Patent Application
20170008776
The present invention relates to a new facility and a new method for treating water pumped in liquid form in a natural environment by evaporation/condensation, in particular such as seawater, lake water or water from a stream, or groundwater. The invention for example makes it possible to desalinate seawater, or to purify water pumped in a natural environment. The invention is also applicable to the use of the thermal energy of water pumped in a natural environment to produce electricity or to treat a gas.
At normal atmospheric pressure (at sea level), water evaporation occurs around 100° C. This evaporation occurs when the outside environment supplies energy to the water having become steam in the form of latent heat Lv. As long as the water stays in its steam state, this energy Lv remains stored in said steam. If the temperature of the steam is decreased, one then witnesses the condensation phenomenon whereby the steam turns into liquid while ceding its stored energy to the outside environment.
The passage from liquid to gaseous state is often referred to indifferently as evaporation and boiling. In reality, these two phenomena are different and appear under different circumstances. Evaporation refers to the appearance of molecules in gaseous state at the surface of the liquid. If energy is supplied quickly at the bottom of the container, the temperature increases gradually over the entire water column, but at the surface in contact with the energy supply, the temperature will quickly exceed the evaporation temperature (100° C. for water at a normal atmospheric pressure). This creates a local evaporation in the form of small bubbles in the water that will escape and rise in the liquid due to the buoyancy. This phenomenon will accelerate with the increase in the temperature of the liquid and the number of bubbles becomes high; the boiling phenomenon is then obtained. Boiling may be said to be three-dimensional or volume-based evaporation, unlike the traditional evaporation that takes place on the surface.
The evaporation of a liquid, and in particular low-pressure water, is also a well-known and controlled method. This evaporation method is related to the fact that the evaporation temperature of a liquid, and in particular of water, decreases with atmospheric pressure above that liquid. For example, at 0.2 bar, the evaporation temperature of water is approximately 60° C.; at 20 mbar, the evaporation temperature of water is approximately 17.5° C. Thus, if one for example places water at 20° C. in a container, for example a beaker, in the short term, nothing happens at atmospheric pressure. If the container is placed in a vacuum chamber connected to a vacuum pump, the water begins to boil abruptly, and the temperature of the water decreases more and more, ultimately finishing at a temperature below zero. After a certain time, the remaining water ends up freezing, thus ending the evaporation. It is therefore possible, by decreasing the pressure sufficiently, to cause water to evaporate and boil at a low temperature, and for example at 20° C.
When a liquid like water evaporates, it needs energy to go from the liquid phase to the gaseous phase: this is the latent heat Lv. The latent heat Lv is equal to 2.25 MJ/kg for water at atmospheric pressure. This energy is supplied by the volume of water in liquid state that does not evaporate and by the container containing the water in liquid state, which supply this thermal energy by decreasing their temperatures. As long as the evaporation continues, the temperature continues to decrease until it drops below 0° C. and the liquid water ends up turning into ice. If the participation of the container is set aside, as a first approximation, it may be considered that the energy is kept between the energy received by the evaporated water and the energy supplied by the liquid water. Eeva=Eliq where Eeva is the energy received by the evaporated water and Eliq is the energy supplied by the liquid water.
E
liq
=m
liq
C
pliq
ΔT
where mliq is the mass of non-evaporated liquid, Cpliq is the heat capacity of the liquid and is equal to 4.18 kJ/kg/K for water and ΔT is the variation of the temperature of the liquid water.
E
eva
=m
eva
L
v
where meva is the mass of evaporated liquid and Lv is the latent heat and is equal to 2.25 MJ/kg for the water at atmospheric pressure.
The conservation of the energy and the material requires that Eeva=Eliq, therefore
m
eva
L
v
=m
liq
C
pliq
ΔT
It is this relationship (Eeva=Eliq) that makes it possible to extract energy from a liquid by evaporation, and for example to extract energy by evaporation from water pumped in a natural environment, in particular seawater, lake water or water from a stream.
This phenomenon of evaporation of a liquid, and in particular water, at low pressure, has been used for many years to produce steam and to use the produced steam to generate electricity.
This electricity produced from steam can be obtained using a turbine, for example as in French patent applications FR 2,515,727 and FR 2,534,293.
