Abstract   This article discusses a class of highly efficient power generating turbines that  convert  solar energy or other forms of heat into electricity through the medium of steam.

Unlike conventional steam turbines, the new class of Latent Power (LP) Turbines are able to exploit the latent heat released when steam condenses, in order to increase their operating efficiency.
The design is very flexible: The turbines can be run on solar power or coupled to fossil fuel or nuclear power station boilers running at lower temperatures, but higher levels of efficiency, compared with existing designs.
LP Turbines may also be run using the waste heat produced when carbon dioxide is captured from fossil fuel power station flue gases.

LP Turbine units powered by solar energy from 1.6% of the World1s deserts could meet all of the world populations current primary energy needs.

Brine can be distilled to drinking water, as a by-product. Alternatively, alcohol can be distilled out of water, reducing the cost of bio-ethanol production.
 

The basic concept

Steam turbines are the work horses of the electricity supply industry. They are the most cost effective devices for converting the energy stored in coal, nuclear fuel, hot underground rocks and sunlight into electricity.

86% of the World’s electricity is produced using steam turbines.

Their design weakness
Steam turbine efficiency increases with boiler temperature and pressure. The most efficient units are found in coal and nuclear powered stations. They run at the extreme temperature and strength limits of modern materials, but they can only deliver 40% efficiency.

The reason for this disappointing performance is that a large amount of energy known as latent heat has to be supplied to convert the boiling water into steam at the boiling temperature.

Conventional thinking on steam turbine design is that the latent heat is trapped inside the steam and can only be released as waste heat at the end of the turbine cycle.

The diagram below summarise the problem.

 Figure 1. Steam has a natural tendency to expand as it moves through a turbine. This accelerates the steam, allowing the turbines to spin rapidly and have a fairly compact design. Unfortunately, expansion also discourages condensation. So the latent heat is not released until the end of the turbine cycle.

 A lesson from nature

Hurricanes generate some of the most powerful forces in nature from apparently benign origins. Their energy source is pleasantly warm water vapour (26.5^oC+) above tropical seas..
Hurricane production is governed by a thermodynamic cycle which is totally different to the steam cycle used in conventional steam turbine systems. Nature’s cycle is more efficient because it exploits the latent heat released when saturated water vapour condenses.

Figure 2. Hurricane production is only possible if the top layer of the sea has a temperature of 26.5^oC or higher. This is cooler than the temperature at which power station cooling towers dump their waste heat into the atmosphere.
When moisture condenses out as rain latent heat is released. This thermally rejuvenates the upward convection currents in the eye of a hurricane, creating higher velocities compared with dry air convection currents.

 If we could tap into the same thermodynamic principles that drive hurricanes, it may be possible to use latent heat to drive turbines. In principle, running turbines on latent heat could at least double the efficiency of steam turbine design. At a stroke, we would reduce the cost of generating electricity and move a long way towards solving the problem of global warming.

A second benefit of imitating nature would that steam turbines could operate very efficiently at temperatures of 100^oC or lower. This would make solar and geothermal heat based steam turbines far more financially attractive.

      Figure 3. The heat source for hurricanes is cooler than a baby's bath water.

 But is it possible to imitate nature?

We believe the answer is "yes". But, in order to capture latent heat, the steam passing through the turbine system has to remain saturated. One way of meeting this condition is to keep the steam pressure constant but reduce its volume, as it passes through a chain of turbines.

Figure 4. The turbines and related apertures decrease in capacity in a calculated way so that the pressures inside the first and final turbines are the same. 
The system will need to be primed in order to create the initial vapour flow and at the far end of the chain a small fraction of the vapour will need to be pumped out in order to maintain a steady state of flow.

For a detailed discussion of this deign please visit our Latent Power Turbine Theory page by clicking here.

Conclusion

We argue that it should be possible to design a steam turbine system that operates at very high efficiency levels by tapping into the latent heat stored inside the steam.

We are currently seeking funding for a proof of concept experiment to be carried out at Lancaster University.

For details of our proposed "proof of concept" experiments click

Figure 5.

