From the University of Colorado at Boulder
New study: US power plant emissions down
Power plants that use natural gas and a new technology to squeeze more energy from the fuel release far less of the greenhouse gas carbon dioxide than coal-fired power plants do, according to a new analysis accepted for publication Jan. 8 in Earth’s Future, a journal of the American Geophysical Union. The so-called “combined cycle” natural gas power plants also release significantly less nitrogen oxides and sulfur dioxide, which can worsen air quality.
“Since more and more of our electricity is coming from these cleaner power plants, emissions from the power sector are lower by 20, 30 even 40 percent for some gases since 1997,” said lead author Joost de Gouw, an atmospheric scientist with NOAA’s Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder. NOAA is the National Oceanic and Atmospheric Administration.
De Gouw, who works at NOAA’s Earth System Research Laboratory (ESRL), and his NOAA and CIRES colleagues analyzed data from systems that continuously monitor emissions at power plant stacks around the country. Previous aircraft-based studies have shown these stack measurements are accurate for carbon dioxide (CO2) and for nitrogen oxides and sulfur dioxide. Nitrogen oxides and sulfur dioxide can react in the atmosphere to form tiny particles and ozone, which can cause respiratory disease.
To compare pollutant emissions from different types of power plants, the scientists calculated emissions per unit of energy produced, for all data available between 1997 and 2012. During that period of time, on average:
- Coal-based power plants emitted 915 grams (32 ounces) of CO2 per kilowatt hour of energy produced;
- Natural gas power plants emitted 549 grams (19 ounces) CO2 per kilowatt hour; and
- Combined cycle natural gas plants emitted 436 grams (15 ounces) CO2 per kilowatt hour.
In combined cycle natural gas plants, operators use two heat engines in tandem to convert a higher fraction of heat into electrical energy. For context, U.S. households consumed 11,280 kilowatt hours of energy, on average, in 2011, according to the U.S. Energy Information Agency. This amounts to 11.4 metric tons per year of CO2 per household, if all of that electricity were generated by a coal power plant, or 5.4 metric tons if it all came from a natural gas power plant with combined cycle technology.
The researchers reported that between 1997 and 2012, the fraction of electric energy in the United States produced from coal gradually decreased from 83 percent to 59, and the fraction of energy from combined cycle natural gas plants rose from none to 34 percent.
That shift in the energy industry meant that power plants, overall, sent 23 percent less CO2 into the atmosphere last year than they would have, had coal been providing about the same fraction of electric power as in 1997, de Gouw said. The switch led to even greater reductions in the power sector’s emissions of nitrogen oxides and sulfur dioxide, which dropped by 40 percent and 44 percent, respectively.
The new findings are consistent with recent reports from the Energy Information Agency that substituting natural gas for coal in power generation helped lower power-related carbon dioxide emissions in 2012.
The authors noted that the new analysis is limited to pollutants emitted during energy production and measured at stacks. The paper did not address levels of greenhouse gases and other pollutants that leak into the atmosphere during fuel extraction, for example. To investigate the total atmospheric consequences of shifting energy use, scientists need to continue collecting data from all aspects of energy exploration, production and use, the authors concluded.
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Authors of the new paper, “Reduced Emissions of CO2, NOx and SO2 from U.S. Power Plants Due to the Switch from Coal to Natural Gas with Combined Cycle Technology,” are de Gouw (CIRES), David Parrish (NOAA ESRL), Greg Frost (CIRES) and Michael Trainer (NOAA).
starzmom:
I write to add detail to your post at January 11, 2014 at 6:26 am.
Importantly, I explain why expensive gas turbine operation – not cheaper combined cycles – are needed to provide back-up to meet rapidly fluctuating demand for electricity.
A steam turbine cycle uses a steam turbine to obtain energy from heat.
A gas turbine uses a gas turbine to obtain energy from heat.
A combined cycle uses a gas turbine and a steam turbine to obtain energy from heat.
The heat is supplied to an operating fluid which is supplied to a turbine. A steam turbine uses superheated steam as its operating fluid. And a gas turbine uses hot gas (often combustion product from burning natural gas, i.e. methane) as its operating fluid.
Extracting heat from the operating fluid lowers the temperature of the fluid. So, energy that can be obtained from the fluid can be increased by increasing the temperature of the fluid supplied to the turbine.
The gas supplied to a gas turbine can be much hotter than the steam supplied to a gas turbine. This is because available materials for making turbines constrain the maximum input temperature of steam turbines.
