AU2016204971B2

AU2016204971B2 - Process for reforming hydrocarbons

Info

Publication number: AU2016204971B2
Application number: AU2016204971A
Authority: AU
Inventors: Kim Aasberg-Peterson; Peter Seier Christensen; Thomas Sandahl Christensen
Original assignee: Haldor Topsoe AS
Current assignee: Topsoe AS
Priority date: 2011-06-29
Filing date: 2016-07-15
Publication date: 2017-01-12
Anticipated expiration: 2032-06-20
Also published as: AU2016204971A1

Abstract

The invention relates to a process for the production of synthesis gas by the use of autothermal reforming in 5 which tail gas from downstream Fischer-Tropsh synthesis is hydrogenated and then added to the autothermal reforming stage.

Description

1 2016204971 15 Μ 2016

Title: Process for Reforming Hydrocarbons

FIELD OF THE INVENTION 5 The present invention relates to a process for the production of synthesis gas used for the production of hydrocarbons by Fischer-Tropsch synthesis. The invention relates in particular to a process for the production of synthesis gas by the use of autothermal reforming in 10 which tail gas from a downstream process, in particular Fischer-Tropsh synthesis, is hydrogenated and then added to the autothermal reforming. In a more general aspect the invention encompasses the removal of olefins in a gas to reduce metal dusting of metal parts in contact with 15 the gas, particularly for the reduction of metal dusting in ATR, CPO or POx and other downstream equipment through which the gas is passed.

BACKGROUND OF THE INVENTION 20

The production of synthesis gas for Fischer-Tropsch synthesis is typically obtained by passing a hydrocarbon feed through primary and secondary reforming stages. The primary reforming is often conducted in tubular steam 25 reformers or heat exchange reformers, while the secondary reforming is typically conducted in autothermal reformers. When combining a heat exchange reformer with a subsequent autothermal reformer, the hot effluent gas from the autothermal reformed is usually used as heating 30 medium in the heat exchange reformer. It is known to recycle tail gas from Fischer-Tropsch synthesis as part of the hydrocarbon feed used to produce the synthesis gas 2 2016204971 15M2016 in the primary and secondary reforming stages. Tail gas can be added prior to the primary reforming or to the primary reformed gas before entering the secondary reforming (typically autothermal reforming). 5

Tail gas from Fischer-Tropsch synthesis contains hydrogen, carbon monoxide, carbon dioxide as well as light hydrocarbons in the form of paraffins such as methane, ethane, propane and not least olefins such as 10 propylene. The tail gas may also include alcohols and other higher hydrocarbons of both paraffinic and olefinic nature. It is known that the addition of such tail gas to the synthesis gas production section enables that there is sufficient carbon dioxide during the reforming to 15 achieve the desired H2/CO molar ratio, typically about 2.0.

As used herein "tail gas" means off-gas from the Fischer-Tropsch synthesis stage which is not re-used in said 20 stage.

Hydrogenation of tail gas is known in the art. For instance, in GB 632386 tail gas from Fischer-Tropsch synthesis is hydrogenated in order to increase the 25 otherwise low heating value of this gas caused by the presence of i.a. carbon dioxide, carbon monoxide and hydrogen. WO-A-0142175 discloses a process in which tail gas is 30 hydrogenated in order to saturate any unsaturated hydrocarbons and is then reformed in a separate steam reformer. The hydrogenation serves to decrease the 3 2016204971 15 Μ 2016 tendency towards coking in the subsequent high temperature treatment of the steam reformer, since the tendency to coking in said reformer is greater when unsaturated hydrocarbons are present in the tail gas. The 5 resulting reformed tail gas may subsequently also be passed to an autothermal reformer. Accordingly, a steam reformer is used between the hydrogenation stage and the autothermal reformer. 10 EP-A-1860063 discloses a process in which off-gas from

Fischer-Tropsch synthesis where olefins present in the off-gas are first hydrogenated and then converted to hydrogen by a reforming process. Olefins are hydrogenated because of carbon deposition or coking of catalysts used 15 in the hydrogen manufacturing unit and which form hot spots on the catalyst and the reformer reactor tubes. Thus, olefins are removed to avoid coking in a steam reformer having reformer tubes such as a fired reformer.

