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Show 3. NEW SYSTEM DESIGN (cont'd) Continuous Emission Monitoring Systems Now that all the major control features have been presented, the NOx emission monitor technique shall be reviewed. In the past the use of a Continuous Emission Monitoring System (CEMS) has been used. This is basically a NOx and oxygen (for correcting the NOx reading to some standard oxygen) analyzer enclosed in a analyzer house. The difference between these analyzers and say, the NOx and oxygen analyzers for control, is that these will be used for reporting compliance to the local regulatory officials. As such, these analyzers have more stringent requirements such as permitting or periodically reporting the following: • Acceptable models and sample methods • Calibration • Calibration gas quality • Maintenance • Testing These are to name a few and the local regulatory department should be contacted for more detailed information. Safety Shutdown Systems In designing any system, safety must be considered. When dealing with combustion equipment such as a fired heater, safety is the number one issue. To insure a safe and reliable system, a safety shutdown system (SSD) is installed. Since a whole paper can be written on this subject, this paper will only touch on the basic choices available. Surveys show that the largest number (> 85%) of heater explosions occur during start-up. The remaining mishaps occurred during upsets or by operator error. The SSD system is deSigned to address the first two causes. The target issue in developing an SSD is to keep it safe, simple, and reliable. To be safe means to protect against any possible deviation that can exist, such as losing a fan, hence combustion. To be simple means not to add all the "bells and whistles" available since, as stated previously, the more complex it is the less it will be used. Lastly, to be reliable means to insure the system doesn't shutdown prematurely (nuisance trips). 11 |
