• Grid reference: TQ6237674479
  • x=562376
  • y=174479
  • 51°26'46"N; 0°20'12"E
  • Civil Parish:Northfleet, Kent

Clinker manufacture operational: 16/02/1970-30/04/2008

Approximate total clinker production: 60 million tonnes (2nd)

Raw materials:

  • Upper Chalk (Seaford Chalk Formation: 85-88 Ma) from Swanscombe Park quarry (559300,173500: Swanscombe parish) and Johnson's quarry (557900,173600: Stone parish). In the latter stages of working both quarries, the underlying Lewes Nodular Chalk Formation (88-90 Ma) was reached. Slurry was made in the Swanscombe Park quarry (at 559379,172938) and pumped to the plant (3.5 km).
  • London Clay (London Clay Formation 48-55 Ma) from Ockendon, Essex (561200,182600), slurried at the quarry and pumped to Swanscombe Park by an 11 km pipeline under the Thames. In later years, clay was partially replaced with pfa in order to reduce alkali input.
  • Minor additions of loam (overlying Reading Beds) and bought-in iron oxide were used to control silica and alumina ratios.


The plant was the only post-war foundation in the area, although the site was “brown-field”: it was built on the long-derelict site of the Crown and London Portland plants, in quarried land that was already worked out (for lime and ballast) long before the cement industry began. The adjacent Bevans site was absorbed, allowing an extended deep water wharf to be operated, handling ships of 60,000 tonnes. An efficient looped rail link was established, accessing the plant through tunnels first driven for quarry access, and this allowed coal and gypsum to be brought in by shuttle trains without the need to reverse. Up to seven 1500 t trains of cement could be shipped out per day to a set of mostly newly-constructed depots around the country. Cement continued to be moved by barge for the central London market.

The project was fundamentally based on the need to replace the increasingly decrepit Thames-side plants with a modern, efficient plant. Comparative cost studies in the 1960s (see Jackson, p 82) showed all the big Thames plants near the bottom of the Blue Circle league table: the best was 16th out of 33. The decision to replace these plants in 1970 with a wet process plant with 50% greater output was based on a number of assumptions: that cheap oil would continue to be available; that the home market would continue the rising trend of the 1960s; that a buoyant export market would allow the plant to continue flat out during home market downturns; and that there were adequate raw material reserves in the Swanscombe Park lands. The price of oil had already risen above that of coal by 1970, and when energy prices began to rise across the board from 1972, an intrinsically inefficient plant was at an immediate disadvantage. The initial workforce of 1200 also compromised the economy of scale, and it turned out that, when the UK market fell after 1973, only minor, "captive" export markets were accessible.

The raw material reserve proved to be significantly lower than anticipated, and the company was taken aback to find the County Council refusing an application to quarry adjacent land to the south. This, and the fall in market, was the justification for scrapping kilns 1 and 3 only ten years after start-up.

The six kilns, at 650 ft × 20 / 18½ ft diameter, were physically the largest installed in Britain (although substantially larger wet kilns were installed abroad). The kilns ran neck-and-neck with Hope B1 and B2 as the largest in capacity until they were overtaken by Platin A2 in 1977, but the kiln performance never reached adequate levels because of poor run-time: the 20 ft diameter burning zones were insufficiently rigid, and caused refractory failure. Burning zone brick life of only a few months added to the unanticipated operating costs.

Conversion of two kilns to semi-wet process was accomplished by providing A2 and A4 with four 15 m3 presses each, in a press-house on the site of kiln A3. The filter cake was fed directly to the kilns, and the considerably increased dust losses were returned by installation of dust scoops just above the fourth tyre.

The semi-wet conversion saved around 1 MJ/kg in kiln fuel energy, offset against the extra electric power and manning cost of pressing.

Following the closure of Rochester in 2000, it was the last cement plant to operate in Portland cement's birthplace in the south-east of England. The site was cleared in 2009-10, and the stacks were finally demolished on 28/3/2010. The western (ex-Johnsons) quarry was redeveloped in the 1990s as the Bluewater Retail Park. The eastern (ex-Swanscombe) quarry awaits redevelopment.

Please contact me with any relevant information or corrections. I am particularly interested in firmer dates and statistics.


  • The Ockendon (Essex) clay plant, sized to process 1.2 million tonnes a year of clay, had four 25’ washmills.(100 kW each). The screened slurry was stored in a 4700 m2 (2200 dry tonnes) tank then pumped at 4.5 MPa pressure under the Thames to Swanscombe Park quarry and received in a set of three similar tanks.
  • The clay and chalk arriving direct from the quarry crushers were ground in three 930 kW 11.6×3.66 m FLS wash-drums. The slurry was screened with through sieve bends, and the oversize re-ground through three 1790 kW FLS Unidan two-chamber ball mills. The resulting slurry was stored in five 4700 m2 (4800 dry tonnes) prior to pumping to the Northfleet plant where it was received in a further six such tanks – a total 17 kiln-days’ capacity.

