Compressor as Expander for power (Rankine Cycle)

[rcarlitos99]

Hi everybody,

It’s the first time in this forum. I’m project engineer from Spain and we are working in a new project, an organic Rankine Cycle for power recovering.

We have an organic fluid (could be R-245fa or R-134) in steam phase (82ºC and 8,3 bar abs) and we want to expand it until 1 bar in winter or 2 bar in summer, both abs.

My questions:

Which are the best devices to use? The screw compressor? Of course, thinking in the efficiency and also in the final price. The turbines are very expensive.

Which is the isentropic efficiency of the device?

And the most important thing, could someone tell me a supplier of these kind of devices (in Europe or in America)?

The idea is to develop devices in the range of 30 to 190 mechanical Kw in the shaft and couple that shaft to an electric generator.

Regards!!

[The Viking]

Sorry,
I can't get my head around your post, I think we need more information..

Organic fluid or refrigerant maybe?

What is it you are planning to use it for?

What does the rest of the refrigerant cycle consist of, evaporator, condensor and so on?

If you just want to reduce the pressure from 8.3 to 1-2 bar then you don't need a compressor, you need a cooler vessel to store it in. But I assume that this wasn't what you wanted to achieve?

[rcarlitos99]

This is what we are planning to do:

We are in the first step of the project but we are assumimg we will use the Honeywell R-245fa or R-134a.
The idea is to use the water from the water circuit of an engine to pass through an evaporator. With this water we are warming up a fluid until 82ºC. This correspond with the saturation pressure of 8,3 bar abs for the R245fa. For pressuring we need a pump.
Then the idea is to use a screw compressor in reverse mode, getting mechanical power in the shaft of the compressor, so the compressor becames an expansor. We will couple the expansor shaft to an electric generator (50 Hz - 400V) and the we will get electric power.
Once the steam is expanded until 1 bar in winter or 2 bar in summer we will pass it through a condenser working in the other side with a cooling tower. The steam becames liquid and then the cycle start again through the pump.

My problem: I can not get a manufacturer of expander. Does anyone can help me with that?

Another question: if we ask for a compressor from 1 to 8,3 bar, if we use it in reverse mode, the efficiency would be the same value?

Thank you!!

[HallsEngineer]

Screw compressors do not run backwards very well. If you put the high pressure gas in the suction you would get no oil feed to make your seals and that would not be good. One big pile of expensive scrap. No refrigeration compressors are just that COMPRESSORS not used to drive but to be driven. I would contact BOC Edwards about a roots pump pssibly but the oil does need to be at a higher pressure than the suction at all times. Best bet is for a steam turbine and a cooling tower to provide the energy back into the refrigerant. Also you are not allowed to just release refrigerants to atmosphere.

[The Viking]

OK,
Now even I understand better.

As Halls states above, no conventional refrigeration compressor will do what you ask for, even if you were able to find one the losses would be to great.
The normal/conventional way to reclaim excess heat is to put a refrigerant evaporator in the heat source and then heat something (normally a building) up with the condenser.

BUT.....

Your project interest me (yes I'm sad, I know).
Is there a reason for the 82 degrees limit?
If you could raise it a bit higher you could use a conventional steam engine to run your generator.

Or why not find some type of Stirling engine?
(see http://en.wikipedia.org/wiki/Stirling_engine )

[rcarlitos99]

Thanks Hall.

And what do you think about the idea of using a dry (oil-free) screw compressor?

The turbines are very expensive and can make the system no rentable. May are better when you have more thermal jump available, but with low temperatures...

Thanks again

[US Iceman]

From a theoretical viewpoint, a screw rotating in one direction is a compressor (suction to discharge and driven by the motor).

If the screw is rotated in the opposite direction by high pressure gas, the energy from the expansion process (high pressure to low pressure) is converted into electrical energy by turning a generator.

The problem becomes one of; is the screw designed to be used as an expander? Most compressors are not to my knowledge. I am however aware of one company that was considering something very similar to what you are thinking about.

