Can Coal Be Clean? Debate & Survey

[jwhf777]

Coal- clean? or dirty?

Hello everyone
I have received a termproject regarding energy myths
and my topic is this:

Can coal be as clean as other fuels?

I personally would say yes but I need some good replies from
you guys for this survey...either the eco side or the capitalist side

Thanks for the help~

 

[TVP45]

You would have to set up some qualifications for how you judge "clean" and which fuels you compare to. I can tell you that our experience here in Pittsburgh (where we have probably burned as much coal as anywhere in the world) is that it is dirty.

 

[russ_watters]

Welcome to PF.

The first thing you need to do is define the term "clean coal".

Clean coal is the name attributed to coal chemically washed of minerals and impurities, sometimes gasified, burned and the resulting flue gases treated with steam, with the purpose of almost completely eradicating sulfur dioxide, and reburned so as to make the carbon dioxide in the flue gas economically recoverable. The coal industry uses the term "clean coal" to describe technologies designed to enhance both the efficiency and the environmental acceptability of coal extraction, preparation and use[1], with no specific quantitative limits on any emissions, particularly carbon dioxide.

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

The definition pretty much determines the answer to the question. It most certainly does make economic and environmental sense to remove impurities from coal and ensure its combustion contains as much CO2 and as little of anything else as possible. Actually capturing and somehow getting rid of the carbon dioxide itself may not even be possible, much less viable.

 

[jwhf777]

thanks for the welcome and
yea i should've put up some qualifications
but in this case, there are none- just coal itself--
its asking could it be clean or not?
I need a variety of answers for the survey
ANY answer or explanations on what you think would be great

 

[cesiumfrog]

Exactly. When the industry says "clean coal" they basically just mean that it doesn't cause smog and acid rain (it releases less unburned particles and sulphur than the "dirty" coal stations do).

But it's still just as bad for global warming (since you're still pumping CO2 from a fossil source into the atmosphere). In theory this could be addressed using coal power plants with "carbon sequestration" (basically zero atmospheric emissions of any type), but of course that would be incredibly expensive (uncompetitive) and produce immense quantities of waste (to be stored forever).

Compared to renewable sources at the moment, the "clean coal" may be bad for the environment but ignoring that it is still cheaper and (importantly) available to be used on demand.

Compared to nuclear sources.. both produce radioactive waste, but normal coal stations just disperse this into the atmosphere whereas nuclear plants can very easily store their small amount of waste. Which to choose depends on whether you include the environmental costs and on the price of public perceptions.

 

[jwhf777]

Thanks for the replies~
Could you guys also have the source if you searched for it?
Thanks~

 

[pixel01]

Compared to other hydrocarbons, coal combustion gives off the most CO2 and you know it's the main green-house gas.

 

[Astronuc]

Thanks for the replies~
Could you guys also have the source if you searched for it?
Thanks~

I'm not sure what the question means. Russ cited the Wikipedia article on clean coal.

Here is the US DOE site on clean coal -

http://www.fossil.energy.gov/programs/powersystems/cleancoal/

NETL webiste - http://www.netl.doe.gov/technologies/coalpower/cctc/index.html

 

[minorwork]

Refined coal is called coke. It burns "cleaner" than raw coal. During the coking process any distilled liquids can be processed at a crude oil refinery, though benzene output is low, and the methane driven off can power, to a degree, the coking process. CO2 sequestration would enable a zero emission burn. That is, the emissions are all captured. What to do with them? As for all waste product, the answer determines the economic cost.

Let's build these cokers and burn only coke for electric power. Let's put Americans to work.

 

[TVP45]

Refined coal is called coke. It burns "cleaner" than raw coal. During the coking process any distilled liquids can be processed at a crude oil refinery, though benzene output is low, and the methane driven off can power, to a degree, the coking process. CO2 sequestration would enable a zero emission burn. That is, the emissions are all captured. What to do with them? As for all waste product, the answer determines the economic cost.

Let's build these cokers and burn only coke for electric power. Let's put Americans to work.

