Chemistry and Mixing Effects in Reburning

Peter Glarborg, Anker Jensen, DTU
Lone M. Schmidt, Niels B. K. Rasmussen, december 2000, R0011

The objective of the work was to develop an engineering model for gas injection systems with detailed chemistry that in a simple manner can be used to simulate processes like Natural Gas Reburning.

The work involves improvement and validation of detailed kinetics models for hydrocarbon oxidation and hydrocarbon/nitrogen interactions, based on flow reactor data covering a wide range of hydrocarbon fuels, temperature and stoichiometry. Furthermore, a systematic analysis and evaluation of different approaches for modeling of jet mixing systems with simplified fluid dynamics and detailed chemistry was planned. The preferred mixing model was to be validated through comparison with literature results on reburning.

The project, planned to last three years, was terminated shortly into the second year, following the discontinuance of the GRI Basic Research Program. The emphasis during the first part of the project has been on the chemistry of the reburn process. The major uncertainties are associated with 1) the hydrocarbon oxidation chemistry, in particular prediction of the concentration of the HCCO radical largely responsible for NO removal in Natural Gas Reburning, and 2) rate constant and product channels for the HCCO+NO reaction.

A comprehensive experimental database on hydrocarbon oxidation in a flow reactor under a wide range of fuels (C1 and C2 hydrocarbons) and reaction conditions (temperature, stoichiometry, pressure) has been established and compared with modeling predictions with our current reburn mechanism as well as GRI Mech 3.1. In general, both mechanisms perform satisfactorily, but important deviations have been identified, which need to be addressed in future work.

In order to characterize HCCO reactions, in particular HCCO+NO and HCCO+O2, flow reactor experiments with a convenient precursor for HCCO, carbon suboxide (C3O2), have been conducted. The oxidation of C3O2 with and without presence of NO was investigated at different temperatures and stoichiometries. Data are interpreted in terms of a detailed chemical kinetic model.

A preliminary mixing model, based on the approach by Zwietering, in combination with the detailed reaction mechanism has provided a satisfactory description of bench and pilot scale data on reburning from literature.