Ammonium Bisulfate (AbS) Measurement for SCR NO_x Control and Air Heater Protection

摘要

Operating an SCR is a delicate balancing act between generating the NO_x reduction ton required to meet emission reduction goals, balance-of-plant issue such a unit availability and reliability and heat-rate. The primary constraint in running the SCR aggrievedly for maximum NO_x reduction is the formation of AbS which is a result of the reaction between Ammonia Slip and SO_3. AbS has a higher dewpoint and condenses in the air heater causing plug gage which can force a unit derate due to ID Fan limitation or a unit shutdown to wash the Air Heater. There are two possible actions that can prevent this situation. One is to run the SCR conservatively resulting in limited NO_x reduction and the other option is to artificially raise the Air heater operating temperatures using Air heater bypass or steam coils resulting is loss of heat rate. This paper will present a unique application of the AbSenor condensable measurement sensor to measures the formation of AbS and an online Air heater thermodynamic model to predict the condensation of AbS in the Air heater. Thee prediction are then used in real-time to simultaneously control Ammonia Injection rates and Air heater bypass damper opening striking a balance between NO_x reduction and Heat Rate. Data will be presented herein to demonstrate operation at improved heat rate at desired NO_x reduction with no BOP impacts.