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A S Jessup-Bould: Field Trials and Design - Production of Synthesis Gas
Synthesis Gas							Sable Chemicals; Zimbabwe
1992:	Process Engineer investigating alternative route for hydrogen production as a feed gas for an Ammonia works.
	Lead Engineer for full size Oxygen blown gasification field trials.
Project Background
Sable chemicals is Zimbabwe's sole producer of ammonia based fertilisers. The basis for Sable's ammonia production is the Haber process. Ammonia plant feeds are Nitrogen produced in an aging cryogenic air separation plant and Hydrogen produced from water in the world's largest electrolysis plant. The electrolysis plant uses a vast amount of power which is a huge economic burden on production costs. Furthermore, if this power could be made available for other users, this would enable the development of other industries within Zimbabwe. My company at that time, OSC, had a presence rehabilitating the coke oven by-products plant at the nearby steel works. They were approached to see if ammonia could be recovered from the coke oven gas and used to produce fertiliser. It soon became apparent that there was far too little ammonia available from this source, however OSC were commissioned to investigate alternative routes to produce ammonia.
Process Selection
Oxygen Blown Coke Gasification A process for synthesis gas was developed that would require the gasification of excess coke from the local steel works to produce a synthesis gas rich in hydrogen and carbon monoxide. Air blown coke gasification technology was already available within Zimbabwe, however to avoid over-sizing of the gasification and downstream processing equipment, oxygen blown gasification was proposed as this would eliminate the presence of large volumes of nitrogen. Oxygen would be available from a new air separation plant which would also be required on account of the need to meet existing obligations to supply oxygen being produced from the electrolysis process to a local steel works, the age of the existing air separation plant and the need for more nitrogen to satisfy increased ammonia production requirements.
I was responsible for executing a series of oxygen blow trials on a full size gasifier in Zimbabwe.
Shift Reactors The process required carbon monoxide to undergo a shift reaction with water to yield more hydrogen. Sulphur tolerant catalyst was required for this part of the process due to the presence, albeit small, of sulphur in the coke feed to the gasifiers. I was also responsible for this section of the process. Carbon Dioxide and Hydrogen Sulphide Removal The Benfield process was proposed for the removal of CO2 and H2S from the gas stream leaving the shift reactors. Pressure Swing Adsorption The final stage in the process was a PSA unit to recover hydrogen for subsequent ammonia production. Cryogenic Air Separation Plant A new air separation plant was required to meet the needs of increased ammonia production, to ensure the continued supply of oxygen to the steel works and for gasification purposes.
Project Outcome
This process was not realised due to the high capital investment required and the discovery of natural gas resources within Zimbabwe which would have eliminated the need for gasification. Subsequent events within Zimbabwe have also prevented further investment in alternative process routes at Sable Chemicals