Process Intensification – High Gravity Reaction Technology (Higee Technology)
Process intensification (PI) is an innovation on process and equipment that results in more efficient of process unit operations and often a dramatic reduction of equipment size. The advantages of PI may include improvement of product quality, energy saving, reduction of operation cost, reduction of resource consumption, minimisation of pollution, and improvement of safety .
High Gravity Reaction Technology (Higee technology) is a practical example of PI that has been commercialised. The Higee technology involves fundamentals of hydrodynamics, mass transfer and micromixing. Its applications include engineering of nanoparticles, reaction process intensification and separation process intensification, which can be applied to different industries such as nanomaterials, chemical industries, energy – oil and gas, environment, and life science [1, 2].
The Higee technology is a combination of static and rotating mixers where inlet fluids are mixed through the packing then disperse into fine droplets or thin film. The dispersion results in intense micromixing between the fluid elements . The interface between the fluids (gas-liquid or liquid-liquid) is renewed vigorously and results in a significant intensification of mass transfer and micromixing . The Higee technology uses centrifugal force to obtain a high gravity environment and is carried out in a rotating packed bed (RPB). A RPB was first invented by Ramshaw and his co-authors in 1979 to intensify the mass transfer and heat transfer for multiphase systems. The rate of mass transfer between a liquid and a gas can reach up to 1-3 orders of magnitude faster in a RPB than in a conventional packed bed [5, 6], which is one of the main aspects of PI. After the first invention of Ramshaw and co-authors in 1979, Higee technology has attracted attention of researchers and industrialists since then [7-22]. Several commercialisation projects of high gravity technology were reported [23, 24]. Schematic diagrams of a RPB used in the Higee technology for both liquid-liquid and gas-liquid processes are shown in the figures below [1, 2]:
[1, 2] (Click to enlarge images)
The rotational speed of a RPB can generate force as 200-1000 times that of gravity force. By increasing the gravitational force, or rotational speed, the mass transfer coefficients increase which results in production of smaller bubbles and thinner films . Having such high efficiency of mass transfer, is useful when generating products with high supersaturated concentrations in gas-liquid phase reaction and precipitation processes.
The Higee technology has been used for the production of nanomaterials such as CaCO3, Al(OH3) and SrCO3 in size range between 1nm and 40nm. The nanoparticles generally have narrow particle size distribution, specific crystal morphology and shape with consistent quality. In addition, the production has been proven to be more cost efficient than conventional nanomaterials production methods .
Compared with conventional technologies, the Higee technology has advantages such as ease of operation, low pressure drop of the gas phase, low power consumption – clean and green energy saving environmental conditions, low liquid holdup (which can be useful for expensive materials, toxic materials, flammable and explosive materials), more effective mass transfer for micromixing, improved metallurgical extraction, and better synthesis of nanoparticles with narrow size distribution and smaller size with low operating cost and high production output. Also, unlike large conventional contacting columns, the Higee technology has reduced size and weight, and low residence times involved (which is good for heat sensitive materials). [3, 7, 21]. The main aspects of PI can be seen to have been achieved in Higee technology with proven research data and commercialisation of the technology.
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