WO2019112492A1

WO2019112492A1 - Evaporative water desalination system, scale build-up prevention method in evaporative water desalination systems and use of water saturated with micro-nano bubbles

Info

Publication number: WO2019112492A1
Application number: PCT/SA2018/050029
Authority: WO
Inventors: Yousef AL YOUSEF; Filip HERMAN
Original assignee: New Energy Transfer Spolka Z Ograniczona; King Abdulaziz City for Science and Technology KACST
Current assignee: New Energy Transfer Spolka Z Ograniczona; King Abdulaziz City for Science and Technology KACST
Priority date: 2017-12-08
Filing date: 2018-11-25
Publication date: 2019-06-13
Anticipated expiration: 2020-06-08
Also published as: WO2019112492A4; PL238498B1; PL423783A1

Abstract

The substance of the invention is the evaporative water desalination system, the method of preventing scale deposition in desalination system and usage of water saturated with micro- nano bubbles in evaporative desalination systems. The system according to the invention comprises the saline make-up water preparation tank (4) connected by the pipeline (12) equipped with the pumping system (14) with the evaporative desalination system (6) comprising the distillate discharge system (5) and the brine discharge system (7), comprising the gas source (1) connected by the pipeline (8) with the gas preparation station (2) connected by the pipeline (9) with MNB generator (3) connected with the pipeline (10) with the saline make-up water preparation station (4).

Description

Evaporative water desalination system, scale build-up prevention method in evaporative water desalination systems and use of water saturated with micro-nano bubbles

The subject of the invention is an evaporative water desalination system, a scale build-up prevention method in evaporative water desalination systems and a use of water saturated with micro-nano bubbles in evaporative desalination systems.

The invention belongs to the field of water desalination systems .

Due to an increased risk of scale deposition on a heat exchanging surface, evaporative desalination systems require a pretreatment of saline feed water. This is connected with formation of carbonates and build-up thereof in a system resulting from saline feed water degassing and separation of carbon dioxide which is removed outside through a vacuum system. Moreover, sulfur and magnesium compounds existing in the saline feed water have properties of effective scale deposition on heat exchanger tubing. Conventional desalination systems rely on adding inhibitors to a saline feed water, usually at the level of 5ppm of the saline water intake. Moreover, a maximum temperature of multi-stage evaporative system operation being approximately 70°C is defined by a chemical composition of feed water, since above this temperature a risk of scaling in heat exchanger piping is very high. The abovementioned circumstances render a continuous operation of evaporative water desalination systems impossible. Operation downtimes result from a necessity to conduct periodic maintenance procedures. Moreover, a solution relying on a dosage of inhibitors aiming at slowing down scale formation and deposition process in desalination system is a costly procedure. Aiman Eid A1. -Rawaj feh, Albara I. Alrawashdeh, Maha Al- Shabatat and others in their article „Inhibitory effect of Hydrex anti-sealant on calcium scale deposition from seawater under multiple-effect distillers' conditions" describe studies aiming at reducing a risk of scale deposition on heat exchanging surfaces leading to efficiency improvement of multiple-effect sea water desalination systems. In the research, a commercial anti-sealant Hydrex 9202 manufactured by Veolia has been used and, depending on a dosage, has inhibited ions of calcium, carbonates and sulfur and contributed to fixing in the solution the carbon dioxide which in turn contributes to forming a scale on heat exchanging surfaces when released from the solution. The substance has been dosed in a concentration ranging from 2ppm to 8ppm and the best results have been obtained at 5ppm. The difference between the present invention and the state of art is that neutral micro-nano bubbles (MNB) are dosed instead of chemicals to influence the inhibition of the ions of calcium, sulfur and carbonates and maintain a solubility of carbon dioxide in the solution. The saline water is saturated with micro-nano bubbles before the intake to MED system using the oxygen, ozone or carbon dioxide.

A.E. A1. -Rawaj feh, H.E.S. Fath i A.A. Mabtouk in their article „Integrated Salts Precipitation and Nano-Filtration as Pretreatment of Multistage Flash Desalination System" describe an application of nano-filtration membranes to lower the concentration of calcium carbonate and sulfur in the saline water delivered to the system, which led to reducing the concentration of sulfur ions by 95% and calcium carbonate by 37% in a stream of saline water delivered for thermal desalination. Although it has nearly doubled the efficiency of desalination process by increasing a maximum temperature of system operation, it has not eliminated a necessity of using chemicals. The difference between the present invention and the state of art is that a dosage of chemicals has been eliminated completely and no element to be replaced due to nanoflitration membrane deterioration or cleaning is applied to the system.

