There are some elements we meet every day and about which in truth we know very few. An example of this could be cement (from Latin “caementum” that is building rough stone), whose coming is generally deemed as one of the most remarkable aspects of our century and whose production, along with that of steel and electrical power, points out the economic and social

MATERIE PRIME PER LA PRODUZIONE DEL CEMENTO
COMPONENTI PRINCIPALI DELLA MISCELA
CALCARI  TUFI	Forniscono alla miscela cruda principalmente calce (C30)
ARGILLE	Sono portatrici soprattutto di silice (SIO2), allumina (AI203) e ferro (Fe203)
MARNE  SCISTI	Apportano in proporzioni diverse i quattro ossidi sopra indicati
ADDITIVI DELLA MISCELA
SABBIE SILICEE  CENERI DI PIRITE  BAUXITI	Apportano soprattutto silice  Conferiscono soprattutto ferro    Forniscono soprattutto allumina
COSTITUENTI SECONDARI DEL CEMENTO
POZZOLANE  LOPPE D'ALTOFORNO  CENERI VOLANTI  CALCARE	Per la preparazione di cementi specializzati

development degree of a country. The discover of the features of the cement is dated back to the XVIII century when the English J. Parker got from the burning of a certain kind of limestone, a material having a remarkable quit setting; the first patent was achieved by another English, J. Aspdin, who, in 1824, patented a cement realized with loam rocks supplying a product alike the stones of the isle of Portland. Starting from the second half of the XIX century, investigation and experimentation to produce an ever higher quality product have brought to perform several kinds of cements nowadays in use, turning surely it into a indispensable row material. Indeed it's employed in several fields, from the residential building to plants building, sporting installations, bridges, harbour works, highways, waterworks etc. In Italy the development started wiuth the construction of the first railways in 1856. In1864 it rose, to constitute later regularly in 1865, the Società Bergamasca for the Production of Cement and Hydraulic Lime, having taken in 1927 the definitive denomination of Italcementi that nowadays represents one of the main operators all over the world. The technologic advances over last years have made that not only it were achieved a higher quality but mainly and overall that the ecological and environment impact due to the production of cement were reduced to the less at an extent that the productive techniques related to cement are numbered among the so called “clean technologies”. So how is the cement obtained? First of all it must be reminded that the cement belongs to the hydraulic bonds class, that is powder materials that, mixed with water, produce pulps able to adhere to lithoidal materials and to harden progressively, even without air, forming this way water proof compact blocks, having a mechanic strength of absolute relevance. The main raw materials employed to get ready the crude mix to produce the cement clinker (table1) are mostly natural and are mined in the ore bodies, placed mostly near the production plants, and previously submitted to a crushing treatment to reduce their size so to ease their transportation to the productive plants. Once inside the cement plant the row material is submitted to a sampling process and sent to single stores, some of them working as places of pre- homogenization. The first processing phase is

COMPOSIZIONE MEDIA DI UNA MISCELA CRUDA DA CEMENTO
COMPOSTI  CaCO3  SiO2  Al203  Fe203	% 81 13 4 2

the preparation of the crude mix that can be damp or dry (the first one being a process already technologically obsolete). In this phase the main raw material, opportunely measured out, and mixed with addictive to get the right ratios between calcium, silica, alumina and iron oxides are convoyed to the mills where, by the means of milling and drying processes, are turned to a very fine and dry powder. The average composition of a crude mix for cement as regard to its basic components is showed at Table 2 The mix opportunely homogenenized in a later phase, is measured out at kilns as a powder (dry way process) or nodulized with nearly the 12% of water (semi-dry way process) depending on the kind of installation. So in the kinks it is carried out the burning phase of the clinker. Throughout complex chemical reactions it is got the sintering of the material followed by a quick cooling, partially recovering the heat in the final phase of the burning process. The product rising from this transformation is the so-called cement clinker, that is a semi-manufactured product, dark grey and having mostly a granular structure, constituted by calcium silicates, illuminates and ferrito having and conferring hydraulic properties to elements. The final phase of the productive process is the milling of the clinker (with plaster to product the cement pure Portland), with plaster and other secondary components according to the kind (table 1) to produce cements fitting for several kind of employ.The burning phase of the clinker is surely the most important within the cement production cycle. It is carried out in the so called “Cement Kiln”, that is a jet engine within which it occurs the heat and mass exchanges by the means of a complex thermo-chemical process, so that, starting from the crude mix, it gets to the clinker. The functions inside the kiln are essentially three:

Drying (if necessary), pre-heating and partial decarbonization of the limestone in the mix, that can be carried out in the first part of the rotary kiln, the long kiln- Fig.1c - in the external cyclone exchangers - Fig.1a - or in the a Lepol grid- Fig.1b;

Completion of the decarbonization and sintering at the temperature of 1.450°C, that in the three kinds of kilns is carried out in the final part of the rotary kiln.

Cooling of the clinker carried out in a heat exchanger, grade kind (as shown in Fig. 3) or tabular or planet one, placed at the clinker discharge point in the kiln.

The thermic energy required by the flaming process is brought by the means of the main burner placed in the kiln at the utmost clinker discharge position; in the external pre-heater kilns (Ill.3, a e b) the supply of primary energy can be also carried out by the secondary burner, opportunely inserted into the pre-heater. It must be underlined as, according to the kind of process and of kiln, the absorbed thermic energy varies from 90% to nearly 100% of the whole thermic energy consumed by the entire cement manufacturing process. Provided the peculiarity of the productive process, it is the utmost important that it undergoes continual controls and that the producing companies achieve certification, world level, as ISO9002. Just to better both the productive process and the product quality, important resources are invested in research and development.

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