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Science Technology

Converting More Heat To Useful Energy 57

Posted by timothy from the use-turkey-gut-oil-and-really-make-out dept.
An anonymous reader writes "New Scientist has an article about a technology proposed by Wow Energies which can nearly double the efficiency of power stations, utilise waste heat from many industrial processes, and reduce toxic pollution. The secret is to use propane vapour, which boils at much lower temperatures than steam, and so can convert more heat to useful energy. Even better, it uses existing pump and turbine technology. Could this be a big weapon in the fight against global warming?"
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Converting More Heat To Useful Energy More

Converting More Heat To Useful Energy

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  • I really hope that this works out, because from the looks of it, it would be a great tool in reducing environmental strains. I like that they don't need to rebuild all the factories, reduce, reuse and recycle.

  • This won't be a weapon in the fight against global warming, oil depletion, rising energy costs, and so on. The reason is that all improvements in efficiency are logarithmic whereas growth is exponential.

    A logarithmic function will increase rapidly at first and then slow as it reaches an asymptotic limit at infinity. In the case of efficiency it starts low and as improvements are made efficiency approaches but never quite reaches 100%. It's logarithmic. Growth on the other hand is exponential. It s

    • Thus in the long run a logarithmic decrease cannot overcome an exponential increase.

      Michael.

      Hey Mike, you miss-spelt your name. It is supposed to read M.A.L.T.H.U.S.

      • The closest that Thomas Malthus [wikipedia.org] came to my post is his belief that the increase of population at a geometric rate and the growth of food supply at an arithmetic rate would lead to starvation. He thus espoused favoured "moral restraint" (including late marriage and sexual abstinence) as a check on population growth.

        As we know, food production can also be exponential. There's nothing intrinsically that makes its growth an "arithmatic rate". Contrast this with efficiency, where it's change in time is alw
        • Both you and Malthus made two mistakes:

          Both your models are overly simplistic and overly pessimistic.

          They are simplistic in thinking that a complex system with feedback loops (population, food supply, energy demands, energy supply) can be modeled with simple math functions.

          They are overly pessimistic in thinking that just because there will be eventual difficulties humanity is doomed and there is nothing we can do, so we should stop trying.

          Malthus believed that people were sex machines and as long as yo
          • "pickmode" = "nit"

            City of God gets a bad rap. Augustine's point was not to tell people to turn their backs on the city of man; after all, people live there! Instead, he was reacting against the idea that "Christendom" == "Rome". By telling Christians that their ultimate hope rested in the city of God, he was encouraging them that the failure of Rome was not an ultimate disaster. He was, in fact, advocating an early form of separation of church and state: two cities, interacting but not comingled.

            "pick
            • See, I knew you and Augustine would get along :)

              That may be one interpretation but another way that "City of God" influenced people was to tell them that material things and spiritual things were seperate. Spiritual things were more important. We are better off taking care of our souls than the material things of the world.

              I would agree that spiritual things are more important in the long run but material things like medicine, sanitation, and defense are important too. Augustine's influence, from my point
              • Agreed on the propane issue. Disagreed on the understanding of the Middle Ages. I'm not a Catholic by any stretch, but the church actually did a fair amount of holding things together after Rome's collapse. This includes preserving ancient documents -- you would never have heard of Aristotle or Plato without the church -- building hospitals, and running a lot of local governments. Nor did the church in the early Middle Ages promote feudalism. Later on, perhaps even as early as Charlemagne, the church b
                • Augustine was alive and wrote during the final decline of Rome. I am not saying he delayed the exit from the Dark Ages, I am saying he encouraged their arrival.

                  I AM a Catholic and I AM of Irish descent and I HAVE read "How the Irish Saved Civilization". I am not saying the Church is bad. In the centuries after Augustine and before Charlemagne the Irish actually managed to create some advances over the status quo but most of what was done was preservation not creation.

                  My major point was that many of the gr

          • I understand now. At first I was puzzled by your reference to "M.A.L.T.H.U.S.". I thought it was a computer (like W.O.P.R. [wikipedia.org] in War Games) and perhaps you were humorously implying that I was being too analytical. After searching for 10 minutes for a computer named "M.A.L.T.H.U.S.," I took a guess and assumed you just meant "Malthus" as in Thomas Malthus [wikipedia.org]. It seems now I was correct, although after reading your post above, I realize now that it was in fact an ad hominem [wikipedia.org] argument, where the use of Thomas Malth
    • Nice logic, buddy.

