At present, wood chip and wood pellet are widely available on
the world market. Wood chip is mainly distributed in the paper
industry. Wood pellet has a potential to be supplied in large
amount to pulverised coal fired power plants. In this work, wood
pellet is employed to develop a mill for woody biomass; wood chip
is used for comparison. First, the grinding performance of a coal
mill without any modification is evaluated. Mill structure and
specification are shown in Fig. 4. The mill operating parameters,
namely air flow rate of 3 t/h, table rotation speed of 42 rpm and
roller hydraulic pressure of 3.5 MPa, are maintained; rotating classifier
is stopped for whole duration of experiments. Results of
grinding experiments are shown in Fig. 5. Plotted points indicate
the measured data, for which stable pulverising could be achieved;
for higher feeding rates, the mill could not be operated continuously.
From Fig. 5 it is seen that this test mill can grind about
2.2 t/h of bituminous coal at 3.5 t/h air flow rate and 90 rpm classifier
rotation. However, for wood pellet, only a maximal feeding
rate of 300 kg/h could be obtained. At 400 kg/h the mill differential
pressure has not been stable and showed continuous rising. For
wood chip this is observed at 250 kg/h. In the experiment with