Patent Application
20150068886
The invention relates to both improved water distillation apparatuses of the type using streams of forced saturated damp hot air and recovery of latent heat of condensation, and methods to maximize the performance thereof. Applications of these distillation apparatuses include desalination of seawater and, more generally, demineralization of any clear water, especially for producing ultra-pure water. The invention also relates to the concentration of various industrial aqueous solutions, to be transformed (food industry) or destroyed (polluted effluent waste) and the separation of certain volatile liquids from their aqueous solvent (ethanols, acids, bases . . . ).
Two water distillation apparatuses, using streams of forced saturated damp hot air with recovery of latent heat of condensation are described and commented on (1) in FIG. 5 of a French patent application of 1975, published under No. 2,281,896, and (2) a U.S. Pat. No. 3,860,492 of the same year.
In the water distillation apparatus of this French patent application,
This water distillation apparatus has been arranged to form these three distillation stages in order to improve heat exchange between streams of hot water and hot air or air and water circulating in opposite directions, taking place in the evaporation chamber and the condensation chamber of the apparatus. Such a solution (not justified in the document) is indeed necessary because, depending on the temperature, the heat capacity CpE of one kilogram of water is constant (4.18 kJ/K), while the apparent heat capacity CpA of one kilogram of dry air at standard pressure, incorporated into saturated hot damp air, increases with temperature and exhibits a hyperbolic branch which tends to infinity at 100° C. With three stages of distillation, the pair of curves representing the enthalpy fluxes of rising and descending air is transformed into two sequences of three festoons. In these conditions, we greatly minimize the variation between, on the one hand, these two series of festoons and on the other hand, the two parallel straight lines representative of the enthalpy flux of the water flowing upwardly and downwardly. The total heat exchange thereby achieved is much higher than it would have been with a single distillation stage and the amount of distilled water produced is, under these conditions, greatly increased. But the performance of such water distillation apparatus is nevertheless far from maximal.
Indeed, in this water distillation apparatus, with a stream of air at initial temperature TA0=20° C. and a stream of water at a temperature Tlow of TE0=20° C. and Thigh of TE2=95° C., we have, at an upper portion of the three stages of distillation of ranks 1 to 3, for air circulating in an open loop: TA1=55° C., TA2=75° C., TA3=90° C., and 35° C. at the lower portion of the condensation column. For water circulating in open loop, at the lower portion of the three evaporation chambers we have, from top to the base of the evaporation column: TE2, 85° C., 65° C. and TE3=40° C. At an upper portion of the three condensation chambers we have, for the water, from the base to an upper portion of the condensation column: TE0, 45° C., 65° C. and TE1=75° C. Under these conditions, the coefficient of performance (CoP) of the apparatus (the ratio between the thermal energy used in distillation and the thermal energy supplied by the water heater), CoP=(TE2−TE0)/(TE2−TE1)=3.75, which is an average value, acceptable when the energy used is cheap. But the question is, is this calculated coefficient of performance (CoP) possible with the apparatus described?
To look into this, we will look more closely at the temperatures announced for the air and water. And we will see that these temperatures (clearly not experimental) are not suitable for producing average performance and a fortiori, high-performance, both from a technical and an economic point of view. This firstly is the case for the air temperatures at an upper portion of the evaporation chambers and at the lower portion of the condensation chambers of the three distillation stages.
Initially, what is involved is choosing the two intermediate air temperatures TA1 and TA2 at an upper portion of the evaporation chambers of rank 1 and 2. This choice is usually made starting out from extreme air temperatures: a low temperature TA0 imposed by the ambient air and a high temperature value TA3 relatively close to TE2, the high temperature of the water distributed at an upper portion of an upper evaporation chamber. As a result of the three distillation stages provided in the distillation apparatus, the curve which it is desired to represent the corrected enthalpy fluxes of the ascending saturated hot damp air streams in the three evaporation chambers is an ideal sequence of three segments of a straight line of slopes A=ΔH/ΔT, with ΔH and ΔT the increases in enthalpy flux and air temperature in each of the evaporation chambers. In fact, the actual curve representing the corrected fluxes is constituted by three festoons which depart from a straight line and which meet angularly at two points. The maximum difference between these two curves, actual and optimal, is the degree of deflection ΔTF of each festoon. For each festoon, the value in degrees of the deflection ΔTF is the quotient ΔH*/A where ΔH* is the difference in enthalpy flux between the middle of the ideal line and the point on the curve for air enthalpy flux at the mean temperature of the chamber. In the case of extreme temperatures of saturated damp hot air in an upper portion and lower portion of the evaporation chambers, announced in the patent concerned, namely 30 (approximately), 55, 75 and 90° C., the values of enthalpy flux for 1 kg/s of dry air, carried away by the stream of saturated damp hot air ascending in each evaporation chamber are given by the table for specific enthalpy H of the saturated damp hot air. For significant temperatures of the damp air (middle and ends of the straight line segments), we have H90=3887 kW; H82.5=1864, H75=1088; H65=600; H55=353; H42.5=179 and H30=100 kW. For the lower festoon, we have ΔH1*=½ (H55+H30)−H42.5=48 kW and A1=(H55−H30)/25=10 kW/K, so that ΔTF1=4.8° C. For the central festoon we have ΔH2*=120 kW, A2=37 kW/K and ΔTF2=3.2° C. For the upper festoon we have ΔH3*=623 kW, A3=187 kW/K and ΔTF3=3.3° C. All these values are unacceptable, for the reason that they are too high. But as the deflection ΔTF1 of the lower festoon is the most significant, it is, therefore, the only one to be taken into account for determining (TE2−TE1). Here, it represents a quarter of the temperature increase required of the water heater, which leads to a corresponding reduction in coefficient of performance (CoP) of the apparatus. By way of conclusion of these initial comments, we see that for water distillation apparatus to be efficient, the number of distillation stages and the choice of air temperatures at an upper portion of the evaporation chambers cannot be determined in an arbitrary fashion even if this does seem to be in line with common sense.
