Replies to This Discussion

Permalink Reply by David on September 8, 2009 at 14:14

The link to the article is here, should you want to read it.

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Permalink Reply by sesport on September 8, 2009 at 18:02

Electro - Aren't the power companies more likely to consider building peak plants to cover the increasing demands? And wouldn't those kinds of plants be more likely to use ng?

IMO, you're right though about this guy's opinion being more of a forward looking statement to boost his company's image.
:0)

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Permalink Reply by Mac Davis on September 8, 2009 at 20:54

I'm unclear on why it's said to be so difficult to switch from coal to gas. It seems to me that burning coal is a lot more complicated than burning natgas. Is it really that difficult to replace the "burner" portion of the boiler? I realize it's a significant change for part of the boiler, not just a "pump natural gas instead of coal" into the burner change. Isn't it mostly a question of replacing coal burners with gas burners, or even adding gas burners to an existing coal burner? Wouldn't it be possible to build new boilers as "dual fuel" burners?

Yes, it would be big bucks, but would it be a significant percentage of the cost of a new boiler?

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Permalink Reply by sesport on September 12, 2009 at 14:42

Mac - See if this article helps. As I understand it, there are no boilers involved in gas powered electric plants.

http://electricalandelectronics.org/2008/10/01/gas-turbine-power-pl...

Also, at the bottom of page on this link is another link to a schematic. It's not easily read because it's so small, but at least it's a visual aid. :0)

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Permalink Reply by sesport on September 12, 2009 at 17:22

Mac - One of my "tutors" called me on this one and I need to clarify. It's only in the instance of gas fired turbines that no boiler is involved. There are gas fired boilers involved in the generation of power in other types of plants, though.

Sorry if this caused any confusion.

:0)

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Permalink Reply by Mac Davis on September 12, 2009 at 17:58

Thanks, sesport, that's useful information.

However, that's a "gas turbine" power plant. It's a bit confusing because we are using "gas" for two things. 1) gas turbine - a turbine using a gas other than steam to turn the blades. and 2) gas - natural gas - mostly methane.

Your "gas turbine power plant" would usually be powered by burning natural gas, but a gas turbine can also be powered by oil, or "syngas" generated from coal.

The other major kind of power plant is a steam turbine power plant. You burn a fuel in a boiler to generate steam and then use the steam to turn a turbine. The fuel is usually coal or natural gas. There are quite a few natgas fired steam turbine plants around this area. 30 years or so, natgas fired steam turbine plants were probably the main kind of power plant around Louisiana, until economics(?) made coal more attractive than natgas.

You're unlikely to convert a coal fired steam turbine plant into a natgas fired gas turbine plant.

I'm wondering if it's reasonable to convert a coal-fired steam turbine plant to a natgas fired steam-turbine plant. You might want to do this if natgas becomes expensive, or if there are regulatory or political pressures to get off of "dirty" coal.

There's also a "combined-cycle" power plant where you run a gas turbine and then use the exhaust from the gas turbine to boil water and run a steam turbine. This usually gives you a better efficiency than a gas turbine or a steam turbine alone. You can even take an existing natgas powered steam turbine plant and put a gas turbine on the front end of the natgas boiler and use the gas turbine exhaust gas to either completely power the boiler or combine turbine exhaust with freshly burned fuel to run the boiler and steam turbine.

There are natgas electrical power plants in LA that have been converted from natgas-steam to natgas combined cycle. I think the one I toured was in Monroe, but I don't remember for sure.

It might be practical to put a natgas turbine on the front end of a coal fired steam turbine power plant and turn it into a combined cycle power plant. It might also be possible to use natgas to fuel the gas turbine and then combine natgas turbine exhaust with coal burner heat to power the steam turbine.

There's yet another possible combined fuel plant option. Some of the coal fired power plants being built are combined cycle power plants, but instead of burning natgas, they "gassify" coal and burn that gas into a combined cycle power plant. (Google IGCC) I suspect an IGCC plant could be easily built to accept either coal gas or natgas at the input to the gas turbine.

This could even be a sneaky way to build a new coal fired plant. Build a combined cycle natural gas power plant, get the permits and approval by claiming it's powered by "clean burning natural gas," then convert the front end to coal by adding a coal gasification plant.

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Permalink Reply by sesport on September 12, 2009 at 18:17

Mac - The closest thing that I've run across re. a conversion was an article about the Little Gypsy plant. The conversion involved switching from ng to petroleum coke, however. I seem to remember that, when ng prices began to free fall, this plan was put on a back burner.

I haven't really researched the topic of conversions, but if I run across something I'll give you priority heads-up. lol

Oh, and the standard disclaimer applies here. That being IINAEE, or any kind of an engineer for that matter. Just an Everyday Joe.

best :0)

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Permalink Reply by mango on September 9, 2009 at 7:26

Gas is so much cleaner than coal, it seems with this administration it would almost become mandatory for power companies to switch. Really what I do not hear debated in the switch to gas from coal argument enough. Is what do you do with the coal ash deposits? But retrofitting systems should not be that difficult if there were incentives to do so.

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Permalink Reply by Mac Davis on September 9, 2009 at 8:26

Mango, I'm not sure what you mean about coal ash. Is there some reason the coal ash deposits keep you from switching to natgas?

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Permalink Reply by sesport on September 9, 2009 at 16:34

Thanks, Electro - I read Mac's comment, and my next response was going to be that I thought the difference is that gas powered plants involve turbines, just needed to rummage through my stack of bookmarked items to verify what I thought.

Hmmmm, I'm thinking I may need to figure out a way to gain access to another person's library card. Electro, when do you take lunch breaks, coffee breaks, when are you most likely to be out of your office? ha, ha

:0)

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Permalink Reply by Mac Davis on September 10, 2009 at 4:33

Natgas power plants are often combined cycle systems. You burn the natgas in a gas turbine system to generate electricity. Then you use the exhaust heat from the turbine to generate steam in a more conventional boiler/steam turbine powerplant system.

This has an efficiency advantage over a simple burner/boiler/steam turbine system. The gas turbine part of the plant can also be designed for "peaking." Coal plants tend to be designed in ways such that you want to run them at a steady load. You need some "peaking" generating capacity in your electrical system that you can turn on and off as needed and let your more efficient base load systems run at a nearly constant load level.

I understand that it's not easy to convert a base load coal-fired power plant to a plant you'd build from the ground up as a gas-fired power plant. What I'm wondering is if you can do a simpler conversion? Change as little as possible to switch fuel from coal to gas? How expensive is it vs. a new natgas plant? How much efficiency do you lose vs. a new natgas plant?

Look at it this way: If you can't get coal to your existing coal-fired plant and had to switch to natgas, how much of the power plant do you scrap and rebuild?

By the way, you can sometimes take an existing natgas boiler/steam power plant and add a gas turbine generator on the front end to increase peaking ability and overall efficiency.

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Permalink Reply by Mac Davis on September 10, 2009 at 15:16

You keep repeating yourself, but you still haven't supplied any information, other than "Electrodynamics says it isn't feasible," and "natgas prices are too volatile."

Gas price volatility is a very valid point. I agree it's a big hurdle. Perhaps it's a sufficiently big problem in itself that the coal to natgas conversion will never take place.

I understand that it may not be technically feasible, but "Electrodynamics says so" isn't really a good enough answer for me.

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