Cement Kilns

Martin Earles

Rhinoceros LogoMartin, Earle and Co. Ltd Rhinoceros Brand.

Location:

  • Grid reference: TQ72836773
  • x=572830
  • y=167730
  • 51°22'56"N; 0°29'1"E
  • Civil Parish: Strood Extra, Kent

Clinker manufacture operational: 1881-1940, 1948-1967

Approximate total clinker production: 6.8 million tonnes

Raw materials:

  • Upper Chalk (Lewes Nodular Chalk Formation: 88-90 Ma) from quarries at 572550,167700, 572450,167800 and 572200,167900
  • Medway Alluvial Clay

Ownership:

  • 1881-1890 John Adams and Co.
  • 1890-1895 Reliance Portland Cement Works Ltd
  • 1895-1911 Martin, Earle and Co. Ltd
  • 1911-1967 BPCM (Blue Circle)

Although many aspects of the plant's history are well documented, evidence regarding the early kilns is slight and unsatisfactory. Please contact me with any relevant information or corrections.

Also called Wickham Works, having been built on the site of Wickham Farm. Aggressively developing the plant around the turn of the century, the company were among the primary promoters of the APCM amalgamation, and yet were excluded from the deal because, characteristically, they greatly over-valued their plant. The plant commenced with seven chamber kilns, making 185 t/week. Ten more (195 t/week) were added in 1895 and another ten (290 t/week) in 1896. Rapid expansion then took place. By the start of 1899 there were 70 kilns, making 1880 t/week. In that year, construction of a further 80 kilns was planned, to bring output to 4200 t/week, but with the market collapse of that year, only 20 of these were constructed, giving a final chamber kiln capacity of 2400 t/week. This phase is described with characteristically absurd hyperbole in a 1899 article. Subsequent developments were of rotary kilns. The company, in collaboration with P. J. Neate and Co., built their own kiln operational in 1901, and the plant was among those alleged to have operated the first successful rotary kiln (see article). They then installed a set of fifteen. The chamber kilns were decommissioned in 1914. With 16 rotary kilns operable, Martin Earles in 1922 proudly claimed to be the largest plant in Europe, although Swanscombe was twice the size. BPCM scrapped the old kilns and installed two Vickers kilns that, although near state-of-the-art, restricted output to 2800 t/week. From then on, the plant was used mainly for top-up capacity, shutting down completely in 1932-1933, 1940-1948 and 1958-1960: most or all of the clinker was moved to Crown and Quarry or Holborough for grinding. The plant made use of both rail and water transport: in the latter years the clinker produced was moved to the grinding sites by barge. From 1962, B2 was used intermittently for lime manufacture, and the plant was turned over entirely to lime in 1967. The kilns finally shut down in 1980, after which bought-in quicklime was hydrated, and the site finally closed in 1986. The site was cleared and is now the Medway Valley Leisure Park. The quarries were abandoned but are now in course of redevelopment.

Rawmills

Washmills were always used, originally on the plant site. With the 1920s rebuild of the plant, a 90 kW washmill and screeners were installed in the quarry, and the chalk slurry was inter-ground with clay in a similar washmill on the quay-side.

Eighteen rotary kilns were installed, in two stages.

Kiln A1

Supplier: Martin Earle/Neate
Operated: 1/5/1901-1904?
Process: Wet
Location: Hot end,: Cold end, : unenclosed.
Dimensions: 60’0” × 5’10½” (metric 18.29×1.791)
Rotation (viewed from firing end): ? - since in the picture the drive appears to be on the near side, it may turn clockwise.
Slope: 1/24 (2.388°)
Speed: ?
Drive: ?
Kiln profile: 0×1791: 18288×1791: Tyres at 3861, 13030: turning gear at 14961
Cooler: None
Fuel: Coal
Typical Output: 26 t/d
Typical Heat Consumption: 10.5 MJ/kg


Kiln A2

Supplier: Earles/Neate
Operated: 1903-1912, 1920-1922
Process: Wet
Location: Hot end,: Cold end, : entirely enclosed.
Dimensions: 90’0”× 6’0” (metric 18.29 × 1.829)
Rotation (viewed from firing end): ?
Slope: ?
Speed: ?
Drive: ?
Kiln profile: 0×: ×: ×: ×: ×: ×: ×: ×: ×: Tyres at , , , ,
Cooler: rotary followed by vertical drum cooler. It seems likely that there were only three of the latter, shared by kilns 2-6, 7-11 and 12-16 respectively.
Fuel: Coal
Coal Mill: indirect: common ball mill for all sixteen kilns
Typical Output: 37 t/d
Typical Heat Consumption: 8.5 MJ/kg