Generally I agree with you. Coke burns much cleaner than coal. However, you still have NOx to deal with.

I think you're a coal worker? I live near where coke is made (Clairton) and it ain't pretty yet. If we can get the government off it's rear end to start supporting pollution controls (that means $), then you should be able to largely clean up coke, but we need energy people in Washington who understand basic engineering.

 

[minorwork]

I retired last year after 31 years underground mining in Central Illinois. Yes. NOx was always monitored on our diesel equipment underground even. The diesels were clean running there, no black smoke, as they were "detuned" to lessen Nox emissions.

Twenty years ago or so I attended a meeting with a Springfield city council woman and others given by two older retired engineers from the now gone Sangamo Electric. They had put up a proof of concept closed system coker near Athens Illinois. The patent was granted and they pursued developement. It involved an enclosed round tank housing 5 or more round pans with a spiral groove that alternately, when rotated, moved the coal from the edge then dropping to the next pan was moved to the center where it dropped to the next then back out to drop, and so on. Initially they fired with propane, but when gasses generated they could turn off the propane and run the "refinery" on its own emissions. They had a 5 foot square model of a producing plant at the meeting. They would not mention the controls for the device however. They said all else could be copied except their controls. They captured the distillates and they were sent to the Joliet refinery.

These guys were desparately in need of a presenter as one old guy kept calling the council woman "honey." She called him on that but he couldn't help himself. My bogus meter was activated when they claimed a grant from the government for a full scale pilot plant was denied because they had solved the problem of "dirty" coal combustion. The grants were given to projects pursuing a solution.

Then they mentioned being offered a large sum by a major corporation to sell the rights. They refused. They were retired old timers even 20 years ago when the meeting occured. They wanted to put Americans to work. They would not back down on that.

 

[mgb_phys]

Compared to other hydrocarbons, coal combustion gives off the most CO2 and you know it's the main green-house gas.

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.

 

[pixel01]

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.

I just talk about CO2. OK, one mole of C will give off 1 mole CO2, but if you use CH4, you will need less than one mole of C to create the same heat compared to coal.

 

[mgb_phys]

I hadn't realized that producing the H2O gave off so much energy - I thought this would be a disdvantage since water's high capcity should reduce the temperature and so the efficency. I thought all that water in the flue gas would be a pain as well.

 

[PRDan4th]

The real question is "what does clean mean?" Coal contains particulates, metals, sulfur and a wide variety of hydrocarbons. Combustion of coal produces CO2, H2O, CO, SOx, NOx, metal oxides, non-combusted hydrocarbons, carbon (soot), and other particulates. We used to think that all of these combustion products except CO2 & H2O were pollutants. Power plants could be designed to control the release of the pollutants by flue gas scrubbing and coal cleaning prior to combustion. How clean is clean? Pollution control and coal cleaning equipment is expensive and requires energy and operation/maintenance labor to operate. Thus making the plant less efficient and more expensive. The most efficient way to produce power from coal in a extremely clean way is a coal gasification combined cycle (CGCC) power plant. A DOE/EPRI sponsored pilot plant called "Cool Water" produced 1000MW in California in an extremely clean fashion. The coal was first gasified in a Texaco gasifier and a clean fuel gas of CO & H2 was cooled and scrubbed prior to combustion in a combined cycle power plant. The project was a technical success but was not economically viable in the 1980s. With oil prices approaching $100/BBL and coal still reasonably inexpensive on a BTU basis this might be a better answer today! CO2 would be separated before combustion and sequestered if the CO2 storage technology is developed. Possibly in deep sea areas or hydrates.

The primary fuel competition today is natural gas! A natural gas combined cycle plant is much cheaper to build and very efficient with CO2 production much less per KWh than a Coal fueled plant. Natural gas supply is limited and more expensive than coal, thus a trade off is required.

CO2 is not considered a pollutant, but it is a greenhouse gas. The economics of CO2 sequestration is not clear today. A carbon tax with offsetting credits for safe storage could be developed. Coal is a very important and abundant fuel resource in the United States, but a high carbon tax could stifle coal production in the US.

