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Ammonium nitrate production and operational experience

Summary

The key to safe ammonium nitrate production lies in the neutralisation section of the reactor. Here, Axel Eben of Krupp Uhde describes various routes towards safe and efficient neutralisation of AN, and Paul Kaupas of Orica Inc gives details of operational experience using such a system.

Abstract

Ammonium nitrate is generally produced from aqueous nitric acid and gaseous am­monia according to the reaction;

HNO3 + NH3 -> NH4NO3 + HR; HRm = 1330~1390 kJ/kgAN

As this reaction is strongly exothermic, the neutralisation has to be done in a circulated AN solution in order to control the reaction temperature. The circulation can be activated by natural forces (thermosyphon) or by means of a pump.

Depending on the concentration of the nitric acid and on the process configuration, a more or less concentrated ammonium nitrate solution is obtained in the neutralisation stage. Depending on the later use (eg granulated AN/CAN, NPK, UAN solution) the solution has to be further concentrated.

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Dumping or commerce?

Summary

The ammonium nitrate industry in Europe has claimed for some years that Russia is selling AN at levels below production cost in European markets, in so-called 'dumping' to gain foreign currency. With progressively more stringent EU restrictions on Russian AN the debate has moved on to the USA, where a Senate investigation is now underway.

Abstract

In April, the International Trade Commission (ITC) received a letter from the US Senate Finance Committee authorising an investigation into ammonium nitrate trade in the US, EU and Russia. The US Senate has asked the ITC to produce a report by October, with particular reference to the US, EU and Russia, and possible ‘dumping’ of below cost AN in the US. The action has been requested by US AN producers, in particular Mississippi Chemicals and El Dorado Chemicals, who claim that EU action on Russian AN dumping has had the knock-on effect of making the cheap AN move to the US market instead.

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Nitrate pollution and sustainable agriculture

Summary

In the late 1980s and early 1990s, 'nitrate pollution' and 'blue baby syndrome' were phrases in common currency, provoking European Community legislation in 1985 and 1991. Since then, however, the issue has dropped out of the public eye. But as legislation on nitrate use in both the US and Europe creeps towards the statute books, Nitrogen & Methanol looks at the ongoing controversy and where we are now.

Abstract

In recent years, there has been concern that the quantity of mineral fertilizers used in agriculture is having adverse effects on the environment. When nutrients are applied to crops they are not all taken up by the plants immediately. There is also concern that some farmers might be applying inappropriate quantities of fertilizer. Depending on the type of nutrient and the existing soil conditions, different kinds of fertilizer input are required in order to maintain a given level of soil fertility. The nutrients applied may leak over time to environments where they can cause pollution. Such losses may occur when nutrients: run off the land as a result of erosion caused by heavy rainfall; are leached through the soil, beyond the root zone, eventually reaching the ground water; or escape into the atmosphere as volatile gases.

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Taking the strain off the reforming furnace

Summary

The primary reforming furnace is the most highly stressed item in conventional ammonia and methanol plants, but better materials of construction and im­proved operating practices are helping to prolong its service life. Meanwhile alternative technologies are being developed to perform its function in much less massive and failure-prone equipment.

Abstract

The true raw material for the nitrogen industry is available in equal abundance at every point on the earth’s surface: elemental nitrogen constitutes 78% of the air we breathe. The only problem is “fixing” it: making it combine with other elements to form nitrogen compounds. The reason there is a problem is that the intrinsic chemical energy of the N2 molecule is very low indeed on account of the tremendous stability of the treble covalent bond which unites it. All compounds of nitrogen with other elements have much higher inherent chemical energy. That is why to create them it is necessary to inject a huge amount of energy in one form or another. It is also the reason why there are so few significant geological sources of fixed nitrogen in the world: for purely thermodynamic reasons, all chemically combined nitrogen will sooner or later return to the atmosphere as the element except under very special climatic conditions (such as those which have long prevailed in the Atacama Desert of Chile) which inhibit the natural biological and chemical pathways by which this normally happens.

Man did not work out how to fix atmospheric nitrogen in significant amounts until the beginning of the present century, and it is one of the miracles of nature that, apart from the high-energy lightning discharges that take place in thunderstorms, the only signi­ficant agent of nitrogen fixation was a living system: micro-organisms in the soil.

Some idea of the scale of the problem is given by the desperate measures employed in the original Birkeland-Eyde nitrogen fixation process of 1901, which aped the natural formation of nitrogen oxides taking place in thunderstorms by passing air through an electric arc. It is no accident that this process was developed in Nor­way, where hydroelectric power was abundantly available at minimal cost. Because of the thermodynamic and kinetic characteristics of the N2-O2-NO system, the specific energy consumption per ton of nitrogen fixed in this process was absolutely prodigious.

The breakthrough which proved to be the foundation of virtually the entire world nitrogen industry of today was, of course, the development by Fritz Haber of BASF of a satisfactory way of synthesizing ammonia from nitrogen and hydrogen – or, in physical chemistry terms, a way of improving the kinetics of the ammonia synthesis reaction at a temperature low enough to attain satisfactory equilibrium conversion. Although the intrinsic chemical energy of the product ammonia is much higher than that of the nitrogen, the reaction of nitrogen with hydrogen is exothermic (a net producer of energy). The reason for that is the extremely high intrinsic chemical energy of hydrogen, which provides the driving force for the reaction.

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