JPS58117307A - Method and device for converting thermal energy - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for converting thermal energy into another form of energy.

Current and future energy trends are leading to efforts to utilize energy sources such as low temperature industrial exhaust, waste liquids, geothermally heated water, and the like. These energy sources were considered to be out of the mainstream and not economically viable as a source of power during the last decade, when fossil fuels were still relatively cheap. Now 11 a method has been developed that can be considered a clearly advantageous proposition,
Devices have also been devised.

Most of these methods are based on the Rankine cycle, well known in the field of thermodynamics, and involve shaft-powered heat engines that exploit the expansive nature of gases or steam. An important challenge in such engines is that the vapor or gas must remain in the same phase during expansion to avoid liquid formation during expansion. This is because most mechanical expanders, such as turbines and reciprocating machines, do not operate well when liquid is present. Steam engines operating on various variations of the basic Rankine cycle often generate a certain amount of moisture during the expansion process. This is either because the water vapor is wet from the beginning, or because the thermodynamic properties of water vapor make the expanding vapor more wet. In such cases, the engine either superheats the steam or flans it to a lower pressure before entering the expander;
Alternatively, they are typically designed to minimize water formation within the expander by separating or removing excess water at intermediate stages of the expansion process. In recent years, the use of polymeric organic fluids in place of steam has been proposed as an important method of reducing the water content of expanding steam in Rankine cycle engines. Such institutions.

Ormat in Israel, The in the United States
rmoelectron, 5undstrand, GE
, Aero jet and other companies, IHL in Japan, M
Itsui, S in France.

ciete bertin, germante wa darn
ier, Italian, Swedish, and Soviet Union companies, all of which generate very little moisture in the expander during their operating cycles. therefore,
Turbine efficiencies are higher than with steam, and this is a major reason for its good performance in low-temperature power generation systems used to recover waste heat or geothermal energy.

However, methods based on Rankine cycles still have a number of deficiencies that impair their efficiency. That is, the entire evaporation portion of the cycle consumes enough thermal energy to raise the liquid temperature not only to the boiling point by -F but even beyond that point. In fact, when using an organic working fluid, it almost always leaves the expander in a superheated state and must be cooled down in a large condenser. A portion of the extracted heat can be recycled and used to preheat the compressed liquid, but this requires an additional heat exchanger known as a regenerator. This drawback can be avoided to some extent by supercritical heating, but this increases feed pump work, which also reduces cycle efficiency. In addition, during the boiler heating process, the temperature of the working fluid increases unevenly, and when using a single-phase fluid such as hot gas or hot liquid flow as a heat source, cycle efficiency is increased and the heat can be used with high efficiency. It becomes impossible to recover.

Clearly, it would be desirable to overcome the shortcomings and deficiencies of the prior art Rankine cycle, by providing a method in which the working fluid only needs to be heated to its boiling point, and the evaporation is carried out by flashing in the expansion section of the cycle. . This eliminates the need for a heat storage chamber and increases the efficiency of converting heat from the mesophase wake into power. For low-temperature heat sources, which are mostly industrial waste heat, solar ponds, geothermal heat, etc., this is a significant cost advantage over the best of Rankine cycle-based devices. To briefly explain, a solar pond is a shallow pool of water, with the upper layer being unsalted water and the r layer being salt water. Salt water is heated to a temperature of around 95 degrees by the radiant heat of the sun, and heat is extracted from this salt water.

According to the present invention, a method for converting thermal energy into another form of energy includes preparing a liquid working fluid having said thermal energy, compressing the working fluid in a substantially adiabatic manner, and operating with the wet working fluid. , substantially adiabatically expanding a hot compressed working fluid by flashing to produce said another form of energy within an expansion machine that can gradually dry said working fluid upon expansion; and working fluid discharged from the expansion machine. It consists of condensing.

Furthermore, according to one aspect of the present invention, a device for converting thermal energy into another energy form includes a device for supplying a liquid working fluid having thermal energy, a pump device for compressing the working fluid substantially adiabatically, and a pump device for compressing the working fluid substantially adiabatically. an expansion device for substantially adiabatically expanding a hot working fluid by flashing to produce another form of energy, the expansion device being operable with wet working fluid; At times, the working fluid can be gradually dried and further the working fluid discharged from the expansion machine can be condensed.

Hereinafter, the present invention will be described by way of examples with reference to the accompanying drawings.

The method according to the invention provides a constant phase thermal engineering source, namely:
These two types are suitable for energy sources that do not undergo a phase transformation when transferring their thermal energy to a working fluid, and are best understood by a detailed comparison with the well-known Rankine cycle, which differs in terms of wood structure. The mechanical components that implement the cycle are almost the same.

