Title of Invention	A PROCESS FOR THE PREPARATION OF AMMONIA SYNTHESIS
Abstract	A process for the preparation of ammonia synthesis gas The present invention provides a process for the preparation of ammonia synthesis gas comprising the steps of mixing a feedstock gas and a flue gas to obtain a mixed gas; and feeding the feedstock gas mixed with the flue gas to at least one pair of reforming reactors, each reactor having a process and fuel side and a combustion side, each pair of reactors being arranged in parallel on the process and fuel side, and in series on the combustion side; wherein a flame temperature in each pair of reactors is controlled by supplying an excess of combustion air to a first reactor of the pair, and oxygen-depleted combustion air to a second reactor of the pair.

Title of Invention

A PROCESS FOR THE PREPARATION OF AMMONIA SYNTHESIS

Abstract

A process for the preparation of ammonia synthesis gas The present invention provides a process for the preparation of ammonia synthesis gas comprising the steps of mixing a feedstock gas and a flue gas to obtain a mixed gas; and feeding the feedstock gas mixed with the flue gas to at least one pair of reforming reactors, each reactor having a process and fuel side and a combustion side, each pair of reactors being arranged in parallel on the process and fuel side, and in series on the combustion side; wherein a flame temperature in each pair of reactors is controlled by supplying an excess of combustion air to a first reactor of the pair, and oxygen-depleted combustion air to a second reactor of the pair.

