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Re: Compressor as Expander for power (Rankine Cycle)
Setting off on an ORC project using a standard (hermetic) refrigeration compressor is not a good idea. To convert a compressor to be an expander requires the removal of the discharge valves (which stop the compressor running backwards), which can only be got to by sawing the hermetic shell!! Even if you did manage to do this and make a safe closure of the shell (very difficult), you'll be battling against oil systems designed to oil the scroll from oil in the hermetic sump. There are other problems too - but just believe me, this is the wrong way to start.
Far better to go for a semi-hermetic car scroll - take a look through the Sanden range for example. Despite warnings that you can't open the scroll and put it back together again, I've never found this a problem - draw a line on the case to aid alignment when putting it back together and be ready for a shower of ball bearings if you open it the wrong way up! With the case open, the discharge valve can easily be removed. Some car scrolls have mechanisms to return oil from the discharge port to the suction side of the scroll - best avoided or blocked off, but not a serious problem. Lubrication when acting as an expander is very easy - oil is carried through with the fluid, whereas in compressors you have to pump or recirculate oil from the discharge to the suction.
Unfortunately you don't have a hermetic system when you go down the car scroll route (shaft seal can be a problem). However there are a number emerging semi-hermetic (no shaft seal) electric car scrolls which may be interesting, but you would need to find out what to do with the electrical side - usually three-phase, permanent magnetic motors - very efficient, but you need to rectify and invert the output for grid use. As with any adaptation, you need to be careful about the compatibility of your working fluid with any seals and insulation materials in the system.
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Re: Compressor as Expander for power (Rankine Cycle)
ORCMAN, I sent you a PM, would love to talk to you a little more about auto type A/C ORC devices. =)
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Re: Compressor as Expander for power (Rankine Cycle)
We developed "HIMM-The Cool Energy" Turbine Generator using R245fa Gas.
We didn't go for scroll compressor or twins screw ones, because it is not easy to redesign any machine to work in reverse conditions. Try driving a car in reverse gear and you will understand.
We can supply "HIMM -the Cool Energy" ORC Turbine Generator up to 1000 KW using R245fa Gas.
The gas is heated to 120C/10 bar and the turbines work without any hitch.
For a 10KW unit, we used 3000 LPH of water at 90C as the heating media. Presently we are discussing with a solar supplier to design a system to use Dowtherm fluid as the heating media and soonest it is ready, I will post it here.
Mizun ORC
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Re: Compressor as Expander for power (Rankine Cycle)
After some moths working in other interesting projects, here I'm again.
I have read all the post in this topic and I really glad of seeing that the topic it is very intereresting.
I still do belive that the best technology for power between 15 and 200 KWe and low temperature (90ºC - 120ºC) is the screw type expander, as it is cheap and robust. The heart of the technology is to make the compressor run backwards, what it is not very complicate.
I have seen the Orcman's post, where he says that also the oil injection system would be a problem. And really it is a problem. My recommendation is to avoid the oil injection system.
Next discussion would be the applications, the heat sources for these systems. I would like to identify industries where the heat is going out to the atmosphere and could be recovered by the ORC systems for low temperature.
After having the machine developt, know I would like to identify the best customers for it.
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Re: Compressor as Expander for power (Rankine Cycle)
Quote:
Originally Posted by
rcarlitos99
After some moths working in other interesting projects, here I'm again.
I have read all the post in this topic and I really glad of seeing that the topic it is very intereresting.
I still do belive that the best technology for power between 15 and 200 KWe and low temperature (90ºC - 120ºC) is the screw type expander, as it is cheap and robust. The heart of the technology is to make the compressor run backwards, what it is not very complicate.
I have seen the Orcman's post, where he says that also the oil injection system would be a problem. And really it is a problem. My recommendation is to avoid the oil injection system.
Next discussion would be the applications, the heat sources for these systems. I would like to identify industries where the heat is going out to the atmosphere and could be recovered by the ORC systems for low temperature.
After having the machine developt, know I would like to identify the best customers for it.
How about the smaller scale? Such as 1~10kW for the domestic applications?
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Re: Compressor as Expander for power (Rankine Cycle)
Nice to revice this thread
Few months ago I redesigned an existing screw compressor by Frascold, and I produced it with reversed thrust bearings for counter rotation. Removed the motor and left the protruding shaft.
It was a prototype, quite promising.
Now I left Frascold, but I'm sure they will be able to give you some help
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Re: Compressor as Expander for power (Rankine Cycle)
Hi all!
Was hesitant to join the forum because my problem isn't strictly a refrigeration problem, then I saw this thread..perfect!
I am designing and building a REALLY low temperature cycle, to study the options available for Ocean Thermal Energy Technology (I am doing this for a start up company called 'Bluerise' in the Netherlands).
