The subject of the invention relates to a low temperature multi-stage seawater distillation system.

The invention relates to the field of water desalination solutions .

Known systems of multi-stage distillation - Multi Effect Desalination (MED) are highly efficient installations for desalination of water and production of distillate suitable for consumption. This type of desalination system is particularly attractive due to the high efficiency of desalinated water production, using the thermal energy to feed the system very efficiently. The principle of operation of the MED system is based on the condensation of the distillate vapors formed in the "n" effect with the simultaneous release of condensation heat in the "n+l" effect. This heat is used to evaporate the next portion of the distillate from the "n+l" effect, and then to condense it in the next effect ("n+2").The cascade is repeated until an effect is obtained with a temperature close to the ambient temperature. In conventional systems, the minimum temperature is 45°C, which is determined by the temperature of the water used to cool the condenser - the element that condenses the vapor from the last effect of the MED system. Due to the limitations dictated by the wear of the installation, the temperature of the first effect is about 70°C. According to this principle, MED systems operate in the temperature range of 70-45°C, which results in the final product (distillate) at a temperature of about 45°C. The implementation of a cooling device for the MED system allows to reduce the minimum operating temperature of the system to lower values, and thus creating the possibility of increasing the number of effects by an additional temperature range, thanks to which there is a significant increase in the production of distillate with a temperature significantly lower than in the conventional solution of the classic MED solution. The consequence is an increase in distillate production from the same amount of energy supplied to the first effect.One of the ideas to lower the temperature of the final effect is to use an adsorption chiller as a cooling device. The adsorption bed can be compared to a condenser, which has an additional advantage - it allows a significant reduction of pressure in the last effect, allowing water to evaporate at a temperature of about 10-20°C below the temperature of a conventional condenser. The sorbent, which is filling the beds of the adsorption device, sucks in and then condenses the vapor formed in the last effect of the Multi Effect Desalination and Adsorption Desalination (MEDAD) system. The MEDAD technology allows the temperature difference to be increased from, for example, 35 K to 58 K by reducing the pressure through the adsorption device, which results in a significant increase in the distillate production and the reduction of the temperature of subsequent effects below ambient temperature .

The specificity of this system is the significant energy consumption of supplying the adsorption device with water at a temperature of 50-90°C in order to prepare the bed for adsorption of another portion of the distillate.

Other known types of multistage distillation systems - Multi-Stage Flash distillation (MSF) - are systems based on the phenomenon of flash evaporation. Flash evaporation is a phenomenon consisting in introducing a liquid into a volume where there is pressure, for which the boiling point of the introduced liquid is lower than its actual temperature. Such liquid suddenly becomes a superheated liquid and boils intensively to bring it to the saturation temperature corresponding to the pressure in the given space.

The MSF system consists of a series of volumes called stages, each containing a heat exchanger and a distillate condensing system. The counter extern stages are called cold and hot ends, while the stages therebetween with respect to the liquid flow have temperatures ranging from the temperature of the last to the temperature of the first effect. Effects have different pressures corresponding to the boiling points of water at the temperature of the effect.Sea water is fed to the last effect (cold end) in a diaphragmatic manner as a heat sink in a heat exchanger acting as a condenser. The seawater receives the heat of condensation of the distillate flowing successively from the last to the first effect. The seawater is then fed to an exchanger supplied by an external heat source, where it is heated to a temperature higher than the boiling point of the first stage. The heated brine is then fed to the interior of the first stage, which has a pressure corresponding to the boiling point of the water lower than the brine temperature. Due to that phenomenon, part of the water in the brine evaporates intensively. The gaseous distillate, due to its lower density than the liquid in its vicinity, rises and directs to previously described condenser, inside which seawater flows. Sea water with a temperature lower than the distillate condensation temperature causes its condensation on the walls of the exchanger. After condensation, the liquid-phase distillate flows into a drip tray and is then received as a final product. The remaining brine increases its salinity and lowers its temperature. Then it is fed to the next stage, where the pressure is lower, so the process repeats itself. The brine from the last stage is removed as the second product of the process.

