Read The Engineer at Grace's Guide.
The following is a transcript of an anonymous article that appeared in The Engineer, 94, 11 July 1902, p 45. It is believed to be out of copyright. It describes the Wouldham plant, around the time that the commissioning of the first-generation rotary kilns was completed. Note on Imperial units of the time: 1 ton = 1.016047 tonnes: 1 ft = 0.304799 m: 1 h.p. = 0.7457 kW.
CEMENT WORKS AT GRAYS
On Friday last a number of the shareholders of the Wouldham Cement Company (1900), Limited (Note 1), and guests visited the works of this company at West Thurrock, near Grays. The company was formed in the early part of 1900 to take over the existing works which had been for some time - we gather for upwards of thirty-five years (Note 2) - engaged in the manufacture of cement on the ordinary chamber kiln principle. The works were then known as the Lion Works, and the name given to the cement manufactured there was the Red Cross Brand. We understand that at the time the works were taken over they were in the hands of S. Pearson and Son, Limited, and, further, that this firm undertook to take all the cement made at the works. The new company at once decided to remodel the whole of its plant, and to install the newest type of machinery available, so as to start operations under the best known conditions. The object of inviting the shareholders and guests to visit the works on Friday was that they might see the new plant in operation, active working of the major part of the machinery having been recently commenced after a stoppage of some months, during which time opportunity has been taken to put everything in working order.
The company possesses its own chalk quarry (Note 3), situated, roughly speaking, half-a-mile from the works' site, and connected to it by two lines of railway approaching the quarry at two different points. Steam locomotives are employed to bring the chalk to the works. The other necessary constituent of cement - clay - is brought in barges from the river Medway, where the company owns land. Excellent arrangements have been made by means of wharves built out on piles into the river Thames - for the company's land has a considerable frontage to the river - whereby not only can this clay, coal, and coke be unloaded, but the cement, flints, &c., be despatched. Moreover, the London, Tilbury, and Southend Railway passes close to the works and in between them and the quarry, and a siding is led on to the site. In fact, taking everything into consideration, the works would appear to be very fairly well placed, both as regards the obtaining of raw material and the disposal of finished cement. The total area of land - leasehold and freehold - is about 138 acres, which includes the chalk land. The amount of chalk available is said to be ample for the whole needs of the company - at all events, during the continuance of the lease - of which, so we gather, there are some fifty years or more to run - and at the full rate of output for which the works are designed, namely, 125,000 tons of cement per annum (Note 4).
At the present time the manufacture of cement is carried out in two different ways - that is to say, so far as the burning is concerned (Note 5); but before dealing with these, we will briefly describe the preliminary arrangements. The chalk is brought from the quarry in trucks, and passes over a weighbridge on its way to the wash mills. The trucks are emptied into the hopper of a crusher, which delivers equally into either of two wash mills, placed side by side, and adjacent to the crusher. The clay meanwhile has been conveyed to elevated structures placed one on either side of the wash mills. Here the proper quantity is weighed out and sent down shoots into the wash mills. The wash mills have, of course, revolving arms driven by bevel gearing worked from two parallel horizontal shafts. The overflow from the first set of wash mills makes its way in each case to second mills adjoining the others, and here the mixture of the two ingredients is further carried on, the resulting slurry flowing to a common sump. From this sump it is elevated by means of a bucket wheel to the stone mills (Note 6), of which there are thirteen, and the discharge from these flows by gravity into two mixers placed side by side. Quite close to these is the "doctor", or small mill, into which either chalk or clay may be shot, depending on whether the analyses, which are continuously being carried out, indicate that either the one or the other is required. The discharge from the "doctor" flows by gravity into the mixers, and the final overflow from these is ready for the operation of burning.
There are in all thirty-two chamber kilns, of which fourteen are of the most recent type. There is no need for us to describe the process of burning cement in these, as it has been done on several occasions in our columns. But, in addition to the chamber kilns, there are six rotary kilns of the latest kind. These, as the majority of our readers are no doubt aware, consist of iron cylinders lined with fire-brick, and mounted at an angle on rollers, so that they can be revolved by means of gearing. These kilns are open at both ends, and are 70 ft. long and 5 ft. in diameter. The slurry is pumped up to such a level that it can be fed into their topmost ends. Burning is brought about by the ignition of powdered coal blown into the lower opening by means of a jet of air (Note 7). The coal is ground on the spot in special machinery (Note 8) and is led up to huge hoppers placed well above the firing-floor level, the coal being supplied to the nozzle through a worm conveyor connecting with the delivery of the hopper. Inside the kiln it is conjectured that a temperature of 3000 deg. Fah. is attained (Note 9). The slurry as it enters the top end gradually gets dried, then heated, and before it gets to the bottom end has been, so it is stated, thoroughly burnt, the time of its passage being some 2½ hours. Our representative saw several of these kilns at work (Note 10). The burnt clinker falls into brick-lined revolving cylinders, through which it gradually passes to ground level, meeting on its way a crusher cooled by a jet of water (Note 11), so that it comes out of the cylinders practically cold, and of a remarkably uniform black colour.
We understand that the working of these kilns has given every satisfaction so far, both as regards cost and also as to the quality of the final cement produced. The tests obtained are stated to be phenomenal.
The clinker, whether produced in the chamber or rotary kilns, is first of all carefully picked and is then crushed. It is then elevated to the top floor of a building which contains in all seven ball and tube mills. Gradually as it descends the cement is ground to the desired fineness, till at length it is finished and is conveyed to the storage bins, which, we were told, were of a total capacity of upwards of 10,000 tons, divided into bins of 160 tons each. Extensive use is made throughout the works of band conveyors, which are put in wherever possible. By an ingenious device one moving band can be made to deliver into any desired bin by means of a specially constructed moveable carriage. Before it leaves the works the cement passes through an automatic weighing and sack-filling machine.
Practically everything, saving the main shafting, is driven electrically. The main machinery consists of eight Davey-Paxman economic boilers of 300 horse-power each. There is a fine horizontal cross-compound engine made by Hick, Hargreaves and Co., Limited, of 1113 indicated horse-power, which drives through gearing on to the main shaft. Subsidiary shafts are driven from this by ropes. Another compound engine by Davey, Paxman and Co., Limited, of 400 horse-power, drives shafting by means of ropes. There are two sets of double air compressors by Walker Brothers, of Wigan, these being for the air jets of the rotary kilns and for other purposes. For lighting and power there is a combined Willans-Electric Construction Company engine and dynamo, the latter delivering 585 amperes at 510 volts when running at 320 revolutions per minute. Tramways run everywhere, and evidently great pains have been taken to so design the works that there may be a minimum of handling of the material, both raw and finished, and there seems every reason to suppose that cement should be produced at these works both economically and well.