June 01, 2004
Propane Drives Turbine To Harness Waste Heat, Reduce Pollution
Currently almost two thirds of heat generated by coal and natural gas to generate electricity is wasted.
When steam is used to turn a generator, it must be pressurised and raised to around 650 °C. Below 450 °C, the process no longer operates efficiently because the steam pressure drops too low. This means that the heat in flue gases below 450 °C cannot be used to generate electricity, and so is lost to the atmosphere.
Two engineers have developed a mechanism using a pair of heat exchangers and propane cycling between liquid and vapor states to drive a turbine to generate more electricity from heat that is currently wasted.
But now Daniel Stinger, a turbine engineer, and Farouk Mian, a petroleum engineer, have developed a surprisingly simple way to harness almost all this waste heat. They calculate that a second turbine, driven by the waste heat from the first, would capture almost all the remaining energy. The first turbine's waste heat would vaporise and pressurise still more propane to drive the second (see diagram).
Daniel Stinger and Farouk Mian have founded Wow Energies and have a patent pending on their invention.
A new patent pending technology is available which replaces the steam turbine system with a Cascading Closed Loop Cycle (CCLC) system producing an increase in MW output of 150% to 600% over a steam turbine system operating at the same heat source temperatures. Click here for comparison chart. The CCLC can also be installed to operate in conjunction with an existing steam turbine system to increase the output by 100% without using additional fuel, the Super CCLC system. If the CCLC turbine system had been installed in place of or with the steam turbines in use today, it is estimated that the U.S. economy could save $100 billion in fuel costs annually. The savings to the economy if the CCLC technology is used to retrofit existing units is conservatively estimated at $35 billion annually.
Other industry proceses are equally inefficient. Industries that depend on burning fossel fuels in boilers, furnaces, ovens, kilns, gas turbines, internal combustion (IC) engines, fuel cells, nuclear power plants, etc. all produce equivalent losses in the form of waste heat exhausted to the atmosphere. Major industries, in addition to the power generation industry, which can benefit from the CCLC technology includes refining, petrochemical, transportation, cement, pulp & paper, metals and pharmaceutical.
Even more dramatic are the corresponding environmental benefits of conservation of non-renewable fuel resources and dramatic reductions or elimination of emissions when installed on an existing waste heat source.
The CCLC system uses off-the-shelf components. The three (3) major components are a pump, heat exchanger and turbo-expander (turbines) that are readily available from numerous suppliers. For example, both axial and centrifugal turbo-expanders are used extensively in the petrochemical and oil & gas industries and are readily available from suppliers such as GE, Atlas Copco, Mafi Trench, Mitsubishi, Siemens and MAN.
Less fossil fuels burned to generate electric power translates into less pollutants released across the board. But there is an additional benefit of their approach. By converting more of the heat into electricity they lower the temperature of exhaust air and that causes many pollutants to condense into liquids and solids instead of being released into the atmosphere.
The CCLC system is so efficient that during the process of converting waste heat to power, it reduces the flue gas temperature to near ambient where conditions are favorable for elimination of pollutants. At these temperatures, vaporized pollutants such as Mercury, Vanadium, Lead, Cadmium, as well as Vaporized Organic Compounds (VOC), can no longer exist in a vaporized state and are “forced” to condense out of the flue gas as a liquid or solid. The remaining SOx and NOx can be removed using a low temperature Final Flue Gas Cleanup (FFGC) system by circulating a dilute water solution of sodium hydroxide and hydrogen peroxide in a scrubber that reacts with any remaining SOx and NOx to form stable salt solutions. The dilute solution also serves to remove PM2.5 and PM10 particulates, returning the flue gas to the environment in a pristine state. Low temperature scrubbers are commonly used in the petrochemical and pharmaceutical industries where they must totally prevent far more dangerous pollutants from entering the environment. Any pollutants escaping their plants would be instantly destructive, whereas the pollutants noted above only slowly but surely damage the environment and destroy our health.
Lower costs and less pollution are double wins for their invention.
