Question

Limestone (CaCO3) is converted to calcium oxide (CaO) in a continuous kiln. The conversion process is represented by the following reaction: CaCO3(s) CaO(s) + CO2 (g) The energy to decompose the limestone is supplied by the combustion of CH4 in direct contact with the limestone using 50% excess dry air. The CaCO3 and air enter the process at 25 °C, and CaO exits at 900 °C. The product gases exit at 200 °C. Using the heat of reaction approach and the heat of formation and sensible heat approach, calculate the maximum number of kg of CaCO3 that can be processed per 1000 m3 of CH4 measured at standard conditions (i.e., 0 °C and 1 atm for gases). Show that the two approaches will produce similar results.

H o f, CH4, gas = -74.84 kJ/mol

Cp (for all gases and vapors): 30 J/mol.K

H o f, CaCO3, solid = -1206.9 kJ/mol Cp,CaCO3(s) = 234.5 J/mol.K

H o f, CaO, solid = -635.6 kJ/mol

Cp,CaO(s) = 111.8 J/mol.K

H o f, CO2, gas = -393.51 kJ/mol

H o f, H2O, gas = -241.83 kJ/mol