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February, 1955

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The British coal-mining industry has been conscious of the need for treating mine dusts with care ever since Buddle suggested the explosibility of fine coal dust in 1803. During the last 10 years or so the emphasis has shifted however, and although due respect is still paid to the explosive properties of the dust, it is becoming increasingly realised that working in dust clouds can do as much damage to the aggregate health of the workers in the industry as the more spectacular hazards.

This realisation has come at a time when increased mechanisation underground has brought an increase in the production of dangerously fine dust. Consequently dust-prevention measures in collieries are now being applied on an unprecedented scale, with particular attention being paid to suppression at source through such means as wet cutting, wet drilling and water infusion. At the same time dust collection during transport and handling has not been neglected and many conveyor-loading and transfer points, tippler stations, skip-loading pockets, and screens have been equipped with devices for controlling dust.

The need for such devices is especially apparent in the newer heapstead arrangements. In many of these, manpower requirements are kept low by the simple expedient of having the shortest possible route for the cars or tubs, and to this end the tipplers are placed comparatively near to the mouth of the winding shaft.

One of the most successful of these new heapstead arrangements is to be found at Lynemouth Colliery* in the No. 3 Area of the Northern (N. & C) Division of the National Coal Board, Here a notable re-organisation scheme is being implemented with a view to increasing output from an original figure of less than 1,000 tons per day to as much as 7,000 tons. At present the scheme may b said to be about half completed as far as the surface arrangements are concerned daly output is in the neighbourhood of 3,000 tons and, although the downcast shaft is currently being widened and re-equipped, the modernisation of the upcast (No. 2) has been completed to the satisfaction of all concerned.

At this shaft the coal is raised, by the only fully automatic a.c. winder in the country**, in Hudson five-ton capacity mine cars which are carried, one at a time, in Head Wrightson steel cages. For handling the cars on the surface the Lofco system, devised and supplied by Qualter Hall & Co. Ltd., is installed, and such is its efficiency that only one man is required for normal coal-winding operation of the entire heapstead including the winding engine. In this system of cage changing, car travel is minimised by the provision of two identical 14 ft. dia. rotary tipplers one on each side of the shaft about 6 ft. from the cage. From each cage the loaded cars brought by alternate winds are propelled, by remotely-controlled oil-hydraulic rams, to the same side of the shaft. After emptying, the car does not go through the tippler but is returned to the cage in time to discharge the next loaded car on to the opposite side of the shaft,

As in all other Lofco installations, breakage is minimised by the provision of two-speed drives and shaped delivery chutes on the tipplers, and to help confine any dust raised during tippling the tippler sides are enclosed in sheet metal. Additional precautions were felt to be necessary, however, because the tipplers are situated inside the airlock building and are therefore under a suction of rather more than 2 in. of w.g. and this suction was expected to prolong the suspension in the atmosphere of any dust raised until the dust was drawn off into the main mine fan. Apart from aesthetic considerations, not only would such a proceeding have a deleterious effect upon the equipment inside the airlock and on the mine fan, its drift and evasee, but as the control cabin for this cage-changing and winding is also inside the airlock it may be expected that poor visibility for the operator would do much to militate against the efficient operation of the plant.

Accordingly the Area Engineering Staff considered how dust from the tipplers could be prevented from entering the airlock, and as a result a contract for dust-control equipment was placed with Thermix Industries Limited, London, S.W.1. In collaboration with Mr. B, Eddershaw, Area Chief Engineer, this firm, specialist in dust control and recovery installations designed a scheme for collecting the dust from the tipplers by means of hoods, ducting and a Tubix multi-tubular collector unit, The equipment was manufactured by Thermix Industries Limited and installed under their supervision by the Area Engineering Staff, Through the kindness of Mr, D. Hindson, Area General Manager, we were allowed to visit the colliery and publish the following description.

A diagrammatic layout of the dust-collection scheme is given in Fig. 1. Along the top of two sides of each tippler are collecting hoods constructed in 1/8 in. steel sheet, there being three such hoods to each side. Each set of three hoods on the south-east side of the tipplers conjoins into a rectangular sheet steel duct 18 in. by 18 in, which in turn joins a 24 in, by 18 in. manifold near a point where the manifold receives from the three hoods in the north-west side of the tippler.