As regards temperatures at the lower portion of condensation chambers, there is no reason for the temperature of the air stream deviated by the two communication paths between the evaporation and condensation chambers of ranks 1 and 2, and the temperatures of the descending air streams in condensation chambers of rank 2 and 3 to be the same. Indeed, as the architecture of the two chambers of a distillation stage is different one from the other, then a priori, their respective heat exchange coefficients are also different. The inequality of these temperatures causes a decrease in coefficient of performance (CoP), if it is not corrected.
In addition, as the shape and dimensions of the cross-sections of the ducts discharging into the condensation chambers, nor the shape of the cross-section of these chambers are not specified, the exact conditions under which air streams deviated by these ducts enter these chambers and mix with the air streams descending from chambers of higher rank is not known. Whatever the case may be, streams of air which actually come into close contact with the coils are, a priori, in very small minority compared to those which do not. This is at the origin, locally, of air/water thermal couplings which are unbalanced and very different one from the other. Overall, the saturated damp hot air is very poorly cooled and vapor is very badly condensed in the condensation chambers equipped with condensing coils. For this to be otherwise, it is necessary that the surface area per unit volume S/V for heat exchange at these coils be relatively high in the condensation chamber. As such a ratio for efficient heat air/water exchange is S/V>150 m2/m3, we can see that this is inconceivable when using conventional zigzag or spiral coils, for which S/V<10 m2/m3. The situation is better when multiple coils or sections of coils are assembled in parallel, with upstream and downstream manifolds. This is something which the cited document does not suggest. In any case, the thread-like structure of conventional coils often leads to unacceptable pressure loss in the water stream. In addition, their cost is often prohibitive since, being a priori of metal, their metal must be insensitive to the corrosive action of seawater The conclusion of these discussions is simple: conventional metal coils are completely unsuitable to fulfil the double function assigned to them in high performance (coefficient of performance (CoP>4) water distillation apparatus, namely: efficiently heat up an ascending seawater stream using a descending stream of saturated damp hot air and condensing the maximum amount of water vapor carried by the air stream under satisfactory economic conditions for the relevant markets.
Moreover, packing wettable artificial nuts into the evaporation column leads to significant pressure losses in the air stream blown in by the fan installed at a lower portion of this column. This leads to a requirement, for the air stream, for relatively high pressures and high local velocities, which inevitably leads to the presence of droplets of brine in air streams entering into the condensation column. In the case of water distillation apparatus treating standard seawater, this leads to the presence of a 1 to 2 g salt content per liter of distilled water produced, making consumption thereof unpleasant. In the case of water distillation apparatus treating polluted industrial water, discharge of which is prohibited, the situation is worse: the distilled water remains polluted and discharge thereof is prohibited.
To complete the discussion of the problems posed by water distillation apparatus disclosed in the cited document, we can still note that the temperature TE2=95° C. provided for the hot water to be distributed at an upper portion of the evaporation column, is a temperature which is too high, in the long run dangerous because it accelerates the precipitation of certain salts dissolved in the water and, as a result, leads to significant limescale deposits within the passages taken, causing disruption and, in the long-term, these finish by blocking the operation of the machine.
The water distillation apparatus according to U.S. Pat. No. 3,860,492 is designed to be an automatic system for concentrating industrial water. It includes a first distillation stage, materialized in a lower half of the two columns, and an indeterminate number of stages arranged thereabove. The wettable components of the evaporation column consist of suspended netting and the hollow heat exchange components of the condensation column are condenser coils. The majority of the above negative remarks apply. In addition, arrow of the festoon of the air enthalpy curve in this first stage is, a priori, notably greater than that in the case discussed above. Higher performance distillation apparatus using eight stages is additionally envisaged, without further details.
To conclude the commentary on these two documents, we can affirm that one major condition to insure the process involved does exhibit high energy performance is that the difference in temperature between the damp air and the water be as small as possible throughout the length of the evaporation and condensation columns. The fact of splitting up each column into several stages, where the damp air flow rates are different and the water flow rate is practically constant already makes possible an overall reduction in the difference in temperature between the damp air and the water. The two documents cited do propose such a solution. The French patent does not give an explanation. The US Patent gives a partial explanation starting from the curve showing the evolution of saturated damp air enthalpy as a function of temperature. But neither of these two patents deals with a way of minimizing the difference in temperature between the damp air and the water within each one of the stages.
Accompanying this major condition there is another condition which is just as important: thermal exchange coefficients which notably result from thermal exchanges in dry air, the mechanism for distributing water vapor into the air and the surface area per unit volume (S/V) of the components of the distillation units, must be as high as possible, in order to be able to sufficiently reduce this difference in temperature between the damp air and the water. But this is all the more difficult when we consider that obtaining good mastery of heat exchanges in saturated damp air is something which is not at all obvious.
The first subject matter of the invention concerns various improved water distillation apparatuses, using forced saturated damp hot air streams with recovery of the latent heat of condensation, including several distillation units adapted to operate under optimal conditions.
The second subject matter of the invention concerns such improved water distillation apparatuses in which, through construction, these optimal conditions are, within the condensation chambers, established by the use of components having a very high thermal exchange coefficient.
The third subject matter of the invention concerns such improved water distillation apparatus in which these optimal conditions, in both chambers of each distillation unit, are established by differences in temperature between the damp air and the water which are as low as possible.