This electricity can also advantageously be produced by condensing steam, and in particular produced water vapor, and by converting the energy recovered during the condensation of the steam into electricity.
More particularly, over the last decade, the conversion of thermal energy from oceans and seas has made considerable progress with OTEC (Ocean Thermal Energy Conversion) technology. OTEC systems are for example described in international patent applications WO 81/02231, WO 95/28567 and WO 96/411079 and in patent U.S. Pat. No. 3,967,449, and convert the thermal energy into electricity by using the temperature difference between the hot seawater on the surface and the cold seawater at greater depths.
Usually, closed-cycle OTEC systems are used that use a thermodynamic cycle of an intermediate working fluid. To that end, three types of thermodynamic cycles exist, namely Rankine, Kalina and Uehara, that are compatible with the principle of the OTEC systems.
This cycle is used with organic liquids that have a boiling point lower than that of water. It is consequently called “Organic Rankine Cycle” (ORC).
http://www.thermoptim.org/sections/technologies/systems/cycle-kalina/
This cycle uses a mixture of water and ammonia as working fluid. The ammonia concentration is variable depending on the need of each step of the cycle. In theory, the effectiveness is 20% higher than that of the ORC cycle. The working fluid (water+ammonia) is boiled using the heat released by the hot source. Next, the fluid penetrates a separator and splits in two:
The Kalina cycle has the particularity of varying the concentrations of heat transfer fluid (water+ammonia) in order to change the operating points. Indeed, at the exchanger, the ammonia concentration is high, which makes the evaporation temperature low. It is thus possible to evaporate the fluid at a lower temperature. If the ammonia concentration is low, this makes the condensation temperature higher and it therefore becomes easier to condense the steam, since the liquid that will be used to condense (cold source) will not need to be very cold.
http:/www.thermoptim.org/sections/technologies/systemes/cycle-uehara
This cycle also uses water and ammonia as the working fluid with a fixed ammonia concentration, but its theoretical effectiveness is greater than Kalina, and this cycle is above all suitable for hot source temperatures between 20 and 30° C.
This electricity production cycle using thermal energy from the sea is an improvement on the Kalina cycle. Its main particularity lies in simplifying the composition change of the water-ammonia mixture by using a staged expansion with withdrawal.
Just like for the Kalina cycle, the interest of this cycle lies in replacing the evaporations and condensations with a constant working fluid temperature with evolutions using a sliding temperature, and therefore reducing the irreversibility of the system.
In this cycle, an ammonia-rich mixture is heated in an economizer and a vaporizer, which it leaves in its diphasic state. The vapor and liquid phases are then separated, the first being expanded to an intermediate pressure in a turbine.
Part of this expanded flow is recirculated at medium pressure, then cooled by exchange with the base mixture, with which it is mixed, to form the working fluid, which is next brought back to pressure.
The main flow leaving the turbine is expanded to the low pressure in a second turbine, then oriented toward an absorber, where it is mixed with the liquid fraction leaving the separator and cooled beforehand in the regenerator by exchange with the working fluid leaving the rich pump, then expanded to the low pressure. Upon leaving the absorber, the obtained base mixture is condensed before being compressed at the intermediate pressure.
In practice, a 100-MW OTEC facility operating with a Uehara cycle has the following characteristics:
Water desalination systems have also been proposed implementing a humidifier (evaporation device) coupled to a dehumidifier (condensation device). These systems are for example described in the publication “A solar desalination system using humidification-deshumidification process—A review of recent research,” Y B Karhe et al., International Journal of modern Engineering Research, pages 966-977, Apr. 30, 2013. In these water desalination systems, the evaporation of the water in the evaporation device is obtained owing to prior heating of the water before it is introduced into the evaporation chamber, in particular by using solar energy, and all of the saltwater introduced into the evaporation device is evaporated, so as to subsequently recover the brine in the bottom of the evaporation device. These water desalination systems do not make it possible to work with high water flow rates, and it is not conceivable for these systems to use the small quantity of water vapor generated to produce electricity.
The invention aims to propose a new technical solution for treating water in liquid form pumped in a natural environment by evaporation/condensation, in particular such as seawater, lake water or water from a stream, or groundwater. The solution according to the invention makes it possible to improve the energy conversion yields and the implementation costs.
