Kyoto – A Perspective (Part 11)

Posted on Tue 04/15/2008 by TonyfromOz

COAL FIRED POWER PLANTS

I was going to go straight into individual methods of finding a replacement for those coal fired power plants, but, first thing, I thought you’d like to see what all the fuss was about.

I debated whether or not to include this, because of the technical nature, and how that might not interest some of you, but I found this relatively simple schematic diagram in the online Wikipedia. This shows you (basically) all the parts that go to make up a Coal fired power plant, and I’m going to explain in as simple a way as possible how it operates.

For those of you with a lower screen resolution, this diagram obviously disappears off the right side of your screen. If you click on the image it will show in full. I have purposely done it like this only for the one reason. If I make the image smaller, the numbers are too small to see. Great diagram, but useless if you don’t know what’s what. You could just scroll across the screen as you read the explanation for some of the aspects here.

Please Click on the above Image to see a larger view. Opens in a new window.

1. Cooling tower	10 Steam control valve	19 Superheater
2. Cooling water pump	11. High pressure steam turbine	20. Forced draught fan
3. Three phase transmission line	12. Deaerator	21. Reheater
4. Step up transformer	13. Feedwater heater	22. Combustion air intake
5. Electrical generator	14. Coal conveyor	23. Economiser
6. Low pressure steam turbine	15. Coal hopper	24. Air preheater
7. Boiler feedwater pump	16. Coal pulveriser	25. Precipitator
8. Surface condenser	17. Boiler steam drum	26. Induced draught fan
9. Intermediate pressure steam turbine	18. Bottom ash hopper	27. Flue gas stack

The place where all the action happens is in the area covered by the numbers 11, 9, 6, and 5.

These are the three stages of the turbine and the generator. All of these are on the one long shaft. The length is around 100 feet, a good 33 paces, about twice as long as the average house. The weight for an average large baseload power generator with the turbine that drives it is around 250 tons, and all this rotates at around 3000 to 3600 RPM. Some plants have three of these onsite. The generator’s rotor is sealed and cooled with hydrogen gas.

I know that figures might seen a little meaningless, so I want you to consider this, and I’ll make a comparison with the operation of this to your family car.
You get in the car and drive to work, and then home again in the evening. You go shopping in it once or twice a week, take the children to sport on the weekend and visit your parents or other family members and friends every so often. Once a year maybe you’ll go on a road trip to a holiday destination and the car actually gets a good continuous run of say eight hours maximum, with one or two breaks. At the end of four or five years of this, you trade up to a new car.

A 250 Ton baseload turbine and generator gets turned on after the whole complex is built. It spins up to 3000 to 3600 RPM, and stays there for the next 35 years, and in some cases, more. Once a year for maintenance purposes, it’s run down but because it is so heavy on the shaft, it must be kept rotating during the servicing, so that weight is not on the shaft, because it will surely bend it. While the maintenance is being carried out the whole 250 Tons still rotates at 3 RPM.
IT DOES NOT STOP ROTATING ………………….. FOR THE LIFE OF THE PLANT.

More often than not there are three of these generating units onsite.

This gives you a good idea of the inertia involved. The speed of this 250 ton rotating behemoth cannot be run up at short notice when ‘peak power’ times arise, so that’s why these large plants are base load plants of large capacity, and they just hum along at basically the one speed all the time.

Let’s look at what keeps all this moving then. The steam is produced by boiling water, and the fuel used is coal. Coal is brought to the plant by rail or truck or even ships that sail right up to the plant. The coal is offloaded onto the site where a conveyor belt carries it to where it is pulverised and then burned, at points 14, 15, and 16 on the diagram. The coal is smashed into smaller pieces around two inches by two inches, and these small pieces are then broken down to a fine powder which is more readily burned.
So, how much coal is used in the process for a typical three generator system?
Normal daily operation uses around, wait for it now, 10,000 tons, and in the Summer peak periods can rise to 30,000 tons per day, as average baseload rises, and so the speed rises to generate the extra power.

Now you can see why these plants provide base load power, just motoring along at the one speed, because at the peak time, they cannot be quickly run up, because increasing the speed of a 250 ton rotating mass needs a lot of extra steam, not easily generated, and the only way to produce that increased amount of steam is by pouring on a lot more coal, so any lead time to get them running faster would be longer than that for when peak time arises.

The following link shows some of these large base load coal fired power plants in Pennsylvania. The large fat round structures are the steam cooling towers and the tall thin chimneys are where the gases are exhausted. If you go here and read about some of the plants, you’ll see that one of the generators at the Cromby power plant at Phoenixville on the Schuylkill River recently celebrated fifty years of operation.

http://www.industcards.com/st-coal-usa-pa.htm

I won’t go into this much further because in a later piece I’ll be discussing in detail another method that might provide a way out while still keeping the coal fired method of power production.
However, the real reason I posted this is because of the following.

You just gotta love Politicians. Point a camera at them and they smile and try to look like they actually know what is happening around them.
Recently there was a photograph showing a noted politician (from Australia, admitted, but the same applies everywhere) at the site of a coal fired power plant. Money had been given to research the possibility of cleaning up the exhaust gases and I’ll get into that in a later post.
Incidentally, this will happen at around point 25 or 26 on the above diagram.

The people concerned wanted a great emotive shot of said politicians and entourage at the site of the coal fired plant, so the TV cameras and still photographs show said smiling politician viewed from shin height, looking up, with that filthy disgusting pollution spewing into the air behind him out of that big fat exhaust stack.
Minders, reporters, TV cameramen, still photographers, hangers on, all smiling profusely.

The photograph was taken in the general vicinity of point 1 on the above diagram.
That filthy white environmental pollution was spewing out the top into the pristine Chinese air. Trouble is that the pollution pouring out of a coal fired power plant from the burning of coal is at point 27 on the above diagram.
What was pouring into the air above that emotive photograph of the politician was the water vapour from condensing steam, or harmless water.

I can see the engineers now.

“Er! Excuse me, but that’s only steam.”
“Don’t worry mate, the public doesn’t know that. Anything else spoils the shot. We know what we’re doing. Butt out”

But then, that’s just how politicians are, I guess.

KPPSTony