Water adsorption desalination process with pressure swing

Abstract

A method of purifying water comprises: • (i) evaporating feed water in an evaporator 220 to produce water vapour, wherein the evaporator 220 is set at an evaporator temperature T ey; • (ii) allowing the water vapour from the evaporator 220 to an adsorption chamber 230 comprising an adsorption apparatus 231, wherein the adsorption apparatus 231 is set at a temperature T SB, wherein T SB is greater than T ey; and • (iii) allowing the water vapour from the adsorption chamber 230 to a condenser 240, wherein the condenser 240 is set at a condensation temperature T cond, wherein T cond is less than T SB. • the method is based on actuating adsorption and desorption in the sorption chamber via a pressure swing, rather than a temperature swing.

Description

[0001] WATER ADSORPTION DESALINATION PROCESS WITH PRESSURE SWING

[0002] Field of the Invention

[0003] The present invention relates to systems and methods for controlling an Adsorption Purification device. In particular, but not exclusively, the invention relates to systems and methods for controlling a heat-powered Adsorption Desalination apparatus, for example to produce purified water.

[0004] Background

[0005] The generation of clean and / or drinking water is a growing concern throughout the world for various reasons, which include, amongst others, pollution, climate change, industrialisation, and increasing population.

[0006] Many water purification systems exist in order to provide a solution when access to clean and / or drinkable water is insufficient. Water desalination is one such available solution, which is particularly attractive in regions of the world where rainfall is low and / or where population density is high.

[0007] Adsorption Desalination (AD) is a heat-driven evaporative technology for the purification of feed water from substances having lower saturation pressure (e.g. salts in seawater). Typically, in its simplest configuration, an AD system is composed of an evaporator to evaporate water from feed water, an adsorption chamber in the form of a Sorption Bed (SB) on which water vapour is adsorbed, and a condenser to condense and collect purified, liquid, water that is released from the SB. The Sorption Bed (SB) typically comprises a nanoporous material in contact with a heat transfer surface such as the external surface of a heat exchanger.

[0008] Examples of AD systems are disclosed in US8535486B2 (Kim Choon Ng et al), US8603223B2 (Bidyut Baran Saha), US20210107807 (Qasem et al), US11311818B1 (Amaltrafi et al), and Olkis et al. (A small-scale adsorption desalinator, Vol 158, 2019, p1425-1430).

[0009] However, conventional operation of adsorption-based water desalination facilities are associated with a number of disadvantages:

[0010] The adsorption / desorption cycle in the adsorption chamber is typically driven by temperature swings, where the chamber is heated to a high temperature, typically around 70-80°C, and cooled down to around 30-40°C. This an energy inefficient step due to the heating / cooling cycles. This is also time inefficient, particularly when no additional energy is used to accelerate heating and cooling.

[0011] The low energy efficiency of these systems contributes to a high carbon footprint for this technology, estimated to be 76 million tons (Mt) of CO2 per year as of 2018 (Muhammad W. Shahzad et a / ; Adsorption desalination - Principles, process design, and its hybrids for future sustainable desalination; 2018; King Abdullah University of Science & Technology (KAUST), Thuwal, Saudi Arabia).

[0012] The heating / cooling temperature cycle tends to hinder the vacuum tightness of the adsorption chamber, which then requires maintenance.

[0013] Muhammad Wakil Shahzad et al (Pressure driven adsorption cycle integrated with thermal desalination; Case Studies in Thermal Engineering 41 (2023) 102608) describes a pressure-driven adsorption cycle in a water desalination system. However, this system relies on the active regulation of the pressure in the adsorption chamber using a vacuum ejector.

[0014] It is an object of the invention to address and / or mitigate one or more problems associated with the prior art.

[0015] It is an object of the invention to improve the efficiency of Adsorption Desalination systems and methods.

[0016] Summary

[0017] The present invention is based on the finding that it is possible to effectively operate an Adsorption Desalination system by actuating adsorption and desorption in the sorption chamber via a pressure swing, rather than a temperature swing.

[0018] Advantageously, because the sorption chamber is not subjected to repeated cycles of high and low temperatures, the main source of heat needed to operate the system does not require the same power levels as in a conventional facility, and the system can use “low grade” heat in order to power the desalination water purification system.

[0019] Low grade heat is typically considered a source of heat supplying a temperature less than about 60°C, e.g. about 50°C. This is advantageous as it enables the AD facility to be associated with and / or combined with existing activities that typically generate this source of low grade heat, which in most cases is discarded or released into the environment. For example, in colder climates, such as in the UK, traditional industries such as whisky distilleries or power stations generate waste heat (<60°C). It was discovered that such waste heat may be sufficient to operate an AD system according to the present methodology. Traditionally, certain distilleries may shut down in the summer, because of the lack of water of sufficiently high quality. The current technology can sustainably extend their operational time since rivers or sea water can be purified up to drinkable quality using the low grade heat generated on site.

[0020] In water climates, for example central and southern Europe, solar radiation is strong enough to provide a source of power which, although typically not high enough to operate a conventional AD system, may be high enough to operate an AD system according to the present methodology.

[0021] According to a first aspect, there is provided a method of purifying water, the method comprising:

[0022] (i) evaporating feed water in an evaporator to produce water vapour, wherein the evaporator is set at an evaporation temperature Tev;

[0023] (ii) allowing the water vapour from the evaporator to an adsorption chamber comprising an adsorption apparatus, wherein the adsorption apparatus is set at a temperature TSB, wherein TSB is greater than Tev; and

[0024] (iii) allowing the water vapour from the adsorption chamber to a condenser, wherein the condenser is set at a condensation temperature TCOnd, wherein TCOnd is less than TSB.

[0025] The method may comprise repeating steps (i)-(iii).

[0026] Advantageously, TSB may be set to be constant or substantially constant. Thus, in the present invention, the adsorption apparatus is set at a temperature TSB which is preferably constant. The term “substantially constant will be understood to account for the potential inherent minor variations in temperature due to temperature control equipment characteristics. For example, if TSB is set to X °C, the actual temperature within an operating range of an associated temperature control means, e.g. temperature controller, may be X°C ± 5°C, e.g. X°C ± 3°C, e.g. X°C ± 2°C, e.g. X°C ± 1 °C.

[0027] However, regardless of the temperature control means being used, it will be appreciated that small changes in the actual temperature of the sorption bed TSB may occur, for example due to the pressure equilibrium being reached with the evaporator and / or with the condenser upon fluid communication between the adsorption chamber and the evaporator or the condenser. For example, the actual temperature of the sorption bed TSB may vary by about 0-5°C, e.g. about 0-3°C. TSB may vary, e.g. between steps (ii) and (iii), by less than 5 degrees C, e.g. by less than 3 degrees C.

[0028] Advantageously, the present method allows adsorption and desorption of water, e.g. water vapour, in the adsorption chamber, e.g. repeated cycles of adsorption and desorption of water to / from the adsorption chamber, based on a temperature-induced pressure swing in the adsorption chamber. The inventors have discovered that this approach is much more efficient than conventional approaches based on a temperature swing.

