Selection of Air or H2 for Generator

A

Thread Starter

Ayed

What is the comparison between hydrogen cold and air cold generator? Looking for which is better for Gas Turbine frame 7 E 60MW.
We need the advantages/ disadvantages between Generator air cold and generator H2 cold.

Thanks

<b>Moderator's Note:</b> Think he may mean air cooled, but not sure.
 
Ayed,

Air or hydrogen?

Hydrogen or air?

For a LOT of equipment the choice was dictated by environment/atmospheres on the site. For example, dust and or fine sand; H2S (hydrogen sulfide); high humidity; etc.

Another factor is the availability of space for the generator and the space required for rotor removal. The size of comparably rated air-cooled and hydrogen-cooled generators can be very different. In general, hydrogen-cooled generators of a particular rating are smaller, in some cases much smaller (25-40%, by volume, as well as length).

Air cooling can be done with or without water-to-air heat exchangers to cool the air being circulated inside the generator casing. There are totally-enclosed, water-to-air (TEWAC) air-cooled generators--but they require cooling water--as do hydrogen-cooled generators.

If using ambient air to cool the generator, the high ambient temperatures in some parts of the world may, at times, limit the generation capability because of the inability to cool the generator sufficiently per the capability- or D-curve for the generator.

If using ambient air to cool the generator, filtration is necessary. And if the ambient is or is at times humid that can be a problem with filter effectiveness as well as contributing to dust/dirt accumulation on generator internals. (No filtration system removes all entrained dust/dirt, and there can be leaks if filters are not properly installed or rupture.)

Hydrogen-cooled generators require a source of cooling water, as well as a source of seal oil (usually lube oil). They also requires constant pressurization to maintain pressure and purity, and a scavenging system to monitor and maintain purity. And a source of gas (usually CO2) to purge the generator during emergency and prior to charging with hydrogen.

Purging and charging require time and patience; with an air-cooled generator that's not required. (Purging and charging and maintaining hydrogen purity also require training and procedures--something in seriously short supply at most power plants these days.) Excessive gas consumption can occur if purging/charging is done too quickly or without following proper procedures.

Hydrogen-cooled generators aren't affected by ambient contaminants (dust/dirt or corrosive or explosive gases).

There is more piping associated with hydrogen-cooled generators (Seal Oil; Lube Oil; hydrogen; CO2; hydrogen vent piping).

If it were my choice, I'd choose an air-cooled generator if possible. A TEWAC, specifically. No need for air filtration, nor seal oil, nor hydrogen nor CO2, less complicated piping, less time to return to service after an outage (no need to purge/charge), less training and procedures.

Hope this helps. The opinions expressed are those of the author.
 
Dear

We have both generators types in our gas turbines. We reached to this decision of selection because of all the hydrogen generators due for rewinding. Our plant has all requirements such as sealing, cooling water and hydrogen plant as well. But for safety concerns we decided to study which type of generator we do select?

We did not have any problem for the hydrogen generator during operation since 1983. All the parameters were maintained even the availability of hydrogen generators.

The thing that lead us for the selection is from safety point of. From my opinion both types of generators are technically accepted.
We need more comparisons between them. I think that the hydrogen generator is compatible for the unit which has more than 100 MW.

Best regards
 
Dear,

Safety.

So, what are your safety concerns, specifically?

Because producing, storing and distributing hydrogen seems pretty risky, not to mention the risk of leaks into a hot Load Compartment or a collector where there have been known to be a spark or three. And the amount of energy required to ignite an explosive concentration of hydrogen in air is very small.

Because when an air-cooled generator doesn't have any of those risks, where's the question?

Inquiring minds want to know--where's the safety risk between air and hydrogen? Unless there's something in the air at your site that you haven't told us about that would make using air to cool the generator unsafe, like say hydrocarbon fumes, or corrosive gas(es)?

What other safety concerns do you have?
 
The advantages of H2 cooling; "Hydrogen has many advantages over air including high heat capacity and very low viscosity. Hydrogen cooled generators also have less windage/friction loss than air-cooled generators. Windage, which is caused by friction between the hydrogen and the rotor, can account for 30-40 percent loss in the efficiency of a generator."

If the H2 purity is kept high; well above the explosive limit it is not a safety issue.
 
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