Gas turbine's stabilty

[gaillee]

Hello, Everyone.

We want to build a big methanol production plant based coal.
We want to use an integrated coal gasification combined cycles plant to provide steam and power for this plant,this idea of coproduction of power and chemicals.

But somebody said a gas turbine have to stop for check the combustor and the blades of turbine every month. This will
disturb the stable production of chemicals.

But i find the such concept is very popular now. And ISAB plant in Italy use IGCC to provide steam and power for chemical plant, this plant can output 522MW power and run very well.

So I just want to ask several questions:
1)the longest time of continuous run of gas turbine;
2)how to avoid the disturb to the chemical plant;
3)If the IGCC have to stop very frequently, the concept of coproduction may be not feasible. But this concept of polygeneration is very popular, such as DOE's EECP, some chemical plants. What are their solutions?
4)we extract some high pressure air to the air separation unit for supplying oxygen to the gasifier, if the gas turbine shut down, the gasififer must be down. Then if we want to start the plant, it will last a long time. Can anyone do me a favor that how a igcc plant solve this problem?

 

[tombmech]

Check with the SOLAR turbine division of Caterpillar. They quote 99% uptime or better with their turbines. The power industry, cogeneration applications, and redundant power backup are a major sales focus. High availability is part of the game.

Of course, every machine must have maintenance, but turbines are among the least demanding in that respect with proper planning. If you cannot afford a redundant turbine for zero outages, SOLAR has been known to stock spares with a contracted minimum downtime replacement.

So essentially, it is a concern that should be addressed, but it is also a common guarantee of turbine power generation sales and service.

 

[toothless]

Depends on the particular unit, but I know many can go 18 months or more between outage inspections. I don't know of any, though, that go past 36 months.

Major inspections requiring longer outages occur every 6 years or so.

 

[davefitz]

The large frame gas turbines require a complete rollout-rollin of combustor components about once per year on some macnines, once per 2500 hrs on others. The compressor needs to be on-lined cleaned routinely, but if the compresssor efficiency is dropping due to accumulations of deposits, then an off-line wash may be required. This may be the issue with your plant , espescially since an oversized compressor is used to supply air to the cryo plant. You may need to provide special provisions to prevent particulate matter entering the compressor so as to extend the time between off line washes.

If the cryo plant and gasifier has a turndown abililty , to perhaps 60% load, then supplying 2 x 60% gas turbines may be an answer.

 

[norzul]

Hi Gaillee,

Talking about IGCC (integrated gasification combine cycle), just remember that we did feasibility study several months ago. The objective of the study was to find out whether should we proceed with the IGCC+Cogen or just proceed with the cogen. The result proved that it is not feasibile to proceed with the IGCC at this point of time. Yu can refer to my new technical blog to see the process flow of IGCC and its relationship with Cogen.

http://technical2005.blogspot.com/

Anyway regarding the gas turbine downtime, based on my knowledge there are 4 kinds of inspection required:
1) Boroscope inspection
2) Combustion inspection
3) Hot gas path inspection (HGPI)
4) Major inspection

The frequency/interval of inspections may vary from one machine to another. It also varies according to the manufacturer. Just to share our experience, we evaluated 3 manufacturers for the 25MW gas turbine range.

1) GE/NP - Frame5 (PG 5371PA)
a) Boroscope : annually (1day)
b) Combustion : 12,000 hrs (5days)
c) HGPI : 24,000 hrs (13days)
d) Major : 48,000 hrs (36days)
2) Hitachi - H25
a) Boroscope/Combustion : 16,000 hrs (5days)
b) HGPI : 32,000 hrs (18days)
c) Major : 64,000 hrs (27days)
3) Simens - GT10B
a) Boroscope/Combustion : 10,000 hrs (3days)
b) HGPI : 20,000 hrs (10days)
c) Major : 40,000 hrs (21days)

This is based on the proposal and for 25MW machine, however the more accurate info need to be sourced from the supplier himself.

Thanks

norzul

 

[sshep]

gaillee,
Scheduled downtime is per turbine manufacturer warrentee. If power generation is electrity, multiple package type units are required with extra capacity, or purchased backup utility power. Steam requirements can be supplemented by direct firing the steam generation unit. There is alot of experience readily available to assist in these evaluations.
best wishes,
sshep

 

[tombmech]

Norzul's 25MW turbines are bigger than what I've personally dealt with, yet, his numbers are interesting.

The shortest time interval for maintenance of any of the three listed is 10,000 hours. That still means constant uptime, without interruption of over one year! (24 x 365 = 8760 hours) Even then, the maintenance time required appears proportional to the maintenance period. For example, the shortest interval - 10K hours - requires only a single day of downtime. One requires 5 days downtime, but the interval is 16,000 hours, effectively two years' worth of 24/7 uptime.

Those are almost magical periods of constant uptime for any machine, period.

Sshep has echoed my original suggestion, too - the uptime is negotiable and is part of the turbine warranty. Also, as he repeats, "There is a lot of experience readily available to assist in these evaluations." Good comments from both.

 

[norzul]

What I've stated previously excluded the off line washing frequency. The offline washing depends on several factors i.e. GT performance,air quality, filter, etc. The interval period could be extended, however it will have some effect on the GT's performance i.e. heatrate may increase over time. There is no standard formula on this.

However, based on my discussion with NP, for frame 5 GT, the offline interval could be 4-6 months. The whole activities will take about 1 day (from stop to start).

The online washing interval could be each month but yu don't have to shutdown the turbine.

 

[davefitz]

It sounds like some kind of a Monte Carlo analysis could be used to determine the risk for having a forced outage of the gasification plant. Still, even if the analysis showed low risk of forced outage, the shutdown -restart costs of a forced outage could be enormous, espescially if it impacts downstream operations of a chemical plant.

Most gasifier reactors are thick refractory lines vessels, over 1.5 ft thick ,and to avoid excessive thermal stresses could need a 2 day warmup period to reach full operating temperature. The exception may be the Shell design , which uses a steam cooled or water cooled vessel with a thinner reractory inner liner.

I understand that typical max operating periods for the refractory lined vessels is 9 months- they would require an inspection to determine the degree of high temp corrosive damage to the refractory after 9 mos. So a major outage that would allow inspection of the gasifiers would be scheduled at least once per 9 mos.

If the committment for product gases is for 365 days per year without scheduled outages, or if one cannot tolerate a forced outage, it would seem practical to design the plant as 2 x 50% or 2 x 60% trains for those pieces of equipment that requrie maintainence outages or have low availabilyt, sych as gasifier trains, hot filters, gas turbines, etc.

Another annoying issue associated with the IGCC's need to operate 24/7 is that there must be a corresponding firm consumer of the product gas on a 24/7 basis. This works if the consumer is a chemical plant, but a power generating gas turbine is usually schedueld to shutdown at nightime to allow the base loaded coal fired plants and nuclear plants to maximize their output during nightime electric demand minimas.

 

[gaillee]

hi norzul,

Thanks very much.

 

[bonzoboy]

The reason that methanol production makes sense in these applications is to take advantage of the availability of the gas turbine, which is usually high, against the gasifier section, which is usually lower. The gasifier can be operating to produce methanol (when the turbine is not running) and the turbine can operate on the methanol, when the gasifier is not running.

The frequent inspection interval is probably due to the use of the syn-gas (CO, H2, +crap, etc). Turbines can burn just about anything, as long as it is clean. If you ONLY ran the turbine on the methanol, you'd have a much better shot at improving your maintenance intervals than if the unit is switched back and forth between different fuels.