[0029] Typically, TCOnd is less than Tev.

[0030] Advantageously, TCOnd may be at or around ambient temperature, e.g. between about 10°C and 35°C, typically between about 20°C and 30°C. It will be appreciated that the preferred TCOnd may depend on the conditions where the process is taking place, e.g. on climatic conditions. By such provision, effective condensation of water, e.g. purified water, can be achieved in the condenser whilst minimising energy expenditure.

[0031] Typically, Tevmay be between about 30°C and about 50°C, e.g. between about 35°C and about 45°C.

[0032] Typically, TSB may be between about 40°C and about 60°C, e.g. between about 45°C and about 55°C.

[0033] Advantageously, this allows the present method to use a source of “low grade” heat to power and / or to regulate the temperature of the evaporator and / or of the adsorption apparatus, advantageously of both the evaporator and adsorption apparatus.

[0034] The adsorption apparatus may typically comprise a sorption bed.

[0035] The method may comprise supplying heat to the evaporator and / or to the adsorption apparatus, preferably to the evaporator and to the adsorption apparatus. The method may comprise supplying heat from a source of energy comprising or consisting of a “low grade” heat source. Advantageously, this allows the method to use a source of “low grade” heat to power and / or to regulate the temperature of the evaporator and / or of the adsorption apparatus, advantageously of both the evaporator and adsorption apparatus.

[0036] As mentioned above, TSB is greater than Tev. Advantageously, TSB may be between 0.5°C and 15°C greater than Tev, e.g. between 1 °C and 10°C greater than Tev. Advantageously, setting TSB higher than, but close to, Tevprovides a significant advantage in the amount of water produced. Setting TSB higher than Tevensures that condensation of water vapour in the adsorption chamber is avoided, thus minimising or preventing damage to the performance of the apparatus. Setting Tevrelatively close to TSB maximises the amount of water vapour generated in the evaporator, thus improving efficiency. It may also reduce or minimise the amount of time required to reach pressure equilibrium between the evaporator and the adsorption chamber, thus further improving efficiency.

[0037] As mentioned above, desorption in the sorption chamber advantageously occurs via a temperature-induced pressure swing, rather than a temperature swing. Advantageously, the pressure swing may occur by providing fluid communication between a / the evaporator and a / the adsorption chamber comprising the adsorption apparatus in an adsorption step, and by providing fluid communication between a / the adsorption chamber and a / the condenser in the desorption step.

[0038] As mentioned above, in step (ii) the method comprises allowing the water vapour from the evaporator to an adsorption chamber comprising an adsorption apparatus, wherein the adsorption apparatus is set at a temperature TSB, wherein TSB is greater than Tev. By such provision, upon providing fluid communication between the evaporator and the adsorption chamber, and upon pressure equilibration between the evaporator and the adsorption chamber, water vapour is adsorbed on the adsorption apparatus with minimal no condensation of water vapour.

[0039] In step (iii), the method allows the water vapour from the adsorption chamber to a condenser, wherein the condenser is set at a condensation temperature TCOnd, wherein TCOnd is less than TSB. By such provision, upon providing fluid communication between the adsorption chamber and the condenser, and upon pressure equilibration between the evaporator and the condenser, water vapour is condensed on the condenser which is at a condensation temperature TCOnd lower than TSB.

[0040] Advantageously, the method does not include using a dedicated pressure control apparatus associated with the adsorption chamber, and / or does not involve independently controlling the pressure in the adsorption chamber using a pressure control apparatus.

[0041] The method may comprise performing step (i)-(iii) sequentially.

[0042] Alternatively, steps (i) and (ii) may be performed concomitantly, and step (iii) subsequently.

[0043] The method may comprise performing step (i-a): (i-a) providing fluid communication between the evaporator and the adsorption chamber. The method, e.g. step (i-a) may comprise opening a first valve within a first conduit provided between the evaporator and the adsorption chamber.

[0044] Step (i-a) may be carried out after step (i).

[0045] Alternatively, steps (i), (ia) and (ii) may be performed concomitantly.

[0046] The method may comprise performing step (ii-a), typically after step (ii):

[0047] (ii-a) ceasing fluid communication between the evaporator and the adsorption chamber. The method, e.g. step (ii-a) may comprise closing the first valve within the first conduit provided between the evaporator and the adsorption chamber.

[0048] The method may comprise performing step (ii-b) after step (ii), preferably after step (ii-a):

[0049] (ii-b) providing fluid communication between the adsorption chamber and the condenser. The method, e.g. step (ii-b) may comprise opening a second valve within a second conduit provided between the adsorption chamber and the condenser.

[0050] Typically, the method, e.g. step (iii), may comprise condensing the water vapour in the condenser.

[0051] In an embodiment, the method may comprise, sequentially:

[0052] (i) evaporating feed water in an evaporator to produce water vapour, wherein the evaporator is set at an evaporator temperature Tev;

[0053] (i-a) providing fluid communication between the evaporator and an adsorption chamber;

[0054] (ii) allowing the water vapor from the evaporator to the adsorption chamber comprising an adsorption apparatus, wherein the adsorption apparatus is set at an adsorption temperature TSB, wherein TSB is greater than Tev;

[0055] (ii-a) ceasing fluid communication between the evaporator and the adsorption chamber;

[0056] (ii-b) providing fluid communication between the adsorption chamber and a condenser; and

[0057] (iii) allowing the water vapor from the adsorption chamber to the condenser, wherein the condenser is set at a condenser temperature TCOnd, wherein TCOnd is less than TSB.

[0058] In another embodiment, the method may comprise: concomitantly: (i) evaporating feed water in an evaporator to produce water vapour, wherein the evaporator is set at an evaporator temperature Tev;

[0059] (i-a) providing fluid communication between the evaporator and an adsorption chamber;

[0060] (ii) allowing the water vapor from the evaporator to the adsorption chamber comprising an sorption bed, wherein the sorption bed is set at an adsorption temperature TSB, wherein TSB is greater than Tev; then sequentially:

[0061] (ii-a) ceasing fluid communication between the evaporator and the adsorption chamber;

[0062] (ii-b) providing fluid communication between the adsorption chamber and a condenser; and

[0063] (iii) allowing the water vapor from the adsorption chamber to the condenser, wherein the condenser is set at a condenser temperature TCOnd, wherein TCOnd is less than TSB.

[0064] The method, e.g. step (i-a) may comprise opening a first valve within a first conduit provided between the evaporator and the adsorption chamber.

[0065] The method, e.g. step (ii-a) may comprise closing the first valve within the first conduit provided between the evaporator and the adsorption chamber.

[0066] The method, e.g. step (ii-b) may comprise opening a second valve within a second conduit provided between the adsorption chamber and the condenser.

[0067] The method may further comprise:

[0068] (iv) ceasing fluid communication between the adsorption chamber and the condenser.

[0069] The method, e.g. step (iv) may comprise closing the second valve within the second conduit provided between the adsorption chamber and the condenser.

