Steam Reforming

In steam reforming, hydrogen is produced by reforming the hydrocarbon feedstock, producing synthesis gas containing a mixture of carbon monoxide and hydrogen. The carbon monoxide is then reacted with steam in the water-gas-shift reaction to produce carbon dioxide and hydrogen. The carbon dioxide is recovered for urea production, exported as co-product, or vented to the atmosphere. In the final synthesis loop, the hydrogen reacts with nitrogen to form ammonia. 

In steam reforming ammonia plants there is a surplus of high-level heat that is produced in primary reforming, secondary reforming, shift conversion and ammonia synthesis. Most of the waste heat is recovered for producing high pressure steam that is used in turbines for driving compressors, pumps and fans. In general, all the high pressure steam will be used in steam turbines for driving the synthesis gas compressor. Modern steam reforming ammonia plants do not import energy for driving the mechanical equipment. Energy is in many cases exported in the form of steam or electricity to other consumers (IPTS/EC, 2007).  

The natural gas use in a an ammonia plant using the steam reforming process ranges between 28 and 35.5 GJ/tonne, of which about 20-22 GJ/tonne of ammonia is used as feedstock, 7.2-9.0 GJ/tonne is fuel consumed in the primary reformer, and the remaining 0.5-4.2 GJ/tonne is used in auxiliary boilers and others. Table below shows the typical breakdown of energy use in steam reforming ammonia plants. 

Estimated energy use breakdown for a typical ammonia plant using natural gas as a feedstock (Appl, 1998; EFMA 2000; Worrell et al. 2000; IPTS/EC 2007; Saygin, 2013)
  Natura Gas
(GJ/t NH3
Heat Input/Output
(GJ/t NH3)
Primary reformer feed 20.4 - 22.3  
Primary reformer 7.2 - 9.0 3.0 - 4.5
Secondary reformer   0.0
Waste heat boiler   -5.0 - -6.0
Shift and CO2 removal   0.8 - 1.2
Methanator    
Synthesis loop   -2.5 - -3.0
Auxiliary boiler 0.3 - 3.5 -0.2 - 3.0
Turbines/compressors   3.9 - 6.3
Other (e.g. flare 0.2 - 0.7  
Total 28.1 - 35.5 0.0

 

There are also a number of steam reforming configurations offered by different technology providers, and currently considered as best available technologies. These include the following:

  • Advanced conventional primary reforming with high duty primary reforming and stoichiometric process air in the secondary reformer. Processes with this configuration are the Kellogg Low-Energy Ammonia Process, the Haldor Topsoe process, the Uhde process, the LEAD process, the Exxon Chemical Process, the Fluor process and the Lumus process (Ullmann’s, 2011).
  • Steam reforming with mild condition in the primary reformer and use of excess air in the secondary reformer. Processes with this configuration are the Braun Purifier process, the ICI AMV process, the Foster Wheeler AM2 process, the Humphreys & Glascow BYAS process, the Jacob Plus Ammonia Technology the Montedison Low-pressure process and the Kellogg’s LEAP process (Ullmann’s, 2011).
  • Heat exchange autothermal reforming with a process gas heat exchange reformer and a separate secondary reformer, or in combination with an autothermal reformer that uses excess or enriched air. Processes with this configuration are the ICI LCA process and the Chiyoda process (Ullmann’s, 2011).

There are also a number of processes in which there is no use of a secondary reformer in which the nitrogen is supplied by an air separation unit. Some examples are the Linde LAC process and the Humphreys & Glasgow MDF process. Claimed energy use values of the different processes are provided in Table below. 

Energy Use in Advanced Steam Reforming Configurations (Ullmann’s, 2011)
Process Name Energy Use
(GJ/t NH3)
Advanced conventional primary reforming
Kellogg Low-Energy Ammonia Process 27.9 (27.01)
Haldor Topsoe Process 27.9
Uhde Process 28.0  (27.0)
LEAD Process 29.3
Exxon Chemical Process 29.0
Fluor Process 32.0
Lummus Process 29.6-33.5
Processes with reduced primary refiner firing
Braun Purifier Process 28.0 (27.01)
ICI AMV Process 28.5
Foster Wheeler AM2 Process 29.3
Humphreys & Glasgow BYAS Process 28.7
Jacobs Plus Ammonia Technology 28.8 (26.81)
Montedison Low-Pressure Process 28.1
Kellogg’s LEAP Process <28.0
Processes without a primary reformer
ICI LCA Process 29.3
Kellogg Brown and Root (KBR) KAAPplus Process 27.2
Chiyoda Process N/A
Processes without a secondary reformer
KTI PARC Process 29.3-31.8
Linde LAC Process 28.5 (29.32)
Humphreys & Glasgow MDF Process 32.82

1: Energy use when steam is exported
2: Energy use when CO2 is recovered. 

