Can Coal Be Clean? Debate & Survey

[pixel01]

About the flue gas : CO2 or H2O is more dangerous?
You all know that the Peace Nobel prize this year is given to Gore for his effort to warn people about the danger of global warming and probably due to the increased CO2 level in the atmosphere.
If you don't take it seriously, you just spew it out because it is easy, it's just a gas and you can save a lot of money for doing nothing. Then the whole world is affected. Nowadays, a lot of efforts are being made in order to capture CO2 in industry, or at least reduce it by some percents.

 

[ShawnD]

About the flue gas : CO2 or H2O is more dangerous?

That's not a simple question. It depends on how much and where. Certain places are not supposed to have high amounts of CO2, and some places are not supposed to have high amounts of water. If you release a huge amount of water into a desert region, it shouldn't be unexpected when it has a major effect on the environment. Desert doesn't just mean areas like Nevada; it also means areas that are dry due to low temperature. It could be some place in Alaska, it could be in Argentina, it could be anywhere. You can't make a blanket statement saying CO2 is bad and water is good.

 

[Paranoia]

Just as a side note, if you are still doing this jwhf777 I would recommend not using Wikipedia, because it would be logical for these corporations to modify the articles; however, using Wikipedia to find sources is still okay.

 

[pixel01]

That's not a simple question. It depends on how much and where. Certain places are not supposed to have high amounts of CO2, and some places are not supposed to have high amounts of water. If you release a huge amount of water into a desert region, it shouldn't be unexpected when it has a major effect on the environment. Desert doesn't just mean areas like Nevada; it also means areas that are dry due to low temperature. It could be some place in Alaska, it could be in Argentina, it could be anywhere. You can't make a blanket statement saying CO2 is bad and water is good.

Sure, it is not a simple question. What I am talking about is based on the current situation. The water vapour in the atmostphere is rather high because there are a lot ot oceans and water surfaces on Earth which provide continuously. Industries add some water of course, but I guess very small portion. But the CO2 natural sources is not as enormous and the industry sources can compare. In additon, of all the glass-house gases, CO2 is the most effective.
I also agree that CO2 is important, we can not survice without it, but if we increase it to an extent, the risk may apprear.

 

[russ_watters]

Hopefully to get you guys back on track, it looks like there was a misunderstanding on page 1 that led to this: in posts 13 and 14, the point was simply that 1 mole of CH4 gives off more energy than 1 mole of carbon because burning the hydrocarbon produces a lot more energy (by burning hydrogen) for the same amount of pollution (CO2). The more hydrogen in the hydrocarbon, the better it is for the environment.

Whereever the discussion went from there, it wasn't initially about electrolysis creating energy.

 

[GTrax]

More than my 2c worth..

For those who would use power station output to split water to get hydrogen to burn .. just look at the sentence, and you know why this does not work. Water is the very bottom product after we have extracted the energy. You put back exactly that energy to haul back the hydrogen, even before you make it useful to safely burn. Its about as bad as those who would feel 'clean and green' driving electric cars without knowing they got the electricity from hydro or wind or nuclear. Its just possible the ultimate carbon spend was worse than using a combustion engine!

Burning hydrogen for any engine or need only makes steam as exhaust, but is inconvenient as a portable fuel, and it involves burning a lot of of other fuel to collect it. Gasoline, on the other hand is highly convenient! A small can of it will push my car more than 40 miles (UK has bigger gallons ) All the fossil fuel we burn is really us trying to get at the hydrogen locked up in it, and to get it to join with oxygen to shove us along in our cars, and heat our homes. Unfortunately, along with the water, it comes with CO2 and other stuff.

When I look at a furnace roaring, gobbling huge amounts of air for the 21% oxygen, I imagine how long that wheatfield out back of my home must soak up sun to grab equivalent CO2 from the air, and put the oxygen back, and lock it up a furnace-worth of carbon in vegetable matter. That tree trunk that took 120 years to grow might weigh a ton extracted from CO2, but our vegetation clawback is dwarfed by the rate we burn the vegetable product of millions of years of sunshine. (There are some who think what makes a tree comes up its roots).

