Title:
Influence of Uneven Fuel Distribution on A Grate on Gas Flow and Combustion Quality
Author(s):
Kiener, M., Nussbaumer, T.
Document(s):
Paper
Abstract:
Grate boilers are widely applied for biomass combustion and achieve high combustion quality in good operation conditions. However, uneven fuel distribution such as e.g. uncovered grate sections can occur due to part load operation or changing fuel properties. Uncovered grate sections influence the flow conditions and are assumed to cause increased emissions from incomplete combustion such as carbon monoxide (CO). The objective of this investi¬gation is to analyse the influence of the grate coverage on the flue gas emissions by experiments and CFD modelling. Experiments are performed on a 1.2 MW moving grate boiler. The grate coverage is varied by different primary air settings. To identify the grate coverage and to derive gas profiles for the CFD calculations, pyrolysis gas measur¬ements (CO, CO2, CH4, H2, O2 and H2O) above the grate with an oil cooled sampling probe are performed. Flue gas analysis is performed with use of CO as indicator for the combustion quality. Experiments and CFD modelling confirm a relevant influence of the grate coverage on the combustion quality. With increasing uncovered area at the end of the grate, CO emissions increase. A change from an ideally covered grate with 80% coverage and CO emissions of 25 mg/m3 at 11 vol.¬% O2 to a highly uncovered grate with 40% coverage, a CO increase by a factor of 2.5 is found in experiments. CFD modelling predicts an increase by a factor of 3.9. Hence modelling is qualitatively validated by experiments and uneven fuel distribution is confirmed as a source of increased emissions. Measures to reduce emissions due to uncovered grates are discussed.
Keywords:
emissions, measurement, modelling, sampling, wood chips, grate combustion
Topic:
R&D on Biomass Conversion Technologies for Heating, Electricity and Chemicals
Subtopic:
Solid biofuel combustion for small and medium scale applications
Event:
20th European Biomass Conference and Exhibition
Session:
2BO.10.2
Pages:
761 - 767
ISBN:
978-88-89407-54-7
Paper DOI:
10.5071/20thEUBCE2012-2BO.10.2
Price:
FREE
