Particle residence time distributions in a vortex-based solar particle receiver-reactor: The influence of receiver tilt angle

We present the first experimental assessment of the influence of receiver tilt angle on the particle residence time distribution (RTD) of a two-phase solar particle receiver. The tracer pulse response method is used to measure the particle RTD within a laboratory-scale vortex-based solar particle receiver, with the particle phase itself used as the tracer. The experimental parameters of particle size, transporting gas inlet velocity and a range of receiver tilt angles – spanning 180° from vertically upward to downward facing – were systematically varied to determine the influence of key controlling parameters on the particle RTD within the receiver. It was found that the Stokes number of the two-phase flow evaluated at the receiver outlet, Skout, has a controlling influence on the residence time and that the influence of the receiver tilt angle is significant for large particles (Skout > 10) but weak for small particles (Skout ~ 1). This implies that it is preferable to operate tower-mounted systems (i.e. with downward facing receiver tilt angles) with Skout ~ 1. Furthermore, a preliminary scale-up assessment suggests that the influence of tilt angle on the residence time of particles 200 µm and smaller will be insignificant for a nominal 50 MW-scale receiver, which will provide flexibility in the design of industrial-scale devices. Finally, the residence time behaviour for the range of tilt angles assessed can be well described by an analytical compartment model consisting of a small plug flow reactor, followed by two continuously-stirred tank reactors in parallel with a second plug flow reactor.