The fourth subject matter of the invention is the realization of such improved water distillation apparatus having a high and/or variable capacity for daily production of distilled water, constituted by modular distillation units which are easy to construct, install and operate.
A fifth subject matter of the invention concerns methods for maximizing the performance of these various water distillation apparatuses.
A sixth subject matter of the invention concerns the construction of such improved water distillation apparatuses which are suitable for demineralizing water, notably desalinated seawater, concentrating industrial waters and separating volatile liquids from their aqueous solvents, with a high energy yield.
In accordance with an enlarged definition of the water distillation apparatus disclosed in the French patent commented on above, the present distillation apparatus is of the type in which:
According to the invention, the improved water distillation apparatus of the broad type defined above is characterized in that:
According to the invention, such water distillation apparatus is further characterized in that it includes N perforated trays adapted to distribute total flow rates of air, respectively entering into the N condensation chambers, into substantially equal partial air flow rates penetrating into the spaces between the hollow plates of these chambers.
According to the invention, such water distillation apparatus is more precisely characterized in that in each of the N distillation units:
These simple provisions are both novel and non-obvious, since they provide practical solutions to concrete non-obvious problems, considering they were overlooked and/or not expressed until now. Firstly, the choice of condensation chambers having a rectangular cross-section is not the only one possible but, clearly, the most rational choice considering that the heat exchange device is constituted by an assembly of rectangular hollow plates, which are the only ones which are currently available on the market. With condensation chambers which have a non-rectangular cross-section, the arrangement of the hollow plates will be done on the basis of the specific geometry or geometries, which the manufacturer has given these plates.
With a horizontal rectangular entrance window, according to the invention, the stream of saturated damp hot air which penetrates into the condensation chamber of each one of the N distillation units, does this in the form of uniform horizontal and parallel veins of air which have overall, an elongated rectangular cross-section (40×10 cm, for example). Under these conditions, in the distillation unit of rank N, such veins of air can correctly spread out above the heat exchange device which is occupying the whole cross-section of the condensation chamber (40×30 cm, for example). In the other units, the two flow rates, the horizontal one and vertical one, which enter into the condensation chamber at the same temperature (below it will be seen why and how this is so) but the mixing thereof sets up disordered movements and excess pressures.
The perforated tray, which is installed without notable lateral leakages, corrects the potential action of these disordered excess pressures, by forcing the total air flow, entry into each condensation chamber, to be redistributed into substantially equal partial flow rates, which penetrate into the spaces separating the vertical hollow plates of the heat exchange device.
Using condensation chambers having a rectangular cross-section and rectangular hollow plates which are assembled at a constant pitch, the perforations of the perforated tray are rows of oblong holes, having the same pitch as these plates. Within each condensation chamber of rank 1 to N, equality of the partial flow rates of air circulating between the plates is a result of the substantial drop in pressure Δρn=½ρnvn2, which is created during their passage through the holes (ρn being the density of the saturated damp hot air entering into the chamber of rank n, and vn is the velocity at which it passes through the holes). As a consequence, the surface areas, both total and individual, of the oblong holes of the perforated distribution and spreading plate of each condensation chamber can be determined further to a simple calculation, done using the total flow rate of incoming air, which itself is calculated, as will be seen below. Additionally, it is possible to replace each row of holes by one or a plurality of slots of an appropriate calculated width, but the distribution of the partial air flows circulating between the hollow plates is in this case less uniform and, inside the condensation chamber, the heat exchange performed is less effective, but generally satisfactory.
Thanks to the arrangements according to the invention, effective heat exchange is performed between, on the one hand, the descending (3 to 6 mm thick) layers of saturated damp hot air, sweeping both faces (30×40 cm for example) of the (4 to 6 mm thick), thin-walled (<1 mm) hollow plates of polymer material and, secondly, the narrow (2 to 4 mm) thicknesses of water which is ascending inside these plates. This is achieved despite the relatively high thermal resistivity of polymer materials. The coefficients of heat exchange and conductance between these air and water streams are significant since they are spread over two relatively large faces of this plurality of thin-walled hollow plates, assembled close to each other, occupying the whole volume of a condensation chamber. This is possible since the surface area per unit volume of the heat exchanger using separated, assembled hollow plates can reach S/V=250 m2/m3, when plate pitch is 8 mm. Thermal conductance here is several tens of times greater than that produced between an air stream which is passing through a condensation chamber occupied by a conventional metal coil, whether this be in zigzag or helical, and the water conveyed therein.
Further, if we do replace these conventional coils of 1975 by their current up-to-date versions, in other words bundles of polymer material tubes, having upstream and downstream manifolds, the surface area per unit volume of such a bundle, (depending on the manufacturer, 15<S/V<110 m2/m3), remains on average three times less than that of a group of assembled hollow plates. If one were to replace the hollow plates by such bundles of tubes, this would lead, on average, to tripling the thicknesses of air and water, and consequently substantially diminishing thermal conductance per unit volume. A further significant and non-obvious comparative advantage of heat exchangers using hollow plates, installed in the condensation chambers of water distillation apparatus will be discussed below, in relation with the temperatures and flow rates of the saturated damp hot air streams inside these chambers.
In addition to these initial advantages specific to hollow plates of polymer material, there is the further advantage provided by the perforated tray according to the invention, in other words the division of the total air flow rate of incoming air in each condensation chamber into substantially equal partial flow rates that circulate between the hollow plates. When it is desired to maximize performance of the apparatus, it is essential to ensure that these partial flow rates are the same. In effect, simple calculation shows that a moderate disequilibrium (<20%) between these partial air flow rates would result in a division by up to two of the efficiency of heat exchange achieved, and consequently of the performance of the apparatus. And this all the more so when we consider when we are seeking a target coefficient of performance which is even higher. As a consequence, thanks to these initial provisions according to the invention, in water distillation apparatus improved in this way, the effective heat exchange achieved inside the condensation chamber of each distillation unit leads to a maximum condensation of vapor and a maximum heating up of the water.
