Experimental Study On Twin-screw Extrusion Of Crop Straw For Animal Husbandry

With the rapid development of animal husbandry in China,developing grain-saving and non-grain types of feed has become an urgent task due to the rapidly increasing demands.China is a large agricultural country with an annual 700-million-ton output of crop straw.However,the feed use of crop straw is affected by a large quantity of hard and poorly palatable crude fiber and lignin contained in,which leads to a low livestock feed intake and digestibility of straw.Currently,the utilization ratio of crop straws can be improved by screw extrusion due to the destruction of crude fiber and lignin structure.Nevertheless,the posterior start of straw extruding in China makes double screw extrusion expansion of crop straw rarely seen in related research.In view of the present situation,this research project aimed at testing the twin-screw extrusion of crop straw for livestock husbandry and studying the flow mechanism of co-rotating intermeshing twin-screw during extrusion process.Twin screw configuration was designed and double-screw flow field was analyzed.The designed twin-screw was used to carry out extrusion test and the raw material was mixtures of rice straw and corn flour.While no more than twenty percent of rice straw was added in total amount,the appearance and expansion ratio of extruded products were put forward as evaluating indicators to obtain process parameters of the best puffing degree.The results provided a theoretical and practical guidance for crop straws twin-screw extrusion to produce feed.This paper attempted to find the law of material movement between the co-rotating intermeshing twin-screw.Firstly,by analyzing the infinitesimal movement of material in C-space under the cylindrical coordinate system,the fluid continuity equation and fluid Navier Stokes equations were established.Then,the expressions of speed for Vr?V??Vz and pressure for P were obtained as well as the average shear rate equation.Finally,the suitable exponent law model was selected to obtain the viscosity expressions and the flow model of the co-rotating intermeshing twin-screw during extrusion process was established.This paper designed the configuration of twin-screw and established its three-dimensional model using the software solidworks.Based on computational fluid dynamics theory,the finite element model of double screw flow field was established and numerical simulation analysis of intact model flow field was carried out.The obtained trajectory of the fluid,temperature distribution and pressure distribution revealed the internal movement law of flow field between twin-screw.The design of screw configuration was verified to meet the requirements and provided equipment support for the subsequent extrusion test.Rice straw and corn flour were used as raw material to carry out single-factor test with five variables including the amount of rice straw,the three-zone temperatures of the extruder,the moisture content of materiel,the speed raes of screw and feeding speed,respectively.The appearance and expansion ratio of extruded products were put forward as evaluating indicators to analyze the influence of above-mentioned five factors.The results show that the maximum addition of rice straw 20%,the moisture content selection 18%-24%,three-zone temperatures of the extruder selections 120 ??140 ?,screw speed rate selection 90r/min?130r/min and feeding speed rate selection 20r/min?24r/min can be the best parameter intervals for a good puffing effect of products.In this paper,the amount of rice straw added was set a fixed value 20%,and four changeable factors including moisture content,three-zone temperatures,screw speed and was feeding speed were designed to carry out quadratic regression orthogonal rotation combination test to revael the influence of variable factors.The test results were regression analyzed by software SAS9.3 and the second regression equation of puffing degree was obtained to validate significance and simulating loses.The results show that under twenty percent of the rice straw amount added,the moisture content 19.85%,three districts temperature of the extruder 128.57 ?,screw speed 110.55r/min and feeding speed 22.1r/min can be the best parameter configuration when the puffing degree reached 1.571.The actual test product puffing degree is 1.587 in test under above best parameter configuration and the relative error with theoretical expansion is only 1.02%,which meets the error requirements.