[0070] Typically, step (iv) may be performed after step (iii).

[0071] The method may further comprise:

[0072] (v) recovering water, e.g. pure water, from the condenser.

[0073] The method may comprise repeating steps (i)-(iii), e.g. steps (i)-(iv), e.g. steps

[0074] (i)-(v). Typically, the method may comprise desalinating (the) water, e.g. the feed water.

[0075] The method, e.g. step (i), may comprise evaporating the feed water to reach a water vapour pressure in the evaporator Pev. Without wishing to be bound by theory, it is believed that, neglecting the boiling point elevation of the feed water due to the presence of impurities, e.g. salts, Pevcan be considered to be or substantially be the saturation pressure of pure water at the evaporation temperature Tev. Without wishing to be bound by theory, it is believed that the presence of impurities do not affect the performance significantly, as can happen in other evaporative technologies (e.g. Multieffect distillation).

[0076] Typically, Pevmay be between about 4.2 and 12.3 kPa (between about 0.04 and 0.12 atm), e.g. between about 5.6 and 9.6 kPa (between about 0.06 and 0.09 atm).

[0077] Typically, when water vapour moves from the evaporator to the adsorption chamber, the pressure of the water vapour in the adsorption chamber is PSB. PSB may typically be lower than the saturation pressure of pure water at the sorption temperature TSB.

[0078] Typically, the saturation pressure of water at temperature TSB may be between about 7.4 and 19.9 kPa (between about 0.07 and 0.20 atm), e.g. between about 9.6 and 15.8 kPa (between about 0.09 and 0.16 atm).

[0079] The system typically operates at a pressure below atmospheric pressure. Advantageously, this may help avoid condensation of water in the evaporator and / or in the adsorption chamber.

[0080] Typically, PCOnd may be or may substantially be the saturation pressure of pure water at the condensation temperature TCOnd. The method may comprise performing the method intermittently, for example as explained above.

[0081] Each cycle may be around 1-200s, e.g. about 10-100s, e.g. about 60s. The duration of each cycle may depend on the specific design of the system.

[0082] The method may comprise performing the method continuously. In such instance there may be provided two or more adsorption chambers in fluid communication with one or more evaporators and with one or more condensers.

[0083] Thus, according to a second aspect, there is provided a method of purifying feed water, the method comprising: (i) evaporating feed water in an evaporator to produce water vapour, wherein the feed water is set at an evaporation temperature Tev;

[0084] (ii) providing fluid communication between the evaporator and a first adsorption chamber comprising a first adsorption apparatus, thereby allowing the water vapor from the evaporator to the first adsorption chamber, wherein the first adsorption apparatus is set at a first adsorption temperature TSB1, wherein TSB1is greater than Tev;

[0085] (ii-a) ceasing fluid communication between the evaporator and the first adsorption chamber;

[0086] (iii) providing fluid communication between the first adsorption chamber and a condenser, thereby allowing the water vapour from the first adsorption chamber to the condenser, wherein the condenser is set at a condenser temperature TCOnd, wherein Tcond is less than TSB1;

[0087] (iv) providing fluid communication between the evaporator and a second adsorption chamber comprising a second adsorption apparatus, thereby allowing the water vapour from the evaporator to the second adsorption chamber, wherein the second adsorption apparatus is set at a second adsorption temperature TSB2, wherein TSB2is greater than Tev;

[0088] (iv-a) ceasing fluid communication between the first adsorption chamber and the condenser;

[0089] (iv-b) ceasing fluid communication between the evaporator and the second adsorption chamber; and

[0090] (v) providing fluid communication between the second adsorption chamber and the condenser, thereby allowing the water vapour from the second adsorption chamber to the condenser, wherein TCOnd is less than TSB2.

[0091] Typically, TSB1and TSB2may be substantially equal. Advantageously, TSB1and TSB2may be constant or may be substantially constant. TSB1and TSB2may vary, e.g. between steps (ii) and (v), by less than 10 degrees C, e.g. by less than 5 degrees C.

[0092] Step (i)-(ii) may be performed simultaneously.

[0093] Typically, steps (i)-(iii) may be performed sequentially. If steps (i)-(ii) are performed simultaneously, step (iii) may be performed after steps (i)-(ii).

[0094] Step (iii) may be performed before, simultaneously with, or after, step (iv).

[0095] Typically, steps (iii-a) and (iv-a) may be performed after steps (iii) and (iv).

[0096] Step (iii-a) may be performed before, simultaneously with, or after, step (iv-a).

[0097] Typically, step (v) may be performed after steps (iii-a) and (iv-a). The method may comprise repeating steps (ii) - (v). Step (v) may be performed before, simultaneously with, or after, step (ii) of the following iteration.

[0098] The method may comprise (v-a) ceasing fluid communication between the second adsorption chamber and the condenser.

[0099] The method, e.g. step (ii) may comprise opening a first valve within a first conduit provided between the evaporator and the first adsorption chamber.

[0100] The method, e.g. step (ii-a) may comprise closing the first valve within the first conduit provided between the evaporator and the first adsorption chamber.

[0101] The method, e.g. step (iii) may comprise opening a second valve within a second conduit provided between the first adsorption chamber and the condenser.

[0102] The method, e.g. step (iv) may comprise opening a third valve within a third conduit provided between the evaporator and the second adsorption chamber.

[0103] The method, e.g. step (iv-a) may comprise closing the second valve within the second conduit provided between the first adsorption chamber and the condenser.

[0104] The method, e.g. step (iv-b) may comprise closing the third valve within the third conduit provided between the evaporator and the second adsorption chamber.

[0105] The method, e.g. step (v) may comprise opening a fourth valve provided between the second adsorption chamber and the condenser.

[0106] The method, e.g. step (v-a) may comprise closing the fourth valve within the fourth conduit provided between the second adsorption chamber and the condenser.

[0107] The method may further comprise:

[0108] (vi) recovering water, e.g. pure water, from the condenser.

[0109] The method may be actuated manually.

[0110] The method may be actuated automatically.

[0111] Each half cycle may be around 1-200s, e.g. about 10-100s, e.g. about 60s depending on specific designs.

[0112] According to a third aspect, there is provided a system for purifying water, the system comprising; an evaporator configured to produce water vapour, wherein the evaporator is configured to be set at an evaporator temperature Tev; an adsorption chamber comprising an adsorption apparatus, wherein the adsorption apparatus is configured to be set at an adsorption temperature TSB, wherein TSB is greater than Tev; and a condenser, wherein the condenser is configured to be set at a condenser temperature TCOnd, wherein TCOnd is less than TsB.

[0113] Typically, TCOnd is less than Tev.

[0114] The evaporator may be in fluid communication with a source of water, e.g. feed water, via a feed conduit. There may be provided a feed valve to control feed of the feed water to the evaporator.

[0115] The system may comprise a first conduit between the evaporator and the adsorption chamber. There may be provided a first valve configured to control flow of water vapour through the first conduit.

[0116] The system may comprise a second conduit between the adsorption chamber and the condenser. There may be provided a second valve configured to control flow of water vapour through the second conduit.