Kiln A3

Operated: 1903-1912, 1920-1922
Location: Hot end,: Cold end, : entirely enclosed.
Identical in all other respects to B1


Kiln A4

Operated: 1903-1912, 1920-1922
Location: Hot end,: Cold end, : entirely enclosed.
Identical in all other respects to B1


Kiln A5

Operated: 1903-1912, 1920-1922
Location: Hot end,: Cold end, : entirely enclosed.
Identical in all other respects to B1


Kiln A6

Operated: 1903-1912, 1920-1922
Location: Hot end,: Cold end, : entirely enclosed.
Identical in all other respects to B1


Kiln A7

Operated: 1903-1914, 1920-1922
Location: Hot end,: Cold end, : entirely enclosed.
Identical in all other respects to B1


Kiln A8

Operated: 1903-1914, 1920-1922
Location: Hot end,: Cold end, : entirely enclosed.
Identical in all other respects to B1


Kiln A9

Operated: 1903-1914, 1920-1922
Location: Hot end,: Cold end, : entirely enclosed.
Identical in all other respects to B1


Kiln A10

Operated: 1904-1916, 1920-1922
Location: Hot end,: Cold end, : entirely enclosed.
Identical in all other respects to B1


Kiln A11

Operated: 1904-1922
Location: Hot end,: Cold end, : entirely enclosed.
Identical in all other respects to B1


Kiln A12

Operated: 1904-1922
Location: Hot end,: Cold end, : entirely enclosed.
Identical in all other respects to B1


Kiln A13

Operated: 1904-1922
Location: Hot end,: Cold end, : entirely enclosed.
Identical in all other respects to B1


Kiln A14

Operated: 1904-1922
Location: Hot end,: Cold end, : entirely enclosed.
Identical in all other respects to B1


Kiln A15

Operated: 1904-1922
Location: Hot end,: Cold end, : entirely enclosed.
Identical in all other respects to B1


Kiln A16

Operated: 1904-1922
Location: Hot end,: Cold end, : entirely enclosed.
Identical in all other respects to B1


Kiln B1

Supplier: Vickers
Operated: 1922-1940, 1952-22/9/1967
Process: Wet
Location: Hot end,: Cold end, : hot end enclosed.
Dimensions: 200’0”× 9’10½”B / 8’10½”B (metric 60.86×3.010/2.705)
Rotation (viewed from firing end): clockwise
Slope: ?
Speed: ?
Drive: ?
Kiln profile: 0×2705: 3124×2705: 4191×3010: 15164×3010: 16231×2705: 60960×2705: Tyres at 2134, 17221, 35509, 53797
Cooler: Rotary 62’6”× 6’6” (metric 19.05 × 1.981) beneath kiln
Cooler profile: 0×1981: 19050×1981: Tyres at 4420, 15392
Fuel: Coal
Typical Output: 1922-1931 201 t/d: 1931-1936 210 t/d: 1936-1940 212 t/d: 1940-1953 227 t/d: 1953-1962 238 t/d: 1962-1967 232 t/d
Typical Heat Consumption: 1922-1931 8.36 MJ/kg: 1931-1936 8.60 MJ/kg: 1936-1940 8.48 MJ/kg: 1940-1953 7.65 MJ/kg: 1953-1962 6.79 MJ/kg: 1962-1967 7.59 MJ/kg


Kiln B2

Operated: 1/1/1926-1940: 1948-22/9/1967
Location: Hot end,: Cold end, : hot end enclosed.
Typical Output: 1926-1931 207 t/d: 1931-1936 209 t/d: 1936-1940 225 t/d: 1940-1953 206 t/d: 1953-1962 241 t/d: 1962-1967 224 t/d
Typical Heat Consumption: 1926-1931 8.28 MJ/kg: 1931-1936 8.39 MJ/kg: 1936-1940 7.83 MJ/kg: 1940-1953 9.28 MJ/kg: 1953-1962 7.16 MJ/kg: 1962-1967 7.63 MJ/kg
Identical in all other respects to B1



Sources: Eve, p 28: Francis, pp 193-195, 257: Jackson, pp 239, 286: Preston, pp 83-84, 172: Pugh, p 47: “The cement works of Martin, Earle, and Co., Limited”, The Engineer, LXXXVII, June 30, 1899, p 644: The Engineer, XCVIII, July 1, 1904, p 22

Read the Engineer articles.



