In any case, I don't understand why you're focusing on pressurizing the gas by pumping air in on it ???

a) that dilutes your fuel...you're wasting storage space

b) it makes it an explosive mixture.

The proper way to do this is to draw the gas through a filter and into a compressor.  The output of the comp. goes right to the tank.

Your thought of using propane tanks is a good one.  They are rated to higher pressure than almost any other commonly available pressure-vessel.

Note that your gas is likely to have some water vapor in it, and propane tanks do not have a water-drain valve on the bottom.  Water will collect in your tank and slowly rust it.  You should be thinking about how you're going to deal with that...

I'd consider the use of wood-gas for a heating boiler as a big waste of time and energy, and fuel-energy too.  The only thing that I use wood-gas for is a diesel gen-set, i.e. something that -needs- a gaseous or liquid fuel.  For heat and hot water, we use solid wood.

notes;  the CO portion of the gas IS a fuel.  You do not want to eliminate it...you want to burn it.

I know of no cheap and easy way to eliminate the nitrogen.  There -are- filters available that will seperate hydrogen from nitrogen, but they are neither cheap nor easy.

you -can- filter out the tars and acids fairly easily with a fairly crude/simple setup; and I highly recommend doing so if you're using the gas to run any kind of engine.  Uncleaned wood-gas will eat up an engine in short order...