CZ155493A3 - Conversion method of heat energy to mechanical energy - Google Patents

Abstract

The method is based on the principle of an energy cycle, where the working medium undergoes phased compression, heat supply from an external source and expansion with concurrent working performance and then cooling. Compression of the medium begins at its critical temperature and at an initial pressure higher than its critical temperature. In the expansion phase of the working media, while supplying heat until the upper temperature of the cycle is reached, heat can be supplied to the medium by exchange directly from the cooling phase and from the external source. In the expansion phase of the working media, after reaching the upper temperature of the cycle and subsequent cooling, heat can be supplied to the medium. In the reducing phase of the working medium volume, before reaching the lower temperature limits of the cycle, heat from the media in the low pressure cycle is transferred by exchange to the medium in the high pressure cycle. Carbon dioxide CO2 can be used as a working medium.<IMAGE>

Description

______ _r _ _______ Methods of converting thermal energy ___ into mechanical

Technical field

The invention relates to a method of converting thermal energy into mechanical energy based on an energy cycle.

BACKGROUND OF THE INVENTION ------------------------------------.......... ..... The conversion of thermal energy into mechanical energy is currently carried out in essentially two ways. In the production of electrical energy, which is obtained by the gradual conversion of thermal energy to mechanical, a steam cycle is used to convert thermal energy to mechanical work. The heat causes the water to evaporate, that is, the conversion of a liquid into a vapor which has a significantly larger volume at the same pressure. This larger volume of steam then does the work, usually in a turbine. The classic steam engine, where work is carried out by increasing the volume under the piston, is almost no longer used for a number of reasons. Heat is supplied to the conversion either by burning fossil fuels, i.e., coal, oil or gas, or by cooling the nuclear reaction in nuclear power plants. The disadvantages of this method are the relatively low efficiency, i.e. the low ratio between the mechanical work obtained and the heat input, where a considerable part of the energy is lost by cooling. The efficiency of nuclear power plants is around 25%, thermal power plants approximately 35%, which is about half of the theoretically achievable value. The reduction is based on the position of the cycle in the temperature-entropy or entropy-enthalpy diagram. The rest of the heat has to be costly removed. In relation to the critical values of the medium used, the steam cycle is constructed so that the lower cycle pressure (that is the lowest medium pressure) is significantly lower than the critical pressure and the lower cycle temperature (the lowest medium temperature) is significantly lower than the critical temperature properties do not determine).

A second method of converting thermal energy to mechanical energy is used in internal combustion engines. Internal combustion engines utilize an increase in the volume of flue gas enclosed under the piston, which is given

Their combustion temperature is higher than the inlet temperature — To achieve greater efficiency, either the fuel mixture or the air itself (compression phase) is compressed, followed by ignition and expansion, which results in mechanical work. Expansion takes place either in the space enclosed beneath the piston, where the subsequent movement of the piston is transferred to the motor shaft, or in a turbine, i.e. a turbomachine.

The disadvantages of the cycle are also its low efficiency and the necessity of using expensive liquid or gaseous fuels. The loss of the cycle is due to the loss of heat in the hot exhaust and cooling. In relation to the critical values of the medium used, the combustion cycle has temperatures significantly higher than the critical temperature and pressures significantly lower than the critical pressure.

SUMMARY OF THE INVENTION

These deficiencies are, to some extent, overcome by a method of converting thermal energy into mechanical energy, based on the principle of an energy cycle, where the medium undergoes phases of compression, heat supply, expansion with simultaneous work and cooling. The essence of the present invention is that the compression of the medium is based on a region of its critical temperature and an initial pressure higher than its critical pressure. This results in higher basic energy efficiency, higher energy densities, and reduced dimensions of the respective equipment for comparable performance compared to turbomachines.

In the expansion phase of the working medium at heat supply until the upper temperature of the cycle is reached, the medium is alternatively supplied with heat directly from the cycle cooling and from an external source. Compared to another alternative, where the heat supply at this stage of the cycle is exclusively from an external source, this increases the conversion efficiency.