The CCLC system uses off-the-shelf components to generate electricity by recovering the trillions of BTUs discharged hourly to the environment in the form of 300 oF to 700 oF waste heat. Instead of vaporizing water to produce steam to drive a steam turbine, the CCLC process vaporizes propane to drive turbo-expanders in a sealed closed loop system. The propane is identical to that used in back-yard grills for cooking, stored in tanks for heating homes, and as a clean fuel for cars, trucks and other vehicles. Propane is not consumed in the process and serves only as the medium to convert thermal energy to mechanical energy; requiring only 130 Btu/lb to vaporize versus 1000 Btu/lb for water. More importantly, propane will vaporize and absorb superheat at low ambient temperatures – not possible with water. Turbo-expanders have been used for decades throughout industry to expand vaporized hydrocarbons, including propane, to produce electrical power. The uniqueness of the CCLC patent pending system is the use of twin turbo-expanders and multiple heat exchangers, in a parallel/series arrangement, resulting in conversion of nearly all the temperature from the heat source to electrical power.
If this turns out to work then consider the implications. Rather than building new electric power generation plants existing plants could be outfitted to generate more electricity from the same amount of fuel. Even nuclear plants could have their electric power output boosted. Plus, the CLCC system could be hooked up to all sorts of industrial processes used in other industries to provide yet more sources of electric power and less pollution to boot.
Seems like simple technology. Similar heat exchangers and low boiling point fluids driving turbines were used to extract energy from the temperature differentials at different ocean depths. What are they offering that is new?
Fly - sounds like you are talking about OTEC, or Ocean Thermal Electric Conversion. Only a few OTEC plants have ever been built, and they generally operated at a net power loss. (There is a lot of pumping overhead to be overcome) OTEC is a very experimental technology that has required government funding (ie NREL here in the US). It has not been shown to be commercially viable. Part of the problem is that it doesn't scale down well, and so requires huge capital costs for experimentation.
(I don't know anything about the new tech being described here, just had to chime in and debunk the OTEC myth. If this system generates positive energy, its a big improvement on OTEC)
Fly, If this wasn't somehow new then we'd already see a lot of effective capture of smaller energy gradients. But energy gradients that are much much larger than ocean gradients can not now be economically harnessed. Hence all the hot water towers and hot water flowing into creeks at nuclear power plants. If these guys really have figured out a way to make low boiling point fluids work more efficiently to drive turbines to capture energy from a few hundred degrees of energy gradients then they have done something new.
The question that remains to be proven in a trial plant is whether they have solved a problem that obviously has not yet been solved.
To be blunt, Wow Energies is a fraud. Their claims are false and their product is snake oil.
First, if it were possible to achieve 60% efficiency from a binary fluid cycle, we would have done this 50 years ago. We tried binary mercury vapor/steam cycles (using the mercury turbine as a topping cycle), but they only achieved about 40% efficiency. The thermodynamics of propane were well-known even then, and engineers are no smarter now; if propane were a better working fluid you can rest assured that we would have been using it.
Second, we can already achieve 50%+ efficiency using combined-cycle systems. Some have touted ammonia as an additive for the improvement of cycle efficiency in steam turbines; I have no specific expertise in this and a quick search did not turn anything up, so I can't say how those claims added up.
Third, their claims about current systems are false. They say
Processes that depend on the combustion of fossil fuel are at best only 35% efficient. The remaining 65% is discharged to the environment as waste heat in the form of high temperature flue gases, vented steam, hot water and other high temperature fluids and gases. The majority of this waste heat is at temperatures between 300 oF and 700 oF.
Stack gas from coal-fired powerplants is often not terribly warmer than the surrounding air, and the steam exhaust from the turbines is often at 100F or less; condenser pressures during winter (when cooling water is coldest) are often at a fraction of a PSI absolute.
Fourth, 650 F is plenty hot to recover energy using a Rankine engine. You can recover significant energy at the atmospheric boiling point of 212 F if you have an external condenser operating at a good vacuum (meaning, cold). The claim "Propane is not consumed in the process and serves only as the medium to convert thermal energy to mechanical energy; requiring only 130 Btu/lb to vaporize versus 1000 Btu/lb for water. More importantly, propane will vaporize and absorb superheat at low ambient temperatures – not possible with water" is half-true (propane does require less heat to vaporize, and it also yields less energy in expansion) and half false (you can superheat water vapor at any temperature or pressure below critical, as any glance at the phase diagram will demonstrate).
