Mid-size gas turbines

[bewdley]

I am looking for gas turbines for a combined cycle unit, to produce steam for a multiple-effect crystallizer, plus mechanical (or electrical) energy for a steam compressor in the same crystallizer.

The problem is, I need some 10 MTPH of LP steam and the electric generator would be rated for approx. 1MWe. Balancing is not a problem, the system would be connected to a general network and in case of steam shortage we would use afterburners.
What puzzles me is the apparent lack gas turbines for this size. There is a gap between microturbines, found up to 200 - 400 kWe, and standard gas turbines, starting at 2-3 MWe. I could use marine diesels, but this seems impractical for many reasons.

Any hint?

 

[taylorg]

bewdley,

What quality and pressure of LP steam do you require (is 7 bar sat steam ok?), and can you clarify that you need 10 tonnes/hr?
Also, is your electrical and steam demand steady, i.e 24hrs per day, 365 days/year base load or is there a varying profile?
Is there a possibility to export power?
Are you using natural gas?

Questions questions!

There are a range of issues and related options which you need to consider in order to get the most suitable solution.
You dismiss diesel engines, but in your case they may actually be a very practical solution! Gas engines are extremely efficient and with an exhaust gas boiler (with supplementary firing to get 10t/h) you would have a very simple plant to look after.

 

[bewdley]

Tks taylorg. Actually, consumption of both energy and steam is quite steady and 7/24, but there should be provision of a parallel board to interconnect with utility.

Diesel engine (converted to Otto) seems to have a relatively high low-temperature output with the cooling fluid, not really usable in the process; I need steam, and 100 - 120 °C water or glycol don't do the job. Moreover, it appears the gas turbine has a higher heat-to-electricity ratio, which is what I am looking for.

It's just puzzling to see that no turbine producer has a good round 1 MWe model (maybe Kawasaki, but they have no assistance in Europe, I gather)

 

[ScottyUK]

Solar's Saturn 20 is about 1200kw with a steam capability of 3.7 - 16.8 tonnes per hour. Seems pretty close to what you wanted.

http://mysolar.cat.com/cda/layout?m=41100&x=7

----------------------------------

One day my ship will come in.
But with my luck, I'll be at the airport!

 

[turboco1]

How does this little GT fit?

Rating = 1.48mw

Recoverable Energy in the Exhaust= 22 mmBTU/hr or 5.87 MJ/s

Steam Production Dry & Saturated
@ 25psig / 1.72 bar=19700 lb/hr

@ 150psig / 10.3 bar = 19000 lb/hr

@ 600psig / 41.4 bar / 750F / 400C = 15600 lb/hr

 

[bewdley]

Thanks ScottyUK and turboco. Saturn 20 probably skipped me. Turboco, who's the manufacturer?

 

[turboco1]

Goto:

http://www.turbinedoctor.com/viking/index.html

tell the doc TurboCo1 sent you

good luck

 

[bewdley]

Thanks gents, all quite useful. Turboco, get a beer if I do something...

 

[EPINT]

you might look at the Turbomachinery magazine. They just came out with their 2006 handbook (Vol. 46 No. 6), which has general spec's for most gas turbines on the market. They have a web site:

http://www.turbomachinerymag.com

This might help.

 

[taylorg]

In recent times most companies in your position have gone for cogeneration using gas engines as their efficiency in open cycle is approx 45% versus less than 30% for an equivalent GT. This is especially true for low output schemes such as the one you are considering. Apologies for giving you the wrong impresion in my last post - the steam is raised from the exhaust gas in the exactly the same way as a GT, not from the cooling water.

You should peruse the cogeneration sections of manufacturers like

http://www.wartsila.com

and

http://www.jenbacher.com

for comparison.

By the way I'm not a manufacturer or salesman for engines (or gas turbines!)
Your best option is to fully assess the technical and economic benefits of all possible solutions as there are several available to you.
Good luck and let us know how you get on...

 

[bewdley]

Thanks, everybody. Just for your info, this is a project for a salt crystallizer : customer has a double effect producing some 27,000 MTPY, and I am proprosing to revamp to triple + mechanical compression to 60,000 MTPY, installing a cogeneration as above.
If ever it is made, I'll tell you...

 

[rmw]

So, are you going to drive the vapor compression with the steam generated by the CT and then use the low pressure exhaust to drive the evaporator train? And, if so, why just triple effect?

Just curious.

rmw

 

[bewdley]

rmw,
Not exactly : I am driving the recompression (via centrifugal compressor) using electricity generated with the GT (I am not brave enough to be the first to propose a directly coupled compressor for this application) and generating steam to operate the triple. Why triple? well, it's a compromise : with reasonable delta Ts in exchangers, I need live steam at 1.5 bar g, meaning a nameplate rating of boiler at, say, 5 bar is OK. I could use a quad lowering the delta T, but at the expense of a (much) larger heat exchange area - unfortunately each effect loses 9 - 10 °C as boiling point rise and short circuit, so in a triple I have a difference between live steam and final vapours saturation temperature of some 60 °C; in a quadruple it would be 80 - 90 °C, obliging to rise boiler rated pressure to 8 - 10 bar, and giving additional corrosion problems (hot saturated brine is no easy customer).

 

[rmw]

Thanks for responding.

I never messed with saturated brine. My experience was with a weak brine (seawater) and we used to use anywhere from 1-24 effects with brine heated to not much more than about 115C. We didn't like it any hotter than that either.

Our delta t per effect was pretty low, obviously.

Are you using rising film or falling film evaporators?

rmw

 

[bewdley]

Film evaporators? would work fifteen seconds and plug. These are crystallizers, and forced circulation (external) to make the good old table salt - actually, not for the table, but for salt blocks -we call them pills, this side of the ocean - to be used in water softeners (mainly for dishwashers). I understand you are in multiple effect (or flash) desalination. Nice field, I tried to enter but units are too big for my humble company.
You do not need to bother with boiling point rise, you lucky guy.

I hope it is not unethical to give the link to our site - there is a number of salt units shown there :

http://www.bewdleytech.co.uk

 

[toothless]

I wouldn't call 1 MegaWatt GT a mid-size. That is tiny. I think a 20-45 MW is mid-size, and 75+ MW is large.