PROCESS DEVELOPMENT IN AMMONIA PLANT by selecting proper process technology and by adjusting the process parameters
Ammonia production
Topsoe's low energy ammonia
process scheme can be optimised for a wide range of operating conditions by
selecting proper process technology and by adjusting the process parameters.
Topsoe's ammonia plant designs are characterised by being highly energy
efficient.
Ammonia process steps
The Topsoe ammonia process scheme
features the following main process steps:
feed
purification
prereforming
tubular
reforming
heat
exchange reforming
secondary
reforming
CO
conversion
methanation
ammonia
synthesis
It is imperative to remove
impurities like sulphur and chlorine efficiently from the hydrocarbon feed in
order to prevent poisoning of catalysts in the downstream (tubular) steam
reformer.
Topsoe's range of feed purification catalysts provides an effective and economical removal of sulphur and chlorine compounds from hydrocarbon feedstocks ranging from natural gas to naphtha.
Topsoe's range of feed purification catalysts provides an effective and economical removal of sulphur and chlorine compounds from hydrocarbon feedstocks ranging from natural gas to naphtha.
Purification steps
The purification section includes
a number of steps:
Hydrogenation
Hydrogenation converts organic compounds into hydrogen sulphide and hydrogen chloride, as the organic compounds are not easily absorbed on downstream absorbents. The hydrogenation process is also applicable for feedstock containing olefins and di-olefins.
Topsoe’s extensive R&D activities within the hydrotreating area have resulted in the development of superior catalysts. Catalysts offered for this application are TK-250 (CoMo type) and TK-261 (NiMo type).
Absorption
After hydrogenation the feed contains hydrogen sulphide and hydrogen chlorine, which are absorbed on a zinc oxide and a chlorine guard respectively. The concentration of these components at the outlet of the absorber is practically nil. The sulphur is removed to very low concentrations (ppb level).
The Topsoe chlorine guard - HTG-1 - offers high chlorine absorbtion capacity at a wide range of temperatures. The range of zinc oxide absorbents, the HTZ series, provides very efficient sulphur removal for all applications.
Final purification
Large variations in the sulphur content in the feed, low operating temperatures, high carbon dioxide or water content may require a final purification step. A solution is to install Topsoe's sulphur guard catalyst ST-101 where a high Cu surface area will remove any remaining hydrogen sulphide as well as organic sulphur in the bottom of the zinc oxide reactor.
Hydrogenation
Hydrogenation converts organic compounds into hydrogen sulphide and hydrogen chloride, as the organic compounds are not easily absorbed on downstream absorbents. The hydrogenation process is also applicable for feedstock containing olefins and di-olefins.
Topsoe’s extensive R&D activities within the hydrotreating area have resulted in the development of superior catalysts. Catalysts offered for this application are TK-250 (CoMo type) and TK-261 (NiMo type).
Absorption
After hydrogenation the feed contains hydrogen sulphide and hydrogen chlorine, which are absorbed on a zinc oxide and a chlorine guard respectively. The concentration of these components at the outlet of the absorber is practically nil. The sulphur is removed to very low concentrations (ppb level).
The Topsoe chlorine guard - HTG-1 - offers high chlorine absorbtion capacity at a wide range of temperatures. The range of zinc oxide absorbents, the HTZ series, provides very efficient sulphur removal for all applications.
Final purification
Large variations in the sulphur content in the feed, low operating temperatures, high carbon dioxide or water content may require a final purification step. A solution is to install Topsoe's sulphur guard catalyst ST-101 where a high Cu surface area will remove any remaining hydrogen sulphide as well as organic sulphur in the bottom of the zinc oxide reactor.
Steam reforming features
Steam reforming is used in the
production of synthesis gas from feedstocks including natural gas, refinery
off-gases, LPG or naphtha. Topsoe's fundamental knowledge of steam reforming
reactions and the complex interaction between heat transfer and reaction
kinetics has resulted in the development of superior steam reforming
technologies and catalysts.
Topsoe's range of steam reforming catalysts are high activity catalysts with excellent poisoning resistance, good mechanical strength and low pressure drop.
Topsoe's range of steam reforming catalysts are high activity catalysts with excellent poisoning resistance, good mechanical strength and low pressure drop.
