Process and plant for producing a converted synthesis gas

Abstract

The invention relates to a process for producing a converted synthesis gas from a crude synthesis gas comprising the essential synthesis gas constituents of hydrogen (H.sub.2) and carbon monoxide (CO), wherein the crude synthesis gas is initially generated in a synthesis gas generation stage and subsequently converted in a multi-stage CO conversion and thus elevated in terms of its hydrogen content. The crude synthesis gas has steam added to it as a reaction partner for the CO conversion and cooling of the converted synthesis gas affords an aqueous condensate.

Claims

1. A process for producing a converted synthesis gas containing hydrogen (H.sub.2) and carbon monoxide (CO), comprising the following process steps: a) providing a first synthesis gas stream having a first H.sub.2/CO ratio and providing a reaction steam stream, b) combining and mixing the first synthesis gas stream with the reaction steam stream, c) introducing the first synthesis gas stream comprising the admixed reaction steam stream into a first CO conversion stage and converting under CO conversion conditions, discharging a second synthesis gas stream having a second H.sub.2/CO ratio, d) providing a first steam generator suitable for generation of a first steam stream by evaporation of boiler feed water and/or an aqueous process condensate, e) introducing the second synthesis gas stream as a heating stream into the first steam generator, discharging a cooled second synthesis gas stream and a first steam stream from the first steam generator, f) introducing the cooled second synthesis gas stream into a second CO conversion stage and converting under CO conversion conditions, discharging a third synthesis gas stream having a third H.sub.2/CO ratio, g) introducing the third synthesis gas stream into at least one cooling apparatus, cooling the third synthesis gas stream in the at least one cooling apparatus to below its dew point, discharging a cooled third synthesis gas stream and the aqueous process condensate, wherein h) the reaction steam stream comprises the first steam stream, i) the generation of the first steam stream in the first steam generator is affected by evaporation of boiler feed water and/or at least a portion of the aqueous process condensate.

2. The process of claim 1, wherein the reaction steam stream is composed of the first steam stream and a fresh steam stream and the generation of the first steam stream is effected in the first steam generator by evaporation of boiler feed water.

3. The process of claim 1, wherein the reaction steam stream is composed of the first steam stream and a fresh steam stream and the generation of the first steam stream is effected in the first steam generator by evaporation of at least a portion of the aqueous process condensate.

4. The process of claim 1, wherein the reaction steam stream is composed of the first steam stream and the generation of the first steam stream in the first steam generator is effected by evaporation of the predominant proportion of the aqueous process condensate, wherein the remaining proportion of the aqueous process condensate is discharged from the process as a purge stream.

5. The process of claim 4, wherein the first steam generator comprises two heat exchangers, wherein the generation of the first steam stream in the first steam generator is effected in indirect heat exchange against the second synthesis gas stream as the heating stream in the first heat exchanger and against a hot fresh steam stream as the heating stream in the second heat exchanger.

6. The process of claim 1, wherein the reaction steam stream is composed of the first steam stream and the generation of the first steam stream in the first steam generator is effected by evaporation of the predominant proportion of the aqueous process condensate and a proportion of boiler feed water, wherein the remaining proportion of the aqueous process condensate is discharged from the process as a purge stream.

7. The process of claim 6, wherein the reaction steam stream is composed of the first steam stream and the generation of the first steam stream in the first steam generator is effected by evaporation of the predominant proportion of the aqueous process condensate and a proportion of boiler feed water, wherein the remaining proportion of the aqueous process condensate is discharged from the process as a purge stream and wherein the proportion of boiler feed water is equal in quantity to the purge stream.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:

(2) FIG. 1 is a schematic representation of a first exemplary embodiment a the process/of a plant according to the invention,

(3) FIG. 2 is a schematic representation of a second exemplary embodiment of a process/of a plant according to the invention,

(4) FIG. 3 is a schematic representation of a third exemplary embodiment of a process/of a plant according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) A particular embodiment of the process according to the invention is characterized in that the reaction steam stream is composed of the first steam stream and a fresh steam stream and generation of the first steam stream is affected in the first steam generator by evaporation of boiler feed water. Such a generation of the reaction steam stream from a plurality of components provides increased flexibility, for example upon startup of the process.