20 SUMMARY OF THE INVENTION 30

We have now found out that the addition of tail gas to the autothermal reformer (ATR), or catalytic partial oxidation reactor (CPO), or non-catalytic partial 25 oxidation reactor (POx), which is desirable in order to adjust the H2/CO ratio in the synthesis gas, has the severe drawback of promoting metal dusting corrosion, particularly in the burner parts of the ATR or CPO, yet by hydrogenation of the tail gas prior to its direct addition to the ATR such metal dusting is significantly reduced. It has come as a surprise to the applicant that the removal of particularly olefins in the tail gas via 4 2016204971 15 Μ 2016 hydrogenation conveys the critical advantage of significantly reducing the aggressiveness of the tail gas and hence reducing or eliminating metal dusting in the ATR, or CPO or POx. At the same time the benefits of 5 using tail gas to adjust the H2/CO ratio are maintained.

The reduction or elimination of metal dusting in an apparatus, e.g. ATR, CPO or POx, according to the simple, economical and elegant solution provided by the present 10 invention translates directly into the reduction or elimination of costly down-time periods in the plant and reduces thereby maintenance costs. Metal dusting has otherwise been mitigated through the use of resistant alloy compositions or metallic coatings that form 15 protective surfaces under metal dusting conditions, and/or by operating the reformer at less metal dusting aggressive conditions but which on the other hand impair the process. Yet even the use of expensive and otherwise effective alloys against metal dusting such as Inconel 20 690 cannot withstand metal dusting attack when exposed to tail gas from Fischer-Tropsch synthesis.

Metal dusting is a type of metallic corrosion that may be encountered when gases containing carbon monoxide come 25 into contact with metals above ca. 400°C, particularly in the range 400-800°C. Metal dusting conveys the disintegration of metals to dust and is described extensively in the literature. 30 Metal dusting is a highly complex corrosion process which is not completely understood. However, it is often represented by the following reaction: 5 2016204971 15M2016 CO + H2 - C + H20 (1)

The formed carbon results in corrosion of the construction material possibly by a mechanism including 5 carbide formation and/or dissolution of the carbon in the metal material.

Carbon formation via the exothermic reactions 2CO"^ C + C02 (Boudouard reaction) and CO + H2 C + H20 (CO-10 reduction) is a precursor for metal dusting (MD) corrosion. The exothermic reactions are favoured at low temperatures. However, the reaction rates are higher at higher temperatures. As a result, the MD potential for a given gas will be highest in a medium temperature range, 15 typically in the range of about 400-800°C.

It has to be appreciated, however, that metal dusting and coking are two different phenomena. While metal dusting refers to catastrophic corrosion of metal parts, coking 20 is associated with the catalyst. Coking refers more 30 specifically to carbon formation negatively affecting the catalyst of a steam reformer such as a tubular reformer due to formation of carbonaceous elements that deposit and dissociate on the nickel surface or support material 25 of the steam reforming catalyst (typically a nickel-based catalyst). This may convey also the development of hot spots in the tubes containing the catalyst. Accordingly, for the skilled person metal dusting and coking are two different phenomena: while it has been known for long that the presence of olefins causes coke deposition in catalyst beds, no one has ever seen nor expected that 2016204971 15 Μ 2016 6 olefins are also responsible for causing such a different phenomenon as metal dusting.

Accordingly, in a first aspect of the invention we 5 provide a process for the production of synthesis gas from a hydrocarbon feedstock with reduced metal dusting potential in at least the burner parts of an autothermal reformer (ATR), catalytic partial oxidation reactor (CPO), or partial oxidation reactor (POx) comprising: 10 passing said hydrocarbon feedstock through an ATR, CPO or POx, and withdrawing a stream of hot effluent synthesis gas from the ATR, CPO or POx, passing tail gas from a Fischer-Tropsch synthesis stage through a hydrogenation stage to produce a hydrogenated tail gas and adding the 15 hydrogenated tail gas directly to said ATR, CPO or POx.

