Calcination, which represents thermal decomposition of CaCO3, is the key reaction in a cement process. Some reactions including heating-up also take place simultaneously in the calcination reactors. Basic thermal performance and dimensions of the reactors in two cases, which are a rotary kiln wih a four-stage cyclone pre-heater and a simple single rotary kiln, were compared. To employ the heat transfer, mass transfer and reaction rate as well as calcination, one-dimensional modeling was conducted in each case. Some simplification about the reactors was described, however, the reliable Nusselt number and heat transfer coefficients on the reactors were used to make results reliable.