Thus, a gas turbine is more efficient than a steam turbine because the operating fluid supplied to the gas turbine is hotter.
However, steam turbines are inherently more efficient than gas turbines at converting heat to energy. This is because of the differences in viscosities, densities and thermal capacities of steam and the gas which the turbines use as operating fluid.
A combined cycle uses these facts to obtain greater efficiency than a gas turbine or a steam turbine alone. High temperature gas is supplied to a gas turbine and the output of gas from the gas turbine is used to boil water and to superheat the resulting steam which is supplied to the steam turbine.
In a combined cycle both turbines operate at less than their maximum efficiency. The gas turbine outputs gas hotter than it could be, and the steam turbine is provided with gas less hot than it could be. But the performances of the two turbines are optimised such that their combination provides more efficiency than either could alone.
Additionally, topping cycles exist. In these the gas turbine and the steam turbine each operates at its maximum efficiency. This is achieved by using additional fuel to increase the temperature of the steam supplied to the steam turbine (i.e. a ‘topping’ of heat is supplied to the steam).
The reason that gas turbines are used as back-up to match peak electricity demand is because they can start-up very fast. They are supplied with gas which is ignited so instantly obtains turbine input temperature, and the turbine rapidly reaches operating temperature.
This use of gas turbines is necessary but gas turbine plants provide much more expensive energy than combined cycle plants because combined cycles are much more efficient.
But steam turbines, combined cycles and topping cycles each need to boil their water and to superheat the steam before they can achieve operating temperature. (Anybody who has boiled a kettle knows this is not instant.) Conventional coal-fired power stations (pulverised fuel, PF, plants) operate steam turbines so take days to start-up from cold. PF plants operate spinning-standby when used as back-up. In spinning- standby a plant burns its fuel to boil the water, to superheat the steam, and to maintain its turbines and etc. at operating temperature. Spinning-standby is very expensive.
I hope this information is useful.
Richard
Why on Earth would you want to reduce co2 emissions when it is so beneficial? Ask an honest geologist whether co2 in the atmosphere is by geologic standards currently high, median or low? Low is the answer you will get.
As for power plants I don’t care what they burn as long as it’s the most economical AFTER reducing real pollutants like nitrogen oxides and sulfur dioxide. Co2 is not a pollutant no matter how hard they pant, huff, puff and wave their arms.
Finally, given the fact that Warmists are so concerned about co2 shouldn’t they be going mad for gas fracking? Of course not, reducing co2 is not their real agenda.
Leonard Weinstein says:
January 11, 2014 at 6:32 am
…. I do not understand where you get the factor of 5 to 10 times, as it is not in the net cost.
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Straight from the article that shows the new power will cost
I will repeat it:
What was the old/present cost of electricity? $16 per megawatt
What is the cost for new production for 2015? $136 per megawatt, $167 per megawatt, $357 per megawatt.
This is the already agreed on price not something pulled out of calculations.
Coal used to produce 42% of the electricity in the USA. Obama has stated he is going to close ALL coal plants using the EPA. Top Obama EPA Official Admits to Plan to Destroy the Coal Industry in America (Video)
The Math:
If you paid $160/month for electric and Obama succeeds in his plans your cost is 60% at the old price plus 40% at the new price. That is $96 for electricity from old capacity plus between $544 and $1428 for electricity from the new capacity.
That means your bill went from $160 to 640 IF you are lucky or from $160 to $1524 if you are unlucky enough to live in Ohio.
Actually it is even worse that that in Ohio because Coal fueled 78 percent of Ohio’s net electricity generation in 2011
Do you think the people in Ohio are going to care about your ” net cost” when the actual cost of shutting down their coal plants hits their bills?
Ohio ‘ahead of the curve’ for closing coal-fired power plants says Union of Concerned Scientists.
Anthony had this chart in one of the articles here at WUWT: Residential Energy Forecast
A minor quibble, someone is sligthly sloopy when it comes to multiplication or something
915 gram/kwh = 0.000915 Metric ton/kwh , so 11280 kwh/household x 0.000915 ton/kwh = 10.32 tons/household (rounded to 2. decimals) not 11.4 metric tons/household per year CO2 emission from coal only plant electricity use . and similiar errors/inaccuracies in other numbers in the article, f.x combined gas is 4.82 metric ton/year not the 5.4 ton/year stated . My guess is somone mixed up his long pants with his his shorts when writing that paragraph
This deserves a separate post. Hopefully every one knows Obama’s goal is closing ALL coal plants (the link is in my above comment – in moderation per usual)
The worst of the problem is the plants are closing faster than the US government thought they would.
