WO2013032484A2

WO2013032484A2 - Conversion of seawater to drinking water at room temperature

Info

Publication number: WO2013032484A2
Application number: PCT/US2011/050263
Authority: WO
Inventors: Kenneth Yat-yi CHEN
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-09-01
Filing date: 2011-09-01
Publication date: 2013-03-07
Anticipated expiration: 2014-03-01
Also published as: WO2013032484A3

Abstract

An apparatus and method for converting seawater to drinking water at room temperature aoci normal atmospheric pressure. The conversion is accomplished using the processes of osmosis, ammonia stripping: ion exchange, and breakpoint chlojlnation, which provide a low-cost alternative to traditional seawater conversion methods.

Description

CONVERSION OF SEAWATER TO DRINKING WATER

AT ROOM TEMPERATURE

REFERENCE TO RELATED APPLICATIONS

Not applicable

GOVERNMENT RIGHTS

Not applicable BACKGROUND OF THE INVENTION

The present invention generally relates to apparatus and methods for seawater utilization and, more specifically, to apparatus and methods for the conversion of seawater to drinking water at room temperature and normal atmospheric pressure.

Typically, seawater is converted to drinking water by distillation, temperature elevation, or reverse osmosis desalinization processes. The elevated temperatures, pressure, and energy requirements of typical seawater conversion processes result in large, expensive, rather energy- inefficient processing plants for large-scale conversion.

As can be seen, there is a need for a less expensive, more energy-efficient process of producing drinking water from seawater.

SUMMARY OF THE INVENTION

In one aspect of the present invention, an apparatus comprises a intake chamber; an osmotic chamber coupled to the intake chamber; at least one ammonia stripping column coupled to the osmotic chamber; at least one ion exchange coupled to the at least one ammonia stripping column; a breakpoint chlorination chamber coupled to the at least one ion exchange column; and an output from the breakpoint chlorination chamber.

In another aspect of the present invention, a method comprises taking seawater into an intake chamber; directing the seawater from the intake chamber into an osmotic chamber; allowing osmosis of water molecules through a membrane located between the seawater and a concentrated ammonia solution in the osmotic chamber; wherein the concentrated ammonia solution is converted to a diluted solution through the osmosis step; adjusting the pH of the diluted solution to 11 or higher; removing ammonia from the diluted solution using multistage air-stripping columns; adjusting the pH of the diluted solution to approximately neutral after the air-stripping; removing ammonia from the diluted solution using at least one ion-exchange column after the air-stripping; and removing ammonia from the diluted solution using breakpoint chlorination after ion exchange.

In yet another aspect of the present invention, a method comprises allowing osmosis between seawater and a second solution, resulting in a diluted solution; stripping ammonia from the diluted solution at an elevated pH level; removing ammonia from the diluted solution using ion exchange; and performing breakpoint chlorination on the diluted solution.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a schematic flow diagram of an embodiment of the present invention; and

Fig. 2 shows an apparatus according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplated modes of carrying out exemplary embodiments of the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.

Various inventive features are described below that can each be used independently of one another or in combination with other features.

Broadly, embodiments of the present invention generally provide an apparatus and method to convert seawater to drinking water by undergoing osmosis with a concentrated ammonia solution, removing ammonia from the solution (ammonia concentration of 500 mg/L or less) using air-stripping columns at an elevated pH, removing ammonia from the solution using ion-exchange methods, and a breakpoint chlorination step to remove any remaining ammonia in the solution.

