Boiler house Heat recovery systems
2
1 m (max.)
2 m (min.)
2.8 4
Drain valve piped to open drain
Fig. 3 Example showing two float traps in parallel when capacity demands
Float trap The build up of water in the flash vessel must be avoided so a float trap with continuous drainage of condensate at saturation temperature is essential. The trap must be fitted so that the float arm rises and falls vertically with the direction of flow as indicated on the body. Where capacity demands two float traps should be fitted in parallel (see Figure 3). The flowrate of residual blowdown through the trap is dependent on the head of water above it. For the full rated capacity of the system the trap should be positioned at least 2 m below the flash vessel as shown in Figure 3. It is usually most convenient to fit the trap at a low level for easy access immediately above the heat exchanger. No more than 1 m of horizontal pipework should be used between the flash vessel and the float trap inlet to prevent the float trap from becoming steam locked. Heat exchanger (see Figure 4) All piping to and from the plate heat exchanger and shut-off valves should match the connection size of the exchanger. Pipes should be fitted so that any thermal expansion does not affect the plate heat exchanger or the fittings. This may be accomplished inherently within the piping or by flexible connections. Valves and piping are to be mounted without tension on the heat exchanger connections. We recommend that the residual blowdown being discharged to drain is visible to provide a means of checking that the system is operating correctly. Use a swan neck to ensure the primary side of the heat exchanger is always full of water. This prevents problems caused by sludge, and damage to gaskets.
Residual blowdown inlet from flash vessel
Heated water outlet to tank
Residual blowdown out to drain
Cold water inlet from tank
Fig. 4 Heat exchanger - Piping
AI-P404-07 AB Issue 7
Page 4 of 8
Boiler Blowdown Heat Recovery Systems - Installation, Operation and Maintenance
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