Old Maps

A detail plan of the plant has been partially completed, but further progress is prevented by lack of information on the layout and modifications of the earlier rotary kiln section.

Approximate capacity: tonnes per year
Martin Earles Capacity


ME Kiln A1
Picture: a much-reproduced image of Kiln A1 in 1901, taken from the original plate. The wrapper around the centre was used as a coal drier. The building immediately behind was the Wickham Farm house, and remained in place until after WWII.


 GeoScenicP207783_CrownCopyright1938
Picture: Crown Copyright 1938: British Geological Survey Cat. No. P207783. This shows kilns B2 (right) and B1 viewed from the firing floor (west end) in 1938.


Martin Earles Picture
Picture: ©English Heritage - NMR Aerofilms Collection. Catalogue number CF266. A high-definition version can be obtained from English Heritage. This was probably taken in the late 1960s, viewed from the southwest. The chamber kilns were beyond the bottom-left corner. The first rotary kiln was located in the space below and left of the centre, and the group of fifteen kilns next installed were in the cleared area in the centre, parallel to kilns B1 (nearer) and B2.

Read The Engineer at Grace's Guide.

The following are transcripts of two anonymous articles that appeared in The Engineer, 87, 30/6/1899, p 644, and 98, 1/7/1904, p 22, both of which are believed to be out of copyright. Note on Imperial units of the time: 1 ton = 1.016047 tonnes: 1 ft = 0.304799 m: 1 in = 25.4 mm: 1 h.p. = 0.7457 kW: 145.037 psi = 1 MPa.

The initially small and failing Whickham cement plant had been taken over by Martin and Earle in 1895, and a programme of rapid expansion ensued. By the time of the first article, the plant had expanded ten-fold, and was planning a further doubling of its output (which due to the 1899 depression, did not happen). The active partner, Edward John Vavasour Earle (1851-1923), was planning to break the exclusive, sclerotic industry Establishment, and was trying to get the other Medway manufacturers to join an alliance that would out-perform the likes of Whites and Hilton, Anderson and Brooks. In this he was out-manoeuvred (see APCM formation), and by the time Martin Earles was taken over by BPCM, he had been ousted. In retrospect, Earle's strategy involved much more brawn than brain, and the fulsome description in the article was no doubt part of the campaign.

A certain amount of ingratiating hyperbole was normal in such accounts, and the first article stands out in this regard. The description is of what is in fact a plant with decidedly backward technology, its only virtue (and that much exaggerated) being its size.

THE CEMENT WORKS OF MARTIN, EARLE, AND CO., LIMITED.

THE Wickham Cement Works of Martin, Earle, and Co., Limited, are situated on the north bank of the river Medway, a little higher up stream than Rochester Bridge. The site could not have been better chosen (Note 1), and it forms an ideal situation for cement manufacture. It is true that coal and coke have to be brought from a distance, but with the exception of these every other requisite is near at hand on the premises. As is, of course, well known, the original ingredients required in the manufacture of cement are chalk and clay (Note 2). These exist in abundance on the company's property; indeed, we are informed, there is sufficient for at least 300 years' working (Note 3). Moreover, both the chalk and the clay are easy to obtain (Note 4), and the machinery has been placed in the most central portion of the works, having regard to all considerations. The foregoing do not by any means form the whole of the advantages possessed by those works, a plan of which we give in our illustration. There is a frontage of about half a mile to the river Medway, and a wharf has been built along the whole of this. When we had an opportunity of visiting the works there was a fleet of no less than twenty-five barges lying by the wharf in the course of being loaded, or waiting to be so. These barges, or some of them, bring coal and coke to the works on their return journeys after discharging their cargoes of cement at their destinations.

