Stockton

Stockton Logo
Nelson's Cock Brand.

Location:

Clinker manufacture operational: 1872 to 5/1945

Approximate clinker production: 1.83 million tonnes

Raw materials:

Ownership:

Sometimes called Nelson’s Works. The site made lime from early times and like Southam had its own dock on the Grand Union Canal. The manufacture of “cement” dates from 1857, but as with the other Warwickshire plants, true Portland cement was not made until later: around 1872 in this case, when two small dry process bottle kilns were employed. The number of small bottle kilns was gradually increased, and a set of chamber kilns may have been added, perhaps around 1889.

A historical account of this plant is hampered by lack of data, and particularly by lack of maps. As with many rural areas, there is no map edition between the 2nd edition County Series of 1909 and the late 1960s revision. This means that no map shows the rotary kilns, and the only evidence for their location are a few poor quality aerial photographs of the 1930s. The fact (if it is a fact) that there were chamber kilns originates from a statement in a valuation document drawn up by a law firm in 1910 (Rugby Archive RS/9/1/5/6) which says “there are several old slurry drying Kilns, no longer required as such, which we understand will be converted into, and used as Clinker Stores.” The 1909 map does not depict anything that can be unambiguously identified as a chamber kiln block. The 1930s aerial photography shows an area where clinker is being stacked, with little indication that it might once have accommodated chamber kilns, but if it did, then a rectangle 98’ × 80’ can be identified, and, as it happens, there is a tall brick stack at one corner. This, depending on orientation, could contain six 22 tonne or four 30 tonne kilns. This information could be regarded as tenuous enough to ignore, were it not for the fact that the maps show the bottle kilns to be very small – the twenty-three amounting to only 302 t/week capacity. With the three Schneider kilns making 240 t/week, some 160 t/week extra capacity is needed to make the 700 quoted by Davis. (Davis is generally very reliable, using his own objective expert assessments of the plants rather than “declared” capacities.) I therefore go for the 6×22 tonne arrangement. Further circumstantial justification is the fact that wet process rotary kilns were chosen. All the Warwickshire manufacturers were watching each other closely at this time, and collaborating to a significant extent. Both Rugby and Harbury had chamber kilns and chose the wet process. Southam had dry process bottle kilns and chose the dry process. Previous experience of making slurry was evidently decisive, and without chamber kilns, Stockton would have had no need to make slurry.

Around 1902, three of the later bottle kilns were converted into Schneider kilns. By 1907 there were 8 lime kilns and 23 cement bottle kilns (305 t/week), six chamber kilns (135 t/week) and three Schneider kilns (240 t/week), totalling 680 t/week, corresponding to Davis’ estimate of 700 t/week. The Schneider kilns were converted to forced-draught (together 450 t/week) in 1908. These used dry-ground briquetted rawmix. The use of static kilns ceased in 1913. New continuous lime kilns were installed at the same time as the rotary kilns, and the plant continued to make a significant amount of Lias lime.

The plant did not expand up to the depression, and Rugby took a share in the near-bankrupt company in 1937. Following complete takeover in 1945, it became clear that there was no point in keeping it as a separate unit alongside the newly modernised Southam, and production ceased immediately, with the plant continuing to function as a depot until it closed in 1949. In addition to the canal, the plant also had a railway connection through the L&NWR Weedon-Leamington branch from 1895. The plant site remained derelict for many years, and was finally cleared of structures in 1968. The canal spur was filled in and the site has remained waste land, with foundations still visible. The quarries are partially back-filled, but mainly flooded.

Although this was the most important Warwickshire plant at the start of the twentieth century, information is hard to come by, and this account is far from satisfactory. Please contact me with any relevant information or corrections. I am particularly interested in firmer dates and statistics, pictures and plans.

Power Supply

The original plant was directly driven by steam engines. These were replaced with gas engines around the turn of the century. From 1910, the plant was converted to electric power, with an on-site generator driven by a 650 IHP Musgrave Uniflow steam engine. A second identical unit was added in 1913. Purchased power was never used.

