System and process for production of synthesis gas

Abstract

A system for production of a synthesis gas, including: a synthesis gas generation reactor arranged for producing a first synthesis gas from a hydrocarbon feed stream; a post converter including a catalyst active for catalyzing steam methane reforming, methanation and reverse water gas shift reactions; the post converter including a conduit for supplying a CO.sub.2 rich gas stream into a mixing zone of the post converter, where the CO.sub.2 rich gas stream in the conduit upstream the mixing zone is in heat exchange relationship with gas flowing over the catalyst downstream the mixing zone; a pipe combining the at least part of the first synthesis gas and the CO.sub.2 rich gas stream to a mixed gas, in a mixing zone being upstream the catalyst; wherein the post converter further includes an outlet for outletting a product synthesis gas from the post converter. Also, a corresponding process.

Claims

1. A system for production of a synthesis gas, comprising: a synthesis gas generation reactor arranged for producing a first synthesis gas from a hydrocarbon feed stream; and a post converter comprising a shell housing a catalyst, said catalyst being active for catalyzing steam methane reforming, methanation and reverse water gas shift reactions; said post converter comprising a conduit for supplying a CO.sub.2 rich gas stream into a mixing zone of said post converter, said mixing zone being upstream said catalyst, where said CO.sub.2 rich gas stream in said conduit upstream said mixing zone is in heat exchange relationship with gas flowing over said catalyst downstream the mixing zone; where said system further comprises a pipe for supplying at least a part of said first synthesis gas from said synthesis gas generation reactor into said mixing zone of said post converter, thereby combining said at least part of the first synthesis gas and said CO.sub.2 rich gas stream to a mixed gas, wherein said post converter further comprises an outlet for outletting a product synthesis gas from said post converter.

2. A system according to claim 1, wherein said synthesis gas generation reactor is an autothermal reforming reactor, a thermal partial oxidation reactor, a catalytic partial oxidation reactor or a steam methane reforming reactor.

3. A system according to claim 1, wherein said conduit comprises a first part arranged for conducting said CO.sub.2 rich gas stream in heat exchange relationship with said product synthesis gas.

4. A system according to claim 1, wherein said conduit comprises a second part arranged for conducting said CO.sub.2 rich gas stream in heat exchange relationship with the mixed gas in said mixing zone.

5. A system according to claim 1, wherein said CO.sub.2 rich gas stream is heated in a fired heater, in an electrically heated heater, by heat exchange with at least part of the product synthesis gas exiting the post converter, and/or by heat exchange with superheated steam prior to being inlet into the post converter.

6. A system according to claim 1, wherein the catalyst is a steam reforming catalyst.

7. A process for production of a synthesis gas, comprising: in a synthesis gas generation reactor producing a first synthesis gas from a hydrocarbon feed stream; supplying a CO.sub.2 rich gas stream into a mixing zone of a post converter via a conduit, where said post converter comprises a shell housing a catalyst, where said CO.sub.2 rich gas stream in said conduit upstream said mixing zone is in heat exchange relationship with gas flowing over catalyst prior to mixing said CO.sub.2 rich gas stream with at least part of the first synthesis gas in said mixing zone, supplying said at least a part of the first synthesis gas from said synthesis gas generation reactor into a mixing zone of said post converter via a pipe, thereby combining said at least part of the first synthesis gas and said CO.sub.2 rich gas stream to a mixed gas, where said post converter, said catalyst being active for catalyzing steam methane reforming, methanation and reverse water gas shift reactions, and where said mixing zone is upstream said catalyst, producing a product synthesis gas from said mixed gas by carrying out steam methane reforming, methanation and reverse water gas shift reactions over said catalyst, and outletting said product synthesis gas from said post converter.

8. A process according to claim 7, wherein said synthesis gas generation reactor is an autothermal reforming reactor, a partial oxidation reactor, a catalytic partial oxidation reactor or a steam methane reforming reactor.

9. A process according to claim 7, wherein said CO.sub.2 rich gas stream is conducted in heat exchange relationship with said product synthesis gas upstream said catalyst.

10. A process according to claim 7, wherein said CO.sub.2 rich gas stream is conducted in heat exchange relationship with the mixed gas in said mixing zone downstream said catalyst.

11. A process according to claim 7, wherein said CO.sub.2 rich gas stream is heated in a fired heater, in an electrically heated heater, by heat exchange with at least part of the product synthesis gas exiting the post converter, and/or by heat exchange with superheated steam prior to being inlet into the post converter.

12. A process according to claim 7, wherein the catalyst is a steam reforming catalyst.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) An embodiment of the present invention is explained, by way of example, and with reference to the accompanying drawing. It is to be noted that the appended drawing illustrates only an example of an embodiment of this invention and is therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

(2) FIG. 1 is a schematic drawing of an embodiment of the system for production of synthesis gas according to the invention.

DETAILED DESCRIPTION

(3) FIG. 1 shows a system 100 for production of a product synthesis gas 12. The system 100 comprises a synthesis gas generation reactor 10 arranged for producing a first synthesis gas 5 from a hydrocarbon feed stream 3. In the embodiment of FIG. 1, the synthesis gas generation reactor 10 is an autothermal reforming (ATR) reactor.

