propane instead of water 1

[macmet]

Has anybody got any experience or thoughts of using LP as a replacement for steam in power generation?

I have been looking for info online and I am having a hard time getting a reasonably unbiased opinion. People selling it say its genius others seem much more hesitant.

Parts of the arguments I read seam reasonable, such as the lower vaporization temp and energy mean that it could be used to produce power at lower temperatures (such as waste heat). What about lower enthalphy though? I would think that propane would produce significantly less power at the same mass flow.

Any comments or experiences would be appreciated.

 

[Eltron]

It seems like you're talking about the organic Rankine cycle. Just google "organic Rankine cycle", and you'll find a plethora of information. In principle it seems like a good idea to change the working fluid to one with a lower B.P. The problem is that most of the really good low-B.P. working fluids are flammable, toxic or environmentally harmful, oh, and they're a lot more expensive than water. The particular advantage of the system would be the recapture of low grade heat energy. According to the DOE the US vents 29 quadrillion BTUs of low grade thermal energy into the atmosphere, lakes, and rivers anually. 29 QUADRILLION BTUs lost. The energy is there to recapture, we just need to come up with better turbines, exchangers, and working fluids to suck it back out.

Hope that helps.

 

[zdas04]

Eltron has described the essence of the issue very well. I do have one question: What is a quadrillion?

A million is 1X10^6
A billion is 1X10^9 (in the US)
A trillion is 1X10^12
so is a quadrillion 1X10^15? I'm just trying to get a feel for the prize. The chemical energy in 1,000 ft^3 (MCF, at "standard" conditions, whatever they are) of methane is 1 million BTU. That would say that we have about 29X10^9 ft^3 of "methane equivilant" in the low-grade heat. That is 29 BCF of Methane. At $10/MCF that is $10 million per year. Sounds like a big number, but in the scale of power generation it is not even in the round off error.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

 

[IRstuff]

Yep, that's what we learned in school, at least, in the US, anyway. Quintillion, etc., supposedly came after that.

TTFN

 

[IRstuff]

But are we doing the same math here?

29E15BTU = 8.5E12kWh

Assuming 12000 kWh/yr per home, that's enough energy for 700 million homes?

TTFN

 

[GenB]

LP as a replacement for steam in power generation?
as we write, LP is actually being used instead of steam in power generation.
genb

 

[Eltron]

One quadrillion = 10^17

These thermal losses in the conversion of fuel to electric power exceed the amount of energy annually consumed by the U.S. transportation sector alone or by the entire Japanese economy. Based on these statistics, fully thirty percent of the energy produced by the U.S. is lost as wasted heat. This translates into approximately 210 billion dollars (US) that is lost each year, or an amount of energy lost that is equivalent to the entire consumption of natural gas (2.2 x 1013 ft3) by the U.S. annually.

 

[IRstuff]

quadrillion must be integer power of 10^3, so can't be 10^17

TTFN

 

[macmet]

GenB,

I have seen a few companies offering systems using lp, but I only seem to find these companies perspectives of the systems. I'm wondering if there are any problems associated with LP that are not seen with steam systems.

Eltron mentioned "flammable, toxic or environmentally harmful" which I expected.

There might not be, but I'd like a more neutral opinion as opposed to someone trying to sell us a system.

 

[Zoobie]

I look at this is a refrigeration system running backwards. Propane as a refrigerant is very common. Systems today can be designed for very low leakage. An installation of this sort would need a relief system, and if large enough, a flare system. If designed and handled properly, the "flammable, toxic, or environmentally harmful" properties can be easily taken care of. I think this system would be far simpler than a steam one...no water treatment, no corrosion or scale, no steam traps.

I think one of the attractive options to this type of system is that it potentially could be operated remotely/unmanned. If steam were used (at least in my jurisdiction) you would need a steam engineer on-site 24/7.

 

[macmet]

In our region too we would need a steam engineer 24/7 and that is one of our main reasons for looking for alternatives.

 

[GenB]

LP as a replacement for steam in power generation?
as we write, LP is actually being used instead of steam in power generation.
genb

 

[Eltron]

IRstuff,

One quadrillion = 10^15, or one thousand trillion.

Sorry for the typo, guys.

 

[IRstuff]

No problems. I was just surprised at the overall amount of energy lost. While it's obviously a small percentage of the total generating capacity; if the math is correct, recovery of that lost energy could help out our overall energy situation.

TTFN