Further, experience has shown that with oblong holes in the perforated tray, having a width which is substantially equal to the distance between two hollow plates (>3 mm), we eliminate the risk of these holes becoming blocked by droplets of condensed water. Additionally, each partial air flow rate exiting from a hole is efficaciously distributed between two plates, when there is a distance of less than about 10 cm separating two rows of holes of a perforated tray.
According to the invention, a method for maximizing the performance of these water distillation apparatuses according to the invention is characterized in that, depending on the conditions of use of the apparatus, it includes the following preliminary steps:
Through the choice of a temperature TE2<90° C. for the hot water to be distributed and spread, scaling of components of the apparatus is minimized. The choice of the value TE2, between 90 and 45° C., depends on the primary heat source available (solar, thermal engines, hot effluent, burners . . . ) and, where applicable, the temperature of boiling of the volatile liquid (ethanol, acid, base) dissolved in the water that is to be separated from the solvent.
To implement the various arrangements of the method according to the invention, we first make use of the table for enthalpy of saturated damp hot air. We saw earlier that the deflection of a festoon which departs from a straight line in a particular evaporation chamber is the difference in degrees, which corresponds to the maximum difference in watts between the curve representing the actual value of the enthalpy flux of the saturated damp hot air, and the deflection it would have if the curve was a straight line segment. Appropriate software makes it possible to draw up a digital chart for the amplitudes of these N festoons which depart from a straight line for every pair of extreme temperatures (TA0, TAN) used for the air stream rising in the evaporation column. In a four-distillation-stage distillation apparatus, with an upper water temperature value of TE2=85° C. and extreme air temperatures of TA4=83° C. and TA0=33° C., the approximated optimum temperature of the air at an upper portion of the evaporation chambers of rank 1 to 3 are substantially: 47.5°, 61° and 73° C. In this case, the four increments ΔTA1 to ΔTA4 between the extreme temperatures of the air in the evaporation chambers are, from top to bottom, 10, 12, 13.5 and 14.5° C., while the departures from a straight line of the festoons are substantially equal to 1.2° C. (to which there should be added an imposed 0.5° C. deviation due to the salinity of the water). If we increase the number of distillation stages, departure from a straight line or deflection of the festoons decreases, but below about 0.5° C. for these deflections, increasing the number N is of little value. In an improved water distillation apparatus according to the invention, the optimal number of distillation stages may range from N=3 to N=6, as a function of the difference between the extreme temperatures of the air (TAN−TA0), ranging from 35 to 65° C. In practice, the number N=4 is suitable in all cases, for technical and economic reasons.
Within the four evaporation chambers, the temperatures TA1 to TA4 as well as the increments ΔTA1 to ΔTA4 being established, the heat capacities CpA1 to CpA4 of the saturated damp hot air, at the average temperatures Tm1 to Tm4 in these chambers are known. Enthalpy fluxes exchanged in an evaporation chamber of rank n are: ΔHAη=QAn. CpAn. ΔTAn and ΔHEn=QEN. CpEnΔTEn. As increments ΔTAn and ΔTEn are substantially equal and QEn only slightly differs from QE0, the approximated mass flow rate of dry air in a stage of rank n is substantially QAn=QE0. CpE/CpAn. Tables giving the density of saturated damp hot air make it possible to know the approximate volume flow rates QS1 to QS4 of this hot air, at average temperatures Tm1 to Tm4 in the four evaporation chambers. From these values, it is easy to calculate, for each condensation chamber, total and individual surface areas of the holes in the perforated tray and the pressure drop to be generated by the presence of the distribution plate.
For example, with QE0=100 g/s and in the evaporation chamber of rank 1, Tm1=41° C., CpA1=8.74 kW/kg·K, QA1=47.8 g/s, we get QS1=43.9 dm3/s. In the evaporation chamber of rank 4, with Tm4=79° C. and CpA4=102.6 kW/kg·K, we get QA4=4.1 g/s and QS4=4.92 dm3/s. These two very different flow rates indicate that the air flows in the condensation chambers of ranks 1-4 have progressively shifted from a turbulent regime to a laminar regime. This leads to very different surface areas for the holes in the distribution plates of ranks 1 to 4. Moreover, this leads to an unobvious additional justification for the exclusive use of heat exchangers having hollow plates in the water distillation apparatus according to the invention.
Indeed, in the case of dry air, thermal exchange coefficients depend on:
In the case of hollow plates, below a certain airspeed, flow changes from one regime to another (from turbulent, it becomes laminar) and the coefficient of exchange no longer depends on velocity but remains relatively high since the characteristic dimensions is small. This is not the case when we are dealing with bundles of tubes, where the transition from one flow regime to another is less sharp and the characteristic dimension is larger than in the case of plates.
With saturated damp air, operating under an evaporation or condensation regime, the apparent thermal exchange coefficient depends on the exchange coefficient for dry air defined above but, additionally, the diffusion mechanism which intervenes in the evaporation or condensation process considerably amplifies this exchange coefficient, and the coefficient of amplification is substantially proportional to the rate of increase in saturated vapor pressure as a function of temperature. As a consequence, in the hottest condensation chamber of the distillation apparatus (rank N), where the equivalent flow rate of dry air (and consequently its speed) is small, a heat exchanger using hollow plates will have significantly better performance than one using a bundle of tubes; and this will be increasingly true as the surface area per unit volume S/V increases. The same will apply more or less for the condensation chambers which are cooler of the distillation apparatus.
