WO2014019610A1 - A method for increasing the capacity of an ammonia plant - Google Patents

A method for increasing the capacity of an ammonia plant Download PDF

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Publication number
WO2014019610A1
WO2014019610A1 PCT/EP2012/064938 EP2012064938W WO2014019610A1 WO 2014019610 A1 WO2014019610 A1 WO 2014019610A1 EP 2012064938 W EP2012064938 W EP 2012064938W WO 2014019610 A1 WO2014019610 A1 WO 2014019610A1
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revamping
ammonia
compressor
method according
synthesis
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PCT/EP2012/064938
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French (fr)
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Ermanno Filippi
Sergio Panza
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Ammonia Casale Sa
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Priority to PCT/EP2012/064938 priority Critical patent/WO2014019610A1/en
Publication of WO2014019610A1 publication Critical patent/WO2014019610A1/en

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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J8/00Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
    • B01J8/02Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with stationary particles, e.g. in fixed beds
    • B01J8/06Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with stationary particles, e.g. in fixed beds in tube reactors; the solid particles being arranged in tubes
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/02Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/025Preparation or purification of gas mixtures for ammonia synthesis
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/02Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/32Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air
    • C01B3/34Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents
    • C01B3/38Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents using catalysts
    • C01B3/382Multi-step processes
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01CAMMONIA; CYANOGEN; COMPOUNDS THEREOF
    • C01C1/00Ammonia; Compounds thereof
    • C01C1/02Preparation, purification or separation of ammonia
    • C01C1/04Preparation of ammonia by synthesis in the gas phase
    • C01C1/0405Preparation of ammonia by synthesis in the gas phase from N2 and H2 in presence of a catalyst
    • C01C1/0417Preparation of ammonia by synthesis in the gas phase from N2 and H2 in presence of a catalyst characterised by the synthesis reactor, e.g. arrangement of catalyst beds and heat exchangers in the reactor
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2219/00Chemical, physical or physico-chemical processes in general; Their relevant apparatus
    • B01J2219/00002Chemical plants
    • B01J2219/00004Scale aspects
    • B01J2219/00006Large-scale industrial plants
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2219/00Chemical, physical or physico-chemical processes in general; Their relevant apparatus
    • B01J2219/00002Chemical plants
    • B01J2219/00018Construction aspects
    • B01J2219/00024Revamping, retrofitting or modernisation of existing plants
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/02Processes for making hydrogen or synthesis gas
    • C01B2203/0205Processes for making hydrogen or synthesis gas containing a reforming step
    • C01B2203/0227Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step
    • C01B2203/0233Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step the reforming step being a steam reforming step
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/02Processes for making hydrogen or synthesis gas
    • C01B2203/0205Processes for making hydrogen or synthesis gas containing a reforming step
    • C01B2203/0227Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step
    • C01B2203/0244Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step the reforming step being an autothermal reforming step, e.g. secondary reforming processes
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/02Processes for making hydrogen or synthesis gas
    • C01B2203/0283Processes for making hydrogen or synthesis gas containing a CO-shift step, i.e. a water gas shift step
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/0415Purification by absorption in liquids
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/0435Catalytic purification
    • C01B2203/0445Selective methanation
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/0465Composition of the impurity
    • C01B2203/0475Composition of the impurity the impurity being carbon dioxide
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/06Integration with other chemical processes
    • C01B2203/068Ammonia synthesis
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/14Details of the flowsheet
    • C01B2203/142At least two reforming, decomposition or partial oxidation steps in series
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/14Details of the flowsheet
    • C01B2203/146At least two purification steps in series
    • C01B2203/147Three or more purification steps in series
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02PCLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00Technologies relating to chemical industry
    • Y02P20/50Improvements relating to the production of products other than chlorine, adipic acid, caprolactam, or chlorodifluoromethane, e.g. bulk or fine chemicals or pharmaceuticals
    • Y02P20/52Improvements relating to the production of products other than chlorine, adipic acid, caprolactam, or chlorodifluoromethane, e.g. bulk or fine chemicals or pharmaceuticals using catalysts, e.g. selective catalysts

Abstract

A method for increasing the capacity of an ammonia plant, the plant comprising a front-end for production of a make-up syngas and a synthesis section for conversion of said make-up syngas into ammonia, the front-end comprising a primary reformer (1), a secondary reformer (2), an air compressor, a treatment section including a CO2 removal section (4), and a syngas compressor (33), the method comprising the following steps: an increase of the hydrogen that is or can be produced by the reforming section of the front-end, by means of replacement of tubes of the primary reformer and/or feeding additional oxygen to the secondary reformer; revamping of said air compressor by means of installation of new statoric and rotoric parts in such a way that the revamped compressor train is able to deliver a larger flow rate of air to the secondary reformer while keeping the same final discharge pressure; revamping of the CO2 removal section; revamping of the synthesis gas compressor; upgrade of the synthesis gas drying unit; revamping of the ammonia synthesis loop..

