Chemical and Process Engineering
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A S Jessup-Bould: Problem Solving and Innovative Skills
All of the projects which I have worked on have required me to solve problems; however there are a number which I found particularly satisfying.
"Puffing Billy":			120,000 m^3 Gas Holder Purging
OSC were in Zimbabwe commissioning a 10 km pipeline to convey surplus coke oven gas from a coke works to a power station. Purging of the system including a vast 120,000 m^3 gas holder was required, however a local supply of nitrogen failed to materialise. Import of the required amount of nitrogen from South Africa would have been a costly option and so I was tasked with finding an alternative solution.
			An inert gas generator was the obvious answer, however the long delivery times quoted by potential suppliers would have had a seriously detrimental effect on the programme. It was however possible to buy a diesel fuel burner quite easily, so I developed a design using the burner that could be fabricated locally. My concept consisted of the burner, firing in to a horizontal carbon steel pipe which was cooled by being submerged in a water bath. The products of combustion were directed, via an elbow at the end of the pipe, in to the first of two vertical towers in which the gas was cooled by water circulated from a nearby lagoon. The combustion tube was a loose fit at the bottom of the tower to allow for thermal expansion and a "Chinaman’s Hat" helped prevent water entering the tube. I prepared the basic sketches and calculated the main parameters. Detailed design was completed at OSC’s Stockport office. The unit was then fabricated on site and the burner incorporated.
"Puffing Billy", as it became known was successfully operated, enabling the project programme to be met and saving the substantial costs of nitrogen imports. Furthermore, the equipment is now available for further use should the need arise.
Sable Synthesis Gas for Ammonia Production Sable Chemicals in Zimbabwe produce hydrogen for their ammonia plant using the world’s largest electrolysis plant. This requires half the electricity available from the Kariba Hydroelectric power station. Not only is this an immensely costly process, but it also deprives the rest of the country from a significant amount of power that could help this developing nation prosper in so many other ways. Sable Chemicals had already been in dialogue with OSC to investigate utilising ammonia from the coke oven gas produced at an installation they had built nearby. The amounts required by Sable were however far in excess of that which could be supplied by this means. I was delegated to be part of a team to investigate other technologies which could be employed to solve this problem. Important criteria were that the solution must neither create undue demands on the technological capabilities within Zimbabwe nor on the amount of foreign expenditure required. My solution was to use coke gasification to produce a synthesis gas containing significant amounts hydrogen and carbon monoxide which could undergo shift reactions to yield more hydrogen. This would be followed by scrubbing out carbon dioxide (Benfield Process) and pressure swing adsorption to extract hydrogen at the required level of purity. The technology for coke gasification was already established in Zimbabwe and there would be a plentiful supply of coke from the local works. The only drawback was that air blown gasification would result in large quantities of nitrogen in the synthesis gas and a correspondingly large plant would be required to handle this until it could be separated at the PSA plant. Nitrogen for ammonia synthesis was already being produced by Sable by cryogenic separation from air, however a larger plant would be required to meet an existing contract to provide oxygen, a by-product from the electrolysis plant, to a nearby steel works. If surplus oxygen could be produced, then this could be used instead of air in the gasifiers to produce a gas devoid of nitrogen. As part of the study I devised a series of oxygen blown gasification trials on an existing 3 metre diameter gasifier in Harare. These trials were undertaken under my supervision and lasted for a month. Oxygen was supplied in liquid form using tankers from the existing air separation plant at Sable Chemicals. The results showed that this technology was feasible subject to sufficient steam being provided with the oxygen.
VERT Hazardous Waste Vitrification The 'VERT' contract required the design of a flue gas treatment system serving a hazardous waste vitrification furnace. The system needed to be capable of processing a flue gas having an extremely wide range of different contaminants and the equipment materials of construction needed to be capable of handling the wide range of corrosive components which might be present. The flue gas treatment plant had to be designed to be transportable for use with the furnace at different locations around Europe. This required special consideration of all items of equipment. One of the most arduous services was the gas-to-gas heat exchanger which was used to cool the hot gases off the furnace in order to enable downstream processing and to use this heat to reheat the cleaned gases to minimise the risk of plume formation at the exhaust stack. Problems encountered in this heat exchanger were high temperatures, differential thermal expansion, a range of oxidising and reducing atmospheres, a range of corrosive chemical contaminants, risk of dewpoint conditions at the heat transfer surface. A wide variety of materials were investigated, but no materials could be guaranteed to be corrosion resistant. If 'exotic' materials were to be used (eg hastelloy) there was still a risk of failure under certain conditions. I decided that the most cost effective solution was to simply use a carbon steel heat exchanger, incorporating a packed floating head removable bundle. Hot and cold flue gases were arranged in co-current flow to avoid tube wall temperatures falling below the lowest predicted dewpoint temperature and corrosion coupons were fitted to provide feedback under actual operating conditions. A spare bundle would provide cover in the event of tube failure, giving time for a replacement bundle to be fabricated, in a more suitable material determined from analysis of the corrosion coupons.