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Conditional Use Permit and, Solid Waste Facility <br />Narrative <br />electricity and operates 24 hours per day. The facility is maintained and operated by 41 <br />full-time employees. <br />The Combustors: <br />Energy is produced through combustion of the fuel in three spreader stoker-fired excess <br />air combustion units (combustors or boilers). The boilers are identified as emission Units <br />1, 2, and 3. Unit 3 is approximately twice the size of units 1 and 2. The units are 128, <br />128, and 268 mmBtu/hr, respectively, which equates to approximately 11.7, 11.7 and <br />24.4 tons of RDF per hour (a smaller feed rate-ton/hr is required when TDF is used to <br />supplement the fuel mix). The combustors can also burn natural gas and fuel oil. Natural <br />gas is used at start-up and as necessary to maintain proper combustion conditions; <br />distillate fuel oil is used as a backup fuel to the natural gas. The combustion units were <br />converted from burning coal to RDF in 1988. <br />Air Emissions Control equipment: <br />All three of the combustion units (boilers) are connected to common emissions control <br />equipment, which are a dry scrubber for the control of acid gasses and a baghouse for <br />the control of Particulate Matter (PM). The dry scrubber uses lime as a reagent in the <br />chemical removal of the acid gasses. The lime is unloaded pneumatically to the lime <br />storage silo, which is protected by a fabric filter baghouse from emitting PM during the <br />unloading process. Exhaust gasses are continuously monitored for Carbon Monoxide <br />(CO), Sulfur Dioxide (SOZ), Nitrogen Oxides (NOX), opacity, and oxygen (02). A number <br />of operating parameters, including scrubber exit (baghouse inlet) temperature, and boiler <br />feedwater flow rate, are also monitored continuously. Air emissions are governed in the <br />state of Minnesota by the Minnesota Pollution Control Agency (MPCA) under the Title V <br />permitting program. ERS's air permit number is 14100003. <br />Other air emission sources on site: <br />Hot water for internal use when boilers 1, 2, and 3 are shut down is occasionally <br />provided by a rented fuel-oil-fired boiler. A natural gas-fired generator currently provides <br />emergency electrical power, for use to recharge an existing battery bank. The System <br />Operations Control Emergency Generator is included in ERS Title V air permit but is <br />maintained and operated by system operations. The Elk River Peaking Station is also <br />included in the MPCA issued Title V air permit #14100003 as an emission source on this <br />site. <br />Water usage and discharge: <br />System cooling is provided by once-through appropriations from the Mississippi River. <br />Discharge and monitoring to the Mississippi is governed by the Minnesota Pollution <br />Control Agency under the National Pollution Discharge Elimination System (NPDES) <br />permitting program. Additional groundwater appropriations are used for scrubber <br />operation and internal wastewater streams. Treatment is provided by a wastewater <br />clarifier which discharges internally to the once-through cooling water discharge. <br />Combustor waste (ash): <br />Fly ash produced in the course of waste combustion is stored in an enclosed area at the <br />facility. A fabric filter baghouse controls PM emissions during the conveyance of the fly <br />ash. The ash is shipped from the site using covered trucks to a permitted ash-only cell in <br />Becker, MN. <br />S:\Legal\Environmental\ERS\City of Elk River\City of ER - Cond.UsePermit\2010Renewal\ER CUP Renewal <br />Narrative.docx <br />Page 2 of 3 <br />