Tweet

---

October, 1930

---

Horden Colliery has a peculiar interest to us in that it was one of the first which we visited when we began these descriptive articles over six years ago. Horden has ever had a well-deserved reputation for up-to-dateness, and we were naturally interested to see what new measures had been taken to maintain this position. We were glad, too, to renew our acquaintance with Mr. A. E. Charlesworth, the Chief Engineer to the Company, who kindly conducted us around the plant. Three notable changes had been made: an extensive dry-cleaning plant had been erected, water-tube boilers for pulverised fuel firing had been substituted for a battery of Lancashires, and new water-softening equipment had been put into commission. As brief particulars of the softening plant (which combines feed-heating arrangements) were given in a recent issue, we shall confine ourselves to the two remaining items.

Dry-Cleaning Plant.

The new cleaning plant, which was constructed and erected by the Birtley Iron Co. Ltd., is the largest of its kind in Europe and is designed to handle 250 tons per hour. All this coal is 2¼ in. or under and is brought from the colliery screening plant either by a belt conveyor, 48 in. wide by 272 ft. long, or alternatively by trucks, discharging into a 200 tons capacity underground bunker (Fig. 2). Two elevators of the continuous bucket type, each driven by a 40-H.P. motor and capable of handling 150 tons per hour, raise the coal from this bunker to the top of the building. Each of the elevators which, by the way, are 104 ft. between the centres of the tumbler shafts, feeds one-half of the plant which is divided into two distinct sections, north and south, each capable of dealing with 125 tons per hour and so arranged that either or both can be operated according to market requirements.

On leaving the north elevator the coal is passed over a Hum-mer vibrating screen fitted with 7/8-in. mesh, the oversize (2 in. - 7/8 in.) being discharged into a sized coal hopper whilst the undersize is passed to a further Hummer provided with 3/8-in. mesh. As before, the oversize (7/8 in-3/8 in.) is delivered to a hopper, the undersize being submitted to final screening over a 3/16-in. mesh double Hum-mer to which it is carried by a 36-in. belt conveyor and a cross-scraper. In this case both the oversize (3/8 in.-3/16 in.) and undersize (3/16 in.-0) are delivered to hoppers.

This arrangement is duplicated on the south side of the plant and the eight sized coal hoppers, each of which has a capacity of about 12 tons, are situated directly over a corresponding number pneumatic separators on the floor below. In the case of the sizes from 2 in. to 3/16 in. the coal is delivered by gravity directly into the feed pan of each of the separators, but before reaching the feed pans of the machines treating the smallest sizes (3/16 in.-0) the coal is passed through cascade-type aspirators in which the bulk of the dust is removed.

The separators are of the standard "Vee" type and are totally enclosed in mild-steel hoods which are connected by trunking to the suction ranges leading to the dust extractor. Inspection doors are provided on each side of the hoods so that separation can be under continuous observation, and any fluctuations in the stone content followed up by the adjustment of the cutting fingers fitted at each side of the machines. The usual three products are made — clean coal, middlings and refuse — these passing down separate chutes to the next door where the collecting belts are installed.

The clean coal is collected on two conveyors, 48 in. wide and 83 ft. in length, each having a capacity of 250 tons per hour, the chutes feeding on to these belts being so arranged that any separator can deliver to either conveyor, thus enabling a sized or mixed product to be obtained. These conveyors deliver into bunkers for loading into trucks or on to a 48-in, wide cross conveyor, 61 ft. long, which discharges into trucks on another road. Middlings are collected on a 24-in, conveyor, 90 ft. in length, and can be delivered direct in trucks or, as is normally the case, discharged to another 24-in, wide conveyor, 83 ft. long, which returns them to the main raw-coal conveyor belt for re-treatment in the plant. The shale is carried by a 20-in, conveyor, 83 ft. long, having a capacity of 45 tons per hour to a further conveying unit having a length of 570 ft., which discharges it into a refuse bunker to be dealt with by an aerial ropeway. These conveyors, in common with all others throughout the entire plant, are fitted with ball bearings throughout, those of the head and tail shafts being self-aligning.