According to the invention, water distillation apparatus of the type in which:
is characterized in that:
In an alternative embodiment, in water distillation apparatus of the type in which:
it is characterized in that:
According to the invention, a method to maximize performance of the first of a series of one or the other of these two distillation apparatuses includes the following additional steps:
The implementation of the method according to the invention can begin as soon as the number N of stages of distillation and the N temperatures TA1 to TAN have been selected, as soon as the hot water has been distributed and spread for a certain amount of time (>1 hour, in view of the thermal inertia of the apparatus), the fan is causing the air to circulate in an open or closed loop, and the partition openings are half closed. This first adjustment is terminated as soon as the intended temperature TA1 is reached. The mass flow rate of dry air QA1, included in the flow rate of air supplied by the fan, is now, just like TA1, at an approximated optimal value. When circulation is taking place in a closed loop, the temperature TE0 of the cold water and the initial state of the port cross-sectional areas of the openings in the partition determine the initial low-temperature TA0 of the air. In this case, TA1 is a provisional predetermined temperature, obtained at the end of this first adjustment step for the flow rates of the air streams circulating in the evaporation chambers.
The second step in the method according to the invention employs means for adjusting cross-sections for air passage. We start with the lowest opening in order to adjust the temperature TA2 of the air stream in the upper portion of evaporation chamber of rank 2. Once this adjustment has been done, we do the same for the evaporation chambers of increasing rank from 3 to N. The operation is restarted at least one second time in order to correct variations in the temperatures TA1 to TAN inevitably brought about by the successive adjustments, since the mass flow rates of dry air QA1 to QAN and their temperatures TA1 to TA1 are independent. In the case of closed-loop air circulation, the low temperature TA0 of the air being blown in at the lower portion of the evaporation column becomes progressively closer to TE0, the initial water temperature.
The third step in the method according to the invention has the aim of respectively bringing to equal temperatures, the temperatures TA1 to TA(N-1) and TA1* to TA(N-1)* of the layers of air circulating at the lower portion of the evaporation and condensation chambers of the (N−1) highest superposed distillation stages. When the air temperature, at the lower portion of a condensation chamber of a given rank is different to that of the lower portion of the evaporation chamber of the same rank, it is not known whether the mass flow rate of dry air concerned, QA1 to QAN at that point is a bit too high, or too low. In practice, we start with the highest stage and increase or reduce the flow rate of air circulating in the evaporation chamber of rank N, by slightly and carefully increasing or decreasing the port cross-sectional area of the communication path between the chambers concerned. It is necessary to wait a short while to see whether this action has resulted in the two temperatures concerned coming closer together. If this is the case, one continues up until the point where they are equal. Otherwise, one does the opposite. If this is not sufficient to obtain the desired equality, the best adjustment is noted and this is supplemented by adjusting the port cross-sectional area of the communication path delimiting the upper portion of the distillation stage of rank (N−1) up until this equality of temperatures is found. One then proceeds in the same fashion for this distillation stage of rank (N−1), adjusting the port cross-sectional area of the opening delimiting the stage of rank (N−2) and then returning to the two openings of higher rank, in order to maintain temperature equality at the bottom portion of the evaporation and condensation chambers of the distillation stages of ranks (N−1) and N. The procedure is renewed for all the stages of lower rank, up to the stage of rank 2. Next, it is a priori necessary to adjust the air flow rate produced by the fan in order to maximize TE1, the water temperature at the outlet from the condensation column.
With air circulating in a closed loop, we will have finally minimized as much as possible the temperature of the air TA0* in the lower portion of the condensation column by causing it to approach TE0, the temperature of the water entering therein and, at the same time, we will have maximized as much as possible the temperatures TAN of the air and TE1 of the water at the top portion of this column, by bringing both of them close to the temperature TE2 of the water being distributed and spread. The air temperatures at the lower and upper portion of the distillation stages would then have optimal set point values TA0C to TANC, slightly different to the initial theoretical optimal temperatures TA1 to TAN, which correspond to the values adopted for the three terms QE0, TE2 and TE0 of one particular piece of distillation apparatus. In the N stages, the representation f(T) of enthalpy fluxes of mass flow rates of water comprise two parallel straight lines having a slope CpE, separated by a number of degrees (TE2−TE1), and the representation f(T) of enthalpy fluxes of the air comprise, between these two straight lines, one single line formed festoons having successive extremities TA0C to TANC, the mean slope of this line being slightly greater than that of these two straight lines. The relations between the extreme temperatures of the water and air are: (TE1−TE0)=(TE2−TE3)<(TANC−TA0C).
To finish, we can note that, in view of the high thermal inertia of the various components of the apparatus, all the operations for implementing the method for maximizing performance of the first piece of distillation apparatus of a series can take several hours, this number of hours being itself directly proportional to the number N of stages.
Under these conditions, by carrying out the method according to the invention, experience has shown that with water distillation apparatus having four distillation stages, constructed in accordance with the invention, it is possible to obtain a coefficient of performance (CoP)>6, for a daily flow rate of distilled water produced which is equal to 3 to 5 times the total volume of the evaporation and condensation chambers of the apparatus.
According to the invention, the first model of a second type of improved water distillation apparatus having the general architecture of the new water distillation apparatus defined above and having N distillation units placed one above the other and forming two columns, one for evaporation and the other for condensation;
is characterized in that
According to the invention, the second model of this second type of improved water distillation apparatus having the general architecture of the new water distillation apparatus defined above, is characterized in that:
According to the invention, a method to maximize performance of the first piece of apparatus of a series of one or the other of the two improved water distillation apparatuses of the second type, is characterized in that it includes the following additional steps:
With these latter provisions, one can construct two particularly useful novel water distillation apparatuses adapted to treat water using fixed inlet parameters: mass flow rate QE0 and high temperature value TE2. Indeed, the N distillation units are substantially identical, except, however, that the rows of holes of the perforated trays are different from one apparatus to another and the N fan controls are set differently. Such water distillation apparatus employing juxtaposed distillation units is of considerable interest when daily production of distilled water is large (>10 m3/day). Indeed, it does make it possible to build distillation units which are identical, of medium height, easier to handle than multi-stage towers having the same number of distillation units.