In the expansion phase of the working medium after reaching the upper temperature of the cycle and the subsequent lowering of its temperature, additional heat can be supplied to the medium in order to increase the conversion efficiency.

In the phase of reducing the volume of working medium before reaching

-3the area of the lower temperature cycle was warmed from .media to. The low pressure ----- cycle converts it into a medium at a higher pressure cycle. This is the case if the expansion of the medium in the working machine does not reduce its temperature down to the lower temperature of the cycle. The heat from this phase of the cycle is directed through the counter-current heat exchanger to the expansion phase of the medium when the heat is supplied at a higher cycle pressure. As a working medium

------- _is - _with -výhodou applicability ekyšrich j "Cart" uhTíčrtefio C0 ₂ '~~~ ~ kterýliá appropriate critical parameters, it is the critical pressure and critical temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained with drawings, which is provided in FIG shows an example of the power cycle for carbon dioxide C0 _2, wherein upon expansion of the heat is supplied to it from an external source, or change from the cooling cycle. Fig. 2 is another example of the energy cycle for carbon dioxide CO ₂ , where in its expansion phase the expansion of the medium is repeatedly interrupted at certain pressure values without heat supply and the medium is again supplied by exchange directly from the cooling cycle and from an external source , then the expansion of the media and subsequent work continues.

DETAILED DESCRIPTION OF THE INVENTION

The new high-pressure energy cycle is designed to achieve higher baseline energy efficiency than current energy cycles, that is, a better ratio between the mechanical work obtained and the heat supplied, resulting in lower cooling losses. This is particularly important for nuclear power plants where efficiency is low due to the low upper cycle temperature.

The cycle works with a closed medium, which may be carbon dioxide, ammonia, isobutane, mixtures of carbon dioxide with lubricants (oils), freons and other substances. The position of the cycle according to temperature and pressure in relation to the critical medium values is important.

-4 ____ critical pressure of the medium is meant the lowest-Tiak when the liquid becomes a párůbež supplies Tepi ^ ⁼ ^ koňštáhtniin RTA ⁼ 'Tiak-u = ^ - and temperature.

For carbon dioxide CO ₂ the critical pressure is 7.52 MPa, for ammonia H ₃ N 11.52 MPa, for isobutane C ₄ H ₁₀ is 3.77 MPa, for monochlorotrifluoromethane CClF ₃ (F13) is 3.94 MPa.

The critical temperature of a medium is understood to be its lowest temperature, where the liquid changes into steam without supplying heat at constant pressure and temperature.

The critical temperature for carbon dioxide CO ₂ is 31.0 ° C, for ammonia-H 2 N - 13.2.4.4 ° C, for example, isobutane is 134 ° C, for monochlorobifluoromethane it is 2878 ° C: - - - - · "·" ·

If CO ₂ is chosen as the medium (according to suitable critical parameters of the medium, this working medium can be chosen; medium in accordance with cooling possibilities and suitable efficiency), then in the energy cycle in Fig. 1 this medium is suitable pump (piston, vane etc.) compresses through a heat exchanger into a hydraulic motor at 300 K (slightly lower than critical) from a pressure of 15 MPa (critical pressure is 7.52 MPa) and a volume of 50.797. 10 ³ m ³ / kmol to a pressure of 40 MPa and a volume of 44.063.10 ^-3 m ³ / kmol. In this area, the working medium is a liquid, so it is a high-pressure liquid pumping. This is followed by an isobaric expansion phase, that is, copper expansion as heat is supplied to the pressurized medium (at a substantially constant pressure of 40 MPa) from an external source, such as a nuclear reaction or fossil fuel combustion, at which its temperature rises to 500 K; the volume increases to 97.09. IC ^-3 m ³ / kmol. Said heat supply increases the volume of the medium at its constant pressure and thus the medium performs work in the respective machine. As a working machine can be used engine with working volume closed (classic engine with pistons, vane engine and the like) or turbine. Heat can be supplied to the working medium from two sources. On the one hand, exchange directly from the cooling cycle and part of the heat from an external source, and on the other hand only from an external source. In this phase of the energy cycle, the temperature of the cycles changes to the upper (highest) level. cycle temperature

-5.a pressure medium. it remains at the upper (not higher) cycle pressure.

