Method and device for generating electricity using low-grade heat transfer fluids

 

(57) Abstract:

Method and device for generating electricity can be used in the energy sector. In the method, including direct energy cycle in which liquid working fluid is compressed, then heated and vaporized, the vapors expand in the turbine with electricity generation and condense, and return the energy cycle in which the refrigerant is compressed in the compressor is cooled by transfer of heat to the working body and the expansion in the expander, the condensation of the working fluid is carried out at a temperature below the ambient temperature, the temperature of the refrigerant before compression in the compressor is reduced below the ambient temperature, the refrigerant in the expander is cooled to a temperature below the condensation temperature of the working fluid and served in a condenser for dissipating heat and the heating and evaporation of the working fluid before the turbine is carried out with the use of low-grade heat carrier. The device includes a power circuit connected in series with pump, heater, turbo-generator and a condenser, and a heat pump with an expander and a compressor connected to the heater, the steam path after heater provided with a heat exchanger d is instore, and the loop steam cycle front of the turbine has an additional heater is connected to an external source of thermal energy. The invention provides improved efficiency of energy conversion of low-grade heat sources, such as electricity, reducing fuel consumption and emissions of flue gases into the environment. 2 S. p. and 16 C.p. f-crystals, 2 Il.

The invention relates to energy, in particular, to the conversion of low-grade thermal energy into electrical energy.

There is a method of generating electrical energy with the use of low-grade heat carrier (1), for example exhaust gases of a heat engine. In this way the working fluid is pre-compressed natural gas coming from the gas line, low-grade heat by the heat source (cooled) to a temperature of 50 - 90oC, then expands in the turbine with electricity generation. After the turbine working fluid is excreted in the temperature range of 0oC to minus 10oC. In this way for 1 kWh of electricity consumed 450 kcal (0,523 kWh) thermal energy.

The disadvantage of this method is the need for a gas pipeline of high pressure.

The disadvantage of this method are the relatively high costs of fossil fuels and environmental pollution flue gases. A device for generating electricity closest in tehnicheskaya are connected to the pump, heater, turbine generator and condenser, and circuit reverse cycle (heat pump) for circulating the refrigerant, which has a compressor and an expander connected to one another through the heater. In this way feedback loop is open-circuited, pipelines entry of air into the compressor and the outlet of the expander is communicated with the atmosphere.

The device operates as follows. The refrigerant (which is air), with the ambient temperature, is compressed in the compressor, its temperature increases significantly, the heater is heated, the refrigerant gives up part of its heat energy boiling liquid steam circuit. Then, the compressed refrigerant flows into the expander, where expanded with performance of external work and is cooled to ambient temperature. Due to the work of the expander are largely borne by energy consumption in the compressor.

The disadvantage of this device is the lack of efficiency of converting thermal energy into electrical energy and pollution.

The aim of the present invention is to increase the efficiency of energy conversion of low grade heat East is P> This goal is achieved by the fact that in the known method of generating electricity, including direct energy cycle in which liquid working fluid is compressed, then heated and vaporized, the vapors expand in the turbine with electricity generation and condense after the turbine, and the reverse energy cycle in which the refrigerant compressed in the compressor, is cooled compressor after transferring heat to the working body and the expansion in the expander with obtaining external work, the condensation of the working fluid is carried out at a temperature lower temperature environment, the temperature of the refrigerant before compression in the compressor is reduced below the ambient temperature by recuperative heat exchange, the refrigerant in the expander is cooled to a temperature below the condensation temperature of the working fluid and submit it to the condenser where it is used as the heat load and the working fluid before the turbine is additionally heated using low-grade heat source.

Another difference is that as a heat source using a heat carrier - liquid or gas with a temperature of 50 to 150oC.

In addition, the refrigerant leaving the compressor, in addition is the expansion of the refrigerant is carried out in several stages.

Another difference is the additional increase in the pressure of the refrigerant after the expander with the help of an additional compressor.

There are other differences, namely, that the cooling of the refrigerant to the compressor spend working fluid direct loop;

the cooled refrigerant to the compressor is conducted additionally refrigerant leaving the condenser;

the cooled refrigerant to the compressor is conducted to the temperature of condensation of the working fluid;

condensation of the vapor of the working fluid is carried out at a temperature of 70 TO 120;

as a working body using light hydrocarbons containing in the molecule from 2 to 4 carbon atoms and having a critical temperature above ambient temperature;

the working fluid after the condenser is compressed to pressures of 2-4 times greater than critical;

before evaporation of the working medium drossellied, reducing its pressure;

as the refrigerant used in the air.

