Introduction
Ammonia is the world’s second-largest manufactured industrial chemical. Ammonia production is the most complicated process, involving the greatest percentage of catalytic steps and four chemicals (ammonia, methanol, hydrogen, and carbon monoxide) that depend on related syngas process for their development. Ammonia is one of the most essential chemical substances globally and 88 percent of it is used as a fertilizer for food production. The remaining 12 percent of ammonia is utilized as a refrigeration fluid and a removal agent of nitrogen oxides (NOx) pollution control of numerous chemical uses including the manufacture of explosive material and polymers.
Fig 1. Annual ammonia usage
Production of ammonia from ambient nitrogen was made possible by the invention of the Haber-Bosch cycle during the first decade of the nineteenth century.
Fig 2. Haber – Bosch process improvement
This was the only scientific achievement recognized by two Nobel Chemistry awards, given in 1918 to Fritz Haber and in 1931 to Carl Bosch. As revealed by Sir William Crookes in 1898, the invention of ammonia synthesis explicitly addressed as the “Wheat Issue,” whereby a lack of available supplies (of wheat) will only enable the population to grow continuously until around two billion, that would be attained in about 1930.
Fig 3. Haber – Bosch process
In 2002, Iceland generated electrolysis of 2,000 tons of hydrogen gas utilizing surplus energy from its hydroelectric projects, mainly for the use of ammonia for fertilizer production. From 1911 to 1971, the Vemork hydroelectric generators in Norway used its excess electricity production to generate reuseable ammonia, which included 15 MWh / ton of nitric acid. The same process is achieved by lightning, which offers a natural trigger to transform ambient nitrogen into soluble nitrates. Currently, the global ammonia output volume is expected to surpass US$ 100 billion, with the largest single plants able to manufacture 3300 metric tons per day (mtpd) or 3640 short tons per day (stpd). To reach that scale, a number of changes have been made in the past 100 years of both process and catalyst technologies (Rafiqul, 2005).
Background
The ammonia process technology has changed significantly over the last 60 years. Plant architectures changed from multi-train layouts to single-train models, often with separate trains at the front end and propagation loops. The processing of synthesis gas at the front end of the plant is improved by raising atmospheric pressure to pressure of 30–50 barg.
Fig 4. Flow scheme of the first commercial ammonia plant
The efficiency of a single train rose from 100 mtpd to as many as 3,300 mtpd. Energy efficiency has also improved with consumptions well above 60 GJ / m.t of ammonia in older plants down to 40–50 GJ / m.t in new plants. Modern plants also applied heat recovery to both the synthesis preparation train and the formulation loop through steam processing at pressures as much as 125 barg.
Fig 5. Worldwide ammonia production
in terms of plant equipment, there has been a change from reciprocating compressors to centrifugal compressors. In the formulation converter, a heat energy exchanger was installed to improve the conversion of H2 and N2 to NH3. Processing of ammonia relies on abundant energy sources, primarily natural gas. Sustainable production is beneficial, leading to the essential function of ammonia in industrial cultivation and other processes. This is possible with the use of renewable energy to produce hydrogen through electrolysis of water. In hydrogen production, the process will be straightforward by converting some produced hydrogen from power to feedstock usage.
Hydrogen recycling from purge gas (in devices like PSA systems) has been used by manufacturers to increase efficiency or reduce plant energy use. Hot feed gas desulphurization systems have also been enacted by designers. The catalysts used in the upgrading, shift transfer, methanation, and ammonia synthesis have been greatly enhanced. Distributed control systems (DCSs) for automated process management, as well as security-instrumented systems (SISs), are now common in ammonia plants to increase process control and safety. Hazard and operability (HAZOP) studies and Layer of protection Analyses (LOPAs) are done before each mechanism goes live.
Fig 6. HAZOP and LOPA studies are done for ammonia plants
Innovations in simulator testing and teaching activities mean that operators and engineers may conduct their duties safely and efficiently. This is only a handful of the thousand technological and safety enhancements that have been introduced to render the ammonia industry as one of the world’s most efficient and stable industries (Sendich, 2008).