[0117] Advantageously, the present system allows adsorption and desorption of water in the adsorption chamber, e.g. repeated cycles of adsorption and desorption of water in the adsorption chamber, based on a pressure swing in the adsorption chamber. The inventors have discovered that this approach is much more efficient than conventional approaches based on a temperature swing.

[0118] The system may be associated with or may comprise a source of energy e.g. heat, configured to provide energy to the evaporator and / or adsorption apparatus and / or configured to regulate heat of the evaporator and / or adsorption apparatus. Advantageously, the source of energy may comprise or may consist of a “low grade” heat source. Advantageously, this allows the method to use a source of “low grade” heat to power and / or to regulate the temperature of the evaporator and / or of the adsorption apparatus, advantageously of both the evaporator and adsorption apparatus.

[0119] Typically, the evaporator may be configured to be set at an evaporator temperature Tevbetween about 30°C and about 50°C, e.g. between about 35°C and about 45°C.

[0120] The evaporator may be associated with a first temperature control means, e.g. first temperature controller, configured to regulate and / or control the temperature Tevof the evaporator. The first temperature control means may be set at an evaporator temperature between about 30°C and about 50°C, e.g. between about 35°C and about 45°C. Typically, the adsorption apparatus may be configured to be set at an adsorption temperature TSB between about 40°C and about 60°C, e.g. between about 45°C and about 55°C.

[0121] The adsorption apparatus may be associated with a second temperature control means, e.g. second temperature controller, configured to regulate and / or control the temperature TSB of the adsorption apparatus. The second temperature control means may be set at an adsorption apparatus temperature TSB between about 40°C and about 60°C, e.g. between about 45°C and about 55°C. TSB may be constant or may be substantially constant.

[0122] The term “substantially constant will be understood to account for the potential inherent minor variations in temperature due to characteristics of the second temperature control means. For example, if TSB is set to X °C, the actual temperature within an operating range of the second temperature control means may be X°C ± 5°C, e.g. X°C ± 3°C, e.g. X°C ± 2°C, e.g. X°C ± 1 °C.

[0123] However, regardless of the temperature controller being used, it will be appreciated that small changes in the actual temperature of the sorption bed TSB may occur, for example due to the pressure equilibrium being reached with the evaporator and / or with the condenser upon fluid communication between the adsorption chamber and the evaporator or the condenser. For example, the actual temperature of the sorption bed TSB may vary by about 0-5°C, e.g. about 0-3°C.

[0124] The condenser may be associated with a third temperature control means, e.g. third temperature controller, configured to regulate and / or control the temperature TCOnd in the condenser. The third temperature control means may be set at a condenser temperature TCOnd between about 10°C and about 30°C, e.g. between about 15°C and about 25°C. TCOnd may be around room or ambient temperature. In such instance, a third temperature control means may not be present.

[0125] As mentioned above, desorption in the adsorption chamber advantageously occurs via a temperature-induced pressure swing, rather than a temperature swing. Advantageously, the pressure swing may occur by providing fluid communication between a / the evaporator and a / the adsorption chamber comprising the adsorption apparatus, and by providing fluid communication between a / the adsorption chamber and a / the condenser. Advantageously, the system does not include using a pressure control apparatus associated with the adsorption chamber, and / or does not involve independently controlling the pressure in the adsorption chamber using a pressure control apparatus. Advantageously, the system may be associated with or may comprise the source of energy, e.g. the “low grade” heat source.

[0126] The source of energy, e.g. the “low grade” heat source, may comprise or may be a renewable energy facility, e.g. a solar heat generator.

[0127] The source of energy, e.g. the “low grade” heat source, may comprise or may be an industrial facility, e.g. a manufacturing facility, a refining facility, a chemical plant, a food processing plant; a power generation facility, e.g. a thermal plant, a nuclear plant, a power generation plant; a HVAC (Heating, ventilation and air conditioning) system; a waste treatment facility, e.g. a waste incineration plant; and / or a data centre. In some embodiments, the source of energy, e.g. the “low grade” heat source, may comprise or may be a distillery, a brewery, or a power plant, or the like.

[0128] The adsorption apparatus may comprise an adsorbent material capable of adsorbing water vapour. Typically, the adsorbent material may comprise a nanoporous material. The adsorption apparatus may comprise the adsorbent material, e.g. nanoporous material, provided on a surface of a heat transfer device such as a heat exchanger.

[0129] The system may be a desalination system.

[0130] When the system comprises one adsorption chamber, the system may be configured to operate, e.g. to generate pure water in the condenser, intermittently, for example according to a method of the first aspect.

[0131] The system may be configured to operate, e.g. to generate pure water in the condenser, continuously, for example according to a method of the second aspect. In such instance the system may comprise two or more adsorption chambers each in fluid communication with one or more evaporators and with one or more condensers.

[0132] Thus, according to a fourth aspect, there is provided a system for purifying water, the system comprising: an evaporator configured to produce water vapour, wherein the evaporator is configured to be set at an evaporator temperature Tev; a first adsorption chamber comprising a first adsorption apparatus, wherein the first adsorption apparatus is configured to be set at a first adsorption temperature TSB1, wherein TSB1is greater than Tev; a second adsorption chamber comprising a second adsorption apparatus, wherein the second adsorption apparatus is configured to be set at a second adsorption temperature TSB2, wherein TSB2is greater than Tev; and a condenser, wherein the condenser is configured to be set at a condenser temperature TCOnd, wherein TCOnd is less than TsB1and TSB2.

[0133] Typically, TCOnd may be less than Tev.

[0134] Typically, TSB1and TSB2may be substantially equal. TSB1and TSB2may be constant or may be substantially constant.

[0135] The evaporator may be in fluid communication with a source of water, e.g. feed water, via a feed conduit. There may be provided a feed valve to control feed of the feed water to the evaporator.

[0136] The system may comprise a first conduit between the evaporator and the first adsorption chamber. There may be provided a first valve configured to control flow of water vapour through the first conduit.

[0137] The system may comprise a second conduit between the first adsorption chamber and the condenser. There may be provided a second valve configured to control flow of water vapour through the second conduit.

[0138] The system may comprise a third conduit between the evaporator and the second adsorption chamber. There may be provided a third valve configured to control flow of water vapour through the third conduit.

[0139] The system may comprise a fourth conduit between the second adsorption chamber and the condenser. There may be provided a fourth valve configured to control flow of water vapour through the fourth conduit.

[0140] The system may be associated with or may comprise a source of energy e.g. heat, configured to provide energy to the evaporator and / or to the first and / or second adsorption apparatus and / or configured to regulate heat of the evaporator and / or first and / or adsorption apparatus. Advantageously, the source of energy may comprise or may consist of a “low grade” heat source. Advantageously, this allows the method to use a source of “low grade” heat to power and / or to regulate the temperature of the evaporator and / or of the first and / or second adsorption apparatus, advantageously of the evaporator and of the first and second adsorption apparatus.

