Lime (calcium oxide) is widely used in the production of cement, steel, medicines, insecticides, plant and animal food, soap, rubber, and many other familiar materials. It is usually produced by heating and decomposing limestone (CaCO3), a cheap and abundant mineral, in a calcinations process: CaCO3 (s) heat → CaO (s) + CO2 (g)

(a) Limestone at 25C is fed to a Continuous calcinations reactor. The calcinations is complete, and the products leave at 900°C. Taking 1 metric ton (1000 kg) of limestone as a basis and elemental species [Ca(s), C(s), O2 (g) at 25°C as references for enthalpy calculations, prepare and fill in an inlet—outlet enthalpy table and prove that the required heat transfer to the reactor is 2.7 x 10° kJ.

(b) In a common variation of this process, hot combustion gases containing oxygen and carbon monoxide (among other Components) are fed into the calcinations reactor along with the limestone. The carbon monoxide is oxidized in the reaction CO (g) + ½ O2 (g) → CO2 (g) suppose

• The combustion gas fed to a calcinations reactor contains 75 mole% N2, 2.0% O2, 9.0% CO, and 14% CO2;

• The gas enters the reactor at 900°C in a feed ratio of 20k mol gas/k mol limestone;

• The calcinations is complete:

• All of the oxygen in the gas feed is consumed in the CO oxidation reaction:

• The reactor effluents are at 900°C.

Again taking a basis of 1 metric ton of limestone calcined, prepare and fill in an inlet—outlet enthalpy table for this process [don’t recalculate enthalpies already calculated in part (a)] and calculate the required heat transfer to the reactor.

(c) You should have found that the heat that must be transferred to the reactor is significantly lower with the combustion gas in the feed than it is without the gas. By what percentage is the heat requirement reduced? Give two reasons for the reduction.