Fig. 23.—Pneumatic Unloading of Coal at Messrs. Boots, Ltd. (Nottingham).
In the first case, immediately the barge is alongside, the flexible suction pipe is lowered into the barge (Fig. [23]), and coal immediately begins to rise in the pipe and is discharged as required. Little or no handling of the coal is required after the suction nozzle has once reached the bottom of the barge; all that it is necessary to do is to bring the barge gradually up to the nozzle, the coal then “avalanching” down to the nozzle. Fig. 24 shows the discharger placed on girders over the bunkers into which it discharges continuously. The coal enters at A and the major portion of the fuel is discharged through the rotary valves B.
The coal discharger itself consists of a cast iron vessel with two King’s patent rotating valves. These are designed in the form of a slightly conical taper divided into four sections, one portion of the circular valve being under vacuum, and the other under ordinary atmospheric pressure. The outlet of the valves is larger than the inlet to allow the coal which is in the valve to drop out easily. Over each valve is also provided a four-armed sweeper to prevent any damp coal from forming a cone inside. The discharger is provided with two inlets with full-way bored valves, so that the coal can be drawn either from the water side or from the land side at will. After the coal has been deposited in the main discharger, there is provided a supplementary discharger consisting of a vessel 6 ft. high by 30 ins. diameter, with two inlet pipes of 8 ins. diameter, to provide a contra-flow, so that any particles of coal dust in the air will meet one another in the 30 ins. box at equal velocity and be deposited. The small particles are delivered by a supplementary rotary discharge valve which is set to run very much slower than the main discharger valves.
Fig. 24.—Discharger for Coal Conveying Plant.
The main discharger valves are driven by worm gearing, the latter having one right-hand thread and one left-hand thread, so that the end thrust on the worms is neutralized. Ball bearings are provided and the small motor which drives all three valves is coupled up with an electrical device designed by the author. This device ensures that if anything happens to the top discharge valves—so that the 3 h.p. motor driving them cuts out, owing to an overload or other cause—then the main motor also is cut out by the opening of its circuit breaker. This prevents any “flooding” of the pipes and dischargers.
It may be mentioned that the valves are so designed that a portion of the weight of each valve is carried by the vacuum, so that the vertical wearing lift on the valves when at work is very slight.
The intake pipes for the coal are 5 ins. diameter, and they are provided with heavy cast iron bends, having extra thick metal on the outside radius to allow for the wearing effect of coal passing at the rate of 20 tons per hour.
The pipe into the barge is provided with a flexible steel pipe at the suction nozzle end, for convenience of handling. India-rubber piping has been tried, but the extra cost does not justify its continued use.