Entrain CO2 under the sea? Hmm.. Maybe power stations (nuclear, wind, hydro) should be used to desalinate, and pump water across parched land to sustain the best self-aligning solar collectors known.. leaves. It can be trees, it can be food, it can be pretty flowers. Way better than semiconductor solar power arrays, it does the conversion job to deal with the CO2 directly. To forcibly reclaim the deserts, and accept that it will modify the climate (for the worse? yes? no? ). Given that so much oil reserve is under desert areas, I am not so sure it matters. Its a pipe dream anyway. I think we are headed for conflicts over water and energy. The mere fact that we instantly invent 'carbon trading' let's us know the divisions will not be equitable. I think there will be 'haves' and 'have-nots', and distasteful stuff like starvation for some.

 

[Sojourner01]

Burning a mole of carbon gives off a mole of CO2 wherever the carbon comes from!

Since coal is pretty much pure carbon (once washed) you could argue that a kg of coal gives off more CO2 than a Kg of oil but that's just because a kg of oil contains less carbon.
The questions should be:
How efficently can you burn coal vs. oil, so how much energy do you get from each mole of CO2 produced.
How easily can you clean the coal/oil so you aren't also burning sulphur, mercury, lead etc.
What conditions does the combustion process require and how much NOx does it produce.

You aren't thinking this through - coal and oil aren't just 'carbon'; they're complex, and different, chemical structures. 1 mole of carbon atoms in a quantity of oil are bonded such that they liberate more energy when combusted than 1 mole of carbon atoms in a quantity of coal. I would suggest that this has something to do with the haphazard crystalline structure of coal - and is reinforced by the idea that while coal is produced mostly from plant matter, oil is mostly animal remains - and animals tend to bioconcentrate chemical energy more than plants do.

 

[mgb_phys]

No, I was wrong about the coal, but the extra energy in oil comes from the huge amount of energy you get when you burn the hydrogen present in hydrocarbon fuels.
Pixel01 pointed out how energetically favourable that is.

The origin and structure of the carbon has no effect - it doesn't matter if it was from animals, planets or diamonds.

 

[LURCH]

..Its about as bad as those who would feel 'clean and green' driving electric cars without knowing they got the electricity from hydro or wind or nuclear. Its just possible the ultimate carbon spend was worse than using a combustion engine!

Not trying to nitpick, but this is kind-of an area of special study for me. I did some research and some figuring regarding driving an electric car that is charged up with electricity produced exclusively by burning coal (assuming that a regular coal-burning powerplant was the only source for the electricity and that plant produced polutants at the national average rate for coal-buring powerplants in the US). According to my calculations, the electric car produces about 1/2 the CO₂ as a gasoline powered Internal Combustion Engine. Maybe a little off-topic, but worth mentioning, I think.

 

[cesiumfrog]

an area of special study for me[..] an electric car that is charged up with electricity produced exclusively by burning coal [..]produces about 1/2 the CO₂ as a gasoline powered[..]

That's very interesting. Did you write an article on it? How did you estimate the inefficiencies of the electric car?

 

[GTrax]

Not trying to nitpick, but this is kind-of an area of special study for me. I did some research and some figuring regarding driving an electric car that is charged up with electricity produced exclusively by burning coal (assuming that a regular coal-burning powerplant was the only source for the electricity and that plant produced polutants at the national average rate for coal-buring powerplants in the US). According to my calculations, the electric car produces about 1/2 the CO₂ as a gasoline powered Internal Combustion Engine. Maybe a little off-topic, but worth mentioning, I think.

Very interesting - so OK, even approximately, how did you figure it?

For me it goes (loosely) like this:
Gasoline car uses x kW*hours energy to do a given journey. Electric car does the same.

For my 1998 Peugeot 108HP. 2.1 litre turbodiesel, which has poorer fuel economy than the HDi models which replaced it, I get around 43-47miles/imperial gallon, which is around 36-39.5 miles/US gallon. I estimate on 2 hours driving I might use 110 kW*hours of energy. This has implications for folks unwilling to spend hours charging a car, and what happens if everybody wants to do it at the same time, but let us gloss over that (for now)

1. Some part of this work was done by electric car having to haul the additional battery mass up and down hills, and accelerating and braking the mass. Figure that some hybrid cars do recover some braking energy by charging back to batteries using the motors as regenerative brakes. The recovery efficiency I don't know, but its not 100%.
Gasoline car is rarely running fully tanked, and batteries are heavy.
We are not yet giving consideration to 'memory effect, self-discharge rate, capacity deterioration, replacement manufacture energy, etc. For the present, let us generously put these aside.

