GB2168718A

GB2168718A - Producing synthesis gas

Info

Publication number: GB2168718A
Application number: GB08427288A
Authority: GB
Inventors: Anthony Horton
Original assignee: Humphreys and Glasgow Ltd
Current assignee: Humphreys and Glasgow Ltd
Priority date: 1984-10-29
Filing date: 1984-10-29
Publication date: 1986-06-25
Also published as: GB8427288D0; GB2168718B

Abstract

High temperature gases leaving a reformer wherein hydrocarbons are converted to gases including oxides of carbon are mixed with carbon dioxide and passed through a catalyst promoting the reaction of carbon dioxide and hydrogen to carbon monoxide and water i.e. in a back shift converter. The stream leaving the converter may be passed through a carbon dioxide removal system, the carbon dioxide removed being heated and recycled to the exit of the reformer.

Description

SPECIFICATION Process for the production of synthesis gas and its utilisation There are many areas ofthe world having cheap natural gas, much of which is flared because it is associated with oil production, and many companies are endeavouring to utilise such gas.

In the present state of the artthere are two main meansforconverting the natural gas to raw synthesis gas: namely tubular steam reforming and, secondly, those processes utilising oxygen or an oxygencontaining gas, commonly referred to as partial oxidation or automatic processes.

In both the presently known processes the raw synthesis gas leaves the primary process unit at a very high temperature. The temperature is so high that very expansive means are needed to contain it, and thus it is usually cooled to a more manageable temperature by means of a waste heat boiler which generates a high pressure steam.

This process does not cool the very high temperature gases bythe aforesaid means but adds to the very high temperature gases carbon dioxide, and then passes the resultant mixture through a catalyst which causes some of the carbon dioxide to react with hydrogen to form additional carbon monoxide. Inasmuch as the reaction of carbon monoxide with water to form carbon dioxide and hydrogen is commonly referred to as the water gas shift reaction, or just the shift reaction, the abovementioned reaction producing carbon monoxide from carbon dioxide may be referred to as back shifting.

There art a nut area numberofpossiblesourcesofthe carbon dioxide which is added. The carbon dioxide may be that which could be removed from the effluent ofthe back shifting reactor. Normallythiswould be carried out after cooling ofthe gases, or the carbon dioxide may comefrom the removal of carbon dioxide fromthe natural gas feed, orthe carbon dioxide may be imported, say from an ammonia or fermentation plant or from a carbon dioxide well, or carbon dioxide may be recovered from flue gas.Alternatively the carbon dioxide may be recovered from a stream which arises in the downstream processing ofthe effluent of the back shift reactor In this invention the carbon dioxide stream which is added to the very high temperature gases may contain other gases but preferably does not contain a high percentage of carbon monoxide or steam.

In the back shift reactor some of the carbon oxides may be methanated which reaction is very exothermic and such exotherm helps supply heat too. Indeed under certain circumstances the temperature during back shifting may even rise because there is an excess of heat release due to methanation over back shifting.

Intheevent that the carbon dioxide stream added to the high temperature stream comes from a carbon dioxide removal unit which is located just downstream of the back shift reactor (after cooling) then the recovered CO2 would probably be compressed and then recycled as above. This arrangement has the advantage both of supplying the necessary carbon dioxide for the back shift reaction and also removing the carbon dioxide from the back shift reactor effluent, leaving a gas rich in carbon monoxide and hydrogen.

Should any carbon dioxide removal unit use a thermal regeneration process there is usuallysufficient low grade heat to effect such regeneration from downstream processes.

As an alternative means of recovering the carbon dioxide a permeable membrane process such as Monsanto Prism Process may be used, for example, the effluent of the back shift reactor after cooling may be passed to such a unit whereupon, possibly after a preliminary hydrogen rich stream has been removed by a permeable membrane unit, a mixed carbon dioxide/hydrogen stream may be removed and this carbon dioxide/hydrogen rich stream may be the stream which is recycled to the very high temperature stream. In this case the presence of hydrogen has an advantageous effect in that it moves the equilibrium of the reaction back towards carbon monoxide, although care must be taken to ensure that it does not simultaneously cause too much methanation, which in turn would result in a loss of carbon monoxide, and indeed a very high heat release.

The effluent from the back shift reaction, preferably after CO2 removal and preferably after adjusting the hydrogen/carbon monoxide ratio by means such as a permeable membrane processora pressure swing adsorption process, maythen be utilised from synthesis processes such as Fischer-Tropsch, and OXO alcohols. For such processes the hydrogen/carbon monoxide ratio would be above .5.

Alternatively, after carbon dioxide removal the carbon monoxidecontent in the gas may be recovered by means such as a selective solvent processes such as the Cosorb process, or by means of pressure swing adsorption, or by cryogenic means.

In this invention feedstock has been referred to as natural gas but a wide range of hydrocarbon materiats may be used, including ethane.

In this application there is provided an invention characterised by A. the reforming of a hydrocarbon to gases, including oxides of carbon B. the addition of a carbon dioxide containing gas to the hot effluent from A C. passing the mixture through a catalyst promoting the reaction of carbon dioxide and hydrogen to carbon monoxide and water.

1. A process characterised by: A. the reforming of a hydrocarbon to gases, inciuding oxides of carbon B. the addition of a carbon dioxide containing gas to the hot effluent from A.

C. passing the mixture through a catalyst promoting the reaction of carbon dioxide and hydrogen to carbon monoxide and water.