The hydrogenation of the tail gas results in a gas that protects the ATR, CPO or POx from metal dusting, particularly for ATR and CPO the burner metal parts 20 located at the inlet of the reactor and thus upstream the catalyst bed, as it unexpectedly turns out that the absence of olefins makes a gas less aggressive with respect to metal dusting corrosion. 25 Hence, there is provided in an elegant and simple manner a solution to the long-standing problem of metal dusting of metal parts in the ATR, CPO or POx, particularly burner parts of the ATR, which were encountered when incorporating tail gas from Fischer-Tropsch synthesis 30 into the process. 7 2016204971 15M2016

As used herein the term "reduced metal dusting potential in at least the burner parts of an autothermal reformer (ATR), catalytic partial oxidation reactor (CPO), or partial oxidation reactor (POx)" means that the metal 5 dusting potential is reduced in any metal part within the reactor being in contact with the process gas fed to the it (ATR, CPO, POx) including burner metal parts, particularly for ATR or POx. It would be understood by the skilled person that ATR and POx imply the use of a 10 burner at the top of the reactor. ATR and CPO use a catalyst bed below the combustion zone. CPO means a catalytic reactor or catalytic gasifier which does not always require the use of a burner, but a mixer instead. Further, in a POx (gasifier) there is no use of catalyst. 15 The term ATR includes secondary reformers.

Since the tail gas contains carbon monoxide, carbon dioxide, hydrogen, various hydrocarbons including olefins and a range of other components as described above, the 20 gas is converted by reducing the olefin concentration by hydrogenation according to the following reaction C3H6 + H2 *-> C3H8. The reaction is given for propylene hydrogenation but hydrogenation of other olefins takes place according to a similar reaction. 25

Catalysts suitable for selectively hydrogenating the olefins to saturated hydrocarbons are preferably based on copper, for instance a Cu/ZnO catalyst, or a combination of copper and a noble metal, for instance platinum or 30 palladium. A copper based catalyst, such as Cu/ZnO catalyst, is particularly active in the selective hydrogenation of olefins to paraffins with reduced 8 2016204971 15 Μ 2016 formation or without the formation of methanol or higher alcohols having two or more carbon atoms in their structure . 5 In connection with the above and below embodiments, the hydrogenation is preferably conducted in a cooled reactor, particularly at a temperature in the range 100-150°C or higher, for instance 185°C. This enables high conversion of olefins such as C3H6 and C4H8 while at the 10 same time avoiding significant formation of methanol or higher alcohols and other by-products. Alternatively, the hydrogenation is conducted in an adiabatic reactor in which the inlet temperature is preferably in the range 70-120°C, more preferably 80-100°C, and the outlet 15 temperature is 120-210°C, preferably 140-190°C, more preferably 150-185°C.

The pressure in the hydrogenation step is in the range 20-70 bar, preferably 20-50 bar, more preferably 20-40 20 bar.

In one embodiment of the invention said hydrocarbon feedstock is a gas that has passed through at least one adiabatic pre-reforming stage. 25

Adiabatic pre-reforming is preferably conducted in a fixed bed reactor containing a reforming catalyst, thereby converting all higher hydrocarbons into a mixture of carbon oxides, hydrogen and methane. This endothermic 30 process is accompanied by the equilibration of exothermic methanation and shift reactions. Removal of higher 9 2016204971 15 Μ 2016 hydrocarbons allows a higher preheat temperature to the subsequent steam reforming.

In another embodiment of the invention said hydrocarbon 5 feedstock is a gas that has passed through at least one steam reforming stage. The steam reforming stage may for instance be tubular reforming (steam methane reforming, SMR) or heat exchange reforming (convective reforming). 10 In yet another embodiment, the invention encompasses also a process wherein said hydrocarbon feedstock is a gas mixture resulting from dividing a raw hydrocarbon feed gas into two streams, passing the first stream through at least one steam reforming stage to form a primary 15 reformed gas, using the second stream as a by-pass stream to said steam reforming stage, and subsequently combining said primary reformed gas with the by-pass stream to form said hydrocarbon feedstock. 20 According to this embodiment, steam reforming is arranged in series with the ATR, CPO or POx.

In a separate embodiment, an arrangement where steam reforming is arranged in parallel with the ATR, CPO or 25 POx, is also provided. Hence, the process comprises dividing a raw hydrocarbon feed gas into two streams, by which one of the streams formed becomes said hydrocarbon feedstock, and passing the other stream through at least one steam reforming stage to form a reformed gas. 30

In another embodiment in combination with anyone of the above or below embodiments, there is provided a process 10 2016204971 15 Μ 2016 wherein the steam reforming stage is heat exchange reforming, and where at least a portion of the hot effluent synthesis gas from the ATR, or CPO, or POx stage is used as heating medium in said heat exchange 5 reforming.