A solar energy driven Latent Power  Turbine unit. The solar version will operate on a mixture of water vapour and air, with the mixture being kept at approximately atmospheric pressure to minimise pressure stresses on the glass roof that covers the trough. As the system warms up the air fraction id gradually bled off. If the trough is filled with sea or brackish water, the power plant can produce distilled water as a by-product.
 

Fossil fuel, geothermal and nuclear powered LP Turbine units

Any source of heat that can generate steam at approximately 100^oC can be used to power an LP Turbine unit. 

Rainforests

It may be economically possible to operate the units using energy extracted from saturated water vapour at temperatures as low as 30^oC. This would make it financially attractive to replant denuded rainforest areas, with the objective of capturing say 1% of energy stored in the moist air and converting it into electricity. The replanted forests would act as massive carbon sinks until such time as they were burned down again or rotted away.
(For comparison, palm oil production in tropical regions, for use in bio fuels, converts about 0.25% of the solar energy falling on the cropping area into transport fuel.)

Frequently asked questions

Q1. Will conventional steam turbines be used?
A. No. Compared with conventional coal/nuclear powered systems, the turbines will be running at relatively low temperatures. This will allow most of their parts to be made from injection moulded plastic and bonded with adhesives.
Baffles need to be added to ensure that the vapour does not expand and move away from saturation conditions. Please click for a more detailed explanation.

Q2. Is there any experimental evidence to support the LP Turbine theory?

A. Yes. The thermal rejuvenation effect we propose to exploit turns out to be a nuisance in turbine based, ozone layer friendly air cooling systems.
If warm moist air is cooled by passing it through a turbine, condensation may occur. This releases latent heat, re-warming the air. On exiting the turbine, the net cooling effect is minimal compared with using the same unit to cool dry air. Researchers at the National Technical University of Athens have investigated this air cooling problem. Their research findings are in good agreement with LP Turbine theory.  Reference:
Roumeliotis and Mathioudakis, Analysis of moisture condensation during air expansion in turbines, International Journal of Refrigeration, 29 (2006) 1092- 1099.

The main difference between air cooling systems and LP Turbines is that the LP Turbine design includes baffles to prevent the vapour expanding.

Q3. What are the main energy losses?

A. Heat losses through the walls of the system, resistance losses in the electrical components and friction losses between moving parts.

Q4. What are the main differences between the hurricane and LP Turbine cycles?

A. LP Turbines copy nature by harnessing the latent heat released when moist air is forced to do external work. This simple analogy is fine for the first turbine, but as explained on the Latent Power Turbine Theory page, additional features need to be added to ensure stability when a chain of turbines is used.

Q5. Are there any existing industrial processes that exploit the thermal rejuvenation phenomenon?
A. Yes, the multi-stage flash desalination process, developed in the 1950's provides a good analogue. In this process, outlined at http://cape.uwaterloo.ca/che100projects/sea/msf.html thermal rejuvenation is used to improve the efficiency of the evaporation desalination process.  Flash desalination uses latent heat release  along a chain of decreasing vapour pressure chambers to evaporate water at successively lower temperatures. Instead of evaporating fresh batches of water, we plan to generate electricity.

Q6. Using the Carnot efficiency equation, I can't see how its possible to exceed the 40% efficiency of a conventional steam cycle, for a maximum operating temperature  of 100^oC.

A. The individual turbo-generators  have a Carnot efficiency of 2 -6%. But, after passing through each turbo-generator, the partial condensation process thermally rejuvenates the moist air, lifting its temperature. This means that the input temperature of the second turbine is higher than the output temperature of the first turbine and so on. 
 

Q7. The kinetic energy of the moist air increases in proportion to the square of its velocity. Are there any limits on the maximum velocity we can use?

A. Yes. Velocities must be kept sub-sonic. If the vapour acquires a super-sonic velocity, as it does in a conventional steam turbine unit, the vapour will expand, moving away from saturation conditions.

Q8. How would the capital  costs of a coal fired LP Turbine unit compare with its conventional equivalent?

