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Development of improved combustion engineering models - applicationto nox reduction processes

Objective


Task 1: Large-Scale Burner Testwork and In-Flame Sample Collection High quality in-flame gas analysis data and particulate samples have been collected for two different coals (Kellingley, a high volatile bituminous coal from northern England and Powder River Basin (PRB), a high volatile sub-bituminous coal from the western USA) during single burner trials (35MW heat input, GCV basis) on a fully instrumented test facility. The particulate samples were subjected to the following analyses: proximate analysis by thermogravimetric analysis, ultimate analysis, particle size distribution and BET N2 surface area.
High quality in-flame gas analysis and particulate samples have been collected from a front wall fired utility boiler furnace (314 MWe). The particulate samples were characterised by ultimate analysis.

Task 2: Laboratory Scale Testwork Isothermal Plug Flow Reactor (IPFR) characterisation of Kellingley and PRB pulverised coals was completed. The characterisation comprised devolatilisation and char burnout tests at several conditions and evaluation of apparent reaction orders, apparent activation energies and apparent frequency factors.

Task 3: CCSEM Analysis of the Particulate Material Samples Computer-Controlled Scanning Electron Microscope (CCSEM) characterisation of the Kellingley and PRB particulate samples collected during the single burner trials and the Kellingley particulate samples collected during the IPFR characterisation was completed. A quantified description of the particle size and composition (carbon, ash, open pores and closed pores) was produced for each char sample. The range of char particle microstructures and changes in the distribution of char particle composition during combustion of the two coals were described.

Task 4: Improvement and Testing of the Coal Combustion Models The Chemical Percolation Devolatilisation (CPD) model was used to describe the coal devolatilisation process. It was validated against the IPFR Kellingley devolatilisation results.

A model of the transient swelling of coal particles during devolatilisation was developed. It was validated against literature data for a wide range of coals, temperatures and heating rates and then used to predict the particle morphology of the IPFR char samples. The results were compared against CCSEM measured data and particle size data. Char combustion models using apparent kinetics, intrinsic kinetics and Langmuir kinetics were compared. An ash inhibition model was included to consider the influence of the ash layer on oxygen diffusion. The thermal annealing model was included for single step reaction kinetics to consider the variation in char reaction order due to variations in heat treatment. The char combustion model was validated against the IPFR Kellingley char combustion results. Simulations of the 35 MW Kellingley coal flame were made using a proprietary Computational Fluid Dynamics (CFD) model with kinetics parameters derived during the project. The results were compared with the 35 MW Kellingley test data and reasonable agreement was achieved.
The principal objective of the project is to develop improved physical and numerical models of the coal particle combustion processes which occur in pulverised coal flames, and to test these models in CFD simulations of full scale industrial burners. CFD models are increasingly applied as an investigative and design method in the power industry, but it is recognised that the current generation of codes are dependent on empirically-derived rate constants to describe many of the key process and as a result they have only correlative rather than truly predictive capabilities. The treatment of the solid phase reactions in CFD codes is considered to be unsatisfactory.
In the proposed project, these issues are addressed in a combined programme of experimental and computational work involving close collaboration between four of the strongest coal combustion research groups in Europe.
The following activities are proposed:
a. A programme of in-flame measurements (gas composition and temperature profiles) and of in-flame particulate material sampling in full scale pulverised coal flames both in a single burner test facility and in a power plant boiler,
b. Detailed characterisation of the coal combustion processes under closely controlled conditions in an isothermal plug flow reactor,
c. Quantitative microstructural analysis of the in-flame particulate material samples and the plug flow reactor products using a computer controlled scanning electron microscope, and by other techniques,
d. Development of novel physical and numerical models of the coal particle devolatilisation, char structure development and char combustion processes suitable for incorporation into the current CFD codes, and
e. Testing of the improved models against the flame structural data from the full scale testwork and against other industrial flame performance.
It is anticipated that the work proposed in this document will represent a significant step forward in the development and application of CFD codes for industrial flame simulation.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

MITSUI BABCOCK ENERGY LTD*
Address
Porterfield Road
PA4 8DJ Renfrew
United Kingdom

Participants (3)

IMPERIAL COLLEGE OF SCIENCE, TECHNOLOGY AND MEDICINE
United Kingdom
Address
Royal School Of Mines, Prince Consort Road
SW7 2BP London
INSTITUTO SUPERIOR TECNICO
Portugal
Address
Avenida Rovisco Pais 1
Lisboa
INTERNATIONAL FLAME RESEARCH FOUNDATION
Netherlands
Address
Wenckebachstraat 1, 3G-25
1970 CA Ijmuiden