NOx reduction control system for boilers

Abstract

The invention uses an input signal directly from a fuel flow device to control the amount of ammonia injected into a flue gas stream for NOx reduction for boilers. The control system receives a signal directly from a fuel flow device that indicates the amount of fuel flow and corresponding NOx emissions. The signal is processed using an algorithm with a multi-loop controller and an ammonia mass flow control valve with temperature and pressure corrections to determine how much ammonia must be injected into the flue gas in the presence of a catalyst to achieve the desired NOx emissions reductions. A dilution air blower transports ammonia to an injection grid and subsequently, the ammonia reacts with the flue gas in the presence of a catalyst to reduce the amount of NOx emissions to the desired level. A bias function that allows a boiler operator to manually increase or decrease the flow of ammonia in order to vary the amount of NOx reduction is included and can be used as an alternate to automatic operation, thus allowing an operator to dictate the amount of ammonia to be injected into the system. Air temperature and pressure correction functions are also included to adjust the ammonia flow based on a given temperature and fuel flow.

1 . A control system, as part of a boiler system, for a selective catalytic reduction system, comprising a device to give a fuel flow input signal from the boiler and a device to give an ambient air temperature input signal, being processed and corrected by a configurable controller which sends an output signal to an ammonia mass flow control valve that sets a specific amount of ammonia to be injected to the ammonia injection skid and catalyst for NOx emissions reductions. 
     
     
         2 . In accordance with  claim 1 , a control system with the option of bias operation. 
     
     
         3 . In accordance with  claim 1 , wherein the control system can be set to hold ammonia control output at zero percent until ammonia demand is satisfied. 
     
     
         4 . In accordance with  claim 1 , wherein the control system includes relay outputs for shutting off of the ammonia when selective catalytic reduction inlet flue gas temperature is below or above a given temperature set-point. 
     
     
         5 . In accordance with  claim 1 , wherein the control system has an algorithm that sets the ammonia flow based on the boiler fuel flow or the boiler load signal.