The heat energy in the sewage can be recovered using a heat pump and utilized for cooling or heating. However, the problems of heat-exchanger blockage and scaling have not been adequately addressed. A defoulant hydrocyclone (DFH) has the advantages of fewer moving components, a simple structure, and high separation efficiency. The separation of particulate matter primarily depends on the external swirling flow that adheres to the wall; however, the external swirling flow is easily converted into an internal swirling flow, causing separation failure. We conducted a simulation to investigate the influence of installing a conical surface (CS) at the locus of zero vertical velocity (LZVV) on separation performance. The numerical simulation results were in good agreement with the experimental data. Simulation studies on the size of the CS revealed that longer CS resulted in a stronger suppression effect on turbulence; the turbulence caused by the transition from external to internal swirl flow was weakened, thereby reducing the system energy consumption. However, the particle trajectory and residence time indicate that a longer CS caused a stronger particle binding effect, making it difficult to separate particles in a timely manner. We changed the axial position of the fixed CS and found that turbulence was most intense at the bottom of the DFH, and the pressure and pressure loss were minimized when the inner cone was installed at a distance of −100 mm from the column cone interface.