[0141] Typically, the evaporator may be configured to be set at an evaporator temperature Tevbetween about 30°C and about 50°C, e.g. between about 35°C and about 45°C.

[0142] Typically, the first adsorption apparatus may be configured to be set at a first adsorption temperature TSB1between about 40°C and about 60°C, e.g. between about 45°C and about 55°C. Typically, the second adsorption apparatus may be configured to be set at a second adsorption temperature TSB2between about 40°C and about 60°C, e.g. between about 45°C and about 55°C.

[0143] The system may comprise a control unit. The control unit may be configured to control one or more of the following:

[0144] - temperature of the evaporator, e.g. via the first temperature controller;

[0145] - temperature of the adsorption chamber(s), e.g. of the first adsorption chamber and / or of the second adsorption chamber), e.g. via the second temperature controller;

[0146] - temperature of the condenser, e.g. via a / the third temperature controller;

[0147] - actuation of a valve, e.g. of the first, second, third, and / or fourth valve.

[0148] The control unit may be configured to be operated manually, e.g. via a user interface.

[0149] The control unit may be configured to be operated manually automatically, e.g. may be controlled by a computer.

[0150] The features described in relation to any aspect of the invention may equally apply to any other aspect and, merely for brevity, are not repeated. For example, features described in relation to compositions can apply in relation to methods, and vice versa.

[0151] Brief Description of Drawings

[0152] Embodiments of the invention are described with reference to the accompanying drawings, in which:

[0153] Figures 1-2 illustrates the use of a first (intermittent) desalination system according to the prior art;

[0154] Figures 3(a)-3(c) shows the measured temperatures and pressures of the various elements of the system of Figures 1-2;

[0155] Figure 4 shows a second (continuous) desalination system according to the prior art;

[0156] Figure 5 is a graph representing computational data showing the temperatures of (a) the evaporator, (b) and (c) the two sorption beds, and (d) the condenser, of the system of Figure 4; Figures 6(a) and 6(b) show performance comparison (Specific Daily Water Production (SDWP) in [kgwater kgSiiicage1day-1] and the dimensionless Performance Ratio (PR)) based on mathematical model predictions, of the system of Figure 4;

[0157] Figure 7 shows a continuous desalination system according to a first embodiment;

[0158] Figures 8(a)-8(c) show the measured temperatures and pressures of the various elements of the system of Figure 7;

[0159] Figures 9(a) and 9(b) shows experimental results comparing the performance of a system as described with reference to Figures 1-2 and a system as described with reference to Figure 7;

[0160] Figure 10 shows a continuous desalination system according to a second embodiment;

[0161] Figure 11 is a graph representing computational data showing the temperatures of (a) the evaporator, (b) and (c) the two sorption beds, and (d) the condenser, of the system of Figure 10 operated with the method according to the present disclosure;

[0162] Figures 12(a) and 12(b) showing performance comparison (Specific Daily Water Production (SDWP) in [kgwater kgSiiicage1day-1] and the dimensionless Performance Ratio (PR)) based on mathematical model predictions, of the system of Figure 10, including heat recovery;

[0163] Figure 13 shows the thermodynamic cycle of one sorption bed during operation of the systems of Figures 7 and 10;

[0164] Figure 14(a) to 14(c) show alternative embodiments of a system according to the present disclosure.

[0165] Detailed Description

[0166] In the present disclosure, reference is made to a number of terms, which have the meanings provided below, unless a context indicates to the contrary.

[0167] The term “comprising” or variants thereof is to be understood herein to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

[0168] The term “consisting” or variants thereof is to be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, and the exclusion of any other element, integer or step or group of elements, integers or steps. The term “about” herein, when qualifying a number or value, is used to refer to values that lie within ± 5% of the value specified. For example, if a temperature is specified to be about 5 to about 13 °C, temperatures of 4.75 to 13.65 °C are included.

[0169] Reference to physical states of matter (such as liquid or solid) refer to the matter’s state at 25 °C and atmospheric pressure unless the context dictates otherwise.

[0170] As explained above, the present inventors have discovered that it is possible to effectively operate an Adsorption Desalination system by actuating adsorption and desorption in the sorption chamber via a pressure swing, rather than a temperature swing.

[0171] Advantageously, because the sorption chamber is not subjected to repeated cycles of high and low temperatures, the main source of heat needed to operate the system does not require the same power levels as in a conventional facility, and the system can use “low grade” heat in order to power the desalination water purification system.

[0172] Figures 1-2 illustrate the use of a first desalination system 10 according to the prior art.

[0173] The system 10 includes an evaporator 20 configured to produce water vapour. The temperature Tevof the evaporator 20 is controlled using an evaporator heater 22.

[0174] The evaporator 20 is in fluid communication with an adsorption chamber 30 comprising a sorption bed 31. The temperature TSB of the sorption bed 31 is controlled using a sorption heater 32.

[0175] Flow of water vapour between the evaporator 20 and the adsorption chamber 30 is controlled by a first valve 25.

[0176] The system 10 includes a condenser 40. The temperature TCOnd of the condenser 40 is controlled using a heat exchanger 42, typically for condensing and cooling the water vapour.

[0177] Flow of water vapour between the adsorption chamber 30 and the condenser 40 is controlled by a second valve 35.

[0178] Figure 1 shows a first stage of a conventional process used in the prior art, in which the first valve 25 is open and the second valve 35 is closed. The evaporator 20 is heated to Tevwhich is sufficient to generate water vapour, typically about 23.5 °C. The water vapour migrates to the adsorption chamber 30 where it is adsorbed on the sorption bed 31. The sorption bed 31 is at an input temperature above Tev, typically about ambient.

[0179] In a second stage illustrated in Figure 2, first valve 25 is closed and the second valve 35 is open, providing fluid communication between the adsorption chamber 30 and the condenser 40. In order to release water vapour from the sorption bed 31, the heater 32 is actuated to increase the temperature of the sorption bed 31 to a higher temperature, typically about 70-80°C, creating a temperature swing which causes the water vapour to desorb from the sorption bed 31 and enter the condenser 40. Typically, the temperature of the condenser may be around ambient.

[0180] This conventional method has a Half Cycle Time of about 600s, mainly due to the long time required to heat then cool the sorption bed 31 in each cycle.

[0181] Figures 3(a)-3(c) shows the measured temperatures and pressures of the various elements of the system of Figures 1-2. It can be seen that, whilst the temperature of the evaporator is low (about 23.5 °C), the temperature of the sorption bed 31 alternates between a low temperature (about 37 °C) when in adsorption mode and a much higher temperature (about 48 °C) when in desorption mode. It will be appreciated that, in order to allow for a meaningful comparison of the performance between a conventional single bed system (Figures 1-2) and a single bed system operated according to the present disclosure (e.g. Figure 7), the temperatures used in the sorption bed were comparable. However, in practice, a conventional single bed system 10 would require higher desorption temperature, typically about 70-80°C.

