Design, Fabrication and Evaluation of a Wet Cattle Manure Size Reduction Machine

Introduction The annually production of cattle manure is estimated around six million tons in Iran. Manure transportation with high moisture and low density recognized as crucial issue. The densification of dry or wet manure is the profound method for decreasing the manure volume which reduces the cost of handling and storage. Besides, the particle size is one of the important factors in the pellet production. Ball mills, vibratory mills, hammer mills, knife mills, two roll mills, colloid mills, attrition mills, or extruders can be used for size reduction of biomass. Specific energy consumption for size reduction of biomass highly depends on moisture content, bulk and particle densities, feed rate of the material, particle size distribution (initial/final particle size) and machine variables. The present study is conducted for wet cattle manure size reduction machine. Furthermore, the relationship between moisture content (35, 40 and 45 %w.b) and drum of special size reduction machine in rotational speed (150, 200 and 250 rpm) considering geometric mean diameter of particle and size distribution of wet cattle manure were investigated. A factorial experiment under randomized complete design method was employed with three replications.   Materials and Methods The main parts of machine include drum, concave, spring and adjusting screw. The main function of this thresher machine is to combine crushing and cutting in order to conduct the size reduction methods, i.e., to apply compressive and shear forces to the cattle manure particles. The drum is also equipped with several rows of sharp-edged milling segments. The spring constants were determined by evaluating the slope of the force vs. deflection curves. The rotational speed of drum was changed in the range of 100-700 rpm during these experiments. In the test of the machine physical properties of grinds such as geometric mean diameter of grind particles and particle size distribution were determined. One kg of cattle manure was grinded in each test and the particle size distribution of grinded cattle manure was determined according to ASAE standard S319.3. The moisture content of cattle manure was obtained according to ASAE standard S358.3.   Results and Discussion The initial and final particle size of the materials are 20 millimeters and less than 5 millimeters, respectively and the angle of nip is 30 degrees (according to the installation space limitations), the diameter of the drum is 310 millimeters. The spring constant was equal to 24.371 N / mm and on the basis of the experiments a drum speed in the range of 150–250 rpm is considered to be optimal settings for the milling for cattle manure disintegration. The results of Table 4 show that for wet cattle manure with 35% (w.b) moisture content at 250 rpm rotational speed of drum (P > 0.05; Skewness = -0.056; Kurtosis = -2.15), 40% (w.b) moisture content at 250 rpm rotational speed of drum (P > 0.05; Skewness = 0.076; Kurtosis = -1.77), 45% (w.b) moisture content at 200 rpm rotational speed of drum (P > 0.05; Skewness = 0.095; Kurtosis = -1.72), in grinds that would potentially produce better compacts. The geometric mean particle size and standard deviation for each test are shown in Table 2. According to Table (2), the lowest geometric mean of particle size is related to rotational speed of 200 rpm and a moisture content of 45% (w.b), and the highest at rotational speed of 250 rpm and a moisture content of 45% (w.b) can be observed.   Conclusions The use of cattle manure of thresher machine reduces the specific energy consumption of cattle manure by 92% compared to the conventional method (using drying and hammer mill) in the pellet production. The lowest geometric mean diameter of wet cattle manure was 1.02 millimeter for drum rotational speed of 200 rpm at 45% (w.b) moisture content and the highest was 1.38 at rotational speed of 250 rpm and a moisture content of 45% (w.b%). The best particle size distribution was observed for milling of wet cattle manure with 35% (w.b) moisture content at 250 rpm rotational speed of drum (P> 0.05; Skewness = -0.056; Kurtosis = -2.15), 40% (w.b) moisture content at 250 rpm rotational speed of drum (P> 0.05; Skewness = 0.076; Kurtosis = -1.77), 45% (w.b) moisture content at 200 rpm rotational speed of drum (P> 0.05; Skewness = 0.095; Kurtosis = -1.72)