Diversified technology provider Johnson Controls’ Sabroe compressors, which power a custom-build ammonia chiller plant, will play an important role in diversified chemicals group Omnia’s newly operational R670-million nitrophosphate plant in Sasolburg.
Omnia lead process engineer Kripal Daby explains that, a core part of the nitrophosphate production innovation is a new more efficient method of crystallisation, which requires the nitrophosphate liquid to be rapidly cooled. “We needed a chiller solution that was not only robust and reliable, but capable of managing variable loads, and able to respond effectively and operate cost effectively.”
He explains that the custom-built Johnson Controls ammonia chiller was not only able to meet functional demands, it was able to offer high energy-efficiency gains, helping to ensure that the new production method was viable and sustainable.
Finding the ideal configuration took collaboration. “Johnson Controls worked closely with the Omnia team through multiple testing phases to engineer and configure the chiller solution for the new nitrophosphate plant,” says Johnson Controls engineering manager Russell Hattingh.
“We are pleased to be part of what we believe is an important innovation in the sector.”
Thestandard nitrophosphate production methodis well known. It comprises dissolution of rock phosphate with nitric acid, crystallisation of the dissolving solution and separation of the crystals from the acid solution. About 40% of the new Omnia nitrophosphate plant process is known—up to the making of the nitrophosphate liquid. The crystallisation process is where the differentiation lies.
“Omnia required different temperature brine streams.” To make the process viable, efficient operation of the chiller is critical, so multiple evaporating temperatures were provided, says Hattingh, adding that, the company settled on the use of four Sabroe screw compressor chillers operating in parallel.
“All of these units have variable speed drives which enable the chillers to operate reliably over a range of conditions, while cutting energy use significantly. A larger swing compressor was added for versatility and redundancy.”
Given the criticality of the solution, the service capability that Johnson Controls can provide was an important factor in winning this deal, he notes.
Further, Daby highlights that the saving for Omnia is significant as “the chillers are able to run at high capacity of 90% and still lower Omnia’s energy use, delivering up to R900 000/y in energy savings”.
In November last year, Engineering News reported that the new facility will have lower emissions and will no longer produce large quantities of gypsum waste and will also improve throughput at Omnia’s nitric acid plant, where capacity use remains below the company’s target level of 90%.
Meanwhile, in Phase 2, Omnia will double the capacity of its nitrophosphate plant, expanding the chiller solution to seven Sabroe compressors, says Hattingh.
“We will continue to work with Omnia to ensure optimal performance of the Johnson Controls ammonia chiller plant, and to customise and refine outputs to meet the requirements of the nitrophosphate plant as it ramps up production.”
He concludes that this is a unique application for an exciting new operation, and that Johnson Controls is pleased to have been able to meet Omnia’s demands.
“It is a great reflection of what becomes possible when we collaborate with our customers, combining deep industry know-how and advanced engineering.”