HEAT CONVERSION INTO MECHANICAL WORK THROUGH ABSORPTION- DESORPTION
DISCRIPTION
RELATED APPLICATION: The usual way of converting heat into mechanical work (and then electricity) is based on the Ranking cycle. A liquid (water) is heated up to s"per heated steam. Expanding the steam through a turbine, work is produced.The saturated steam at the turbine exit is condensed, at the same time rejecting heat to the ambient and subsequently compressed to a higher pressure level before being heated again.
In an improv ent o'f Ranking cycle a system of rnulticomponent working fluid is utilized. This system operates on the principle that a binary working fluid is pumped as aliquid to a higher pressure level.
It is heated in a steam generator to partially vaporize the working fluid. The vaporized working fluid is expanded through a turbine to transform its energy to usable form. The remaining liquid working fluid returns to an absorber where it is mixed with the expanded gaseous working fluid, to regenerate the initial rnulticomponent working fluid.
Applicant has improved the above system mainly by adding the following processes:
Preheating of the pumped rnulticomponent working fluid by heat recovered from the evaporated gaseous working fluid leaving steam generator;
reheatings of the expanded through the turbine gaseous working fluid , from the absorber or another heat source that has a temperature equal or lower the ambient temperature. reexpanding of the reheating gaseous working fluid. NEW? A rnulticomponent working fluid consisting of a lower boiling point component "solute" dissolved in higher boiling components "absorbant", is pumped as a liquid to a high working pressure. The liquid is heated up in a steam generator and is partially evaporated, splited into a gaseous working fluid consisted mainly from the lower boiling component and a lean solution with respect to lower boiling component, After successive reheatings and expansions the gaseous working fluid is absorbed by the lean solution returning to absorber. The purpose of this procedure is to increase the thermal efficiency of the cycle by expanding the gaseous working fluid to a low temperature and by reducing the heat amount rejected to ambient.
This invention relates to a method of generating energy in the form of useful energy from a heat source. The new ther odynamic cycle developed from this method has an improved heat utilization effeciency, compired with thermodynamic cycles which are in commercial application now and utilize heat sources
available at the same temperature.
In accordance with one aspect of this invection, a method of generating energy comprises:
(a) Pumping an initial rnulticomponent working fluid streamin liquidstate having an initial composition of lower and higher boiling components to relatively high pressure;
(b) Su. jecting said rnulticomponent working fluid stream to partial distillation in a dist illation system^ called steam generator, by means of heat to generate working fluid fractions of differing compositions;
(c) recovering heat from the one working fluid fraction which is a liquid lean solution and is impoverished with respect to the lower temperature boiling component, by heating aportion of the pumped initial rnulticomponent working fluid stream ;
(d) recovering heat from the second working fluid fraction, hich is a gaseous working fluid,and is enriched with respect to a lower temperature boiling component, by heating a portion of the initial pumped rnulticomponent working fluid;
(e) expanding the said liquid lean solution at a pressure relatively lower that the distillation pressure; (f) expanding the said cooled gaseous working fluid through a turbine to transform its energy to useable form.
(g) condensing the spent gaseous working fluid in a main absorption stage by dissolving it with cooling in the lean solutio-n at the pressure of the expanded liquid lean solution. The expansion of the lean solution can be executed through a hydro-turbine which helps in pumping the initial rnulticomponent fluid, or through an expansion alve.
The gaseous working fluid released in the steam generator may be flashed to separate high and low boiling working fluid, depending on the conditions of temperature, pressure and comcentration prevailing in .the steam generator as well as the particular rnulticomponent working fluid. Inan embodiment of the invention, the gaseous working fluid released in the steam generator may be super heated instead of cooled. the other steps of the method remaining the same. Cooling of tne gaseous working fluid released in the steam generator, by means of heat recovery from the rnulticomponent working fluid, decreases the heat requirments of the cycle and increases the thermal efficiency cf the cycle.
The expanded gaseous working fluid may be successively reheated and expanded one or more times. When the gaseous working fluid is expanded to a temperature lower than the ambient temperature, reheating may take place from a heat source at ambient or even lower temeprature. In this way,
cogeneration of power and refrigeration is possible. Besides, a power cycle which rejects condensation heat at a temeprature lower than the ambient temeprature and a thermodynamic cycle converting heat of the ambient to useable work has been achieved.
Applicant believes thatthis is an improvement of existing systems.
