Book - School of Science and Technology

Electricity 313Table 11.12 Flow of LPG in steel and copper pipesLitre per second in pipes having stated nominal size (mm)Paper mrunMedium steel (BS 1387)Copper (BS 2871 (Table X))8 15 20 25 6 10 12 22 284 0.030 0.23 0.46 0.93 0.006 0.044 0.075 0.39 0.785 0.034 0.26 0.53 1.11 0.007 0.049 0.083 0.42 0.897 0.039 0.31 0.63 1.32 0.008 0.059 0.103 0.54 1.0610 0.047 0.38 0.75 1.61 0.010 0.072 0.122 0.66 1.3115 0.058 0.46 0.92 2.00 0.012 0.091 0.156 0.83 1.6420 0.068 0.53 1.08 2.33 0.015 0.107 0.183 0.99 1.9425 0.076 0.60 1.22 2.61 0.017 0.121 0.208 1.11 2.1930 0.083 0.66 1.33 2.89 0.019 0.135 0.230 1.25 2.4740 0.097 0.77 1.56 3.33 0.022 0.158 0.272 1.47 2.8650 0.108 0.86 1.74 3.75 0.025 0.178 0.306 1.67 3.3170 0.119 0.95 1.93 4.17 0.027 0.201 0.342 1.86 3.6480 0.139 1.11 2.25 4.86 0.032 0.236 0.403 2.17 4.310.3 0.5 0.7 1.3 0.1 0.3 0.4 0.7 1.0Notes: single resistances.For approximate purposes, equivalent lengths may be taken as lengths in metres as listed in the bottom line of the table for each bend, tee, etc.A pressure drop of about 250 Pa between the second stage regulator and the point of use isthe accepted criterion. Once again, retaining the kilowatt as a basis for calculation, a unitflow of propane (1 litre/s) is equivalent to an energy supply of 95 kW.ElectricityThe latest statistics available (1999*) show that in the British Isles, the output of the majorelectricity generating companies produced by coal fired/steam turbine power stations hasreduced to 28% (from 48% in 1995). Natural gas fired stations contributed the largestoutput at 38.5% and 24.5% was produced by nuclear power; Imports accounted for 4%of the total. Each of these main types has a different capital/running cost relationship and,in consequence, each is best suited to contribute to a particular pattern of loading.Nuclear stations, for instance, are more economical when meeting the base load andcombined cycle gas-turbine stations for dealing with a short term peak load. Furthermore,stations of the same type will have differing costs of production depending upon age,design, etc.Growth in generation from renewable sources is increasing, albeit slowly, with about2% of the national electricity generation currently from these sources, of which hydroaccounts for about half of this total.A typical load curve has a morning peak which usually extends from 8 a.m. onwardsuntil about noon with a lesser peak in the late afternoon. Such changes in demand, insofaras they relate to motive power and lighting, etc., are inevitable but nevertheless createproblems for the supply industry. While electricity, uniquely among energy supplies,cannot be stored as such it can be converted without loss into heat which may then be* Digest of UK Energy Statistics 2000, DTIpublication.