Rawmills

Originally Collis and flat stone mills were used, grinding stone brought from the quarry by tramway. By 1905, they had 3 tube mills (size unknown) for wet grinding. In 1919, a wet "combination" tube mill was installed at the quarry, and the Lias was pumped to the plant as a slurry. At the plant, a second combination mill ground the slurry with added bought-in sweetener limestone.

Two rotary kilns were installed:

Kiln A1

Supplier: Edgar Allen
Operated: 6/1910-5/1945
Process: Wet
Location: hot end 444199,264766: cold end 444187,264725: totally enclosed
Dimensions: 140’0” × 8’0”B / 7’0”CD (metric 42.67 × 2.438 / 2.134)
Rotation (viewed from firing end): anticlockwise
Slope: 1/24 (2.388°)
Speed: ?
Drive: ?
Kiln profile: 0×2134: 2134×2134: 3658×2438: 8230×2438: 11278×2134: 42672×2134: tyres at 1448, 12344, 24384, 37338: turning gear at 25146.
Cooler: rotary 55’0”× 4’0” (metric 16.76 × 1.219) beneath kiln
Cooler profile: 0×1219: 16764×1219: tyres at 1829, 13716: turning gear at 13868.
Fuel: Coal
Coal mill:

Exhaust: via drop-out box to stack.
Typical Output: 1910-1921 54 t/d: 1922-1933 60 t/d: 1934-1945 75 t/d
Typical Heat Consumption: 1910-1933 9.48 MJ/kg: 1934-1945 9.03 MJ/kg


Kiln A2

Operated: 1913-5/1945
Location: hot end 444204,264765: cold end 444192,264724: totally enclosed
Rotation (viewed from firing end): clockwise
Identical in all other respects to A1



Sources:

The Warwickshire County Record Office holds sales ledgers from Charles Nelson & Co's plant at Stockton (temporary catalogue numbers RS 9/5/1-5). I present the data here because it represents an exceptionally long (over 50 years) time series of uniformly-gathered data, and because it refers to the idiosyncratic history of the Warwickshire industry. In Warwickshire, the Blue Lias district produced "engineering-grade" hydraulic limes from the 18th century, and these became popular throughout Britain when the building of canals allowed them to be distributed nationwide. When Portland cement began to be produced from the 1840s onwards, Blue Lias Lime was one of the established products with which it had to compete, and the reliability of this lime ensured that it remained in favour for certain applications well into the 20th century. Its production continued at the Warwickshire plants until WWII.

The Stockton plant was established on a site previously worked for lime in 1844. Portland cement made with a ground rawmix commenced production in 1872, and by 1886 its capacity was 15000 t/year of Portland cement and 25500 t/year of lime - about 63% lime. The lime was marketed in three forms: lump lime, ground lime and Selenitic lime. The vast majority (80-90%) was sold as ground lime, which is the familiar Blue Lias hydraulic lime, made by grinding the lump product without any slaking. Lump lime was probably made from stone from known high-carbonate floors. Selenitic lime was made by adding 5% gypsum at the grinding stage as a retarder, and was used in mortars. By the start of the following records in 1897, the relative position of lime and cement had reversed, with lime down to around 40% of tonnage.

