Recovery Act - Terahertz Imaging in Kraft Recovery Boilers

Recovery boilers are a key component of all Kraft pulp mills and are the production bottleneck in most such mills. Formation of deposits on the outside of heat transfer tubes can cause plugging of the gas passages within the convective sections of the boiler leading to unscheduled outages and lost production. High pressure steam lances (sootblowers) used to clean the outside of these heat transfer surfaces consume as much as $1 million in steam per year per boiler, but the lack of adequate real-time inspection capability in large sections of the boiler prevent effective and efficient use of these sootblowers to remove deposits leading to excessive steam usage. The proposed project will develop and demonstrate a terahertz measurement/imaging system that can be used to produce clear images of the interior of an operating kraft recovery boiler at all locations within the boiler, allowing for much more efficient use of sootblowing steam and potential savings of ~0.0116 Quads of energy and $210 million per year nationwide. The energy savings is accompanied by reductions in pollutants associated with the production of that saved energy and amounts to ~36 MM lbs of SO2 and 7 MM lbs of NOx per year nationwide. This same terahertz measurement system will also provide quantitative measurements of the thickness and size of saltcake deposits on heat transfer tubes and it will provide information on the chemical composition of those deposits. In the proposed Phase I project we will customize an existing terahertz measurement system developed by our collaborator, Professor Antao Chen at the University of Washington, to enable that system to perform proof-of-concept experiments in an operating Kraft recovery boiler at the Simpson Tacoma Kraft pulp mill in Tacoma, WA. Enertechnix will model the propagation of terahertz waves through the particle-laden recovery boiler gases and we will develop suitable housings and air-purged probes to allow the terahertz system to operate in the recovery boiler environment. The University of Washington will adapt its existing terahertz measurement system to accommodate the available inspection port geometry and the increased working distance imposed by the separation between the inspection port and the heat transfer tubes inside the furnace. Commercial Applications and Other Benefits: The proposed technology has potential commercial applications in virtually all the process industries. In addition to making measurements and providing clear images in high temperature processes, a terahertz measurement system can provide measurements of gas composition in a wide variety of situations such as detecting and visualizing gas leaks in petrochemical plants and can be used to inspect products for quality assurance purposes.