Low energy ejector desalination system

Abstract

Systems and methods for treating a raw wastewater feed stream using a low energy ejector, which works as a heat pump to increase the pressure and temperature of a two-phase distillate stream used, in part, to heat the raw wastewater feed stream. The systems and methods utilize heat from a liquid distillate stream and a concentrated liquid wastewater stream to pre-heat the raw wastewater feed stream and produce a liquid distillate product stream.

Description

FIELD OF THE DISCLOSURE

The present disclosure generally relates to treatment and desalination of seawater, produced water, and other high salinity water; it also has applicability to treatment of nuclear wastewater and other treatment processes requiring evaporator-based treatment. More particularly, the present disclosure relates to use of a low energy ejector desalination system (LEEDS), employing a static liquid-gas ejector (with no moving parts) and maximum heat integration in a water treatment system.

BACKGROUND

Thermal desalination processes that use steam as a heating medium typically use a vapor conditioning system to extract heat from the available steam through heat transfer. When these processes use vapor compression, either thermal or mechanical, they typically require auxiliary steam for start-up and to enhance normal operations.

The auxiliary steam for start-up and to enhance normal operations generally requires a fossil-fuel fired boiler to make the steam. The boiler for the auxiliary steam will usually require an air emissions permit to address emissions from fossil fuel combustion, which can include carbon monoxide, nitrogen oxides, and carbon dioxide. Permitting the boiler can be a challenge for facilities that do not normally produce steam (such as LNG) or facilities in environmentally sensitive areas or in other areas where air emission permits are difficult to obtain. Eliminating the need for the boiler has the further advantage of avoiding combustion of the boiler fuel and the associated emissions.

BRIEF DESCRIPTION OF THE DRAWING

The present disclosure is described below with references to the accompanying drawing, and in which:

FIG. 1 is a schematic diagram illustrating one embodiment of a LEEDS process according to the present disclosure.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT

The subject matter of the present disclosure is described with specificity, however, the description itself is not intended to limit the scope of the disclosure. The subject matter thus, might also be embodied in other ways, to include different structures, steps and/or combinations similar to and/or fewer than those described herein, in conjunction with other present or future technologies. Although the term “step” may be used herein to describe different elements of methods employed, the term should not be interpreted as implying any particular order among or between various steps herein disclosed unless otherwise expressly limited by the description to a particular order. Other features and advantages of the disclosed embodiments will be or will become apparent to one of ordinary skill in the art upon examination of the following FIGURE and detailed description. It is intended that all such additional features and advantages be included within the scope of the disclosed embodiments. Further, the illustrated FIGURE is only exemplary and is not intended to assert or imply any limitation with regard to the environment, architecture, design, or process in which different embodiments may be implemented. All streams described are carried by physical lines. To the extent that temperatures and pressures are referenced in the following description, those conditions are merely illustrative and are not meant to limit the disclosure.

The present disclosure overcomes one or more deficiencies in the prior art by providing a process for treatment and desalination of wastewater that does not require auxiliary steam during start-up or to enhance normal operations, thus eliminating the need to use (and obtain an air emissions permit for) a boiler for the auxiliary steam. The ability to treat high salt content wastewater without requiring steam augmentation is a primary component that sets the process apart from conventional processes in the market. The process also allows maximum use of pumps to convey streams. These are principally accomplished by use of the static liquid-gas ejector (with no moving parts) and maximum heat integration in the water treatment system.

In one embodiment, the present disclosure includes a system for treating a raw wastewater feed stream, comprising: i) a heat exchanger to heat a wastewater stream and create a two-phase stream; ii) a column in fluid communication with the heat exchanger for separating the two-phase stream into a vapor distillate stream and a concentrated liquid wastewater stream; iii) an ejector in fluid communication with the column for combining the vapor distillate stream from the column and a liquid distillate stream to produce an ejector two-phase stream; iv) a separator in fluid communication with the ejector that separates the ejector two-phase stream into another vapor distillate stream and the liquid distillate stream, wherein the vapor distillate stream and the another vapor distillate stream are in fluid communication; v) a pump in fluid communication with the ejector to send the liquid distillate stream as a motive fluid to the ejector; and vi) another pump in fluid communication with and positioned downstream from the column for pumping at least a portion of the concentrated liquid wastewater stream to the heat exchanger.

In another embodiment, the present disclosure includes a method for treating a raw wastewater feed stream, comprising: i) heating a wastewater stream to create a two-phase stream; ii) separating the two-phase stream into a vapor distillate stream and a concentrated liquid wastewater stream; iii) combining the vapor distillate stream and a liquid distillate stream to produce another two-phase stream with a temperature higher than a temperature of the vapor distillate stream, wherein the liquid distillate stream is recirculated through a column, a distillate tank, and an ejector; iv) separating the another two-phase stream into another vapor distillate stream and the liquid distillate stream; and v) pumping at least a portion of the concentrated liquid wastewater stream to the heat exchanger.

