Furnaces
Improved combustion control via advanced CO laser sensor Lieke de Cock, Marco van Kersbergen, Joost Laven and Sjon Brouwer discuss the achievement of improved combustion control in glass furnaces by the application of a CO and O2 laser sensor.
C
ombustion control is of key importance to ensure stable and profitable operation of glass melting furnaces. Most furnaces are fired on >1% O2 excess to be safe and not find any CO in the regenerators. This results in higher NOx values and lower efficiencies, 1% higher oxygen excess ~1% more energy. Understoichiometric firing is not recommended, due to increased refractory corrosion, increased chance of clogged chambers (more evaporation) and higher SOx emissions. The thermic most efficient point can be found just above stoichiometric conditions (~0.5% oxygen excess). Close to stoichiometric conditions, the CO concentrations can vary significantly (+/- 500 ppm) while the oxygen level remains within the accuracy of the oxygen measurements. Small variations in air leakage, temperature or gas composition are not visible in the measured O2 levels, but can easily be detected by the measured CO concentration. Therefore, control is
only possible based on CO concentration measurements when operating at optimal near stoichiometric conditions.
Optimal combustion control There are a series of key factors to achieve optimal combustion control. Measurements of flue species in the flue gas should be taken as close to the combustion process as possible to avoid influences like air leakages (additional O2) and post combustion (decreasing CO). The reaction time of the measurements should be fast and sensitive, especially when operating near stoichiometric combustion. The measurements should also be representative for the real values in the furnace. Most glass producers currently choose to be on the safe side and control on higher O2 excess values to ensure low CO levels. That is why measuring CO is that important. “Combustion control is changed from controlling O2 only to CO control. Target is to
achieve a complete combustion with various settings for the individual burners to achieve an optimized setting for each zone in the furnace. – Sjon Brouwer, Batch and Furnace manager, Ardagh Moerdijk.” Some furnaces are still operating without any measurement of O2 or CO. Concentrations up to 8% of excess oxygen and 4% of CO are observed at these furnaces. Most furnaces are equipped with O2 sensors measuring only at one point (normally the top of the regenerator). In Fig 1 the O2 concentrations in the burner port are shown (range 0-2%). A point measurement does not give a representative value for the O2 values. In the top of the regenerator even larger differences can be seen due to the large flue gas circulations. The laser sensor gives you the average value for the whole width of the burner port which results in a value that is Continued>>
� Fig 1. Oxygen distribution in the burner port of an end-port
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fired furnace (range 0-2%).
33 Glass International March 2018