| The slagging problem with coal-fired furnace is very common, which is now a tough problem to ensure boilers to operate safely and economically. In our country, the quality of coal for utility boiler is low and varying too much, the boiler capacity and efficiency of combustion are reduced by 20% and 2.5% respectively because of slagging. If taking into account of the down time, repair and renovation fee of boilers, the economic loss resulted from slagging is astonishing.Slagging is a very complicated physical and chemical process which deals with several scientific courses such as combustion, multi-phase flow , heat and mass transfer etc. During the operation of boilers, the causes of the slagging are rather complicated; they are related to not only the characteristics of fossil fuel, but to the architecture and operational condition of boilers. Anyhow the slagging is formed in the combustion process, the slagging is closely related to and cannot be separated from the process of combustion. Here the paper is composed of two sections. The first part concerning the improvement of numerical modeling to the combustion process, the other section is to build the mathematical modeling of fuzzy comprehensive judgment of slagging and to predicate the distribution of slagging on the heated surface on the basis of numerical modeling and by utilizing theory of fuzzy mathematics.Compared with other general CFD software, the numerical modeling software of combustion process improved by the author of this paper has following features: (1) It can adjust the corresponding parameters and manipulating methods according to furnace architecture, operational parameters and fuels etc.; (2) It can arrange the nodes of grid flexibly and also make special calculation to certain nodes, which cannot be accomplished by the general commercial software; (3) In the boundary(water-cooled wall) condition processing, the third boundary condition is selected for the temperature calculating, linking the combustion process inside the furnace with the flow and heat exchange of water inside the water-cooled wall, so the heat absorbing and the influence of the water-cooled wall to combustion process and heat transfer of furnace are explicitly explained . The software has been used to do numerical calculation for many boilers; Quantitative analysis on the temperature deviation around the exit of furnace of tangentially-fired boilers is also conducted; So is the research on distribution of slagging on the heated surface , which provides thetheoretical basis for boiler design, optimal operation, renovation planning etc.The paper analyzes the mechanism of slagging in the coal-fired combustion process; it creates the mathematical modeling of fuzzy comprehensive judgment of slagging by utilizing the theory of fuzzy mathematics. The modeling considers not only the characteristics of fuel (including ash composition and melting point), but also takes into account of the influence of operational conditions (gas velocity, atmosphere, temperature) on slagging to avoid the unilateralism of other methods of judgment to the slagging.The fuzzy judgment of slagging described in the paper can provide the distribution of slagging on the heated surface and make judgment of the slagging condition on any spot of the furnace wall. Because the model used in the paper is different from other methods of judgment to slagging, all the variables affecting slagging are assigned the local values resulted from numeric calculation (in other methods, the parameter to affect slagging can only use one flag value ). Hence, the judgment to the slagging condition on any specific node of the grid can be made, so that effective and timely measures can be taken during operation. The combination of the fuzzy judgment of slagging a numerical modeling of combustion process provides the distribution of slagging on the heated surface, all the above methods have not been found in domestic and international publishing.Tangentially coal-fired boilers have a large market share even...
|
PDF Full Text Request