Latent Power Turbines

A more detailed technical discussion

This theory page is written from a historical perspective, explaining how the Latent Power Turbine concept has been developed over many years.

Overview

Back in the 1960’s Bill Courtney studied Thermodynamics at university and meteorology as a hobby.

He was taught the standard engineering belief that we are doomed to live in a world where the heat engines we build to generate electricity will always waste at least 40% of their thermal energy because the Carnot equation tells us so.

This argument was excellently summarized in New Scientist, The Last Word, “Rising heat”, 15 September 2010.
http://dou407.ru/article/mg20727782.500-rising-heat.html

However his spare time studies of tropical hurricanes and the Foehn mountain wind revealed that nature creates heat engines that that are far more efficient than the Kelvin temperature version of the Carnot equation predicts.

He argued that if nature can find a way round the limitations of the Carnot equation then why can’t humans?

In 2009 small scale research at Lancaster University supported these.

Now, after fifty years of arguing his case and being ridiculed he has won £98,400 Innovate UK funding funding to test his assertions on a larger scale

1  The misinterpretation of the Carnot equation

A heat engine is a system for converting heat or thermal energy into mechanical energy.

This class of engines includes the steam engines used to power early railway trains, the internal combustion engines used in most modern cars and the gas and steam turbines found in the majority of electricity generating power stations.

The theoretical maximum efficiency h of a heat engine is given by the Carnot equation.

h = 1 - QC

QH

Where QH is the amount of heat absorbed from the hot reservoir and QC is the amount of heat rejected into the cold reservoir.

“Fortunately”, if the thermodynamic temperature scale is used, the ratio of any two temperatures is equal to the ratio of the quantities of heat taken in and then rejected by a reversible heat engine operating between the same two temperatures. This allows engineers to use the more convenient form of the Carnot equation,

h = 1 - TC

TH

Where TC is the kelvin temperature of the cold reservoir and TH is the kelvin temperature of hot reservoir.

This convenient form of the Carnot equation has led heat engine designers to believe that,

(i) in order to maximise thermal efficiency, a heat engine must operate at the highest possible temperature that its construction materials can tolerate,
(ii) even then the maximum efficiency will be low, with the maximum efficiency of steam turbines being about 50% and more complex combinations of gas and steam turbines having a maximum efficiency of around 60%.

Since the 1960’s Bil has argued that if the values of QH and QC were extended to include latent heat, then it should be possible to develop highly efficient heat engines without the need for correspondingly large temperature differences. His case was based on the observation that tropical hurricanes, a natural form of heat engine, rely on the release of latent heat at temperatures of about 28oC to generate devastating amounts of kinetic energy. He argued that if nature can create heat engines that operate efficiently at balmy tropical temperatures acceptable to humans, then humanity should be capable of inventing something similar.

In 2009 he formed a company with technology business consultant, Dick West to develop a cool running heat engine.

Acknowledgement. Dick West has contributed to LP Turbine theory and design. Bill would not have been able to develop the concepts outlined on this website without his input. From 2009 onwards "we" means Bill Courtney and Dick West.

2  Evidence to support Courtney's arguments

With the aid of Innovate UK funding they performed a series of experiments at Lancaster University to develop their theory. A throttling constriction was used to amplify the kinetic energy of moving air masses before comparative samples of moist and dry air at around laboratory air temperature were passed through a small turbine coupled to a generator.

Figure 1. The Lancaster University heat engine

As expected, the moist air allowed the engine to run at a higher efficiently than the Kelvin temperature version of the Carnot equation predicted. But to their delight, the dry air also delivered an efficiency greater than the equation predicted.

Here is a summary:

Figure 2a. Summary of Lancaster University research results.

The moist air results were reassuringly in line with expectations
but the dry air results required some explaining.

This is what we concluded.

Figure 2b. Two mechanisms combine to create the illusion that
the dry air turbine is more efficient than a Carnot engine.

In addition heat is generated as work is done
against drag as the air transits the turbine blades.

These mechanisms had no obvious practical application but
mulling over the problem opened up our minds to new ideas.

Serendipity!

