CA1160844A - Synthesis gas for ammonia production - Google Patents
Synthesis gas for ammonia productionInfo
- Publication number
- CA1160844A CA1160844A CA000350435A CA350435A CA1160844A CA 1160844 A CA1160844 A CA 1160844A CA 000350435 A CA000350435 A CA 000350435A CA 350435 A CA350435 A CA 350435A CA 1160844 A CA1160844 A CA 1160844A
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- Prior art keywords
- gas stream
- nitrogen
- hydrogen
- pressure
- raw gas
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
- C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
- C01B3/025—Preparation or purification of gas mixtures for ammonia synthesis
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Combustion & Propulsion (AREA)
- Inorganic Chemistry (AREA)
- Hydrogen, Water And Hydrids (AREA)
- Industrial Gases (AREA)
- Catalysts (AREA)
- Separation By Low-Temperature Treatments (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
ABSTRACT
SYNTHESIS GAS FOR AMMONIA PRODUCTION
A process for producing a gas stream for ammonia synthesis in which a gas stream containing hydrogen and nitrogen in excess of ammonia synthesis requirements, e.g. obtained by partial oxidation of natural gas, coal or oil, is treated to remove other component gas and thereafter subjected to a separation stage, e.g. in a cryogenic separator, to separate a hydrogen-nitrogen stream having the desired hydrogen:nitrogen ratio which is injected into the reactor for ammonia synthesis, and a waste nitrogen stream which may be utilized in power generation or washing stages.
SYNTHESIS GAS FOR AMMONIA PRODUCTION
A process for producing a gas stream for ammonia synthesis in which a gas stream containing hydrogen and nitrogen in excess of ammonia synthesis requirements, e.g. obtained by partial oxidation of natural gas, coal or oil, is treated to remove other component gas and thereafter subjected to a separation stage, e.g. in a cryogenic separator, to separate a hydrogen-nitrogen stream having the desired hydrogen:nitrogen ratio which is injected into the reactor for ammonia synthesis, and a waste nitrogen stream which may be utilized in power generation or washing stages.
Description
SYNTHESIS GAS FOR AMMONIA PRODUCTION
This invention relates to a method for producing a gas containing hydxogen and nitrogen which is particularly suitable for use as an ammonia synthesis gas.
Commercial production of hydrogen is frequently carried out by a succession of process steps which essentially comprise:
~i) the production of a gas containing carbon-oxides and hydrogen as its principal constituents by reaction of the hydrocarbon feedstock with oxygen and/or air and/or steam, (ii) oxidation of the carbon monoxide with steam to carbon dioxide and hydrogen ('shift conversion'), (iii) removal of carbon dioxide, leaving a substantially pure hydrogen stream, (iv) final purification as appropriate to remove residual impurities.
Two major variants of this process sequence currently in use are:
A. Catalytic Steam Reforming This process is presently restricted by the availability of suitabla catalysts to use with natural gas, naphtha and similar light feedstocks. The catalysts .~
are sulphur-sensitive and accordingly the hydrocarbon must be rigorously desulphurised prior to contact with the catalyst. The desulphurised feedstock is mixed with 2 to 4 moles steam/atom carbon and then passed over the catalyst, leaving at high temperature as a mixture containing chiefly hydrogen, carbon oxides, residual methane and unreacted steam. The heat needed to raise the reactants temperature to the exit temperature and to provide the endothermic heat of reaction is supplied by enclosing the catalyst in tubes which are heated externally in a furnace.
The steam reEorming process can alternatively be carried out wholly or partially autothermically, by admission of air and/or oxygen to allow combustion within the catalytic reactor. Specif:ically in the production of ammonia synthesis gas from natural gas indirect heat supply to the reactants in the primary reformer is supplemented by internal combustion of air i~ the secondary reformer which supplies inter alia the nitrogen requirement of the ammonia synthesis process.
In another steam-reforming process all the high temperature heating necessary is provided by the auto-thermic combustion of oxygen or oxygen-enriched air in the catalyst zone and there is n.o indirectly heated reformer at all.
=4=
The reformer product gas is subjected to CO
shift conversion, CO2 removal and ~inal purification such as methanation in accordance with the requirements of individual applications.
B. Partial Oxidation The partial oxidation processes are based on the combustion of the hydrocarbon feed in a restricted supply of oxygen or air. ~xamples include some such as the Texaco and Shell processes that are capable of accepting the full range of hydrocarbons from natural gas to coal and others such as the Koppers Totzek and Lurgi Processes that are specific to coal.
Since no catalyst is used in these processes, the sulphur content of the feed hydrocarbon is not critical.
The product gases from the partial oxidation processes contain hydrogen, carbon oxides, residual methane and steam in various proportions, with sulphur compounds, chiefly hydrogen sulphide, to the extent that sulphur is present in the feed and other trace impurities. Particularly in the case of the Lurgi and other processes in which coal is maintained in the gasifier at relatively low temperatures, the product gases can contain substantial amounts of high molecular weight organic material such as benzole and tars.
~.~
8~
=5=
The desirability of freeing the product gas of trace impurities, combined with the difficulty in operating a low temperature (about 200 to 250C) carbon monoxide shift catalyst on sulphur-laden gases, has frequently led to the choice of nitrogen wash for final gas purification after shift and carbon dioxide and hydrogen sulphide removal cf. the use of methanation with steam reforming.
It will be recognised that in the application of the partial oxidation processes and of the autothermic steam reforming processes as outlined above, the employ-ment of air as the internal oxidant is restricted by the degree that the resultant nitrogen present is acceptable in the product gas.