martin earles 1899 plan

By means of the river, too, lighters are sent down loaded to an ocean-going steamer, the property of a small affiliated company, which can come up to just below Rochester Bridge. By thus doing its own carrying, as it were, the Cement Company can deliver its goods with the least possible expenditure. Most of the long distance traffic is done by water, but the local demand is satisfied by means of the two railways - the South-Eastern and the London, Chatham, and Dover - which run actually through the property. Sidings have been constructed in connection with these railways, one of which the - South-Eastern - comes right through the manufacturing portion of the works and between it and the chalk pit, while the Chatham and Dover lies a few hundred feet farther north of the South-Eastern, and only the large scale of our illustration prevents it being shown. The company owns seventy acres of land, with possession of all mining rights of all kinds, while it leases thirty acres in addition, with power to remove the chalk from these. Good water is present in large quantity at but a small distance from the surface, and altogether it may be said that the site has been chosen with the utmost skill, and developed with every regard to utilising all these advantages to the utmost, and with an eye to future developments.

Referring to the plan, the chalk lies to the northward of the railway, and is approached by two tunnels underneath this, while a third is shortly to be constructed. The chalk is at the present time being worked down to a depth of some 80ft. from the ground level, which brings the working level down to a little higher than the level of the works, so that loaded trolleys can travel on the small tram lines which are laid down from the chalk workings into the works almost by themselves. There is a depth of chalk of some 30ft. below this level, however, which could be worked if necessary. We have previously stated that there is a supply sufficient for 300 years, so probably it will be many years before this portion of the chalk is touched. The chalk itself is of considerable purity, averaging, we are told, about 92 per cent. of carbonate of lime, and it is very homogeneous in character, and varies but little over a large number of samples. At present it is brought from the pit into the works by hand labour, the incline rendering the force necessary to propel the trolleys or trucks very small - not more than one man can easily manage. When empty there is no difficulty in returning them up the incline; but shortly this is all to be done by means of endless ropes. This system is also being adopted for a method of aerial conveyance of chalk, where it will no doubt be very successful. This is for taking the chalk from the pits to places from which it can be carted or taken from the works by other means, for the company is in the enviable position of being able to supply chalk to cement manufacturers who are unfortunate enough to have run through their supply of this necessary to their manufacture - a not unfrequent (sic) occurrence among the makers in the surrounding district. This in itself forms no inconsiderable item in the revenue of the company (Note 5).

The process of manufacture of the cement, as carried out at these works, is as follows:- As the chalk is quarried it is taken on tram lines to what are known as "wash mills". These are circular brick-lined pits, in each of which revolves a "spider", the arms of which carry implements much like harrows in construction. As the spider revolves, the harrows catch the lumps of chalk and break them up. With the chalk is added a certain amount of clay, the proportions being, roughly, two-thirds of chalk to one of clay. The addition of the water allows of an intimate mixture of these two substances, and when sufficiently mixed the "slurry" escapes through a grating into a catch pit. From this it is taken up either by bucket wheel, or by an endless chain of bucket wheels to a higher level and delivered into the "rough mills", formed of rough " burr " stones placed horizontally (Note 6). From these it flows in a thick cream, and is led to the "mixers", which are in sets of two. They consist of circular pits, like the "wash mills", and in them revolve four-armed spiders carrying "stirrers". In the "mixers" at present at work these "stirrers", of which there is but one to each "mixer", revolve in one direction. Shortly, however, each "mixer" is to be provided with two stirrers mounted on the same axis, but made to revolve in opposite directions, by which means the time taken to obtain a perfect mixture will be materially lessened. The slurry flows from one "mixer" to the other - the two closely adjoining one another - and, during its progress through these, samples are taken every half an hour to the testing shop so that a continuous check is kept on the composition of the mixture. The "slurry" is now ready for drying previous to "burning". Both these processes are conducted at one operation in one kiln, the method adopted varying slightly with the different type of kiln. A description of one will suffice for the whole, for, though they differ in detail (Note 7), the general principle remains the same. Speaking generally, the kilns consist of two parts - the kiln proper, and the drying tank or floors.

