Boosting Gas Turbine Power Output 4

[EmmanuelTop]

Good evening to forum members,

I am looking for some guidelines on expanding gas turbine power output. Any useful information is appreciated, especially if it comes based on first-hand experience(s).

Since the turbine inlet temperature is a limiting factor in all gas turbines, there are several systems developed long time ago with the purpose to lower the air inlet temperature: evaporative coolers, fogger systems, inlet air chillers, and so-called "wet compression" (injection of water mist into axial compressor suction).

The plant where I am based is area of high humidity (>95%) where evaporative cooling simply doesn't work. Budgetary proposal for air chilling system is one with the sky-high cost, so it has been eliminated after cost-benefit analysis. The only thing which remains is wet comression, but I've heard from Mechanical guys this system is as bad as it is cheap - it usually ends up with rotor damage. That's at least what these guys are saying, I don't have any experience with wet compression systems.

I was also thinking about the possibility of replacing the existing turbines with aero-derivative type of turbines (higher efficiency), but these machines we have here are so big (hundreds of megawatts) that I doubt this can be a good solution for boosting power output to refrigerant compressors.

Any hints on this topic?

 

[rmw]

If you are in a high humidity area chilling is your best option. If the cost benefit ratio isn't there, then you are just stuck. I am with your mechanical guys about wet compression. It is done and it works, but I think the cost/benefit ratio if you have to replace a compressor section is something you have to think about.

Is your humidity still high when your power demand peaks? In the part of the world where I live, the humidity is high but on those hot summer days when the power peak is at its highest, the humidity falls off in the heat of the afternoon so that at least fogging works.

rmw

 

[EmmanuelTop]

Hi RMW,

I am based in West Africa, Bioko island. The humidity is high all-year-round, we just can't do much about it.

What about propane cooling/evaporation coils inside the axial compressor? Is there any possibility to inject something else apart from water? I guess light hydrocarbon liquids are eliminated due to explosive mixture hazards?

There are some other inlet air cooling systems, however I don't know anyone with hands-on experience with these units.

Thanks,

 

[ApC2Kp]

EmmanuelTop,

There are gas fired turbines that serve as the topping cycle of a more conventional steam turbine system. The exhaust heat of the gas turbine is used in a heat recovery steam generator (HRSG) to power the steam turbine. There is significant capital involved.

The benefits of the steam turbine could be considered in several ways. First, the steam turbine could run a generator for a refrigeration system to chill the inlet air of the gas turbine, or 2) the steam turbine could drive another (refrigerant) compressor. 3) surplus electric power could be used/sold to the Bioko Island electric power grid?

The steam from HRSG could be used in a steam jet vacuum chiller system that could provide 40 deg F chilled water, without the capital for a steam turbine / refrigeration system. The condensed water from the steam jet vacuum condenser system might be run as part of a water distillation operation?

 

[ApC2Kp]

EmmanuelTop,

One further followup to the possibility of refrigeration for inlet air cooling - Was the proposal and costs for a refrigeration system based on mechanical compression cycle or an ammonia absorption chiller? There are ammonia absorption chillers run with waste low pressure steam - the gas turbine exhaust would be much hotter and probably need some dilution air to bring it within range of the ammonia absorption chiller equipment. The capital cost would still be significant but the operating costs likely much lower. The other consideration for an inlet air chiller would be the storage of ice for the cooling of inlet air only during the peak power intervals or peak air temperature intervals. The size of the chiller system would be optimized to make ice during the off-peak intervals (night time).

 

[GTstartup]

what type/manufacturer? Some of the manufacturers have upgrades (compressor, turbine etc) that can improve output by as much as 10%.

 

[tgmcg]

Steam injection for power augmentation is another possibility. Utilizes a HRSG to generate steam for injection into the combustor. The increased mass flow results in increased power output. Will also lower NOx, which may or may not be an issue in West Africa.

There may also be metallurgical upgrades to the hot end, including coatings that may allow higher firing temperatures.

Does the fuel contain any sulfur?

Best regards,

Tom McGuinness, PE
Turbosystems Engineering

http://www.turbosynthesis.com

 

[zuccus]

Chilling the air inlet will be the best bet, however if you aren't getting paid for the extra capacity, it is hard to justify. There are a couple of options to help keep your capitol and operating cost lower, such as TES tanks and/or not chilling all the way down to the best inlet air temperature.

ApC2Kp gave you some good options too, but I bet chilling is the best $/mw value.

Have you gotten (recent) bids from the major inlet chilling manufactures?

