On 08/09/2016 7:59 AM, Markem wrote: ...
There've been "mine-mouth" plants for years; the biggest difficulty in doing it universally is that for the most part the coal isn't where the demand for power is.
On 08/08/2016 9:04 PM, John McCoy wrote: ...
Ummmm...well don't see why it _couldn't_ be arranged but certainly having the fuel already in gaseous form is convenient as they're currently designed around NG.
But, attacking the problem from another direction, there's a redesigned/upgraded plant in Denmark operating a "ultra" supercritical cycle that runs at a thermal efficiency of 47% (LHV basis) for the generation side and counting the residual waste heat used for residential heating has an overall plant heat efficiency of some 90-91%. This was done retrofitting an existing plant; one would expect a few more percentage points could be squeezed of of new designs. Hence, the overall advantage of combined cycle needn't be as large as is when compared to conventional coal-fired boilers (which in US _average_ at over 40 years of age and while I've not computed it recently, is probably closer to 50 by now although there have been a number of the really, really old plants forced offline so perhaps they've reduced the geriatrics some. It's now been 15 yr since returned to the family farm and stopped the active consulting so I've gradually dropped behind on current data, sorry...
That is the beauty of Tesla'a AC, easier than Edisons DC.
dpb wrote in news:nocnl5$n09$ snipped-for-privacy@dont-email.me:
I know at one time pulverized coal was tried in a turbine and was abandoned because it was too abrasive on the turbine blades. I don't know if that problem has been solved.
That (47%) is remarkable for a single cycle plant. But even so it's less than combined cycle, which I beleive is now close to 60%. And of course the waste heat benefit is only available in certain places (wouldn't exist in S Fla, where I am, for example).
This, to my mind, is the real reason coal demand is dropping. If you own a power plant that's 40+ years old and intend on replacing it, at this time you wouldn't consider coal. You'd go for natural gas, most likely combined cycle, because it's going to be cheaper to build and operate. Even without the enviromental regulations, you'd go with natural gas.
John
"Easier" initially isn't necessarily all the issue...AC transmission line losses are a major problem; in fact new long-distance lines (and many existing from the massive hydro generation in Canada to the NE US) are now DC. Possible primarily owing to the advances in solid state that make large-current voltage transformers practical now that weren't in TAE's time.
snipped-for-privacy@slp53.sl.home (Scott Lurndal) wrote in news:wSkqz.29043$NH5.25351 @fx38.iad:
The one I learned on was built in 1913 and converted to oil before WW1.
About 10% of US steam locomotives burned oil. Generally it was used in places where oil was abundant and coal wasn't, because everything being equal (i.e. including the cost of shipping) coal was cheaper.
John
On 08/09/2016 9:52 AM, John McCoy wrote: ...
We'll have to agree to disagree on the totality of that conclusion...there would be several coal-fired plants under construction or already completed if it hadn't been for the interventionists backed by the current and previous administrations that made the licensing process as difficult as nuke was in the '80s for essentially, imo, very similar hysteria-driven reasons as opposed to real.
Our local generation co-op has had a two-unit plant on the drawing boards and ready to build for several years and would begin construction tomorrow if the aforementioned issues weren't in the way. We looked at alternatives closely, it is to be located at a site with an existing unit so most of the infrastructure is there whereas NG would require a new pipeline and the local supplies are depleting so the source would have to come from afar. The unit was designed to meet and exceed _all_ even current emissions limits and includes a biofuel (algae) demo facility with it as well and still isn't enough to pass the permitting hurdles thrown up. Meanwhile the region is being stifled in economic growth by lack of additional, economical power.
The local utility company recently built a NG plant. What many don't realise is that these are gas turbine units and are only useful for peak draw generation and not base load generation. Graham
Are we setting a new record for posts on a single topic?
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While they are good for that (and coal-fired isn't), the "veritable plethora" of these being installed is in part owing to the need to have them as standby for the increasing wind generation that is extremely unreliable, down to the minute unreliable as it is never certain that a wind shift or drop in wind speed won't happen.
I've done a study of the output from a local large wind installation here in SW KS where the wind is about as reliable as it gets outside a few very localized areas in the world and the maximum capacity factor in some seven years' of operation is roughly 37% of nameplate rating over a month; midsummer it's closer to 20%. This implies that on average on the best of months one needs to build almost 3X the target capacity to be able to have that much generation in the best of times and more like
4-5X that capacity on an annual basis. This, to say the least, is _not_ particularly cost-effective, and is even more so when one factors in that it cannot replace either ready-reserve _nor_ baseload generation so in order to ensure a reliable grid the utility has to maintain as operational and staff capacity as much as 10X actual grid load.