The first object of the invention is thus a facility for treating water pumped in a natural environment by evaporation and condensation. Said facility includes an evaporation device, which comprises an evaporation chamber intended to contain water in liquid form, and allowing only a portion of the water contained in the evaporation chamber to be evaporated, and gas supply means making it possible to inject a gas into the water in liquid form contained in the evaporation chamber, so as to form gas bubbles in that water. Said facility further includes a heat exchanger, which includes cooling means and which makes it possible at least to condense the water vapor coming from the evaporation chamber. Said facility comprises water supply means, which make it possible to pump water in liquid form in a natural environment, and in particular seawater, lake water or water from a stream, or groundwater, to send said water in liquid form pumped in a natural environment through said cooling means or place it in contact with said cooling means, so as to allow the cooling of the water vapor coming from the evaporation chamber, and to supply the evaporation chamber with that water in liquid form pumped in a natural environment after that water in liquid form has been heated while having traversed or been placed in contact with said cooling means. The evaporation chamber includes means for discharging part of the water in liquid form contained in the chamber which, in combination with the water supply means, allow a renewal of the water in liquid form inside the chamber such that the temperature of the water in liquid form contained in the chamber is kept at a sufficient temperature to maintain the evaporation of part of the water contained in the evaporation chamber.
More particularly, the facility according to the invention may include the following additional and optional features, considered alone or in combination with one another:
The invention also relates to a method for treating water in liquid form, by evaporation/condensation, in which only part of the water in liquid form contained in an evaporation chamber of the evaporation device is evaporated in that evaporation chamber, and the water vapor coming from the evaporation chamber is condensed using a heat exchanger, in which a gas is injected into the water in liquid form contained in the evaporation chamber, so as to form gas bubbles in that water, in which water in liquid form is pumped in a natural environment, and in particular seawater, lake water or water from a stream, or groundwater, said water in liquid form pumped in a natural environment is sent through said cooling means or placed in contact with said cooling means, so as to allow the cooling of the water vapor coming from the evaporation chamber, and the evaporation chamber is supplied with that water in liquid form after that water in liquid form has been heated while having traversed or been placed in contact with said cooling means, wherein part of the water in liquid form contained in the evaporation chamber is discharged so as, in combination with the supply of water of the evaporation chamber, to renew the water in liquid form contained in the evaporation chamber such that the temperature of the water in liquid form contained in the chamber is kept at a sufficient temperature to maintain the evaporation of part of the water contained in the evaporation chamber.
More particularly, the method according to the invention may include the following additional and optional features, considered alone or in combination with one another:
The water contained in the evaporation chamber is not heated using an additional heating means.
The invention also relates to a use of the aforementioned facility or method:
The features and advantages of the invention will appear more clearly upon reading the following detailed description of specific alternative embodiments of the invention, the specific alternative embodiments being described as non-limiting and non-exhaustive examples of the invention, and in reference to the appended drawings, in which:
This device 1 includes:
The supply means 12 more particularly include a compressor 121, an intake duct 120 making it possible to supply the compressor 121 with ambient air, and an outlet duct 122, connected at one end to the outlet of the compressor 121, and having its other end submerged in the liquid 11, such that the air produced by the compressor 121 is injected into the liquid 11, near the bottom of the chamber 10.
The passage of a gas, such as air, through the liquid 11 causes forced boiling at a low temperature (in the case at hand, at ambient temperature), which makes it possible to improve the evaporation yield. This can be explained by the fact that the gas bubbles 13, which are created in a forced manner in the liquid by the gas, become charged with vapor (water vapor if the liquid 11 is water), while withdrawing latent heat Lv from the liquid 11 and thus cooling the liquid in the chamber 10. Under the effect of the buoyancy, the bubbles 13 of gas charged with vapor rise increasingly quickly to burst on the surface of the water.
It should be noted that the gas may simply be air or any other gas, and for example, non-limitingly and non-exhaustively, an air-based gaseous mixture, or an inert gas, and in particular helium.
The device of
The curves of
Thus, the injection of a gas, and in particular air, into the liquid 11 contained in the evaporation chamber 10 advantageously makes it possible to create gas bubbles 13, and more particularly air bubbles, which allow the acceleration of the evaporation.
