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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]Not ApplicableSTATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0002]Not ApplicableREFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISK APPENDIX[0003]Not ApplicableBACKGROUND OF THE INVENTION[0004]The embodiment is in the technical field of boiler steam generation emissions control. More particularly, the present invention is in the technical field of controlling the amount of NH3 (ammonia) present as part of a selective catalytic reduction (SCR) system. Selective catalytic reduction is a post-combustion control technology that involves the injection of ammonia in the boiler exhaust gases in the presence of a catalyst to significantly reduce and control airborne contaminants of NOx, the cumulative emissions of nitric oxide (NO) and nitrogen dioxide (NO2) and trace quantities of other nitrogen-bearing species generated during combustion. Ammonia must be present for the selective catalytic reducti...

AI Technical Summary

Benefits of technology

[0012]The present invention is a NOx reduction control system designed to control the amount of ammonia used with a NOx reduction catalyst as part of a selective catalytic reduction system for boilers (package boilers, whether firetube and watertube type, indicating that the boiler is shipped to an end user completely assembled and includes a burner and controls, thus the NOx control system described here is ideal for package type boilers). This approach can be applied to new boiler application or as a retrofit to an existing boiler system in order to improve the overall operation of ammonia flow control and NOx reduction capabilities.

Problems solved by technology

Ammonia must be present for the selective catalytic reduction process to occur, however if not controlled, it can lead to what is known as “ammonia slip”, the term used when ammonia is not consumed in the reaction and passed through to the atmosphere.

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