Patent Application
20200339439
The invention relates to positive displacement, reciprocating, rotary or linear motion compressors of Mechanical Vapor re-Compression (MVC) used in multi-stage heat-pumps and water treatment systems, (desalination, condensation of aqueous solutions, etc.).
Positive displacement centrifugal and rotary compressors (gears, lobes, sliding vanes, screws, etc.) are used by heat-pumps and existing single-stage and multi-stage Mechanical Vapor re-Compression (MVC) systems in desalination, industrial waste, condensation of aqueous solutions in industry, etc. The centrifugal ones are most often used. Such applications are noted e.g. at:
U.S. Pat. No. 1,150,713 και U.S. Pat. Nos. 1,200,996, 5,676,801, WO2014/115079, U.S. Pat. Nos. 5,676,801, 5,772,850, DE3327958, JPS6483890, WO2007/148338, U.S. Pat. No. 5,520,008, WO2016/138343, U.S. Pat. No. 2,589,406, DE4431887, WO01/98665, etc.
An important role in the development of heat-pumps have both, (a) the compressor and (b) the efficient multi-stage systems.
Regarding the centrifugal compressor, its growth and size is limited by (a) the very large specific volume of the vapor as the state-of-the-art systems require in a single phase the movement of significant volumes of low temperature vapors and (b) the peripheral speed of the compressor blade's tip which cannot exceed certain limitations (noise, etc.).
The energy for the operation of the heat-pump is mainly the energy for the compressor. For the immediate start-up of the process it is additionally necessary (and only for the start-up phase) to pre-heat the feed-water by an external source until it reaches the boiling temperature of the system. The process then continues and is maintained only by the mechanical energy provided by re-compression of the vapors by the compressor.
In their multi-stage version, (MVC) systems are mainly Multi-Effect Evaporation/Desalination (MEE/MED) type and are usually comprised of, a) a centrifugal compressor (or, more rarely, a positive displacement lobe-type compressor) for the whole system, b) an external multi-stream pre-heat exchanger of the feed-water and c) evaporation and condensers/heat-exchangers chambers with a brine spray system. More specifically:
The brine circulates from the first to the last stage, evaporates continuously, while gradually, its temperature decreases and its salinity increases. In order to maintain boiling and evaporation in all stages, the vacuum is increased from the first to the last stage, whereby the boiling point of the brine is progressively reduced.
In the state-of-the-art Mechanical Vapor re-Compression Systems (MVCs), the vapor produced at the last and coldest stage is sucked and compressed by, the single mechanical compressor, becomes superheated, its temperature rises to the system's highest temperature, the vapor runs externally around the entire system and is fed to the heat-exchanger of the first and warmest stage, where it is condensed to desalinated water, transferring sensible and latent heat for the boiling of the brine of the first stage and the production of its saturated vapors. This saturated vapor is directed and flows into the heat-exchangers of the second stage, heating and evaporating its brine and producing its saturated vapor, which in turn is fed to the next stage, and so on.
The brine of each stage is pumped and sprayed by a grid of nozzles within the same stage, mainly spraying externally the surface of the heat-exchanger in the interior of which the saturated vapor, produced in the previous stage, is flowing, with its temperature corresponding to the temperature conditions of the previous and warmer stage.
The disadvantages of these multi-stage systems are many and significant, such as: at the thermodynamic aspect itself, at the control and coordination of the state/thermodynamic conditions and also at the constructional/manufacturing level. In particular:
a) Significant increase of entropy, since in a single phase and with a single compressor, the vapor is compressed with a very high compression ratio CR (>1.8) in order to cover, the total temperature difference ΔTmax required for the whole multi-stage system/unit (e.g. by a three-stage system/unit, the total temperature difference required, is 10-12° C. which significantly increases the entropy),
b) great difficulty in determining, regulating, coordinating and maintaining the required temperatures and salinities of the brine and in particular the temperatures of the vapor produced at each stage and being fed for condensation to the next one,
c) bulky vapor ducts connecting the stages, since vapors circulate by natural draft between the stages.
d) bulky and of low-efficiency heat-exchangers, since vapors circulate in the heat-exchangers (except the heat-exchanger of the first stage) by natural draft (low velocity) with all that it implies.
(e) reduced vapor amount (and production thereof) due to the loss of vapor pressure in the droplet separators and connecting ducts, which due to natural draft, reduces the active pressure (head and energy loss) for the vapor circulation.
Substantial disadvantages that reduce production, increase the volume and cost of the installation/plant, over-complicate the standardization and control, and increase the minimum temperature difference (Δtν) for the operation of the different stages and overall energy consumption. The latter (increase of minimum temperature difference) drastically reduces the number of stages that can be served by a single compressor with an obvious reduction in the plant's efficiency.
The above disadvantages arise from the fact that a single compressor is used for the entire system/unit which must raise the temperature of the vapor by re-compressing it from the boiling point of the last and colder stage to the highest temperature Tmax of the system (first stage).
For these reasons, the state-of-the-art technologies, using a single compressor, have to face very unstable conditions, balancing between many contradictory parameters, since:
a) the temperature differences between stages (Δtν) must be very small/low, as should the maximum temperature difference ΔTmax of the system be as well, in order not to increase entropy, while at the same time ΔTmax must be high enough to be sufficient and to serve as many stages as possible (since ΔTmax=ΣΔtν), in order to increase the system's overall efficiency [low temperature differences (Δtν) are obviously, for the state-of-the-art, very difficult to control, maintain and coordinate].
b) there is a limitation on the increase in the speed of rotation as well as the increase in the rotor blade radius of the centrifugal compressor since the peripheral speed of the blade's tip must not exceed a certain maximum value. Difficult task, when all energy-pressure head must be created by a single compressor. If a positive displacement lobe compressor is used instead, the volume and costs are much higher while the benefits and yields are considerably lower.
Since the above conditions are difficult to be combined, the maximum number of stages that can be served and achieved is very small compared to the corresponding classical multi-stage thermal systems without vapor re-compression, such as the Multi-stage Flash Evaporation (MSF) and the Multi-Effect Evaporation/Desalination (MEE/MED).
