WO2004055352A1

WO2004055352A1 - A method of utilizing low temperature heat

Info

Publication number: WO2004055352A1
Application number: PCT/DK2003/000884
Authority: WO
Inventors: Allan Thomsen
Original assignee: Dantaet Electronics A/S
Priority date: 2002-12-16
Filing date: 2003-12-16
Publication date: 2004-07-01
Also published as: AU2003287902A1

Abstract

When, according to the invention, the heat energy from e.g. a solar collector system is utilized and the heated air (2) is allowed to drive a turbine and a generator (3) in the manner according to the invention, where the air (7) from the surroundings is supplied to a heat exchanger (14) to heat the air before the air (16) is supplied to the solar collector (1), the source of hot air is utilized in an expedient manner to achieve a power excess.

Description

A METHOD OF UTILIZING LOW TEMPERATURE HEAT

State of the art

The invention relates to a method of utilizing air which is heated in a solar collector or another heat source to a temperature below 100 °C, said heated air being supplied to a turbine or piston engine in a system which drives an electrical generator.

The increased pollution caused by the use of fossil fuel for the production of electricity, etc. has resulted in a requirement for the greatest possible reduction of this use.

Alternatives are either nuclear power systems, which, however, also involve a source of pollution in the form of spent uranium staves which are to be disposed of.

Environmentally friendly installations include wind and wave power systems which operate when the winds so allow.

Finally, there is utilization of the solar energy for the production of electricity by heating the heat in a solar collector and utilization of the pressure increase to drive a turbine, which produces power via an electrical generator.

An example of such a system is known from US 5 300 817, which describes a solar collector which heats atmospheric air supplied via channels through a compressor part with blades and turbine blades that cause the turbine shaft to rotate to drive the generator.

This system requires a certain pressure drop because of the updrift of the heated air, and therefore the efficiency is not sufficiently great to make the system profitable.

Object of the invention

The object of the invention is to improve the efficiency, and this is achieved according to the invention by a method, wherein the heated air is supplied to the turbine or a pressure chamber of the piston engine, and air from the surroundings is supplied and heated either via a heat exchanger in case of turbine operation or via cooling fins of the piston engine in case of engine operation before the air is supplied to the solar collector.

When the heat energy is used in this manner for the heating of the air supplied to the solar collector, an unprecedentedly high efficiency is achieved. The reason is that the method allows more energy to be recovered in the turbine or the piston engine than is required to drive the compressor and the fan, and thereby provides a relatively great power excess.

When, as stated in claim 2, a heat exchanger is used in a turbine-driven system, the air supply will serve as a carrying medium to raise the tem- perature of the working air in the system in an effective manner.

Finally, as stated in claim 3, a system with a piston engine will utilize the heat given off by the engine in a simple manner to heat the atmospheric air supply before the air is supplied to the heat source.

The drawing

Embodiments of systems for the performance of the methods according to the invention will be described more fully below with reference to the draw- ing, in which fig. 1 shows a system with a turbine-driven electrical generator, and

fig. 2 shows a system with a piston engine-driven generator.

Description of embodiments of the method

The working principle of the systems is to utilize a source of heat in the best possible manner to heat air, which will generate a positive pressure in the first instance because of the expansion and then convert the positive pres- sure into useful work by allowing the air to expand through a turbine.

To achieve the greatest amount possible of useful work in such a continuous process it is necessary to reduce the supply of energy to the system, which will be described in the form of a turbine-driven and a piston engine- driven system.

Figs. 1 and 2 schematically illustrate how the constituent components of the system are connected.

Fig. 1 shows a system comprising a turbine 3 which is coupled to an electrical generator (not shown), said turbine 3 being connected by a pipe 2 with a solar collector 1 or another form of energy source, such as a waste heat and the like.

The air in the solar collector 1 is heated and expands via a pipe 2 to the turbine 3, from where 5 it is conveyed through a pipe 4 to a heat exchanger 14, in which it is cooled and thereby generates a negative pressure, contraction, relative to the air in the pipe 2 before the turbine 3. The cooled air 24 is then discharged to the atmosphere.