The solution referred to in SG193372 "Regenerative Adsorptive Distillation System" shows the characteristics and possible configurations of the "MED-AD" system with a double bed adsorption chiller. In the solution according to the invention, the distillation system is a hybrid system and not only a MED system. In addition, the heat of the vapor adsorption serves to pre-heat the water intended for desalination and the type of adsorption chiller is different, preventing continuous operation of the system at low adsorption pressure.

The invention described in the application US203.7072336 "Apparatus and method for multifunction adsorptive distillation" shows possible configurations of the MED-AD system with a multi bed adsorption chiller. In the solution according to the invention, a fixed bed chiller cannot be used because it is necessary to ensure a consistently low condensing pressure throughout the process. Additionally, for the solution according to the invention, it is crucial, unlike in the above appl cation, to combine MED-MSF systems with the use of water vapor absorption heat for pre-heating the desalination water, acting as an energy regeneration system significantly reducing primary energy consumption by the desalination system.

The invention CN1Q5441101 - "A method of refining an antifibrillation solution by combining enzymes, distillation and adsorption" - presents a method of purifying chemical compounds using a combination of various processes, including adsorption. In the solution of the present invention, the adsorption bed is used to absorb water vapor to reduce pressure and use the heat of adsorption to preheat the water to be desalinated.

In the CN application 204625229, entitled "Seawater desalination unit incorporating MED heat pump" refers to a seawater desalination solution using an absorption heat pump connected to the MED system. In this case, the heat produced by the absorption heat pump is used to heat the brine supplying the MED system, while in the proposed solution there is only an adsorption cooling device, so the solutions differ, because in the solution according to the invention we simultaneously use two functions of the adsorption chiller - adsorption and heat reception from this process for the heating of water intended for desalination.

It follows from the above that the prior art describes both absorption heat pumps, MED desalination systems, two-bed and three-bed chillers, and a combination of the MED system with an Absorption Heat Pump, or MED with an adsorption chiller. However, the system combining the adsorption chiller with a moving bed, the MED system and the use of flash evaporation vessels based on the flash evaporation process used in MSF systems is not known.

The object of the invention is a system enabling the process to be carried out at much lower temperatures than the solutions used so far. A very important advantage of the operation of the system in the low temperature range is the reduction, and even the exclusion of salt deposits on the exchanger surface and their clogging, i.e. scaling and fouling phenomena. At low temperatures, the range of operating parameters at which these phenomena do not occur is greater than at higher temperatures used in the systems in the known state of the art.

The second advantage is the reduction of the reguirements for the properties of the required materials and fittings, resulting in lower investment costs of the device. Heat exchangers in typical MED and MSF systems are usually made of GR2 titanium, the cost of which is about PLN 120/kg. On the other hand, AW6060 aluminium can be used for the proposed system, which, like titanium, is resistant to chemical corrosion and pitting caused by chlorides. The price of this material is about PLN 12/kg, so ten times less. In addition, A 6060 aluminium has a lower density ~2700kg/m ³ compared to titanium GR2 ~4450kg/m ³ , thanks to which less weight is needed to build the exchanger.

Another important advantage is the almost ten times higher w thermal conductivity of aluminium 200 compared to titanium

W

22 - , which favours the heat transfer process and leads to many times lower investment costs for the device.

Another important aspect is the low final temperature of the process. It makes it possible to obtain a effluent with a lower temperature, and hence with a higher brine concentration. The higher the effluent concentration also means the greater the amount of distillate obtained per unit of feed solution. A lower final temperature of the process also means a low final temperature of the distillate. Solutions according to the known art in the vast majority of cases produce a distillate with a relatively high temperature, often exceeding 40°C, which in most cases requires additional cooling of the obtained products.

