An In-House Computational Fluid Dynamics (CFD) solver is developed for dealing with the gas–solid flow. The Finite Volume Method (FVM) is the basis of the numerical method utilized by the solver, and the Fortran language is used for building the code. The code relies on the Cartesian coordinate system. In order to analyse the effects of varying the simulation parameters, the developed code is tested to solve gas–solid flow simulation inside a circular riser. The simulation parameters which are employed in this study are three different drag models, two different radial distribution function models, two different coefficient of restitution values, and two different time steps of 0.0001 s and of 0.00015 s. In total, 24 variations of the simulations are calculated up to 6 s and its results are compared with each other. From the simulations, the numerical results can be categorized into several groups. The simulations using time step of 0.00015 s, the radial distribution function of Syamlal model, and coefficient of restitution of 0.70, with three different drag models, Gidaspow, Syamlal, and Wen-Yu, showed the best numerical results which will afterwards be fully simulated up to 40 s.