DESC:TECHNICAL FIELD
[0001] The instant disclosure is in the field of chemical sciences, more particularly towards sour water/spent water purification. The present disclosure relates to methods for separating impurities including oil/tar, and suspended or dissolved solids from sour water, and systems thereof.

BACKGROUND OF THE DISCLOSURE

[0002] Poor run length of sour water filtration system due to chocking of pre-filter and filter element by oily materials and suspended solids is a concern for steam crackers (both gas & naphtha crackers) operation. This reduces the run length of process diluent generator along with addition of extra operating cost for frequent changing of filter elements which supposed to provide several months service and also increases Effluent Treatment Plant (ETP) load due to bypassing of entire filtration system during maintenance. Even filtration system upgradation and also use of additives like emulsion breaker, dispersant, pH modifier, etc. are not effective in solving the issue completely.

Steam Cracker Process
[0003] In steam crackers, cracked gas effluent from the cracking furnaces goes to cracked gas compressor through quench water tower. Spent quench water stream typically consist of tars, hydrocarbons including heavy aromatics, dissolved & suspended oils and solids. After separation of oil rich spent quench water as a side cut from the bottom of quench water tower, the spent quench water is processed in the oil water separator (de-oiler) where free oil is withdrawn from the top. Water with emulsified oil and other inorganic impurities is passed through sour water filtration system followed by sour water stripper before fed to process diluent generator.

Sour Water Filtration System
[0004] Generally sour water filtration system includes Pre-filter and Filter followed by Coalescer in series and are operated in one on-line and one in standby mode. Oils present in the water are separated in the coalescer after removal of > 50µm particles in pre-filter followed by > 10µm in filter. All solids present in the oil less spent quench water are trapped by the sacrificial pre-filter followed by filter to reduce the solid load in the coalescer and protect the costliest elements of it. The life of filtration elements depends on solid loads in the feed and also on other factors which affects filtration efficiency e.g. oil, tar / gummy materials, etc. present in the feed.

Operational Issues Related to Sour Water Filtration System
[0005] Due to containing of more solids and oil and grease in the feed of sour water filtration system both pre-filters and filters get chocked which requires frequent cleaning of the filtration system. Instead of expected run time of several months, the filtration system is being taken in maintenance within few days to change the filter elements and during that time whole system is bypassed to ETP. This phenomenon of poor run length of the filtration system not only affects the performance of process diluent generator system but also increases the ETP load and operating cost due to frequent change of filter elements.
[0006] Therefore, there is a need to develop a simple, easy to implement, cost-effective, improved/efficient and green method/process for separating impurities such as oil, tar, and dissolved or suspended solids from water stream. The present disclosure tries to address said need.

SUMMARY OF THE DISCLOSURE
[0007] Provided herein are methods and systems for removing impurities from spent quench water. Also provided herein are methods and systems for cracking hydrocarbons.
[0008] In some embodiments, a method for removing impurities from spent quench water comprises: (a) providing spent quench water from quenching of a cracked hydrocarbon effluent in a quench water tower; and (b) mixing said spent quench water with an organic solvent, wherein impurities from said spent quench water are extracted by the organic solvent to produce a solvent-extracted spent quench water; and (c) feeding the solvent-extracted spent quench water to a sour water filtration system.
[0009] In some embodiments, provided herein is a method for cracking hydrocarbons, comprising: (a) mixing a hydrocarbon stream with a steam stream to produce a mixed hydrocarbon stream; (b) cracking the mixed hydrocarbon stream in a cracking furnace to produce a cracked effluent; (c) quenching the cracked effluent in a quench water tower with quench water to produce a quenched effluent stream and a spent quench water; (d) mixing said spent quench water with an organic solvent, wherein impurities from said spent quench water are extracted by the organic solvent to produce a solvent-extracted spent quench water; (e) feeding the solvent-extracted spent quench water to a sour water filtration system to produce filtered spent quench water; (f) feeding the filtered spent quench water to a sour water stripper to produce stripped spent quench water; and (g) feeding the stripped spent quench water to a dilution steam generator to produce a clean steam stream.
[0010] In some embodiments, the organic solvent is selected from a paraffin, an aromatic solvent, or a solvent comprising both paraffin and aromatic compounds. In some embodiments, the organic solvent is selected from the group consisting of: n-hexane, toluene, light naphtha, and a mixture thereof.
[0011] The methods and systems of the present disclosure provide a significant reduction in impurities from spent quench water. In particular, the methods and systems provide a significant reduction in the amounts of oil, grease, suspended solids, and dissolved solids. The methods and systems of the present disclosure also provide a significant reduction in turbidity and chemical oxygen demand of spent quench water.
[0012] Organic solvents used in the methods and systems of the present disclosure can be recycled and reused for subsequent extractions with same contaminant removal efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Figure 1 illustrates a simplified block diagram showing Sour Water Filtration System with Solvent Extraction System according to an exemplary embodiment of the invention.
[0014] Figure 2 shows results of the SIMDIST analysis, carried out according to Industry Standard Method ASTM D 2887, of separated oil in Example 1.

