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Waste Tire-Fired Bubbling Fluidized Bed Boiler

Introduction

Waste tires, with a high heating value of 33,700 kJ/kg, are being considered as an alternative fuel to coal, which has a heating value of 25,500 kJ/kg. Handing of bead wires in tires is a very serious problem for the adoption of waste tires as a fuel. There are two ways of dealing with this. One is to make chips from tires after bead wires have been removed; another is to divide tires into sixteen segments (for automobile tires) or 32 segments (for truck tires) without removing bead wires. When the latter method is adopted, the pretreatment process becomes easier, and we can get waste tires at a lower cost compared with the former method.
When waste tires are used as fuel in a fluidized bed boiler, bead wires must be discharged from the furnace without leaving sedimentation at the bottom of the bed for stable fluidized bed combustion to be achieved.
MHI's waste tire-fired bubbling fluidized bed boiler is based on technology combining waste fluidized bed incinerators with high-temperature, high-pressure fluidized bed boilers.

Features of MHI's waste tire-fired bubbling fluidized bed boiler

1. Stable discharge of wires
The slope of the bed bottom is optimized and air nozzles are made cylindrical with tapering rather than short, preventing sedimentation at the bottom of a bed or twisting around air nozzles.
2. Low environmental pollution
Emission of CO, NOx, and DXNs is reduced due to M-STAR*
*M-STAR: Mitsubishi Multi-Stage Air Re-Firing Method
3. Transport of and separation process for wires
The screw pitch and clearance between the screw and casing are optimized for the feeding mechanism to prevent wire from clogging the passage.
Three magnetic drum separators are installed to ensure high reliability of wire separation.

Verification tests of waste tire-fired bubbling fluidized bed boiler

Development of a fluidized bed boiler for waste tires was achieved through verification tests as shown in the following results.
Hot model test
A large-scale demonstration plant
A large-scale demonstration plant
  • Bead wires were stably discharged without leaving sedimentation at the bottom of the bed or twisting around air nozzles.
  • Waste tires were burned stably in the fluidized bed.
  • Emission of CO, NOx, and DXNs was remarkably reduced due to M-STAR when waste tires were combusted in the fluidized bed.
Cold model test
The cold model test equipment
The cold model test equipment
In this test, the discharge, transport, and separation of bead wires was confirmed with integrated test equipment.
  • Bead wires were stably discharged.
  • Clogging of the passage by wires was prevented when the screw pitch and clearance between the screw and casing were optimized.
  • Wires were completely separated from sand with a magnetic drum separator.

Business contact: Network

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