CO2 and NG

Tim_34

I have planted hundreds of trees in my lifetime and hopefully they will help reduce climate problems even after I am gone.

I am trying to ask a serious qustion about how much CO2 is produced when NG is burned.

Tim_34

CO2 and NG

Don't want to get political here, but I was wondering what the answer to this qustion would be:

If I burned 5000 therms of natural gas how much CO2 would I be putting in the atmosphere?

jp_2

planting trees

I want to know, how many trees does it take to off set that 5000 therms, and I thought they slept during the winter?

Brad White_9

Typically

about 120,000 lbs. per 1 million cubic feet burned. Your 5,000 therms (500,000 CF at 100 CF per therm) would emit about 60,000 lbs. of plant food.

Interesting in that the weight of the gas itself is about 22,200 lbs. The mass increase is because of the greater amounts of air required, over 17:1 by weight.

The following is from an essay I wrote when teaching:



For natural gas, comprised principally of methane (CH4, 70 to 95%) and associated gasses (ethane, CH6, 1 to 14%) and (propane, C3H8, 0-4%). Butane, hexane, pentane plus other inert gasses make up a range of no more than 2% each. Methane has the highest O2/air requirements of any of them, so the methane figures will govern. Methane alone requires 3.99 lbs. of O2 and 17.24 lbs. of air per lb. burned. Butane, propane and ethane all require less than 94% that of methane. Complete theoretical methane gas combustion yields carbon dioxide and twice as much water vapor (CH4 + 4 O2)=(CO2 & 2-H20).

jp_2

mitch,

I wasn't trying to be funny, I think my question is as interesting as yours, sorry you thought differently.

they do go together as mr gore would imply, but still an interesting question.

jp_2

confused brad

you say 60,000lbs but only 22,000 lbs of co2 gas?

then isn't the real answer 22,000lbs of co2 produced from 500,000cf ch4? Or 166,500 cf co2?

don't forget to properly balance your equation CH4 + 2O2

Brad White_9

JPaul

60,000 lbs. of CO2 given the typical rate of 120,000 lbs. of CO2 per 1 million CF burned. 5,000 therms is half a million CF so half of the 120,000 rate per million.

EDIT: So, specifically, the 5,000 therms would yield 60,000 lbs. of CO2, yes.

Thanks for the check-in on the equation; I had not meant it to be the formula but should have been. None of my students picked that up but you on the other hand.... . It is actually 4:1 (3.99 call it 4 lbs. oxygen per pound of methane by weight). The balance of course goes to NOx (air being 78% nitrogen) and actually can make recombinant CH4, not to mention CO and ice sculptures if you do it right

cattledog

CO2 and NG

Combustion of natural gas produces about 12 pounds of CO2 per 100 cubic feet(approximately 100,000 btu).

These conversion factors come from the U.S. Department of Energy and the Energy Information Administration, Instructions for Form EIA 1605B, Voluntary Reporting of Greenhouse Gas Emissions, Appendix B. (Natural gas = 12.0593 lbs. of CO2/CCF and 11.708 lbs. of CO2/Therm, Oil = 22.384 lbs. of CO2/Gallon, Propane = 12.669 lbs. of CO2/Gallon.)

Tim_34

Thank you guys

My head is spinning from the math but I surely appreciate your answers.

So, Brad, are you saying that 5000 therms of NG would emit about 60,000 lbs of CO2 mhen burned?

I'm going to go plant more trees ;-)

I apologize to you, JPaul. I meant no disrespect regarding your 1st post.

Jim Davis_7

Does it go up??

CO2 has a molecular weight of 44. Air O2 + 4N has a molecular weight of approx 30. CO2 starts out hot but as soon as it cools in the air in becomes much heavier than air. Therefore does it actually go into the atmosphere??

Brad White_9

I suppose like any gas in suspension

it does as it damned well pleases..

Convection, osmosis, the Coreolis effect, winds, etc. all play a role. The atmosphere is not one of those bartender drinks where each layer of a given density knows it's place -until shaken, not stirred.

If the density hypothesis were true, the upper atmosphere would be entirely hydrogen, helium and other lighter gasses, if I grasp your thinking.

