Technical | Steam-plant  | Boilers  >  accumulator

Section under development

The exhaust-steam turbine generators which were first installed at Pleasley around 1911 required a steady supply  for their operations. Up to 1922, there was a constant exhaust output from the fan engine, although this would probably not have been sufficient alone to operate them and the supply would have been supplemented by the exhaust from the winders. The discharge from the winders was intermittent, however, and some means of maintaining the supply to the turbines would have been required. The standard means for achieving this at British collieries was by means of  the steam accumulator which stored the intermittent discharges of the exhaust steam and then delivered it to the turbines at a steady rate. 

No details of the arrangement are known until 1923 when four old Lancashire boilers were converted for use as accumulators. They appear to have been adequate since, in addition to the existing machines, they also supplied a new larger mixed-pressure turbine. Within a couple of years the steady input from the fan engine disappeared after this was replaced by an electric motor  although the operation of the larger winder installed in 1922 would have partly compensated for this.

The standard procedure for converting Lancashire boilers was to remove their flues, fit an internal baffle and blank the ends off.  They would be kept 3/4 full of water and the steam would discharge below water level through a series of nozzles. The steam was thus thoroughly  mixed with the water which, as a result, was heated to the saturation temperature of the steam.

Accumulator -m

General arrangement of a  Lancashire boiler based steam-accumulator

The pressure within the accumulators would be held at about 5 psi above atmospheric and the temperature would have been about 109 degC / 228 degF.  The pressure is believed to have been maintained by a relief valve tee’d off the exhaust main, the excess steam released by the valve being discharged to atmosphere by passing it through the economiser tank, thus pre-heating the boiler feed water up to a temperature of  about 100 C / 212 F.


Exhaust back-pressure  relief valve

The basic operation of the accumulator is as follows. Each winder would be producing exhaust steam for about half of each wind and this would go to charging the accumulator, increasing the pressure and saturation temperature within it. Meanwhile, the turbines would be drawing steam from the accumulator and once the exhaust discharge from the winders ceased the pressure would begin to drop.  The water temperature, however, would then be above the saturation temperature for that pressure and the water would rapidly boil, thus providing steam for the turbines.  A fresh input of exhaust steam would recharge the accumulator and the cycle would repeat.

The scenario described above represents the operation under normal coal winding conditions, but what is unclear is what happened outside of coal winding. At night, when demand was low, the electricity would have been provided by a mixed-pressure turbine using high pressure steam from the boilers. At other times, however, such as when winding men or materials,  much longer delays would occur between each wind and the rate of recharge of the accumulator could have been inadequate for the demands from all the turbines.  The mixed pressure turbines would probably switch to high pressure operation in order to conserve the accumulator steam for the dedicated exhaust turbine, since it is unlikely that the dedicated exhaust turbine would be shut down for short periods. In the first quarter of the 20th century an eight hour shift was in operation and coaling was performed on only one shift.


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08 Apr, 2018


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