 

[mgb_phys]

The primary fuel competition today is natural gas! A natural gas combined cycle plant is much cheaper to build and very efficient with CO2 production much less per KWh than a Coal fueled plant. Natural gas supply is limited and more expensive than coal, thus a trade off is required.

That has been the problem in the UK - the dash for gas.
When the market was deregulated the drive was to build a plant as quickly and cheaply as possible, the actual energy production cost didn't matter because of the way the price was set.
Now that North Sea gas is running out they are having to face bringing LPG tankers into large cities or building pipelines to Russia/Iran.

 

[PRDan4th]

This is true! Utility energy pricing is cost based, but capital has to be raised to develop new plants. The utility has to build new plants fast to follow the demand cycle and gas plants can be installed quickly. New gas needs to be found and developed to fuel these plants and this requires capital to be raised by private industry with no assurance that they will find or develop new fields (risk). There is plenty of Natural gas in the world, its just not here where it is needed and transporting gas is expensive and storage is difficult.

In the long run, however, natural gas can be a significant factor in mitigating the global warming problem. What is needed: sub-sea methane hydrate development (safely) and CO2 sequestration, perhaps under the same sub-sea hydrate field that was ued to produce the methane. This is a long-term developmental solution, IMO.

 

[mgb_phys]

The problem is that natural gas ( methane) is the best fuel for domestic heating. It doesn't make sense to burn it to generate electricity at 50% efficiency then transmit that electricity to homes to run electric heating. Well it does if you are power company of course!

The privatisation wasn't well designed (politics) it basically worked that who ever built the plants first got a monopoly - whatever the eventual cost. A lot of the plants have had to be replaced already becuse they were built under capacity cheaply.

 

[TVP45]

That has been the problem in the UK -

I wondered why you thought coal was just carbon, till I saw the UK. You guys have been spoiled by good coal. Here in the US we have lots of coal that's little more than dark rock. They have much of the same in China except it's not even dark, but brown.
We have some small specialty plants now that are trying to clean up some of the really bad fuel and it turns out they're less polluting than many of the old, high quality coal plants. Our politics here favor old plants since they can literally run forever without modernizing under our so-called clean air act.

 

[TVP45]

I retired last year after 31 years underground mining in Central Illinois. Yes. NOx was always monitored on our diesel equipment underground even. The diesels were clean running there, no black smoke, as they were "detuned" to lessen Nox emissions.

We run our coal plants around 2-2.5% excess oxygen to do that. At one plant (I'm not making this up) they've got an old-timer in the control room who can look at the smoke and adjust the fire for minimum pollution. And, he could stay in EPA guidelines.

Our cokeworks here in western PA capture a lot of the gases and either use them for fuel for other processes or else (like with ammonia) sell it. Still the plants are old and leaky and cranky.

 

[pixel01]

I hadn't realized that producing the H2O gave off so much energy - I thought this would be a disdvantage since water's high capcity should reduce the temperature and so the efficency. I thought all that water in the flue gas would be a pain as well.

So now you know it. Have you ever heard about H2 energy? Burning H2 gives off a lot of energy and the flue gas is just water!, so clean ever. The more H atoms in the hydrocarbon, the less CO2 emission over a heat unit gained. Coal has no H atom.

 

[pixel01]

One more disadvantage of coal is that, combusting solid fuel is always more complicated compared to liquid rivals.

 

[brewnog]

So now you know it. Have you ever heard about H2 energy? Burning H2 gives off a lot of energy and the flue gas is just water!, so clean ever. The more H atoms in the hydrocarbon, the less CO2 emission over a heat unit gained. Coal has no H atom.

So, pixel. Where do you get all this H2 from?

 

[ShawnD]

So now you know it. Have you ever heard about H2 energy? Burning H2 gives off a lot of energy and the flue gas is just water!, so clean ever. The more H atoms in the hydrocarbon, the less CO2 emission over a heat unit gained. Coal has no H atom.

A bit of a chemistry lesson to add to this.