Hence, one preferred embodiment is a process in which a heat exchange reformer is arranged upstream and in series with an ATR or CPO, preferably an ATR. The raw 10 hydrocarbon feed, for example desulphurised natural gas, is mixed with steam and the resultant mixture is directed to the catalyst side of the heat exchange reformer. In the heat exchange reformer, the gas is then steam reformed according to the reactions: CH4 + H20 «-> CO + 3H2 15 and CO + H20 «-» C02 + H2. The gas leaving the heat exchange reformer is close to chemical equilibrium for the reactions above. Typically, the exit temperature is 600-850°C or preferably 675-775°C. The primary reformed gas leaving the heat exchange reformer is passed to the ATR 20 or CPO. In the reactor (ATR or CPO) also oxygen and in some cases a small amount of steam is added. Synthesis gas is formed by a combination of steam reforming and partial oxidation in the reactor. The gas leaving the reactor is free of oxygen and generally the above 25 reactions are close to chemical equilibrium. The temperature of this hot effluent gas from e.g. an autothermal reformer is between 950 and 1100°C, typically between 1000 and 1075°C. 30 This hot effluent gas leaving the reactor comprises carbon monoxide, hydrogen, carbon dioxide, steam, residual methane, and various other components including 11 2016204971 15 Μ 2016 nitrogen and argon. This synthesis gas is passed to the non-catalytic side of the heat exchange reformer, where it is cooled by supplying heat to the catalytic side of the heat exchange reformer by indirect heat exchange. The 5 exit temperature from this side of the heat exchange reformer would typically be in the range from 500-800°C.

It also follows that in another preferred embodiment a heat exchange reformer is arranged in parallel with an 10 ATR, CPO or POx, preferably an ATR, and hot effluent synthesis gas from the ATR, CPO or POx is used to provide heat for the endothermic reforming reactions in the heat exchange reformer. 15 In the parallel arrangement said hot effluent synthesis gas is combined with said reformed gas before, during or after said hot effluent synthesis gas has delivered heat to the heat exchange reforming. Preferably, said hot effluent synthesis gas is combined with said reformed gas 20 before it has delivered heat to the heat exchange reforming.

In yet another embodiment in combination with one of the above or below embodiments, the process comprises also 25 adding a stream comprising steam to said hot effluent synthesis gas, said reformed gas, or the combined stream of hot effluent synthesis gas and reformed gas.

Hence, regardless of whether the heat exchange reformer 30 is arranged in series or in parallel with the ATR, CPO or POx, steam is introduced to the gas from the ATR, CPO or POx delivering heat to the heat exchange reformer. This 2016204971 15M2016 30 12 enables reduction of metal dusting in the metal parts, particularly the shell side, of the heat exchange reformer, particularly where the heat exchange reformer is in series arrangement with the ATR, CPO or POx. This 5 stream comprising steam contains preferably more than 90 vol% of steam (H20 in the vapour phase), more preferably more than 95%, and most preferably more than 99%. Preferably, the temperature of the hot effluent synthesis gas is 950 to 1050°C, more preferably 1025°C, while the 10 steam added is preferably at 271°C at 55 barg, thus resulting in a temperature of the mixed stream, i.e. hot effluent synthesis gas combined with stream comprising steam, of 900 to 990°C. 15 In a further embodiment in combination with anyone of the above or below embodiments, the at least one adiabatic pre-reforming stage is conducted prior to dividing said raw hydrocarbon feed. Hence, prior to dividing the raw hydrocarbon feed gas in separate streams in the series or 20 parallel arrangements, adiabatic pre-reforming of the raw hydrocarbon feed (typically comprising methane and higher hydrocarbons) is conducted.

In an another embodiment in combination with anyone of 25 the above or below embodiments, the process comprises also mixing the hydrogenated tail gas with the hydrocarbon feedstock prior to conducting reforming in the ATR, CPO or POx; or alternatively, adding the hydrogenated tail gas to the ATR, CPO or POx as a separate stream. 13 2016204971 15 Μ 2016

In connection with the operation of the series arrangement as described above, there is also provided a process comprising mixing the hydrogenated tail gas with said by-pass stream prior to conducting reforming in the 5 ATR, CPO or POx; or alternatively, mixing the hydrogenated tail gas with said primary reformed gas.

In yet a further embodiment in combination with anyone of the above embodiments, the process further comprises of 10 converting the synthesis gas into liquid hydrocarbons, particularly diesel via Fischer-Tropsch synthesis.

In a second aspect the invention encompasses the use of hydrogenated tail gas from a Fischer-Tropsch synthesis 15 stage as means for reduction of metal dusting in an autothermal reformer (ATR), catalytic partial oxidation reactor(CPO), or partial oxidation reactor (POx).