A.  Very favourably because LP Turbine units do not require cooling towers or other water cooling systems. The turbines will larger because they are operating at lower pressures and temperatures but manufacturing costs will be reduced because injection moulded plastics can be used for many components.

Q9. How about comparative running costs for coal fired  units?

A. LPT systems should offer big savings.
Solving the latent heat problem will dramatically increase thermal efficiency, reducing fuel and fuel storage costs. Cooling water will not be squandered, pumping it into the air and a desalination option will become available to earn extra revenue.

FAQ10. Would an open cycle system be better? i.e., Is it worth while, in energy terms, compressing the low pressure vapour back to atmospheric pressure?
A Yes because almost twenty times as much energy would be required to produce the same mass of new vapour by evaporation.
Sample calculation, assuming 1 kg of steam is compressed from 20% atmospheric pressure to one atmosphere.
Values used
Latent heat stored in 1 kg of steam at 1 atmosphere, 100^oC= 2.3 x 10⁶ Joules.
Atmospheric pressure = 10⁵ N/m²
Steam density at 100^oC = 1.3 kg/m³, so 1 kg of steam occupies 0.77 m³ at final pressure and 5 x 0.77 = 3.85 m³ at its initial pressure

Work done compressing vapour
= ½ x 80% of atmospheric pressure x change in volume
= ½ x 8 x 10⁴ x (3.85 – 0.77)
= 12.3 x 10⁴ Joules.
Ratio latent heat/work done = 2.3 x 10⁶/ 12.3 10⁴
                                      = 18.9

LP Turbines  PART 2

A more detailed discussion of the various LP Turbine designs

You now have the choice of two options for learning more about LP Turbine.

i) The article below takes a very broad look at the LP Turbine concept, discussing designs for generating electricity in cool and warm climates.

OR

ii) For a discussion that concentrates on desalination and power generation in hot, dry climates go to the following web page on our site:

Using LP Turbine systems to clean coal fired power station flue gases, before they are returned to the atmosphere

The difference between a gas and a vapour is that a vapour can be converted to a liquid by compression alone, provided that its latent heat is extracted. Sulphur, and nitrogen dioxides, mercury and steam are all vapours at a LPT generator operating temperature of 100⁰C. Carbon dioxide is also a vapour below 31^oC. This suggests that LP Turbine systems could be used to liquefy the main flue gas pollutants, with the latent heats liberated in the process being used to generate electricity. The soot particles in the flue gases would provide ideal vapour seeding centres.

The pressures required are quite high. The flue gases would need to be compressed to about 100 atmospheres. The compression process would heat up the gases, but this heat of compression could be recycled using LPT type power units. After the pollutants have been stripped out, the residual oxygen depleted air would still be compressed to approximately 80 atmospheres. By expanding this depleted air back to one atmosphere, via a turbo-generator, a considerable cooling effect would be produced. This would be used to cool the carbon dioxide well below its critical temperature of 31^oC.

Distillation of drinking water from brine If brine is used as the water source in the evaporation chamber, then it can be distilled out to produce drinking (potable) water. The water distillation process consumes a negligible amount of energy compared with running the system using fresh water (Some energy is consumed in delivering fresh brine to the system and pumping away concentrated brine)

Brine is corrosive, so the capital cost of building a power plus drinking water generator will be higher than for a system running on fresh water. However, the costs can be recouped by selling off the drinking water in regions where this is a scarce commodity. The figure of 0.4 litres/ second/ MW of electricity output, given at the beginning of this article, is based on a calculation of the energy required to raise 0.4 kg of water from 5⁰C to 100⁰C and evaporate it.

But, if you refer back to Figure 15, you will see that the solar LPT generator includes a positive thermal feedback loop. This means that more energy is circulating round the system than is actually extracted as electricity. If the feedback loop starts at 70⁰C, as shown, the water output increases to 0.5 litres/ second/ MW of electricity output.  If we close down the loop at 81⁰C, when the saturated vapour pressure of water is 0.5 atmospheres, the water output increases to 0.6 litres per second/ MW output.