The basic Rankine cycle for water vapor is T in Figure 1.
The basic Rankine cycle for organic working fluids, such as those used in Ormat systems, is shown in the T-s diagram of FIG.

The operating sequence in FIG. 1 is liquid compression (1→2), heating and evaporation (2→3), expansion (3→4), and condensation (4→1). Note that in this case the water vapor exits the expander in a wet state. Regarding Figure 2, the organic fluid, by its nature, often leaves the expander in a superheated state at point 4, resulting in the vapor temperature having to be reduced as shown in Figure 2 (4→5). .

This desuperheating is accomplished with a large condenser.

The mechanical components that carry out this operating sequence are shown in FIG. 3 and include feed pump 2o, boiler 22 . It includes an expander 24 (turbine, reciprocating machine, etc.), an attemperator and condenser 26.

FIG. 4 shows that the compressed liquid is preheated using at least a part of the rejected superheat reducer (4→5 in FIG. 2 2→7),
It shows how to reduce external heat requirements. This is physically accomplished by providing the circuit with an additional heat exchanger 28, known as a regenerator, as shown in FIG.

In the T-s diagram used throughout this specification,
The area enclosed by the lines connecting the cycle points represents the amount of work.

Now, it is a well-known result of the laws of thermodynamics that when heat is obtained from a constant temperature heat source or an infinite heat source, the ideal heat engine cycle becomes the Carnot cycle shown in Figure 6.

As can be seen by examining Figure 1.2.4, the Rankine cycle is very close to the ideal Carnot cycle due to the large amount of heat supplied at a constant temperature during the evaporation process shown in Figure 1. This process takes place in a boiler, and in almost all cases the amount of heat supplied is considerably greater than that required to raise the temperature of the working fluid to its boiling point. Naturally, the evaporation of the fluid in an Or m a' t type system is
In fact, it is an important feature of the sequence of processes involved in some Rankine cycles. However, if the heat is not supplied by an infinite or constant temperature source,
The Carnot cycle is not necessarily an ideal model. Now consider the flow of hot liquid or gas that you are discarding. When cooling this stream, the heat transferred therefrom depends on the temperature low F as shown in the temperature versus heat transfer coordinate cooling curve of FIG.

Boiler heating process (2 → 3 in Figure 1.2, 7 groan 3 in Figure 4)
) is shown in FIG. 8. In this case, the large amount of heat required to evaporate the working fluid in a Rankine cycle φ boiler limits the maximum temperature that the working fluid can achieve to a value much lower than the maximum temperature of the fluid stream being cooled. I understand.

To achieve a fairly desirable conversion of heat into mechanical power, the working fluid being heated in the boiler follows a temperature versus heat transfer path that exactly matches that of the cooling fluid stream that heats it. good. This ideal case is shown in FIG. 9, which results in the ideal heat engine cycle shown in the T-s coordinates of FIG.

At first glance, this seems to be the inverse of the ideal Carnot cycle concept. However, it should be understood that the Carnot cycle is ideal only for constant temperature or infinite heat sources, whereas here the heating source temperature changes throughout the heat transfer process. Another way to visualize the cycle shown in FIG. 1O is to think of it as a series of micro Carnot cycles, each receiving heat at a slightly different temperature as shown in FIG.

For such cycles, the large heat of vaporization required in Or m a t type cycles is quite disadvantageous. Therefore, after the completion of evaporation, the steam can be superheated to obtain the cycle shown in Figure 12, or the inlet/outlet pressure can be increased to obtain the cycle shown in Figure 13.
It has been proposed to improve the T-type conflict cycle. This is because these results in a Rankine cycle shape that is close to the ideal. However, both of these cycles typically require large desuperheating, which means that a large storage chamber is required if efficiency is to be maintained, which also means an increase in cost. Both cycles
Typically, the working fluid is expanded as a dry vapor, but it is implied to some extent that the vapor becomes somewhat wet during the expansion process. It is little known that supercritical cycles usually require very heavy feed 3 2 pump water, especially if there is little superheat reduction of the steam leaving the expander. This reduces cycle efficiency.

The new cycle according to the invention is shown in Figure 14.15.
It is shown in the entropy coordinates, and includes liquid compression (l → 2) similar to that in the Rankine cycle, heating of only the liquid phase (2 → 3), and expansion accompanied by a phase transformation from liquid to vapor as already explained. (3→4), consisting of condensation back to 1. As can be seen in FIG. 15, for some organic fluids, expansion produces completely dry vapor at the outlet of the expander. The sequence of components required for this cycle is shown in FIG.

