CO shift catalyst, while smaller crude syngas flows may be sent to the subreactor containing the smaller volume portion of the CO shift catalyst. The advantage is that in start-up and shutdown scenarios in which the single reformer and/or gasifier stages in a multi-stage reformer and/or gasifier plant are started up or shut down successively, the deviation from the design value for the optimum space velocity is smaller compared to a situation where either large or small flow rates of crude syngas are routed to the same catalyst volume, for example in an arrangement where two subreactors are symmetrically filled with the same amount of catalyst. This leads to less temperature overshooting and thus to less thermal stress on the catalyst and reactor materials.

BRIEF DESCRIPTION OF THE DRAWINGS

Further developments, advantages and possible applications of the invention can also be taken from the following description of exemplary embodiments and examples and the drawings. All features described and/or illustrated form the invention per se or in any combination, independent of their inclusion in the claims or their back-reference.

In the drawings:

Fig. 1 schematically shows a CO shift process and plant according to

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PCT/CN2015/073621 the prior art (comparative example),

Fig. 2 schematically shows a CO shift process and plant according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

In Fig. 1, a crude syngas stream, received from a multi-stage coal gasification unit comprising three gasifier stages, not shown in the figure, is routed via line 1 to heat exchanger 2, which serves for adjustment of temperature to CO shift reaction temperature. After passing heat exchanger 2, the crude syngas stream is directed via line 3 to the CO shift reaction section, consisting of two symmetrical subreactors 7 a,b. The flow of the crude syngas stream to subreactors 7 a,b via lines 5 a,b is controlled by valves 6 a,b. Both subreactors comprise two catalyst beds, each of which comprises an identical catalyst volume relative to the other catalyst beds. Thus, the total catalyst volume present in both subreactors with regard to the optimum space velocity is distributed over four catalyst beds with equal catalyst volumes. Furthermore, both subreactors are equipped with bypass lines 11 a,b and valves 12 a,b in order to bypass the crude syngas stream around the respective first catalyst bed in flow direction.

The treated synthesis gas stream from the CO shift reaction section depleted in carbon monoxide and enriched in hydrogen and carbon dioxide with regard to the crude synthesis gas stream is withdrawn via line 8 a,b and valve 9 a,b, collected in line 10 and routed to optional further processing stages, e. g additional CO shift stages, which are know per se and are not shown in the figure.

The complete CO shift reaction section may be bypassed via line 10 by

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PCT/CN2015/073621 shutting off valves 4 a,b and optionally valves 9 a,b and opening valve 13 which is closed in normal operation.

On start-up of the three parallel stage gasifier stages, the single stages are normally started up successively. Thus, there will be modes of operation where the gasifier unit runs at one third or two thirds of its full production capacity, with either one or two out of three gasifier stages in operation. The processing of the crude syngas streams received in these operation modes in the downstream CO shift section is difficult in terms of adjustment of the optimum space velocity. In the one third production capacity scenario, the operator has the choice to either direct the crude syngas stream completely to one or two catalyst beds, both choices being suboptimal with regard to adjustment of the optimum space velocity, or, alternatively, to adjust the flow rate of the crude syngas stream to one subreactor by means of regulating valve 6 a,b. The performance of the latter methods critically depends on operator experience and skillfulness and is prone to operator errors.

Likewise, in the two thirds production capacity scenario, the operator has the choice to either direct the crude syngas stream to two catalyst beds, e. g. one complete subreactor, or to three catalyst beds, e. g. to the complete first subreactor plus to the downstream bed of the second subreactor, the upstream bed of the latter being bypassed. Again, both choices are suboptimal with regard to adjustment of the optimum space velocity.

In Fig. 2, schematically showing a CO shift process and plant according to the invention, a crude syngas stream, received from a multi-stage gasifier unit comprising three parallel gasifier stages, not shown in the figure, is routed via line 1 to heat exchanger 2, which serves for adjustment of temperature to CO shift reaction temperature. After passing heat exchanger 2, the crude syngas stream is directed via line 3 to the CO shift reaction section, consisting of two

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PCT/CN2015/073621 subreactors 7 a,b which exhibit different catalyst volumes. Both subreactors comprise only one catalyst bed each, wherein reactor 7a comprises two thirds and reactor 7b one third of the total catalyst volume with regard to the optimum space velocity. In this example according to the invention, there are no bypass lines 11 a,b, and no valves 6 a,b and 12 a,b.

As in the comparative example in Fig. 1, the treated synthesis gas stream from the CO shift reaction section depleted in carbon monoxide and enriched in hydrogen and carbon dioxide with regard to the crude synthesis gas stream is withdrawn via line 8 a,b and valve 9 a,b, collected in line 10 and routed to optional further processing stages which are know per se and are not shown in the figure.

Again, the complete CO shift reaction section may be bypassed via line 10 by shutting off valves 4 a,b and optionally valves 9 a,b and opening valve 11 which is closed in normal operation.

