Kyoto – A Perspective (Part 14)

Posted on Mon 04/21/2008 by



AES Ironwood – Fuel: natural gas, 710-MW
Lebanon, PA USA
Photograph courtesy of Siemens

natural gasAgain it seems that I’ve strayed from the Kyoto title, further proving that this just goes to the heart of the matter, that it is more complex than it seems on the surface.
First we have the expectation from the protocol itself, that Western countries, and in the main, the US will be contributing the proposed hundreds of billions, and probably more, towards those developing countries to either bring them up to the same standard that we have with regard to access to electric power, or to fund their ability to attract the technology and then to construct power plants other than coal fired plants.
On top of that there will be the inevitable carbon tax. Conservative estimates might place this at around $1000 per person, so that equates to the vicinity of 300 billion dollars, but some estimates now put it into the trillions of dollars, numbers unheard of outside of the Defence Budget.
Then on top of that is the amount to actually replace coal fired plants for something less polluting, which is where we are here, discussing methods that might be used to replace coal fired power plants.

I mentioned how psychology plays a part, and this method of producing power fits into that area neatly, and some may think I’m drawing a long bow, so I’ll explain how I come to that conclusion.
This form of generation uses Liquified Natural Gas.
Politicians again find their way to the forefront to explain how this might just be one method that can prove to be less polluting, and really, that may be so, but only in the short term. Those politicians know that if engineers are put up to explain it then the message might be lost in technical detail, so party followers coach politicians in what to emphasise when they explain it to the public through the media.
The will concentrate (with appropriate expressive hand movements) on the words ‘renewable’, and ‘less polluting’ with regard to greenhouse gases.
The real truth might actually lie elsewhere.
Those real renewable methods are in the realm of being unproven, or unreliable on a large scale, and will take long lead times to implement, and most probably at huge cost. Even Hydro and Nuclear electricity generation have long lead times.
One thing to keep in mind here is something inherent within Western Society that is not so much of a problem in developing countries, and that is the cost of labour itself. In those developing countries, between ten and twenty workers will attract the same money as one worker might in the US and those western countries, and the restrictions on the manner of the work will be a lot more lax in developing countries as well.

A Natural Gas turbine power plant can be constructed from the foundations being laid down to coming on line in around 18 months, and, as opposed to those other already established methods, that is attractive. It’s also why this form is the one that currently makes up the greater number of constructed plants in the US, and also of those under construction and in the planning stages.
True, they cannot supply the huge base load plants that coal and nuclear might be able to provide, so that means that more of them need to be constructed.

So, how does it work then?
The turbine itself is similar to an aircraft engine, but notice that I only said similar to. They are larger, and operate on a longer basis.

However, in a very clever manner, they are also more efficient than most other forms.
The turbine is fuelled by liquified natural gas which is piped onto the site. The gas turbine itself drives the generator and the electricity is produced.

However, the clever part is this.
The superheated exhaust from the turbine is used to generate steam to drive a second turbine attached to another generator. These plants are called Combined Cycle Power Plants. This is why they are so efficient, because in this manner the two forms of power production can be added to each other, effectively getting two results from the one fuel.
This, combined with the speed and ease of plant construction make this method very attractive, and that is why the vast number of new plants being constructed in the US are these Gas Turbine Combined Cycle plants.

The major drawback is that it still uses a fossil fuel in the production of that power.

The gas itself is found in much the same manner as is the drilling for oil, and is more often than not found with oil deposits. The gas is refined in much the same manner and different forms of the gas produced, Propanes Butanes and other gases. The gas is liquified because that way it takes up only one six hundredth of the space. This liquid is then transported to the plant where it is turned back into a gas to drive the turbine. Being similar to the process of refining oil, it is therefore quite expensive in the current market, and as has been seen, that price can only go in the one direction, and as much as the wish thinks it might eventually come down again, that wish is just that. Hence, the cost to the consumer of this form of electric power is quite expensive, as costs of the construction, maintenance and the fuel itself are passed on to the end consumer in higher charges for electricity.

So, as you can see, this is where the psychology is needed from those politicians selling it to the public. They use that one word, ‘CLEAN’ and mention that by extrapolation, that is going to mean that there is a cost for just that.

Because the plants themselves are not huge, when compared with coal plants or even nuclear plants, they are also used mainly for peak power situations, but the larger ones can be used for base load power. What this effectively means is that instead of the one huge plant with two or three turbine/generators on site, this will be replaced by three or four of these Gas turbine plants. Economically there are usually two combined cycle units on the one site, so total power production might be in the range of 600 to 1000 MW per plant for some of the bigger ones.

I will mention something here that might seem a little abstract, but it is a very important factor to be taken into account, that being the efficiency of power production, and this is something that a lot of people just cannot grasp.
The Gross Power number on the makers nameplate is the 100% theoretical maximum that the unit can provide. However each method has inherent losses in that system. Some methods are more efficient than others, and as we go along, I’ll explain the efficiency of these individual methods.
With respect to this method Combined Cycle Gas Turbine, the efficiency is in the general vicinity of 85%.

As you can see from these photographs of some of these , the plants look a lot newer and cleaner without the black dust from the coal staining everything.

Remember though, these plants still use fossil fuels and the cost of power production is more expensive. Don’t believe the spin when an important face on the television tells you that this is the clean way of the future. Their hand is still in your pocket.