Capstone Turbine

[alexit]

Hello,

Has anyone first hand information regarding this capstone microturbine? I wanted to know if power is generated through inverter to high-speed brushless motor or if is using speed reducer and 3600 rpm genset. Also, what is good/bad about this? (I have downloaded for web a cost analysis for one installation in Canada, but there must be someone else using these...)

Thanks,
Alex

 

[jtkirb]

I do not thing there is a gearbox in them or run synchronus gens. I'm pretty sure they are induction based generators.

I've installed them, but never opened the case, sorry.

JTK

 

[stevenal]

They run at high frequency. Power is rectified and inverted to the supply frequency.

 

[davidbeach]

What stevenal said. They are high speed/high frequency (in the kHz) PM synchronous machines with the output run through a rectifier and inverter.

 

[ccjersey]

Anyone have any experience with the Parallon (Honeywell) turbines? I understand they pulled the plug on that line a while back. Looked like a great idea to me until NGas prices went through the roof. Still would be great if they would run on digester gas etc. I have heard there is a problem with the contaminates in digester gas.

 

[jtkirb]

we have a pilot project in the works locally to run a capstone on digester gas. landfil gas is fairly nasty, but digester gas shouldn't be that bad.

I'll have to check on the project...

JTK

 

[alexit]

jtkirb,

I understand these units can be jetted for different fuels, is this something user-changable?

Do you know the difference in the sizes (are turbines different or is only synchronous motor/inverter sized different?) The weight and dimensions listed are too big for me, I have a project requiring a smaller unit (15kW/30kW). I wonder if this equipment is possible to downsize...or split the mounting of several components to better fit my installation.

Thanks fo your comments.

 

[jtkirb]

capstone turbines are a box you hook up some wires and a pipe to. They are sold as a complete product and are not designed to be modified other than maybe adding some heat recovery.

Not sure on the sizes they sell, but I'm sure the website will inform.

 

[aolalde]

One of this system advantages is a design with a single rotating shaft (generator-turbine) high speed, with air bearings. Attempts to modify the architecture will be unpractical and probably detrimental.

 

[UKpete]

Hello alexit, you originally asked about the pros and cons of direct drive and gearbox step down to conventional speed generator. It is well known but here goes.

The high speed (direct drive) alternator has extremely good power to weight ratio but is expensive, because they are difficult machines to engineer and commission, and the component and assembly costs are high. On top of this of course, the sales volumes are low. They have very high efficiency: 97-98%, including windage losses but not including bearing losses, compared to say 92% for a conventional 30kW generator.

I believe that high speed gearboxes (and we are talking say 80krpm down to 1800rpm) are specials but are available, no personal experience of these. Overall I think the low speed generator option uses the more proven technology but is heavy/bulky and less efficient.

Neither am I a combustor expert! but I have listened in the past to people who are and I remember that it is not straightforward to change fuels without redesigning the combustor, particularly if emissions are a factor. Also combustor life is an issue even with natural gas - perhaps even as low as 10,000 hours.

At 30kW you are below the typical 100kW ratings of Combined Heat and Power units (Turbec, Elliott-Ebara, Bowman Power) but a bit above the automotive developments (energy recovery from exhaust gases, fuel cell energy recovery). However, there may be truck or bus equivalents of around that power - an 8 litre engine at full power may have up to 50kW available for recovery from exhaust gases.

 

[UKpete]

Obvious omission from my pros and cons - with an 1800 or 3600rpm generator you don't need a relatively large and expensive rectifier/inverter to produce 60Hz.

 

[davidbeach]

One advantage of the high speed machine - rectifier/inverter combination is that the machine can be a PM generator and there is no need for an excitation system; generator output is what it is.

 

[alexit]

Capstone markets a 30kW electrical generator with 60kW heat recovery unit. This is too big for my application (too heavy and large) so I was inquiring if a modification of this was possible to downsize/relocate components/derate output of this. I also would like to have ability to change fuels (or possibly multi-jetted) as diesel, natural gas, and LPG each become scare at times...hopefully though not all at once.