Full Text	This invention relates to a process for the prep¬aration of ammonia synthesis gas. Summary of the Invention The present invention provides a process for the preparation of ammonia synthesis gas. The process includes the steps of mixing a feedstock stream and a flue gas so as to obtain a mixed gas, and feeding the mixed gas in a split stream to at least one pair of reforming reactors. Each reactor has a process and fuel side, and a combustion side. Each pair of reactors is arranged in parallel on the pro¬cess and fuel side, and in series on the combustion side. The flame temperature in each reactor is maintained below about 14 00°C. The feedstock gas typically is desulphurized. Typically, the flue gas consists mostly of COj, HjO and N2 having been withdrawn from a second of each pair of reactors. The amount of flue gas is selected so as to obtain a predetermined H2/N2 ratio in the synthesis gas. The feedstock stream can further be mixed with steam. Preferably, the temperature in the first reactor is maintained by supplying air in a large excess, e.g. about 105% excess. Flue gas from the first reactor is supplied as combustion air for a second reactor of each pair of reac¬tors. The flue gas is oxygen depleted, which limits the flame temperature to below about 1400°C. Overall air excess is kept low, to about 5%. According to a preferred embodiment, the mixed gas is fed to at least two pairs of reactors. Each reactor is connected in parallel on the process gas side. Each pair of reactors is connected to another pair of reactors in series on the combustion side. The main advantages of the inventive process over the prior art are as follows: stoichiometric synthesis gas from NH3-production is produced in a heat exchange reforming reactor without use of enriched air or cryogenic separation of excess nitrogen; use of two reforming reactors in series on the combustion air side provides flame temperature control without excessive overall surplus of combustion air; release of NOx from the reforming process to the atmosphere is minimized; release of SO2 is eliminated; CO2 and steam formed by the combustion are partly used as reformer feed, reducing overall steam demand; and power for compression of combustion air is partly recovered by expansion of excess flue gas. In addition, steam reforming of feed gas being admixed with nitrogen and carbon dioxide-containing flue gas from a subsequent heat exchange steam reforming process step provides higher steam reforming conversion rates of carbon hydride feedstock, and thus a lower concentration of unconverted carbonhydrides in the reactor effluent. In the steam reforming reactor, necessary heat for the endothermic steam reforming reactions is provided by indirect heat exchange with pressurized flue gas. To provide the flue gas for use in the heat exchanging steam reforming process, fuel is combusted with excess of air in a first heat exchange steam reforming step air resulting in lower combustion temperatures in the reactor. Oxygen-containing flue gas is then withdrawn from the first reforming step, intermediately cooled, and fur¬ther combusted with additional fuel in one or more subsequently reforming steps. Other features and advantages of the present inven¬tion will become apparent from the following description of the invention which refers to the accompanying drawings. Accordingly the present invention relates to a process for the preparation of ammonia synthesis gas comprising the steps of mixing a feedstock gas and a flue gas to obtain a mixed gas; and feeding the feedstock gas mixed with the flue gas to at least one pair of reforming reactors, each reactor having a process and fuel side and a combustion side, each pair of reactors being arranged in parallel on the process and fuel side, and in series on the combustion side; wherein a flame temperature in each pair of reactors is controlled by supplying an excess of combustion air to a first reactor of the pair, and oxygen-depleted combustion air to a second reactor of the pair. The invention will now be described more in detail with reference to the accompanying drawings, in which; Brief Description of the Drawings Fig. 1 is a diagram of the process according to the present invention. Fig. 2 is a diagram of an alternative embodiment of the process of the present invention. Detailed Description of the Invention Referring to Fig. 1, a simplified form of the process of the present invention is illustrated. Feedstock 20 typically is natural gas being desulphurized and split into two streams. The feedstock is mixed with steam 30 and a predetermined amount of deoxygenated, pressurized flue gas 40 (see below) to obtain the correct Hj/Nj ratio requested in the syngas being produced. The.gas mixture is used as process gas in two heat exchange reforming reactors 60,80 arranged in parallel on the process and the fuel side and in series on the combination air side. Exit tempera¬tures from each catalyst bed 62,82 being arranged in the reforming reactors is high to ensure reasonably low CH4-leakage. Air 100 is compressed to a pressure slightly higher than the pressure of the process gas upstream the heat exchangers. The air is first used as combustion air in the first heat exchange burner 64, which operates on large excess of air (about 105% excess) to keep the flame tem¬perature below 1400°C. After having exchanged heat with reformer tubes in the first reactor, the pressurized flue gas 102 (at about 600°C) is further used as combustion air in the second reactor 80. The combustion air is oxygen-depleted, which limits the flame temperature to below about 1400°C, while the overall air excess is kept low, about 5%. Flue gas 104 from the second reactor is split into two streams 106,108. Stream 106 is expanded to provide part of the power required for air compression. The residual amount of flue gas 108 is passed to a deoxygenator for removal of remaining traces of oxygen and further to the feed stream to the reactors as described above. Referring to Fig. 2, a further specific embodiment of the invention is illustrated, according to which methane in a process gas is steam reformed in four heat exchange steam reforming reactors I, II, III and IV. The reformers are of the conventional bayonet tube type with an inner tube coaxially arranged in an outer sheath tube. Steam reforming catalyst is loaded in an annular space defined between the walls of the inner tube and the outer tube. Necessary heat for the endothermic steam reforming reactions proceeding in the process gas is thereby provided by hot flue gas passing externally along the wall of the sheath tube. Prior to introduction of process gas 2, the gas is mixed with flue gas 4 consisting mainly of CO2, H2O and N2. Flue gas 4 is withdrawn from reactor II after having sup¬plied heat to the steam reforming reactions proceeding in the reactor. Flue gas 4 is admixed into the process gas in an amount to obtain the required Nj/Hj ratio to the syn¬thesis gas being prepared by steam reforming in reactors I through IV. Reactors I through IV are connected in parallel as concerns introduction on the mixed process gas 6. On the combustion/flue gas side the reactors are arranged in groups of reactors I, II and III, IV. The two reactor groups are connected in series. Reactors I and II are heated by burning fuel with pressurized air 8. Combustion in reactor I is carried out with excess of air to achieve a suitable combustion tem¬perature and to provide the necessary oxygen content in flue gas 10 being withdrawn from reactor I and introduced into reactor II for further combustion with fuel. Flue gas 12 being withdrawn from reactor II is cycled to deoxygenator 14 with a bed of conventional oxidation cata¬lyst in order to remove residual amounts of oxygen in the gas. From oxygenator 14, flue gas 4 consisting substan¬tially of nitrogen, carbon dioxide and water is cycled to and admixed with feed gas 2. Reactors III and IV, being connected in series on the flue gas side, are heated by burning fuel at atmos¬pheric pressure. Flue gas 16 leaving reactor III is passed to combustion in reactor IV. After having supplied heat to reactor IV, the flue gas is passed to conventional waste heat recovery. Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications will become apparent to those skilled in the art. Therefore, the present invention is to be limited not by the specific disclosure herein, but only by the appended claims. WE CLAIM: 1. A process for the preparation of ammonia synthesis gas comprising the steps of mixing a feedstock gas and a flue gas to obtain a mixed gas; and feeding the feedstock gas mixed with the flue gas to at least one pair of reforming reactors, each reactor having a process and fuel side and a combustion side, each pair of reactors being arranged in parallel on the process and fuel side, and in series on the combustion side; wherein a flame temperature in each pair of reactors is controlled by supplying an excess of combustion air to a first reactor of the pair, and oxygen-depleted combustion air to a second reactor of the pair. 2. The process as claimed in claim 1, wherein the flame temperature is maintained below about 1400°C. 3. The process as claimed in claim 1, wherein air in an excess of about 105% is supplied to the first reactor. 4. The process as claimed in claim 1, wherein oxygen-depleted flue gas fi-om the first reactor is supplied as combustion air for the second reactor of each pair of reactors, for limiting a flame temperature in the second reactor, an overall air excess in the second reactor being kept to about five per cent. 5. The process as claimed in claim 1, wherein the combustion air supplied to the first reactor is compressed to a pressure slightly higher than a pressure of the feedstock gas located upstream of the rectors. 6. The process as claimed in claim 1, wherein the flue gas from the second reactor is expanded to provide at least part of the power required for compression of the air. 7. The process as claimed in claim 1, wherein the flue gas mixed with the feedstock gas is withdrawn from a second of each pair of reactors. 8. The process as claimed in claim 1, wherein the mixed gas is fed to at least two pairs of reactors, and each pair of reactors is connected to another pair of reactors in series on the combustion side. 9. The process as claimed in claim 1, wherein the amount of flue gas mixed with the feedstock gas is selected so as to obtain a predetermined H2/N2 ratio in the synthesis gas. 10. The process as claimed in claim 1, wherein the feedstock is desulphurized. 11. A process for the preparation of ammonia synthesis gas substantially as herein described with reference to the accompanying drawings