In addition, a single compressor for all stages has considerable volume and high cost because it carries large quantities of large specific volumes of vapors, while in the case of placing an independent compressor for each stage, while being thermodynamically sound, will pose enormous constructional issues and raise the costs even higher.
Moreover, vapor is required to run twice the entire length of the unit, once internally by transferring the saturated vapor from stage to stage, and once externally in the reverse direction, from the last and coldest stage to the first and warmest. This results in heat and pressure losses, higher energy consumption, regulatory/adjustment difficulties, reduced production, large volume and unit costs, and inability to standardize (modulation) of the stages (manufacturing and transportation-wise issues).
For all these reasons, manufacturers prefer to install a plurality of parallel-linked single-effect evaporator desalination units, two-stage or at most three-stage units, in order to increase the daily production, since with the smallest number of stages per unit, they have better control over the operating conditions (more precise control over the small differences of thermodynamic state conditions required between stages), and encounter the issue of transporting them. The brine in these applications does not circulate sequentially from unit to unit, but is rejected independently from each unit, resulting in reduced overall efficiency of the parallel array of units.
Reciprocating positive displacement compressors for Mechanical Vapor re-Compression (MVC), with multiple independent dual action chambers used in multi-stage heat-pumps of water treatment systems, (e.g. desalination, industrial waste) or condensation of aqueous solutions, etc.
They are applicable to all known thermal desalination Mechanical Vapor re-Compression systems (e.g. MVC-MEE/MED, MVC-MSF, etc.) and are of two variants a) reciprocating-rotational and b) reciprocating-linear motion, where:
a) in their rotational version, the compression chambers are radially arranged cylindrical sectors based on concentric circular sectors extending at the same central angle, with compression pistons of radially arranged flat vanes of corresponding surface which rotate reciprocally in the compression chambers, being mounted on a common rotor/shaft and
b) in the linear version, the successive compression chambers as well as the respective pistons/vanes are linearly arranged and preferably of circular form and the pistons/vanes move linearly reciprocally being mounted on a common shaft.
The surfaces of the vanes/pistons, as well as the respective compression chambers, preferably differ from each other, since operationally each compression chamber has preferably its own and independent pair of evaporation and heat-exchanger chambers/areas, from and to the compression chamber sucks, compresses and discharges, and the fluids/vapors being dispensed are under different thermodynamic state conditions. Each compression chamber adjusts its own flow rate and its compression ratio CR (and reheating Δtν) independently of the others.
The rotary-radial compressor is studied herein in a multi-stage (four-stage) version of a flash evaporation desalination process with mechanical vapor re-compression (MVC-MSF), wherein:
The four evaporation chambers of the unit are enclosed by two coaxial cylindrical shells, an outer one and an inner sleeve-cylinder of smaller diameter in comparison, between of which are developed four radially arranged chambers (cylindrical sectors) which are laterally separated from each other by four crosswise arranged vertical spacers.
The roofs of the evaporation chambers of the stages are covered by a common and uniform, preferably horizontal circular roof cover. The bottoms of the evaporation chambers are preferably a circular horizontal plane common for all stages.
On top of the evaporation chambers is located the compressor with four compression chambers, each one of which corresponding to the evaporation chambers, being also radially arranged cylindrical sectors and based on almost the same circular sectors with the evaporation chambers. They are separated by approximately the same crosswise arranged vertical spacers that project upwards.
Inside the compression chambers are developed two for each chamber, identical and narrow, opposite facing collection chambers (based on circular sectors) which are restricted laterally, internally by two radially arranged vertical spacers and externally by the crosswise arranged radial vertical spacers of the respective compression chamber.
All collection chambers are extending at the same acute central angle β°, are restricting, sideways, at an area corresponding to two-fold the central angle β° (=2*β°) in total, the active area of the respective compression chambers and are dividing by an intermediate horizontal flat partition in two sub-chambers: the lower or suction sub-chambers and the upper ones or compression sub-chambers.
The roofs of the compression chambers are preferably, gradually and stepwise increased, with the roof of the first stage to be lower than that of the second, and the second lower than that of the third and so on.
The compression chambers as well as the collection chambers are enclosed externally by a preferably common cylindrical housing, the height of which is preferably not uniform as it follows the height of the roofs of the respective compression chambers.
Inside the compression chambers rotate the vanes mounted on a cylindrical rotor which rotates freely inside an inner sleeve-cylinder of small diameter and terminates (the rotor) in a vertical shaft by which it is driven. The surfaces of the vanes are progressively increasing and correspond to the cross-sections of the compression chambers.
The shaft exits from the main area of the stages and terminates in a toothed wheel (pinion) which connects it to the transmission systems of the reciprocating-rotational drive systems preferably located at the base of the unit.
The suction sub-chambers of the two collection chambers of each stage communicate directly with the underlying evaporation chamber of the respective stage through their bottoms which are identical or independent surfaces but in contact with the roof of the respective evaporation chamber of the stage and remains permanently open over the droplet separators.
Both suction and compression sub-chambers communicate with the respective compression chambers through the suction and compression check-valves respectively.
The check-valves are activated automatically, preferably by varying the pressures in the compression chambers. The compressor of this variant, because it sucks directly from the underlying evaporation chamber, does not necessarily have a suction pre-chamber as in other applications (e.g. MVC-MEE/MED).
Just below the evaporation chambers and having approximately the same plan-view circular-section area, are developed the respective four condensation chambers with the water-vapor heat-exchangers and are connected, in order for the superheated vapor to be transferred, with the overlying compression chambers of the stage through vertical ducts. The water-vapor heat-exchangers are connected in series and pre-heat the feed-water before it enters the unit and the evaporation chamber of the first and warmest stage.
The compressor creates a lower pressure in the suction sub-chambers, sucks the saturated vapors from the respective underlying evaporation chambers, compresses and superheats them to a specific, for each stage, temperature and finally directs them through the vertical ducts to the condensation chambers with the heat-exchangers for pre-heating the feed-water.
