Continuous processing using OFM
Continuous processing involves superimposing an oscillatory flow onto a steady throughput using a mechanical oscillator. This gives control of mixing independent of the bulk flow. A noteworthy feature of the mixing is that each inter-baffle zone behaves as a unit stirred tank, so mixing over the length of the tube is the cumulative effect of all the discrete mixing units. For example, the typical reactor geometry as shown in the diagram includes some 100 discrete mixing units. This means the residence time distribution (RTD) can be optimised to give a very close approach to plug flow in reactor tubes, even where the mean residence time is long (i.e. a number of hours).
Another feature is that the residence time can be fixed, but control over RTD and heat removal is maintained. This could be very important, for example, in an exothermic reaction where control and efficient mixing are important for the optimum (and safe) operation of the reactor.
New reactors for industry
The control of mixing possible in an oscillatory flow reactor should help industry gain the full benefit from continuous flow production schemes, which inherently offer more flexibility than batch production. In speciality chemicals manufacture, for instance, many applications would benefit from improved control of mixing and enhanced chemical performance. Current manufacture typically uses stirred tank, batch processing technology, which is inherently inefficient. For example, a 2 tonnes/hour process on a 12 hours batch cycle would require a 24 cubic meter reactor vessel. Equivalent additional volume is required for reactants and products, and overall this makes large demands on heating and cooling services. Converting to a continuous process based on a 2 hours reaction time, a reactor of only 4 cubic meters would be necessary: this would correspond to a significant reduction in the reactor’s volume.
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| Cut-away schmatic of a concept design for new industrial scale 20-pass, 0.5m3 continuous OFM reactor using servo-hydraulilic actuators. |