2. A process as claimed in claim 1 wherein the carbon dioxide containing gas is recovered from the effluentofthe back shifted reactor.

3. A process as claimed in claim 1 wherein the carbon dioxide containing gas is recovered by removing from the hydrocarbon feed.

4. A process as claimed in claim 1 wherein carbon dioxide is supplied from a well or a carbon dioxide

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Process for the production of synthesis gas and its utilisation There are many areas ofthe world having cheap natural gas, much of which is flared because it is associated with oil production, and many companies are endeavouring to utilise such gas. In the present state of the artthere are two main meansforconverting the natural gas to raw synthesis gas: namely tubular steam reforming and, secondly, those processes utilising oxygen or an oxygencontaining gas, commonly referred to as partial oxidation or automatic processes. In both the presently known processes the raw synthesis gas leaves the primary process unit at a very high temperature. The temperature is so high that very expansive means are needed to contain it, and thus it is usually cooled to a more manageable temperature by means of a waste heat boiler which generates a high pressure steam. This process does not cool the very high temperature gases bythe aforesaid means but adds to the very high temperature gases carbon dioxide, and then passes the resultant mixture through a catalyst which causes some of the carbon dioxide to react with hydrogen to form additional carbon monoxide. Inasmuch as the reaction of carbon monoxide with water to form carbon dioxide and hydrogen is commonly referred to as the water gas shift reaction, or just the shift reaction, the abovementioned reaction producing carbon monoxide from carbon dioxide may be referred to as back shifting. There art a nut area numberofpossiblesourcesofthe carbon dioxide which is added. The carbon dioxide may be that which could be removed from the effluent ofthe back shifting reactor. Normallythiswould be carried out after cooling ofthe gases, or the carbon dioxide may comefrom the removal of carbon dioxide fromthe natural gas feed, orthe carbon dioxide may be imported, say from an ammonia or fermentation plant or from a carbon dioxide well, or carbon dioxide may be recovered from flue gas.Alternatively the carbon dioxide may be recovered from a stream which arises in the downstream processing ofthe effluent of the back shift reactor In this invention the carbon dioxide stream which is added to the very high temperature gases may contain other gases but preferably does not contain a high percentage of carbon monoxide or steam. In the back shift reactor some of the carbon oxides may be methanated which reaction is very exothermic and such exotherm helps supply heat too. Indeed under certain circumstances the temperature during back shifting may even rise because there is an excess of heat release due to methanation over back shifting. Intheevent that the carbon dioxide stream added to the high temperature stream comes from a carbon dioxide removal unit which is located just downstream of the back shift reactor (after cooling) then the recovered CO2 would probably be compressed and then recycled as above. This arrangement has the advantage both of supplying the necessary carbon dioxide for the back shift reaction and also removing the carbon dioxide from the back shift reactor effluent, leaving a gas rich in carbon monoxide and hydrogen. Should any carbon dioxide removal unit use a thermal regeneration process there is usuallysufficient low grade heat to effect such regeneration from downstream processes. As an alternative means of recovering the carbon dioxide a permeable membrane process such as Monsanto Prism Process may be used, for example, the effluent of the back shift reactor after cooling may be passed to such a unit whereupon, possibly after a preliminary hydrogen rich stream has been removed by a permeable membrane unit, a mixed carbon dioxide/hydrogen stream may be removed and this carbon dioxide/hydrogen rich stream may be the stream which is recycled to the very high temperature stream. In this case the presence of hydrogen has an advantageous effect in that it moves the equilibrium of the reaction back towards carbon monoxide, although care must be taken to ensure that it does not simultaneously cause too much methanation, which in turn would result in a loss of carbon monoxide, and indeed a very high heat release. The effluent from the back shift reaction, preferably after CO2 removal and preferably after adjusting the hydrogen/carbon monoxide ratio by means such as a permeable membrane processora pressure swing adsorption process, maythen be utilised from synthesis processes such as Fischer-Tropsch, and OXO alcohols. For such processes the hydrogen/carbon monoxide ratio would be above .5. Alternatively, after carbon dioxide removal the carbon monoxidecontent in the gas may be recovered by means such as a selective solvent processes such as the Cosorb process, or by means of pressure swing adsorption, or by cryogenic means. In this invention feedstock has been referred to as natural gas but a wide range of hydrocarbon materiats may be used, including ethane. In this application there is provided an invention characterised by A. the reforming of a hydrocarbon to gases, including oxides of carbon B. the addition of a carbon dioxide containing gas to the hot effluent from A C. passing the mixture through a catalyst promoting the reaction of carbon dioxide and hydrogen to carbon monoxide and water. CLAIMS

4. A process as claimed in claim 1 wherein carbon dioxide is supplied from a well or a carbon dioxide producing process such as an ammonia plant or a fermentation process.

5. Products produced from gases produced from the aforementioned processes.

Newclaimsoramendmentstoclaimsfiled on 13 Feb'86.

Superseded claims 1 only.

1. A process characterised by: A.the reforming of a hydrocarbon to gases, including oxides of carbon B.the addition a carbon dioxide containing gasto the hoteffluentfrom A C.passing the mixture through a catalyst promoting the reaction of carbon dioxide and hydrogen to carbon monoxide and water but which does not promote the formationMecomposition of methane.

3. A process as claimed in claim 1 wherein the carbon dioxide containing gas is recovered by removing itfromthe hydrocarbon feed.