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1. State of the art ammonia production
2. Energy requirements
3. Carbon dioxide emissions – low carbon ammonia – carbon footprint
4. Ammonia from renewable sources: energy storage and potential as fuel

State of the art ammonia production

Large scale integrated ammonia – urea – nitric-acid complexes have been developed and implemented in which the daily ammonia production can be up to 3.000 t/d. These are huge commercial plants with investment costs in the order of up to 1.5 billion US $ for the ammonia section only.

In general, an ammonia manufacturing facility can be split into two major sections. First, there is a large section in which hydrogen is produced, today primarily through methane steam reforming, and in which nitrogen from the air is purified.

Second, there is the true ammonia synthesis by reacting purified hydrogen and nitrogen catalytically at elevated temperatures and pressures to produce NH₃. The NH₃ produced is separated from the gas circulation loop through cooling and subsequently stored at low temperatures or under pressure.

Details of such installations have been described (UNIDO / IFDC, 1998) and can be obtained from dedicated engineering companies. The International Fertiliser Society offers a wealth of data and information and a dedicated USB is available for past ammonia proceedings.

The various ammonia processes and technologies and their associated emissions are described in the IPPC reference document on the BREF LVIC-AAF (2007). This document offers background information and emissions data.

FerTechInform will not detail these modern-day processes but instead refers to AmmoniaKnowHow for further specific and expert descriptions and advice.

Energy requirements

It is remarkable that, at around 1908, Haber-Bosch won the battle with Frank-Caro, in part because of the energy efficiency of the Haber-Bosch process.

The Frank-Caro process of reacting calcium carbide with nitrogen at high (> 1.000°C) temperatures produced calcium cyanamide and carbon; upon addition of water, lime and ammonia are formed. The calcium cyanamide process was considered to be very energy-intensive and to be, in this respect, inferior to Haber-Bosch. In case low-cost energy is available, the cyanamide process can prevail and even today such units are in operation successfully (Reuvers, 2017).

Around 1980, about 3. 109 t/year of hydrogen were produced worldwide by direct coal gasification and used mainly for ammonia synthesis. 90 per cent of this hydrogen was generated with Koppers-Totzek gasifiers; this process is very suitable for a comparison of several ways of synthetic gas generation from different feedstocks. The figure shows a comparison of the production cost of ammonia on the basis of various feedstocks for a plant with a capacity of 1,000 tons/day NH₃ (Teggers, 1980).

Since that time, coal has in many cases been replaced by natural gas as a reliably available, often cheaper, and cleaner raw material.

In 2022, rather similar price comparisons of raw material sources for hydrogen were performed, this time comparing renewable energy sources with fossil sources like natural gas (Western Europe) and coal (Asia).

Times have changed and the Haber-Bosch process is now often considered far too energy intensive. In the existing catalytic process for ammonia, clearly a minimum amount of energy is required. Even if all required supporting energies are, theoretically, eliminated, there remains a basic energy requirement of at least 18,6 GJ per tonne (Kirova-Yordanova, 2004; 2012; Noelker and Ruether, 2011). This number represents the methane feedstock chemically bound in one tonne of ammonia. Present technology, however, converts nitrogen and hydrogen at elevated temperatures and pressure and thus requires mechanical work. There is also a loss of energy in the energy conversion from steam to mechanical power.

Available literature delineates precisely the limits of energy demands for ammonia synthesis (Kirova-Yordanova, 2012): The theoretical minimum energy consumption has been calculated as 22,2 GJ per tonne of ammonia, including feedstock and indispensable additional fuel consumption (Noelker and Ruether, 2011).

Today, a realistic baseline for the energy demand for ammonia production is about 27 GJ per tonne (Kirova-Yordanova, 2012). Therefore, instead of minimising energy consumption, optimisation of energy use is key. Using heat generated in the process of ammonia production for other on-site purposes may, for example, be best practice. Optimisation also refers to the balancing of capital investment and operational cost, and one needs to consider the impact of climatic conditions on energy demands.

