Cement Kilns

Sundon in 1913

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The following is a transcript of an anonymous article that appeared in The Engineer, 116, 15 August 1913, p 167. It is believed to be out of copyright. It describes the Sundon plant after the installation of the second rotary kiln. Note on Imperial units of the time: 1 ton = 1.016047 tonnes: 1 ft = 0.304799 m.

Sundon Cement Works, Harlington, near Dunstable

The works of this firm, which is associated with the British Portland Cement Manufacturers, Limited, are situated at Harlington. about 15 miles from Bedford and 5 miles from Luton.

The works were first constructed with 14 Johnson chamber kilns, but in 1901 Schneider kilns were erected, the flues of the chamber kilns being roofed in and covered with cast iron plates to provide a floor to dry materials for the Schneider kilns. In 1902 (Note 1) an American rotary kiln, 60 ft. by 6 ft., was installed by F. L. Smidth and Co., of Copenhagen, and in 1908 (Note 2) an order was placed with Edgar Allen and Co., of Sheffield, for a rotary kiln 150 ft. long by 7 ft. 6 in. diameter.

The manufacture of cement at these works is carried on progressively in the following order:

From the chalk quarry the materials consisting of chalk and marl (mixed in the necessary proportions determined by chemical analysis) are conveyed to the wash mill by an endless chain hauling gear (Note 3). Here they are fed through rolls into the mills, where they are washed through gratings and elevated to the wet mill. This contains three sets of Clarke's mills, through which the slurry passes into the mixers by gravity. From the mixers it is distributed to the rotary kiln slurry storage tanks by Taylor's three-throw pumps, and then it is pumped direct into the kiln through reducing nozzles. The No.2 kiln, installed by Edgar Allen and Co., Sheffield, is 150 ft. long by 7 ft. 6 in. diameter, with an enlarged burning zone 8 ft. 6 in. diameter (Note 4). The heat given up by the clinker as it passes through the cooler is used to dry the coal (Note 5). The clinker is delivered on to a shaker conveyor and then elevated and conveyed direct to the grinding plant or storage ground. In the grinding plant the clinker, after passing through steel roller crushers, is elevated to storage bins, where it passes by gravity to the Kominor Mills. Here it is prepared for the tube mills, which do the final grinding. It is then elevated and conveyed to a cement warehouse, which consists of a series of bins each of 1000 tons capacity (Note 6). The power plant consists of two twin-cylinder and one single-cylinder gas engines by the National Gas Engine Company, developing 800 brake horsepower. There are seven suction gas plants. There is a well-equipped laboratory and testing-room, where the materials are tested at various stages of manufacture. The number of men employed at these works is about 150.


Note 1. As so often, this date is deceptive. The kiln was commissioned in 1905, and what is more, FLS list the order date as 1905 as well. It was No.52 on their list of rotary kilns supplied world-wide. It is referred to as "American" because, as with all the early FLS kilns, it was constructed largely to the specifications of Lathbury & Spackman.

Note 2. It was commissioned some time in 1909.

Note 3. The deposit at Sundon was physically divided between Grey Chalk above and Chalk Marl below by a 3-4 m band of Totternhoe stone. Both the Grey Chalk and the Marl varied more or less linearly in calcium carbonate content: the chalk varied from around 78% at the base to 88% at the top, while the marl varied from 77% at the top to about 60% at the bottom. In extracting the deposit, advantage was taken of this linear vertical variation by scraping the material with a harrow, from the top downwards, to form a fairly shallow sloped cut. As the thickness of the Grey Chalk varied, the length of the cut downwards into the marl was varied in order to keep the overall chemistry of the cut close to the target value (76%, rising in later years to 78.5%). This ensured that the material arriving at the washmill rarely varied from target chemistry by more than 1-2%. The reliability of this process contributed much to the success of the plant in the early years. Later, as the use of quarry faces worked by draglines and face shovel was developed, management of the quarry became much more complex.

Note 4. Kiln 2 was at the time of installation Britain's biggest kiln. The Swanscombe kilns had been lengthened to 130 ft in 1907, but the Sundon kiln had a greater diameter and had a rated output 30-50% greater. The kiln was Edgar Allen's first.

Note 5. Failure to recycle cooler heat to the kiln was a feature of many of the early kiln designs, and was a basic mistake made by Allen. The continental suppliers, as they introduced their own large kilns in the next few years, tried to use cooler air appropriately. The Sundon cooler air was later introduced into the kiln hood in the normal way, compensating for the very narrow cooler throat by pressurising the cooler.

Note 6. The six box-like cement bins, with extraction screws at the base into which the cement had to be persuaded by trimming from the front with long rakes and air-lances, remained a quaint feature of the plant until it closed in 1976. Concrete silos for cement began to be erected around 1910.

Picture: ©English Heritage - NMR Aerofilms Collection. Britain from Above reference number EAW013474.
Britain from Above features some of the oldest and most valuable images of the Aerofilms Collection, a unique and important archive of aerial photographs. You can download images, share memories, and add information. By the end of the project in 2014, 95,000 images taken between 1919 and 1953 will be available online. View in High Definition.
Picture: ©English Heritage - NMR Aerofilms Collection. Britain from Above reference number EAW013475.
View in High Definition. These two images were taken much later - in 1948 - but the structure of the early plant is still clear. A bank of 14 chamber kilns with two stacks, and a block of four Schneider kilns adjacent, with communication with the chamber floors for transfer of raw material. Kiln 2, and later Kiln 3, were built into the middle of the chamber kiln block. After installation of kiln 3 in the 1920s (when the chamber kilns were decommissioned), a kiln feed mixer was built into the southern kiln chambers.

Original content © Dylan Moore 2014: commenced 19/07/2014: last edit 02/02/2017.

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