On start-up of the first gasifier stage of the three parallel-stage gasifier unit in the process and plant according to the invention in Fig. 2, which corresponds to the one third production capacity scenario described above, the crude syngas stream is routed completely to subreactor 7b, comprising one third of the total catalyst volume with regard to the optimum space velocity. Thus, subreactor 7b is automatically operated in the optimum space velocity regime.

Likewise, in the two thirds production capacity scenario, with two out of three gasifier stages in operation, the crude syngas stream is routed completely to subreactor 7a, comprising two thirds of the total catalyst volume with regard to the optimum space velocity. Thus, subreactor 7a is automatically operated in the optimum space velocity regime.

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In contrast, on shutting down the first gasifier stage of the three-stage gasifier unit in the process and plant according to the invention in Fig. 2, which corresponds to the two thirds production capacity scenario described above, the crude syngas stream is routed completely to subreactor 7a, comprising two thirds of the total catalyst volume with regard to the optimum space velocity. On shutting down two gasifier stages of the three-stage gasifier unit, corresponding to the one third production capacity scenario described above, the crude syngas stream is routed completely to subreactor 7b, comprising one third of the total catalyst volume with regard to the optimum space velocity. Once more, subreactor 7b is automatically operated in the optimum space velocity regime.

In the following table, different options and scenarios of distributing the crude syngas flow to the two CO shift subreactors, together forming the first CO shift reactor, are collected in dependence of the number of gasifier stages in operation. It will be understood by the skilled practitioner that the one third and two thirds production capacity scenario as described above can also be realized by partially reducing the flow to one or both of the parallel subreactors, e. g. by means of regulating valves 5 a,b. These options, denoted as Option A1, B1, and B2 in the table, may for example be employed in situations where one of the reactors need to be removed or isolated from service. However, in the context of the present invention, it is clearly preferred to employ Options A2, B3 and C1, underlined in the table, and corresponding to modes of operation where the catalyst bed load factor is 0 and/or 1, i.e. the corresponding subreactor receives zero or full flow.

Table: Different options of distributing the crude syngas flow to the two parallel CO shift subreactors forming the first CO shift reactor

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No of gasifier stages in operation	Subreactor 7a (2/3 of catalyst volume)	Subreactor 7b (1/3 of catalyst volume)	Total capacity
Crude syngas feed flow	Catalyst bed load factor	Crude syngas feed flow	Catalyst bed load factor
A: 1 gasifier	Option A1: 33.33%	0.50	Option A1: Closed	0	33.33%
Option A2: Closed	0	Option A2: 33.33%	1Ό	33.33%
B: 2 gasifiers	Option B1: 33.33%	0.50	Option B1: 33.33%	1.0	66.67%
Option B2: 43.33%	0.65	Option B2: 23.33%	0.70	66.67%
Option B3: 66.67%	1Ό	Option B3: Closed	0	66.67%
C: 3 gasifiers	Option C1: 66.67%	1Ό	Option C1: 33.33%	1Ό	100.00%

Industrial Applicability

With the invention, there is proposed a process and a plant for converting a crude syngas stream into a treated syngas stream depleted with regard to carbon monoxide, but enriched with regard to hydrogen and carbon dioxide. Compared to known prior art processes, the proposed process and plant are more flexible with regard to turnarounds in the upstream syngas generation plant, e. g. a multi-stage reformer and/or gasifier plant. The asymmetric split of the first CO shift reactor in direction of flow of the crude syngas stream into two or more subreactors with different catalyst volumes allows for greater flexibility during start-up or shutdown of the single syngas generation stages, while operating in the or next to the optimum space velocity regime in the single catalyst beds in the CO shift subreactors.

WO 2015/131818

PCT/CN2015/073621

List of Reference Numerals

[1]	line
[2]	heat exchanger
[3]	line
[4 a,b]	valve
[5 a,b]	line
[6 a,b]	valve
[7 a.b]	CO shift subreactor
[8 a,b]	line
[9 a,b]	valve
[10]	line
[11 a,b]	line
[12 a,b]	valve
[13]	valve

2015226629 07 Aug 2018

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A process for producing a treated synthesis gas, containing carbon oxides and hydrogen, the process comprising the following steps:

5 (a1) gasifying a carbonaceous feed stream in at least one gasifier stage to produce a crude synthesis gas stream, or (a
2) reforming a hydrocarbonaceous feed stream in at least one reformer stage to produce a crude synthesis gas stream, (b) routing the crude synthesis gas stream to a CO shift reaction section,

10 comprising at least a first shift reactor, containing a shift catalyst, and converting the crude synthesis gas stream under CO shift conditions in contact with a CO shift catalyst to a treated synthesis gas stream under CO shift conditions, (c) withdrawing a treated synthesis gas stream from the CO shift reaction section depleted in carbon monoxide (CO) and enriched in hydrogen (H₂) and carbon

15 dioxide (CO₂) with regard to the crude synthesis gas stream, wherein the first shift reactor comprises at least two subreactors which are operated in parallel, wherein the at least two subreactors contain different volumes of the shift catalyst.

