R020932J1, Install Manual

Section I I I

NOTE Clayton feedwater receivers are sized for proper flow and chemical mixture. If a customer’s condensate system creates large surges in returns at start up or while in operation, it may cause the feedwater receiver to overflow. Proper evaluation of the condensate return system and final feedwater receiver sizing is the customer’s responsibility.

3.5 DEAERATOR (DA) Effective control of the pressure in the deaerator is essential to proper performance and operation of the Clayton steam generator system. Most deaerators have high and low pressure condensate return inlet connections. The high temperature condensate should be introduced into the DA through a sparger tube. Condensate returns affect the pressure and water temperature in the DA. Introducing condensate return increases the pressure in the DA and, conversely, reducing the amount of condensate return decreases the pressure in the DA.

CAUTION When the quantity of condensate return is insufficient to maintain the desired water level in the D/A, relatively cool makeup water is admitted. This results in a pressure drop (sometimes sudden) in the D/A. This distorts the saturation pressure-temperature relationship causing the high temperature water in the D/ A to flash, releasing steam. Some amount of the water in the supply line to the feedwater pump also flashes. This condition may result in cavitation of the feedwater pump, impeding feedwater delivery to, and resulting in an overheat condition of the heating coil.

On the other hand, if the water in the DA is overheated due to an excessive amount of condensate return, some of this heat is vented off as steam to prevent over-pressurizing the DA. Pressure regulating valves, PRV/BPR, are used to maintain a stable pressure in the DA. A Pressure Regulating Valve (PRV) is used to inject steam into the DA when a pressure drop is sensed. The PRV for this service is typically pilot operated. The downstream sensing line should be connected to the deaerator head rather than the PRV downstream pipe line. This will prevent any control variations due to the pressure loss in the line. A Back Pressure Regulator (BPR) is used to vent steam during periods of overpressure. When large amounts of hot condensate are returned, an amount of steam will be released momentarily—this is normal. Clayton uses a separator with dual steam traps on deaerator applications to minimize this condi- tion. With intermittent conditions of condensate returns at different temperatures and cold makeup, it may not be possible to absorb all the heat from the hot condensate. Deaerator pressure fluctuations should be con- trolled to within 2-3 psig maximum.

3-5

07/10/2015

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