Full Text

This invention relates to a process for the prep¬aration of ammonia synthesis gas.
Summary of the Invention
The present invention provides a process for the preparation of ammonia synthesis gas. The process includes the steps of mixing a feedstock stream and a flue gas so as to obtain a mixed gas, and feeding the mixed gas in a split stream to at least one pair of reforming reactors. Each reactor has a process and fuel side, and a combustion side. Each pair of reactors is arranged in parallel on the pro¬cess and fuel side, and in series on the combustion side. The flame temperature in each reactor is maintained below about 14 00°C. The feedstock gas typically is desulphurized.
Typically, the flue gas consists mostly of COj, HjO and N2 having been withdrawn from a second of each pair of reactors. The amount of flue gas is selected so as to obtain a predetermined H2/N2 ratio in the synthesis gas.
The feedstock stream can further be mixed with steam. Preferably, the temperature in the first reactor is maintained by supplying air in a large excess, e.g. about 105% excess. Flue gas from the first reactor is supplied as combustion air for a second reactor of each pair of reac¬tors. The flue gas is oxygen depleted, which limits the flame temperature to below about 1400°C. Overall air excess is kept low, to about 5%.
According to a preferred embodiment, the mixed gas is fed to at least two pairs of reactors. Each reactor is connected in parallel on the process gas side. Each pair of reactors is connected to another pair of reactors in series on the combustion side.

The main advantages of the inventive process over the prior art are as follows:
stoichiometric synthesis gas from NH3-production is produced in a heat exchange reforming reactor without use of enriched air or cryogenic separation of excess nitrogen;
use of two reforming reactors in series on the combustion air side provides flame temperature control without excessive overall surplus of combustion air;
release of NOx from the reforming process to the atmosphere is minimized; release of SO2 is eliminated;
CO2 and steam formed by the combustion are partly used as reformer feed, reducing overall steam demand; and
power for compression of combustion air is partly recovered by expansion of excess flue gas.
In addition, steam reforming of feed gas being admixed with nitrogen and carbon dioxide-containing flue gas from a subsequent heat exchange steam reforming process step provides higher steam reforming conversion rates of carbon hydride feedstock, and thus a lower concentration of unconverted carbonhydrides in the reactor effluent.
In the steam reforming reactor, necessary heat for the endothermic steam reforming reactions is provided by indirect heat exchange with pressurized flue gas.
To provide the flue gas for use in the heat exchanging steam reforming process, fuel is combusted with excess of air in a first heat exchange steam reforming step air resulting in lower combustion temperatures in the reactor. Oxygen-containing flue gas is then withdrawn from the first reforming step, intermediately cooled, and fur¬ther combusted with additional fuel in one or more subsequently reforming steps.
Other features and advantages of the present inven¬tion will become apparent from the following description of the invention which refers to the accompanying drawings.

