Measurements of NOx precursor concentration profile above the bed at a full scale W-t-E plant and the effect of precursor speciation on the NOx formation

Satisfactory result from CFD modelling of NOx formation during combustion of waste in grate-fired waste-to-energy plants relies heavily on an accurate description of the temperature field in the free-board, this is a consequence of the high dependency of the temperature on the fuel NOx chemistry [1,2].

Modelling of the temperature field in the free-board in a CFD code relies on an accurate determination of the boundary conditions from the bed into the computational domain, e.g., species concentrations, gas temperature and gas velocity. Most CFD models of grate-fired waste-to-energy plants use a stand-alone model of the bed, describing the waste devolatilisation and the partial oxidation of volatiles, which have been coupled with the CFD model.

The drying, devolatilisation and volatile oxidation in the bed is strongly coupled with the combustion of gaseous species in the free-board due to the radiation onto the bed as indicated in figure 1. The devolatilisation of the fuel and partial oxidation of the volatiles in the bed, generated during devolatilisation, has been coupled with the combustion of gaseous species in the freeboard and been applied with success in previous studies [3, 4].