466258 Innovations, Interactions and Integrations in Fluid Particle Systems; Memories and Future Tasks
Memories and Future Tasks
Tokyo University of Agriculture and Technology
The early history of fluidization was inseparable from the huge innovation of the catalytic cracking technology. Such a tradition has been active until recently and we have been committing quite a few challenging developments in environment, energy, materials and pharmaceutical fields. As discussed elsewhere [1, 2], researchers of the fluid-particle engineering field were entering the second 30 years’ period of scientific breakthrough at the time of early 1970s. During this second 30 years period our peer engineers have developed several commercialized and some partially commercialized processes and a few candidate processes that could be deployed in the coming future. However, shapes of industries are expected to change drastically for year 2050 and further from both necessities for environmental sustainability by mitigating global warming and for economic sustainability by developing a compromise among global, national and local economies. Also important is the sustainability of fluid particle education to keep our knowledge and technology active, interesting and renewable. Or in other words, fundamental scientific and engineering knowledge on fluid particle systems need to become more popular so that our classical achievements in the technical/engineering field can be inherited safely for long. Therefore, it would be worth discussing the shape of industries in the future and the shape of academia to prepare for a big transformation of the present social energy metabolism and the transition to the low-carbon and humanistic society. In this respect it should be stressed that innovations in the near future are becoming not just technical but also social. Both engineers and academic researchers would need more knowledge on social issues in the near future.
The era started early in the 1970s, which was the time I enjoyed most with my students and with many friend researchers in the world, was indeed a critical period of fluidization and fluid particle engineering in terms of innovations, interactions and integrations, but in several different senses as indicated above.
Concerning interactions, we have been concerned about several different categories of interactions: fluid-particle interactions, particle-particle interactions, hydrodynamics-plant interactions, chemical reaction-hydrodynamic interactions, and even the interactions among different branches of academia and between industries and academia.
Concerning integrations, we have achieved the integration of previously separated modes of fluid-particle systems including fixed/moving bed, bubbling fluidized bed, turbulent and fast fluidization, entrained bed and pneumatic transport, the integration of microscopic phenomena into mesoscopic and macroscopic ones and integrations of different branches of fluid-particle reaction engineering.
In the present paper let me take some memorable experiences of mine and discuss the three ‘I’s by leaving my thoughts.
2. Interactions — Incident of L-valves
When the license of multi-solid FBC boiler was imported and scaled-up by Mitsui Engineering & Shipbuilding (MES) from Battelle Columbus Laboratories, one of the most difficult issues was L-valve control. The original picture of the L-valve was beautiful in recycling solids from the external heat exchanger either by cold recycle or hot recycle to control the combustor temperature as desired. However, L-valves for the hot recycle were quite like a group of unruly children flowing free even in the no-aeration conditions. At that time the plant was waiting for the final transfer to the customer at the site. While discussing with an engineer from MES a suspicion came to my mind that some gas generation took place by chemical reactions. We started making a rough evaluation of CO formation and found out it was sufficient to fluidize the stand pipe.
There I learned that interactions between hydrodynamics and chemical reactions are two-way interactions, not just one way from hydrodynamics to chemistry, and chemical reactions to hydrodynamics could be critical particularly in high temperature processes. But from this incidence I was also convinced that any business risks have chances to be tightly related to some very fundamental phenomena and that relevant scientific knowledge has a potential to save them. Moreover, I re-acknowledged the importance of industry academia collaboration for the progress of technologies as well as engineering sciences.
3. Integrations — Two topics
1) DEM simulation
It is a talent required for researchers to look at phenomena always as integrated things. So, it is their common habit to decompose things into elements or essential laws and to find some structures composed of them behind the superficial phenomena. The decomposition is not always easy. And even when it is done well, we should not use the style of reductionists, but search for solutions or suggestions on the macroscopic level of phenomena re-constructing things by integration.