Accordingly the present invention relates to a process for the preparation of ammonia synthesis gas comprising the steps of mixing a feedstock gas and a flue gas to obtain a mixed gas; and feeding the feedstock gas mixed with the flue gas to at least one pair of reforming reactors, each reactor having a process and fuel side and a combustion side, each pair of reactors being arranged in parallel on the process and fuel side, and in series on the combustion side; wherein a flame temperature in each pair of reactors is controlled by supplying an excess of combustion air to a first reactor of the pair, and oxygen-depleted combustion air to a second reactor of the pair.
The invention will now be described more in detail with reference to the accompanying drawings, in which;

Brief Description of the Drawings
Fig. 1 is a diagram of the process according to the present invention.
Fig. 2 is a diagram of an alternative embodiment of the process of the present invention.
Detailed Description of the Invention
Referring to Fig. 1, a simplified form of the process of the present invention is illustrated. Feedstock 20 typically is natural gas being desulphurized and split into two streams. The feedstock is mixed with steam 30 and a predetermined amount of deoxygenated, pressurized flue gas 40 (see below) to obtain the correct Hj/Nj ratio requested in the syngas being produced. The.gas mixture is used as process gas in two heat exchange reforming reactors 60,80 arranged in parallel on the process and the fuel side and in series on the combination air side. Exit tempera¬tures from each catalyst bed 62,82 being arranged in the reforming reactors is high to ensure reasonably low CH4-leakage.
Air 100 is compressed to a pressure slightly higher than the pressure of the process gas upstream the heat exchangers. The air is first used as combustion air in the first heat exchange burner 64, which operates on large excess of air (about 105% excess) to keep the flame tem¬perature below 1400°C.
After having exchanged heat with reformer tubes in the first reactor, the pressurized flue gas 102 (at about 600°C) is further used as combustion air in the second reactor 80. The combustion air is oxygen-depleted, which limits the flame temperature to below about 1400°C, while the overall air excess is kept low, about 5%.
Flue gas 104 from the second reactor is split into two streams 106,108. Stream 106 is expanded to provide part of the power required for air compression. The residual

amount of flue gas 108 is passed to a deoxygenator for removal of remaining traces of oxygen and further to the feed stream to the reactors as described above.
Referring to Fig. 2, a further specific embodiment of the invention is illustrated, according to which methane in a process gas is steam reformed in four heat exchange steam reforming reactors I, II, III and IV.
The reformers are of the conventional bayonet tube type with an inner tube coaxially arranged in an outer sheath tube. Steam reforming catalyst is loaded in an annular space defined between the walls of the inner tube and the outer tube.
Necessary heat for the endothermic steam reforming reactions proceeding in the process gas is thereby provided by hot flue gas passing externally along the wall of the sheath tube.
Prior to introduction of process gas 2, the gas is mixed with flue gas 4 consisting mainly of CO2, H2O and N2. Flue gas 4 is withdrawn from reactor II after having sup¬plied heat to the steam reforming reactions proceeding in the reactor. Flue gas 4 is admixed into the process gas in an amount to obtain the required Nj/Hj ratio to the syn¬thesis gas being prepared by steam reforming in reactors I through IV.
Reactors I through IV are connected in parallel as concerns introduction on the mixed process gas 6. On the combustion/flue gas side the reactors are arranged in groups of reactors I, II and III, IV. The two reactor groups are connected in series.
Reactors I and II are heated by burning fuel with pressurized air 8. Combustion in reactor I is carried out with excess of air to achieve a suitable combustion tem¬perature and to provide the necessary oxygen content in flue gas 10 being withdrawn from reactor I and introduced into reactor II for further combustion with fuel. Flue gas

