Help On Lowering Suction Air Temperature

[TommyPhan]

Hello All,

New member here, but creeped the site for some time now. Thought I'd post a problem that I'm currently facing at work on two gas engines we have. We have two twin turbo V-20 natural gas engines that are coupled to generators to generate electricity for the site. The problem we see during the summer is high suction air temperature that causes the engine to de-rate 15%. Engine intake is exposed to atmosphere and although it's under a metal roof with shade, outside temperatures get very hot with the humidity (South West Louisiana and the current heat index outside is 102F). This de-rating by 15% requires us to pull from the electrical grid the electricity we aren't generating and can become costly.

There is an intercooler after the turbochargers and it does it's job, but it is still no match for the heat outside. I've thought of having a air/water heat exchanger prior to the intake duct, but am afraid of a tube failure and having water in the intake.

Have any of you dealt with this issue in the past?

Thank you,
Tommy Phan

 

[BrianPetersen]

How does engine air intake temperature compare to outside air temperature? If your engine air intake is in the coolest place you can find, there's not much more you can do for the turbo compressor air intake temperature.

For your intercooler, what are the temperatures on the high-pressure side going in and out of the intercooler?

 

[Lou Scannon]

Maybe your intercooler is fouled. Something to check, anyway. Did the engine manufacturer supply instructions for cleaning the intercooler?

Also, have you done a health check on the turbos, air filters, and the engine generally?

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[dicer]

For stationary installs like gen sets, you could use a much larger intercooler, and use an independent cooler or chiller to supply the intercoolers coolant.

 

[catserveng]

I've worked on several installations of large gas engines in high ambient conditions, frankly I wouldn't consider your conditions extreme. I guess the first best question to ask is if a cooling system audit was performed per the manufacturers recommendation to make sure the engine would perform as expected in those conditions?

Was the unit properly sized? Many customers will purchase a unit rating assuming that the hottest part of the year really isn't that long and they can get by.

Most newer gas engines are using two stage aftercoolers, first stage uses jacket water (or HT circuit as called some suppliers)and the second stage uses an aftercooler (or LT) circuit sized to meet the inlet manifold temperature specs for the unit.

What does your dealer have to say? Have you discussed this with them?

Determining what the real problem is likely would require a considerable amount of time to review the entire system, but some additional questions are,

How old is the unit, in years and in operating hours?

What are the actual temperatures? How are you measuring them?

What is generating the derate, the on board engine controls or some other system control?

Are you having any other performance issues, such as high emissions, detonation, instability, etc?

Some more specific information may get you some better answers.

MikeL.

 

[MikeHalloran]

Put a water/water HX in the engine cooling water circuit before it reaches the intercoolers, and pump swamp water through it, to cool the intercoolers a bit more.
Also, as mentioned, do clean the air side of the intercoolers once in a while.

And while you're at it, clean the dust and bugs out of the air side of the engine radiator and make sure the fan is moving air through it as designed.




Mike Halloran
Pembroke Pines, FL, USA

 

[TommyPhan]

Thank you all for pitching in.

Brian, the suction is unfortunately at the best place in that area. It's under an insulated roof with open sides for cross breeze. I don't have a way of measuring the pressure before and after the intercooler, unfortunately. The engine manufacturer did not give us that measurement.

Hemi, we know that this isn't due to fouling because the issue started the very first summer we oeprated these engines. I'm thinking that this is a design issue since these engines are the very first ones in North America. Original manufacturer is in Europe and their largest customer base is in Spain, much different climate.

Dicer, a larger intercooler is a good solution but right now I'm searching for lower cost options that can supplement the current design.

Cat, I'm not sure if the unit was designed properly, but my guess right now is that it's not. I've spoken with this to the manufacturer and they are looking into possible solutions. The unit is 5 years old 30,000 hours, but the problem started the first year's summer. Temperatures are measured with thermocouples and the derate is triggered by the engine's process logic controls. No other issues, other than high inlet air temperatures.

Mike, currently we are using filtered, softened, swamp water to cool the intercooler. After that it goes 3 large fin fans that is part of a closed loop system. Only concern I have with cooling down the intercooler even more is introducing more condensate into the air header. We are constantly spewing out condendate at the end of the header through a small tube.

We've looked at renting air chillers to shoot straight into the intake, but we were quoted ~$20K a month flat fee. I appreciate all of the input; this site has been very helpful.

