ANSI FCI 13-1-2016 pdf free download – Determining Condensate Loads to Size Steam Traps.
Many steam trap manufacturers design and test steam trap flow capacities to stringent standards. Steam trap hot condensate flow capacities can be measured in accordance with ANSI/ASME PTC 39 or ISO 7842 standards. Steam trap manufacturers should publish capacity tables or graphs according to the aforementioned standards in order for users to select the correct steam trap to discharge the condensate load required by their application. Calculation of the condensate load requirement that the steam trap needs to discharge is just as important as having an accurate flow capability. Under-sizing of the steam trap due to poor load information can lead to poor process performance or dangerous water hammer.
Over-sizing the steam trap also serves little purpose, and in the case of certain types of traps, may cause steam leakage under low flow conditions. Steam traps are often considerably over-sized, which may result in removal of condensate; however, it may also shorten steam trap life in addition to possible unnecessary steam loss as referenced above.
If the equipment manufacturer lists the heat output of the steam equipment that needs to be drained, the estimated condensate rate can be easily calculated. Generally, equipment manufacturers provide the BTU/hr output. In that case, divide the BTU/hr output by the operating steam pressure latent heat (Table 1) to estimate the condensate generation rate from that equipment. (For more exact calculation, the steam quality / wetness has to be considered to adjust for actual lowered latent heat available at the process). Example: 2,500,000 BTU/hr @ 30 psig steam When selecting the trap type, size, and required discharge capacity, consideration still has to be given to whether the steam pressure is steady state or modulating. The calculation shown in the example above is maximum condensate load at full pressure.
When the heat output rates from the equipment are unknown, estimated calculations for heat load using other sources of data can be utilized.
3. DEFINITIONS
3.1 Steam trap – An integral, self actuated valve which automatically vents air in the steam system and drains condensate from a steam containing enclosure while remaining tight to live steam. Most steam traps will also pass non-condensible gases while remaining tight to live steam.
3.2 Condensate – The fluid created after steam has given up its latent heat energy and becomes liquid phase.
3.3 Capacity – The manufacturer’s rated capability of a steam trap to discharge condensate. Capacity is typically stated in the manufacturer’s product specifications, illustrated through either charts or tables.
3.4 Drip Points – Vertical piping pockets located along the steam main pipe where condensate is collected for the purpose of draining from the system. These points are commonly referred to as collecting legs, drip points/legs/pockets, or drain pockets. In the formulas contained here-in this standard these locations are referred to as drip points.
4. GENERAL FORMULAS FOR DETERMINING CONDENSATE LOADS
4.1 Glossary of Abbreviations and Terms
A = area of heating surface, sq ft
BTU = British thermal unit
Cp = specific heat, BTU/lb (Table 4)
CFM = air flow, cubic feet/minute
d = density of air, lb/ft 3 (Table 3)
D = diameter of dryer, ft
EDR = effective direct radiation, sq ft
ft = length, Feet
G = volume, gallons
GPM = flow, gallons/minute
L = latent heat BTU/lb (Table 2, saturated steam latent heat value, adjust for wetness %)
Ll = latent heat of lower pressure, BTU/lb
Lot = length of tubes, ft
N = number of tubes
P = sq ft of surface area per lineal foot of pipe (See Table 1)
Q = condensate generated, lb/hr
Qi = Incoming condensate flow, lb/hr
R = rate of condensation, (lb/sq ft-hr), (typical 7 lb/sq ft-hr)
s.g. = specific gravity @ 60◦F
S = sensible heat, BTU/lb
Sh = sensible heat, higher pressure, BTU/lb
Sl = sensible heat, lower pressure, BTU/lb
t = time, hours
Ta = ambient air temperature, ◦F。ANSI FCI 13-1 pdf download