[0182] Figure 4 shows an alternative desalination system 110 according to the prior art. The system 110 of Figure 4 is generally similar to the system 10 of Figures 1-2, like parts denoted by like numerals, but incremented by ‘100’. In Figure 4, the system 110 has two adsorption chambers 130a, 130b. This arrangement allows a more continuous water production by allowing adsorption of water vapour from the evaporator 120 into one adsorption chamber 130a, whilst allowing desorption of water vapour from the other adsorption chamber 130b into the condenser 140. In this system, whilst the temperature parameters are generally similar to those described in relation to Figures 1-2, some of the time required to heat / cool one of the adsorption chambers 130a can be used to cool / heat the other adsorption chamber 130b. However, this approach is still time consuming due to the heating and cooling cycles of each sorption bed, and inefficient due to the large amount of energy required to each sorption bed 131 a, 131b during each cycle.

[0183] This inefficient temperature swing approach is represented in Figure 5 showing the temperatures of: (a) the evaporator, (b) and (c) the two sorption beds, and (d) the condenser, of the system of Figure 4. This represents computational data that illustrate a temperature swing of around 45°C between heating and cooling each sorption bed 131 a, 131b during each cycle.

[0184] Figures 6(a) and 6(b) illustrate the performance (using Specific Daily Water Production (SDWP) in [kgwater kgSiiicage1day-1] and the dimensionless Performance Ratio (PR)) based on mathematical model predictions, of the system of Figure 4, when silica gel is used in the sorption bed.

[0185] The Specific Daily Water Production (SDWP) in [kgwater kgSiiicage1day-1] is defined using equation (1):

[0186] Where QCOnd is the condensation heating power in [kW], Lwater is the latent heat of water in [kJ] at TCOndenser, mSiiicagei the dry mass of silica gel loaded in SB in [kg] and N is the number of cycles per day.

[0187] The dimensionless Performance Ratio (PR) is defined using equation (2):

[0188] Where Qheat is the heating power to the SB in [kW], Lwater is the latent heat of water in [kJ] at TCOndenser and rhdist is the mass flow rate of pure water (distillate) produced in [kg s’1].

[0189] These results from mathematical models of a heat-integrated conventional process are the maximum achievable with silica gel. High TSB (still <60°C) and very long half-cycle times (e.g. 600s) lead to reaching SDWP ~6 and PR -0.49.

[0190] Figure 7 shows a desalination system 210 according to a first embodiment.

[0191] The system 210 of Figure 7 is generally similar to the system 10 of Figures 1-2, like parts denoted by like numerals, but incremented by ‘100’.

[0192] In the embodiment of Figure 7, the system 210 has a single adsorption chamber 230, as in Figures 1-2, which is therefore operated intermittently. In this embodiment, the system 210 is operated by actuating adsorption and desorption in the sorption chamber 230 via a pressure swing, rather than a temperature swing as operated in the system 10 of Figures 1-2. Advantageously, because the sorption chambers 230 is not subjected to repeated cycles of high and low temperatures, the main source of heat needed to operate the system does not require the same power levels as in a conventional facility, and “low grade” heat can be used in order to power the desalination water purification system 210.

[0193] The evaporator 220 is heated to Tevwhich is sufficient to generate water vapour, in this embodiment about 38.5°C.

[0194] In this embodiment, the sorption bed 231 is maintained at adsorption temperatures TSB, which is greater than Tev. Advantageously, Tss is between 0.5°C and 15°C greater than Tev, e.g. between 1°C and 10°C greater than Tev. In this embodiment, TSB was set at about 48°C. Advantageously, setting TSB higher than, but close to, Tevprovides a significant advantage in the amount of water produced. Setting TSB higher than Tevensures that condensation of water vapour in the adsorption chambers 230 is avoided, thus minimising or preventing damage to the sorption bed 231. Setting Tevrelatively close to TSB maximises the amount of water vapour generated in the evaporator 220, thus improving efficiency. It may also reduce or minimise the amount of time required to reach pressure equilibrium between the evaporator 220 and the adsorption chamber 230, thus further improving efficiency.

[0195] In a first step, fluid communication is provided between the evaporator 220 and the adsorption chamber 230 comprising the sorption bed 231, by opening first valve 225 in first conduit 226. This allows the water vapour from the evaporator 220 to the adsorption chamber 230 where it is adsorbed on the sorption bed 221. In this stage the second valve 235 between the adsorption chamber 230 and the condenser 240, is closed.

[0196] Subsequently, once the sorption bed 231a is adsorbed with water vapour, first valve 225 is closed, thus closing respective conduit 226.

[0197] Then, second valve 235 is opened to allow water vapour to desorb from the sorption bed 231. Because the condenser 240 is at a condenser temperature TCOnd, wherein TCOnd is less than TSB, opening second valve 235 causes desorption from the sorption bed 231 due to the difference in the water pressure between the sorption bed 231 and the condenser 240. The present system and method allow more efficient water production by controlling successive cycles of adsorption and desorption through pressure switches in the adsorption chamber 230, rather than temperature switches.

[0198] This allows much shorter cycles than using a conventional method. Using the system of Figure 7, each half cycle was around 60s, whilst a method described in Figure 3 had a half cycle of around 600s.

[0199] Figures 8(a)-8(c) show the measured temperatures and pressures of the various elements of the system of Figure 7. As can be seen, using the present methodology, the lowest temperature is that of the condenser TCOnd. Importantly, as explained above, Tev. Is lower, but close to TSB which is kept constant, the slight changes in the temperatures of the sorption bed TSB being due to the pressure equilibrium being reached with the evaporator and the condenser upon each adsorption / desorption cycle.

[0200] Figures 9(a) and 9(b) shows experimental results comparing the performance of a system according to Figures 1-2 using a conventional method, and a system according to the embodiment of Figure 7. The measurement parameters used for this comparison were the Specific Daily Water Production (SDWP) in [kgwater kgsilicagel-1day-1] and the dimensionless Performance Ratio (PR). While the SDWP is an indicator of productivity, the PR is an indicator of energy efficiency. Figure 9 shows the clear advantage from operating the AD system 210 according to the method described above both in amount of water produced (due to much shorter cycle times) and overall energy efficiency, even when using similar TSB.

[0201] Figure 10 shows a desalination system 310 according to a second embodiment.

[0202] The system 310 of Figure 10 is generally similar to the system 110 of Figure 4, like parts denoted by like numerals, but incremented by ‘200’. However, the system 310 of Figure 10 is operated in similar fashion to the system 210 of Figure 7, albeit continuously rather than intermittently.

[0203] In the embodiment of Figure 10, the system 310 has two adsorption chambers 330a, 330b, in order to permit continuous water production by allowing adsorption of water vapour from the evaporator 320 into one adsorption chamber 330a, whilst allowing desorption of water vapour from the other adsorption chamber 330b into the condenser 340.

[0204] In this embodiment, the system 310 is operated by actuating adsorption and desorption in the sorption chambers 330a, 330b via a pressure swing, rather than a temperature swing as operated in the system 110 of Figure 4. Advantageously, because the sorption chambers 330a, 330b are not subjected to repeated cycles of high and low temperatures, the main source of heat needed to operate the system does not require the same power levels as in a conventional facility, and “low grade” heat can be used in order to power the desalination water purification system 310.