This facility includes an evaporation device 1° by forced boiling, connected to a heat exchanger 3, which, in this alternative, more particularly allows the production of electricity from the condensation of the water vapor coming from the evaporation device 1′.
The evaporation device 1′ includes an evaporation chamber 10 intended to contain water 11, which has been pumped in liquid form in a natural environment.
This evaporation chamber 10 includes:
This evaporation chamber 10 includes a bottom 100 in which an opening 100a is arranged to supply it with water pumped in liquid form in a natural environment.
In the upper part, the evaporation chamber 10 also includes an opening 10c for discharging liquid water 11 contained in the chamber.
The heat exchanger 3 for producing electricity makes it possible to carry out a closed thermodynamic cycle, of the Rankine cycle type.
It includes a condensation unit 30, comprising a condensation chamber 300. which communicates with the discharge opening 10a of the evaporation chamber 10, and which allows the condensation of water vapor coming from the evaporation chamber 10.
The recovery of at least part of the condensation energy of the water vapor and its conversion into electricity are done by an energy conversion system of the Rankine type, which includes a closed circuit 31 in which a heat transfer working fluid circulates in a closed loop. This closed circuit 31 comprises an evaporator 310 for said working fluid (cold source of the Rankine cycle), which has a serpentine shape, and which is positioned in said condensation chamber 300, and a condenser 311 for said working fluid (hot source of the Rankine cycle), which has a serpentine shape, and which is positioned outside the condensation chamber 300. In a manner known itself, a compressor 312 is further inserted on the journey of the working fluid between the outlet of the condenser 311 and the inlet of the evaporator 310.
The heat exchanger 3 also comprises a turbine 32, which makes it possible to produce electricity using the working fluid F, and which is mounted on the journey of the working fluid, between the evaporator 310 of the working fluid and the condenser 311 of the working fluid.
The working fluid F is for example a mixture of water and ammonia.
The facility also includes supply means 12 allowing the forced injection of air into the water 11 contained in the enclosure 10.
These supply means 12 include a compressor 121 whereof the intake is connected to the discharge opening 10a of the evaporation chamber 10 by a duct 120, and the outlet of which is connected to an inlet of the condensation chamber 300 by a duct 122, and an air flow rate control valve 123 that is mounted on the intake opening 10b of the evaporation chamber 10.
More particularly, a filter (not shown) can be mounted at the outlet of the evaporation chamber 10, and upstream from the compressor 121, in order to avoid dirtying of the facility downstream from the evaporation device 1′.
The facility also includes water supply means 14, including a hydraulic pump 140, which makes it possible to pump water L in liquid form in a natural environment, for example seawater, lake water, water from a stream, or groundwater.
This hydraulic pump 140 is connected at its outlet to one end of a water supply duct 141. The other end of the water supply duct 141 is connected to the intake opening 144a of a cooling circuit 144, which is in contact with the condenser 311, and which makes it possible to cool the working fluid F circulating in the condenser 311. The discharge opening 144b of this cooling circuit 144 is connected to one end of a duct 142, which is connected at its other end to the opening 100a in the bottom 100 of the evaporation chamber 10.
The facility also includes a vertical discharge duct 143 that is connected to the opening 10c of the evaporation chamber, and which allows the discharge by gravity of part of the water 11 contained in the chamber 10.
The outlet 143a of this discharge duct 143, which is situated below the evaporation chamber 10, is for example, but not necessarily, submerged in the same natural water source (sea, ocean, lake, stream, etc.) as that in which the hydraulic pump 140 pumps water.
During operation, the hydraulic pump 140 is used to pump cold water L in liquid form at a temperature Tf in a natural environment, and in particular seawater, lake water or water from a stream, or groundwater; this water pumped in a natural environment is circulated in the cooling circuit 144, which makes it possible to cool the condenser 311, and to condense the heat transfer fluid F during its passage in the condenser 311. This water L is thus reheated as it passes in the cooling circuit 144.
This water L in liquid form and reheated to a temperature Tf+ΔT1 is then reintroduced into the evaporation chamber 10, through the intake opening 100a in the bottom 100 of the chamber 10, which makes it possible to renew and reheat the water in liquid form contained in this chamber 10.