YearOwn Product Sold tonnesPurchased Materials Resold tonnesTotal Sales tonnes
Lump LimeGround LimeSelenitic LimeOPCRHPCLump LimeGround LimePlasterCementLump LimeGround LimeSelenitic LimePlasterCement
18974741404280015574020664484347730425401852680034722878
1898953148071062209520252648185124476347919625106251225428
1899911137121118205070197840985005120288917810111850025627
1900465119531471204800189357055578152235817658147155728632
1901802130051182209550110349556826883190517960118268227838
190287812138158820533079428635636455167215001158856326988
1903170614241103422717068428574367686239017098103443630403
1904171115582110622397035724573686755206818039110636829152
190531989661943238800271950395471234691061194339528592
19062314115668322774104361275419466827501284183241932409
1907281997119312370307016642241032889987793142227806
1908256576297102001509046237132072655809171037123222
190919198461792166640140023024302059846179223019094
191031139507651251570210061124193323950765161127576
19112040735354632171032212769730402362748054669735211
19121158710844041042015710123125451315720944023143587
191377455466344047705802184433832554663421844910
19141580420716939679081014253201661420716914244999
1915583263614531530012121125251704263814511236781
19163914161152933505409819889314161159831323
19176391357251980101991188573932579127083
19186710058123776015893957821013819324733
191914798462358203562062059498044620625641
1920716455726703053026030896016455726029792
192136016102732319408811241891448162127324124085
192233421611413364605611491142390216214114934788
19233146675883677203415112202634866908811238798
1924246344648306470390152176028534464815232407
19254293563973678504815148125047735789714838035
192628326106732894013911203108042226216720333974
1927257269831355880616021427287326983121435860
192823825282837634002525642323825532825638057
192918525373931954064030547524925373930532429
1930181381974335940761044526725738297444533861
1931442292089323530221266928446429328966932637
193220223167233312034070817623623167270833488
1933226344078349570211249223424734527849235191
1934336287884354740710791194072878847935593
19353443005131377270681680219412300613168037946
19367973720125477290125440818440922416012581848169
1937860380318950645115890326465289950412918946552092
1938216369380489621739306817117124637618017150872
193934321211456166196297448349543328611448358623
1940832566194640824555884066708826541940649533
1941101440104148021501096494472015361049443677
19420125103537926249153414183091404041439833
1943071603160319200268354450984035433568
1944077702980515590030900777030931364
194504970235091460022125182520718025133221
19460193013711300538313352900731031336791
1947000000723298370250723029837025
1948000000572213278170572021327817
194900000016062696701600626967

It is noticeable that, particularly in the earlier period, a large proportion of the lime and cement sold was not made by Nelsons. The majority of these materials were sold at remote sales points, particularly London, and were packed under the Cock logo by other producers - mainly the other Warwickshire producers.

stockton sales
stockton lime

The total tonnage produced on site varied remarkably little during the period, and never rose very much above the 40,000 tonnes capacity in 1886. However, the amount of lime in the mix consistently fell. It is noticeable that lime production was set aside during both World Wars. Other Blue Lias Lime producers ceased manufacture earlier: Rugby in 1932, Barrow and Southam in 1935, Barnstone in 1938, Aberthaw and Harbury in 1939.

Prototype Atritors

Most early rotary kilns were indirect-fired, which involved a complicated coal preparation system typically consisting of:

The BPCRA research reports show that these systems were a major contribution to the poor efficiency of early rotary kilns. Particular challenges included:

While the usual response was to make modifications to the systems to eliminate the more salient defects, it became increasingly apparent that a direct firing system was desirable. Several systems that could simultaneously dry and grind wet coal and propel it into the kiln were developed after WWI. By far the most successful system developed in this period was the Atritor, and the original development of this mill took place at Stockton. Its application in the cement industry, and in many other applications, followed rapidly afterwards.

An anonymous article on this development appeared in Engineering (114,14/7/1922, pp 42-3, 46). In addition to a description of the prototype as manufactured by Alfred Herbert Ltd., it also provides information on the otherwise poorly-known Stockton kiln system. The original design and the terminology are remarably similar to those of the familiar mature equipment of later years.

Powdered coal, about which much has been written lately in connection with boiler furnace work, has for many years been commonly used in the cement industry for firing rotary kilns. In this application it has been very successful. In this country the material has not been used to any considerable extent for boiler work, although elsewhere, and particularly in the United States, a fair amount has been done with it. The advantages claimed for pulverised coal are very complete combustion, low labour costs, and the fact that low-grade coal can be employed with good results. Among its disadvantages are the costliness of the plant necessary and the inadvisability of storing the powdered fuel, as well as the difficulty and cost of carrying the material to the various furnaces when a central pulverising plant is used in a large installation.