[0205] The evaporator 320 is heated to Tevwhich is sufficient to generate water vapour, in this embodiment about 38.5°C.

[0206] In this embodiment, both first sorption bed 331a and second sorption bed 331 b are maintained at respective adsorption temperatures TSBI , TSB2 which are greater than Tev. Advantageously, TSBI and TSB2 are between 0.5°C and 15°C greater than Tev, e.g. between 1 °C and 10°C greater than Tev. In this embodiment, TSBI and TsB2were set at about 38.5°C. Advantageously, setting TSBI and TSB2 higher than, but close to, Tevprovides a significant advantage in the amount of water produced. Setting TSBI and TSB2 higher than Tevensures that condensation of water vapour in the adsorption chambers 330a, 330b is avoided, thus minimising or preventing damage to the sorption bed 331a, 331 b. Setting Tevrelatively close to TSBI and TSB2 maximises the amount of water vapour generated in the evaporator 320, thus improving efficiency. It may also reduce or minimise the amount of time required to reach pressure equilibrium between the evaporator 320 and the adsorption chambers 330a, 330b, thus further improving efficiency.

[0207] In a first step, fluid communication is provided between the evaporator 320 and the first adsorption chamber 330a comprising the first sorption bed 331a, by opening first valve 325a in first conduit 326a. This allows the water vapour from the evaporator 320 to the first adsorption chamber 330a where it is adsorbed on the sorption bed 321a.

[0208] At the same time, fluid communication is provided between the second adsorption chamber 330b comprising the second sorption bed 331b and the condenser 340, by opening fourth valve 335b in fourth conduit 336b. This allows the water vapour which has been adsorbed in the second sorption bed 331 b to be desorbed and condensed on the condenser 340. Because the condenser is at a condenser temperature TCOnd, wherein TCOnd is less than TSB1and TSB2opening fourth valve 335b causes desorption from the second sorption bed 331b due to the difference in the water pressure between the second sorption bed 331b and the condenser 340. In this embodiment, TCOnd was at ambient temperature, in this case at about 23.5°C.

[0209] During the above step, second valve 335a within second conduit 336a provided between the first adsorption chamber 330a and the condenser 340, and third valve 325b within third conduit 326b provided between the evaporator 320 and the second adsorption chamber 330b, are both closed.

[0210] Subsequently, once the first sorption bed 331a is adsorbed with water vapour, and the second sorption bed has been desorbed, first valve 325a and fourth valve 335b are closed, thus closing respective first and fourth conduits 326a, 336b.

[0211] Then, second valve 335a is opened to allow water vapour at to desorb from the first sorption bed 331a. Because the condenser 340 is at a condenser temperature Tcond, wherein TCOnd is less than TSB1and TSB2opening second valve 335a causes desorption from the first sorption bed 331a due to the difference in the water pressure between the first sorption bed 331a and the condenser 340.

[0212] At the same time, third valve 325b is opened to provide fluid communication between the evaporator 320 and the second adsorption chamber 330b comprising the second sorption bed 331b. This allows the water vapour from the evaporator 320 to the second adsorption chamber 330b where it is adsorbed on the sorption bed 331a.

[0213] The present system and method allow more efficient water production by controlling successive cycles of adsorption and desorption through pressure switches in the adsorption chambers 330a, 330b, rather than temperature switches.

[0214] This allows much shorter cycles than using a conventional method.

[0215] Experimental system

[0216] The experimental AD system described in relation to Figure 10 was set up using four 316L stainless steel vessels 330a, 330b embedding two sorption beds (SBs) 331 a, 331b, one evaporator 320 and one condenser 340. Inside each vessel, one aluminium heat exchanger 332a, 332b is connected to the heating and cooling water system. Electro-pneumatic valves 325a, 325b, 335a, 335b (Pfeiffer Vacuum GmbH, Germany) connected each vessel to the evaporator and condenser. All fittings follow the ISO-KF standard for vacuum equipment. Pressure was measured in each vessel with pressure transducers (WIKA Alexander Wiegand SE & Co. KG, Germany, 0.25 % accuracy). Both the evaporator 320 and the condenser 340 feature viewports (Pfeiffer, Germany) to check the water level and the formation of vapour bubbles during evaporation. The evaporator and condenser were equipped with T-Type thermocouples (Omega Engineering, USA, 0.4 % accuracy) measuring the temperatures on both vapour and liquid phases. Additional thermocouples are at the outlet and inlet of all heat exchangers. The thermocouples were used to measure the temperature difference of the heating and cooling water supplied to the heat exchangers. The aluminium heat exchangers (RC Racing Radiators, Italy) in the SBs were filled with micro-porous beads of silica gel (Siogel Oker-Chemie GmbH, Germany), which had a diameter of 0.5-2.0 mm. Siogel silica gel is a benchmark material in AD. The silica gel beads was secured inside the heat exchanger with a 290 pm polymer mesh (Plastok Meshes & Filtration Ltd, UK) with an open area of 50%. Each heat exchanger had a weight of 226 g and is filled with 145 g of silica gel resulting in a metal to adsorbent weight ratio of about 1.6. The flowrates of the heating and cooling water loops were set by means of three rotameters (Nixon Flowmeters, UK, 1.6 % accuracy). The three temperatures (Tev, TCOnd, TSB) were set in three thermostatic baths (Julabo, Germany). All sensors were connected to data acquisition and control boards (Advantech Co. Ltd., USA) and monitored on a Labview software (National Instruments Corp., USA). The software was specifically designed to allow adjustments of the cycle times, actuation of all solenoid valves switching the heating and cooling water loops and of the electropneumatic valves.

[0217] Figure 11 is a graph representing computational data showing the temperatures of (a) the evaporator 320, (b) and (c) the two sorption bed 331 a, 331b, and (d) the condenser 340, of the system of Figure 10. As can be seen, the range of temperature of the sorption bed 331 a, 331b is much narrower than in Figure 5 (when using a conventional method as described with reference to Figure 4) thus improving efficiency and reducing cycles time. Although this graph shows relatively high Tevand TSB1and TSB2, (in order to permit representative comparison between Figures 5 and 11), the inventors found that these could be reduced, as shown in Figure 8, to further improve energy efficiency.

[0218] Figures 12(a) and 12(b) showing performance comparison (Specific Daily Water Production (SDWP) in [kgwater kgSiiicage1day-1] and the dimensionless Performance Ratio (PR)) based on mathematical model predictions, of the system of Figure 10. Figures 12(a) and 12(b) mark the maximum theoretical performance achievable in a process featuring two sorption beds and heat recovery. The comparison between Figure 12 and Figure 6 shows an improvement of the SDWP and PR across the whole temperature and half-cycle time ranges, with PR that can reach values beyond 0.9 if long half-cycle times are allowed. The trend of the PR is flat across the temperature range, showing that PR is independent of the regeneration temperature for a large range of half-cycle times. The results suggests there is no need to increase the regeneration temperature, unless seeking for an increase of the SDWP (pure water productivity).