Even crawling along the ground is in the atmosphere too as I see it

Lurkin' Murkin'

True - I've been crawling along the ground and "lost in the ozone again", at the same time...

jp_2

winds

ever hear the stories of new york skyscraper workers getting hit by wheat kernals from the midwest?

apparently CFC's get up there too, much heavier than CO2.

then, think about dust! ever sit in a room where the sunlight is just right that you can see dust particles dancing around in the air, thousands of time heavier than air?

or even Hail, and how its formed, billions of times heavier than air,CO, CO2 and CFC's.

even in that very 'still' room with dust, those 'air' molecules average 1,000 mph!

Jim Davis_7

mixes evenly

Apparently CO2 mixes evenly from ground to sky and is at a current level of about 330ppm. This is supposed to be increasing about 1 ppm each year. Also read an article that said elevated CO2 helpls some trees endure adverse weather conditions better. And just for the record, Mother Nature produces over 97% of all greenhouse gasses.

Christian Egli_2

No Jenny Craig here, but the pounds have to go

Since when is it customary to speak of gasses in pounds? Chemistry only talks of grams. Utilities sell us our fuel by the volume, we burn the stuff in volumetric metering devices and no one has a clue on how many pounds go through the gas meter.

What goes through the gas meter is not even half the story, measure it's weight if you wish, but then also, weigh the remaining of the comburant gasses and weigh the combustion gasses as well. Necessary air for combustion ways tons. Add excess air and you have mega tons. How many pounds of CO2 is there you say? The number is a mind numbing trick to sell us a bill of goods.

Grocery stores know all about this.

Which will be cheapest? the product that sells a dollar for twelve ounces or ninety-nine cents for three hundred and forty milliliters. Buy it by the pint and we'll get drunk together.

For an accurate and more earth grounded number on what sort of smoke comes off your boiler stack, look at the chemical combustion process. For each one volume of natural gas you enter into the equation, you very exactly get only one volume of carbonic gas. The idea that our whizzing gas meters are pumping out mountain piles of CO2 is plainly skewed - the mound of gas only amounts to a mole. --- 22.4 liters.

Are you horrified by the 500,000 cubic feet of gas you burned? (This is a large amount that would possibly take five to ten small homes to consume in a whole season , keep that in perspective) You won't be horrified then that you've only put out a volume of 500,000 cubic feet of CO2. Put your visualizing goggles on, and this staggering volume full of zeroes only amounts to the atmosphere contained within the walls of an ordinary grocery store, compared to clouds and stuff, it is nothing. It took a boiler in an apartment building a whole season to put out a cloud that a tree breathe through in one day, without even much wind.

1 volume CH4 + 2 volume O2 = 1 volume CO2 + 2 volume H2O vapor

16 g CH4 + 64 g O2 (notice this heavy weight whopper) = 44 g CO2 (notice where the O2 sits now, see what's relatively heavy?) + 36 g water

CO2 is a heavy weight molecule, simply because of its O2 fat content. I find it most scientifically discriminatory to go ahead and make targeted weight comments while pointing fingers at the Junoesque CO2. But we shouldn't be surprised in a world of political correctness.

You think numbers don't add up -

The highly offensive idea touted behind the fat CO2 weight based tax is that we should start looking for weight equivalents. We convert twenty two gazillion pounds of CO2, and the idea painted into our head is that there is no way we can grow that sort of tree in our backyards......... hmmm......... the thing is, trees are skinny, they don't do in heavy body mass indexes, beyond operating water, they largely contain no heavy oxygen.

Trees breathe-in huge pounds of CO2, trash the heavy oxygen part, reject it to the atmosphere (and if you're a tree, these emissions are super pollutants), then they build something beautiful out of the precious carbon which we should all love. It's all a cycle, getting all boogey eyed on one aspect of the wheel makes no sense.

The carbon cycle through the atmosphere is not balanced, hasn't ever been I suspect. For all practical purposes there is no surplus free (measured in tiny PPM) amount of CO2 in the air that gets cast aside like pennies in the street. There is a huge shortage of the stuff, CO2 can't be produced fast enough for all forms of natural processes to gobble up the stuff.