Topsoe's steam reforming
portfolio
Topsoe's steam reforming
portfolio includes several technologies:
Prereforming features
Prereforming is used for
low-temperature steam reforming of hydrocarbon feedstocks ranging from natural
gas to heavy naphtha.
Converting higher hydrocarbons in the prereformer results in stable and mild operating conditions for a downstream tubular reformer and thus ensures reliable operation of the tubular reformer.
Prereforming allows operation at low steam to carbon ratio and thereby reduces the overall energy consumption. The prereformer also increases the lifetime of the tubular reformer and the shift catalysts, as the sulphur present in the hydrocarbon feed and process steam is absorbed by the prereforming catalyst.
Converting higher hydrocarbons in the prereformer results in stable and mild operating conditions for a downstream tubular reformer and thus ensures reliable operation of the tubular reformer.
Prereforming allows operation at low steam to carbon ratio and thereby reduces the overall energy consumption. The prereformer also increases the lifetime of the tubular reformer and the shift catalysts, as the sulphur present in the hydrocarbon feed and process steam is absorbed by the prereforming catalyst.
Prereforming process layout
The prereformer is placed
upstream of the tubular reforming unit. In order to obtain the required
steam to carbon ratio, feedstock is mixed with process steam before entering
the prereformer. In the prereformer, all higher hydrocarbons are converted into
a mixture of carbon oxides, hydrogen and methane at equilibrium based on the
methanation and water gas shift reactions
Topsoe's reforming designs are
based on the side-fired furnace concept, which ensure optimum use of high alloy
tube materials and maximum heat flux. Accurate temperature control and an even
heat flux ensures long lifetime of the reformer tubes.
Topsoe's tubular reforming
technologies
Topsoe offers two tubular
reforming technologies depending on plant application:
the side-fired tubular reformer
for ammonia, methanol and hydrogen plants
the Topsoe Bayonet reformer for
hydrogen plants
A range of catalysts designed for
the reforming processes provide optimal plant performance.
Side-fired tubular reforming
features
With its ability to control the
temperature profile along the tube length the side-fired tubular reformer is
the only reformer which can run at a low steam to carbon ration as well as at a
high outlet temperature.
The development of improved tube materials and reforming catalysts combined with a solid understanding of heat transfer and the influence of temperature levels and temperature gradients have made it possible to design and operate tubular reformers for tube wall temperatures up to 1050ºC/1920ºF.
Topsoe designs steam reformers with average heat fluxes close to 100,000 kcal/m3h in plants producing more than 200,000 Nm3 hydrogen equivalent in a single steam reformer.
The development of improved tube materials and reforming catalysts combined with a solid understanding of heat transfer and the influence of temperature levels and temperature gradients have made it possible to design and operate tubular reformers for tube wall temperatures up to 1050ºC/1920ºF.
Topsoe designs steam reformers with average heat fluxes close to 100,000 kcal/m3h in plants producing more than 200,000 Nm3 hydrogen equivalent in a single steam reformer.
Side-fired tubular reforming
advantages
The side-fired tubular reformer
offers the following advantages:
uniform and higher heat flux
fewer tubes and longer tube life
no risk of flame impingement
safer and more reliable operation
Application
Depending on plant capacity
one or two radiant chambers are installed with tubes placed in a single row
along the centerline of the furnace chamber.
Radiant wall burners are typically placed in the furnace walls, and flames are directed backwards to the furnace wall, eliminating the risk of flame impingement. Also, the short flames in the side wall fired furnace ensure very low NOx levels in the flue gas - typically below 50 ppm for reformers without combustion air preheat.
Hot flue gas leaves at the top of the radiant chambers through a refractory-lined duct, and the heat is used in the convection section. In modern plants with a large combustion air preheater the convection section is normally placed at ground level.
Radiant wall burners are typically placed in the furnace walls, and flames are directed backwards to the furnace wall, eliminating the risk of flame impingement. Also, the short flames in the side wall fired furnace ensure very low NOx levels in the flue gas - typically below 50 ppm for reformers without combustion air preheat.
Hot flue gas leaves at the top of the radiant chambers through a refractory-lined duct, and the heat is used in the convection section. In modern plants with a large combustion air preheater the convection section is normally placed at ground level.
Focal points
Topsoe's range of catalysts for
the reforming process may be combined to ensure optimal performance.
