• Energy Research

Abstract An integrated methodology for the simulation of practical combustion systems and NOx prediction is presented. It is based on 3D CFD simulation coupled to a postprocessor which yields reactor networks, extracted from 3D fields, as ‘equivalent’ simplified flow models for which it is possible to use a detailed reaction kinetics. The study of two glass melting furnaces is presented to illustrate the methodology. The furnaces were experimentally characterised, then CFD simulations were performed, setting the suitable boundary conditions for the radiative heat exchange and the sub-model for the chemistry. From each CFD simulation, a chemical reactor network was extracted to perform the computation of the secondary product combustion species by means of a complex kinetics mechanism. An evaluation of the models was given comparing the measurements with the temperature of the CFD field and the NOx prediction. Finally, an estimate of the effect of some NOx reducing techniques was given.

Abstract An extended Eddy Dissipation Concept (EDC) local extinction model is proposed to take into account the effects of finite-rate chemistry, normally occurring in Moderate to Intense Low oxygen Dilution (MILD) combustion, on the extinction limits. Local extinction is predicted when the local fine structure residence time is below a local critical value that is determined theoretically in the present study. The proposed model has been evaluated against experimental data reported for CH 4 /H 2 jet-in-hot and diluted coflow flames. Comparison with the standard EDC extinction model is also presented. Results show that prediction of extinction threshold in MILD combustion conditions is attainable only through the application of the extended EDC extinction model on a well-resolved turbulence–chemistry interaction field. The effect of penetrating surrounding air into the reaction zone with subsequent flame cooling at downstream is also captured by the proposed extinction model. Despite its simplicity, the extended EDC extinction model is able to describe many features of localized extinction under MILD combustion as well as conventional combustion conditions.

Two supply chains for biomethane are here analyzed and modeled: gasification of short rotation forestry (SRF) poplar wood chips and anaerobic digestion of two species of microalgae, Chlorella vulga...

Biomass fuels represent a renewable energy source, they are CO2 neutral fuels, and their use reduces the consumption of fossil fuels and limits the emissions of SOx, NOx, and heavy metals. They are...

This work proposes a simple and accurate tool for predicting the main parameters of biomass gasification (syngas composition, heating value, flow rate), suitable for process study and system analysis. A multizonal model based on non-stoichiometric equilibrium models and a repartition factor, simulating the bypass of pyrolysis products through the oxidant zone, was developed. The results of tests with different feedstocks (corn cobs, wood pellets, rice husks and vine pruning) in a demonstrative downdraft gasifier (350kW) were used for validation. The average discrepancy between model and experimental results was up to 8 times less than the one with the simple equilibrium model. The repartition factor was successfully related to the operating conditions and characteristics of the biomass to simulate different conditions of the gasifier (variation in potentiality, densification and mixing of feedstock) and analyze the model sensitivity.

Abstract In this paper we describe and test the use of a thermogravimetric technique for measuring the ignition temperatures of thin layers and beds of coal particles, and we report the results of such measurements on a South African coal, a Polish coal and two chars. The technique is to compare weight-temperature curves in air and inert (N2) atmospheres in order to evaluate the ignition temperature; the results are used to test the existing theory and to obtain kinetic constants for the reactions.

Abstract Flameless combustion is able to provide high combustion efficiency with low NO x and soot emissions. The present work aims at investigating the role of closure sub-models for the modelling of a flameless furnace, as well as the main NO formation paths. Among the different turbulence models that were tested, modified k – ɛ provides the best agreement with the experimental data, especially for temperature measurements. Reynolds stress model leads to smaller deviation for radial velocity predictions. Since in flameless combustion regime the turbulence–chemistry interaction as well as the kinetic mechanism play a fundamental role, the Eddy Dissipation Concept (EDC), coupled with four different kinetic schemes (JL, KEE58, GRI 2.11 and GRI 3.0) was considered. The GRI 2.11 and KEE58 mechanisms perform better, thus confirming the necessity of turbulence/chemistry interaction models accounting for finite-rate chemistry when flameless combustion is studied. As far as NO emissions are concerned, the N 2 O intermediate NO mechanism is found to play a major role, while thermal NO formation mechanism is not as relevant as in traditional combustion regime. An assessment of the uncertainty related to the choice of boundary conditions as well as to the choice of the parameters of the physical models is also performed. Finally the operation characteristics (such as the recirculation rate and the location of the reaction zone) of the furnace are evaluated.

This work presents a pilot-scale investigation aimed at assessing the feasibility and reliability of biomass pellet gasification. Wood sawdust and sunflower seeds pellets were tested in a 200 kW downdraft gasifier operating with air as gasifying agent. The gasification of pelletized biomass led to rather high and unstable pressure drops, reducing the gasifier productivity and stability. Furthermore the generation of fine residues compromised the operation of wet ash removal systems. On the other hand, good syngas compositions (H(2) 17.2%, N(2) 46.0%, CH(4) 2.5%, CO 21.2%, CO(2) 12.6%, and C(2)H(4) 0.4%), specific gas production (2.2-2.4 N m(3) kg(-1)) and cold gas efficiency (67.7-70.0%) were achieved. For these reasons pelletized biomass should be considered only as complementary fuel in co-gasification with other feedstock.