Another WUWT regular Chris Wright says (of the UK)
Just what we need rolling blackout in coming winters because the “Planned Economy’ Third Way idiots royally messed up.
http://www.thirdway.org/about_us
Forgot first link: Impact of EPA’s Regulatory Assault on Power Plants: New Regulations to Take 34 GW of Electricity Generation Offline
Apparently, this study is only referring to those power plants that burn somethng and does not include any other type of electrical power plants or generators (nucear, hydro, wood, etc).
This article is therefore quite misleading.
Leonard Weinstein says:
January 11, 2014 at 6:32 am
Leonard, we are told the cost of building a gas- or coal-fired generating station is $800 to $1.2 billion. If your numbers are correct and the cost of the energy over the life time of that plant is only $25 million, then (as Gail Combs claims) construction of the plant far outweighs the operating costs.
Richard,
Thanks for all that.
Certainly Grangemouth could handle any product – the Forth currently handles over 50M tonnes of crude export and product export per annum and Longannet pit would still have been producing coal but for the terrible flood a few years ago – but all hypothetical as you say.
But all fascinating stuff.
$800 million to $1.2 billion.
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Scott says:
January 11, 2014 at 5:54 am
One big difference between natural gas and coal is that natural gas seems to be a “just in time” type of fuel (being a gas, not easy to store without liquefying it) while coal plants can stock up a big pile of coal that can last for a few months.
***
Yes, that’s a concern for me. Gas plants have to rely on an instantaneous supply of pressurized gas, powered by compressors upstream in the supply pipeline. If power goes out on the compressors — that’s it. Coal is stockpiled and can supply power independently, for weeks at least.
Richard–You are very right, and went into far more detail than I. The point I was trying to make is that as back up generation to renewables, primarily wind, the combined cycle function is not permitted by the EPA, as these plants (gas turbines) reach high enough temperatures that many require NOX control, and the warmup times associated with the waste heat boiler is not compatible with using the NOX control system. So the waste heat boilers–the second part of the combined cycle–can’t be used and that efficiency is lost. But your description of the operation is excellent.
Oldseadog:
Thankyou for your post at January 11, 2014 at 7:58 am.
You brought back a personal memory when you said
Yes, Longannet pit supplied its coal directly into the power station via a drift. True efficiency.
I still possess a set consisting of an engraved silver hip flask, an engraved whisky glass, and a small bottle of whisky which Longannet pit presented to me when I accepted an invitation to visit them long. long ago. Thankyou for making me recall the memory although it is tainted by the loss of Longannet.
Richard
beng says: @ur momisugly January 11, 2014 at 7:19 am
Decommissioning working coal plants is a stupid, greenie-driven waste….
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Agreed although we need to build new generating capacity.
The biggest problem is building new capacity is a regulatory nightmare and very very costly and very very time consuming so we can expect to see more of this: On January 6, 2014, ERCOT [Texas] announced an Energy Emergency Alert, asking the public to conserve energy by…
Message for mod’s and or Anthony etal,
Congressman Ralph Hall of Rockwall Texas was at a deal where this poster and others were at early today. He advised to me that he and other Congress members have evidence of $ being frowarded to most if not all of the people who signed the consensus letter.
I will be at a deal with Senator Ted Crus around 11:00 today before one of his town hall deals.
I will pass the info to he/his staff and make sure Ralph’s info is in the hands of Ted Cruz also.
Lies kill.
Truth is life.
starzmom:
Thankyoui for your emphasis of your point in your post addressed to me at January 11, 2014 at 8:02 am.
I copy from your post to add support for the importance of your point in case others missed it.
Hopefully, the importance of your point has been exemplified by my brief introduction to the reasons for the different thermodynamic cycles.
Of course, I could now explain the issues of SOx and NOx and the various power plant technologies to address them, but I see no value in doing that here.
The important issue is that intermittent renewables are expensive and pointless addition to power generation and they raise costs of grid operation for several reasons an important one of which you have explained.
Richard
Beng – I know that SOME natural gas pipelines burn natural gas to power their compressors. But I suppose that now THOSE must have EPA compliance as well, so maybe gas transport is also screwed up. Things could really get interesting if fossil fuel transport had to be powered by renewables. Please don’t pass this concept on to the “regulating” class….