In the device for generating electricity, including the direct path loop for circulation of the working fluid, which are connected to the pump, heater, turbine generator and condenser, and circuit reverse Zilla after the heater is equipped with an additional heat exchanger for cooling the refrigerant, included in the circuit feedback loop to the compressor, the expander is connected to the capacitor, and the circuit of the direct cycle before the turbine has an additional heater is connected to an external source of thermal energy.

Another distinctive feature of the device is that the loop reverse loop contains an additional compressor which is connected with the condenser and the heat exchanger for cooling the refrigerant.

Another distinctive feature of the device is that in the circuit of the reverse cycle is set to an intermediate heat exchanger is connected on one side to the compressor and the expander, and the other to the capacitor and the additional compressor.

The following distinctive feature of the device is that the feedback loop equipped with a regenerative heat exchanger communicates on one side with a heat exchanger for cooling the refrigerant and the compressor, and on the other, with an intermediate heat exchanger and an additional compressor.

In addition, the distinctive characteristic of this device is that the expander contains several stages, connected to the condenser.

Another distinctive feature of the device is that the direct path loop before additional heater of are significant to achieve the objectives of the invention. In particular, as a direct cycle it is advisable to use steam Rankine cycle, approaching on the efficiency of the Carnot cycle. The reduced condensing temperature to values of 70 - 120 allows you To significantly increase thermodynamic efficiency of the direct cycle compared to conventional steam power plants with condensing temperature of about 300 K.

For the heat pump, which removes the heat of condensation in the proposed method provides for the use of a reverse triangular cycle Lorentz constant temperature heat source (the working fluid in the condenser) and variable temperature heat load (working fluid compressed by the pump after the condenser). thermodynamic efficiency of the triangular loop Lorentz in the temperature range 100 - 300 K is almost three times higher than the efficiency of the ideal Carnot cycle /3, 4/. With increasing temperatures, this ratio increases to 10 times or more /3/.

For conducting the reverse cycle with minimum energy losses (i.e., to reduce external and internal irreversibility of the real cycle), the proposed method provides a number of operations, including: 1 - cooling of the refrigerant before compression in the compressor; 2 - use the following compression in the compressor until the temperature of the working fluid; 4 - increase the refrigerant pressure in the condenser with the use of an additional compressor that increases the pressure difference in the expander and the consistency of the temperatures of the working fluid and refrigerant; 5 - multistage compression and expansion of the refrigerant.

The energy efficiency of the proposed method and devices can be relatively high and the generation of electricity in a direct cycle may significantly exceed the cost of energy in the reverse cycle. This also contributes to the choice of the working fluid with a relatively high critical temperature and increase the degree of compression of the working fluid in the pump. These factors allow multiple increases heat the working fluid after the condenser and, therefore, reduce the temperature of the refrigerant in the reverse cycle, the Lorentz determine its coefficient of performance. In particular, for liquid propane (C3H8), which has a critical pressure Pkr= 4,21 MPa, the critical temperature Tkr= 369,9 To the heat of vaporization Qto480 kJ/kg at T 100 - 150 K, the average specific heat at constant pressure Cpin the temperature range 100 - 200 K at pressure P/Pkr3 is according to /5/ of 6.7 kJ/kgK.

The amount of heat that can kJ/(KGC)100K = 670 kJ/kg .

Refrigeration coefficient of triangular cycle Lorentz for this range of temperatures T1= 100 K and T2= 200 K can be calculated as follows /3, 4/.

< / BR>
The work consumed in the reverse cycle, even taking into account the low efficiency of the real process = 0,7 , we can estimate the value of A equal to A = Qto/(g) = 480/(3,2590,7) = 210 kJ/kg .

In this case, the quantity of heat Q2transmitted heat pump (reverse cycle) a working body, is equal to Q2= Qto+ A = 480 + 210 = 690 kJ/kg, practically equal to the value of Q1required for heating the flow of liquid propane from 100 K To 200 K.

Electricity generation in a direct cycle when expanding vapor propane having an average value of the heat capacity Cp= 1,5 kJ/kgK, in the temperature range 400 - 100 To taking into account the efficiency of the turbo-generatort= 0,75 possible to estimate the value of At= 1,5 (400 - 100) 0,75 = 337,5 kJ/kg.

Thus, the generation of electricity in a direct cycle (337,5 kJ/kg) may exceed the energy consumption in reverse cycle (210 kJ/kg) on practically meaningful value.

To drive the compressor in the reverse cycle, you can also use a heat engine, and the energy generated exhaust gases using the Liceo, and the degree of conversion of fuel energy into electrical can be 80 - 90%.

