If anyone could give me any insight or ideas about this, it would be appreciated.

"Several geothermal power plants are in operation in the United States and more are being built since the heat source of a geothermal plant is hot geothermal water, which is "free energy."  An 8-MW geothermal power plant is being considered at a location where the geothermal water is at 160 degrees Celcius is available.  Geothermal water is to serve as the heat source for a closed Rankine power cycle with refrigerant-134a as the working fluid.  Specify suitable temperatures and pressures for the cycle, and determine the thermal efficency of the cycle.  Justify your selections."


UPDATE:

I figured what size of pump I need.

I need to know how much a pump for geothermal power generation would cost.  It needs to be able to handle a flow rate of atleast 300 kg/sec with pressures up to 1.6 MPa.  It needs to handle temperatures up to 160 degress Celcius.  The fluid being pumped is Refrigerant 134a.

Does anybody know how much something like this would cost or if it is even feasible.

I also need to know if binary geothermal power plants use any reheat or feedwater heaters.

Thanks

Scott

Why bother with freon at all?  I would use a tesla bladeless turbine for a first stage, then recover the steam into a low pressure conventional turbine since all the minerals and crap came out in the first stage.  Then vent to atomoshere.  If I need recovery or make up water I would pump surface water back in at a deeper location.  Hopefully I could find some dry rock at that temperature and use water without all the limestone.  This way I do not have to deal with cooling towers.

But I think what they want to hear is you pump the cold down deep and vent the hot side into a heat exchanger to boil the freon.  Vent that into a low pressure turbine and condense it back to a liquid with a cooling tower.  That way the limestone and crap stays suspended in the primary loop and dosen't plug up your plumbing.

I think butane would be better since it has a lower boiling point and will give you a higher working pressure.  the only problem is when something goes wrong, it goes BOOM!

Any thermal plant, be it a gas, oil or coal fired steam plant, a nuclear steam generator or geothermal all have limitations with heat transfer surface.

In the case of coal fired steam plants, the fouling problem is dealt with by using tubes cast into a slightly conductive refractory, keeping the metal temperatures within limits for the pressure involved yet the refractory surface is maintained at relatively high temperatures to keep fouling at a minimum.  Since coal fire temps are in the 1600 C range, all that is needed for the design is thickness of the refractory.

Same in gas fired plants.  And peak shaving aero-derivative gas turbine plants have little fouling problems from the very pure, but expensive, natural gas/propane.  Fouling here is pof principle concern to the turbine blades which is why atomized coal, while a possible fuel for gas turbines, isn't practical.  Gas fire cogeneration still has a problem with corrosive condensation on the final heat recovery stage, limiting the overall efficiency.

For the nuclear plant, all heat transfer fluids are kept very clean, preventing any fouling.  The temperatures are somewhat lower on the primary heat transfer surfaces but the efficiency high because of the clean fluids.

Not so in geothermal.  Geothermal water is HIGHLY contaminated with minerals and dissolved gas, some of which are highly corrosive.  Couple the very low temperature means a low boiling point fluid must be used, hence the reference to R134a.  Where the coal fired plant has a practical solution with refractory-covered primary tubes, this is not possible with geothermal due to the low availability of the source.  Primary heat transfer surface fouling is the problem.

I cant use anything but refrigerant 134a as the working fluid.

Also refrigerant 134a is not freon.

Is cost a function?  TCO?  

What about the condensor?  Temperatures?

Without knowing the sink temperature, efficiency is an unknown.

Think of this as a modified steam cycle.

And this is why I went comp-sci instead of sticking with engineering.  Thermo is annoying.

Quoted: Is cost a function?  TCO?   What about the condensor?  Temperatures? Without knowing the sink temperature, efficiency is an unknown. Think of this as a modified steam cycle.

Yes, cost can be included.  This is suppose to be "real life" according to my professor.

I put my plant in Iceland, so let's set a suitable lower temperature as 20 C (room temperature) and 160C (heated water temp) as the upper limit.

These temperatures result in reasonable working pressures of 300 psig on the heat exchanger outlet (hot side) and 24 psig at the outlet of the condenser (cold side).  The pressure differential of 276 psig.  All well within the working strengths of normal materials.  

Thermal efficiency = Q out/Qin

I think I need info about R-134A here.

You could look at it this way, absolute highest possible efficiency = deltaT/Tmax, where temps must be converted to degrees Kelvin.

Max Possible Efficiency = 140K/433K = .32 (32%)


I hope this does not get you in trouble with your prof.  You are supposed to do your own homework.

