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View Full Version : Hydrogen power is not as clean as promised.



dapted
2002-Apr-20, 06:02 AM
I find it interesting to listen to people saying hydrogen burns clean producing only water as a byproduct. This is only true if you burn hydrogen in the presence of only pure oxygen. In reality hydrogen will be burned in normal earth atmosphere. It will of course combine with oxygen to form water, but the heat in the process, and possibly compression, will cause some oxygen to bond to nitrogen yeilding a good amount of Nitrus Oxide. While it will be harmfull to us, at least we'll have a good time when we are exposed to it. (Laughing Gas). There will be other byproducts as well, but the NO2 will be the biggest likely problem.

2002-Apr-20, 09:39 AM
I've always had a problem with vehicles that would produce water as exhaust. That could end up being just as bad as the carbon monoxide produced today. Imagine a billion vehicles all over the Earth producing water as exhaust. Wouldn't be long until we start changing the entire ecosystem! (sheeesh! I sound like a tree hugger!) Deserts would soon become lush tropical zones,humidity would rise warming the planet. Am I wrong about this???? I hope so!!

Phobos
2002-Apr-20, 10:28 AM
On 2002-04-20 05:39, trusty wrote:
I've always had a problem with vehicles that would produce water as exhaust. That could end up being just as bad as the carbon monoxide produced today. Imagine a billion vehicles all over the Earth producing water as exhaust. Wouldn't be long until we start changing the entire ecosystem! (sheeesh! I sound like a tree hugger!) Deserts would soon become lush tropical zones,humidity would rise warming the planet. Am I wrong about this???? I hope so!!


Well lets assume that alll water output from the car enters the atmosphere. Bearing in mind that if the fuel that generated the water "polutant" was not manufactured into car fuel, then it would probably be part of some lake where it would evaporate and end up in the same place.

Bottom line is that the output of water into the environment would be benine.

Phobos

John Kierein
2002-Apr-20, 12:04 PM
I don't think we'll create hardly any nitrous oxide. And hydrogen power is actually likely to DEPLETE the amount of water, but increase the amount of oxygen in the environment. The hydrogen is expected to be created by using solar electric power to electrolyze water into hydrogen and oxygen. The hydrogen is kept in the fuel tanks and the oxygen escapes into the atmosphere. So all the unburned hydrogen in the tanks came from water and it won't be replaced in the environment until it's burned. More likely to create deserts. The whole process also puts heat into the environment. Still, it's miuch better than what we're doing now!

2002-Apr-20, 02:38 PM
<a name="20020420.8"> page 20020420.8 aka Earths Atmosphere
ahha..HIStory {oh My} 1? I wonder what the current rate of
power consumption / per capita ? world wide would be?
2. And how fast that numbers increasing
3? I've seen animations of this "Green" planet
showing the color changes over the centuries
and its truly scary 4now also when I was in school
LONG AGO the estimated oil reserves were predicted
to be exaustable in umteen score of years?
whats the current guess when the gas pumps dry?

David Hall
2002-Apr-20, 03:08 PM
On 2002-04-20 10:38, HUb' wrote:
3? I've seen animations of this "Green" planet
showing the color changes over the centuries
and its truly scary

That animation sounds very interesting. I'd like to see 'em. Do you have any links?



also when I was in school LONG AGO the estimated oil reserves were predicted
to be exaustable in umteen score of years?
whats the current guess when the gas pumps dry?


I have no idea exactly, but I remember hearing the same things when I was growing up. I think though that since then there have been quite a few advances in oil production and they've opened up vast reserves that nobody had forseen existing or being tappable. So I think the forcast has been pushed far into the future for now.

Jim
2002-Apr-20, 03:51 PM
On 2002-04-20 10:38, HUb' wrote:
also when I was in school LONG AGO the estimated oil reserves were predicted
to be exaustable in umteen score of years?
whats the current guess when the gas pumps dry?

On 2002-04-20 11:08, David Hall wrote:
I have no idea exactly, but I remember hearing the same things when I was growing up. I think though that since then there have been quite a few advances in oil production and they've opened up vast reserves that nobody had forseen existing or being tappable. So I think the forcast has been pushed far into the future for now.


Those estimates may need to be drastically revised:

Deep underwater, and deeper underground, scientists see surprising hints that gas and oil deposits can be replenished, filling up again, sometimes rapidly.