I could go on, but how much information do you need to know that these people are either completely wrong-headed or lying? Either way, keep your hand on your wallet.
Direct carbon conversion fuel cells are likely the the best way to double powerplant efficiency.
"The reaction yields 80 percent of the carbon–oxygen combustion energy as electricity. It provides up to 1 kilowatt of power per square meter of cell surface area—a rate sufficiently high for practical applications. Yet no burning of the carbon takes place.
"“What if we could nearly double the energy conversion efficiency of fossil fuels in electric power generation over the conversion efficiency of today’s coal-fired power plants—which is about 40 percent—and thereby cut the carbon dioxide emissions per kilowatt almost in half?” asks lead researcher John Cooper, scientific capability leader for electrochemistry and corrosion in Lawrence Livermore’s Chemistry and Materials Science Directorate. “And what if we could produce a pure carbon dioxide byproduct for sequestration or industrial use at no additional cost of separation while avoiding the air pollution problems associated with combustion?”
And there's no advantages to large scale operations so powerplants could be much closer to users, cutting distribution/transmission costs while making the whole system much more robust.
Very interesting link Jos. Thanks.
Why are such large cooling towers and so much river water used if there is not a significant amount of high temperature fluid to condense. Granted, 300F-700F does sound like an awful lot of waste to have ignored for the last 30 years of high energy awareness. But if the quality of the steam below that temperature is low, it would kill the turbine blades. Anyone have any more specific information, I'd love to hear more.
UTC, United Technologies Corporation, has a product called Clean Power that uses a carbon based liquid, probably a hydrofluoro carbon like R123a in a Rankine boiled liquid vapor turbine cycle, that is intended to generate electricity from waste heat sources like large stationary engines or turbines.. They also have a product that uses the waste heat from a small gas fired turbine generator to cool a building whilst generating its power. Holland and New Zeeland are giving meager government support for such projects in the home so that electricity is created as a cheap byproduct of the heating of the home and the hot water used in it. Different varieties of Stirling engines are being proposed and tested for this purpose because of their long life and quiet operation. One could use a small natural gas powered engine for this purpose, but the maintenance and noise repel possible customers even if there is a cost saving far greater than the savings of using solar cells. The nitrogen oxides produced by and engine as well as the hydrocarbons and carbon monoxides must also be controlled by catalysts even when burning clean natural gas in the engine. The UTC turbine without catalysts are cleaner when burning diesel than are natural gas vehicles with catalysts. john
Because the CCLC uses a closed loop of propane, it will need to condenced the propane for re-use after it has expaned to spin the turbine generator. Where is the engergy to compress the gas comming from? How does it compair with the electric energy generated?
Almost everything stated and shown in the Stinger-Mian Propane-based Waste-Heat Rankine Cycle is demonstrably WRONG. The errors are so numerous and glaring as to be laughable... so numerous, I won't waste my time demonstrating into them. Instead, get yourself a thermodynamic analysis tool like CyclePad and see for yourself! I will only summarize a few of the Stinger-Mian flaws: Ignores real-world facts such as temperatures, costs, corrosion by condensates in combustion gasses; Uses flawed logic; Performance graph is BACKWARD from reality.
See this comparison of 2 designs which are identical except for temperature:
http://www.qrg.northwestern.edu/thermo/design-library/KenRank/turank.html ... higher temperatures result in higher efficiency, contrary to the implication of Stinger & Mian that more heat would be thrown away and result in LESS efficiency!
Notice also that the waste heat of a realistic power plant (CYCLE Tmin) is discharged from the turbines at no more than 40 degrees CELSIUS (104 F)
The CyclePad software itself is here: http://www.qrg.northwestern.edu/software/software.htm
What a bunch of ignoramuses.
For a start Engineer Poet. You don't know what you are talking about. All you need to do was check their patents for the worked examples. Obviously you never even checked the schematic they provided to see how it owrked but just shot your big mouth from the hip. First who said 60%?? Already CCGT are 60%. Wow is a bottoming cycle (no, I am not talking about the part of the pond where you live), and sopicks up with a higher efficiency than the rankine cycle. So, instead of the LP part of the Steam Turbine, it is substituted with the WOW technology. Not necessary to replace all the steam part from a manufacturing and economic perspective it is fine. But instead of dumping 66% of the heat because of waters latent heat, the 1/7th of the latent heat of propane is dumped. Granted, much higher mass flow is reqired to transport the heat around, but the nett effect is that only half the leatent heat is vented to the environment.