Thus in the usual natural gas based ammonia process, the amount of air admitted to the secondary reformer is limited to the supply of nitro~en required for the ammonia synthesis step. Also in the partial oxidation and autothermic reforming operations, recourse to at least partial supply of the oxidant in the form of substantially pure oxygen is usually necessary, except when the process is to be used only to produce a low grade fuel gas. The necessity for the supply of substantially pure oxygen means that an air separatlon plant must be provided. The additional capital and i, ~
=6~ 4~
running costs incurred thereby results in such processes appearing less attractive as a means of producing hydrogen rich gases except when the feed hydrocarbon is very cheap or complete flexibility of feedstock source is desired.
One exception to this restriction is in the Braun "Purifier" Process for the manufacture of ammonia by steam reforming, according to which a larger quantity of air than that necessary to supply the synthesis nitrogen is introduced into a secondary reformer and the resulting excess of nitrogen over synthesis requirement is condensecl out downstxeam of the reformer~
It is an ob~ect of the present invention to provide a method of producing a gas stream sui-table for the synthesis of ammonia.
lS In one broad aspect, the invention comprises a process for producing a feed gas stream for the synthesis of ammonia which process comprises la) partia:lly oxidizing a substance selected from the group consisting of oil, coal, natural gas or any combination thereof in the presence of air at a pressure of 15 to 150 bar and a-t a temperature of 300 to 2,000C, to produce a raw gas stream containing hydrogen and nitrogen, with a stoichiometric excess of nitrogen based upon that needed for ammonia synthes.is, together with carbon oxides, methane and hydrogen sulphide if sulphur was present in the oil, coal or gas. The process also includes (b) treating the raw gas stream from step (a) to remove substantially all componen-t gases other than hydrogen and nitrogen, (c) clrying the raw gas stream from step ~b) if wa-ter is present, and d) subjecting the raw gas stream from step (c) at a pressure of lS to 100 bar to a separation stage to separate (1) a hydrogen-nitrogen feed gas stream at a pressure of 15 to :ln0 bar, the raw gas stream having a pxedetermined nitrogen:
hydrogen ratio suitable for ammonia syn-thesis and (2) a . ~ ~
`.~;;~ nitrogen-rich gas stream at a pressure of S to 50 bar.
=7=
(e) The hydrogen~nitrogen feed gas stream from step (d~
is injected into a reactor for ammonia synthesis, (f) the nitrogen-rich gas stream from step (d) is heated, still at a pressure of 5 to 50 bar, to a temperature of 500 to
This invention relates to a method for producing a gas containing hydxogen and nitrogen which is particularly suitable for use as an ammonia synthesis gas.
Commercial production of hydrogen is frequently carried out by a succession of process steps which essentially comprise:
~i) the production of a gas containing carbon-oxides and hydrogen as its principal constituents by reaction of the hydrocarbon feedstock with oxygen and/or air and/or steam, (ii) oxidation of the carbon monoxide with steam to carbon dioxide and hydrogen ('shift conversion'), (iii) removal of carbon dioxide, leaving a substantially pure hydrogen stream, (iv) final purification as appropriate to remove residual impurities.
Two major variants of this process sequence currently in use are:
A. Catalytic Steam Reforming This process is presently restricted by the availability of suitabla catalysts to use with natural gas, naphtha and similar light feedstocks. The catalysts .~
are sulphur-sensitive and accordingly the hydrocarbon must be rigorously desulphurised prior to contact with the catalyst. The desulphurised feedstock is mixed with 2 to 4 moles steam/atom carbon and then passed over the catalyst, leaving at high temperature as a mixture containing chiefly hydrogen, carbon oxides, residual methane and unreacted steam. The heat needed to raise the reactants temperature to the exit temperature and to provide the endothermic heat of reaction is supplied by enclosing the catalyst in tubes which are heated externally in a furnace.
The steam reEorming process can alternatively be carried out wholly or partially autothermically, by admission of air and/or oxygen to allow combustion within the catalytic reactor. Specif:ically in the production of ammonia synthesis gas from natural gas indirect heat supply to the reactants in the primary reformer is supplemented by internal combustion of air i~ the secondary reformer which supplies inter alia the nitrogen requirement of the ammonia synthesis process.
In another steam-reforming process all the high temperature heating necessary is provided by the auto-thermic combustion of oxygen or oxygen-enriched air in the catalyst zone and there is n.o indirectly heated reformer at all.
=4=
The reformer product gas is subjected to CO
shift conversion, CO2 removal and ~inal purification such as methanation in accordance with the requirements of individual applications.
B. Partial Oxidation The partial oxidation processes are based on the combustion of the hydrocarbon feed in a restricted supply of oxygen or air. ~xamples include some such as the Texaco and Shell processes that are capable of accepting the full range of hydrocarbons from natural gas to coal and others such as the Koppers Totzek and Lurgi Processes that are specific to coal.
Since no catalyst is used in these processes, the sulphur content of the feed hydrocarbon is not critical.
The product gases from the partial oxidation processes contain hydrogen, carbon oxides, residual methane and steam in various proportions, with sulphur compounds, chiefly hydrogen sulphide, to the extent that sulphur is present in the feed and other trace impurities. Particularly in the case of the Lurgi and other processes in which coal is maintained in the gasifier at relatively low temperatures, the product gases can contain substantial amounts of high molecular weight organic material such as benzole and tars.
~.~
8~
=5=
The desirability of freeing the product gas of trace impurities, combined with the difficulty in operating a low temperature (about 200 to 250C) carbon monoxide shift catalyst on sulphur-laden gases, has frequently led to the choice of nitrogen wash for final gas purification after shift and carbon dioxide and hydrogen sulphide removal cf. the use of methanation with steam reforming.
It will be recognised that in the application of the partial oxidation processes and of the autothermic steam reforming processes as outlined above, the employ-ment of air as the internal oxidant is restricted by the degree that the resultant nitrogen present is acceptable in the product gas.