20 2. A process according to claim 1, wherein in case the crude synthesis gas stream is produced by gasifying a carbonaceous feed stream in at least one gasifier, and the crude synthesis gas stream comprises at least 50 mol-% CO and acidic gas components, the crude synthesis gas stream is routed to a CO sour shift reaction section, containing a sour shift catalyst.
3. A process according to claim 2, wherein the crude synthesis gas stream comprises 60 to 70 mol-% CO and acidic gas components.
4. A process according to claim 1, 2 or 3, wherein the first shift reactor consists of

30 two subreactors which are operated in parallel, wherein the catalyst volumes in the two subreactors are present in a ratio of one third in the one subreactor to two thirds in the second subreactor.

2015226629 07 Aug 2018
5. A process according to claim 4, wherein the crude synthesis gas stream is produced in a multitude of gasifier stages and/or reforming stages which are operated in series and/or in parallel.

5
6. A process according to claim 4, wherein the crude synthesis gas stream is produced in three gasifier stages and/or reforming stages.
7. A process according to any one of claims 1 to 6, wherein the at least two subreactors in the first shift reactor are adiabatic reactors.
8. A plant for producing a treated synthesis gas, containing carbon oxides and hydrogen, the plant comprising the following units:

(a) at least one gasifier stage or at least one reformer stage to produce a crude synthesis gas stream,

15 (b) a CO shift reaction section in fluid connection with the at least one gasifier or reformer stage, comprising at least a first shift reactor, containing a shift catalyst, the CO shift reaction section being suited for converting the crude synthesis gas stream under CO shift conditions in contact to a treated synthesis gas stream under CO shift conditions,

20 (c) means for withdrawing a treated synthesis gas stream from the CO shift reaction section, wherein the first shift reactor comprises at least two subreactors which are operated in parallel, wherein the at least two subreactors contain different volumes of the shift catalyst.
9. A plant according to claim 8, wherein in case the crude synthesis gas stream is produced by gasifying a carbonaceous feed stream in at least one gasifier, and the crude synthesis gas stream comprises at least 50 mol-% CO and acidic gas components, the CO shift reaction section contains a sour shift catalyst.
10. A plant according to claim 9, wherein the crude synthesis gas stream comprises 60 to 70 mol-% CO and acidic gas components.

2015226629 07 Aug 2018
11. A plant according to claim 8, 9 or 10, wherein that the first shift reactor consists of two subreactors which are operated in parallel, wherein the catalyst volumes in the two subreactors are present in a ratio of one third in the one subreactor to two thirds in the second subreactor.
12. A plant according to claim 11, wherein the crude synthesis gas stream is produced in a multitude of gasifier stages and/or reforming stages which are operated in series and/or in parallel.

10
13. A plant according to claim 12, wherein the crude synthesis gas stream is produced in three gasifier stages and/or reforming stages.
14. A plant according to any one of claims 8 to 12, wherein the at least two subreactors in the first shift reactor are adiabatic reactors.
15. A method for starting up a plant for producing a treated synthesis gas, the plant comprising (a) at least three gasifier or reformer stages to produce a crude synthesis gas stream,

20 (b) a CO shift reaction section in fluid connection with the gasifier or reformer stages, comprising at least a first shift reactor, containing a shift catalyst, wherein the first shift reactor comprises at least two subreactors which are operated in parallel and which contain different volumes of the shift catalyst, (c) means for withdrawing a treated synthesis gas stream from the CO shift 25 reaction section, wherein (d) on start-up of the first gasifier or reformer stage, the crude synthesis gas stream is routed to the subreactor containing the smaller volume of the shift catalyst, (e) on start-up of all gasifier or reformer stages, the crude synthesis gas stream 30 is routed to all subreactors.
16. A method for shutting down a plant for producing a treated synthesis gas, the plant comprising

2015226629 07 Aug 2018 (a) at least three gasifier or reformer stages to produce a crude synthesis gas stream, (b) a CO shift reaction section in fluid connection with the gasifier or reformer stages, comprising at least a first shift reactor, containing a shift catalyst, wherein the

5 first shift reactor comprises at least two subreactors which are operated in parallel and wherein the catalyst volumes in the two subreactors are present in a ratio of one third in the one subreactor to two thirds in the second subreactor, (c) means for withdrawing a treated synthesis gas stream from the CO shift reaction section,

10 wherein (d) on shutdown of the first gasifier or reformer stage, the crude synthesis gas stream is routed to the subreactor containing two thirds of the total volume of the shift catalyst.

WO 2015/131818

PCT/CN2015/073621

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Fig. 1

Fig. 2