Although it sounds too good to be true, increasing evidence from the Gulf of Mexico suggests that some old oil fields are being refilled by petroleum surging up from deep below, scientists report. That may mean that current estimates of oil and gas abundance are far too low.

http://www.chron.com/content/archive/qsearch.hts?operation=getdoc&database=2002%3B2001%3B2000%3B1999%3B1998%3B1997%3 B1996%3B1995%3B1994%3B1993%3B1992%3B1991%3B1990%3B 1989%3B1988%3B1987%3B1986%3B1985%3B&databases=2002%3B2002%3B2002%3B2002%3B2002%3B2002% 3B2002%3B2002%3B2002%3B2002%3B2002%3B2002%3B2002%3 B2002%3B2002%3B2002%3B2002%3B2002%3B2002%3B2002%3B 2002%3B2002%3B2002%3B2002%3B2002%3B&docid=88235&docids=26565%3B26524%3B26463%3B26444%3B26088%3B260 43%3B26042%3B25763%3B25716%3B25705%3B25627%3B25605 %3B25172%3B25057%3B25047%3B25044%3B24938%3B24837%3 B24699%3B24607%3B24600%3B25816%3B25459%3B24641%3B2 4460%3B&query=petroleum+NOT+3:RSEC&pos=8&numhits=25&start=&type=&user=houston&sview=1&hview=2&dview=1

Kaptain K
2002-Apr-20, 04:47 PM
First of all, nitrous oxide is N2O, not NO2 (nitric oxide).
Second, oxides of nitrogen (generically NOx) are formed whenever air is the oxidiser. We have the catalytic converter technology to deal with them, whatever fuel is used (hydrocarbon, alcohol, hydrogen or other).
Third, the biggest advantage of H2 as a fuel is the lack of CO and CO2 (greenhouse gases) in the exhaust.
Fourth, incomplete combustion of petroleum fuels (gasoline, diesel) produces unburned hydrocarbons in the exhaust. this is the primary component of the brown haze that we call smog. With no carbon component, unburned HCs are not a factor with hydrogen fuel.
Fifth, whatever fuel is used, water is the primary component of exhaust (by volume).

_________________
When all is said and done - sit down and shut up!

<font size=-1>[ This Message was edited by: Kaptain K on 2002-04-20 12:49 ]</font>

John Kierein
2002-Apr-20, 11:37 PM
Actually, the more I think about it, I'm not so sure the whole process adds heat to the environment, especially if solar energy is used to produce the hydrogen from electrolysis. The waste heat from the electrolysis process and the waste heat from burning hydrogen may be less than the energy extracted from the sun to create the electricity for the electrolysis.

<font size=-1>[ This Message was edited by: John Kierein on 2002-04-20 19:39 ]</font>

Jigsaw
2002-Apr-21, 02:24 AM
Yo, Jim, your link just brings up their Archives page, not an article. What should I look under?

Donnie B.
2002-Apr-21, 05:49 PM
Good points, all. Oxides of nitrogen can be limited by careful control of the combustion process, combined with catalytic conversion.

What's more, it's entirely possible that a hydrogen-based fuel cycle would involve fuel cells, not combustion.

Fuel cells don't burn the H, they recombine it with oxygen in a reverse-osmosis process, producing electricity and water. The electricity could be used to spin motors. The water can be collected and placed into the waste-treatment stream, if there's any concern about its release to the atmosphere -- though I suspect that evaporation from the oceans would dwarf the release of water from all combustion processes combined.

While fuel cells do operate at high temperatures, they aren't high enough to generate oxides of nitrogen. One goal of fuel-cell research is making them operate efficiently at lower temperatures.

Jim
2002-Apr-21, 06:41 PM
On 2002-04-20 22:24, Jigsaw wrote:
Yo, Jim, your link just brings up their Archives page, not an article. What should I look under?


Try this link to the same story instead:
http://www.newsday.com/mynews/ny-dsspd2670369apr16.story

Jigsaw
2002-Apr-22, 02:04 AM
Okay, thanks. /phpBB/images/smiles/icon_smile.gif Fascinating stuff.

Another Phobos
2002-Apr-24, 09:35 PM
On 2002-04-20 05:39, trusty wrote:
I've always had a problem with vehicles that would produce water as exhaust. That could end up being just as bad as the carbon monoxide produced today. Imagine a billion vehicles all over the Earth producing water as exhaust. Wouldn't be long until we start changing the entire ecosystem! (sheeesh! I sound like a tree hugger!) Deserts would soon become lush tropical zones,humidity would rise warming the planet. Am I wrong about this???? I hope so!!


Here's a thought...water vapor is a bigger greenhouse gas than carbon dioxide. Hmm...

DaveC
2002-Apr-24, 10:04 PM
"Here's a thought...water vapor is a bigger greenhouse gas than carbon dioxide. Hmm..."

Maybe - but unlike CO2, water vapour won't build up in the atmosphere. It maintains an equilibrium defined by the dew point. However, you raise an interesting thought. If CO2 emissions cause elevated temperatures, there will be more water vapour held in the atmosphere, contributing to higher temperatures. Like a chain reaction IF water is indeed a greenhouse gas. I hadn't heard that before.