Thus in the usual natural gas based ammonia process, the amount of air admitted to the secondary reformer is limited to the supply of nitro~en required for the ammonia synthesis step. Also in the partial oxidation and autothermic reforming operations, recourse to at least partial supply of the oxidant in the form of substantially pure oxygen is usually necessary, except when the process is to be used only to produce a low grade fuel gas. The necessity for the supply of substantially pure oxygen means that an air separatlon plant must be provided. The additional capital and i, ~
=6~ 4~
running costs incurred thereby results in such processes appearing less attractive as a means of producing hydrogen rich gases except when the feed hydrocarbon is very cheap or complete flexibility of feedstock source is desired.
One exception to this restriction is in the Braun "Purifier" Process for the manufacture of ammonia by steam reforming, according to which a larger quantity of air than that necessary to supply the synthesis nitrogen is introduced into a secondary reformer and the resulting excess of nitrogen over synthesis requirement is condensecl out downstxeam of the reformer~
It is an ob~ect of the present invention to provide a method of producing a gas stream sui-table for the synthesis of ammonia.
lS In one broad aspect, the invention comprises a process for producing a feed gas stream for the synthesis of ammonia which process comprises la) partia:lly oxidizing a substance selected from the group consisting of oil, coal, natural gas or any combination thereof in the presence of air at a pressure of 15 to 150 bar and a-t a temperature of 300 to 2,000C, to produce a raw gas stream containing hydrogen and nitrogen, with a stoichiometric excess of nitrogen based upon that needed for ammonia synthes.is, together with carbon oxides, methane and hydrogen sulphide if sulphur was present in the oil, coal or gas. The process also includes (b) treating the raw gas stream from step (a) to remove substantially all componen-t gases other than hydrogen and nitrogen, (c) clrying the raw gas stream from step ~b) if wa-ter is present, and d) subjecting the raw gas stream from step (c) at a pressure of lS to 100 bar to a separation stage to separate (1) a hydrogen-nitrogen feed gas stream at a pressure of 15 to :ln0 bar, the raw gas stream having a pxedetermined nitrogen:
hydrogen ratio suitable for ammonia syn-thesis and (2) a . ~ ~
`.~;;~ nitrogen-rich gas stream at a pressure of S to 50 bar.
=7=
(e) The hydrogen~nitrogen feed gas stream from step (d~
is injected into a reactor for ammonia synthesis, (f) the nitrogen-rich gas stream from step (d) is heated, still at a pressure of 5 to 50 bar, to a temperature of 500 to
2,000C, and (g) the high pressure nitrogen-rich gas stream from step (f) is expanded in a turbine to generate power.
The invention further comprehends a process for producing a feed gas stream Eor the synthesis of ammonia which process comprises ta) partially oxidizing a substance selected from the group consisting of oil, coal, natural gas, or any combination thereof in the presence of air at a pressure of 15 to 150 bar and at a temperature of 300 to 2,000C, to produce a raw gas stream containing hydrogen and nitrogen with a stoichiometric excess of nitrogen based upon that needed for amrnonia synthesis, together with carbon oxides, rnethane and hydrogen sulphide if sulphur was present in the oil, coal or gas. The process further includes (b~
passing the raw gas stream from step ~a) over a shift catalyst and reacting the raw gas stream with steam at elevated temperatures to convert the carbon monoxide present to carbon dioxide and hydrogen, (c) treating the raw gas stream from step Ib) to remove carbon dioxide in a wash solution, (d) treating the raw gas stream from step (c~ to rernove sub-stantially all component gases other than hydrogen and ~5 nitrogen, (e) drying the raw gas strearn from step (d) if water is present, and ~f) subjecting the raw gas stream from step (e) at a pressure of 15 to 100 bar to a cryogenic separation stage to separate (1) a hydrogen-nitrogcn feed gas stream at a pressure of lS to 100 bar, the feed gas stream havin~
a predetermined nitrogen:hydrogen rat.io suitable for ammonia synthesis, and (2) a nitrogen-r:ich gas stream at a pressure oE 5 to 50 bar. (g) The hydrogen-nitrogen feed gas =8=
stream from step (f) is injected into a reactor for a~nonia synthesis, (h) with the nitrogen-rich gas stream produced by the cryogenic separator in step (f) still at a pressure oE
5 to 50 bar, being used to strip a substantial part of the carbon dioxide from the wash solution produced in step (c).
(i) The combined nitrogen and carbon dioxide stream from step (h) ls heated still at a pressure of 5 to 50 bar, to a temperature of 500 to 2,000C, and (j) expanding the combined nitrogen and carbon dioxide stream from step (i) in a turbine to generate power.
The invention is based on the fact that hydrogen and nitrogen mi~tures can be separated with ease in view of the large difference in their properties and hence the nitrogen content of such mixtures may be accurately control-led. The simplest method o~ separating the gases is bycryogenic treatment al-though other separation metho~s which rely on the difEerence in molecular size of the gases, e.g.
differential adsorption methods or di~fusivity, may also be used. The invention allows any gas which predominantly contains hydrogen and nitroyen to be used and the source gas may therefore be derived from the partial oxidation of oil, coal or gas in air.
In a preferred embodiment the desired amount of nitrogen is separated in a cryogenic separator. The separator may use Joule Thomson cooling and regenerative heat exchanye, low temperature work expanders, supplementary refrigeration or any combination thereof. Suitable cryogenic separators are well known and commercially available. T~le separated hydrogen containing the desired quantlty of nitrogen normally leaves the cryogenlc separator at a slightly lower pressure than its inlet pressure and is injected into a system for ammonia synt~esis.
=9=
The nitrogen stream normally leaves the cryogenic separator at a somewhat lower pressure than its inlet pressure but nevertheless may still give useful power when heated and passed through an expansion turbine.