In the case where both parameters QE0 and TE2 are variable (solar energy), an interesting situation also exists. Indeed, as noted above, for any group of input parameters QE0, TE2, TE0 and TA0, as soon as temperatures TA1 to TAN have been set, it is easy to calculate QA1 to QAN as well as QS1 to QSN and thus the operating conditions of the fans. When using fans with synchronous motors, one thus determines the frequencies F1 to FN of their supply voltages. This implementation of the method according to the invention, in order to maximize the performance of water distillation apparatus having N juxtaposed units, is particularly easy, using a computer and establishing correspondences between the frequencies F1 to FN and setpoint temperatures TA1C to TANC to be obtained, as soon as the four values QE0, TE2, TE0 and TA0 are input. To do this, an experimental database is set up, by performing at least three operations to get optimum settings for each of the four input parameters QE0, TE2, TE0 and TA0. Then we develop software that associates these data to the N optimal set point temperatures TA1C to TANC and to the N frequencies F1 to FN of motor supply voltages. These frequencies will be determined by computer, from the values chosen for QE0, TE2, TE0 and TA0, and then manually or automatically adjusted.
In order to be able to properly dimension the evaporation and condensation chambers of the N distillation units of the different types of water distillation apparatus discussed above, according to the desired flow rate of distilled water from the apparatus to be constructed, it is necessary to determine their thermal conductance CT (watts per degree) and/or their thermal resistance RT (degrees per watt). To do this, they are calculated. This is done as a function of the respective components and architectures contemplated for construction of the two columns of the distillation apparatus. One then calculates the thermal conductance of an elementary slice of the evaporation and condensation chambers. These results are then integrated over the height of each of the two chambers of each one of the N distillation stages, in order to finally draw up charts for thermal conductance and resistances of the two columns. The accuracy of these calculations is estimated to be 10%. Having chosen the structures of the two columns, the next step is to respectively provide appropriate thermal resistances to the two chambers of the N distillation stages. This is done in accordance with equal enthalpy fluxes ΔHE and ΔHA to be exchanged in the two chambers of a given distillation stage. From one stage to another, these fluxes are, or are not, equal. The same applies to the thermal resistances of the two chambers of a distillation unit, in line with practical considerations imposed by the geometry of the apparatus.
The characteristics and advantages of the invention will become clearer from the following description, made with reference to the accompanying drawings in which:
The partition 18 is 240 cm high and includes two wide openings: one 24 at its top and the other 26 at its base. The partition 18 further includes three identical intermediate openings 28, 30 and 32, and each of these openings is a horizontal row of vertical slots, 10 cm high and 2 mm wide, having the same pitch (15 mm) as plates 20 of evaporation column 14. Such a row of slots is shown in
The opening 26, arranged at the lower portion of the partition 18, is equipped with a fan 34 for drawing in air from the bottom of the condensation column 16 and propelling it upward in evaporation column 14 (arrow 36). The electric motor of the fan 34 is for example of the synchronous type and is powered by a variable frequency voltage. The graph giving the maximum flow rate and pressure of the air supplied by the fan 34, as a function of supply frequency, is available. The upstream manifold of heat exchanger 221 of condensation column 16 is connected by a polymeric conduit 38 to a storage tank providing it with seawater to be distilled, at an appropriate mass flow rate QEo. This seawater constitutes the cold source of the apparatus. The downstream manifold of heat exchanger 226 of condensation column 16 is connected by a conduit 39 in polymer to the inlet of water heater 40, equipped with heating means, constituted by a heat exchanger 42, similar to exchangers 221-6. This exchanger 42 is supplied by two upstream and downstream pipes 44-46, in which a heat transfer fluid circulates, supplied by an external primary hot heat source (not shown). The water heater 40 has an outlet weir 48, from which hot seawater 50 trickles, entering a basin-like member 52. This basin-like member 52 has its bottom perforated with forty pairs of collared holes, corresponding to forty distribution troughs (not shown) covering an upper portions of the forty plates 20 of evaporation column 14. At the base of condensation column 16, there is installed a container 54 for collecting the distilled water 56; this container 54 is provided with walls in the form of a widely-opening V, and an evacuation conduit 58. Evaporation column 12 and tower 10 include, at their common base, a container 60 for collecting the concentrated seawater, this container 60 being provided with an evacuation conduit 62. Arrows 64-66-68 represent the ascending air streams in the evaporation column, and the arrows 70-72-74 show the air diverted through openings of the partition 18. The arrows 76-78-80 represent air streams descending down condensation column 16 and arrow 82, the stream entering the column 16, through opening 24 arranged at an upper portion of the partition 18.
In this first piece of apparatus 10 of a series of identical distillation apparatuses several thermocouples measuring the temperature TA1 to TA4 and TA1* to TA4* defined above, are installed at significant locations of the distillation apparatus; they are represented by black dots with a white center and are connected to a digital conversion circuit and display, not shown. Two thermocouples, respectively installed in hollow metal inserts sealingly fitted into holes through the wall of the inlet conduit 38 and outlet conduit 39 of condensation column 16 measure TE0 and TE1 and a third thermocouple in water heater 40 measures TE2. Five thermocouples, respectively located in front of upper opening 24, lower opening 26, and intermediate openings 28, 30, 32 of the partition 18, measure TA0 and TA4. Three more thermocouples, located respectively at the lower portion of heat exchangers 223, 225, 226 and adjacent the outer wall of the condensation column 16, measure TA1*, TA2*, and TA3*. Three thermocouples, respectively fitted into metal inserts pass through the wall of the conduits connecting the heat exchangers 222-223, 224-225 and 225-226, measuring at intermediate openings 28, 30, 32, the temperatures of the water ascending in the condensation column.