Fans by Standard & Pochin Pros. Ltd. supply the air to the separators and are situated on the floor below the conveyors ; each fan is arranged vertically beneath its separator. The fans are driven by two 90-H.P. motors, one for the north and the other for the south side, clutches being provided for shutting down any fan if required.

The coarse dust from the aspirators is delivered to trucks for use in the pulverised-fuel plant, or mixed back with the clean coal as desired. The air-borne dust from the aspirators, together with that from the separator hoods, is taken to the main suction ranges whence it is collected in four Waring-type filters. Each filter is provided with a cyclone in which the larger particles of dust are deposited, and a bag filter mounted directly above the cyclone in which the finest dust is collected. The dust-extractor fans, which are housed in a separate building, are arranged on the suction side of the filters so that they only deal with clean air. Valves are arranged on the top of each collector casing so that they earn be turned from "suction" to "atmosphere" for the purpose of cleaning the fabric filter bags.

The dust is automatically discharged by means of balanced flopper valves from the bottom of the cyclones into a bunker situated immediately below the collectors, whence it is elevated to the boiler house for use in the pulverised-fuel plant.

The electrical equipment consists of 21 motors ranging from 3 to 95 B.H.P. of the "Metrovick" high-torque squirrel-cage type, controlled by a main contactor board and operated by push buttons from the separator floor, the contactors being so arranged that on the operation of a single push button the whole of the motors start up in correct sequence at 3-second intervals. A single "stop" push button closes down the complete plant and a further "stop" push button is provided for each motor, the contactors being so interlocked that in the event of a key motor being stopped, other predetermined motors in the sequence of the key motor will also stop, thus preventing flooding at any point in the system.

The building itself consists of a steel framework with brick panels and reinforced-concrete floors ; special glazing which is not subject to damage from variation in temperature and set in non-corrodible bars is provided in the roof and sides of the structure.

Pulverised-Fuel Boiler Plant.

The new steam-raising plant consists of three Babcock & Wilcox standard land-type water-tube boilers, each having a heating surface of 9,860 sq. ft., and designed for a safety-valve loading of 205 lb. per sq. in. Each unit is capable of evaporating 50,000 lb. of water per hour from feed at a temperature of 90° F. into steam of 200 lb. pressure superheated by 100° F.

The pulverising plant is arranged on the unit system, i.e., a separate pulverising mill to each boiler. Single disc-type pulverisers, each capable of dealing with 5 tons of fuel per hour, are in service, and the fuel burners are of the horizontal forced-draught dispersive type, the equipment being complete with the necessary fans, pipe lines, air ducts for the admission of primary and secondary air, and flat suspended arches of the Liptak type. Adequate ash, furnace and inspection doors are provided in the furnace to enable the closest possible inspection of furnace conditions at all times.

Each boiler is set separately and has four 54-in. longitudinal steam and water drums, so that ample steam reserve is provided against sudden demands for load. The units are complete with Babcock & Wilcox integral super-heaters, arranged to provide a final steam temperature of 490°.

Each boiler is fitted with a Green's economiser of the tri-tube type, composed of 300 pipes and fitted with circulators to ensure equalisation of temperature. Arrangements have been made for by-passing the economisers when this is considered desirable.

Each boiler is entirely self-contained, having its own self-supporting steel chimney of the gussetted type, 6 ft. in diameter and 70 ft. high, together with a motor-driven induced-draught fan. The boiler plant is equipped with a full complement of accessories, including two Weir feed pumps, Kent's water meters, draught gauges, Electroflo CO2 recorders and steam flow meters. The boilers are also equipped with feed-water regulators of the Thermofeed type.

The boilers are fitted with Babcock calorised Diamond soot-blowers in order to obtain a maximum continuous efficiency, and an interesting arrangement has been adopted in connection with the supply of water to the hot-well. Feed water is pumped from the pit, and in addition to being heated by exhaust steam in the heat exchanger mentioned in our previous article it is also circulated through the cooling jackets of the air compressors. The boilers are fitted with a continuous blowdown, the sludge being discharged to an underground tank.

