Method of treatment of amine waste water and a system for accomplishing the same

Disclosed herein is a system comprising an evaporation unit comprising a first heat exchanger in fluid communication with a second heat exchanger; where the first heat exchanger is operative to heat an effluent stream comprising an amine solvent and/or amine byproducts and water and to discharge the effluent stream to the second heat exchanger; where the second heat exchanger is operative to convert the effluent stream into a distillate stream and a concentrate stream; and a reverse osmosis unit in fluid communication with the evaporation unit; where the reverse osmosis unit comprises a first reverse osmosis unit that is operative to receive the distillate stream and to separate water from byproducts of the amine solvent such that the water has a purity of greater than 95%, based on the weight of the distillate stream.

FIELD OF THE INVENTION

This disclosure is related to methods of treatment of waste water containing amines. In particular, this disclosure is related to methods of treatment of waste water containing amines where the waste water is obtained from an amine based post combustion carbon dioxide capture plant.

BACKGROUND OF THE INVENTION

The combustion of a fuel, such as coal, oil, peat, waste, and the like, in a combustion plant such as a power plant, generates a hot process gas stream known as a flue gas stream. In general, the flue gas stream contains particulates and gaseous contaminants such as carbon dioxide (CO2). The negative environmental effects of releasing CO2to the atmosphere have been recognized, and have resulted in the development of processes adapted for removing or reducing the amount of CO2from the flue gas streams. One such system and process is directed to the utilization of amine-containing solutions. Amine-containing solutions can efficiently remove CO2, as well as other contaminants, such as sulfur dioxide and hydrogen chloride, from a flue gas stream.

Treatment of the flue gas stream with amine-containing solutions results in an effluent stream that may be regenerated and recirculated throughout the system. However, there are often degradation products produced by the reactions between the amine-containing solution and the contaminants present in the flue gas stream. Those degradation products should be removed as they impact the ability and the effectiveness of the regenerated and recirculated amine-containing solutions to absorb CO2.

To safeguard the efficiency of the system, and to comply with emission standards, treatment or removal of the degradation products from the system is desired.

SUMMARY

Disclosed herein is a system comprising an evaporation unit comprising a first heat exchanger in fluid communication with a second heat exchanger; where the first heat exchanger is operative to heat an effluent stream comprising an amine solvent or byproducts of the amine solvent and water and to discharge the effluent stream to the second heat exchanger; where the second heat exchanger is operative to convert the effluent stream into a distillate stream and a concentrate stream; and a reverse osmosis unit in fluid communication with the evaporation unit; where the reverse osmosis unit comprises a first reverse osmosis unit that is operative to receive the distillate stream and to separate water from byproducts of the amine solvent such that the water has a purity of greater than 95%, based on the weight of the distillate stream.

Disclosed herein too is a method comprising discharging an effluent stream comprising an amine solvent or byproducts of the amine solvent and water to a first heat exchanger; heating the effluent stream in the first heat exchanger; discharging the effluent stream from the first heat exchanger to the second heat exchanger; separating the effluent stream into a distillate stream and a concentrate stream; discharging the distillate stream to a reverse osmosis unit that comprises a first reverse osmosis unit; and separating the water from amine byproducts in the first reverse osmosis unit; where the water has a purity of greater than 95%, based on the total weight of the distillate stream.

DETAILED DESCRIPTION

Amine based post-combustion processes produce different types of amine containing waste waters (hereinafter “effluents”) due to the degradation of amines, undesirable accumulation of amines in wash systems, backwash of filters and purges, and the like. These effluents are further treated to avoid expensive external treatment. Systems have been designed and developed to remove amines and their byproducts from effluent streams. Some of these waste water treatment systems remove amines to a certain level, but are insufficient to effectively remove substantially all of the amines and their byproducts from the waste water streams.

