Background of the Invention Field of the Invention

This invention relates to an apparatus and process for energy production, and more particularly to an osmotic membrane distillation apparatus for energy production and a method thereof. Description of Related Arts

The global need for renewable and clean energy is much in demand. The current practice of burning fossil fuels for producing energy has been shown to have extremely negative environmental effects, and is responsible for the emission of greenhouse gas into the atmosphere which is strongly linked to global climate change. One such form of clean and renewable energy is osmotic energy. Osmotic energy utilizes the osmotic pressure difference between two liquids to create a hydrostatic pressure that can be converted to useful energy such as generating electricity. For example, International Publication No. 2012/1 18369 A2 disclosed a method of converting thermal energy into mechanical energy using a direct contact membrane distillation method. A working fluid is preferably obtained from membrane distillation of seawater. A stream of the working fluid is a stream of pressurised distillate produced by evaporation and condensation using a direct contact membrane distillation unit. Said stream pressurised distillate having a pressure of at least one bar. A converter is used for generating mechanical energy from said stream of said pressurised distillate, and a generator is connected to the converter for generating electricity. However, the drawback of this cited art includes several steps for producing the stream of pressurised distillate which make the process more cumbersome. As is well known, forward osmosis is a process where water flows through a permeable membrane from a solution with relatively high water concentration (feed solution) to a solution with relatively low water concentration (draw solution). In recent years, forward osmosis methods for producing energy are actively studied as exemplified by U.S. Patent Application Publication No. 2005/0016924 A1. The cited art disclosed a system for producing energy, comprises a solvent chamber, a pressure chamber and a semi-permeable barrier separating the solvent chamber from the pressure chamber. The solvent chamber contains a solvent, whereas the pressure chamber contains a solute solution. The semi-permeable barrier is permeable to solvent molecules and impermeable to solute molecules. Solvent molecules diffuse across the semi-permeable barrier into the solute solution in the closed pressure chamber to increase the pressure of the pressure chamber, thereby generating energy in the form of hydrostatic pressure. A conversion device may convert the increased pressure in the pressure chamber to energy. The solute solution may be expelled and recycled after use.

However, membranes for forward osmosis have been under investigation for many years. It remains challenging to provide high water flux in combination with other desirable membrane properties, such as low solute flux, resistance to fouling, good mechanical handling properties, etc. One such membrane is described in U.S. Patent Application Publication No. 2012/0080378 A1 , disclosed a forward osmosis membrane has a hydrophilic support layer and a first polyamide rejection layer. The hydrophilic support layer and the first polyamide rejection layer are incorporated into a thin film composite membrane. The forward osmosis further comprises a second polyamide rejection layer, wherein the hydrophilic support layer is sandwiched between the first polyamide rejection layer and the second polyamide rejection layer. The forward osmosis membrane in flat sheet and hollow fibre configurations are possible. However, the development of the thin film composite membrane is complicated and time-consuming.

Accordingly, it can be seen in the prior arts that there exists a need to provide an apparatus incorporated with an improved membrane for forward osmosis. In addition, it would be an advancement in the art to provide an alternative method for energy production.

Summary of Invention

It is an objective of the present invention to provide an improved membrane for forward osmosis process.

It is also an objective of the present invention to provide an alternative method for energy production, so as to reduce negative environmental effect such as air pollution caused by combustion of fossil fuels.

It is yet another objective of the present invention to provide an osmotic membrane distillation apparatus for energy production. It is a further objective of the present invention to provide a simple method for energy production.

Accordingly, these objectives may be achieved by following the teachings of the present invention. The present invention relates to an osmotic membrane distillation apparatus (100) for producing energy, characterised by a first chamber

(101 ) containing a heated feed solution; a second chamber (102) containing a draw solution; a membrane (103) separating the first chamber (101) and the second chamber (102); a mechanical system connected to the second chamber

(102) for generating mechanical energy from diluted draw solution, wherein the diluted draw solution is a mixture of distilled feed solution and the draw solution.

The present invention also provides a method for producing energy using the osmotic membrane distillation apparatus (100), characterised by the steps of heating the feed solution to produce vapour that across the membrane (103) into the second chamber (102); maintaining the draw solution in the second chamber (102) at a lower temperature than the feed solution in the first chamber (101 ) to enable condensation of the vapour in the second chamber (102), thereby diluting the draw solution; directing the diluted draw solution through the mechanical system for generating mechanical energy.

