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Colliery Engineering

January, 1934

Machinery

All the creepers are of similar construction, having two strands of mild steel chain with cast-steel rollers mounted on hollow steel spindles. Enots nipples are fitted for grease-gun lubrication, and the carrying horns are pitched at 8 ft. centres.

In order to take full advantage of the reception sidings, the retarders have been designed to enable them to continue working and at the same time allow the tubs to stand up the incline. As soon as the track brakes at the bottom of the retarders are released, to allow the tubs to run to the tipplers, the tubs are immediately under the control of the retarders. Each creeper and retarder is driven by an independent motor, through cast-steel machine-cut spur reduction-gears. All shafts are fitted with Skefko self-aligning ball-bearings in dustproof housings. The main creepers, A, on each of which it is possible to have fifteen tubs, have automatic brake gear fixed on the head-shaft, which is interlocked with the starting clutch; thus, in the event of the creepers stopping when full, the chains are prevented from running back. As an additional precaution, safety catches are fitted and act on the body of the tubs.

The tipplers are of the side-revolving type and arranged to take either one long tub or two short ones. A special feature of the design is the provision of doors, which are directly over the tubs and only open when the tippler has turned through about 150°. By this means the coal is kept under control and only allowed to slide gently out of the tubs. The whole of the tippler operation is under automatic or manual control at will. When under automatic control it is only necessary to keep a supply of full tubs in front of any tippler for that tippler to deal with them continuously.

In order to effect this, the tipplers are loaded by pneumatic rams, the full tubs being locked in position by the outgoing empty tubs. On their return stroke the rams set the tippler in motion, and when it has completed its revolution it unlocks the empty tubs and operates the controls both of the rams and the chocks holding the full tubs in front of the tippler; the whole cycle then begins again.

Each jigging screen is set at a small angle and is capable of accurately sizing ten tubs of coal per minute. The screen is built in two balanced sections, each carried by a series of ash hangers and driven by eccentric sheaves and straps through mild-steel connecting rods. Each driving shaft is fitted with heavy flywheel driving pulleys and a friction clutch operated from a distance.

The picking belts are 51 ft. centres, by 4 ft. 6 in. wide, and consist of two strands of short-pitched chain and mild-steel joggled plates, carried on cast-iron rollers running in self-aligning ball bearings. The belts are driven at the delivery end through a single train of cast-steel machine-cut gearing, through the intermediary of a Ferodo-lined friction clutch, provision being made for remote control. An interesting feature about the belts is that they are totally enclosed, steam pipes being provided between the top and bottom plates for heating purposes, in order to secure greater comfort for the pickers. This little forethought will doubtless increase the efficiency of the men in cold weather.

Pulsating loaders are fitted at the end of each picking belt, and consist of two interlinked sections. The first is fitted with a screen plate to take out any small coal which may be made during the process of cleaning, and the second consists of a plain steel trough, pivoted and fitted with gear enabling it to be lowered into the wagons, thus delivering the coal without any drop. The motion of the trough is such that the stroke or traverse varies inversely with the angle of slope, thus keeping the travelling speed of the coal constant whatever the position of the trough in the wagon. The loaders are raised and lowered by means of power-driven friction gear.

The conveyors for dealing with the stone and intergrown coal are of the double-trough scraper type, arranged for conveying on both upper and lower troughs simultaneously. The inclined stone conveyor to the hopper and the inclined intergrown coal conveyor to the crusher are of similar design, but of the single-trough type. All the remaining conveyors dealing with the coal are of the troughed-band type, varying in size from 18 in. to 30 in. wide. Both top and bottom idlers have machined faces and are fitted with Timken bearings throughout, arranged for grease-gun lubrication.

Main inclined conveyors to the various cleaning plants are fitted with automatic cam gear which prevents them from running back if the power is cut off while the conveyors are loaded. Those conveyors running outside the main buildings are supported in totally enclosed gantries. The refuse conveyor from the Birtley plant is of the troughed-band type, 18 in. wide by 195 ft. long, and delivers to a scraper conveyor 24 in. wide by 250 ft. long, the latter acting as common refuse conveyor for the spirals and the washing plant.