Just to be fair to the original poster, I might work for one of them.

 

[EmmanuelTop]

Thanks to all of you for your inputs. One of the options considered is coating of turbine internals, allowing for higher firing temperatures. Do you have any first-hand experience with this subject?

I did a little research on the topic, and I found - at least according to those references - that high pressure fogging (as suggested by RMW) could be an option regardless of high humidity, particularly in those areas where high ambient temperatures between 11AM-4PM do not coincide with high humidities. Just as an illustration, we experience 95% humidity in early hours when ambient temperature is below 27C (design T for turbines), while humidity drops to 75-80% during hottest hours, between 11AM and 4PM, when ambient temperature reaches 32-33C. This results in approx. 6C difference between the wet bulb and the dry bulb temperature. Is this sufficient for high-pressure fogging application, taking into account some average system efficiencies?

In addition, there is something called "supercharging" = installing a fan upstream of air intake system and raising inlet air pressure for 40-80 inches H2O, thereby increasing mass flow. Is someone familiar with this application?

I think inlet air chilling is out of the game because it is not required 24hrs per day, 365 days per year, and therefore it would be hardly justified - when knowing the price for this system is sky high.

 

[FOURe]

I guess you do not have many options available to help you increase the existing gas turbine power output ...

http://www.engineering-4e.com

 

[VikingUK]

To be honest, chilling the inlet air will not improve efficiency by any great degree. You will spend more than you will gain. If your goal is to increase power you need to upgrade your generators

 

[rmw]

Tell that to the hundreds, and several thereof of combustion turbines out there that have inlet chilling. Those poor chumps; wasted their money. Tisk tisk.

I think you better recheck your facts. You have missed something somewhere.

rmw

 

[ApC2Kp]

VikingUK,

The mis-understanding of the problem that occurs with the combustion turbines and high air temperatures could result in overlooking a number of possible solutions for users like EmmanuelTop. The question is not 'efficiency' but the reduction of output power when the mass flow is reduced by the less dense inlet air flow.

If the inlet of turbine had some adjustment device to allow increased opening for less dense air, then a turbine might be able to then compensate for air density and generate a more uniform output power despite air temperature change. The maximum opening of such an adjustable inlet would need to to be varied so that power output would not exceed the machine's limit before suffering mechanical damage or overspeed.

Inlet air chilling is applied with economic benefit on the many combustion turbine generator sets used in 'peaking' service, during the time intervals when the power produced has a much greater value than the baseline power production. This is not a new technology, as RMW points to its use by hundreds of installations. The September 1992 issue of 'Power Engineering' had a 2 page article titled 'Ice Storage System Boosts CT efficiency' where it was applied to a pair of turbines alrady equipped with evaparative inlet coolers. The use of on-line chilling of inlet air was not justified due to high cost of $400 to $600 per Kw - ca. 1992, its parasitic load on the generator, and peaking application operation. The turbines were GE Frame 7 rated 62.5 Mw, reduced to 53.1 Mw at 100 deg F. The evaporative coolers gave the turbines a rating of 57.8 Mw when ambient air was otherwise 100 deg F. The ice chiller cooled the inlet air to 40 deg F. for 67.1 Mw output from each turbine. Ice would be made for 20 hours per day 23ton/hr and ice melted for 4 hours per day. The refigeration system included a 700 hp compressor in an equipment package costing $2.2M that also included a fuel conversion to natural gas. The result was less than $200/Kw incremental capacity gained. The cost of the ice chiller was small compared to the turbine operating fuel costs.

Vogt Heat Transfer Division used their Vogt ice makers in conjunction with some of their HRSG units installed with gas turbines for projects in the 1990s.

 

[dcasto]

I've done the calculations and you can get a head with propane refrigeration chilling on a turbine inlet air.

 

[rmw]

And, if you get a leak in the chiller coil in the AF housing, you can launch the thing.

rmw

 

[zuccus]

rmw,

I don't believe dcasto is talking about putting propane directly in the coils in the filterhouse.

dcasto,
While propane refrigeration in inlet chilling does make sense, conventional chillers are much more economical and efficienct.

Zuccus

 

[dcasto]

You'd make chilled water and coils in the intake. We seriously looked at this. We had steam condensate spraying on the inlet air system which helped us, but we were either going to add coils or just chill the water spray down to 50 degrees.

 

[VikingUK]

I stand by what I said previously. The cost of chilling (both energy and plant purchase)is not as efficient as upgrading the generator. And I've worked in Malabo on Bioko, Equatorial Guinea so I know how hot it is.