Condensation column 106 includes four heat exchangers 1201-4, having hollow rectangular plates 121 and upstream-downstream manifolds, similar to the exchangers 221-6 of
The partition 108 is of expanded polymer. The lowest portion of this partition 108 does not include any fittings and the remaining part thereof is occupied by four independent transit chambers 1441-4, provided with elongated rectangular inlets, formed by rows of vertical slots, shown in
As air streams, deviated by the inlets of the transit chambers 1441-4, usually carry drops of industrial water, which is concentrated to a greater or lesser degree, these inlets include droplet separators, formed by baffles 1451-4 and deflectors 1461-4, which are hook-shaped, and co-operate to trap water droplets and bring them back into evaporation column 104. Beyond these baffles, lines are arranged leading to rotary valves 1481-4 then to the intervals 1501-4 which separate heat exchangers 1201-4 and water heaters 132. Inside rotary valve 1481-4, rotating cylinders, with diametrically opposed longitudinal openings (black in the figure) are equipped with manual control means, not shown. Rotary valve 1484 is opened to the maximum and the pressure drop created by chamber 1444 is negligible.
The conduit 118 for evacuating concentrated contaminated water produced by the distillation apparatus 100 is connected to a device 119 for natural cooling of the water, which discharges above a storage tank 152. This tank 152 has two outlet pipes, one of which 154, is connected to the inlet of a pump 156, and the other of which 158, is provided with a solenoid valve 160, for discharging this concentrated water to a industrial storage cistern. To close the loop of water circulation in the distillation apparatus 100, a pipe 162 connects the outlet of the pump 156 to the upstream manifold of heat exchanger 1201 of condensation column 106. The industrial apparatus which is producing the polluted water to be concentrated is connected to the distillation apparatus 100 through a conduit 164 discharging above storage tank 152, this conduit being provided with a solenoid valve 166. Like the distillation apparatus 10 in
When, in distillation apparatus 100 according to
In discussing operation of the first piece of apparatus 10 or 100 of one or the other of the two series-production distillation apparatuses concerned, it is considered that distillation apparatus 100 is, initially, virtually simplified and arranged to operate in the same way as distillation apparatus 10. The fundamental data are the mass flow rate QE0 of water that is spread and distributed and water temperatures TE0, TE2 and air temperature TA0. For example, QEo=100 g/s and TE2=85° C., for both pieces of apparatus. As distillation apparatuses 10 and 100 both operate with closed loop air streams and open loop water streams, then we have TE0=20° C. and then TA0=27° C. and TA4=83° C. From these data, we can carry out the adjustment procedure described in detail above for the fan and the cross-sections of the openings in the partition. We start by determining the temperatures of the air streams we need to establish at the rows of slots 28, 30, 32 of partition 18 of the distillation apparatus 10 and the similar rows of partition 108 of the distillation apparatus 100. With extreme temperatures of 27 and 83° C., we will have successively (approximately) 45, 61, and 73° C. and local steps of substantially 18, 16, 12 and 10° C. Next, we spread and distribute hot water, for a fairly long period to bring the components of each piece of apparatus to a suitable temperature, and then turn on the fan 34 or 116. As evaporation column 16 is provided with vertical plates, having wettable or hydrophilic surfaces juxtaposed on a constant pitch and column 104 having wettable artificial nuts loosely packed, the passages offered to air streams and the pressure drops therein are very different. Under these conditions, the same thing applies to the excess pressure of the air to be produced by the fans: from 100 to 200 Pascals for the fan 34 of the distillation apparatus 10, and from 300 to 500 Pascals for fan 116 of distillation apparatus 100. Indeed, in the distillation apparatus 10, the ascending air streams have uniform velocities and are unlikely to be carrying water droplets, which enables the rows of vertical slots 24, 26, 28, 32 to directly open into the condensation column 16. However, the same thing does not apply in the distillation apparatus 100, since here the air streams can have significant local velocities carrying along droplets of water and brine, notably in the row of slots arranged upstream of the entrance to transit chamber 1411 of the distillation stage of rank 1 These carried-along drops of water and brine necessitate the presence of droplet separators 1451-4-1461-4, that trap and return them to the evaporation chambers.
The flow rates of the fans 34 or 116 are adjusted to temporarily bring the temperature TA1 of the air passing through the row of slots of rank 1 of partitions 18 or 108 of distillation apparatuses 10 and 100 to 45° C. Then, using the covers 174 or rotary valves 1481-3 we adjust the port cross-sectional area of the openings 18 of the partition concerned of the distillation apparatus 10 or those of the partition 108 of the distillation apparatus 100 to have temperatures TA2=61° C. and then TA3=73° C., at the tops of the evaporation chambers of ranks 2 and 3. Then we re-adjust the settings of covers 174 or rotary valves 148 of rank n, so that the temperature TAn at the entrance to the evaporation chamber of rank n becomes equal to the temperature TAn* at the outlet of the condensation chamber of the same rank. These temperatures then constitute optimal setpoints TA1C, TA2C and TA3C, which only differ from the initial temperatures by a difference <1 5° C. After this, we slightly correct the speed of the fan to maximize the temperature TE1 of the water at the outlet of the condensation column and to bring it as close as possible to TE2, up to TE1=0.75° C. for example.