[0219] Figure 13 shows the thermodynamic cycle during operation of one sorption bed during operation of the systems of Figures 7 and 10. Pvp(T) is the vapour pressure of the feed water solution at temperature T. The curves parallel to the vapour pressure curve mark the water isostere of the sorption bed, curves at constant water uptake 0 = q / qswhere q is the amount of water in the material in [kgwater / kgdrymateriai] and qsis the maximum amount of water the material can contain when it is saturated with water vapour.

[0220] Figure 14(a) to 14(c) show alternative embodiments 410,510,610 of a system according to the disclosure.

[0221] For the purpose of these illustrations, each of these systems is shown using a single sorption bed (430,530,630), as in the system 210 of Figure 7, but alternatively could include multiple sorption bed as described in Figure 10.

[0222] As shown in Figure 14(a), the system 410 has a heater 450 (H) which heats the heat exchanger 432 of sorption bed 430 first. Therefore, the temperature of heat exchanger 422 of the evaporator 420 to which heat is supplied after passing through heat exchanger 432 of sorption bed 430 is expected to be slightly lower than that of heat exchanger 432, meeting the requirements explained above in relation to Figure 7. A cooling system 460 (C) is connected to heat exchanger 442 of condenser 440 in order to dissipates heat at ambient temperature. Such cooler may or may not be required depending on the conditions of the system 410. However, the configuration of Figure 14(a) runs a low risk of condensation of water vapour from the evaporator 420 in the nanoporous material if heat transfer surfaces of the sorption bed 430 are not carefully designed.

[0223] In order to address this risk, the system 510 (like parts being denoted by like numerals, incremented by ‘100’) of Figure 14(b) has a cooler 562 with controllable heat power to allow to setting the inlet temperature of the heat exchanger 522 in the evaporator 520 at a specific value.

[0224] The system 610 (like parts being denoted by like numerals, incremented by ‘200’) of Figure 14(c) is another alternative in which the inlet temperature of the heat exchanger 622 in the evaporator 620 is controlled by using heat generated by the heat exchanger system of the condenser 640, using additional heat exchanger interface 670. This may provide additional energy efficiency by reducing loss of heat in different heat exchangers which are not otherwise connected.

[0225] Advantageously, the heater (450,550,650) comprises or is associated with a source of low grade heat supplying a temperature less than about 60°C, e.g. about 50°C, which may be an industrial facility such as a distillery, a brewery, a power plant, or the like.

[0226] It will be understood that the present embodiments are provided by way of example only, and that various modifications can be made to the present embodiments without departing from the scope of the invention.

Claims

CLAIMS:1 . A method of purifying water, the method comprising:(i) evaporating feed water in an evaporator to produce water vapour, wherein the evaporator is set at an evaporator temperature Tev;(ii) allowing the water vapour from the evaporator to an adsorption chamber comprising an adsorption apparatus, wherein the adsorption apparatus is set at a temperature TSB, wherein TSB is greater than Tev; and(iii) allowing the water vapour from the adsorption chamber to a condenser, wherein the condenser is set at a condensation temperature TCOnd, wherein TCOnd is less than TSB.

2. A method according to claim 1 , comprising repeating steps (i)-(iii).

3. A method according to claim 1 or claim 2, wherein TSB is set to be constant or substantially constant.

4. A method according to any preceding claim, wherein TCOnd is less than Tev.

5. A method according to any preceding claim, wherein Tevis between about 30°C and about 50°C, optionally between about 35°C and about 45°C.

6. A method according to any preceding claim, wherein TSB is between about 40°C and about 60°C, optionally between about 45°C and about 55°C.

7. A method according to any preceding claim, wherein TSB is between 0.5°C and 15°C greater than Tev, optionally between 1 °C and 10°C greater than Tev.

8. A method according to any preceding claim, wherein the method comprises supplying heat to the evaporator and / or to the adsorption apparatus, from a source of energy comprising or consisting of a low grade heat source.

9. A method according to any preceding claim, comprising performing step (i)-(iii) sequentially.

10. A method according to any of claims 1 to 9, wherein steps (i) and (ii) are performed concomitantly, and step (iii) subsequently.

11. A method according to any preceding claim, further comprising:(iv) ceasing fluid communication between the adsorption chamber and the condenser; and(v) recovering water from the condenser.

12. A method according to any preceding claim, wherein desorption of water vapour from the adsorption apparatus occurs via a pressure swing in the adsorption chamber during steps (ii) and (iii).

13. A method of purifying feed water, the method comprising:(i) evaporating feed water in an evaporator to produce water vapour, wherein the feed water is set at an evaporation temperature Tev;(ii) providing fluid communication between the evaporator and a first adsorption chamber comprising a first adsorption apparatus, thereby allowing the water vapor from the evaporator to the first adsorption chamber, wherein the first adsorption apparatus is set at a first adsorption temperature TSB1, wherein TSB1is greater than Tev;(ii-a) ceasing fluid communication between the evaporator and the first adsorption chamber;(iii) providing fluid communication between the first adsorption chamber and a condenser, thereby allowing the water vapor from the first adsorption chamber to the condenser, wherein the condenser is set at a condenser temperature TCOnd, wherein Tcond is less than TSB1;(iv) providing fluid communication between the evaporator and a second adsorption chamber comprising a second adsorption apparatus, thereby allowing the water vapor from the evaporator to the second adsorption chamber, wherein the second adsorption apparatus is set at a second adsorption temperature TSB2, wherein TSB2is greater than Tev;(iv-a) ceasing fluid communication between the first adsorption chamber and the condenser;(iv-b) ceasing fluid communication between the evaporator and the second adsorption chamber; and(v) providing fluid communication between the second adsorption chamber and the condenser, thereby allowing the water vapor from the second adsorption chamber to the condenser, wherein TCOnd is less than TsB2.

14. A system for purifying water, the system comprising; an evaporator configured to produce water vapour, wherein the evaporator is configured to be set at an evaporator temperature Tev; an adsorption chamber comprising an adsorption apparatus, wherein the adsorption apparatus is configured to be set at an adsorption temperature TSB, wherein TSB is greater than Tev; and a condenser, wherein the condenser is configured to be set at a condenser temperature TCOnd, wherein TCOnd is less than TsB.

15. A system for purifying water, the system comprising: an evaporator configured to produce water vapour, wherein the evaporator is configured to be set at an evaporator temperature Tev; a first adsorption chamber comprising a first adsorption apparatus, wherein the first adsorption apparatus is configured to be set at a first adsorption temperature TSB1, wherein TSB1is greater than Tev; a second adsorption chamber comprising a second adsorption apparatus, wherein the second adsorption apparatus is configured to be set at a second adsorption temperature TSB2, wherein TSB2is greater than Tev; and a condenser, wherein the condenser is configured to be set at a condenser temperature TCOnd, wherein TCOnd is less than TsB1and TSB2.

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