Referring to Figures 1 -2, the conversion apparatus may include several chambers for different processing stages described in the process 10. The first chamber may be a seawater intake chamber 50, which may be equipped with a microstrainer 1 1 , typically for removal of objects measuring at least 5 microns. The intake chamber 50 may be connected to an osmotic chamber 12. The osmotic chamber 12 may have an osmotic membrane 14 with a seawater tank 16 on one side and an ammonia tank 18, containing a concentrated ammonia solution, on the other side. The seawater may enter the seawater tank 16 from the intake chamber 50, and using the osmotic membrane 14, water molecules may migrate into the ammonia tank 16 to a solution that may typically contain approximately 10 molar ammonia as a solute. The concentration of ammonia in the ammonia tank 18 may be greatly diluted, e.g. 5 times, through the osmotic process. The pH of the diluted solution may then be adjusted to 1 1 or higher, typically using sodium hydroxide.

The solution may then be introduced to multistage air-stripping columns 20 to remove ammonia, typically to a concentration of 500 mg/L or less. The column packing material may be specially designed to achieve ammonia removal efficiency of 85% or better when using air for the stripping operation. The gas stream 22 coming out of the ammonia stripping columns 20 may be a mixture of ammonia, oxygen, nitrogen, and water vapor. This gas stream 22 may then be passed through condensation tube 24, which may typically be a series of longitudinal conduits designed to condense the ammonia and the moisture content in the gas stream, allowing oxygen, nitrogen, and a low concentration of ammonia to escape. Subsequently, the escaped (post-condensation) gas stream 26 may be directed to a heating chamber 28, and the heated gas 30 may then be recirculated back to the ammonia stripping columns 20. The condensate 32, containing water and ammonia, may then be recirculated back to the ammonia solution in the osmotic chamber 12.

The pH of the water after ammonia stripping may then be adjusted to almost neutral (typically 6.5 to 7.5), typically using sulfuric acid. The water may then be passed through a series of ion exchange columns 34 for ammonia removal, typically decreasing the ammonia concentration in the water to less than 5 mg/L. The ion exchange resin may be regenerated using concentrated sulfuric acid. This solution can be recirculated until the solution is almost saturated with ammonium sulfate, and it may then be discharged through a recirculating fluid output 36. Concentrated sodium hydroxide solution may be used to adjust the pH of the solution to above 11 , and ammonia gas may eventually be removed by air stripping columns 38. The gas 40 from the air stripping columns 38 may be directed to the condensation tube 24. The spent solution 42 may contain high concentrations of sodium ion, sulfate, and some residual ammonia, and the solution can be diluted with seawater before discharging back to the ocean.

The water may then undergo breakpoint chlorination, typically in a chamber 44, in which the remaining ammonia in the water may be oxidized to nitrogen gas and chloramines using chlorine gas or hypochlorites. The resulting water product may typically contain total dissolved solids of 150 mg/L or less with a free chlorine level of 0.2 mg/L to 1 mg/L.

In the process according to an embodiment of the present invention, the ammonia concentration of the solution exiting the osmotic chamber may be in the range of 30,000 mg L even after 5-time dilution through the osmotic process. The physical process of condensation may be used to separate most of the air from the ammonia. The ammonia condensate may be completely recirculated to the ammonia solution in the osmotic chamber, and the escaped air stream may be recirculated to the air stripping columns. A heat-exchange system may be used to extract heat from the condensation process. The extracted heat may be used to heat the recirculated air stream.

Traditionally, the removal of ammonia from wastewater and industrial wastewaters using air-stripping methods has been practiced in relatively low concentrations (tens to hundreds of mg/L). The resulting air/ammonia mixture is typically directly discharged into the atmosphere or treated with the biological processes of nitrification denitrification, which is prohibitively expensive at high ammonia concentrations.

Thus, the seawater conversion process of the present invention may include the following steps, as described above:

1 ) Natural osmosis between solutions of different concentrations,

2) Ammonia stripping at an elevated pH level, 3) Ion exchange to remove a moderate level of ammonia in solution, and

4) Breakpoint chlorination.