Essentially the high pressure gas flows into what we would consider the discharge flange on the compressor. The expansion process occurs when the high pressure gas is reduced by flowing out off what we would consider the suction flange on the compressor.

The picture posted by HallsEngineer is also similar to the geothermal energy system used in Hawaii for generating power, except they are using ammonia instead of the R-134a or R-245fa. However, this application is using turbines I believe.

If you have something different in mind from the flow diagram posted, please share it with us.

[US Iceman]

Here is a nice article describing a similar system. This is based on the use of turbo compressors being used as expanders.

http://www.yourownpower.com/Power/grc%20paper.pdf

[rcarlitos99]

Iceman, the picture posted by HallsEngineer is what we are planning to build.

The solutions with turbine are more expensive than with an screw compressor.

Viking, the reason for not go up than 82ºC is that the thermal source is the jacket circuit (cooling circuit) of a internal combustion engine, comming from the engine at 90ºC maximum. Furthermore, the most important value for the project is that we want to recover energy from low temperature. Solutions for higher temperatures are built with turbines.

But is very difficult to fin a dry screw expander between compressors manufacturer.

Regarding the fluid, is not defined yet and maybe is better to use a natural refrigerant as amonia (but that means to expand from high pressure, 40 bar, to 3 bar and a single stage dry compressor may not support that pressure).

We are trying to build an economical system for power recovery and we have aou minmds focused in the dry screw compressor manufactures. Maybe we are in the wrong direction but I hope no.

[US Iceman]

Howden compressors may be the best option I can think of for a twin screw expander. I know they have a dry screw compressor.

The problems are not just imposed by oil injection. If a twin screw rotates in reverse the thrust bearings are on the wrong end of the rotors. In effect, if you want to run a twin screw backwards as an expander you have to build it in reverse. Oil injection, thrust bearings, slide valve, etc.

A single screw may be able to do this duty with the minimum amount of changes. In the version I am thinking of there are no thrust loads on the bearings, only radial loads.

[HallsEngineer]

What about those new danfoss turbocor compressors with magnetic bearings?

[Josip]

Hi, rcarlitos99

maybe you can find something useful here:

http://www.staff.city.ac.uk/~ra601/oportsvi.pdf

also good for other members to learn something new..

Best regards, Josip

[squil]

Compressors running as expander are a good solution for ORC, especially in small units. Turbo machines have the drawback of a very high shaft speed, and thus the need for a transmission gear, faster bearing friction and deterioration, etc.
Oil-free compressor are easier to transform into expanders, but have a higher leakage area and thus a deteriorated isentropic efficiency.
On the other hand, lubricated compressors have the drawback of the oil injection and oil separation at the outlet.

Among positive displacement machines, i think the best solutions are the scroll and the screw expanders because of their availability, robustness, good behavior under two-phase conditions, high pressure ratio, price, etc

[bruceboldy]

rcarlitos
This is an intersting project.
When i was with Frick we did some work on screw expanders. It has been some time ago. I will see if I have any old contacts who can tell me where to get the machines you need. I believe they are available.
bruce

[rcarlitos99]

Thank you in advance bruce

[US Iceman]

Next week I wil be talking to a friend who might be able to offer some details. Do you have a quantity of units that may be required? How many of these do you think you can sell in each capacity range?

[rcarlitos99]

US Iceman,

thank you. I have sent you an email through your web site's contact page with my e-mail to contact directly with me. I can send you more information about my requirements using the private e-mail.

THX

[talour]

hello I am talour a student of Chile and it interests the subject to me because I am haciedo a work on screw compressors and scroll operating like expansor using flowed organic fluid like of work, serious good that pudieramos to interchange information.

[squil]

Hi
You can have a look at this location : Experimental study and modeling of a low temperature Rankine cycle for small scale cogeneration
They used a scroll compressor working as an expander and they explain how they transformed it to make the system work.