Incremental improvements have continuously reduced the energy requirement over the past 20-40 years. Can we go below the realistic limit of 27 GJ given by the present process, or do we need a new synthetic approach to achieve this? Can we go from an incremental approach to a new process with lower energy demands? Considering that stand-alone green-field world-scale ammonia plants have an interesting price tag in the order of 0.5 – 1.5 billion dollars or euros, do we need not only ideas, innovation and initiative but also a lot of courage? In about 1912, BASF put all its financial resources behind Haber-Bosch and barely survived.

Detailed information on practical actions that can be taken to improve the energy efficiency of existing ammonia, and other, production plants is provided on the FertInform page covering Fertiliser production energy efficiency.

Carbon dioxide emissions – low carbon ammonia – carbon footprint

In the decade up to 2022, priorities have changed again and now the emissions of, in particular, carbon dioxide from the ammonia manufacturing processes are in focus.

Most hydrogen today is produced from fossil fuels – steam methane reforming of natural gas, partial oxidation of coal or oil residues – and entails large CO₂ emissions. This hydrogen from fossil sources is often called “grey hydrogen”, sometimes also referred to as brown hydrogen. The same colour scheme applies to the ammonia produced from this hydrogen, called “grey ammonia”, or “brown ammonia”. The exact carbon footprint depends on the fuel used and the efficiency of the facility, so one could easily identify many shades of grey.

To avoid a further increase in global warning, the reduction of green-house gas emissions is the main objective of global, European and national strategies. Emissions of carbon dioxide from steam reforming processes are inevitable. Existing commercial integrated sites cannot be changed rapidly, as just the erection of such sites may take up to 3-5 years, let alone the time required for a certain return on investment.

To reduce or altogether eliminate such CO₂ emissions, another source of hydrogen is needed which is obtainable from renewable energy. Wind energy, solar energy, or hydropower may be sources of electricity that, in turn, can be used to produce clean hydrogen from plain water. This electrolysis, on a scale never imagined before, is now under rapid development (Brown, IFA, 2018). The transport of the electricity required may be another challenge.

The electrolysis process for manufacturing hydrogen for ammonia plants is not new. Such processes were engineered and implemented, for example, in Egypt (Aswan, 1960, BASF; see Feiler, 1952), Norway (Rjukan, 1913, Norsk Hydro; see Halasa, 2021), Spain (Valladolid, NICAS, prior to 1990), India (Nangal, 1962-1990), Canada (Trail, British Columbia, 1931 onward), and Zimbabwe (Kwekwe, Sable Chemicals, 1972-2012; see Anonymous, 2012). Generally, these plants were built at locations where low-cost hydroelectric power was available. The ammonia production can be a by-product from the production of chlorides (from electrolysis) for other value chains.

Most of these plants have been closed due to the increased cost of electricity and because the overall energy requirement was higher than for natural gas-based plants. Thus, although the carbon footprint was much reduced, the overall energy demand was higher for these early green ammonia facilities. Without the production of by-product carbon dioxide, the establishment of an integrated ammonia-urea site is not feasible.

For the fertiliser plant at Aswan, Egypt, designed for the production of 400.000 t/y of calcium ammonium nitrate, all the required hydrogen was obtained by electrolysis. At the time, this water electrolysis installation, designed and build by a consortium headed by BASF, was the largest of its kind in the world. Electricity was delivered from the hydroelectric power station at the old Aswan dam.

The ammonia produced from hydrogen obtained by electrolysis and without co-production of carbon dioxide is called green ammonia.

If the co-generation of carbon dioxide is not avoided, however, the CO₂ produced is captured, transported, and stored underground, the resulting ammonia is referred to as blue ammonia.

One more ammonia colour needs to be explained. This is the colour of hydrogen from methane pyrolysis, a process that directly splits methane into hydrogen and solid carbon. As such, no carbon dioxide results and the solid carbon is potentially a raw material resource for other value chains. Hydrogen produced by this process is called turquoise, or green-blue; if this hydrogen is used for ammonia manufacturing, turquoise ammonia results.

In the world of ammonia manufacture, various intermediate and site-specific processes are possible. For example, in 2018, a new ammonia plant was commissioned in Freeport, Texas. This world-scale ammonia plant uses no fossil fuel feedstock. The plant produces 750,000 metric tons of ammonia per year using hydrogen and nitrogen delivered directly by pipeline. The primary supply of hydrogen is by-product hydrogen from other non-fertiliser chemical installations, rather than hydrogen produced from fossil fuels; as such the Freeport plant can claim that its ammonia has a significantly reduced carbon footprint.