Plant processes improvements
Several changes have been made in ammonia plant technology during the first few years of the 21st century, enabling current plants to raise output volumes and to construct new plants with greater and greater capacities. Competition amongst suppliers of technology is very intense. The market is currently dominated by three technology licensors – KBR (Kellogg Brown and Root), Haldor Topsøe, and ThyssenKrupp Industrial Solutions (TKIS).
Fig 7. Major ammonia technology licensors
Another company, Ammonia Casale, is an industry pioneer in revamping mature plants, providing axial-radial catalyst bed construction.
KBR (Kellogg Brown and Root) plant design
Most of KBR’s newly built ammonia plants use its Purifier method, which incorporates the main reformer, an upstream liquid nitrogen wash purifier to eliminate impurities and change the H2: N2 ratio, a patented thermal energy boiler system, unitized coolers, and a horizontal ammonia synthesis converter. The energy intake may be as small as 28 GJ / m.t based on plant configuration. Since the secondary reformer requires excess air, the main reformer might be smaller than in existing methods. The ammonia concentration that leaves the horizontal low-pressure converter is 20–21 percent, which decreases the recycle compressor’s energy demands. KBR also provides low pressure ammonia loop with which uses a combination of magnetite catalyst and its patented ruthenium catalyst (Abughazaleh, 2002).
Fig 8. Modern ammonia plant by KBR
Haldor Topsøe designed plant
Except for its patented side-fired visionary, which utilizes radiant burners to provide fuel for the transforming reaction, it is very conventional. Haldor Topsøe also sells a patented iron-based synthesis catalyst, one-, two- or three-bed radial-flow adapters, and a patented bayonet-tube waste-heat burner. More recent innovations include the prototypes of the S-300 and S-350 converters. The S-300 conversion is a three-bed radial-flow system with internal heating systems, while the S-350 design incorporates a single-bed S-300 conversion with a single-bed S-50 device with waste heat between converters to optimize ammonia (Mark Fecke, 2016).
Fig 9. Haldor Topsøe’s ammonia plant design
ThyssenKrupp plant design
Uhde now known as tkIS (ThyssenKrupp Industrial Solutions) is another company with a long innovative history in the ammonia industry with its first ammonia plant built-in 1928. Uhde developed its dual-pressure process for large-scale plants in late 2001. The first plant based on this technology was the SAFCO IV ammonia plant in Saudi Arabia, which was commissioned in 2006.
Dual-pressure ammonia synthesis loop with a distinctive secondary reformer design, specialized waste heat boiler, radial flow converters. Nowadays, the TKIS dual pressure process can accomplish a production rate of 3.300 mtpd.
Fig 10. ThyssenKrupp’s dual pressure design
The Linde Ammonia-Concept (LAC)
The Linde Ammonia Concept (LAC) is an established industrial process scheme with more than 25 years of work experience in plants with capacities ranging from 200 mtpd to over 1750 mtpd. The LAC design scheme substitutes a traditional ammonia plant ‘s expensive and complex front end with two well known, efficient control units (Grasham, 2019):
- The manufacturing process of ultra-high-purity hydrogen from a PSA-purified steam methane reformer
- Ultra-high-purity nitrogen output by a cryogenic nitrogen generating station, also recognized as an air separation unit (ASU)
Fig 11. The Linde Ammonia-Concept (LAC)
Other technologies
Several manufacturers of equipment have proposed gas-heated reformers (GHRs) to generate ammonia in small-scale plants or to expand efficiency. While traditionally designed plants use a combination of primary reformer and secondary reformer, plants with GHRs use the secondary reformer hot-process gas to provide power to the primary reformer. While some ammonia manufacturers promote dispersed processing of ammonia in small ammonia plants, most businesses tend to construct massive facilities near to inexpensive sources of raw material and deliver the commodity to customers by truck, rail, or pipeline.
