OPERATING PARAMETERS TO MINIMIZE EMISSIONS DURING ROTARY KILN EMERGENCY SAFETY VENT OPENINGS

Certain designs of hazardous waste incinerator systems include emergen cy safety vents (ESVs). ESVs (also called dump stacks, vent stacks, em ergency by-pass stacks, thermal relief valves, and pressure relief val ves) are regarded as true emergency devices. Their purpose is to vent combustion gases directly from the combustion chambers to the atmosphe re in the event of a failure of other system components. This is done for operator safety as well as to protect the incinerator and other do wnstream equipment from damage. ESVs are typically required for rotary kiln and hearth incinerators which process a portion of their waste l oad as bulk solids or contained liquids introduced continuously or in batch charges. Research has been performed at the U.S. EPA on a 73 kW (250,000 Btu/hr) rotary kiln incinerator simulator examining optimum s ettings of kiln operating parameters so as to minimize emissions durin g an ESV opening event. Experimental results are interpreted in the li ght of previous research results on transient ''puffs.'' Mechanisms go verning both the release of volatile matter during an ESV event and th e subsequent pyrolysis and oxidation in the residual sorbent bed are i dentified. From a practical point of view, results indicate that alter ation of operator-controllable kiln parameters during the onset of cer tain ESV opening events can have a significant effect on emissions of both organics and hydrogen chloride (HCI). A low air flow rate results in lower emissions of both organics and HCI. This hypothetical low ai r flow rate could possibly be equal to the flow rate induced by the na tural draft coupled with air in-leakage. Rotational speed (RPM) appear s to have slightly different effects on organics and HCl. Whereas emis sions of HCI are minimized at a very low or non-existent RPM, emission s of organics exhibit a minimum at a low (but non-zero) RPM, with incr easing emissions at both zero and high RPM. The use of a small afterbu rner to simulate an in-stack flare during an ESV event dramatically re duced organic emissions.