hydrogen cooling system

8/3/2019 Hydrogen Cooling System

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I want to know how a hydrogen coolingsystem for GE frame6 generator works.Anyone who can provide me drawing or a

brief tutorial will be helping me.

And my email address is seshu_inst [at] yahoo.co.in,Reply to this post...

The concepts of a hydrogen-cooled generator are very simple. As current flows in aconductor, heat is generated. A generator has a lot of conductors and a lot of currentflowing through the conductors, generating a lot of heat. If that heat isn't "removed"then the windings will be damaged (insulation "blisters"; conductors grow and elongatecausing clearance and balance issues; etc.). In addition, in a synchronous generator(alternator), there are high currents flowing in the rotor windings, which also generatesheat which must be "removed".

Air can be used to cool a generator, by circulating it through the generator to absorbheat and then exhausting the air to another area outside the generator. A continuousflow of air from outside the generator, through the generator, to another area outsidethe generator will cool the generator and rotor. (The presumption is that the airentering the generator is cooler than the generator.)

Another way to cool the generator is to use hydrogen gas circulated through thegenerator and around the rotor to cool things. Hydrogen is seven to ten timesbetter at transferring heat than air. This means that for the same size generator, ifit's cooled with hydrogen versus air that more current can flow in the stator and rotorwindings which means that more power can be produced. Or,

Thinking about it a little differently, the same about of power can be produced with asmaller generator cooled with hydrogen than one cooled with air, which is the typicalreason for using hydrogen cooling--to reduce the physical size (and cost) of thegenerator.

The "problem" with using hydrogen as a cooling medium is that it's explosivewhen mixed with air and exposed to an ignition source. However, if the purity ofthe hydrogen is maintained at a very high level, meaning there is very little or noair in the generator casing to mix with the hydrogen, then even if there was a "spark"there won't be an explosion.

So, to use hydrogen to cool a generator it's necessary to prevent air from
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contaminating the high-purity hydrogen used to fill the generator casing after displacingthe air. And that's important, displacing as much of the air inside the generator casingbefore filling it with high-purity hydrogen.

The hydrogen gas inside the generator is usually at a pressure of approximately

2 barg (30 psig), which means that air cannot leak "into" the generator casingwhere the hydrogen is. In effect, this is the primary method of preventing air fromgetting into the casing and contaminating the hydrogen.

The hydrogen is circulated by fans on the ends of the generator rotor, and asit's circulated around the generator it passes over coolers which have watercirculating through them. The heat which is absorbed by the hydrogen gas as itpasses through the generator and around the rotor is transferred to the water in thecooler. As the hydrogen exits the coolers, it's recirculated back to the generator androtor, in a continuous cycle.

Another important consideration is to keep the hydrogen from leaking out ofthe generator, mixing with air and causing an explosion- or fire hazard where it mightleak out of the generator.

The generator rotor rotates where it passes through the end-shields and that is thearea that must be sealed to keep the hydrogen in and not allow it to leak out. Ahydrogen-cooled generator uses "seals" to keep the hydrogen gas inside the generator.

The hydrogen seals are on the two shaft "ends" that pass through the generator end-shields. Oil is typically used as the sealing medium, and is sprayed on the

shaft around the entire circumference of the shaft. The "seal oil" is at a higherpressure than the hydrogen inside the generator casing. Some of the seal oil flowsout of the seal area along the shaft to the "air" side of the generator andsome of the oil flows out of the seal area along the shaft into the "hydrogen"side of the generator.

The oil that's used as the seal oil is generally the same lubricating oil that's used for thebearings.

That oil is normally in contact with airwhen it's in the lube oil tankand thebearing drains. So, air (in the form of small bubbles) can be entrained in the lube oil,

and when sprayed on the generator shaft that air can be liberated from the oil thatflows into the hydrogen side of the seal area. That air, if not "removed" somehow,can continue to collect inside the generator casing and reduce the purity ofthe hydrogen, and cause a safety concern.

