Steam Trap characteristics for main line applications
Steam traps find their important place in almost all the parts of a steam system. Steam traps play an important role at all the locations and ensure that the processes take place in efficient way. Though different parts of a steam system need steam traps, different kinds of traps should be used at different parts depending on the process requirement. If a wrong type of trap is selected for any particular application, it will not operate in the most desirable and efficient way resulting in reduced productivity, longer process timings and higher maintenance costs. Thermodynamic traps are always recommended on main line application. A large number of plants can be found using inverted bucket trap for mainline applications though it is not recommended. This article highlights the characteristics of a trap required for its proper functioning on main line applications.
Main line applications
As steam travels through mainline, some heat is lost on account of radiation losses. As a result, condensation takes place in main lines. The condensate thus formed, should be removed from the steam system. If not removed, this condensate increases the chances of water hammer in the steam system. At the time of start-up, as the pipe work is cold, rate of condensation is higher and hence, the trap used should be able to discharge large amounts of condensate. There are many other parameters which should be considered while selecting a trap for main line applications. Some of these characteristics are-
1. Radiation losses
The working trap has its temperature higher than the surroundings. As a result, it will radiate heat which accounts for the loss of energy. Radiation loss reduces as the exposed area of the trap is reduced. Hence, for mainline applications, the trap selected should be compact with minimum area exposed to surroundings.
2. Loss of live steam
Live steam is the useful steam which the trap vents away resulting in the wastage of energy. Traps used on mainline should have zero loss of live steam.
3. Number of moving parts
Any trap which is being used should have minimum number of moving parts. Higher the number of moving parts, more the trap will be prone to failure.
4. Ability to handle dirt
The traps working on main line applications should have the ability to handle the dirt. They should not clog too frequently.
Comparison of Thermodynamic trap and Bucket trap on mainline applications-
As we have already seen, larger the exposed surface area of a trap, more will be the radiation losses from the trap. Size of the inverted bucket trap for an equivalent capacity is 3 to 4 times more than that of thermodynamic trap having same capacity. Thus radiation loss through inverted bucket trap is two times more than those through thermodynamic trap of same capacity.
2. Number of moving parts
The inverted bucket trap has linear bucket movement with a linkage for opening/closing orifice. The linkage and the bucket are subject to wear and tear on account of repeated cycles. In-case of a thermodynamic trap, there are no moving parts other than a free disc. Thus inverted bucket trap is requires more maintenance and is also more prone to failure.
3. Water hammer
On account of lesser number of moving parts, thermodynamic traps can withstand water hammers better than inverted bucket traps on account of their robust design.
4. Loss of water seal
For a condensate with a higher ratio of Steam:Condensate mixtures, the water seal of the inverted bucket trap is exposed to a steam surges resulting in loss of water seal thus the trap fails open.
5. Operating cost
Operating cost of a trap is determined using two parameters-
a. Loss through trap- The steam loss happening on the account of opening and closing the trap
b. Loss from the trap- This is the energy lost on account of radiation losses taking place in a trap
In case of thermodynamic trap, both of the above losses are lesser than the inverted bucket trap. Hence, operating cost of thermodynamic trap trap for mainline applications is always less than that of an inverted bucket trap.
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