John Rumm wrote:
Natural gas as supplied for fuel is about 90% methane CH4, most of the
rest being ethane C2H6 and a little CO2 and N2.

Is the natural gas we have piped naturally in that mixture or is it
blended that way for a reason?

It has to meet a lot of requirements, that were originally based on the
gas that was available in the 1960s:

* within a specified range of calorific value

* within a specified range of density (along with the CV, this ensures
that the gas will deliver a known amount of energy when metered through
a nozzle - Google for "Wobbe number"or "Wobbe index")

* not too much hydrogen (to avoid light-back)

* not too much inerts (to maintain flame stability)

* not too much heavier hydrocarbons (to avoid sooty flames).

Most of those requirements are inter-related, but it all started out
quite easy because the standards had been written to match the gas. I
don't know how much additional effort it requires using present-day
feedstocks.


--
Ian White