A millimeter-wave imaging system for kraft recovery boilers

In this paper we present the findings of an effort to create a millimeter-wave radar system to image the internal structure of a kraft recovery boiler as well as measure the dielectric coating on the pipes. A kraft boiler is used by the paper industry to reclaim inorganic salts used in the pulping of wood. The bio-mass and salt structure of the fuel combusted in the boiler causes rapid deposition on the boiler pipes reducing the efficiency of the heat-transfer mechanism. A large portion of the generated steam is used to mitigate the build-up of the salts (using sootblowers), commonly referred to as saltcake. The steam used for maintenance consumes a substantial portion of the energy generated in the boiler. A millimeter-wave radar system capable of measuring the saltcake could add a feedback path for an intelligent sootblower mechanism. We investigate the optimal center frequency as well as required bandwidth for an effective imaging/measuring device.