A machine which is claimed to eliminate many of the disadvantages of the ordinary pulverising plant, and which has in practice shown very valuable reductions, both in the cost of pulverising and in the class of fuel necessary for a definite duty, is illustrated herewith and on the opposite page and page 46. This coal pulveriser, which has been named the "Atritor", is the invention of Mr Charles E. Blyth, of Messrs Charles Nelson and Co.; cement makers of Stockton, near Rugby. It is manufactured by Messrs Alfred Herbert, Limited, of Coventry (Note 1). The machine is in the form of a small self-contained unit which dries, pulverises and propels the coal direct into the furnace, so that there is no storage of pulverised fuel and no long transmission of the product. The machine is continuous in action, and the drying and pulverising go on together, the coal being burned immediately after pulverisation so that there is no opportunity for it to absorb moisture. There are no screens in the plant, so that there is no question of appliances of this kind clogging. In view of the fact that no auxiliary machinery is necessary in connection with the pulveriser, other than some method of supplying the receiving hopper with coal, its cost is very moderate, while maintenance, labour and power required are all brought down to a low figure.

figures 1 to 5
figure 6

The general lines of the machine will be followed from the illustrations. Figs. 1 to 5 are various outside views, Fig. 6 is a cross-section, and Figs. 10 to 12 are from photographs of an actual machine and some of its parts. Coal is fed into the receiving hopper which can be seen at the top of the machine in many of the figures and which is indicated by the letter F in Fig. 6. This hopper is fitted with a feed screw at the bottom, indicated by G in Fig. 6, which is driven from a cone pulley as shown. A lever-operated slide, shown at H in Fig. 6, is also fitted to regulate the flow of coal. The operating lever can best be seen in Fig. 10. The coal from the hopper passes down a chute, as shown by the arrow in Fig. 6, and into the separator I. This separator is simply a sloping passage up which a cold air supply enters the machine from the passage K. The air current carries the coal with it, while any pieces of metal or other material of a higher specific gravity than coal pass down the separator and fall out of the machine. The air supply is drawn through an opening in the front of the machine, to be seen in Figs. 2 and 10, the amount of opening being adjusted by a sliding cover which can be seen in these figures and is indicated by the letter C in Fig. 1. The cold air is drawn into the machine by a fan fixed on the far side of the rotor, which serves to deliver the pulverised coal to the outlet. The incoming air current delivers the coal to the rotor, which pulverises it, and the amount of air is adjusted so that all coal passes into the machine and all metal or similar undesirable matter is rejected.

There is a second inlet to the machine, shown at L in Fig. 6, through which air at about 500°C is drawn. This air supply is drawn from the rotary cooler of the kiln, as shown in Figs. 7 to 9, which illustrate an "Atritor" installation in connection with two 140 ft by 8 ft rotary cement kilns. This hot air dries the coal, and it may be noted that coal containing 25% of moisture has been successfully dealt with by the machine. The coal which is carried into the machine by the cold air current meets the hot air current on the face of the rotor and is dried as it is broken up. The hot air current is regulated by a regulating lever shown at A in Fig. 1, and provided with a clamping screw B. The coal is broken by coming in contact with an inter-meshing series of hard metal pegs. These can be seen in Fig. 6, and their general form and arrangement will be clearly understood from the views of the opened-out casing and the rotor which are given in Figs. 11 and 12. As the rotor revolves, the coal is caught between the various distributed pegs and is effectively pulverised. It is an essential feature of the "Atritor" that the coal goes through two different sets of pegs in its passage through the machine. Pegs are fixed on each wall of the casing and on each side of the rotor, and it will be clear that the coal in its traverse from the position M of Fig. 6 to the position N will receive two treatments. These treatments are known respectively as the "first effect" and the "second effect".