So, because the hydrogen inside the generator casing is at a higher pressure thanoutside the generator casing, air can't leak into the generator. And, because oil, which


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will have entrained air in it, is used as the sealing medium, the air released from the"seal oil" that flows into the hydrogen area can reduce the hydrogen purity if notremoved. So, the primary source of air to reduce hydrogen purity (contaminate thehydrogen gas inside the generator) is air liberated from the oil used to keep thehydrogen inside the generator from leaking out along the shaft.

So, there is a system to remove the air which is liberated from the seal oilthat flows into the hydrogen side of the generator seal. That system is

typically called a "scavenging" system.A small amount of gas is allowed tobe vented from the seal oil enlargement tank, where the entrained airliberated from the seal oil is hopefully contained. That vent is normallypiped to a safe area of the atmosphere away from any ignition source sinceit will have hydrogen gas in it as well as air.

Because a small amount of gas (air and hydrogen) is continually being vented to

atmosphere through the scavenging system, the pressure inside the generator would

decrease if nothing else were done. However, there is a pressure regulator from asource of high-purity hydrogen that maintains the pressure by flowing asmall amount of high-purity hydrogen into the generator casing to maintainthe pressure.

There is usually a hydrogen purity monitoring system which can be used to detectchanges in purity during operation. Again, the presumption is that the hydrogen purityis high to begin with (after the generator casing is purged of air and filled ("charged")with hydrogen). But because of the air which can be liberated from the oil used as thesealing medium to keep the hydrogen from leaking out of the generator, it is necessaryto have a means of monitoring the purity, usually at multiple points in the generator, tobe sure that the purity is maintained to prevent a possible explosion or fire.

The scavenging flow rates must also be set and monitored to prevent excessivehydrogen consumption (to replace the hydrogen lost with the air that's being vented toatmosphere).

The seal oil that flows into the hydrogen side of the seal area is usually directed to anarea called and "enlargement tank" and that's where it's hoped the entrained air is

liberated and "contained", and vents from the enlargement tanks are directed throughcalibrated flow-meters to atmosphere (the scavenging system). The hydrogen puritymonitors are usually capable of monitoring the purity of the gas in the top of theenlargement tanks that's vented through the scavenging system.

The hydrogen purity monitor can also be set to monitor the purity inside the casing(which should be higher than the enlargement tanks, theoretically).


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Usually, when the hydrogen purity monitor indicates the purity is decreasing, then itincreases the scavenging flow-rate to try to increase the purity, but venting more"contaminated" gas to atmosphere and replacing it with high-purity hydrogen.

If the hydrogen purity drops below a certain level (around 80% or so, depending on

manufacturers' recommendations), then usually the generator and prime mover arestopped and then the generator is purged of hydrogen. (CO2 is usually used as themedium for purging air from the generator when filling with hydrogen, and also whenpurging the hydrogen from the generator.)

Presuming the hydrogen being used to maintain the pressure while scavenging is highpurity, and because the casing pressure is usually two barg, the most likely way thatpurity can be decreased is from the air entrained in the seal oil. If the seal oil flow-rates (usually monitored with a single (unfortunately) flow meter) increase, then theair liberated from the seal oil will increase and that is the primary source ofcontamination and decreased purity. (This presumes that the purity monitors areworking correctly.) So, it's very, very important to monitor seal oil flow-rates to detectan increase which would usually result in a decrease in purity. But, with only a singleseal oil flow-rate meter for seals at two ends of the generator, it's difficult to detectwhich seal is degrading and consuming more oil which is liberating more air (but thedecreased purity in a particular enlargement tank is the key ).

That should be enough of a description for a newbie or novice. If you have specificquestions, we'll try to help. If you're working at a site with a hydrogen-cooledgenerator, you should be able to find the seal oil piping schematic (P&ID) which shouldbe helpful in understanding the seal oil system. If the generator was manufactured by

GE, it will usually have some drawings in the Instruction Manuals that are very helpfulin understanding the systems in use on the generator at the site (though most are verysimilar, there can be subtle, but important, differences).Reply to this post...

Posted byDEV on 26 February, 2010 - 4:33 am

Hai,

I read your message and simply superb. I am having small doubt that "What are thebasic reasons for improvement of seal oil flow of the generator to maintain the same DPacross the seal oil and the Hydrogen in side the Generator"

Please help me..ByReply to this post...
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Posted byCSA on 26 February, 2010 - 10:17 am

DEV,

Sir, I sincerely hope you do not have a doubt. You have a question.