Conventional steam reforming of natural gas includes desulphurization, primary reforming and secondary reforming processes. 

Desulphurization: 

The feedstock used for the production of ammonia may contain sulphur and sulphur compounds which are harmful for the catalyst used in subsequent process steps and therefore need to be removed. Typically, feedstocks may contain up to 5 mg S/Nm3 of sulphur compounds. In desulphurization, the pre-heated (350-400oC) and untreated feed-gas enters a vessel that usually contains a cobalt molybdenum catalyst where the sulphur compounds are hydrogenated to H2S. The hydrogen needed for the reaction is usually recycled from the synthesis section. The hydrogenated sulphur compounds are then adsorbed on pelletized zinc oxide. After desulphurization, the feed-gas sulphur concentration drops to less than 0.1 ppm. 

Primary Reforming:

The feed-gas, after being treated in a desulphurization vessel, is mixed with process steam. The preheated mixture enters the primary reformer at a temperature of 400-600oC. In certain new and revamped ammonia plants the preheated steam/gas mixture is passed through an adiabatic pre-reformer before entering the primary reformer, where it is then reheated in the convection section (EFMA, 2000). 

Primary reformers consist of a large number of high-nickel chromium alloy tubes which are filled with a nickel-containing reforming catalyst (see Figure 3). In conventional steam reforming, the hydrocarbon conversion rate in the primary reformer is about 60%. The reaction is highly endothermic: 

Natural gas or other types of burners provide heat to the process. About half of the heat supplied to the primary reformer is consumed in the reaction. The remaining half is contained in the flue gases and used in the convection section of the reformers for the preheating of process streams. The flue gases leaving the primary reformer convection section compose the most significant source of the plant’s emissions. These emissions mainly consist of CO2, NOx, and small amounts of SO2 and CO (EFMA, 2000).

The typical fuel use in the primary reformer (including steam generation) ranges between 7.2 and 9.0 GJ/tonne of ammonia (IPTS/EC, 2007). Natural gas consumption in energy efficient ammonia plants is about 6.8 GJ/tonne of ammonia (Ullmann’s, 2011).

Secondary Reforming: 

In secondary reforming the nitrogen needed for the production of ammonia is added and the reforming of the hydrocarbon feed is completed (only about 60% of the feed-gas was reformed in the primary reformer). In order to increase the conversion rate, high temperatures are required. This is achieved with the internal combustion of part of the reaction gas and the process air, which is also the source of nitrogen, before it passes over to the nickel containing catalysts. The supplied air is compressed and heated at the convection section of the primary reformer at a temperature of 500-600oC. The gas outlet temperature is about 1000oC and about 99% of the primary reformer hydrocarbon feed is converted. The residual methane content is about 0.2-0.3% (dry gas base). Heat is removed with the use of a waste heat boiler and the gas is cooled down to approximately 330-380oC (IPTS/EC, 2007). 

Steam ReformingSchematic

Steam ReformingTechnologies & Measures

Technology or MeasureEnergy Savings PotentialCO2 Emission Reduction Potential Based on LiteratureCostsDevelopment Status
Using Improved Materials for Reformer Tubes

Replacement of the reformer tubes in the Indian plant required an investment of Rs. 50 million. The payback time was 40 months (PCRA,, 2009 p.335).

Indian Flag  Investments for a 1 300 tpd plant are around US $ 2 million [2011 values] (FAI, 2013).

Commercial
Heat Recovery from Reformer Flue Gas

Reducing the stack temperature by 100˚C will result in energy savings of approximately 0.4 GJ/ t NH3 (Christensen, 2001).