The invention will now be described with reference to the accompanying drawings, in which:
Figure 1 represents a flow diagram of a process in accordance with the invention, Figure 2 represents a flow diagram of an alter-native process in accordance with the invention, and Figure 3 represents a diagram of a high temperature open cycle gas turbine suitable for use in the process of the invention.
Referring to Figure 1, natural gas, oil or coal or a combination thereof is partially oxidised with air or oxygen enriched air which is generally preheated and pressurised. The resulting gas stream contains hydrogen, nitrogen, carbon oxides, methane and hydrogen sulphide i~
sulphur is present, the nitrogen:hydrogen ratio being in excess of that required for ammonia synthesis. The partial oxidation process is conducted at a pressure up to 150 bar generally 15 to 150 bar, preferably 30 to 100 bar and a temperature of 300 to 2000C generally up to 1000C. The oxidation may be conducted at atmospheric pressure in which case the yas stream may be pressurised at a later stage in the treatment process.
The resulting gas stream is passed over a shift catalyst, e.g. iron oxide or cobalt molybdate, generally at a temperature in the range 200 to 500C to convert the -10=
carbon monoxide present to carbon dioxide and hydrogen.
The gas stream is then treated to remove carbon dioxide and hydrogen sulphide impurities. There are many types of process for such gas removal including scrubbing with hot potassium carbonate e.g. at 70 to llO~C and the Rectisol process. The sulphur content of the gas may be removed at any prior stage. Any residual carbon oxides present may be removed by methanation, generally at 250 to 450C. The resultant gas comprises a mixture of hydrogen and nitrogen, with methane, inert gases such as argon and water vapour as the chief impurities. This gas is then dried by cooling initially and subsequently by contact with drying medium e.g. molecular sieve adsorbent (which would also remove any remaining traces of carbon dioxide). The dried gas is then passed to a cryogenic nitrogen/hydrogen separator, e.g. which uses Joule Thomson cooling and regenerative heat exchange. The gas is contacted with heat exchange elements which cool the gas to about 100 K. In the cryogenic condenser, the nitrogen content of the hydrogen is reduced to the level required ~or the ammonia synthesis gas, typically 25~ N2 for ammonia synthesis. The cryogenic nitrogen condensation will result in partial depletion of the methane and argon and content of the inlet gas, the impurities removed appearing in the waste nitrogen stream. The hydrogen-nitrogen stream which leaves the condensor at a pressure slightly less than the inlet pressure of the gas strec~m is injected into an ammorlia synthesis system.
~, ~ `.j`~ !
=11=
In the embodiment depicted in Figure 2, the nitrogen condenser incorporates a form of liquid nitrogen washing to remove residual carbon monoxide to a level acceptable for ammonia synthesis. This expedient enables methanation to be dispensed with and allows the convenient use of a higher CO level from the shift conversion resulting in a final synthesis gas substantially free of CH4 and inert gases. The pure nitrogen needed for the washing may conveniently be obtained from the condensed nitrogen in the cryogenic separator, thus there would be no dependence on an external source of liquid nitrogen as in the classical nitrogen wash plants.
It is also possible for the cryogenic nitrogen condensation to be placed upstream of methanation in Figure 1~
In all applications it is advantageous for the waste nitrogen to be discharged from the cryogenic condenser at near ambient temperature and at an elevated pressure up to 50 bar, generally 5 to 10 bar since it may then be heated to a representative inlet temperature for a high-temperature turbine and expanded therein to near atmospheric pressure, thus generating a useful proportion of the power needed for pressuxing the gas stream, e.g. to compress the process air for the partial oxidation or steam reforming steps.
~1 =12=
The waste nitrogen may be heated to the turbine inlet temperature, e.g. 500 to ~000C, generally 500 to 1000C, by indirect heat exchange and/or by direct combustion of its combustible content, i.e~ traces of methane, hydrogen, carbon monoxide with supplementary air and additional fuel if required upstream of the turbine.
In the arrangement of the expansion turbine shown in Figure 3 the hot gas expansion turbine is the turbine element of an open cycle gas turbine. The nitrogen is mixed with supplementary fuel and fed to the combustion chamber of the gas turbine as fuel. At the same time the process air requirement for the partial oxidation or reforming processes is bled from the gas turbine compressor discharge. By this expedient approximate parity is maintained between the mass flows in the compressor and expander sections of the gas turbine and an efficie~t means of compression and expansion provided using developed industrial equipment designs.
Alternatively the waste nitrogen may be expanded at a low temperature, e.g. ambient temperature to generate power and may be used for refrigeration of desirable parts of the ammonia synthesis plant.
~7 =13=
If the waste carbon dioxide from the acid gas removal plant may be discharged to the atmosphere in impure form it is expedient to use the waste nitrogen under pressure from the cryogenic separator to strip a substantial part of the carbon dioxide from the wash solution and then to pass the combined nitrogen and carbon dioxide stream still at high pressure to heating and work expansion.
In summary, the following advantages are offered for the air oxidation/nitrogen condensation/nitrogen expansion system described over current practice involving oxidation of feedstock:
l. elimination of air separation plant, oxygen compressors, pipework, etc.