The method may include repe titions of the steps of
(a) reheating the expanding gaseous working fluid; (b) expanding the reheated gaseous working fluid through a turbine to transform its energy into useable form.
The heat required for the reheatings may be selected from one or more members of the group comprising:
(a) a portion of the heat released in the absorber during condensation (absorbtion) of the gaseous working fluid;
(b) a heat source at ambiant temperature like ambient air or water.
(c) a heat source at a temperature lower than the ambient temperature.
(d) a heat source from another power cycle from the steam generator heat source, or any other heat source at convenient temperature.
When reheating from the absorder takes place, the absorber may be divided into two stages. The first stage rejects heat to the ambient and the second stage rejects heat to the gaseous working fluid. The second stage may therefore be kept at a temperature lower than the ambient temperature. This lower temperature gives the ability to increase the concentration in lower boiling cc-iponent of the initial multicomponet fluid or to decrease the pressure of a portion of the condensing gaseous working fluid.
The method may include the steps of:
(a) dividing the absorber into two stages;
(b) reheating the gaseous working fluid which has been expanded to a temperature below the ambmient temperature, from the second stage of the absorber;
(c) expanding the gaseous working fluid through a turbine to transform its energy to useable energy while a portion of the gaseous working fluid leaves the turbine from an intermidiate stage^ (d) reheating the gaseous working fluid from the second stage of the absorber;
(e) condensing a portion of the gaseous working fluid in the first stage of the absorber and the other pirtion in tne second stage of the absorber) (f) pumping the reformed liquid working fluids from the two stages of the absorber to a common pressure level;
(g) mixing the two portions to reform the initial rnulticomponent working fluid.
Depending on the particular application, the temperature of the absorption may be high enough, to be used for space heating or objects heating.
The method may include the step of transfering the' energy released in the absolber to use it for space or objects heating.
The heat source which is used in the steam generator to heat and partially evaporate the multi- component working fluid may be selected from one or more members of the group comprising; (a) The heat released at the absorber of another thermodynamic cycle as it has been described above; (b) the heat released at the condender of a Ranking power cycle.
(c) the heat released from an internal combustion engine including heat released for cooling the engine and flue gases heat; (d) solar, geothermal or any other heat source,like fuel ' burningor stored heat.
The initial rnulticomponent working fluid may be totally or partially evaporated.
The evaporated working fluid is superheated and expanded through a turbine. The expanded working fluid is cooled, so that a liquid consisted mainly of the higher boiling working fluid is greated.
The remaining gaseous working fluid consisted of the lower boiling working fluid is expanded through a turbine to a lower pressure level than that of the higher boiling working fluid condensation pressure. The condensed working fluid is subcooled and expanded to a lower pressure level where the lower boiling working fluid is finally absorbed.
The gaseous working fluid released in the absorber may undergo a multithermal, compression so that the working pressure will be increased.
The method may conveniently include the repeated steps of:
(a) absorbing the gaseous working fluid released at steam generator (Gi) by a multicomponent working fluid; (b) pumping the liquid working fluid greated by the absorption;
(c) heating the working fluid by heat recovered from the lean solution leaving steam generator (Gi + 1) and gaseous working fluid leaving steam generator (Git 1); (d) Partially evaporating the working fluid to produce a lean liquid solution and a gaseous working fluid.
The working fluids involved in this multi heat compression are not necessarilly the same.
To avoid heat of vaporization a modification can be made to the method based on different solubility of a working fluid in an intermediate absorbent fluid.
At least two different substances are used in solutions with a common working fluid.
The first solution is a weak absorbent fluid and the second is an intermediate absorbent fluid. The intemediate fluid is used in one stage of the absorber to concentrate the weak absorbent solution by solvent extraction.
T.iis method includes the steps of:
(a) absorbing a gaseous working fluid by weak asborbent fluid)
(b) concentrating the absorbent fluid by absorbent extraction using an intermediate absorbent fluid which absorbs part of the dissolved gaseous working fluid;
(c) using again the weak absorbent fluid to absorbe the gaseous working fluid^
(d) pumping the intermediate absorbent fluid which is enriched in dissolved gaseous working fluid to a higher pressure level;
(e) heating said enriched intermediate absorbent fluid to a higher temperature, generating two fluid streams; the first condisted of the liquid phase of the component used as gaseous working fluid and the other condisted of impoverished intermediate absorbent fluidj
(f) exhanging heat between impoverished intermediate absorbent fluid going to absorbent and enriched intermediate absorbent fluid going to separator,
(g) Pumping the liquid phase of the said gaseous working fluid to a higher pressure level or expanding it to a lower pressure level, (h) heating said liquid phase of the gaseous working fluid to generate super heated steam in the form of a gaseous working fluid;
(i) expanding said gaseous working fluid (super heated steamj to tramsform its energy to useable form. (j) absorbing said expanded gaseous working fluid in an absorber to generate initial weak absorbent fluid. In general, standard equipments such as heat exchargers, tanks, pumps, turbines and fittings of the type used in a typical Ranking cycle may be employed in carrying out the method of this invention. Applicant believes that the constraints upon materials of construction would be the same for this invention as for coventional Rankine cycle power or refrigeration systems.
