Division 1.4.1 Emissions to air
United Kingdom
| Technique | Description |
|---|---|
| Biofilter | A biofilter degrades organic compounds by biological oxidation. A waste gas stream is passed through a supporting bed of inert material (e.g. plastics or ceramics) on which organic compounds are oxidised by naturally occurring microorganisms. The biofilter is sensitive to dust, high temperatures or high variation in the waste gas inlet temperature. |
| Bioscrubber | A bioscrubber is a biofilter combined with a wet scrubber that preconditions the waste gas by removing dust and lowering the inlet temperature. Water is recycled continuously, entering the top of the packed bed column, from where it trickles down. Water collects in a settlement tank where additional degradation takes place. Adjustment of pH and the addition of nutrients can optimise degradation. |
| Cyclone | A cyclone uses inertia to remove dust from waste gas streams by imparting centrifugal forces, usually within a conical chamber. Cyclones are used as a pretreatment before further dust abatement or abatement of organic compounds. Cyclones can be applied alone or as multicyclones. |
| Cyclofilter | A cyclofilter uses a combination of cyclone technology (to separate coarser dust) and bag filters (to capture finer dust). |
| Electrostatic precipitator (ESP) | Electrostatic precipitators operate such that particles are charged and separated under the influence of an electrical field. The ESP is capable of operating over a wide range of conditions. |
| Wet electrostatic precipitator (WESP) | The wet electrostatic precipitator consists of a wet scrubber stage, which scrubs and condenses the waste gas, and an electrostatic precipitator operating in wet mode in which the collected material is removed from the plates of the collectors by flushing with water. A mechanism is usually installed to remove water droplets before discharge of the waste gas (e.g. a demister). Collected dust is separated from the water phase. |
| Bag filter | Bag filters consist of porous woven or felted fabric through which gases pass to remove particles. The use of a bag filter requires the selection of a fabric appropriate for the characteristics of the flue-gas and the maximum operating temperature. |
| Catalytic thermal oxidiser (CTO) | Catalytic thermal oxidisers destroy organic compounds catalytically over a metal surface and thermally in a combustion chamber where a flame from combustion of a fuel, normally natural gas, and the VOCs present in the waste gas, heat the waste gas stream. The incineration temperature is between 400 °C and 700 °C. Heat can be recovered from the treated waste gas before release. |
| Regenerative thermal oxidiser (RTO) | Thermal oxidisers destroy organic compounds thermally in a combustion chamber where a flame from the combustion of a fuel, normally natural gas, and the VOCs present in the waste gas, heat the waste gas stream. The incineration temperature is between 800 °C and 1 100 °C. Regenerative thermal oxidisers have two or more ceramic packed bed chambers where the combustion heat from one incineration cycle in the first chamber is used to preheat the packed bed in the second chamber. Heat can be recovered from the treated waste gas before release. |
| UTWS dryer and combustion with heat exchanger and thermal treatment of discharged dryer waste gas | UTWS is a German acronym: ‘Umluft’ (recirculation of dryer waste gas), ‘Teilstromverbrennung’ (post-combustion of partial directed dryer waste gas stream), ‘Wärmerückgewinnung’ (heat recovery of dryer waste gas), ‘Staubabsheidung’ (dust treatment of air emission discharge from the combustion plant). UTWS is a combination of a rotary dryer with a heat exchanger and a combustion plant with recirculation of dryer waste gas. The recirculated dryer waste gas is a hot vapour stream that enables a vapour drying process. The dryer waste gas is reheated in a heat exchanger heated by the combustion flue-gases and is fed back to the dryer. Part of the dryer waste gas stream is continuously fed to the combustion chamber for post-combustion. Pollutants emitted from the wood drying are destroyed over the heat exchanger and by the post-combustion. The flue gases discharged from the combustion plant are treated by a bag filter or electrostatic precipitator. |
| Wet scrubber | Wet scrubbers capture and remove dust by inertial impaction, direct interception and absorption in the water phase. Wet scrubbers can have various designs and operating principles, e.g. spray scrubber, impingement plate scrubber or Venturi scrubber, and can be used as a dust pretreatment or a stand-alone technique. Some removal of organic compounds may be achieved and can be further enhanced by using chemicals in the scrubbing water (achieving chemical oxidation or another conversion). The resulting liquid has to be treated by separating the collected dust by sedimentation or filtration. |