Nearly all the challenges we faced have been touched upon so far in the thread, but we have the added headache of ammonia as our working fluid - actually an ammonia/water mix.
1) We found a few company selling low power scroll/screw expanders (which I suppose at the time this thread started weren't yet on the market). Our output power needs to be less than 1kW, and it is especially difficult to find anything on this scale. Turbo-expanders are out of the question for other reasons aswell, but even scroll/screw are hard to source. Any ideas what we can use for this prototype? It obviously doesn't have to be something which scales up well, we are not interested in what will be feasible as an expander on larger scales, only that the cycle works...it needs to expand saturated ammonia vapour btw!
2) Another smaller, detail, what kind of tubing should I think of? Obviously nothing contained copper, would PVC do? The temperature is really low, between 0-30 degrees (yes we want extract energy from that hehe!)
3) Lastly, we need to separate the ammonia-water mixture when it is at a state of around 35% vapour. I realise this presents a rather high liquid loading for any potential separator, higher than anything I've found anyway.
We were thinking of simple knock out drums with mesh pads, or impingement+vane type...could you offer any further insight?
Our flow rates are also very low, less than 1.5kg/min, pressures between 4 and 8 bar...
Thanks for this immensely useful forum!
Regards
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Re: Compressor as Expander for power (Rankine Cycle)
Hi all,
As I know, ORC binary recovery started commercializing so early. But due to low efficiency caused by low diff. temp., the equipment cost is so high if going with power generating grade equipment ( steam, turbine,...), then it is feasible if going with ready made refrigeration ones. Carrier built one derived from their centrifugal chiller may be in Alaska (UTC Power).
Refrigerant selection depends on source/sink temp. and expander must have Vi suitable to source/sink pressure for best eff. for expander itself. There's a software from an university built for calculating all para. of such cycle.
For power around 10 kWe or lower, scroll comp. modified as expander is possible - remove dis. check valve and refit the oil pump. The weak point is low Vi with AC scroll, refrigeration scroll with higher Vi but lower power.
Higher power needs a screw one. Problem only higher press.oil pump and oil separator. All bearing are on the right way because of same axial load force direction (dis.port - inlet; suction - outlet) and we can adjust Vi if it built-in.
Listen to your comments
Regards
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Re: Compressor as Expander for power (Rankine Cycle)
Hello, maybe you start looking at producers of ORC Cycle systems, like Turboden in Italy, Carrier, GEN
and look what they use, there are many. I have heared of some scroll expanders for ORC cycles some years ago,
could find not much in my library though. See the literature index of http://www.plastverarbeiter.de/ai/re...ddb4ff7835.pdf. This article in german is about screw expanders used in big size refrigeration systems instead of solenoid valves. Scroll expanders and screw expanders need anyway a cycle oriented construction or they have a poor output. You can browse the website of http://www.bios-bioenergy.at/en/ too, they have ... or had nice information. In germany we had to switch to Kalina Cycles, as Organic Refrigerants are unwanted nowadays. Those are Ammonia Water binary cycles. They can use common water/steam expansion machines which makes them less expensive.
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Re: Compressor as Expander for power (Rankine Cycle)
oh, the company "Svenska Rotor Maskiner" in Stockholm might have the right screw expander for your
project :) but I guess you need to call them, they build such machines.
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Re: Compressor as Expander for power (Rankine Cycle)
190kW shaft output power from the expander is very large. Working on a isentropic efficency of around 0.6 ish, enthalpy change will be around 66kJ/kg and therefor mass flow will be around 2.88kg/s giving a volume flow at the expander inlet of around 2.88cum/s and around 26.5cum/s at the outlet. With these sorts of flow you have no option but to go for turbo compressors/expanders and large ones as well.
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Re: Compressor as Expander for power (Rankine Cycle)
Too funny this was an email I was reading the other day when we had a request for such a project.
We have a screw compressor designed as a steam expander roughly generating 100-200 kW with 250-275 psi steam.
I have just started my research on the unit now so I have limited answers but have not problem digging more answers for you if need be.
Iceman
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Re: Compressor as Expander for power (Rankine Cycle)
Hi everyone.
I am studying and developing a ORC with 1 kWe as output, using a car air conditioning scroll compressor as expander.
How can I work out the values of flow rate needed, knowing the inlet and outlet pressure??
Thank you.
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Re: Compressor as Expander for power (Rankine Cycle)
the simple way, roughly, ET?, CT?, refrigerant? then you get know EP, CP, depending on ET, efficiency around 10%; you get the flow. You can search online a thermodynamic software/formular for that calculation
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Re: Compressor as Expander for power (Rankine Cycle)
forget the compressor idea.
You will need something running on steam like a steamengine or a turbine.
water will boil at 85 degrees when the pressure is lowered a little.
Your water from the engine under pressure can be relieved into a expanding vessel, the liquid pumped back to motor and the vapour is used in a steamengine. The vapour is condensed and also pumped back to the motor.
this way no need for heatexchangers so the efficiency is high.
