Boiler house Heat recovery systems
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Safety information Your attention is drawn to Safety Information sheet IM-GCM-10 as well as to any national or regional regulations concerning boiler blowdown. In the UK guidance is given in HSE Guidance Note PM60. General information This information describes the Spirax Sarco heat recovery system which is designed to recover the heat in discharged boiler water from automatic TDS control systems, and a proportion of this water in the form of flash steam. The heat recovery system must only be used to recover heat from the TDS blowdown. There will be another blowdown point on the bottom of the boiler used for the intermittent removal of precipitates. This should be kept entirely separate from the heat recovery system. Refer to separate literature for system selection details. This equipment is designed to save energy. All pipework and the flash vessel should be lagged. As water passes through the blowdown valve it is reduced in pressure. Flash steam is formed and the pipework downstream of the valve will contain a mixture of steam and blowdown water travelling at high velocity. If the pipeline to the flash vessel is too small in diameter the result may be erosion of the pipework with turbulence and carryover as it enters the flash vessel. The best arrangement is to increase the size of the pipework after the blowdown valve: - Install the flash vessel at a high level adjacent but not bolted to the feedtank. - Fit the pressure gauge set, safety valve and vacuum breaker as shown in Figure 2. - Pipework from the flash vessel to the feedtank should match the vessel’s vent size. - The safety valve should always be fitted with the centreline of the spring housing vertically above the valve. - The discharge pipework must be installed so that undue stresses are not imposed upon the safety valve that could cause distortion and leakage. - Discharge pipework should be as short and straight as possible and discharge where it can not cause damage or injury to property or persons. - Discharge pipework must not be smaller in diameter than the valve outlet. Where it is necessary to install discharge pipework over a longdistance lowering of the performance and possible chatter can be avoided by fitting larger diameter pipe. - There must be no shut-off device on the inlet or outlet of the safety valve. - The size of pipework to drain should match the flash vessel drain connection size. - The vacuum breaker must be installed in a vertical position above the flash vessel in the flash steam line to prevent a vacuum forming when the blowdown valve shuts off. Installation Flash vessel
2.8 3
Vacuum breaker
Flash steam to feedtank
Safety valve fitted on a full bore swept bend. Discharge piped to a safe area.
Pressure gauge, gauge cock and 'U' syphon
Auto TDS blowdown inlet
Residual blowdown to drain
Fig. 2 Flash vessel
AI-P404-07 AB Issue 7
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Boiler Blowdown Heat Recovery Systems - Installation, Operation and Maintenance
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