Detecting burner instabilities using joint-time frequency methods whilst co-firing coal and biomass
- Authors: Valliappan, Palaniappan , Thai, Shee Meng , Wilcox, Steven , Ward, John , Tan, Chee Keong , Jagietto, Krzysztof
- Date: 2011
- Type: Text , Conference paper
- Relation: ASME/JSME 2011 8th Thermal Engineering Joint Conference, AJTEC 2011
- Full Text: false
- Reviewed:
- Description: Conventional coal-fired burners are designed to operate within specific limits that, in part, result from the need to efficiently burn the fuel. These designs have been developed to ensure stable combustion, lower NOx emissions and increase the combustion efficiency through techniques such as air staging and adding swirl to the combustion air. Recent requirements to reduce CO 2 emissions from coal-fired boiler plant has focussed on the co-firing of biomass, primarily wood, either by delivering the pulverised biomass with the coal or through separate burners. To date this approach has typically taken place at substitution levels of around 5% by mass and at these levels the operation of the burners and boiler is not adversely affected. However, as the proportion of biomass increases the fuel characteristics of the blend moves further away from the burner design parameters. This can lead to combustion instabilities and in extreme cases extinction of the flame. In order to co-fire higher concentrations of biomass a system or technique is required that can detect the onset of these instabilities and warn before the combustion conditions become dangerous. In this paper a novel technique based around the Wigner-Ville transform is presented that shows promise at being able to temporarily resolve the conditions that could result in the onset of burner instabilities for three cases; the first will present results from the combustion of 100% bituminous coal, whilst the second and third cases will present the results from experiments where the proportion of biomass was set at 10% and 20% by mass with the same bituminous coal. In each experiment the secondary combustion air was first reduced from a nominal stable condition and then subsequently increased from the same stable condition. It was found that the Wigner transform was able to resolve flicker frequency changes as the airflow rate was reduced. These changes were subsequently used in a neural network to automatically detect drastic changes in the air flow rates to the burner and could provide a means by which utility operators could detect dangerous flame instability conditions in real-time. Copyright © 2011 by ASME.
The monitoring and control of burners co-firing coal and biomass
- Authors: Valliappan, Palaniappan , Jagietto, Krzysztof , Wilcox, Steven
- Date: 2012
- Type: Text , Conference paper
- Relation: ASME 2012 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference p. 139-149
- Full Text: false
- Reviewed:
- Description: The monitoring and control of combustion systems co-firing coal and biomass is a critical consideration when aiming to increase the proportion of biomass being combusted. This is because it is likely that the combustion will become increasingly unstable as the biomass proportion increases. In order to develop a flame monitoring and control system, flame signal data sets were collected from combustion measurements taken on a 500kW pilot scale combustion test facility. The sensors used were photodiodes with sensitivities in the UV, visible and IR wavelengths. The analysis of these data, identified flame features that can be related to operational parameters such as flame stability, excess air level, NOx and CO emissions. These features were then applied in the development of an intelligent flame monitoring and optimisation system for individual burners based on these low cost sensors. The testing of the monitoring and control system on a pilot scale burner and at full scale are described in this paper.