K. Ehrhardt

Modeling of NOx reburning in a pilot scale furnace using detailed reaction kinetics

Abstract A Zone Model has been developed for the prediction of NO reduction by “reburning” in turbulent diffusion flames. The computations of fluid dynamics are decoupled from those of detailed combustion chemistry including those of the nitrogen species. The calculations begin with the computations of the stream function, heat release, temperature, and major species concentration distributions using a commercial CFD code and simple, one or two step chemistry. The modeled space is then subdivided into volume elements (zones) bounded by streamlines and some axial coordinate. The sizes of these zones are much larger than those of a computational grid so that it is practicable to use detailed chemistry for the calculation of progress of reaction within such a zone. In the experimental investigation natural gas with and without additive NH3 was used as “reburn” fuel. It was injected axially into the NO bearing combustion products of a 335 kW natural gas-air flame to obtain a parabolic flow which can be modele...

Continuous generation and air-assisted atomization of fuel oil-water-emulsions

In the present work a simple and inexpensive device for continuous generation of emulsified liquid fuels has been developed, which can for instance be used for NO-reduction in gas turbine application. The emulsification process was based on liquid-in-liquid atomization, hence water and oil were injected into a cell by means of pressure-swirl nozzles. The use of a nozzles for each stream ensured, in contrary to just one nozzle for one of them, fine emulsification in wide control ranges. The emulsions were sufficiently stable so that no surfactant was required. Jets of water-in-oil emulsions disintegrated easily and significantly faster than the pure substances or oil-in-water emulsions. This property of water-in-oil emulsions leads to significantly finer air-assist atomization.

Assessment of Atomization Quality with Respect to Burnout for the Incineration of Organically Contaminated Waste Waters

abstract Three different air-assist nozzles were investigated with a Phase-Doppler-Analyzer and high speed photography in a cold environment and then used in a pilot scale furnace at a thermal input of 200 kW. Waste water was simulated by a water-glycol mixture. Measurements showed temperatures above 1100°C and homogeneous oxygen concentrations except close to the burner. With such conditions evaporation and, hence, atomization quality set the limits on burnout, as oxidizing reactions are fast. The Sauter Mean Diameter (SMD) did not correlate closely with burnout since SMD indicates a mean droplet size while performance is limited by the number oflarge droplets present. Betteragreement was achieved for D90%. which is a parameter that represents the upper end of the size distribution. High speed photography is recommended to detect and measure the largest droplets in the spray. Their size correlated closely with the onset of incomplete burnout and is, therefore, an appropriate parameter to characterize ato...

Modeling of NOX reduction by reburning

Reburning is a powerful and relatively inexpensive technique to reduce the NO x emission from industrial incinerators or coal fired power plants. NO x reduction is achieved by means of secondary fuel injection. The aim of the reported theoretical and experimental investigations has been to develop modeling tools for combustor design and layout. Detailed kinetic models from the literature have been tested and modified to describe species interconversion under practical reburning conditions. Furthermore, a hybrid model has been developed which allows calculation of the NO reduction in practical flows. It separates the computation of the turbulent flow from the computation of NO reduction. The latter is performed by a postprocessor using detailed kinetics. Both models have been validated against experimental data from test facilities in semi-technical scale, and their predictions agree satisfactorily with the experiments.

Experimental study on the dependence of burnout on the operation conditions and physical properties in wastewater incineration

The incineration of wastewater was investigated in a pilot-scale furnace with respect to burnont. The existence of two regimes was proved. At temperatures higher than approximately 900°C, burnout is controlled only by evaporation, as the oxidation kinetics of carbon monoxide and hydrocarbons are fast. Below approximately 850°C chemical kinetics limits burnout, provided that atomization is fine and, therefore, evaporation of droplets is fast. For evaporation-controlled conditions, the influence of volatility was investigated for alcohols dissolved in water as well as for oil-in-water emulsions. For solutions, the lighter species deplete during droplet evaporation due to distillation processes, and activity coefficients must be considered for a proper assessment of volatility. For emulsions, the disperse oil phase evaporates very fast so that fuel oil#2 exhibited the same volatility as methanol. This effect was attributed to a phase separation during droplet evaporation. Under reaction-controlled conditions, the oxidation of alcohol vapors, CH4, and CO was investigated and the data were evaluated assuming global reactions of first order. CH4 and CO required temperatures of 790 and 850°C, respectively, to allow a destruction efficiency of 99% by oxidation within one second. The thermal stability of the alcohol vapors was significantly smaller. The measured oxidation rates of CH4 and CO were accurately modeled with detailed reaction mechanisms, whereas some global rate expressions gave unreasonable results for the investigated conditions.