Book - School of Science and Technology

308 Fuels, storage and handlingTable 11.7 Flow of oil in steel pipes (BS 1387: medium)Value of factor for pipes having stated nominal bore (mm)Grade of oil 10 15 20 25 32 40 50 65 80D 0.56 0.19 0.06 0.02 0.01 ± ± ± ±E ± 7.69 2.43 0.96 0.32 0.17 0.07 0.02 0.01F ± ± 3.04 1.19 0.40 0.22 0.08 0.03 0.02G ± ± 4.86 1.91 0.64 0.34 0.13 0.05 0.03Notes:Factors apply to oil at handling temperature, Table 11.4.Single resistances:For approximate purposes, equivalent lengths of bends, tees, etc., may be ignored.The viscosities and velocities encountered in oil distribution piping are normally suchthat the flow is streamline or laminar. The consequent loss in pressure may be calculatedfrom a simplified approximate equation:wherep ˆ :Qp ˆ pressure drop per m run (Pa/m) ˆ a factor read from Table 11:7Q ˆ boiler power, at 75% efficiency (kW)Subsidiary storage and handlingThe subject of roof-top boiler houses has been referred to in the preceding chapter,particularly in the context of multi-storey buildings. In such cases, it is usual for the mainoil store to be retained at ground level and for a supply to be pumped to a small dailyservice tank in or near the boiler house, as shown in Figure 11.7. The size of the servicetank is dictated by regulations as are the methods of control for the transfer pumpingequipment. Pumps are usually provided in duplicate and arranged to be started by handbut stopped by a level control fitted in the service tank.Natural gasNatural gas from the UK continental shelf and on-shore production is providing effectivelyall of the national `mains' supply in the British Isles and, in consequence, manufacturedgas need be considered only in the context of history and as a basis for comparison.The latest energy statistics show that the United Kingdom has been a net exporter ofnatural gas since 1997. For distribution from import terminals, a high pressure pipenetwork has been created to serve the various areas of the mainland. To cater for theinevitable diurnal fluctuations in demand, the not inconsiderable volumetric capacity ofthe primary high pressure distribution pipework is supplemented at national level fromstorage underground and, for local low pressure storage, by the familiar above-groundgasometers.In order to make provision for exceptional peak demands upon the system, special`interruptible' tariffs have been offered to large industrial users, the arrangement being