Cement Kilns

Rotary Kiln at Gillingham

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The Gillingham plant, founded in 1874, was bought out by J. B. White & Brothers Ltd in 1893, and subsequently became part of APCM. Due to relatively poor communications and restricted raw material reserves, it was not selected as one of the few plants for development, and it was closed down in 1911. The site was in 1920 sold to a renewed Gillingham Portland Cement Company Ltd, under the condition that rotary kilns would not be installed for ten years. The company planned to have a rotary kiln ready for use on the anniversary date in 1930. The kiln was obtained from Edgar Allen, and a contract for the purchase was drawn up in 1925. The contract is to be found in the Rugby Archive, held at the Warwickshire County Records Office, temporary catalogue number RC/11/3/3.

The contract itself is of typical format and is of little interest, but the list of equipment to be supplied is included in the appended Schedule, and this is given below. It gives an impression of the scope of equipment required to convert a static kiln plant to rotary operation, and shows the order of magnitude of the cost. £1 (1925) is approximately £50 (2016). 1 ft = 0.304799 m. 1 HP = 0.7457 kW.

THE SCHEDULE above referred to
Drawing No. 12242 - General Arrangement (Note 1).
Drawing No. 12220 - Survey Plan.
Item No.DescriptionPrice
1.Three 18 ft dia. Wash Mills for Chalk in the Quarry (Note 2), complete with Harrows, Grids and Screens, Driving Gear, Lay Shaft and Supporting Girders in Rolled Steel Sections. Vertical Shafts to have Ball Thrust Footsteps, and Fast Driving Pulleys supplied on Lay Shaft.£1,25300
1a.One Set of 8" x 16" Three Throw Slurry Pumps for Quarry Washmill (Note 3).£30000
2.One 18 ft dia. Washmill for Clay on Wharf with Gearing and Screens interchangeable with existing Clay Washmill. Complete with Line Shafting, Driving Pulley, Throw-out Clutch Gear (Note 4), and top Supporting Girders for gearing in rolled steel sections. £41500
3.One Set of Three Throw Slurry Pumps 8" dia x 16" stroke, for finished Slurry, with Double Spur Gearing, including Pinion for Washmill Line Shaft (Note 5). Exclusive of Suction and Delivery Piping (Note 6).£29100
4.Two Sets of Ironwork for 40 ft dia. Concrete Mixer Tanks, 12 ft depth of Slurry (Note 7). Consisting of Vertical Shafts with Gearing and Footsteps with Ball Bearings, Mild Steel Stirring Grids, Line Shaft, Double Reduction Gearing, and Fast & Loose Pulleys. Top Supporting Girders for gearing in Rolled Steel Sections.£93400
5.Two Sets of Three-throw Slurry Pumps 8" dia x 16" stroke, complete with Line Shaft, Second Reduction Gear and Driving Pulley, with Throw-out Pinions on the Pumps, exclusive of Suction and Delivery Piping (Note 8).£60000
6.Complete Suction, Delivery, and Overflow Piping Connections for Slurry Pumps, consisting of 6" dia. Cast Iron Flanged Piping, with Bolts, Jointing material, Stop Valves etc (Note 9).£21500
TOTAL FOR SECTION 1 . . .£4,00800
Note - Item 6 refers to the Connecting Pipes for the Kiln Pumps Item 5. No Suction and Delivery Piping is included for the Single Set of Pumps Item 3.
Item No.DescriptionPrice
1.One Automatic Slurry Feeding Apparatus for the Rotary Kiln, complete with Supports and Worm Reduction Gearing (Note 10).£11100
2.One Rotary Kiln 9 ft dia., by 200 ft long parallel, ¾" shell, four Cast Steel Tyres and Rollers, Mild Steel built-up Bedplates (Note 11), Cast Steel Driving Gear with machine-cut teeth with the exception of the large Ring and Pinion which would be machine moulded, Counter-shaft and Driving Pulley, Slurry Lifters (Note 12) fitted to the Inlet end of Kiln.
One Mild Steel Hood on wheels.
Extra for Enlarged Burning Zone, 10 ft dia (Note 13).£30000
3.One Set of Fittings for Brick Chamber of Rotary Kiln, including Damper and Operating Gear, Draught Ring, Slurry Feed Pipe, four Cleaning-out Doors, and Inspection Door.£27700
4.One Set of Tie Rods and Buckstays for brickwork to Rotary Kiln Dust Chamber (Note 14).£22400
5.One Rotary Cooler 6 ft dia. x 61 ft long, with Cast Steel Supporting Tyres and Rollers, similar to Rotary Kiln, together with Fittings for brickwork chamber.£1,36400
6.One set of Tie Rods and Buckstays for Brickwork Chamber for Cooler Hood (Note 15).£6000
7.One Set of Firebrick Linings for the Rotary Kiln, Cooler, and Kiln Hood.£1,02500
TOTAL FOR SECTION 2 . . .£10,56600
Note - Chimney for Rotary Kiln not included.
Item No.DescriptionPrice
1.One Inclined Band Conveyor for raw Coal, 18" wide by 190 ft centres of Drums, complete with Driving Gear, Tension Gear, Fast & Loose Pulleys, Troughing and Return Rollers, Mild Steel Framing, Rubber and Canvas Band, exclusive of Supports from ground level, and Throw-off Carriage, but including 4 Mild Steel Ploughs for Throwing off the coal on top of the Silos (Note 16).£69900
2.One Mild Steel Feed Hopper including Supports to ground level, and one Discharge Shoot at end of Conveyor.£9100