(6) An alternative embodiment of the process according to the invention is characterized in that the reaction steam stream is composed of the first steam stream and a fresh steam stream and generation of the first steam stream is affected in the first steam generator by evaporation of at least a portion of the aqueous process condensate. In this way the condensate obtained is utilized and treatment/disposal cost and complexity is reduced. This also makes it possible to reduce the consumption of boiler feed water.

(7) Preference is given to a particular embodiment of the process according to the invention which provides that the reaction steam stream is composed of the first steam stream and the generation of the first steam stream in the first steam generator is effected by evaporation of the predominant proportion of the aqueous process condensate, wherein the remaining proportion of the aqueous process condensate is discharged from the process as a purge stream. This avoids enrichment of unwanted disruptive components within the steam generation circuit.

(8) In a further particular embodiment of the process according to the invention, it is provided that the first steam generator comprises two heat exchangers, wherein the generation of the first steam stream in the first steam generator is effected in indirect heat exchange against the second synthesis gas stream as the heating stream in the first heat exchanger and against a hot fresh steam stream as the heating stream in the second heat exchanger. The utilization of two different heating streams in the first steam generator to generate the first steam stream increases process mode flexibility, for example during startup of the process. Furthermore, utilization of the hot fresh steam stream as the heating stream in the second heat exchanger allows complete condensate evaporation even in the case of high condensate generation since the flow of the fresh steam can be chosen to be correspondingly large while by contrast the flow of the second synthesis gas stream as the heating stream in the first heat exchanger is determined by the flow of the crude synthesis gas. After its utilization as a heating stream, the now-cooled fresh steam stream may still be employed as a feedstock/in terms of its heat content in adjacent process stages or plant parts, for example in the generation of the crude synthesis gas, for example by steam reforming.

(9) In a particular embodiment of the process according to the invention, the reaction steam stream is composed of the first steam stream and the generation of the first steam stream in the first steam generator is effected by evaporation of the predominant proportion of the aqueous process condensate and a proportion of boiler feed water, wherein the remaining proportion of the aqueous process condensate is discharged from the process as a purge stream. In this way boiler feed water and fresh steam are saved and the obtained process condensate is used as a feedstock, wherein recycling of the process condensate advantageously results in disruptive components present therein being at least partially catalytically decomposed over the CO conversion catalyst.

(10) It is preferable when the reaction steam stream is composed of the first steam stream and the generation of the first steam stream in the first steam generator is effected by evaporation of the predominant proportion of the aqueous process condensate and a proportion of boiler feed water, wherein the remaining proportion of the aqueous process condensate is discharged from the process as a purge stream and wherein the proportion of boiler feed water is equal in quantity to the purge stream. This provides a simple option for controlling, and especially keeping constant, the steam generation circuit.

(11) A particular embodiment of the plant according to the invention is characterized in that it further comprises means which allow the reaction steam stream to be composed of the first steam stream and a fresh steam stream and the generation of the first steam stream to be affected in the first steam generator by evaporation of boiler feed water. Such a generation of the reaction steam stream from a plurality of components provides increased flexibility, for example upon startup of the plant.

(12) An alternative embodiment of the plant according to the invention is characterized in that it comprises means which allow the reaction steam stream to be composed of the first steam stream and a fresh steam stream and the generation of the first steam stream to be effected in the first steam generator by evaporation of at least a portion of the aqueous process condensate. In this way the condensate obtained is utilized and treatment/disposal cost and complexity is reduced. This also makes it possible to reduce the consumption of boiler feed water.

(13) Preference is given to a particular embodiment of the plant according to the invention which provides that means are comprised which allow the reaction steam stream to be composed of the first steam stream and the generation of the first steam stream in the first steam generator to be effected by evaporation of the predominant proportion of the aqueous process condensate, wherein the remaining proportion of the aqueous process condensate is discharged from the process as a purge stream. This avoids enrichment of unwanted disruptive components within the steam generation circuit.