The same rotary-radial compressor, but with suction pre-chambers at its base instead, is also applied to multi-effect evaporation/desalination units (MVC-MEE/MED), where:
As far as the evaporation chambers are concerned, around the narrow inner cylindrical sleeve shaped for the passing of the rotation rotor/shaft, an intermediate spacious vertical duct riser develops, terminating at the roof of the evaporation chambers.
The evaporation chambers, in the MVC-MEE/MED application, are of complex form with water-vapor heat-exchangers consisting preferably of bundles of vertical falling-film tubes. They are covered both from above and below by horizontal flat frontal plates (tube sheets) and internally and circumferentially from the intermediate vertical duct riser which isolates the spaces of the evaporation's saturated vapors from the spaces of the compression's superheated vapors.
Externally and circumferentially the heat-exchangers are open in order for the superheated vapor to descend from the compression chambers into the channel, which develops at the periphery of the evaporation chambers and to access the spaces of the heat-exchangers.
Within the differences, is included the brine pumping system, that pump the brine from the bottom of the evaporation chambers and spray it inside the vertical tubes, outside of which the superheated vapor flows.
The vapor is condensed to desalinated water, portion of the brine is evaporated and the saturated vapor produced descends to the bottom where, due to the lower pressure created in the suction pre-chamber, it rises again through the intermediate vertical riser duct and enters the compression chamber.
There, it is compressed, its temperature rises and is directed downwards again as superheated vapor to the above-mentioned water-vapor heat-exchanger of the stage, etc. The brine which has not evaporated is transferred to the next stage to undergo a corresponding independent process.
In another variation of MVC-MEE/MED the same rotary-radial compressor is used with the following differences:
(a) at the four evaporation chambers which are parallelepipeds and are arranged in pairs and in two parallel rows and
(b) at the vapor-water heat-exchangers inside the evaporation chambers consisting of a bundle of horizontal tubes.
The bundle of tubes terminates in two narrow vertical collectors/chambers, the inlet collectors of the superheated vapor, and the outlet collectors of the condensate, both extending over the entire width of the stage.
On top of the heat-exchangers there is a brine spraying system, while in the lower part, the brine basin is developed.
Between the inlet collectors of the superheated vapor and the wall with which the stages are joined in pairs frontally to each other, a narrow flattened vertical duct-chamber develops, extending parallel to the inlet collector of the superheated vapor connecting the brine basin to the compressor's suction pre-chamber, corresponding to the stage.
From the center of the system, i.e. the junction of the four parallelepiped stages, the cylindrical shell-sleeve passes through with the rotation shaft at its center and the rotary-radial compressor at its top.
The double opposite compression sub-chambers of the compressor are connected to the inlet collectors of the heat-exchangers of the superheated vapor through ducts, that terminate on the two opposite sides on the top of the inlet collectors, discharging the superheated vapor from two opposite points.
The operation of this variation is similar to all MVC-MEE/MED applications. The brine is pumped from the bottom of the evaporation chamber and is sprayed externally onto the bundle of the horizontal tubes of the heat-exchangers and the saturated vapor is sucked, compressed, etc., as per known in the MVC-MEE/MED applications.
The stages/effects in all MVC-MEE/MED applications are independent from each other with respect to the medium that provides the energy of evaporation, since the vapor-medium comes from the stage/effect itself, unlike the state-of-the-art of purely thermal systems MEE/MED (as well as MVC-MEE/MED), where the vapor-medium and the thermal energy of evaporation of each stage, are derived from the previous and warmer stage.
In another embodiment of multi-stage flash evaporation desalination with Mechanical Vapor re-Compression (MVC-MSF) the reciprocating positive displacement, dual-action compressor, differs as it is comprised of cylindrical compression chambers sequentially and in series arranged and carries corresponding circular vanes.
The vanes are mounted to a common horizontal shaft perpendicular to their surface that moves reciprocally and linearly by a drive mechanism. The evaporation chambers, like the condensation and heat-exchanger chambers, are arranged linearly instead of radially. The surfaces of the vanes as well as the volumes of the respective cylindrical compression chambers are also preferably gradually and stepwise increased.
There are also present the relevant suction and compression check-valves of the compressor as well as the suction and compression ducts which communicate with the evaporation chambers for the suction of the saturated vapors and with the condensation chambers and heat-exchangers to pre-heat the feed-water as described at the Flash Evaporation Desalination (MVC-MSF).
The ratio of compression (CR) of vapor volumes, as well as the temperature rise, are also adjustable attributes here, and the operation of the new application is completely analogous to what has already been described in the MVC-MSF with rotary-radial compressors.
The system can also function as a multi-stage compressor where a chamber sucks from the former and re-compresses the pumped medium to the next by gradually increasing the pressure from stage to stage. It can also be used as a multi-stage compressor in refrigeration applications or as a multi-stage compressor of any gaseous medium.
a show the cross-sections 1-1, 2-2 and 2a-2a respectively of compact four-stage Flash Evaporation Desalination with Mechanical Vapor re-Compression (MVC-MSF).
The unit is enclosed by two coaxial cylindrical shells, an outer shell 1 and an of smaller diameter inner sleeve-cylinder 2, between of which the four radially arranged evaporation chambers eν (e1, e2, e3, e4) of the respective stages are developed, which are laterally separated from each other by the four crosswise arranged vertical spacers 3ν (31-34).
The roofs of the evaporation chambers of the four stages-segments are covered by a common and uniform, preferably horizontal, airtight roof cover 4ν (41-44) below of which are developed the respective droplet separators 5ν (51-54) for holding the droplets of brine.
The bottoms 31ν (311-314) as well as the roof covers 4ν of the evaporation chambers of all stages are preferably for all stages a common and uniform circular horizontal plane divided into four circular sectors.
On to the roofs covers 4ν of the evaporation chambers is located the compressor 6 with the four compression chambers 7ν which are radially arranged above the evaporation chambers eν corresponding one by one to them.
Similarly to the evaporation chambers eν, the compression chambers 7 are separated by the same vertical spacers 3 extending upwards.
