Looking into the fire with infrared …
Infrared cameras can now be used to follow fires in the combustion chamber of waste incineration plants (MVA). Dr. Martin W alter from the Ruhr University in Bochum has developed a way to significantly optimize waste incineration in his "Investigation of processes for the continuous analysis of waste incineration in grate furnaces using infrared thermography". Infrared images provide information about the location of the main fire zones and the development of the fire over time. The operators of the waste incineration plant can thus better control the incineration processes. The aim of further research by Dr. W alter was the online evaluation of the infrared images and the integration into the automatic process control.
In waste incineration plants, the waste falls through a shaft onto the combustion grate and is then transported through the combustion chamber. The air passed through the grate and the high temperature - over 1000°C - dry the waste until it ignites and burns out completely on its way through the firebox. Infrared cameras in the combustion chamber now provide the operator with direct information about the ongoing combustion process. He can then regulate the optimal firing temperature by varying the air supply on the combustion grate or by changing the transport speed and the amount of waste in the combustion chamber. The infrared cameras record the thermal radiation and provide information about the temperature distribution of the waste on the incineration grate.
In experiments at the waste incineration plant in Hamburg Stapelfeld, the scientist from the Ruhr University Bochum found out which factors influence combustion. There is therefore a clear connection between the location of the fire in the combustion chamber and the amount of air flowing in. He used this knowledge for a new control strategy based on online processing of the infrared images: The position of the main burn-out zone is calculated and the individual sources of fire on the combustion grate are identified. The results are fed into a process control computer which automatically optimizes the firing conditions. So far it has only been possible to exploit the influence of these factors indirectly; one was dependent on the measurement results of smoke gas development and emissions during a combustion process and could only control the fire afterwards.
Operators of waste incineration plants have difficulties in adapting the firing process to the - largely unknown - waste mixtures. The composition of the waste is constantly changing, partly due to mixtures from different catchment areas, partly due to seasonal fluctuations. As a result, the incineration properties of the waste also change continuously. Wet garbage, for example, takes a long time to dry; it ignites later than dry waste and burns out much more slowly. There is thus a risk that wet waste will not burn out completely and the resulting slag cannot be further utilized. On the other hand, very dry waste can ignite in the feed chute in front of the combustion chamber and cause a fire there. The operation of incineration plants therefore requires intensive observation by the staff and has so far led to generously dimensioned and expensive plants. The use of infrared technology means that combustion operations are made significantly easier.
Dr. W alter's analysis methods will be used in a further developed version at a new waste incineration plant in Hamburg. The infrared recordings are used online by a fire power control concept that works with fuzzy logic. This methodology allows intermediate values to be defined between normal yes/no ratings. They become mathematical equations that computers can use to process statements such as "pretty warm" or "pretty cold." In this way, human-like ways of thinking and empirical knowledge are transferred to computer programming. This technology is particularly suitable for controlling systems that cannot be described exactly using mathematical models, but can be perfectly controlled by human operators. The new waste incineration plant will go into operation at the end of the year.