(14) In a further particular embodiment of the plant according to the invention, it is provided that the first steam generator comprises two heat exchangers, wherein the generation of the first steam stream is effected in the first steam generator in indirect heat exchange against the second synthesis gas stream as the heating stream in the first heat exchanger and against a hot fresh steam stream as the heating stream in the second heat exchanger. The utilization of two different heating streams in the first steam generator to generate the first steam stream increases process mode flexibility, for example during startup of the plant. Furthermore, utilization of the hot fresh steam stream as the heating stream in the second heat exchanger allows complete condensate evaporation even in the case of high condensate generation since the flow of the fresh steam can be made correspondingly large while by contrast the flow of the second synthesis gas stream as the heating stream in the first heat exchanger is determined by the flow of the crude synthesis gas. After its utilization as a heating stream, the now-cooled fresh steam stream may still be employed as a feedstock/in terms of its heat content in adjacent process stages or plant parts, for example in the generation of the crude synthesis gas, for example by steam reforming.

(15) In a particular embodiment of the plant according to the invention, means are comprised which allow the reaction steam stream to be composed of the first steam stream and the generation of the first steam stream in the first steam generator to be effected by evaporation of the predominant proportion of the aqueous process condensate and a proportion of boiler feed water, wherein the remaining proportion of the aqueous process condensate is discharged from the process as a purge stream. In this way boiler feed water and fresh steam are saved and the obtained process condensate is used as a feedstock, wherein recycling of the process condensate advantageously results in disruptive components present therein being at least partially catalytically decomposed over the CO conversion catalyst.

(16) It is preferable when means are also comprised which allow the reaction steam stream to be composed of the first steam stream and the generation of the first steam stream in the first steam generator to be effected by evaporation of the predominant proportion of the aqueous process condensate and a proportion of boiler feed water, wherein means are also comprised which allow the remaining proportion of the aqueous process condensate to be discharged from the process as a purge stream and wherein the proportion of boiler feed water is equal in quantity to the purge stream. This provides a simple option for controlling, and especially keeping constant, the steam generation circuit.

(17) Further features, advantages and possible applications of the invention are also apparent from the following description of a working and numerical example and from the drawings. All the features described and/or depicted; on their own or in any combination, form the subject-matter of the invention, irrespective of their combination in the claims or their dependency references.

(18) The controlling, gating and conveying devices, for example valves, gate valves or pumps, shown in the figures, are shown merely by way of example to help elucidate the process sequence. A person skilled in the art will know to accordingly provide any further devices of the abovementioned types if required or advantageous.

(19) In the embodiment shown schematically in FIG. 1 of a process/a plant 1 according to a first exemplary embodiment of the invention, crude synthesis gas is supplied from a plant for synthesis gas generation (not shown) via conduit 10. Since in the present working example synthesis gas generation is carried out by coal gasification, the generated crude synthesis gas still contains sulfur components such as for example hydrogen sulfide (H.sub.2S). The crude synthesis gas is therefore subjected to a desulfurization in desulfurization reactor 11. This may be affected for example by adsorptive or absorptive binding of the sulfur to suitable sorbents, for example zinc oxide (ZnO). A dedusting filter (not shown) is often arranged upstream of the desulfurization reactor.

(20) Depending on the type of catalysts used for the CO conversion, it is also possible to use other process embodiments in which the desulfurization reactor is arranged downstream of the CO conversion stages, arranged between a plurality of CO conversion stages or eschewed entirely. In the literature this process mode is also referred to as crude gas shift or acid gas shift while the embodiment described hereinabove is also referred to as a sweet gas shift.