This new ammonia plant demonstrates three truths. First, low-carbon merchant ammonia is available for purchase in industrial quantities today; this is not just technically feasible but also economically competitive. Second, carbon intensity is measured in shades of grey, not black and white. Ammonia is not necessarily carbon-free or carbon-full, but it has a carbon intensity that can be quantified and, in a carbon-constrained economy, less carbon content equates to higher premium pricing. Third, the ammonia industry must improve its carbon foot-printing in order to be rewarded for producing green ammonia (Brown, 2018).

High cost of ammonia production, for example due to high raw material cost, such as high cost of electrolysis or to high natural gas pricing, may prompt manufacturers to curtail production. This reduces the output of carbon dioxide, which, however, may be needed for other value chains such as the food and beverage sector.

Ammonia from renewable sources: energy storage and potential as fuel

Renewable energies can provide electricity which can be converted into hydrogen and other chemicals. One challenge to be overcome is the need to intermittently store this energy. The search for capable batteries is ongoing.

The storage of hydrogen faces both energy and safety challenges. To liquefy hydrogen, much of its energy content is used, e. g. about 70 % of the energy content of hydrogen is required to condensate the gaseous hydrogen at very low temperatures or under pressure. Energy is required to maintain this liquid state. The storage of large volumes of flammable hydrogen requires elaborate and costly safety precautions.

Liquid ammonia may offer a more practical and energy efficient alternative. To liquefy gaseous ammonia, at around – 33 °C, much less energy is needed, about 30 % of its energy content. Ammonia can be catalytically decomposed in nitrogen and hydrogen with very high conversion rates at rather normal pressure and temperature conditions. Liquid ammonia thus is a possible energy / hydrogen carrier and as such is under discussion as fuel, for example, for maritime transport.

Ammonia has a pungent smell and therefore is detected at very low levels (5-10 ppm), which provides for an early warning in contrast to hydrogen.

The successful use of solar energy in small-scale sustainable ammonia production for direct agricultural use has been demonstrated (Schmuecker, 2015).

References

Anonymous. (2012). Zimbabwe Independant – 05.04.2012.

Appl, M. (1999). Ammonia: Principles and Industrial Practice, Wiley ISBN 3-527-29593-3.

Brown, T. (2018). https://www.ammoniaenergy.org/articles/yara-and-basf-open-their-brand-new-world-scale-plant-producing-low-carbon-ammonia/, 27.04.2018.

Brown, T. (2018). Innovations in Ammonia, International Fertiliser Association, Global Technical Symposium, Madrid, Spain, 09.-12.04.2018.

Feiner, J. (1952). The Aswan dam development project. Middle East Journal, Vol. 6, No. 4 (autumn), pp. 464-467.

Hager, T. (2008). The Alchemy of Air. Harmony Books, New York, United States of America. ISBN 978-0-307-35178-4. OCLC 191318130.

Halasa, M. (2021). Yara Glomfjord nitric acid plant from 1955 – 66 years of continuous improvement, International Fertiliser Society webinar.

IPPC. (2007). Integrated Pollution Prevention and Control, Reference Document on Best Available Techniques for the Manufacture of Large Volume Inorganic Chemicals – Ammonia, Acids and Fertilisers, August 2007; a revision and update of this document is ongoing (2021-2025).

Kirova-Yordanova, Z. (2004). Exergy analysis of industrial ammonia synthesis. Energy, 29, 12, December 2004, 2373-2384.

Kirova-Yordanova, Z. (2012). Energy integration and cogeneration in nitrogen fertilizers industry: Thermodynamic estimation of the efficiency, potentials, limitations and environmental impact. Part 1: Energy integration in ammonia production plants. Proceedings of ECOS 2012 – The 25th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems, June 26-29, Perugia, Italy, 138-152.

Korkhaus, K. and Bachtler, M. (2013). The Ammonia Process – A Challenge for Materials, Fabrication and Design of the Components. AIChE Ammonia Technical Manual Vol 54.

Noelker, K. and Ruether, J. (2011). Low energy consumption ammonia production: Baseline energy consumption, options for energy optimization. Nitrogen & Syngas Conference, Düsseldorf, Germany.