We concluded that our engine was a hybrid heat and mechanical engine that converted heat and kinetic energy into electricity. This led to us speculate on the advantages of placing a heat engine inside a mechanical engine.

Eventually our speculations produced the following hypothesis.

A closed loop mechanical engine can be constructed that converts ambient temperature heat into electricity with 100% thermal efficiency, provided that the engine simultaneously functions as a refrigerator, so that its internal temperature is below ambient.

With the aid of joint funding from the EPSRC and Innovate UK this hypothesis is now being tested.

3 Theoretical justification for the hypothesis

A Latent Power Turbine engine can be considered as a mechanical engine with a heat engine inside it.

Figure 3.  By installing a heat engine inside a mechanical engine it should be possible to recycle rejected heat instead of wasting it.

The diagram below summarises the essential features of our proof of concept LP Turbine.

Figure 4. For experimental convenience, thermally insulating thick walled plastic pipes are used outside the constriction region.

LP Turbines can never achieve 100% mechanical efficiency because a fan is required to ensure that air continuously circulates round a closed loop of pipes.

However they are obliged to achieve a true thermal efficiency of 100% without violating the laws of thermodynamics because they have three novel design features.

1. They run at a temperature below their surrounding environment. This means that heat can flow into the engine but heat cannot escape to the environment without violating the first law of thermodynamics.
2. The temperature drop across the turbine is very low, so the efficiency of the heat engine calculated using the Carnot equation is also very low.

Example

Using efficiency h = 1 - TC

TH

Taking the temperature of the air entering the turbine as 170C (=290.15 K) and assuming the temperature drop across the turbine is a modest 1 K, the efficiency h = 0.003.

This means that 99.7% of the heat is rejected.

However, because we are using a closed loop system the rejected heat can be “topped up” to 170C  and reused indefinitely. This means that the heat absorbed by the LP Turbine is converted into electricity with100% efficiency. It cannot be less than 100% thermally efficient because this would require the cold LP Turbine to pump heat into its warmer environment.
The operation of the electrical components and the work done against friction all generate low grade heat but this does not equate to a net heat loss because any heat leaking into the environment from externally mounted components can be drawn back into the engine again.

1. Expansion of the working fluid is a key feature of existing steam/gas turbine design. Recycling of the rejected heat would be a futile exercise for these engines because work would have to be done compressing the steam/gas back to its hot reservoir conditions.
LP Turbines overcome this problem by preventing the air from expanding as it flows through the heat engine. However, using a fan in combination with throttling as a substitute for expansion means that LP Turbines are bulky compared with existing steam/gas turbine designs.

4 An additional counter-intuitive feature:
Power output cannot be increased by raising the external temperature

If the external environment temperature increases by Dq, there is a temporary increase in the rate of heat flow into the engine until the internal temperature has also risen by Dq.

If the external environment temperature falls by -Dq, there is a temporary reduction in the rate of heat flow into the engine until the internal temperature has also fallen by -Dq.

Consequently, unlike free standing heat engines, increasing the temperature of the hot reservoir does not improve performance. We refer to LP Turbines as mechanical engines because the only way of increasing the electricity output from a given engine is to increase the speed at which the air flows through the internal heat engine.

[This argument is only true to a good first approximation because the thermal properties of the air and metal walls change with temperature.]

An enthalpy-pressure chart for LP Turbines

In order to construct an experimentally viable thermodynamic chart that emphasizes the primacy of mechanical action, it will be necessary to modify the pipe work loop, so that heat is drawn in after the electricity has been generated.

Figure 5. All parts drawn in blue are lagged so that heat only enters the loop after the engine has done external work.

Lagging the parts offers no practical benefits but is convenient for separating out the heat flow processes in a manner that can be experimentally verified.

Figure 6. Enthalpy – Pressure chart with heat flow processes separated out.

For ease of explanation, we have assumed that the temperature at B will be ambient. It is possible that this temperature will need to be slightly below ambient for the temperature gradient across the bare metal walls to draw in replacement heat. This simplification does not affect the shape of the chart.

A            At A the fan does work on the air so the air warms to above ambient temperature. Prior to A, the air inside the conduit is assumed to be at ambient temperature.