(4) A hydrocarbon feed stream 3 to the ATR reactor 10 is made up of a stream of hydrocarbon gas 1, such as natural gas, which is combined with a stream 2 of steam and possibly CO.sub.2. The combination of the hydrocarbon gas 1 and the stream 2 of steam and possibly CO.sub.2 is the hydrocarbon feed stream 3 let into the ATR reactor 10.

(5) An oxygen containing stream 4, such as air, a stream of steam and oxygen, an oxygen rich stream or substantially pure oxygen, is inlet into the ATR reactor 10 via an inlet. In the ATR reactor 10, partial combustion of the hydrocarbon feed stream 3 by sub-stoichiometric amounts of oxygen in the oxygen containing stream 4 is followed by steam reforming of the partially combusted feedstock in a fixed bed 11 of steam reforming catalyst, thereby producing the first synthesis gas 5 comprising hydrogen, carbon monoxide, and carbon dioxide. The first synthesis gas 5 exiting the ATR reactor 10 typically has a temperature of between about 900° C. and about 1100° C., such as about 1000° C.

(6) The system 100 moreover comprises a post converter 20 comprising a shell 22 housing a bed of catalyst 21.

(7) The system 100 comprises a pipe (not shown in FIG. 1) for supplying at least a part of the first synthesis gas 5 from the synthesis gas generation reactor into a mixing zone 20c of the post converter 20. The post converter 20 also has a conduit 23 for supplying a CO.sub.2 rich gas stream 6 into the mixing zone 20c of the post converter 20, so that the CO.sub.2 rich gas stream in the conduit upstream the mixing zone 20c is in heat exchange relationship with gas flowing over the catalyst 21, viz. downstream the mixing zone, prior to being mixed with the at least part of the first synthesis gas 5 in the mixing zone 20c. In the embodiment shown in FIG. 1, the catalyst 21 is housed within shell of the post converter 20 and outside the conduit 23, i.e. between the shell 22 and the conduit 23.

(8) The post converter 20 comprises three zones or parts: a mixing zone 20c, a catalyst zone 20b and a product gas zone 20a. Correspondingly, the conduit 23 has three parts: a first part where the CO.sub.2 rich gas stream 6 is conducted within the conduit 23 in heat exchange relationship with product synthesis gas in the product gas zone 20a; a second part where the CO.sub.2 rich gas stream 6 is conducted within the conduit 23 in heat exchange relationship with gas in the catalyst zone 20b; and a third part where the CO.sub.2 rich gas stream 6 is conducted within the conduit 23 in heat exchange relationship with mixed gas in the mixing zone 20c. The extent of the mixing zone 20c and/or the product gas zone 20a along the longitudinal axis (not shown in FIG. 1) may be relatively small, e.g. in a case where the catalyst zone 20b is relatively large.

(9) The post converter 20 also comprises an outlet for outletting a product synthesis gas 12 from the post converter 20.

(10) In the system 100, the first synthesis gas 5 is used as the source of heat in the post converter 20. However, the CO.sub.2 rich gas stream 6 may be preheated prior to being let into the post converter 20 via the conduit 23.

(11) The catalyst 21 carries out steam methane reforming, methanation and reverse water gas shift reactions of the mixed gas, thereby providing a product synthesis gas 12. Downstream the catalyst zone 20b, the product synthesis gas undergoes heat exchanges with the CO.sub.2 rich gas stream 6 within the first part of the conduit 23.

(12) The arrows 25 indicate the direction of the flow of the CO.sub.2 rich gas stream 6 from within the conduit 23. Within the mixing zone 20c, the first synthesis gas 5 and CO.sub.2 rich gas stream 6 are mixed to a mixed synthesis gas.

Example

(13) An example calculation of the process is given in Table 1 below. A hydrocarbon feed stream comprising a hydrocarbon gas, CO.sub.2 and steam and having a S/C ratio of 0.6 is fed to the ATR reactor 10 of the invention as shown in FIG. 1. The hydrocarbon feed stream is heated to 650° C. prior to being let into the ATR reactor 10. An oxygen rich stream 4 is added and the amount is adjusted such that the temperature of the first synthesis gas 5 is 1050° C. The ATR reactor 10 produces a first synthesis gas 5.

(14) The total flow of all components in all inlet streams to the ATR reactor and the flow of all components in the first synthesis gas 5 are given in the column headed “ATR 10” in Table 1.

(15) A CO.sub.2 rich gas stream let into the conduit and is heated in the conduit to a temperature of 988° C. by heat exchange with the gas flowing between the conduit and the shell, within the mixing zone 20c, the catalyst zone 20b and the product gas zone 20a. The CO.sub.2 rich gas stream is mixed with the first synthesis gas to form a mixed synthesis gas, having a temperature of 1038° C.