Disclosed herein is a system and a method for treating an amine containing waste water stream. The system advantageously comprises an evaporation unit in fluid communication with a reverse osmosis unit. Effluents discharged from the plant are discharged to the evaporation unit to produce a concentrate, which is then safely disposed of. The evaporation unit advantageously removes anions, cations, salts and other solids in the range of about 95 to about 99% from the effluent. The reverse osmosis system can be a single pass or double pass cell and advantageously removes about 95 to about 99% of the amines present in the effluent.

TheFIG. 1discloses a system100that comprises an evaporation unit200in fluid communication with a concentrate storage unit300and a reverse osmosis unit400. Both the concentrate storage unit300and the reverse osmosis unit400are located downstream of the evaporation unit200. In one embodiment, the evaporation unit200also lies upstream of the reverse osmosis unit400. In other words, the evaporation unit200and the reverse osmosis unit400are lie a recycle loop—products discharged from the evaporation unit200are discharged to the reverse osmosis unit400and products discharged from the reverse osmosis unit400are discharged to the evaporation unit200.

With reference now once again to theFIG. 1, the evaporation unit200comprises a first heat exchanger202in fluid communication with a second heat exchanger204, a water separator206and a compressor208. In one embodiment, the heat exchanger202is in a recycle loop with the second heat exchanger204, i.e., the second heat exchanger204lies upstream and downstream of the first heat exchanger202. In another embodiment, the second heat exchanger204lies in a recycle loop with the water separator206, i.e., the second heat exchanger204lies upstream and downstream of the water separator206. In yet another embodiment, the second heat exchanger204is also in a recycle loop with the water separator206via the compressor208, i.e., the compressor208lies upstream and downstream of the water separator206. In an exemplary embodiment, the evaporation unit200is an electrically driven mechanical vapor recompression (MVR) evaporator comprising a feed distillate heat exchanger202(the first heat exchanger), a shell and tube heat exchanger204(the second heat exchanger204), a water separator206and a compressor208. Additional details of the evaporation unit200are provided below.

The reverse osmosis unit400comprises a first optional pump402in fluid communication with a first reverse osmosis unit404. A first recycle loop414discharges the retentate from the first reverse osmosis unit404to an effluent stream103at a point upstream of the pump202. This retentate comprises water and amine solution byproducts. An optional second pump406and an optional second reverse osmosis unit408lie downstream of the first reverse osmosis unit404and are in fluid communication with the first reverse osmosis unit404. The second reverse osmosis unit408, if present, lies downstream of the second pump406. A second recycle loop416recycles the retentate from the second reverse osmosis unit408to the evaporation distillate stream401at the inlet of the first reverse osmosis unit404.

As detailed above, power generation facilities generate a flue gas stream that contains carbon dioxide. The carbon dioxide is removed from the flue gas stream in a carbon capture system. The removal of carbon dioxide from the flue gas stream in the carbon capture system generates a stream of carbon dioxide that is released from the carbon capture system for further use or storage (not shown). Removal of carbon dioxide from the flue gas stream also generates a cleaned flue gas stream. The cleaned flue gas stream may be released to the atmosphere via a stack (not shown) or sent to another section of the system for further processing and/or treatment (not shown).

Using an amine-containing solution to remove carbon dioxide from the flue gas stream results in the formation of an effluent stream103(seeFIG. 1) that contains products from the degradation of the amine-containing solution, residual amines and other compounds that reduce the efficacy and efficiency of the amine-containing solution when it is regenerated for re-use within the carbon capture system. The effluent stream103contains amines (primary, secondary and/or tertiary), aldehydes, amides, nitrosamines, anions, cations, other solids in addition to water. As noted above, it is desirable to treat the waste water stream103to remove substantially all of the amines (primary, secondary and/or tertiary), aldehydes, amides, nitrosamines, anions, cations, other solids (hereinafter also referred to as “contaminants”).

