Co-generation

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steve66

steve66

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Location
Illinois
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Engineer
I'm starting to look at a cogeneration project. I don't have any specific question, but I would appreciate any general info, advice, or warnings anyone has. Also, any good articles or books or websites would be appreciated.

I really don't know much about cogen except the very basics: natural gas is used to turn a trubine that generates electricity, and the waste heat is used to produce steam for hot water, and building heating and cooling. If you're also new to co-gen, you now know as much as I do :D

Thanks in advance:
Steve
 
Re: Co-generation

If you're an IEEE member, go to the IEEE Xplore website, and search back copies of the Industrial Applications Society (IAS)Transactions using cogeneration, generator, generation as key words. A lot of good overview articles were written in the 1982-1996 time frame and several more recently. I found copies at the local university library.

Check the trade magazines: EC&M magazine had some overview articles. Back issues of ?Power? and ?Power Engineering? or ?Consulting and Specifying Engineer? are other good sources.

Good luck, it is an interesting field.

The subject is too big to discuss here.
 
Re: Co-generation

In addition to steve's questions, I will ask one. Is there any particular location/application where cogeneration is more beneficial to use? Such as in a factory setting, or in general is it good for regular old medium voltage distribution?
 
Re: Co-generation

One of the least obvious concepts with Co-gens is that the electricity is actually the "by-product." In other words, you probably needed to justify the steam for process requirements or heat recovery from a HVAC chiller system first. Two-Stage generation systems where gas turbine heat is recovered through a Heat Recovery Steam Generator (HRSG) and then used to drive a steam turbine for an electric generator are technically not Co-gens.

I've installed small co-gens where the steam was used in food processing. I've also installed fairly large systems for refineries that used both high and low pressure steam for various process uses. Low-pressure steam was usually generated through a letdown turbine that either drove process equipment or another generator.

In both cases, since it was the steam that was valuable, we also had to have a package steam generator for when the genset was down.

The utility interface, if any, was generally medium voltage.
 
Re: Co-generation

I guess the biggest question is can it pay given the prices of natural gas and electricity.

That would get down to an analysis of utility rates, demand for electricity and heat as well as the ownership and maintenence costs of the cogen equipment.

Jim
 
Re: Co-generation

Hence, can it be said that co-gens are for efficiency operations and not for redundacy operations?
 
Re: Co-generation

You get efficiency in terms of more use out of the input fuel. You get power, and you get steam. But as Bob pointed out, if you don't need the steam for other purposes anyway, then co-gen isn't going to raise your efficiency.

One other benefit is not having to pay the utility for the power to run your facility. In one sense, it does provide a level of redundancy. If your generator dies, than you still have the utility available.
 
Re: Co-generation

In many locations any excess power can be sold back to the utility. I suppose that it varies in each state how that transaction takes place but
you may be able to make a few bucks if you have excess generation.
 
Re: Co-generation

In many locations any excess power can be sold back to the utility.
Click to expand...
That's true, but I'm also finding in many places the client has a contract with the POCO that prohibits them from selling power back, or even generating power on site.

Apparently our client has a 10 year contract with their cost of electricity locked in. But their contract prohibits them from even starting construction on a generating plant until the contract expires (in a year or two).

I guess these 10 year contracts were pretty common back when the utility companies saw deregulation coming.

Steve
 
Re: Co-generation

Originally posted by steve66:
In many locations any excess power can be sold back to the utility.
Click to expand...
That's true, but I'm also finding in many places the client has a contract with the POCO that prohibits them from selling power back, or even generating power on site.

Apparently our client has a 10 year contract with their cost of electricity locked in. But their contract prohibits them from even starting construction on a generating plant until the contract expires (in a year or two).

I guess these 10 year contracts were pretty common back when the utility companies saw deregulation coming.

Steve
Click to expand...
This is true. Con-Ed is suing a number of property owners in Manhattan for using their backup generators to run their A/C and express elevator systems. It seems they can generate power cheaper than Con-ed's rates which fluxuate to sometimes peak over .25 Kwh during the hotter days.
 
Re: Co-generation

As a utility we have several large combined cycle natral gas power plants. One of them is placed near a few food processing plants and sells steam. I know we worked with a shipyard recently and they were thinking of making a co gen plant but it proved un economical because their steam source was too low pressure. As for a new install I have never been involved in 1. However, I could see it being economical because most power prices are mostly set by natral gas prices.

[ September 09, 2005, 08:06 PM: Message edited by: MJJBEE ]
 
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