I don't know if it can be in Iceland since the problem talks about the US.  I will have to check on that.


Scott

It seems to be a simple Rankine cycle problem.  There should be examples that you can follow in the book.  Just use the 134a as the working fluid, and assume that you can heat it to about 85% of 160C (heat exchanger efficiencies).  If this fits the Rankine cycle well then use it; if not suggest another working fluid.

I suggest that you dig into your text book and figure it out on your own, it's the best way to learn.

Good luck.

M.L.

Yeap, classic Therm 1 problem, change the numbers on the example in your book and you're set.

Kharn

I know its a Rankine Cycle.  I know how to do the homework problems.  It is a design problem requiring a write up and report.  It doesn't have to be simple Rankine cycle.  It can have regeneration and reheating.


Scott

Quoted: I don't know if it can be in Iceland since the problem talks about the US.  I will have to check on that. Scott

LOL! ! !   Location irrelevant.

.

Quoted: If anyone could give me any insight or ideas about this, it would be appreciated. "Several geothermal power plants are in operation in the United States and more are being built since the heat source of a geothermal plant is hot geothermal water, which is "free energy."  An 8-MW geothermal power plant is being considered at a location where the geothermal water is at 160 degrees Celcius is available.  Geothermal water is to serve as the heat source for a closed Rankine power cycle with refrigerant-134a as the working fluid.  Specify suitable temperatures and pressures for the cycle, and determine the thermal efficency of the cycle.  Justify your selections."

location: the colder year round temp the better.
pressures: min-slightly below condensation point for r134a. max-depends on how much superheat you will get from the delta-T
temps: max=geo water temp, min=environment temp+waste heat
efficiency=1-Tmin/Tmax (IN ABSOLUTE TEMP SCALE)

Also, I need to use a binary cycle as the water is not the working fluid.  The geothermal water needs to pass its heat off to the refrigerant in heat exhanger chamber.

Quoted: Also, I need to use a binary cycle as the water is not the working fluid.  The geothermal water needs to pass its heat off to the refrigerant in heat exhanger chamber.

That is the reality bite.  You need hourly scrubbing of the HX because the temperature difference  required for heat transfer will dictate HEAVY fouling of this surface.

HEY!,  I think I said all that.

Only in a cold climate could you keep the low temp down around a comfortable, room temperature (that's why I placed mine in Iceland).  It doesn't say you have to be in the USA.

Iceland generates a lot of electricity and hot water using geothermal energy.

Mammoth Mountain, California is a geologically active area and they have geothermal electricty generation there.

btt for the night crew

you know about carnot and rankine cycles, right? Just start with that, plug in values that you know based on the properties of the fluid, and calculate the rest.

What is this R-134 you speak of?  My books are so old all I have is R-12.

Kent

Hmmmm, I think I can rig an old refrigerator to generate power. Thanks guys!

Sold all of my books including the steam tables and refrigerant tables. No help here.

Hey, I had to design my own power system in thermo.

Stop cheatin !  

Quoted: Hey, I had to design my own power system in thermo. Stop cheatin !

Pretty damn funny post considering your sig line.  I'd help if I could but I'm at work.  (BTW, what was the solution to the last homework you posted - I'm still curious about that one).  

Quoted: What is this R-134 you speak of?  My books are so old all I have is R-12. Kent

R-134 is the new age stuff that replaces freon.

Quoted: Quoted: Hey, I had to design my own power system in thermo. Stop cheatin !   Pretty damn funny post considering your sig line.  I'd help if I could but I'm at work.  (BTW, what was the solution to the last homework you posted - I'm still curious about that one).

I will have to look it up.

btt

Great topic! Very topical and electic.  And people say gun nuts are stoopid!  HA!

Does anyone know where do look for how much turbines cost?  Or how much the geothermal plant costs in general?

Did you try google? Took me 3 seconds to find that one out.

Quoted: Did you try google? Took me 3 seconds to find that one out.

+1
Most college students just use Google to solve their problem, especially when searching for commercial solutions to their design problem.

Kharn

I already tried google.  I can't find the cost of a turbine.  

Quoted: I already tried google.  I can't find the cost of a turbine.

Go to the Chem Eng computer lab, find a senior, ask if you can borrow his Process Design book, it will have the pricing information you need in the form of an equation based on size/flow and constant-year dollars (for example, the book will have year 2000 dollars, use inflation to get 2005 dollars).

Kharn

up

The only thing I know about thermodynamics is that when the heat's on someone else, it's not on me.

Quoted: up

Couldnt find a senior and his Design book?

Kharn

no