2. reduction in gross installed power of plant compressors,
The invention further comprehends a process for producing a feed gas stream Eor the synthesis of ammonia which process comprises ta) partially oxidizing a substance selected from the group consisting of oil, coal, natural gas, or any combination thereof in the presence of air at a pressure of 15 to 150 bar and at a temperature of 300 to 2,000C, to produce a raw gas stream containing hydrogen and nitrogen with a stoichiometric excess of nitrogen based upon that needed for amrnonia synthesis, together with carbon oxides, rnethane and hydrogen sulphide if sulphur was present in the oil, coal or gas. The process further includes (b~
passing the raw gas stream from step ~a) over a shift catalyst and reacting the raw gas stream with steam at elevated temperatures to convert the carbon monoxide present to carbon dioxide and hydrogen, (c) treating the raw gas stream from step Ib) to remove carbon dioxide in a wash solution, (d) treating the raw gas stream from step (c~ to rernove sub-stantially all component gases other than hydrogen and ~5 nitrogen, (e) drying the raw gas strearn from step (d) if water is present, and ~f) subjecting the raw gas stream from step (e) at a pressure of 15 to 100 bar to a cryogenic separation stage to separate (1) a hydrogen-nitrogcn feed gas stream at a pressure of lS to 100 bar, the feed gas stream havin~
a predetermined nitrogen:hydrogen rat.io suitable for ammonia synthesis, and (2) a nitrogen-r:ich gas stream at a pressure oE 5 to 50 bar. (g) The hydrogen-nitrogen feed gas =8=
stream from step (f) is injected into a reactor for a~nonia synthesis, (h) with the nitrogen-rich gas stream produced by the cryogenic separator in step (f) still at a pressure oE
5 to 50 bar, being used to strip a substantial part of the carbon dioxide from the wash solution produced in step (c).
(i) The combined nitrogen and carbon dioxide stream from step (h) ls heated still at a pressure of 5 to 50 bar, to a temperature of 500 to 2,000C, and (j) expanding the combined nitrogen and carbon dioxide stream from step (i) in a turbine to generate power.
The invention is based on the fact that hydrogen and nitrogen mi~tures can be separated with ease in view of the large difference in their properties and hence the nitrogen content of such mixtures may be accurately control-led. The simplest method o~ separating the gases is bycryogenic treatment al-though other separation metho~s which rely on the difEerence in molecular size of the gases, e.g.
differential adsorption methods or di~fusivity, may also be used. The invention allows any gas which predominantly contains hydrogen and nitroyen to be used and the source gas may therefore be derived from the partial oxidation of oil, coal or gas in air.
In a preferred embodiment the desired amount of nitrogen is separated in a cryogenic separator. The separator may use Joule Thomson cooling and regenerative heat exchanye, low temperature work expanders, supplementary refrigeration or any combination thereof. Suitable cryogenic separators are well known and commercially available. T~le separated hydrogen containing the desired quantlty of nitrogen normally leaves the cryogenlc separator at a slightly lower pressure than its inlet pressure and is injected into a system for ammonia synt~esis.
=9=
The nitrogen stream normally leaves the cryogenic separator at a somewhat lower pressure than its inlet pressure but nevertheless may still give useful power when heated and passed through an expansion turbine.
The invention will now be described with reference to the accompanying drawings, in which:
Figure 1 represents a flow diagram of a process in accordance with the invention, Figure 2 represents a flow diagram of an alter-native process in accordance with the invention, and Figure 3 represents a diagram of a high temperature open cycle gas turbine suitable for use in the process of the invention.
Referring to Figure 1, natural gas, oil or coal or a combination thereof is partially oxidised with air or oxygen enriched air which is generally preheated and pressurised. The resulting gas stream contains hydrogen, nitrogen, carbon oxides, methane and hydrogen sulphide i~
sulphur is present, the nitrogen:hydrogen ratio being in excess of that required for ammonia synthesis. The partial oxidation process is conducted at a pressure up to 150 bar generally 15 to 150 bar, preferably 30 to 100 bar and a temperature of 300 to 2000C generally up to 1000C. The oxidation may be conducted at atmospheric pressure in which case the yas stream may be pressurised at a later stage in the treatment process.
The resulting gas stream is passed over a shift catalyst, e.g. iron oxide or cobalt molybdate, generally at a temperature in the range 200 to 500C to convert the -10=
carbon monoxide present to carbon dioxide and hydrogen.
The gas stream is then treated to remove carbon dioxide and hydrogen sulphide impurities. There are many types of process for such gas removal including scrubbing with hot potassium carbonate e.g. at 70 to llO~C and the Rectisol process. The sulphur content of the gas may be removed at any prior stage. Any residual carbon oxides present may be removed by methanation, generally at 250 to 450C. The resultant gas comprises a mixture of hydrogen and nitrogen, with methane, inert gases such as argon and water vapour as the chief impurities. This gas is then dried by cooling initially and subsequently by contact with drying medium e.g. molecular sieve adsorbent (which would also remove any remaining traces of carbon dioxide). The dried gas is then passed to a cryogenic nitrogen/hydrogen separator, e.g. which uses Joule Thomson cooling and regenerative heat exchange. The gas is contacted with heat exchange elements which cool the gas to about 100 K. In the cryogenic condenser, the nitrogen content of the hydrogen is reduced to the level required ~or the ammonia synthesis gas, typically 25~ N2 for ammonia synthesis. The cryogenic nitrogen condensation will result in partial depletion of the methane and argon and content of the inlet gas, the impurities removed appearing in the waste nitrogen stream. The hydrogen-nitrogen stream which leaves the condensor at a pressure slightly less than the inlet pressure of the gas strec~m is injected into an ammorlia synthesis system.
~, ~ `.j`~ !
=11=
In the embodiment depicted in Figure 2, the nitrogen condenser incorporates a form of liquid nitrogen washing to remove residual carbon monoxide to a level acceptable for ammonia synthesis. This expedient enables methanation to be dispensed with and allows the convenient use of a higher CO level from the shift conversion resulting in a final synthesis gas substantially free of CH4 and inert gases. The pure nitrogen needed for the washing may conveniently be obtained from the condensed nitrogen in the cryogenic separator, thus there would be no dependence on an external source of liquid nitrogen as in the classical nitrogen wash plants.
It is also possible for the cryogenic nitrogen condensation to be placed upstream of methanation in Figure 1~
In all applications it is advantageous for the waste nitrogen to be discharged from the cryogenic condenser at near ambient temperature and at an elevated pressure up to 50 bar, generally 5 to 10 bar since it may then be heated to a representative inlet temperature for a high-temperature turbine and expanded therein to near atmospheric pressure, thus generating a useful proportion of the power needed for pressuxing the gas stream, e.g. to compress the process air for the partial oxidation or steam reforming steps.