      Except, you've taken an argument that would establish the fact that this won't solve global warming, oil depletion, rising energy costs, and so on, while the statement was that it would be a "weapon in the fight against global warming." M-16s solely can't win a war, nor can tanks, Apaches, aircraft, crew served weapons, effective intelligence, secure supply routes, or anything else by itself win a war. But an effective application of several weapons can.

      Besides, global warming ISN
    • Thus in the long run a logarithmic decrease cannot overcome an exponential increase.

      This is true, which means the only long-term solutions are either solar or fusion. Any fossil fuel-based plan is doomed from the start. Solar can be anything from using ocean thermals to tapping the Sun's core itself, but it has to use the Sun's output in real-time.

      • Solar Component (Score:4, Insightful)

        by Bob_Robertson ( 454888 ) on Saturday May 29, 2004 @05:53PM (#9286946) Homepage
        Ok, how about using solar as the heat source for the propane-vapor turbine?

        The problem remains one of thermal difference, in that there has to be a way to cool the propane back down for liquification, to complete the cycle. This might be a way for people near slow rivers to use the river water since they cannot use it for hydroelectric.

        Bob-

        • Re:Solar Component (Score:3, Insightful)

          by Mr. Piddle ( 567882 )
          This might be a way for people near slow rivers to use the river water since they cannot use it for hydroelectric.

          There is a tree-hugger for every type of pollution...even thermal pollution in rivers. Sigh. Still, using solar heat to drive a turbine is a good idea, and I think there are steam-driven ones somewhere (I recall picture of a desert with many many mirrors).
    • Population is not really expected to continue growing at current rates. IANAD[emographer], but they [prb.org] say growth is starting to decrease, and by 2070 it will be almost flat. The link has a nice graph too.

    • Re:Logarithmic versus Exponential (Score:5, Insightful)

      by barakn ( 641218 ) on Saturday May 29, 2004 @07:51PM (#9287461)
      Anyone who has seeded a sterile medium with bacteria realizes that growth is only quasi-exponential. After a while the population hits carrying capacity, stalls out, then crashes.

      • Re:Logarithmic versus Exponential (Score:4, Interesting)

        by Michael.Forman ( 169981 ) * on Saturday May 29, 2004 @10:49PM (#9288042) Homepage Journal

        Exactly! That curve you describe is a Gaussian curve. It occurs when there is an exponential draw on a finite resource. It can be seen in the population of bacteria over time when bacteria are grown in a finite medium. It can be seen as the Hubbert curve [wikipedia.org] which describes accurately oil production as a function of time.

        With these three functions (logarithmic, exponential, and gaussian) one can draw several conclusions about the future of humanity. Ultimately unlimited exponential growth is not possible. Whether it is energy consumption, human population, or the economy, they all must stop growing eventually. One of the arguments that people reach for when arguing for unlimited exponential growth is improvement in efficiency or conservation. Unfortunately, those functions are logarithmic and cannot offset exponential growth indefinitely. Thus the only alternative is an end to exponential growth. Whether steady state manifests itself as constant, oscillatory, or a descent to zero as in a Gaussian, it must happen.

        Michael. [michael-forman.com]
    • Actually, logarithmic functions do not have a limit or an asymtote. They keep increasing to infinity, but do so much more slowly than exponential functions.

  • safety? (Score:3, Insightful)

    by LWATCDR ( 28044 ) on Saturday May 29, 2004 @03:47PM (#9286400) Homepage Journal
    A leak of heated propane could be very exciting.

    • Re:safety? (Score:5, Informative)

      by s0l0m0n ( 224000 ) on Saturday May 29, 2004 @05:12PM (#9286814) Homepage
      It's not a scary as you might think.

      I'm a bladesmith, and I work with a propane fired forge on a regular basis. Even my properly aspirated burners don't burn well without containment and back pressure. If you pull a burner out of the forge, it sputters real bad and doesn't produce nearly as much heat.

      Most of the time, a straight propane leak (without
      proper aspiration) will blow it self out, even with an open flame nearby. Sure, it's stinky, and if you get the mix with atmostphere wrong it could blow up if contained properly, but generally, LPG is pretty safe stuff.