Since the Capstone unit is provided as a single piece, with rectifier and inverter co-located I expect I must find another solution to fit my envelope. Your list of the larger combined providers is helpful, I had not contacted Turbec previously.

Does anyone know of a small on-demand combined heat/power unit for 10-15kW power and 13kW min heat? I am able to accept a larger overall package provided that the fuel-burning unit remains smaller than 0.9m x 0.6m x 0.5m and weighs less than 190kg. A seperate controller/rectifier/inverter is actually desired as these components can then be located out of the weather. IF the controller allows output to synch with utility mains it is even better. Efficiency is greatly desired, if we could keep consumption below 2.0L/hr (diesel) this would be perfect.

Looking forward to your comments.
Thanks, Alex

 

[waross]

A rule of thumb for diesel motor sets is 13 KWHr per Gallon of diesel. You may have to lower your fuel consumptions expectations. What is the controlling demand? Heat output or electric power output?
yours

 

[alexit]

Is for road-mobile application, possibly need not to run (but is better if can) while in transit but to survive rough travels:

Unit is always running, at low heat demand when mains are present unit can draw power from mains for to keep rotation to turbine to minimize fuel consupmtion (is at idle state hope very small fuel use <0.5l/hr.)

When mains lost, unit must achieve self-sustaining running and generate power, load to vary from 1-15kW hope fuel is consumed dependent on load. Heat output can be any, have cooling system to keep temperature between setpoints

If heat demand increases (from temperature drop in cooling system) unit to increase fuel consumption to maintain temperature within setpoints...if can generate power to mains synchronously when present is best.

Can stop unit regularly for maintenence and if needed to change fuel source to other type. Best if unit can use both liquid or gaseous fuel, I can accept change in output/consumption from other sources than diesel.

Does this help?

Thanks,
Alex

 

[waross]

If you have to meet a heating demand you may consider electric heaters in addition to your exhaust heat extraction. Switching on a heater will give you direct heat and the increased load will also make more heat available to be extracted from the exhaust.

 

[UKpete]

alexit, your consumption figure is realistic I think, based on published specific fuel consumption figures for natural gas microturbines:

http://services.bepress.com/cgi/viewcontent.cgi?article=1026&context=eci/heatexchangerfall2005

(quite an interesting article, it mentions the main players in the microturbine market although it is about 5 years out of date)
- this will equate to a diesel consumption of about 0.1litre/kWhr mechanical output, with an efficiency of 30% and calorific values of 50MJ/kg and 40MJ/kg for natural gas and diesel respectively. So 2 litres/hr should give you up to 20kW elec and 45kW heat (although of course not all that heat energy could be recovered usefully).

If only I could be positive about sourcing a unit! As stated in the above-mentioned article, Capstone are at the bottom end of the microturbine CHP market in terms of kW output. Bowman Power did produce some mobile power units close to your rating for a military application here in the UK I think (hope I don't get in trouble for mentioning that!) but it wasn't in series production. Development times and costs are high, you will have to have high volumes in mind to make it viable.

 

[alexit]

Good to see our calculations are close! I had 2.0l/hr =15kW electrical and 30kW thermal based upon Capstone literature...problem is this is half size of their small unit.

My volume is too low for special production (under 520/yr) and only for short run ~2-3yrs.

I expect efficiency of larger turbine if only running 1/2 (or less) of rated output will be bad, must require minimum fuel/speed so I am probably out of luck there.

Thanks everyone!

 

[itsmoked]

500/year for that kind of product sounds like a number you could get some serious "custom" interest in.

 

[itsmoked]

Hi Alex,

I am confused... You have mentioned "lost mains" and "controller allows output to sync with utility mains"
and "when mains lost".

But you are also saying this is a "small mobile unit"?!?!

Is this stationary or mobile?