These components are essentially the same as those used in the basic Rankine cycle (with the exception of the smaller condenser 30), but unlike the Rankine cycle, the liquid heater 22 has minimal evaporation and preferably Wet steam differs significantly from the Rankine cycle in that it must operate without any evaporation, and the function of the expander also differs from that of the Rankine system described above.

4. Compared to the supercritical Rankine cycle shown in FIG. 13, in which the heating is equivalently carried out in a single phase, the cycle according to the invention also differs in that the fluid is heated at supercritical pressure,
As mentioned earlier, the expander is also different from the Rankine cycle expander. If this cycle is used with a complex liquid refractory/volatile liquid working fluid as in MHD, then in temperature-entropy coordinates,
Due to the large heat capacity of the liquid metal, the line of expansion will be more inclined to the right as shown in FIG. Thus, the volatile fluid becomes drier at the expander outlet.

The cycle according to the invention has a number of advantages over extremely modified forms of the Rankine cycle, such as in supercritical systems:

l) Little or no desuperheating is required, so no heat storage is required.

2) Fewer feed pumps are required than in the supercritical Rankine cycle.

3) Cycle efficiency is higher for constant phase heat flow.6 4) More heat can be transferred when, unlike in the Rankine cycle, there is no limit to the temperature at which the constant phase flow can be cooled.

The efficiency of the cycle according to the present invention 1 is determined by the cycle efficiency before work is generated in the expander, as shown in step 3-4 of the T-S diagram in FIG. 18 and reference numeral 32 in the block diagram of the components shown in FIG. is significantly enhanced by carrying out the initial stage of expansion in a flushing chamber.

This ensures that the first part of the expansion does not have to occur at a rate determined by the required rotational speed of the expander, and that this process in the flushing chamber 32 is at equilibrium before further expansion begins. Sufficient time may be allowed to mix the steam mixture well. Furthermore, the volumetric expansion ratio of the expander is considerably reduced, making the design work considerably easier.

On the surface, it would seem that such a modification of the basic wet steam cycle would lead to a loss of usable energy, offsetting any theoretical advantage over the Rankine cycle. However, when we examine the expansion process more precisely, we find that the adverse condition of power loss due to such a change is very small, on the order of a few percent of the solder, but the extra amount is due to the working fluid and Depends on the temperature range in which it expands.

The reason is that the initial liquid volume is l compared to the final volume of vapor.
”・Because it is great. Since flow work is equal to the integral of the product of pressure drop and volume, it is appropriate for only a fraction of the work accounted for by an expansion ratio of 3 or more in the initial stage or a smaller expansion ratio in the final expansion stage. . This is confirmed by accurate calculations.

In research on recovering power from geothermal water at 100'O, we performed calculations using a computer program. The results of this 34 calculation were compared with the Run Hour Cycle ◆ system.

The assumptions were the same except that the Rankine turbine efficiency was 85% and the efficiency of the appropriate screw expander was 80%. This is pretty much the same thing, although we didn't do anything about circulating geothermally heated water.

76 It seemed to be slightly larger than the one in the Rankine cycle. The hot water flow rate was 75 Kg/s. In all cases, cold tofu R114 was chosen as the working fluid to maximize all analyses.

Power from the Rankine system was 717 kWe.

Wet steam systems 8 In these cases, the expander volume ratio is quite low and by doubling the fluid volume in flushing 3
It is possible to perform a complete expansion with a single stage screw m-expander with power losses of less than %. If the volume is tripled by flushing, a single-stage vane expander can also perform expansion if this output can be used as a basis.

If the overall volume ratio were higher, the power loss penalty would be less. Even the numbers in the last column, where the expander volume ratio is very conservative, are only 9 points worse than the Rankine system.

In other cases n-pentane was chosen as one working fluid to optimize all analyses.

The power as a Rankine system is equal to 746 kWe.

Wet steam systems In these cases, the expander volume ratio is such that by increasing the fluid volume at the flood ring by a factor of 8, full expansion is possible with a single stage screw expander with a power loss of 8%. It is a kimono.

When flushing increases the volume by a factor of 12,
If this output can be used as a basis, a single-stage vane type expander can also perform expansion.

If the overall volume ratio is high, the adverse conditions of power loss will be less.

To evaluate the possible advantages of this cycle over the Rankine system, a very detailed study of the power recoverable from hot rock geothermal heating water was performed assuming a water flow rate of 75 to 9/sec. . All systems were fully optimized using computer programs developed over 10 years for each of the many working fluids.

