Research On The Characteristics Of Venturi Scrubber Purifying Biomass Gas

Pyrolysis and gasification technology could convert low-grade solid-state biomass into high-grade combustible gas, increasing energy density and combustion characteristics, which was a substitute for natural gas as a clean energy for production and living activities. It could resolve storage and transportation issues of abundant waste biomass resources in rural and forestry area, so that it is an important technical means for large-scale resource utilization of biomass. However, tar and other by-products are inevitably produced in gasification process, which need to deepen the study of the biogas purification technology so as to explore the mechanism of decoking and reasonable parameters for the biogas quality prediction, and provide the basis for the optimization of decoking equipment.This paper presents the purification of biomass gas with venturi scrubber. The interaction effect between purification medium, detergent, and tar droplet particles in biomass gas was researched through the analysis of the flow field in venturi tube internal. Based on the basic laws of fluid mechanics, the flow field characteristics of fluid motion were obtained, which showed that the decontaminated area of the internal flow field is turbulent flow, in line with the flow characteristics of continuous medium. Continuity equation, momentum equation, turbulent kinetic energy equation and turbulent dissipation rate equation of different k-ε model wear analyzed and standard k-s model was suitable for the calculation of the venturi tube gas-liquid turbulence flow field, which provided the mathematical model for complex hybrid simulation of the flow field.Based on CFD calculation method, the venturi model was established according to the basic principle and need to pay attention to the factors for design. It break through the multiple opening holes on venturi wall of experimental research in the past, which impact the internal flow field, to simulation study the efficient removal mechanism and purification process of the fine tar particles from biogas. The static pressure field and velocity distribution field showed obvious layer distribution characteristic. Fluid circulation section contraction in the contraction segment and the throat segment accelerates airflow violent, and increases the relative motion and the collision probability between airflow and detergent. The dynamic pressure and turbulent kinetic energy contours showed that a strong turbulent zone was formed by tar particles carrying with gas stream impacted detergent droplet, which promoted purification efficiency of tar. but also caused pressure loss of venturi scrubber.In order to improve the purification efficiency and reduce the pressure loss, the paper set up a biomass gasification and gas purification system and the purification performance of venturi scrubber was experimentally studied. The test results showed that the suitable geometry parameters of venturi scrubber are pipe segment length for80to100mm, contraction angle for24°and diffusion angle for6to7°and found primary and secondary order of the main operating parameters of venturi is throat speed, liquid-gas ratio, inlet tar content, which affect the purification efficiency and pressure drop. That is to say the higher throat speed and the greater liquid to gas ratio, the higher purification efficiency and the greater overall pressure drop. This study considered both factors and concluded that the tar content has little effect on the purification performance, the suitable range of throat speed is90to120m/s with the optimal level of90m/s, the reasonable interval of liquid gas is1-2L/m3with the optimal level of2L/m2. The purification efficiency is90%and the overall pressure drop is7kPa when venturi scrubber was worked at optimal level conditions. Compared with throat speed for120m/s and the liquid to gas ratio for3L/m3, purification efficiency is slightly decreased, while the pressure drop is reduced by about6kPa. The study could improve the purification performance of venturi scrubber purifying biomass gas and laid the foundation for the design and engineering application of venturi scrubber equipment.