Indian Flag By installing a feed pre-heat coil in the low temperature convection section of the reformer flue gas duct, a plant in India was able to reduce flue gas temperature of the reformer from 170˚C to 148˚C and eliminated the need for a fired heater, resulting in energy savings of 0.17 GJ/t NH3 (Nand and Goswami, 2009). 

Indian Flag Another Indian installed a natural gas heating coil to recover the heat from the reformer flue gas. The reformer flue gas temperature was reduced from 190˚C to 160˚C, saving 0.18 GJ/t NH(Nand and Goswami, 2009). 

At an ammonia plant in Pakistan, a demineralized water preheating coil was installed to recover heat from the flue gas (240˚C). The temperature of the flue gas was lowered to 137˚C, recovering approximately 44 GJ/hour of waste heat from the flue gases (Yousaf, 2011)

Heat recovery in the Pakistani plant saved $ 2 Million/year (Yousaf, 2011)

Indian Flag For a 1 300 tpd plant, the required investments are estimated to be around US $ 700 000 [2008 values] (FAI, 2013).

Commercial
Using Improved Catalyst Designs for Primary ReformingCommercial
Improving the Design for Induced Draft Fan Ducts

Indian Flag For a 1 500 tpd plant, investments are estimated at around US $ 200 000 (FAI, 2013).

Commercial
Heat Exchange Autothermal Reforming

The investment cost are stated to be 303 Yen/tonne ammonia, resulting in a payback time of one year (1999 figures) (ECCJ, 1999, 148).

Commercial
Increasing Reformer Operating PressureCommercial
Modification of Burners in Primary Reforming

Indian Flag  Replacement of burner nozzles for a 1 500 tpd plant is estimated to cost around US $ 0.4 million [2012 values] (FAI, 2013)

Commercial
Using an Adiabatic Pre-reformer

Energy consumption can be reduced by 4-10% (IPTS/EC, 2007; Nieuwlaar, 2001; Patel et al., unknown date)

Dutch flag In Netherlands, a plant in Rozenburg, energy savings of about 4% were realized with the installation of an adiabatic pre-reformer. (Worrell and Blok, 1994). 

For a 2 000 t/day plant, the investment cost associated with the installation of a pre-reformer is reported to ¥280 million, resulting in a payback time of 1.7 years (ECCJ, 1999 p. 156). 

According to Nieuwlaar (2001) the investment cost is estimated at €7.5/GJ. 

Dutch flag For the plant in Netherlands, the installation costs for the adiabatic pre-reformer was estimated as $6/tonne ammonia, and the payback time was estimated to be  one to three years (in 1990 dollars) (Worrell and Blok, 1994).

Indian Flag For a 1500 tpd plant, the investments are in the range of US $ 10 million (2000 values) (FAI, 2013).

Commercial
Insulation of Reformer Furnace

An assessment for an Australian ammonia plant estimated that the payback time for improving insulation on reformer furnace will have a payback time of less than one year (Australian Government, 2009). 

Commercial
Improved Design of Secondary Reformer Burner

Indian Flag The cost of replacing burner nozzles in a 1 500 tpd plant is reported to be around US $500 000(FAI, 2013).

Commercial
Using Improved Catalyst Designs for Secondary ReformingCommercial
Shifting Reformer Duty

This measure increases the capital costs (FAI, 2013). 

Commercial
High Emissivity Coating of Radiant Section Refractory

Indian Flag For a 1 500 tpd plant, the implementation costs are estimated to be around US $ 25 000 FAI, 2013). 

Commercial
Heat Exchanger Reformer
Lower Steam to Carbon Ratio on ReformerCommercial
Installing a Feed Gas SaturatorCommercial
Increasing Mixed Feed Preheat Temperature

Indian Flag For a 1 500 tpd plant, an investment in the range of US $ 500 000 is required to preheat fuel gas using low grade recovered heat (FAI, 2013)..

Commercial

Steam Reforming Reference Documents

Reference Document on Best Available Techniques for the Manufacture of Large Volume Inorganic Chemicals - Ammonia, Acids and Fertilisers

Prepared by the Institute for Prospective Technical Studies of European Commision, this document provides detalied information on Best Available Technologies applicable to Ammonia production – as well as on the production of Acids and Fertilizers.  

Page Number: 

39-41