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This unit serves a dual purpose. It functions both as a condensate return unit and a large flash tank. It is designed to handle condensate at temperatures up to 300°F and under 50 psig without steam flash losses. The unit converts high-pressure condensate to a low-pressure state and cools the high-temperature condensate before it is pumped back to a boiler.
The unit eliminates the need for coolers and traps in a steam system; it also eliminates the need for flash tanks to reduce the temperature of condensate. It is typically recommended when the back pressure at the pump discharge will always be greater than the internal pressure of the receiver. Because of its design, less heat is wasted, less space and piping are required, and operating costs are lower because the condensate does not need to be reheated as much as in a vented system.
As the pressurized, high-temperature condensate enters the receiver, it hits the inlet cascade baffle. The purpose of the baffle is to slow the flow of the incoming condensate minimizing water turbulence inside the tank. The condensate flows out the sides of the baffle and drops into the receiver. A portion of the high-temperature condensate also flashes into steam. This flashing occurs when high-temperature condensate that is under pressure is discharged into the lower pressure receiver.
The size of the tank must be sufficient to prevent the low-pressure receiver from becoming over pressurized. The size of the receiver depends upon both the flow of condensate and the input steam pressure. Because the unit is considered a pressure vessel, it must be constructed in accordance with ASME code and is supplied with a pressure relief valve. The tank is also elevated 27" above the floor level.
The water level rises in the receiver tank from the returning condensate causing the float to rise.
The thermostatic vent trap serves a dual function. At startup, the low pressure inside the receiver forces air and non-condensable gases, that might have accumulated within the receiver, out through the thermostatic vent trap.
The check valve located in the piping between the receiver and the thermostatic vent trap prevents air from entering the receiver if the system should go under a vacuum. The gate valve in the drain piping is always closed except when the condensate needs to be drained from the receiver.
During operation, the thermostatic vent trap functions as a mechanical trap. When steam reaches the trap, the thermostatic air vent closes in response to higher temperature -- keeping the steam inside the unit. However, as the temperature of the steam in the piping between the check valve and the thermostatic vent trap drops below the saturation point, the steam condenses. A small amount of condensate accumulates in the piping above the trap. At a certain point, the trap opens an orifice and discharges the condensate into the drain piping.
When the rising float reaches the high water position, the pumping phase begins. The float switch sends an electrical signal to turn on the pump sending condensate out the discharge of the pump.
As the condensate is pumped out the discharge of the pump, the water level of the receiver drops.
When the float reaches the low water position, the float switch sends a signal to turn off the pump. The fill/pump cycle repeats.
The unit is often used in applications with steam absorption equipment. The unit is piped directly to the outlet of absorption equipment. It handles the condensate at the same pressure or vacuum that the absorption unit operates at. In this application, the condensate flows by gravity to the unit's receiver.