If you live in the suburbs, your trees and lawn probably eat up all the CO2 you can feed them. If there's any left, the oceans will swallow it up. If you don't even live near an ocean, watch out for rocks and how they throw themselves at the CO2 gas. Yes rock, what do you think calcium CARBonate is? The layers and layers of limestone and marble we have our feet planted on represent carbon deposits that make coal a laughably small stash.

Now business talk

Please send me your carbon credit money, and I'll go water some rocks on your behalf. I'm totally serious, as a business we do grow artificial refractory rocks and we do eat up carbon dioxide here; and it's a thing that can't be done without steam and without money. We take pounds Sterling...

Brad White_9

That is osmosis at work

All fluids eventually find equilibrium and go where they are not.

A professor once told me that if you took a cup of water and evaporated it in the Houston Astrodome (starting at zero percent humidity and in a vacuum) each molecule of water vapor would find a place at practically the speed of sound and equidistant apart.

They just know, those smart little antisocial buggers.

You are essentially correct as to what Mother Nature does. Whether we like it or not. Actually, Mother nature produces about 97% of all CO2, 99.999% of all water vapor and in it's natural state, methane. So all told as far as so-called greenhouse gasses are concerned, she makes over 99.99 (take your pick of decimals) percent of them.

Brad White_9

When all seems in despair

Mr. Egli, Poet Laureat of The Wall once again sets things straight.

The mixing of volume and weight is indeed head-spinning, enough to burrow like a mole...

Thanks Christian- erudition never sounded so great.

Brad

JimH

Jim Hansen...

Brilliant NASA scientist, or misguided tool of the Liberal Hollywood Elite?

You be the judge:

http://en.wikipedia.org/wiki/James_Hansen#Opposing_Greenhouse_Skeptics

At the top of the list of things I take away from this article is that right now co2 is the least of our worries (though a worry, nonetheless). Here's a quote:

"He notes that warming observed to date is largely due to non-CO2 gases. This is because CO2 warming is offset by climate-cooling aerosols emitted with fossil fuel burning and because non-CO2 gases, taken together, are responsible for roughly 50% of greenhouse gas warming."

The eruption of Mount Pinatubo in the 1991 put a lot of sulfur in the air, producing cooling effects which were quite noticeable in North America. There is some evidence that sulfur emissions from fossil fuels masked the warming effects of co2 and particulates, and now that sulfur emissions are much lower the effects of the particulates and co2 are more pronounced.

-JimH

JimH

osmosis??

Osmosis implies a membrane, does it not?

http://en.wikipedia.org/wiki/Osmosis

You're just checking to see if we're awake, right?

:->

-JimH

jp_2

mitch,

no offense taken, could have seemed as if I was an eco wacko!!!

Bob Harper

Brad, could you explain this quote?

Brad wrote: "For natural gas, comprised principally of methane (CH4, 70 to 95%) and associated gasses (ethane, CH6, 1 to 14%) and (propane, C3H8, 0-4%). Butane, hexane, pentane plus other inert gasses make up a range of no more than 2% each. Methane has the highest O2/air requirements of any of them, so the methane figures will govern. Methane alone requires 3.99 lbs. of O2 and 17.24 lbs. of air per lb. burned."

How do you figure methane has the highest O2/ air requirement of any of these?
methane- 10/1 air to fuel
propane- 24/1
butane-31-1

Shouldn't that have read "lowest" meaning it takes less air volume for proper combustion than the heavier compounds? The ratio means methane is a higher percentage of the mixed combustion fuel/air load per batch, if you will but the overall air requirements are higher for the heavier alkanes. If you measured one cubic foot of methane/ air versus propane/ air at stoichiometric mixes, there would be more air and less fuel with the propane than the methane, which is how we make fuel conversions yet maintain the BTU input rating.
thx,
Bob

JimH

do boilers run @ stoichiometric?

Hi, all my combustion experience is in the area of automobile fuel injection, where thing are run slightly
rich, to lower temps and oxides of nitrogen. Are boilers tuned to run right at stoichiometric?

