How to live with Coal while saving the planet

[Artful Dodger]

PRELUDE:

There has been a lot of fancy sciencey talk and arm-waving about the Evils of Coal, but few people have even come close to presenting a potential solution to the main problem associated with the recent growth in coal-fired generation in many parts of the World (ie: China, India, Netherlands). That is, how to capture C02 from combustion, aka Carbon Sequestration and Storage (CCS). This single sticking point is IMO largely responsible for the inability of recent Conference of Parties meetings (ie: COP17 Durban) to produce climate change action.


*** As is often the case, the solution is to avoid the problem. ***

One of the major technological hurdles with CCS is how to capture CO2 from a relatively low concentration stream of power plant exhaust. However, there IS technology available to produce a high concentration stream of CO2 from coal fired power plants, to avoid those hurdles. It's called Oxyfuel with flue-gas recirculation.

Instead of burning coal with atmospheric gases, coal is burned with (nearly) pure oxygen (O2). Normally, the extremely high temperatures produced would actually improve the Carnot efficiency of the heat cycle, but oxy-fuel burns so hot that it will actually melt steel (btw, a ceramic liner in the furnace and boiler allow hotter temps and higher efficiency, but let's not get ahead of ourselves)

That's where the flue-gas recirculation comes in. Part of the exhaust stream of pure C02 is diverted back into the furnace, in sufficient proportion to reduce combustion temperature to the optimal level (C02 won't burn a 2nd time, so it's effectively inert during combustion). Hence, no super expensive metals are needed for the furnace, just some more piping to handle the C02 recirculation.

The benefits of oxy-combustion are three-fold:

• zero Oxides of Nitrogen (toxic NOx air pollution) produced since no nitrogen is present during combustion, no acid rain, and no Asian brown cloud
• a highly concentrated stream of CO2 (near 100% concentration) can be used directly as a feed source to make concrete, or to feed to a green house, and
• a stream of hot water can be condensed from the flue gases yielding both a source of heat for distributed domestic hot water heating, and a source of usable water for irrigation, or domestic grey water.
  

Here's the bottom line: any City that needs electricity, heat, water, concrete, and food could benefit from an oxy-fuel coal-fired power plant. Best of all, oxy-fuel combustion can be retrofitted to existing coal-fired generation and once in production the extra cost could be as little as 2 cents per KWH of electricity.

So why aren't we requiring this OBVIOUS solution for existing plants? And for new Natural Gas-fired plants, which have many of the same issues? Simple: Because Engineering execs also have MBAs, who tell them it's CHEAPER to buy off politicians and lie to the public.

So that's the REAL reason: It's not the concentration of CO2, it's their concentration on $$$. Funny that, because I think I could sell the water, food, concrete, domestic hot water and space heating for a wee bit more than 2 cents.

Care to add your 2 cents worth? 

[Artful Dodger]

*** PLACEHOLDER to provide additional info & answers ***


Q. Where does the stream of nearly pure oxygen comes from?

A. The atmosphere, through Industrial oxygen concentrators


Q. Isn't Pure Oxygen explosive?

A. Goddammed right. So was Hurricane Sandy. Except we get to choose where we burn oxy-fuel.


Ask more questions, and I'll keep the answers up to date here. 

[slow wing]

That's a very interesting idea, thanks for presenting it. A couple of questions to start with:

1) where does the 2c/kWh estimate come from? Is there a source for it in a paper?

2) How would net CO2 be used up in making concrete? Making cement gives off CO2 rather than absorbing it. Heated calcium carbonate sheds CO2 to become the calcium oxide that is combined with silicates in portland cement. The hydration of the cement forms the concrete. See
http://matse1.matse.illinois.edu/concrete/prin.html .



Thanks.

[Neven]

Never heard of this one before. Thanks, Lodger.

[Vergent]

The CO2 associated with Portland cement manufacture falls into 3 categories:
Source 1. CO2 derived from decarbonation of limestone,
Source 2. CO2 from kiln fuel combustion,
Source 3. CO2 produced by vehicles in cement plants and distribution.
Source 1 is fairly constant: minimum around 0.47 kg CO2 per kg of cement, maximum 0.54, typical value around 0.50 worldwide.[citation needed] Source 2 varies with plant efficiency: efficient precalciner plant 0.24 kg CO2 per kg cement, low-efficiency wet process as high as 0.65, typical modern practices (e.g. UK) averaging around 0.30.[citation needed] Source 3 is almost insignificant at 0.002-0.005. So typical total CO2 is around 0.80 kg CO2 per kg finished cement. This leaves aside the CO2 associated with electric power consumption, since this varies according to the local generation type and efficiency. Typical electrical energy consumption is of the order of 90-150 kWh per tonne cement, equivalent to 0.09-0.15 kg CO2 per kg finished cement if the electricity is coal-generated.

