CIRCULATING WATER SYSTEM

TIR JOHN POWER STATION
 

Under an agreement with the Great Western Railway Co., the circulating water for cooling Tir John Power Station was drawn from the King's Dock and, after passing through the power station’s condensers, it was returned to the Queen's Dock. The quantity of water required for the first section of the station, i.e. 120,000 kw., was of the order of six million gallons per hour. As the Kings Dock and Queens Dock are inter-connected, the total cooling surface area was in excess of 200 acres.
 

The circulating water was conveyed from King's Dock to the power station and back to Queen's Dock in two deep underground tunnels terminating in vertical shafts at either end of each tunnel. Sections of the tunnels and shafts are shown on the drawings below. The tunnels, which remain in place to this day, are of horseshoe cross-section about 9 feet in diameter, and are lined with 9 inches of concrete. They were driven in rock at a depth of 300 feet below ground level at the power station end, and 250 feet and 240 feet at the King's Dock and Queen's Dock ends respectively. The difference in levels is due to the gradients given to the tunnels for the purpose of drainage during construction. The length of the intake tunnel from King's Dock to the former Tir John site is about half a mile, and the length of the discharge tunnel from the site to Queen's Dock is about three quarters of a mile.
 

The vertical shafts, today filled and capped, were 14 feet in diameter, and the two at the power station end were sunk through solid rock and lined with concrete. At the docks end, the upper sections of the two shafts had to be lined with cast iron where they passed through the water-bearing strata to the rock below, and from that level down they too were concrete lined. The sinking of the shafts at the Tir John end and the boring of the tunnels to the docks offered no great difficulties, but the sinking of the intake and discharge shafts at the docks end called for special treatment. The water-bearing strata had to be passed before solid rock could be reached, and the overall depth of the strata between the surface and the rock was around 130 feet. This was too great a depth for the use of compressed air, so a freezing process was adopted. This process consisted of a ring of borings of the required depth into which pipes were inserted. Then a freezing mixture was circulated through the pipes until a circular ice wall of the necessary thickness was formed. The shafts were sunk and permanently lined inside this wall, after which the ground was allowed to thaw out.
 

TURBINE ROOM EQUIPMENT.