Halogenated compounds in landfill gas can be removed either by chilling the gas or by passing it through granular activated carbon (GAC). Chilling looks the better prospect where the gas also needs drying, but the supplier’s advice was to prove it with a small on-site test first. This short post summarises that advice from a note to a landfill gas power generator, and says plainly where the evidence ends.
The challenge: an unusual contaminant
Halogens in landfill gas are, by the supplier’s own account, a relatively infrequently encountered problem. That has a consequence. The company had good data on chillers removing ammonia and moisture from landfill gas, but had not previously had to review performance on halogens.
The two options
Gas chilling
A high level of moisture removal may reasonably be expected to remove some halogens too. A suggested system would raise the gas pressure to between 1 and 3 bar and chill it to around 3°C. The refrigeration can come from an absorption chiller running on landfill gas, so electrical demand would be minimal.
The supplier suggested a small-scale site test first, using a sample gas chiller and a flame ionisation detector (FID). By measuring halogen removal against the amount of moisture removed, the supplier could then predict what an optimised chiller would achieve with some precision.
Granular activated carbon
Tests with various forms of GAC showed that certain types can be quite effective. A typical system would be a twin-column unit alternating between duty and regeneration. There is a catch:
- Chemical washing regeneration creates a waste that needs disposal.
- Heat regeneration returns the halogens to a gas that is released to atmosphere.
Which is preferable
The supplier considered the chiller to offer the best chance of meeting the requirement, while stating that the data on halogens specifically was limited and a trial was the sensible next step.
What to consider for your own project
- Identify the halogenated compounds and the limit you must meet (for example an engine manufacturer’s specification).
- Run a pilot test before committing to a full-scale system.
- Count the waste. GAC regeneration generates a waste stream or moves the problem to the air.
- Look for double duty. Chilling also removes moisture.
FAQ
Will a chiller remove halogens?
Probably some, in proportion to moisture removal, but this needs on-site testing.
Can activated carbon be regenerated?
Yes, by chemical washing or heat, each with a drawback.
Contaminants in your gas?
Send us your gas analysis and we will suggest a trial. Related: landfill gas well monitoring.