For reforming of light feedstocks such as natural gas Topsoe's R-67-7H catalyst meets all the requirements of today's demanding processes.
The R-67-7H catalyst provides a combination of high mechanical stability of the carrier and a large surface area, which results in a high catalytic stability and activity for the reforming reaction. High activity ensures that the reforming reaction is close to equilibrium at the outlet from the reformer. Furthermore, the high activity of R-67-7H results in lower tube wall temperatures, which prolongs life expectancy of reformer tubes, or alternatively allows operation at higher rates.
When operating in high-flux top-fired steam reformers and on feedstocks ranging from heavy natural gas to naphtha, R-67-7H is combined with Topsoe's series of RK-200 alkali-promoted catalysts. The RK-200 catalyst installed in the top part of the tubes offers protection against carbon lay-down
For reforming of light feedstocks such as natural gas Topsoe's R-67-7H catalyst meets all the requirements of today's demanding processes.
The R-67-7H catalyst provides a combination of high mechanical stability of the carrier and a large surface area, which results in a high catalytic stability and activity for the reforming reaction. High activity ensures that the reforming reaction is close to equilibrium at the outlet from the reformer. Furthermore, the high activity of R-67-7H results in lower tube wall temperatures, which prolongs life expectancy of reformer tubes, or alternatively allows operation at higher rates.
When operating in high-flux top-fired steam reformers and on feedstocks ranging from heavy natural gas to naphtha, R-67-7H is combined with Topsoe's series of RK-200 alkali-promoted catalysts. The RK-200 catalyst installed in the top part of the tubes offers protection against carbon lay-down
Secondary reforming features
In ammonia plants the methane
reforming reaction from the tubular reformer is continued in the secondary
reformer via the introduction of air to the reactor. The combustion of the
air produces temperatures around 1,250ºC (2,300ºF)which result in further
reforming of the methane.
Topsoe's nozzled ring burner
Topsoe has developed a nozzled ring type burner for secondary reforming. The nozzled ring type burner is equipped with specially designed and patented nozzles installed on each of the air distribution holes, and has the following benefits:
Topsoe's nozzled ring burner
Topsoe has developed a nozzled ring type burner for secondary reforming. The nozzled ring type burner is equipped with specially designed and patented nozzles installed on each of the air distribution holes, and has the following benefits:
controlled and effective mixing
at the burner nozzles
low metal temperatures of the
burner
equal gas and temperature
distribution at the inlet to the catalyst bed
protection of the refractory
lining from the hot flame core
Focal points
The improved Topsoe designed
burner has since 1993 proven its excellent performance and high reliability
with minimised maintenance in a large number of plants.
In a secondary reformer the thermal stability of the catalyst is of great importance. For this application Topsoe has developed the RKS-2-7H catalyst with high thermal resistance and stable activity.
In a secondary reformer the thermal stability of the catalyst is of great importance. For this application Topsoe has developed the RKS-2-7H catalyst with high thermal resistance and stable activity.
CO conversion
CO conversion features
The shift section is designed to
maximise the hydrogen output and reduce the CO level in the synthesis gas, thus
reducing the inert level in the ammonia synthesis.
The shift section consists of a high temperature shift reactor (HTS) followed by a low temperature shift reactor (LTS).
The shift section consists of a high temperature shift reactor (HTS) followed by a low temperature shift reactor (LTS).
CO conversion process
The CO conversion section in an
ammonia plant is located downstream the secondary reformer.
The performance of the carbonmonoxide (CO) conversion section strongly affects the overall plant energy efficiency, as unconverted carbonmonoxide will consume hydrogen and form CH4 in the methanator, reducing the feedstock and increasing the inert gas level in the synthesis loop.
The performance of the carbonmonoxide (CO) conversion section strongly affects the overall plant energy efficiency, as unconverted carbonmonoxide will consume hydrogen and form CH4 in the methanator, reducing the feedstock and increasing the inert gas level in the synthesis loop.
CO conversion catalysts
The HTS and LTS catalysts convert
the carbon monoxide (CO) to carbon dioxide (CO2) and produce more
hydrogen. Topsoe's HTS catalyst SK 201 2 is proven in industry to provide
exceptional long lifetime due to its high activity and strength. The LTS
catalysts LK-821-2 and LK-823 (low temperature shift) are market leaders in the
ammonia and hydrogen plant industry.