T. Okazaki, Z. Kawara, T. Yokomine and others in their article Enhancement of MSF Using Microbubbles" investigate an efficiency of evaporation in one of thermal desalination methods based on application of micro bubbles to the saline make-up water delivered to the system with the smallest bubble diameter of 0.05mm. The application thereof allowed to improve the evaporation efficiency ratio, so that at superheating by 7.3°C a similar effect has been obtained to one, when superheating by 11°C without application of micro bubbles. The difference between the present invention and the state of art is the bubble generation technology since the smallest bubble dimeter in MNB technology is 0.005mm, i.e. ten times less than in micro bubble technology which results in more intensive atomization and substantial increase of water/gas heat exchange surface .

Patent application No. CN106944400 (A) by ZHANG TIANZHU; ZHANG HUI JUAN; XUE XIAOLI; YANG WENHUA; WU NA; ZHAO YUEGANG; REN QIANG describes a method of cultural relics cleaning by spraying the water with dissolved MNB particles using a hand held spray gun. The difference between the present invention and the state of art is that a mixture of make-up water and MNB is fed to water desalination system with the purpose of improving the efficiency and reliability of evaporative desalination process at a pressure lower than atmospheric pressure .

Patent application No. WO2017127636 (Al) USE OF MICRO AND NANO-BUBBLES IN LIQUID PROCESSING by AMAMCHARLA JAYENDRA [US]; LI BINGYI [US]; LIU ZHE [US] presents application of MNB to a liquid with a purpose to reduce its viscosity and eventually reduce pumping costs. This solution is especially well suited for a food industry (for example pumping of milk) thanks to a favorable influence of MNB on dissolving of milk additives while reducing pumping costs. The invention provides dosing of MNB to a low viscosity liquid containing over 90% of pure water to maximize a heat exchange as well as cleaning and disinfecting properties .

The present invention, unlike other known from the prior art and conventionally used chemical dosing stations (for example inhibitors), utilizes MNB (Micro Nano Bubble) technology based on saturating a saline make-up water with bubbles of oxygen, ozone, carbon dioxide or a mixture thereof, having a diameter of less than 0.1mm to reduce scale formation and improve energy efficiency of a system. Breaking micro-nano bubbles generate ultrasonic waves having a cleaning effect on all solid surfaces. Breaking of micro-nano bubbles results in emergence of OH* hydroxyl radicals being very strong oxidants, stronger than ozone and atomic oxygen. Hydroxyl radicals destroy all microorganisms such as bacteria or viruses and have a positive effect on an existing scale - breaking MNB' s mechanically clean a heat exchanging surface by protecting it against build-up of carbonates and similar scale forming minerals as well as protecting from formation of biofilms. Additionally, presence of MNB' s in water changes a solubility of minerals and shifts a saturation point thereof, thus greatly benefiting evaporative desalination systems. In the same time, radicals emerging at MNB breakdown enhance evaporation due to a large number of nucleation sites in water.

In MSF (Multi Stage Flash) systems a temperature of saline make-up water supplied to effects is always higher than a temperature of saturation, therefore it is a superheated saline water which has to be cooled down so that it is delivered to heat exchange tubes at the temperature of saturation of given MED effect in order to condensate a vapor flowing inside tubes and not to superheat it. Whereby a superheated make-up water is evaporated before getting to heat exchanger tubes after its prior saturation with MNB and atomization in spray nozzle, the production of distillate increases by 4.3% which in case of a system having an output of 100.000m³ per day results in additional production of 4.300 m³ of distillate from the same amount of energy supplied to a multi-effect evaporation system.

The substance of the present invention is an evaporative water desalination system comprising a saline make-up water preparation tank connected by a pipeline including an integrated pumping system to an evaporative desalination system containing a distillate discharge system and a brine discharge system, characterized by that it contains a gas source connected by a pipeline with a gas preparation station connected by a pipeline with MNB generator connected by a pipeline with a saline make-up water preparation station.

In a favorable embodiment the source of gas is an air inlet unit or gas tanks.

