The exhaust gas exiting the sulphonation reactors is processed to reduce the level of pollutant to values widely accepted by the most stringent international standards on emissions to atmosphere.
The maximum content of the polluting agents guaranteed at plant stack is the following:
- SO2: 5 ppm (vol.)
- SO3: 15 ppm (vol.)
- Organic mist: 25 mg/m3
The exhaust gas undergoes two subsequent steps of treatment before being released to the atmosphere: reduction of organic mist content and final washing with a caustic soda solution to reduce the amount of free SO2 discharged.
This latter step is carried out in a suitable SO2 scrubber, while for the elimination of the organic mist Desmet Ballestra can offer two alternative technological solutions having the same efficiency:
- Electrostatic precipitator (ESP)
- Wet brink filter (NEGT)
New Generation Electrostatic Precipitator (ESP)
The latest generation ESP is characterized by:
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fixed electrode rods, granting much longer operation and no risk of rupture
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upper and lower fixation of the electrode rods, completely avoiding the maintenance problems related to the traditional counter-weights and eliminating the risk of swinging
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round-shaped tubes bundle, designed to ensure the proper gas speed and having higher tube thickness, so ensuring longer life time
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integrated blowers for upper insulators flushing, directly installed on top of the machine
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lower insulators flushing by means of dry process air, so preventing any risk of moisture condensation
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high voltage transformer, able to work up to 60 kV, providing higher efficiency
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electronic controller, able to select the best operating conditions in terms of voltage according to the detected electric field
Wet brink filter (NEGT)
The new unit is based on a special Multicartridge High Efficiency brink filter constantly washed with fresh organic raw material.
This new system, while guaranteeing the same performances of the ESP (in terms of cleanness of the gas at the stack outlet), allows the complete recovery of the sulphonic acid carried over by the exhaust gas.
As additional advantage, the NEGT system enables the recovery, as finished product, of the organic drippings, otherwise normally wasted. For this reason, the system is optimized for processing LABS and MES.