When the water level in the evaporation chamber 10 is sufficient, part of the water contained in the chamber 10 is automatically discharged through the opening 10c and through the duct 143. The temperature (Tf+ΔT1) of the water in liquid form entering the evaporation chamber 10 is higher than the temperature (Tf−ΔT2) of the water in liquid form leaving the evaporation chamber 10 through the opening 10c. The water contained in the evaporation chamber is thus continuously renewed, and the temperature of the water in liquid form L contained in the chamber 10 is constantly kept at a sufficient temperature to maintain the evaporation of only part of the water contained in 10 the evaporation chamber, without it being necessary to heat the water in the chamber 10 using an additional heating means or to heat the water before it is injected into the chamber 10 by an additional heating means. “Additional heating means” refers to a heating means using an energy source outside the system, i.e., an energy source other than the energy coming from the water pumped in a natural environment, and for example a solar or electrical energy source.
The flow rate of the pump 140 is adjusted or regulated automatically, so as to continuously supply a sufficient quantity of thermal energy to keep the volume of water 11 in the chamber 10 at a high enough temperature for the evaporation phenomenon not to stop.
This flow rate of the pump 140 may be fixed or can advantageously be regulated automatically, for example from a liquid level detection in the chamber 10, in order to keep a minimum liquid level in the chamber over time, and/or for example from a detection of the liquid temperature 11 in the chamber 10, so as to keep the temperature of the liquid above a minimum temperature threshold conditioning the evaporation of the liquid over time.
In parallel, the compressor 121 operates and aspirates gas (in the case at hand, air) and water vapor in the upper part of the evaporation chamber 10, and creates a vacuum in the evaporation chamber 10 above the water level. This vacuum allows an aspiration of the air from outside the evaporation chamber through the valve 123 and the intake opening 10b of the chamber 10, and thus allows the forced injection of air coming from outside the chamber 10 into the volume of liquid water 11 contained in the chamber 10.
Comparably to what was previously described, this air forms air bubbles 13 (forced boiling) in the liquid water 11 that rise to the surface of the water and favor the evaporation of the water.
By adjusting or regulating the air flow rate entering the chamber 10 using the air flow rate control valve 123, the quantity of vapor produced over time is advantageously controlled.
The vacuum inside the chamber created by the compressor 121 and this forced boiling of the liquid water in the chamber 10 advantageously allow the production of water vapor with water at a low temperature, and for example with water at ambient temperature (Tf+ΔT1 for example comprised between 15° C. and 60° C.).
The air and the water vapor produced in the upper part of the evaporation chamber 10 are aspirated by the compressor 121, and are discharged by the compressor 121 into the condensation chamber 300, while having been heated by several degrees Celsius in the compressor 121.
The water vapor is condensed in the chamber 300 in contact with the evaporator 310 and cedes part of the calories to the working fluid F, which reheats and evaporates the working fluid F in the evaporator 310.
This working fluid F in vapor form makes it possible to rotate the turbine 32 that produces the electricity.
Once it has passed through the turbine 32, the working fluid F in vapor form is cooled in the condenser 311, then is recirculated toward the evaporator 310 by the compressor 312 inserted between the outlet of the condenser 311 and the inlet of the evaporator 310.
The water coming from the condensation of the water vapor in the chamber 300 is collected in the lower part of the chamber 300 and is discharged through the outlet 300a. The dry air after condensation is discharged from the condensation chamber 300 through an air outlet 300b.
When the hydraulic pump 140 withdraws saltwater (water taken from the sea or an ocean), the water coming from the condensation of the water vapor in the chamber 300 and collected in the lower part of the chamber 300 is fresh water, the facility thus making it possible, in addition to producing electricity, to produce fresh water by desalinating seawater. This fresh water can advantageously be recovered while being discharged from the condensation chamber 300 into a freshwater recovery circuit.
Additionally, regarding saltwater or fresh water taken from a natural environment, and which may contain pollutants, the evaporation/condensation of this water in the facility makes it possible to recover, at the outlet 300a of the evaporation chamber 300, cleaned purified water.
