ABSTRACT
An alternative for fossil-fired boilers for steam power plants was to incorporate boiler circulation pumps (BCPs). This measure significantly reduced the size of the boiler compared to free-convection boiler designs for the same capacity and thus also significantly reduced the boiler first cost. Since it is easier to seal liquid water than steam, special measures were employed to ensure that flashing to steam does not occur in the seal leakage flow path. Accordingly, it is necessary to tap seal injection water off the boiler feed pump discharge manifold. Boiler feed pump discharge water is the only water available with a high enough pressure to force flow into the boiler, through the BCP impeller seal ring clearance. As a reference point, seal leakage calculations were made by assuming smooth sealing annulus surfaces and that seal annulus entrance and exit pressure drops are small compared to the pressure drop within the seal fluid annulus.