Topsoe's HTS catalyst SK-201-2 and LTS catalyst system LK-821-2/LK-823 offer the combination of excellent mechanical strength and superior activity and selectivity, which ensures optimal and efficient performance of the shift section.
In addition the SK-201-2 comes with a negligible content of sulphur and hexavalent chromium which makes the initial activation of the catalyst fast and smooth as neither a desulphurisation period nor a reduction procedure for reducing the hexavalent chromium is required.
The LK-823 is a low-methanol catalyst and industrial experience has shown that an eight-fold cut in methanol by-product formation is achieved without any sacrifice of activity or mechanical strength.
Topsoe's HTS catalyst SK-201-2 and LTS catalyst system LK-821-2/LK-823 offer the combination of excellent mechanical strength and superior activity and selectivity, which ensures optimal and efficient performance of the shift section.
In addition the SK-201-2 comes with a negligible content of sulphur and hexavalent chromium which makes the initial activation of the catalyst fast and smooth as neither a desulphurisation period nor a reduction procedure for reducing the hexavalent chromium is required.
The LK-823 is a low-methanol catalyst and industrial experience has shown that an eight-fold cut in methanol by-product formation is achieved without any sacrifice of activity or mechanical strength.
Methanation
Methanation features
In order to ensure that the feed
is free from carbon oxides, it passes through the methanator,
which converts any traces of carbondioxide and unconverted carbonmonoxide
(CO) from the shift section into methane (CH4).
The carbonmonoxide and carbondioxide content in the feed is normally reduced to a few ppm before the feed passes to the ammonia synthesis converter.
The carbonmonoxide and carbondioxide content in the feed is normally reduced to a few ppm before the feed passes to the ammonia synthesis converter.
Methanation catalyst
To counter problems of carbon
monoxide and carbondioxide leakage, Topsoe has developed a methanation
catalyst, PK-7R, which operates at inlet temperatures down to 190ºC/375ºF while
ensuring that CO and CO2 are fully converted at inlet
temperatures down to 190ºC/375ºF.
The superior activity and
stability of the PK-7R catalyst enables operating at low temperatures which
provides the client with long cycle length and significant energy savings.
With its ring shape, the PK-7R catalyst achieves a 50% reduction in pressure drop relative to the conventional spherical or cylindrical shaped methanation catalysts.
With its ring shape, the PK-7R catalyst achieves a 50% reduction in pressure drop relative to the conventional spherical or cylindrical shaped methanation catalysts.
Low temperature methanation
catalyst PK-7R (346 KB)
Ammonia synthesis
Topsoe's radial flow converters
Topsoe’s ammonia synthesis
technology is based on radial flow converters.
Topsoe offers three radial flow converters adapted to client needs and plant requirements for the most efficient plant operation.
The Topsoe S-200 converter
The Topsoe S-200 ammonia converter is a two-bed radial flow converter with indirect cooling between the catalyst beds. Since the introduction of the S-200 ammonia converter in 1976 this converter type has been used in more ammonia plants than any other competing converter design.
The Topsoe S-300 converter
The recent development of the S-300 converter with three beds offers a higher conversion of ammonia or alternatively a reduced catalyst volume compared to the S-200 converter. The S-300 is the recommended solution for all new plants.
The Topsoe S-50 converter
When an even higher conversion is desired the one-bed S-50 converter can be installed in series with the S-200 or the S-300 converter.
Topsoe offers three radial flow converters adapted to client needs and plant requirements for the most efficient plant operation.
The Topsoe S-200 converter
The Topsoe S-200 ammonia converter is a two-bed radial flow converter with indirect cooling between the catalyst beds. Since the introduction of the S-200 ammonia converter in 1976 this converter type has been used in more ammonia plants than any other competing converter design.
The Topsoe S-300 converter
The recent development of the S-300 converter with three beds offers a higher conversion of ammonia or alternatively a reduced catalyst volume compared to the S-200 converter. The S-300 is the recommended solution for all new plants.
The Topsoe S-50 converter
When an even higher conversion is desired the one-bed S-50 converter can be installed in series with the S-200 or the S-300 converter.
