Edited from material supplied by Bill Courtney, Cheshire Innovation
The Newcomen engine concept presented by TecEco and Cheshire Innovation follows from the original steam engine invented around 1712 by Newcomen and is named after him. With the application of modern technology heat exchangers, condensers pumps, turbine technology and a few other ‘smarts’ Newcomen engines are potentially very efficient at capturing low grade heat and condensation pressure differentials and converting them to higher value forms of energy such as electricity.
The Rankine and Newcomen Engine Cycles
In contrast to Rankine cycle engines Newcomen engines capture the pressure change and heat released in the transition from a vapour back to a liquid. Newcomen engines can be retrofitted to existing fossil fuel and nuclear power stations and as a bonus produce distilled water.
Newcomen Engine Technology and the Green Energy Problem.
The world's resources of low grade heat, both natural and man-made far exceed our energy requirements. To date, these resources have been disregarded, because low grade heat cannot efficiently be used to drive conventional turbine generators. Newcomen engines utilise the large volume differences when water vapour collapses to form a liquid. Low grade heat can be used in contrast to the high grade heat required to create the necessary excess gas pressures to drive steam turbo-generators. The basic idea is not new as in the table below
|EARLY "ATMOSPHERIC" STEAM ENGINES E.G. NEWCOMEN'S MINE ENGINE 1712
|FOSSIL FUEL and NUCLEAR BASED MODERN STEAM ENGINES
|MODERN NEWCOMEN ENGINES
|THE KEY IDEAS BEHIND HOW THEY WORK
|The collapse in volume and pressure caused by steam at atmospheric pressure condensing into water can be harnessed as useful mechanical work
|The steam is raised to a very high temperature. A large fraction of the collapse in volume and pressure takes place prior to condensation
|Go back to the early "atmospheric" steam engine concept but include new designs of heat exchangers to capture the latent heat
|THEIR THERMAL EFFICIENCY PROBLEM
|Large amounts of latent (hidden) heat are liberated as low grade thermal energy. The early engines were only about 2% efficient
|At least 50% of the energy used to heat the steam is still wasted because latent heat must be given up, when the steam condenses
|Any heat engine incurs energy losses, but by minimising latent heat losses, high levels of efficiency can be achieved
Steam Cycles Compared
The figure below illustrates the basic concepts behind a solar energy powered Newcomen engine generator system. To reduce the visual clutter, the thermal feedback loop has been omitted.
Basic Concept Sketch of a Solar Powered Newcomen Engine Generator
Newcomen engine generator systems require two physically separated masses of water vapour. Primary vapour is generated in a large evaporation chamber. When it collapses, on cooling, inside the turbo-generator, electricity is generated. Secondary vapour is generated inside the turbine, when latent heat is extracted from the primary vapour.
In the next figure below, brine in the evaporation chamber is heated:
- directly by solar energy and
- by heat liberated when secondary vapour condenses in the underlying condensation chamber.
Fresh brine is continuously added at the cold end of the trough, with hot, concentrated brine being drawn off at the hot end. The heat stored in the concentrated brine is re-cycled, to pre-heat the turbine cooling water.
At the cool end of the condensation chamber, the secondary vapour always ends up transferring its latent heat to the overlying brine, because the vapour pressure builds up until it reaches its dew point.
A Solar Energy Powered Newcomen Generator
In order to re-cycle the heat stored in the secondary vapour at the highest possible temperature, the latent heat in the primary vapour needs to be drawn off in several fractions. The figure below shows a vertical cross section through a turbo-generator that draws off the secondary vapour in three fractions.
A Newcomen Engine Turbo Generator that Extracts Heat from Three Fractions of Primary Vapour
In the first figure, the primary vapour is pulled through the rotor by a suction process. In the figure above this is converted into a push process, by cooling the primary vapour, before it hits the first rotor.
How the push process works
- The mass of vapour per second passing through each successive set of turbine blades falls off, as primary vapour condenses out.
- The condensation of vapour along the length of each stator tunnel produces a pressure drop. This accelerates the emerging vapour plus air, giving it kinetic energy, for transfer to the following rotor.
Engineers familiar with steam turbine design will spot two other design features:
- The push process eliminates the need for Laval nozzles.
- Application of Bernoulli's equation suggests that a three stage cooling system would be too effective, because the exit velocity from each stator would be very high. In reality, more than three cooling stages are likely to be required.
The figure below shows how a single condensation chamber under the evaporation chamber, can accept several fractions of secondary vapour, at different input temperatures.
A Multiple Input Condensation Chamber
Distillation of Drinking Water from Brine or Seawater Using Newcomen Engines
A second water distillation circuit can be built into the Newcomen Generator design by using brine as the cooling water inside the turbine unit. 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)
Because brine is corrosive the capital cost of building a power plus drinking water generator will be higher than for a system running on fresh water. The costs can however be recouped by selling the drinking water in regions where it is a scarce commodity.