Inside the compression chambers 7ν, at both ends of them and in contact with the vertical spacers 3ν, are developed two for each compression chamber identical, narrow, opposite facing, collection chambers 8ν (81-84) which are restricted laterally, internally by two also radially arranged vertical spacers 9ν (91-94) which extend over the entire height of the compression chamber 7ν, and externally by the radial vertical crosswise arranged spacers 3ν of the respective stage.
All collection chambers 8ν are cylindrical sectors extending at the same, for all the stages, area corresponding to the central angle β° and are restricted circumferentially and internally by the inner sleeve-cylinder 2 of smaller diameter. The two inward facing vertical spacers 9ν are extending, in the present application of the four-stage version, at a central angle α°=90°−2*β° and restrict the active area of the compression chambers 7ν and respectively the range/stroke of the reciprocating-rotational motion of the vanes 20ν (201-204). The compression chambers are cylindrical sectors based on circular sectors of the same central angle 90° (=α°+2*β°).
The collection chambers 8ν are also divided by intermediate horizontal flat partitions 10ν (101-104) into two smaller chambers: the lower or suction sub-chambers 11ν (111-114) and the upper or compression sub-chambers 12ν (121-124).
Roofs/covers 13ν (131-134) of the compression chambers 7ν (as well as of the corresponding collection chambers 8ν) show preferably a gradual and stepwise increase in the height, with the roof 131 of the first stage being lower than the corresponding 132 of the second and the second lower than the third, etc.
The compression chambers 7ν are encircled externally by a preferably, common for all stages, cylindrical housing 18 the height of which varies gradually stepwise and follows the height of the roofs 13ν of the respective compression chambers 7ν.
The roofs 13ν also form the upper cover of the compact four-stage unit. Inside the four compression chambers 7ν, move the radially arranged flat vanes 20ν (201-204) of the rotor 14 of the compressor 6, projecting through the permanently open openings 122ν of the sleeve-cylinder 2 as will be described below.
The two opposite facing suction sub-chambers 11ν of the two collection chambers of each stage, communicate with the underlying evaporation chamber eν of the respective stage through their bottom which is identical to the roof 4ν of the evaporation chamber of the respective stage and which remains permanently open above the droplet separators 5ν.
Both suction sub-chambers 11ν and compression sub-chamber 12ν, communicate with the respective compression chambers 7ν of the compressor 6 of their stage, through suction and compression check-valves 22ν (221-224) and 21ν (211-214) respectively. The valves operate automatically and preferably by varying of the pressures in the respective compression chambers.
Evaporation chambers are empty spaces and do not contain any heat-exchangers. Just below the evaporation chambers eν, and with almost the same circular-sector plan-view, are developed the respective four condensation chambers Cν (C1-C4) with the water-vapor heat-exchangers eCν (eC1-eC4), which are preferably comprised of vertical tubes 30ν (301-304) and are connected to the compression chambers 7ν of the above lying compressor of the stage through the vertical ducts 19, of the superheated vapor. The heat-exchangers eCν pre-heat the feed-water 40 before it enters the system.
In
The surfaces of the four vanes 20ν (201-204) preferably differ from one another as they progressively increase corresponding to the cross-sections of the four compression chambers 7ν within of which they are rotated. The rotor 14 terminates on a vertical shaft 16 that exits the main body of the stages and the sleeve-cylinder 2 and terminates on a toothed wheel (pinion) 17 which connects it to the reciprocating-rotary drive transmission systems.
It concerns an embodiment of sealing the rotation of the rotor between the adjacent compression chambers 7ν by sealing the openings 122 within of which the vanes 20ν move/stroke. the openings 122ν within of which the vanes 20ν move/stroke. The sealing is a series of concentric closed frames of horizontal and vertical bars 23 projecting slightly around the openings 122ν on the inner cylindrical surface of the sleeve-cylinder 2 creating between them the peripheral channels and the labyrinth conditions of trapping the vapor.
Correspondingly, there are also the parallel rows of rolled bars 23a circumferentially and sequentially arranged below and above the openings 122ν. The bars 23a also cooperate with respective equal number of parallel rows of rolled bars 23b deployed on the opposed convex portion of the rotor 14 and are interposed one by one between the bars 23a, creating a double labyrinth seal (the latter is e.g. applicable to compression chambers' version of
At the top of the inner sleeve-cylinder 2, around the upper-end and right before the top bearing of the shaft 16, there is also an auxiliary water-vapor heat-exchanger for the additional pre-heating of a portion of the feed-water 40 on the walls of which the vapor, which escapes from the labyrinth bars, condenses and flows, collected as desalinated water at the bottom of the sleeve-cylinder 2. The heat-exchanger is not designed.
In
At the center of the vane 120ν, the adjustable (sliding) aperture 123ν (by-pass) exists to adjust the discharge of the compression chamber by by-passing of a portion of the vapor from the high-pressure side in the low-pressure side of the vane, that are continuously alternating.
There might be other mounting and sealing systems of vanes as well as dividing in parts, prefabrication and assembling of the compressor chambers, etc.
The main factors of each stage (i.e. compression 7ν, evaporation eν, condensation Cν, and heat-exchangers eCν chambers) correspond and are located one directly above the other, in such a way that the four stages can be prefabricated as four independent cylindrical sectors (modules) and assembled during installation creating the cylindrical body of the unit. Correspondingly, the vanes and obviously the chambers could be, in particular in the variant of
What will remain to complete the installation of the unit, is the external connections of the ducts 19ν with the condensation chambers Cν, and the in-series external hydraulic connections of (a) the heat-exchangers' eCν, (b) the brine and (c) the desalinated water, that will be removed.
The rotary-radial compressor 6, due to its shape and motion, is characterized as a “fan” type.
The reciprocating-rotary motion of the rotor 14 functions as a multi-compressor of four independent compression chambers. Creates a lower pressure at the inlet of the multi-compressor, sucking the vapors from the evaporation chambers eν, and transferring them to the compression chambers 7ν where it compresses and superheats them before leading them to the condensation chambers Cν. Similar operation with the “supercharger” system of internal combustion engines, hence the significant thermodynamic and technological improvement that the present multi-compressor offers, among other things, in thermal desalination, etc.