(16) Within the catalyst zone 20b of the post converter 20 the combined stream is equilibrated, viz. it undergoes reverse water gas shift, methanation and reforming reactions to equilibrium. The exit temperature of the product synthesis gas 12 exiting the post converter 20 is around 995° C., which is well below the methane decomposition equilibrium temperature for the gas of 1349° C. and above the Boudouard temperature for the gas of 860° C. Consequently, the product synthesis gas 12 does not have potential for carbon formation.

(17) TABLE-US-00001 TABLE 1 Catalyst bed of Post Exit of Post ATR 10 CO.sub.2 6 converter 20 converter 20 Inlet T [° C.] 650 180 1038 Outlet T [° C.] 1050 988 995 853 Inlet P [kg/cm.sup.2g] 35.5 35.5 34.5 34 Outlet P [kg/cm.sup.2g] 34.5 34.5 34 33.5 Outlet T(MDC) [° C.] — — 1349 Outlet T(BOU) [° C.] 891 — 860 Inlet: N.sub.2 [Nm.sup.3/h] 26 245 CO.sub.2 [Nm.sup.3/h] 8487 11615 17583 CH.sub.4 [Nm.sup.3/h] 18695 373 H.sub.2 [Nm.sup.3/h] 394 31372 H.sub.2O [Nm.sup.3/h] 11321 16988 CO [Nm.sup.3/h] 0 20842 Oxygen inlet: O.sub.2 [Nm.sup.3/h] 10735 N.sub.2 [Nm.sup.3/h] 219 Oxygen feed T [° C.] 371 Outlet: N.sub.2 [Nm.sup.3/h] 245 245 245 CO.sub.2 [Nm.sup.3/h] 5968 11615 12720 12720 CH.sub.4 [Nm.sup.3/h] 373 392 392 H.sub.2 [Nm.sup.3/h] 31372 26451 26451 H.sub.2O [Nm.sup.3/h] 16988 21870 21870 CO [Nm.sup.3/h] 20842 25685 25685 Total outlet flow [Nm.sup.3/h] 75788

(18) Thus, when the system and process are used, it is possible to provide a product synthesis gas having a relative high amount of CO. In the example of Table 1, the H.sub.2/CO ratio is 1.0, while the H/C and O/C ratios are 2.5 and 1.9, respectively.

(19) In this context, the methane decomposition temperature (T(MDC)) is calculated as the temperature where the equilibrium constant of the methane decomposition into graphite (CH.sub.4.Math.C+2H.sub.2) equals the reaction quotient (QC) of the gas. Formation of graphitic carbon can take place when the temperature is higher than this temperature.

(20) The reaction quotient QC is defined as the ratio of the square of the partial pressure of hydrogen to the partial pressure of methane, i.e. QC=P.sup.2.sub.H2/P.sub.CH4.

(21) The Boudouard equilibrium temperature (T(BOU)) is calculated in a similar way, but from the Boudouard reaction (2CO.Math.C+CO.sub.2) and in this case formation of graphitic carbon can take place when the temperature is lower than this Boudouard equilibrium temperature.

(22) A comparative example of the corresponding numbers for producing a similar synthesis gas in system with an ATR reactor but without an adiabatic post converter, here denoted “a stand alone ATR reactor”, is shown in Table 2. In this case, all CO.sub.2 is added up-front the ATR reactor which operates at a S/C of 0.6. Comparing the examples shows that more oxygen is needed in the standalone ATR reactor.

(23) TABLE-US-00002 TABLE 2 Stand alone ATR Inlet T [° C.] 650 Outlet T [° C.] 1050 Inlet P [kg/cm.sup.2g] 35.5 Outlet P [kg/cm.sup.2g] 34.5 Outlet T (MDC) [° C.] — Inlet: N.sub.2 [Nm.sup.3/h] 26 CO.sub.2 [Nm.sup.3/h] 18678 CH.sub.4 [Nm.sup.3/h] 18967 H.sub.2 [Nm.sup.3/h] 400 H.sub.2O [Nm.sup.3/h] 11494 CO [Nm.sup.3/h] 0 Oxygen feed: O.sub.2 [Nm.sup.3/h] 11739 N.sub.2 [Nm.sup.3/h] 240 Oxygen feed T [° C.] 371 Outlet: N.sub.2 [Nm.sup.3/h] 266 CO.sub.2 [Nm.sup.3/h] 11807 CH.sub.4 [Nm.sup.3/h] 153 H.sub.2 [Nm.sup.3/h] 26493 H.sub.2O [Nm.sup.3/h] 23029 CO [Nm.sup.3/h] 25685 Total outlet flow [Nm.sup.3/h] 87433

(24) From Table 1 and Table 2, it is seen that the outlet flow from the ATR reactor in the case of the present invention is smaller than with a stand-alone ATR. This means that a smaller ATR can be designed by using the concepts of the invention. This also means that in case of revamps, the production of carbon monoxide can be boosted without the need for enlarging a given ATR reactor. This is done by adding the post converter to form a system and to operate a process according to the invention.

(25) The oxygen consumption (calculated as O.sub.2 consumed/CO produced [Nm.sup.3/Nm.sup.3]) is 0.418 versus 0.457 for the stand-alone ATR. Hence, oxygen is saved according to the invention which reduces the capital cost of the air separation unit for producing oxygen.