For driving purposes the plant is arranged in units of convenient sizes, each driven by a separate motor. Adjacent units can be coupled together so that two units can be driven by one motor in case of emergency. In all the sections of the plant the motors are controlled by contactor panels located in dustproof houses. By this means stop and start buttons can be placed in most convenient positions for the separate units. All shafting is mounted in Skefko self-aligning ball bearings with dust-proof housings, and friction clutches are fitted for easy control of picking belts and screens, &c. Throughout the gearing is of machine-cut cast-steel.

Spiral plant

To avoid breakage the inclined conveyors UU deliver the coal to the bunkers by spiral chutes. These bunkers have sufficient capacity to absorb all fluctuations in quantity and provide a steady supply for the screens, which are pitched at a small angle to give accurate sizing and run at 160 r.p.m. The screens are made in two balanced sections, carried on ash hangers and driven by two pairs of eccentrics set at 180° on the main shaft, which is provided with flywheels and driving pulleys. The small coal below 1 in. is removed and the remainder, sized into doubles, trebles and cobbles, is delivered to the spirals which automatically remove stone and intermediates, the clean coal being passed to flat bands arranged as inspection conveyors. These bands deliver the coal to wagons by the pulsating loaders.

Air cleaning plant

This plant was installed to deal with 140 tons per hour of 1 in. to zero coal. At the head of the plant, the raw coal feed is discharged on to the scraper conveyor which distributes the load over two type-60 Hum-mer screens, each 8 ft. x 4 ft. and fitted with 0.375 in. mesh. The undersize from each of these screens is discharged to a pair of similar Hum-mer screens equipped with 0.095 in. X 3 in. screen-cloths. The 0.375 in. oversize and the 0.375 in. to 0.095 in. product are each fed to a pair of mild-steel storage hoppers which in turn feed the pneumatic. separators. These latter comprise two Birtley standard "VEE" separators which treat the 1 in. to 0.375 in., and two similar machines treating 0.375 in. to 0.095 in. material. Each separator turns out two final products, and approximately 10 per cent. of the feed is recirculated as middlings. The clean coal is taken by means of a belt conveyor to a grading plant, where it is normally sized into singles, pearls and peas. Facilities are also provided for mixing any of these sizes, adding the undersize from the Hummer screens if desired. This grading plant is quite distinct from the cleaning plant, and enables any desired grade of coal to be made to suit the market requirements quite independently of the grades necessary for cleaning purposes.

Middlings are recirculated by means of chutes to a belt conveyor which discharges on to the incoming raw coal conveyor. Refuse is fed by means of chutes to a belt conveyor which delivers to the main refuse conveyor T. Undersize from the 0.095 in. screens can be delivered direct to wagons, by means of a belt conveyor, either separately or with the filter dust, or, alternatively, it can be added to the clean coal as previously mentioned. The four separators are enclosed in mild-steel hoods which are connected by means of air-ducts to two Birtley Waring filters. These, the bodies of which are reinforced concrete, are connected to a single fan, and both filters are equipped with reversing valves for cleaning purposes. The collected dust at the bottom of the reinforced-concrete cones is conveyed from the plant by means of worm conveyors.

All the motors are arranged for contactor starting, the contactor panel being housed on the ground floor, whilst the whole of the plant can be controlled from a pushbutton panel on the separator floor. The whole system is interlocked so that should any unit stop due to the operation of the push-button, overload, or leakage, all previous motors in the sequence will shut down simultaneously.

Washing plant

The Rheolaveur washery is designed to treat 225 tons per hour of 4 in. to zero steam coal, 50 tons per hour of 4 in. to zero house coal, and 10 tons per hour of intermediates from the spiral plant. Provision is also made so that, if required at some future date, a complete further installation for treating 125 tons per hour of 0.875 in. to zero coal could be installed with very little modification.

It is necessary for the house and the steam classes from 0.375 in. upwards to be washed and kept entirely apart, and for this reason it was necessary to instal two complete coal-washing units together with the necessary de-watering and classifying screens, separate storage, &c. In conjunction with these two installations there is one common re-wash trough for treating the shale and middlings evacuated by the first Rheo-boxes in each trough.