The feed-water 40 is pumped and passed through the multi-stream external heat-exchangers (not designed) where it is pre-heated in the multi-stream heat-exchangers of the desalinated water 44ν and the brine 36ν which are removed. The pre-heated feed-water 40 enters under pressure from the fourth and coldest stage through the bundle of vertical tubes 30ν of the water-vapor heat-exchangers eCν, runs all the stages where it is gradually pre-heated, by the superheated vapors which correspondingly condense, and finally the feed-water enters the evaporation chamber e1 of the first stage. The condensed, desalinated water is collected in the bottom of the condensation chambers Cν and is removed.
Upon entry of the feed-water 40 into the evaporation chamber e1 of the first stage, part of it is subjected to flash evaporation and the vapor produced, in saturation state, is intensively sucked, entering through the permanent openings of the roof cover 41 and passes to the two suction sub-chambers 111 of the double collecting chamber 81 of the first stage after passing through the droplet separators 51.
Whenever the vane 201 of the first stage begins the reciprocating stroke from one of its two terminal positions, which are identical to the two opposed vertical spacers 91, lower pressure is created in the suction sub-chamber 111 of the collecting chamber 81 behind the vane.
The lower pressure opens the suction check-valves 211 and the vapor enters at high speed into the compression chamber 71 of the first stage of the compressor, following the vane's 201 motion. The intense suction reduces the vapor pressure in the evaporation chamber e1 and causes more intensive evaporation.
After the stroke of the vane 201 and the suction phase have been completed, the vane 201 moves in the opposite direction. Part of the compression chamber 71, which was previously under lower pressure conditions, is now at higher pressure conditions, the suction check-valves 211 close behind it, while at a certain point on the new stroke and when the required high pressure has been reached, the compression check-valves 201 open-up at the opposite (in the vane movement) compression sub-chamber 121. Due to the dual-action of the vane, vapors are sucked and compressed continuously.
With the compression, the vapor temperature rises and superheated and under considerable higher pressure is guided through the permanent opening of the compression sub-chamber 121 in the peripheral channel 151 and from there through the common vertical duct 191, of the first stage, descends into the condensation chamber C1 and the water-vapor pre-heating exchangers eC1 of the feed-water 40.
The superheated vapor transfers its sensible and latent heat to pre-heat the feed-water 40 and condenses on the outer surfaces of the tubes 301 of the heat-exchanger, while the condensate 441 descends to the circumferential channel 421 at the bottom of the chamber C1 of the first stage.
The brine portion 361 which is not evaporated in the first stage, has lost temperature and from the bottom of the evaporation chamber e1 is fed to the next evaporation chamber e2 of the second stage. Herein the same flash evaporation process and compression of the vapors is followed, with the exception that since the brine 362 is colder and the vapor pressure lower, the vacuum at this stage is higher.
Furthermore, because the specific enthalpy (kJ/kg) is reduced while the specific volume (m3/kg) of the saturated vapor is greater, the circulation of a larger volume is required in order to have the same production as the first stage.
For this reason the surface of the vane 202 is larger. Therefore, the suction volume, the compression ratio (CR) and the rise in the vapor temperature, have different values compared to the first stage.
The process is repeated in the third and fourth (last) stage with the surface of the vanes 20ν being gradually increased, the brine 36ν circulating and becoming colder and more saline and the temperature of the compressed vapors also gradually decreasing.
The feed-water 40, following a reverse course in regards to the brine, is pre-heated gradually in the heat-exchangers eCν which are connected in-series, so that the temperature ta (corresponding to the boiling temperature of the brine 361 of the first stage) is finally reached before entering the first stage.
The desalinated water, by following the reverse direction relative to the feed-water, is collected and removed after it has passed through the multi-stream external water-water heat-exchanger of the initial pre-heating of the feed-water 40.
In order for the flow of the brine and the desalinated water to be moved preferably by gravity, the levels of the bottoms 31ν of the evaporation chambers may be gradually stepped. Also, the volumes of the evaporation chamber eν, of the condensation chambers Cν, as well as the surfaces of the water-vapor heat-exchangers eCν, may not be the same, but they change gradually from stage to stage.
This application of the four-stage unit resembles that of
They have the same rotary-radial compressor 206 with the vanes 220ν, the rotor 214, the collection chambers 208ν, the vertical spacers 203 and 209ν, the horizontal flat partitions 210ν in the sub-chambers 211ν and 212ν with the respective suction and compression check-valves 221ν and 222ν and the circumferential channel 215ν. Finally, the compression chambers 207ν, with the flat roofs 213ν of gradually and stepwise increased heights and the cylindrical housing 218, complement the compressor 206.
The unit has the same radial arrangement of the evaporation chambers dν with the common roof cover 204ν, the peripheral cylindrical shell 201, the inner sleeve-cylinder 202, with the bases of the chambers dν occupying the four circular bottom segments 231.
With regard to the differences with the aforementioned variation MVC-MSF of
Regarding the evaporation chambers dν (d1-d4), between the peripheral cylindrical shell 201 and the narrow inner sleeve-cylinder 202, is interposed a larger coaxial cylindrical shell 236ν. Between the latter cylindrical shell 236 and the sleeve-cylinder 202, an intermediate vertical duct riser 46 is formed, terminating at the top of the roofs 204ν.
The evaporation chambers d contain heat-exchangers 32ν, preferably water-vapor, consisting of vertical tube bundles 33ν of falling brine film. They are developed within the chambers dν and are covered from top and bottom by horizontal flat frontal plates (tube sheets) 34ν and 35ν respectively and internally peripherally from the large cylindrical shell 236ν.
The flat frontal plates (tube sheets) 34ν and 35ν and the cylindrical shell 236ν isolate the spaces of the saturated vapor, from the spaces of the superheated one.
Externally and peripherally, the heat-exchangers 32ν are open in order for the superheated vapor, descending from the compression chambers 207ν, to access the spaces of the heat-exchangers 32ν.