2. It was delivered via electric motors of efficiency E1. That came from batteries. That can involve efficiency Eb. 66% for NiCd. 75% for lead acid, something else for Li-ion. Choosing say a generous 80%, we now need 1.33x

3. Then you have the charger efficiency E3. The best get over 90%. Requirement is now 1.48x.

4. That electricity was delivered to a charge point at a (relatively) safe voltage. UK has 240V. USA has 110V. Copper and connection losses are proportional to the square of the current. USA losses are 4x higher, but assume good kit everywhere. Say a transformer 3kV to 100V has efficiency Et1 at 98%. Let us generously ignore the high current copper losses on the secondary side. We are at 1.51x

5. The substation 33kV to 3kV - another transformer, another Et2=98%. Now 1.54x. I don't know how many transformers might be involved here, but there will be at least one more at the power station. If the got up to a very low loss 300kV, then at least another 2 transformers would be used. I feel OK about 1.6x.

6. I don't know how much is lost in electricity transmission. It can only make the figure worse.

7. Then we come to the power station. This is what you get to choose from -> http://www.aie.org.au/melb/material/resource/pwr-eff.htm" Choosing the efficient Japanese station value 38.4% (and pausing to wonder at that Swedish power station!), we now need 4.22x of energy for the journey.

8. The energy density of liquid fuel is extremely high. That 2 hours worth can fit in a can I can carry, and the fraction of the 3000 gallon transporter energy that carried it to the gas station is going to be tiny.

Maybe in the end, they are comparable, the efficiency of the combustion engine counted (in effect putting the burning part at the end of the chain), and that heat was used up in dragging off the fuel fraction. Even so, I am having a hard time reconciling how using an electric car discounts the 4.2x back to less than 0.5 *[what the car would have used] - or have I missed something very basic?

 

[russ_watters]

Not trying to nitpick, but this is kind-of an area of special study for me. I did some research and some figuring regarding driving an electric car that is charged up with electricity produced exclusively by burning coal (assuming that a regular coal-burning powerplant was the only source for the electricity and that plant produced polutants at the national average rate for coal-buring powerplants in the US). According to my calculations, the electric car produces about 1/2 the CO₂ as a gasoline powered Internal Combustion Engine. Maybe a little off-topic, but worth mentioning, I think.

The calculation is pretty straightforward - what efficiencies and energy capacities did you use? Your result is surprising.

I just found a website that says coal has an energy capacity of 12,000 btu/lb (1.6 kwh/kg) and another that says that gasoline is 2.6 kwh/kg.

Here are my efficiency assumptions (feel free to nitpick):
Car tank-to-wheels efficiency: 15%
Coal plant mechanical/thermodynamic efficiency: 45%
Generator efficiency: 95%
Transmissin efficiency: 92%
Charging efficiency: 90%
Storage efficiency: 85%
Electric motor efficiency: 95%
Drivetrain efficiency: 90%

So, 1 kg of gasoline puts .39 kWh of energy to the ground in a car.
1 kg of coal puts .41 kWh of energy to the ground in a car.

Now I'm going to guess that gasoline is about 80% carbon by mass, so to get the same amount of CO2 as in a kg of coal, you need 1.25 kg of gas. So that's .39*1.25= .49 kWh/kg.

I really didn't plan that, but I got that gasoline and coal->electricity produce pretty close to the same amount of CO2 to power your car (20% more for the coal plant).

[edit: Saw gTrax's post after writing mine, didn't realize battery storage efficiency was so bad, re-adjusted my numbers)

 

[russ_watters]

Maybe in the end, they are comparable, the efficiency of the combustion engine counted (in effect putting the burning part at the end of the chain), and that heat was used up in dragging off the fuel fraction. Even so, I am having a hard time reconciling how using an electric car discounts the 4.2x back to less than 0.5 *[what the car would have used] - or have I missed something very basic?