Description

A method for increasing the capacity of an ammonia plant

DESCRIPTION

Field of the invention

The invention relates to the field of preparation of ammonia, based on the reforming of hydrocarbons. The invention discloses a method for increasing the capacity of certain ammonia plants.

Prior art The preparation of ammonia requires a synthesis gas comprising hydrogen (H2) and nitrogen (N2) in a suitable ratio of 3:1 . A synthesis gas suitable for preparation of ammonia is also called "ammonia syngas".

It is known in the art to produce ammonia syngas from the reforming of a hydrocarbon (HC) feedstock. Said HC feedstock is generally a raw source of hydrogen and carbon, such as for example methane, natural gas, naphtha, GPL (liquefied petroleum gas) or refinery gas and mixtures thereof. Usually, the feedstock is natural gas or methane.

In a well known process, desulphurized hydrocarbons are mixed with steam in a suitable ratio and the resulting mixture is admitted at a primary steam reformer in which most of the hydrocarbons in the feed are converted into a mixture of carbon monoxide, carbon dioxide and hydrogen by passage over a suitable catalyst at a moderate pressures, in the range of 15 to 35 bar, and high temperatures in the range of 780°C to 820°C.

As said, this conversion is endothermic. The catalyst is contained in a multiplicity of catalytic tubes which are heated externally by the heat of reaction supplied by the combustion of a gaseous fuel with air. The pressure outside the tubes is normally close to atmospheric. The gas product exiting the primary reformer is fed to a secondary reformer usually containing a suitable catalytic bed and a reaction space overlying the catalytic bed. The secondary reformer also receives a flow of air in a controlled amount to supply the nitrogen required for the downstream ammonia synthesis. This air is typically supplied by an air compressor driven by a steam turbine or by an electric motor; as alternative some plants use an Air Separation Unit to supply enriched air to the secondary reformer.

The oxygen reacts in the reaction space above the catalyst bed with the combustible components of the product gas coming from the primary reformer and the resulting combined product gas enters the catalyst bed at elevated temperature.

During passage down through the catalyst, the residual methane reacts endothermically with steam, resulting in a typical exit temperature of the secondary reformer outlet gas of around 1000 °C with over 99% of the hydrocarbons feed converted to carbon oxides and hydrogen.

The reformed gas exiting the secondary reformer is then typically treated in a series of down-stream equipments to remove carbon oxides and obtain a gas composition suitable for ammonia synthesis (i.e. having a H2/N2 molar ratio close to 3:1 ). These equipments include at least shift converters, a CO2 washing column and a methanation reactor.

The shift converters usually comprise a high temperature CO shift converter followed by a low temperature shift converter, where most of the carbon monoxide (CO) of the reformed gas is catalytically converted with unreacted steam to carbon dioxide plus an additional volume of hydrogen. In the CO2 washing column, the carbon dioxide is removed by scrubbing the gas with an appropriate solvent such as an aqueous solution of an amine or of potassium carbonate, so obtaining a gas flow comprising nitrogen and hydrogen in an approximately 3:1 H2 to N2 molar ratio and traces of methane, carbon oxides and argon. In the methanation reactor, the residual carbon oxides are catalytically converted to methane, to avoid poisoning of the downstream ammonia synthesis catalyst by oxygen-containing compounds.

The ammonia syngas is then obtained at low pressure, typically 15-30 bar, and is compressed to reach the pressure of the ammonia synthesis loop, generally in the range of 80 to 300 bar and typically around 150 bar. This compression is made with a main syngas compressor.

The capacity of an ammonia plant is given by the amount of ammonia which is or can be produced and is measured e.g. in metric tons per day (MTD). The capacity is related to a given hydrocarbon-containing feedstock In a process for upgrading an existing ammonia plant, efforts are made to increase the capacity, from an original capacity to a considerably larger target capacity, for the same or an equivalent feedstock. However, the existing plant normally reveals a number of so-called "bottlenecks". Bottlenecks are limitations of the existing plant that would not allow the achievement of the target capacity. A bottleneck may arise, for example, from the capacity of a certain section of the plant or from the capacity of a machine, such as a compressor. The bottlenecks of a complex plant, however, are not self-evident. In the prior art, the upgrade takes place basically by replacing certain existing equipments with new and bigger ones, and the bottlenecks are overcome one by one through the time, as soon as they become evident. In other words, the plant is first modified to overcome the first bottleneck, than re-started increasing the throughput until another bottleneck is revealed.