I have a central heating working with a stirling engine, that is another way to produce power.
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Re: Compressor as Expander for power (Rankine Cycle)
What about using a piston powered fridge compressor instead of a turbine? The expanding gas can increase cylinder pressure and force the piston down, and then it would reciprocate and do the same again, causing rotation.
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Re: Compressor as Expander for power (Rankine Cycle)
Can do but have to modify its valves controlled by crankshaft like an old train engine
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Re: Compressor as Expander for power (Rankine Cycle)
Yes, the flap valves must be reversed. Basicly the valve plate must be installed upside down.
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Re: Compressor as Expander for power (Rankine Cycle)
you all have no idea how a steamengine is working.
read the book
reversing will not help.
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Re: Compressor as Expander for power (Rankine Cycle)
I don't know who you're talking to, but I was referring to a reciprocating piston semihermetic compressor for refrigeration. Not a steam engine.
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Re: Compressor as Expander for power (Rankine Cycle)
so you say turn the flaps, the piston will go down at that moment, and how do you think to close the flaps and let the piston go up again ????
you are really missing some basic here.
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Re: Compressor as Expander for power (Rankine Cycle)
Quote:
Originally Posted by
shooter
so you say turn the flaps, the piston will go down at that moment, and how do you think to close the flaps and let the piston go up again ????
you are really missing some basic here.
Yes, you're right. My mistake. The intake and discharge must be commanded with a gear train, not a flap.
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Re: Compressor as Expander for power (Rankine Cycle)
Ya, He's talking the one who's talking about recip expander (recip steam engine) means no idea on steam engine history, look back on this with engineer brain. "Bitter medicines fix remedies" (Vietnamese proverb)
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Re: Compressor as Expander for power (Rankine Cycle)
All,
I ran across this thread doing some research online. I happen to work at a company called Air Squared, Inc. that manufactures and designs scroll expanders. I think someone else mentioned us in an earlier comment. I believe we are one of the only companies that offers them.
Because of the all the interest surrounding our scroll expanders for waste heat recovery, we actually put our 1 kW and 5 kW scroll expanders into full production. The expander is in use in a numer of ORC applications (mostly university projects so far). The test data has been great.
Anyway, thought I would share the info. You can find more on our site at htto://airsquared.com. Hope this helps and good luck.
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Re: Compressor as Expander for power (Rankine Cycle)
I just got cad plans for a tesla turbine has anyone thought of that . Cheap to build. Also has anyone thought of using the cold gases like hydrogen which they use to cold the windings on large generators at power plant. My first orc will use co2. Any thoughts on that let me know please
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Re: Compressor as Expander for power (Rankine Cycle)
A question and another idea. Why in orc do most want to use open or closed loop steam . Isn't there a lot more wasted heat then closed loop refrigerant based system . Yes I know the pressures get very high but one could make the system stronger aand gain the high efficiency . Now the idea open loop steam orc . One could make hydrogen easily with the wasted steam to store for use in a furnas at night instead of using batteries. Tell me your thoughts on that.
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Re: Compressor as Expander for power (Rankine Cycle)
Hello Everyone,
I am working on building a 1.5kW electrical output ORC system. The heat input is around 10kW.
A good source for small scale expanders is Infinity Turbine. They make units from 1kW, 10kW to over 100kW.
Almost ready to start assembling the circuit. Does anyone know where I can purchase small quantities of R245fa refrigerant (<5kg)?
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Re: Compressor as Expander for power (Rankine Cycle)
Hello Tanner,
I am also building a 1.5kW electrical output ORC system. If I was to use R245fa refrigerant, I figure I will need a mass flow rate of 0.04kg/s to achieve about 1kW net electrical output. This is with the evaporator working at 1700kPa absolute and the condenser working at 287kPa absolute.
I can look up some pressure-enthalpy diagrams if you need some info. I chose to use custom expanders made by Infinity Turbine which are hermetically sealed and do not require oil lubrication. More expensive, but better efficiency then converting Copeland scrolls.
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Re: Compressor as Expander for power (Rankine Cycle)
I guess the best technology is the compressor working as expander
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Re: Compressor as Expander for power (Rankine Cycle)
Have you seen the ORC from ENERBASQUE (http://www.enerbasque.com/en/orc.html). It is based on compressor working as expander. They have a 25 KWe unit and I think, also, it is possible to subcontract his services as ORC consultants or order and stand-alone expander for your project.
Our company has worked with them in this area and we are really happy with their services. They are really experts in this ORC world and they know the most appropiate technology and design options for each project.
Just an option for the projects I have seen here. They are really interesting!!
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Re: Compressor as Expander for power (Rankine Cycle)
Hello
I think that a small steam turbine is indicated that much of a screw compressor ..