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Cartridge Catalysts for ammonia oxidation

Summary

PGP Industries has introduced a new Cartridge Catalyst system, offering improved performance in the production of nitric acid. J. Cranston discusses the results obtained from six years of commercial operation in various types of nitric acid plants.

Abstract

PGP Industries, Inc., was founded in 1970 and is today one of the world’s leading refiners and fabricators of platinum group metals. PGP originally entered the North American nitric acid market in 1984 and has since initiated a variety of fabrication techniques aimed at improving the performance of the standard woven gauze.

Much of PGP’s research has culminated in the production of specially fabricated woven gauzes, (e.g. quick start gauze, special weave gauze and low pressure drop catalyst gauze). All these changes were aimed at improving the performance of a commodity gauze. Although customization of the catalyst pack did show minor improvements, PGP believed that any significant benefits required either a change in the gauze structure or a compositional change in the catalyst alloy. After evaluating the performance improvements resulting from both the application of knitting techniques to the fabrication of catalyst gauzes and a change in the total composition of PGP’s new Cartridge Catalyst system, PGP decided to concentrate its efforts on the Cartridge Catalyst.

The objective in designing the Cartridge Catalyst was to manufacture a product that would be capable of reducing the costs associated with producing a ton of acid. The factors associated with the catalyst that directly affect production costs are listed as follows:

  • Conversion efficiency
  • Production rate
  • Production run length
  • Costs associated with the catalyst:
    • intrinsic metal costs
    • net losses of platinum group metals (PGM) from the catalyst

 

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Central European fertilizer outlook

Summary

Central Europe is a region still emerging from the doldrums of post-Cold War economic restructuring. However, some countries have managed the change with far greater ease than others, creating a new divide in a politically turbulent region.

Abstract

It has now been eight years since Mikhail Gorbachev announced that the then Soviet Union would no longer stand in the way of political change in central Europe. The euphoria of the dismantling of the ‘Iron Curtain’ and the reunification of Germany has given way to painful economic realities caused by the transition from state to market-run economies for the countries of the region.

There is continuing political uncertainty, too. The ending of the Soviet military occupation of the region has allowed national and ethnic tensions that had been buried for most of this century to move back to the fore. Czechoslova- kia and Yugoslavia, both creations of the 1919 Versailles treaty, have each seen the industrialised northwest of their respective nations cut loose from the agrarian southeast. In Czechoslovakia’s case the move was achieved peacefully and with few recriminations in the so called ‘Velvet Divorce’. In Yugoslavia it required a bloody four-year civil war until the combatants were exhausted enough that peace could be imposed by the United States. Albania’s recent collapse into anarchy could easily be repeated on a larger scale in Bulgaria if the April elections there do not produce a government prepared to grasp the nettle of economic restructuring. And old ethnic tensions smoulder on, such as between Serbs and Albanians in Yugoslavia’s southern Kosovo region.

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The fertilizer industry in China

Summary

China is the largest consumer of fertilizer in the world, and the major destination for the world's urea exports. However, in the first months of 1997, China stayed out of the urea market, and urea imports may drop by 30% this year. Is the giant close to achieving its dreams of self-sufficiency?

Abstract

Much of China’s fertilizer infrastructure is a relic of the country’s troubled past. When the communists came to power in 1949, they inherited a poor, backward nation ravaged by half a century of civil wars and foreign invasions. Mao Zedong’s new regime began a programme of industrial development intended to meet the peoples needs on a region by region basis. Some fifty fertilizer facilities formed part of this modernisation programme. However, much of the siting of plants was done on a political rather than economic basis, rewarding those areas and local leaders that had supported the communist regimes rise to power.

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Johnson Matthey diversifies its product range

Summary

Nitric acid producers are faced with a bewildering choice of catalyst, with many types of catalyst based on knitting technology. This article informs and advises on the parameters which should be considered before reaching a conclusion and introduces Johnson Matthey's new range of knitted catalyst gauzes.

Abstract

In the past, the catalyst traditionally used in the industry for the manufacture of nitric acid was a woven, 1024-mesh, precious metal catalyst gauze with a wire diameter of 0.076 mm or 0.060 mm. This woven catalyst design was the industry standard for some 70 years until the early 1990s, when Johnson Matthey was the first company to develop and market a new type of precious metal catalyst based on knitting technology. Since then all manufacturers have developed structures based on the knitting technique and it has quickly become the standard for many plants.

