Movement and Mixing of Crushed Straw Material in Rotary Drum with Straight Plates

ZHOU Jingzhi;FENG Junxiao;ZHOU Zhixing;LI Shizhong;School of Energy and Environmental Engineering,University of Science and Technology Beijing;Beijing Key Laboratory for Energy Conservation and Emission Reduction in Metallurgical Industry;Institute of Nuclear and New Energy Technology,Tsinghua University;

rotary drum;;straight plate;;crushed straw material;;movement mode;;image analysis

Annual production of straw is 600 to 800 million tons in China. Dr. LI Shizhong solid-state fermented crushed straw material to acquire ethanol. However,the fermentation heat in bed often over accumulate and kill the yeast,as crushed straw material has low heat conductivity. Dr. Li use rotary drum with straight plates as fermentation drum to solve the problem. The length of plates and the number of plateshasgreat influence on movementand mixing of crushed straw material. However,there is less study in this area. In order to study the influence,section test platform was designed referred to laboratory level rotary drum. The drum can connect 1/2/4 plates andthe length of plates can adjust to 15%/35%/55%/75% ratio of drum( R). The material filling ratio and rotary speed is the same as laboratory level rotary drum: 50%,1 r/min. Some of the material was colored black while the other remains uncolored. They are laid in drum orderly to form acolored and an uncolored material layer. The two layers will mix with drum rotation,and the bed section color will change at the same time. Therefore,the section color can measure the mixing degree of colored and uncolored material. The faster the section color turn uniform grey,the faster thematerial totally mixed. The faster the material totally mixed,the greater the promoting effect of plates on averaging bed's fermentation heat. The method to measure mixing degree was built based on image analysis,as shown in figure 2. Mesh the bit-mapped picture and calculate the number of uncolored material grids( N0) and all material grids( N) as the black pixeldensity interval between themare different. The quotient( Imix) of N0 divided by N is dimension less and will turn to 0 from 0. 5 along with mixing and can mark the mixing degree. The time Imix-time fitting line turn 0 is the complete mixing time of colored and uncolored material( Tc). Data analysis resultshows that: Imixis the most accurate in the case of grid size 8 mm; black pixel density [0. 1,0. 7]marks the uncolored material grid,[0. 1,1]marksall material grid. The software to calculate Imixwas programmed with Visual Studio. Thirteen section-mixing tests were done: 1/2/4 plate( s) with length 15%/35%/55%/75% ratio of drum. The control group is 0 plate. Each test were done 5 times to obtained the average Tc. The results show that:( 1) The length of plates has greater influence on Tcthan the number of plates,they are in the same order of magnitude and have strong coupling effects.( 2) Tcis the smallest under influence of 4 × 0. 55 R plates.( 3) Synthetically,Tcchange like cos function along with longer plates,change like exponential function along with more plates.( 4) Tcdecrease under influence of single long plate or multi middlelength plates,increase under influence of multishort plates or multilong plates. The movement modes of material were studied. From 0 to 4 plates,0. 15 R to 0. 75 R,there is no one unique mode for every test condition. All the movement modes,the influence of plates on mixing and the mixing mechanismhave been analyzed and classified which is shown in table 2. The research can guide designing of plates of laboratory level rotary drums. It can also deepen the understanding of complex movement of crushed straw material in rotary drum with plates. However,for industrial level rotary drums,the conclusions above can not be used uncritically as the drums become much bigger. Tests need to be done on industrial level drums with methods above to acquire conclusions of bigger drums. Furthermore, two important conclusionsfor any kind of mixing process were put forward.( 1) There are only two ways to mix material A and B. The first way is to let material group that totally comprised of Aleaves Amaterial layer and embed in B material layer. The second way is to break and mix material group which contains both material A and B. The first can happen in any part of the material bed,while the second can only happen in interface of material A and B.( 2) If there is no permanently blocking area,the more material falling areas the material bed has,the faster the colored and uncolored material mix.