R016600x

SUPPLEMENT I - SCR

1.1 SEMI-CLOSED RECEIVER SYSTEMS (SCR) 1.1.1 Requirements

A Semi-closed Receiver (SCR) system is used when condensate can be returned at rela- tively high pressure and temperature. The pressure of the receiver tank is determined by the con- densate return system. When the system is warm and operating at its normal “balanced pressure” the back pressure regulator and pressure regulating valve may be set. The SCR systems typically operate between 50–125 psi and must be at least 50 psi below the anticipated steam pressure. Because of these higher operating pressures/temperature (feedwater will be between 300°– 350° F) feedwater chemical treatment is reduced but not eliminated. Because of the elevated feed- water temperature, cooling water is circulated over the pump heads in the feedwater pump. This helps keep the pump diaphragms cool thereby extending the life. The pump head cooling water does not have to be softened water unless it is returned to the hot-well. Installation of cooling water lines to the pump head connections is the responsibility of the installing contractor. 1.1.2 Components of an SCR System refer to Drawing R-16596 The SCR must be sized to a total capacity of 1.5 gallons per boiler horsepower. Multiple generators may be operated from one receiver if the installation is operating at a common pres- sure. The receiver tank must comply with the ASME Section VIII Code specifications for unfired pressure vessels. There must also be a large valved drain line in the bottom of the receiver to per- mit periodic draining and flushing of the tank.

NOTE Receiver must be installed to provide sufficient NPSH to the feed- water pump(s). See Section 2.11.

1.1.3 Water Level Gauge Glass A sight glass must be mounted on the receiver for visual verification of the operating water level. This glass must be rated for the operating pressure/temperature and be at least one foot long. 1.1.4 Steam Trap An overflow steam trap is required to control the maximum water level, when above nor- mal amounts of condensate are being returned. The trap inlet must have a priming drip leg at least eighteen inches long. The trap discharge must be piped to the make-up tank.

SI-1

07/10/2015

Supplmt01_SCR_c.fm