With respect to theFIG. 1, the effluent stream103is first contacted with an acid in a dosing system104, where the acid is operative to adjust the pH of the effluent stream to about 5 to about 9. In addition to reducing the pH, the addition of the acid to the effluent stream103produces salt and water and also results in an improvement of the amine and aldehyde removal efficiency from the effluent stream103. The effluent stream103is then discharged from the dosing system104at a temperature of about 40 to about 50° C. to the evaporation unit200where it is introduced into the first heat exchanger202. The evaporation unit200facilitates the evaporation of amine containing effluents.

In an exemplary embodiment, the first heat exchanger202is a feed distillate heat exchanger. The first heat exchanger202exchanges heat between the effluent stream and a distillate stream401emanating from the second heat exchanger204. The effluent stream enters the first heat exchanger at a temperature of about 40 to about 50° C. and absorbs heat from the distillate stream401that has a temperature of about 85 to about 90° C.

The second heat exchanger204can be either a steam driven type or an electrical driven type. Examples of the second heat exchanger204are a shell and tube heat exchanger, plate heat exchanger, adiabatic wheel heat exchanger, plate fin heat exchanger, pillow plate heat exchanger, dynamic scraped surface heat exchanger or a phase-change heat exchanger. One or more of these heat exchangers may be used if desired. As noted above, an exemplary second heat exchanger204is a tube and shell heat exchanger.

The second heat exchanger204receives the effluent stream103from the first heat exchanger202at a temperature of about 70 to about 80° C. The second heat exchanger204facilitates the separation of the water from the contaminants (amines (primary, secondary and/or tertiary), aldehydes, amides, nitrosamines, anions, cations, other solids) in the effluent stream103by evaporation. A wet steam stream205leaves the second heat exchanger204and is guided to a water separator206. The water separator206separates residual water from the steam. A (separated) water stream207re-circulated to the second heat exchanger204. A dry steam stream209leaves the water separator206and enters a compressor208. The compressor208delivers the required energy for evaporation of effluent stream103and ensures the desired circulation. A steam stream210leaves the compressor208and is guided to the second heat exchanger204. In the second heat exchanger204, the steam stream210is condensed to a distillate stream211and guided to the first heat exchanger202, transferring the heat to the effluent stream103. The water leaves the first heat exchanger202as the evaporation distillate stream401(hereinafter the distillate stream), while the contaminants leave the second heat exchanger204as a concentrate stream403. Both of these streams will be addressed in detail below.

The second heat exchanger204is in fluid communication with the water separator206and the compressor208. Steam is the heating medium used in the second heat exchanger204. The water separator206receives the wet steam stream205from the second heat exchanger204at a temperature of about 85° C. to about 95° C. The wet steam stream205entering the water separator206is separated into vapor and liquid. The water separator206contains a demister. The vapor is discharged from the top of the water separator206to the compressor208as the dry steam stream209and recycled to the second heat exchanger204, while the water is discharged from the bottom of the water separator206to the second heat exchanger204as the separated water stream207.

The first heat exchanger202receives the distillate stream211from the second heat exchanger204. As noted above, it exchanges this heat with the effluent stream103raising the temperature of the effluent stream103prior to its entry to the second heat exchanger204in the process.

The distillate stream211(now identified as401but having essentially the same composition as stream211) leaving the first heat exchanger202is discharged to the reverse osmosis unit400, while the concentrate stream403, which contains those contaminants extracted from the effluent stream is discharged to the concentrate storage tank300.

The distillate stream401is directed to reverse osmosis unit400via an optional heat exchanger410and a second dosing unit412. The optional heat exchanger410reduces the temperature of the distillate stream if desired, while the second dosing unit412introduces additional acid into the distillate stream401. The optional heat exchanger410is employed to reduce the temperature of the distillate stream403to minimize damage to the membranes employed in the reverse osmosis unit400. The addition of acid converts amines and neutralizes other basic ingredients into salts, which are more easily separated from the distillate stream than the amines.

