The E2SL Regenerative Thermal Oxidiser (RTO)

PROCESS DESCRIPTION:

The RTO extracts fume laden exhaust gas from the carbon electrode baking furnace flue system via an inlet duct at a temperature of 70-150°C, and a slight negative pressure.

During routine operation, the kiln exhaust gas is routed into and up a hot regenerator tower. Above the top of the tower two modulating burners automatically keep the temperature of the now preheated gas entering the top of the selected exit tower to approximately 850°C.

Each combustion zone provides an average gas residence time of around 1.0 seconds ensuring good burn out not only of pitch fume and other organic compounds but particularly – carbon monoxide.

The gases passing into and down the selected exit tower are cooled as they heat up the tower packing. The ultimate discharge temperature varies throughout the cycle but the ID fans and all diversion/control dampers should never have to handle gas hotter than 350°C.

As the exit tower discharge temperature rises to 300°C the next ‘cold’ tower in sequence is brought on stream as an exit tower and incoming gas is diverted from the now cooled inlet tower to the recently heated exit tower, which becomes an inlet tower.

The heating and cooling periods and sequential rotation of towers are automatically controlled by the computer based control system – using all three towers in normal operation.

In the case where the dirty inlet gas is at 100°C the average clean gas outlet temperature will be approximately 230°C. This means that fuel is only needed to raise the gas temperature by 130 degrees Centigrade instead of 750 degrees Centigrade. Consequently regenerative systems use only 17% of the energy a simple thermal oxidiser would need.

This 83% saving is equivalent to 21 litres of oil per 1000 standard cubic metres of gas treated. So, for example a plant treating 50,000 standard cubic metres per hour, running for 8,600 hours per year will save 9 million litres of oil per year. The corresponding saving in CO2 emissions is enormous!

Key Benefits:

• No Residues to handle and treat prior to disposal.
• Low energy consumption relative to conventional thermal oxidising systems
• High level of equipment redundancy enabling excellent kiln availability

The Regenerative Thermal Oxidiser in Action

The plant featured left was a new purpose designed plant installed on a turnkey basis for around £1,000,000.

Completed in August 1998 the above Regenerative Thermal Oxidiser (RTO) processes 30 tonnes per hour [24,000 nm3/hour] of flue gas from a tar & bitumen type plant. Environmental problem solved!

The RTO shown extracts fume laden gas via a 1m-diameter inlet duct at up to 30 tonnes per hour [24,000 Nm3/hour], at a temperature of 70-150°C, and a slight negative pressure. The selected level of suction is maintained by a continuous automatic pressure control loop varying the speed of the Induced Draught fan that discharges to the chimney.

During routine operation the exhaust gas is routed into and up a hot regenerator tower. Above the top of the tower two modulating gas burners automatically keep the temperature of the now preheated gas entering the top of the selected exit tower to approximately 850°C. Each combustion zone provides an average gas residence time of around 1.0 seconds ensuring good burn out not only of pitch fume and VOC’s but particularly – carbon monoxide.

The gases passing into and down the selected exit tower are cooled as they heat up the tower packing. The ultimate discharge temperature varies throughout the cycle but the ID fans and all diversion/control dampers should never have to handle gas hotter than 300°C. As the exit tower discharge temperature rises to 300°C the next ‘cold’ tower in sequence is brought on stream as an exit tower and incoming gas is diverted from the now cooled inlet tower to the recently heated exit tower, which becomes an inlet tower.

The heating and cooling periods and sequential rotation of towers are automatically controlled by the computer based control system – using all three towers in normal operation. The striking benefit of regeneration is that it uses around 15% of the fuel a system without it would use – producing 85% less CO2!

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