Six rotary kilns were installed:

Kiln A1

Supplier: Vickers Armstrong
Operated: 16/02/1970 to 26/02/1981
Process: Wet
Location: Hot end 562318,174392: Cold end 562369,174583: unenclosed.
Dimensions: 650’0”× 20’0”B / 18’6”CD (metric 198.12×6.096/5.639)
Rotation (viewed from firing end): clockwise.
Slope: 1/40 (1.433°)
Speed: 0.5-1.5 rpm
Drive: 2 × 580 kW
Kiln profile: 0×5637: 1067×5637: 4877×6096: 44501×6096: 48768×5639: 198120×5639: Tyres at 7163, 35966, 75743, 113843, 152857, 186690: Turning gear at 108814
Cooler: Fuller 825S1050H grate: sloping part originally 5° - later reduced?
Fuel: Coal 1970, 1974-1981: Mixed (10% Oil) 1971-1973
Coal mill: Direct: MPS140 roller mill (one per kiln plus two spares)
Exhaust: Parallel pair of Lodge Cottrell electrostatic precipitators, then ID fan. Two spare precipitators were available - one shared by kilns 1-3, and one by 4-6.
Typical Output: 1970-1973 1725 t/d:1974-1981 1948 t/d
Typical Heat Consumption: 1970-1973 6.67 MJ/kg: 1974-1981 6.25 MJ/kg

Kiln A2

Operated: 08/05/1970 to 3/5/2008
Process: 1970-1983 Wet: 1983-2008 semi-wet: chained kiln fed with filter cake
Location: Hot end 562333,174388: Cold end 562384,174580: unenclosed.
Dust return at 124358 mm added 1985
Fuel: Coal, 1974-2008: Mixed (10% Oil) 1971-1973: from 1990, coal was partially or totally replaced by Petcoke.
Typical Output: 1970-1973 1750 t/d: 1974-1983 1934 t/d: 1983-2008 1940 t/d
Typical Heat Consumption: 1970-1973 6.65 MJ/kg: 1974-1983 6.20 MJ/kg: 1983-2008 5.31 MJ/kg
In all other respects identical to A1

Kiln A3

Operated: 17/12/1970 to 26/01/1981: cleared to make way for the semi-wet process filter press house.
Process: Wet
Location: Hot end 562354,174383: Cold end 562405,174574: unenclosed.
Typical Output: 1970-1973 1751 t/d: 1974-1981 1926 t/d
Typical Heat Consumption: 1970-1973 6.80 MJ/kg: 1974-1981 6.25 MJ/kg
In all other respects identical to A1

Kiln A4

Operated: 24/03/1971 to 3/5/2008 (Mothballed 6/1992 to 4/1994)
Location: Hot end 562368,174379: Cold end 562420,174570: unenclosed.
Typical Output: 1971-1973 1780 t/d: 1974-1983 1952 t/d: 1983-1992 1923 t/d: 1994-1995 1697 t/d: 1996-2008 1890 t/d.
Typical Heat Consumption: 1971-1973 6.74 MJ/kg: 1974-1983 6.21 MJ/kg: 1983-1992 5.21 MJ/kg: 1994-1995 6.80 MJ/kg: 1996-2008 5.27 MJ/kg.
In all other respects identical to A2

Kiln A5

Operated: 04/07/1971 to 1983 (date?)
Process: Wet
Location: Hot end 562389,174373: Cold end 562440,174565: unenclosed.
Typical Output: 1971-1973 1816 t/d: 1974-1983 1969 t/d
Typical Heat Consumption: 1971-1973 6.60 MJ/kg: 1974-1983 6.19 MJ/kg
In all other respects identical to A1

Kiln A6

Operated: 15/12/1971 to 1991 (date?)
Process: Wet
Location: Hot end 562404,174369: Cold end 562455,174561: unenclosed.
Typical Output: 1971-1973 1850 t/d: 1974-1983 1948 t/d: 1983-1991 1804 t/d
Typical Heat Consumption: 1971-1973 6.42 MJ/kg: 1974-1983 6.18 MJ/kg: 1983-1991 6.37 MJ/kg
In all other respects identical to A1

Sources: Jackson, pp 246, 289: Pugh, pp 172-175

More precise information - particularly dates - is urgently sought. Please contact me with any relevant information or corrections.