A significant advantage of the system according to the invention is also the fact that a system of this type could also be used for the separation and recovery of sodium chlori.de from wastewater produced in the pharmaceutical industry, which is a very significant advantage, as there are no systems that implement this process in an economic manner.

Additionally, another significant advantage of the proposed system is the fact that it is fed only with low-temperature heat, which can come directly from sea water. Therefore, it can also be supplied with waste heat from other installations or systems. This fact has a significant impact on the economic aspect related to the costs of operating the system and has an impact on the sustainable development of areas requiring the use of the desalination process for drinking water production.

Low operating and supply temperatures of the device also result in greater safety of the operation, service and renovation personnel due to the inability to suffer burns.

In the MED technology, which is a technology more effective than the MSF technology (the average energy consumption of MED is 80-90 kWh/m ³ of produced distillate, while for MSF this coefficient is 120 kWh/m ³ of heat input to the installation), the scaling effect becomes problematic, the genesis of which is as follows: as a result of brine concentration due to the evaporation of distillate from the solution, and as a result of evaporation temperatures in conventional installations, calcium, magnesium and sodium ions together with sulphides form the so- called hard scaling - that is, the solution produces a chemical compound in the form of magnesium sulphide, sodium sulphide and calcium sulphide, which permanently covers the heat exchange surfaces, significantly reducing the heat transfer efficiency coefficient. In order to remove the formed salt formations, an energy-consuming heat exchanger heating procedure is used, with simultaneous supply of solutions of various acids to the "acidification" of the installation. The above process Is time- consuming (generates interruption in the supply of desalinated water) , is expensive and energy-consuming (increases the cost of the water produced) and does not guarantee 100% efficiency, so the efficiency of heat exchange is never restored to the level of a new device, which deteriorates the efficiency of the system over time and increases the cost of producing desalinated water. To counteract the above, MED installations maintain the salinity of the discharge brine at the maximum level of 62,500 mg/1.This is a barrier that some manufacturers sometimes cross, necessitating the use of anti-hard scaling chemicals - they are not the same agents used in every device to counteract soft scaling - which are designed to reduce surface tension on the heat transfer surface to "slide off" the potential crystal formations. The above-mentioned phenomena determine the necessity to maintain low values of salts dissolved in the waste brine after the recovery of the distillate from seawater, which forces the fresh brine flow several times greater than the distilled water obtained, determining the need for increased electric consumption for circulation pumps supplying brine to the installation.Another consequence of the low condensation capacity of the brine, which is then returned to the sea, is the fact that this type of installation cooperates very costly with Zero Liquid Discharge installations, whose task is to maximize the recovery of drinking water and maximize brine concentration in order to recover salt and eliminate the need to discharge saline water into sea reservoir. The expensiveness lies in the fact that low-concentrated discharge brine is subjected to thickening processes before the crystallization process, which is achieved in a very ineffective manner, which determines a very extensive installation made of extremely expensive materials resistant to high chloride concentrations.The proposed solution according to the invention, due to the fact that the first desalination effect is fed with a temperature of 35°C and less, leads to the fact that the risk of hard scale precipitation is practically negligible, while obtaining the concentration of salts dissolved in the discharge brine at the level of 122500 mg/1 thanks to whereby, in order to obtain the same amount of distilled water as in the case of conventional solutions, a much smaller flow of inlet brine is required.The above, additionally reduces the consumption of electric energy twice, and thus also reduces operating costs and the cost of producing distilled water. In addition, the lack of the risk of deposition of compounds described as "hard scaling" eliminates the need for time-consuming and energy-consuming acid treatment, thanks to which the installation according to the invention operates approximately 336 hours longer per year than conventional installations, increasing the annual production capacity by approximately 3.8%. All these advantages are additionally increased due to the fact that the heat transfer efficiency in the device according to the invention is always kept at the design level.