Hence, according to this aspect the invention encompasses 20 the use of a known substance (hydrogenated tail gas) to obtain the surprising technical effect of reduced metal dusting in an ATR, CPO or POx. Alternative expensive methods such as the provision of resistant alloy compositions or metallic coatings that form protective 25 surfaces under metal dusting conditions are thus avoided.

Tail gas from Fischer-Tropsch synthesis is hydrogenated, thereby converting olefins (alkenes) into alkanes, and thus unexpectedly results in reduction of metal dusting 30 in at least the burner parts of the reactor compared to a situation where the tail gas is added directly, without being hydrogenated. Since the use of tail gas is 14 2016204971 15 Μ 2016 desirable in order to adjust the H2/CO ratio in the synthesis gas, this is now possible without risking expensive downtime periods and maintenance costs in the ATR, CPO or POx due to metal dusting issues. 5

The hydrogenated tail gas contains preferably less than 1 mol% olefins, more preferably less than 1 mol%, most preferably below 0.5 mol%, such as less than 0.2 mole %, or less than 0.1 mole %. 10

The hydrogenated tail gas is added directly to the ATR, CPO or POx, as illustrated in the enclosed Figures. The term "directly" means without any intermediate processes which change the chemical composition of the hydrogenated 15 tail gas, e.g. without a steam reformer between said hydrogenation stage and said ATR, CPO or POx.

In a broader aspect the invention encompasses also a method for reducing metal dusting in an apparatus, said 20 apparatus containing an off-gas, said method comprising the removal of olefins from said off-gas. In particular, olefins are removed by hydrogenation thereof. The method is particularly useful for the reduction of metal dusting in ATR, CPO or POx and other downstream equipment through 25 which off-gas is passed. The invention encompasses a method for the reduction of metal dusting in an ATR, CPO or POx and further downstream equipment by removing the content of olefins in an off-gas to be passed through the ATR, CPO or POx. 30

Preferably, said step of removing the content of olefins is a hydrogenation stage. 15 2016204971 15 Μ 2016

As used herein the term "further downstream equipment" means waste heat boiler and/or steam superheater located downstream the ATR, CPO or POx and which are used for 5 cooling the synthesis gas under the production of steam.

As used herein the term "removing the content of olefins" means reducing the content of olefins in the gas to less than 0.2 mole %, preferably less than 0.1 mole %. 10

As used herein the term "off-gas" means any gas containing hydrocarbons and olefins, which has to be reformed in the ATR, CPO or POx to form a synthesis gas comprising hydrogen and carbon monoxide. The off-gas is 15 preferably tail gas from Fischer-Tropsch synthesis or tail gas from downstream process for production of gasoline, such as a process in which gasoline is produced from oxygenates comprising methanol and dimethyl ether, for instance via the so-called TIGAS process as disclosed 20 in US Patent 4520216 and US 4481305.

The invention encompasses also the use of a gas free of olefins as means for the reduction of metal dusting of the metal parts of apparatus in direct contact with the 25 gas. Preferably the apparatus in direct contact with the gas is an ATR, CPO or POx. Preferably, the gas is an offgas; i.e. the waste gas from an industrial process such as gasoline synthesis as defined above. 30

As used herein and in accordance above the term "gas free of olefins" a gas with less than 0.2 mole %, preferably less than 0.1 mole % olefins. 2016204971 15M2016 16

As used herein the term "in direct contact with the gas" means that the gas free of olefins is added directly to the equipment or to a separate hydrocarbon feedstock 5 without first being passed through an intermediate stage of reforming, such as steam reforming.