After interruption of the medium supply to the working area of the working machine (eg a hydraulic motor), the medium continues its work by its expansion in the working machine, where its volume increases up to 164.42. 10 “ ³ m ³ / kmol and its temperature drops to 400

K and pressure to 15 MPa (lower cycle pressure). In the event that

- “expansion of the medium does not reduce its temperature up to the area of the lower cycle temperature, it is necessary to transfer heat from the medium at the lower pressure to the medium at the upper pressure (countercurrent heat exchanger) by heat exchange.

In the next phase of the cycle, the medium must be cooled at 15 MPa to return it to its original state. This cooling down of the medium is carried out in two ways. First, by common-cooling,?

for example by means of a water-carbon dioxide exchanger, which represents losses of the working cycle, and on the other hand, by more energy-efficient heat exchange with a counter-current exchanger into a pressurized medium at a pressure of 40 MPa. During cooling, sea or river water, evaporation process (similar to current power plants), air and special cooling processes can be used.

Fig. 2 shows a modification of the high-pressure energy cycle of Fig. 1. When the medium (carbon dioxide CO ₂ ) is at a pressure of 40 MPa and a temperature of 500 K, it is partially expanded and the medium is working. When its pressure drops to 30 MPa, the medium is re-supplied with heat (either from an external source or by heat exchange from the duty cycle). The temperature of the medium now rises again up to 500 K, followed by the expansion of the medium, the medium again working at a constant and subsequently decreasing pressure and this process can be repeated several times.

The high pressure energy cycle of the present invention, which is utilized in converting thermal energy to mechanical energy, is placed in the supercritical region of the working medium. This area can be chosen to cool down losses. The critical temperature of the medium must be so much higher than the temperature of the chilling 6- ni ^ .. ^ _J ABV, the medium can cool down the area of the critical Lup - tions. ,

The critical pressure of the medium should be as low as possible in order to make the device for converting heat to mechanical energy as simple as possible (high pressure shaft seals, movement seals, lubrication of systems). Working media such as carbon dioxide (CO ₂₎ and possibly freons (which have adverse environmental effects) best meet these requirements. the design of this high-pressure energy cycle essentially corresponds to the conventional design.

cycle (high pressure pump, hydraulic motor, heat exchangers). However, since the mechanical energy conversion device in this case operates at high pressures, _{t of the} order of magnitude higher than the steam cycle, the energy density is also higher and hence the equipment is smaller for the same outputs. By utilizing the high pressure energy cycle of the present invention, efficiency shifts can be achieved for both nuclear and thermal power plants.

Industrial applicability of the invention

Method for converting thermal energy to mechanical according to this

The invention is particularly applicable in the energy sector, in conventional thermal and nuclear power plants, in the field of marine and automobile propulsion.

Claims (5)

PATENT CLAIMS 1. A method of converting thermal energy into mechanical energy, based on the principle of an energy cycle, wherein the working medium undergoes phases of compression, supply of heat from an external source and expansion with simultaneous work and cooling, characterized in that critical temperature and from an initial pressure above its critical pressure. Method for converting thermal energy into mechanical energy according to claim 1, characterized in that in the expansion phase of the working medium at the heat supply until the upper cycle temperature is reached, heat is supplied to the medium by exchange directly from the cycle cooling and from an external source. Method for converting thermal energy into mechanical energy according to claim 1 or 2, characterized in that in the phase of expanding the working medium after reaching the upper temperature of the cycle and subsequently reducing its temperature, additional heat is supplied to the medium. Method for converting thermal energy into mechanical energy according to any one of claims 1 to 3, characterized in that in the phase of reducing the volume of the working medium before reaching the lower cycle temperature range, the heat from the medium at the lower cycle pressure is transferred in exchange to the medium at the higher cycle pressure. Method for converting thermal energy into mechanical energy according to one of claims 1 to 4, characterized in that CO ₂ is used as the working medium.