Robust optimal control of a natural gas-fired burner for the control of oxides of nitrogen (NOx)

Tightening requirements on industrial boilers and furnaces will require hands-free techniques to (1) assure peak performance with respect to emission, and (2) assure an ability to achieve peak performance throughout a load duty cycle, In the present paper, robust optimal control of a model industrial, swirl-stabilized, natural gas-fired burner is explored as a strategy to attain and maintain low flute-gas nitrogen oxide concentration ([NOx]) concomitant with high combustion efficiency (eta(c)). A performance index, J, is defined such that the maximization of J correlates to optimal burner performance, with respect to [NOx] and eta(c). Two parameters, swirl intensity (S') and excess air (EA), are made amenable to control and incorporated as variable burner inputs. For a given load, the settings of EA and S' are automatically adjusted by a specialized search algorithm in order to maximize the performance index, thereby optimizing eta(c) and [NOx]. The robustness of the approach is demonstrated and evaluated by initiating a change in load and observing the reaction of the modified control system. The control scheme is shown to effectively increase and maintain overall burner performance. Implementation of robust optimal control to practical systems is discussed in terms of challenges outstanding and opportunities to integrate with overall system performance.