Oxford English Dictionary defines doubt as a feeling of distrust or disbelief; to questionthe truth of.

Nothing we say here is intended to mislead anyone. And it's perfectly acceptable inpolite company to say, "I have a question", or, "I would like moreclarification." But, to express doubt is to express distrust or disbelief.

I will answer the questionof what would increase seal oil flow rates, and that isthat the "seal" is actually a brass ring with an inner diameter slightly larger than theouter diameter of the alternator rotor. It is held tightly around the shaft withsprings. Oil is admitted through ports and grooves in the seal rings and "sprayed"onto the shaft.

The brass rings and holding springs can wear or even fail over time. Dirty oil can alsocause wear of the seal rings. The generator rotor shaft, as all shafts in journal bearing,moves as it is accelerated and even axially with the application of torque and electricalforces (though axial movement is generally very small, as is the radial movement).Unattended high vibrations of the generator shaft can also cause problems, as caninduced voltages that are not properly grounded (through the shaft grounding brush).

Also, the seal oil pressure regulators do require maintenance and adjustment and canbe the source if increased seal oil flow rates.

We are happy to answer questions here at control.com. I imagine on occasion somequestionable information is provided but never intentionally. The form of your questionsuggested it was not caused by any doubt, rather that you sought further informationand clarification. Which we are happy to provide when asked, but not so happy toprovide when requested by expressing doubt.Reply to this post...

Posted byDEV on 26 February, 2010 - 3:44 pm

Hai,

I got useful information from you technically as well as personally.
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ThanksReply to this post...

Posted by csa on 26 February, 2010 - 6:39 am

A lot of thanks for your information sir. I got a great information.Reply to this post...

Posted by Luis Phillippe on 8 June, 2010 - 3:13 am

Depending on the price for H2 bottles, the process will be costly and you have a good

opportunity to improve it.

Could you approach any solution for the H2 purity decreased ? Like using a vacuumtreatment for the seal oil...

In other hand, instead of solving the main problem, installing a H2 generator connectedto the H2 supply line would be a feasible solution. Do you have any experience with thiskind of system?

Cheers

Reply to this post...

Posted byCSA on 8 June, 2010 - 12:01 pm

The problem with having a separate seal oil system is that at some point the seal oiland some of the bearing lube oil will eventually mix, and so I believe that's why thesame medium (lube oil) is used for both bearing- and seal oil. Treating a portion of thelube oil is going to be costly and difficult, at best.

Decreasing H2 purity is primarily a function of seal oil flow rate, and it can be affectedby moisture in the H2 and from leakage from the cooling water used in the H2 coolers.There are dryers and desiccants used to help remove moisture but a lot of machinesdon't have the dryers and only very small desiccant dryers which are rarely, if ever,properly maintained. Also, oil in the belly of the generator (from improperly chargingmethods and internal leaks) can also cause H2 contamination.

One has to remember: The casing is usually maintained at approximately 2 barg, or at
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some pressure above atmospheric. So, air can't leak "into" the generator; H2 can onlyleak out. So, the only real source of air is from the lube oil used as the seal oil medium.Presuming the purity monitors don't drift (and that's NOT a given with the old manualWheatstone bridge used in many H2-cooled generator purity monitoring systems) aboutthe only source of air is what's liberated from the seal oil.

Most H2 usage comes not from the scavenging replacement, but from leaks--leaks ofH2 out of the generator casing that cause the pressure to decrease. Actually, thisshould help increase the H2 purity because of the higher replenishment rate due to theleakage, because, again, air cannot leak into the generator.

There are many sites around the world which have opted for on-site H2 generation. Itjust adds another system to be operated, monitored, and maintained. And in myexperience, they were never operated or maintained properly and so most of themwere soon shut down and bottled H2 was used for the generators.Reply to this post...

Posted by David on 12 June, 2010 - 2:55 pm

Great submission ....thanks.

A question: What can be the possible causes for excessive H2 entrained in the seal oildrain to the enlargement tanks?Reply to this post...

