FIELD OF INVENTION

The present invention relates to a method for concentrating brine.

More particularly, the present invention relates to a method for concentrating brine by means of a desalination process.

BACKGROUND TO INVENTION

According to literature, brine is water, saturated or nearly saturated with salt (usually sodium chloride). Furthermore, natural brine wells are the source of a large percentage of the world's bromine, lithium, and boron and lesser amounts of potash, trona (sodium carbonate), Glauber's salt (sodium sulfate), and magnesium. In addition, artificial brines are produced by dissolving formations containing soluble minerals such as halite (rock salt; sodium chloride), potash, trona, and boron.

For various reasons, brine needs to be concentrated. However the known methods for concentrating brine are not sufficient as they do not provide the required concentrations or are uneconomically and energy inefficient.

It is an object of the invention to suggest a method for concentrating brine which will assist in overcoming these problems.

SUMMARY OF INVENTION

According to the invention, a method for concentrating brine includes the steps

(a) of concentrating brine by means of freeze desalination to form concentrated brine and separated ice crystals representing the desalinated water; and

(b) of melting the separated ice crystals by means of the hot side of a refrigeration system. Also according to the invention, a method for concentrating brine includes the steps

(a) of concentrating brine by means of freeze desalination to form concentrated brine and separated ice crystals representing the desalinated water; and

(b) of utilising the separated ice crystals as cooling of processes and/or cooling of a mine.

Yet further according to the invention, a arrangement for concentrating brine includes

(a) freeze desalination means adapted to form concentrated brine and separated ice crystals representing the desalinated water; and

(b) cooling and/or melting means adapted to utilise the separate ice crystals.

The cooling and/or melting means may include the hot side of a refrigeration system and/or cooling in processes and/or cooling of a mine.

The methods may include the step of treating the concentrated brine in an eutectic freezing process to remove salt crystals by means of the reduction of brine temperatures.

The methods may be adapted to optimize energy usage and/or improve operational energy cost to a minimum.

The methods may be adapted to allow for the production and storage of ice in the form of "cold" energy, also called Thermal Energy Storage (TES).

The stored energy may be used to cool down mines, buildings or any process or environment..

Heat may be recovered by means of the refrigeration system both by means of de- superheating hot gas, or by means of an oil cooling system.

Depending on the application, heat recovery may also be achieved by means of a condenser, and may be used to increase the temperature of bulk low salinity dam water to optimize evaporation in such dams.

The arrangement may be adapted to be used for a continuous process. The method may be a continuous process. BRIEF DESCRIPTION OF DRAWING

The invention will now be described by way of example with reference to the accompanying schematic drawing.

In the drawing there is shown a schematic layout of a method for concentrating brine in accordance with the invention.

DETAILED DESCRIPTION OF DRAWING

Referring to the drawing, a method for concentrating brine in accordance with the invention is shown.

A method for concentrating brine in accordance with the invention includes the steps

(a) of concentrating brine by means of freeze desalination to form concentrated brine and separated ice crystals representing the desalinated water; and

(b) of melting the separate ice crystals by means of the hot side of a refrigeration system.

Also a method for concentrating brine in accordance with a second embodiment of the invention includes the steps

(a) of concentrating brine by means of freeze desalination to form concentrated brine and separated ice crystals representing the desalinated water; and

(b) of utilising the separate ice crystals as cooling of processes and/or cooling of a mine.

The methods include the step of treating the concentrated brine in an eutectic freezing process to remove salt crystals by means of the reduction of brine temperatures.

The methods are adapted to optimize energy usage and/or improve the operational energy cost to the minimum.

The methods are adapted to allow for the production and storage of ice in the form of "cold" energy, also called Thermal Energy Storage (TES). The stored energy can be used to cool down mines, buildings or any process. This is often called demand side management and could be used to manage peak demand power by means of the storage of energy in the form of ice.

Heat can be recovered by means of the refrigeration system both by means of de- superheating the hot gas, or by means of the oil cooing system.

Depending on the application, heat recovery is also be achieved by means of the condenser, and may be used to increase the temperature of bulk low salinity dam water to optimize the evaporation in such dams.

This allow the Mine, process or facility to provide cooling and at the same time provide water treatment in the form of a concentrated brine that could be processed further to commercially exploit the extraction of different salts.

Mine water, industrial effluent, acid mine water drainage, toxic effluent from mine or industrial processes are all applications where the methods according to the invention can be used to treat the water by means of the freezing of fresh water and filtering of the pure ice from the dirty stream, resulting in the concentration of the resultant stream to higher salt concentrations.

The concentrate is then further treated by means of an eutectic freezing process, where the brine is reduced in temperature even further to facilitate the freezing separation of salt crystals from the brine stream.

The different salt crystals can be removed by means of temperature regulation and reduction of brine temperatures to extract as much as possible of different salt from the stream.

The system therefore achieves the following:

(a) Brine concentration by means of the removal of ice with freeze desalination process;

(b) Production of desalinated water to allow further processing into industrial or potable water; (c) Eutectic Freezing to facilitate the extraction of different salts at different brine temperatures;

(d) The removal of salts allow the possibility to commercially exploit the salt harvested from the brine; and/or

(e) The volume of brine reduced to a smaller volume that could be treated further.

The main objective of the invention is to treat waste water streams and produce desalinated water at the lowest cost possible and produce a concentrated brine. Further cooling of brine will facilitate the separation of salt crystals called Eutectic Freezing.

At the same time we are able to provide Thermal Energy Storage (TES) for the use in mine cooling, air-conditioning or process cooling.

Heat is available from the refrigeration system by means of the recovery of high temperature superheated ammonia and oil cooling. We also have heat available by means of the removal of heat in the condensation process of ammonia in the refrigeration cycle. This heat could be used in any process required.

This provides a holistic approach to power management and savings that will benefit the power usage more than an individual approach to desalination.

The objective not only provide an holistic approach to desalination, brine concentration and eutectic freezing and removal of salt crystals from a concentrated brine solution to be commercially exploited . The arrangement also allows to manage energy usage by means of a Thermal Energy Storage (TES) system. Heating and cooling is available by means of the recovery of heat available from the refrigeration system and the ice produced allows for the cooling of the mine, process or building. The melted ice from this process is the desalinated water that could be recovered for operational purpose.

The principle operation is based on freeze desalination, where most of the salt is removed from the brine.

Ice crystals are formed in a heat exchanger (EverTube™).The microscopic ice crystals are then delivered to a large separation tank and the pure ice crystals with low salt content separated from the brine and delivered to the thermal energy storage tank where the secondary load or other heat loads will melt the ice.

The water at low salt content could be further processed with a standard processes to produces potable water or used as industrial water.

The technology is simple in design and operation, and easy to maintain. Lower maintenance cost can be seen, because the first step of freeze desalination do not have filters and do not require cleaning. Thermal energy storage is not an unique concept. The difference with the EverTube™ generator is that it has the advantage to be up-scaled to very large capacities and manufactured cost effectively with a small foot print compared to conventional slurry systems on the market.

The system generally consists of the following main components:

A) Compressor , to increase the ammonia vapour pressure from a low pressure to a higher pressure

B) Heat exchanger for heat recovery, to recover heat from the superheated ammonia gas.

C) Shell and tube condenser, to condense the ammonia to a liquid form at a higher vapour pressure delivered by the compressor.

Dl) Heat exchanger to improve refrigeration system efficiency (COP, coefficient of performance) by sub-cooling the high pressure liquid ammonia to a lower temperature, with the waste brine stream.

D2) Heat exchanger to pre-cool the make-up water. This heat exchanger is optional, and can be used depending individual system requirements to perform the best possible efficiency.

E) Expansion devise as part of the ammonia refrigeration cycle to act as a pressure reducing valve between high pressure liquid from the condenser, and the feed of low pressure and temperature ammonia to the ice producing heat exchanger called the EverTube™.

Shell and tube evaporator (EverTube ) to produce microscopic ice crystals from a brine solution. Heat is absorbed in the evaporator by the evaporation of ammonia, outside the tubes on the shell side, at a lower temperature and pressure. Ice crystals forms inside the tubes on the water side, in the heat exchanger and is pumped by means of by a circulation pump circulating brine by means of the heat exchanger.

The heat exchanger has multiple spirals driven with a geared motor on the outside of the water cover, and connect each spiral individually by means of multiple gears aligned to each tube spiral. The gear will be running in the water with special material suitable to operate in water. The geared drive on the outside will be equipped with a shaft and shaft seal extending by means of the water end cover to the inside. The geared motor will drive the centre gear and the centre gear mesh with the other gears surrounding the centre. All gears will mesh perfectly in a square format, and the loads meshing is balanced.

Concentrator to concentrate the ice, and separate the higher brine solution from the slurry stream. The slurry steam delivered by the brine circulation pump, trough the evaporator (EverTube™), to the ice concentrator.

The Ice concentrator has two compartments, the top or upper compartment where the ice is filtered with a special filter mounted in the upper part of the centre or multiple stand pipes in the upper compartment. The bottom compartment is the storage and level control of the brine drained from the top compartment. Brine would be pumped from the bottom compartment trough the evaporator (EverTube™) and entering the top compartment, where the ice would be pushed upwards with pump pressure and the brine separated, by means of the filtration section in the drain pipe and gravity feed by means of to the bottom brine compartment. The ice would be at a high concentration, and will be washed with a fresh water sprayer mounted on the ice scraper or rake. The ice rake will be fitted above the upper compartment and driven with a geared motor.

The remaining brine holding on to the ice crystals will be replaced with the fresh water.

As the ice cake moves upwards, the rake would remove the ice and deliver to tank "H".

Ice melting tank (Thermal energy storage tank) to be used to store the ice produced and absorb external heat load available at the time. This tank will act as the energy storage for variable heat load conditioned.

Heat exchanger to provide external heat load from air conditioning, process cooling etc.

Delivery of water and recovery of energy by means of heat exchanger by pre- cooling make-up saline water with melted water from Ice storage and melting tank noted above in "H"

The recovered water can used as is, depending on the application, or could be further processed by means of a low pressure reverse osmoses system and treated for use as potable water

Some of the water could be heated by means of the heat recovery heat exchanger for domestic or other applications.

Water delivered from a brackish source or from sea water where the cold deep water would benefit the overall efficiency more.

The condenser will be fed with cooling water preferably delivered from deep level sea water to provide the coldest water for best efficiency and lowest condensing temperatures. The cooling water can also done with a cooling tower or other methods of condensing the ammonia. We can also utilize melt the Thermal energy store (ice storage) by means of the heat from the condensing side of the refrigeration system and therefore improve the efficiency of the refrigeration system.

The invention focus on the holistic approach of cooling, heating and desalination with the added advantage of thermal energy storage and energy management.

The same basic concept could be used in the mining industry to desalinate acid mine water and deliver a concentrated brine which could be further processed with Eutectic freezing by means of the same EverTube™ heat exchanger. All the benefits of energy management and heat recovery is available to the user of the system.

This invention can also use waste heat by means of an absorption refrigeration system to provide the cooling effect to produce ice. The EverTube™ evaporator could also be used along with the absorption refrigeration system. In case of absorption system, the advantage would be "free" heat available to produce the cooling effect, and therefore produce slurry ice to be separated and handled in the same way as the process described above.