Hopewell Power Station - Executive Summary |
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Hopewell Power Station (HPS) is a cogeneration power plant that produces electricity and process steam for sale. The facility includes two coal-fired stoker boilers each equipped with selective non-catalytic reduction (SNCR) and an overfire air system for the removal of nitrogen oxide (NOx) emissions. In the SNCR process nitrogen oxide emissions are reduced by chemical reaction with ammonia whereby nitrogen oxide is transformed into harmless nitrogen and water. The ammonia used in the SNCR process is liquid anhydrous ammonia. Liquid anhydrous ammonia is stored at the facility in a 15,000 gallon tank with a maximum fill capacity of 12,750 gallons. The tank, piping system, and safety devices are designed and constructed to comply with federal codes and regulations. All tank process connections are equipped with internally mounted excess flow valves and a check valve on the liquid fill line to shut off the flow of liquid or vapor should a pipe rupture occur. The tank is enclosed by a c oncrete berm and contains chemical sensors to detect small releases. The tank is also equipped with other safety devices: pressure relief valves, for overpressure protection; check valves, to shutoff the flow of fluid in case of an emergency; an overpressure alarm system; an emergency shut-off system; and pressure, temperature, and level indicators. The tank working pressure is normally between 50 to 60 psig and a vaporizer helps maintain these pressures. HPS has maintained a strong safety and accidental release prevention program. The facility's ammonia storage and handling is subject to OSHA's Process Safety Management (PSM) requirements. HPS operating procedures are written and followed with specific detail for safely conducting activities involving the unloading, storage, and handling of anhydrous ammonia. In addition, each employee involved in operating the ammonia process is further trained in emergency operations. Plant personnel strictly adhere to the written maintenance proc edures to ensure the mechanical and functional integrity of the tank, piping system, and emergency shutdown systems. These activities include periodic inspections, testing, and replacement of parts consistent with the manufacturer's recommendations and good engineering practices. Furthermore, HPS ensures that any changes to the ammonia process or plant equipment and systems are managed by implementing a hazard analysis, a root cause failure analysis, and safety procedures before modifications occur. HPS has taken great care to ensure the anhydrous ammonia system is properly designed, maintained, and operated. As a result, HPS has never had a reportable accident. Under the 40 CFR Part 68 requirements, facilities must identify the maximum possible area that might be affected under unspecified catastrophic conditions (the worst-case release scenario). It further requires facilities to identify a more likely scenario (the alternative release scenario). EPA's RMP*Comp (Ver.1.06) modeling program was chosen to estimate the distance to toxic endpoint for the worst-case and alternative case release scenarios. As dictated by the regulation, the worst-case release scenario at the HPS facility involves an unspecified failure of the ammonia tank with a release of its maximum content of 12,750 gallons over a 10 minute period coupled with very unlikely stable atmospheric. Using RMP*Comp with these conditions yields a distance to toxic endpoint that is presented in Section 2 of this plan. According to the EPA's Risk Management Program Guidance for Ammonia Refrigeration (Doc. EPA-550-B-98-014), the distance to toxic endpoint is defined as the distance to ensure that no potential risks to public health are overlooked and that the estimated distance under the worst-case conditions should not be considered a "public danger zone." The EPA further states that the low wind speed and calm atmospheric conditions required in the worst-case release models "are uncommon and if weather conditions are different, the distance would be much smaller." In addition to the worst-case scenario, several alternative release scenarios were evaluated for potential off-site consequences. The alternative scenario with the greatest distance to toxic endpoint was chosen for this plan. This alternative scenario consists of a hypothetical release resulting from a tanker truck transfer hose disconnecting from the fill line, coupled with the failure of the ammonia tank check valve, and immediate evaporation of the liquid ammonia upon release. It should be noted that the ammonia tank check valves and other safety devices are regularly inspected, tested, and replaced in accordance with the manufacturer's recommendations and best engineering practices. Using RMP*Comp for this alternative release scenario yields a distance to toxic endpoint that is presented in Section 3 of this plan. HPS has an emergency response program that has been coordinated with the Hopewell Local Emergency Plan ning Committee (HLEPC). In the event of a release the program includes immediate notification of local responding agencies, state and federal agencies, the ammonia supplier, and plant management. The program further includes evacuation procedures and leak isolating procedures, if it is safe to do so. Because the ammonia storage and handling is subject to OSHA's PSM requirements, audits and inspections are performed periodically to identify changes to improve safety. These changes are evaluated and implemented as required by the regulation. |