Tronox operate a Fluid Bed Product Dryer for the drying of synthetic rutile at their Chandala site. The heat source is a natural gas fired hot gas generator. Gas is exhausted from the dryer chamber through a mechanical collector and then wet scrubber before discharge into a stack. There is only a single dryer and therefore reliability is paramount to achieving production targets.
By 2006 the installed hot gas generator was reaching the end of it's useful life and one was a major cause of plant down time. We worked with Hatch and Associates to determine an overall upgrade plan for the dryer. The hot gas generator requirements to achieve the longer term production targets were as follows:
- A maximum air flow into the dryer of 22,000Nm³/hr.
- A temperature limit into the dryer of 750°C.
- The hot gas generator had to operate against a positive pressure to overcome the losses through the dryer tuyeres and product depth.
- A nominal gross maximum heating capacity of 30GJ/hr.
The decision to proceed with the hot gas generator upgrade was taken in February 2007 and the intallation and commissioning had to be planned to coincide with the plant shut of June through July 2007. We were contracted to carry out the design and commissioning.
The combustion chamber was manufactured and assembled on a cradle off site for ease of installation. (Mass with refractories ±20,000kg.) Special sole plates were designed to allow some movement in the feet for expansion. The combustor chamber has a double shell through which the fluidising air is introduced to keep the skin temperature cool.
Air is introduced through the burner as combustion air and through the chamber as front wall air and end of chamber mix air and through the hot gas generator as final mix air. This ensures an optimum combination of excess air through the burner, a combustion chamberr temperature of around 1000°C and a windbox inlet temperature of 700°C. Refractory castable is incorporated in the burner throat, front wall and outlet areas and insulation and high alumina bricks in the combustion chamber. Air distribution is by a distribution box which also supplies air to cool the dryer tuyeres.
The burner is a North American Wide Flame Magna-Flame size 4796-20. Natural gas flow at design conditions is around 800Nm³/hr. The burner operates at high excess across a large turndown range.
The gas train and burner management system was supplied by Complete Combustion Industrial Gas Services of Western Australia. A Siemens LMV5 burner management system together with Siemens block and control valves inb the main gas line were selected.
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