The solution according to the invention also has a number of energy advantages. From the point of view of heat transfer, conventional MED systems, due to evaporation temperatures above the fresh brine temperature, record heat losses resulting from the need to heat the brine to saturation conditions. In the case of the solution according to the invention, the evaporation temperatures are below the temperature of the inlet brine, so there is no heat loss of heating to saturation conditions, and what is more, the enthalpy of the brine after introducing it to the effect causes its flash evaporation, in the expansion chamber generating an additional amount of distillate vapor. The use of expansion chambers is also intended to protect the heat exchange surface against the abrasive activity of salt crystals precipitated in the expansion process, which, without the use of these chambers, would inevitably lead to mechanical destruction of the exchanger under the spray pressure. The configuration of the system according to the invention with "Zero Liquid Discharge" systems has the advantage that the brine is concentrated from the level of 122500mg/l to the crystal ization conditions, i.e. in a way that requires less energy than concentrating the same amount of brine from the concentration of 62500 g/l for crystallization . The solution according to the invention fills the gap between evaporative and osmotic technologies and the Zero Liquid Discharge technology, which is clearly noticeable today.

Summarizing, the LTMAD technology solves many engineering and economic problems, what has been shown above.

The essence of the invention is a water desalination system containing a source of seawater, a set of desalination effect blocks, an adsorption chiller with a moving bed, a feed collector, characterized in that each of the desalination effect blocks consists of an effect based on the flash evaporation technology placed above the effect based on the boiling technology where these effects are connected with each other by a brine channel attached to the bottom of the effect based on the flash evaporation technology and the upper part of the effect based on the boiling technology, and from each of the effects a vapor channel is led out to a vapor channel connecting successive desalination blocks by connecting successive effects, the vapor channel of the last desalination block is connected to the adsorption chamber of the adsorption chiller with a moving bed, moreover, from the bottom of each effect there is a brine pipeline terminated with brine discharge; moreover, the desorption chamber is connected to the heat source by means of a pipeline; and a seawater pipeline equipped with a pump is connected to the first effect and discharged as a chilled water pipeline and connected to the pipeline between the discharge valve drain valve and the control valve, where the pipeline is connected to the adsorption section of moving bed adsorption chiller, and then led out as a heated water pipeline, supplied to the buffer tank from which brine pipelines with valves are connected to the effects; and the discharge brine pipeline and the distillate receiving pipeline are derived from the last effect .

The subject of the invention in a preferred embodiment is shown in the drawing presenting a diagram of the system with connections and its elements.

The system consists of:

- a set of desalination effects (15) based on boiling technology, in number of 5 made of AW6060 aluminium; a set of desalination effects (9) based on the flash evaporation technology with a volume of about 1 m ³ , in number of 5 made of AW6060 aluminium;

- buffer tank (7) with a volume of about 5 m ³ made of acid resistant steel Duplex 2304 type;

- adsorption chiller (19) with a moving bed, with a supply temperature of 55°C and recovery of the adsorption heat of 30°C;

- a seawater pipeline (2) feeding the first exchanger (15a) made of acid resistant steel Duplex 2304 steel;

- a seawater return pipeline (3) supplying first effect made of acid resistant steel Duplex 2304 steel;

- a seawater pipeline (4) for supplying the buffer tank (7) made of acid resistant steel Duplex 2304 steel, consisting of three sections: a first section of pipeline (4a) supplying the moving bed adsorption chiller and a second section of pipeline (4c) supplying the buffer tank;

- the distillate receiving pipeline (20);

- brine receiving pipeline (21);

- a bypass line (24); - heat source (26);

- heating water supply pipeline (26a);

- heating water return pipeline (26b);

- a set of (five) sea water supply pipelines (10);

- a set of (five) sea water supply pipelines (13);

- a set of (five) distillate vapor pipelines (14);

- a set of (five) distillate vapor pipelines (16);

- a set of (four) brine pipelines (17);

- a set of (three) liquid distillate pipelines (18); and auxiliary elements:

- a centrifugal circulation pump (1) with a capacity of about 160 m ³ /h;