~1 =12=
The waste nitrogen may be heated to the turbine inlet temperature, e.g. 500 to ~000C, generally 500 to 1000C, by indirect heat exchange and/or by direct combustion of its combustible content, i.e~ traces of methane, hydrogen, carbon monoxide with supplementary air and additional fuel if required upstream of the turbine.
In the arrangement of the expansion turbine shown in Figure 3 the hot gas expansion turbine is the turbine element of an open cycle gas turbine. The nitrogen is mixed with supplementary fuel and fed to the combustion chamber of the gas turbine as fuel. At the same time the process air requirement for the partial oxidation or reforming processes is bled from the gas turbine compressor discharge. By this expedient approximate parity is maintained between the mass flows in the compressor and expander sections of the gas turbine and an efficie~t means of compression and expansion provided using developed industrial equipment designs.
Alternatively the waste nitrogen may be expanded at a low temperature, e.g. ambient temperature to generate power and may be used for refrigeration of desirable parts of the ammonia synthesis plant.
~7 =13=
If the waste carbon dioxide from the acid gas removal plant may be discharged to the atmosphere in impure form it is expedient to use the waste nitrogen under pressure from the cryogenic separator to strip a substantial part of the carbon dioxide from the wash solution and then to pass the combined nitrogen and carbon dioxide stream still at high pressure to heating and work expansion.
In summary, the following advantages are offered for the air oxidation/nitrogen condensation/nitrogen expansion system described over current practice involving oxidation of feedstock:
l. elimination of air separation plant, oxygen compressors, pipework, etc.
2. reduction in gross installed power of plant compressors,
3. taking into account the high potential efficiency of the waste nitrogen containing gas expansion and conventional associated heat recovery, a substantial reduction in the total energy requirement for the whole plant.
The pressures referred to herein are gauge pressures.
~,
The pressures referred to herein are gauge pressures.
~,
Claims (10)
1. A process for producing a feed gas stream for the synthesis of ammonia which comprises:
(a) partially oxidizing a substance selected from the group consisting of oil, coal, natural gas or any combination thereof in the presence of air at a pressure of 15 to 150 bar and at a temperature of 300° to 2,000°C to produce a raw gas stream containing hydrogen and nitrogen with a stoichiometric excess of nitrogen based upon that needed for ammonia synthesis, together with carbon oxides, methane and hydrogen sulphide if sulphur was present in the oil, coal or gas, lb) treating the raw gas stream from step (a) to remove substantially all component gases other than hydrogen and nitrogen, (c) drying the raw gas stream from step (b) if water is present, (d) subjecting the raw gas stream from step (c) at a pressure of 15 to 100 bar to a separation stage to separate (1) a hydrogen-nitrogen feed gas stream at a pressure of 15 to 100 bar, said raw gas stream having a predetermined nitrogen:hydrogen ratio suitable for ammonia synthesis and (2) a nitrogen-rich gas stream at a pressure of 5 to 50 bar, (e) injecting said hydrogen-nitrogen feed gas stream from step (d) into a reactor for ammonia synthesis, (f) heating said nitrogen-rich gas stream from step (d), still at a pressure of 5 to 50 bar, to a temperature of 500° to 2,000°C, and (g) expanding said high pressure nitrogen-rich gas stream from step (f) in a turbine to generate power.
(a) partially oxidizing a substance selected from the group consisting of oil, coal, natural gas or any combination thereof in the presence of air at a pressure of 15 to 150 bar and at a temperature of 300° to 2,000°C to produce a raw gas stream containing hydrogen and nitrogen with a stoichiometric excess of nitrogen based upon that needed for ammonia synthesis, together with carbon oxides, methane and hydrogen sulphide if sulphur was present in the oil, coal or gas, lb) treating the raw gas stream from step (a) to remove substantially all component gases other than hydrogen and nitrogen, (c) drying the raw gas stream from step (b) if water is present, (d) subjecting the raw gas stream from step (c) at a pressure of 15 to 100 bar to a separation stage to separate (1) a hydrogen-nitrogen feed gas stream at a pressure of 15 to 100 bar, said raw gas stream having a predetermined nitrogen:hydrogen ratio suitable for ammonia synthesis and (2) a nitrogen-rich gas stream at a pressure of 5 to 50 bar, (e) injecting said hydrogen-nitrogen feed gas stream from step (d) into a reactor for ammonia synthesis, (f) heating said nitrogen-rich gas stream from step (d), still at a pressure of 5 to 50 bar, to a temperature of 500° to 2,000°C, and (g) expanding said high pressure nitrogen-rich gas stream from step (f) in a turbine to generate power.
2. A process according to Claim 1 wherein the separat-ion stage in step (d) is performed in a cryogenic separator.
3. A process according to Claim 1 wherein said nitrogen-rich stream is mixed with supplementary fuel and fed to the combustion chamber of a gas turbine as fuel.
4. A process according to Claim 3 wherein said process air requirement for the partial oxidation is bled from the gas turbine compressor discharge.
5. A process according to Claim 2 wherein said raw gas stream resulting from the partial oxidation is passed over a shift catalyst and reacted with steam at elevated temperatures to convert the carbon monoxide present in said raw gas stream to carbon dioxide and hydrogen.
6. A process according to Claim 5 wherein said raw gas stream, after passing over the shift catalyst, is subjected to scrubbing with hot potassium carbonate at a temperature of 70° to 100°C to remove the acid gas content prior to the separation stage.
7. A process according to Claim 6 wherein said raw gas stream, after scrubbing with hot potassium carbonate is subjected to methanation to remove any carbon oxides prior to the separation stage.
