Book - School of Science and Technology

Boiler firing ± gaseous fuel 291Normally openNormally closedOilBurnersPilotGasControlDamperactuatorsPilotgovernorPressureregulatorOil pumpFilterMaingovernorOil inGas inFigure 10.25 Schematic connections for dual-fuel burnerGas boostersIn certain circumstances it may be found necessary to provide pressure boosting equipmentto serve burners which require a fuel supply at a pressure higher than that availableat the meter. Such a situation may arise in particular where a dual-fuel burner is selectedand the pressure at which the combustion air is provided exceeds that at which gas isavailable. Pressures higher than normal offer advantages in that piping, automatic controlvalves, etc., may be of smaller size but it would rarely be economic to introduce boostingequipment for such reasons alone.Booster equipment may take the form of one centrifugal unit per burner or a commonunit serving a range of burners. Since operation must be fully automatic and cross-linkedwith the burner control systems, physical booster/burner connections to provide standbysupport may be difficult to arrange and may dictate the overall arrangements for a givensituation. The circuit arrangement illustrated in Figure 10.26 applies to a single boosterserving two burners.Safety precautionsIn addition to the various devices incorporated in burner control systems, a numberof further items must be considered. These apply equally to oil and gas fired plants, asfollows:. Automatic fuel shut-off at the entry to the boilerhouse, either by a solenoid or deadweightoperated valve. The valve is usually held open by thermal links located aboveeach boiler, plus emergency push/lock-off buttons at each boilerhouse exit.