Further, atmospheric air 7 is supplied to the heat exchanger 14 via a com- pressor 10, whereby the air 11 is heated in the exchanger 14 and is supplied in a heated state 16 via a pipe 15 to solar collectors 1 , following which the cycle is repeated.

To illustrate the mode of operation of the system, an idealized system will have the following characteristics, viz.:

the solar collector 1 can yield 10 kW at a discharge temperature of maximum 95 °C, - the heat exchanger 14 is assumed to have an efficiency of 50%, flow resistance in pipes, heat exchanger 14 and solar collector 1 is disregarded, and the embodiment is free of limitations in terms of space and weight, and loss in the compressor 10 and the turbine 3 is neglected.

In these circumstances, the following operational conditions are assumed to apply with reference to the system shown in fig. 1

Measurement point Temp. °C Positive pressure kPa Flow l/s

Compressor inlet 7 20 0 394

Compressor outlet 11 20 30 394 Heat exchanger outlet 16 57.5 30 453 Solar collector outlet 2 95 30 512 Turbine outlet 5 95 0 512

The resulting power excess will be 3.5 kW at 30 kPa (512-394) l/s.

Fig. 2 shows a basic sketch of a system with a piston engine which drives a generator. In this case, too, the heat source is a solar collector, but other examples of heat sources might be used, such as hot cooling water or air, etc.

The heated air 2 from the heat source 1 is supplied via a controlled valve 27 to an engine chamber 22 of a piston engine. The piston 17 is at the top of the cylinder 18, as indicated, and when the valve 27 opens, it will be able to admit hot air, as the flywheel 21 of the piston engine moves the piston 17 downwards in the cylinder 18.

Then the valve 27 interrupts the air supply 2, and the piston 17 will be moved down in step with the cooling of the air, contraction, in the chamber

22.

The air in the chamber 22 is hereby displaced, and this takes place by the opening of a one-way valve 23 to discharge the air which exceeds the counter pressure of the valve as outflowing air 24.

The piston 17 with a connecting rod 20 is connected with a crankshaft 26 and a flywheel 21 which drive an electrical generator (not shown).

The atmospheric air 7 to be supplied to the system flows past the cooling fins 19, 25 of the engine, where it is heated before being conveyed via a fan 12 as heated air 16 via a pipe 15 to the heat source 1. This working cycle is then repeated.

The controlled valve 27 is connected synchronously with the crankshaft 26 in a generally known manner to control the flow of hot air to the engine.

Of course, it is possible to construct the engine as a multi-cylinder engine and to dimension according to the capacity of the heat source.

Claims

PATENT CLAIMS

1. A method of utilizing air which is heated in a solar collector or another heat generator to a temperature below 100 °C, said heated air being supplied to a turbine or a piston engine in a system which drives an electrical generator, characterized in that the heated air (2) is supplied to the turbine (3) or a pressure chamber (22) of the piston engine, that air (7) from the surroundings is supplied and heated either via a heat exchanger (14) in case of turbine operation (3) or via cooling fins (19) of the piston engine in case of engine operation before the air (16) is supplied to the solar collector (1) again.

2. A method according to claim 1 , wherein the system comprises a turbine, ch a racterized in that the discharge air (5) from the turbine (3) is supplied to a heat exchanger (14) to give off heat to the supplied ambient air (7), which is supplied via a compressor (10) to the heat exchanger (14), following which the heated air (16) is supplied to the inlet end (15) of the solar collector (1 ) or another source of hot air.

3. A method according to claim 1, wherein the system comprises a piston engine, characterized in that the heated air (2) from the solar collector (1) or another source of hot air is supplied via a controlled valve (27) to the engine, while its piston (17) is descending, following which the hot air supply is interrupted by the valve (27) so that cooling and subsequent con- traction of the air in the cylinder (18) caused by the supply of ambient air (7) causes the piston to be pressed upwards by the external atmospheric pressure, whereby energy is transferred to the flywheel (21) of the engine until the pressure difference has been balanced, and then excess air is discharged through the non-return valve (23), while the heated ambient air (16) is conveyed to the inlet port (15) of the solar collector (1) or another source of hot air by means of a fan (12).