Features of the invention: 10 The invention is also disclosed by the below features in correspondence with the appended claims. 1. Process for the production of synthesis gas from a hydrocarbon feedstock with reduced metal dusting 15 potential in at least the burner parts of an autothermal reformer (ATR), catalytic partial oxidation reactor (CPO), or partial oxidation reactor (POx) comprising: passing said hydrocarbon feedstock through an ATR, CPO or POx, and 20 withdrawing a stream of hot effluent synthesis gas from the ATR, CPO or POx, passing tail gas from a Fischer-Tropsch synthesis stage through a hydrogenation stage to produce a hydrogenated tail gas and adding the hydrogenated tail gas directly 25 to said ATR, CPO or POx. 2. Process according to feature 1 wherein said hydrocarbon feedstock is a gas that has passed through at least one adiabatic pre-reforming stage. 30 17 2016204971 15 Μ 2016 3. Process according to feature 1 or 2 wherein said hydrocarbon feedstock is a gas that has passed through at least one steam reforming stage. 5 4. Process according to any of features 1 to 3 wherein said hydrocarbon feedstock is a gas mixture resulting from dividing a raw hydrocarbon feed gas into two streams, passing the first stream through at least one steam reforming stage to form a 10 primary reformed gas, using the second stream as a by-pass stream to said steam reforming stage, and subsequently combining said primary reformed gas with the by-pass stream to form said hydrocarbon feedstock. 15 5. Process according to any of features 1 to 3 comprising dividing a raw hydrocarbon feed gas into two streams, by which one of the streams becomes said hydrocarbon feedstock, and passing the other 20 stream through at least one steam reforming stage to form a reformed gas. 6. Process according to any of features 3-5 wherein the steam reforming stage is heat exchange 25 reforming, and where at least a portion of the hot effluent synthesis gas from the ATR, CPO, or POx is used as heating medium in said heat exchange reforming. 30 7. Process according to feature 5 or 6 wherein said hot effluent synthesis gas is combined with said reformed gas before, during or after said hot 18 2016204971 15 Μ 2016 effluent synthesis gas has delivered heat to the heat exchange reforming. 8. Process according to feature 6 or 7 comprising 5 adding a stream comprising steam to said hot effluent synthesis gas, said reformed gas, or the combined stream of hot effluent synthesis gas and reformed gas. 10 9. Process according to any of features 4 to 8 wherein the at least one adiabatic pre-reforming stage is conducted prior to dividing said raw hydrocarbon feed. 15 10.Process according to any of features 1 to 9 comprising mixing the hydrogenated tail gas with the hydrocarbon feedstock prior to conducting reforming in the ATR, CPO or POx. 20 11.Process according to any of features 1-9 comprising adding the hydrogenated tail gas to the ATR, CPO or POx as a separate stream. 12. Process according to any of features 4, 8 and 9 25 comprising mixing the hydrogenated tail gas with said by-pass stream prior to conducting reforming in the ATR, CPO or POx. 13. Process according to any of features 4, 6, 8 and 9 30 comprising mixing the hydrogenated tail gas with said primary reformed gas. 19 2016204971 15 Μ 2016 14.Process according to any of features 1-13 further comprising converting the synthesis gas into liquid hydrocarbons via Fischer-Tropsch synthesis. 5 15.A method for reducing metal dusting in an apparatus, said apparatus containing an off-gas, said method comprising the removal of olefins from said off-gas. 10 16.The method according to feature 15, wherein olefins are removed by hydrogenation thereof. 17. The method according to any one of features 15-16 wherein the apparatus is an ATR, CPO or POx 15 18. The use of a gas free of olefins for the reduction of metal dusting of the metal parts of apparatus in direct contact with said gas. 20 19.The use according to feature 18, wherein the apparatus in direct contact with the gas is an ATR, CPO or POx. 20. The use according to any one of features 18-19, 25 wherein the gas is a tail gas from a Fischer

Tropsch synthesis. 21. The use according to any one of features 18-20, wherein the gas free of olefins is obtained by 30 hydrogenation of said olefins to alkanes.

BRIEF DESCRIPTION OF THE DRAWINGS 20 2016204971 15 Μ 2016

The invention is further illustrated by reference to the accompanying figures. Fig. 1 shows a schematic view of the invention when using a stand-alone autothermal 5 reformer yet including a pre-reformer. Fig. 2 shows heat exchange reforming and autothermal reforming in series with hydrogenated tail gas addition to the primary reformed gas. Fig. 3 shows a process with by-pass of the primary reforming stage, with addition of hydrogenated 10 tail gas to the by-pass stream, or to the combined stream of primary reformed gas and by-pass stream.