12 being withdrawn from reactor II is cycled to deoxygenator 14 with a bed of conventional oxidation cata¬lyst in order to remove residual amounts of oxygen in the gas. From oxygenator 14, flue gas 4 consisting substan¬tially of nitrogen, carbon dioxide and water is cycled to and admixed with feed gas 2.
Reactors III and IV, being connected in series on the flue gas side, are heated by burning fuel at atmos¬pheric pressure. Flue gas 16 leaving reactor III is passed to combustion in reactor IV. After having supplied heat to reactor IV, the flue gas is passed to conventional waste heat recovery.
Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications will become apparent to those skilled in the art. Therefore, the present invention is to be limited not by the specific disclosure herein, but only by the appended claims.

WE CLAIM:
1. A process for the preparation of ammonia synthesis gas comprising the steps of mixing a feedstock gas and a flue gas to obtain a mixed gas; and feeding the feedstock gas mixed with the flue gas to at least one pair of reforming reactors, each reactor having a process and fuel side and a combustion side, each pair of reactors being arranged in parallel on the process and fuel side, and in series on the combustion side; wherein a flame temperature in each pair of reactors is controlled by supplying an excess of combustion air to a first reactor of the pair, and oxygen-depleted combustion air to a second reactor of the pair.
2. The process as claimed in claim 1, wherein the flame temperature is maintained below about 1400°C.
3. The process as claimed in claim 1, wherein air in an excess of about 105% is supplied to the first reactor.
4. The process as claimed in claim 1, wherein oxygen-depleted flue gas fi-om the first reactor is supplied as combustion air for the second reactor of each pair of reactors, for limiting a flame temperature in the second reactor, an overall air excess in the second reactor being kept to about five per cent.
5. The process as claimed in claim 1, wherein the combustion air supplied to the first reactor is compressed to a pressure slightly higher than a pressure of the feedstock gas located upstream of the rectors.

6. The process as claimed in claim 1, wherein the flue gas from the
second reactor is expanded to provide at least part of the power required for
compression of the air.
7. The process as claimed in claim 1, wherein the flue gas mixed with
the feedstock gas is withdrawn from a second of each pair of reactors.
8. The process as claimed in claim 1, wherein the mixed gas is fed to at
least two pairs of reactors, and each pair of reactors is connected to another pair of
reactors in series on the combustion side.
9. The process as claimed in claim 1, wherein the amount of flue gas
mixed with the feedstock gas is selected so as to obtain a predetermined H2/N2
ratio in the synthesis gas.
10. The process as claimed in claim 1, wherein the feedstock is desulphurized.
11. A process for the preparation of ammonia synthesis gas substantially as herein described with reference to the accompanying drawings

Documents:

2187-mas-1997 abstract-duplicate.pdf

2187-mas-1997 abstract.pdf

2187-mas-1997 claims-duplicate.pdf

2187-mas-1997 claims.pdf

2187-mas-1997 correspondence-others.pdf

2187-mas-1997 correspondence-po.pdf

2187-mas-1997 description (complete)-duplicate.pdf

2187-mas-1997 description (complete).pdf

2187-mas-1997 drawings.pdf

2187-mas-1997 form-19.pdf

2187-mas-1997 form-2.pdf

2187-mas-1997 form-26.pdf

2187-mas-1997 form-4.pdf

2187-mas-1997 form-6.pdf

2187-mas-1997 petition.pdf

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Patent Number

201026

Indian Patent Application Number

2187/MAS/1997

PG Journal Number

8/2007

Publication Date

23-Feb-2007

Grant Date

19-Jun-2006

Date of Filing

01-Oct-1997

Name of Patentee

M/S. HALDOR TOPSOE A/S

Applicant Address

NYMOLLEVEJ 55, DK-2800 LYNGBY

Inventors:

#	Inventor's Name	Inventor's Address
1	henrik otto stahl	STRANDVAENGET 30, DK-2960 RUNGSTED KYST
2	IB DYKJAER	NDR. FRIHAVNSGADE 25, 3.T. DK-2100 COPENHAGEN O,
3	CARSTEN LAU LAURSEN	SKJOLDGARDSVEJ 6A, DK-2920 CHARLOTTENLUND

PCT International Classification Number

C01B3/02

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	60/027,639	1996-10-04	U.S.A.