In the kiln are placed alternate layers of coke and dried " slurry." The burning creates a great heat, and the heated gases are led either under or over the tank or floor into which the "slurry" has been pumped to a depth of some 9 in. or 10 in. The action of the kilns is therefore twofold: burning one "charge" while drying and preparing the next charge for burning. The period necessary for adequate "burning" varies somewhat, but it may certainly be taken that three complete "charges" can be passed through each kiln in a fortnight (Note 8). The clinker is now removed, and the slurry, which is now dry and cracked all over, is dug out of its tank and placed in its turn in the kiln, with alternate layers of coke. The slurry tank is again filled, the furnace closed, and the process repeated. The heat used is just below that of the fusing points of the materials, and it is here where, with the exception of the mixing, the greatest skill is required. The burning has, of course, to be carefully watched day and night, and the temperature regulated by means of dampers. Laying the "fire" also requires considerable experience, for there must be just enough coke, and not too much. "Enough", because under-burnt clinker is useless for cement, both in colour and properties; and "not too much", for otherwise the heat is too intense, fusion takes place, and the resulting material rendered of no use on this account. The, clinker, as it eventually comes from the kilns, is grey in colour, and extremely hard. It is also porous, and is not unlike light-coloured coke in general appearance (Note 9), being pierced with numberless minute holes. One is tempted to ask, when looking at this clinker, "How much coke remains in its composition?" so great is the resemblance of the one to the other. And the answer received is, "None at all". All gets burnt away, as a fact, though from appearances it would seem otherwise.

The clinker stage arrived at, there yet remains the crushing, grinding, and production of the cement proper, and to this branch of the subject the company has evidently given the greatest amount of consideration and thought. There is practically no machine which it has not tried, and several kinds are now at work. These are of widely different character. One is not unlike the ordinary mortar mill in general principle (Note 10); another, the "ball mill", consists of a large cylinder containing balls, which as the cylinder revolves are lifted up and fall on the clinker as it passes through the cylinder. The type, however, which meets with most general approval resembles in construction a pestle and mortar. This machine is of American design, and the company is so satisfied with its performances that it is just about to install a large number of this type of machine. The practical result is to do away with sieves - that is to say, sieves as separate machines to the grinders, for they produce an extremely large proportion of "flour" (Note 11). One of these machines is now at work producing cement, and the parts of a large number of others are on the premises awaiting erection. As regards the numbers of the various kinds of machines, &c., which are now at work there are four "wash mills", ten "rough mills", four "mixers", and nearly a hundred kilns(Note 12), besides numerous crushers, grinders, sieves, &c. The general output at the present time is about 2000 tons per week. Extensions of the buildings and machinery are, however, in course of construction which will in a short time allow this output to be doubled, and then this will be without doubt the largest single cement factory in the world (Note 13).

The motive power for all the machinery throughout the works is obtained from steam engines. There are two principal engine-houses. One contains three vertical triple-expansion engines of 600-horse power each. These drive on to shafting by means of cotton ropes. Steam is generated here in four marine type boilers. In fact, one might almost imagine oneself in the engine-room or stokehold of a ship, such an air of the sea is there about all the arrangements. The engines are condensing, and the water is obtained from wells sunk on the premises, the water, after it has been through the condensers, being allowed to flow back into the wells again. The second engine-house contains an old beam engine, which, though old, is still doing excellent work. It is supplied with steam from three Lancashire boilers, only two of which are at work at one time.

The works are very imposing to look at. There are already seven large chimneys, varying from 180ft. to 220 ft. in height, and others are in course of erection. Most of these are for receiving the gases from the flues of the kilns. The arrangements of both the old and the new buildings is excellent, and we may here say that in our illustration the extensions in course of construction are shown by dotted lines (Note 14). The working portion is in each case kept as near to the chalk as possible, so as to save carriage of this further than is necessary. Then when the cement is made, and is in such a form that it can be more easily carried, it is taken to the " stores " in conveyors. The stores are situated on the quay, along which run steam-worked travelling cranes. The quay has recently been very largely extended by the company, having been taken some 300 or 400 yards down stream to the opposite shore of a small bay in the river. The land enclosed by this wharf is now being reclaimed, the filling-up material being obtained from another portion of the works, which is being levelled for building the extensions. This will be a large gain to the company, and will enable it to extend its buildings without encroaching on land which will yield either clay or chalk. It is evidently intended to expand as much as possible, as is shown by the work now in progress, and by the expressed intentions of the directors. Moreover, the company is its own builder, and is itself carrying out the erection of its new buildings. These will contain, as will be seen from the plan, eighty new kilns, with their necessary "wash mills", "crushers", "grinders", engines, boilers, &c., and also of five new stores, capable of holding together some 9000 tons of cement. The present storage capacity is about 7500 tons, so that in a short time the combined storage capacity will be some 16,500 tons.