The potable water bonus In many industrialised countries, including the UK, France, Germany and the USA, up to one third of fresh water usage is accounted for in cooling power stations, with the resultant warm water vapour being dumped into the atmosphere. When calculating the fresh water savings delivered by LPT systems, we need to take into account the fresh water saved by dispensing with cooling towers, as well as the potable water generated.

 Corrosion Electrolytic corrosion involving different types of metals is a big problem in any system used to process warm brine. The improved Newcomen engine runs at temperatures of 100^oC and lower. This is about 500 degrees cooler than for conventional steam turbines. This will  allow many traditional turbine parts to be made from injection moulded plastic, reducing the metal content and consequent corrosion problems. Modern dielectric adhesives can also be used instead of metallic welds for bonding components. One interesting design option is the use of Pelton wheel type turbine units.

Low cost bio-ethanol production: LP Turbine units could also be used for other distillation processes, for example, the separation of alcohol from water, following fermentation. Up to 10% ethanol can be added to gasoline, for use as a vehicle fuel, without any modifications being made to the engine design. So LPT generators could be used to produce cleaner fuels that also help solve oil supply problems.

Primary energy sources

Any source of low grade heat that can be used to heat large quantities of water to about 100^oC can be used to power LP Turbine systems. Suitable sources of such heat include waste heat from industrial processes, solar and geothermal energy.

Nuclear Power LP Turbine systems

Compared with existing nuclear power station designs, a nuclear powered LPT Generator system offers many advantages, including the following:

•          The design is more efficient than a conventional nuclear power station, because it does not reject low-grade heat. This cuts down on the nuclear fuel costs for the power station and reduces the mass of nuclear waste produced, per unit of electricity generated.

•          The improved Newcomen engine can operate efficiently with a maximum temperature in the region of 100^oC. This gives nuclear engineers an opportunity to re-think the reactor presser vessel design, with the possibility of simplification, by allowing it to operate at lower temperatures, without net efficiency loss.

•          Low-grade nuclear fuel, which is only emitting thermal energy a few degrees above ambient temperature, could play a useful thermal regenerative role in the invention. This extends the working life of the fuel rods and reduces the nuclear waste storage costs.

•          The relatively small size, low operating pressures and temperatures of the nuclear energy plant required for the present invention, reduce the costs and publicly perceived problems associated with designing a nuclear power plant, which is secure against earthquakes, terrorist and other forms of attack.

•          It may be possible to postpone the decommissioning date for existing nuclear power stations, by running them at reduced temperature and steam pressure, to power LP Turbine systems.

Running LP Turbine systems on industrial waste heat

TecEco, internationally famous for their carbon dioxide absorbing Eco Cement are giving serious consideration to the incorporation of an improved Newcomen Engine, based on Cheshire Innovation designs, in their future manufacturing processes. Visit http://www.tececo.com/projects.carbonsafe.php for details.

Green transport  systems running on hydrogen
In principle, hydrogen is very appealing as a clean transport fuel.

A merit of hydrogen is that it can be produced locally by passing an electric current through water. But this source of energy is only clean if the electricity is also produced cleanly.
LP Turbine systems especially solar powered units, could be the answer.

Greening the deserts

Fig. 6. above is a vertical cross section through  a solar powered steam generator at right angles to its length. An important feature of this design is the use of (Fresnel) micro-prisms to focus solar energy. It offers similar super-heating of the trough water to that provided by converging mirrors, but without the complexity of a mechanical sun tracking system. Instead of moving mirrors, the vapour is drawn off in different fractions from the array of troughs, throughout the day. Dust laden air in desert regions is abrasive, so by keeping all of the moving parts under cover maintenance problems are reduced. Unlike a conventional greenhouse, the glazing diverts the solar energy away from the cropping zones causing cooling. The cropping zones are only illuminated by scattered sunlight from the sky. In effect, the inner glazed zone, occupied by the troughs, acts like a giant heat pump, shunting heat away from the cropping zones. Evaporation of water from the leaves of the plants provides further cooling. This system will allow people to live in comfort in the desert, without the need for air conditioning.