In most cases, the primary reformer is modified with the installation of more tubes. The air supply to the secondary reformer is typically increased through installation of a new air compressor in parallel to the existing one or, in some cases, with an air compressor booster which is installed upstream of the existing air compressor. This approach, however, is often more expensive than necessary and then it is poorly efficient and not satisfactory. Hence there is still the need to find a convenient method for increasing the capacity of an ammonia plant. Summary of the invention

The present invention discloses a method for increasing the capacity of an ammonia plant, comprising a front-end for production of a make-up syngas and a synthesis section for conversion of said make-up syngas into ammonia. The synthesis section comprises at least an ammonia converter. The front-end includes basically: a primary reformer comprising a plurality of tubes filled with a catalyst; a secondary reformer receiving the effluent of the primary reformer and a flow of an oxidant; a first compressor arranged to deliver said oxidant to the secondary reformer; a train of equipments for treatment of the effluent of said secondary reformer, said train including at least a CO-shift converter, a carbon dioxide removal section and a methanator; a synthesis gas drying unit; a synthesis gas main compressor for raising the pressure of the synthesis gas to the pressure of the synthesis section, comprising a given number of stators and rotors. The method for revamping the above plant comprises at least the steps listed in the attached claim 1 . A first step is an increase of the capacity of the reforming section. This capacity is understood as the flow rate of hydrogen that is or can be produced by the reforming section. Said increase is achieved by one or more of the following: - replacement of the tubes of said primary reformer with new tubes with improved construction material, the new tubes having substantially the same outer diameter and having a smaller thickness than the original ones, in order to increase the internal tube diameter; and/or - installation of an oxygen source and the O2 enrichment of the air feed directed to the secondary reformer, with the oxygen delivered by said source.

Further steps according to the invention are:

- revamping of said first compressor by means of installation of new statoric and rotoric parts in such a way that the revamped compressor train is able to deliver a larger flow rate of air to the secondary reformer while keeping the same final discharge pressure;

-revamping of the CO2 removal section;

- revamping of the synthesis gas compressor, by means of replacing at least the rotors of said compressor and reducing the number of stages;

- upgrade of the synthesis gas drying unit;

- revamping of the ammonia synthesis loop.

The applicant has found that the above method is able to achieve a considerable increase of capacity, for example at least 40%, with a relatively small number of interventions. In particular, the present invention provides a way to increase the efficiency in various sections of the plant without necessarily requiring a size increase of the involved equipment. The invention provides a combination of steps which is able to increase significantly (more than 40%) the plant production. Some preferred embodiments are listed in the dependent claims and will be discussed hereinbelow.

In some cases, the existing CO2 removal section is equipped with two absorbers and two regenerators. Hence, the revamping of said CO2 removal section preferably includes that said two regenerators are made to operate at different pressure, so that a first generator is operated at a first pressure and a second generator is operated at a second pressure. More preferably, an ejector is installed to connect said two regenerators.

In other cases, the existing CO2 removal section is equipped with only one absorber and only one regenerator. Hence the revamping of the CO2 removal includes preferably the installation of one or more additional reboiler(s) and condenser(s) and a revamping of the internals of said absorber and regenerator. According to a further option, said CO2 removal section with one absorber and one regenerator is modified by means of installation of a new LP flash tower plus revamping of the internals in the existing absorber and regenerator. In some embodiments, the synthesis gas drying unit is a molecular-sieve unit, and upgrade of said synthesis gas drying unit comprises the provision of a new absorbent having more drying capacity than the original absorbent of the unit, or installation of an ammonia washing unit capable to remove oxygenated compounds.

The step of revamping the ammonia synthesis loop comprises preferably the installation of either axial-radial or radial internals in an existing converter of said loop. In some embodiments, revamping the synthesis loop comprises a revamping of the existing ammonia converter, using any of the following: multi- bed, radial or axial radial, adiabatic or isothermal technologies. These technologies will be discussed in a greater detail in the following description.

According to other embodiments, revamping the ammonia synthesis loop comprises the installation of an additional converter in parallel or in series to the existing one. Where the ammonia synthesis loop comprises a hydrogen recover unit, revamping the ammonia synthesis loop may comprise the upgrading of said hydrogen recovery unit.

The capacity of the front-end to produce hydrogen can be increased with any of the following: installing a pre-reformer upstream said primary reformer, or providing an extension of a radiant box of said primary reformer, or installing an air separation unit, and enriching the air feed to the secondary reformer with oxygen produced by said unit. In some embodiments, also the burner of the secondary reformer is replaced. Adding an air separation unit has also the advantage that hydrogen production is increased without a revamping of the air compressor, since the air compressor is already included in the air separation unit.

In some embodiments of the invention, the steam-to-carbon ratio in the front- end is reduced, preferably to a value in the range 2.7 to 3.1 .