  • Limited application (Score:5, Informative)

    by Smidge204 ( 605297 ) on Saturday May 29, 2004 @03:55PM (#9286451) Journal
    *puts on skeptic's hat and steps up on soapbox*

    The design here seems to scavange heat off of the flue gas. The problem with this is that you can only remove so much energy from the waste gasses before you create problems.

    Combustion of either coal or oil procudes carbon dioxide, water, soot (unburnt carbon) and nitrogen and sulphur compounds (From impurities in the fuel).

    The boilers of the power plant are typically designed very well to remove as much heat as possible from the fuel and resulting gaseous waste. Easly over 80% efficient. (80% is par for most large commercial boilers as used in schools and office buildings. Some can get up to 90%). So while the temperature may be 450F, remember this is a gas. Temperature is only half the story when you talk about energy.

    Attempting to extract this energy causes two big problems: draft and condensation. The whole point of a chimney is to create a draft from the hot waste gas rising up (which uses energy in the process... so the gas is cooling as it rises). This draft helps stoke the fire and prevents the fumes from accumulating inside the plant. Removing too much energy from the stream will DESTROY the draft, which means you will need a fan to make up for it (which will use more energy than you extract!) Remember that the waste is mostly water vapor? Removing too much heat will cause this to condense. Also remember that the gas cools as it rises up the chimney, so there is a minimum temperature at the chimney base that is required to maintain your draft and prevent condensation.

    Condensation is a real issue, too. The now liquid water starts to absorb those sulphur and nitrogen compounds to create some very strong acids. If you get this, it won't be long before that chimney rots out. You can line the chimney with stainless steel to help prevent this, but it needs to be a specific alloy (oil and gas burners require different materials because of the different products they create). But you still have to deal with the acid itself and even a stainless steel lining won't last without regular maintenance. They estimate the flue gas will be "a relatively cool 55C", and they correctly state that nearly ALL the water will condense out. At least they plan to treat the waste properly...

    So how much energy can you really extract from the flue gasses? Certaintly not 20% of the plant's total output!

    The biggest problem I have is the second stage turbine they propose. Supposedly they plan to use the leftover heat from the first propane stage to power a second stage to "capture almost all the remaining energy." Clearly this second stage must operate at a MUCH lower pressure than the first, because if there was enough energy in the propare at outlet of the first turbine to boil more propare, it would still be a gas and not a saturated mix like it should be. Pressure drops, operating temperature drops, efficiency drops, output drops.

    I would be extremely impressed if they managed to increase a plant's efficiency by 5%, let alone the 20-35% they are claiming.

    *takes off hat, steps down*
    =Smidge=

    • Re:Limited application (Score:4, Informative)

      by pfdietz ( 33112 ) on Saturday May 29, 2004 @04:02PM (#9286501)
      If you read the article, you see that they want stuff to condense out. The NOx and SOx, for example, get reacted with alkali solutions, with hydrogen peroxide added to oxidize them to nitrate/sulfate. These reactions go better at the lower temperature of the cooled flue gases than they would in the current hot flue gases.

      Even better, the cold gas will cause mercury, lead, cadmium and other metal oxides to condense. Mercury pollution from coal burning is a major environmental issue right now.
      • And if had read my post, you would have noticed that I ackowledged that they want to condense the flue gasses. But that doesn't make the highly corrosive condensate any less of a problem. You're still going to have acidic vapor rising up your chimney.

        =Smidge=
        • I see. You run the flue gases through an alkali spray, and the vapors are still acidic? Sure.

          In any case, at 55 C there are plenty of materials available that are extremely resistant to corrosion, even in strong acids or bases. Teflon, for example (although that's probably overkill.)

    • Re:Limited application (Score:4, Informative)

      by pfdietz ( 33112 ) on Saturday May 29, 2004 @04:26PM (#9286610)
      Oh, one other thing...

      As I understand it, the first stage does not expand the propane to saturation (and neither does the second stage). They've presumably optimized the design and determined it was counterproductive to do that.

      See the pressure-enthalpy diagram on page 13 of this set of slides [wowenergies.com].

    • Condensation is a real issue, too. The now liquid water starts to absorb those sulphur and nitrogen compounds to create some very strong acids.

