Safety, Equipment & Systems – Ammonia-tank leak-suppression

Protecting personnel and neighbors

Terry Bundy Generating Station

Lincoln Electric System

175-MW, gas-fired, 3 × 1 combined cycle located in Lincoln, NE
Plant manager: Brad Hans
Key project participants: Jim Dutton, operations supervisor; Vern Cochran, maintenance supervisor; Tom Davlin, project engineering manager

Challenge.

The Terry Bundy Generating Station is a four-unit combined-cycle facility which uses selective catalytic reduction to control NOx emissions from three LM 6000s. SCR is a post-combustion control process in which anhydrous ammonia is injected in the exhaust gas, upstream of the catalyst, to convert NOx emissions to nitrogen and water. The site’s air permit restricts NOx emissions to 3.5pp mvd (30-day rolling average). During the plant’s last Risk Management Program review, the potential for a catastrophic spill from a 12,000-gal ammonia storage tank was identified as a major concern. A large release of ammonia from the site has the potential to impact facility staff as well as surrounding residences.

Solution.

Plant personnel evaluated the potential for installing an ammonia-spill remediation system to reduce the impact of a tank breach. After reviewing remediation options, a water spray system was identified as the most economical solution. It has 34 nozzles configured on six lines surrounding the tank to provide 75 ft2 of spray coverage. The system was designed to NFPA 15; spray density is 0.25 gpm/ft2. The spray system requires a nominal minimum flow of 700 gpm at 120psig, which is supplied by the fire pump. Multiple ammonia detectors monitor the site’s various ammonia systems and are used to alert plant operators to any releases. As soon as an operator confirms a major ammonia release from the storage tank, the spray system would be activated manually to minimize the size and concentration of the resulting ammonia cloud. Fig 30 shows the final flow test.

Results.

Successful demonstration of the system proves it significantly reduces both risk to plant personnel and the potential for offsite exposure. With the successful demonstration, the utility has budgeted for 2011 the installation of similar systems at the Rokeby Generating Station which has two large ammonia systems associated with turbine inlet air chillers.