Ancillary modifications involving equipment like heat exchangers, separators or other items are not listed, since they have only a limited impact in the plant capacity increase of an ammonia plant. According to further embodiments:

- the shift conversion section can be also revamped;

- a water chilling unit can be installed to provide the required cooling to the ammonia plant. - ammonia absorption sections can be revamped or installed as new, in order to provide the required cooling capacity to the ammonia plant.

The features and the advantages of the invention will be now elucidated with reference to preferred embodiments and to Fig. 1 .

Detailed description Fig. 1 discloses an example scheme of an ammonia plant. The plant comprises a front-end section delivering a make-up synthesis gas to an ammonia synthesis loop 6. The main items of the front-end are: a reforming section comprising a primary reformer 1 and a secondary reformer 2; one or more shift converters 3, a CO2 washing column 4, a methanator 5. The make-up syngas 42 is elevated to the high pressure of the synthesis loop with a main syngas compressor 33. Said compressor delivers high-pressure syngas 31 to said synthesis loop 6.

The circulation in the loop 6 is provided by a further compressor (not shown) also termed circulator. The operation, in a greater detail, is as follows. A mixture 9 of steam 8 and a suitable hydrocarbon source 7, such as natural gas, is heated to around 500 °C in a pre-heater 10 and then the preheated gas 1 1 is catalytically reacted in the tubes of the primary reformer 1 .

The product gas 13 leaving the tubes of the primary reformer 1 is further oxidized in the secondary reformer 2 with the aid of an air supply 14. Said air supply 14 is delivered by a suitable air compressor. The secondary reformer 2 comprises a reaction zone 2b and an underlying catalytic zone 2a. In the upper reaction zone 2b, the gas 13 reacts with the oxygen contained in the air supply 14. To this purpose, the secondary reformer 2 comprises a burner. The product gas 17 leaving the secondary reformer 2 is treated in the shift converters 3, carbon dioxide washing column 4 and methanator 5, with intermediate gas cooling in the heat exchangers 16, 19 and 26, and re-heating in the heater 23 upstream the methanator 5. Liquid separation takes place in the separators 21 , 28.

Block 40 denotes removal of water contained in the synthesis gas. Said block 40 may include a drying unit which technology is based either on molecular sieve that adsorb selectively the water or is based on ammonia washing unit. This block 40 in many existing plant is not present. The loop 6 may also include a hydrogen recovery section. Said section is able to recover a hydrogen-rich stream from a purge gas taken from the loop itself. Said hydrogen-rich stream is preferably recycled at the suction of the circulator, to minimize the energy requirements for compression.

The method of the invention is now elucidated in a greater detail and with reference to a preferred embodiment.

Reforming capacity

A first step of the invention is the increase of the primary reforming capacity, i.e. the production of hydrogen in the primary reformer 1 . This is accomplished by installing new tubes with a reduced thickness, and therefore without changing the number of the catalytic tubes. New tubes have substantially the same outer diameter but a smaller thickness and, hence, they have a larger inner diameter compared to existing tubes. Preferably, tubes with improved metallurgy are adopted, e.g. the newly-installed tubes are micro-alloy tubes, so that they are able to safely operate under the required pressure and temperature, despite the reduced thickness.

The above is in contrast with the conventional revamping techniques which usually teach to increase the number of the catalytic tubes in order to cope with a larger capacity. The invention increases the capacity of each single tube, by means of reducing the thickness, so that a larger flow rate can pass through each tube. Preferably, the primary reformer capability is further increased by means of a steam to carbon ratio reduction. Preferably, the steam to carbon ratio is reduced to a value in the range 2.7÷3.1 (mol/mol). By reducing said ratio, more natural gas is steam reformed to hydrogen and carbon oxides. The applicant has found that the above reduction of the SC ratio turns out to be an advantage, despite the worse equilibrium.

In a conventional revamping according to the prior art, the steam to carbon ratio is typically left unchanged or is only slightly reduced, in order to avoid operational issue with the downstream CO2 removal section. The invention provides that the reduction of the SC ratio has a synergistic effect with the carbon dioxide removal section, as discussed below.

Nitrogen source

Nitrogen is typically introduced with the air supply of the secondary reformer, for example with air flow 14 in Fig. 1 . This air supply needs a respective air compressor train. An aspect of the invention is that said air compressor train (compressor and turbine) is revamped by means of installation of new compressor internals (rotoric and statoric parts). Optionally, the secondary reformer 2 is fitted with a new burner.

Referring to the figure, the secondary reformer 2 comprises a burner in the reaction stage 2b, which provides a combustion of the gas feed 13 (from the primary reformer) and air 14. A new secondary reformer burner, according to an aspect of the invention, will be designed to decrease the air side pressure drop, and to shift the equilibrium toward a higher concentration of hydrogen and carbon oxides. In some embodiments of the invention, an ASU is installed to provide oxygen for the enrichment of the air supply 14 directed to the secondary reformer 2. This ASU can also be used as a source for nitrogen.

