The Convector Generator
The products of combustion are carbon dioxide, water vapour, unused nitrogen and excess air. The hot gases rise because they are lighter than air. The individual molecules are moving at high velocity and have a large amount of kinetic energy. Their collision against any surface creates pressure. The continuous upward flow of combustion products could rotate a turbine or wind vane producing electricity.
Hot gases rise because of gravity. The atmosphere is held around the earth by gravitation. Cold air is like water in its response and seeks the lowest level. Cold air is pulled towards the earth and will displace warm air or any lighter gas. In the domestic coal fire, the combustion products rise because fresh air which is denser forces the hot gases upwards. Hot air rising is not the primary action – it is a reaction to cold air being pulled down by gravity forcing the lighter combustion products upwards.
In any process of continuous combustion, there will be a regular flow of the hot gaseous products. It creates a force vertically upwards. If the flow is along a uniform pipe the constant push from the flow can be used to cause rotation and to generate electricity. It is like harnessing the energy of the wind. If wind vanes are placed in the path of the rising hot gases, the molecules will lose some of their kinetic energy in collisions with the vane surface causing rotation. Heat energy is converted into rotational energy which can generate electricity.
In this way the combustion products themselves can directly rotate a vane or turbine. There is no need to use the heat energy to turn water into steam. The technologies developed for harnessing the energy of air flow or water flow can be adapted to the generation of electricity from convection currents. Windmills, steam turbines, hydroelectricity and wave power all extract energy from moving gas or liquid. Every design developed could be adapted for use in a Convector Generator, harnessing the energy of a continuous flow of rising hot gases to produce electricity.
At its simplest:
The combustion products will rise, their molecules colliding with the surface of the vanes causing rotation. There should be a series of vanes or obstructions to maximise the number of collisions and the absorption of energy. The turbine at ground level will generate electricity. An alternative arrangement based on the waterwheel would be:
The flue gases may contain considerable energy, so a more efficient system would involve heat recovery from the exhaust gases to pre-warm incoming air.
There is an endless array of options for the rotational mechanism. It is a case of absorbing energy from a flow of gas under pressure to produce rotation and converting this into electricity. The variety of technologies in harnessing wind power, those involved in hydroelectricity or in the design of turbines or jet engines are all relevant and could be adapted.
A particularly interesting recent development is the Wells turbine which can achieve efficiencies of up to 90% in converting wave energy into air flow and into electricity. A novel feature of the Wells turbine is that it continues to rotate in one direction irrespective of the direction of the air flow. It may apply to the convector generator as below:
In the apparatus as drawn there must be a certain distance between the level of the flue gas exit and that of incoming air. The greater is this "head", the faster will be combustion and the greater the capacity of the system but it will be at some cost to energy efficiency.
Convector generators as depicted above should be able to achieve efficiency of conversion of heat energy into electricity of above 80%, as there is very little loss of energy. The residual energy in the flue gases could be further recovered using the principles of the condensing gas boiler or used to heat water as in combined heat and power systems to give an overall efficiency of over 90%.