This program takes into account all internal losses and inefficiencies in detail. The results of this study are summarized in the table below.

1 As clearly seen from this table, the "wet steam" cycle of the present invention is significantly larger at a lower cost per unit of output than the Rankine cycle system.

Perform proper power recovery.

In addition, power is recovered from the solar pond and heat collector. We conducted research on cryogenic systems used for.

It has been found that nearly three times the output power of the Rankine cycle system is possible here.

Further advantages of the "wet steam" cycle according to the invention are explained below.

In many industrial processes, especially in chemical plants, large quantities of hot fluids ultimately have to be cooled. Such a plant requires a large heat exchanger to extract the heat, which may, of course, constitute the boiler for the power plant according to the invention as described above. Another method of using this process heat is to omit the Mumu sepoiler and use the hot liquid itself as the working fluid, either directly or through a flushing chamber, into the expander, where it is expanded and cooled to do work. . Although the final heat extraction still requires a pump to recompress the liquid and a condenser after this extraction stage, such a process "wet steam" expander system is not suitable for boilers or liquid heaters. Since there is no need for Q, installation is cheaper than a growth engine,
Efficiency is achieved in that there is no temperature drop in transferring heat from one fluid to another within a boiler or heater.

This principle can be used with wet steam expanders when recovering power from hot rock geothermal or other heat sources where the circulating fluid does not need to be limited to water.

As mentioned earlier, one of the fundamental differences between the "wet steam" cycle of the present invention and the Rankine cycle is that in the former:
Phase transformation during the expansion process is the most woody characteristic, and in the latter case it must be avoided as much as possible. Additionally, when moisture is generated in a Rankine cycle system, the moisture content of the steam gradually increases during the expansion process, whereas in the "wet steam" cycle of the present invention, the steam dries out as expansion progresses.

As a result, conventional turbines and reciprocating machines are unsuitable for the expansion phase of the "humid fff! steam" cycle according to the invention. This causes the droplets to corrode the turbine blades (L%), reducing the aerodynamic efficiency of the turbine, and washing lubricating oil from the cylinder walls of the reciprocating expander, promoting mechanical wear and seizure. It is from. There are other machines that can be used for this purpose. For example: l) Positive evacuation machines such as rotary vane type, screw set expanders. If liquid is present in this, lubrication is promoted and leakage is reduced. Very efficient small vane machines are available.

2) Two-layer turbine.

3) MHD (magnetohydrodynamic) duct through which the working fluid flows. In this case, the fluid consists of a mixture of a volatile liquid that changes phase and a non-volatile liquid such as a liquid metal or other conductive fluid. This non-volatile liquid is propelled through the rectangular cross-section duct by the expanding volatile liquid. If the two opposite walls of the duct generate a magnetic field between them, and the other pair of opposite walls contain electrical conductors, a direct current can be generated by this means. Refrigerant II for use in "wet steam" process expansion systems, 12.21.
30.113.114.115, toluene, thiophene, n-pentane, pyridine hexafluorobenzene,
Various working fluids were investigated including Fe12, monochlorobenzene, and water. The main disadvantage of water is the very large volume ratio required for expansion, and n-pentane, along with R11, R12 and other refrigerants, has a much more desirable volume ratio and can be used in either one or two stages depending on the operating temperature limits. This expansion ratio can be obtained with any number of expansion stages among three, three, and four.

To increase system efficiency, if possible, both the expander and the flushing chamber should be provided with means to facilitate the flushing process. Such means are known per se, but include turbulence promoters that create vortices in the fluid before it enters the expander, inoculants that increase nucleation points and create bubbles within the fluid, and surface tension of the working fluid. A wetting agent that weakens and increases the rate of bubble growth during the early stages of flushing.

6 including combinations of these means.

Furthermore, the mechanical efficiency of the expander can be improved by adding suitable lubricants to the working fluid to reduce friction on the contact surfaces of the moving parts.

Although organic fluids are preferred as working fluids, suitable inorganic fluids may also be used. The heat source is generally a liquid, with a view to keeping the size of the heat exchanger within reasonable limits, but may also be a vapor or a gas.