Carbon dioxide removal section Another aspect of the invention is to increase the capacity of the CO2 removal section (item 4 in Fig. 1 ) which usually is not capable to cope with a significantly increased capacity.

The modifications to be accomplished depend on the type of the CO2 removal technology installed in the plant to be revamped. The most common technology used for this section is based on amine (especially activated MDEA) or potassium carbonate solution. A carbon dioxide removal section includes basically an absorption subsection and a regeneration subsection. Each of said subsections may include one single tower or a plurality of towers, e.g. two towers.

In some cases, the existing CO2 removal section is equipped with two absorbers and two regenerators. In such a case, an aspect of the invention is that the two regenerators will be operated at different pressure, in such a way to realize a first stage at a first pressure and a second stage at a second and lower pressure.

More preferably, a suitable equipment such as an ejector will be installed to connect the two regenerators. The required modifications can be limited to the pipe re-routing in order to operate the two regenerators at different pressure, and to the installation of simple equipment such as an ejector, which purpose is to connect the two regenerators installed in this section.

In some other case, the existing carbon dioxide removal section is equipped with only one absorber tower and only one regeneration tower. Hence, the revamping will basically increase the heat input to the existing towers, involving the installation of additional reboilers and condensers plus internals revamping in said towers. The modifications required are in this case deeper than in the previously discussed embodiment, and include preferably: upgrade of internals of the towers, to avoid the flooding conditions; increase of the regeneration condensing capacity; increase of the reboiling capacity increase and/or the installation of a solution/solution exchanger. Another embodiment provides the installation of a LP flash tower. Said LP flash tower decreases the capacity of reboiling section and condensing section.

It shall be noted that the operational change of the steam to carbon ratio described above (reduction up to 2.7÷3.1 ) has an important outcome on the boiling duty of the CO2 removal section. Actually, the reduction of the steam to carbon (SC) ratio decreases significantly the available heat, and this has discouraged so far the reduction of the SC ratio. In the present invention, however, the specific energy consumption of the CO2 removal section is reduced (in other words, the CO2 removal section is made more efficient), allowing for a lower SC ratio which, as seen above, has an advantage in terms of the production of hydrogen.

Synthesis gas compression

The syngas compressor (item 33 in Fig. 1 ) usually has a limited spare capacity and therefore needs to be upgraded. The syngas compressor may comprise several stages and several rotors (also called wheels) for each stage, due to the relevant compression ratio. According to preferred embodiments, said compressor is revamped by reducing the number of rotors (wheels) per stage; the new wheels will be bigger than the original ones, in this way the pressure ratio of the compressor stages will be reduced but the flow rate compressed will be increased. The reduction in stage number will also enhance the compressor efficiency by reduction of the bypass among the wheels.

The above mentioned options such as reduced SC ratio and installation of a new burner also have a positive effect on the syngas compressor. In fact, an increase of capacity generally causes additional pressure drop in the front-end. The capacity of the syngas compressor is then reduced because of the larger front-end pressure drop. The present invention solves this problem with modifications by keeping almost unchanged the syngas compressor suction pressure. More specifically, the steam to carbon ratio reduction decreases the front-end pressure drop since less water is flowing in the front- end equipment and, as a consequence, the duty of the main syngas compressor is reduced. The installation of a new burner of the secondary reformer might also help to reduce the duty of the compressor, since the new burner can be designed in order to increase the hydrocarbon steam reforming so that the specific input of natural gas (natural gas vs. output of ammonia) is reduced.

Synthesis gas drying unit

In addition to the synthesis gas compressor train, another item to be installed as new (if not originally installed), in order to reach the target capacity, is the synthesis gas drying unit (block 40 in figure 1 )

This equipment is provided in order to remove the water contained in the synthesis gas, and to supply the reacting gas directly to the ammonia converter. The drying operation can be accomplished by means of an ammonia washing unit, where the synthesis gas is washed with liquid ammonia, or by means of molecular sieve, which are able to selectively remove water from a gas current.

If a molecular sieve drying unit is already installed, then a first option of the invention is that the absorbent of said drying unit is replaced with a new absorbent having a bigger drying capacity (absorbent bed type replacement). Another option, as alternative to the absorbent bed type replacement, is the replacement of the existing section with a brand new ammonia washing unit.

If no drying unit is installed, then a new unity is installed, to remove the oxygenated compounds from the synthesis gas. This newly-installed unity is either a syngas drying unit based on molecular sieve, or an ammonia washing unit. The drying units can be installed in the syngas compressor inter-stage or at the suction of this machine.

Synthesis loop

Normally the synthesis loop (item 6 in Fig. 1 ) can bear only a limited increase of capacity, i.e. is not able to process a substantially larger flow of make-up gas coming from the revamped front-end. Therefore modifications are required to upgrade its performances and to overcome the relevant bottleneck.

