Comparison of Two Designs for the Spiral Casing of the Fan Grinding Mill. Porovnání dvou konstrukčních variant spirálové skříně ventilátorového mlýna

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1 Comparison of Two Designs for the Spiral Casing of the Fan Grinding Mill Porovnání dvou konstrukčních variant spirálové skříně ventilátorového mlýna Richard KLUČKA 1 Abstract: This work deals with comparison of two design variants of the spiral casing for the fan grinding mill, according to the stress and deformation states. Computer modelling was used for solutions of this problem (i.e. the Finite Element Method FEM with application of sub-modelling principle). In the begining, the creation of computational models is described. From the results of analyses was determined that both variants had almost the same values of displacements. The important differences are only in the distributions of equivalent stresses (von Mises) and plastic strains. Finally, the comparison of both variants is evaluated and the new design, which considers the use of skid plates in the lower part of the casing, is proposed. Abstrakt: Práce se zabývá srovnáním dvou konstrukčních variant spirálové skříně ventilátorového mlýna z hlediska stavů deformace a napjatosti. Pro řešení úloh bylo využito počítačového modelování (metoda konečných prvků MKP s využitím principu submodelingu). V úvodu je popsána tvorba výpočtových modelů. Z analýz výsledků bylo stanoveno, že obě varianty mají téměř shodné velikosti posuvů. Významné rozdíly jsou v rozložení redukovaného napětí (HMH) a plastických deformací. V závěru je provedeno zhodnocení obou variant a je navržen nový design uvažující využití kluzných desek v dolní části skříně. Keywords: FEM, fan grinding mill, elastic foundation, thermal loads, strength analyses, plastic strain, submodelling, thermal power plant Klíčová slova: MKP, ventilátorový mlýn, pružný podklad, teplotní zatížení, pevnostní analýzy, plastické deformace, submodelling, tepelná elektrárna 1. Introduction Fan grinding mill activity consists of the milling of lignite (by discarding on cabinet walls with using grinding wheel, which is stored briefly) and the blowing of resulting powder into the separator. The powder then goes to the boiler, where it starts burning. The resulting heat is used to steam production and then to spin of turbine and generator for electricity production. The goal of this article is to compare two structural variants in the terms of stresses and deformations (total displacement) resulting from the treatment of lignite. The results are applied in the reconstruction of thermal power plant Pruneřov in the Czech Republic (IVITAS company). 2. Technical system The technical system consists of several components (see Fig.1). The entire system is stored on a concrete foundation (which is simplified by elastic foundation, modulus of the 1 M.Sc. Richard KLUČKA, VŠB - Technical University of Ostrava, Faculty of Mechanical Engineering, Department of Mechanics of Materials, Ostrava, Czech Republic, +420 xxxxx, xxx@vsb.cz

2 foundation K = 14.7 Nmm -3, see references [5] to [7]) and fixed against spontaneous movement by a set of anchoring elements. Weight of the whole system is 50 tons. This complicated and huge technical system puts demands on the quality of foundation. Therefore, elastic foundation was applied instead of simple rigid supports. Sorter Sorter Gate Drive Gate Foots of the mill Spiral casing Ventilator-mill-wheel Fig.1 Scheme of the Fan Grinding Mill. The fan grinding mill is made of steel (i.e. elasto-plastic - bilinear isotropic material model, see Fig. 2). Yield limit 300 MPa Tangent modulus 300 MPa Fig.2 Bilinear Isotropic Material Model. 3. Finite Element (FE) Model The basic loads are temperature loads of the milled mixture (up to 300 C) and its own weight. ANSYS Workbench v12 software is used (coupled analysis, submodelling, see reference [7], [8] and [9]). Finite element mesh (i.e. combination of volume elements and shells elements, nodes and elements) is shown in Fig.3. Two variants (designs) A and B of the FE model were solved and evaluated.