Posted byCSA on 13 June, 2010 - 12:11 am

Failing hydrogen seals; improperly installed hydrogen seals; failing or broken hydrogenseal springs; excessive Seal Oil pressure are the usual culprits. Dirt/debris has also beenknown to get into the seals and cause problems, usually the brass rings get scored andsometimes the shaft, also. This is an extreme case, but has happened.


Posted bybhola on 29 June, 2010 - 12:52 am

thanks a lot sir,

it is really very helpful for me. sir i have one question, what is the function of liquid
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level detector (i am fresher in CCPP and working in the Maintence side, ours is ge 9famachine)? is this any how related with float trap assembly).

thanks in advance.Reply to this post...

Posted byCSA on 29 June, 2010 - 7:27 pm

A liquid level detector is for detecting any liquid in the generator casing.

There shouldn't be any liquid in the generator casing under normal operatingconditions.

Sources of liquid could be leaking hydrogen coolers and excessive seal oil flows.

Please find the Generator Hydrogen System P&ID drawing. Also, if you have a unitpackaged by GE you should have a section in the Instruction Manuals that describes, invery brief detail, how the system works. It's not much, but it's better than nothing.

Learn to use the available documentation at your site. We can fill in gaps and detailshere at control.com.Reply to this post...

Posted by Jeff on 29 April, 2011 - 4:26 pm

Very interesting information. Any chance you know (or can point me in the rightdirection) to learn about how much power the whole cooling system draws? That is,how much recirculating power is there?

Thanks.

> The concepts of a hydrogen-cooled generator are very simple. As current> flows in a conductor, heat is generated. A generator has a lot of conductors and a lot

of current flowing through the>conductors, generating a lot of heat.

---- snip ----Reply to this post...
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Posted by Maroun Slaiby on 1 September, 2011 - 8:27 am

Hello my Name Is Maroun and i am planning to an invention of Hydrogeen coolingsystem for House kitchens, any tips on that? I am not that experienced in that Field but

just have the Idea to develop. Thank youReply to this post...

Posted byRetired on 13 June, 2010 - 2:34 pm

I have a PowerPoint presentation I can send you but I do not know how to addattachments to the site, Do you know?


Posted bypeg ferraro on 13 June, 2010 - 5:43 pm

Hi,

Your friendly local moderator here. The forum does not do attachments. People canpost and include their email addresses and ask for the PowerPoint presentation; we willpost the messages to the list.

Regards,Peg FerraroReply to this post...

Posted by Paragkumar on 14 June, 2010 - 2:01 am

Dear CSA,

Can we use nitrogen instead carbon dioxide to purge the hydrogen? as bothnitrogen & carbon dioxide are inert gas, but the density of CO2 is higher thanthe nitrogen. but nitrogen is still heavier than hydrogen.

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Posted byCSA on 14 June, 2010 - 10:07 am

People have tried it before with very mixed results. It depends on several factors, first,the patience of the people purging and charging the generator (which is usually not

very good, and neither is that of management waiting for the purge and charge to becompleted).

Second, the instrumentation available. Usually one of the meters is set to read CO2 inAir, or something similar, so I believe it's not really expecting anyinert gas.

Third, I think it's particularly difficult to purge the casing of air with nitrogen beforecharging it with hydrogen.

In my personal opinion, purging and charging (regardless of the gases andinstrumentation used/available) needs to be done slowly if for no other reason than to

reduce the mixing of gases during the processes. Slow and steady wins this "race": therace to purge the casing of one gas as completely as possible and then fill it withanother as quickly as possible with the highest purity possible. Leaving any air in thegenerator casing when charging, whether CO2 or nitrogen was used for purging, is notdesirable.

A lot of people ask why the purity goes down during initial operation after apurge/charge, and it's likely because of two things. First, the scavenging rates need tobe adjusted, and second, because it's likely that the purge and charge wasn't aseffective as believed because of the rush to complete it. So, it usually takes a little more

scavenging to get the purity up, and then it can be adjusted lower.

That's the part that most people don't understand about scavenging: It's b>NOT 'set-it-and-forget-it.' It needs to be adjusted over time to maintain purity, and ANYadjustment needs to be logged for tracking and trending purposes which can be veryuseful when trying to determine if hydrogen usage becomes excessive. And adjustmentcan be to decrease scavenging as well as to increase it. Remember: The adjustmentsare made to maintain purity. And any adjustment is probably going to take severalhours to seen any effect; it's not immediate.

