Book - School of Science and Technology

310 Fuels, storage and handlingTable 11.8 Properties of natural and manufactured gasItem Natural gas Manufactured gasSpecific masskg/m 3 at 15 C 0.78 0.6re air ˆ 1 0.6 0.48Calorific value (MJ/m 3 )gross 41.6 20.9net 38.7 18.6Wobbe No. 49.9 27.0Burning velocity (m/s) 0.35 0.8Ignition temperature ( C) 650 600Operating pressure (kPa) 2 1Toxicity Nil ToxicConstituents (% volume)methane 92.6 33.5ethane 3.6 ±propane 0.8 ±butane 0.2 ±pentane and above 0.1 ±hydrogen ± 47.9nitrogen 2.6 ±CO 2 0.1 4.9CO ± 13.7PipeworkFrom the meter outlet, the gas supply distribution system becomes the responsibility ofthe building owner. The Guide Section C4 provides data in tabular form for flow of gas inpipes and Table 11.9 is a digest from this, for steel pipes. Retaining the kilowatt as a basisof calculation, a unit flow of natural gas (1 litre/s) is equivalent to an energy supply of39 kW (strictly 38.6). Thus the input requirement, in kW, of any boiler or other appliancemay be converted into gas flow by using this equivalence. Alternatively, makers' listssometimes give input gas rates volumetrically and these may be used.In terms of pressure loss, it is usual to limit this to between 75 and 125 Pa from themeter to the point of use. Thus, for example:Input rating to boiler ˆ 750kWNatural gas rate ˆ 750/39 ˆ 19:2 litre/sPressure available, say, ˆ 100PaPipe run from intake to boiler ˆ 30mPressure available/m run ˆ 100/30 ˆ 3:3PaThus, from Table 11.9, pipe size ˆ 65mmThe pressure available for distribution of gas within a building is bound up withgovernor settings, requirements for burner intake pressure and with demands for boostingequipment. Such matters need investigation in the light of manufacturers' applicationdata in individual cases and with the gas suppliers.