The two manifolds lead into the Tubix dust-collector unit. Although widely used in other industries in this country and in collieries overseas this form of dust collector is not, as yet, well known in British collieries. Basically it is a multi-tubular separator and utilises a principle already well known for the separation of dusts from gases. The Tubix incorporates a number of patented refinements however, which enables the manufacturers to claim for their product exceptionally high recovery efficiencies together with low maintenance costs and trouble free operation. In the actual cyclones there are no guide vanes to wear and require replacement for example, the necessary spiral motion being imparted to the particles by means of a specially shaped inlet slot, Moreover, in the dust-collection chambers the cyclones are arranged in a manner which allows the coarser particles to be decanted from the air stream without passing through the cyclones.

The construction and principle of the Tubix device will be apparent after reference to Fig. 2 which represents a simplified cross-section through a basic unit, As will be seen it consists of a number of small cyclone tubes arranged in parallel at an angle of 45 to the horizontal and welded between two tube plates. Dust-laden air enters at the left-hand opening which although shown in the vertical plane in Fig. 2 could, if required to suit the ducting, just as well be in the horizontal plane. Having passed through the opening into the space between the tube plates the larger particles (usually those above B.S. Sieve No. 325) fall through the spaces between the cyclone tubes into the right-hand side hopper — the decantation hopper.

Meanwhile the finer particles entrained in the air current enter the Tubix cyclones by way of the inlet openings at the side of each and pass into the annular space formed between the inner and the outer tube of each cyclone. The air and fine particles follow a helical path in a downward direction, the particles being separated from the air stream by centrifugal force which directs them against the periphery of the outer tube, where they descend in a spiral path and are discharged through a conical opening in the bottom of the tube into the left-hand-side hopper, the centrifugation hopper. The cleaned air rises and leaves the cyclone through the inner tube into the outlet opening which is at the top right-hand-side of the unit, and which, like the inlet opening, could be arranged in the horizontal plane if considered desirable,

The number of cyclone tubes, their inclination and the material of the construction depends upon the particular duty, and in the Lynemouth installation they are constructed of heavy gauge mild steel. A total of 80 tubes is inclined at 45° and arranged in two equal banks,

Emptying the separated-dust hoppers may be done manually if required, but the collector at Lynemouth is emptied automatically, being fitted with rotary discharge valves. These, which are also of Thermix manufacture, are driven by a Metrovick motor controlled by Allen West switchgear, and dust leaving the collectors travels by gravity through ducts to the main conveyor delivering to the coal-preparation plant.

Air is drawn from the tipplers through the dust collection unit by a centrifugal fan, which is driven through vee belts by a Metrovick motor controlled by Reyrolle switchgear. This fan exhausts sufficient air to produce a depression of 2 in, of water gauge and, as Fig. 1 indicates, is arranged so that no dust-laden air passes through to cause excessive wear on the fan blades and casing; exhaust air is ducted into the upcast shaft. To ensure that the air drawn by the fan consists of that taken from only that tippler which is actually tipping, Thermix Industries Limited have incorporated a butterfly valve in each of the twin manifold ducts. These valves are pneumatically operated through Climax cylinders which are automatically controlled by valves mounted on the tipplers. Any tendency of the dust cloud to blow back through the car opening in the tippler is prevented by "curtains" of used conveyor belting which the car pushes aside on entry and exit but which remain in the closed position during the rotating period.

The dust collector unit, together with the fan, its motor and control panel, is housed in a separate room, Thus, which is pleasantly decorated in cream and blue and conforms with the general architectural features of the new surface, is positioned immediately behind the winding-control cabin and immediately above the main conveyors serving the coal-preparation plant.

Because the dust-collection unit discharges directly on to the conveyors daily weighings of the dust recovered are not now made. During the acceptance test period, however, figures showed that over 97 per cent, of the dust picked up from the tipplers was recovered by the Tubix plant. At the same time it was noted that nearly 30 tons of dust, which would otherwise have been distributed into the atmosphere to waste, or to disfigure and damage equipment inside the airlock and main fan installation, were diverted to the washery each week; maintenance charges during the year the plant has been installed have been negligible. Perhaps the most apt indication of the satisfaction given by the Tubix plant may be obtained, however, from the fact that a second installation may be ordered for the Lynemouth No. 1 shaft heapstead which is currently being re-equipped with Lofco car-handling plant.

* See Colliery Engineering, page 93, March, 1951 and page 503, Dec., 1953.

** See Colliery Engineering, Page 503, Dec., 1953.

Drawings and Photographs accompanying the article