- sea water flow control valve assembly (8);

- the bypass control valves (23);

- the main control valves (29);

- a set of (five) temperature sensors (12);

- a set of (five) pressure sensors (11);

Seawater at a temperature of 30-35°C, from the seawater source (5), which is the seawater intake, is supplied through a pipeline made of fiberglass with a diameter of DN350 (2) via a centrifugal circulation pump (1) with a titanium impeller and housing with duplex steels to the first evaporative effect (15a). This water is used as a heat source for the first evaporative exchanger (15a) to generate saturated steam used in the subsequent evaporative effect as a heat source. Inside the evaporative exchanger (15a) with an evaporation power of lOOOkW, there is a low-pressure brine in a saturated state, with a water evaporation temperature of 27°C and a dissolved salt content in the range of 20,000 - 100,000 mg/1. The temperature difference leads to heat transfer in the exchanger, from sea water to brine. As a result of contact with the aluminium pipes of the exchanger, the outer diameter of which is 16mm, with a wall thickness of lmm and a length of 2000mm, in which seawater flows, the distillate evaporates and the brine is concentrated. As a result, the sea water inside the exchanger tubes cools down and at the same time, concentrates the sea water outside the exchanger tubes .

Sea water, after heat dissipation in the evaporative exchanger (15a) goes to the first effect return pipeline (3) made of fiberglass and of DN350 in diameter. The first effect return pipeline (3) is then split into two other pipelines: the bypass pipeline (24) made of PVC with a diameter of DN200 equipped with a valve (23) and the first section of the pipeline supplying the buffer tank (4a) also made of PVC and of DN100 diameter. A portion of the seawater stream transported through the pipeline (3) is discharged out of the system by the bypass pipeline (24) in a quantity that can be regulated depending on the exact salt content and the required salt content in the effluent after the evaporation process. The second part of the seawater stream transported by the pipeline (3) flows through the first section of the pipeline feeding the buffer tank (4a). The flow through both pipelines is regulated by the operation of the valves:

- a bypass control valve (23) provided in the flow line of the bypass line;

- a main control valve (29) located in the flow line of the first section of the pipeline supplying the buffer vessel (4a);

The above-mentioned control valves regulate the flow using the indications of the flow meters installed in pipeline 24 and 4, the conductivity sensor installed in pipeline 4 and the conductivity sensor installed in the concentrated brine discharge pipeline (21) and based on the setting of the required brine concentration at the outlet, the valves regulate how much brine goes to the evaporation process, while the amount returns to the brine source.

The first section of the pipeline supplying the buffer tank (4a) is connected to the adsorption chiller (19) with a moving bed in such a way that seawater flows through the adsorption chamber exchanger (19a), in which the sorbent is cooled before the process of water vapor adsorption resulting from the last effect, evaporative (15n), connected to the last evaporative effect by a vapor channel (16n) made of carbon steel, 1500mm in diameter. The flowing sea water is used to receive the heat of sorbent cooling from the adsorption device (19).The return from the adsorption device is led through the second section of the pipeline (4b) supplying the buffer tank (7) made of duplex 2304 acid-resistant steel with a volume of 20m ³ . In order to regenerate the sorbent in the desorption chamber (19b) of the adsorption chiller (19) with a moving bed, it is fed writh hot water supplied by means of a supply pipeline (26a) and a return pipeline (26b) from a heat source (26) being a field of solar collectors .

The water level in the buffer tank (7) must Joe kept constant. The water level is regulated by using the main control valve (29). From the buffer tank (7), there are five pipelines made of PVC with a diameter of DN50, forming a set of sea water supply pipelines (10). There is a valve in the flow line of each seawater supply pipeline (10) to control the flow of seawater. These valves form a set of seawater flow control valves (8). Each of the seawater discharge pipelines goes to one of five flash evaporation tanks (9) made of duplex 2304 acid-resistant steel with a volume of 2m ³ .