      Only with older boilers. Modern boilers have an efficiency of over 100%. This is because with older boilers the latent heat in water vapor was concidered lost because the condensation would corrode the boiler. Modern boilers aren't effected by this corrotion and therefore are designed to have the water vapor condensate and so release more energy. Since they used t

      • this results in over 100% efficency.

        BULLSHIT - Put in 100 Ergs and get 101 Ergs out? Fine, if you are converting matter to energy (a la E=mc^2.) If we're talking about non-nuclear reactions, bullshit.
        • Nope. Originaly 100% was the best efficency a boiler could have, but this already took the loses because of the escaping water vapor in account. This didn't mend that 100% of the energy was transferd from fuel to hot water.
          Newer boilers allow the water to condensate and retrieve some of the latent heat. This latent heat was originaly considered lost and wasn't included in the way they calculated efficiency. Since these new boiler retrieve that energy, but their efficency is still calculated in the same way
    • The boilers of the power plant are typically designed very well to remove as much heat as possible from the fuel and resulting gaseous waste. Easly over 80% efficient. (80% is par for most large commercial boilers as used in schools and office buildings. Some can get up to 90%).

      The article mentions 35% effficiency, so somebody's smoking some crack, and I suspect it's you.

    • Re:Limited application (Score:4, Informative)

      by DerekLyons ( 302214 ) <fairwater@NOSPAM.gmail.com> on Sunday May 30, 2004 @01:40AM (#9288512) Homepage
      The design here seems to scavange heat off of the flue gas. The problem with this is that you can only remove so much energy from the waste gasses before you create problems.
      The other problem is that significant heat is already scavenged from the flue gas. In every commercial steam powerplant in the world, water exits the condenser, and is routed through a heat exhanger to preheat it before it's sent back to the boiler. (Warmer water in means less work to raise the temperature to a given level, which means a more efficient plant.)
      Attempting to extract this energy causes two big problems: draft and condensation. The whole point of a chimney is to create a draft from the hot waste gas rising up (which uses energy in the process... so the gas is cooling as it rises). This draft helps stoke the fire and prevents the fumes from accumulating inside the plant.
      Commercial plants are forced draft, because natural draft varies with firing rate and atmospheric conditions. Forced draft allows for finer control of fuel burning and greater heat being produced at a higher effiency rate.

  • Nuclear should do even better with this (Score:5, Interesting)

    by pfdietz ( 33112 ) on Saturday May 29, 2004 @03:58PM (#9286472)
    Nuclear reactors are currently even less efficient than coal-burning powerplants, and produce even more medium grade waste heat. This technology should be especially useful there. It should help fusion power even more, since the cost of a fusion core (per thermal MW) is projected to be many times that of a fission core, so getting the most power out of it will be very important.
    • One would hope the next generation of reactors is more efficient, thermodynamically. A lot of the Gen IV effort is oriented towards supercritical water as the working fluid. Other options include liquid metal or high temperature gas.
      • Making the reactor core even hotter would boost efficiency, but you still have that medium grade waste heat at the end to dispose of, so an organic bottoming cycle like this could increase the efficiency still more. It would also be nice to get higher efficiency without having to operate the core at a temperature that could reduce safety margins or pose materials problems.

  • Big savings (Score:3, Insightful)

    by $exyNerdie ( 683214 ) on Saturday May 29, 2004 @03:59PM (#9286481) Homepage Journal
    Stinger estimates the US alone could add over 200 gigawatts of generating capacity - almost 20 per cent of its power needs

    Now I don't know the figures but US consumes like a 4th or 5th of entire power consumption on the planet. This could definitely help increase the life of available non-renewable energy resources...

  • I love how the stories on /. line up sometimes. If we take this tech and the mechinical computing not too far down the page we can get more computation for our effort. That has to count as over clocking... or at least cool on the geek factor.
  • Can u imagine what happens when the sparks fly? nice thing to choose a volatile gas as a heat exchanger it will never be safe.
    • I think you mean a flammable gas rather than a volatile one. Volatile means that something easily turns into gas or vapor at relatively low temperatures, which is exactly what you want for heat exchange. It doesn't imply anything at all the flammability of the substance.

      To be fair, most commonly encountered volatile chemicals are also flammable, and once something is in a gaseous state (and mixed with air) it gets a lot easier to ignite, but the volatility and flammability aren't the same.