As a casual observer I never thought much about the actual numbers. They pretty much suck at 37% at best. Costly to install even though you use "free" fuel. I guess we won't see a windmill on every roof.
graham wrote in news:noctb4$bnf$ snipped-for-privacy@dont-email.me:
Might be - gas turbines have been used for peaking for many years. In that application low efficiency isn't a major concern.
But it's more likely it's a combined cycle plant, that uses a gas turbine as the first stage and the exhaust heat from that to boil water for a steam turbine second stage. That's "state of the art" right now, and most new power plants are using that design. Combined cycle approaches 60% efficiency, which is what you want for base load plants.
John
On 08/09/2016 4:54 PM, John McCoy wrote: ...
I'd venture that also depends on where it is...peaking units are popping up like daisies out here because of the legislated "green" fraction the utilities are being mandated to put on grid; without them their reliability is going to go to pot or they can't meet the required percentages -- catch 22. :(
And, there are areas of the country where forced shutdowns of fossil has lead to cases where these peaking units are now being operated as baseload generation causing two further issues--1) reduced reliability for lack of peaking capacity since it's already being used instead of being on standby or idling and 2) they suck in efficiency even in relation to the older units they replaced.
dpb wrote in news:nocr7p$41r$ snipped-for-privacy@dont-email.me:
Well, I'd agree with you that that case (which is more of an expansion of an existing facility than a complete new installation) is kind of the exception that proves the rule. With you being relatively close to the coal mines and having the infrastructure already in place, it makes sense coal would be the more economical choice.
It's a pity there isn't some flexibility (and common sense) in the rules to handle cases like that.
John
Ed Pawlowski wrote in news:QP-dnZ5oCazQ3jfKnZ2dnUU7- snipped-for-privacy@giganews.com:
A typical fossil fuel power plant converts about 37% of it's input fuel into electricity, so wind isn't doing so bad in that regard.
The problem with wind is it's not a constant 37%, it varies from 100% to essentially 0 as the weather changes. To be viable, wind needs to be installed in many places (because the weather isn't the same everywhere); have a high capacity grid connecting everything (some days half the wind turbines in west Texas are idle, because Texas isn't well connected to the rest of the country and the power can't be sent out of state); and be supplemented by techniques like pumped storage that can smooth the cycle.
John
But it converts 100% of it nameplate capacity into power at a very high fraction of it's operating time so it takes 3X the installed capacity to get 1X the output.
Not to mention that Wolf Creek say, generates 1000 MWe at annual capacity factors of 100% for a calender year on occasion when the reload falls outside the year on less than 640 A. The Gray County wind farm has 117 towers that only have 112 MWe if were operating at 100% and is spread out over 12,000 A and visually pollutes the skyline and adds night light pollution from 20-30 mi around it.
All of which effectively reduces that efficiency even further when one considers all the losses and duplication in generation required.
It seems to me, the solution is simple. Ask people with knowledge, like maybe one or two people living in the White House and get expert opinion and ignore all them engineer type guys advice.
You can trust the government to make the right decision for us. That's why we elected the smartest guy in thw world to be our President.
We did that once - his name was Tom Jefferson. But he couldn't get elected today, the evangelicals would barf at his deism.
On 08/09/2016 5:06 PM, John McCoy wrote: ...
Those were monthly averages for the facility, looking specifically for cyclical patterns owing to the nature of wind patterns over the year. Turns out it's very observable and repetitive (as one might expect) over the seven full years at the last time I updated the analysis.
It also showed that the output was _not_ demand-limited as also compared the generated output vs nearby NWS average daily windspeeds which had a very high correlation of >85% which, if the units were being kept offline for a high fraction of the time the output would have been more-or-less independent of the average windspeed variation.
Also, just a point of interest, the output doesn't vary just from 0-100% but 0-100-0 as they can only operate between range of 14-55 mph; below there's insufficient force, above they have to be feathered. While the fraction >55 mph is small, it's not zero and while I don't know their operational procedures in detail, I'd venture they go ahead and feather in thunderstorms on general principle rather than wait for a trip and risk the 80 mph gust front ripping through first...
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I wouldn't argue that so much if it were a _reliable_ 37% in the month (or day of month or even minute of the day), but it isn't; it's more-or-less random. Consequently, the utilities can't not keep all the other generation facilities both base load and peaking and add even _more_ peaking in order to be able to provide the grid reliability. The alternative is to then rely on buying spot power (try that in mid-TX summer heat wave for price if can even get it).
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