Abstract
Log-wood furnaces with constant-flow air supply have complete combustion only during short periodes. Variable wood composition and irregular descending of the wood into the pyrolysis zone cause the air excess to vary and leads to incomplete combustion over long periods. Hence to reduce emissions, control of the combustion is needed. As a control variable, various concentrations of flue gases can be used (CO{sub 2}, O{sub 2}, CO), but these measurements need expensive equipment. Because there is a clear relationship between the flame temperature and the air excess the former may also be used as a control variable. Although the air excess is not the only parameter determining the flame temperature, keeping the flame temperature stable reduces the variation in the air excess and hence reduces the emissions. Only the primary and secondary air can be used as a controlled variable. Controlling the secondary air has a more immediate impact on the air excess, but only the primary air reaches the pyrolysis zone and can influence the quality of embers. Hence, to control a log-wood furnace primary air should be used. The setpoint of the flame temperature has been determined through extensive measurements burning soft- and hardwood of various humidities and
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Citation Formats
Kerschbaumer, D.
Control of the combustion in log-wood furnaces; Regelung einer Stueckholzfeuerung.
Switzerland: N. p.,
1990.
Web.
Kerschbaumer, D.
Control of the combustion in log-wood furnaces; Regelung einer Stueckholzfeuerung.
Switzerland.
Kerschbaumer, D.
1990.
"Control of the combustion in log-wood furnaces; Regelung einer Stueckholzfeuerung."
Switzerland.
@misc{etde_10104487,
title = {Control of the combustion in log-wood furnaces; Regelung einer Stueckholzfeuerung}
author = {Kerschbaumer, D}
abstractNote = {Log-wood furnaces with constant-flow air supply have complete combustion only during short periodes. Variable wood composition and irregular descending of the wood into the pyrolysis zone cause the air excess to vary and leads to incomplete combustion over long periods. Hence to reduce emissions, control of the combustion is needed. As a control variable, various concentrations of flue gases can be used (CO{sub 2}, O{sub 2}, CO), but these measurements need expensive equipment. Because there is a clear relationship between the flame temperature and the air excess the former may also be used as a control variable. Although the air excess is not the only parameter determining the flame temperature, keeping the flame temperature stable reduces the variation in the air excess and hence reduces the emissions. Only the primary and secondary air can be used as a controlled variable. Controlling the secondary air has a more immediate impact on the air excess, but only the primary air reaches the pyrolysis zone and can influence the quality of embers. Hence, to control a log-wood furnace primary air should be used. The setpoint of the flame temperature has been determined through extensive measurements burning soft- and hardwood of various humidities and at different power levels. It is shown that the optimal setpoint depends only on the power level of the furnace, and is independent of humidity and type of wood. A normal proportional-integral controller is suffficient to achieve good performance. Based on the steps responses of the flame temperature a simple model of the combustion was constructed. The parameters of the controller were found by simulation; a gain of 0.5 (m{sup 3}/h)/{sup o}C and 300 s integrating time gave the best results. In a time-discrete implementation a sampling time of 1 s was found to be fast enough. The results of many measurements made with this controller show a significant improvement in the combustion quality. (Abstract Truncated)}
place = {Switzerland}
year = {1990}
month = {Dec}
}
title = {Control of the combustion in log-wood furnaces; Regelung einer Stueckholzfeuerung}
author = {Kerschbaumer, D}
abstractNote = {Log-wood furnaces with constant-flow air supply have complete combustion only during short periodes. Variable wood composition and irregular descending of the wood into the pyrolysis zone cause the air excess to vary and leads to incomplete combustion over long periods. Hence to reduce emissions, control of the combustion is needed. As a control variable, various concentrations of flue gases can be used (CO{sub 2}, O{sub 2}, CO), but these measurements need expensive equipment. Because there is a clear relationship between the flame temperature and the air excess the former may also be used as a control variable. Although the air excess is not the only parameter determining the flame temperature, keeping the flame temperature stable reduces the variation in the air excess and hence reduces the emissions. Only the primary and secondary air can be used as a controlled variable. Controlling the secondary air has a more immediate impact on the air excess, but only the primary air reaches the pyrolysis zone and can influence the quality of embers. Hence, to control a log-wood furnace primary air should be used. The setpoint of the flame temperature has been determined through extensive measurements burning soft- and hardwood of various humidities and at different power levels. It is shown that the optimal setpoint depends only on the power level of the furnace, and is independent of humidity and type of wood. A normal proportional-integral controller is suffficient to achieve good performance. Based on the steps responses of the flame temperature a simple model of the combustion was constructed. The parameters of the controller were found by simulation; a gain of 0.5 (m{sup 3}/h)/{sup o}C and 300 s integrating time gave the best results. In a time-discrete implementation a sampling time of 1 s was found to be fast enough. The results of many measurements made with this controller show a significant improvement in the combustion quality. (Abstract Truncated)}
place = {Switzerland}
year = {1990}
month = {Dec}
}