Method and device for generation of electric power and cold using low-potential heat sources

Abstract

A method for generating electricity and cold and a device for realizing same, consists in a closed absorption cycle in which a working body is a mixture of a low-boiling (refrigerant) component and a high-boiling (absorbent) component. The method involves evaporating a strong solution in a steam generator, thus forming a refrigerant vapor and a weak solution, expanding the refrigerant vapor in a turbine, thus producing work, and, after the turbine, absorbing spent vapor in an absorber, forming a strong solution. A distinguishing feature of the method consists in changing the concentration of a strong solution using two stages, including not only evaporation but also filtration. The proposed method and device allow for significantly increasing the efficiency of systems for generating electricity relative to analogous known methods.

Claims

1. A method for producing electric energy and cold using low-potential heat sources, comprising circulation of a solution comprising a refrigerant as a low-boiling component and an absorbent as a high-boiling component, with periodic heating and cooling said solution, evaporation of a high concentration the solution during heating with formation of a steam flows of the refrigerant and a weak solution of elevated temperature and pressure, using of the refrigerant steam flow in a heat engine with formation at a turbine exit of an exhaust steam of reduced temperature and pressure, decrease in temperature and pressure of the weak solution, absorption of the exhaust steam by the weak solution under cooling with formation of a strong solution, increase in pressure of the strong solution and feeding of the solution for evaporation, wherein the strong solution is divided into flows with increased concentration of the absorbent and flows with increased concentration of the refrigerant, whereas the flow with increased concentration of the absorbent being used as weak solution during absorption, while the flow with increased concentration of the refrigerant being employed during the evaporation as a high concentration solution after an additional increase in pressure and temperature.

2. The method as defined in claim 1 wherein the separation of the strong solution into the flows with various concentration is carried out by the strong solution filtration using semipermeable membranes.

3. The method as defined in claim 1 wherein the separation of the strong solution into the flows with various concentration is carried out by applying the centrifugal and gravitational effects.

4. The method as defined in claim 1 wherein the pressure of the refrigerant steam during the absorption rises due to the utilization of potential energy of the weak solution in a vapor-liquid ejector.

5. The method as defined in claim 1 wherein the high concentration solution delivered for evaporation is heated, whereas the weak solution being formed in the course of evaporation is cooled owing to a recuperative heat exchange between these flows.

6. The method as defined in claim 1 wherein for filtration of the strong solution the membranes with the selectivity no more than 0.75 are employed.

7. The method as defined in claim 2 wherein for filtration of the strong solution the membranes with the selectivity no more than 0.75 are employed.

8. The method as defined in claim 1 wherein the weak solution which has been formed during evaporation, after a decrease of its pressure and temperature, mixes with the high concentration solution being formed during filtration.

9. The method as defined in claim 1 wherein mixtures of the components differing in their capacity to permeability through a semipermeable membrane are applied as absorbent.

10. The method as defined in claim 1 wherein the exhaust steam before absorption is used for cooling external facilities.

11. A device for producing electric energy and cold comprising an absorber, a pump, a solution heat exchanger, a steam generator, a separator and a turbine with an electric generator, connected in closed cycle of solution motion, in which the turbine connects at an inlet with the separator for delivering steam, and at an outlet from the turbine with the absorber, and the separator connects both to the steam generator and to the absorber with a thermoregulation valve, wherein filter elements have been mounted in a solution motion cycle between the absorber and the steam generator, said filter elements are connected on an one hand to the absorber with the possibility of delivery to the filter elements of the strong solution and return into the absorber of the weak solution, and on an other hand to the steam generator with the possibility of supply to the steam generator of a higher concentration solution passed by the filter elements.

12. The device as defined in claim 11 wherein the separator at the exit of weak solution is connected by means of a control valve and a supplementary expansion valve to the filter elements for entry into it of the weak solution.

13. The device as defined in claim 11 wherein after the filter elements a supplementary pump has been installed, and a recuperative solution heat exchanger has been mounted between the supplementary pump and the steam generator.

14. The device as defined in claim 11 wherein between the turbine and the absorber a vapor-liquid ejector has been installed.

15. The device as defined in claim 11 wherein as filter elements the membranes for Nano filtration are employed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The essence of the proposed method is illustrated with a schematic diagram of the plant for the production of electric energy and cold which is shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

(2) Such a device includes:

(3) 1steam generator as boiler, 2separator,

(4) 3turbine with an electric generator also called heat engine,

(5) 4absorber, 5pump,

(6) 6filter elements,

(7) 7supplementary pump, 8solution heat exchanger,

(8) 9injector, 10control valve,

(9) 11expansion valves also called throttle valves.

(10) The proposed method can be implemented as follows.

(11) In the steam generator 1 the higher refrigerant concentration solution heats up, separating therewith into the flows of the refrigerant and weak solution steam.

(12) From the generator 1 the flows of steam and weak solution enter the separator 2 where a more complete separation of vapor and liquid occurs.

