Presently, the use of bituminous coals as a heating source in the cement industry has led to an increase in carbon dioxide emissions. In this study, the thermal flow characteristics inside a waste combustion chamber constituting multiple thermal plasma jets was numerically analyzed. The waste combustion process was applied as a heating source to produce the raw materials of cement. The design and operation of the waste combustion process were optimized through numerical analysis using the magnetohydrodynamics and computational fluid dynamics code. The thermal flow characteristics inside the waste combustion chamber were numerically analyzed in accordance with adjusting the chamber width, injection angle of the torch, and combustion air temperature. As a result, the temperature in the range of 1,600–2,200 K was widely distributed at the center of the chamber. The optimized conditions are as follows: 400 mm chamber width, 20° injection angle, and 1,000 K combustion air temperature. The waste combustion chamber constituting multiple thermal plasma jets was constructed based on the numerical results. It was concluded that plasma jets generate a sufficient temperature to treat waste plastics.