Waste plant material is dried out in the glazed cropping areas to release its trapped water content. The waste is burned in the late afternoon, to provide additional low grade heat, as the solar intensity declines. The carbon dioxide produced by the burning process is pumped into the uninhabited cropping zone, to enrich its carbon dioxide content and accelerate plant growth. The plant ash is used as a potash fertiliser.

By combining solar powered LP Turbine and gas turbine units, 24 hour/day electricity generation will be possible. The combustion gases for the gas turbines would be compressed hydrogen and oxygen, with the gases being produced during daylight hours from the electrolysis of water. Such gas turbine units would be far more efficient than conventional gas turbines, which waste a lot of energy compressing air, (only one fifth oxygen) in preparation for injection into the combustion chamber. The steam produced by the combustion process can be condensed out to a vacuum, further increasing efficiency, compared with conventional gas turbines. The latent heat released by the condensation process would help to keep the solar powered LPT unit warm overnight, ready for firing up the next morning.

Fig. 7. Parallel solar steam generators may be grouped under a common Fresnel lens canopy. Additional internal shading can be provided for pedestrians, cyclists and horse riders.

The solar LP Turbine unit concept can be adapted to meet a range of desert community needs. The diagram below shows a unit adapted for sewage treatment.

Fig. 8. The re-cycled sewage materials are used to fertilise an enclosed meadow. The condensed evaporate from the liquid sewage is used as drinking water for the cattle.

Fig. 9. The World’s desert assets. In addition to the true deserts shown, all the populated continents have extensive tracts of semi-arid scrublands. These could become economically productive regions if solar LP Turbine systems were introduced.

What fraction of the deserts need to be colonised by solar LP Turbine units to meet our total energy needs?

“The suns intensity at the Earth’s surface depends on latitude and season. The average value over a 24 hour period across the whole of the Earth’s surface is about 300 watts per square metre.”  Holkham, T, The Last Word, New Scientist, p105, 2006.

For the following calculations we will make the cautious assumption that solar powered LP Turbine units deliver 250 watts per square metre, for eight hours/day, 300 days/year, giving an annual output per square metre of 600 kilowatt hours/year (600 x 10⁶ kW hours/km³/year)

Information sources:

Desert areas, The Guinness World Data Book, ISBN 0-85112960.9

Primary energy statistics, USA Energy Information Administration, http://www.eia.doe.gov/

The above table assumes that during bright sunshine daylight hours the LP Turbine outputs exceed current demands, with surplus electricity being used to liberate hydrogen and oxygen by passing an electric current through water. These gases are stored and used to fire gas turbines during periods of darkness or high cloud cover.

Producing bio-fuels form algae, the LPT way

Green micro-algae can be used as the primary material for the production of bio-diesel and ethanol.  The algae needs to be fed on a diet of nutrient, CO₂, sunlight and water. Details of the bio-fuel production process can be found in the literature                                                                                   [e.g. Paul McKenna "From smokestack to gas tank", New Scientist, p 28-9, 7 October 2006]

The following aspects of the algae to bio-fuel process will benefit from incorporation into LPT technology:

• Algae don't need strong sunlight for photosynthesis, so bioreactors can take the form of stacked culture plates, in the optical shadow of solar LPT units.
• The algae has to be dried, consuming energy, before processing.
• The dried algae cake consists of  (i) fatty oils, the basis of bio-diesel and (ii) starch, which is fermented to produce ethanol.
• Solvents are used to extract the fatty oils from the algae cake. Separating the solvent from the oil requires further energy.
• Distilling the ethanol out of water requires a third input of energy.
• All three energy inputs trap latent heat, so they are amenable to LPT type energy extraction.
• The nutrients required by the algae can be obtained from sewage liquor, which fits in well with the sewage treatment version of LPT..
• The CO₂ could be obtained by burning a mixture of power station fuels, including dried sewage solids and other waste materials, dried in an LPT evaporation chamber.

