Roof falls

Turbo-Tray Dryers The turbo-tray diyer is a continuous diyer consisting of a stack of rotating annular shelves in the center of which turbo-type fans revolve to circulate the air over the shelves. Wet material enters through the roof, falling onto the top shelf as it rotates beneath the feed opening. After completing one revolution, the mate-... 

At the start to walk stooping is rather a joke, but it is a joke that soon wears ojf. I am handicapped by being exceptionally tall, but when the roof falls to four feet or less it is a tough job for anybody except a dwarf or a child. You have not only got to bend double, you have also got to keep your head up all the while so as to see the beams and girders and dodge them when they come. 

It should however be pointed out that the principal source of colliery accidents is not explosion but roof falls. Rogers [22] gives the following annual figures for 1923-59 in Great Britain (Table 92) ... 

Maintenance of machinery of government under rocket bombardment, 245 Manod Quarry, 232, 233, 238 Abandonment, 242 Access road, 240 Air conditioning, 241 Cold war improvements, 242 Conversion, 241 Description, pre-war, 240 Powerhouse, 241 Risk of roof falls, 241 Transfer of paintings from country houses, 240 Master General of Ordnance, 12, 14... 

Nagy, J. Kawenski, E.M. 1960. Frictional ignition of gas during a roof fall. U S. Bureau of Mines. Report of investigations 5548, Washington. 

The prevention of coal-gas dynamic disasters in coal mines is the worldwide problem (He 2010), and threat seriously the safety of the underground hves of mine workers and high production efficiency. Coal-gas dynamic disasters include coal and gas outburst, gas (and coal dust) explosion, rock burst and larger roof fall, etc, and affected by coal distribution, minefield layout, mining technology and other factors. 

The simulation assumes that the gas emission position locates at the top of the roof-fall carving in the return airway. The relative methane emission rate is 1.78 mVt and the absolute rate is 0.0033 mVs. According to the Coal Mine Safety Regulations, the gas concentration of airflow in return airway... 

According to Figure 2 and Figure 3, the gas concentration accumulating at the top of the roof-fall area is about 0.3%, which is consistent with the on-site data. 

Figure 7 and Figure 8 show that the gas concentration distribution in roof-fall area under air velocity of 1 m/s. It shows that the gas concentration rises up to 3% from 0.3%, when air velocity goes down from 2.03 m/s to 1 m/s at 720 m and 380 m. For the... 

Fig. 9 and Fig. 10 show the gas concentration distribution in roof-fall area under the wind velocity of 4 m/s. It can be concluded that the gas concentration in roof-fall area has basically no different under speed of 4 m/s from that of 2.03 m/s (showen in Fig. 2 and Fig. 3). The gas layer in roof-fall area at 380 m top-caving is thicker than that of 720 m top-caving.

CFD physical model was proved to be effectively verified the simulation of the gas accumlation in the roof-fall area of the airway ... 

Gas concentration in top-caving area would go down if airflow velocity is continuously increased. But when air velocity is over a certain hmit, the gas will tent to keep constant concentration as airflow velocity goes up. On the contrary, with the decrease of the airflow velocity, the gas accumulated in top-caving area and the gas concentration reached the dangerous level of the gas explosion triangle and spontaneous combustion appeared in the roof-fall area, which gas explosion disasters will happen. 

---