Brief Description of the Drawings

The features of the invention will be more readily understood and appreciated from the following detailed description when read in conjunction with the accompanying drawings of the preferred embodiment of the present invention, in which:

Fig. 1 is a drawing showing an osmotic membrane distillation apparatus; and Fig. 2 is diagram showing passage of vapour from a first chamber across membrane into a second chamber.

Detailed Description of the Invention

As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting but merely as a basis for claims. It should be understood that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the invention is to cover all modifications, equivalents and alternatives falling within the scope of the present invention as defined by the appended claims. As used throughout this application, the word "may" is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words "include," "including," and "includes" mean including, but not limited to. Further, the words "a" or "an" mean "at least one" and the word "plurality" means one or more, unless otherwise mentioned. Where the abbreviations or technical terms are used, these indicate the commonly accepted meanings as known in the technical field. For ease of reference, common reference numerals will be used throughout the figures when referring to the same or similar features common to the figures. The present invention will now be described with reference to Figs. 1 and 2.

The present invention relates to an osmotic membrane distillation apparatus (100) for producing energy, characterised by:

a first chamber (101 ) containing a heated feed solution;

a second chamber (102) containing a draw solution, wherein the draw solution has a higher solute concentration and lower temperature than the feed solution to enable osmotic distillation of the feed solution into the second chamber (102);

a membrane (103) separating the first chamber (101 ) and the second chamber (102), wherein the membrane (103) is a hydrophobic and semi-permeable nanofibre membrane;

a mechanical system connected to the second chamber (102) for generating mechanical energy from diluted draw solution, wherein the diluted draw solution is a mixture of distilled feed solution and the draw solution.

In a preferred embodiment of the osmotic membrane distillation apparatus (100), the feed solution is water. In a preferred embodiment of the osmotic membrane distillation apparatus (100), the draw solution is brine.

In a preferred embodiment of the osmotic membrane distillation apparatus (100), the membrane (103) is made of polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, or any combination thereof.

In a preferred embodiment of the osmotic membrane distillation apparatus (100), the apparatus (100) further includes a heating means (104) for heating the feed solution.

In a preferred embodiment of the osmotic membrane distillation apparatus (100), the heating means (104) is a heat exchanger. In a preferred embodiment of the osmotic membrane distillation apparatus (100), the osmotic membrane distillation apparatus (100) further comprises a valve (105) connected to an outlet of the second chamber (102) for directing the diluted draw solution to the mechanical system.

In a preferred embodiment of the osmotic membrane distillation apparatus (100), the valve (105) is a check valve. In a preferred embodiment of the osmotic membrane distillation apparatus (100), the mechanical system comprises a turbine ( 06).

In a preferred embodiment of the osmotic membrane distillation apparatus (100), the mechanical system comprises a turbine (106) and a generator (107) for converting mechanical energy to electrical energy.

The present invention also provides a method for producing energy using the osmotic membrane distillation apparatus (100), characterised by the steps of: heating the feed solution to produce vapour, wherein the vapour passes across the membrane (103) into the second chamber (102);

maintaining the draw solution in the second chamber (102) at a lower temperature than the feed solution in the first chamber (101) to enable condensation of the vapour in the second chamber ( 02), thereby diluting the draw solution;

directing the diluted draw solution through the mechanical system for generating mechanical energy.

In a preferred embodiment of the method for producing energy using the osmotic membrane distillation apparatus (100), the feed solution is heated to a temperature in a range of 40 °C to 70 °C. 7

In a preferred embodiment of the method for producing energy using the osmotic membrane distillation apparatus (100), the mechanical energy is converted into electrical energy using a generator (107). Below is an example of an osmotic membrane distillation apparatus (100) for energy production and a method thereof from which the advantages of the present invention may be more readily understood. It is to be understood that the following example is for illustrative purpose only and should not be construed to limit the present invention in any way.