The superheated vapors, from the peripheral channel 215ν of the compressor and through the vertical ducts 37ν, end up in the troughs 41ν which develop at the periphery of the evaporation chambers dν and from there in the space of the heat-exchangers 32ν.
Regarding the compressor, between the roofs 204 of the evaporation chambers dν and the compression chambers 207, are developed four suction pre-chambers 246ν (2461-2464) which are located below their respective compression chambers 207, (and bellow their collection chambers 208ν). The suction pre-chambers correspond exactly to the compression chambers and are also an integral part of the compressor's housing, occupying the entire circular surface under it and are peripherally enclosed by the common cylindrical housing 218.
At the upper-end of the vertical duct 46ν, inside the evaporation chamber and before the suction pre-chambers 246ν, brine droplets separators 205, are developed.
Within the differences are included the pumping system 36ν of the brine which pumps the brine from the bottom of the evaporation chambers dν by the pumps 38ν and sprays it through the spray/nozzle systems 39ν onto the flat frontal plates (tube sheets) 35ν in the upper portion of the evaporation chambers and above the bundle of the vertical tubes 33ν of the water-vapor heat-exchangers 32ν. The surfaces of the heat-exchangers are gradually changed from stage to stage.
The
The feed-water 40 is pumped at ambient temperature, is pre-heated at the specific temperature to in the multi-stream external heat-exchanger (not designed) from the removed brine 36ν and the desalinated water 44ν and is fed to the evaporation chamber d1 of the first stage.
The inlet temperature to is slightly lower than the temperature t1 of the boiling point of the brine which corresponds to the specific vacuum prevailing in the evaporation chamber d1 of the first stage.
From the bottom of the chamber d1, the brine 361 is sucked by pump 381 and sprayed through the spray system 391 at the inner surfaces of the falling film tubes 331 of the water-vapor heat-exchanger 321, wherein a portion of the brine is evaporated by the sensible and latent heat transferred by the superheated vapor S1 flowing onto the outer surfaces of the tubes 331. In particular:
Whenever the vane 2201 of the first stage of the compressor 206 begins the reciprocating stroke from one of the two of its terminal positions, as per known, lower pressure is created in the suction sub-chamber 2111 of the collection chamber 2081 which happens to be behind the vane.
The lower pressure opens the suction check-valve 2211 and the saturated vapor produced in the evaporation chamber d1 is strongly sucked following the stroke of the vane, enters the suction sub-chamber 2111 of the collection chamber 2081 of the first stage, after having ascended through the vertical duct 461, having dismissed the brine droplets at the separator 205 and having entered in the suction pre-chamber 2461 of the compressor.
After the vane's stroke 2201 and the suction phase have been completed, the vane 2201 moves in the reverse direction, as per known from the previous embodiment of the
The compression ratio CR1 corresponds to the required temperature rise of the superheated vapor of the first stage. The saturated vapor is compressed, superheated and its temperature is raised from t1 to t1+Δt1, wherein the portion Δt1 covers:
a) the rise α1 of the boiling point of the brine of the first stage due to increased salinity and
b) the temperature difference D1 which will increase the enthalpy of the superheated vapor S1 to cause a relatively quick evaporation of the brine.
For the overall required temperature rise of the vapor at the first stage, the relationship holds: Δt1=α1+D1, or in general for the stages that follow: Δtν=αν+Dν.
The superheated vapor S1, after the heat transfer in the heat-exchanger, is cooled-down and condensed. The condensate and desalinated water 441, descends to the bottom of the peripheral channel 411, from where it is pumped along with the corresponding condensates of the other stages and is directed to the multi-stream external water-water heat-exchanger of the pre-heating of the feed-water 40 and from there to the storage space.
The brine, which has not been evaporated in the first stage and is colder, is passed to the next evaporation chamber d2 of the second stage. There it follows the same evaporation and compression process. In order to achieve the same production of desalinated water 44ν at each and every stage, the surface of the vane 2202 and of the corresponding compression chamber are larger, compared to the first stage (or, in generally, to the previous stage).
The compression ratio CR2 also varies in order to achieve the required temperature rise Δt2 of the superheated vapor S2. The saturated vapor having the temperature t2 of the brine of the second stage, is sucked into the compression chamber 2072 of the stage, is compressed, superheated and is guided through the corresponding peripheral channel 2152 and the vertical duct 372 in the second stage heat-exchanger at a lower temperature t2+Δt2, compared to the corresponding one of the first stage t1+Δt1 (the relationship holds: tν+Δtν< . . . <t2+Δt2<t1+Δt1).
The process is repeated in the third and the fourth (last stage), with the brine circulating from stage to stage becoming colder and saltier and the temperature of the superheated vapor Sν becoming also gradually lower.
The unit instead of an electric motor can use an internal combustion engine, so there will simultaneously be a permanent supplementary and auxiliary heat supply, significantly improving the start-up and the efficiency of both drivetrain and desalination.
They have the same rotary-radial compressor 306, with the four chambers and the vanes 320ν, the collection chambers 308ν, the vertical spacers 303ν and 309ν, the horizontal flat partitions 310ν, the two sub-chambers 311ν and 312ν, the suction check-valves 321ν and compression check-valves 322ν and the suction pre-chambers 346ν (3461-3464).
Collection chambers 308ν and compression chambers 307ν, have as their bottom the partition plane 345ν under which the four suction pre-chambers 346ν are developed. The suction sub-chambers 311ν are connected directly, via their permanently open bottoms, with their corresponding pre-chambers 346ν.
The compressor is also covered by flat roofs 313ν of gradually and stepwise increased heights, enclosed by a cylindrical housing 318, while the bottom 347ν forms its lower outer cover and at the same time the bottom of the suction pre-chambers 346ν. The surfaces of the vanes 320ν are gradually and stepwise increased as are the cross-sections of the compression chambers 307ν.
This is therefore the same system compared to that of
The four evaporation chambers Lν, with the inside incorporated heat-exchangers, are longitudinal and of parallelepiped shape, arranged in pairs and in two parallel rows. The two rows are located adjacent to each other forming a common parallelepiped consisting of the four parallelepipeds, all of which having a common junction point.
