Through the first stage of the experiment on the traditional design of hammermill using no screen and with screen at 5 size holes diameters (12, 14, 16, 18 and 20 mm). The results showed that, the use of screen with all holes size had shallow decreased production and clogging the screen holes after short time from the beginning process. While without screen condition, the productivity was increased to 897.50 kg/h. In addition, to optimize the chopping process under no screen condition, it should be increase the chopping and fragmentation time by controling the rotation track length.
Figure 4A shows the effect of FR on MWD of MR at different DS when the average MR moisture reached to 54%. From the figure, it could be seen that FR has inversely relationship with the MWD. These results mean that the effect of drum speed is higher than the effect of feeding rate. The data cleared that the increase in FR from 500 to 900 kg/h causes decrement in MWD about 0.299 and 0.920 mm, but it was recorded about 1.065 and 1.190 mm when DS increased from 1500 to 3000 rpm in short and long track, respectively. At the multiple regressions, the relationship between MWD and the each of FR and DS shows the highly significant effect (0.0002 F sig.) at short track. Also, the formula with the coefficient of each factor can be described as:
$${\text{MWD}} = 7.899{-}0.00075{\text{FR}}{-}0.00069{\text{DS}}\,\left( {R^{2} = \, 0.9409} \right)\,{\text{at}}\,{\text{short}}\,{\text{track}}.$$
This formula cleared that both of the FR and DS are an inversely proportional to the MWD. Also, the DS has the highly significant effect on MWD (P > 0.0001), while the FR has a significant only (p > 0.03).
Fig. 4Effect of RT, FR and DS on mean weight diameter, A sun drying after one and B two days
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At the long track, the multiple regressions the relationship between MWD and the each of FR and DS show the highly significant effect (0.00076 F sig.). Also, the formula with the coefficient of each factor can described as:
$${\text{MWD }} = { 8}.{77 }{-} \, 0.00{\text{23FR }}{-} \, 0.000{\text{79DS }}\left( {{\text{R}}^{{2}} = \, 0.{9}0{88}} \right){\text{ at long track}}.$$
This formula cleared that both of the FR and DS had an inversely proportional to the MWD. Also, the DS has the highly significant effect on MWD (P > 0.0008), while the FR has a significant at (p > 0.003).
When the average MR moisture reached to 43%, the effect of FR on MWD of MR at different DS is presented in Fig. 4B. It can be understood from Fig. 4B that the relation between FR and MWD is a reverse relation. These results mean that the effect of drum speed is higher than the effect of feeding rate. Data showed that the increase in FR from 500 to 900 kg/h causes decrement in MWD about 0.728 and 0.660 mm, but it was about 0.25 and 0.51 cm when the DS increased from 1500 to 3000 rpm in short and long track, respectively. At the multiple regressions, the relationship between MWD and the each of FR and DS shows highly significant effect (0.054 F sig.) and (0.0057 F sig) at short and long track, respectively. Also, the formula with the coefficient of each factor can be described as:
$$\begin{aligned} {\text{MWD}} & = 7.67{-}0.00061{\text{FR}}{-}0.000466{\text{DS}}\,\left( {R^{2} = 0.82} \right)\,{\text{at}}\,{\text{short}}\,{\text{track}}. \\ {\text{MWD}} & = \, 7.64{-}0.0013{\text{FR}}{-}0.00041{\text{DS}}\,\left( {R^{2} = \, 0.62} \right)\,{\text{at}}\,{\text{long}}\,{\text{track}}. \\ \end{aligned}$$
Both formulae cleared that both of the FR and DS are an inversely proportional to the MWD. Also, the DS has the highly significant effect on MWD (P > 0.02) and (P > 0.006) while the FR have a significant only (p > 0.3) and (p > 0.01) at short and long track, respectively.
Figure 5A shows that the power consumed for chopping MR was increasing by increasing DS and FR for hammermill at the two rotation tracks. The figure clarified that the power consumed from the short track is slightly decreased compared with that from the long track. The lowest value of the power consumed was 1102.24 and 1195.10 W at feeding rate of 500 kg/h using DS 1500 rpm for short and long tracks, respectively. These data were observed on the MR with 54% moisture content.
Fig. 5Effect of RT, FR and DS on power consumption A sun drying after one and B two days
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At the multiple regressions, the relationship between power and the each of FR and DS showed highly significant effect (0.00057 and 0.00000137 F sig.) at short and long track, respectively. Also, the formula with the coefficient of each factor can be described as:
$$\begin{aligned} {\text{Power}}\,{\text{consumption}} & = 414.099 + 0.66{\text{FD}} + 0.219DS.\,\left( {R = 0.92} \right)\,{\text{at}}\,{\text{short}}\,{\text{track}}. \\ {\text{Power}}\,{\text{consumption}} & = 605.465 + 0.66{\text{FD}} + 0.161{\text{DS}}.\,\left( {R = 0.98} \right)\,{\text{at}}\,{\text{long}}\,{\text{track}}. \\ \end{aligned}$$
These equations cleared that both of the FR and DS are directly proportional to the power. Also, the DS has a highly significant effect on power (P > 0.002) and (P > 0.000004) at short and long track, respectively, while the FR has a significant only (p > 0.0007) and (p > 0.000003) at short and long track, respectively.
