From escalating global concern over the exhaustion of non-renewable energy sources comes an imperative need for the use of renewable resources. Biomass pyrolysis has emerged as a very promising renewable alternative for fuel and chemical production. Previous work has shown that the most effective biomass pyrolysis processes require a careful control of temperature and residence times, and downer reactors appear to be the best technology to achieve such goals. Ongoing research at the Institute for Chemicals and Fuels from Alternative Resources (ICFAR) has led to the development of a new downer reactor design for the pyrolysis of biomass feedstock. However, this process requires a gas-solid separator that achieves a minimum spread of the gas residence time distribution – i.e., as near to plug flow as possible.

As a result, a novel integrated gas-solid inertial separator has been designed for implementation in the downer reactor. This new separator combines both primary separation and solids stripping within the same device. This is intended to decrease the product vapor residence time and to reduce the severity of vapor overcracking compared to other fast separation methods. The gas-solid separation section of the new device features a uniflow configuration and a vertical, axial entry with either swirl vanes or a deflector cone.

In the current study, various geometry configurations and operating conditions were tested for their effect on separation efficiency and pressure drop. A 70 mm-diameter separator was tested under cold flow modeling conditions using silica sand, glass beads or FCC catalyst particles as solid material. The sand, glass beads and FCC particles had Sauter mean diameters of 200 μm, 63 μm and 43 μm, respectively. Air was used in all cases with a gas inlet velocity varying from 0.95 to 13 m/s and solid loadings ranging between 0.075 and 19 wt/wt. The separation length was adjusted from 0.1 to 2 separator diameters.

Initial cold flow experiments using silica sand revealed that the separator performance was influenced greatly by the separator geometry. The measured separation efficiency was greater using flow deflector blades (i.e. swirl vanes) than all tested cone deflectors. Solids recovery in excess of 99.99% was achieved. Particle collection efficiency decreased steadily as the separation length increased, but was in general not as strongly affected by solid loadings or gas inlet velocity. Experimental cold testing of glass beads in air gave typical efficiencies above 98.50%. Recovery of the lighter and smaller FCC catalyst was also very high, with a minimum measured efficiency of 98.80%.