In the mid-90s we developed DEM (Discrete Element Model) to simulate macroscopic bed behaviors from laws governing microscopic phenomena. However, the computer capacity of that time was much smaller than now and it was difficult to conduct realistic scale computation. However, we conducted a variety of demonstration for beds of sticky particles to see agglomeration behavior, for beds of immersed tubes to see contact packet renewal over the tube surface, for beds of polymer particles in reaction to see distribution of temperature of individual particles, and for beds char combustion to see surface temperature of burning char which is important for NOx formation and reduction. With these small scale computation we could have tested innovative ideas in the macroscopic level, which is produced from freewheels thinking. Actually the real scale computation may not induce innovative ideas nor quick design as long as it takes much computational effort. Macroscopic models and correlations would be still valuable for quick actions as well as deep understanding of the phenomena of concern. Furthermore, with scaling laws we can conduct scaled down experiments as well as scaled-up computations for the integration.
2) Cluster and agglomerate size prediction
Prediction of mean cluster or agglomerate sizes is another challenge of macroscopic modeling. Here, I use the term a ‘cluster’ as a group of particles brought together by external (not particle-particle) effects and an ‘agglomerate’ as a group of particles held together by direct interparticle forces as proposed by myself and Professor R. Clift .
In the dilute region of CFBs and in the freeboard of bubbling beds we have clusters that are group of drifted particles. In bubbling beds of sticky particles we have agglomerates. In both cases the force fields changing dynamically are the key factors, one in a dilute suspension with turbulent gas motion and another in a dense bed with frequent compaction and sharing due to bubble passage. We have proposed models  and  for prediction of cluster and agglomerate sizes, respectively, but both models should be examined in more detail for validation.
The key technological approaches for sustainability are low carbon transportation, zero emission buildings with highly insulated walls, biomass material utilization, solar heating, lighting and PV power generation, renewable energy utilization and process intensification, integration for low exergy losses. To reduce GHG emissions from transportation we need to avoid unnecessary carbon foot prints and induce local production and consumption. In terms of energy the scheme of decentralized local generation and consumption should be encouraged more to reduce emissions from centralized mineral energy conversion systems. Moreover, in many countries, their megalopolises consume much more energy than they can locally produce. In this respect encouraging people and industries move to areas rich in renewable energies is promising . It is a counter action against the over-urbanization of the last 50 – 60 years. All of these indicate that decentralization and community empowerment should be the necessary trend in the coming decades for countries having centralized systems.
Destination of decentralization is also confirmed by thoughts on the global economy. So far the size of financial economy is said to be much larger than real economy. More money is invested for the sake of profit and there is a definite world trend of widening disparity and increase of poverty. Circulation of local investment in the local economy is one of the current issues to stabilize modern society. So, from economic viewpoint de-centralization of some extent and community economy empowerment are necessary.
Keeping these destinations in mind, the future practices of chemical and fluid-particle engineering should be newly defined. In the last part of my paper I would discuss their features-to-be.
1. M. Horio, Fluidization Science, its Development and Future, Particuology, 8, No.6, 514-524, 2010
2. M. Horio, 1. Overview of Fluidization Science and Fluidized Bed Technologies, ‘Fluidized-bed Technologies for Near-zero Emission Combustion and Gasification,’ ed. by F. Scala, Woodhead Publishing, 3-41, 2013
3. M. Horio, R. Clift, A Note on Terminology: ‘Clusters and agglomerates’, Editorial, Powder Technology, 70, pp.196, 1992
4. M. Horio, M. Ito, Prediction of Cluster Size in Circulating Fluidized Beds, J. Chem. Eng. Jp., 30, pp.691-697, 1997
5. Y. Iwadate, M. Horio, Prediction of Agglomerate Sizes in Bubbling Fluidized Beds of Group C Powders, Powder Technology, 100, pp.223-236, 1998
6. M. Horio et al., The Potential for Massive GHG Reduction by Mass Rural Remigration (The Renewable Energy Exodus): A Case Study for Japan, Applied Energy, 160, 623-632, 2015
See more of this Group/Topical: Particle Technology Forum