I thought the article on vehicle emissions was well written and hopefully helps raise awareness that understanding on the costs of our actions. However, I’m not sure that vehicles are the largest producers of CO2 in the US. America’s electricity is over 50% coal fired! Here’s my wonky stats work, feel free to haggle on it. Referenced from the Union of Concerned Scientists : http://www.ucsusa.org/CoalvsWind/c02c.html
600 coal plants in US (avg 500MW) x 3,700,000 tonnes of carbon dioxide / year = 2.22 billion tonnes CO2/yr
or
the equivalent of cutting down 96 billion trees per year. :eek:
This is just CO2, not the other chemicals released through the process. The stat I found the most shocking was the average 500mw plant requiring 40 traincars of coal PER DAY!
Caveat: How do we compare vehicle emissions to coal emissions, etc? Every expert slices the data to their own bias I suppose. My bias was merely to raise awareness that energy with low financial costs has costs elsewhere, some of which aren’t talked about too much.:smack:
Welcome to the SDMB, and thank you for posting your comment.
Please include a link to Cecil’s column if it’s on the straight dope web site.
To include a link, it can be as simple as including the web page location in your post (make sure there is a space before and after the text of the URL).
Tourist makes a solid point. We often ignore power plants when looking at the overall picture of pollution, greenhouse gases, and such. Some folks who drive electric cars think they are making no pollution. In fact, they are just moving it. The electricity for their daily recharge comes from a big power plant somewhere. They may think it comes from a wind farm, but no! I’m using that wind farm stuff right here in my computer. Ha!
The fact that animals have been around for a few billion years rather tends to indicate that the green plants on balance produce more oxygen than they consume.
(Indeed, oxygen is a very active chemical – one of the greatest corrosives in nature. A largely oxygen atmosphere is simply not a stable situation, even in a world without animals.)
The CO2 figures on the page aren’t bad. However, the figures for NOx, SO2, mercury, and other emissions which are quoted on that page assume NO emissions controls are in place on their “average” coal plant (which is not accurate), and that no heavy metal capture is done via the precipitator and/or fabric filter units, or via scrubbers.
How big is a “traincar” of coal? Anywhere from 80 tons to 110 tons, depending on the style of car, the rail route selected, and the type of coal. Assuming an average of 100 tons, we get 4000 tons of coal per day, or about 167 full-load tons per hour. Well, if you’re assuming 500 MW is “average” sized, then that’s not too far off.
Hell - I’ve seen a plant that, at full-load in the Summer, had 2-1300 MW units that burned nearly 300 cars of Wyoming coal per day. With unit trains being 100 cars in length, that’s three trains per day! :eek:
Point well taken, Anthracite. The scrubbers you refer to do reduce many of the additional chemicals that were once just released. However, I’ve never heard of a CO2 scrubber on a coal plant (no engineer here, just a lonely hypocrit haha). I figure that the worst waste is simply the efficiency of coal plants, the latest cogeneration technology still cannot get us from the 30-35% efficiency of coal. Compare this to the efficiencies from combined cycle gas plants and there you go, course gas is alot more expensive, but isn’t that the whole tradeoff? Cheap power versus clean power ?
Again, thanks for all your replies, I learn most from them
But according to Cecil’s article, “[e]ach year humans release about 6.7 billion tons of carbon into the atmosphere.” American coal plants can’t be responsible for 1/3 of the world’s CO2 emissions so there must be a mistake somewhere. I’d guess that a majority of those 600 plants are smaller than the “typical coal plant” described in the article (the one linked to in the OP).
[QUOTE]
*Originally posted by scr4 *
[American coal plants can’t be responsible for 1/3 of the world’s CO2 emissions
I thinks that’s the whole point. America is responsible for aproximatly 1/3 of the world’s CO2 emmissions.
With such a county and resources American should be leading the way not arguing about signing some accord. It should have been called the Columbus Accord (New World) you should have written it and really put your weight behind.
I was disputing the actual numbers, not the overall point. To claim that American coal plants alone produces 1/3 of the world’s CO2 emissions is ridiculous.
In fact I found some statistics on this. I have no idea how reliable or subjective this is (that’s the problem with web searches) but it says that the US produces 25.2% of the world’s CO2, and coal accounts for 34.4% of that, or 560 million tons. It’s still a lot, but much smaller than the 2 billion ton figure quoted in the OP. (Yes, I know it was just a back-of-the-envelope guess, nothing wrong with that.)
For coal, in the US, 2002 - carbon-equivalent emissions:
Residential: 0.3 million metric tons
Commerical: 2.3 million metric tons
Industrial: 51.1 million metric tons
Transportation: 0 million metric tons
Electric Power: 494.6 million metric tons
Total (2002): 548.4 million metric tons from coal, carbon equivalent.
Convert to CO2:
548.4*((32+12)/12) = 2,011 million metric tons = 2.011 billion metric tons CO2
Note that petroleum carbon outweighs coal carbon…
scr4 - the difference which you see on your link is in comparing carbon-equivalent versus carbon dioxide. They refer to this on that table as “MTC”.
CO2 scrubbers do exist, but I know of none actually installed at an operating plant.
Well, how clean is natural gas? It still is a greenhouse gas emitter, and it still produces NOx and some SO2 (although not much SO2 at all, relative to coal).
The power has to come from somewhere.
FTR - hibernicus and I were just discussing efficiencies of our plants, and his gets nearly 40% on bituminous coal. I have seen very well-run and well-maintained supercritical-pressure coal plants burning very low moisture fuel which can get to 42%.
