Anti-icing protection of gas turbine during startup transients

[alcor30]

Dear all,

We are about to commission a gas turbine in a northern Europe area. The site is exposed to low temperatures and high humidity, so that icing phenomenas may occur in the gas turbine air intake.

The gas turbine core engine is protected from icing by hot air injection bleeded from the compressor (bleed heating). This bleed heating air is injected downstream of the filters.

We have an additional anti-icing system installed upstream of the filters. This anti-icing system is aimed at preventing ice formation on the filter panels themselves.

Our filtration system is a static type, in a 3 stages arrangement : humidity coalescing filters + prefilters + filters.

The additionnal anti-icing to protect the filters is a heat exchanger fed by steam bleeded from the Combined Cycle HRSG.

However, steam will not be available at the very beginning of startup transients. During cold and warm startups, we will have to wait approximately 40 minutes until the HRSG water/steam circuits reach sufficient conditioning levels.

Therefore, we are afraid that icing particles may develop and cause obstruction of the filtering panels during these first 40 mn of the starting procedures... before our steam anti-icing heat exchanger gets effective for good.

From your experience, is such an icing issue likely to happen during startup transients ?
Or can we assume that icing is an intrinsically a slow and progressive mechanism... which could not induce blocage of the filters within as short as 40 minutes ?

Any advise/recommandation would be welcome, especially if derived from field experience.

Thank you.

Alcor30

 

[GTstartup]

I have commissioned gas turbines as far north as Northern Canada and those particular units had a the Anti Icing system bled from the compressor last stage via an orifice and introduced to the airstream upstream of the filters. I don't have any experience of warm air being introduced after the filters.

But I have to ask. Why two anti icing systems? Seems simpler to have one that handles icing on filters and compressor blades together.

Now to answer your question on ice propogation. It's my experience (talking about compressor blades and vanes only) that it comes fast. I've been watching the first row, took my eyes off for a few seconds and went back and a layer of ice was evident. How it affects filters, I don't know, but I expect that you would see some ice build up before the anti icing system becomes effective.

I would suggest you contact the GT manufacturer. Ask them the pros and cons of having two separate systems. (I am guessing that they will turn off the GT system when the filter system is available to increase GT efficiency and output). Nevertheless they should have some experience in these matters.

If there is any concern I suggest supplementing the filter anti icing system during startup with the GT anti Icing system. It will take an additional MOV and some piping but may be worth it.

 

[abeltio]

During acceleration the flow is much lower, but it cannot be sure that ice will not form.

I know of a site in Northern Europe that has both heaters as described in the post. Inlet Bleed Heating (IBH) is also used as means to control downturning of the Dry NOx control to achieve lower loads while in low emissions mode.

Curves can be developed showing at what temperatures/loads the IBH acts as anti-icing and as downturn support.

Formation of ice on static filtration systems, specially if mechanical separation of droplets is implemented, is less than on pulsing systems


saludos.
a.