So, patience is the key.

But, to answer your question simply, it's your machine and you're free to try it. It'sbeen done with mixed success, and if you're willing to take the chance and live with theconsequences, then it would seem to be feasible. But, then, a lot of things look easy"on paper", don't they?Reply to this post...
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Posted by chaitu on 30 June, 2010 - 7:29 pm

Hi Mr.Retired

can u send the presentation to me. my mail address is

chaitu4u_k [at] yahoo.com.

tyReply to this post...

Posted by Bud on 30 June, 2010 - 9:18 pm

Honeywell has made a thermal conductivity analyzer for hydrogen cooledgenerators for decades. The thermal conductivity cell has not changed since the 1970's.

The electronics box is known as a Triple Range Analyzerbecause it providesconcentration readings for running and purge cycles.Range 1: 0 to 100 % CO2 in AirRange 2: 0 to 100 % H2 in CO2Range 3: 0 to 100 % H2 in Air

The electronics that determine the concentration from the thermal conductivity on-linecell raw data definitely expect H2, CO2 or air. not nitrogen in place of CO2. That doesn'tNitrogen can't be used, but any thermal conductivity analyzer expecting CO2 willread wrong when used with nitrogen.Reply to this post...

Posted by Ghassan Sleiman on 3 December, 2010 - 12:54 am

This is a great thread. Does anyone have any data on the effect of hydrogen purity of

the Generator. What would be loss of efficiency of a Generator if the purity of H2begins to decrease.

On another note. I have worked on many station in the middle east where they have onsite Generation. What I found was that if you select the right Company, you can makeyour own hydrogen for years and years. But there are many more failed On-site
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Generation Companies. Make sure you select the right one. There are only 3 that cometo mind.Reply to this post...

Posted by uma_799 on 7 May, 2011 - 7:14 am

Why the amount of CO2 required for replacing air & hydrogen is different. I readsomewhere that less amount is required to purge air from generator casing. Cananybody help me?Reply to this post...

Posted by al on 6 December, 2010 - 1:56 pm

> I have a PowerPoint presentation I can send you but I do not know how to addattachments to the site, Do you know? > I have a PowerPoint presentation I can send you but I do not know how to addattachments to the site, Do you know?


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Posted by sardar9 on 29 April, 2011 - 11:48 pm

> I have a PowerPoint presentation I can send you but I do not know how to add> attachments to the site, Do you know?

Hello!!

Can you send me this presentation please. My e mail address issim_4144[at]yahoo[dot]com

Thanks in advanceReply to this post...

Posted byDave Wolff on 30 April, 2011 - 9:20 am

>> I have a PowerPoint presentation I>can send you but I do not know how to>add>> attachments to the site, Do you>know?

>

I would be very appreciative of a copy of the presentation on hydrogen cooling. My e-mail is dave(dot)wolff(at)protonenergy.comReply to this post...

Posted by Phil Corso on 7 May, 2011 - 2:08 pm

Uma...I suggest you go to ABB's website.

Regards, Phil CorsoReply to this post...

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> I have a PowerPoint presentation I can send you but I do not know how to add> attachments to the site, Do you know?

Hello !!! May I request your power point presentation. My e mailsim_4144[at]yahoo[dot]com

Thank for your timeReply to this post...

Posted by heyram on 21 July, 2011 - 4:37 pm

> I have a PowerPoint presentation I can send you

Dear Sir,

I would like to have your power point presentation. Would you kindly send me powerpoint file to my email add: [email protected] to this post...

Posted by sardar9 on 21 July, 2011 - 8:58 pm

> I have a PowerPoint presentation I can send you but I do not know how to add

attachments to the site, Do you know?

Hi Mr retired,

please send me power point attachment for H2 cooling, I really appreciate that. My email is sim_4144[at]yahoo[dot]comReply to this post...

Posted by sardar9 on 2 August, 2011 - 11:43 pm

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Thanks. My e mail:[email protected] to this post...

Posted bysavage42 on 10 August, 2011 - 5:15 am

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