In this study tank holdup method was usedto model the distillation column which contained a mixture of methanol-water- ammonium carbonate. This involved two stages: first, the development of a MATLAB code that was used for mathematical modeling with NRTL activity coefficient for liquid phase and PR equation of state for gas phase of the tower. Also Yildiz equations for mass and energy balances with some assumptions and then making them in form of algebraic equations were employed. In the second stage, the aim wa to calculate the optimum reflux ratio for reduction of processing costs and for increasing the purity of methanol in distillated product to at least 90 ercent and achieving the recovery of at least 90 ercent. For one distillation tower including the solid component of ammonium carbonate with a few free degree that could e used for minimizing the processing costs and also in achieving the desired aims. The reflux ratio can affect the steady –state point of operation and so the daily costs. In this study the aim was to get closer to product with desired characteristic in minimum operation time and with minimum costs with access of available relationship between reflux ratio with purity of product and Capacity Factor. With maximizing of this factor desired product can be achieved. Maximizing this parameter with considering the other parameters، we can get the greater recovery. At last with these factor for this column after simulation with Matlab-Program we can reach to purity about 90 percent and recovery about 90 percent with having optimum internal reflux ratio of ، 0.875 in a mount ، CAP of 175.72 and reboiler heat duty of about 900KJ/hr. Keywords: Tank Holdup، Recovery،Capacity Factor ,Internal Reflux Ratio,Steady-State Operating Point