-JimH

Mitch_4

names

Hi Mitch.

Just as an aside, I have been using the name for 4 years here.

I am going to start using Mitch B to avoid confusion. Existing user names are not checked.

You may want to use mitchman like you email addy, or like mitchS and now myself with Mitch B use your last init to avoid confusion.

Mitch (now Mitch

Lurkin' Murkin'

I don't know of any oil or gas burners that run at stoichiometric, but some emmision values are corrected relative to that. Most burners run cleanest with 10 to 50 %excess air. I was wondering, though, about the values in this discussion - if they are based on stoichiometric combustion?

Christian Egli_2

Erudition? Word eruption - let the mojo flow

As always, Brad, thanks for the encouragement.

We should know, trying to line up those smart little antisocial buggers you mention in your post below in order to make them enter our radiators is already plenty hard enough. I can't see how we can make them do tricks up in the sky.

Meanwhile, from the depth of my subterranean boiler room, I'll be controlling the universe at the turn of a rusty valve. Bwaah ha ha ha. Bwaaah ha ha. Bwaaaah ha ha ha. Who needs "laser" beams anyways?

OK, cool it now, here's your meeelion pounds.

On that note, and for the sheer perspective of things. The 500,000 cubic feet yearly gas bill for the apartment building, if bagged in plastic (paper won't do) would represent a bag the volume of a whole grocery store - all the air inside that you normally breathe, replaced by natural gas. It's not a gigantic and unmanageable amount to grasp. One store for one entire year.

Once burned, besides the excess air and water vapor, if you could separate all the CO2 gas faster than the trees will inhale it out your chimney, you'd have a bagged volume the exact same size the previous grocery store was. Again, not that big a deal to manage.

Breathing wise, we can easily sense how quick the air would go stale in this store if we were to shut down ventilation and lock up the shoppers. Replace grocery goers by potted palm trees, and the speed at which things go stale in a carbonic gas environment remains entirely comprehensible. Boilers putting out CO2 does not come no where near the dooming effect portrayed in Hollywood.

And here, weight-wise, we were worried about getting run over by a 60,000 pound semi tractor trailer rig loaded with 5000 therms worth of CO2.

Have you ever wondered how much all the air inside a grocery store weighs? No? Let me oblige. It's far from nothing as we'd be inclined to think.

The air (taken at a standard density of 1.293 kg/m³) contained within one 500,000 cubic feet grocery store weighs about 18 tons!!!!!!! A staggering amount of stuff we swim through while pushing our caddies towards the bakery counter, it weighs the equivalent of about a dozen ordinary cars, all suspended in air, all just floating. So, while you have nothing but doughnuts on your mind, think of all the heavy cars you're bumping on your way... the workout is worth a treat.

The same volume of air replaced with CO2, as described by the excellent posts above comes up to 60,000 pounds, about 27 tons. CO2 has a heavier density than air.

Confrontation with the mediatised 27 tons seems at once bewildering. In contrast to the dainty flower bed in the front lawn, it is easy to imagine the ravages caused by an out of control rig coming down your driveway. Shriek in horror, run for cover - that's the traditional movie mantra where all things explode in balls of fire.

Fall for it if you want, I think that knowing now what plain air weighs, there is nothing out of line or out of proportions with any of our CO2 outputs. If 18 tons of air is good enough for a few humans to breathe, 27 tons of carbonic gas is good enough for a few more trees to breathe. The oxygen we need comes delivered on equally heavy loaded rigs; we don't worry about that, do we?

We converted that CO2 from combustion air and natural gas. How much did the 5000 CCF of natural gas originally weigh? Well, I'm glad you ask. 500,000 cubic feet of methane will weigh about 10 tons.

Whacky politicians are attempting to vilify carbon, they keep on harping how bad carbon is (never mind the carbs within my beloved bakery goods). Following the sensational math above, we should feel guilty about putting out the 27 tons it took to maintain heat in the apartment building full of people. But... did you follow the inflationary tricks? We start out with 10 tons of natural gas, to which we mix lots and lots of combustion air, air that weighs 18 tons, a portion of which is transformed into CO2, and we get 27 tons of that in the end.

