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May, 1957
Coal preparation at Horden
To increase the mechanical coal-cleaning facilities at Horden Colliery, a 210 tons per hour coal-preparation plant erected by the Fraser & Chalmers Engineering Works of The General Electric Co. Ltd. has recently been commissioned. This plant, together with the existing Baum washer and Birtley dry cleaner, cleans the whole of the coal from the pit
Horden Colliery, situated in the No. 3 Area, N.C.B., Durham Division, obtains coal from four seams, Five Quarter, Main, Low Main and Hutton, all of which have been yielding a good quality gas coal since the turn of the century. The bulk of the coal is worked by longwall methods and is won by hand and loaded on to conveyors, although a proportion is obtained by bord and pillar mining. It is not known exactly how far the seams extend out under the sea bed, but the coal faces are at present between two and three miles from the coast. The whole of the output is raised through two shafts, North and South, each 400 yards deep. A third shaft, the East, also 400 yards in depth, is used for the transport of men and materials.
Previously only coal below 2¼ in. in size has been mechanically cleaned, by a Baum washer and dry cleaning tables, the larger, or 2¼ in. plus coal, being hand cleaned on a battery of six picking belts. Due mainly to changes in mining methods, it became necessary to clean more of the coal mechanically.
In March, 1953, the N.C.B. decided to order a Chance coal-preparation plant from The Fraser & Chalmers Engineering Works of the G.E.C. to clean the whole of the 8 in. by 1½ in. coal. The plant has been designed to work in conjunction with the existing raw coal tipplers and screens, but a new screen and picking belt were to be provided for hand cleaning the plus 8 in. fraction.
The plus 1½ in. coal is cleaned at the rate of 210 tons per hour, 170 tons per hour of 8 in. by 1½ in. passing through the Chance cone and the remaining 40 tons per hour constituting plus 8 in. coal.
The run-of-mine coal is wound in tubs of 11 cwt. capacity which are discharged by six rotary tipplers on to jigger screens. The existing tipplers and screens dictated the position of the new washery, but the colliery was extremely congested in this vicinity and considerable thought had to be given to the problem of installing the new washery in the space available. It was only by removing one of the rail tracks to accommodate the basement of the washery that the scheme could be carried out. It was inevitable that the installation of the new plant would deplete still further the already limited "fulls" wagon standage space and present yet another problem. A solution was found by loading the clean coal to wagons from conveyors running in the opposite direction to the travel of the wagons. This arrangement would not permit the use of orthodox boom-loading practice for the clean sized coals, but it did at least provide standage for three additional wagons on each loading track. Although at the time it was appreciated that this method of loading must unavoidably result in the creation of more degradation than desirable in the clean coal, it was considered that, because the coal would be used for carbonisation purposes, it was of greater importance to obtain maximum wagon standage at each loading point.
Although the conditions of the site were not all that could be desired from a constructional point of view, virtually no interference was caused to the normal colliery working during the alterations to the existing and the construction of the new plants.
Flow of coal
Run-of-mine coal is discharged by six rotary tipplers.* From these tipplers the coal passes over screens, Fig. 1, where the minus 1½ in. round fraction is removed. Oversize, or plus 1½ in. is collected by belt conveyor V and passes to conveyor U for subsequent discharge to a further screen. This screen separates the coal at 8 in. round and in addition removes any minus in. degradation created by previous handling. The plus 8 in. material, after hand picking on picking belt S, is loaded to wagons by means of boom loader Q. Meanwhile 8 in. by 1½ in. coal is carried from the screen to belt conveyor P to feed direct into the Chance cone.
The Chance cone has been initially installed for a single gravity-clean coal and refuse — separation although provision has been made in its construction for the addition of middlings extraction equipment.
From the Chance cone the clean coal is separated at 2½ in. round; the smaller fraction discharges on to conveyor E and the larger to conveyor G. Both products are loaded to wagons direct from these belt conveyors.
Refuse discharged from the cone is de-sanded and de-watered, after which belt conveyors B and A carry it to a 1,200 cu. ft. capacity bunker whence it is loaded to wagons for disposal by tip.
Provision has been made in the design of the plant for the raw coal to be diverted to wagons in an emergency via conveyor Y, thus avoiding interference with the normal winding rate from the pit. This outloaded coal can be re-introduced into the plant by means of conveyors X and W collecting from a track hopper.
Belt conveyor Y, in addition to its use in an emergency, could be used as a picking belt for preparing large hand-selected coal for sale since a two-speed worm reduction gear box has been fitted into its drive.
Effluent bled from the Chance sand and water system is pumped to the Baum washer for treatment with the minus 1½ in. coal. For dealing with effluent from the Baum plant a bank of froth flotation cells and a rotary vacuum filter have been installed by Unifloc Limited in the new washery building. After de-watering, the particles of small coal in the form of filter cake, pass out for mixing with the clean small coal from the Baum washery.
Services available
Water and air required for the plant is provided through the normal colliery services, the amount of makeup required being of the order of 50 g.p.m. of water and 150 cu. ft. of free air per min. compressed to 60 lb. per sq. in. The air is necessary for the completely automatic operation of the refuse gates.
The sand required for the washing medium is brought to the plant by rail and unloaded direct into a concrete pit. From the pit the sand is introduced to the plant by a motor operated hoist. Approximately 3 lb. of sand per ton per hour of coal feed to the Chance cone is adequate for the satisfactory operation of the plant.
Guarantees
Guarantees submitted to the National Coal Board took the following form:-
(1) That with the washery working on a specific gravity of 16 the ash content of the clean coal would not differ from that theoretically possible by more than 025 per cent.
(2) That an average sample of the discard from the plant would not contain more than 1 per cent. of floating material in a gravity of 16. Since the commissioning of the plant, part of the cobbles, 8 in. by 2½ in. coal, after treatment in the washery has been marketed for household purposes.
In consequence the washery has been operating at a sp. gr. of between 150 and 155 in order to prepare a satisfactory domestic coal. The results of tests which have since been carried out have proved that the washery is operating well within the guaranteed limits.
Future plant
Although the Chance cone at Horden has initially been installed for single gravity, two-product separation, allowance was made in its design for the addition in future of middlings extraction equipment if required. The addition of this middlings extraction plant would not in any way prevent the Chance cone from operating at a single gravity if desired at times, for it is an extremely simple matter to convert the cone from a single-gravity to a two-gravity separation and vice versa. Moreover, the changeover can be made as often as necessary through the shift, for the reaction of the sand and water mass in the cone is instantaneous.
* "Dust Control at Tipplers and Screen Houses" Colliery Engineering, p. 72, Feb., 1955.
Drawings and Photographs accompanying the article
Article reproduced from a copy of the magazine held at National Mining Museum Scotland, Newtongrange, Midlothian.
Contains public sector information licensed under the 
