7EA best practices focus on performance improvement, safety

Sharing experiences among users is the primary goal of CCJ’s Best Practices Program, now in its 13th year. Think of it as an extension of the information you glean from user-group meetings delivered directly to your computer or mobile device. Two best practices from 7EA owner/operators were among the scores of entries submitted to Senior Editor Scott Schwieger in 2017. They focused on performance improvement and safety—two of the most popular categories in the annual judging.

Don’t miss the opportunity to share your plant’s best practices/lessons learned with colleagues worldwide and to be recognized among the industry’s leaders by entering the 2018 Best Practices Program. Entries, which take only an hour or two to prepare, are due by Jan 31, 2018. Details are on the CCJ website.

Monitor spark-plug performance to prevent failed starts

The ignition systems for Ferndale Generating Station’s 7EAs rely on spark plugs to initiate combustion. The engine model installed has two independent ignition circuits, each with its own spark plug. A unit will start as long as one circuit works properly. If both plugs fail to deliver an adequate spark, the unit won’t start. An unsuccessful start resulting from a “failure to ignite,” is indicated by a control system alarm.

Although this potentially indicates a spark-plug system malfunction, it’s not an absolute indicator, as other problems can trigger a “failure to ignite.” The only way to determine whether an individual spark plug is functioning properly is to remove and test it. Dissatisfied with this reactive and tedious approach, Ferndale’s staff looked for a means of assessing spark-plug health in-situ on an ongoing basis to avoid costly failed starts, reliability impacts, and impromptu repairs. After researching the possibilities, they found no industry solution that would achieve this objective.

An employee theorized that the current flow in the spark-plug cable during ignition should indicate whether the spark plug is functioning properly. If current flow in the cable between the ignition transformer and plug could be measured in-situ, staff could determine if each circuit was delivering an adequate spark without having to pull and test the plug. Using this diagnostic, plant personnel could be alerted to an ignition-circuit failure regardless of whether it stemmed from a shorted, open, or dead circuit.

They proved the theory with a testing program conducted in the plant shop and derived the expected current of a properly functioning plug. By simulating known failure modes, personnel learned that, in all cases, current flow was significantly reduced compared to that of a healthy circuit. For a short circuit, current flow quickly decays to zero following an initial increase.

To measure spark-plug cable current flow in the installed system, the plant purchased small current transformers which provide a 4- to 20-mA current loop output proportional to current flowing in the cable. They were installed in the unit’s ignition-transformer cabinet with a spark-plug cable fed through them. Each transformer’s 4-20-mA output was wired to the respective GT’s Mark V control system and the input signal scale was configured thusly: 4 mA = 0%, 20 mA = 100%.

The control system was configured to monitor spark-plug cable current during the ignition sequence and to generate an alarm when the current drops below the designated value for more than three seconds. This alarm remains uncleared until the operator performs a master reset on the respective GT’s Mark V. 

When a 7EA is shut down, the plugs are positioned with their tips penetrating into the combustion can liner ID. After the purge phase of startup is complete and the unit is at firing speed, the control system energizes the ignition circuits for 60 seconds while fuel is admitted to initiate combustion. When proper ignition is achieved, the control system gradually accelerates the unit to operating speed.

During acceleration, pressure builds in the combustion cans and the spark plugs auto-retract by overcoming insertion spring pressure. During the subsequent unit shutdown and coast down, the pressure in the combustion can reduces to a point where spring pressure is able to reinsert the spark plug, preparing it for the next unit start.   

Staff configured the system to passively monitor spark-plug performance during every start, so no operator intervention is required. During the three years the systems have been in service, they have proven extremely effective in identifying ignition-circuit issues, generating around 10 alarms collectively. In every case, when the corresponding spark plug was removed and tested, personnel confirmed that a malfunction had occurred resulting in a degraded spark or no spark at all.

Ferndale is operated by NAES Corp for owner Puget Sound Energy. The 270-MW, gas fired 2 × 1 combined cycle is located in Ferndale, Wash. Tim Miller is the plant manager.

Portable CO2 cylinder skid eliminates ergonomic hazards

Plant Manager Frank Meade and his safety-conscious staff at the Eagle Point Power Generation Facility challenged themselves to reduce the potential for personal injury in the handling of CO2 cylinders stored at the plant’s hydrogen-cooled generators for routine and emergency purging.

When individual cylinders are emptied, new ones must be moved from a storage area located far from the point of use. Each 175-lb cylinder has to be lifted and maneuvered into position inside the restrictive storage cabinet provided for each generator (Fig 1). Between eight and 12 cylinders are used during a routine purge. This creates several hazards—such as ergonomic issues associated with awkward body positioning and pinch points. Plus, with relatively few operators on shift, the existing procedure can take excessive time in an emergency situation.

Operations department personnel developed a solution by rethinking the existing cylinder handling system. They designed a six-cylinder crate which can be moved by forklift. A 10-ft hose is used to connect cylinders in the crate to the generator for purging (Fig 2). The crate remains outside the cylinder compartment during purging. Two cylinders are retained in the cabinet for emergency use. After a purge is completed, the empty cylinders are moved back to the storage area by forklift.

Eagle Point, a 250-MW, gas-fired 2 × 2 combined cycle located in Westville, NJ, is operated by NAES Corp for owner Rockland Capital Assets.

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