It looks to me like you didn't separate out the efficiency of the car engine and passed it along through the electricity calculation. If the car's actual thermodynamic tank-to-wheels (taking drivetrane and idling losses into account) efficiency is about 20% (say your car is better than average), that 4.2 now becomes .84 and your numbers start looking similar to mine.

 

[russ_watters]

You aren't thinking this through - coal and oil aren't just 'carbon'; they're complex, and different, chemical structures. 1 mole of carbon atoms in a quantity of oil are bonded such that they liberate more energy when combusted than 1 mole of carbon atoms in a quantity of coal. I would suggest that this has something to do with the haphazard crystalline structure of coal - and is reinforced by the idea that while coal is produced mostly from plant matter, oil is mostly animal remains - and animals tend to bioconcentrate chemical energy more than plants do.

No, I was wrong about the coal, but the extra energy in oil comes from the huge amount of energy you get when you burn the hydrogen present in hydrocarbon fuels.
Pixel01 pointed out how energetically favourable that is.

The origin and structure of the carbon has no effect - it doesn't matter if it was from animals, planets or diamonds.

Some clarifications: The crystal structure of the material effects the bond strength, so the tighter the bond, the more energy is required to break the bond before combustion. Coal's bonds are weak, which is why it might yeild more energy than the carbon in a hydrocarbon. But the reason that oil produces more energy per kg than coal is quite simply because it has hydrogen in it and hydrogen produces a lot more energy per kg than carbon does.

Here is enthalpy of formation data for some substances: http://itl.chem.ufl.edu/2045_s00/lectures/lec_8.html

The calculation is pretty simple. If you take 1 mole of methane (CH4), the chemical reaction looks like this:

CH4+3O2->C+4H+60->CO2+2H2O

The first step is simply breaking-up the structure of the reactants. For noble gases, no energy is needed to break them apart. For CH4, it is +75 kj/mol (minus enthalpy of formation[/b]). The second step is making the CO2 and H2O, which yields -393 and -242 respectively.

So the reaction yields 75-393-2*242=-802 kJ/mol
The calculation yields the new internal energy of the substance: 802 kJ/mol lower because that's the energy released.

Surprisingly (from above), diamond has a positive enthalpy of formation, so burning it would release more energy than burning non-crystalline carbon.

 

[LURCH]

That's very interesting. Did you write an article on it? How did you estimate the inefficiencies of the electric car?

No article, just an e-mail to a couple of my profs. Finding a starting point for the EV efficiencies was kinda difficult, so I just went with the one EV I knew of that is in production and on the road, the Tesla. Using that as my baseline, here's what I came up with (the first half was about price, but it establishes the Equivalent Gallon on which the polution calcs are based)...

As can be seen from this site...

http://www.teslamotors.com/efficiency/well_to_wheel.php

...the Tesla requires about 110Wh to travel 1km. This translates to about 160Wh/m. According to the EPA, the average passeneger vehicle gets about 25mpg, so multiplying 160Wh/m by 25mpg, we get 4000Wh = 1gal. This is to establish what I call the Equivalent Gallon (or EqG); which is the amount of electrical energy required to drive the same distance as 1 gallon of gasoline, 4 kWh.
Looking at my electric bill from last month, I see that I am paying about 10 cents per kilowatt hour, including all taxes and service fees. So...
(financial clacs deleted)
...It can also be seen from this DOE web site:

http://www.eia.doe.gov/cneaf/electricity/page/co2_report/co2report.html#electric

that burning coal to generate electricity creates about 2 pounds of CO2 per kilowatt hour. Multiplying by 4 kWh, this renders about 8 pounds of CO2 per EqG. By comparison, according to this EPA web site:

http://www.epa.gov/otaq/climate/420f05001.htm

burning gasoline generates approximately 20 pounds of CO2 per gallon; roughly double the amount.

This also takes into account the fact that the Tesla, a sports car, is built for performance only. Later "family car" versions will probably get better mileage.

GTrax, are you really getting 36mpg (US gallons)? That's extraordinary! I wonder, if an EV were built with fuel economy as a priority, cuold we get 35-40 m/EqG from it?