Strathclyde Fluidised Bed
Composite recycling
Design
Heating System
The heating system design was required to define the airflow into the system and how it and the sand bed would be heated. The design was required to enable the sand bed to be heated to temperatures ranging between 450˚C and 650˚C.
Many heating system configurations were considered. These included: standard air preheaters; custom designed air preheaters; and external heaters for the sand bed. Initially a custom air preheater was designed. This system was based on shell-tube heat exchangers used in many applications. The design was costed but was discarded during the design review stage.
This initial design was replaced by a standard external heater which would be used to heat the sand bed directly. This offered a number of advantages and overcame heat transfer issues between the airflow and sand. The system specified in the design was two ‘Fibrothal half shells’ as supplied by Kanthal Ltd (owned by the Sandvik Group). A fan-blower was sourced supplying airflow of 190 m3/hour at a pressure of 8.5 KPa.
Separation System
A separation system was designed to separate the decomposed components of the composite material from the expelled airflow of the fluidised bed reactor.
A Stairmand cyclone was chosen as the separation system. This decision was based on the beneficial characteristics that this model possesses: wall friction coefficient; ease of production; and cost effectiveness.
The Stairmand cyclone design is based on the cut diameter of the particles that are to be extracted from the airflow. A number of equations can be used to calculate the required geometries of the cyclone from this cut diameter. These equations were applied to produce the cyclone design for the project. Being a unique cyclone design the manufacturing company (Malakoff Ltd.) machined the cyclone from a solid block of metal.
Overview of full rig
Initially it was planned to attach the heating, airflow and separation subsystems to the pre-existing rig. As the project developed it was decided to produce a new rig from scratch to improve versatility. The full rig design (including airflow, heating and separation systems) can be seen in the diagrams below.
Fan Blower: Air is supplied to the rig by means of the fan-blower.
Main Reactor: The reactor holds the sand bed which is fluidised during operation. It is within the reactor that the decomposition of the composite material takes place.
Heating System: The heating system consists of two ‘fibrothal half shells’. These surround the main reactor to heat the sand bed directly.
Composite Feeding Pipe: The composite scraps are fed into the sand bed through the feeding pipe once fluidisation is achieved.
Cyclone: The cyclone has been designed to separate the fibres, released from the composite material, from the air outflow from the reactor.
Extraction system: Exhaust gasses are dangerous and will be feed into an extraction system after passing through the cyclone.
Control System: A system has been designed to allow control rig temperature.
 Fluidised bed design |  Fluidised bed components |  Fluidised bed components |
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 Fluidised bed components |  Fluidised bed components |  Fluidised bed components |
 Fluidised bed components |  Fluidised bed components |  Fluidised bed components |
 Fluidised bed components |  Fluidised bed components |  Fluidised bed components |