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Nitrogen 2000 conference report

Summary

The Nitrogen 2000 International Conference and Exhibition, organised by British Sulphur Publishing was held at the Hotel Inter-Continental, Vienna, Austria, from Sunday 12th March to Tuesday 14th March 2000.

Abstract

Vienna hosted the Nitrogen 2000 conference at a time when fertilizer prices seemed to be finally moving back upwards again. As delegates gathered in the Hotel Inter-Continental, the mood was more upbeat that in had been last year.

The conference began with a cocktail reception on Sunday, February 28th, kindly hosted jointly by Synetix and Krupp Uhde, before moving to the papers proper the next morning.

Conference director and Nitrogen & Methanol publisher John French, opening the conference, commented that he hoped the current upturn in fertilizer prices might be the beginning of a longer trend. There was also a presentation made by Nitro­gen & Methanol magazine to James Crocco, in recognition of long service to the methanol industry (see page 25).

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Laughing gas: not a laughing matter

Summary

In an ammonia-nitric acid-ammonium nitrate complex the biggest contributor to the "greenhouse effect" is not the carbon dioxide from the ammonia plant but nitrous oxide in the tail gas from the nitric acid plant. Getting rid of it is, at present, not nearly as simple as conventional NOx abatement.

Abstract

Because of a peculiar quirk of nitrogen chemistry the oxides of nitrogen normally formed in the catalytic oxidation of ammonia are not the true anhydrides of nitric acid. That means that their conversion into nitric acid is much less efficient than, for example, the by no means trouble-free conversion of sulphur trioxide into sulphuric acid.

In the wave of environmental consciousness that began thirty or more years ago, the nitric acid industry was one of the first targets for emission regulations. By a combination of better absorber design and the application of selective catalytic reduction (SCR), the NOx levels of both new and most existing nitric acid plants have now been reduced below the threshold of visibility, taking these plants very largely out of public scrutiny.

Out of sight, as the saying goes, is out of mind, and that certainly applied until recently to another oxide of nitrogen, always present in nitric acid plant tail gas but unbeknownst to the public. This is nitrous oxide – the good old “laughing gas” of the dentist’s surgery. This is formed by side reactions in the high-temperature catalytic oxidation of ammonia. Because it is inert and virtually insoluble in water, there is no mechanism by which, once released into the air, it can be removed or destroyed. Like chlorofluorocarbons, it therefore diffuses up into the stratosphere, where it is broken by ultraviolet radiation into free radicals, which in turn destroy ozone. Like chlorofluorocarbons also, it is a strong “greenhouse gas” (GHG) – about 310 times as powerful as carbon dioxide, in fact. A fairly recent paper1 ascribed to nitrous oxide 26% (74 million t/a CO2-equivalent) of the greenhouse effect of the world fertilizer industry’s estimated total emissions of GHGs (283 million t/a CO2-eq.) and no less than 56% (34 million t/a CO2-eq.) of the greenhouse effect of the estimated emissions of GHGs (60 million t/a CO2-eq.) from fertilizer manufacturing operations in Europe, where a far higher proportion of nitrogen fertilizer production is ammonium nitrate-based. Fertilizer production accounts for about 1.2% of total world emissions (1.8% of total European emissions) of all GHGs from man-made sources.

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Knitting for victory

Summary

Now that the problem of tail gas NOx is essentially solved, attention has been shifting back to the efficiency of ammonia oxidation. The design of the catalyst gauze is crucial and has been undergoing radical development in recent years.

Abstract

Considering the chemical nature of the product, it is perhaps inevitable that the manufacture of all the three mineral acids used in quantity by the fertilizer industry gives rise to environmental and health concerns. In the case of phosphoric acid, the primary concern is the acidity and toxicity in the fumes given off in the main reaction and remaining in the waste phosphogypsum, which has to be dumped into the environment in prodigious quantities because of the lack of any economic uses for it. In the case of sulphuric acid, it is the escape into the atmosphere of gaseous sulphur dioxide and sub-micron sulphuric acid mist. In nitric acid production, it has traditionally been emissions of acid-forming oxides of nitrogen.

Nitrogen has a number of different oxides, and none of the three that predominate in the product of industrially applicable nitrogen oxide-producing chemical reactions is the true anhydride of nitric acid. Because virtually the only industrial source of chemically “fixed” nitrogen is ammonia, the catalytic oxidation of ammonia is effectively always the first stage in the manufacture of nitric acid. At the high temperature needed for oxidation of ammonia, nitric oxide (nitrogen monoxide, NO) predominates (equation 1), but this oxide is inert towards water and virtually insoluble in it, so before any nitric acid can be produced it has to be cooled and further oxidized to nitrogen dioxide, NO2 (equation 2), which is then brought into contact with water to produce nitric acid (equation 3).

  1. 4NH3 + 5O2 -> 4NO + 6H2O
  2. 2NO + O2 -> 2NO2
  3. 3NO2 + H2O -> 2HNO3 + NO

 

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