(21) The desulfurized and optionally deducted crude synthesis gas leaves the desulfurization reactor as the first synthesis gas stream having a first H.sub.2/CO ratio via conduit 12 and is combined with a steam stream as reaction steam stream which is supplied via conduit 18. The combined gas streams are heated in heat exchanger 20 in indirect heat exchange against hot reactor product gas from the reactor 25 and via conduit 21 enter into reactor 25 which forms the first CO conversion stage. Effected here under CO conversion conditions is a first partial reaction of the CO present in the first synthesis gas stream with the added steam to obtain a second synthesis gas stream having a second, elevated H.sub.2/CO ratio which is discharged from the reactor 25 via conduit 26. Due to the exothermicity of the CO conversion reaction, the temperature of the gas stream leaving the reactor 25 is higher than that of the gas stream entering the reactor and therefore a portion of the liberated heat energy is transferred via a heat exchanger 20 to the gas stream supplied via conduit 12.

(22) Via conduit 28 the second synthesis gas stream is discharged from the heat exchanger 20 and introduced into a heat exchanger integrated into a first steam generator 30 as a heating stream. In the first steam generator 30 a further portion of the heat energy from the second synthesis gas stream is utilized for steam generation, in particular for generation of the reaction steam required for CO conversion. The boiler feed water required therefor is passed to the first steam generator 30 via the conduits 56, 57, 58, 60 and control valve 59. Via conduits 33, 35, 16, 18 and control valves 34, 17 the generated steam is discharged from the first steam generator and supplied to the first synthesis gas stream in conduit 12. In addition, superheated high-pressure steam is supplied via conduits 13, 15 and control valve 14 and combined with the steam stream in conduit 35.

(23) Via conduit 32 the further cooled second synthesis gas stream is discharged from the heat exchanger of the first steam generator and supplied to a first heat exchanger integrated into a second steam generator 40. In the second steam generator 40 a further portion of the heat energy of the second synthesis gas stream is utilized for steam generation, wherein the steam thus generated is discharged from the second steam generator via a conduit (not shown) and may be supplied to external consumers for example. The boiler feed water required therefor is passed to the second steam generator 40 via the conduits 56, 57, 62 and control valve 61.

(24) Via conduit 42 the further cooled second synthesis gas stream is discharged from the first heat exchanger of the second steam generator and supplied to a reactor 50 which forms a second CO conversion stage. Effected here is a further partial reaction of the CO present in the second synthesis gas stream under CO conversion conditions with steam still present to obtain a third synthesis gas stream having a third, further elevated H.sub.2/CO ratio which is discharged from the reactor 50 via conduit 51. Due to the exothermicity of the CO conversion reaction, the temperature of the gas stream leaving the reactor 50 is higher than that of the gas stream entering the reactor and therefore the third synthesis gas stream is supplied to a second heat exchanger likewise integrated into the second steam generator 40. Thus, in the second steam generator 40 a portion of the heat energy from the third synthesis gas stream is likewise utilized for steam generation.

(25) Via conduit 52 the cooled third synthesis gas stream is discharged from the second heat exchanger of the second steam generator and introduced into a heat exchanger 55. Effected therein is the further cooling of the third synthesis gas stream in indirect heat exchange against cold boiler feed water which is supplied via conduit 56 to the heat exchanger 55 and, now heated, discharged therefrom via conduit 57. The further cooled third synthesis gas stream is then supplied via conduit 65 to an air cooler 66. Effected therein is a further cooling of the third synthesis gas stream to below its dew point in indirect heat exchange against ambient air. The further cooled third synthesis gas stream, now cooled to below its dew point, is subsequently discharged from the air cooler via conduit 68 and supplied to a phase separator 70. Effected therein is separation of the third synthesis gas stream into a gaseous, converted synthesis gas product which is discharged from the process/from the plant via conduit 72 and supplied to a conditioning or further processing that is not discussed further here.

(26) A liquid, water-containing condensate is discharged from the phase separator via conduit 74. It contains typical trace components such as CO, CO.sub.2, H.sub.2, CH.sub.4, NH.sub.3 and methanol and must therefore be sent for special workup or disposal.