The clean coal passing over the ends of the troughs is delivered to main sizing screens, the cobbles and trebles being screened out and de-watered, and delivered by means of spiral chutes to their respective bunkers while the undersize is delivered to secondary screens. On these secondary screens the doubles, singles and pearls from both washing installations are kept apart and stored in their respective hoppers, while the undersize, together with the water extracted by both screens, is delivered to the re-wash cistern. From this cistern the material is elevated to the double fine-coal washing installation fitted with open-discharge-type Rheo-boxes. The clean coal passing over the ends of the first two troughs is de-watered on the peas de-watering Zimmers and stored in hoppers.

Drainage water is collected in the pump sump and raised by centrifugal pumps to the settling tanks for clarification. The fine-coal precipitating in this tank is piped to the two duff-washing installations, the washed duff passing over the ends of the troughs being de-watered on Zimmer screens and delivered direct to hoppers. A mixing conveyor runs the full length of the building and enables singles, pearls, peas and duff to be mixed together in any proportions, instead of being loaded as separate products. Shale is de-watered and delivered to the main refuse conveyor.

The accompanying flow-sheet illustrates the course of the coal through the washery, and it will be appreciated that the sizes of the grades mentioned can be varied within wide limits. Although this plant was designed for a total capacity of 285 tons per hour, we understand that it has under a prolonged acceptance test, treated 416 tons per hour without in any way affecting the washing efficiency of the plant, and the final washed product, together with the final shale was well within the guaranteed figures. Generous clarification area has been given and the reinforced concrete settling tank is fitted with an overflow ring to assist the process further. The clarified water is taken from this ring to supply the horizontal and the vertical currents in the washery, while the make-up water is introduced into circulation through the sprays utilised for spraying the washed coal. In the base of the settling tank structure is housed the re-wash cistern, and adjoining the structure is the house in which are the three main washing pumps, each having a capacity of 3,000 g.p.m. Two of these pumps are required to deal with the normal load of washery.

Refuse ropeway

The ropeway for the disposal of all the refuse from the three cleaning plants has a capacity of 60 tons per hour and is of hi-cable type. It is 2,464 ft. long, the carrying ropes being of lock-coil construction 1.375 in. diameter and the haulage rope of flattened-strand Langs-lay construction, 0.875 in. diameter. The buckets, which have a capacity of 15 cwt. each, are fitted with gravity-type hauling-rope grip and are automatically tipped by a movable gear. A self-righting gear at the loading terminal turns the buckets before they come under the loading-spout ready for filling. The standards on the sections arranged for tipping are 100 ft. high and the maximum rope span is 710 ft.

Buildings

The buildings are designed for ample floor loads and wind pressure, and particular care has been given to convenience of access and intercommunication. The number of stanchions and foundations has been reduced to a minimum, the floor girders being arranged to span two wagon-roads and the conveyor gantries having clear spans between houses; all possible clearance is thus provided on the ground for the sidings and wagons. Similar buildings are provided for the Duke pit heapstead, and the combined heapstead for the Carl and Bothal pits.

The buildings are steel-framed with 4½ in. brick-panelled sides; floors throughout are of reinforced concrete and the roofs are covered with corrugated asbestos sheets. Side windows in steel sashes, and roof lights in patent sash-bars, provide ample illumination. The roofs over the various picking belts are of north-light pattern. Wired-glass is used in all the roof lights, and cleaning platforms are provided.

The design and general layout of the whole of the reconstruction scheme were carried out by the engineering staff of the Ashington Coal Co. Ltd., in conjunction with Goodall, Clayton & Co. Ltd., of Leeds, with whom the order was placed for the manufacture and erection of the whole of the screening and grading plants, gantries, buildings, etc. The washery was also manufactured and erected by Goodall, Clayton & Co. Ltd., to the design of the Rheolaveur Company. The Birtley Co. Ltd. was responsible for the air cleaning-plant, and the aerial ropeway for the disposal of refuse was provided by R. White & Sons Ltd., of Widnes.

Drawings and Photographs accompanying the article