  • Reality Check (Score:4, Informative)

    by Anonymous Coward on Saturday May 29, 2004 @09:09PM (#9287728)
    There are several problems with the technology proposed in the article:

    1) The efficiency limit of *ANY* thermal cycle is determined by the source temperature and the sink temperature, and are independent of the working fluid used in the cycle (water or propane). The source temperature is limited by the highest temperature in the gas stream and by the sink temperature (the condenser cooling water).

    2) Working fluids other than water have been discussed in engineering textbooks for many years. The use of Propane as proposed in the article is NOT a new idea. I remember working problems using propane, mercury, water, freon(s) and others back in the mid 1970s. The Mercury cycle was actually built as a topping cycle for a (very) few power plants in the early 1950s or so. Thankfully these are now retired! Ammonia was used as the primary working fluid for refrigeration in the early days and abandoned for safety reasons. I expect these same safety reasons would work against propane or other flamable hydrocarbon as the working fluid in any industrial or larger scale plant.

    3) Current (from the 1950s to present) technology for steam based power plants is able to reduce flue gas temperatures below the acid and water dew points. We often had a stack temperature of 180F, and had to keep it UP to prevent water condensation from turning the flyash to mud and bringing everying to a halt.

    4) The sink temperature has a reasonable limit of about 100F based on cooling towers and the wet bulb temperature of the air in summertime. Anything below about 100F is *VERY* expensive in extra hardware.

    With the water/steam cycle able to exploit the environmental limits of sink temperature and extract heat from any source up to the thermal limits of alloy steel piping (1000F steam temperature), there are few reasons to invest in a working fluid that is flamable.

    • Re:Reality Check (Score:3, Informative)

      by pfdietz ( 33112 )
      Your point (1) ignores the fact that the efficiencies of steam cycles used today are well below the theoretical Carnot limit for the given steam initial temperature and cooling water temperature. This invention is purporting to offer a way to avoid some of the inefficiencies.
    • I wonder if the most useful application for this propane cycle business is in new kinds of nuclear reactors. If his fluid can work with a cooler running system, the extra safety gear and auxiliary systems could be built lighter and cheaper. Of course many of these systems would have to run in parallel to get the same output, but it's an interesting idea at least.

      I rremember picking up apromo brochure from GE a while back and they were crowing about a 1 or 2 percent increase in the efficiency of their indus
  • Think about this.

    Combustion Plant A combusts C3H8(g) as a fuel. The heat generated from combustion turns C3H8(l) into pressurized C3H8(g) to turn turbines - thus generating power. C3H8(g) is released through a stack vent.

    Combustion Plant B captures C3H8(g) from A's stack vent, and combusts it as a fuel. The heat generated from combustion turns C3H8(l) into pressurized C3H8(g) to turn turbines - thus generating power. C3H8(g) is released through a stack vent.

    Combustion Plant C captures C3H8(g) from B's st

  • Alternate Heat Engine Cycles (Score:4, Informative)

    by wjwlsn ( 94460 ) on Saturday May 29, 2004 @11:00PM (#9288085) Journal

    A combined cycle gas turbine uses the waste heat from a Brayton gas-turbine cycle as the heat source for a Rankine steam cycle. In the "cascading closed-loop cycle" described in the article, a similar idea is used except that two Rankine cycles are involved -- they just use different working fluids. This should work, both in theory and in the real world, but I wonder about the cost and the additional complexity.

    Another alternative that is proven, and makes good use of waste heat, is the combined heat and power cycle... for example, the waste heat can be used for district heating. Still another alternative that extracts more usable heat in the first place is the Kalina cycle, which uses a variable mixture working fluid.

    Here's some basic info on heat engine cycles that may be useful for comparison purposes:

  • So.... (Score:3, Funny)

    by Rhinobird ( 151521 ) on Saturday May 29, 2004 @11:09PM (#9288108) Homepage
    So what does this mean for Sim City? Will there be a new option in powerplants? or maybe an upgrade option to tranform my coal fired plants into ultra effriecient/low polluting rigs?
  • steam and water are quite corrosive
    so your parts can be cheaper
    and last longer.
  • Propane? Pfft! I gots an even better low boiling point liquid in mind! See? I just spilled some acetone right over... Damn! Where'd it go?

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