On cost: According to the EIA, the average delivered price of fuel to US plants in 2002 was:
Coal: 121.9 cents/MBtu
Gas: 346.6 cents/MBtu
Petroleum: 352 cents/MBtu
Biomass: from 70 to 285 cents/MBtu (difficult to track, and not really comperable)
Nearly three-to-one is a big difference.
It’s also not just a matter of cost: in general, natural gas plants are not designed to provide the baseload power generation required for a stable electrical grid. Oh, they can, and they are used in that way - but they don’t compare in terms of their equivalent availability and capacity factors to coal or nuclear plants.
Those are some great resources Anthracite, thanks!
On the topic of “what can we do about it?” I submit the following:
Working in the biz, I acknowledge the edict that supply must match demand, so I agree, the power must come from somewhere. Having to fulfill that demand for peak hours, especially when the demand gets quite “peaky” (ie low System Load Factor) creates a huge inefficiency at the system level. What I mean by that is that if the peak demand of a control area starts to reach the limit of system capacity (demand is demanding all the supply available and more, for a short “peak” period), a whole new power source must be found/created to satisfy that peak demand, regardless of how low demand gets during the offpeak times. However if the peak only lasts a short time during each day, that new source isn’t needed most of the time.
However, those who built that source want a return on their investment, so whether it’s needed or not, it has to run! (What’s a coal plant cost? Well factoring out things like governmental approvals, coal transportation, transmission lines to the plant, etc, and sticking to raw dollars for just the plant, I’d estimate in the neighborhood of 1-1.5 million (USD) per MW of capacity. That’s alot of jack for a plant that may only be needed for a short period each day.)
What causes low system load factor? Alot of things, some of which we, as consumers, have control over (in the aggregate). Many forms of information dissemination are out there telling us to delay turning that dishwasher/washer/dryer on until before you go to bed and not right after supper (the superpeak).
But imho, while we are billed on an average or aggregated usage, regardless of whether we did delay that dishwasher, we have no strong motivation to change our behaviour (for you economists out there, the free rider effect - freedom of the individual versus responsibility to the group/society).
My wonky answer? I hearken to the day when a real time power price is connected directly to our appliances via the internet, billing us per use. (waits for laughter from the audience). Is it so difficult to do? Perhaps immediately, but what is the cost of fibre to the home versus another 500MW of generation that could be delayed until we really need it 24/7? Personally, I’d love a system that would charge me, say $10 to run the dishwasher right during the superpeak versus 50cents at 4am. If I really needed those dishes clean, I’d Accept the charge and not penalize my neighbors for it.
Most public sources agree with your figures for US plants. Given that many are being proposed with SCR and FGD systems, $1500 per kW ($1.5 million per MW) is more commonly seen.
Lately I’ve been running the diskwasher at night, and the dryer a lot, so the waste heat will help out some at night.
I don’t think it’s a wonky answer, nor is it not possible to do.
One thing that has prevented it is that, quite simply, power in the US is very, very cheap. Even the 2025 forecasts done by the EIA recently show electrical power cost decreaseing steadily (as measured in constant 2001 dollars) all the way to 2025 and beyond. There just isn’t much incentive to change. Many of the demand-side management schemes of the early 1990’s were driven more by an odd response to deregulation, rather than an actual concern over leveling the load out.
Our power is really cheap, and the EIA and EPRI both believe that it will get even cheaper. I would be more than happy to have power costs stay the same in real dollars, and apply a conservation or renewables tax/incentive scheme that helped reduce CO2 emissions and dependence on nonrenewable resources.
Your professor was correct. Plants get the energy they need to power their life processes by using sunlight to synthesize sugars out of water and carbon dioxide. They then burn the sugar, often at night, releasing the carbon dioxide again.
However, plants also use some of the sugars they’ve made to create cellulose, the main ingredient in wood. Plants don’t magically make carbon dioxide go away, they store it, in the form of cellulose. A plant only shows a net uptake of carbon dioxide when it’s gaining mass. So growing trees does absorb carbon dioxide, but then once the tree is grown then what? If the wood is burned or allowed to rot, it just returns the carbon dioxide to the atmosphere again. Thus most people are surprised to learn that the Amazon rain forest on average removes zero carbon dioxide from the air.
[hijack]Anthracite and tourist, I am glad to know that we have experts in our midst. Do you (or anyone) know the average percent power loss of electricity due to transmission through power lines? I remember 50% from my Sustainability class, but I could be wrong. I think this should be considered when comparing Electricity to other energy storage mediums such as hydrogen.
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Do you know the delivered price of nuclear derived energy? How does that compare to the others. I was told it is expensive.
Isn’t natural gas easier to clean? I understand that modern natural gas power plants release very little emmisions.
Lumpy, It’s true that the Amazon doesn’t remove any carbon dioxide from the air, but burning it sure does release the carbon back INTO the air. And that’s a lot of carbon!
That’s actually a very difficult number to arrive at. Transmission conditions and line conditions vary so much across all parts of the US, and there are a lot of variables to take into account. It also depends on whether or not the lines are AC, DC, their voltage, the temperature outside, etc.
That having been qualified - I too see the “greater than 50%” number used a lot in the industry. Even though I work with people who design these things, they still can’t give me a better overall number.
What about the people who say, “Well, the earth has been polluting its OWN atmosphere since the beginning of time, with innumerable sulfurous geysers and volcanoes belching forth billions of tons of chemicals like CO2 and ozone, for billions of years. Life has evolved along with it. What we add is infinitesimal by comparison.” It sounds weird. Is there any validity to that?
On the whole, the system, including Life, has been relatively balanced and stable until now. Now the “Life” side of the boat is tilting down, and is soon going to go gunwale-under.
