Residual ash is dumped at the end of the grate into an ash pit, and combustion gases go out the top of the boiler. The problem in this application was that a considerable amount of unburned wood was being entrained by the gas and carried through the steam-generating banks. Technicians at the plant tried adjusting the boiler's operating parameters. Above the windswept spouts, the combustion air is introduced into the boiler through four rows of overfire air ports, two on the front wall and two on the rear wall. Each row has seven or eight ports with 4-inch nozzles, with the front wall ports opposing the rear wall ports.
Undergrate air is introduced under the stoker grate through a compartmentalized wind box.
Technicians at the boiler site tried changing the airflow distribution as well as increasing and decreasing the fuel intake through different spouts without any success. They turned the problem over to analysts at McDermott Technology Inc. in Alliance, Ohio, a unit of McDermott International Inc., a leading provider of engineering, procurement, and project-management services. McDermott analysts have used CFD for the last decade to analyze airflow and combustion inside power boilers. A CFD analysis provides fluid velocity, pressure, and temperature values throughout the solution domain for problems with complex geometries and boundary conditions. As part of the analysis, a researcher may change the geometry of the system or boundary conditions such as inlet velocity and flow rate, then view the effect on fluid-flow patterns or concentration distributions.