Steam Trap Maintenance

Condensa.te Return Systems. Ia a process plant, steam traps are used to drain and return condensate. Given proper appHcation and continuous maintenance, these can operate with minimal steam leakage. Correct iastaHation is also important (12). 

High maintenance co.st.s. Leaks must be repaired and steam traps must be checked and replaced if they have failed. Numerous studies have shown that, due to the energy lost through leaks and failed steam traps, an extensive maintenance program is an excellent investment. Steam maintenance costs are so high that for low-... 

Steam traps are automatic mechanisms that remove low heat-content air and condensate from the steam delivery system. The lack of steam traps or use of traps that fail to function properly leads to a gradual decline in heat-transfer efficiency, waterlogged heat exchangers, and water hammer (which may in turn result in ruptured pipes). When adequate maintenance of steam traps is neglected, this ultimately leads to a serious overall loss of operating efficiency. There are various types of steam traps, each designed for a specific function. Some common variations are discussed in the following sections. 

Production of heat energy at Rohm Haas has been improved by better control of combustion in boilers, cleaning and maintenance of boilers and process heaters to maintain their efficiency, elimination of steam leakages, steam trap maintenance, and improved condensate recovery (4). 

Pressure tests of pipelines, jackets, steam coils, and arrangement to isolate and take out coils for maintenance are necessary. Steam traps shall be selected for the removal of condensate as soon as formed. There shall be no cooling of condensate in the jacket or coils (unless system is specially designed to recover heat from hot condensate also). 

It is often said that most process analyzer problems can be traced to the sample system. While some progress has been made in modularizing sample systems, generally the type of maintenance that must be performed has not changed. In many cases, steam-traced hnes have been replaced with electrically heated lines, which eliminate maintenance related to steam traps and steam supply. However, filters must still be replaced, valves must still be maintained, and materials of construction that corroded in the past will still corrode. 

Do not forget the basic energy management, which includes maintenance, steam leaks, steam trap management, condensate return, and insulation. These elements are very visible on site and the energy loss can be estimated. Typically, around 10% steam production can be reduced in steam boilers from better housekeeping management. 

Steam Leaks from Steam Straps (Invisible) The purpose of a steam trap is to separate steam and condensate. It is designed in such a way that it opens to allow condensate to go through, but closes when presented with steam (hence trapped ). If operating properly, steam traps have negligible loss of steam. However, when steam traps stick in the open position, steam passes through the trap valve directly to the condensate system. There are many hundreds of steam traps all over the place in a site and many of them could operate in poor conditions if there is no proper maintenance in place. 

There are hundreds of steam traps all over the place in a site and many of them could malfunction if there is no best practice of maintenance in place. That is the reason why the most common energy waste is steam leakage from bad steam traps. 

The objective of a steam trap is to remove noncondensable and condensate from steam with minimal loss of useful steam. While accomplishing this objective, a good steam trap should posses the following does not freeze in cold weather, adaptable to the full range of loads for the given application, requires minimal maintenance, and lasts a long time. 

It is important to know that steam traps should not be sized based on pipe size. A common problem is poorly sized traps that cause premature failure through excessive cycles and wear on internal parts as well as excessive steam leaks. Therefore, steam traps are selected primarily on duty second, on duty variation for transient cases and third, on equipment requirement (Kenny, 1989). Proper installation and maintenance together with regular vendor service can maintain good steam trap performance and long life. 

Replace steam traps with steam venturis where applicable. Venturi devices are engineered and must be accurately sized for the application. The benefit is that there are no moving parts to wear out, reducing maintenance and steam losses. 

Inverted-bucket and float-type steam traps are highly susceptible to mechanical damage. If the level arms or mechanical linkages are damaged or distorted, the trap carmot operate properly. Regular inspection and maintenance of these types of traps are essential. 

Most of the failure modes that affect steam traps can be attributed to variations in operating parameters or improper maintenance. Table 22.1 lists the more common causes of steam trap failures. 

Poor maintenance practices or the lack of a regular inspection program may be the primary source of steam trap problems. It is important for steam traps to be routinely Inspected and repaired to assure proper operation. 

Use of steam condensate receivers. In many plants steam traps require considerable maintenance and have significant leakage. The use of steam condensate receivers instead of traps reduces maintenance and steam losses. 

Indirect systems often require relatively larger equipment and much more costly instrumentation plus the maintenance and supervision that goes with that instrumentation. Direct heated vaporizers require simpler controls than indirect heaters plus avoid any danger of condensate fireezeup except if the steam trap gets blocked and traps condensate inside the shell. Desuperheaters can be added to give maximtun flexibility to exit vapor control temperature. 

Steam condensate removal is most commonly achieved by traps—devices that, in efFea, are very simple level controllers. Many plants have experienced the need for high maintenance with these. Sometimes enough steam leaks through to impair the accuracy of steam-consumption estimates based on steam flow metering. In addition, as pointed out by Mathur, a rapid closure of the steam valve may cause a vacuum in the shell and pull back condensate through the trap with possible hammering and vibration in the shell. As a result, some reboilers, particularly large ones, are now equipped with condensate seal pots. These pots then have conventional level controllers. 

Steam condensate and return systems. Corrosion of steam condensate and return systems presents a twofold problem to power-generating and steam-heating plants. Equipment damage and frequent replacement of lines, valves, and traps result in a serious maintenance problem. In addition, corrosion products frequently formed are carried back into the steam-generating equipment and deposited there. The result is plugging of lines, localized overheating, and promotion of corrosion in the boiler system itself. 

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