We have previously mentioned that the slurry is tested continuously. This also applies to the cement, and the test of the briquettes made the week previous to our visit gave an average breaking strain of 485 lb. to the square inch (Note 15). We witnessed the test of a briquette selected at random by ourselves. This had been made just over a year, and it did not break until subjected to a strain of 1000 lb. to the square inch. The tests are carried out in a small building neatly fitted up as a laboratory. The offices are contained in an unpretentious building constructed entirely of cement, the inside fittings being of pitch pine.

A feature in cement manufacture is, of course, the large amount of money which it is necessary to expend on repairs and upkeep, not only of the kilns, but of the machinery. We are informed that until recently the bill at the Wickham works for this latter item amounted to no less than £700 a month. The company, being naturally desirous of paying as little as possible for these necessary repairs, instituted the idea of erecting an engineering shop, so as to do the work itself. This turned out to be so successful that this part of the works has been largely extended ; and now an engineering business has been added to the manufacture of cement, it having been found that plenty of work can be and has been obtained to keep a large establishment busy. Among other things now in course of construction are a pair of 600-horse power triple-expansion engines, destined for the extension of the cement works, and a considerable amount of outside work. The saving of expense in regard to the repairs alone is said to amount to as much as £400 a month. The formal opening of these engineering works took place on the 17th inst., the ceremony being performed by Lord Cranborne (Note 16). The works consist of a large erecting and fitting shop, driven at present by a Davey-Paxman horizontal engine. The building is lightly but substantially erected of steel girders and corrugated galvanised iron, and is exceptionally well lighted. One noticeable feature is that the shafting for actuating the machinery, instead of being overhead, is down on a level with it, and placed well out of the way. A number of machines are already at work, and many more are on order. There is also a foundry and smith's shop, and the beginnings of a boiler shop, for the company evidently intends to do all its work itself. A pattern and carpenter's shop adjoins these buildings, and close by are the offices, contained in a substantial brick structure ; all of these being in a most forward state. A line of railway connects the engineering shops with the cement works and thence to the railway, a distance of some few hundred yards. It certainly is a novelty to find a cement works developing an engineering business, but this is what has happened here (Note 17).

- o - O - o -

Only twenty of the eighty projected new kilns were constructed because of the economic downturn that took place in 1899. By the time the market showed signs of picking up, it became clear that rotary kilns were "the next thing", and the land at the east end of the plant earmarked for four blocks of fifteen chamber kilns was instead used to accommodate a set of sixteen first-generation rotary kilns. Although up-staged by the larger installation at Swanscombe, this was by far the largest such installation among the "independents".

SOCIETY OF ENGINEERS. - A highly interesting visit was made by the president - Mr D. B. Butler - and members of the Society of Engineers, on Wednesday, June 29th, 1904, to the Portland cement works of Martin, Earle and Co., Limited, at Wickham, Rochester, where they witnessed the manufacture and testing of cement made by the ordinary method and by the new rotary kiln system. These works have already, in part, been described in our columns - see our issue of June 30th, 1899. Since that description was published the company has installed rotary kilns, of which there are now sixteen installed, and which give an approximate output of 2500 tons per week. The rotary kiln-house is a large brick building, in which the sixteen kilns are arranged in line. The kilns are provided with slurry agitators and coal-firing apparatus. Some are also fitted with apparatus for drying sufficient fuel - which is finely powdered coal - for the entire battery. The body of each kiln is 90 ft. in length, constructed of mild steel, and lined with basic fire-brick. The remarkably large output of 200 tons of clinker per week can be obtained from each kiln, maintaining an average of 25 cwt. per actual running hour of the kiln (Note 18). The clinker discharged from the kilns is transferred to horizontal revolving coolers, whence it is transmitted by conveyors to the crushers, and is afterwards elevated to cooling towers. The dry mill-house is situate behind the cooling towers, and the milling is there done by "Griffin" mills arranged in separate batteries of six mills each, which receive the clinker from overhead hoppers through shutes. The finished cement is conveyed from the dry mill-house by ordinary screw conveyors to the warehouses. Three sets of engines are employed to drive the wet plant, the dry mill, and the coal mill plants respectively, all of which are identical in size and type. Each engine is of the triple-expansion marine type, designed for mill work, with rope drives, and working with surface condensers and centrifugal circulating pumps. The company justly pride themselves upon the fact that the whole of the engines and machinery for the plant were turned out in its own engineering shops, the control of which devolves upon Mr A. T. Macfarlane, who designed the engines, machinery, and rotary plant.