DETAILED DESCRIPTION OF FIGURES 15 The accompanying Fig. 1 shows a general schematic view of an embodiment for the production of synthesis gas for Fischer-Tropsch synthesis using a stand-alone autothermal reformer. Clean (free of sulphur and other poisons to reforming catalysts) hydrocarbon feed gas 100 such as 20 natural gas or other hydrocarbon containing gas source is mixed with process steam 110, optionally partly via saturator/humidifier. The mixture is preheated and prereformed adiabatically in pre-reformer 300 in order to convert any higher hydrocarbons into H2, CO, C02 and CH4. 25 This resulting hydrocarbon feedstock mixture 120 is fed to the autothermal reformer 400 together with oxygen 130, protection steam 140 and hydrogenated tail gas 150. From the autothermal reformer 400 at hot effluent of synthesis gas 160 is withdrawn and further processed to form the 30 synthesis gas feed to the downstream Fischer-Tropsch section 500. Liquid hydrocarbons 170 are produced and tail gas recycle stream 180 is passed through 2016204971 15M2016 30 21 hydrogenating stage 600 prior to entering the autothermal reformer 400. Notably, hydrogenated tail gas is added directly from the hydrogenator to the autothermal reformer 400. 5

In Fig. 2, a mixture of the raw hydrocarbon feed gas and steam 10 is passed to heat-exchange reformer 25 where it is catalytically steam reformed and thereafter leaves the heat-exchange reformer as stream 30. The primary reformed 10 gas stream 30 is mixed with hydrogenated tail gas 65 from Fischer-Tropsch section 150 forming the ATR feed stream 70. The mixed stream 70 is fed to an autothermal reformer 75 with oxidant 80 and protection steam (not shown) also being supplied. The primary reformed gas is partially 15 combusted and brought towards equilibrium over reforming catalyst in the autothermal reformer 75. The hot effluent synthesis gas 110 from the autothermal reformer is passed through the heat exchange reformer 25. The synthesis gas is cooled by heat exchange with the gas undergoing 20 reforming over the catalyst in the heat-exchange reformer 25. The thus cooled synthesis gas leaves the heat exchange reformer as stream 120 and is further processed to form the synthesis gas feed to the Fischer-Tropsch section 150 downstream. Liquid hydrocarbon products 140 25 are withdrawn together with a tail gas recycle stream 60. The tail gas recycle stream 60 passes through hydrogenator 160 to form hydrogenated tail gas stream 65 before being combined with primary reformed gas 30. Notably, hydrogenated tail gas is added directly from the hydrogenator to the autothermal reformer 400. 22 2016204971 15 Μ 2016

In Fig. 3, a mixture of raw hydrocarbon feed gas (10) is divided into two streams 20 and 40. The first stream 20 is fed to the heat-exchange reformer 25 where it is catalytically steam reformed and thereafter leaves the 5 heat-exchange reformer as primary reformed gas 30. The second stream 40 is preheated in a heat exchanger 45 and bypasses the heat exchange reformer. The primary reformed gas 30 is mixed with the preheated second stream 50. Hydrogenated tail gas 65 is added to this mixed stream or 10 to the preheated second stream 50 thus forming the ATR feed stream 70. The ATR feed stream is fed to the autothermal reformer 75 to which oxidant 80 and protection steam (not shown) are also supplied. The ATR feed stream is partially combusted and brought towards 15 equilibrium over reforming catalyst in the autothermal reformer 75. The hot effluent synthesis gas 110 is passed through the heat exchange reformer 25. The mixture stream is cooled by heat exchange with the gas undergoing reforming over the catalyst in the heat-exchange reformer 20 25. The thus cooled synthesis gas leaves the heat exchange reformer as stream 120 and is further processed to form the synthesis gas feed to the Fischer-Tropsch section 150 downstream. Liquid hydrocarbon products 140 are withdrawn together with a tail gas recycle stream 60. 25 The tail gas recycle stream 60 passes through 30 hydrogenator 160 to form hydrogenated tail gas stream 65 which is then combined with primary reformed gas 30 or by-pass stream 50. Alternatively, the hydrogenated tail gas 65 may also be added to the primary reformed stream 30. Notably, hydrogenated tail gas is added directly from the hydrogenator to the autothermal reformer 400. 2016204971 15 Μ 2016 23

EXAMPLE

Two tests were made in the same experimental setup:

An 800 mm long sample of Inconel 690 was placed in a 5 reactor. The reactor was placed in an oven with three heating zones. The temperature of the Inconel 690 sample varied with the position in the oven. The sample temperatures were 200 to 640°C. The sample was exposed to a continuous flow of gas with the composition given in 10 Table 1 as Test 1. The flow rate was 100 Nl/h. The pressure was 29 barg. The conditions were kept for 626 hours. The sample was examined after the test using stereo microscope and scanning electron microscope. The sample was attacked by metal dusting corrosion. 15