[ORC]

Hi,

I'm a student in mech engineering. I'm also working on a project similar to yours (same fluid conditions). So far, the best solution I got is to use a scroll compressor widely use in car A/C (cheap option).
Otherwise you can have a look at these compagny:
eneftech.
or
airsquared
Unfortunatly they are too expensive for me

[swaminathan van]

hi all, this is very interesting. i have seen similar arrangements in oilfield equipment web sites where they use turbines similar to axial fans fitted in series in the gas lines which help use the kinetic energy of the gas and also produce electrical energy which is used elsewhere.
also if the recovered enengy is going to be used for climate control then an absorption unit or an adsorption unit should be able to use the heat to produce cooling.
hope this helps.

[renewablejohn]

I am also going down this route using thermal oil and a steam evaporator to produce steam. I have seen the following unit however I cannot find out the manufacturer and I only require the compressor /generator system not the boilers etc which go with it.
As I have not made 15 posts I cannot give you the url but if you look up mawera.at and their cogeneration products you will see the screw generator I am talking about.

[tomireland]

Hi Guys, yep interesting, just a few observations, I may be wrong... The amount of energy lost in overcoming the inertia and maintaining motion in the screw compressor, given its typical mass would make it the most uneconomical at these relative low pressures, the best way might be to look at a steam/pneumatic pump type system scaled up to take advantage of the power resource availble, the lighter the components involved in the compression process, the greater the conversion of power in to power out,COP is suppose. There are quite a few innovative machines on the market at the moment which might meet your requirements, with a little upscaling and attention to seals etc...I cant post urls just yet, but try this for brain fodder, quasiturbine.promci.qc.ca and look at the pneumatic turbine, they have the right idea, and I would say are approachable to new ideas. Worth a try...

[rcarlitos99]

Hi guys,
wonderfull. I have run the compressor as expander and the machine is running properly after some problems during some months. Now we are happy.

Maybe someone can help me to find out what I need now.

For an especific fluid (refrigerant) with a given mass flow and inlet pressure and temperature to the expander, how can I define the rotation speed of the comppressor to get the best efficiency and also to select the best machine size between a range for that flow? Is there any mathematic formula?

Thank you in advance.

[renewablejohn]

rcarlitos99

Pleased to hear your compressor as expander is running properly. Any chance of expanded on what sort of problems you had and how you solved them.

tomireland
have looked in the past at the quasiturbine but came to the conclusion that screw expanders are a more robust technology for the mass market.

[rcarlitos99]

Yes, we had a lot of problems with the compressor due to the seizing because of the bad lubrication.
Right now, the compressor has run for 100 hours, with a lot of stops and start-ups.

We have made the first adjust of the machine and the thermal power we have recovered is about 8% with water at 90ºC.

[renewablejohn]

Yes, we had a lot of problems with the compressor due to the seizing because of the bad lubrication.
Right now, the compressor has run for 100 hours, with a lot of stops and start-ups.

We have made the first adjust of the machine and the thermal power we have recovered is about 8% with water at 90ºC. The cost of the machine, including the liquid and frames, less than 2000€/KWe.

If there is someone interested in Europe I can show him the machine running with all the sensors. At this moment, we want to industrialize the product and we are looking for financial support to do it.

Have you seen the electratherm machine I would post an Url but not able to as yet. They seem to be using a twin screw expander at a similar temperature to what you are using

[rcarlitos99]

Right now, the compressor has run for 100 hours, with a lot of stops and start-ups.

We have made the first adjust of the machine and the thermal power we have recovered is about 8% with water at 90ºC.

[kristinsoffia]

Hi all

I'm currently working on a waste heat recovery project. I'm looking into both Kalina and ORC and using a Scroll\Screw expander. rcarlitos - how did you get yours to finaly work and where did you get it from.
One other thing - has anyone scaled a circle down to ao total volume of 0.064 m3?

[Jerrysjz]

congratulations! And I have a question that where did you buy the proper screw compressor and the volume capacity of it.

