CH4+H2O Ice Clathrates as alternative to LNG transport?

[kriesel]

Originally Posted by LaurV

+1. Problem with the LPG in US is that they have none.

What!?
US exported 1.3 million barrels of propane per day, 3/4 derived from natural gas, 1/4 from petroleum. (~75.E6 cubic meters / year, ~41.e6 metric tons. That's not quite as much as Germany's ~66.E6 metric tons of natural gas consumption, but it's not "none".)

"The increase in propane exports was driven by strong petrochemical and heating demand in Asia"

https://www.eia.gov/todayinenergy/detail.php?id=47036
https://www.argusmedia.com/en/news/2...o-grow-in-2022
Maybe we should withhold it from Thai residents that pretend it does not exist.

I very briefly considered LPG / LP as possible alternative fuel for import to Germany from the US, as it does not require as much pressure, but its higher US cost would seem at first glance to make it less appropriate. I haven't spent the time to look deeply into transportation cost per unit energy or what capital budgets might be required, or difference between producer and consumer price. People spend careers on these aspects. Some of them were my classmates.

[LaurV]

Originally Posted by kriesel

What!? US exported 1.3 million barrels of propane per day, 3/4 derived from natural gas, 1/4 from petroleum.

Yep, they just have a lot of refineries. Nobody said US is not a big industrial power. They are, and we respect that. But, to use the same site you pointed, extracted LPG, they mainly import ... (or... grrr... they used to...)
They also make shampoo from petrol. But extracting shampoo from the soil, I don't know... Do they?
(love tickling this guy! now I imagine him looking for statistics of how much shampoo US extracts yearly... )

[Dr Sardonicus]

Originally Posted by ewmayer

I considered this sort of thing, but the numbers seem to make it impractical. Let's use Germany as an example. Someone please check my math:
<snip>
Per this site, Germany natgas imports ~155 billion cubic meters / yr
<snip>

The 155 billion m^3/yr figure appears to be a mistake caused by the table using a bizarre choice of units. The table you cite for your 155 billion cubic meters/yr lists imports in units of Cub m mn.

The figures in the table are in the 155,000 range, a bit below 170K. I spent some time seeking an explanation of "Cub m mn" to no avail. So, I assumed "mn" was a time unit, and guessed.

Guessing that "Cub m mn" means "cubic meters per minute, 155493 Cub m mn gives a figure of about 82 billion cubic meters per year:

? 155493.*60*24*365
%11 = 81727120800.000000000000000000000000000

This is in line with the 90 billion Statista figure you used. Good instincts, there.

I was able to check using the import figures given in energy units. Recent gas imports from Russia in terajoules/month are shown here. About 200,000 terajoules per month. I used one of the figures given for the energy in a cubic meter of gas to convert to cubic meters.

? 200000*10^12/(38.3*10^6)
%13 = 5221932114.8825065274151436031331592689
? %*12
%14 = 62663185378.590078328981723237597911227

This is of the same order of magnitude but somewhat lower, and may indicate how much gas Germany is importing from non-Russian sources.

[kriesel]

Originally Posted by LaurV

they mainly import

5.M barrel/month import, export 1.3M/DAY ~40.M/month. Units matter. You might want to quit while you're behind, and stop embarrassing yourself.

[kriesel]

Originally Posted by ewmayer

That got me wondering

Other systems are also possible. Ethanol and methanol also are capable of containing considerable mole fraction of methane at pressure. But their trade volumes are also inadequate for the large scale of methane involved. And adding up 1% of use by this, 0.x% by that, etc to get to 100% or greater capacity seems pretty unlikely to succeed.

[ewmayer]

Good discussion, all, but let's please try to keep the bickering to a minimum - it's not about a given post/claim being right or wrong, it's about trying to find viable solutions to a very real technological problem with huge economic implications.

Getting back to "optimizing the clathrate approach" - the phase diagram at Wikipedia shows that at temps lower than -5C or so (what the quote in the OP refers to as "ordinary freezer temperatures"), clathrates require little or no pressurization. The phase diagram does not inform to what extent pressurization may be needed to form the clathrate structure to begin with, but it seems likely that the needed pressures at the temps of the left end of the phase diagram would be very large. One possible efficiency would be to install the relatively modest (vs LNG) processing facilties along shipping routes in the far northern US and Canada, and use natural cooling to chill things. Of course that would need pipeline infrastructure to pipe the natgas north. Another efficiency: given a large enough bulk carrier, one might not even need any refrigeration equipment on same - large storage compartments lined with (say) a decently-thick layer of insulating foam would seem to suffice. Not so different from the old straw-lined barns used to store ice blocks cut from frozen lakes in the upper midwest back in the old days.