Energy and Mass
Fire is always oxidation, and oxidation can be described as "adding oxygen" or "removing hydrogen" from a molecule. Molecules with hydrogen, such as methane, have more burning energy than things without hydrogen, such as coal. Molecules with oxygen, such as ethanol, have less burning energy than those without.
http://en.wikipedia.org/wiki/Heat_of_combustion
Hydrogen - 141.9 MJ/KG
Methane - 50.009 MJ/kg
Methanol - 19.937 MJ/kg

The trend continues based how much it can be oxidized.
Sulfur - 9.163 MJ/kg (it doesn't oxidize very much)
Carbon - 32.808 MJ/kg (no hydrogen, no oxygen, no nitrogen)
Coal - 15-27 MJ/kg (contains sulfur, nitrogen, oxygen, hydrogen, other things)

Energy and Volume
It gets trickier when you throw density into the mix. I keep posting over and over again that hydrogen is a horrible fuel for cars because it's not dense at all; it takes huge volumes of it to get enough mass to power anything. The same problem applies with industrial applications for whatever fuel you want to look at. Coal is an excellent fuel source because of its high density.
Carbon - 2.267 g/mL (as graphite)
Carbon - 3.513 g/mL (as diamond, but you don't burn these obviously)
Gasoline - 0.688 g/mL (as isooctane)
Diesel - 0.850 g/mL (varies)
Hydrogen - 0.07 g/mL (less than 10% the densityof diesel fuel)My post might not have a lot to do with this specific topic, but it helps to know some basics before we guess at which fuel should be used. Coal is great because 1 truck full is a lot of energy.

 

[mgb_phys]

So now you know it. Have you ever heard about H2 energy? Burning H2 gives off a lot of energy and the flue gas is just water!, so clean ever. The more H atoms in the hydrocarbon, the less CO2 emission over a heat unit gained. Coal has no H atom.

I thought it took roughly the same energy to split the C-H bond in the fuel as you got back from forming the O-H bond.
Water, especially hot water loaded with lots of dissolved NOx COx is a real pain in an industrial exhaust.

One more disadvantage of coal is that, combusting solid fuel is always more complicated compared to liquid rivals.

In a fluidised bed you are burning dust - burning dust has never been a problem. Stopping it burning is quite a trick sometimes, ask any flour mill.

 

[TVP45]

So now you know it. Have you ever heard about H2 energy? Burning H2 gives off a lot of energy and the flue gas is just water!, so clean ever. The more H atoms in the hydrocarbon, the less CO2 emission over a heat unit gained. Coal has no H atom.

Pixel01, you're right on. Fully saturated hydrocarbons (as many H's as possible) generally have more combustion energy and lower pollutants than unsaturated ones. Thus a mole of natural gas yields about 800 kJ while producing a mole of CO2. A mole of good coal yields about 470 kJ and produces a mole of CO2. The mole of natural gas has greater mass, of course, and some people compare it that way but it still comes out better in terms of energy. If you're looking for a power plant fuel, you have to compare on a per kJ basis.

The other advantage to methane in this use is that, in order to provide peak electricity for 6:00 am breakfast, you have to start ramping a pulverized coal plant about 3:30 am. Methane comes very close to being on demand (only the thermal inertia of the boiler water slows it down).

The water produced by methane is generally pretty clean (except for NOx and sometimes some SOx), while the coal requires precipitators, bag houses, scrubbers and so on.

The big problem is simply quantity available (and therefore cost). We have lots of coal in the world and not so much methane. No matter what, we are stuck with coal for many, many years and we therefore have to develop cleaner technologies.

 

[ShawnD]

The big problem is simply quantity available (and therefore cost). We have lots of coal in the world and not so much methane. No matter what, we are stuck with coal for many, many years and we therefore have to develop cleaner technologies.

T'other way 'round. I'm in Edmonton, Canada and there are 3 refineries in the area. Each of the refineries has a methane fire going 24/7 because methane is worth literally nothing. They can't sell it to anybody, so they just burn it. If it was worth something, they would sell it.