27 is bigger and scarier than just 10. But those numbers say nothing about what, where, and how much carbon we're actually peddling. The 10 tons of methane isn't even all carbon, by weight, only three quarters of it are... Nifty inflationary tricks at hand: 7.5 = 10 = 18 = 27 = aiiiiiiiiiiiiiiiiii!!!!!!!!!!!!!!!!

The muddy footprints hysteric housekeepers are screaming about while they magnify the facts by 27, turn out to be only little specs of 7.5 tons of carbon.

7.5 tons of carbon is only a pile as little as a dump truck load, and from all that, we efficiently kept 5 to 10 families warm throughout the winter season.

Be very worried about institutions all concerned about your shoe soles and wanting you to go bare feet, you will get your dignity violated. Meanwhile, I will remain proudly attached to the American No Shoes, No Shirt, No Service; it is a profound concept.



***************



How did we get at all this math?

It couldn't be easier to do it all yourself at home with a tiny amount of stoichiometry. Sounds smart, doesn't it?

We're all familiar with chemical symbols that represent molecules of stuff we can analyze from the lab. Armed with no more than the table of elements, we can crack all this open by writing chemical combustion equations that are about just as much fun to solve as the level one Sudoku puzzles.

The fun party goers in our red lighted boilers are oxygen and methane. Their bio: O2, is a same-atom couple of oxygen and oxygen, and CH4, is a partnership molecule of one atom of carbon and four of hydrogen - here five atoms doing their thing together in the privacy of their penthouse - I know, you and I both don't want to know how... I don't even want to look. When you're on fire, you're hot and for molecules, things get so kinky that there is a whole lot of swinging going on.

Not just platonic love.

To the beat of the pulsating burner, new embraces start emerging from the atomic dance floor. The results of this combustion are grounds for divorce. The Oxygen couple handily seduced dear old Carbon; he lost himself, upon which, his four Hydrogen wives slapped him in the face and left - this is why things get really hot when carbon families break up. Alone on the dance floor, the victims of this divorce all found their fun elsewhere. The Carbon guy joined in on his two new Oxygen buddies, while the Hydrogen ladies went on with their couple busting rampage and tore apart other happy Oxygen pairs, dividing up the studs between two Hydrogen gals each, the ménage à trois. Oh là là.

I told you this would be obscene. Wait for the Hollywood movie of all this.

For there to be enough atoms on the dance floor, we necessarily had to have two each of the two atom oxygen couple, and one carbon atom and his four hydrogen harem. For natural gas, those are the only proportions in which the clubbing goes on. Nobody just vanishes from this dance floor, only relationships change in arguments that can be heated. There were nine atoms going in, and there are nine atoms going out. The Oxygen dudes really did strike out: the carbonic oxide couple picked up one atom of fun Carbon, and the reformed single again Oxygen guys left each in the embrace of two steamy hot Hydrogen beauties. Lucky them.

The fun is short lived though... Public opinion does not much approve of these horny molecules once out in the open air where the sun shine hits.

Apparently, what the carbonic gas guys are doing to each other offends our green trees enough that they soon pour the cold chlorophyl on them. Humping a tree is never a good idea and the penitent carbon accepts his fossilization fate.

The clouds of steamy water vapor try their three-way thing as best they can, but as is obvious to all of us, those relationships get stormy up in the sky.

Enough of the soaps, now, with less romance all this gets written out as: read an arrow in the place of the = sign

1 CH4 + 2 O2 = 1 CO2 + 2 H2O

That's for chemistry and relationships.

We can quantify all of this through stoichiometry. Science being the beautiful thing it is, makes it so that a set number of molecule of any gas will occupy a volume of 22.4 liters (under atmospheric conditions - no vacuum pump trickery). Look up Avogadro's number for further insight on this and what moles are.

Next, because the table of elements is meant to be convenient, we can read off the exact weight each of those set numbers of atoms tip the scale at. That set number, or set quantity, is referred to as a mole... just because scientists didn't want to make a mountain out of a mole hill. (Science is also fun) Buy your doughnuts by the dozens, and buy your chemical elements by the mole, that's all there's to it.

