Research On Pneumatic Conveying Simulation For Fertilizers And Pipeline Structure Optimization For A Paddy Side-Deep Fertilization System

As an important grain crop in China,rice plays an important role in ensuring China’s food security.In order to ensure the high yield and stable yield of rice,the technique of side-deep fertilization for rice paddies has been widely popularized and applied because of its characteristics of low fertilization quantity,low cost and high fertilization efficiency.This technology is realized by rice transplanting mechanically and side-deep fertilization concurrently,but in the process of operation,there will be problems of fertilizer blockage and inequal fertilization quantity in different rows,which will directly affect the yield of rice.Considering the requirement of side-deep fertilization for rice paddies in Yangtze River,structural improvement and structural parameters optimization of the key components of the pneumatic conveying line for fertilizers—fertilizer tube and a gas-volume distribution line were carried out,using the ways of theoretical analysis,simulation and orthogonal experiment.The structure with excellent performance was selected from circumgyrating Venturi fertilizer tube and straight Venturi fertilizer tube.The working principle of Venturi effect to convey fertilizers was described,their structural features were compared and analyzed,and their key structural parameters were designed:diameters of the airflow inlet and outlet are both 24 mm,diameter and length of the throat are both 16.8 mm,cross-sectional area of the end contraction is221 mm²,angle of the contraction and the diffusion are 21°and 8°,respectively.The airflow fields and fertilizers motion were simulated using computational fluid dynamics-discrete element modelling（CFD-DEM）coupling simulations.The results revealed that straight Venturi fertilizer tube could provide better acceleration for airflow and better suction for fertilizers.Fertilisers in the straight Venturi fertilizer tube flows fluently,and quickly,so the straight Venturi fertilizer tube has a better ability of anti-blocking.The above revealed that the straight Venturi fertilizer tube with its structure of flat shrinkage and straight through-tube is more suitable to convey fertilizers.Structural improvement and parameters optimization of straight Venturi fertilizer tube were carried out.To take full advantage of the acceleration effect of the fertilizer’s own gravity in its motion direction,the structural improvement of the straight Venturi fertilizer tube was carried out,angleβand diameter D of the non-horizontal section,and horizontal length L of the contraction section were selected as key structural factors affecting the test index（fertilizer flow velocity v_x）.Parameters optimization test was carried out using the method of CFD-DEM coupling simulations and quadratic regression orthogonal rotation combination test.The regression model between the test index and various factors is obtained using this test,and the order of the factors affecting the test index in order of priority are L,βand R,and there is no interaction between any two factors;Whenβ=13.7°,R=21 mm,and L=40 mm,the maximum velocity v_xwas obtained.The theoretical and simulation values were 3.186 m/s and 3.30 m/s,respectively,and the deviation rate was 3.45%,the regression model was proved to be accurate,and the bench test was carried out using a high-speed camera.The average velocity=3.04 m/s at the end of the non-horizontal section was obtained,and the deviation rate from the simulation value was 8.55%,it can be concluded that the two results are basically the same,which revealed that the simulation model is reasonable and the regression model and parameter optimization results are credible.Structural improvement and parameters optimization of the gas-volume distribution line were carried out.Based on ventilation engineering,the mechanism of gas flowing in the gas-volume distribution line was described,the front section of the branch pipe was improved into the airflow equalizer,and the branch pipes were located along the duct at equal distance,thus,a gas-volume distribution line was designed to improve consistency of the sectional gas velocities in different rows（σ₁）.Structural parameters（notch angle A,extended length B）and the position parameter（Distance between adjacent branches C）of the branch pipe along the duct were selected as the key factors affectingσ₁.The reasonable ranges of the factors were selected,which are notch angle of 120-180°,extended length of 24-36 mm,distance between adjacent branches of 120-160 mm,using single-factor tests.Parameters optimization test was carried out using Fluent simulation and orthogonal test.The results of range analysis and variance analysis were consistent with each other,and the order of the factors affectingσ₁was extension length,notch angle×extended length,distance between adjacent branches,Notch angle,the optimized parameters combination is the notch angle of 150°,the extended length of 24 mm and the distance between adjacent branches of 140 mm.The simulation without the optimized airflow equalizers is carried out as a control test.The trend of sectional gas velocities were similar in three tests,i.e.a simulation test without the airflow equalizers,a simulation test with the airflow equalizers,and a bench test with the airflow equalizers.The sectional gas velocities all gradually increased as the branch number increased.Theσ₁in those three tests were 20.69%,7.07%,9.53%,it showed that the optimized airflow equalizers could improve the consistency of the sectional gas velocities in different rows..The validity of the simulation model and the reliability of the optimization result of the pipeline structure were carried out,and the performance of pneumatic conveying line for fertilizers with equal-gas-volume based on the gas-solid coupling simulation was carried out.The results revealed that there is less fertilizer in total mass sensor,and the consistency of fertilizer quantity in different rows（σ₂）is 4.25%,which is 8.51%lower than that of the traditional device.These revealed that the structure has good performance to convey fertilizers,and can significantly improve the consistency of fertilizer quantity in different rows.