Hi Luke, We know that pressure in a gas is a result of the random motion of gas molecules colliding with the walls of a vessel (simple explanation; not every gas molecule has the same kinetic energy and the energy is proportional directly to mass as well as to the square of the velocity and distributed according to Maxwell’s distribution). We also know that the atmosphere on Earth is held in place by gravity. We all know about ‘escape velocity’. At a given temperature, a gas will have a certain bulk property called kinetic energy. Individual gas molecules that are heavier can have the same energy as a gas that is lighter but moving faster. The lightest gas is H2 which has a tendency of some part of its velocity distribution to reach escape velocity and head for the sun.
So, using this as an example: To fight diffusion, first it helps to slow the average temperature of a gas down so that the transfer of kinetic energy between molecules is reduced. The closer one gets to absolute zero, the easier this becomes. As the temperature of a gas increases, so does the mean velocity of gas molecules and so does the propensity of a gas to diffuse with other species. (It takes longer.) Sorry there’s no magic number, because there are no “Maxwell’s Demons” in charge of things, separating slower, higher-mass molecules from faster, lower-mass molecules. One other thing to consider: if a field force such as gravity (even if “simulated” by a centrifuge) is used, separation efficiency is proportional to mass difference, not to molecular weight (relative mass) ratios. N2 and O2 are only about 13% different in weight, so centrifugal separation would be more difficult than, say, separating H2 and N2. Just for another reality check, gas centrifuges often operate at 100,000 rpm, with mag bearings and electromagnetic pulse drives (and are heated to create a convective flow inside their chambers for separated gas collection). Mark From: Luke Gardner [mailto:[email protected]] Sent: Saturday, March 05, 2011 11:04 PM To: [email protected]; Discussion of biomass pyrolysis and gasification Subject: Re: [Gasification] sidebar Ideal Gas Law for engineering Mark, how many G's does it take to overcome diffusion, say for example to round up the majority of lighter H2 atoms of producer gas in one region vs its other heavier constituents? Luke ----- Original Message ----- From: Mark Ludlow <mailto:[email protected]> To: 'Leland T Taylor' <mailto:[email protected]> ; 'Discussion of biomass pyrolysis and gasification' <mailto:[email protected]> Sent: Saturday, March 05, 2011 10:45 PM Subject: Re: [Gasification] sidebar Ideal Gas Law for engineering …and the phenomenon of diffusion. It’s not a theoretical impossibility, either, given several thousand ultra-high-speed gas centrifuges cascaded together. From: [email protected] [mailto:[email protected]] On Behalf Of Leland T Taylor Sent: Saturday, March 05, 2011 9:53 PM To: Discussion of biomass pyrolysis and gasification Subject: Re: [Gasification] sidebar Ideal Gas Law for engineering Except for the moving atmosphere, thermal effects of circulation etc. Tom Taylor -- Sent from my Palm Pixi _____ On Mar 5, 2011 8:08 PM, Mark Ludlow <[email protected]> wrote: Hi Toby, I think I see what you mean by the “balloons”. So I would ask this question: “If a mixture of gases (as represented by the ‘normal’ Earth’s atmosphere) would stratify as you suggest, wouldn’t one expect the atmosphere to have a different composition at every discrete altitude?” Or: “Wouldn’t all the CO2 have suffocated us by now, even if it is only 0.035% of the atmosphere? (If the atmosphere were 100,000 ft thick, that would still be 35-feet.)” Intended to be a thought experiment. Sometimes though experiments can save time and money. Best regards, Mark From: [email protected] [mailto:[email protected]] On Behalf Of Toby Seiler Sent: Saturday, March 05, 2011 3:54 PM To: [email protected] Subject: [Gasification] sidebar Ideal Gas Law for engineering Daniel and all, That's a great explanation and helps a lot. I see the proportionality in relation to absolute pressure and temperature. It validates use of an inter-cooler and away from heated incoming air, even into ones gasifier, I believe, as far as putting oxygen into the device. I'm speculating here, but thinking of making and trying an oxygen enhancing low pressure system, from lots of long tubular balloons? Oxygen, being a slight bit lighter than nitrogen, could be taken from the low point, and since under pressure, have some portion of the rejected nitrogen and combined air-nitrogen discharged through an orifice at the high point. I see at the end of your post that air, with gasoline fuel at 12-1 and 15-1 ratio, has 2.4 and 3 lbs of oxygen per pound of fuel respectfully (rounding to 20% O/air). Isn't the target ratio of producer gas to oxygen one to one in an IC engine? Or is that 1lb air, thus 1/5 the oxygen or a 5-1 ratio for producer gas to air? The car guys are generally using a 50% air and 50% producer gas ratio, which would seem to validate the 5-1 ratio of gas to oxygen by weight. I'm sure with the numbers you provided I can figure flow rates at each stage. I will verify my flow so sizing is correct before cutting/welding. I purchased some 4" and 6" dia 304 stainless pipe at a salvage company and have a SS air tank for some of the hot section heat recovery from the second stage reactor (and I think enough for a steam superheater... part of final gas cooling). Gas out starts at about 1800f from the x-flow reactor, as gas from stage one is burned and reformed into synthesis gas going through the char bed. The gas outlet is direct coupled to the heat recovery, flowing first to heat stage one incoming fuel, then to a steam superheater and then to a water boiler. It's a CHP arrangement, since massive amounts of heat have to be removed in prooducer-synthesis (prosyn) gas cooling. Thanks for your explanation. Mole remains a small fuzzy creature. Toby Seilertechco _____ _______________________________________________ Gasification mailing list to Send a Message to the list, use the email address [email protected] to UNSUBSCRIBE or Change your List Settings use the web page http://lists.bioenergylists.org/mailman/listinfo/gasification_lists.bioenergylists.org for more Gasifiers, News and Information see our web site: http://gasifiers.bioenergylists.org/
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