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

Cement does absorb CO2 when it cures changing CaO into calcium carbonate, but this is only retrieving a small portion of the emitted.

The real question is what to do with the CO2 after you have captured it? for every ton of coal, you end up with three tons of CO2. And, how do you replace the oxygen in the atmosphere?



For every trainload of coal, you end up with three trainloads of CO2. Where are they going?

[Wipneus]

*** As is often the case, the solution is to avoid the problem. ***

One of the major technological hurdles with CCS is how to capture CO2 from a relatively low concentration stream of power plant exhaust.

Lodger, let me first state that I have some professional experience with combustion processes,  coal firing and electricity generation. I hope for more than 2 cents.

First you solve a problem of capturing a low concentration CO2 ( about 16%) by capturing O2 from air which has concentration only 4% higher!
If the concentration is not such a big deal, there ARE advantages of doing it on the air side. Flue gasses are hot and at the temperature extremely corrosive and poisonous (for catalysors at least). So if it can be shown to be more cheaper on refining the oxygen than that would be the way to go.
Flue gas re-circulation is a well known technique for improvements of the combustion and as you say influencing the temperature of the flue gasses.

Now the feasibility. You need more than half a million cubic metres of pure oxygen per hour per GW installation. The example "industrial" oxygen concentrators in the wiki measure their output in milli litres. I have not heard that the existing industrial nitrogen/oxygen separation plants (that use a liquid air and a fractional distillation) are now redundant.

In the end it comes down what is the process that produces the cheapest useful output.

Now your proposed use of the clean CO2 stream. Using them for concrete hardening and improving glasshouse ventilation efficiency, is NOT reducing CO2 output. Those processes would take CO2 from the air, which is not happening at all. Net result is zero, except more efficient operation which can be achieved by other means. You have to put the CO2 somewhere unused and that is going to add to the cost. Not even mentioning safety.

[Wipneus]

My calculation:

C + O₂ -> CO₂  + 32.8 MJ/kg-C

atomic number give that 12 kg of C burns using 32 kg of oxygen. So per kg of oxygen we have:
Here is my calculation:

32.8 * 12/32 [MJ/kg-O₂]

Electric generating plants come per GW-electric. One GW of generated electric power, at 40% efficieny is 2.5 GW of fuel.

2.5 GW = 2.5 GJ/s = 2500 MJ/s = 2500 * 3600 = 9,000,000 MJ/hr

So we get 9,000,000 / (32.8*12/32) = 731,700 kg-O₂ per hour

Since 1 kg oxygen is about 1 cubic meter we need a million cubic meters oxygen (from 5 million m3 air) each hour for each installed GW-e plant.

[Vergent]

Lodger

http://www.devilbisshealthcare.com/files/A-525%20Rev%20E-FINAL.pdf

It takes 310 watts to generate 5 liters per min. or 300L/hour. It would take about 1000 watts to generate 1 M^3 /hour. It would then take a GW to supply the O2 for this plant. In other words this idea is a nonstarter.

A m^3 of O2 weighs about 3kg so it would take 300MW to supply the plant. However if there were some way to use the waist heat to compress the air it could work, and there is.

low pressure steam was used to pump large volumes of water to a low rise. A large chamber is filled with steam, then sealed, cold water is sprayed in condensing the steam and creating a vacuum. water is then sucked into the chamber. steam is let in forcing the water out(on the other side of the floodwall).


Instead of  water, the steam could act on huge vertical piston that is attached to a slightly smaller piston below(so you can get to 2 atmospheres, the pressure needed to concentrate O2). The vacuum lifts the pair of pistons. When the steam is let in the weight of the pistons compress the air.

Whiles it is feasible to concentrate the O2, I still do not see what you can do with the now concentrated CO2. You could compress it in a similar fashion. That would let you pipe it a short distance. Liquefying it would require the entire output of the power plant. You could pipe it to a huge algae farm, but the farm could just as well get the CO2 out of the air.

Interesting idea though. Keep thinking outside the box, that is where the new ideas come from.

Verg

[TerryM]

Lodger

I'll be dining with one of the engineers from Babcock Wilcox on the 1st. They build/retrofit most of the big coal & gas plants, at least in the west. He's been in charge of installations & retrofits around the world & should be aware of any projects on the drawing board.


Are there any questions you'd like me to ask him about the process?


Terry