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Post by Ramprasad »

I have a doubt on methanator section .
Why are you not using the adsorbers in the place of methanator for absorbing the methane carbon monoxide ,crbondioxide and argon .
It will helps the decrease the consumption of the hydrogen and reduce the load on synthesis gas compressor.
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Re: Methanator

Post by PKS1964 »

I think that reaction help to convert CO and CO2 to CH4 which we removed as inert and use as fuel.
For adsorption there will be some issue in ammonia plant
1- Operation energy of adsorption tower for handling of big quantity of gas for CH4 adsorption.
2- Where we use this adsorbed CH4. because for adsorption there will be some adsorbing media.

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Re: Methanator

Post by Zubairtalha »

Following could be some Reds,

1- There will be no savings on Capitals. You need Two or more vessels for Dryers in comparison to Methanator. Size of the vessels will be huge as Stream is saturated with water ( may require chilling to remove free water),Loading of CH4, CO2 and CO is much higher. And further we are trying to completely remove CO (difficult).
2- For regeneration, probably treated outlet stream will be utilized which will contain Hydrogen far more than Methanator consumption?
3- Increased number of Instruments and Control valves. A single passing valve can ruin the complete regeneration cycle of dryers.
4- Requirement of filtration at main stream to avoid dust carry over to Synthesis section. Similarly burners chocking issue for usage of Waste gas as fuel if no filtration.
5- requirement of chillers (Cooling step of adsorbers), putting load on refrigeration circuit and Heaters (for heating cycle), ie more Steam demand.
6- Replacement frequency of Molecular sieve is high while Methanator catalyst lasts for Years.
etc. etc. etc.

Zubair Talha
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Re: Methanator

Post by naseemce »

It will be very expensive and methanator catalyst life is more than 15 years and generated CH4 will work as fuel instead of wasting .
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Re: Methanator

Post by astromo »

Assuming that this question is reviewing the trade off between a pressure swing adsorber as the final step of syngas production versus a methanator, then the answer lies in the process advantages and compromises that the original designer drives for.

I'd say that once that decision has been made, the magnitude of the sunk capital (especially when you consider the intricacy of an ammonia plant's energy recovery and exchange systems) is such that a retrofit of one technology for the other is unlikely. Maybe there's a project report out there that can be shared?

A PSA requires multiple vessels plus a buffer drum to smooth the pressure cycles so that the off gas can be supplied to the plant's fuel gas system. Intuitively, one of the key advantages that a PSA provides in terms of the process energy balance is that it reduces the inert loading in the make up gas to the syngas compressor and avoids the need for additional treatment and heat exchange to deal with the moisture and temperature rise that a methanator reintroduces to the syngas.

How that sits with the other trade offs at play, will come down to economics. For some, such as Linde, it works. For others, methanator technology wins.

If an in-depth study write up is available that reviews the CAPEX/OPEX trade-offs, then it would make good reading provided that the author(s) were not commercially motivated. Every process licensor will go to all sorts of lengths to convince you why their process is a winner and there are all sorts of reporting tricks that can be used to sway the argument.

Process licensors (generally) have a slate of technology in which they're strong and they will favour those technologies, rather than necessarily developing a process that is the ultimate best of the best. This latter hypothetical approach would invariably require using someone else's unit operation that would need to be licenced (assuming that it can be released because the owner doesn't see a competitive threat). Practically, this is not seen very often.
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