Referring now to FIG. 1, the system 100 is a low energy ejector desalination system for processing a pre-treated or pre-conditioned raw wastewater feed stream 102, which may comprise aqueous feed streams with or without saline water and/or a high concentration of suspended and/or dissolved solids. The pre-treatment or pre-conditioning of the raw wastewater feed stream 102 minimizes scaling and corrosion in the heat exchangers and other associated equipment. The pre-treatment or pre-conditioning may include chemical precipitation, coagulation, and flocculation, softening by precipitation and ion exchange, addition of anti-sealant and anti-corrosion chemicals, pH adjustment, and other means to prevent scaling and corrosion in the associated equipment.

The raw wastewater feed stream 102 is sent to a heat exchanger system 104 where heat is recovered from the distillate and the concentrated wastewater streams and transferred to the raw wastewater feed stream 102 to produce a heated aqueous feed stream 108. The heated aqueous feed stream 108 is mixed with a concentrated liquid wastewater stream 112 exiting an outlet in the bottom of column 122 to produce a mixed aqueous feed stream 114 that may be pumped through to a falling film heat exchanger 116 positioned in column 122 using a pump 126. The concentrated liquid wastewater stream 112 may also be pumped through heat exchanger system 104 to heat the raw wastewater feed stream 102. As it passes through the heat exchanger system 104, the concentrated liquid wastewater stream 112 is cooled and becomes a liquid wastewater product stream 162 for collection. A flow regulator 110, which may be a valve, may be used to control the flow of concentrated wastewater stream to the heat exchanger system 104 to heat the feed stream 102.

The mixed aqueous feed stream 114 is distributed through the falling film heat exchanger 116, which heats the mixed aqueous feed stream 114 and creates a two-phase mixed aqueous feed stream. A hot vapor distillate is separated from the two-phase mixed aqueous feed stream in column 122 after it leaves the falling film heat exchanger 116. The hot vapor distillate collects above the falling film heat exchanger 116 in column 122 and exits an outlet in the top of column 122 as a hot vapor distillate stream 132. Concentrated liquid wastewater, which may include brine, is separated from the two-phase mixed aqueous feed stream in column 122 after the hot vapor distillate leaves the falling film heat exchanger 116. The concentrated liquid wastewater collects below the falling film heat exchanger 116 in column 122 and exits the outlet in the bottom of column 122 as the concentrated liquid wastewater stream 112.

The hot vapor distillate stream 132 is drawn into an ejector 134 by suction, where it is mixed with and compressed by a high-temperature liquid distillate stream 142, which functions as a motive fluid. Preferably, the ejector 134 is a static liquid-gas ejector (with no moving parts). The ejector 134 produces a two-phase distillate stream 136, which is at a temperature slightly higher than that of the hot vapor distillate stream 132. The two-phase distillate stream 136 is ejected into a separator 137 in the falling film heat exchanger 116. The separator 137 separates the two-phase distillate stream 136 into the liquid distillate stream 142 and another hot vapor distillate stream 146.

The hot vapor distillate stream 146 enters a hot side inlet of the falling film heat exchanger 116 and rises upward through individual heating elements to heat the mixed aqueous feed stream 114 distributed downward between the individual heating elements and create the two-phase mixed aqueous feed stream. The hot vapor distillate stream 146 combines with the hot vapor distillate from the two-phase mixed aqueous feed stream above the falling film heat exchanger 116 in column 122 and exits the outlet in the top of column 122 as the hot vapor distillate stream 132. The liquid distillate stream 142 falls downward through the individual heating elements and exits an outlet near the bottom of column 122. The liquid distillate stream 142 is then sent to a distillate tank 138 where it is collected and heated during start-up operations.

The liquid distillate stream 142 exits an outlet in the bottom of the distillate tank 138 and is pumped through to the ejector 134, to function as a motive fluid, using a pump 140. A portion of the liquid distillate stream 142, once at the predetermined temperature and level, is pumped through the heat exchanger system 104, to heat the raw wastewater feed stream 102, using a pump 152. As it passes through the heat exchanger system 104, the liquid distillate stream 142 is cooled and becomes a liquid distillate product stream 156 for collection. Another flow regulator 150, which may be a valve, may be used to control the flow of the liquid distillate stream 142 from the distillate tank 138 to the heat exchanger system 104 to heat the feed stream 102.