Reuvers, J. G., Brightling, J. R. and Seldon, D. T. (2013). Ammonia technology development from Haber-Bosch to current times. Proceedings International Fertiliser Society, 747.

Reuvers, J. G. (2017). Changes, Challenges and Opportunities in Fertilizer-Manufacturing Processes: A personal Review and Outlook. Proceedings International Fertiliser Society, 803.

Schmuecker, J. (2015). My solar hydrogen and ammonia, and ammonia tractor fuel and fertilizer system. Presented at the 2015 NH3 fuel conference, September 20–23, Argonne National Laboratory, Chicago, USA.

Teggers, H. (1980). Prospects for chemical syntheses based on gas from coal, (a) application of the Koppers-Totzek Process for ammonia synthesis, in Oils and Gases from Coal, a Symposium of the United Nations Economic Commission for Europe, held at Katowice, Poland, 23.-27.04.1979, Pergamon Press.

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Related IFS Proceedings

89, (1965), Manufacture of Ammonia, P W Reynolds

167, (1977), An Integrated Process for Ammonia-Urea Manufacture, V Lagana, U Zardi

168, (1978), Catalysts in Ammonia Production, J D Rankin

184, (1979), Coal Gasification – Routes to Ammonia and Methanol, F C Brown, H G Hargreaves

191, (1980), New Concept Ammonia Process with Higher Efficiency, W F van Weenen, J Tielrooy

307, (1991), Stress Corrosion Cracking of Carbon Steel Storage Tanks for Anhydrous Ammonia, L Lunde, R Nyborg

308, (1991), Ammonia Storage Inspection, S Hewerdine

319, (1992), Development & Operation of the Leading Concept Ammonia (LCA) Technology, K J Elkins, A J Gow, D Kitchen, A Pinto

382, (1996), Control of Stress Corrosion Cracking in Liquid Ammonia Storage Tanks, R Nyborg, L Lunde, P-E Drønen

401, (1997), Ammonia: Safety, Health and Environmental Aspects, K D Shah

446, (2000), Revamping Ammonia Plants: Case Histories of Capacity and Energy Improvements, P Orphanides

479, (2001), Energy Conservation: Key to Survival for Fertiliser Producers, W D Verduijn, J J de Wit

482, (2001), De-Commissioning of Ammonia Cold-Storage Tanks, J Kristensen, R Fogg

484, (2001), Energy Audits of Fertiliser Production Plants, I R Barton, J Hunns

582, (2006), IPPC: The BAT Reference Document (BREF) for the Manufacture of Ammonia, Acids and Fertilisers, B Serr

601, (2007), Ammonia Production: Energy Efficiency, CO2 Balances and Environmental Impact, J D Pach

602, (2007), Ammonia Plant Energy-saving Project: Design and Implementation, W T Nobel, R B J Waggeveld, M J Walton, P A Sharp

603, (2007), Inspection of Atmospheric Ammonia Storage Tanks; New EFMA Recommendations, H A M Duisters

604, (2007), Safety Issues in Ammonia Handling and Distribution, K D Shah

639, (2008), GHG Emissions and Energy Efficiency in European Nitrogen Fertiliser Production and Use, F Brentrup, C Pallière

647, (2009), Developments in Ammonia Plant Contracting, P Kummann

671, (2010), By-Product Formation in Ammonia Plants, J D Pach

691, (2011), Advanced Spun Cast Material for Steam Reformer Furnace Tubes, S Venkataraman, D Jakobi

745, (2014), Detection and Localisation of Leakages in Toxic/Flammable Chemicals Pipelines Using Distributed Fibre Optic Sensors, D Inaudi, R de Bont, R Walder

749, (2014), First Practical Experience with Robot Inspection of Ammonia Storage Tanks, K Bakli, O N Mortensen, C Valand

788, (2016), Improvements in Nitrogen Addition to the Fertiliser Production Flowsheet, I Blazsek and M J Cousins

801, (2017), Opportunities for small scale ammonia production, J P Vrijenhoef

817, (2018), Opportunities created by the innovative revamping of a methanol plant, E Strepparola and A Scotto

843, (2020), Occupational and Process Safety in Ammonia Plants – Pitfalls to Avoid, H Duisters