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August, 1933
Combined Washing and Dry-Cleaning Plant at Backworth Colliery
Backworth Collieries Limited have erected Birtley Washing and Dry-Cleaning Plant to deal with 150 tons of coal per hour from 4-in. to zero size.
Although the Maude and Eccles pits at Backworth Colliery are only a few hundred yards apart, the classes of coal raised are used for quite different purposes, and it was necessary, therefore, in erecting the new cleaning plant, to make provision for treating the two outputs separately. The coal from the Maude pit is used exclusively for steam and domestic purposes, while the Eccles output is for the most part shipped as unscreened gas coal. Both pits are highly mechanised (See article on complete system of machine mining at Backworth Colliery, Nov., 1930), and although the greater output is derived from the Maude pit, practically the whole of the coal is drawn from the Eccles shaft. As the Eccles screening plant was of obsolete design, it was decided to take the run-of-mine coal straight from the tipples to a new screening plant at the Maude pit, two belt conveyors being installed for this purpose.
The whole of the output is raised in six hours, and in order to accommodate a suitable reserve two bunkers were erected, that for Eccles coal being designed for a capacity of 250 tons, while the Maude bunker has a capacity of 150 tons. The cleaning plant for the Eccles coal is capable of handling 85 tons per hour, that for the Maude coal having a capacity of 65 tons per hour.
As a general principle, it was decided to wash the larger sizes and to dry clean the smaller ones, provision being made in the washery design for handling coal up to 4 in., a size which cannot be economically cleaned by a pneumatic process.
Referring to Fig. 2, the raw coal from the Eccles pit tipplers is fed on to the raw coal conveyor Y (36-in. x 230-ft. centres), which delivers on to conveyor Y1 (36-in. x 142-ft. centres) whence it is discharged to the Maude pit screens. Here, smalls below 3 in. are screened out and carried by conveyor Y2 (30-in. x 160-ft. centres) from the existing cross-conveyor to the 250-ton concrete storage bunker. Raw coal from the Maude pit is screened in a similar manner and fed by an existing cross-conveyor to the conveyor Z (30-in. x 160-ft. centres) and then discharged into the 150-ton storage bunker. From the bunkers the flow of the coal is similar for each half of the plant. The bunkers discharge into double-trunk continuous bucket elevators (each 74-ft. centres). At the head of the plant each elevator delivers into a rotary screen C (7 ft. 6 in. x 11 ft. 3m.) which divides the coal into 3 in. to 1 in. and 1 in. to zero. Undersize passes over a Type 60 Hum-mar vibrating screen equipped with three V 16 vibrators and having an area of 28 sq. ft. in the case of the Maude pit, the coal is divided into 1 in. to 3/8 in and 3/8 in. to zero, and in the case of the Eccles pit, 1 in. to 3/16 in. and 3/16 in. to zero. Both products are collected in mild-steel surge bunkers, whence the larger size is fed by gravity to a Birtley standard "Vee" pneumatic separator on the Maude side and a super "Vee" pneumatic separator on the Eccles side. The fines in each case are passed through an aspirator to remove the dust, after which the de-dusted coal is treated on a standard "Vee" separator on the Maude side and a super "Vee" separator on the Eccles side.
The cleaned coal from each separator, in the case the Maude pit, can be delivered direct to trucks as singles, 1 in. to 3/8 in., and duff in. to zero with or without dust. In the case of the Eccles coal sized products are not made, and the cleaned product from both separators is discharged to the belt conveyor B and then to a scraper conveyor. whence it is discharged into wagons along with the hand-picked round coal to be shipped as unscreened gas. Middlings from the separators are returned to the elevator for recirculation by means of the belt conveyors R and R1.
Refuse is taken by means of conveyors N, N1 and N2 to a bunker W alongside the plant, whence it is discharged into colliery company's wagons. All these belt conveyors run at a speed of 300 ft. per minute.
All four pneumatic separators, together with the two aspirators and the surge bunkers, are linked up by means of mild-steel trunking to a pair of Birtley-Waring dust filters, where the whole of the air used in the plant is de-dusted, the clean air being handled by a special type of fan on the suction side of the filter. Each filter is equipped with a reversing valve, so arranged that either filter can be turned over from the fan suction to atmospheric pressure, and the filter cleaned without mixing the clean and dirty air streams. The aspirated dust from the Eccles coal can be discharged on to the clean coal conveyor B, or, alternatively, to the scraper P (which is of the totally enclosed type) and which also handles the dust from the Maude pit coal. By-pass chutes are provided so that the dust can be re-mixed with the cleaned coal in either case, or, alternatively, taken out of the plant and burnt under boilers.
The oversize (3 in. to 1 in.) coal from the rotary screen is delivered by means of a launder to the wash box S. In the case of the Eccles coal, the washed product is passed over the drainage screen U and mixed with the dry-cleaned 1-in, to zero smalls. After washing, the Maude pit coal passes over a drainage screen and is then sized by means of the jigging screen V into 3 in. to 2 in. and 2 in. to I in.
Refuse from the washery is discharged by means of elevators along with the refuse from the dry-cleaning plant. In view of the fact that only nuts sizes are washed, the amount of slurry made is very small, and the concrete settling ponds provided are quite adequate for dealing with it.
With regard to the construction of the plant, the building consists of a mild-steel framework having brick-filled panels and ample glazing. The elevators in use are of the continuous positive-discharge type, so designed that the following bucket discharges on to the back of the leading bucket at the elevator head. All the belt conveyors are enclosed by mild-steel covers, the troughing idlers, which are of the five-shaft type, being provided with ball bearings arranged for grease-gun lubrication. Also, self-aligning ball races are fitted in the take-up gear.
The motors for driving the various units are of the squirrel-cage high-torque type, totally enclosed or enclosed ventilated according to the situation. Those of under 20 H.P. are arranged for direct starting, but the higher powered units are resistance-controlled. The switchgear consists of an open-type contactor panel housed in a separate room on the ground floor, and is operated from a push-button panel on the separator floor. As is now standard practice with Birtley plants, all the motors are arranged for sequence starting, push-buttons being provided for stopping individual motors.
Drawings and Photographs accompanying the article
Article reproduced from a copy of the magazine held at National Mining Museum Scotland, Newtongrange, Midlothian.
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