3.Two 3 ft dia. Table Feeders under Silos, complete with Mouthpieces and Slides suitable for fixing to customers Ferro-Concrete Silos, including Mild Steel Shoots to Band Conveyor.£13600
4.One Band Conveyor under Silos, 18" wide by 50 ft long, complete with Driving Gear, Fast & Loose Pulleys, Framing etc.£21700
5.One Inclined Continuous Bucket Elevator 12" wide Buckets x 30 ft centres, complete with Driving Gear, Fast & Loose Pulleys, Framing, Rubber and Canvas Belt, and including Mild Steel Head Shoot and Inlet Supports for same.£25900
6.One Rotary Coal Dryer 4'6" dia., by 40 ft long, large enough for drying coal for two Rotary Kilns (Note 17). Complete with Driving Gear, Cast Steel Tyres, supporting Rollers and Beds, Furnace Fittings, Inlet Hood and Outlet Shoot, Draught Rings for brickwork and short Connecting Flue in Mild Steel to Chimney Base, Damper and Frame.£83000
7.One Mild Steel Chimney for Dryer 3'9" dia. by 60 ft high.£19200
8.One Set of Tie Rods and Buckstays for Coal Dryer Brickwork (Note 18).£7900
9.One 12" dia. Spiral Conveyor in Mild Steel Casing 30 ft long with Fast & Loose Pulleys.£8600
10.One Vertical Steel Cased Elevator 55 ft centres, for dried Coal, complete with Buckets, Chain, Driving Gear, and Fast Driving Pulley, Inlet and Head Shoots.£20900
11.One 12" dia. Spiral Conveyor in Mild Steel Casing 30 ft long, with Gearing and Fast & Loose Pulleys.£10100
12.One Mild Steel Hopper for dried coal, approximately 30 tons capacity (Note 19), exclusive of structure to ground level, but including Connections to Turbo Pulverisers.£25200
13.Two C.R.5 Turbo Pulverisers (Note 20) for Coal Firing the Kiln, exclusive of Motor.£1,60000
14.One Set of Piping Connections for Turbo Pulverisers connecting Cooler to Kiln.£16400
15.Shafting for the Coal Plant, consisting of two Countershafts with Turned Steel Shafting, Self-Oiling Bearings, Soleplates, Pulleys etc.£5000
TOTAL FOR SECTION 3 . . .£4,96500
Item No.DescriptionPrice
1.One Mild Steel Discharge Shoot from Cooler with Supports.
One Mild Steel Hopper to Clinker Weigher.
One Automatic Clinker Weighing Machine.
2.Two Vertical Steel Cased Elevators for Clinker, 45 ft centres, complete with Driving Gear, and Fast & Loose Pulleys, Buckets and Chain. One Elevator to take from Cooler, and one from Yard Stock heap.
Two Mild Steel Feed Hoppers for Clinker at Elevator Boots.
Two Mild Steel Head Shoots.
3.One Mild Steel Hopper for filling Clinker Trucks on Yard Gantry, complete with Outlet Door but exclusive of Supports.£2500
4.One Steel Band Conveyor for Clinker 18" wide by 95 ft centres of Drums, complete with Driving Gear and Pulley, Tension Gear, Framing, Drums, Idlers, V-Plough over first Clinker Hopper, and Mild Steel Discharge Shoot at end, exclusive of Gantry and Supports to ground level.£32200
5.One Mild Steel Clinker Hopper about 30 tons capacity, including Supports to ground level, and one 4 ft dia. Table Feeder for Clinker to Cement Combination Mill, and 21" dia. Table Feeder for Gypsum (Note 21).£45000
6.One Allen's "STAG" Combination Tube Mill 6 ft dia. x 32'6" long for Clinker grinding, with three compartments, including Cast Steel and Cast Iron Bar Linings, machine cut Cast Steel Helical Wheel and Pinion, short Countershaft and Flexible Coupling (Note 22).£2,52000
7.One Charge of Metallic Grinding Media for the above Mill.£49600
8.One 12" dia. Spiral Conveyor in Mild Steel Casing 48 ft long with Driving Gear, Fast Pulley and Mild Steel Breeches Shoot (Note 23).£13500
9.Shafting consisting of One Countershaft for driving Clinker Elevator and Band Conveyor.£4400
TOTAL FOR SECTION 4 . . .£4,61200
Fifteen Motors and Starters and Controllers, as follows:-
A.C., 3 Phase, 400 Volts, 50 Cycles.
H.P.R.P.M.Slip Ring or Squirrel CageLocationSpeedPrice (Note 24)
One30720S.R.Kiln Slurry Pumps and two Mixers.Constant£100
One720/240S.R.Slurry FeederVariable£17
One50720/360S.R.Rotary Kiln.Variable£240
One20720S.R.Rotary CoolerConstant£70
One20720S.R.Coal Dryer and ElevatorConstant£70
One120570S.R.3 Chalk WashmillsConstant£420
One40570S.R.Clay Washmill & PumpsConstant£140
One10720S.C.Coal Band ConveyorConstant£40
One10720S.C.Two Clinker ElevatorsConstant£40
One10720S.C.Band Conveyor under Coal Bunkers.Constant£40
One10720S.C.Dried Coal Elevator and ConveyorConstant£40
One350250SynchronousClinker Combination MillConstant£1820
Two901460S.R.Turbo PulverisersConstant£460
One10720S.C.Clinker Band ConveyorConstant£40
TOTAL FOR SECTION 5 . . . £3,537. 0. 0.
Best Balata Driving Belts from Motors to the machines specified in our Tender including Drives from Countershafts to Elevators etc.£22500
TOTAL FOR SECTION 6 . . .£22500
Section 1 -Slurry Washing & Mixing Plant.£4,00800
Section 2 -Rotary Kiln Plant.£10,56600
Section 3 -Coal Plant£4,96500
Section 4 -Clinker Grinding Plant.£4,61200
Section 5 -Fifteen Motors and Starters£3,53700
Section 6 -Driving Belts£22500
TOTAL . . .£27,91300

