OCR Text |
Show of conditions. A specialized optimization algorithm is applied to control the fuel-air mixing process via swirl intensity and excess air in order to optimize burner performance, which is defmed in terms of combustion efficiency and NOx concentration, measured in the exhaust gas. An active control scheme has been postulated in order to continuously monitor NOx concentration ([NOxJ) and combustion efficiency (llc), and adjust the fuel-air mixing process to maintain optimum performance of the burner as boundary conditions vary. Given a constant burner geometry, and a set of variable input parameters (in this case swirl intensity, S', and excess air, EA), the active control system should be able to find some combination of those parameters such that a desired performance, the optimum condition, is attained and maintained. APPROACH The approach adopted was to implement the active control hypothesis in four steps: (1) development of the experiment; (2) definition of performance in quantitative terms; (3) achievement of a "proof-of-concept" phase demonstrating the viability of the active control scheme; and (4) exploration of a more advanced control algorithm and of the control scheme's reaction to a large scale change in boundary conditions (in this case, fuel load). Experiment. The burner facility and associated control hardware are shown schematically in Figure 1. Given a fixed fuel flow (load), the two inlet parameters (EA and S) are variable by adjusting the amount of air flowing through the axial and swirl air streams. First, the sum of the two air streams (mcp + me) determines the overall excess air (EA) provided for combustion. Second, the percentage of flow through the swirl air stream with respect to the total amount of air flow uniquely defines the swirl intensity (S) for this burner. To facilitate computer control of the air and fuel flow, sensor/valve Figure 1. Burner facility. 2 |