Drinking water, industrial water, and water for recreational usage may be produced by the process of the present invention. Moreover, the process could be used for industrial wastewater treatment. The chemicals involved are acid, base, ammonia, and chlorine. Chlorine may be used in very small concentrations, recovery of ammonia is almost 100%, and air may be recirculated within the process. The spent water, which may be discharged back to the ocean or source, contains mostly sodium sulfate, some base, and trace amounts of ammonia. The present invention may be capable of reducing the cost of desalinization of seawater to that of obtaining drinking water from freshwater sources.

The process of the present invention may eliminate the need for temperature elevation or the application of high pressure for the desalinization of seawater, except for the case in which "room temperature" is below freezing.

The present invention may provide a completely closed system without releasing any ammonia to the atmosphere. The adaptation of physical separation of air from ammonia is essential to achieve the primary goal of low cost seawater conversion.

It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.

Claims

WE CLAIM:

1 . An apparatus, comprising:

an osmotic chamber;

at least one ammonia stripping column coupled to the osmotic chamber;

at least one ion exchange coupled to the at least one ammonia stripping column;

a breakpoint chlorination chamber coupled to the at least one ion exchange column; and

an output from the breakpoint chlorination chamber.

2. The apparatus according to claim 1 , wherein the osmotic chamber comprises:

a seawater tank;

an ammonia tank; and

an osmotic membrane interposed between the seawater tank and the ammonia tank.

3. The apparatus according to claim 1 , wherein the ammonia stripping column is configured to achieve ammonia removal efficiency of 85% or better when using air.

4. The apparatus according to claim 1 , wherein:

the at least one ammonia stripping column comprises a gas output;

the gas output is coupled to a condensation tube having a condensate output; and the condensate output is coupled to the ammonia tank in the osmotic chamber.

5. The apparatus of claim 4, further comprising:

at least one air-stripping column having an input, a gas output, and a solution output;

wherein the at least one ion-exchange column comprises a recirculating fluid output;

wherein the recirculating fluid output is coupled to the input of the at least one air-stripping column; and

wherein the gas output of the air-stripping column is coupled to the condensation tube.

6. The apparatus of claim 5, wherein the spent solution output is discharged to the ocean.

7. A method, the steps comprising:

directing the seawater into an osmotic chamber; allowing osmosis of water molecules through a membrane located between the seawater and a concentrated ammonia solution in the osmotic chamber;

wherein the concentrated ammonia solution is converted to a diluted solution through the osmosis step;

adjusting the pH of the diluted solution to 11 or higher;

removing ammonia from the diluted solution using at least one multistage air-stripping column;

adjusting the pH of the diluted solution to approximately neutral after the air-stripping;

removing ammonia from the diluted solution using at least one ion-exchange column after the air-stripping; and removing ammonia from the diluted solution using breakpoint chlori nation after ion exchange.

8. The method according to claim 7, further comprising the step of removing objects measuring at least 5 microns from the seawater using a microstrainer.

9. The method according to claim 7, wherein the step of removing ammonia using multistage air-stripping columns further comprises:

producing an exiting gas stream comprising ammonia;

condensing ammonia from the exiting gas stream; and directing the condensed ammonia and moisture into the concentrated ammonia solution in the chamber.

10. The method according to claim 7, wherein the step of removing ammonia from the diluted solution using at least one ion- exchange column is performed until the ammonia concentration of the diluted solution is decreased to less than 5mg/L

1 1. The method according to claim 7, wherein the diluted solution comprises 150 mg/L of dissolved solids or less after the breakpoint chlorination step.

12 The method according to claim 7, wherein the diluted solution comprises a free chlorine level of 0.2 mg/L to 1 mg/L after the breakpoint chlorination step.

13. A method, the steps comprising: allowing osmosis between seawater and a second solution, resulting in a diluted solution;

stripping ammonia from the diluted solution at an elevated pH level;

removing ammonia from the diluted solution using ion exchange; and

performing breakpoint chlorination on the diluted solution.

14. The method according to claim 13, further including the step of removing objects measuring at least 5 microns from the seawater.

15. The method according to claim 13, further comprising the step of returning stripped ammonia to the second solution.