Is there dangerous, catastrophic global warming going on? It does not seem that is the case; global temperatures are lower than forecasted by GCMs and have gone down to zero increase or even a slight cooling trend.
Is there dangerous, catastrophic global cooling going on? No, but but cooling seems to progress more rapidly than warming in the geological records, so we’ll have less warning from temperature measurements.
Could we stop or even slow down either of these? It seems to me that the amount of CO2 in the air does not positively affect the amount of water vapor, and that it is the shading by clouds that dominates the energy input/output, not the delaying of outgoing long wave radiation that water vapor and to an incredibly lower extent CO2 causes.
So, adaptation makes sense, not mitigation.
Adaptation requires energy, lots of energy, cheap (not just affordable) energy.
Adaptation requires inventiveness; Freedom, not regulation. Good information, not lies.
And in Europe, their climate/enviro madness has led tothe refusal to develop natural gas. Due to the inevitable, predicted failure of wind and solar, and the irrational fear of nuclear, Germany is now returning to coal.
Bob Greene says: @ur momisugly January 11, 2014 at 6:49 am
@ur momisuglyGail Combs: The PJM market clearing price numbers sound more like entry prices for peaking plants in their day-ahead market, not baseload pricing….
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Then explain the newest information:
Or this direct from the Report on 2013 auction: (Remember the old price was $16)
The second page shows a chart for RPM Prices for Annual Resources
The prices range from $136.00 to $357.00 for the year 2015/2016 and $59 to $219 for the year 2016/2017.
Sure doesn’t look like they are talking about only energy need for peak.
Oh goodie. We had widespread sporadic power outages here in the Deep South with that last Arctic Outbreak. I’d expect more with the next Arctic Intrusion this weekend!
CCGT is intended for base load, with individual units ranging from about 400MW to now 700MW. A newer Siemens 680 MW unit actually achieved 61% efficiency averaged over a year (2012). Supercritical coal is at best 41%, and the US coal average is 34%. It is mostly older, least efficient coal plants that are being shuttered, since uneconomical even though depreciated. CCGT takes three years to construct and has a capital cost about 2/3 that of equivalent new SC coal, which takes 4 years to construct. The switch from baseload coal to base load CCGT is being driven by economics. Faster to build, less capital, much higher efficiency, lower fuel cost even if gas prices go back above $6 by 2015, which will be the general area needed to keep the fracking supply steady or increasing due to the steep individual well decline curves of shale gas.
The data cited places the decrease from 1997 83% coal to 2012 59%.
Based on everything I’ve read in the above comments, I believe I can see power blackouts in this nation’s future with the huge costs to the economy to go along with it. If and when it happens, it seems quite clear that the EPA and Obama will be to blame. The idiocy of ill-conceived and poorly thought out government regulations and agendas will get you every time.
And the worst part of it will probably be that the MSM in this country will blame anybody but Obama and the EPA for it.
Rud Istvan:
In your post at January 11, 2014 at 8:57 am you say of the US situation.
You may be right, but I would welcome more information before I agree.
A nuclear plant provides electricity with negligible fuel cost because capital, operating and decommissioning costs are almost all its electricity cost.
A conventional or supercritical PF coal-fired plant provides electricity with its fuel cost being about half of its electricity costs.
A CCGT plant burning natural gas has its fuel cost as almost all its electricity cost because its capital and operational costs are very low.
Hence, economics does decree that a new power station will probably be CCGT because initial return on capital is high.
So, as coal plants reach the end of their lives they will probably be replaced by CCGT plants burning natural gas. But reaching the end of its service life is not the only reason why a coal-fired plant may be closed.
An old coal-fired power station with e.g. ten years of remaining life will have payed off its capital so – although it is much less efficient than new CCGT – it will produce cheaper electricity than new CCGT which has high fuel cost. But such a coal-fired power station will be made uncompetitive – so will be shut – by need to retrofit emission constraints. For example, flue gas desulphurisation (FGD) adds ~20% to the plant’s capital cost and ~10% to its operational cost. The capital expenditure of the retrofit must be recovered over the remaining life of the plant despite the increased operating cost. (UK coal-fired power stations are being closed solely as a result of this effect of tightened emission constraints.)
Closure of coal-fired power stations by tighter emission constraints with probable replacement by new CCGT is similar to throwing away a 2-year-old Ferrari and buying a Ford because the Ford has better miles per gallon. The saving from operating the replacement is less than the loss of what was replaced.
Richard