Division BAT 38 In order to prevent or reduce emissions of treatment chemicals from pressure processes (autoclaves), BAT is to use all of the techniques given below.
United Kingdom
| Technique | Description | |
|---|---|---|
| (a) | Process controls to prevent operation unless the treatment vessel door is locked and sealed | The treatment vessel door is locked and sealed once the treatment vessel is loaded and before treatment takes place. Process controls are in place that prevent the operation of the treatment vessel unless the door is locked and sealed. |
| (b) | Process controls to prevent the treatment vessel from opening while it is pressurised and/or filled with preservative solution | Process controls display the pressure and whether liquid is present in the treatment vessel. They prevent the opening of the treatment vessel while it is still pressurised and/or filled. |
| (c) | Catch-lock for the treatment vessel door | The door of the treatment vessel is equipped with a catch-lock to prevent the release of liquids in the event that the treatment vessel door needs to be opened in an emergency situation (e.g. door seal is broken). The catch-lock permits the door to be partially opened to release the pressure while retaining liquids. |
| (d) | Use and maintenance of safety relief valves | Treatment vessels are fitted with safety relief valves to protect the vessels from excessive pressure. Discharges from valves are directed to a tank of sufficient capacity. Safety relief valves are regularly inspected (e.g. once every 6 months) for signs of corrosion, contamination or incorrect fitting and are cleaned and/or repaired as required. |
| (e) | Control of emissions to air from the vacuum pump exhaust | Air extracted from pressure treatment vessels (i.e. the vacuum pump outlet) is treated (e.g. in a vapour-liquid separator). |
| (f) | Reduction of emissions to air when opening the treatment vessel | Sufficient time for dripping and condensation is allowed between the depressurisation period and the opening of the treatment vessel. |
| (g) | Application of a final vacuum to remove excess treatment chemicals from the surface of treated wood | To avoid dripping, a final vacuum is applied in the treatment vessel before opening it to remove excess treatment chemicals from the surface of treated wood. Application of a final vacuum may not be necessary if the removal of excess treatment chemicals from the surface of treated wood is ensured by the application of an appropriate initial vacuum (e.g. less than 50 mbar). |