The installation of the falling film heat exchanger 116 inside column 122 and incorporation of the separator 137 in the falling film heat exchanger 116 significantly reduces the footprint of the system 100 and further reduces heat loss. The column 122 also allows venting of non-condensable gases. The ejector 134, which works as a heat pump, increases the pressure and temperature of the two-phase distillate stream 136. This provides an additional heat contribution to the vapor compression evaporation process.

The system 100 is unique, simple, and environmentally friendly. The system 100 is made more efficient by using heat from the liquid distillate stream 142 and the concentrated liquid wastewater stream 112 to heat the raw wastewater feed stream 102. The system 100 further yields a value-added liquid distillate product stream 156 and liquid wastewater product stream 162.

While the present disclosure has been described in connection with presently preferred embodiments, it will be understood by those skilled in the art that it is not intended to limit the disclosure in those embodiments. In addition to the treatment of wastewater, LEEDS can be applied to treat other aqueous streams with a high concentration of suspended solids such as the production of high quality distilled or demineralized water, the reduction of volume of aqueous streams, and the recovery of products where evaporation is employed. It is therefore, contemplated that various alternative embodiments and modifications may be made to the disclosed embodiments without departing from the spirit and scope of the appended claims and equivalents thereof.

Claims

1. A system for treating a raw wastewater feed stream, comprising: a heat exchanger to heat a wastewater stream and create a two-phase stream;a column in fluid communication with the heat exchanger for separating the two-phase stream into a vapor distillate stream and a concentrated liquid wastewater stream;an ejector in fluid communication with the column for combining the vapor distillate stream from the column and a liquid distillate stream to produce an ejector two-phase stream;a separator in fluid communication with the ejector that separates the ejector two-phase stream into another vapor distillate stream and the liquid distillate stream, wherein the vapor distillate stream and the another vapor distillate stream are in fluid communication;a pump in fluid communication with the ejector to send the liquid distillate stream as a motive fluid to the ejector; andanother pump in fluid communication with and positioned downstream from the column for pumping at least a portion of the concentrated liquid wastewater stream to the heat exchanger.

2. The system of claim 1, wherein the column encloses the heat exchanger and the separator.

3. The system of claim 1, wherein the raw wastewater feed stream is an aqueous stream comprising suspended solids.

4. The system of claim 1, further comprising another heat exchanger or heat exchanger systems to heat the raw wastewater feed stream using the liquid distillate stream and the concentrated liquid wastewater stream.

5. The system of claim 4, wherein the column is in fluid communication with the liquid distillate stream.

6. The system of claim 5, further comprising a distillate tank in fluid communication with the column and the ejector for collecting the liquid distillate stream.

7. The system of claim 2, wherein the heat exchanger is a falling film heat exchanger.

8. The system of claim 1, wherein the raw wastewater feed stream is an aqueous stream comprising dissolved solids.

9. The system of claim 4, further comprising a flow regulator for controlling a flow of the concentrated liquid wastewater stream to the another heat exchanger or heat exchanger system.

10. The system of claim 4, further comprising a flow regulator for controlling a flow of the liquid distillate stream to the another heat exchanger or heat exchanger system.

11. The system of claim 1, wherein the ejector is a static liquid-gas ejector.

12. A method for treating a raw wastewater feed stream, comprising: heating a wastewater stream to create a two-phase stream;separating the two-phase stream into a vapor distillate stream and a concentrated liquid wastewater stream;combining the vapor distillate stream and a liquid distillate stream to produce another two-phase stream with a temperature higher than a temperature of the vapor distillate stream, wherein the liquid distillate stream is recirculated through a column, a distillate tank, and an ejector;separating the another two-phase stream into another vapor distillate stream and the liquid distillate stream; andpumping at least a portion of the concentrated liquid wastewater stream to the heat exchanger.

13. The method of claim 12, wherein the wastewater stream is heated by the another vapor distillate stream in a falling film heat exchanger.

14. The method of claim 12, wherein the raw wastewater feed stream is an aqueous stream comprising suspended or dissolved solids.

15. The method of claim 12, further comprising heating the raw wastewater feed stream using the liquid distillate stream and the concentrated liquid wastewater stream.

16. The method of claim 12, wherein the column separates the two-phase stream into the vapor distillate stream and the concentrated liquid wastewater stream.

17. The method of claim 12, wherein the distillate tank collects the liquid distillate stream from the column.

18. The method of claim 12, wherein the ejector combines the vapor distillate stream and the liquid distillate stream to produce the another two-phase stream.

19. The method of claim 12, further comprising sending the liquid distillate stream from the distillate tank to the ejector as a motive fluid.