The second test was made analogous to the first test, with the exceptions that the gas composition used was as given in Table 1 as Test 2 and the conditions were kept for 672 hours. Examination of the sample after the test 20 showed that the sample was not attacked by metal dusting corrosion. 2016204971 15M2016 24

Table 1 Gas compositions (mole %) Component Test 1 Test 2 Hydrogen 12.1 12.1 Water 22.6 22.6 Carbon 6.9 6.9 monoxide Carbon 7.8 7.8 dioxide Ethylene 0.14 0 Ethane 0 0.14 Methane 49.8 49.8 Propane 0.45 0.45 1-Butene 0.21 0 Butane 0 0.21

The two gas compositions in the two tests are identical 5 with the exception that the gas in test 1 contains the olefins (alkenes), whereas the gas in test 2 contains the corresponding alkanes. Metal dusting attack occurs in Test 1 but not in Test 2, which is of longer duration. 10 The presence of alkenes makes a gas more aggressive with respect to metal dusting corrosion. Thus, the use of a hydrogenated tail gas conveys the reduction or elimination of metal dusting compared to a situation where tail gas is used without being hydrogenated. 15

Claims

1. Process for the production of liquid hydrocarbons from a hydrocarbon feedstock comprising: a. passing said hydrocarbon feedstock through an ATR, CPO or POx, and withdrawing a stream of hot effluent synthesis gas from the ATR, CPO or POx, b. converting the synthesis gas into liquid hydrocarbons via Fischer-Tropsch synthesis, c. passing tail gas from the Fischer-Tropsch synthesis stage through a hydrogenation stage to produce a hydrogenated tail gas containing less than 1 mol% olefins, and d. adding the hydrogenated tail gas directly to said ATR, CPO or Pox; e. optionally recovering the liquid hydrocarbons produced.

2. Process according to claim 1 wherein said hydrocarbon feedstock is a gas that has passed through at least one adiabatic pre-reforming stage.

3. Process according to claim 1 or 2 wherein said hydrocarbon feedstock is a gas that has passed through at least one steam reforming stage.

4. Process according to any one of claims 1 to 3 wherein said hydrocarbon feedstock is a gas mixture resulting from dividing a raw hydrocarbon feed gas into two streams, passing the first stream through at least one steam reforming stage to form a primary reformed gas, using the second stream as a by-pass stream to said steam reforming stage, and subsequently combining said primary reformed gas with the by-pass stream to form said hydrocarbon feedstock.

5. Process according to any one of claims 1 to 3 comprising dividing a raw hydrocarbon feed gas into two streams, by which one of the streams becomes said hydrocarbon feedstock, and passing the other stream through at least one steam reforming stage to form a reformed gas.

6. Process according to any one of claims 3-5 wherein the steam reforming stage is heat exchange reforming, and where at least a portion of the hot effluent synthesis gas from the ATR, CPO, or POx is used as heating medium in said heat exchange reforming.

7. Process according to claim 5 or 6 wherein said hot effluent synthesis gas is combined with said reformed gas before, during or after said hot effluent synthesis gas has delivered heat to the heat exchange reforming.

8. Process according to claim 6 or 7 comprising adding a stream comprising steam to said hot effluent synthesis gas, said reformed gas, or the combined stream of hot effluent synthesis gas and reformed gas.

9. Process according to any one of claims 4 to 8 wherein the at least one adiabatic pre-reforming stage is conducted prior to dividing said raw hydrocarbon feed.

10. Process according to any one of claims 1 to 9 comprising mixing the hydrogenated tail gas with the hydrocarbon feedstock prior to conducting reforming in the ATR, CPO or POx.

11. Process according to any one of claims 1-9 comprising adding the hydrogenated tail gas to the ATR, CPO or POx as a separate stream.

12. Process according to any one of claims 4, 8 or 9 comprising mixing the hydrogenated tail gas with said by-pass stream prior to conducting reforming in the ATR, CPO or POx.

13. Process according to any one of claims 4, 6, 8 or 9 comprising mixing the hydrogenated tail gas with said primary reformed gas.

14. Process according to any one of claims 1-13, wherein the hydrogenated tail gas of step c) contains below 0.5 mol% .

15. Process according to any one of claims 1-13, wherein the hydrogenated tail gas of step c) contains less than 0.2 mo1e % .

16. Process according to any one of claims 1-13, wherein the hydrogenated tail gas of step c) contains less than 0.1 mole %.