John Kierein
2002-Apr-24, 10:12 PM
But the hydrogen economy SUBTRACTS water from the ecosystem. The water is converted to hydrogen which is stored until it's used (plus some released oxygen). So all that stored hydrogen repesents water taken out of the ecosystem. Maybe this will cause us to freeze?
Actually the dewpoint argument given by Dave C. is the right one. As we take water out of the ecosystem more evaporates to keep the humidity about the same and as we put vapor in, it deposits as rain and dew. So the greenhouse gasses don'tchange from a hydrogen economy.

<font size=-1>[ This Message was edited by: John Kierein on 2002-04-24 18:27 ]</font>

<font size=-1>[ This Message was edited by: John Kierein on 2002-04-24 18:28 ]</font>

Jim
2002-Apr-24, 11:55 PM
On 2002-04-24 18:04, DaveC wrote:
"Here's a thought...water vapor is a bigger greenhouse gas than carbon dioxide. Hmm..."

... I hadn't heard that before.

Yup.

On a clear day, water vapor can comprise 60 to 70 percent of the greenhouse effect. Next in line, carbon dioxide contributes an additional 25 percent.

http://www.pbs.org/wgbh/nova/ice/greenhouse.html

(Fixed BB Code.)
_________________
<font color=000099>Never attribute to malice what can be adequately explained by ignorance or stupidity.</font>
Isaac Asimov

<font size=-1>[ This Message was edited by: Jim on 2002-04-24 19:57 ]</font>

roidspop
2002-Apr-25, 03:18 AM
For any science teachers out there, a little demo that's fun...probably completely wrong, but interesting.

You fill an empty fish tank (no fish, ok?) with CO2 and invite your kids to feel the greenhouse effect; one by one they stick their hands into the CO2. The sensation of warmth is very distinct (probably completely misleading too, but neat).

Sorry. Now go back to your argument.

<font size=-1>[ This Message was edited by: roidspop on 2002-04-24 23:21 ]</font>

David Hall
2002-Apr-25, 12:38 PM
On 2002-04-24 23:18, roidspop wrote:

one by one they stick their hands into the CO2.

Just make sure it's only their hands, okay? Don't want any kids turning purple (or worse). /phpBB/images/smiles/icon_smile.gif

DaveC
2002-Apr-25, 06:48 PM
I tried the CO2 in the fish tank experiment- it was warm. What I don't understand is why when I tried it with water it felt cold if water is a bigger greenhouse gas. Did I miss something? My brother the wannabe physicist says if I had used dry ice as a source of CO2 I would have gotten better results.

As I recall, CO2 is at about 350 ppm in the atmosphere and water vapour must be in the several percent range. This suggests that water is not a more effective greenhouse gas than CO2, it just has a bigger effect because of its much higher concentration. What about on a cloudy day? Do clouds reflect IR radiation back into space before it gets a chance to raise the atmospheric temperature?

roidspop
2002-Apr-25, 09:26 PM
Here is an interesting article about clouds and the greenhouse effect:

http://science.nasa.gov/headlines/y2002/22apr_ceres.htm?list151878

As to the tank experiment, I suspect the difference in concentrations (nearly 100% as opposed to a few percent), difference in specific heats, and difference in densities all contribute to the effect. I leave the details to the alert reader (ie...I don't understand it m'self)

Phobos
2002-Apr-25, 11:29 PM
The water felt cold to you because water is a beeter conductor of heat. Conduction, convection and radiation are the three known methods of heat transfer.

In the case of water the principle method is conduction. We say water is a good conductor of heat because it allows heat to transfer well from one medium to another through it.

Being a good conductor of heat doesn't only mean that it absorbs heat quickly - it will release it quickly as well (ever been burnt from the steam from a kettle, or burnt yourself getting into the bath too soon ?).

Phobos


<font size=-1>[ This Message was edited by: Phobos on 2002-04-25 19:57 ]</font>

John Kierein
2002-May-01, 06:25 PM
As I understand it, the reason someone can run over a bed of hot coals is because the coals, while hot, are not good conductors of heat. Don't try running over a bed of hot iron!

ToSeek
2002-May-01, 06:40 PM
On 2002-04-25 19:29, Phobos wrote:
The water felt cold to you because water is a beeter conductor of heat. Conduction, convection and radiation are the three known methods of heat transfer.

In the case of water the principle method is conduction. We say water is a good conductor of heat because it allows heat to transfer well from one medium to another through it.

Being a good conductor of heat doesn't only mean that it absorbs heat quickly - it will release it quickly as well (ever been burnt from the steam from a kettle, or burnt yourself getting into the bath too soon ?).

Phobos


Actually, my understanding is that water is a poor conductor of heat but a good reservoir of heat (high specific heat capacity). You can get burned easily with water because there's so much heat there to be burned with - the steam doesn't cool off immediately in the air as it would if it had a low specific heat capacity.