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).
4.2 Steam Main: Steam mains in various applications may operate in saturated or superheat conditions. When the steam main is superheated, the start-up load may be high to bring the pipe to temperature, but then very little or no condensate is generated when operating at full superheat. In low steam velocity conditions, such as very low demand or in a (stagnant flow) collecting leg, flow reduces to the threshold where the heat loss of the main exceeds the BTU’s of superheat available. Then, condensate will again be created and must be removed from the system. In instances where the superheated steam flow is stopped, the main or collecting leg can revert first to saturated steam, and then to wet steam, depending upon the amount of time for the flow cessation. For that reason, a steam trap is required at the drip points along the pipe with either saturated or superheated steam. Steam mains generally operate more than 90% of the time in the full operational mode. The condensate load produced during normal operation is known as “Running Load”, whereas the condensate load generated during the time when the main is brought up to full operation is known as “Start-up Load”. Start-up times of the main should not be so short as to generate large amounts of condensate that could cause water hammer. Another issue with short start-up times is that large steam traps need to be used to handle the over-large start-up load, and then those traps could be grossly oversized in the normal operating mode.