 

The major benefits of knitted catalyst to the nitric acid producer are as follows:

  • increased surface area giving improved conversion efficiency;
  • reduced metal loss;
  • extended campaign length;
  • reduced surface contamination;
  • increased strength;
  • lower rhodium oxide formation.

During the last year, a new range of knitted catalysts from Johnson Matthey that provides improved performance has been on trial in Europe and the USA. The new catalysts form part of the Inter-Lok range of knitted catalyst. The new catalysts became available commercially in March 1997.

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Boosting nitric acid production

Summary

Direct oxygen injection can provide a low cost alternative for nitric acid producers who want to increase their production rate without increasing NOx emissions. It can also be used to reduce NOx emissions, maintain colour quality, increase acid strength, provide flexible operation and, in some cases, reduce utilities consumption. Praxair has optimized this technique and has demonstrated it in several commercial units in recent years.

Abstract

Nowadays, environmental regulations are such that most nitric acid producers cannot increase their nitrogen oxide (NOx) emissions under any circumstances. Therefore, any pro-cess change must be achieved without increasing NOx. If NOx emissions are to remain the same while boosting production, intervention is needed because increasing production will increase the amount of NOx in the absorption tower. If this NOx is not reoxidized in the tower, the NOx emissions will rise. Maintaining NOx while increasing production can generally be obtained in one of four ways: direct oxygen injection, the installation of additional absorption tower height, boosting plant pressure, or increasing the capacity of the NOx treatment unit. Of these options, direct oxygen injection, requires the least capital outlay.

The concept of using oxygen addition to enhance the performance of a conventional nitric acid plant is not new. It has been used to boost production by what is now Hydro Agri Europe in several nitric acid plants in Norway during the 1980s. More recently, Praxair Inc., the leading supplier of industrial gases in North and South America, has developed and optimized the technique and, to date, has demonstrated it in ten commercial nitric acid plants.1

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New concept optimizes energy recovery

Summary

A new concept called the Saturated Nitric Acid Process has been developed by dk-Technik and Kemira Denmark. The new process is designed to offer superior performance in a less complex plant than the conventional nitric acid process. This results in a process design that is more energy efficient and less capital intensive.

Abstract

The Saturated Nitric Acid process is a new concept based on a simple yet significant modification of the conventional nitric acid process. The modification comprises saturating the tail gas at elevated temperature before it enters the tail gas expander and systematically optimizing the operating parameters. This allows an improved match between heat release and heat absorption, especially at high temperature.

The new process has been developed with energy efficiency in mind. In fact, it is claimed to have a superior cost/energy efficiency ratio for all cost levels. The reason for that is a simpler design from which the steam cycle in many cases can be omitted.

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Flash evaporation provides a new alternative

Summary

Urea solutions are often concentrated in a two-stage evaporation section. According to M. Rijckaert and A. Biermans of DSM Research, DSM/Stamicarbon has developed a new method for concentrating the urea solution which is not only less sensitive to fouling but also reduces the water content in the urea melt. In the second evaporation stage, dry urea is now obtained by flash evaporation. The urea solution is flashed to pressures and temperatures at which the liquid phase is no longer stable and will therefore spontaneously split into solid urea and water vapour.

Abstract

Urea is synthesized from ammonia and carbon dioxide. Ammonium carbamate is formed in the first step and then partially converted to urea and water. The first step is fast and exothermic and goes nearly to completion. The second step is slow and endothermic, the equilibrium is reached at a CO2 conversion of about 65%.

2NH3 + CO2 <-> NH2COONH4

NH3COONH4 <-> NH2CONH2 <-> H2O

In the DSM/Stamicarbon process most of the unconverted ammonium carbamate is separated from the urea solution in a stripping section with CO2 as the stripping agent. Further concentration by removal of water is established in a two-stage evaporation section. The urea solution is concentrated from 75 wt-% to 95 wt-% urea in the first stage and further concentrated to 99.7 wt-% in the second stage. The second stage is especially sensitive to fouling, caused by physical and chemical entrainment. Chemical entrainment is caused by the decomposition products of urea in the vapour phase (ammonia and isocyanic acid). NH2CONH2(l) NH4NCO(l) <-> NH3(g) + HNCO(g)

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