From the table we read that a mole load of C, carbon atoms weighs 12 grams. O, oxygen is beefier at 16 grams a pile. H, hydrogen is more delicate at 1 gram per mole. For N, nitrogen, it's 14, and so one for everything in grams per mole where a mole of gas is a volume of 22.4 liters. For solids like pure coal, which is carbon, we'll know the weight, but the 22.4 convenience won't hold.

C - 12; O - 16; H - 1

Put two and two together, and you compute the weight per cubic foot of any gas on the corner of a cocktail napkin... This supposes you're not eyeing the vapory molecules on the dance floor.

Do some math and the collective weight of one amount of the CH4 molecule adds up to 12+1+1+1+1 = 16. One mole of methane, which, as a gas occupies a volume of 22.4 liters, weighs 16 grams. Period.

O2 is not so slender at 16+16 = 32 grams per mole.

CO2 is a slob at 44 grams per mole, where, as before, this mole of gas still occupies a volume of 22.4 liters

Lastly, H2O, you do the math, comes only to 18.

1 CH4 + 2 O2 = 1 CO2 + 2 H2O

Going back to our Dr. Ruth description of the combustion equation, we see at once, that it took one volume of gaseous CH4 to produce one volume of gaseous CO2; in the process we required the participation of two volumes of O2. The proportionality of these volumes being a key factor.

Weight wise, it took one amount of 16 grams of CH4 to combine with two amounts of 32 grams of O2, thus 64 grams of oxygen (and we have a total entering weight of 16+64=80 grams). The results broke down into one amount of 44 grams of CO2, and two amount of 18 grams of H2O, thus 36 grams (the total leaving weight combined at 44+36=80 grams). Nothing gained, nothing lost, whew, we did not violate any conservation principle. Science, unlike environmental politics, is the ultimate conservation game.

Note how this idealizes the perfect combustion. We did not have one single extra atom of anything that we didn't use. In reality, playing matchmakers on such a level only works if there is a load of excess air just to provide a margin of operation. We choose excess air, because air is free and natural gas is costly, our goal is to match all of the carbon and hydrogen containing molecules and not worry too much about the oxygen we need to pull out of thin air. As we remember from earlier, the oxygen partners are already having plenty fun together and we don't really want to look at what they're doing.

So, if our boilers are not set anywhere near perfect stoichiometric relations, this is to guarantee the goal of near total (paid for) fuel combustion. For all the natural gas we burn, we get all the computed amount of combustion gasses. We also give the excess air a free ride, and a free warm up, as it travels through the boiler. The excess air is the chaperon at this boiler party, that's all.

Testing theoretical numbers for reality

Remember from above, we said CO2 (12+16+16) weighed 44 grams per mole, which, as a gas, occupies a volume of 22.4 liters.

Take yet these needed conversion factors: 1 pound weighs 454 grams, 1 lb per 454 g; also, it takes 28.3 liters to fill a cubic foot, 28.3 l per 1 ft³; lastly, the usual ton is spoken of in lieu of approximately 2200 pounds, 1 T per 2200 lb.

Throw all this together:

44 g CO2 / mol * 1 mol / (22.4 l) * 28.3 l / ft³ * 1 lb / (454 g) = 0.122 lb / ft³

To get a targeted weight for 500,000 cubic feet from our 5000 therms of gas:

500000 ft³ * 0.122 lb / ft³ = 61200 lb

or

61200 lb * 1 T / (2200 lb) = 27.8 T

There

Isn't all this worth the Sunday crossword puzzle? For the rest of the afternoon, you can entertain yourself by solving the balanced combustion equation for burning propane, C3H8, together with oxygen, O2, then by plugging in added mole values, you'll get a ton of fun. Coal is nothing but single C (less the impurities). Acetylene is C2H2. The combustion results are always CO2 and H20 (except for pure coal) - nothing magic, nothing toxic.

Oh, and CH is for Christian and I hope you had plenty fun reading all this.