| OCR Text |
Show sce oxygen system is mainly responsible for active control of transient emissions. The continuous emissions monitoring (eEM) system extracts and analyzes the gas sample downstream from the baghouse. The oxygen level signal is transmitted to the sce oxygen system for controlling the amount of oxygen flow. The extractive sampling system creates a lag time of about 30 to 40 seconds. Such a lag time is undesirable but not detrimental. The control system typically can maintain an oxygen level within +/- 1.5 percentage points of the desired set points. Water injection is also used in the sec to control temperature; up to 4000 lb /hr of water injection has been used successfully. The use of these oxygen systems improved the throughput of waste materials by over 60% while significantly reducing the transient CO problems. Waste feed shutdowns, due to high CO levels, were virtually eliminated with the use of the OLS. The substitution of oxygen for air reduced the velocity of kiln gas. Due to the decrease of kiln gas velocity which reduced particulate carryover and improved temperature control of the kiln and SCC, the slagging problem was also mitigated with the use of oxygen combustion. Continual effort is being made in order to further improve the performance and reliability of the control system. One remaining problem is that the air infiltration rate between the sce and the sampling point is quite significant and also variable over time. For example, the control system would normally operate perfectly with the oxygen concentration maintained above 12% at the baghouse. However, occasional CO excursions would occur even with over 14% oxygen readings due to excessive air leakage. Air leakage after the combustion chambers does not participate in combustion but does increase the oxygen readings which can fool the control system. Operators have to be alert to such deviations by temporarily raising the set point of the stack oxygen level and correcting the problem. An option currently being investigated is to use a fast response oxygen analyzer to measure the oxygen level at the exit of sce. This option should allow direct control of sec oxygen level by eliminating the interference of non -participating air leakage, while providing a more responsive control. However, due to the hostile environment at the sampling location (temperature up to 2400oF, high particulate loading and slagging), the reliability of such an analyzer will be a critical issue. CONCLUSIONS According to the extensive data analyzed, the oes has proven to be an essential component for both improved capacity and increased availability of the EP A Mobile Incinerator. This analysis has documented the actual operational experience when burning trash/soil mixtures and the significant improvement achieved by the implementation of the oxygen system. Through the use of the OCS, the MIS provided better system response to transient combustion behaviors and, therefore, significantly reduced transient kiln puffs :resulting from the incineration of combustible materials. Such a conclusion is consistent with observations reported by operating personnel famjliar with operational - 12 - |
