R016600x

STEAM GENERATOR & FLUID HEATER INSTALLATION MANUAL

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.

If the water in the D/A is overheated due to an excessive amount of condensate return, some of this heat is vented off as steam to prevent over-pressurizing the D/A. Pressure regulating valves, PRV/BPR, are used to maintain a stable pressure in the D/A. A Pres- sure Regulating Valve (PRV) is used to inject steam into the D/A 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 condition. 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 controlled to within 2-3 psig maximum. The deaerator should be installed horizontally. The higher the D/A can be elevated above the booster pump(s) the less sensitive the feedwater delivery system will be to pressure variations. Other fac- tors, such as friction loss in the feedwater supply line and the Net Positive Suction Head (NPSH) charac- teristics of the booster pump(s), should be considered when planning the deaerator installation. Clayton requires booster pumps for most D/A installations. The D/A can be insulated to maximize heat retention. Descriptions for the water treatment and accessory components, as shown in drawing R-16595 are provided in Section VII (Optional Equipment) and/or in the Clayton Feedwater Treatment Manual.

NOTE All piping to and from the deaerator must remain the same size or larger than the tank connection. Always check feedwater pump pipe size requirements and follow the larger pipe size. See Table 3-4 below and the feedwater supply re- quirements and pipe sizing guidelines discussed in Sections 2.8, 2.9, 2.10, and 2.11.

3-6

Sect03_FeedwtrSys_xx4_g.fm

07/10/2015