The single-car shuttle kiln operates up to 1600°C, with a maximum capability of 1650°C. The car’s setting dimensions are 1.75m long, 3m wide, and 3m high. The kiln chamber features an oxidizing atmosphere, with a reduction atmosphere (which is part of the process) introduced above 800°C. For the reduction firing phase, NUTEC Bickley has designed an atmosphere control system that maintains oxygen levels at close to 0% for prolonged high-temperature treatment.
Alberto Cantú, NUTEC Bickley’s Vice-President, Ceramics, said: “Our client’s electrically conductive firebrick has come about after years of research and trials by materials experts, and we are excited to have been chosen as an industry partner for what promises to be a groundbreaking product in the vanguard of decarbonising ultra-high-temperature processes. Our advanced combustion and control technology will ensure a smooth production flow and conformance to tight tolerances.”
Given the unique nature of the firebrick material, and the fact that the average load in the kiln will weigh in at 19,320kg, a long firing cycle is required. The kiln is heated gradually over 65 hours to the peak temperature of 1600°C – where it dwells for just over 40 hours, before reducing to 20°C for a further 35 hours.
Nozzle-mix burners
The gas-fired kiln is fitted with eight high-velocity nozzle-mix burners, firing in lanes along the length of the kiln; these lanes are staggered between the product loads. The high-performance burners provide excellent turbulence and heat transfer, promoting excellent temperature distribution and uniformity throughout the product. There are four temperature groups, and the combustion system can fire in two distinct modes of operation. In fuel-only mode, the burners fire with a constant air volume while the control system regulates the gas input by modulating the impulse-bleed valves of each zone. This mode of operation provides low temperature capability, the highest burner velocity for recirculation and excellent temperature uniformity, as well as a continuous oxidising atmosphere.
In proportional (ratio control) mode, the impulse-bleed valves are driven full closed providing a closed loop impulse to the burner gas regulators that operate in a direct cross-link fashion to the combustion air valves. The control system regulates the temperature by modulating each of the combustion air zone valves so that the air and gas stream together. The result is maintenance of stoichiometric combustion. This firing mode provides the most fuel-efficient method of operation, used at higher temperatures when larger heating outputs are required, thus maintaining correct velocities for temperature uniformity. This mode of operation is activated by a set point program event. If the cycle requires a variable level of excess air, it is operated at a prescribed value in the firing profile and is completely independent of the temperature set point. The system can also be adjusted to fire at excess gas.
NUTEC Bickley is always careful to pay special attention to insulation, designing with the appropriate system for optimum operation and fuel efficiency. In this part of the project, it is able to draw upon the decades of experience in insulation materials provided by another member of NUTEC Group.
Further Equipment
This shuttle kiln’s walls are fully lined using a high-temperature ceramic fiber module system for excellent insulation and long life coupled with low maintenance. Low-mass ceramic fibre modules allow faster heating and cooling than brick linings, thus reducing cycle time and increasing kiln throughput. Polycrystalline fiber modules are resistant to thermal shock, making them ideal for rapid thermal cycling conditions.
The kiln car lining comprises various refractory materials. The top layer consists of large prefired high alumina brick shapes. These are backed up with both dense bubble alumina and insulating refractory materials.
This is a two-door shuttle kiln. The doors are of pneumatic swing-out design and include all safety circuits to ensure they cannot be opened during firing. When the door is in position, a pneumatic set of cylinders tightens the doors to ensure correct closing.
