Numerical modeling of torrefaction reactor integrated in energy technological complex

Highlights: • Energy-technological unit with torrefaction reactor heated by exhaust gas simulated. • Direct heating torrefaction reactor with recirculation of heat carrier is considered. • Influence of operating variables on process and quality of torrefied pellets defined. • Recommendations on advisability of using recirculation of the heat carrier supposed. • Energy and economic efficiency in cogeneration and trigeneration modes analyzed. -- Abstract: The paper presents the calculated performances of an energy-technological complex (ETC) consisting of an electric generator based on a gas piston unit (GPU), a torrefaction reactor and a heat-recovery boiler (HRB) for incinerating torrefaction volatile products. A one-dimensional mathematical model was used to simulate the operation of the torrefaction reactor with direct heating and recirculation of the heat carrier. The heat carrier consisted of exhaust gases from the GPU and torrefaction volatile products. The reactor operated in a cycle mode with periodic unloading/loading of feedstock. It is shown that the degree of mass losses during torrefaction depends not only on the temperature but also on mass flow rate of the heat carrier at the reactor inlet. An optimal value of the mass flow rate was obtained. The reduction in the duration of the unloading/loading cycle leads to an improvement of the torrefied pellets quality and the smoothing of the fluctuations in the HRB operating parameters. Using the recirculation halves the consumption of natural gas for the production of torrefied pellets. Based on the comparative analysis of the ETC operation in cogeneration and trigeneration modes, it is shown that economic efficiency of schemes with recirculation is higher than schemes without recirculation.