The expansion of the working fluid from a charged high pressure level to a spent low pressure level to transform its energy to useable form may be effected by any suitable conventional means known to those skilled in the art.
In a preferred embodiments of the invention, the working fluid may be expanded to drive a turbine of conventional type.
In accordance with another aspect of this invention, a sol¬ vent is solid state is used instead of a liquid phase. he solvent cousists of peaces so that the contact area with the absorbed gas is greater.The heat transfer from absorber - cold tank - and to steam generator - heat tank - can be per¬ formed with any way known to those dealed in the art.
The equilibrium pressure increases with temperature.
When a substance in solid state that has absorbed a sub¬ stance with low boiling point is heated up, the substance with low boiling point is released in gas phase.
The gas may expanded to couver its energy to useable form. he expansion takes place through a machine like a tur¬ bine to produce mechanical work.
In the exit of the turbine the gas is absorbed by ano¬ ther substance in solid state.Cooling by heat rejection takes place in the same time and this substance is called cold tank. The substance which is heated to release gas is called heat tank.
The couple of the substances i.e. the heat tank and the cold tank may have the same or different composition.
The role of the two tanks is reversed.
The tank that has been cooled to absorb the gas is now heated to release the gas.The gas is expanded again through the turbine.In the exit of the turbine, the gas is absorbed by the other tank which is now cooled (which in the first step was heate ) .
These steps are repeated.
In this case no pump is used.
DRAWINGS FIG. 1. shows a schematic representation of one system for carry out the method of the invection. FIG. 2. shows a schematic representation of another system for carry out the method of the invection recovering absorption heat in order to heat the initial multicomponent working fluid.
FIG. 3. shows a schematic representation of another system for carry out the method of the invention, using an intermediate absorbent fluid.
FIG.1 of the drawings, refers generally to one embodiment of a thermodynamic system or cycle in accordance with this invention.
This system or cycle comprises a πain steam generating stage q..1 a first turbine 1.1 and a second turbine 2.1 , a first absorption stage -.1. and a second absorption stage 3.1, a hydroturbine 5.1, a first heat exnanger 6.1. and a second heat exchanger 7.1. a flashing system 11.1 and another heat exchanger 12.1.
In use, using an ammonia - water working solution as a binary working fluid,liquid solution of ammonia- water at lower pressure is pumped from the first 4.1. and second 3.1- absorption stages through a hydro- turbine 5.1. to the higher steam generator pressure level.
This is an enriched in ammonia, liquid solution. This solution is splitted into two streams .
The first stream is heated through the heat exchanger 6.1. by the lean solution that flows along line 13.1 to the absorber.
The second stream is heated through the heat exchanger 7.1. by the gaseous working fluid which leaves steam generator. 9.1. along line 14.1.
The two preheated stream are driven to the stea . generator 9.1. along line 15.1. the solution is heated in the steam generator by a heat source 8.1.__. In this way two fluids of differing composition are created. The first one is a lean liquid solution which is impoverished in ammonia.
The second one is a gaseous working fluid enriched in ammonia. The lean solution having a high temperature and pressure is cooled through heat exchanger 6.1. , where its heat is recovered by the rich solution, then expanded through hydro-turbine 5.1. and finally enters absober along line 13.1.
The gaseous working fluid, is cooled through heat exchanger 7. , where its heat is recovered by the rich solution, flashed through flashing system 11.1. and enters turbine 1.1. It is expanded through the turbine 1.1. transforming its energy to mechanical work. The gaseous working fluid exits turbine at a temperature lower than the absorber temperature and is reheated from the second stage of the absorber 3.1. through a heat exchanger. The reheated gaseous
working fluid is expanded through the turbine 2.1 to transform its energy to mechanical work, reheated through absorption stage 3.1. and enters absorber where it is absorbed by the lean solution and forms the initial rich solutions.