A main bottleneck for a significant (>40%) increase of the capacity is the ammonia synthesis converter. If conversion across the converter is too low, there is a significant increase of the synthesis loop circulation and related operating pressure; on the other hand the synthesis loop cannot exceed a design pressure.

To avoid the previous drawbacks, the invention provides that the existing ammonia synthesis converter is revamped or, as an option, that an additional ammonia converter is installed in parallel or in series to the existing one.

Preferably the existing converter is revamped according to adiabatic or isothermal scheme.

Preferably, a converter revamped according to the adiabatic scheme has a radial or axial/radial multi-bed configuration, i.e. comprises a plurality of catalytic beds traversed by an axial or axial/radial mixed flow of reagents. Inter- refrigeration between the catalytic beds can also be adopted.

A converter revamped according to the isothermal scheme comprises a heat exchanger (e.g. tubes or plates) immersed in the catalytic bed(s). In such a case, a single-bed configuration is also convenient, since the temperature can be controlled along the catalytic bed.

Other options

In some cases, the induced draft (ID) fan train and/or the forced draft (FD) fan train are revamped. The ID fan train is particularly used to evacuate the flue gas from the primary reformer. The FD fan train is used to provide, on forced draft basis, the combustion air to the burners of the primary reformer. In both cases, the revamping may concern both the blower and the turbine of the fan train.

According to some embodiments, also the high temperature and/or the low temperature shift converters are revamped. This is appropriate in the cases where the shift converters are found to provide a main bottleneck for a load increase. A preferred way of revamping said shift converters is the use of the radial or axial/radial technology.

In order to increase the production of hydrogen in the front-end, another adopted solution is the O2 enrichment of air to secondary reformer. In order to carry out this modification, an oxygen source is required; an example of O2 source is the installation of an air separation unit, in this case it might happen that the revamping of the existing air compressor is no longer required, because additional air is supplied by a new air compressor belonging to the air separation unit package. An increase of oxygen concentration in the process air fed to the secondary reformer, will create a Nitrogen shortage in the synthesis gas, therefore the ASU shall also provide nitrogen at the required pressure to the synthesis loop in order to operate the ammonia synthesis loop with optimal Hydrogen to Nitrogen ratio of 3 to 1 . In some embodiments, the Hydrogen recovery unit of the synthesis loop is expanded or modified. This unit is going to separate mainly hydrogen from the other gases in order to reduce the inerts content in the synthesis loop. The hydrogen recovery can be done using molecular sieve or a cryogenic unit; if capacity of these units is significantly expanded, then the ammonia converter revamping could be avoided, however the ammonia plant not necessarily could have a benefit from the energetic point of view.

For plants where 100% cold ammonia production is required, a significant increase capacity of the capacity calls for a revamping of the refrigerant compressor train, to make this item suitable for the new operating conditions. As an alternative to the revamping of said compressor, an embodiment of the invention comprises the installation of chilled water units, e.g. working with Lithium-Bromide units. For plant equipped with ammonia absorption sections instead of refrigerant compressor, shall be considered the upgrading of these units (or the installation of additional sections) in order to provide the required cooling to the ammonia plant. The present invention is particularly suitable to revamp the so-called Russian GIAP and Toyo ammonia plant.

Russian plants GIAP have a capacity of 1360 MTD; they were designed on classic scheme with primary reformer and have some basic differences: CO2 removal section operates with MEA or MDEA solutions with high carbonization degree and original designed equipment (absorber, regenerator); the ammonia cooling and separation stages use absorption-cooling units instead of ammonia compressor. In these units low-potential process heat is used.

Russian plants TOYO were based on Kellogg's classic scheme of ammonia synthesis from NG and based on two stages reformers, two stages shift conversion, CO2 removal section (Carsol or Benfield process), ammonia synthesis at 320 kg/cm2. The capacity of these plants was 1360 MTD.

A 4 (four) stages plus circulator synthesis gas compressor is used in the GIAP and Toyo ammonia plants in order to operate the synthesis loop at pressure in the range 200÷300 bar gauge.

Example

The following example relates to revamping of a Russian Toyo plant as defined above.

The existing tubes of the primary reformer, based on HK-40 material and having an internal diameter of 85 mm, have been replaced with microalloy catalytic tubes having an internal diameter of 92 mm. In this way, the volume of the catalyst can be increased by 15÷20%. To provide further spare capacity to the primary reformer the steam to carbon ratio has been reduced from 3.8 up to 3.0 (mol/mol). The secondary reformer has been revamped replacing the internal burner with a new burner having a frusto-conical end section with a diverging open end (trumpet-like) as disclosed in EP 1531 147. This burner is capable to reduce the pressure drop of the process air (for example the air pressure drop is reduced by 1 bar) and to improve the gas distribution in the catalytic bed in order to increase the hydrogen production and to decrease the methane slip. The existing air compressor has been revamped by means of the statoric and rotoric part replacement; this lead to polytropic efficiency about 81 % for the low pressure compressor body and about 77% for the high pressure compressor body, compared to former efficiencies of 70% and 65%, respectively. Similar modifications have been done for the air compressor turbine.

The CO2 removal section based on potassium carbonate solution was originally based on two absorbers and two regenerators; the revamping of this section has been accomplished by operating the two regenerators in series at two different pressures; more specifically the first regenerator has been operated at 1 .4 bar abs, while the second regenerator has been operated at 2.1 bar abs.

The wet CO2 vapours coming from the low pressure regenerator are compressed by means of an ejector using the vapours coming from the high pressure column as motive stream. The final discharge pressure from this ejector is 1 .55 bar abs. The specific energy consumption of the CO2 removal section is the reduced from 950 Kcal to 700 Kcal per each Nm3 of CO2.

The plant is already equipped with a syngas drying unit; in order to make this section suitable for a 40% capacity increase, the old molecular sieve type has been replaced with the Z4-01 supplied by Zeochem that has a higher water adsorption capability, no other hardware modification have been done on this unit.

The syngas compressor and the relevant turbine have been revamped by means of statoric and rotoric parts replacement; in particular the compressor revamping have been accomplished installing less wheels in each compressor stages; on the other hand these wheels were capable to provide a higher polytropic efficiency to the compressor. The reduced wheel stage number decreases the final discharge pressure from the compressor and reduces the internal bypass/leakage among the wheels (less wheels means less leakage among them). After revamping, the polytropic efficiency in the low pressure body is about 80%, in the high pressure body is 76% and the circulator polytropic efficiency is about 78%. The averaged old polytropic efficiency was less than 70%.

The synthesis loop originally equipped with two axial adiabatic ammonia converters have been revamped by means of internals replacement in both the reactors; the new internals operate with axial-radial flow to improve the reactor ammonia conversion and to reduce the converter pressure drop. The operating pressure of the loop (at circulator discharge) is 240 bar abs (the original operating pressure of the loop was close to 300 bar) and the average ammonia concentration in the synthesis gas downstream the converters is 16.4% mol. The converters pressure drop is less than 5 bar.

The final production of the plant after revamping is about 2000 MTD.

Claims

1 . A method for increasing the capacity of an ammonia plant, the plant comprising a front-end for production of a make-up syngas and a synthesis section (6) for conversion of said make-up syngas into ammonia, wherein said front-end includes: a primary reformer (1 ) comprising a plurality of tubes filled with a catalyst; a secondary reformer (2) receiving the effluent of the primary reformer and a flow of air (14), an air compressor arranged to deliver said air (14) to the secondary reformer; a train of equipments for treatment of the effluent of said secondary reformer, said train including at least a CO-shift converter (3), a carbon dioxide removal section (4) and a methanator (5); a synthesis gas drying unit; a synthesis gas main compressor (33) for raising the pressure of the synthesis gas to the pressure of the synthesis section, said compressor comprising a given number of stators and rotors; and wherein the synthesis section comprises an ammonia converter, the method comprising at least the following steps: a) an increase of the hydrogen that is or can be produced by the reforming section, by means of: a1 ) replacement of the tubes of said primary reformer with new tubes, the new tubes having substantially the same outer diameter and having a smaller thickness than the original ones, in order to increase the internal tube diameter; and/or a2) installation of an oxygen source and the O2-enhchment of the air feed directed to the secondary reformer, with the oxygen delivered by said source; b) revamping of said air compressor by means of installation of new statoric and rotoric parts in such a way that the revamped compressor train is able to deliver a larger flow rate of air to the secondary reformer while keeping the same final discharge pressure; c) revamping of the CO2 removal section; d) revamping of the synthesis gas compressor, by means of replacing at least the rotors of said compressor and reducing the number of stages; e) upgrade of the synthesis gas drying unit; f) revamping of the ammonia synthesis loop.
A method according to claim 1 , wherein the existing CO2 removal section is equipped with two absorbers and two regenerators, and wherein the step of revamping said CO2 removal section includes that said two regenerator are made to operate at different pressure, so that a first generator is operated at a first pressure and a second generator is operated at a second pressure.
A method according to claim 2, wherein an ejector is installed to connect said two regenerators.
A method according to claim 1 , wherein the existing CO2 removal section is equipped with only one absorber and only one regenerator, and wherein the step of revamping said CO2 removal includes the installation of one or more additional reboiler(s) and condenser(s) and a revamping of the internals of said absorber and regenerator.
A method according to claim 1 , wherein the existing CO2 removal section is equipped with only one absorber and only one regenerator, and said CO2 removal section is modified by means of: installation of a new LP flash tower; revamping of the internals in the existing absorber and regenerator.
6. A method according to any of the preceding claims, wherein the synthesis gas drying unit is a molecular-sieve unit, and said step of the upgrade of said synthesis gas drying unit comprises the provision of a new absorbent having more drying capacity than the original absorbent of the unit, or installation of an ammonia washing unit capable to remove oxygenated compounds.
7. A method according to any of the preceding claims, wherein said step of revamping the ammonia synthesis loop comprises the installation of either axial-radial or radial internals in an existing converter of said loop. 8. A method according to any of the preceding claims, wherein said step of revamping the synthesis loop comprises a revamping of the existing ammonia converter, using any of the following: multibeds, radial or axial radial, adiabatic or isothermal technologies.
9. A method according to any of the preceding claims, where said step of revamping the ammonia synthesis loop upgrading comprises the installation of an additional converter in parallel or in series to the existing one.
10. A method according to any of the preceding claims, where the ammonia synthesis loop comprises a hydrogen recover unit and said step of revamping the ammonia synthesis loop comprises the upgrading of said hydrogen recovery unit.
1 1 . A method according to any of the preceding claims, wherein hydrogen production is increased by installing a pre-reformer upstream said primary reformer, or by an extension of a radiant box of said primary reformer.
12. A method according to any of the preceding claims, wherein hydrogen production of the front-end is increased by means of installing an air separation unit, and enriching the air feed to the secondary reformer with oxygen produced by said unit.
13. A method according to any of the preceding claims, wherein the burner of the secondary reformer is replaced.
14. A method according to any of the preceding claims, wherein the steam-to- carbon ratio in the front-end is reduced, preferably to a value in the range 2.7 to 3.1 .
15. A method according to any of the previous claims, wherein the capacity of the plant is increased by at least 40% compared to original capacity.
PCT/EP2012/064938 2012-07-31 2012-07-31 A method for increasing the capacity of an ammonia plant WO2014019610A1 (en)

