The new concept of "high-density riser/circulating fluidized bed" was first proposed in 1993 as a new operating regime within gas-solid fluidization, by our group to address a gap in fluidization theory that I realized through my Shell experience: While many circulating fluidized bed reactors in the petrochemical industry had been operating at much higher density (≥10%)and solids flux (≥400 kg/m2s), all academic research by then was still on low flux (<200 kg/m2s) and low density (<5%) that follows the conditions for circulating fluidized combustors. We then experimentally established this new concept and the differences with the “low density riser”. This concept has been widely accepted and our papers have >1000 citations. Presentations on "high-density riser" now appear at every major fluidization conference. More recently, we have reached extremely high solids flux (≥1000 kg/m2s) that has never been achieved.
Our group also works on the more conventional gas-solid circulating fluidized beds and our contributions include the studies on the influence of particle properties, on the fundamental understanding of gas-particle interaction, on using mathematical tools such as chaos and wavelet analyses to quantify the flow properities, on the understanding of clusters, on fully characterizing the optical fibre probes etc. For example, we were the first to comprehensively show the effects of chaning particle properties on the hydrodynamics inside a GSCFB. We also fully studied the mechanisium of the optical fibre probes and proposed the best practice in calibrating those probes.
The fluidized bed downer reactor was proposed in the 1980s by Texaco and Mobil, as an alterantive to riser reactor, given the perceived benefits of reduced solids backmixing. As there was little research on downers by then, my "Shell Hat" helped me to quickly see its potential, so that we begun to conduct a series of comprehensive studies. The first ever review paper on downer65 was published by us in 1995, which also reported on our theoretical analyses. Through our continued work, we have fully characterized this new type of fluidized bed reactor, with both gas and particles flowing concurrently downwards. Studies in a large scale downer unit on almost every major aspect of the downer (hydrodynamics, heat and mass transfers, reactor performance and modelling etc.) have well established Western as one well-known leading downer study research site in the world.
Our work on conventional gas-solid circulating fluidized beds also includes mathematical modelling and the development of correlations.
We also work on conventional fluidized bed (non circulating).
Another new concept of "circulating turbulent fluidized bed" (CTFB) was proposed by us in 2006. Among fluidized bed reactors, turbulent fluidized beds (TFB) and circulating fluidized beds (CFB) cover most of the key commercial applications given their specific hydrodynamic features. However, they both have their own limitations. TFB reactors provide high reaction intensity and compact size as well as high mass transfer, but suffers from particle backmixing, while CFB reactors have less backmixing and high mass transfer, but are more dilute, bulky and costly to build. In the past few years, we have developed this new concept of circulating turbulent fluidized bed (CTFB) reactor that combines the benefits of both. Our work has shown the realization of CTFB and its key advangases over both CFB and CTFB, such as much higher bed density. CTFB is also shown to be different than the high-density CFB as well as dense phase pneumatic transport in that it has very high bed density (30% or more) and can be operated continuously in a complete particle circulation loop. Circulating turbulent fluidization is a new regime, independent of turbulent, fast fluidization and dense suspension upflow.
One recent major development in fluidization is the expansion of the gas-solid circulating fluidized bed to liquid-solid and gas-liquid-solid circulating fluidized beds. We are the largest group in developing those two new fluidized bed reactors and are leading the field, by a large margin, with 85 published papers66-150 reporting on the flow structure, operating regime and various applications, out a total of less than 300 journal publications one can find. We also hold 3 clusters of original patents. And we also published the only two review papers73,85 on this subject. With several reactor units set up at Western, and with the advanced instrumentation available in our laboratory, full radial and axial profiles of local solids concentration and liquid velocity were obtained and key understandings about these two new type of reactors have been obtained. A new circulating fluidization flow regime was proposed. We have also applied this new apparatus for technology developments biochemical processes and on waste water treatment, with 3 clusters of patent groups – see the next two groups of publications.
The LSCFB technology (above) was applied to biochemical separations, such as efficient protein extraction, heavy metal recovery, green house wastewater recovery/recycle etc. Compared to the conventional methods, the new technology provides significant savings and make the process much simpler. This technology with two issued patents has been licensed to Renix (www.renix.ca) which has marketed it as a CFIX (fluidized bed continuous ion exchange) technology and successfully developed new applications for various industries.
The (G)LSCFB technology (above) was also adopted for an efficient wastewater treatment process. Referred to as CFBBR (Circulating Fluidied Bed Bioreactor), this technology introduces a large quantity of suspended fine particles in the wastewater process to immobilize microbs which are key to the treatment. Mibrobs immobilized on fine particles do not flow out the processor with wastewater flow so that the treatment intensity is greatly enhanced, to 8-10 times. Two clusters of patents have been issued and large scale demos (50 – 1000 ton/day) are being tested or planned to be tested in the very near future. A spin-off company established by my former PhD studet in Beijing, ReGear, will take this on for commercialization in China (http://www.regear.com.cn/).
New types of liquid-solid and gas-liquid-solid fluidized beds have been developed, including various types of inverse L-S / G-L-S fluidized beds and gas-driven L-S / G-L-S fluidized beds.
Our work on liquid-solid and gas-liquid-solid fluidized beds also includes mathematical modelling and the development of correlations.
Notoriously known for extremely difficult to handle but yet very useful, extensive research has been carried out in the past 15 years to achieve smooth fluidization and to increase the handlability of ultrafine powders for direct industrial applications. Using nano technologies developed in house, particles below 30 m can be readily fluidized, essentially overcoming the flow issue. This formed the foundation for several key applications to be listed separately right after.
The ultrafine powder coating technology produces superb surface quality comparable to that of liquid paint, something that have not been achieved by anyone before in the coating industry. It also yield much thinner film, when needed, to provide extra savings. This technology has now been commercialized by an powder coating company in China to replace coarse paint powders, resulting in significantly enhanced surface finish and wider range of products, plus 40-50% savings on powder usage.
The same ultrafine powder coating technology was also applied to pharmaceutical processes, to develop new technologies. The tablet dry powder coating process saves 70-80% energy compared to liquid coating as there is no need to overcome the latent heat during the curing process and is also more environmentally friendly when replacing solvent coating. This is expected to replace the current liquid coating process to become the industry' standard. A spin-off company is being established with an approved OCE commercialization grant. Another technology is a new pulmonary drag delivery system, which does not require any excipients, unlike those on the markets which uses 80-90% inert particles (excipient) to improve the flow of the fine drug particles. The latter technology has been transferred to Western spin-off company InhaChina who is going through regulatory approval process, in collaboration with Shanghai Institute of Pharmaceutical Engineering.
In collaborating with partners at CANMET - Natual Resources Canada, and Guangzhou Institute of Energy Conversion - Chinese Academy of Scienses, we have worked on biomass gasification and other related projects and developed suitable models for those processes.