Acids used in the dosing units104and412can be any type of acids. A suitable example of an acid is a mineral acid. Examples of such acids are sulfuric acid, nitric acid, hydrochloric acid, acetic acid, citric acid, carbonic acid, phosphoric acid, oxalic acid, or the like, or a combination comprising at least one of the foregoing acids. An exemplary acid for purposes of dosing the effluent stream103or the distillate stream401is sulfuric acid.

The distillate stream401is pumped via a pump402into the first reverse osmosis unit404. Reverse osmosis (RO) is a membrane-technology filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side. To be “selective,” this membrane should not allow large molecules or ions through the pores (holes), but should allow smaller components of the solution (such as the solvent) to pass freely.

Suitable membranes for the first reverse osmosis unit404are aromatic polyamide membranes or thin film composite type membranes that include aromatic polyamides. The distillate stream401is pressurized to a suitable desired pressure prior to entry into the first reverse osmosis unit404or during the operation of the first reverse osmosis unit404. The pressure varies depending upon the type of membrane and the desired recovery rate. The temperature of the distillate stream401prior to entry into the first reverse osmosis unit404is about 50 to about 60° C.

The solute from the first reverse osmosis unit404is recycled to the effluent stream103via stream414. In one embodiment, water obtained from the distillate stream401after being separated from the solute in the first reverse osmosis unit404is substantially free from impurities and can be used as make up water for a carbon capture plant or for a power plant. In one embodiment, the water obtained after the first reverse osmosis unit404is about 95 to about 99.9% free of amine based impurities, based on the total weight of the distillate stream401.

In another embodiment, the stream of fluid emanating from the first reverse osmosis unit404may need to be subjected to a second reverse osmosis process. The second reverse osmosis unit408is arranged in series with the first reverse osmosis unit404and lies downstream of it. A second optional pump406can be used to pressurize the fluid emanating from the first reverse osmosis unit404. The pressure of the fluid prior to entering the second reverse osmosis unit or during the operation of the second reverse osmosis unit is dependent on the type of membrane and the desired recovery rate. The temperature of the fluid prior to entering the second reverse osmosis unit is about 50 to about 60° C.

In order to facilitate purifying the water in the distillate stream to the maximum content possible, the solute (also termed the retentate) from the second reverse osmosis unit408may be optionally recirculated back to the distillate stream401upstream of the pump402. The reverse osmosis unit400can thus be utilized as a multi-array double pass reverse osmosis unit. The water obtained from the second reverse osmosis unit408has a purity of greater than 97%, specifically greater than 99% and more specifically greater than 99.9%, based on the total weight of the distillate stream401. As noted above, the water obtained by this method of separating amines and their byproducts from the water may be reutilized in a carbon capture plant or in a power plant.

The contaminants (hereinafter termed the “concentrate”) are discharged from the second heat exchanger204to the concentrate storage tank300as the concentrate stream403. From the concentrate storage tank300they are optionally pumped by a pump302to a disposal facility304. From the concentrate storage tank300, the solids may be disposed of by an external recycling company or alternatively, the concentrate may be used for co-incineration in a boiler of the combustion plant.

This method of removing water from an effluent stream containing amines is advantageous in that the water is purified to greater than 97%, specifically to greater than 99.9%, based on the total weight of the distillate stream. No waste streams are emitted to the environment. The process is also inexpensive and efficient.

The term and/or is used herein to mean both “and” as well as “or”. For example, “A and/or B” is construed to mean A, B or A and B.

The transition term “comprising” is inclusive of the transition terms “consisting essentially of” and “consisting of” and can be interchanged for “comprising”.

While this disclosure describes exemplary embodiments, it will be understood by those skilled in the art that various changes can be made and equivalents can be substituted for elements thereof without departing from the scope of the disclosed embodiments. In addition, many modifications can be made to adapt a particular situation or material to the teachings of this disclosure without departing from the essential scope thereof. Therefore, it is intended that this disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosure.