Design of supporting system on rotary drum bioreactor for solid-state fermentation and finite element analysis

Abstract: The technology of advanced solid state fermentation (ASSF) from sweet sorghum to produce fuel ethanol has broad prospects under the background of shortage of energy. In order to realize the large-scale, automatic and continuous production of the process, a type of rotary drum bioreactor is developed. The supporting system of the bioreactor is mainly composed by friction ring, supporting wheel and wheel shaft, which is the most decisive factor for the safety and stable operation of bioreactor. The pattern design of bioreactor supporting system refers to the rotary kiln used in metallurgical or construction material industry. However, due to the differences in construction, stream characteristics and the load condition between two types of equipment, the analysis of the supporting systems are distinguishing. The bioreactor and its supporting system is failure in operation mainly caused by fatigue crack on the surface of welding joint and stiffness deficiency of cylinder. By analyzing the rotating characteristics of sweet sorghum bagasse in bioreactor, the load condition on the friction ring and cylinder, which considered as a whole element due to two parts welding together, was determined. Based on APDL programing in ANSYS, a three dimensional multi-body model for three parts of supporting system with complex loading of distribution was modeled according to the actual dimension of the parts. The contact elements were used on the interface of friction ring and supporting wheel and the interface fit of wheel and its shaft. SOLID186, a three dimensional element with 20 nodes was selected to build entity. TARGE170 and CONTA174, the interface contact element provided by ANSYS, were selected to simulate the relative motion of parts in the system. Using the manner of key points and lines controlling in the meshing, 5 400 elements were divided. Numerical simulations of contact nonlinear finite elements were presented on the mechanical behavior of the supporting system in the working condition. The stress distribution of friction ring, supporting wheel and the shaft was solved. Cylinder deformation and fatigue failure were focused in finite element analysis. Through the method of path analysis, the maximum deformation on the cylinder was determined, which was combined with welding deformation to be considered as a control condition in the process of design and manufacture of cylinder. The design parameter refers to the deformation deviation of external pressure vessel on Chinese standard. The generation and diffusion of fatigue crack on the end surface of wheel shaft and the welding joint between friction ring and cylinder were predicted. Reducing the welding residual stress and the stress concentration on key parts was an effective method to avoid fatigue damage, which could be carried out by improved specification on fabrication drawings of equipment. High stress concentration was shown in contour at the internal discontinuity of supporting wheel. So fillets were designed at the connection of the ribs and the inner wheel on fabrication drawing. Electrical stress measurement method was used to indicate the effectiveness of finite element analysis of supporting system. The results showed that the maximum simulation error was 8.61% and the stress distribution obtained by finite element calculation was of high accuracy. These findings can apply as instructions for the design of similar rotary equipment applied in agriculture.