trivial question:coal train to transmission line efficiencycomparo

[Electic]

This is not a serious question, but something to debate over beer and pizza.

Having recently observed huge unit coal trains in Wyoming State, how does the efficiency of these railroad trains compare to mine-mouth plants using high voltage transmission lines? I am curious what the power lost represents as a percentage of power transported.

 

[itsmoked]

Well, for sure, a sack of electricity weighs less than a sack of coal! However because electricity is so small some leaks out along the way. Of course, the longer The Way the more leaks out, so you probably need to specify what kind of distances you mean.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[rbulsara]

You need many more power stations spread out throughout the region for reliability and ease of distribution, than you would have the number of coal mines in region. So most of the time, there are other compelling reasons than the transportation losses.

Rafiq Bulsara

http://www.srengineersct.com

 

[cranky108]

If CSX is correct, they can move a ton of freight 250 miles on a gallon of fuel.
However, a coal train of say 100 cars, at 130 tons per car, not including the car weight, should consume 52 gallons per mile. Also if we consiter that the railroads use more expencive power units for coal trains, that use less fuel (AC traction instead of DC traction) I would presume the 52 gallons per mile is to high.

Also consiter Wyoming where most of the coal comes from dosen't have that many power lines, the savings would have to be reduced by the cost of building transmission lines. Which currently exceeds a $1M a mile.

 

[Electic]

Thank you Gentlemen, for the good answers.

Like itsmoked stated, I was initially inclined to assume electricity weighs much less than coal and therefor has the obvious advantage.

However, someone else completely uninformed with either trains or powerlines told me, "power line losses are huge" which prompted me to think a little further.

I'm not familiar with operating transmission lines however, it is not unusual for a distribution line to experience 10% voltage drop from source to final destination, which represents 10% energy loss in a say a 10 mile length. I would expect similar losses over greater distances with higher voltage transmission lines. It would seem unthinkable for a 100 car train to consume 10 carloads of 'equivalent energy' for 5-700 mile journey, Cranky108's approximation would be about 36,400 gallons of diesel fuel.

100 x 130 tons of coal is approx. 260,000,000,000 BTU's of energy delievered in one coal train.

36,400 gallons of diesel is approx. 4,914,000,000 BTU's of energy consumed in delivering one coal train.

That is about 1.9% (if I didn't slip a decimal point). That would seem achievable by a short transmission line but probably lower than typical line losses for a 700mile distance. I would now guess that based on transportation losses, the railroad wins.

(There are other considerations as Rbulsara stated, including the labor to operate either systems)

 

[itsmoked]

Note that CSX moves a ton not 250 miles but 436 miles on a gallon of fuel..

Keith Cress
kcress -

http://www.flaminsystems.com

 

[rmw]

Well,

Let's look at the logic.

There's lots of coal in Wyoming and to a somewhat lesser extent, Montanta, Colorado, Utah and New Mexico. Labor is relatively cheap there and the workforce has a good work ethic-farm boys. Plants should be less expensive to build out there where the real estate isn't in high demand.

So why aren't the power plants all located there and instead of two rails stretching to far flung points, aren't there 3 conductors stretched in all directions to the same markets? Even though there are some power plants in Utah and New Mexico that do generate power specifically for the California market.

Must be that it is cheaper to ship coal to where the electricty demand is and generate it when it is needed than to generate the electricity where the coal is and ship the electrons way far away.

And repeat the logic for where the Natural Gas is located on the Gulf coast.

And repeat the logic for locating the nuclear plants all out in the desolate west where it would be in nobody's back yard and...

It tells me that there is a practical limit as to how far you can transmit power. I am a ME, not an EE, so that is the only way I can look at it.

rmw

 

[cranky108]

And we can put wind farms off the coast of Martha's Steward's vineard.

I think stability limits would nix your idea.

 

[redfurry]

If you consider using HVDC then there are no stability issues or intrinsic issues with maximum AC transmission distances.

So the question is still valid.

 

[Electic]

To add fuel to the debate, there are minemouth generating plants in Montana and other remote locations, so both methods have proven viable.

Approximately 30 years ago I was told that invester owned utilities favored mine mouth plants whereas public utilities often desired generators local to their service area. That might have been a trend before licensing requirements became overwhelming.

 

[cranky108]

Good point, why would I want to put my assets hundreds of miles from my customers? Can I find quilified employees there? What additional construction costs will I incure?

And why would I want to pay taxes to a community, or state that my customers don't live in? (Even more of a question if you are a tax exempt utility).
It's sort of like taxation without represation.

 

[oldfieldguy]

I personally appreciate every one of those natural gas fueled plans in the northeast and in Florida. Keeps the pipeline full and makes my employer happy.

old field guy

 

[racookpe1978]

I've asked generic loss questions for HV power lines, and the have answers varied quite a bit.

Bottom line depends on the HV AC voltage itself, but seems to come out that you loose 20% of your power if you "ship it" 750 miles. Ship it 1200 miles, and you've lost just under 50% of the power you have created.

But - remember, that distance would be thinking like a piping engineer (fluid in must equal fluid out). With the grid, it's more like each regional power plant supplies it's own (nearby 50 - 200 mile) local area, and outside plants are connected to the grid and sharing voltage, but the current (energy) is used locally. So in each grid region (large area) losses are NOT equal to that 750 or 1200 mile percent.