Newcomen generators could also be used for other distillation processes such as, for example, the separation of alcohol from water, following fermentation.
Solar Powered Newcomen Generators and the Hydrogen Economy
There are several thousand miles of desert coastline throughout the world. If Newcomen Generators are used to generate fresh water to green the desert, then a surplus of electricity will be produced. This spare capacity could be used to liberate hydrogen from sea water. The hydrogen could be exported and used as power station fuel, instead of natural gas.
If hydrogen fuel cells ever become economically viable, hydrogen from solar powered Newcomen Generators could be used to split water electrolytically as the primary hydrogen supply.
Integrated Newcomen Engine Generator and Conventional Steam Turbo-Generator Systems
Existing fossil fuel and nuclear power station systems that incorporate steam turbo-generators are less than 50% efficient. They dump at least half of the energy they consume back into the environment as waste heat. By using Newcomen systems similar to those described above to capture the waste heat, the wastage could be minimised. The figure below shows a compact design of an evaporation plus condensation chamber for use with fossil fuel and nuclear power stations.
A Compact Design of Evaporation plus Condensation Chamber Unit for Use with Fossil Fuel/Nuclear Power Stations
In many industrialised countries, including the UK, France, Germany and the USA, approximately one third of fresh water usage is accounted for in cooling power stations, with the resultant warm water vapour emitted by cooling towers being dumped into the environment. By using the waste heat productively, to drive Newcomen generator systems, even fresh water Newcomen generators will contribute significantly to preserving fresh water.
Integrated Newcomen Engine Generator and Carbon Capture Systems
Carbon capture systems extract the carbon dioxide from fossil fuel power station flue gases, compress the gas for ease of transportation and bury it deep underground, for example in depleted oil reservoirs. The compression process is wasteful when used with conventional power station systems because compression generates low grade heat that must be disposed of. In contrast, Newcomen generator systems are designed to work using low grade heat, so by combining a Newcomen generator with a suitably designed carbon capture plant the capture process can be made more cost effective. The figure below shows a notional plant design, with the turbines described earlier, being replaced by compressors.
A Carbon Capture System that also Captures Sulphur Dioxide
The essential argument made in the above figure is that by incorporating an alternating series of compression pumps and heat extraction units, Newcomen Generator systems can be used for energy efficient carbon capture.
The pressure drops caused by the condensing out of the carbon and sulphur dioxides could be used to drive turbo-generators similar to those described previously.
Non Water Rankine Engines
The Rankine cycle system is the opposite to a Newcoment engine cycle and uses a liquid that evaporates when heated and expands to produce work, such as turning a turbine, which when connected to a generator, produces electricity. The exhaust vapour expelled from the turbine condenses and the liquid is pumped back to the boiler to repeat the cycle. The working fluid most commonly used is water, though other liquids can also be used more efficiently as it is then no longer necessary to get over the hydrogen bonding energy holding water together as a liquid.
Non water Rankine cycle engines are similar to the large steam Rankine cycle engines found in coal-burning electric power plants. The main difference is that they utilize heavier working fluids such as organic compounds (in which case they are referred to as Organic Rankine Cycle engines or ORCE’s) which result in superior efficiency over steam Rankine cycle engines for low temperature heat sources (below around 627 deg. C.) Non water Rankine cycle engines typically require only a single-stage expander in the turbine stage, making them much simpler than multi-stage expanders typical of the steam Rankine engines.
One of the main advantages of non water Rankine engines is their mechanical simplicity which gives them obvious manufacturing and reliability advantages over other types of small engines that are more mechanically complex such as typical two or four-stroke engine generators, multistage gas turbine engines and reciprocating Stirling engines.
In the past several decades, thousands of non water Rankine engines have been developed and used for remote terrestrial applications with power outputs ranging from 1 to 1000 kW. A few examples of remote applications that have used efficient, reliable, unattended ORCE type power sources include communication stations, data gathering buoys, satellite communication power supplies, as well as irrigation pumps, air conditioners, and turbo generators.
More recently non water Rankine engine technologies have focused on using the following three renewable energies as heat sources:
- Waste Heat
Several ORCE’s powered by solar energy have been successfully built and demonstrated including solar dish-engines. Two advantages of non-water Rankine engines over photovoltaic generated electricity are higher efficiency and smaller space requirements. Non water Rankine engines used to produce power from geothermal resources or waste heat streams resulting from industrial processes have also been developed and used.
Non water Rankine engines are a more appropriate power system alternative over some of the other types listed above (e.g., fuel cells) for applications that:
- Seek to directly utilize a renewable energy source.
- Require direct shaft power (e.g. heat pumps, chillers, irrigation pumps, flywheel technologies, etc.)
Non water Rankine engines will find a potentially large market for waste heat utilization which will continue to increase as a result of the ongoing international effort to reduce the net emissions from greenhouse gases and are potentially useful for capturing waste heat in the Gaia Engineering process