The four chambers are mounted with their largest surface on an elevated frame below which there are pipelines, pumps and all the auxiliary machinery and devices. Not designed.
The outer coverings 101ν of the evaporation chambers Lν are slightly convex in order to increase stiffness due to vacuum conditions prevailing within. Inside the evaporation chambers Lν, vapor-water heat-exchangers 132ν are developed, consisting of a bundle of horizontal preferably flattened tubes 133ν which terminate in two narrow vertical collector-chambers, the inlet collector-chambers 110ν of the superheated vapor, and the outlet collector-chambers 111ν of the condensates 44ν, with the corresponding vertical and flat frontal plates (tube sheets) 134ν and 135ν respectively. The inlet collector-chambers 110ν, are restricted by the frontal plates (tube sheets) 134ν and by their external side walls 112ν.
Above the heat-exchangers, there are the brine spray systems 139ν, while in the lower part, the brine basins 131ν are developed.
Between the external side walls 112ν of the inlet collector-chambers 110ν and the outer coverings 101ν with which the stages are in contact in pairs frontally to each other, develop narrow, flattened vertical duct-chambers 114ν. They extend over the entire width and height of the evaporation chamber Lν, in parallel to the inlet collector-chambers 110 connecting the upper part of the basins 131ν with the suction pre-chamber 346ν of the compressor 306 corresponding to the stage.
The duct-chambers 114ν correspond to the vertical ducts 46ν, rising upwards, of the saturated vapors of the corresponding variant of
From the center of the unit, namely from the four-stages' common junction, passes the already known narrow sleeve-cylinder 102 with the rotation shaft 316 and the rotor at its center and the compressor 306 at the top.
The double compression sub-chambers 312ν are connected to the inlet collector-chambers 110ν of the heat-exchangers 132ν through the double ducts 337, which terminate on the two opposite sides of the inlet collector-chambers 110ν directing alternately, due to the dual-action, the superheated vapors from two different and opposite points of the collector-chambers, increasing the heat transfer coefficient and the overall efficiency of the heat-exchanger. See also
In another variation there may be only a single vapor duct 337ν from each sub-chamber 312ν to the corresponding inlet collector-chamber 110ν.
The similarities of the operation of the compressor 306 and the MVC-MEE/MED of
The feed-water 40 is pre-heated at the known specific temperature by both the rejected brine 1364 of the fourth stage and the desalinated water 44ν and is supplied to the evaporation chamber L1 of the first stage.
The brine 1361 is pumped from the bottom of the evaporation chamber L1 and is sprayed through the overlying spray nozzle system 1391 externally onto the bundle of horizontal tubes 1331 of the water-vapor heat-exchangers 1321 in the interior of which flows the superheated vapor of the first stage, which descends through the ducts 3371 and is distributed to the tubes 1331 via the inlet collector-chamber 1101.
The saturated vapor produced, descends along with the sprayed brine in the basin 1311, where, due to the lower pressure created at the compressor's suction side, is sucked up vigorously and rises through the vertical duct-chamber 1141 in the suction pre-chamber 3461 to be compressed.
The superheated vapor condenses and as a condensate and desalinated water 441, flows along the length of the horizontal tubes 1331 and descends to the bottom of the opposite terminal collector-chamber 1111 of the condensates. The process is repeated in the other stages, as per known.
In another variation, the evaporation chambers dν and Lν, as already developed in the two previous embodiments of MVC-MEE/MED, with the heat-exchangers incorporated in their interior, the intermediate vertical duct 46ν/114ν and the compressor with the suction pre-chambers 246ν/346ν, could also be used for MVC-MSF applications.
As such, the water-vapor heat-exchangers eCν of the pre-heating feed-water 40 of MVC-MSF, will take the place of the vapor-water heat-exchangers 32ν/132ν inside the evaporation chambers dν and L and no particular condensation chamber Cν will be required.
The condensate (desalinated water) is collected, as in the case of MVC-MEE/MED, from the bottom of their heat-exchangers' eCν in the peripheral channels 41ν/111ν. Obviously the pumping and sprayer system of the brine is not needed in the MVC-MSF application and will be removed.
The vanes are parallel to each other and are mounted to a common horizontal shaft 51, perpendicular to their surface, which moves reciprocally and linearly by a drive mechanism.
The operation of the new embodiment is absolutely analogous to that already described in
The compression chambers 52, are developed in the upper part of the unit and preferably outside the evaporation chambers bν (b1-b3). Under the evaporation chambers b, are located the condensation chambers of the water-vapor heat-exchangers 54ν (541-543) corresponding to the stages, while in the present variation the heat-exchangers are a bundle of straight horizontal long tubes 53 into which feed-water 40 circulates and is gradually pre-heated.
There are also here the relevant vapor suction and compression both, check-valves 524ν and 525ν, as well as ducts 543a and 543b respectively, communicating with the evaporation chambers bν (b1-b3) and the respective condensation chambers of the heat-exchangers 54ν (541-543).
The feed-water 40, after being pre-heated, enters initially the collector 555, is distributed to the long tubes 53, is pre-heated gradually to the known specific temperature ta (corresponding to the boiling temperature of the brine of the first stage) and through the terminal collector 556, the pipe 47 and the control-valve 548, enters the evaporation chamber b1 of the first stage, where the known flash evaporation and condensation process follows, as described in
The compression ratio (CR) as well as the temperatures rise, are also here independently regulated parameters.
In another variation the compressor 506 and the compression chambers are located between heat-exchanger chambers 54ν (541-543) and evaporation chambers bν (b1-b3), whereby the lengths of the ducts 543a and 543b will be significantly shorter. Not designed.
In another variation, the chambers of the heat-exchangers 54ν are located in the same plane and adjacent to the evaporation chambers bν of the respective stages. Not designed.
In another variation the evaporation chambers bν are cylindrical, the compressor 506 and the cylindrical compression chambers are located within the respective evaporation chambers bν, and the heat-exchangers 54ν with the horizontal long tubes of the bundle of feed-water are developed on a peripheral cylindrical sector-sleeve coaxially around the evaporation chambers bν covering them along the entire length. Not designed.
