Deposits formation on heat transfer surfaces, namely slagging and fouling, is one of the main problems associated to biomass combustion. Reducing deposits formation can optimize plant operation. Literature review and experience show a clear research demand to wards methods for on line detection of deposits in large-scale boilers. A system consisting of a monitoring model and an on-line measurement method is presented. Results of testing campaigns show the appropriateness of the model to visualize deposit tendencies, and the possibility to determine the influence of ash deposits on heat transfer using the measurement method.
Dynamic adsorption experiments have been carried out with the help of an FT-IR (Fourier-Transform InfraRed) spectrometer. Fixed bed adsorption breakthrough curves were obtained for n-butane, SO 2 and NO 2 gases as well as for the reaction products NO, N 2 O and CO 2 . The adsorption of SO 2 and NO 2 on activated carbon was studied both during single-and co-adsorption experiments at 30ºC. The activated carbon used exhibited a disadvantage towards NO 2 adsorption in that it was partly converted to NO and immediately desorbed as NO. A further reaction to N 2 O could also be observed. The activated carbon was rapidly altered and lost a notable part of its loading capacity as a result of the presence of water and oxygen. During co-adsorption, SO 2 reacted with NO 2 (both as adsorbed species) and produced an additional amount of NO. An ash-tree spherical activated carbon with an extended surface area (1000 m 2 /g) was used in all experiments.
Dynamic modeling and simulation of steam power plants is often adopted as a tool for control design, personnel training, efficiency improvement and on-line diagnostic. The boiler is possibly the most complex component of the thermal power plant. A usual boiler configuration is the so-called Once-Through arrangement. A common problem in 2-phase systems modeling is the correct calculation of the phase boundary. This is technically interesting in such boilers: the location of the phase transition changes rapidly depending on load conditions and temperature distribution along the walls. A lumped parameters, one-dimensional evaporator model implementing a moving boundary approach is presented and first validation results are discussed. The model takes into account the influence of radiation and convection on the gas side. The flow inside the pipes is divided into 3 regions (sub-cooled, 2-phase, superheated) and the model calculates the locations of the 2-phase transitions and the average steam quality along the pipes. The system is discretized using a staggered grid for higher numerical stability and is implemented in the computer program Aspen Custom Modeler (ACM). Results include the calculation of the system response to input signals simulating a load variation and a validation by comparison with a model implemented in a commercial software for power plant simulations (MMS). Input data, parameters and geometry are taken from an existing plant operating in Uppsala, Sweden.
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