NOTES

Note 1. As stated in the previous sentence, the plant was upstream of Rochester Bridge, which was impassable to large or even medium-sized vessels, so product being shipped in and out by water (which was most of it) required double-handling, expensive in both energy and manpower. In fact, it was one of the worst-sited cement plants.

Note 2. A chauvinistic attitude to local materials was normal among south-eastern manufacturers. Of course, many raw materials are preferable to chalk and clay, and certainly today, chalk would never be used because of its high moisture content, leading to unnecessary high energy costs and CO2 emissions.

Note 3. A back-of-the-envelope calculation indicates that, if all the 100-acre site were worked out to -20 ft OD (unlikely in itself), it would yield 17 million tonnes of chalk, equivalent to 10 million tonnes of clinker. At the current (not the projected) capacity of 100,000 tonnes per year, this would be 100 years. The effectiveness of this statement relies on the hope that few readers would do a back-of-the-envelope calculation.

Note 4. No doubt this was not the quarry-men's opinion - the raw materials were hand-dug.

Note 5. This was easy money, but in view of Note 3, another nail in the coffin of the plant's raw material reserves! Anyone can sell raw materials to their competitors, until they run out.

Note 6. Did they really call them this? In normal parlance, the "rough mill" is the first-stage washmill. In this application, mill stones had to be fairly smooth if they were to work.

Note 7. No two kiln blocks were the same, but all had "double-deck" chambers, variants of the Batchelor, Hilton and Michele designs. See details of kilns below.

Note 8. Maybe this could be done when under pressure, with extra manning, but, as with all such claims, it doesn't represent real practice. The claimed capacity indicates one cycle per week at the most.

Note 9. Those familiar with modern rotary kiln clinker must realise that static kiln clinker was dug out of the kiln in large, irregular-shaped pumice-like lumps.

Note 10. These were "edge-runner" mills of the types made by the local firms of Neate and Collis.

Note 11. Furthermore, the Griffin Mill had an integral sieve. Within the following ten years, Griffin Mills ceased to be used, because the increasingly fine cement in demand in the 20th century could at that time only be produced by ball- and tube-mills.

Note 12. Well, I suppose seventy is getting on for a hundred.

Note 13. Medway producers (but Martin Earles in particular) were fond of making daft statements like this. The proposed doubling of capacity did not take place until rotary kilns were installed in 1904. By contrast, Swanscombe was in 1899 already making 5000 tonnes per week, and was by no means the world's largest plant. As late as 1921, Martin Earles was claiming to be "the largest cement works in Europe" although three British plants - Swanscombe, Burham and Wouldham - were bigger.

Note 14. I have added colour coding to emphasise the various stages.

Note 15. Assuming this is a neat cement test, it corresponds to a modern EN 196 compressive strength of 5 MPa.

Note 16. Viscount Cranborne (James Edward Hubert Gascoyne-Cecil) was Tory MP for Rochester 1893-1903.

Note 17. They went on to make their own rotary kilns. This innovation took place at exactly the time in industry history when it became clear that only specialist suppliers could provide the quality of engineering required in the modern industry.

Note 18. The output numbers are intriguing. A kiln making 25 cwt per hour will make 200 tons in 160 hours, implying 5% down-time in a 168-hour week. However, to make 2500 tons per week in total, only 12.5 kilns are required. It's clear that the kilns were not expected to have an availability of more than 74%. Early kilns often needed re-bricking every few days, although the better operations were achieving over 90% runtime by 1910.

The precise layout of the rotary kiln installation is critical to the understanding of the plant. Plans exist in the Blue Circle archive, which is currently inaccessible and under threat. Please contact me with any relevant information.

Here is a rough estimate of the size of the various chamber kilns finally installed:

block commissioned no. kilns kiln dia ft chamber length ft drying area m2 clinker capacity tonne
11881718.04013426.4
218951015.04011119.5
318961022.05020429.0
41896519.54014528.0
51897718.05016727.1
61897819.04515928.1
71898621.04015629.2
81898718.54013727.9
918991019.04014128.5
101899614.04511718.3
1118991419.54516329.3

ME Kiln A1
Picture of Martin Earles' first rotary kiln in 1901, taken from the original plate.

Original content © Dylan Moore 2011: commenced 19/07/2011: last edit 12/06/2017.

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