Fig.10. Integrating moist waste disposal, sewage treatment, power and bio-fuel production. The power generation chain of turbines would be coupled with the most prolific type of vapour, probably water, with latent heat given up by the other condensing vapours being fed into the water evaporation circuit. Additional side-lighting using plane solar tracking mirrors accelerates the rate of photosynthesis. The mirror system shown has a variable geometry prism shape, allowing it to service two adjacent LPT units.

How LPT generators could reduce international tensions

Iran It’s a bit of a paradox, but at a time when we are considering an expansion of nuclear power in the West, to reduce CO₂ emissions, our politicians are flying round the planet, in an effort to prevent nuclear proliferation in Iran. LPT generators could help resolve this paradox. Iran has semi-arid regions where solar energy is going to waste. LPT generators could produce clean energy for the Iranian people at a lower cost than nuclear power stations, with potable water being distilled out as a by-product. The Iranian people have a long and proud tradition of using engineering skills to cope with their hot, arid climate. These skills could be used to improve on the current solar powered LPT generator designs.

Palestine and Israel’s other neighbours
LPT generators could bring prosperity to the agriculturally poor lands of the Gaza strip.

The possibility of Israel obtaining low cost energy and desalinated water from LPT generators would help free up thinking on the strategic importance of the Golan Heights, which overshadow Israel’s currently crucial fresh water supplies, obtained from the Sea of Galilee LPT generators would be an ideal compliment to Israel’s exiting desalination techniques, which are impressive in their ability to produce potable water, but consume electricity in their operation.

North Korea lies on a volcanically active peninsular, so it may well be an ideal region for building geothermal energy based LPT generators.

LPT generators coupled to freeze-desalination units

If a container of sea water is partially frozen, the water and salts separate out, so that the ice formed is fairly salt free. An attractive feature of freeze desalination processes is that because the temperatures are low compared with evaporation desalination, the corrosion and salt scaling problems are reduced.

Latent heat of fusion has to be extracted from the brine to freeze the water, so conventional freeze desalination processes are energy intensive. But, by coupling a freeze desalination and LPT generator together we can reduce the energy penalty. Large combined units may even be capable of producing a net output of electricity.

Fig. 11. Chart showing freeze desalination unit coupled to a LPT generator. If the energy extracted from the sea water exceeds the energy losses from the total system, a net output of electricity is possible. The energy required to melt the ice may be usefully employed as a resource. For example, in in hot climates, for cooling urban heat islands.

Capturing CO₂  from the atmosphere using freeze desalination units
CO₂ can be extracted from the air as a liquid if the air is compressed beyond its critical pressure of 73 atmospheres and cooled to below its critical temperature of 31.1^oC.  The captured CO₂  could be buried deep underground, for example, to offset CO₂ emissions from aircraft flights.

Freeze desalination units are discussed in detail in our patent literature.

Current state of LPT generator development

•  We are working with West & Co www.west-consulting.co.uk on the early stages of a European Seventh Framework research funding bid.

• Preliminary mathematical modelling by graduate students at Lancaster University supports the theory outlined in the attached document.

• The Australian company TecEco, www.tececo.com internationally noted for its Eco Cement is promoting the LPT concept in the Southern hemisphere.

• We have also been approached by an American company based in Arizona, enthusiastic about the prospect of developing LPT generators in the USA.

Please Contact us if you have any business, academic or media interest in LPT generators. If you want to tell your networking contacts about LPT, or add a link to your own web site, the URL for this page is http://www.cheshire-innovation.com/Sky%20Tube.htm

Links to other Cheshire Innovation proposals, for improving the environment:

1. Eco-friendly tidal barriers Extracting energy from sea water without damaging marine and bird life in river estuaries.

2. Cryocoolers, low temperature refrigerators. These could be used to improve the efficiency of a wide range of electrical devices and reduce long distance power transmission costs. In conjunction with the recently discovered magnesium diboride superconductor, they could form the basis for superconducting pipelines, moving liquid hydrogen and electricity from remote LPT generators to city centres.

3. A transport Internet. A radical proposal for cutting the number of vehicle miles driven, without car owners losing their freedom to drive. Please go to the following page on our innovation dedicated web site.  http://website.lineone.net/~billcourtney/Theme%205%20Transport%20Internet.htm