In another variation the heat-exchangers 54ν are located within the evaporation chambers bν. Not designed.
In another general variation the heat-exchangers instead of being tubular are plate-like.
There will also be variants of Multi-Stage Desalination units MVC-MEE/MED where the compressor is of cylindrical type 506.
The complete independence of the stages allows them to be divided in smaller, standard and prefabricated modules, in order large plants/units to be easily transported in containers.
In another variation, the vanes' surfaces of the rotary-radial compressors are trapezoidal or of another shape, whereby the roof of the compressor is of a correspondingly shaped surface.
In another variation of the rotary-radial compressors, instead of gradually and stepwise increasing the height of the compression chambers, by keeping constant the length of the radius of their vanes, the radius is stepwise increased by keeping constant the height of the compression chambers. Also the evaporation chambers may be of different types e.g. of dynamic type with moving-rotating parts, etc.
A common feature of all the variants of MVC-MEE/MED and MVC-MSF of the present invention is that the multi-stage desalination, resembles and consists essentially of an array of co-operating independent single-effect desalination units arranged and connected in series, with simple common connections and synergies with each other, such as:
a) the brine 36ν circulating from stage to stage, b) the desalinated water 44ν circulating from stage to stage, c) the pre-heating of the feed-water in the common multi-stream external heat-exchanger, d) the pre-heating of the feed-water from the last to the first stage through a common water-vapor heat-exchanger.
The last synergy/feature d) is the main one for the variants MVC-MSF, but it could also exist as complementary to MVC-MEE/MED variants.
Additionally, the three main elements of each stage (e.g. compression chambers, evaporation and heat-exchanger chambers) of the variants of
The same thing happens in the case of parallelepiped evaporation chambers of linear arrangement.
Increased production for the same vapor suction volume, since both independent suction of the saturated vapor of each stage and compression/condensation of the superheated vapor within the same stage, occurs. Meaning that vapors of clearly higher temperatures and therefore of lower specific volume (containing a greater mass of water vapor) are sucked in comparison to the prior art which sucks saturated vapor by a single compressor, only from the last and colder stage, whose vapor has the largest specific volume of the unit and contains therefore the smallest mass of water vapor.
Increased production due to augmented suction volume as the suction is more intense due to lower pressure created at the inlet of each suction sub-chamber of the compression chambers.
Reduced heat-exchangers' surface, due to increased overall heat transfer coefficient (caused by the increased velocity and forced movement of superheated vapors in the condenser/heat-exchanger areas).
Reduced energy cost per unit produced (m3 of desalinated water) due to reduction of entropy, because of independent and partial compression in very small steps (smaller CRs and smaller temperature differences Δtν between the stages).
More precise control of the state's conditions and the smallest permissible temperature differences (Δtν) because of independent control, adjustment and operation of the stages {a smaller overall temperature difference ΔTmax (since ΔTmax=ΣΔtν) and a reduction of the specific energy consumption, is achieved}.
Increased number of stages for the same overall maximum temperature difference ΔTmax (=ΣΔtν) of the unit (higher efficiency) due to easier and more effective control of very small temperature differences (Δtν).
Faster startup of process, as suction and compression are performed simultaneously from multiple chambers and smaller CRs.
Reduce volume of the unit and ability to manufacture and transport more productive units.
Apart from the obvious balance of the preferably dissimilar (gradually increased) surfaces of the rotor's vanes, there are also methods to compensate, the rotational and reciprocating masses-movements of the system, caused by the rotating torques that are continuously changing direction, minimizing the vibrations.
In the case of installing more than one unit, every two similar units mounted to a common frame, will rotate synchronized, at the same time, in opposite directions.
In another variation a unit is placed exactly above the other (arrangement in pagoda layout), both units are mounted in a common frame with rotors and shafts laying in the same vertical axis, driven by the same drive mechanism, which transmits, at the same time, opposite rotational torques to both rotors.
Also two units could be installed horizontally, in series, on a single and common base frame with a common drive transmitting opposite rotational torques. Not designed.
In the case of cylindrical reciprocating compressors 506 wherein the movement is linear, there are provided:
a) a mass attached to the drive mechanism which moves, at any time, opposite to the main movement of the compressor shaft 51, or b) (in the case of more than one unit) every two similar and aligned units (with the horizontal shafts 51 laying in the same axis) with a common frame, are moved synchronized, but opposite to each other, having the same drive unit positioned between them and at the center of their straight and aligned arrangement (boxer layout). Not designed.
The compression ratio (CR) adjustment system includes and utilizes all the known techniques of the reciprocating compressors of positive displacement for gases and vapors, such as: the adjusting techniques of the opening and closing pressures of the suction 21, and compression 22 check-valves, etc.
The adjustment of flow rates is usually done by varying the size of the surface of the vanes, the reciprocating movement frequency, but also by varying the cross-section of: a) the internal by-pass of adjustable sliding openings 123 onto the vane surface or b) the external by-pass ducts with adjustable control-valves, affecting accordantly the recirculated flow rate portion. Not designed.
In reciprocating motion systems of constant frequency (mainly at units of very large sizes), the adjustment of the flow rates is set in discrete steps and rates of the nominal flow, e.g. at 100%, 75%, 50%, 25% or 0% of it.
Applications: a) in the chemical industry and the food industry for the condensation of aqueous solutions by the gradual evaporation and condensation of a substantial part of the water or other solvents, b) in the environment protection by further condensation of the brine rejected from reverse osmosis desalination plants {Zero Liquid Discharge (ZLD)} or by evaporating water from aqueous solutions of toxic and industrial waste in order to reduce their volume and facilitate their transport and neutralization.
Particularly in desalination, wherein due to the highest quality of desalinated water achieved (≥5-6 ppm TDS) it can be used throughout the broad spectrum of the chemical industry where high quality water is required.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20170100407 | Sep 2017 | GR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GR2018/000043 | 9/7/2018 | WO | 00 |