The pegs in the "first effect" are carried completely across the passage through which the coal travels as a result of centrifugal force and the draught caused by the fan, and as a consequence there is no possibility of any coal getting through without being broken. In the "second effect" through which the coal is drawn by the fan draught, the rings of pegs on the rotor are carried only half across the chamber, leaving a free passage at one side except for the presence of the stationary pegs fixed to the casing. The innermost ring of pegs on the rotor is, however, carried right across the chamber. This inner ring is composed of thin pegs which enter a recess in the casing on the other side. This ring acts as a rejector for coal particles which may still be too large for use and throws them back into the "second effect" where they are further broken up. The draught from the fan combined with the paddle effect of the pegs causes a set of eddy currents towards the centre on the side of the casing, and towards the periphery up the side of the rotor disc, with the result that a circulation is set up and the coal does not pass on until the particles are so small that they are drawn by the fan and propelled into the furnace.

The suction and blower fan is carried on the main rotor shaft, as will be seen from Fig. 6. This fan delivers to a scroll leading to the outlet to the kiln, as is best seen in Fig. 3. A ring with circular ports is carried on the face of the fan casing, as shown in Fig. 3. This ring regulates the opening of auxiliary cold-air ports. It is operated by the handle D of Fig. 2, and locked in position by the screw E. The full capacity of the machine is 1,800 lb of coal an hour. For this output the slide under the coal hopper should be full open and the feed screw run at its highest speed, the auxiliary ports on the delivery side being kept closed. For a smaller output the coal supply slide is partially closed, and the air supply regulated until no coal is thrown out by the separator. For a still smaller output it is necessary to open the auxiliary air ports to give sufficient air for combustion. The machines may, of course, be driven in any convenient way.


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In the installation illustrated in Figs. 7 to 9 an individual motor drive is used for each pulveriser, while in the plant shown in Fig. 13, the machines are driven by belt from a line shaft. Each machine of this size takes about 30 hp when dealing with coal of a size not exceeding ¾" in any direction, but it is recommended that 40 hp motors should be installed. The machine is guaranteed to give an output of 1,800 lb of coal an hour pulverised, from ¾" lumps to a fineness such that 95% will pass a British standard 100 by 100 mesh screen.

The first "Atritor" was put into commission at the Stockton works about twelve months ago, and since that time has been put to very complete practical tests. The cost of pulverisation by the "Atritor" at Stockton is about 2s. 7d. per ton, while by the old installation it was 5s. 3d. per ton. We understand that this latter figure was a very good one and that figures ranging from 6s. to 10s. 6d. per ton are common. It has also been found that a lower grade of coal can be successfully utilised since the installation of the "Atritor" pulverisers. The difference in cost between the lowest grade coal it was possible to utilise with the old plant and that which can be burned quite satisfactorily with the "Atritor" is from 10s. to 7s. 6d. per ton delivered at the works. A method of working which has been developed in connection with the plant and has been patented, lies in the addition of a small amount of paraffin to the coal during pulverisation. This is said to have a remarkable effect when using coal of poor quality. The amount of paraffin used is very small, 0.07% by weight of the fuel burned, or about 1½ pints for 1,800 lb of coal. In some cases the paraffin can be shut off when full heat is attained, but in the case of very inferior coal may be maintained during the whole of the firing period.

Notes

Note 1. Thomas Phillip Blyth (b. 1833, Poplar, d. 1896) was a London lime merchant taken into partnership with the Nelsons in 1870. Three of his sons - George Blackstone Blyth (b. 1868 Hampstead, d. 1950), Harold Francis Blyth (b. 1869 Galle, Sri Lanka, d. 1960) and Charles Edward Blyth (b. 20/12/1870 Stockton, d. 3/6/1940) - became directors of the company in 1894. Charles married Alfred Herbert's sister, Fanny, in 1901. Charles was an active participant in BPCRA and was one of the few outside Blue Circle to benefit from it.