Colmac Energy, Inc. - Executive Summary |
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The Colmac Energy power plant consists of two biomass-fired boilers to supply steam to a single turbine generator producing 47 MW of electric power which is sold into the electric grid. The facility is located on the Cabazon Band of Mission Indians Reservation near Mecca, California. Ammonia, the only regulated substance present at the facility, is required by a permit condition for the purpose of reducing nitrogen oxide emissions (NOx) in the combuster flue gas using a process referred to as Thermal DeNOX. The Thermal DeNOx system consists of one 12,000 gallon (9,840 gallon working capacity) ammonia ASME code pressure vessel, one liquid ammonia vaporizer, ammonia injection system, and associated piping, fittings, valves, instruments, and controls. The storage tank is equipped with 265 psi safety valves to control overpressure in the tank and excess flow valves to control leaks that could be caused by potential breaks in the piping. The ammonia NOx control system operates at a press ure of 45 psig. The maximum amount of ammonia present on the site is 55,800 lbs. Ammonia is delivered to the site by truck. The ammonia system is a fully automatic system equipped with numerous sensors to monitor system performance on a real time basis and to control or shut in the system if necesarry. Alarms include storage tank high and low pressure, high and low temperature, high and low level; vaporizer high temperature and isolation valve failure to close; ammonia tank vapor outlet failure to close; and ambient ammonia high (3 sensors). One ambient ammonia sensor is installed on the top of the ammonia tank and one near each boiler at the point of injection into each respective hot cyclone. Tripping of the ambient ammonia sensor will automatically alarm the control room, isolate the vaporizer by closing valves, and shut off flow of ammonia from the storage tank by closing a valve. Prior to construction of the plant in 1991, a Risk Management and Prevention Program (RMPP) was developed that, among other things, included a Hazop study, seismic assessment, offsite consequence analysis, and review of of the facilities auditing and inspection procedures, record keeping procedures, contingency planning, and training. The RMPP was reviewed and recertified in June, 1999. It was found that the design and operation of the ammonia system had not changed since the installation and that the entire ammonia system was refurbished in April, 1998. The refurbishment included the draining, inspection, and refurbishment of the tank, and the inspection and maintenance of the safety valves, flow regulators, level indicators, and control system. Colmac interfaces with both the Cabazon Band of Mission Indians Fire Department and Riverside County Fire Department regarding emergency response at the facility. Colmac has developed Emergency Response procedures to be utilized in the event of an emergency at the facility. Training for the ammonia system, including response to a mmonia releases, is provided by the supplier and consists of hands on activities. In accordance with RMP regulations, the worst case toxic release consists of the release of the entire contents of the ammonia system (55,800 lbs) over a ten-minute time period. Atmospheric conditions were assumed to be those that would result in the largest downwind distance to the endpoint concentration of 0.14 mg/L (200 ppm). These were stability condition F with 1.5 m/sec wind. The topography was determined to be "rural". Using EPA protocols, the distance to the endpoint was determined to be 4.4 miles. This would overlap the unincorporated area of Mecca. The alternate toxics release was assumed to be a release of ammonia from one of the pressure relief valves on the ammonia storage tank. It was assumed that the release would last for one minute. The release rate was calculated to be 174 lbs/min. The endpoint was calculated for more typical atmospheric conditions consisting of atmospheric st ability D and 3 m/sec wind. The distance to the endpoint was determined to be 0.3 miles which extended slightly off site to the south. No populated areas were overlapped. There have been no reportable accidental releases of ammonia from the facility during the past five years. It was determined that no changes to improve safety are warranted. |