What should we use for final stage filtration on a gasifier-engine system?
Many use paper filters, but these are sensitive to water and resist passing gas once wet. They are also surface packing, so tend to tolerate smaller particulate loads before clogging. The paper ones also cannot be cleaned easily, which is a problem for remote areas. Ideally we'd like the filter to be tolerant of water, particulate loading, and easy to clean when out in the boonies and not able to buy a new one.
Considering the above, we started considering cleanable K&N type off road filters. Which then lead to considering Uni type motorcyle filters. But what are the relative merits of these two cleanable filter types?
Here below are some threads from the off-road toys motor toys world on the relative merits on each type. The summary is the paper filters are the best performing filters, but clog faster and can't be cleaned. Of the cleanable type, the foam are better filters than the cotton gauze, which is commonly the K&N. The K&N filter breathes slightly better than all of them, but not an amount that really matters much. Many seem concerned with the filtering ability of the K&N in very dusty conditions.
http://www.rhinoforums.net/engine/38703-k-n-air-filters-vs-foam.html
http://www.thumpertalk.com/forum/archive/index.php/t-389759.html
http://www.ds450hq.com/forums/engine-efi-drivetrain/2237-k-n-foam-filter.html
http://www.kfx450hq.com/forums/engine-efi-drivetrain/6288-air-filters-foam-k-n.html
http://ltr450.theatvchannel.com/invision/index.php?showtopic=7283
http://www.race-dezert.com/forum/arch
Info on the Uni foam filter, the standard foam filter. the uni is made from open cell polyurethane foam. this is also called "reticulated foam". it is often two stage- 45ppi and 65ppi. the classic green sock ones are one stage 65ppi.
http://www.unifilter.com/whoisuni.html
http://www.unifilter.com/online%20catalog/accessories.html
the different pores per inch (ppi) of different layers. many are done as two stage filters. coarse on outside. fine on inside.
http://www.technilube.com/twin_air/index.php
* Standard Twin Air dual-stage foam filter has 45 pores per inch (PPI) on the outer and 60 PPI on the inner foam
* Total thickness of the foam layers when bonded together equals 15mm
* Twin Air foam layers are not glued together, they are laminated
* The lamination process does not restrict airflow between the two layers
* Twin Air foam is open cell polyester foam
if you get serious in off-road racing in very dusty situations, the choice seems to be the ump super filter. these are paper filter cartridges in nice ss housing. they are the big industrial size catridge like common on big forklifts.
http://www.racereadyproducts.com/air-filtration/ump-super-filters/
Here's some sources for bulk reticulated foam. If you want onesies and twosies, likely get it from Uni directly. They sell bulk foam for homemade filter making.
all thomas net suppliers. http://www.thomasnet.com/products/reticulated-foam-30684500-1.html
http://www.newenglandfoam.com/filter.html
http://www.pacfoam.com/appl.htm in so cal. big filter maker
http://www.bobsfoam.com/detail.html#reti in hayward. big foam warehouse
http://www.merryweather.com/polyurethanes.asp#reticulated
http://www.ufpt.com/united-foam/applications/filter-foam.asp
http://www.canalrubber.com/
http://www.ndi-us.com/Reticulated-Filter-Foam.cfm
http://www.polytechinc.com/products/filters.php
http://www.airfiltersupply.com/ in sacramento
http://www.appliedairfilters.com/index.html in fremont
http://www.williamsfoam.com/products.html in sylmar
http://www.procycledepot.com/AIR_FILTER_FOAM_SHEETS-8-10434-91724.html