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The conventional methods for recovering effluent gas in polyethylene processes include compression condensing, membrane separation, cryogenic separation systems and pressure swing adsorption. Since the effluent gas content varies with the process, there is no single recovery technic can meet all effluent gas content conditions. Therefore, a systematic strategy is needed to guide the selection of recovery technologies. This article introduces a method to select the best recovery system for certain compositions of effluent gas. After searching the feasible content region for the recovery systems according to the specified concentration of recycle stream and outlet streams, it shows PSA system has the largest feasible region while compression condensation system has the smallest one. In comparison of economic and exergetic performance, the cryogenic separation system shows its outstanding peculiarity to recover the effluent gas. The obtained result is effective in guiding the design of recovery system. [ABSTRACT FROM AUTHOR]

The performance of gas-solid fluidized bed reactors (FBRs) strongly depends on the behavior of gas bubbles. Mechanical agitation is widely used in industrial FBRs to enhance gas-solid mixing; however, its influence on bubble behaviors has been poorly studied, especially in experimental study. Pressure fluctuations in a 300 mm inner diameter plexiglas column fluidized bed of Geldart D particles with an arch agitator were measured under various gas velocities and agitation speeds. The bubble sizes were evaluated by incoherent analysis of pressure fluctuations. The effects of mechanical agitation on axial bubble growth, bubble sizes, regime transition velocity and fines elutriation were comprehensively investigated. Results show that mechanical agitation promotes bubble growth at 1.7 Umf but reduces the bubble sizes with increasing gas velocities. The axial maximum bubble size with increasing gas velocity occurs at 1.2 m/s without agitation and 1.0 m/s with agitation speeds of 14 and 21 rpm. Interestingly, mechanical agitation leads to a small increase in minimum fluidizing velocity and a slight decrease in critical turbulent velocity. Furthermore, the entrainment rate is reduced with mechanical agitation, due to the decreasing bed height and small fines ejection at the bed surface. The arch agitator helps to reduce the channel flow, enhance the gas-solid contact efficiency and improve the fluidization quality. [ABSTRACT FROM AUTHOR]