Each plant assumes it's local distribution losses are around 3 - 6%. (That included the big plant transformers, the local small transformers, and the small telephone pole transformers, the total copper line losses, and the AC reactive current "resistance" that comes into play at high voltage.

Very high volt DC connections are normally used to cross-connect grid regions, Complicated pro's and con's there, but very high volt DC can be economic over long distances as well under some circumstances. (For example, HV DC can get by with smaller vertical and horizontal clearances for wires than HV AC, so the right-of-way purchases can be much lower. Over 800 miles, that difference in land cost alone can add up to a lot of money.)

Anyway, if you build wind farms in deep west Texas, or solar panels in AZ or NM, or coal plants in upstate ND or SD or Montana almost all of your power will get lost as heat loads and resistance before it crosses the Mississippi River. Much less get all the way to NYC or upstate Michigan. Triple the size of your power plant in AZ, triple the size and number of your copper "pipelines" across country, and you "might" end up with a single power plant's worth of unreliable (lightening storms en route!) electricity at the end of your very, very expensive HV AC extension cord.

(By the way, remember the difference between just getting "voltage" across country, or restarting a grid from long distance power plants (when you really, really, really don't care about about efficiency at all!), and getting "POWER" delivered cross country.)

I can run a 1/2" garden hose for 50 feet, and get reasonable flow at 20 psi. Run a 3/4" garden hose for 120 or 150 feet, and I start seeing significant flow loss and only pressure at 10 - 12 psi. Try to run that 3/4" hose for 500 feet, and I see almost no flow and no pressure when the valve is open. But pressure (at zero flow) will still be 20 psi. Pressure (voltage) at long distances is not energy transmitted long distances.

 

[redfurry]

The losses for HVDC are estimated to be 1.5% at each end for conversion plus 3% per 1000km in losses.

http://www.renewableenergyworld.com...und-hvdc-power-costs-no-more-than-ugly-towers

So, energy generated in the middle of the US and shipped to either coast (~2000km) would have a guestimated loss of around 9%

 

[cranky108]

What HVDC has no stability issues? What about the production of vars?
We require our plants to produce vars during voltage excursions, if we ever have any.

How many lines would be required to avert regional storms from killing all power to the East and West cosasts? Or cascading events from a single line outage (does the new york blackout ring a bell?)?

Have you ever tried to buy right of way? The land owners don't think like it's thinner so it should cost less. They think more like you are intruding on my land, so you must pay what I want.
So a 30 FT or 50 FT right of way costs about the same.

 

[redfurry]

Er.. I'm pretty sure HVDC has no VAR issues and no issues with frequency stability.

 

[BJC]

There is a coal gasification plant in NoDak that make 145 million cubic feet of synthetic gas per day.
That much Gas was enough to run a 6 or 700 MW power plant.
It was spposed to be cheaper to gasify the coal in North Dakota put it in a pipe and generate power in detroit than it was to generate power with int in North Dakota and put it on the wire an deliver it to Detroit.
The coal was not worth hauling anywhere. It was 37% water and about 12,000 BTus /lb.
It might be more efficient to run a fuel cell in Detroit than put the gas in a turbine.
I don't have the paper any longer.
I expect to see more gasificatio plants in The Dakotas and eastern Montana. The reason would be the gas which would be the CO2 produced is in demand to recover oil from the Bakken oil field. There is supposedly enough coal in the area to power the US for 400 years or so. The Bakken oil field has 3 or 4 billion barrels of oil.
In addition to all that the wind fields that run from Alberta down the Dakotas/Montana boarder into Nebraska have the potential to power ALL the US. We could wind up with lots of power in a small area. How do you get it out??

http://www.dakotagas.com/

http://www.engineeringsights.org/Si...id=ND&view=s&name=North+Dakota&page=1&image=0

 

[oldfieldguy]

BJC--

The bottom has dropped out of the pricing on REAL out-of-the-ground natural gas here in the USA. Huge reserves have been discovered to be economically feasible in north Texas, north Louisiana, the northeast US (Pennsylvania - upstate New York) and if I remember correctly, the northwestern plains states. I've heard numbers in the 60-250 year range for reserves.

It put a severe crimp on the people who were spending a lot of money to build plants to receive LNG from overseas.

I would also figure they can develop the gas deposits and lay pipelines cheaper than coal can be gasified. I just haven't seen the numbers on that equation.

old field guy

 

[cranky108]

I honestly don't believe the bottom has droped out of the natural gas market. It may have droped some, but not out.
If it had droped out, they would have switched our coal plants to run on gas (dual burners are nice).
Also I haven't seen real low numbers in my gas bill.

The thing I don't see is if the power plants were located close to the customers, then district heating might be more usable. Although it isen't.

Some power plants are located close to the customers so they can supply electricty, steam, cooling water, and sometimes recieve fuel.
And since many power companies started as city power companies, or as ice companies, they would be located close to there customers.

Another thought is that many power plants, while not located close to there fuel source, they are located close to water.

Now that I think of it, most of the coal fields are not close to water.

Would transporting water cost less than transporting coal?

 

[rcw retired EE]

Since the OP said this not a serious question.- here's my thought:

Wyoming coal fields are at higher elevations than Midwest power plants. The coal coasts downhill and the empty train cars come back up. Electricty can't coast downhill.



Our power plant developer clients tell us that it is a lot easier and cheaper to bring the fuel to the plant than the power to the load. For example, they could place the power plant near the country border where the gas entered the country and build trasnmission lines to the major loads or build closer to the loads and run pipelines. The latter design alwasy won.