[Peter]

As @RNGinsight says regenerative systems are the lowest operating cost long term when you are treating very contaminated gas. In some cases the biogas flows on smaller agricultural projects will never justify the upfront cost of a regenerative system. In lower flow cases carbon costs can be managed by using carbon for siloxane, turpine, and voc removal only with iron based media beds and in situ iron treatment used for sulfur removal. We give some rules of thumb for when to consider a regenerative system for sulfur removal in this article: https://azuraassociates.com/three-risks-of-h2s-at-rng-plants/

azuraassociates.com

Three Unexpected Risks of Hydrogen Sulfide at RNG Plants – AZURA

Three Unexpected Risks of Hydrogen Sulfide at RNG Plants – AZURA

[Peter]

Not sure it they are the top three, but three I think are worth mentioning.

1) Lack of RNG off-take certainty slowing FID

2) Insufficient detail in initial design basis leads to change orders, and delays

3) Regulatory delays related to environmental compliance, gas safety approvals, and pipeline interconnection

[Peter]

@atkinsrealis_fatma What sort of RNG projects do you typically encounter?

[Peter]

Once at the commissioning phase there can still be many challenges some covered in our article <b itemprop=”headline”>Digester Startup and Commissioning https://azuraassociates.com/digester-startup-and-commisioning/.

azuraassociates.com

Digester Startup and Commissioning – AZURA

Digester Startup and Commissioning – AZURA

[Peter]

The answer is feedstock dependant and in short thermal hydrolysis processes that use heat and pressure to break up cells can be worth considering where digester solids are costly to dispose of and feedstocks are slow to break down.

For recalcitrant feedstocks like waste activated sludge and agricultural residues it can get a 15% improvement in gas and in solids destruction.

Anecdotally, most commercial digesters processing manure or food waste have looked at it, done the financial analysis, and determined that the capital and energy cost do not justify the small increase in gas production. Municipal digesters use it because biosolids are costly to dispose of and it can reduce the amount of solids they need to truck away.

Biological processes like an acidogenic thermophilic hydrolysis tank do not generally increase biogas production, but can shorten stable retention times by a few days depending on the feedstock.

[Peter]

Thanks @RNGinsight , What is the minimum flow and concentration where these regenerative VOC and siloxane removal systems are cost effective? How do they respond to high turpine concentrations?

[Peter]

Thanks Fatma, With your broad view of the industry where do you see project get hung up after they have a business case that looks promising?