The water flow is regulated on the basis of input signals in the form of pressure in the flash evaporation tank (9), known by the pressure sensor (11) placed in it, and the temperature of sea water in the supply pipeline (13). If the seawater temperature is noticeably higher than the seawater saturation temperature for a saturation pressure equal to the pressure measured by the sensor (11), the water flow at the seawater flow control valve (8) is reduced.

The pressure in the flash evaporation vessel tank (9) is low. Due to the low pressure, the water evaporation temperature for the first flash evaporation tank is 27°C, and for the subsequent ones: 23°C, 19°C, 15°C and 11°C respectively. Sea water, flowing into the tanks through the sea water supply pipelines (10), has a temperature above 30°C, therefore the phenomenon of flash evaporation occurs, i.e. intense evaporation of distillate from seawater, until it reaches the saturation temperature. As a result of the phenomenon, we obtain distillate vapor and seawater with a lower temperature and a highier salt concentration .

Each of the flash evaporation tanks (9) is connected directly to one evaporative exchanger (15) through a supply pipeline (13) made of PVC with a diameter of DN50, together forming five "effects". The supply pipeline (13) is used to supply sea water from the flash evaporation tank (9) to the duplex 2304 acid-resistant drip tray located inside, in the upper part, of the evaporative exchanger (15). In evaporative exchangers (15), seawater dripping from the drip tray hits the pipes in which the distillate flows at a higher temperature. As the water is saturated, it evaporates and absorbs heat, thereby producing a gaseous distillate.

Each of the flash evaporation tanks (9) has an additional distillate vapor pipeline (14) made of 316L acid-resistant steel with a diameter of 400mm, connected in its upper part. Through this pipeline, the gaseous distillate obtained in the flash evaporation vessel (9) goes to the inter-effect distillate vapor pipeline (16). The connection is also intended to maintain an even pressure in a given effect. Each of the five inter-effect distillate vapour pipelines (16) is made of 316L acid-resistant steel with a diameter of 1500mm, is led out from the upper part of the evaporative exchanger (15) "n" and goes to the next evaporative exchanger (15) "n+1", passing through it to provide heat. The exception is the last evaporative exchanger (15), from which the inter-effect distillate vapour pipeline goes to the adsorption device. The distillate flowing in the inter-effect gaseous distillate pipeline (16) is not in direct contact with the liquid inside the evaporative exchanger into which it flows. There is only heat exchange between the fluids without mass exchange. As a result of the heat transfer from the distillate to the fluids inside the evaporative exchanger (15), the distillate condenses. The condensed distillate then flows out through the liquid distillate pipeline (18) made of PVC with a diameter of DN50. The liquid distillate pipeline (18) then enters a subsequent evaporative exchanger (15) where it connects with the distillate fed through the inter-effect gas distillate pipeline. Both streams supply heat to the next evaporative exchanger.

From each, except the last, evaporative exchanger (15), leaves a brine pipeline (17) made of PVC with a diameter of DN50, which flows into the next evaporative exchanger (15). From the last evaporative exchanger (15) leaves the brine collection pipeline (21) made of PVC with a diameter of DN80 and is used for the final collection of brine.

From the last evaporative exchanger (15), due to the lack of subsequent effect, does not leave the distillate pipeline (18), but the distillate receiving pipeline (20) made of 316L stainless steel with a diameter of DN50, used to receive the final distillate.

From the last evaporative exchanger (15), due to the lack of subsequent effect, the distillate vapor pipeline (16) goes to the adsorption bed of the adsorption device. As a result of the adsorption device operation, we obtain a condensed distillate.

The adsorption device is supplied with the heat at a temperature of 55°C through the hot water supply pipeline (26a) made of carbon steel with a diameter of DN250, in which the flow of heating water is maintained by a centrifugal circulation pump. After heat dissipation, the water returns through the hot water return pipeline (26b) made of carbon steel with a diameter of DN250 to the heating water source (26).