B            The air starts to cool as soon as it enters the throttling throat. B is the point at which the temperature has fallen back to ambient.

C            This is the point immediately after the air has transited the turbine. The air has cooled thanks to throttling and also because the turbine has done work, powering the generator. There has also been some heating due to friction as the conduit tapers and as the air passes through the narrow gaps between the turbine blades.

C’           Is the lowest point on the enthalpy-pressure chart that would have been reached if there had been no heating and corresponding pressure increase due to friction. ( Enthalpy-Pressure chart only.)

D            At the end of the lagged throttling constriction the air temperature is below ambient because the air has done net work driving the turbine.

E            Heat flows in through the conduit walls so that (in this ideal analysis) the air temperature has been restored to ambient. DH is the net heat extracted from the environment during the cycle.

Appendices

LP Turbines can harness sensible or latent heat from their surroundings. For some applications it makes sense to convert sensible heat into an equivalent amount of latent heat to reduce the size of the industrial plant.

The most convenient source of latent heat is the heat released as steam condenses into water.

In Appendix 1 we will outline three different methods of generating steam.

Then, in Appendix 2, we will suggest five applications.

1 Cooling Data Centers

2 The hydrogen economy

3 Improving the energy efficiency of the amine carbon capture process

4 Improving the energy efficiency of the cryogenic carbon capture process

5 A proposal for creating negative carbon footprints

Appendix 1

Generating steam at 100oC for use as LP Turbine fuel

This is what an LP Turbine system running off steam at one atmosphere pressure will look like:

Figure 7. This is a daisy chain of LP Turbines inside a steam chamber. As the steam condenses, its pressure drops, drawing in more steam.

Fuelling LP Turbines with steam at 100oC has several attractions:

• The pressures throughout the system are similar to the external air pressure. So pressure stresses are very low.

• When 1 kg of steam condenses, 2.3 x 106 Joules of latent heat is released. So steam movement into the chamber can take place at a gentle pace.

• The lagging will also offer good sound insulation. So the working environment will be quiet.

However, the real benefit of this form of fuel delivery is that it can be combined with three different types of steam generator, to turn a wide range of industrial problems into profitable energy generating opportunities.

Type 1 steam generators exploit the heat produced by compressing a gas or vapour to generate steam.

Type 2 steam generators exploit the heat released when fluids cool from any high temperature down to about 20oC, to generate steam.

Type 3 steam generators use the waste heat produced by any refrigeration process to generate steam.

A1.1

Type 1 steam generators

These exploit the heat generated when a gas or vapour is compressed, to produce steam at 100oC.

Figure 8. The simplest type of steam generator can be used to cool a compressed gas or vapour to 100oC.

In principle, the design could be used to cool the compressed fluid to a lower temperature, but this would also require the LP Turbine chamber to operate at a pressure below one atmosphere.

A1.2

Type 2 steam generators

These can generate steam at 100oC, while simultaneously cooling a fluid from a high temperature, well above 100oC, down to about 20 oC.

The fluid travels inside a heat transfer pipe that passes through a series of chambers. Each chamber is partially filed with the water that boils at progressively lower pressure and temperature along the chain.

Figure 9. In principle, a single chamber could be used to cool the fluid to 20oC, but this would be inefficient because the compression pump would need to compress very large volumes of steam from very low pressures. We show a total of three chambers, but more chambers, with finer pressure gradations may be used.

The lowest temperature of 20oC is purely arbitrary. Temperatures down to just above 0oC can be reached, but the vapour pressures become very low, and the corresponding compression ratios very high. Temperatures below 0oC can be reached if the water in the chambers is replaced by a low boiling point organic liquid. (The organic liquid vapour can then be condensed out using a standard Type 2 steam generator.)

A1.3

Type 3 steam generators

These exploit the heat extracted during any refrigeration process to generate steam at 100oC

Figure 10. Type 3 steam generators convert the waste heat from any refrigeration process into steam at 100oC.

Appendix 2

Illustrative applications

A2.1 Cooling Data Centers

Data centers are used to house large computer systems for telecommunications, data processing and storage. The power consumed by the systems generates a large amount of waste heat. This needs to be disposed of using air conditioning units that consume more power.

