Rheological And Heat Transfer Characteristics Of Biogas Production During Horizontal Flow Reactors Fed With High Organic Solid Waste

With the improvement of people’s living standards and the continuous improvement of the garbage collection system,the output of solid waste in my country is increasing.Solid waste can be divided into municipal solid waste,industrial solids,and hazardous waste.In 2014,the total amount of urban solid waste in China reached 220 million tons,and the volume of urban solid waste removal was 190 million tons.It is expected that the output of urban solid waste will reach 2020 324 million tons,an average growth rate of 6.7% in six years.At present,there are a variety of organic solid waste treatment methods in China.Solid anaerobic fermentation does not require aeration and has a small footprint.It has become a new method for urban organic solid waste treatment.In this paper,the aim is to achieve the harmless disposal of high-inherent organic solid waste and the comprehensive recovery of resources / energy.This paper takes the high-inherent organic solid waste horizontal flow anaerobic fermentation reactor as the research object to enhance the heterogeneous organic solid The mass transfer / heat transfer of waste is the goal.The experiment starts from simulating the rheological characteristics of high-inherent organic solid waste in a horizontal flow anaerobic reactor.The CFD simulation is used to compare the reactor’s paddle type,paddle diameter,pitch diameter ratio,The effects of stirring speed and shaft eccentric setting on fermentation efficiency were used to optimize the design of the reactor;on this basis,a method to simulate its internal temperature field was proposed,and the mechanism of mass transfer in the reactor was analyzed.Through the measurement of the viscosity and shear stress of different solid content in the horizontal flow reactor at different temperatures and different shear rates under high solids content,the shear stress and shear rate of the material by the power law equation were found.The fitting effect is the best.The solid content rate has a great influence on the rheological characteristics of the material.With the increase of the solid content rate(5% ～ 30%),the consistency coefficient of the fluid increases significantly(0.134 ～ 117.440),the rheological index decreases(0.532 ～ 0.224),The fluidity is decreasing,and the characteristics of non-Newtonian fluids are more and more obvious;in contrast,the temperature(29 ℃ ～ 45 ℃)has little effect on the rheological properties of the material,and it can be ignored compared to the solid content.Through CFD modeling and simulation,different design of the reactor was simulated and compared through research indicators such as stirring efficiency,area ratio in low speed area,torque,power,etc.,and finally determined the horizontal flow anaerobic fermentation reactor(cylindrical shape,diameter D)The best design parameters of the machine are the screw-type stirring paddle with a pitch of 0.6 D;the pitch of the screw is 0.75 D,and the stirring shaft is set vertically eccentrically downward by 0.15 D.It is recommended that the reactor be operated at a low stirring speed,not more than 10 rpm.In order to achieve the purpose of saving energy consumption,such as running at a speed of 10 rpm,the energy consumption per unit volume of the homogenized reactor is 48.20 k J / m3.The rheological properties of the material have little effect on the mixing time.The mixing time is basically stable at 550 s above 10 rpm,and has a great influence on the stirring shaft torque.Therefore,the homogenization of high-solids materials requires more energy.The simulation of the temperature field of the reactor is better with the Euler bidirectional flow double-precision method.Because there is no insulation at both ends of the reactor,there is a temperature gradient with the environment.The stirring of the screw reactor can obviously homogenize the temperature field and prevent the reactor Local temperature is too high;materials with different rheological characteristics have little effect on the flow state of the reactor when it reaches a steady state,and the resulting flow field is similar,but it has a great impact on torque power consumption.The higher the consistency coefficient,the lower the rheological index.,The greater the power consumption required.Through the above research,the mass transfer situation of anaerobic fermentation with high organic solid waste can be more clearly recognized,and the energy consumption of the reactor system can be reduced as much as possible on the premise of ensuring the effect.The conclusion provides a certain reference and reference for anaerobic reaction engineering.