There has been a lot of dialogue and discussion lately on transitioning to hydrogen from natural gas. Much of this discussion is centered on reusing the incredible natural gas pipeline network the USA (and others) have. The simple vision is to ultimately replace natural gas from those pipelines with hydrogen. It does sound simple, but there are a number of technical issues that are overlooked in this simplified view.
First, hydrogen is much lighter and less dense that natural gas. This leads to higher pressure drops in these existing pipelines for the same energy delivery. For example, see the table below where there is an existing 8″ pipeline currently moving 50 MMSCFD of natural gas with an inlet pressure of 1,000 psig. Over the 10 miles it operates there is a pressure drop of 223 psid such that the outlet pressure is 777 psig. Under these conditions the pipeline is currently delivering ~50 BBtu/day.
If hydrogen replaces the natural gas in this same pipeline and the pressure drop remains the same, there will only be ~42 BBtu/day of energy delivered. That is a 16% decrease in delivered energy to the downstream users. Bottom line is if we replace natural gas with hydrogen in our current pipeline system we will need more pipelines or more compression just to deliver the same quantity of energy as we do now with natural gas. This is often overlooked in the energy transition discussion.
| Composition | Flow (MMSCFD) | Flow (klb/hr) | Delivered BTU’s (MMBtu/day) | Outlet Pressure (psig) |
| C1 | 50.0 | 88.1 | 50,120 | 777 |
| H2 | 156.4 | 34.6 | 50,120 | 657 |
| H2 | 130.1 | 28.8 | 42,152 | 777 |
In a future blog we’ll address some of the other issues such as compression, metallurgy, and flammability.