Your idea is good though. Using that gas to supply peak energy demands would make a lot of sense, but it doesn't happen. It probably has something to do with lack of infrastructure, and not enough reason to build said infrastructure. If there was kind of tax incentive to use methane, it would happen right away, but it would mean increased energy costs to everybody (that's really bad for the economy).

 

[TVP45]

How close are you to Alberta? They sell us some gas; maybe you could piggyback on them.

Canada, like Russia, has lots of methane. It's coals to Newcastle.

 

[mgb_phys]

How close are you to Alberta? They sell us some gas; maybe you could piggyback on them.

canada just passed a law requiring oil fields to recover and pipe out methane even if it isn't economic to sell.
Ironically this has led to oil companies filing enviromental objects to their own pipeline plans to stall the constuction!

 

[TVP45]

canada just passed a law requiring oil fields to recover and pipe out methane even if it isn't economic to sell.
Ironically this has led to oil companies filing enviromental objects to their own pipeline plans to stall the constuction!

If a proper big pipeline is ever built, that might ease the problem, although I understand the environmental impact that might have. In the meantime, we in the US really want methane. Right now we're paying about $10 (US) per thousand cubic feet. That's predicted to almost double in the next few years.

 

[PRDan4th]

Natural gas @ $10/ MCF is cheap when compared to crude oil at $100/BBL. One barrel of oil has the same energy content as 6000 cubic feet of gas, therefore gas price is roughly $60/BOE (barrel of oil equivalent). But gas is much more efficient and cleaner than oil, plus it produces less CO2 when burned.

 

[pixel01]

So, pixel. Where do you get all this H2 from?

So I guess your background is not chemistry. After all this is physics forum.
H2 can be extracted by electrolysis. Well let say at a power plant that electricity is redundant. The problem is not where to get H2, but how to transport it !

 

[pixel01]

I thought it took roughly the same energy to split the C-H bond in the fuel as you got back from forming the O-H bond.
Water, especially hot water loaded with lots of dissolved NOx COx is a real pain in an industrial exhaust.


In a fluidised bed you are burning dust - burning dust has never been a problem. Stopping it burning is quite a trick sometimes, ask any flour mill.

=========
I will show you the bond C-H can be broken quite easily when burning.
Heating value of Coal : 0.4092 MJ/mole
----- H2 : 0.2838 MJ/mole
---- of ... CH4 : 0.88

So if I burn 1 mole C and 2 mole H2 separately, I will have 0.4092+2*0.2838 = 0.9768MJ
You can compare with heating value of CH4 = 0.88 MJ/mole, the deficit is not much.
But you can never take out any energy from CO2 or H2O. The bonds are so strong.

OK, the CFB burner is quite easiy to operate, but it can not compare to a liquid run bunner. Have you ever seen a heat turbine run on solid fuel?

 

[brewnog]

So I guess your background is not chemistry. After all this is physics forum.
H2 can be extracted by electrolysis. Well let say at a power plant that electricity is redundant. The problem is not where to get H2, but how to transport it !

So, from where do you get the electricity for electrolysis?

I don't know of much electricity made at power stations which is 'redundant', and I certainly know of none which hasn't been made from nuclear, fossil fuel, or renewable sources. The fact is that hydrogen is only a solution for energy storage, not for power generation.

So while your comment about the combustion of hydrogen giving off only water may be chemically correct (even with your allegation of my lack of a chemistry background), it is misleading to suggest that hydrogen provides an energy solution with no environmental impact.

 

[pixel01]

So where do you get the electricity?

I don't know of much electricity made at power stations which is 'redundant', and I certainly know of none which hasn't been made from nuclear, fossil fuel, or renewable sources. The fact is that hydrogen is only a solution for energy storage, not for power generation.

You can imagine a hydropower plant. The water is redundant, some cases they have to drain water for free for safety reason. The lines can not take on more electricity. Then if only you can store it . Very simple, you split H2O into O2 and H2, then H2 is the energy.

Oh, you misunderstand my idea. They do not produce energy by H2, just to store it. But anyway, at oil refinery, there is a lot of H2 gas as by product.