8. A process according to Claim 6 wherein said raw gas stream, after scrubbing with hot potassium carbonate is subjected to liquid nitrogen washing to remove carbon monoxide in said raw gas stream prior to the separation stage.
9. A process according to Claim 8 wherein the separation stage is conducted in a cryogenic separator and the liquid nitrogen and the washing step is obtained from the nitrogen condensed in the cryogenic separator.
10. A process for producing a feed gas stream for the synthesis of ammonia which comprises:
(a) partially oxidizing a substance selected from the group consisting of oil, coal, natural gas, or any combination thereof in the presence of air at a pressure of 15 to 150 bar and at a temperature of 300° to 2,000°C
to produce a raw gas stream containing hydrogen and nitrogen with a stoichiometric excess of nitrogen based upon that needed for ammonia synthesis, together with carbon oxides, methane and hydrogen sulphide if sulphur was present in the oil, coal, or gas, (b) passing said raw gas stream from step (a) over a shift catalyst and reacting said raw gas stream with steam at elevated temperatures to convert the carbon monoxide present to carbon dioxide and hydrogen, (c) treating said raw gas stream from step (b) to remove carbon dioxide in a wash solution, (d) treating the raw gas stream from step (c) to remove substantially all component gases other than hydrogen and nitrogen, (e) drying the raw gas stream from step (d) if water is present, (f) subjecting the raw gas stream from step (e) at a pressure of 15 to 100 bar to a cryogenic separation stage to separate (l) a hydrogen-nitrogen feed gas stream at a pressure of 15 to 100 bar, said feed gas stream having a predetermined nitrogen:hydrogen ratio suitable for ammonia synthesis, and (2) a nitrogen-rich gas stream at a pressure of 5 to 50 bar,
10. A process for producing a feed gas stream for the synthesis of ammonia which comprises:
(a) partially oxidizing a substance selected from the group consisting of oil, coal, natural gas, or any combination thereof in the presence of air at a pressure of 15 to 150 bar and at a temperature of 300° to 2,000°C
to produce a raw gas stream containing hydrogen and nitrogen with a stoichiometric excess of nitrogen based upon that needed for ammonia synthesis, together with carbon oxides, methane and hydrogen sulphide if sulphur was present in the oil, coal, or gas, (b) passing said raw gas stream from step (a) over a shift catalyst and reacting said raw gas stream with steam at elevated temperatures to convert the carbon monoxide present to carbon dioxide and hydrogen, (c) treating said raw gas stream from step (b) to remove carbon dioxide in a wash solution, (d) treating the raw gas stream from step (c) to remove substantially all component gases other than hydrogen and nitrogen, (e) drying the raw gas stream from step (d) if water is present, (f) subjecting the raw gas stream from step (e) at a pressure of 15 to 100 bar to a cryogenic separation stage to separate (l) a hydrogen-nitrogen feed gas stream at a pressure of 15 to 100 bar, said feed gas stream having a predetermined nitrogen:hydrogen ratio suitable for ammonia synthesis, and (2) a nitrogen-rich gas stream at a pressure of 5 to 50 bar,
Claim 10 - cont'd ...
(g) injecting said hydrogen-nitrogen feed gas stream from step (f) into a reactor for ammonia synthesis, (h) using said nitrogen-rich gas stream produced by the cryogenic separator in step (f) still at a pressure of 5 to 50 bar, to strip a substantial part of the carbon dioxide from the wash solution produced in step (c), (i) heating the combined nitrogen and carbon dioxide stream from step (h), still at a pressure of 5 to 50 bar, to a temperature of 500° to 2,000°C, and (j) expanding said combined nitrogen and carbon dioxide stream from step (i) in a turbine to generate power.
(g) injecting said hydrogen-nitrogen feed gas stream from step (f) into a reactor for ammonia synthesis, (h) using said nitrogen-rich gas stream produced by the cryogenic separator in step (f) still at a pressure of 5 to 50 bar, to strip a substantial part of the carbon dioxide from the wash solution produced in step (c), (i) heating the combined nitrogen and carbon dioxide stream from step (h), still at a pressure of 5 to 50 bar, to a temperature of 500° to 2,000°C, and (j) expanding said combined nitrogen and carbon dioxide stream from step (i) in a turbine to generate power.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7914200 | 1979-04-24 | ||
| GB7914200 | 1979-04-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1160844A true CA1160844A (en) | 1984-01-24 |
Family
ID=10504734
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000350435A Expired CA1160844A (en) | 1979-04-24 | 1980-04-23 | Synthesis gas for ammonia production |
Country Status (14)
| Country | Link |
|---|---|
| JP (1) | JPS5938161B2 (en) |
| AU (1) | AU543957B2 (en) |
| BE (1) | BE882949A (en) |
| CA (1) | CA1160844A (en) |
| DE (1) | DE3015640A1 (en) |
| DK (1) | DK156638C (en) |
| FR (1) | FR2454998A1 (en) |
| GB (1) | GB2048840B (en) |
| IN (1) | IN154518B (en) |
| IT (1) | IT1141316B (en) |
| NL (1) | NL8002358A (en) |