(Twenty seven thousand, nine hundred and thirteen pounds)

Sealed in the presence of:

Wm CrosbyDirector
W Y ColesDirector
E R BurkinshawSecretary

In addition to the work done by Allen, various items were provided by the plant or other contractors. My rough estimate of the 1925 cost of these follows (Note 25):

Quarry Pipeline£2,540
Pipeline from wharf to kiln feed mixers£730
Kiln feed mixer vessels£200
Pump house£75
Back end building£350
Back end chamber£160
Four kiln piers£375
Kiln motor house£20
Kiln and cooler building£1,300
Cooler chute£70
Coal store and drier building£640
Cooler piers£30
Clinker elevator structure£295
TOTAL . . .£6,785

This raises the total cost to £34,698, which can be split between three sections:

Raw milling£2,855£3,270£6,125
Finish milling£5,4510£5,451

The kiln produced about 160 t/d, or 54,400 tonnes for a 340 day year, so the total cost was £0.6378 per annual tonne, or about £32 in 2016 money. Allen were at the time in cut-throat competition with Vickers and had lost several orders to them, so Gillingham may have got a fairly favourable deal, at least for the main items of equipment.

The Gillingham company is discussed at some length in Lesley Cook's book. Having started up in 1920 in time for the brief early-1920s boom, the Gillingham company after five years operation could probably have raised most of the cost of the project from revenue, but a certain amount of debt was taken on. Commissioning of the plant was promptly followed by the 1931-1933 downturn, and large losses were made in 1930-1932. After this, modest profits were made, but any thought of expansion was abandoned, and the company began to look for prospective buyers. The company was finally sold to the Amalgamated Roadstone Corporation in 1937 for less than £100,000. It was sold on to Rugby in 1939 and promptly closed. The kiln was transferred to the Rugby plant as part of Kiln 4.

A 1935 photograph shows the location of many of the items in the Allen list.

