Confined Swirled Flows for Processes Intensifications
XXI International Conference on Chemical Reactors
22-25 Sep 2014
|| Kuzmin Andrey Olegovich
Boreskov Institute of Catalysis SB RAS
Novosibirsk State University
Various chemical processes in multiphase reacting and non-reacting systems are widely presented in industries. The choice of the multiphase contactor depends on the field of application and being affected by specific process requirements such as residence time, required number of stages, desired throughput capabilities, ability to treat specific liquids or operate under high pressure, the necessity to handle with corrosive/flammable substances and etc.
There are many different thoroughly studied conventional multiphase contactors utilized for carrying out the multiphase processes: mechanically stirred vessels, centrifugal and jet mixing apparatuses, packed and sieve-tray columns, static or pipeline mixers, fluidized bed reactors and many others purposefully developed to meet the specific process requirements. Along with many advantages, all types of conventional contactors also have some well-known shortcomings. For different kinds of devices they derive from either maintaining the rotating machinery, or high cost, or slow mass-transfer and sufficient dimensions, or non-uniformity of multiphase medium or large residence time and so on. For instance the large dimensions of packed or sieve-tray column make it unsuitable for modularization and substantial efforts may be required to put up the column and to make the connections. Moreover, the capabilities of further intensification of interphase exchange processes quite often are limited by the stability loss problem arising at enhancing the physical impact on treated medium with subsequent multiphase chemical system structure disruption.
Although the substantial efforts continue to be applied in studying and improving existing technologies, the development of the new designs of multiphase contacting equipment is still welcome. The new approaches for process intensifications are very desirable to be studied and discussed with developing the new devices on their basis that may be compact and provide the high performance.
Turbulent confined swirled or vortex flows are widely encountered in chemical practices and being developed both for applications in nonreacting and reacting systems. The performance of these devices relies on exploitation of some advantages and peculiarities of swirled flows: regulable field of centrifugal forces excessing the gravity by many times, the turbulent and high shear stressed flow patterns facilitating the dispersing/mixing and interphase surface renovation with dramatic accelerating the exchange processes, elongation of particle trajectories with comparison with linear translation movement, achievement of high values of slip velocities for particles motion in fluid environment and high values of velocity difference at the gas-liquid interfaces leading to their efficient contacting, some another special features of vortex flows. The one of the main advantages consists in the possibility of over intensification of interphase exchange processes due to the stabilization of the multiphase system in the vortex flow field giving the chance to sufficiently enhance the value of energy introduced into and dissipated inside the system.
The following well-known applications of confined vortex flows and the variety of practical devices on their basis are being the subjects of only short mentioning in the current presentation and include the cyclones, high-gravity ultrasound and vortex tube separators, spraying and jet devices, various combustion systems, agitated flows used for mixing.
The main topic of present lecture is devoted to review and discuss the various approaches for making contact in multiphase chemical environment and intensifying the interphase exchange processes with utilizing the strained confined swirled flows produced in vortex chambers and in the rotating devices in various processes. Vortex chamber basically is a substantially cylindrical shell having the top and the bottom with fluid flow entering the body via a swirler located at the periphery. Swirler typically consists of a ring with multiple tangential speeding up slots or nozzles designed to convert the pressure energy to rotational motion.
Special attention will be paid to the survey of intensification approaches for gas-liquid processes including the using of the vortex contactors and vortex plates for packing columns, for carrying out of gas-solid processes including the drying devices and the discussion of the new data and ideas for industrial processes intensification in fluidized bed layers, for liquid-liquid contacting for extraction and another applications, for sophisticated liquid-solid-gas mixtures treatment including the bio-chemical applications and etc.