Topsoe's ammonia synthesis
catalyst
Topsoe’s ammonia synthesis
catalyst KM is a high-quality and versatile catalyst, which is characterised by
high and stable activity, unmatched mechanical strength and high poison
resistance. The ammonia synthesis catalyst also comes in a prereduced version,
KMR, which enables a more rapid commissioning compared with a charge of
unreduced KM.
Market experience
Topsoe has installed more than 250 ammonia converters and since the introduction
of the S-300 basket in 1999 this has been the industry’s preferred converter
solution.
Topsoe's
air pollution control technologies provide energy efficient and reliable
solutions for the cleaning of air, flue- and waste gases:
SCR
DeNOx - removal of nitrogen oxides
WSA - removal of sulphurous compounds
SNOX™ - combined removal of sulphurous compounds and nitrogen oxides
CATOX - removal of CO and volatile organic compounds
WSA - removal of sulphurous compounds
SNOX™ - combined removal of sulphurous compounds and nitrogen oxides
CATOX - removal of CO and volatile organic compounds
NOx removal - SCR DeNOx
SCR DeNOx for removing nitrogen
oxides
The SCR (Selective Catalytic
Reduction) DeNOx process is the most efficient process for removing nitrogen
oxides - NOx - from gases, offering NOx-reduction
efficiencies up to 99%. In the SCR process NOx reacts with ammonia
injected into the gas over a catalyst to form molecular nitrogen and water
vapour without creating any secondary pollutants.
Topsoe's SCR DeNOx technology and DNX® catalyst series are the results of extensive in-house research and development and can be tailored to meet any client or legislative requirements.
Topsoe's SCR DeNOx technology and DNX® catalyst series are the results of extensive in-house research and development and can be tailored to meet any client or legislative requirements.
SCR DeNOx applications
Topsoe’s SCR DeNOx process and
catalysts are suitable for treating off-gases from a long range of different
industries and applications including
fossil-fuel fired boilers (coal,
gas, oil, lignite)
biomass-fired boilers
gas turbines
oil-refining and chemical
plants
stationary and marine engines
waste incinerators
SCR DeNOX catalysts
Topsoe is a leading supplier of
SCR DeNOx catalysts, which are tailored to suit a comprehensive range of
applications. The DNX® catalysts are based on a corrugated, reinforced titanium
dioxide carrier which is homogeneously impregnated with the active components -
vanadium pentoxide and tungsten trioxide.
In a fully-automated manufacturing process, the DNX® catalyst obtains a well-defined and controlled porous structure that provides the DNX®catalyst with a large number of active sites, resulting in a high activity.
Catalyst features
The unique catalyst design is the
key to
high NOx removal rates with
minimal ammonia slip
low SO2 oxidation
activity, minimising ABS fouling issues in downstream equipment
unmatched resistance towards poisoning,
providing a long service life
low pressure drop, minimising
power consumption
fast response to changes in
operating conditions, ensuring emission compliance also during load changes
extreme high-temperature
resistance in special, patent-pending catalyst formulations
The SCR DeNOX process
The SCR process for removing
nitrogen oxides is based on the reaction between NOx and ammonia:
4 NO + 4 NH3 + O2
→ 4 N2 + 6 H2O
NO + NO2 + 2 NH3
→ 2 N2 + 3 H2O
Ammonia is injected into the
NOx-containing gas and the mixture is passed through a flow distribution system
and one or several catalyst layers. The main components of an SCR DeNOx system
include a reactor with catalyst and an ammonia storage and injection system.
The ammonia source can be either anhydrous ammonia, ammonia water or a solution of urea. The ammonia is evaporated and subsequently diluted with air or a flue gas side stream before it is injected into the flue gas duct upstream the SCR reactor. Direct injection of ammonia water or a urea solution is also possible. The SCR process requires precise control of the ammonia injection rate and a homogeneous mixing into the flue gas to ensure efficient NOx conversion without an undesirable release of unconverted ammonia referred to as ammonia slip.
The ammonia source can be either anhydrous ammonia, ammonia water or a solution of urea. The ammonia is evaporated and subsequently diluted with air or a flue gas side stream before it is injected into the flue gas duct upstream the SCR reactor. Direct injection of ammonia water or a urea solution is also possible. The SCR process requires precise control of the ammonia injection rate and a homogeneous mixing into the flue gas to ensure efficient NOx conversion without an undesirable release of unconverted ammonia referred to as ammonia slip.
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