Fluidised bed granulation of ammonium sulphate – a new process

Sulphur fertilisers are becoming increasingly important. Sulphur dioxide emissions have reduced over the last few decades, due to changed environmental regulations. This has resulted in less acidic rain and a sulphur deficiency in soil, in many areas. Ammonium sulphate is a popular fertiliser, especially in granular form.

This paper covers the development by thyssenkrupp of a fluidised bed granulation process to produce a granular fertiliser from ammonium sulphate solutions. The systematic scale-up approach is described, starting with a laboratory batch scale plant (~5 kg/hr) to identify the influence of key parameters on the process. It continued with a technical scale plant (~20 kg/hr), to further optimise the operational conditions and determine the first design parameters of the granulator. These results were the basis for the design of a pilot plant (~500 kg/hr). Here, any weaknesses were identified and overcome, and strengths were identified. The final product has a premium quality and the next stage, an industrial scale plant, is in sight.

The main advantage of this fluidised bed granulation is the conversion of by-products into a premium product. These by-products are ammonium sulphate solutions with a high water content (~60 wt%) which arise in caprolactam or coke plants, and as scrubber solutions. Therefore the new process enables the customer to convert low-cost feedstock into a premium product. A product which is easy to handle and spread, providing soil with the sulphur it requires.

Dr. Christian Renk and Peter Banik, thyssenkrupp Industrial Solutions AG, Essen, Germany.

27 pages, 16 figures, 5 plates, 1 table, 8 references