I should note that the Wikipedia entry concludes with a pessimistic note re. the viability of the idea:

Natural gas hydrates versus liquified natural gas in transportation

Since methane clathrates are stable at a higher temperature than liquefied natural gas (LNG) (−20 vs −162 °C), there is some interest in converting natural gas into clathrates rather than liquifying it when transporting it by seagoing vessels. A significant advantage would be that the production of natural gas hydrate (NGH) from natural gas at the terminal would require a smaller refrigeration plant and less energy than LNG would. Offsetting this, for 100 tonnes of methane transported, 750 tonnes of methane hydrate would have to be transported; since this would require a ship of 7.5 times greater displacement, or require more ships, it is unlikely to prove economically feasible.[citation needed]

OTOH given the likely size of the just-created European market here, an investment in bulk carriers would be justified. And given the simplicity of clathrate-transporting carriers, the cost comparison vs one carrying a similar amount of natgas in LNG form might not be unfavorable.

[Dr Sardonicus]

For methane extracted from seabed deposits, I had the whimsical notion of shipping clathrate in the form of floating icebergs rather than by loading it onto ships. I have no idea whether the notion could be made practicable.

I also note that methane released into the atmosphere naturally does a "slow burn" with a half life of around 90 years. That is supposedly good news, since methane is many times better at trapping heat than CO₂.

But whether it burns fast or slow, the complete combustion of a molecule of methane produces 1 molecule of CO₂ and two molecules of H₂O. So each ton of methane which is completely oxidized produces 2.75 tons of CO₂. This is only slightly less bad than for hydrocarbons C_nH_2n+2 which for large n produce about 22/7 (3.14) tons of CO₂ for each ton of hydrocarbon completely oxidized.

[kriesel]

A better comparison would be CO2 produced per MJ of energy. Other than H2, NH3, N2H4, the H/C ratio is maximized at CH4.

[chalsall]

Originally Posted by kriesel

A better comparison would be CO2 produced per MJ of energy. Other than H2, NH3, N2H4, the H/C ratio is maximized at CH4.

Thanks for that.

What are you telling us?

[ewmayer]

Originally Posted by Dr Sardonicus

But whether it burns fast or slow, the complete combustion of a molecule of methane produces 1 molecule of CO₂ and two molecules of H₂O. So each ton of methane which is completely oxidized produces 2.75 tons of CO₂. This is only slightly less bad than for hydrocarbons C_nH_2n+2 which for large n produce about 22/7 (3.14) tons of CO₂ for each ton of hydrocarbon completely oxidized.

Yes, but the CO2 produced per unit of heat released and heat released per unit fuel mass are lowest for CH4 among the hydrocarbons. Numbers from Wikipedia:

Compared to other hydrocarbon fuels, methane produces less carbon dioxide for each unit of heat released. At about 891 kJ/mol, methane's heat of combustion is lower than that of any other hydrocarbon. However, it produces more heat per mass (55.7 kJ/g) than any other organic molecule due to its relatively large content of hydrogen, which accounts for 55% of the heat of combustion[28] but contributes only 25% of the molecular mass of methane.

(I see Ken noted similar above).

The crux of the matter would appear to lie in the cost of transoceanic transport of the roughly 8x greater volume of the stuff vs LNG. The transport-vessel tech is much simpler than for LNG, but it's still an order of magnitude more bulk needing to be carried. You'd also need fire-suppression safeguards, though perhaps a layer of CO2 piped into the storage compartments would suffice - the methane ice keeps the CO2 on top of it chilled and thus preventing any lighter O2 from getting near the CH4.

[chalsall]

Originally Posted by ewmayer

Yes, but the CO2 produced per unit of heat released and heat released per unit fuel mass are lowest for CH4 among the hydrocarbons. Numbers from Wikipedia...

I would like to point out that we have a perfectly safe fusion reactor available to most of us for several hours per day.

Take the photons. Take the wind. Take the tides.

This is both a very complicated, and a very simple, problem space.