- o - O - o -


Note 1. Unfortunately, these two plans are apparently not present in the archive. They may be around somewhere, and are obviously of great interest.

Note 2. Prior to this, chalk was brought from the quarry by tramway. The 120 HP motor for these (see Section 5) was sufficient to drive two of the three. It may be that these were two rough mills, used alternately, and a screening mill.

Note 3. No reference is made to any storage capacity before the pumps, or to the 770 m pipeline to the plant wharf. These may already have been present, or were supplied by the plant. All four pumps in the schedule are 8" dia x 16" stroke three-throw pumps. These have a displacement of 0.0395 m3 per revolution, and working at 20 rpm and 90% volumetric efficiency would deliver 42.7 m3/hr. Slurry at 42% water content contains 0.913 tonnes of solids per cubic metre, so 42.7 m3/hr = 39 t/hr solids, equivalent to about 24 t/hr of clinker, well in excess of the 7 t/hr rating of the kiln, so the day's pumping could be done in 7 hours. Flow from the quarry was aided by a 13 m drop in altitude.

Note 4. References to clutches and fast-and-loose pulleys show that the plant still had much equipment sharing motors through layshafts.

Note 5. It shared a drive with the clay washmill.

Note 6. The line to the kiln feed tanks was about 225 m and supplied by the plant.

Note 7. The stirrer mechanism and delivery pipework is listed, but the plant had to supply the mixer vessels. From photographs, the mixers had simple rotating stirrer beams, and not a sun-and-planet design. There is no indication of any other finished slurry blending equipment. A 40 ft mixer had a nominal capacity of 414 m3, equivalent to 236 tonnes of clinker - about 34 hours of kiln run. Evidently slurry production would have to be at least six days a week. The tanks were probably swapped every morning, with one being filled during daylight hours, while the other fed the kiln, having been stirred overnight to homogenise the slurry. Such a system would inevitably give hit-and-miss chemical control, and tank swapping would always be disruptive. Capacity was tight, allowing little latitude for rawmill breakdowns. With the later uprating of the kiln, the capacity was insufficient. However, this deficiency must have become apparent at an early stage, because by 1932 another mixer (45 ft, capacity 294 clinker tonnes) had been installed next to the wharf washmills.

Note 8. The two pumps and two mixers were all driven by a single common 22 kW motor. Two pumps are provided because pumping is continuous, and a second pump is necessary to continue work during breakdowns and maintenance. Each pump could supply two kilns.

Note 9. The two slurry mixers were close to the kiln feed end, with the pump house in between. The total pipe run for feed and overflow was about 50 m, with an 11 m lift.

Note 10. This was a spoon feeder.

Note 11. The piers were concrete and were supplied by the plant.

Note 12. These were simple channel lifters. By 1930, Allen were providing kilns with slurry sprays.

Note 13. Allen were labouring this point, since an enlarged burning zone had already been selected. They continued to encourage "straight" kilns.

Note 14. The masonry of the dust chamber was provided by the plant.

Note 15. The masonry of the cooler chute was provided by the plant.

Note 16. The support structures of all the conveyors, the buildings and the silos (size not known) were provided by the plant.

Note 17. This is the only intimation that a second kiln was contemplated. Turbo pulverisers were always provided with driers, although the mills themselves were said to be able to cope with high-moisture coal, and an extra level of complexity was involved. The need for a dry feed was probably more to do with handling and maintaining a constant flow.

Note 18. The masonry of the end hoods and piers was provided by the plant.

Note 19. 30 tons capacity would give around 15 hours run.

Note 20. These were made by Clarke, Chapman & Co of Gateshead. They were supplied mainly for boiler firing, particularly in ships, and were available in a range of sizes. I have been unable to find the significance of "CR5". Allen claimed to have exclusive rights for their use on cement kilns. They were also installed at Harbury, Dunstable, Rugby, Barnstone and Sundon, and all these were subsequently replaced with Alfred Herbert Atritors.

Note 21. This is the only mention of gypsum, and arrangements for its handling are unclear.

Note 22. Identical mills were installed at Chinnor and Harbury, although the Harbury mill had a 400 HP motor.

Note 23. The screw was only long enough to plumb into the existing cement conveyor system, which extended over ten bins.

Note 24. Prices of individual motors were not given. This column gives the total value roughly apportioned.

Note 25. There may be items I have missed or got wrong: I shall be glad to hear of these.

Text and notes for this article are in preparation.
Original content © Dylan Moore 2016: commenced 15/07/16: last edit 25/08/16.

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