The substance of the present invention is a method of preventing a scale build-up in evaporative desalination installations specific in that a saline make-up water is supplied to a make-up water preparation tank through a pipeline connected to a water intake from a water basin or tank and a pumping system, wherein its saturation with micro-nano bubbles (MNB) occurs through a MNB generator. After being saturated with MNB in a saline make-up water preparation tank, a make-up water is supplied through a pipeline by a circulation pump to an evaporative desalination system.

The substance of the present invention is that a mixture of water and salt saturated with bubbles of ozone or oxygen or carbon dioxide with diameters not exceeding 0.1mm in the range from 2mg/kg to 5mg/kg of saline water is used in an evaporative water desalination process, by using a mixture of water and salt as a substrate for desalinated water (distillate) production . The solution according to present invention consists of MNB application to a desalination system has the advantage that, apart from having a function of atomizing the saline make-up water intake, micro-nano bubbles provide an accumulated energy which generates an additional stream of energy resulting from a breakage of bubbles. The substance of the present invention is that an atomizing chamber is connected with an evaporation chamber and a spray and tray heat exchanger, thus enhancing a vapor generation in a multi-stage evaporation system by over 4% compared to MSF without MNB system.

Positive effects, mainly connected with cleaning properties and heat exchange efficiency improvement can also be noticed in other evaporative systems, like MED (Multi Effect Desalination) where positive effects are obtained in connection with improved availability and limitation of energy consumption by water desalination system.

A usage of MNB allows to substantially limit maintenance procedures and reduce system downtimes for maintenance purposes from 14 days to 2 days i.e. sevenfold. In case of a system with a production capacity of 100,000 m³ per day it will result in a yearly increase of distilled water production by 1,200,000 m³ while reducing financial expenditures for chemicals added to a make-up water thus successfully providing investment spending for system upgrading.

With an average cost of chemicals at the level of $0.04 per 1 ton of desalinated water a yearly saving of $1,452,000 can be obtained in case of a system with a production capacity of 100, 000 m³ per day due to chemicals saving only while an increase of water production capacity is an added value.

MNB's can be produced in many different ways. One of the most popular is carried out as follows: In a gas source an ambient air is sucked from the outside by an intake fan through filtering layers. A gas source has an option of gas uptake from cylinders which can be used for transporting a gas to a system operation site. A gas collected from a source is delivered through a gas pipeline to a gas preparation station where three subsequent processes are carried out to prepare a gas for a process of saturating a saline make-up water with micro-nano bubbles (MNB) . In the most popular case a gas is firstly dehumidified with a use of a sorption technology through absorbing a humidity by an activated carbon. Afterwards a dry gas is supplied to an oxygen separator where a pure oxygen is obtained. In case of ozone bubbles injection, a pure oxygen is delivered to ozone generator where a pure ozone is produced from the supplied oxygen. In case of using carbon dioxide micro- nano bubbles, gas cylinders are delivered and connected to a system in a gas source, bypassing a gas preparation station. A prepared gas is further transported through a gas pipeline to MNB generator which compresses a prepared gas and transports it through a gas pipeline to a make-up water preparation tank. The saturation process itself takes place in the tank using a device resembling a shell-and-tube heat exchanger, where the saline make-up water is directed into the tube space, whilst the previously prepared pressurized gas is supplied by the gas pipeline to the extratubular space. The tubes are made of membranes which allow the gas to pass from the extratubular space to the saline water flowing inside the tubes. As a result of mixing the gas with the saline water and earlier application of gas under the overpressure conditions, bubbles are formed with diameters of 0.1mm and less. Since a volume of gas supplied to the saline water depends on the volume of saline water subject to desalination process and not the salt content, the valve which doses the gas to MNB generator is adjusted in such a way that approximately 5mg of gas are added to each kilogram of saline water. The saline water itself, containing a particulate matter at a level of approximately 42g/kg of water, is supplied by the pipe line equipped with the circulation pump to the make-up water preparation tank, to be eventually saturated with the gas.

The system according to the invention is depicted on the drawing (Fig.l) which presents a block diagram of the water desalination system according to the invention.

