Date of Award
2004
Degree Type
Thesis
Degree Name
Master of Engineering Science
Program
Mechanical and Materials Engineering
Supervisor
Chao Zhang
Second Advisor
Jin Jiang
Third Advisor
Dr. Youmin Zhang
Abstract
This thesis reports research work carried out to construct on-line real-time dynamic feedback controllers that will reduce the NOx emission in an industrial furnace. The work began with a detailed analysis of the mechanisms for NOx formation. Based on the knowledge gained, a low NOx furnace was designed using CFD modeling techniques to optimize the furnace configurations. The arrangement of the mixing box for recirculated flue gas and fresh air has been determined using numerical simulations. The research has shown that flue gas recirculation (FGR) is an effective way to reduce NOx. To gain a better understanding of the dynamic characteristics of the furnace, the sensitivity of the furnace to the variations of different furnace inputs has been evaluated in the frequency domain by superimposing sinusoidal signals onto the following three furnace inputs: combustion air flow rate, combustion air temperature, and the pressure head of the recirculation fan. The furnace outputs considered were the mole fraction of NOx and the mass fraction of oxygen. Frequency domain based system identification techniques have been used to convert the frequency responses to a set of transfer function representations in an effort to facilitate the control system design. Four transfer functions have been constructed and the accuracy of these transfer functions are further evaluated by means of CFD simulations. It was concluded that these transfer functions can indeed provide an accurate representation of the dynamic behaviours of the furnace around given operating conditions. To ensure that the furnace operates around the designed operating conditions most favourable to NOx minimization under various disturbances or uncertainties, possible regulation of the furnace inputs through feedback control has been investigated. Based on the knowledge gained of the dynamic relationships between the furnace inputs and outputs, a control system composed of one PID and two PI controllers has been synthesized by using nonlinear optimization techniques. The performance of the closed- loop control system has been evaluated based on both the linear models and full-scope nonlinear CFD models. In both cases, satisfactory results have been obtained. The main contribution of the thesis was to develop a methodology for the design and analysis of feedback control based NOx reduction technologies for industrial furnaces.
Recommended Citation
Jiang, Qing, "Modeling and Simulation of an Industrial Furnace with Flue Gas Recirculation for NOx Control" (2004). Digitized Theses. 4976.
https://ir.lib.uwo.ca/digitizedtheses/4976