The ideas outlined above can be scaled up to the dimensions of power stations or miniaturised to apply to car engines. The principle is that rising combustion gases should themselves directly rotate a turbine. If linked to a heat recovery system using the energy of the spent flue gases to pre-heat incoming air, then a conversion efficiency of over 80% heat into electricity should be possible. At its simplest the design could be as follows:
The heavier is the material of the wheel the greater the heat capacity and angular momentum. Thus for a high capacity generator of 100MW - dimensions could be 10 m diameter, 20 m length, 100 sectors and total weight 100 – 1000 tonnes. If it is found that a rotating wheel such as above gives only about 50% efficiency, then a second, third ... wheel could be constructed to extract maximum energy from the rising hot gases. This should raise efficiency to above 80%.
An alternative would be to use a heat exchanger to recover the energy of the spent flue gases to preheat incoming air.
In every design represented there are no pumps. It is expected that each apparatus works at normal pressure and is driven by convection currents alone. The latter two descriptions may involve inconveniently tall units or sections that are well above ground level. The power station could be built on a hillside or under a mountain cf Dinorwic, for structural stability and reduced environmental impact eg
Building such an underground power station would also minimise heat losses – it would in effect be supra insulated by the ground above.
There may be some question over the dimensions of a power station that uses air at atmospheric pressure and relies on convection currents alone. Modern industrial combustion equipment using solid fuel at atmospheric pressures can achieve an energy density of 600 kilowatts per square metre of combustion area. This would indicate that for a 1000MW power station, an area of combustion of 40 metres by 40 metres may be needed.
There may also be some question about the temperature of the combustion gases and its effect on the rotating materials in the hot exhaust stream. The turbo effect is extremely important here. There must be a large excess of air for combustion to lower the temperature of the combustion gases. If only a stoichiometric amount of air is present, the exhaust gases will be at 2000° C – a three fold excess of air is needed to reduce this temperature to 500° C. Any design of combustion units must allow for this 2 – 5 fold excess of air.
Electricity generation using incoming air may be possible using the following configuration:
Perforations in the chimney above the combustion chamber will allow air to be drawn through the Convector Generator. The volume drawn in through the CG may be 5 –10 times that drawn in for combustion. The heat content of the flue gases is used to preheat incoming air – the latter then generates electricity with an efficiency that should be over 80%. The advantages of using incoming air would be that it is non-corrosive and the lower temperature will mean a longer life for the convector generator.
When we consider that natural gas is now the leading fuel for electricity generation in Britain and that modern power stations have such high controllability, the following arrangement could provide highly efficient generation:
A magnet could be designed of suitable geometry and with buoyant light materials surround so that it rotates efficiently and ‘weightless’ under the upthrust of the rising incoming gas flow. There are no major energy losses in the above configuration. The heat content of the combustion gases is transferred to the incoming air that rotates the magnet and generates electricity. Any residual heat is absorbed in the water exchanger. An overall efficiency of over 90% should be possible.