In addition to the boiler plant, Babcock & Wilcox Ltd. have been responsible for the manufacture and erection of the whole of the steelwork utilised in connection with the boiler-house building, steel coal bunkers, and a complete coal- and ash-handling plant.

The boilers are, of course, fired with the "air-borne" and "aspirated" coal dust extracted at the coal-cleaning plant. The "air-borne" dust is collected in a ferro-concrete receiving hopper, where it is elevated and discharged on to a dust-tight drag-link distributing conveyor, which delivers it to the overhead coal bunkers. Each hunker has a capacity of 90 tons of fine coal. The "aspirated" dust is conveyed by wagons from the pneumatic cleaning plant and discharged into a receiving hopper below ground, whence it is delivered by an inclined chain and bucket elevator to the distributing conveyor. Provision is also made for dealing with mixed lump coal, a 4-roll breaker being provided to reduce it to 1½ in. cube before it is passed to the bucket elevator. The coal-handling plant is designed to deal with 30 tons of coal per hour. Each of the coal bunkers in the boiler house is provided with a dual outlet, one of which is arranged to feed direct to the pulverising mills and the other into a portable dust-tight automatic weighing machine. This machine is mounted on rails and can be fixed under any bunker as desired for the purpose of carrying out a test on any individual boiler.

The ash-handling plant consists of a water-immersed scraper conveyor, into which the ash and clinker is discharged from the furnace hoppers. This feeds an inclined automatic skip hoist arranged with a vertical lift of about 60 ft. to discharge into an ash storage bunker having 30 tons capacity.

The plant is designed to operate with fuel having a calorific value of 8,500 B.T.U.s per lb., and while rated for a normal evaporative output of 50,000 lb. of steam per hour, each boiler is capable of carrying an over load of 20 per cent. continuously if required.

The necessary main steam piping, comprising 9-in., 12-in, and 15-in. main headers with 7-in. branches to the boilers, together with auxiliary mains, mild-steel feed piping and blow-down piping, was also manufactured and supplied by Babcock Wilcox Ltd. The necessary boiler feed supply is provided by two Weir turbine-driven rotary feed pumps, each capable of delivering 20,000 gallons of water per hour. Each of the induced-draught fans is coupled direct to a 60-H.P. electric motor, running at 580 r.p.m. and designed to operate at 2,800 volts, 3 phase 40 cycles.

The main dimensions of the boiler-house building are approximately 122 ft. long, 68 ft. wide, and 35 ft. 6 in. high from firing-floor level to eaves. The pulverising mills, ash conveyor, &c., are placed in the basement, the floor of which is 12 ft. 6 in. below the firing-floor level. The firing floor, shown in Fig. 13, is laid with interlock steel flooring to provide light in the basement.

As the fusing point of the ash is very low, care has to be taken that the furnace temperature is not excessive even so an efficiency of 81 per cent. is obtained under normal working conditions.

For the sake of completeness we may reiterate that the softening plant for these boilers is of the lime-soda solution type, and is capable of handling 200,000 lb. of water per hour. It was supplied by William Boby & Co. Ltd. and comprises a heater softener and a mechanically cleansed gravity Silex filter, combined with continuous blowdown and heat recovery equipment. The water supply is derived from the pit and has an initial hardness approaching 28 degrees after passing through the treatment plant the water is passed to the boilers with a hardness in the order of 5 degrees. The use of a heater softener, of course, results in great economy in softening reagents.

IMPROVEMENTS AT HORDEN COLLIERY. — It has been pointed out to us that in our article under this title in the October issue we were in error in stating that the initial hardness of the water (28°) was reduced to 5° after passing through the softening plant. We are informed that, as a matter of fact, the hardness is reduced to much below this, the results of 50 tests averaging 1.8° hardness and 4.1° alkalinity.

Drawings and Photographs accompanying the article