Grate furnace

The traveling-grate furnace requires less labor, increases the output per unit of grate area, and produces more uniform product than the WetheriU. furnaces. The traveling grate is an endless chain of cast-iron bars, driven by sprockets, which traverses a firebrick chamber. Anthracite briquettes are fed to a depth of ca 15 cm. After ignition by the previous charge, the coal briquettes are covered by 15—16.5 cm of ore/coal briquettes. The latter are dried with waste heat from the furnace. Zinc vapor evolves and bums in a combustion chamber and the spent clinker faUs into containers for removal (24,25). 

Clinker treatments are additives designed to reduce the amount of clinkering formations that takes place in boilers fired by bark, bagasse, and similar low-calorific-value fuels. These fuels can give rise to considerable amounts of noncombustible deposits that must be continuously or regularly removed from the furnace area. Clinker treatments are formulated for use with various types of furnace, including slant, pin hole, and chain grate furnaces. 

The roasting process mostly applied to sulfidic sources is carried out in appliances of different types with different design features. Without describing their features and constructional details, it may simply be mentioned here that some of the widely acclaimed roasting units are traveling grate furnaces, multiple hearth furnace, rotary kilns, and fluid-ized-bed roasters. 

Thermal Biomass Conversion and NOx Emissions in Grate Furnaces... 

A popular small-scale thermal biomass conversion method is combustion in grate furnaces. To meet the emission regulations for such a furnace, the operating conditions and design of the furnace have to be chosen carefully. Numerical models, known as computational fluid dynamics (CFD), can support the making of these choices, provided that accurate sub-models for the phenomena occurring in the oven are available. 

Fig. 8.5 Sketch of the processes occurring during solid fuel combustion in a grate furnace.

Fig. 8.10 2D predicted profiles of (a) mean mixture fraction, (b) mean temperature and (c) mean NO mass fraction for the biomass grate furnace. 

The present research has treated important parts of the modeling of combustion and NOx formation in a biomass grate furnace. All parts resulted in useful approaches. For all these approaches successful first steps were taken. Currently, more research is underway to obtain improved results NH3 production is measured in the grid reactor with the tunable diode laser, detailed kinetics will be attached to the front propagation model, including the measured NH3 release functionalities, and for the turbulent combustion model heat losses are taken into account. In addition, the fuel layer model has to be coupled to the turbulent combustion model in the furnace. 

Albrecht, B.A., Bastiaans, R.J.M., van Oijen, J.A., de Goey, L.P.H. NOx emissions modelling in biomass combustion grate furnaces, in Proceeding of the 7th European Conference on Industial Furnaces and Boilers (INFUB ), Reis, A., Ward, J., Leuckel, W., (Eds.), Porto, Portugal, ISBN 972-99309-1-0, (2006). 

Scharler, R., Fleckl, T., Obernberger, I. Modification of a Magnussen constant of the Eddy Dissipation Model for biomass grate furnaces by means of hot gas in-situ FT-IR absorption spectroscopy,... 

The objective of Lamb et al s experimental work [4] was to obtain measurement data on burning rates (conversion rates) of a simulated crosscurrent moving bed. The experimental data would be applied to the combustion process in an inclined grate furnace. 

Ford N., Cooke M.J., and Pettit M.D.,"The use of a laboratory fixed-grate furnace to simulate industrial stoker-fired plant", J. of the Institute of Energy 65, 137-143 (1992)... 

A pigment-grade zinc oxide rotary kiln uses high temperature to produce pigment-quality zinc oxide and makes possible higher recovery than a grate furnace. 

Figure 13.2 Sketch of a large-scale, continuous moving grate furnace.

Management of bottom ash is a relatively less severe problem. In the case of a continuous moving grate furnace, bottom ash is discharged at the bottom of the... 

For general use, the application of macrokinetic data has to be excluded. As has been shown by [7] for the pyrolysis of wood, the influence of the heat transfer in the particle cannot be neglected if particle diameters are in the range of several milimeters. Thus, the assumption of homogenous temperature distributions over the particle is not valid and a different set of macrokinetic data for each particle diameter would be needed to cover the influence. In understoker and grate furnaces the wood particles used are typically sized between 5 and 25 mm. which requires the heat and mass transfer depending on the size of the particles to be taken into account to avoid macrokinetic data. 

The authors want to acknowledge the financial support by the European Union research project Reduction of Nitrogen Oxide Emissions from Wood Chip Grate Furnaces (JOR3CT960059). Moreover thanks are addressed to C. Lopez and E. Herrero performing part of the calculations. 

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