In Fig. 1 shows a schematic diagram of a device for implementing the method, and Fig. 2 - T-S-diagram of the forward and reverse cycles of the proposed method, where T is the absolute temperature, S is the absolute entropy.

The device includes a direct path loop 1, containing a pump 2, a heater 3, a heat exchanger 4, the throttle 5, additional heater 6, the turbine 7 generator 8, a capacitor 9 and a circuit reverse cycle (heat pump) 10 containing the compressor 11 with step 12, the expander 13 with step 14, the intermediate heat exchanger 15, the regenerative heat exchanger 16 additional compressor 17 to the actuator 18.

To implement the method as a working body, it is advisable to use a mixture of hydrocarbons with a content of from 2 to 4 carbon atoms in the molecule, and as a refrigerant in air or nitrogen.

The method may be carried out as follows. Liquid working fluid with a temperature below ambient temperature, for example, 100 K ( - 173oC) after the capacitor 9 is compressed by the pump 2 to a pressure above the critical and transported along the contour of the direct cycle 1, where posleoperatsi 220 K (-53oC), drossellied working the body from lowering its pressure up to values close to critical in the inductor 5.

This throttling reduces the heat capacity of the liquid working fluid, accompanied by increasing its temperature. Next, the working fluid is heated, evaporated and overheat pair of working fluid in the additional heater 6 by using an external source of thermal energy, and the resulting hot vapors, for example, at a temperature of 400 K (+127oC) expand in the turbine 7 with electricity generation by the generator 8. Passing the turbine, the steam is expanded and cooled to the condensation temperature, for example 100 K. After the turbine 6 pairs served in the condenser 9, which is cooled by the refrigerant reverse cycle.

The refrigerant circulates in the loop reverse loop 10. The refrigerant enters the compressor 11 is cooled to a temperature close to the temperature of condensation, for example. 110 K. In the speed of the compressor 12 increases the compression ratio of the working fluid, for example, 2 to 8 times, with intermediate cooling of the refrigerant working fluid in the heater 3. After the compressor the refrigerant is additionally cooled to the condensation temperature, for example, 100 To, in the intermediate heat exchanger 15 a refrigerant, vyhodami is expanded and cooled in stages 14 with intermediate heating of the refrigerant in the condenser 9. The work produced by the expander is consumed for driving the compressor. Next, the refrigerant is heated up sequentially in the intermediate heat exchanger 15, for example, to a temperature of 108 K, the regenerative heat exchanger 16, for example, to a temperature of 135 K, and squeeze additional compressor 17 to a pressure of the refrigerant, for example, 2 to 10 times, and temperatures, for example up to 200 To 220 K. Then, the refrigerant is cooled, for example, to a temperature of 140 To 150 K, the working fluid in the heat exchanger 4, the refrigerant in the regenerative heat exchanger 16 and returns to the compressor at a temperature close to the temperature of condensation of the working fluid.

Is depicted in Fig. 2 chart T-S direct - steam power and refrigeration cycles explains their interaction with each other.

In Fig. 2 - marked: T is the absolute temperature of the refrigerant; S is the absolute value of entropy; Tn, TO.and Ttorespectively the absolute temperature of the vapor of the working fluid, the environment and the temperature of the condensing vapor of the working fluid.

In an ideal direct steam power cycle in Fig. 2 presents the following processes:

1-2 - adiabatic compression of the liquid working fluid pump;

2-3 - heating Rabo body orifice 5;

5-6, 6-7, 7-8, respectively heating, evaporation and superheat the vapor of the working fluid in the additional heater 6;

8-9 - the expansion of the vapor of the working fluid in the turbine from electricity generation in the generator 8;

9-1 - condensation of vapors of the working fluid in the condenser 9.

In a reverse refrigeration cycle of Fig. 2 presents the following processes:

10-11-12 - multistage compression of the refrigerant in the compressor 11 with intermediate cooling in the heat exchanger 3;

12-13 - cooling of the refrigerant in the intermediate heat exchanger 15;

13-14 is a multistage expansion of the refrigerant in the expander 13 with intermediate heating in the condenser 9;

14-15 - heating of the refrigerant in the intermediate heat exchanger 15;

15-16 - heating of the refrigerant in the regenerative heat exchanger 16;

16-17 compression of the refrigerant in the secondary compressor 17;

17-18 - cooling of the refrigerant in the heat exchanger 4;

18-10 - cooling of the refrigerant in the regenerative heat exchanger 16.