The first stage of the absorber -i . 1 . is cooled by a working fluid stream like airor water through 10.1.
FIG. 2. of the drawings refers generally to another embodiment ofa thermodynamic system or cycle in accordance with this invention.
This system or cycle comprises a steam generating stage 9.2, a turbine 1.2 a first absorption stage -\ .2 and a second absorption stage 3.2, a hydro-turbine 5.2. heat exchangers 6.2. and 7.2 and a flashing system 11.2 In use, using an ammonia water working solution as a binary working fluid, initial solution in liquid state, of ammonia-water at low pressure is pumped from the first -\ .2 and second 3.2. absorption stages through a hydro-turbine 5.2. to the higher steam generatςr pressure level along line 15.2. The said liquid solution is preheated through the absorption stages
-1.2. and 3.2. and then it is heated through a steam generator. 9.2. Two fluid streams are generated. The first one is a lean liquid solution which is improverishec in ammonia and which is cooled along line 13.2 by initial solution and or ambient air in heat exchanger 6.2. and expanded through a hydro-turbine or an expansion value 5.2.
The second fluid stream is a gaseous working fluid enriched in ammonia which is cooled along line 14.2 by initial solution or a biant air in heat exchanger 7.2. The gaseous working fluid is expanded through the turbine 1.2 to produce useable work, and then it is reheated through absorption stage 3.2, and enters absorber 4.2. and 3.2. where it is absorbed and condensed to generate initial solution.
Fig. 3 refers to another embodiment of a thermodynamic system or cycle in accordance with this invention.
The system or sycle represented by this figure comprises a first stage of an absorber 4.3, a second stage of an absorber 3.3. a hydro-turbine 5,3 a pump 15.3 a first stage of a sepasator 16.3 a second stage of a separator 17.3. a steam generator 9.3 and a turbine 1.3,
In use, using water as a liquid-gaseous working fluid, LiBr-water as a weak absorbent and acetophenone as anintermediate absorbent, a gaseous working fluid is absorbed by the weak absorbent in the first stage of absorber 4.3.
The intermediate solution absorbs water from the weak solution in the second stage absorber 3.3- The consentrated weak solution impoverished in water, flows along line 18.3, to be used again for absorbing the gaseous working solution. The enriched
in water intermediate absorbent is pumped to the separator 16.3 where it is heated.
The solubility of water is decreased when temperature increases and a fluid stream of impoverished in water intermediate absorber returns to absorber 3.3. along line 19-3 after haVing been expanded through hydro- turbine 5.3, while water is pumped through pump 15.3 along line 20.3 to steam generator 9.3» Water is heated in steam generator and a gaseous working fluid in the phase of superheated steam is generated. The gaseous working fluid is expanded through the turbine 1 -3 and enters absorber.
A case study was prepared to illustrate the advantages of the system in accordance with this invention. The multicomponent system is a binary system of ammonia-water. The lower boiling component is ammonia and the higher boiling component is water.
The parameters for the theoretical calculations which were performed again utilizing standard ammonia- water enthalpy/concentration diagrams are setout in Table 1 below . The points refered are in accordance with FIG. 1.
No heat losses have been considered. Flashing of the gaseous working fluid has been neglected.
The work produced is the sum of the work produce.d from turbine 1.1 and turbine 2.1 This work is the enthalpy change between turbine inlet and outlet.
Wr ^ W2 = (698 - 620) ÷ (700 - 600) = 178 Btu/lb. = 98,9 Kcal/Kg
The heat requirment has been estimated to be Q=505
Kcal/kg The thermal efficiency is equal to 0.19
Another example is presented where the solvent is solid statephase and no pump is -required .
The solid substance is a metalic hybride.lt is LaNi 4.,_7,A10Λ,3_, having absorbed a substance of low boiling point.This substance is hydrogen (H2). The equilibrium pressure is: Up _*_ + 12.84
Applying the temperature of Tn =473 K as a high temperature at the heat tank and the temperature T =273 K as a low tempe¬ rature at the cold tank the following pressures result: Ph=66,2 bar at the heat tank and Pc= 0,11 bar at the cold tankd. The work produced by the turbine is w=740 Kcal/Kg. The heat required at the heat tank to release hydrogen is:
Q=ΔH=16870 Kl/kg =4035 Kcal/kg. The therual efficiency is = 0,18
Let's note that all the processes are considered ideal.