The plant as installed was configured as follows:
Anhydrite, crushed at the mine to -100 mm, was received by rail (in a fleet of 150 26 t hopper-bottom trucks, and held in a 3000 t covered store, with an open-air stockyard as overflow. From this it was extracted and passed through cone crushers (Nordberg) to -12 mm and stored in rawmill feed bunkers.
Shale, sand (later dropped from the rawmix) and coke were received from local sources and stocked in the open air. Shale was passed through one of two hammer crushers (British Jeffrey Desmond) before feeding through one of two rotary dryers (Head Wrightson) heated by light fuel oil. The sand and coke were passed to the dryers as received. Dried materials were stored in separate rawmill feed bunkers.
The raw materials were extracted and weighed (Richard Simon) onto common rawmill feed belts, and conveyed to two 450 kW tube mills (Ernest Newell). The raw meal was ground to typically 7% >150 μm, at typically 14 t/hr. The coarse grind was intended to reduce kiln dust pickup, but also contributed to the very low outputs and high fuel consumptions of the kilns. The raw meal was stored in a set of 9 1000 t silos common to the two kiln systems. Meal was blended by recirculation with elevators and air-slides.
There were two Edgar Allen kilns of dimensions 355 × 13 / 10 / 13 ft, running on 6 tyres, and driven by a 113 kW motor through a fluid coupling to a spur wheel just above the 3rd tyre, giving speed variable from 0.50 to 1.05 rpm. The kilns were sloped at 1 in 25, and discharged into reflex planetary cooler tubes.
The meal was fed by pipe to the kiln back ends. The kilns were bricked throughout and had no other internals. The kilns were originally indirect-fired with coal, but were converted to oil firing in the mid-1960s.
Each kiln’s exhaust gas, containing around 9% SO2, was ducted through a cyclone returning most of the dust to the kiln feed elevator. It then passed through a conditioning tower to cool it and remove further dust. The water effluent was stripped of most of its dissolved SO2 by treatment with hot air in counter-current, and the latter was returned to the process. The cooled gases were passed through a set of mist precipitators (Power Gas Corporation: 10 for each kiln) to remove mist and the remaining dust. Finally, the moist gas was passed through scrubber dryer towers fed with sulphuric acid to remove the remaining water.
The cool gas now consisted only of nitrogen, SO2, CO2 and oxygen. The gas was further diluted with air to give around 6.5% SO2 content, so that there was about a two-fold excess of oxygen present. At this stage the gas passed through fans (“blowers”: Bryan Donkin, 113 kW, 3 per kiln) which supplied the sole gas-flow energy for the entire process.
The gas now passed into the converter unit in which SO2 was oxidised to SO3 by contact with a V2O5 catalyst at 420-450ºC. The process is exothermic, and the inlet gas was heated to reaction temperature, and the outlet gas cooled, by passing them through a counter current heat exchanger. Yield was maximised by repeating the process 4 times, after which the gas was passed through a cooler to the absorber towers, located next to the scrubber dryers mentioned above. Here the SO3 was dissolved in re-circulated 98% sulphuric acid, with water bled in to maintain a constant strength.
The acid was passed through coolers and stored in six 750 t tanks for 98% acid and three 500 t tanks for 20% oleum. From here it was pumped to road and rail loading points.
Finally, the remaining gas, which contained a fraction of a percent of residual SO2, was water scrubbed and passed through a precipitator before emission to atmosphere.
The clinker from the coolers dropped onto shaker conveyors via vibraflows to a set of five 1000 t bunkers and an 18,000 t covered store. The extraction points under the store marked the start of the APCM part of the process. The clinker was conveyed to the feed hoppers of two Vickers Armstrong open circuit 3-chamber finish mills: No1 900 kW, making 28 t/hr and No2 450 kW, making 14 t/hr on OPC. The product was conveyed by drag conveyor and elevator to two 1800 t bulk silos and four 1000 t packing silos. The plant had rail and road loading facilities, and could bring in conventional process clinker to “sweeten” the USAC product.