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2930141A1 (en) * 2014-04-08 2015-10-14 Casale Sa A method for revamping a front-end of an ammonia plant
WO2017144850A1 (en) * 2016-02-25 2017-08-31 Johnson Matthey Public Limited Company Process for revamping an ammonia plant
WO2019220074A1 (en) * 2018-05-14 2019-11-21 Johnson Matthey Public Limited Company Process

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1531147A1 (en) 2003-11-06 2005-05-18 CASALE ChEMICALS S.A. Catalytic secondary reforming process and reactor for said process
EP2022754A1 (en) * 2007-08-08 2009-02-11 Ammonia Casale S.A. Process for producing ammonia synthesis gas
EP2284125A1 (en) * 2009-08-13 2011-02-16 Ammonia Casale S.A. Process for revamping an ammonia plant with nitrogen-based washing of a purge stream
EP2404869A1 (en) * 2010-07-06 2012-01-11 Ammonia Casale S.A. Process for producing ammonia synthesis gas

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1531147A1 (en) 2003-11-06 2005-05-18 CASALE ChEMICALS S.A. Catalytic secondary reforming process and reactor for said process
EP2022754A1 (en) * 2007-08-08 2009-02-11 Ammonia Casale S.A. Process for producing ammonia synthesis gas
EP2284125A1 (en) * 2009-08-13 2011-02-16 Ammonia Casale S.A. Process for revamping an ammonia plant with nitrogen-based washing of a purge stream
EP2404869A1 (en) * 2010-07-06 2012-01-11 Ammonia Casale S.A. Process for producing ammonia synthesis gas

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
"Ullmann's Encyclopedia of Industrial Chemistry", 15 October 2011, WILEY-VCH VERLAG GMBH & CO. KGAA, Weinheim, Germany, ISBN: 978-3-52-730673-2, article MAX APPL: "Ammonia, 3. Production Plants", XP055056405, DOI: 10.1002/14356007.o02_o12 *

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2930141A1 (en) * 2014-04-08 2015-10-14 Casale Sa A method for revamping a front-end of an ammonia plant
WO2015155374A1 (en) * 2014-04-08 2015-10-15 Casale Sa A method for revamping a front-end of an ammonia plant
RU2664941C2 (en) * 2014-04-08 2018-08-23 Касале Са Method for revamping front-end of ammonia plant
US10287174B2 (en) 2014-04-08 2019-05-14 Casale Sa Method for revamping a front-end of an ammonia plant
WO2017144850A1 (en) * 2016-02-25 2017-08-31 Johnson Matthey Public Limited Company Process for revamping an ammonia plant
WO2019220074A1 (en) * 2018-05-14 2019-11-21 Johnson Matthey Public Limited Company Process

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