Thanks,
Tommy

 

[MikeHalloran]

How about posting some photos of the installation?


Mike Halloran
Pembroke Pines, FL, USA

 

[gruntguru]

A few items.
1. Are the engines lean-burn or stoichiometric?
2. Is the de-rate triggered by intake temp or charge air temp?
3. It is probably worth the effort to instrument at least one engine yourself. Drill and tap as necessary to get pressure and temp pre and post turbo compressor.
4. I assume you have high ambient humidity. This is unhelpful for reducing CAT (cooling towers won't help much) but should be helpful for detonation control. The mfr has probably not considered this factor when de-rating.

je suis charlie

 

[Panther140]

Get a meth injection kit and have your PLC trigger it when IAT goes above your specified temp.

Low cost or ideal. Pick.

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

 

[EdStainless]

First, I suspect that the system is sized wrong. If you told the supplier where you are located then he either didn't bother to look up climatic data or decided to cheat on the rating.
Second, this is a huge issue with large turbine power plants. In humid locals where spray can't be used for cooling most of them actually have absorption chiller systems. They use waste heat from the engines for the hot side, and the evaporators are used to cool the inlet air. Sometimes they even spray cold water into it after that.

http://www.turbineinletcooling.org/intro.html

google this gas turbine inlet chilling

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P.E. Metallurgy, Plymouth Tube

 

[dicer]

I agree with Panther 140, and also add water spray to spray over the intercoolers, cheaper that renting a chiller.

 

[gruntguru]

"add water spray to spray over the intercoolers, cheaper that renting a chiller."

Won't help if local humidity is high.

je suis charlie

 

[TommyPhan]

Here is a link with a picture of the engine I'm dealing with. We have two of these.

http://www.ngvjournal.com/rolls-royce-lng-powered-engines-achieve-25-million-operating-hours/

Grunt, the engines are lean burned and the derating is triggered by charge air temperature. In the picture, the intercooler is bolted onto the block and behind a bunch of insulation. We have measurements before the intercooler, but drilling taps afterwards doesn't seem possible since there isn't really piping after the intercooler. From the intercooler, the air is dispersed through cavities in the block to the cylinders. And yes, the humidity here is ridiculous. Some days you can feel the water in the air.

Panther, the meth injection seems like a cool idea, but these engines consume A LOT of air and they derate for 8 hours + a day. I don't know how much the meth injection costs are, but I can assume that's a lot over a summer's course.

Ed, we also have a turbine that I looked into getting forced chilled air. The cost was too high and the payback period was not low enough. I will assume they will same the same for these engines.

Thank you all for your help, these are all very interesting ideas.

Tommy

 

[dgallup]

We buy methanol at a local speed shop for about $5/gallon. I'm sure it's much cheaper by the barrel.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[Panther140]

You can use a water/meth combination. Find the best ratio of water:meth through testing. I'm not sure at what rate, duty cycle, or frequency you would need to spray.

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

 

[burningDiesel]

What is the increase in charge air temperature? 15% derating is high. 102F is not that high, so it seems mostly to be a cooling issue because of the high humidity?
If your engine has knock protection and you can follow up on everything, I'd just derate less (depending on charge air temp, ~ 5% per 10° over the nominal).

The rest is speculation and depends on your running conditions:

Lower/change the thermostat on the cooling circuit (check if the oil cooling is also on this circuit and if it is thermostatically controlled or not), or use an external electric pump with higher flow rate to pump more water through the engine. If you can cool this water of course.
Make sure your cooler isn't running full of water, if it has a drain hole, make it bigger.
Water droplets can have bad effects on the combustion chamber component lifetime, does the cooler have a watermist catcher?

If all else fails, if you have the space and capabilities, change the air ducts from after the turbocharger to the biggest air cooler you can find, and back to the engine and remove the cooler in the engine.

 

[EdStainless]

Tommy, the payback for a chiller system depends on how many hours you fall short of power and what the replacement power (or lost output) is costing you. Most of the cases that I have seen had payback that was less than 2 years. In many cases people realized that there were other uses for the chillers when they didn't need inlet chilling.

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P.E. Metallurgy, Plymouth Tube

 

[Panther140]

Where is your intercooler located? What are the ambient temps usually at where the intercooler is? What is the airflow like?

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

 

[utkuselamoglu]

you can tune your engines for better efficiency without overheating your engine.