Having done this, container 54 or 126 receives an amount of 40 liters per hour of distilled water and with the values given above for TE0, TE1 and TE2, the coefficient of performance (CoP)=6.5. The thermal power supplied to the apparatus by the water heater is Pch=3.8 kW and that used in distillation PDist=24.7 kW, whereby the apparent overall thermal conductance of the evaporation and condensation columns of the distillation apparatus 10 or 100 is given by CT=PDist/(TE2−TE1)=2470 W/K.
Then, the values of the settings of the controls of fans 34 and 116 are noted as are the settings for the port cross-sectional area of the communication paths between chambers of the distillation units and these values are used as constructional specifications for series production apparatus. This will be frequency for the synchronous motors of the fans and values, accurate to one-tenth of a millimeter, for the four rows of vertical slots of the apparatus 10 and the horizontal slots of the four partitions replacing the valves which have been adjusted of apparatus 100. As for the dimensions of the holes in distribution plates 2514 and 12314, these are calculated for each condensation chamber, as a function of approximated volumetric flow rates of saturated damp hot air QS1 to QS4 circulating in these four chambers.
The thus constructed water distillation apparatuses are designed to operate with inlet parameters QE0 and TE2 which are constant. As long as this is so, the coefficient of performance (CoP) of the apparatus is at a maximum, but when for any reason the value of one and/or the other of these parameters deviates somewhat from its initial value, the overall performance of the distillation apparatus is moderately lowered while nevertheless remaining satisfactory.
In the case of a simplified distillation apparatus 10 or distillation apparatus 100, both treating seawater or brackish water, notably fossil, the distilled water is collected and converted into drinking water, by adding appropriate mineral salts, while seawater with a low salt concentration is directly discharged into the sea.
In the case of the distillation apparatus 100 described, operating to produce a concentrate of industrial water, the air stream circulates in an open or a closed loop and the water stream in a closed loop. The concentrate, pre-cooled in device 119 (which becomes the sole cold source when the air circulates in a closed loop) is collected in tank 152 and is recycled until its concentration is sufficient. To do this, the contaminated water, becoming progressively concentrated in the tank 152, is drawn in by the pump 156 and injected into the manifold upstream of heat exchanger 1201 of condensation column 106. When this concentration is sufficient, pump 156 is stopped, the solenoid valve 160 for emptying the tank 152 is operated and a given volume of process water, highly concentrated (5-10 times), is stored in a remote cistern, awaiting collection. At the end of this operation, a fresh volume of industrial water is poured into the storage tank 152 by actuating the solenoid valve 166 for an appropriate period of time. Following this, pump 156 is restarted. The cycle of these operations is determined by trial, depending on the efficiency of the apparatus; solenoid valves 160 and 166 and pump 156 are controlled cyclically, by a programmed controller. The cost of getting rid of a concentrate of polluted water is reduced in correspondence with the degree of concentration achieved. For its part, the distilled water can be collected for local use or rejected into nature. Making use of the same supplementary subassemblies, a distillation apparatus 10, having an evaporation column fitted with evaporation plates with wettable surfaces can be converted into apparatus to produce a concentrate of industrial waste water. And, vice versa, distillation apparatus 100 can be used to produce distilled water and highly concentrated brine.
In each of the evaporation chambers of these units, there are arranged vertically, at a constant pitch of 15 mm, one-hundred non-metallic plates 210 having wettable surfaces as a result of the presence of suitable reliefs, 6 mm thick, 80 cm wide and 125 high cm. The total surface area for exchange of the plates is 200 m2 and the volume of an evaporation chamber is 1.5 m3. In each of the condensation chambers, the heat exchanger 212 is of the same type as those in
This distillation apparatus having four juxtaposed distillation units is well suited to large quantities of daily production of distilled water. With a power for water heater 226 of 120 kW and a mass flow rate QEo of 4.5 kg/s of water to be distilled, daily production is around 30 m3/day for the distillation apparatus 200. In addition the latter is notably well suited to situations in which the amount of thermal energy available is variable notably over the course of one day, thereby imposing mass water flow rates which more or less follow the same trends. In this case, a computer with the appropriate software defined above, supplies the adjustments for the motor blocks, once the parameters QE0, TE2, TE0 and TA0 have been entered. These settings are then made in two possible ways: (1) read on the computer screen values for the setpoints of the dials associated with the controls for these four frequencies, and manually display these values on the dials or (2) program the computer to directly set the control means to these four frequencies.
The modifications to be introduced into the distillation apparatuses 10 and 100 using distillation units placed one above the other shown in
The invention is not limited to the embodiments described with reference to
Indeed, the components of the evaporation and condensation chambers can be different from those presented (plates having hydrophilic or wettable faces, wettable nuts in ceramic or polymer material). In all cases, these components will be non-metallic in order to avoid problems of corrosion and too high cost. Regarding the evaporation chambers, these can be any thin planar support, notably formed by a stretched woven hydrophilic sheet, or yet again, artificial nuts of baked clay. Regarding the condensation chambers, one can use heat exchangers which are formed by commercially-available alveolar plates provided with primary manifolds, connected to secondary upstream and downstream manifolds. In distillation apparatus 200, using juxtaposed distillation units, the evaporation chambers can be filled with wettable artificial nuts and communications between the pair of chambers of each unit can include droplet separators. In addition to standard distillation apparatus which is manufactured pre-set, apparatus which is identical to a first one of each series, including the majority of the measurement and adjusting means can obviously be put on the market in order to satisfy individual customers.
| Number | Date | Country | Kind |
|---|---|---|---|
| 12 00 985 | Apr 2012 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2013/056964 | 4/2/2013 | WO | 00 |
