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Focus on absorption

Summary

The environmental benefits of further improving the efficiency of the modern nitric acid plant absorber scarcely merit the marginal cost. But now it is possible to produce acid at azeotropic strength directly.

Abstract

The main thrust of recent de­velopment work in nitric acid production processes has been towards improving the efficiency of the catalytic ammonia oxidation stage1, in which nitric oxide is gen­erated, and on limiting the generation of nitrous oxide, which is a topical concern on account of its very strong effects as a “greenhouse gas” in the atmosphere.2 But 20 years ago, when global warming seemed to be nothing more than a theory, the main concern was the more obvious residual acid-forming oxides of nitrogen that passed through the absorption section and, thanks to the exceedingly intense brown colour of nitrogen dioxide, appeared as an unmistakable brown plume on the top of the exhaust stack.

Today the absorption section of an up-to-date high-pressure or medium/ high dual-pressure plant is about as efficient as it is going to get. That is not because it is impossible to im­prove it further but because it is not cost-effective to do so. Achievable emission levels are already so low that further improvements can never yield a return in any way commensurate with the extra investment required. If the authorities were to demand emission levels lower even than they are today, there could be more economical ways of achieving them, based on de­struction rather then recovery of the marginal nitrogen oxide values.

Though the absorption section is today technologically one of the most mature parts of a nitric acid plant, at­taining contemporary efficiency levels was not a particularly straight-forward matter. So, as the industry and its tech­nology suppliers strive to close the efficiency gap at the front end of the plant, it is not at all inappropriate to take another look at one their most notable past achievements: closing the efficiency gap at the other end.

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A new configuration

Summary

The advent of knitting techniques literally added a new dimension to ammonia oxidation catalyst gauze technology, opening up almost endless possibilities for optimization. Here J. Neumann, H. Goelitzer and A. Heywood of dmc2 (Degussa Metals Catalysts Cerdec AG) show how the latest version of dmc2's Multinit® three-dimensional catalyst gauze can achieve the same ammonia oxidation performance as formerly with 15–20% less precious metal installed.

Abstract

The efficiency of platinum-rhodium alloy catalyst gauzes in the ammonia oxidation process generally depends on a large number of inter-related factors, including the catalyst geometry and configuration and specific operating conditions of the particular plant.

The most significant parameter is the primary loss of precious metals by volatilization. Platinum is especially prone, as it undergoes an appreciable degree of oxidation and the oxide is rather volatile. That causes gradual rhodium enrichment on the catalyst surface, which reduces the activity of the catalyst. Under specific operation conditions the extent of the primary platinum losses is a function of the temperature gradient within the cata­lyst. Consequently the geometry and configuration of the catalyst gauzes plays the most critical role in de­termining the conversion efficiency, the extent of primary platinum losses and the amount of N2O formation.

Because of its three dimensional spatial structure, Multinit® catalyst gauze is characterized by a shallow temperature gradient, which results in reduced primary platinum loss and an extended campaign length with simul­taneous higher selectivity of the catalyst. This three-dimensional struc­ture therefore enables a further increase in catalytic activity to be achieved without the disadvantage of increasing precious metal losses.

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Lacking the will to reform?

Summary

India's fertilizer industry has come under increasing criticism from successive governments because of the ever-expanding subsidy regime which keeps it afloat. Now the ruling BJP has made the first concrete moves towards reining in the subsidy programme, but it remains to be seen whether India truly has the will to reform its agricultural sector.

Abstract

If anyone had any doubts that the global fertilizer industry was one driven as much by politics as economics, they need only glance at the Indian urea sector. A country with barely enough oil and gas reserves to run domestic electricity generation uses 30% of its scarce natural gas to produce fertilizers which are unable to compete with urea on the international market, and now is considering using even more expensive imported liquified natural gas as a feedstock. Yet even when the government subsidises domestic urea producers to the tune of a net $100/t, they are still unable to make a profit. How did things get this way?

India’s policy during the 1970s and 80s was to expand food production to meet the demands of a growing population, and to ensure security of supply. To this end, financial incentives were introduced to stimulate the growth of domestic fertilizer production. In particular, in 1977 the Retention Pricing Scheme (RPS) was introduced, which guaranteed a fixed return on investment for fertilizer producers irrespective of production cost. At the same time, domestic producers were cushioned from imports via a quota-based system of imports, controlled through three government bodies; STC, MMTC, and IPL. The system formed part of what became known as the ‘Quota Raj’, India’s scheme of import restrictions designed to protect domestic industry.

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The economics of catchment systems

Summary

In the September/October 2000 issue of Nitrogen & Methanol, Darren Bryce described the use of catchment systems for catalysts in nitric acid plants. Here, David Kelley presents an alternative point of view.

Abstract

The use of a catchment system (or getter) for recovering spent precious metal from the converter catalyst presents the nitric acid producer with a complex decision. The use of catchment systems certainly merits consideration since there can economic benefits to the producer. This paper attempts to clarify which criteria must be taken into consideration when trying to calculate the economic implications of running with or without a catchment system. Every plant is different and what applies to one doesn’t necessarily apply to the other; however, the basic criteria for calculating the economic benefits of a catchment system are universal, and the methodology explained in this paper applies regardless of plant type or design.

Any time producers are faced with ranking projects and deciding whether or not they should be accepted and undertaken, several criteria factor into the decision. Many methods are used to rank projects such as:

  • Simple payback
  • Net present value (NPV)
  • Internal rate of return (IRR)
  • Return on investment (ROI)

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