O&M

Steam Trap Monitoring Slashes Energy Waste

Issue 4 and Volume 105.

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In steam distribution systems, steam traps can be blamed for wasting a large amount of energy. Traps are put into place to capture and remove condensate water from the lines in order to avoid problems such as water hammer (pressure rise) and thermal shock (thermal stress) in the system, as well as downtime and off-spec production. When a trap inevitably fails, instead of simply draining the system’s condensate, live steam is vented or condensate is allowed to pass back into the system, both of which inhibit heat transfer needed for process temperature control.

Consider a typical plant with a trap population of 1,000. During a visual steam trap audit, assume 100 traps (10 percent) were found failed open. Napier’s Equation can then be used to determine that 100 leaking traps with an orifice size of 0.1015 inches, in a system that operates at 100 psig, together will waste 47.73 pounds of steam per hour. Much of this energy loss can be attributed to the steam trap and the design of traditional steam trap monitoring systems.

The typical steam trap monitoring system includes a total of three valves: one isolation valve upstream of the trap, and two valves (one test and one isolation) located downstream. These are usually gate-type valves. It is difficult to visually determine whether the valves are open or closed – an important distinction since during a normal test, the operator shuts off the downstream isolation valve and then turns on the test valve. If the trap is functioning properly, condensate removed from the system will drain. The operator can then close the test valve and reopen the downstream isolation valve. But, if nothing is emitted from the test valve, the trap has failed closed. In testing, when live steam is emitted, the trap has failed opened, placing a greater load on the boiler. In either case, the trap has malfunctioned, and the operator must then close the upstream isolation valve and tag the trap for repair.

While gate valves are used in industry and accepted, they pose potential problems when used for monitoring steam trap performance, according to Gene Viola, marketing specialist with Swagelok Co., which manufactures a steam trap test station relying on a ball-valve design. Relative to gate valves, the use of ball valves in steam trap test assemblies offer many distinct advantages including 1/4-turn actuation, visual inspection of their position and a variety of end connections for easier maintenance and replacement.

The test assembly’s valve body features an integral vent port to aid the operator in visually monitoring the performance of the trap. As a 1/4-turn actuation ball valve, it both isolates and vents, thereby replacing the two downstream valves of the traditional set-up. When testing, the operator only needs to actuate one valve-the test valve-1/4 turn. If condensate water drains from the vent test port, the trap is working. If there is “no flow” or if live steam is emitted, the trap has failed (either closed or open, respectively). If the trap is functioning properly, the operator then reopens the valve. If the trap has malfunctioned, the operator actuates the upstream 1/4-turn isolation ball valve and tags the trap for repair or replacement.

Using a steam trap monitoring system based on this design can provide rapid economic benefits. For the plant cited above with the 100 failed traps, implementing the Swagelok steam trap test solution will cost $52,200, which accounts for the cost of all product, installation materials, and labor. Comparing this with the annual steam leakage costs, a payback period of 5.5 months is determined. Replacing the remaining 900 trap systems with the Swagelok design would further improve system efficiency and reduce costs.


Corrections:

It was incorrectly reported in the January issue that construction is nearing completion on Calpine’s Towantic Energy Center in Oxford, Conn. Construction has not yet begun on the facility.

The February issue mistakenly reported that President Bush had named Glenn McCullough to replace Craven Crowell Jr. as chairman of TVA. While there are strong indications that McCullough will be named to succeed Crowell, as of press time there had been no official announcement.