Division BAT 20: In order to reduce emissions to air of dust and CO from the decoking of the cracker tubes, BAT is to use an appropriate combination of the techniques to reduce the frequency of decoking given below and one or a combination of the abatement techniques given below.
United Kingdom
| Technique | Description | Applicability | |
|---|---|---|---|
| Techniques to reduce the frequency of decoking | |||
| a. | Tube materials that retard coke formation | Nickel present at the surface of the tubes catalyses coke formation. Employing materials that have lower nickel levels, or coating the interior tube surface with an inert material, can therefore retard the rate of coke build-up | Only applicable to new units or major plant upgrades |
| b. | Doping of the raw material feed with sulphur compounds | As nickel sulphides do not catalyse coke formation, doping the feed with sulphur compounds when they are not already present at the desired level can also help retard the build-up of coke, as this will promote the passivation of the tube surface | Generally applicable |
| c. | Optimisation of thermal decoking | Optimisation of operating conditions, i.e. airflow, temperature and steam content across the decoking cycle, to maximise coke removal | Generally applicable |
| Abatement techniques | |||
| d. | Wet dust scrubbing | See Section 12.1 | Generally applicable |
| e. | Dry cyclone | See Section 12.1 | Generally applicable |
| f. | Combustion of decoking waste gas in process furnace/heater | The decoking waste gas stream is passed through the process furnace/heater during decoking where the coke particles (and CO) are further combusted | Applicability for existing plants may be restricted by the design of the pipework systems or fire-duty restrictions |