Chapter 5, Problem 5.61P

Most of the concrete used in the construction of buildings, roads, dams, and bridges is made From Portland cement, a substance obtained by pulverizing the hard, granular residue (clinker) from the roasting of a mixture of clay and limestone and adding other materials to modify the setting properties of the cement and the mechanical properties of the concrete.

The charge to a Portland cement rotary kiln contains 17% of a dried building clay $\left(\text{95}\text{wt\%,}{\text{SiO}}_{\text{2}}\text{,}\text{16\%}{\text{Al}}_{\text{2}}{\text{O}}_{\text{3}}\text{,}\text{7\%}{\text{Fe}}_{\text{2}}{\text{O}}_{\text{3}}\text{,}\text{1}\text{.7\%}{\text{K}}_{\text{2}}\text{O,}\text{3}\text{.3\%}{\text{Na}}_{\text{2}}\text{O}\right)$and 83% limestone ( $\text{95}\text{wt\%,}{\text{CaCO}}_3\text{,}5\text{\%}$impurities). When the solid temperature reaches about 900°C, calcination of the limestone to lime (CaO) and carbon dioxide occurs. As the temperature continues to rise to about 1450°C, the lime reacts with the minerals in the clay to form such compounds as $\text{3CaO}\cdot {\text{SiO}}_{\text{2}}\text{,}\text{3CaO}\cdot {\text{Al}}_{\text{2}}{\text{O}}_{\text{3}}$, and $\text{4CaO}\cdot {\text{Al}}_{\text{2}}{\text{O}}_{\text{2}}\cdot {\text{Fe}}_2{\text{O}}_3$. The ?ow rate of CO₂from the kiln is 1350 m³/h at 1000°C and 1 atm. Calculate the feed rates of clay and limestone (kg/h) and the weight percent of Fe₂O₃in the ?nal cement.