Two papers written by IFRF staff and collaborators and based on research carried out in the last two years have been accepted for oral presentation at one of the foremost events in the international combustion calendar. The two IFRF contributions which will be presented at this year’s 13th International Symposium on Combustion in Beijing, China are “Oxidation model for 24 bituminous coal chars: variable or constant activation energy?” and “Retrofitting oxy-fuel technology in a semi-industrial plant: flame characteristics and NOX production from a low NOX burner fed with natural gas.”
The papers both represent attempts to revisit previously reported IFRF raw data to get new insights into fundamental and applied combustion issues.
The contribution “Oxidation model for 24 bituminous coal chars: variable or constant activation energy?” by Oskar Karlström, Anders Brink, Jarek Hercog, Mikko Hupa and Leonardo Tognotti is the result of a collaboration between Abo Akademi in Finland and IFRF.
In the study, the oxidation of 24 bituminous coal chars is modelled with variable activation energy for each coal char and constant activation energy for all chars. Modelled burnout history, from 0 – 70% of burnout, are compared to experimental measurements obtained by IFRF in the last 20 years (see IFRF Doc. No D 10/y/01), by means of an isothermal plug flow reactor operating at temperatures and heating rates typical of pulverized fuel industrial combustion. The kinetic parameters used in the model are determined from fitting burnout history to the experimental measurements. The results show that a constant apparent activation energy of 74 kJ/mol is suitable for most of the 24 chars. Since most comprehensive CFD codes for modelling of pulverized fuel combustion use simple kinetic/diffusion char models, these findings provide additional confidence in achieving predictivity, at least for the main combustion regions of the boiler where most of the heat is released by pulverized fuel. This is not the case for late stages of char oxidation that should be treated by means of a more detailed and uncoupled post-processed approach to predict carbon in ash or mineral matter effects and transformations.
An extended version of the paper, with all the data and calculations, will be published as an IFRF report shortly, in the frame of the project “IFRF Solid Fuel Database”. Readers are reminded that one of the objectives of the project is to provide common solid fuel characterisation guidelines and procedures, and launch a benchmarking activity on solid fuel characterisation through the EFRI programme. The IFRF’s online SFDB Forum will carry information on related initiatives in the near future and details will be announced in MNM.
The paper “Retrofitting oxy-fuel technology in a semi-industrial plant: flame characteristics and NOX production from a low NOX burner fed with natural gas” comes from one of the main IFRF activities, generating new semi-industrial data sets for validation of comprehensive combustion models. New technological drivers are in the field of CCS (Carbon Capture and Sequestration), in particular oxy-combustion.
Resulting from the ongoing collaboration between IFRF (G. Coraggio, L. Tognotti) and ENEL, Engineering and Innovation Division, Technical Area Research, the paper reports part of the results of the campaigns performed last year (IFRF Doc. No. F 110/y/01) on a low NOX burner, firing natural gas in oxy-fuel conditions. The results of combustion tests on burning natural gas with different flue gas recycle rates are presented, with a particular emphasis on NOX production that might affect retrofitting of oxy-fuel technology in conventional boilers.
The process and flame characterisation performed on natural gas provides a valuable set of experimental data for the technological development of oxy-combustion burner technology with recycled flue gas, especially in retrofitting scenarios. The data can be used to develop a better understanding of the chemical and physical phenomena involved in oxy-fuel combustion and can provide modellers with a valuable hint for the development of specific sub-models for oxy-combustion simulation. Since it seems technologically unfeasible to reduce down to zero the presence of nitrogen in recycled flue gases, due to air in-leakages, the presence of relatively small amounts of nitrogen in crucial location in the burner provides a thermal NOX source, depending on local levels of temperature and oxygen concentration.
IFRF, together with certain Member Organisations, is using past and new IFRF reports on reference burners in conventional and oxy-combustion in FO.SPER/Furnace #1 as the database for model validation and benchmarking. An important milestone will be the CFD Validation Workshop to be held on Wednesday 16 June in Renfrew, Scotland, immediately prior to the Joint Committee meeting. Valuable information has already been published via the IFRF’s online CFD forum.
For access to any of IFRF’s three online forums – CFD, EFRI, SFDB, please contact Tracey Biller.