Harbor Generating Station - Executive Summary |
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Accidental Release Prevention and Emergency Response Policies: The City of Los Angeles Department of Water and Power (LADWP) accidental release prevention policy involves a unified approach that integrates technologies, procedures, and management practices. All applicable procedures of the California Accidental Release Prevention (CalARP) Program and U.S. Environmental Protection Agency (EPA) Prevention Program are adhered to. The LADWP emergency response policy involves the preparation of response plans that are tailored to each facility and to the emergency response services available in the community, and is in compliance with the State and Federal Emergency Response Program requirements. General Description of the Stationary Source and Regulated Substance: Harbor Generating Station (HGS), located at 161 North Island Avenue in Wilmington, California 90744 is a gas-fired electricity generating facility that supplies electrical power to the LADWP system. The facility consists of two main 80 megawatt (MW) natural gas combustion turbines that are equipped with two identical selective catalytic reduction (SCR) units to control emissions of nitric oxides (NOx), a combustion byproduct that is a precursor to ozone. In the presence of a catalyst housed in the SCR units, ammonia (NH3) gas that is a reducing agent, is injected into the flue gas to react with NOx to form water vapor and nitrogen gas (N2), an inert gas and the abundant component of atmospheric air. The ammonia solution storage and supply system (ammonia process) has the dual function of injecting ammonia in combustion turbine exhaust to control nitric oxides emissions and controlling the pH level of boiler feedwater. The ammonia process consists of three subsystems: ammonia handling and storage, emission control, and chemical feed. The ammonia handling and storage subsystem supplies ammonia solution to the nitric oxides emissions control catalyst in the SCR and to the Chemical Feed subsystem. Ammon ia solution is used instead of anhydrous ammonia because the latter has some serious inherent safety hazards requiring significant precautions and safety equipment in handling and storing. The health and safety risks related to anhydrous ammonia outweigh the higher costs for transportation and storage of ammonia solution. Ammonia solution at 29% concentration (29% ammonia and 71% water) is stored in two 30,000 gallon, aboveground tanks. The maximum inventory is 25,000 gallons per tank. The tanks are each 20-foot high cylinders with 18-foot diameters and are surrounded by a containment system consisting of 6 inch thick, 50 feet long, 30 feet wide, and 3 feet high concrete walls. Two 0.7-gallon-per-minute (gpm) pumps, each fully redundant, dispense ammonia solution from each tank to the emission control equipment. Other safety equipment associated with these tanks are: pressure/vacuum relief valves, liquid level alarms, two ammonia vapor scrubbers, quick fill connections, vapor rec overy system, and seven strategically-located ammonia vapor detectors. Ammonia solution is delivered by truck into the storage tanks through a quick fill connection, located behind safety/collision barriers. The truck parks within a diked containment area, which drains to a sump in the adjacent containment dike. A truck-mounted vapor recovery system is connected to the tank vapor recovery system during the unloading. The storage tanks are equipped with pressure and vacuum relief valves and the tanks are maintained at ambient temperature and atmospheric pressure and protected from direct exposure to the sun. The loading operator is provided with a readily accessible water supply to wash spills quickly into the 8-foot trench for rapid containment. All spills are conveyed to a wastewater sump for treatment prior to discharge. Flashing lights and audible alarms at the storage area and in the main control room are activated when the ammonia gas monitors detect the gas concentration a bove 20 parts per million in the surrounding area. Ammonia solution is pumped from storage tanks to two evaporator and air mixing chamber systems, one for each SCR. Heated air is provided to the systems by dilution air fans and heaters. The air/water vapor/ammonia mixture is then injected in the flue gas that enters the SCR bed where the catalyst promotes the reaction. The turbine load and exhaust flow rate, and the nitric oxides concentration in the exhaust control the feed rate of ammonia solution. Ammonia solution from the storage tanks is also automatically fed to a 200-gallon dilution tank where the solution is further diluted to 0.3%. The diluted solution is pumped to the boiler feedwater system to control pH level. Offsite Consequence Analysis (OCA) Results: The OCA is conducted in accordance with the latest software program RMP*Comp (Version 1.06) that has been developed by the USEPA in conjunction with the National Oceanographic and Atmospheric Administration. The OC A is performed to determine the distance traveled by the ammonia released before its concentration decreases to the "toxic endpoint" of 0.14 mg/l, which is the Emergency Response Planning Guideline Level 2 (ERPG-2). The worst-case release scenario involves the failure of a bulk storage tank containing 25,000 gallons of ammonia solution; this storage quantity corresponds to 83% of the designed tank volume of 30,000 gallons. The entire volume of the solution from one tank is contained within the secondary containment system and has a maximum surface area for evaporation of 1500 square feet. The RMP*Comp regulatory default meteorological parameters including wind stability F, wind speed 1.5 m/s, air temperature of 770 F, 50% average humidity and urban surroundings, were used. The toxic endpoint distance for the worst-case release is reported to be at 0.1 miles (0.16 kilometers) from the ammonia storage area. Because the RMP*Comp reports all distances shorter than 0.1 miles as 0.1 mil es, the distance may be less than 0.1 miles. The only population potentially affected within this distance includes part of a metal recycling yard located 450 feet directly north of the storage area. The alternative release scenario involves the spill of the ammonia solution as a result of the rupture of a 3 inch diameter, 20 feet long flexible fill line during the bulk transferring of the solution from a tanker truck to the storage tanks. The transfer pump is shut off ten minutes after the leak has been detected. The volume of spilled solution is estimated to be 250 gallons. The spill is collected in a trench drain and discharged to a 5' x 5' x 4'D collector sump. The regulatory default meteorological conditions used for this scenario were: wind stability D, wind speed 3.0 m/s, air temperature of 770 F, 50% average humidity, and urban surrounding. The distance to the toxic endpoint reported by the RMP* Comp for this scenario is less than 0.1 miles from the ammonia storage area. For the purpose of identifying the distance for in-plant health and safety planning, a refined air dispersion modeling was performed using the United States Air Force Toxic Chemical Dispersion model (AFTOX). The model identified the distance to be at 0.01 miles, the shortest distance reported by the model, using local meteorological conditions and urban surroundings. Summary of the General Accidental Release Prevention Program and Ammonia Accidental Release Prevention: The general LADWP accidental release prevention program is based on the following key elements: 7 High level of training of the operators in safe handling of chemicals, 7 Effective preventive maintenance program, 7 Use of state-of-the-art process and safety equipment, 7 Use of accurate and effective operating procedures, written with the participation of the operators, 7 Performance of a hazard review of equipment and procedures, and 7 Implementation of an auditing and inspection program. Other specific steps to pr event accidental ammonia releases include: 7 The extensive training of the operators in the safe handling of ammonia, with emphasis on the hazardous and toxic properties of the chemical, 7 Required ammonia safe handling training of tank truck drivers from suppliers as well as their equipment preventive maintenance program, 7 The availability of self-contained breathing apparatus (SCBA) at close proximity to the storage tanks, 7 The installation of tank liquid levels alarm, pressure levels alarm, pressure/vacuum relief valves, vapor recovery system, gas scrubbers, and ammonia gas detectors around the storage area. 7 The installation of secondary containment system and sumps 7 Water deluge system to dilute and wash spilled ammonia solution into the sumps equipped with a high liquid level alarm. Summary of the Five Year Accident History: No accidental releases of ammonia gas or solution have occurred at this facility for the past five years. Summary of the Emergency Response Program: The facility has an emergency response program, which includes an emergency response decision tree and a notification plan. Emergency response drills and drill evaluations are conducted every year; emergency operation and response procedures are also reviewed at that time. Planned Changes to Improve Safety: Twenty-one minor changes to enhance the ammonia process safety were identified as the results of a Hazard Operability (HAZOP) study session with the facility management, operations and maintenance, and plant engineering. These recommended changes have been either completed or evaluated for implementation as required. |