Investigation On The Mechanism Of Fluid Flow In The Radial Flow Adsorber

As the world economy continues to develop, there is a dramatic increase in industrial gas demand in metallurgy, chemical and other large-scale industry, which urges oxygen plants to feature in large-scale and less energy consumption. Radial flow adsorbers with the advantages of lower bed pressure drop, smaller area coverage, and less heat energy regeneration, have been widely used in large-scale oxygen plants worldwide. However, nonuniform flow distribution along the radial direction usually exists in radial flow adsorbers, which will decrease the utilization of adsorbent and the switching time, increase the valve switching loss and may even result in operating safety problems in oxygen plants. Currently, investigations on the mechanism of fluid flow in the radial flow adsorber, the corresponding multi-dimensional numerical simulations and the scale-up technology are not complete and also lack of direct measurement on the velocity filed. In response to these problems, research work is carried out on the following sections:1. A one-dimensional mathematical model is derived which determines the non-dimensional axial velocity profile in the outer channel of the radial flow adsorber. A universal radial flow adsorber design concept is proposed based on the systematic and in-depth study of the impact of structural parameters and operating conditions on the velocity profile.Based on the pressure drop analysis in the outer and inner channels of the radial flow adsorber and the one-dimensional radial pressure drop equation, the individual non-dimensional axial velocity profile u(y) equation is derived under different radial flow patterns. By comparing the experimental data from the literature, the effectiveness of the equation is verified. Take the Z-flow type single bed radial flow equation as an example, the impact of structural parameters and operating conditions on the velocity profile are investigated and the results show that an increase of bed axial height and particle diameter will result in the axial velocity profile u(y) more nonlinear and deteriorate the flow distribution inside the bed. Under the specific structural parameters and operating conditions, the flow rate and cross-sectional area of the outer channel have no effect on the velocity profile. Therefore, a universal radial flow adsorber design concept is proposed based on the above analysis:under the given operating condition, by solving the individual equation, one can get the non-dimensional velocity profile u(y) in the outer channel under specific structural parameter combination. The radial velocity distribution in the bed is can be derived from the conversion of the velocity profile and from which non-uniformity can be deduced. If the non-uniformity satisfies the design requirement, end the design process. If not, re-select a set of structural parameters and repeat the processes above. The above design concept can be applied to optimize the structural parameters, thus will reduce the non-uniformity of the flow field and improve the operating performance of the adsorber.2. A two-dimensional fluid flow numerical model on radial flow adsorbers is established and the flow field characteristics in the radial bed are investigated under different flow rates and particle diameters. Based on the above simulations and analysis, a new method is proposed to improve the flow distribution in the adsorber.Computational fluid dynamics (CFD) method is used to establish a two-dimensional fluid flow numerical model in the Z-flow type radial flow adsorber. The flow field characteristics in the radial bed are investigated systematically under different flow rates and particle diameters. The results show that the flow rate has no effect on the flow distribution and as the particle diameter decreases, there will be a decrease of the non-uniformity. Based on the above results and analysis, a new method is proposed to improve the flow distribution:by inserting a tube into the inner channel to change the variations of pressure drop in the inner and outer channels, the non-uniformity in the adsorber can be considerably reduced. The simulation results showed a perfect accordance to this theory. As a result, this method can be applied to improve the flow distribution in the adsorber and further improve the operation performance of the adsorber.3. A PIV investigation experimental setup on Z-flow type radial flow adsorber for flow distribution is built and a preliminary PIV experiment is carried out with air as the working fluid.A Z-flow type radial flow adsorber experimental setup for flow distribution PIV investigation is built which mainly include an adsorber, an air compressor, a buffer tank and a measuring system. The velocity field in the outer channel and radial pressure drop along the axial direction are acquired through a preliminary PIV experiment with air as the working fluid. By comparing the experimental data with the theoretical value, the validity of the theoretical models are verified and the causes of the deviations are also analyzed. Based on the above analysis, a preliminary analysis is conducted to investigate the effectiveness of the non-uniformity of the pressure filed for characterizing the non-uniformity of the velocity field. Experimental results and analysis show that in order to achieve a good accordance of the two non-uniformities, the axial velocity in the outer channel should not be too large. This result can serve as a theoretical guidance for a reasonable design of the adsorber.