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General comment Early strength cement where the 3rd day compressive strength is greater than 15 MPa and the 28th day compressive strength is 32.5 MPa. Industrial solid waste that contains silica and flue gas desulfurized (FGD) gypsum is used in cement manufacture instead of clay and gypsum. The main stream of cement production – new suspension preheater (NSP) – is applied in the Chinese cement industry. There are three primary production processes: The pulverized coal and raw material preparation process, including the transfer, grinding, homogenization, and storage of raw materials, and the grinding and storage of coal. In the incineration process, the ground and mixed raw materials are inputted into the preheater and then the calciner and decomposed with 60% coal at 950 ◦C. The limestone decomposes to about 95% in the calciner and 5% in the kiln. The decomposed materials fall into the kiln and are incinerated to clinker with 40% coal at a temperature of over 1400 ◦C. In the finishing process, the cement is produced when the clinker, mineral additions, and gypsum are granulated finely by a grinding mill. The raw materials are suspended and heated by recycled hot air in the preheater. |