Energy Management program
Energy management programs regulate long-term energy challenges and create business consistency by reducing energy consumption by 3% to 10% per year. Energy management also decreases waste and emissions which may be expensive to monitor.
- More than 80 percent of energy consumed in the nitrogen fertilizer industry is actually for manufacture of ammonia. The next phase of maximum energy usage is the processing of urea.
- Much of the fuel used in the ammonia synthesis is used in the main reformer (about 78 percent) and the remainder-in auxiliary boilers. The usage of natural gas for energy purposes contributes to 66 percent of overall electricity expenditure (excluding utilization of feedstock).
- The biggest cost of ammonia manufacturing is natural gas. Based on the scale of an ammonia plant and pricing of natural gas, the electricity and feedstock expenditure of natural gas accounts for 72-85 percent of the overall cost of output.
Future of ammonia production
Ammonia not only fertilizer but also a transporter of hydrogen, with consumer opportunities in the production and delivery of renewable resources, as a fossil-free power. The energy market is best known on NH3’s three hydrogen atoms while the fertilizer industry only represents its one nitrogen atom. Recognizing this current potential ammonia demand is critical because the huge size of the sector fundamentally shifts the investment factors and investment outlook for renewable ammonia development technologies. The global oil industry is greater than the ammonia market today. “Technologies to be established” introduce gradual changes to the existing Haber-Bosch method and entirely new systems that utilize electrochemical and chemical processes.
- Sustainability: use water, rather than natural gas or other fossil sources, as a source of hydrogen, reducing carbon pollution.
- Energy efficiency: to generate the same volume of ammonia utilizing fewer resources (fuel and feedstock).
- Modular interoperability: sizing of industrial processes to be configured for inputs of renewable energy rather than fossil energy.
- Economic factors: that every innovative system’s capital and operational costs so it can cope with the existing systems(Soloveichik, 2017).
Electrochemical synthesis of ammonia
Future Technologies
Coal-related processing of ammonia requires more resources than the development of ammonia dependent on natural gas, with heavy fuel oil and naphtha. All these energy-intensive feedstocks should be substituted by natural gas to achieve the 2050 target of improving energy efficiency at 25 percent. By 2050 ammonia through biomass gasification would be as energy-intensive as currently the coal-based processing is, but will be carbon-neutral. As for every plan for diversifying, this phase would be guided according to the risk tolerance in the sector. And, as in any research plan, there would be first-mover benefits and drawbacks. The first movers are now making their steps: for a conventional Haber-Bosch synthesis process, there are no less than four separate green ammonia model plants presently under construction, each attempting to use green resources to power electrolyzers to generate hydrogen (Ikäheimo, 2018).
Characteristics of technologies to be developed:
Cost-effective fuel synthesis
- Hydrogenation reactions (better, modular Haber-Bosch)
- One-step reactions using water as a hydrogen source
Efficient power generation from fuels
- Direct conversion to electricity
- Combustion in thermal engines
- Intermediate hydrogen formation
Electrochemical vs. thermal (catalytic) technologies
- Higher efficiency >> energy savings
- Higher selectivity >> less purification needed
- Lower temperature and pressures >> lower Blow Out Preventer (BOP)
- Liner Scalability >> better suited for small to medium scale
Conclusion
Even at the most advanced ammonia plants, the basic method of ammonia production and catalysts designed by Haber-Bosch and Mittasch are still easily recognizable. Nevertheless, the plant efficiencies and environmental safety have increased significantly in the last 100 years, most noticeably in synthesis gas processing, supporting both ammonia output and other processes dependent on syngas. Because energy usage is similar to the theoretical level within industrial systems, actual energy use may only be decreased slightly, if at all. Many new approaches and designs have been developed and incorporated to help modern ammonia plants manage the cost and decrease energy consumption. With the advancement of technology, more developments and improvements are expected in the future.
Bibliography
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