As will be clear to those skilled in the art, the invention is not limited to the details of the previously illustrated embodiments, but can be embodied in other special forms without departing from its woody character, and therefore , these Examples are in all respects for illustrative purposes only, and reference should be made to the claims, and the inventors do not intend to understand the meaning and equivalence of the claims. All changes of similar scope are intended.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the T-S (temperature/entropy) diagram of the Rankine cycle using water vapor, Figure 2 is a diagram showing the T-s diagram of the Rankine cycle using organic liquid, and Figure 3 is the diagram shown in Figure 2. Figure 4 shows a block diagram of the mechanical components used to perform the sequence shown; Figure 4 shows a T-s diagram similar to Figure 2 for a reject superheater used to preheat compressed liquid; Figure 5 is a block diagram showing the use of a heat storage chamber, Figure 6 is a diagram showing an ideal Carnot cycle T-s Gui 7g, Figure 7 is a hot liquid or hot gas to be disposed of. Figure 8 is a diagram illustrating how this cooling effect can be combined with the heating part of the cycle shown in Figure 1.2.4; FIG. 9 is a diagram similar to FIG. 8 showing the desired matching; The $IO diagram was obtained from the matching shown in FIG. Z'1 T- of the novel triangular "wet steam" cycle according to the invention
s diagram, Figure 11 shows how this cycle can be considered as a series of micro Carnot cycles, and Figures 12 and 13 show a conventional method for improving the Rankine cycle to recover power from constant phase steam. Figure 14.15 is a diagram showing a T-s diagram including a saturated envelope, which explains the "wet steam" cycle in more detail, Figure 16 is a T-s diagram similar to Figure 14. Figure 17 shows a block diagram of the mechanical components used to produce the T-s of the present cycle when combined liquid/metal/volatile liquid working fluids such as those used in MHD are used. Figure 18 is a diagram showing the practical form of a wet steam cycle (7); Figure 19 is a diagram showing the mechanical structure used to generate the T-S diagram of Figure 18; FIG. 9 is a diagram showing a block diagram of the constituent elements. 20--Pump, 22--Boiler, 24--φ expander, 26--Kensha superheat reducer and condenser, 28--Rei◆
Heat exchanger, 30 years old/+1 condenser Applicant:
Solmets Corporation N,V Agent: Masaru Okabe
Yuki I - Mitsugu Kuribayashi Yuyama 1) Takashi - Noboru Kato 0 Ftc, 1 entropy 7IC/G, 2 entropy FtG, 4° entropy heat transfer/47, 7 nσ9 heat transfer F/G-8° entropy/'/, IO. Entropy /'/, /1 entropy FIG, /J: entropy FIG, /2° entropy MG, /4° entropy Ftc, /s. Ftc, /6 Entropy Ftc, /7 FIG, β Ftr:;, /9

Claims (1)

[Claims] (1) A method for converting thermal energy into another form of energy, which comprises: preparing a liquid working fluid having the above-mentioned thermal properties; compressing this working fluid in a substantially adiabatic state; expanding a hot compressed working fluid substantially adiabatically by flashing to produce said other form of energy within an I11 heavy machine operating with a wet working fluid and capable of gradually drying said working fluid upon expansion; A method characterized in that the working fluid discharged from the expansion machine is condensed. (2. The method according to claim 1, characterized in that the flushing is started before the flushing is introduced into the expansion machine. (3) The method according to claim 1 or 2. A method according to claim 3, characterized in that the condensate is recycled for recompression. (4) A method according to claim 3, in which the working fluid is adiabatically compressed from a cold saturated state, A method characterized by heating by heat transfer from a thermal energy source. (5) A method according to claim 3 or 4, wherein the working fluid is an organic fluid or a suitable inorganic fluid, preferably is refrigerant 11.12.21.30.11
3,114,115.1-luene, thiophene, n-pentane, pyrideno, hexafluorobenzene, Fe1
2. A method characterized by selecting from a group containing monochlorohenzene and water. (6) The method according to claim 3 or 4, wherein the working fluid is a mixture of a liquid conductive substance and a volatile liquid, and the working fluid is adiabatically l11 in the magneto-hydrodynamic duct I. A method characterized by stretching. (7) A method according to any one of the preceding claims, including the step of accelerating the flushing process by creating turbulence in the working fluid in the flow of the tensioning machine. (8) A device for converting thermal energy into another form of energy, the method comprising: a device for supplying a liquid working fluid having thermal energy; and a device for supplying a liquid working fluid having thermal energy; and an expansion device for substantially adiabatically expanding the hot working fluid by fluffing to produce said other form of energy, said expansion device operating with a wet working fluid. An apparatus characterized by being capable of gradually drying the working fluid during expansion, and further condensing the working fluid discharged from the expansion machine. (9) Claim 8: 2. The device according to claim 1, wherein the flow of the expansion device includes a device for causing the flashing to wither and wither. (io) A device according to claim 8 or 9, characterized in that the expansion device is a rotary vane machine or a screw expander.