When steam travels through equipment and transfers heat, it reverts to a liquid phase called steam condensate. Returning this hot condensate to the boiler is important for several reasons. As more condensate is returned, less make-up water is required, saving fuel, water, and chemical treatment costs. Significant fuel savings occur as most returned condensate is relatively hot (130°F.-225°F.), reducing the amount of cold make-up water (50°F-60°F.) that must be heated to make steam.
When the hot condensate returns to the boiler, it gets stored in a vessel that is known as a condensate or return tank (see illustration). When the boiler requires make-up water, the hot condensate is pumped into the boiler. If the level of the water in the tank drops below the required level, fresh water is fed into the tank.
Components of the condensate return system:
1. Condensate Return Tank. This is the vessel that holds the condensate that will be fed into the boiler as make-up water.
2. Float Valve. The float valve maintains the water level in the tank. When the water level drops below the desired level, the float valve will let fresh water into the tank until the correct level is reached.
3. Sight glass. The sight glass will show the level of condensate that is in the tank.
4. Condensate pump. When the boiler requires make-up water, the condensate pump pumps the condensate from the tank into the boiler.
5. Strainer and strainer cleanout. The strainer is a screen that traps debris such as sediment and rust, keeping it out of the pump and boiler.
6. Condensate return flash tube. This is where the hot condensate enters the return tank.
7. Vent. The vent allows pressure to be released from the tank and keeps the return system from “air locking” by displacing lost water with air.
8. Drain valve. This valve is to be opened when the tank is drained.
9. Shutoff valve. This valve shuts off the flow of water to the pump. This valve is normally open. It is closed when the pump is to be serviced or removed.
1 The return tank should be examined for signs of leaks (from corrosion). The tank should be drained out periodically to remove any rust or sediment.
2. If the water level is not being maintained, or if the tank overflows, the float valve may need to be adjusted or replaced. The float works on the same principle as the float valve found in toilet tanks.
3. If the sight glass is leaking, it must be replaced.
4. Check the pump for leaks. If the pump leaks, the seals must be replaced. Listen for any grinding sounds. This could mean that sediment has collected in the impellers. Lubricate the pump as instructed.