I would guess the natural gas is quite purified by that point, but for the fuel cell to work you need to combine it with air (or to be precise, the oxygen in the air) and a lot of it. So for the fuel cell membranes not to clog with dust and gunk they will have to clean in in some way to prevent issues, ideally without to much extra-energy use or expense per unit of air filtered.
alt Hacker News
I would guess the natural gas is quite purified by that point, but for the fuel cell to work you need to combine it with air (or to be precise, the oxygen in the air) and a lot of it. So for the fuel cell membranes not to clog with dust and gunk they will have to clean in in some way to prevent issues, ideally without to much extra-energy use or expense per unit of air filtered.