Development of an up-scalable rotary kiln design for the pyrolysis of waste tyres

Abstract

This paper shows how a design of an indirectly heated rotary kiln for the pyrolysis of waste tyres can be developed based on numerical simulation results. The design is up from a laboratory scale tyre particle mass flow to an industrial scale tyre particle mass flow, preserving the heat- and mass-transfer characteristics. This ensures that findings from the laboratory scale mass flow kiln, which is relatively cheap to build and to operate, are meaningful and representative for the industrial scale mass flow kiln. Due to high cost the scaled-up industrial scale design cannot be tested in advance. The development process based on numerical simulation minimizes the risk that scaled up designs do not reach desired performance values.A one-dimensional simulation model is described, enabling simulation of the temperature and mass flow profiles of the particle bed and the gas phase along the axis of the indirectly heated rotary kiln. The simulation considers the bed height development and the influence of fouling. The model is successfully validated against experimental measurements. It is then used to develop several rotary kiln designs covering a tyre particle mass flow range of two orders of magnitude, from laboratory up to industrial scale, fulfilling a variety of pre-formulated requirements. It is found that the kiln designs increase in slenderness as the bed particle mass flow increases, while the inclination and rotational speed can be kept constant.