(13) Thereupon the steam flow is fed into the turbine 3 where it expands with the work being done. After the turbine the exhaust steam enters the absorber 4 either directly or with its preheating in the course of heat exchange with the external facilities under their cooling.

(14) In its turn the weak solution flow emerging from the separator or from the steam generator is precooled in the recuperative solution heat exchanger 8 and, after reduction of its pressure in the expansion valve 11, also enters the absorber 4.

(15) In the absorber 4 the exhaust steam is taken up by the weak solution with the formation of the strong solution. External heat-transfer agent removes the thermal energy released during the absorption.

(16) Furthermore, the strong solution after the increase of its pressure by the pump 5 is divided by means of the semipermeable membrane 6 also called filter elements into flows with various concentration of the refrigerant. One of these flows, which has not passed through the membrane, has a lower concentration of the refrigerant and after the reduction of its pressure in the expansion valve 11 or the injector 9 is used in the course of absorption as weak solution.

(17) The other flow, which has passed through the filter elements, has a comparatively higher concentration of the refrigerant and is then delivered to the steam generator 1 where it is used during the evaporation as high concentration solution.

(18) Before the steam generator, the pressure and temperature of the high concentration solution are preliminary increased by means of the pump 7 and the recuperative solution heat exchanger 8, respectively.

(19) In this method, the possibility of delivery of the weak solution from the steam generator or separator not only to the absorption stage, but also to the filtration stage is provided for as well. In that case, the weak solution from the separator is delivered to the membrane from the side of the high refrigerant concentration solution allowed to pass by the membrane. In so doing both flows are mixed.

(20) For regulating the delivery of the weak solution formed in the steam generator a control valve 10 serves in that event.

(21) Such a technique allows in a number of instances to reduce the osmotic pressure difference of the solutions before and after the membrane.

(22) Besides, to decrease the osmotic pressure of the strong solution to comparatively small values, approximately 5-10 bar, it is proposed in the method to employ mainly semipermeable membranes for nanofiltration or ultrafiltration, for example such as nanofiltration membranes of ESNA series characterized by a comparatively low operating pressure and selectivity about 60-80% or other similar membranes produced serially [4].

(23) At the same time, in this case the reverse osmosis membranes can be also used because the osmotic pressure arising in this method may be regulated over wide limits by choosing the semipermeable membranes of comparatively low selectivity, e.g. 30-70% as shown in [5].

(24) Moreover, a two-stage change in the strong solution concentration proposed in this method makes it desirable to employ also and the filtration methods of electrodialysis [6] and shock electrodialysis [7], what promotes a reduction of the overall dimensions of the system.

(25) The proposed method can be implemented through the use of known working medias (solutions) considered in the absorption cycles of refrigerators and heat engines.

(26) In particular, it makes sense to use as refrigerants the substances with a comparatively low boiling temperature, for example such as methanol, water, ammonia, R134a, R245fa, etc. as well as their mixtures.

(27) As absorbents, it is worthwhile using the solvents having a comparatively high molecular weight, approximately more than 100 D, and a comparatively high normal boiling temperature, approximately more than 150 C. To such absorbents relate TEG (triethylene glycol), PEG-300 (polyethylene glycol), ionic liquids [8], TEG-DME (tetraethylene glycol dimethyl ether) and other known absorbent.

(28) Some characteristic parameters of the proposed method with the use of the solution of methanol (CH.sub.3OH) and ionic liquid [MMIm]DMP (C.sub.7H.sub.15N.sub.2O.sub.4P) are listed in Table 1.

(29) This ionic liquid [MMIm]DMP has a molecular weight of 222.179 g/mole, registration number CAS-RN: 654058-04-5, and is recommended for the employment in modern absorption refrigerators [8].

(30) TABLE-US-00001 TABLE 1 Some characteristic parameters of the proposed method Denomination of Parameter Magnitude of parameter Working medium CH.sub.3OH [MMIm]DMP Steam pressure before/after the turbine, 2.96/0.028 bar Steam temperature before/after the .sup.100/minus 5 turbine, C. Absorption temperature: initial/final, 22/33 C. Filtration pressure, bar 6 Concentration of refrigerant in solution, wt. %: in absorber at the inlet/outlet 16.7/25.2 in steam generator at the inlet/outlet 50.0/20.sup. Specific work of turbine or else ~331.6 enthalpy difference at inlet and outlet, kJ/kg Specific work of turbine with 263.5 efficiency of 0.85, kJ/kg Specific work consumed by pumps at no more than 1.0 efficiency of 0.75, kJ/kg Specific thermal load of steam generator, ~1200 kJ/kg Theoretical efficiency, % 27.5 Potential practical effectiveness, % 21.9 Theoretical efficiency of Carnot cycle, % 19.8

(31) The proposed method enables one significantly to improve the effectiveness of generation of electric power and cold as compared with other analogous methods.

(32) In particular, the effectiveness of such cycles can exceed the maximum magnitude of this parameter allowable today in the corresponding Carnot cycles because in this case the rules of equilibrium thermodynamics are obeyed not strictly enough owing to thermodynamic peculiarities of non-equilibrium absorption systems.

REFERENCES

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