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53 comments on National Renewable Ammonia Architecture Update

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joule on May 15, 2009 - 11:20am Permalink | Subthread | Comments top

A very informative and nicely done piece.

One highly desirable feature of the general scheme of producing ammonia from wind-generated electricity is that the ammonia doesn't have to be used right away and can be relatively easily stored in various forms. As such, short-term supply and demand can be more or less decoupled, something that is very difficult to do when supplying electrical power to a grid.

However, there is another technical issue regarding the variability of wind power that I'm not sure has been sufficiently addressed. And that is how well the day-to-day operations of an ammonia plant (even the so-called 'solid-state' processes briefly discussion in the paper) will be able to cope with a power supply that can vary from over 100% of what is needed down to virtually zero in a relatively short period of time. I would think that this variability would play havoc with any sort of large electrolysis system for producing hydrogen as well as with whatever system is used to separate nitrogen from air.

A mini-grid might smooth things out a bit but not totally, and building such a grid sort of defeats the whole concept of using stranded wind.

In general, the operation of a large chemical plant (and an ammonia plant is just that) entails much complexity, which is why they like to operate at a steady rate and cannot easily tolerate highly variable and large unpredictable inputs of either materials or power.

I'd be interested in seeing this issue addressed in more depth.

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SacredCowTipper on May 15, 2009 - 12:40pm Permalink | Subthread | Parent | Comments top

There are good answers to that whole variability concern, but the patent filings are getting in the way of me talking about it :-)

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joule on May 15, 2009 - 12:59pm Permalink | Subthread | Parent | Comments top

SacredCowTipper -

Well, your cryptic remark indicates that the variability problem is recognized and that at least someone has been working on it.

Mind you, the problem of power variability does not just affect the actual N2 and H2 production units, but rather the entire operation, i.e., all the pumps, compressors, controls, safety features, etc., etc. As such, I would think that regardless of how you tweak the process to make it more flexible with respect to varying power, there still needs to be as least some on-site electricity storage, perhaps an amount sufficient to run the plant at normal capacity for several hours. It's either that or a back-up generator. Regardless of which is used, they both represent additional capital cost that must be factored into the overall economics.

One other perhaps minor technical issue comes to mind. While my knowledge of electrochemistry is quite rusty (not that it was all that great in the first place), is it not true that to operate an electrolysis cell efficiently, the solution has to have a fairly high conductivity which in turn requires a fairly high salt content? If so, would you not have to include salt as one of the process inputs? Not very expensive, but an additional cost nonetheless.

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SacredCowTipper on May 15, 2009 - 3:39pm Permalink | Subthread | Parent | Comments top

You're correct in stating that an ammonia production facility can not run entirely off grid. The amounts of grid to wind and particulars are trade secrets :-)

Electrolysis unit O&M cost is something we need to get a better handle on, but it's true that there is periodic maintenance required.

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Roger Arnold on May 16, 2009 - 2:34am Permalink | Subthread | Parent | Comments top

There are no technical issues with any of the electrolysis technologies (that I know of) in switching the cells from full to partial power levels at the drop of a hat. The cells mey even be reversible, allowing them to produce or consume power as needed.

There are at least three different groups proposing to use variable power to electrolysis cells for grid regulation. (That's three that I know of. There are probably a bunch more. It seems to be a pretty obvious and popular idea.)

The various proposals differ in the electrolysis technologies that they propose to use, and in how they propose to use the hydrogen (and oxygen, let's not forget!) that they produce. I'm intrigued by the "solid state synthesis of ammonia" covered here because of its supposed low capital cost and high efficiency. If it's for real, it would be really great!

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53 comments on National Renewable Ammonia Architecture Update

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