3 Fig.3 FE Model of the Fan Grinding Mill 4. Results A. First criterion: Distribution of temperatures (see Fig.4) Fig.4 Temperature Distribution [ C] for Variant A (Left) and B (Right).

4 Both variants give nearly the same results (i.e. design of structure doesn t affect the distribution of surface temperatures). B. Second criterion: Total displacement (see Fig.5, 6 and 7) Both variants are nearly the same in size and direction of displacements. In the variant A there are greater shifts towards the inside of the cabinet. Fig.5 Total Displacement [mm] of the Variant A. Fig.6 Total Displacement [mm] of the Variant B.

5 Fig.7 Top view Total Displacements [mm] (Variants: A Upper, B Under). C. Third criterion: Distribution of equivalent von Mises stresses (see Fig.8 and 9) Fig.8 Equivalent von Mises Stresses [MPa] (variant A).

6 In the variant A, the higher values of stresses occurs in areas of foots of the mill. Fig.9 Equivalent von Mises Stresses [MPa] (variant B). D. Fourth criterion: Distribution of equivalent plastic strains (Fig.10) mill. Fig.10 Equivalent Plastic Strains [1]- Variant A (Left) and B (Right). In the variant A, the higher values of plastic deformations occurs in areas of foots of the 5. Conclusions The results of both variants are shown in Tab.1. According to the most important criteria (equivalent von Mises stresses and equivalent plastic strains, see Fig.8, 9 and 10) is evident that variant B gives lower (better) results. Hence, variant B was recommended as suitable for the reconstruction of thermal power plant Pruneřov.

7 Design of the Fan Grinding Mill: Variant A: Variant B: Max. Temperature [ C]: Max. Total Displacement [mm]: Max. Equivalent von Mises Stress [MPa]: Max. Equivalent Plastic Strain [1]: Tab.1 Results. For more information, see references [1] to [4], [7] and [9]. 6. Acknowledgements Allow me to thank prof. Ing. Jaroslav Zapoměl, CSc and our employees and the IVITAS company. Their useful advice and recommendations significantly contributed to the creation of this work. References [1] Technická dokumentace spirálové skříně ventilátorového mlýna a přilehlých komponent [2] MATOUŠŮ P., MĚCHURA V.: Vývoj energeticky nenáročné mlýnice šetrné k životnímu prostředí souhrnná zpráva za rok 2009 k projektu TIP FR-TI1/309, MORE 2009 [3] KUBOŇ Z.: Zpráva EPRU T24/2009 Posouzení stavu materiálu stěny skříně ventilátorového mlýna elektrárny Prunéřov, Ostrava červen 2009 [4] KUBOŇ Z.: Zpráva EPRU T17/2009 Posouzení stavu materiálu kola ventilátorového mlýna elektrárny Prunéřov, Ostrava květen 2009 [5] FRYDRÝŠEK, K.: Nosníky a rámy na pružném podkladu 1, Faculty of Mechanical Engineering, VŠB - Technical University of Ostrava, ISBN , Ostrava, Czech Republic, 2006, pp.463. [6] FRYDRÝŠEK, K., JANČO, R.: Nosníky a rámy na pružném podkladu 2, VŠB - Technical University of Ostrava, ISBN , Ostrava, Czech Republic, 2008, pp.516. [7] FRYDRÝŠEK, K., NIKODÝM, M.: Nosníky a rámy na pružném podkladu 3, VŠB - Technical University of Ostrava, ISBN , Ostrava, Czech Republic, [8] ANSYS Release 12 Documentation [9] KLUČKA R.: Deformační a napěťová analýza spirálové skříně ventilátorového mlýna, Ostrava 2008, Bakalářská práce, VŠB Technická univerzita Ostrava, Fakulta strojní, Katedra mechaniky, Obor aplikovaná mechanika, pp.63. Reviewer: doc. Ing. Karel FRYDRÝŠEK, Ph.D., ING-PAED IGIP, VŠB - Technical University of Ostrava, Czech Republic