Examples

Referring to Fig. 1 , the osmotic membrane distillation apparatus (100) comprises a first chamber (101 ) and a second chamber (102). The first chamber (101 ) is preferably connected to a heating means (104) for heating the feed solution, wherein the heating means (104) is preferably a heat exchanger. In a preferred embodiment, the feed solution is heated by the heat exchanger by means of solar energy, geothermai energy or any waste heat discharge, prior to entering the first chamber (101 ) through an inlet of the first chamber (101 ). In a preferred embodiment, the first chamber (101 ) contains the feed solution, which preferably is fresh water. In a preferred embodiment, the second chamber (102) contains draw solution, which preferably is brine. The first chamber (101 ) and the second chamber (102) are separated by a membrane (103), wherein the membrane (103) is a hydrophobic and semi-permeable nanofibre membrane. The membrane (103) is permeable to the vaporised feed solution but impermeable to liquid feed solution and solute molecules.

It is preferable to make the surface of the membrane (103) completely hydrophobic, for example by means of a coating or other surface modification. In an exemplary embodiment of the present invention, the membrane (103) is preferably made of polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, or any combination thereof. In a preferred embodiment, the membrane (103) has pores (109) of 0.1 to 1.0 micron to allow the water vapour to pass through from the first chamber (101 ) into the second chamber (102). In a preferred embodiment, the membrane (103) is preferably configured in a flat sheet form.

Referring to Fig. 2, heating the feed solution in the first chamber (101 ) causes the liquid feed solution to evaporate at a first vapour-liquid interface (108a) at the opening of the membrane (103) pores (109) on the side of the first chamber (101). Due to a difference in solute concentration between the feed solution and the draw solution, the vapour passes across the membrane (103) into the second chamber (102).

The draw solution in the second chamber (102) is maintained at a temperature below that of the feed solution, preferably below 40°C. In a preferred embodiment, the draw solution is preferably supplied from a desalination plant, for example seawater reverse osmosis (SWRO) plant. The draw solution is left in the ambient temperature prior to sending into the second chamber (102).

When the vapour reaches the second vapour-liquid interface (108b) at the opening of the membrane (103) pores (109) on the side of the second chamber (102), the vapour condenses to form the distilled feed solution. The distilled feed solution mixes with the draw solution, which dilutes the draw solution and increases the pressure in the second chamber (102). The draw solution in the second chamber (102) is thereby osmotically pressurised using the osmotic membrane distillation apparatus (100).

Said second chamber (102) is connected to a mechanical system. In a preferred embodiment, the mechanical system is a turbine (106). Said second chamber (102) is connected to the turbine (106) via a conduit. The pressurised and diluted draw solution from the second chamber (102) drives the turbine (106) for generating mechanical energy. In a preferred embodiment, the mechanical system comprises the turbine (106) and a generator (107). The pressurised and diluted draw solution from the second chamber (102) drives the turbine (106), which in turn drives the generator (107) for generating electricity.

In a preferred embodiment, the osmotic membrane distillation apparatus (100) further comprises a valve (105), preferably a check valve, connected to the second chamber (102) for directing the diluted draw solution in a one-way direction to the mechanical system.

A method for producing energy using the osmotic membrane distillation apparatus (100) as described above starts with heating the feed solution to produce vapour. In a preferred embodiment, the feed solution is preferably heated to a temperature in a range between 40 °C to 70 °C. Then, the vapour passes across the membrane (103) into the second chamber (102). The draw solution in the second chamber (102) is maintained at a temperature below that of the feed solution, preferably below 40°C. This enables the vapour to condense to form the distilled feed solution, which mixes with the draw solution to produce the diluted draw solution. The diluted draw solution is directed to the mechanical system for generating mechanical energy. In a preferred embodiment, the mechanical system comprises the turbine (106) for generating mechanical energy, which is in turn converted into electrical energy using the generator (107). The membrane (103) with suitable porosity will be selected by an ordinary person skilled in the art based on the pressure of the diluted draw solution and the porosity strength of the membrane material. Membrane (103) cleaning to reduce fouling will help to maintain the efficiency of the apparatus (100). Additionally, the membrane (103) may be replaced every three years to maintain efficiency of energy production.

Although the present invention has been described with reference to specific embodiments, also shown in the appended figures, it will be apparent for those skilled in the art that many variations and modifications can be done within the scope of the invention as described in the specification and defined in the following claims. Description of the reference numerals used in the accompanying drawings according to the present invention:

Reference

Description

Numerals

100 Osmotic membrane distillation apparatus

101 First chamber

102 Second chamber

103 Membrane

104 Heating means

105 Valve

106 Turbine

107 Generator

108a First vapour-liquid interface

108b Second vapour-liquid interface

109 Pores