woodburner wrote:How big are the spaces between molecules in HDPE pipe? Thickness will not make much difference if the gaps are large enough fo H2 to get through the gaps. For pipes that meet the requirement https://avt.inl.gov/sites/default/files ... endixc.pdf
The link you posted concerns lines working as high as 8000 psi. That is something for a lab or factory or perhaps a rocket engine. Stainless steel is the thing there.
For gas transmission mains from supplier to city gate the pressure is usually 1500 psi or less and local distribution lines to your meter run as low as 3 psi.
I'm not chemist enough to know the pore space dimensions in a HDPE pipe but I'm pretty sure they are a lot less porous then grey cast iron or even ductile iron pipes.
Wasn't the old coal gas mainly hydrogen? With a massive project to convert the country to natural gas? Can't see the government paying for this and getting the users to pay is hardly a vote winner.
The exact composition of coal gas varied from one district to another, but yes hydrogen was almost always the largest component.
The iron or steel pipes used for coal gas were leak proof if ONLY the pipes them selves were considered.
The joints were a continual source of trouble being typically of tar or compound and fibrous material, or for large pipes of lead wool hammered into the joints.
When natural gas replaced coal gas, leakage was a huge problem, again not from the actual pipes but from the joints.
Coal gas tended to contain a lot of water vapour, and any absolutely minute leakage from a joint tended to keep the hemp or teased oakum damp and therefore more or less gas tight. Natural gas is very dry, and any originally minute and inconsequential leakage tended to very slowly dry out the packing material and make the leak worse.
This caused a number of fatal explosions and as a result all new gas mains are of welded plastic pipe for low and medium pressures, or welded steel for high pressures.
Hydrogen wont leak from the joints of modern gas mains as these are welded and consist of the same material as the rest of the pipe.
I do wonder if the plastic used might be slightly pervious to hydrogen though.
Many plastics are slightly pervious, examples include the evaporation of petrol stored in plastic cans. Offensive smells sometimes escape from plastic pipes carrying sewage, no matter how perfect the joints are.
Orange juice is supplied in tetra packs that incorporate a thin layer of aluminium foil, plastic lined cardboard alone would be slightly pervious to oxygen which would slowly oxidise and spoil the product.
"Installers and owners of emergency diesels must assume that they will have to run for a week or more"
clv101 wrote:Point is the H molecule is much smaller than CH4, it happily fits through gaps CH4 won't. He is the same - inflate a rubber balloon with He and it escapes pretty quick (compared with N and O2) which is why foil balloons are used.
I seem to remember the school chemistry teacher saying it was all about the mass. Graham's Law of diffusion/effusion was why they leaked. Hydrogen (H2) molecules are lighter than methane and effuse (it was diffusion when I was a lad) faster.
Chemistry recollection over for the year.
On another point making it from methane seems to make no sense. Why not electrolysis? I suppose it is government policy after all.
clv101 wrote:Point is the H molecule is much smaller than CH4, it happily fits through gaps CH4 won't. He is the same - inflate a rubber balloon with He and it escapes pretty quick (compared with N and O2) which is why foil balloons are used.
I seem to remember the school chemistry teacher saying it was all about the mass. Graham's Law of diffusion/effusion was why they leaked. Hydrogen (H2) molecules are lighter than methane and effuse (it was diffusion when I was a lad) faster.
Chemistry recollection over for the year.
On another point making it from methane seems to make no sense. Why not electrolysis? I suppose it is government policy after all.
The electric energy needed would be more valuable fed directly into the grid. It takes on the order of 65 KWHs of electricity per kg of compressed Hydrogen.
Production from natural gas is cheaper.
There is no point in producing hydrogen from electric power under present UK conditions (except on a small scale for laboratory or workshop use, when it compares favourably with the cost and time/trouble of purchasing and handling cylinders of the gas)
The electricity would indeed be more valuable fed into the grid, or not taken from the grid and thereby reducing the natural gas consumed for power generation.
The day may eventually come when we have so much renewably generated electricity, that use of any surplus to generate hydrogen MIGHT be worthwhile.
That however is in the far future.
At present we burn a great deal of natural gas to generate electricity, even at off peak hours. Eliminating that should be a higher priority.
"Installers and owners of emergency diesels must assume that they will have to run for a week or more"
I don't think it has to be all or nothing. My understanding is that in Germany they are underway with adding hydrogen into the existing natural gas supply system. The hydrogen is generated at night from spare wind capacity, so if done by electrolysis, could be renewable. And at concentrations of up to 10% can be used in existing natural gas pipelines without significant leakage - and without a requirement to change anyone's home cooking or heating systems.
If we ever get to 10% hydrogen, then we have to solve how to go higher.
I can see what they they are thinking about using an existing gas network for hydrogen. I do agree with Trevor though about using wind turbines and electrolysis. Given the reasonable storage that vtsnowedin said about 65kWh in 1 kg of hydrogen there may even be a little bit of storage of wind turbine intermittency in the gas pipeline network. We once ran a gas turbine generator for several hours on the gas stored in a 20km section of gas pipeline in China.
TrevorL wrote:I don't think it has to be all or nothing. My understanding is that in Germany they are underway with adding hydrogen into the existing natural gas supply system. The hydrogen is generated at night from spare wind capacity, so if done by electrolysis, could be renewable. And at concentrations of up to 10% can be used in existing natural gas pipelines without significant leakage - and without a requirement to change anyone's home cooking or heating systems.
If we ever get to 10% hydrogen, then we have to solve how to go higher.
Welcome to powerswitch.
At present we never have any "spare" wind power in the UK, however in the future the idea of using spare wind power to produce hydrogen has some merit, and as you point out, modest volumes of hydrogen may be added to natural gas without problems.
"Installers and owners of emergency diesels must assume that they will have to run for a week or more"
Yes that does sound like a reasonable strategy when you get to the point that you have enough wind or other renewables to cause grid overload problems. You could have the electrolysis plants turned on or off by the grid controllers as needed as there need be no employees present and allow your base load plants to idle along at the ready for when the wind dies.
One other point about gas leaks. Most American cities have distribution lines that average between fifty and a hundred years old and they are riddled with small leaks. In the Boston area the gas company estimates it is losing 2.7% of the gas it puts into the lines to leaks and that that gas amounts to 10% of local green house gas emissions. These lines need changing but of course it has been pushed off for decades. If they leak Natural gas switching to a hydrogen rich mix would just make that problem worse until the upgrades are accomplished.
I think it's definitely worth investigating to see if we can get the efficiencies up. I also have a suspicion that heat pumps are going to prove problematic so we might well need another source of heat for buildings.
adam2 wrote:
At present we never have any "spare" wind power in the UK,
I don't think that is quite true - there have been times when some Scottish wind turbines have been paid to not produce, though this has mostly been because the connecting transmission lines were not adequate.
adam2 wrote:
At present we never have any "spare" wind power in the UK,
I don't think that is quite true - there have been times when some Scottish wind turbines have been paid to not produce, though this has mostly been because the connecting transmission lines were not adequate.
Yes, I should perhaps have said "we have very seldom had a surplus of wind power, and when we did it was only for a few hours. This was in unusual circumstances that are most unlikely ever to be repeated, unless we vastly increase wind power capacity in Scotland"
No one is going to invest a lot of capital in electrolysis plant and related infrastructure unless there is REGULARLY going to be enough very cheap electricity to profitably run said plant.
"Installers and owners of emergency diesels must assume that they will have to run for a week or more"
