Natural gas + H2 blend calculation

I received some comments on the last edition and was asked for the source of my info. I like to calculate things from first principles, to make sure the math checks out. It is dangerous when people just cut and paste what others say without fact checking. When conference speakers were stating that displacing 20% of natural gas in the pipeline with hydrogen equals a 20% reduction in carbon emissions I just knew this could not be right because they were mixing apples and oranges.

So I'll show my calculations here. Hydrogen is indeed the highest energy carrier by weight (usually given as mega joules per kilogram MJ/kg). But unfortunately it is not dense, much less dense than natural gas. Now natural gas being 'natural' is not pure methane (CH4) and can contain some higher hydrocarbons like ethane, propane and butane. Therefore natural gas heat content can vary across North America but not by a huge amount. For the average in British Columbia I found 40.9 megajoules per cubic meter (or 40.9 MJ/m3).

But hydrogen, on a volume basis, is only 12.7 MJ/m3 i.e. about one quarter that of natural gas, the 'orange' in the apple pipeline ?? or the watered down booze example in my previous edition.

But we are only blending the hydrogen at 20% so for 1 m3 of blended gas, the hydrogen is only contributing 12.7 X 0.2 = 2.54 MJ/m3. But the original natural gas was 40.9 MJ/m3 so the hydrogen is 20% of the volume but only 7.2% of the energy 2.54/35.26 = 0.072. So that is the CO2 emission reduction, only 7.2 % based on the B.C. heat values. In the last edition I used slightly different values and came up with 7%. Either way a far cry from the purported 20% that was promoted at the conference.

Then, just to be safe, I used an old engineering trick. If you can logically reason it out a different way and still calculate the same answer then you know your reasoning is sound. So again, assume it is winter and you are burning natural gas to keep a room warm. One m3 of natural gas would contribute 40.9 MJ. But our one m3 of 20% blend of hydrogen mixed with natural gas only provides 35.26 MJ (40.9X0.8 + 12.7X0.2). So we are missing 5.64 MJ (40.9 - 35.26). So we need to burn a bit more of the blend to get the same heat (i.e. drink a bit more of the watered down booze to get the same kick as the untampered libation). How much more? Well we are missing 5.64 MJ and the blend contains 35.26 MJ/m3 so we need to burn an additional 0.16 m3 of the blend (5.64/35.26) to get the additional heat. But 80% of that extra blend is natural gas of 0.128 m3 (0.16X0.8). And it is the natural gas that emits the CO2 when burned.

Drum roll please: So the 1 m3 blend with hydrogen has only 0.8 m3 of natural gas but we need to burn an additional 0.128 m3 of natural gas for a total of 0.8 + 0.128 = 0.928 m3 of natural gas. So the unblended natural gas would be 1 m3 of natural gas but even with the blend we still need to burn 0.928 m3 of natural gas in the blend to get the same heat content. Therefore from a carbon emission point of view we are saving 1 - 0.928 = 0.072 or 7.2%. Again same answer and it is not 20%.