For further explanations of the effects of combinations of cycles in Fig. 2 shows diagrams of the following is equivalent to the degree of thermodynamic perfection of cycles Carnot;

19 - direct steam cycle of the proposed method;

2 is a first cycle with a heat output low-level environment;

22 - direct power cycle, which is a combination of a direct cycle with the number 19 and reverse cycle number 20.

The shaded plot of cycle number 22 characterizes the additional energy effect of the proposed method.

In addition, a broken line in Fig. 2 describes a multi-stage processes of compression and expansion of the refrigerant.

Thus, it follows that the proposed method is new, involves an inventive step and can be effectively applied in the industry.

List of used sources

1. E. Grechnev, And. Gricevich. The project of introduction of environmentally friendly technologies JSC Creator", "Energy efficiency", M, Center for energy efficiency (CENEf), N 5, c. 12 - 13.

2. The rustle P. Fiftieth anniversary of one idea. "Science and life", 1993, N 2, S. 152 - 153.

3. C. S. Martynovskyi. Cycles, diagrams and specifications of thermotransformators, - M, Energy, 1979, S. 50 - 55.

4. G. Heinrich, H. Najork, Century, Nestler. Heat pump installation for heating and hot water. - M, stroiizdat, 1985, S. 37 - 45.

5. N. L. Staskevich, D. J. Vyhdorchyk. Handbook of liquefied gases. - L., N. the rum liquid working fluid is compressed, then heated and vaporized, the vapors expand in the turbine with electricity generation and condense after the turbine, and the reverse energy cycle in which the refrigerant compressed in the compressor with increasing pressure, cooled compressor after transferring heat to the working body and the expansion in the expander with decreasing pressure of the refrigerant, characterized in that the condensation of the working fluid is carried out at a temperature below ambient temperature, the temperature of the refrigerant before compression in the compressor is reduced below the ambient temperature by recuperative heat exchange, the refrigerant in the expander is cooled to a temperature below the condensation temperature of the working fluid and served in the condenser for removal of heat of condensation, and the heating and evaporation of the working fluid before the turbine is carried out with the use of an additional heat source.

2. The method according to p. 1, characterized in that as an additional heat source using a fluid (liquid or gas) to a temperature of 50 - 150oC.

3. The method according to p. 1 and 2, characterized in that the condensation of the vapor of the working fluid is carried out at 70 to 120 K.

4. The method according to PP.1 to 3, characterized in that the refrigerant before sati is the action scene themes the cooled refrigerant to the compressor spend compressed working fluid.

6. The method according to PP.1 to 5, characterized in that the cooling of the refrigerant to the compressor is conducted additionally refrigerant leaving the condenser.

7. The method according to PP.1 - 6, characterized in that the cooling of the refrigerant after the compressor is conducted additionally refrigerant leaving the condenser.

8. The method according to PP.1 to 7, characterized in that the pressure of the refrigerant after the expander increases with additional compressor.

9. The method according to PP.1 to 8, characterized in that the compression and expansion of the refrigerant is carried out in several stages.

10. The method according to PP.1 to 9, characterized in that the working medium is light hydrocarbons with 2 to 4 carbon atoms in the molecule which have critical temperatures above the ambient temperature.

11. The method according to PP.1 to 10, characterized in that the working medium after the condenser is compressed up to the pressure, 2 to 4 times greater than critical.

12. The method according to PP. 1 - 11, characterized in that as the refrigerant used in the air.

13. Device for producing electric power comprising a direct path loop for CMA and the capacitor, and loop reverse loop for circulation of the refrigerant, in which the compressor is connected to the expander through the heater, characterized in that the contour of the direct cycle after heater provided with a heat exchanger for cooling refrigerant is included in the circuit of the reverse cycle before the compressor, the expander is connected to the capacitor, and the circuit of the direct cycle before the turbine has an additional heater is connected to an external source of thermal energy.

14. The device according to p. 13, characterized in that the contour of the reverse cycle contains an additional compressor which is connected with the condenser and the heat exchanger.

15. The device according to PP.13 and 14, characterized in that the contour of the reverse cycle is set to an intermediate heat exchanger is connected on one side to the compressor and the expander, and the other to the capacitor and the additional compressor.

16. The device according to PP.13 to 15, characterized in that the circuit is equipped with reverse cycle regenerative heat exchanger communicating with one side of the heat exchanger and the compressor, and on the other, with an intermediate heat exchanger and an additional compressor.

17. The device according to PP.13 to 16, characterized in that the expander contains carried the R direct cycle before additional heater includes a choke.

 

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