Now, es_sen , what a lazy butt-ass you are. Jump in, tell everyone how to solve the problem, conclude it doesn't work on what...that you smoked somthing first and it gave you the idea? For a start cyclepad does not even have peropane thermodynamic properties. How dumb are you...there isn't any combuistion in the suggested by Wow!! And what costs? Frankly you are a blockheaded jack-ass posing as a fool.
I recall this idea of a secondary turbine with early nuclear power: an ammonia turbine would capture waste heat from a water steam loop. Apparently nuclear generators were and still remain abysmally inefficient (about 30%). Don't write this off just yet as a crackpot scheme. Binary and trinary fluids would increase the efficiency of the WOW loop by as much as 20% (Einstein even patented a safe refrigeration system based on the concept). A water-chlorine cycle was explored by MIT. Ultimately, no secondary loop is needed for a well designed generator. Steam-bypass condensation has been used for many years. The idea is to condense 5% of the steam on the exit side of the turbine, to create a vacuum. This pressure differential increases efficiency by 15%. But since many existing plants are straining for capacity, and trading for pollution credits and controls, the propane loop addon might be a profitable retrofit. So what is the payback period for this investment, and the savings per annum of overall capital costs between the original and the propane turbines?
I have read quite a bit about the rankine cycle proceses and the effective usage of D'arsonval thermal gradient approaches other than OTEC.
UTC just delivered, in the last year or so, such a reverse refrigeration plant to Alaska.
They are using a refrigerant, slightly less volatile than propane, as their working fluid. It seems to me more work should be done utilizing torr differential approaches in getting the power on.
These guys are merely extending upon basic processes which have existed for ages. It is in the technological approaches and the selection of their technology, just like UTC where they will succeed or fail.
My limited knowledge of working with volatile compounds and mixtures of compounds says the physics and the chemistry is on their side. It is a question, as the author has stated, as to the ability to find off-the-shelf solutions, to enable quick to market reactions.
At the primary market size (retrofits) and the secondary locations (industrial heat producing locations)he mentioned, if adequate captal could be found by them, they literally could afford a special design and fabrication to support their theoretics.
Unfortunately, capitalization to achieve engineered products, especially for start-ups is simply either non-existant or non-compensatory to the entrepreneur.
It however, does not make the author a fraud or incorrect simply because he can/cannot find capital to prove his point in the market place. Again look at the UTC approach in Alaska.
can this be used to improve the efficiency of small engines say 100hp
What type of expanders are best for small ratings? recip or rotary. Who makes these?
To answer Ken's question: what type of expanders are best for small ratings?
Screw Expanders are much better suited to small-scale power production than turbines because :
The cost of a screw expander is up to 1/10th that of a comparable turbo expander. The net result is a total power system cost savings of 35% or more in sizes below one megawatt (MW).
Screw expanders operate at roughly one-tenth the rotational speed of turbo expanders, making for high efficiency and robust, reliable performance with less maintenance.
The twin screw expanders start and stop the generators as soon as hot and cold sources are turned on or off. There is no “warm-up” delay like there is in turbine operation.
Screw expanders operate without high speed turbine’s expensive gear boxes and/or electronics in caustic environments that would severely damage high speed turbine systems.
Screw expanders are more versatile, able to operate in environments that severely damage high-speed turbo expanders, leading to higher plant efficiencies and more reliable operation. Twin screw expanders are not damaged by liquids or wet vapor (impossible with Turbines) allowing ElectraTherm’s patented process lubrication system which eliminates the need for traditional oil pump, tank, lines and filter. .
The twin screws are positive displacement expanders that operate like ball bearings and do not “scuff” to drive a generator. Operating life is increased.
To answer Ken's question: Who makes these:
ElectraTherm Inc. (www.electratherm.com) has a patented twin-screw expander that is the most efficient in the world by a significant margin.