Targeting Improving Performance and Conversion Efficiency in Nitric Acid Plants

Keywords: process modelling, gauze analysis, catalyst, conversion efficiency, nitric acid

In October 1916, Johnson Matthey (JM) supplied its first ever platinum group metal (pgm) gauze pack to the UK Munitions Invention Department. Ever since JM has worked closely with producers to overcome the numerous challenges a nitric acid (HNO3) plant faces. Today in 2016, JM is celebrating its first centenary of gauze manufacture, as well as preparing for the 200th anniversary of JM in 2017.

The latest manifestations of this accumulated experience are the Eco-CatTM systems, which combine platinum group metal with complex ternary alloys and knit structures. This combination generates a number of quantifiable performance improvements, compared to standard catalyst packs. They reduce the overall weight of the gauze pack, with a reduced platinum content, extend campaign lengths, and maintain or improve campaign conversion efficiency, whilst minimising metal loss.

These developments have been facilitated by careful analysis of spent gauzes, to identify surface restructuring. In turn, this indicates the degree to which nitric acid plants are being run optimally. It was identified that traditional gauze packs had spare capacity and reductions in the installed weight could be made confidently. As a result the weight of the gauze pack was reduced to optimise the use of precious metals.

The next stage of development was the introduction of an internal metal recycling mechanism, which used ternary alloys. Repeated use of JM’s ammonia oxidation test rigs enabled an iterative process of fine tuning the content and structure of the gauze packs to be progressed.

This paper details two case studies that demonstrate how JM’s expertise and technology has been deployed to develop a customised Eco-Cat system for a European nitric acid producer and to design solutions for a nitrous oxide abatement containment system that improved abatement performance and overall conversion efficiency.

JM has built on this experience to further develop its reaction modelling capability. Its expertise and knowledge of gauze design, established through a gauze development programme, is being used to create an increasingly robust model. A combination of theoretical concepts, proprietary JM data and design knowhow, along with complex kinetic and pressure drop calculations will be used to further improve the model’s performance.

Oliver Kay and Torsten Buennagel, Johnson Matthey Noble Metals, Orchard Road, Royston, Hertfordshire, SG8 5HE United Kingdom

31 pages, 19 figures, 1 table, 4 plates, 30 references