Stella Power Stations - Design and Specification

Design and Specification

The main visible features of the stations were their large boiler houses, turbine halls, cooling towers and pairs of chimneys; other facilities on both sites included offices, coal sorting areas, small fire stations and workshops. The power stations had the "brick-cathedral" style of design popular for power stations in the 1930s and 1940s and, as of 2009, still tenuously surviving at Battersea power station in London.

The main buildings of the South station had a total length of 130 m (430 ft) and a width of 81 m (266 ft); their tallest point, the roof of the boiler house, was 44 m (144 ft) high. The main buildings of the North station were of a similar length and height, but in total slightly narrower as the station had one less generator unit. This also meant it had a smaller generating capacity; it was sometimes erroneously termed the South station's "B" station.

The boiler houses and turbine halls were all-welded steel structures, consisting of box-type main columns and roof girders, clad with brick and glazed in parts. Each of their four chimneys was made of brick and stood 120 m (390 ft) tall, weighing about 5,000 tonnes. The North station's four 73 m (240 ft) cooling towers were made from reinforced concrete and were of the typically hyperbolic, natural-draft design.

The South station had five generating sets and the North station had four. Each generating set had a bunker for 1,250 tonnes of coal, fed by a conveyor from the coal store. This conveyor belt system was built by E. N. Mackley & Co, Gateshead. Each bunker fed coal into a pulveriser, manufactured by Raymond. From here it was fed into a boiler in powder form and burned. All of the boilers were suspended from the boiler houses' steel frames, and were made by Clarke Chapman Group Ltd, Gateshead. The boilers were forged in Sheffield, the first of the nine arriving at Stella South in 1953. At 62 tonnes, the boilers were at the time the largest ever made in the UK. The boilers were of the radiant-heat type, comprising a water-cooled combustion chamber, controlled-type superheater and an economiser. Each of the boilers had an evaporation rating of 550 kL/h, a steam pressure of 950 psi and a steam temperature of 925 °F. Each boiler was equipped with two forced and two induced Howden fans, twenty-two electrically operated Clyde soot blowers, an automatic control system made by Bailey and Sturtevant electrostatic precipitators. Each station was designed to burn 2,000 tonnes of bituminous coal a day.

Each boiler powered a turbo generator, made by Parsons, Newcastle upon Tyne. These were three-cylinder reaction type steam turbines operating at 3,000 rpm, generating 60 MW of electricity. The stations used them because of a Statutory Order of the Ministry of Supply in November 1947 that all turbo alternators made for the home market could only be of 60 MW at advanced steam conditions. Stella South had a total generating capacity of 300 MW and Stella North originally 240 MW (later recorded as only 224 MW). The stations were the first to use silica removal beds in their turbines, a development which became standard within the CEGB's power stations for some time. In 1967, one of the sets at Stella South became the world's first in commercial operation to use brushless excitation. The set was modified by Parsons to use A.C. exciters and silicon diode rectifiers. The stations' switchgear was manufactured by A. Reyrolle & Company.

The power stations were illuminated by what was then the most powerful lighting installation in North East England. The North station was lit up by 60 flood lights, 15 on each of four towers; the South station also had four towers, but each held 26 flood lights. The Central Electricity Authority justified the use of 194 flood lights over the two sites as "economical, safe and much more efficient than lighting the stations at street level".