REGULATIONS COMPLIANCE Metal cleaning waste streams Table 4 – Proposed ELG for Bottom Ash Transport Water NSPS  The proposed ELG outlines Average of daily values for a new guidelines for metal cleaning Pollutant Maximum for any 1 day 30 consecutive days shall not exceed wastes. The guidelines have been separated into two categories, TSS (mg/L) 100.0 30.0 “nonchemical metal cleaning Oil and grease (mg/L) 20.0 15.0 wastes” and “chemical cleaning metal wastes.” The former is discharge water from plain washing Table 5 – A Once-Common NPDES Example of steam generator components, while the latter obviously refers to Average of daily values for a Pollutant Maximum for any 1 day waste discharge from actual chem30 consecutive days shall not exceed ical cleaning processes. TSS (mg/L) 100.0 30.0 The BAT effluent limitations Oil and grease (mg/L) 20.0 15.0 for nonchemical metal cleaning wastes are shown in Table 2. Free available chlorine (mg/L) 0.5 0.2 The NSPS guidelines for pH (range) 6.0 – 9.0 6.0 – 9.0 chemical cleaning wastes are a bit more detailed, as outlined in Table • Total dissolved solids (TDS) 3. • Sulfate (SO42-) The document goes on to give the following guidelines, • Copper (Cu) detailed in Table 4, for bottom ash transport water. • Phosphorus (primarily as phosphate, PO4) And, the following text includes, “There shall be no dis• Ammonia (NH3) charge of wastewater pollutants from fly ash transport water.” • Quantity of discharge The highly publicized failures of ash storage ponds in recent years, along with increasingly stringent regulations, are moving the remaining coal plants toward dry handling systems.
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Wastewater treatment at combined-cycle plants What about combined-cycle power plants, which obviously burn a much cleaner fuel and do not exhibit the environmental complexity of coal plants? Apart from those plants equipped with air-cooled condensers, the primary constituents of a wastewater stream might consist of some or all of the following. • Cooling tower blowdown (typically represents the largest wastewater stream) • RO reject • Evaporative cooler blowdown • Quenched boiler blowdown • Plant drains In the past, a discharge permit might have looked like the data in Table 5. With regard to new guidelines, on a national level the EPA has proposed limits of 0.2 ppm for chromium and 1.0 ppm for zinc in cooling tower blowdown. However, other parameters are appearing in new state discharge permits, including the following:
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APRIL 2015 ENERGY-TECH.com
Heat Exchangers – Retrofit/Rebuild/Equipment Upgrade – Bearings – Turbine Tech: Steam – ASME: Combined-Cycle Plants