(27) In the embodiment shown schematically in FIG. 2 of a process/a plant 2 according to a second exemplary embodiment of the invention, the plant parts having reference numerals 10 to 74 correspond to what is recited above in the discussion of FIG. 1 in terms of their structure, functions and properties unless otherwise stated. Now newly included are the conduits 75, 77, 78, 80 and also pump 76 and control valve 79 through which at least a portion and optionally the entirety of the condensate obtained in the phase separator save for a small purge stream is passed to the first steam generator 30 where it is used for generation of a portion of the reaction steam required for the CO conversion. Before entry into the first steam generator the recycled condensate is heated in indirect heat exchange against the third synthesis gas stream in the additional heat exchanger 64 which is connected to the heat exchanger 55 via the newly included conduit 63. It is advantageous in this embodiment of the invention that the trace components present in the condensate are partially decomposed and thus reduced in terms of their concentration upon renewed contacting with the CO conversion catalysts present in the reactors 25 and 50. The amount of condensate discharged from the process/the plant and thus the cost and complexity for disposal or external workup of the condensate is further reduced. A significant amount of boiler feed water is also saved.

(28) In the embodiment shown schematically in FIG. 3 of a process/a plant 3 according to a third exemplary embodiment of the invention, the first steam generator is provided both with boiler feed water and with recycled condensate in contrast to the previously discussed embodiments of the invention according to FIGS. 1 and 2. The reaction steam required for the CO conversion is exclusively generated in the first steam generator and combined with the first synthesis gas stream in conduit 12. In order to provide the greater amount of energy required for the evaporation of the now greater amount of liquid in the first steam generator, the first steam generator is provided with a second integrated heat exchanger into which superheated high-pressure steam is introduced via conduits 13, 81 and control valve 14. Once heat exchange has taken place the cooled steam is discharged from the second integrated heat exchanger via conduit 82. In contrast to the embodiments of the invention discussed with reference to FIGS. 1 and 2 the supplied high-pressure steam is not used as a feedstock but utilized only in terms of its enthalpy content. It may subsequently be supplied to external consumers as heating steam or process steam, thus providing additional economic advantages.

(29) The table which follows summarizes and compares typical operating parameters of the embodiments of the invention discussed hereinabove in order to verify numerically the advantages mentioned hereinabove in the discussion of the individual embodiments.

(30) TABLE-US-00001 TABLE Typical operating parameters of the embodiments of the invention, FIGS. 1 to 3 Mass flows t/h) FIG. 1 FIG. 2 FIG. 3 Steam to 5 5 5 conduit (13) Steam from 0 0 5 conduit (82) Steam 5 5 0 consumption as feedstock Condensate from 10 5 <1 conduit (74) Condensate recycling 0 5 >9 conduit (75) Steam from (30) 5 5 10 conduit (35)

(31) The invention provides a process for producing a converted synthesis gas/a corresponding plant allowing resource-efficient, energetically optimized generation of reaction steam for CO conversion with low apparatus complexity. Recycling of the obtained condensate for production of reaction steam reduces the consumption of boiler feed water and of high-pressure steam. The discharged amount of condensate and the cost and complexity for disposal or external workup of the condensate are reduced. Furthermore, the trace components present in the condensate are partially decomposed and thus reduced in terms of their concentration upon renewed contacting with the CO conversion catalysts.

LIST OF REFERENCE NUMERALS

(32) 1,2,3 Plant 10 Conduit 11 Desulfurization reactor 12 Conduit 13 Conduit 14 Control valve 15 Conduit 16 Conduit 17 Control valve 18 Conduit 20 Heat exchanger 21 Conduit 25 Reactor (first CO conversion stage) 26 Conduit 28 Conduit 30 First steam generator 32 Conduit 33 Conduit 34 Control valve 35 Conduit 40 Second steam generator 42 Conduit 50 Reactor (second CO conversion stage) 51 Conduit 52 Conduit 55 Heat exchanger 56 Conduit 57 Conduit 58 Conduit 59 Control valve 60 Conduit 61 Control valve 62 Conduit 63 Conduit 64 Heat exchanger 65 Conduit 66 Air cooler 68 Conduit 70 Phase separator 72 Conduit 74 Conduit 75 Conduit 76 Pump 77 Conduit 78 Conduit 79 Control valve 80 Conduit 81 Conduit 82 Conduit