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New technologies for ammonia plants

Summary

Research and development continues to yield novel concepts for ammonia production and some of these are now ready for their first commercial application. In this article, we report on new technologies and process enhancements from Ammonia Casale, Haldor Topsøe and KBR.

Abstract

Casale ammonia plant design
Casale’s policy has long been based upon the development and application of new advanced technologies to get the best improvements in ammonia plant performance in terms of energy consumption, capacity, or a combination of the two.
Many articles have been written on Casale technologies for plant revamping, whose application can lead to a capacity increase of 50% or more, and a significant energy saving. For this reason, this article presents the new technologies developed by Casale for new ammonia plants only.

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Process condensate stripper performance in ammonia plants

Summary

A project was recently completed on the development of an alternative process route for the removal of methanol, ammonia and carbon dioxide from process condensate in an ammonia fertilizer plant. As part of this project, a performance analysis study on three representative process condensate strippers operating under different conditions in Indian fertilizer plants was initiated and results compared. Steady state simulation runs on these stripper variants using CHEMCAD simulation software were carried out. The effect of stripper operating pressure and temperature and steam tonnage on the stripper performance is reported by S. Krishnaswamy, S. M. Nazir, P.V.K. Srikanth and K. Ponnani of BITS, Pilani – Goa Campus.

Abstract

In the ammonia manufacturing process, when syngas is cooled after the low temperature shift (LTS) step, the unreacted steam (used in reforming and shift conversion) forms a condensate stream which contains impurities, the major ones being ammonia (NH3), methanol (CH3OH) and carbon dioxide (CO2). The syngas from this step goes to a CO2 separation step where another stream containing mostly water and an equilibrium amount of CO2 is formed. This stream normally known as “Benfield” condensate is subsequently pressurised and added to the condensate stream obtained at the end of the LTS step. The resultant stream called “process” condensate1, 2 typically contains ammonia, methanol and carbon dioxide, each in the range of 300 to 2000 ppm by weight, depending on the variations in process and operating conditions in a plant. A comprehensive analysis and characterisation of process condensate has been carried out by the investigators earlier and reported.3
The current method of treating process condensate involves steam stripping to reduce the ammonia, methanol and carbon dioxide content to below 5 ppm by weight for each and re-use the purified condensate as boiler feed water (BFW).  The stripper has to operate under severe operating conditions where a large amount of superheated steam is consumed making it a highly energy intensive operation. Even then, the BFW specifications for recycle are hard to achieve. This can result in degradation of condensate to lower duty or rejection and increase of stripper steam.

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Ammonia in the Mediterranean

Summary

The gas-rich nations of North Africa have become a southern adjunct to the European market, supplying ammonia and other downstream products to the European market. However, some production continues in southern Europe, mainly in the hands of large, integrated companies like Yara and Fertiberia.

Abstract

The Mediterranean Sea has long been one of the major crossroads of the world, and continues to be so, with both natural gas and downstream products crossing it in increasing volumes. This has become particularly so of the ammonia industry, as capacity has closed in Europe and begun to migrate to lower gas cost locations which increasingly include the countries of North Africa.
As Table 1 shows, natural gas reserves are concentrated on the North African side of the Mediterranean, with Egypt, Libya and Algeria holding large reserves. Europe has long been a net consumer, and in fact much of the gas consumption in southern Europe is fed from those three north African states, via pipelines that cross the sea from Algeria to Spain and Italy, and from Libya to Sicily. There is also LNG export from all three of the resource-rich states, although Libya’s export is relatively minor compared to the larger volumes from Algeria and Egypt.

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Methanol: the future remains bright

Summary

Nitrogen+Syngas reports from the IHS World Methanol Conference in San Diego, held in December 2011, on how the rapidly changing market for this important syngas derivative is shaping up.

Abstract

It is just short of 100 years since Dr Alwin Mittasch of BASF made the first synthetic methanol from carbon monoxide and hydrogen at Luwigshaven. By the time that his invention reaches its centenary in 2013, the methanol market will exceed 50 million tonnes per annum. Most of that growth has occurred in the past 40 years, as countries discovered natural gas in remote parts of the world and used methanol as a way of monetising it, replacing older, higher cost capacity in Europe, North America and Japan, as gas costs there rose. Methanol derivatives, however, still tended to be produced in the developed world, and so a large seaborne methanol trade developed.
As we move into the 21st century, the market is changing more rapidly than at any time since the 1970s. Now consumption of derivatives is moving to newly industrialising countries, particularly China, and economies of scale and falling production costs mean that new end uses like fuel blending and even on-purpose propylene production are coming to the fore.

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New approach to secondary catalyst installation

Summary

Secondary N2O abatement in nitric acid plants with high nitrogen loading can be challenging. S.P. Roe of Johnson Matthey Noble Metals reports on the development of a new design approach to secondary catalyst installation utilising axial radial technology. Following extensive development and testing a new system design is being fabricated for installation in 2012.