On the other hand, when the dried MR moisture reached to 43%, the power consumed from the short track is slightly decreased compared with that from the long track. The lowest value of the power consumed was 827.688 and 859.019 W at FR 500 kg/h using DS 1500 rpm for short and long track, respectively (Fig. 5B).
At the multiple regressions, the relationship between power and the each of feeding rate as well as drum speed shows highly significant effect (0.00155 and 0.0063 F sig.) at short and long track, respectively. Also, the formula with the coefficient of each factor can be described as:
$$\begin{aligned} {\text{Power}}\,{\text{consumption}} & = 453.28 + 0.127{\text{FD}} + 0.167{\text{DS}}. \, \left( {R = \, 0.94} \right)\,{\text{at}}\,{\text{short}}\,{\text{track}}. \\ {\text{Power}}\,{\text{consumption}} & = 631.63 + 0.027{\text{FD}} + 0.206{\text{DS}}. \, \left( {R = \, 0.90} \right)\,{\text{at}}\,{\text{long}}\,{\text{track}} \\ \end{aligned}$$
These equations cleared that both of the FR and DS are directly proportional to the power. Also, the DS has a highly significant effect on power (P > 0.00078) and (P > 0.002) at short and long track, respectively, while the FR has a significant only (p > 0.04) and (p > 1) at short and long track, respectively.
Figure 6A, B concludes that the increase in feeding rate resulted in decrease in the hammer mill specific energy (kW h/Mg), for both tracks using dried MR with 54% of moisture. Figure 6A illustrates that drum speed at 1500 rpm and feeding rate 900 can be obtained under the lowest specific energy 1.43 kW h/Mg in the short track. But, in the long track, the three drums speed got slightly similar specific energy in the same feeding rate, while, in short track (Fig. 6A), the multiple regressions of the relationship between specific energy and the each of feeding rate and drum speed show highly significant effect (0.0078 F sig.). Also, the formula with the coefficient of each factor can be described as:
$${\text{Specific}}\,{\text{energy}} = - 6235.46 + 2438.11{\text{FD}} + 4.95{\text{DS}}.\,\left( {R = 0.89} \right)\,{\text{at}}\,{\text{short}}\,{\text{track}}.$$
This equation cleared that both of the FR and DS are directly proportional to the specific energy. Also, the DS has the highly significant effect on specific energy (P > 0.0067), while the FR has a significant only (p > 0.0026), whereas at long track the relationship between specific energy and the each of FR and DS shows highly significant effect (0.017 F sig.). Also, the formula with the coefficient of each factor can be described as:
$${\text{Specific}}\,{\text{energy}} = - 9004.07 + 6.66{\text{FD}} + 3070.72\,{\text{DS}}.\,\left( {R = 0.86} \right)\,{\text{at}}\,{\text{long}}\,{\text{track}}.$$
This equation cleared that both of the FR and DS had a directly proportional to the specific energy. Also, the DS has a highly significant effect on specific energy (P > 0.006), while the FR has a significant only at (p > 0.0099).
Fig. 6Effect of RT, FR and DS on specific energy A sun drying after one and B two days
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From the other side, the average of MR moisture reached to 43%. In the short and long track, Fig. 6A illustrates that feeding rate 900 kg/h and drum speed 1500 rpm could be acquired to the minimum energy requirements which were 0.9939 and 1.0060 kW h/Mg, respectively. At the multiple regressions, the relationship between energy and the each of feeding rate and drum speed shows highly significant effect (0.0088 and 0.0077 F sig.) at short and long track, respectively. Also, the formula with the coefficient of each factor can be described as:
$$\begin{aligned} {\text{Specific}}\,{\text{energy}} & = - 7250.233 + 6.19FD + 3360.76DS.\,\left( {R = 0.89} \right)\,{\text{at}}\,{\text{short}}\,{\text{track}}. \\ {\text{Specific}}\,{\text{energy}} & = - 6747.49 + 5.82{\text{FD}} + 3087.44\,{\text{DS}}.\,\left( {R = 0.89} \right)\,{\text{at}}\,{\text{long}}\,{\text{track}}. \\ \end{aligned}$$
These equations cleared that both of the FR and DS are directly proportional to the specific energy. Also, the DS has the highly significant effect on specific energy (P > 0.00566) and (P > 0.0026) at short and long track, respectively, while the FR has a significant only (p > 0.003) and (p > 0.0054) at short and long track, respectively.