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Colliery Engineering

June, 1924

The Wilputte Plant.

Sixty ovens capable of coking 6,000 tons of dry coal per week comprise the battery. The oven chambers have an overall length of 40 ft., are 10 ft. 6 in. high and have a tapered width averaging 17¾ in. An interesting view of the silica brick work during course of erection is shown in Fig. 9. Fig. 14 gives a very comprehensive sectional view of the flues and regenerator chambers, with the air and gas inlets and the flue-gas outlets.

One of the chief merits of the Wilputte design is the efficiency of the heating arrangements. There is a separate regenerator for every flue and the ovens are heated from both sides, there being fifteen vertical flues on the coke side and thirteen on the ram side. When gas is burning in the vertical flues on one side of the battery the products of combustion pass along the horizontal flue at the top down corresponding flues on the other side, and through the regenerator. At the end of half an hour this process is reversed, air being drawn through the heated regenerator to meet the gas which is burnt to heat the walls and the regenerator on the opposite side. The temperatures make an interesting comparison with those obtained in the usual English practice; at the bottom of the ascension flues, where the gas and air meet for heating the oven walls, the temperature is 1,340° C.; about half way up the walls it averages 1,140° C., while in the regenerators a figure some 100° C. below the latter is attained. About 40 per cent, of the gas produced-some 170,000 cub. ft. per hour-is used for heating the ovens; the remaining 60 per cent. forms saleable product and in this case is consumed in the Company's adjoining steelworks for heating the soaking pits.

The whole of the battery is controlled from a chart room situated under the charging platform of the coal bunker. Here a pyrometer gives a graphical register of the temperature (290 to 300 deg.) of the waste gases at the bottom of the stack, while the gas pressures, the stack draught and the gas consumption to the battery are similarly recorded graphically. A view is shown in Fig. 16. The room also contains all the switch gear for the electrical plant on the battery. Gear for the changing over arrangements is situated in an adjoining apartment, but the adjustable automatic control forms one of the many interesting pieces of apparatus in the chart room and may be seen in the background of the illustration last mentioned. The air pressure to the ovens is created by a Keith fan driven by a Robey engine. This set, with a duplicate set which acts as a standby, is situated on the ground floor underneath the storage bunker and is thus immediately below the chart room. The governors and throttle valve of the engines protrude into the apartment above and are thus under the immediate observation of the chart room attendant. A few details of the special change-over gear may be of interest. An ordinary clock periodically makes and breaks electrical contacts to reverse the flue circuits. This is done through the intermediary of a small pilot motor driving a commutator shaft furnished with contacts, which start and stop the change-over motors in their proper time and order. The entire operation is automatic. First of all the gas is shut off from one side of the battery by a small 5-h.p. motor coming into action; in a short interval of time-about 15 seconds — a second 15-h.p. motor reverses the air and waste heat valves and dampers and the decarbonizing valves; about 15 seconds interval after this operation a third 5-h.p. motor opens the gas cocks on the opposite side of the ovens. Normally, this reversal takes place every thirty minutes. A view of one of the galleries showing the air main, the fuel gas main and the interconnected cocks will be seen in Fig. 31. The large main flues for the burnt gases run along each side of the battery below regenerator level.

The Gas Circuit.

Gas leaves the ovens by short ascension pipes about one-half the length usual in ordinary practice, and passes into two hydraulic mains. Branches from these meet at some distance away and a large single main, 38 in. in diameter, conducts the gas to the two sets of primary atmospheric coolers. A very comprehensive view of the latter, showing the main, will be seen in Fig. 19. The working temperature of the gas through the by-product plant may be controlled by regulating the quantity of cooling water and by varying the number of tubes in use. There is a third battery of the tubular serpentine coolers in the circuit immediately in front of the oil scrubbers. All three batteries are mounted over concrete trays; and the heated water is conducted to a small cooling tower situated on a lower level. The exhausters, as are the tar extractors and saturators, are in duplicate and are capable of dealing with 500,000 cub. ft. of gas per hour. They are constructed on the Root's blower principle, and were manufactured by the Connersville Blower Company. Direct coupled to 108-h.p. twin-cylinder vertical steam engines by Messrs. Marshall, they make 156 r.p.m. Fig. 20 gives a view of both the units. The tar extractors are of the rotary type and are driven electrically through worm drives. Saturators of the "direct" type constructed of cast iron lead lined and finished with central distributing pipes, are installed. Each is provided with a baffle dryer at the outlet through which the gas passes to secondary coolers and scrubbers.