Abstract

Industrial production of nitric acid uses the Ostwald process. The first stage of this process is the production of nitric oxide by oxidation of ammonia by reaction 1.
 4NH3 + 5O2 → 4NO + 6H2O  (1)
This process is carried out in the presence of a catalyst (most commonly Pt based) with a range of temperatures and pressures according to plant design. The combination of reaction conditions and catalyst design can give a range of selectivity’s for the oxidation process which is usually between 92 and 98%. The non-selective products are nitrogen and nitrous oxide according to the reactions 2-4 below:
 4NH3 + 3O2 → 2N2 + 6H2O  (2)
 4NH3 + 4O2 → N2O + 6H2O  (3)
 4NH3 + 6NO → 5N2 + 6H2O  (4)

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OCI and Yara: old and new

Summary

Nitrogen+Syngas looks at two leading figures of the nitrogen industry – one a long-established player, the other a new entrant that has grown rapidly by acquisition to become one of the largest fertilizer companies in the world.

Abstract

Yara International
Yara International is the world’s largest publicly traded nitrogen fertilizer supplier, with a truly global reach. It operates production facilities on six continents and has sales or other operations in more than 50 countries, selling its products to 150 countries around the world. In sales terms it is a world leader, with global sales of 65.37 billion krone ($11.0 billion) in 2010, and EBITDA of 15.32 billion krone ($2.6 billion). Total sales of ammonia and finished fertilizers were 17.20 million tonnes, an increase of 3% on 2009.
More recently, 3Q 2011 results announced in October 21 saw an 85% rise in net income after non-controlling interests to 3.57 billion krone ($634 million), compared with the same period for 2010, and .EBITDA excluding special items of 4.21 billion krone ($710 million).

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Plant Manager+: Problem No. 10 High CO2 content in liquid outlet of a high pressure CO2 stripper in urea synthesis

Summary

It is well known that the high pressure CO2 stripper efficiency in a urea plant is defined by the ammonia content in the liquid bottom outlet. The ratio NH3/CO2 in the bottom outlet is determined by equilibrium equations. Problems have been experienced with a relatively high CO2 content. Several possible causes are explored. One cause could be that CO2 slips through with the liquid bottom outlet due to a defective level measurement in the stripper bottom. Measuring the liquid level is not an easy task due to the corrosive nature and the risk of crystallisation. Sometimes a delta-P level transmitter is applied with flushes in its legs, but this is not a reliable option. Radioactive level measurements are often used but still safety risks, complicated calibrating procedures, limited lifetimes and maintenance costs are significant concerns. The radar level measurement developed by Stamicarbon offers a new and reliable solution.

Abstract

Mr Joko Raharjo of PT Petrokimia Gresik in Indonesia introduces an interesting topic to the round table:
In March 2010 we carried out some maintenance on our high pressure CO2 stripper due to high NH3 content in the liquid bottom outlet. After start-up, the NH3 outlet improved (down from 15.8 wt-% to 14 wt-%, while the design figure is 12.8 wt-%). However, CO2 is still high (before shutdown 16.4 wt-%, now 16.2 wt-%, design is 13.38 wt-%). Now our recovery section is getting hotter.
In my opinion, the higher the decomposition rate of carbamate in the stripper, the lower the NH3 content in the bottom of the stripper, as with CO2. However in my case, the NH3 content in the outlet is lower but the CO2 is still high… I welcome comment on what’s going on with this high CO2 problem.

 

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Ammonia catalysts show continuous improvement

Summary

The performance of ammonia catalysts continues to improve with the growing demand for this key chemical. S. Gebert, Y. Cai, and B. Kniep of Süd-Chemie AG discuss the high performance of the wustite-based ammonia synthesis catalyst AmoMax®-10 that offers much improved performance compared to conventional systems.

Abstract

Ammonia is one of the world’s most valuable industrial and agricultural chemicals. It serves as the basis for the production of fertilizers that are in high demand to meet the global food production needs. Süd-Chemie is actively engaged in addressing the process demands for this product.
The very heart of the ammonia process is the iron synthesis catalyst, which enables the fixation of nitrogen from air with hydrogen. The industrial success of commercial ammonia production would not have been possible without the appropriate catalyst choice. Though different catalysts were tested during the early stages of the process nothing has approximated the advantages of iron (magnetite) for industrial ammonia production. For more than 90 years iron catalyst has supported this industry with very few significant changes1,2.

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Combating corrosion in cooler condensers

Summary

The tube-sheet and the inlet of the tubes of the cooler condenser in nitric acid plants are often subject to corrosion. As the bulk gas temperature is much higher than the surface temperature of the tube-sheet and the inlet of the tubes, condensation and reboiling of acid takes place resulting in corrosion. Even when using special materials the lifetime of the cooler condenser is often limited. In this article, Sandvik Materials Technology, ATI Wah Chang and Yara report on their experiences and solutions to this common corrosion problem in nitric acid plants.

Abstract

Most of the nitric acid produced world-wide is manufactured by the oxidation of ammonia over a platinum catalyst (gauze) to form nitric acid and water. During the production of nitric acid, conditions in the cooler condensers generally range in the 50-60% concentration range at temperatures exceeding the boiling point.
Nitric acid is a strong mineral acid and is highly corrosive to stainless steel if the temperature or concentration is sufficiently high. Fortunately, the inexpensive stainless steel 304L has very good general corrosion properties in weak nitric acid production. However, in heat exchangers like cooler/condensers, tail gas preheaters and boiler feed water heaters 304L has a tendency towards corrosion. When hot NOx gas condenses local corrosion on 304L is very common.

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