| OCR Text |
Show oxygen enrichment could aggravate transient emissions by increasing the waste volatization rate. Therefore, oxygen enrichment, per se, is not an ideal solution to the transient puff problem. Advanced combustion systems are required to maximize the benefits of oxygen, to overcome the problems associated with conventional oxygen combustion technologies and to achieve simutaneous control of excess oxygen level and temperature (~). Finally, an oxygen system has to use oxygen efficiently to make it economically attractive. DESCRIPTION OF OCS The LINDE OCS was developed to advance hazardous waste incineration technology. The OCS includes a patented "A" Burner, flow control piping skids and a micro-processor-based control console. A unique feature of this burner is that flame temperature can be adjusted by replaceable nozzles that vary the diameter and direction of the oxygen jets, thus allowing the user to achieve reduced flame temperature. As a result, the oes minimizes NOx emissions and local overheating. The oes was designed to achieve the simultaneous control of temperature and oxygen levels with a unique feedforward-feedback control logic (14). Either dynamic water spray for cooling, or liquid and gaseous fuel for heating are used for dynamic temperature control. Water, instead of dilution air, is used to absorb the excess heat from waste burning. Water vapor contains approximately twice the enthalpy per unit volume as nitrogen at around 1800oF. Therefore, for a given heat load, the flue gas volume is smaller when using water spray than when using excess air. Linde also conducted laboratory tests to develop the know-how necessary to achieve uniform temperatures while using large quantities of water and oxygen injection. The BTU input rates of fuel and liquid waste when available, are continuously fed forward to the control system for temperature and oxygen control. However, because there is no reliable way of predicting the heat content of each batch of solid waste and, therefore, its combustion behavior, feedback control is most essential to this puff control strategy. An oxygen analyzer is used to detect the oxygen level with a minimum delay. Using rapid feedback of this signal, the control system continuously adjusts the oxygen feed rate to keep the oxygen level close to the desired setpoint. Therefore, the system is able to dynamically follow the trend of oxygen demand to avoid oxygen deficient conditions, without prior knowledge of the waste feed. The DeS controls the flow rates of oxygen and fuel independently, based on the calculated requirements from both the temperature and the oxygen level control loops. Because the oes has a firing rate turndown ratio of greater than 10 to 1, the burner can range from 100% of the stoichiometric ratio to more than 1000% with stable combustion. When burning high-heat-content waste, the fuel input is often reduced to a minimum, while excess oxygen is provided through the burner to combust with combustible vapors released from the waste. This control system was demonstrated in the EPA Mobile Incineration System. - 4 - |