Example 1

The implementation example of the system according to the invention provides the ambient air supply from the gas source (1) being an atmospheric air intake. The gas source (1) is equipped with filtration layers being removable filters and centrifugal fan sucking the air from the outside. The gas source (1) is connected by the PVC pipeline (8) with the gas preparation station (2) where a sequence of gas preparation processes take place to prepare the gas to the process of saline make-up water saturation with micro-nano bubbles (MNB) . Firstly, the gas is dehumidified with a use of a sorption technology through absorbing a humidity by an activated carbon. Afterwards it is supplied by the pipeline to adsorption oxygen separator, where the pure oxygen is obtained. The oxygen generator directly feeds the ozone generator. The gas preparation station (2) is connected by the PVC gas pipeline (9) with MNB generator (3) and by the PVC gas pipeline (10) with the saline make-up water preparation tank (4) . The saline make-up water preparation tank is made of duplex steel 1.4404 and has a volume of 6m³. As a result of mixing the gas with the saline make-up water and earlier application of gas under the overpressure conditions, the bubbles have been formed with diameters of 0.1mm and less Since a volume of gas supplied to the saline make-up water depends on the volume of saline water subjected to desalination process and not the salt content, the valve which doses the gas to MNB generator (3) is adjusted in such a way that approximately 5mg of gas are added to each kilogram of make-up water. The saline make-up water itself, containing a particulate matter at a level of approximately 42g/kg of water, is supplied by the PVC pipeline (11) equipped with the circulation pump (13) to the make-up water preparation tank (4), where the saturation with the gas takes place. The saline make-up water preparation tank (4) provides the make-up water enriched with MNB' s to the evaporative water desalination system (6) based on MED (Multi Effect Desalination) technology through the PVC water pipeline (12) equipped with the pump (14) . During the evaporation process, resulting from decompression, micro-nano bubbles allow the atomization of sprayed make-up water and substantially increase the surface of effective heat exchange thus increasing the process efficiency. The evaporative water desalination system (6) is equipped with the fiberglass distilled water pipeline (7) used for distillate discharge and the PVC brine discharge pipeline (5) used for discharging a concentrated brine after the distillate separation process.

The advantage of this solution is that micro-nano bubbles are generated in a device comprising no moving parts which substantially simplifies the operation and eliminates a risk of the aggressive brine contacting rotary elements of centrifugal generators. Moreover, saturating a saline make-up water delivered to evaporative desalination systems reduces the need for using chemicals, shortens the system downtimes for maintenance purposes and improves the efficiency of thermal exchange due to the atomization of saline make-up water supplied to the system and substantial enlargement of effective heat exchange surface. The production of distilled water in the described system increases from 123t per day to 128, 7t per day with the same energy input whilst reducing the downtimes of the evaporative water desalination system (6) from 10 days per year to 2 days per year which additionally increases the yearly distillate production volume by 2.3% and reduces the financial expenditures for chemicals necessary for preparation of make up water.

Example 2

The implementation example of the system according to the invention provides the ambient air supply in the gas source (1) through the filtration layers via the fan sucking the air from the outside. The air taken from the source (1) is supplied by the gas pipeline (8) to the gas preparation station (2), where a sequence of gas preparation processes take place to prepare the gas to the process of make-up water saturation with micro- nano bubbles (MNB) . Firstly, the gas is dehumidified with a use of a sorption technology through absorbing a humidity by an activated carbon. Afterwards the dried gas is supplied to the oxygen separator, where the pure oxygen is obtained which in its turn is supplied to the ozone generator, where a pure ozone is produced from the supplied oxygen. The prepared gas is transported by the gas pipeline (9) to MNB generator (3) which compresses the prepared gas and transports it by the gas pipeline (10) to the saline make-up water preparation tank (4) . The saturation itself takes place in the tank (4) using a device resembling a shell-and-tube heat exchanger, where the saline make-up water is directed into the tube space, whilst the previously prepared pressurized gas is supplied by the gas pipeline (10) to the extratubular space. The tubes are made of membranes which allow the gas to pass from the extratubular space to the saline water flowing inside the tubes. As a result of mixing the gas with the saline water and earlier application of gas under the overpressure conditions, bubbles are formed with diameters of 0.1mm and less. Since a volume of gas supplied to the saline water depends on the volume of saline make-up water subject to desalination process and not the salt content, the valve (3) which doses the gas to MNB generator is adjusted in such a way that approximately 5mg of gas are added to each kilogram of saline make-up water. The make-up water itself, containing a particulate matter at a level of approximately 42g/kg of water, is supplied by the pipe line (11) equipped with the circulation pump (13) to the saline make-up water preparation tank (4), to be eventually saturated with the gas. The make-up water saturated with micro-nano bubbles is thus delivered to the Evaporative Water Desalination System (6) and subjected to evaporation process. The evaporation occurs as a result of flashing effect as well as heating of the saline make up water saturated with micro-nano bubbles on the surface of the tube heat exchanger. With regard to a possibility of scaling on heat exchangers' surfaces due to precipitation of salts from the saline water during heat reception as well as degassing in desalination system, micro-nano bubbles contained in the saline water break at a contact with heat exchanger surface or other elements of heat exchanger chamber, thus generating an ultrasonic wave which efficiently breaks down any scale formed on heat exchanging surfaces. In addition to that, following the breakage of bubbles, metal heat exchange surfaces are subject to additional oxidation which provides an additional reinforcement of metal structure in the breakage area and complete protection thereof against potential effects of cavitation .