The gas is measured by three Venturi meters supplied by George Kent Limited; one gives the total gas yield, a second records the amount of surplus gas by-passed to the steelworks, and the other measures that required for fuel to maintain the carbonising heat, which also passes through a small gas holder to ensure a constant pressure at the ovens.

Mechanical Arrangements.

The coal charging lorry, with the rest of the travelling gear used in the ovens, is electrically driven by 250-volt direct-current motors. The latter have considerably more power than is usual in English plants, and the gear is operated at a higher speed. This is desirable in view of the fact that the ovens work to a definite and speedy time schedule. Wellman, Smith Owen Engineering Corporation Ltd. were the manufacturers of all these machines. To guide the coke into the coke car across the gas gallery is a machine, seen in Fig. 25, which runs along the bench immediately below the sole level. It is furnished with a patent mechanism, operated by two 5-h.p. motors, for quickly lifting and removing the oven doors, and it also carries the clay boxes from which the doors are luted. The pushing and levelling machine runs on a track on the same level as the bottom of the regenerators. Separate direct-coupled motors are used for each operation, a system lending itself to much quicker operation than the usual clutch drives. The ram and the locomotion gear are each operated by 50 h.p. motors, while the leveller and door-lifting machine are provided with a 30-h.p. and two 5.-h.p. motors respectively.

The coke car, a view of which can be seen in Fig. 18, is hauled by an electric locomotive driven by two 80-h.p. motors. It is substantially constructed, having a steel frame mounted on two bogies. The chute-like receptacle for the coke is lined with cast iron and is of ample capacity to receive the maximum single oven charge. The car is set into slow motion immediately the pushing operation is commenced, and when it has received its full charge it is quickly run under the quenching tower. Here the coke is deluged with some 2,500 gallons of water and is effectively quenched in a period of about a minute. This arrangement is desirable in view of the large volumes of steam generated suddenly, which if quenched at the ovens gives rise to objectionable working conditions and might be harmful to the oven fabric. The system, however, is by no means a disadvantage, since the handling is rapidly effected and the vicinity of the ovens is quite free from the usual heavy clouds of steam. Furthermore, the oven maybe discharged in a minimum of time — from 35 to 40 seconds. The surplus water draining from the coke during and after quenching gathers in a series of three settling tanks, whence it is re-pumped to the elevated tank and used again. Electrically-driven centrifugal pumps accomplish this work. They are controlled by automatic floats, limit switches and contactor gears of The Igranic Electric Company's design. An electric crane with a grab bucket attachment removes the coke sludge from the collecting pits and dumps it into the wagons.

The quenched coke is tipped on to the wharf through the side gates which are operated from the cab by compressed air. Regulating gates at the bottom of the wharf pass the coke, which is now also handled by rotary pocket feeders, to a rubber belt conveyor. The wharf is normally required to bold about 18 tons of coke and extends along a third of the battery length. Twice this amount, or the contents of four ovens, could, however, be accommodated.

An unusual feature of the coke-handling plant is the belt conveyor, already mentioned, which carries coke to the screens through a total vertical height of 55 ft. It is a 5-ply canvas and rubber belt, 36 in. wide, 600 ft. long, and travels at a speed of 150 ft. per minute ; its capacity is 75 tons per hour. Curiously enough the hot coke does not appear to have the devastating effect on it that might be expected.

A screen of the cascade grizzley type receives the coke from the conveyor. All above the 2 in. size is passed to rubber cross belt and delivered into wagons for the Company's blast furnaces. The undersize is conducted to a conical rotary screen and further separated into "nut" size (2 in. to ¾ in.) for domestic fuel and breeze (¾ in. to dust) is taken direct to the hoppers above the boilers. Views of the screening plant, which was supplied by Messrs. Fraser & Chalmers Engineering Works, are shown in Figs. 26 and 27. The housing is erected over a three-line railway siding having a self-acting gradient.

By-Product Plant.