| NO (1) | NO156603C (en) |
| SE (1) | SE449740B (en) |
| ZA (1) | ZA802258B (en) |
Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4524056A (en) * | 1983-07-05 | 1985-06-18 | Foster Wheeler Energy Corporation | Process for the production of ammonia |
| CA1229485A (en) * | 1984-01-23 | 1987-11-24 | Toyo Engineering Corporation | Process for refining an ammonia synthesis gas |
| US4592860A (en) * | 1984-02-07 | 1986-06-03 | Union Carbide Corporation | Process and apparatus for ammonia synthesis gas production |
| EP0214991A1 (en) * | 1984-06-30 | 1987-03-25 | Stamicarbon B.V. | Process for preparing ammonia |
| NO171966C (en) * | 1991-01-23 | 1993-05-26 | Norsk Hydro As | PROCEDURE FOR PURIFICATION OF SYNTHESIC GAS FOR AMMONIA PRODUCTION |
| JP4013007B2 (en) * | 1998-08-28 | 2007-11-28 | 大阪瓦斯株式会社 | Method and apparatus for producing hydrogen-nitrogen mixed gas |
| DE10055818A1 (en) * | 2000-11-10 | 2002-05-23 | Ammonia Casale Sa | Catalytic production of ammonia, especially for direct conversion into urea, using nitrogen-hydrogen starting gas mixture obtained from natural gas by autothermal reforming and catalytic conversion |
| EP1778585A4 (en) * | 2004-07-29 | 2011-08-03 | Fluor Tech Corp | Improved ammonia plant |
| DE102004049774B4 (en) * | 2004-10-12 | 2007-04-26 | Lurgi Ag | Process for the production of urea from natural gas |
| DE102011008931B4 (en) * | 2011-01-20 | 2016-08-18 | Hans Walter Kirchner | Water vapor-air over-pressure gasification with cryogenic gas separation |
| CN103641069B (en) * | 2013-11-25 | 2015-07-01 | 张周卫 | Low-temperature flash evaporation gas-liquid separator for waste nitrogen |
| CN109516445B (en) * | 2018-12-05 | 2021-07-23 | 四川大学 | Closed circulation process for preparing nitric acid by combining electrolysis water and air separation |
Family Cites Families (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2795559A (en) * | 1954-04-01 | 1957-06-11 | Texas Co | Production of hydrogen-nitrogen mixtures |
| US2866321A (en) * | 1954-08-06 | 1958-12-30 | Chemical Construction Corp | Purification of gases by partial condensation |
| DE1135020B (en) * | 1960-04-14 | 1962-08-23 | Linde Eismasch Ag | Process and device for the low-temperature decomposition of a hydrogen-rich gas mixture |
| GB1134621A (en) * | 1965-01-20 | 1968-11-27 | Humphreys & Glasgow Ltd | Improvements in or relating to the manufacture of ammonia |
| US3442613A (en) * | 1965-10-22 | 1969-05-06 | Braun & Co C F | Hydrocarbon reforming for production of a synthesis gas from which ammonia can be prepared |
| US3572046A (en) * | 1965-10-22 | 1971-03-23 | Braun & Co C F | Apparatus for purification of raw ammonia synthesis gas |
| CH482916A (en) * | 1967-09-12 | 1969-12-15 | Prvni Brnenska Strojirna Zd Y | Control device of a combined gas and steam turbine system |
| FR2118300A6 (en) * | 1970-12-16 | 1972-07-28 | Cem Comp Electro Mec | Hydrocarbon conversion - to produce ammonia synthesis gases with waste gases driving a gas turbine |
| DE2235323B2 (en) * | 1972-07-19 | 1974-11-28 | Metallgesellschaft Ag, 6000 Frankfurt | Process for the production of synthesis gas for ammonia synthesis by pressure gasification of coal with water vapor and air |
| JPS5137078A (en) * | 1974-09-24 | 1976-03-29 | Taiyo Kaken Co | Tadanko kisosetsushokusochi |
| US3929429A (en) * | 1974-09-26 | 1975-12-30 | Texaco Inc | Fuel gas from solid carbonaceous fuels |
-
1980
- 1980-04-16 ZA ZA00802258A patent/ZA802258B/en unknown
- 1980-04-17 AU AU57562/80A patent/AU543957B2/en not_active Expired
- 1980-04-23 DK DK173280A patent/DK156638C/en active IP Right Grant
- 1980-04-23 CA CA000350435A patent/CA1160844A/en not_active Expired
- 1980-04-23 GB GB8013446A patent/GB2048840B/en not_active Expired
- 1980-04-23 DE DE19803015640 patent/DE3015640A1/en not_active Ceased
- 1980-04-23 NL NL8002358A patent/NL8002358A/en not_active Application Discontinuation
- 1980-04-23 SE SE8003073A patent/SE449740B/en not_active IP Right Cessation
- 1980-04-23 NO NO801174A patent/NO156603C/en unknown
- 1980-04-23 FR FR8009135A patent/FR2454998A1/en active Granted
- 1980-04-23 IT IT21606/80A patent/IT1141316B/en active
- 1980-04-24 BE BE0/200348A patent/BE882949A/en not_active IP Right Cessation
- 1980-04-24 JP JP55054827A patent/JPS5938161B2/en not_active Expired
- 1980-07-29 IN IN552/DEL/80A patent/IN154518B/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| NO801174L (en) | 1980-10-27 |
| AU543957B2 (en) | 1985-05-09 |
| BE882949A (en) | 1980-10-24 |
| DK156638C (en) | 1990-01-29 |
| SE8003073L (en) | 1980-10-25 |
| DK173280A (en) | 1980-10-25 |
| AU5756280A (en) | 1980-10-30 |
| IN154518B (en) | 1984-11-03 |
| ZA802258B (en) | 1981-04-29 |
| IT1141316B (en) | 1986-10-01 |
| GB2048840B (en) | 1983-12-21 |
| JPS5938161B2 (en) | 1984-09-14 |
| DE3015640A1 (en) | 1980-11-06 |
| FR2454998A1 (en) | 1980-11-21 |
| JPS55144401A (en) | 1980-11-11 |
| NO156603C (en) | 1987-10-21 |
| NO156603B (en) | 1987-07-13 |
| SE449740B (en) | 1987-05-18 |
| GB2048840A (en) | 1980-12-17 |
| DK156638B (en) | 1989-09-18 |
| IT8021606A0 (en) | 1980-04-23 |
| NL8002358A (en) | 1980-10-28 |
| FR2454998B1 (en) | 1983-11-18 |
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