The advantage of this solution as a possibility to clean heat exchange surfaces and inner elements of a heat exchanger and protect them against scaling is that a necessity of using chemicals can be fully eliminated. Additionally, a protection of the above-mentioned surfaces is provided, thus reducing costs resulting from system downtimes due to maintenance works as well as costs of regular purchases of chemicals. A significant advantage is a fact of constant protection and cleaning of heat exchange surfaces and inner elements of heat exchanger allowing to increase a maximum temperature of evaporation which has been reduced up to now due to a substantial risk of scale formation. Additionally, a ratio of distillate recovery from a saline water will be increased from the present 35% to 60 which means that whilst 0.35 kg of distilled water is currently recovered from 1 kilogram of saline water, 0.6 kilogram of distilled water will be obtained from 1 kilogram of saline water after implementation of the proposed technology. In the above described example, the application of MNB resulted in removal of 1.5mm thick scale formed on the tube surface in a time shorter fourfold (15 minutes instead of 1 hour) while leaving a protective layer effectively preventing a scale formation. With no MNB applied no scale reduction on the tube surface was observed.

Example 3

Ihe example of using a mixture of water and salt saturated with ozone bubbles, wherein the saturation occurs in the tank (4) with the use of device in the shape of shell-and-tube heat exchanger wherein the saline water taken from the Persian Gulf is directed to the tube space whilst the previously prepared pressurized gas is supplied to the extratubular space by the gas pipeline (10) . The tubes are made of membranes which allow the gas to pass from the extratubular space to the saline water flowing inside the tubes. As a result of mixing the gas with the saline water and earlier application of gas under the overpressure conditions, bubbles are formed with diameters of 0.1mm and less. Since a volume of gas supplied to the saline water depends on the volume of saline make-up water subject to desalination process and not the salt content, the valve (3) which doses the gas to MNB generator is adjusted in such a way that approximately 5mg of gas are added to each kilogram of saline water. The saline make-up water itself, containing a particulate matter at a level of approximately 42g/kg of water, is supplied by the pipe line (11) equipped with the circulation pump (13) to the saline make-up water preparation tank (4), to be eventually saturated with the gas. Feeding of Evaporative Water Desalination System on a continuous basis with a mixture of saline water and micro-nano bubbles has resulted in the absence of scale deposits on heat exchange surfaces over the yearly cycle of the system operation.

Claims

1. Evaporative water desalination system comprising a saline make-up water preparation tank (4) connected by a pipeline (12) featuring a pumping system (14) with the evaporative desalination system (6) comprising a distillate discharge system (5) and a brine discharge system (7) specific with that it contains a gas source (1) connected by a pipeline (8) with a gas preparation station (2) connected by a pipeline (9) with the MNB generator (3) connected by a pipeline (10) with a saline make-up water preparation tank (4) .

2. System according to Claim 1 specific with that a source of gas (1) is the air intake or the gas tanks.

3. Method of preventing a scale deposition in evaporative water desalination systems specific with that the saline make-up water is supplied to the saline make-up water preparation tank (4) by a pipeline (11) connected to the water intake from the water basin or water tank and pumping system (13) where it is saturated with micro-nano bubbles

(MNB) by the MNB generator (3) . The saline make-up water after being saturated with MNB in the saline make-up water preparation tank (4) is supplied by a pipeline (12) equipped with a circulation pump (14) to the evaporative desalination system (6) .

4. Usage of water and salt mixture containing from 2mg to 5mg of ozone or oxygen or carbon dioxide bubbles, with diameters not exceeding 0.1mm, per 1 kilogram of saline water in the process of evaporative water desalination by utilizing the water and salt mixture as a substrate for production of desalinated water - distillate.