[hahaw000]

congratulations!Now I am working on screw expander,Maybe we willl manufacturing a expander in 2010 for ORC system

[Frostyguy]

Wow, I just joined, and its amazing how this very subject is exactly what Ive been researching. I must say, though the concept of these forums is a good one, how great would a real life sit down be in a think tank of all the talent apparent here.

Ill only comment briefly and also poss a question to you all.
RColitos: As I have gathered by your post you have also found it difficult to locate a smaller version of a, true "Turbo-Expander" for your application so you turned to manipulating a scroll type compressor. I also had contacted some companies who manufacture turbo-expanders for much larger, mega watt outputs, and they had even conceded to funding R&D for smaller units in the capacity your working on but had to pull the plug do to economy backslide. They even mentioned the refrigerants you referring too. This ones exciting, I hope to hear more see where this one gos..

Heres an idea. If your looking to figure what your required flow rate, volume and pressure needs to be to meet the required torque, rpm, etc., of the turbine for your generator, why not hook up a decent sized air compressor, and tweak the pressures and volume along with any other parameters you need to meet to get a range you know your refrigerant will need to achieve.

[aaronf]

Hi there, there is a lot of interest in this thread. I have been looking for a screw-expander manufacturer and haven't been successful. Can anyone make any recommendations? I have looked at the names suggested previously in this forum and haven't found what I'm looking for. Regards, Aaron

[sedgy]

hi 20 years ago , westinghouse made a centrif to do what you want it was called a templifier lancaster uni had one installed , the <chilled< water was sent down the double skinned flues of the heating boilers and the water cooled condence water was used to heat the building ,

[mizun]

We can supply you ORC turbines. We tried with screw compressors but didnt succeed and when switched over to turbine using R245fa gas, the operation is successful. Presently 10KW is being tested. Gradually we will be able to introduce higher capacities. Mizun ORC

[ssk1962]

Can u expailn why screw type expander did not work - Kumar

[Orcman]

Making automotive scroll compressors work as expanders is not difficult. One of the many micro CHP offerings was based on an automotive scroll expander running backwards with minor modifications - see Genlec.

Lubrication is the key. In an ORC cycle, provided you choose your oil properly, it will be dissolved in the working fluid at the condenser, help increase the viscosity of the fluid for the pump, then separates out in the evaporator to be carried through the expander by the vapour. Relatively large quantities of oil can be carried through the circuit, the only disadvantage of carrying a lot of oil being poorer performance in the evaporator and condenser. Some superheat is essential to 'dry' the oil and obtain the viscosity required for the expander.

Getting hold of an efficient, long-life pump that will survive the low viscosity of refrigerants is more of a problem - try looking for 'espresso coffee machine rotary vane pump'.

Having succeeded with scroll expanders, I'd be very keen to hear anyone's experiences with screw compressors as expanders. The difficulty with standard scroll expanders is the relatively low expansion ratio - screw expanders should give a better expansion ratio, but inevitably will tend to be for larger projects than domestic micro CHP (~1kWe) unless anyone out there knows better?

[aupanner]

I think he is meaning using waste heat in the rankine cycle to produce electric. If you type into utbe "Rankine cycle generator" you will see what he is trying to do.

[Orcman]

Take a look at the Energetix Genlec unit - 1kWe ORC micro CHP (commercial product), using automotive-type scroll expander.

[franko9]

This is a great forum! Let us assume that I have a waste heat source that is a constant 70 degrees C and ideally I want to generate 3 to 5 kW.
1. What size copeland scroll compressor should I use as reverse induction generator?
2. any suggestions on size of heat exchange?
3. ***** or propane? Quantities?

[Orcman]

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.

[slader99]

ORCMAN, I sent you a PM, would love to talk to you a little more about auto type A/C ORC devices. =)

[mizun]

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

[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.

[Jerrysjz]

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？

[NoNickName]

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

[fadiga]

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

[dvtruc]

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

[zeotrope]

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.

[zeotrope]

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.