Keeping the air cool and at optimum humidity adds significantly to the cost of running data centers, especially in warm humid climates.

LP Turbines combined with Type two steam generators would turn this problem on its head. The thermal energy extracted from warm moist air could be used to generate electricity, to power the systems, before the cooled air was fed into the center.

A2.2 The hydrogen economy

Hydrogen will need to be compressed to about seventy times atmospheric pressure in order to make it compact enough for storage in vehicle fuel tanks. Traditional compression processes are energy intensive, increasing the price of hydrogen vehicle fuel.

Type one steam generators can be used to recover the heat of compression and reduce fuel costs.

The alternative to compression is to liquefy the hydrogen and store it at atmospheric pressure in insulated fuel tanks. But, liquefying hydrogen consumes more electricity than compressing it. So, according to existing practices, fuel costs also increase. However, using the liquefaction processes described below for cryogenic carbon capture, liquid hydrogen may be cheaper to produce than compressed hydrogen.

A2.3 Improving the energy efficiency of the amine carbon capture process

In this process carbon dioxide (CO2) is removed from combustion gases by passing them through an amide stripper system.

The CO2 leaves the top of the stripper at about 80oC mixed with saturated water vapour at the same temperature. We propose a system for capturing the heat released when both the water vapour and CO2 condense out.

Key facts to help you understand the following diagram:

• CO2 Will liquefy at one atmosphere pressure at its boiling point, -57 oC

• CO2 can be liquefied at higher temperatures up to its critical temperature of +31.1 oC but the pressure has to be increased to its critical value of 74 atmospheres.

Figure 11. LP Turbines can reduce the cost of carbon capture by converting thermal energy from the capture process into electricity.

A2.4 Improving the energy efficiency of the cryogenic carbon capture process

The LP Turbine version of the amine process first separates the CO2 from the other flue gases and then liquefies it.

The LP Turbine cryogenic process does things in reverse: All of the flue gases are compressed and then cooled together so that the CO2 condenses out.

This eliminates the complexities of the amine stripper process but comes at a price. The partial pressure exerted by the CO2 has to be lifted to at least 74 atmospheres for a useful fraction of the CO2 to condense out. But, the CO2 makes up less than 20% by mass of the flue gases, with the main flue gas being nitrogen. Other gases present include SO2, NO2 and possibly Hg vapour.

So the downside of the cryogenic process is that the flue gases need to be compressed to somewhere around 370 atmospheres. But there are several compensations:

• The complexity of the amine process is eliminated.

• Soot particles, SO2, NO2 and Hg vapour can be captured.

• The cool compressed nitrogen than is left at the end of the pollutant capture processes can be further cooled to form the basis of an energy storage system.

Various combinations of compressors and coolers are possible. Here is one of them.

Figure 12. The cryogenic method of flue gas capture can be used to strip out a number of pollutants.

The compressed nitrogen can be liquefied for storage by passing it through a further Type 3 steam generator.

During periods of peak power demand unwanted heat can be added to convert the nitrogen back into a highly pressurized gas for driving a secondary turbine. The required heat could come from a wide range of industrial processes including server centre cooling, food chilling, freeze desalination of sea water and the production of synthetic snow and ice for year round winter sports centers.

A2.5 A proposal for creating negative carbon footprints

Domestic rubbish and other forms of bio fuel could be burned in an atmosphere of pure oxygen and the carbon captured by the cryogenic method. Burning in oxygen would reduce the gas compression required because nitrogen would be eliminated from the flue gases.

The electricity generated would be used to split water into oxygen and hydrogen, with the hydrogen being used as vehicle fuel.

Additional water splitting with the aid of electricity generated by other LP Turbine systems (e.g., geothermal) would provide a total output of oxygen sufficient to burn all of the bio fuel in pure oxygen.

If the captured CO2 was sequestrated, this would create a net drop in atmospheric CO2.

There are many variations possible on this theme. For example, in warm climates excess heat from horticultural glasshouses could be used to drive the supplementary LP Turbines, to provide the balance of oxygen. Some of the CO2 could be fed back into the glass houses to improve plant growth rates.