ESP MODELLING : FROM UNIVERSITY STUDIES TO INDUSTRIAL APPLICATION

The need to understand variations in the performanc e of an electrostatic precipitator, in order to rem ain in compliance with the regulations whatever coal is burned, leads us to place at the disposal of the operator a user-friendly expert investigation tool based on a complete description of the phenomena involved during the dust collection. The code used, obtained from much work in universities, calculates the dust collection efficiency per size class, as a function of the inlet velocity dis tribution and the ESP operating conditions. Before this code can be used on any industrial site , two actions must be taken : the performance of a "blind" validation test on a 250 MW plant and the r eduction of code calculation time to fulfil the operator's requirements. To test the code, a one-day test was performed on a recently renovated ESP. A limited number of data (gas flow rate, inlet dust concentration and size d istribution, ESP geometry, voltage) was provided to permit the efficiency calculation. The values calcu lated by the software were then compared with the values measured : secondary current intensity, outl et dust concentration and size distribution. The comparison between the calculations and measurements shows a difference of less than 15% for the majority of these variables. New context for old ESP In a Power Plant, between producing the initial kWh and finally shutting down the unit, different changes can occur in the operating conditions (coal from different origins, greater air input due to the ageing of the material, installation of low NOx burners, restriction on rates of unburnt carbon in the ashes in order to sell them) or in the regul ation (reduction in the limit of dust emissions, restriction of SO 2 and NO x contents…). In order to respect to the new dust emissions limit , the operator has several solutions from renovation, often involving large investment costs, to lowering the charge, penalising the viability of the unit. A compromise consists in studying the origin of the deterioration in performance, then quantifying the effectiveness of several improvemen ts using a user-friendly simulation tool, relying on a comprehensive description of the phenomena occurring when the dust is trapped in an electrofilter : corona effect, electric field, p article charging, migration, collection and evacuation. The model used, derived from numerous university studies carried out by the team of Pr. Gallimberti in collaboration with ENEL [1-5] ev aluates the effectiveness of dust capture per granulometric class, taking into account the veloci ty cartography and the operating conditions of the electrofilter. The validation of this tool in an industrial config uration has been carried out by means of tests realised under stabilised conditions on a 250 MW un it using a recently retrofitted electrofilter; the input data necessary for the model have been obtain ed together with the output data, which allows the results of the modelling to be compared to the industrial measurements.