The forced injection of air into the evaporation chamber 10 advantageously makes it possible to generate water vapor at a low temperature (for example, at a temperature below 20° C.), without it being necessary to create a vacuum in the evaporation chamber 10. As an example, the vacuum created by the compressor 121 inside the evaporation chamber above the water level can for example be comprised between 0.1 bars and 0.5 bars.
This low-temperature vapor advantageously allows a more effective heat transfer by condensation, and consequently allows the implementation of a source (working fluid in the evaporator 310) that is less cold, to recover, by condensation, the energy stored in the vapor in order to convert it into electricity. It is therefore no longer necessary, unlike the traditional OTEC systems, to pump very cold water, and in particular seawater, at very great depths to cool the condenser 311, but this less-cold water (Tf for example comprised between 15° C. and 30° C.) can advantageously be pumped near the surface, and the energy conversion yields are improved.
The use of water vapor with forced boiling also makes it possible to reduce the need, in terms of structure and number, for pumps (the OTEC 100-MW systems currently require pumps with a cumulative flow rate of 111 m3/s to pump the hot seawater). In the facility of
The invention thus makes it possible to extract thermal energy from water in the natural environment, and in particular from seawater, with a lower energy consumption than the traditional OTEC systems.
The performance of the facility according to the invention depends on the temperature of the water that is pumped in a natural environment by the water pump 140. The performance of the facility according to the invention can be improved by increasing the temperature of the air injected into the liquid 11, since this hot air will cede its excess energy to the water vapor.
In one alternative of the invention, the walls of the evaporation chamber 10 can also be heated with an additional heating system.
In another alternative, the air injected into the chamber 10 can be replaced by another gas, and for example an air-based gaseous mixture, or an inert gas, and more particularly helium.
The facility of
In another alternative illustrated in
The facility can work in a closed circuit as illustrated in
This modification makes it possible to reduce the electricity consumption of the compressor(s) 121. Indeed, the use of a compressor in a closed circuit requires less energy, since the same air is used continuously for the operation of the system.
One or several temperature sensors ST can be positioned within the air circulation circuit, in order to control the working air temperature and automatically steer the air intake solenoid valve EV, if it proves necessary to bring ambient air into the circuit in order to increase the temperature or completely change the working air.
This facility of
This heat exchanger 3′ includes a condensation unit 30, which includes a condensation chamber 300 communicating with the evaporation chamber 10 of the evaporation device 1′, and a cooling circuit 301 with a serpentine shape, which is positioned in the evaporation chamber 300, and in which a heat transfer liquid circulates.
In the facility of
During operation, the hydraulic pump 140 makes it possible to pump water from a natural environment at a temperature Tf, to circulate this water pumped in a natural environment and serving as heat transfer liquid for the cooling circuit 301, in the cooling circuit 301. At the outlet of the cooling circuit 301, the water that has been heated (temperature Tf+ΔT1), following the heat exchanges resulting from the condensation in the chamber 300 of the water 20 vapor coming from the evaporation device 1′, is injected into the evaporation chamber 10 through the intake opening 100a.
The same advantages previously described for the facility of
It is possible to modify this facility of
More particularly, when this gas is a hot gas and/or a gas containing pollutants, the evaporation device 1′ in that case allows the cooling of that gas and/or the dissolution in the liquid 11 of the pollutants contained in the gas. After passage in the liquid 11, the gas is cooled and/or cleaned.
This device may for example be used to cool and clean a gas coming from an incinerator and which may have a temperature of several hundred degrees, the passage of the gas in the liquid making it possible to block the spread of the pollutants into the atmosphere.
In this alternative, the pump 142 makes it possible to pump, in a natural environment, water L in liquid form at a temperature If. and to introduce that water directly into the evaporation chamber 10, such that the condenser 311 of the heat exchanger 3″ is submerged in the water in liquid form 11 contained in the evaporation chamber 10. When it passes in the condenser 311, the working fluid F is thus cooled by the water 11 contained the evaporation chamber 10, then is returned in liquid form by the compressor 312 into the evaporator 310 to allow the condensation of the water vapor coming from the evaporation chamber 10.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1450612 | Jan 2014 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2015/050155 | 1/22/2015 | WO | 00 |
