The work is devoted to the using of modern program packages for simulation of the aerodisperse systems hydrodynamics of equipment with directional motion of the fluidized bed for the chemical industry. The criteria for selecting the design for this type of equipment are substantiated. New forms of organization of flow motion in the fluidized bed regime are proposed. The mechanisms of motion and residence time control of the disperse phase in the working space of the devices are described. The results of computer simulation of hydrodynamic conditions of the directed gas stream and a two-phase aerodisperse system motion are presented. An algorithm for optimizing the calculation of equipment based on the results of computer simulation (by example of the unit for the porous ammonium nitrate with nanostructured porous layers production) is shown.
TopIntroduction
Among various dispersed flows, fluidized bed plays the most significant role in modern technology. The fluidization technique has become widely used due to high intensity of processes.
Disadvantages of the fluidized bed device can include (Philippsen et al., 2015), (Haron et al., 2017), (Huili et al., 2017): different residence time of a particle in the device, a need for thorough cleaning of the exhaust air and material entrainment (in particular it is applicable to small particles of the system). In addition, a significant drawback is the return of fine particles back in the fluidized bed zone. The analysis of various fluidized bed granulation equipment in chemical (Caiyuan et al., 2004), food (Patel et al., 2011) and pharmaceuticals (Agrawal and Naveen, 2011) industries showed the urgent need to organize the mutual flow motion, which will enhance the quality of the final product.
It is rational to use the same device for multiple processes in low-tonnage and multi-assortment production in order to reduce the range of the equipment. Implementation of the new forms to organize mutual flows motion (while keeping the same principles of the fluidized phases contact), which would intensify processing of the dispersed materials without considerable increase in the energy costs, is a promising direction for the development of heat and mass exchange processes in the heterogeneous systems (Artyukhov et al., 2019), (Van Ommen et al., 2012).
Among the major techniques of controlling the polydisperse particles residence time in the device, one should notice the following:
- 1.
To develop a direct movement of particles using accelerating elements (gas distributors of vortex type) (Sklabinskyi and Artyukhov, 2013).
- 2.
To design the device with a variable cross-sectional area applied to the granulation, cooling and dedusting process (Ostroha et al., 2019).
- 3.
The promising direction to reduce financial and energy costs on the heat and mass transfer processes in the fluidized bed is the application of sectioning (vertical and horizontal) to create different conditions for the particle heightwise (lengthwise) motion in the device (Yukhymenko et al., 2016).
TopBackground
There are various possibilities to apply suspended layer (fluidized bed, weighted layer). There are many successful cases regarding the introduction of this method in industrial practice, while in others it is at the stage of laboratory research. The processes taking place in heterogeneous systems using the suspended layer method have a great industrial application. It can be used to stove sulphide, arsenic and antimony ores to facilitate the extraction of gold or silver, for pyrite and pyrrhotine roasting to obtain SO2 in the production of sulfuric acid.
The suspended layer is in great demand in metallurgy for stoving of copper, cobalt and zinc sulfide ores to obtain valuable metals.
Fluidized bed devices for drying solid materials (coal, cement, limestone, etc.) are known in the whole world. Economic considerations make the use of these devices particularly interesting when large-tonnage materials are to be processed. A suspended layer dryer can also be used as a classifier since the drying and classification processes take places simultaneously in the device.
The way to obtain granulation products in the fluidized bed (suspended layer) is used by the world well-known manufacturers of fertilizers and pharmaceutical products: Urea Casale S. A. (Switzerland), Kahl Group (Germany), Stamicarbon (Netherlands), Toyo Engineering Corporation (Japan), Changzhou Xianfeng Drying Equipment Company Ltd (China) Glatt (Germany), Uhde Fertilizer Technology (Netherlands), Rottendorf Pharma (Germany) (Saikh et al, 2013).