The overflow of the pitch cistern, together with condensates from the coolers, is collected and partially separated in two condensate tanks from which supplies of flushing tar or liquor are drawn and pumped over the collecting main. The remainder of the condensates is pumped into a large mixed liquor tank which decants ammoniacal liquor into another tank alongside and tar into two other similar tanks. These four tanks are each 22 ft. 9 in. diameter by 20 ft. high and are constructed of reinforced concrete ; they may be seen in Fig. 11. It may be mentioned that the Industrial Constructions Ltd. were responsible for the design and erection of the tanks as well as the other reinforced concrete structures in the plant.

The small quantity of liquor made is worked up in a vertical still with lining section of usual pattern, and the NH3 vapour is admitted into the main gas stream entering the saturators. This still, the two saturators with duplicate steam, scum and mother liquor tanks occupy one-half of the by-product building. Upstairs in this same bay is found the lead-lined, cast-iron draining tables and two centrifugal salt dryers, seen in Fig. 28, while the other half of the building houses the exhausters and extractors. Overhead hand-power cranes are provided in each bay.

Tar can be loaded into road or rail wagons. The majority of this product will he treated at the Consett Company's new tar-distillation plant of Coppée design, which is now nearing completion at Templetown. Suitable provision is made for ample storage of acid for finished sulphate salt. At an early date it is intended to install a drying, neutralizing and bagging plant for the salt.

Benzol and Crude Plants.

The crude and rectifying plants are housed in one large building; overhead runway joists and lifting tackle are placed over the larger pieces of apparatus to facilitate easy and rapid handling. The recovery of benzols from the coke-oven gas is effected in the large tower scrubbers seen in Figs. 10 and 11. In the gallery below these scrubbers are found a number of electrically-driven pumps for circulating the various liquids around the plant.

Before entering the benzol house proper the rich oil passes through three heat exchangers and then on to the preheater and crude still; vapours pass to the dephlegmating column, crude condenser, benzol receiver and on to measuring and intermediate storage tanks; the stripped oil returns from the still to the scrubber circulation via the heat exchangers and final tubular coolers. Condensates from the fractionating portion of the dephlegmating column pass through a syphon and into an open tank in a fireproof shed adjoining the benzol building. From this tank water is separated and sent to waste, and oil passes into three shallow crystallising pans. Drainage from these is duly returned into the oil circulation and the crystallised naphthalene is removed for further draining and storage.

Rectifying Plant.

This consists of a blow-over boiler still with high fractionating column, dephlegmator and twin condensers. Distilled products are then washed in the usual form of agitating washer, which is completely partitioned off from the remainder of the main building, and are finally distilled in a boiler still and condensing set similar to the one previously mentioned. If required, washing can be effected on either the crude or once-run product. It might be mentioned that the rectifying plant is designed to treat about 2,300 gallons per day of crude benzol from outside sources, in addition to about 2,500 gallons per day made on this site. The chief final product will be motor spirit; this is stored in tanks on the lowest level of the plant and then filled into drums at the drum washing, filling and weighing station. Every precaution is taken to have this spirit sent out ready for motor users, to which end careful and continual tests are made-in a well-equipped chemical laboratory.

Acid regeneration is simply and conveniently effected by collecting the washer residues in a large lead-lined cast-iron pot, which is easily, transferred to a rail bogie by means of an overhead runway and then taken to a steaming station away on the outskirts of the plant. Recovered acid is blown back to the storage tanks for use in the sulphate plant.

Boiler Plant.

The steam required for the plant is made in three Babcock & Wilcox water-tube boilers, one being a spare, each fitted with Underfeed Stoker Co's. chain grate stokers. Coke breeze from the screening plant is delivered to the stoker hoppers by means of chutes from the overhead storage bunkers. Connections have been installed for burning surplus gas under the boilers, but it was impossible to show them in Fig. 34 on account of the difficult lighting.

Clinker and ash is collected in water-sealed ash hoppers placed under the back end of each fire grate and carried by an electrically-driven scraper conveyor, working in a reinforced concrete trough, to a cross conveyor and then into a small ash storage hopper conveniently placed over an adjacent railway siding. Feed water is measured in a Lea recorder apparatus and delivered by either of two Weir feed pumps.

Acknowledgments.

We have to acknowledge the very courteous assistance we have received from the Consett Iron Co. Ltd. in the preparation of this article. Also to the Coppée Co. (Great Britain) Ltd. we are indebted for details of the Wilputte ovens and the by-product plant, and for the use of photographs.

Drawings and Photographs accompanying the article