Standard Technical Features of BTG System for Supercritical 660 ...

Standard Technical Features of BTG System for Supercritical 660/800 MW Thermal Units8.5.11 Materials of constructionThe material of construction of wear parts shall be selected taking into accounthighly abrasive nature of coal resulting from coal contamination with silicasand and Alpha-quartz as specified.Mill componentSpecificationi) Classifier cone Lined with minimum 15 mm thickceramic tiles on both inside and outsidesurfaces of the coneii) Grinding rings/ race Material with hardness 550 BHN (min.) atsurface (with adequate chilled depth)iii) Grinding balls/ rolls Material with hardness 350 BHN (min.)iv) Minimum difference in 100 BHNhardness of rings/ rolls andrace/ balls8.5.12 Minimum guaranteed life of coal pulverizer wear partsThe guaranteed life of different mill components in "equivalent hours" ofcontinuous mill operation at its rated capacity, while firing the specified rangeof coals and without requiring any in between repair or replacement shall be asunder:Item Minimum life inequivalent hoursi) Grinding elements (rolls/ balls and rings/ 7200 [See notesrace)below]ii) Mill discharge valves 15000iii) Seals 20000iv) Classifier cone and other items lined with 25000ceramic materialNotes:a) The expected wear life of mill grinding elements (rolls/ balls and rings/race) in equivalent hours, under conditions stipulated above shall be in therange of 7200 to 8000 hours.b) A curve indicating the variation in guaranteed wear life with variation inYGP index of coal fired (measured as per BS Standard BS-1016 Part-111)shall be furnished. Separate curves for different wear elements of millshall be furnished e.g. for grinding rolls, grinding rings, clearly indicatingits relationship with YGP index of coal.8.5.13 Minimum mill turn-down ratio of 2:1 shall be ensured.67