DESCRIPTION OF THE DISCLOSURE
Definitions
[0015] While the following terms are believed to be well understood by one of ordinary skill in the art, the following definitions are set forth to facilitate explanation of the presently disclosed subject matter.
[0016] The term “a” or “an” refers to one or more of that entity, i.e. can refer to a single or plural referent. As such, the terms “a” or “an”, “one or more” and “at least one” are used interchangeably herein. In addition, reference to “an element” by the indefinite article “a” or “an” does not exclude the possibility that more than one of the elements is present, unless the context clearly requires that there is one and only one of the elements. For example, “an” organic solvent as used herein refers to a single organic solvent or a mixture of two or more organic solvents.
[0017] Unless the context requires otherwise, throughout the present specification and claims, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to”.
[0018] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment may be included in at least one embodiment of the present disclosure. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification may not necessarily all refer to the same embodiment. It is appreciated that certain features of the disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.
[0019] The term “impurities” as used herein refers to impurities present in sour water or spent quench water generated in petrochemical refineries or hydrocarbon cracking plants. Such impurities include, but are not limited to, oil (dissolved and suspended), grease, tar, heavy aromatic compounds, total dissolved solids (TDS), and total suspended solids (TSS).
[0020] As referred to herein, the term “Run Length Improvement” of a system encompasses increasing the durability of; lengthening or prolonging the run time of; increasing life of; reducing equipment costs of; or reducing operating costs of sour water filtration system and/or dilution steam generator system used in petrochemical refineries or hydrocarbon cracking plants.
[0021] The terms “sour water” and “spent quench water” are used interchangeably throughout this disclosure.
[0022] The term “hydrocarbon” as used herein encompasses liquid as well as gaseous hydrocarbons.
Methods
[0023] In a hydrocarbon cracking plant, a hydrocarbon stream is mixed with a steam stream to produce a mixed hydrocarbon stream. This mixed hydrocarbon stream is cracked in a cracking furnace to produce a cracked hydrocarbon effluent. The cracked hydrocarbon effluent is quenched in a quench water tower to produce quenched hydrocarbon effluent and spent quench water. Said spent quench water comprises impurities such as oil (dissolved and suspended), grease, tar, heavy aromatics, TDS, and TSS. Said spent quench water is processed in a sour water filtration system where spent quench water passes through pre-filters and filters to remove particulate matters.
[0024] The present disclosure provides methods and systems for removing impurities from sour water or spent quench water before spent quench water is processed in a sour water filtration system. More particularly, the disclosure provides methods and systems for extracting sour water or spent quench water with organic solvents to separate impurities including oil/tar, suspended solids, and dissolved solids, from said water before processing said water in a sour water filtration system. The methods described herein improve run length of sour water filtration and process diluent generator systems used in petrochemical refineries, hydrocarbon processing plants, etc.
[0025] Analysis of spent quench water from hydrocarbon crackers shows the presence of impurities including oil and grease (O&G), suspended solids (also referred to herein as “total suspended solids” (TSS)) and dissolved solids (also referred to herein as “total dissolved solids” (TDS)). When spent quench water is passed through the sour water filtration system, these impurities (e.g., paraffins, olefins and aromatics) deposit on the filters and pre-filters of the sour water filtration system and plug the filter elements. Inorganic solids of TSS coated with oils also get stuck in the filter elements. This clogging of filter elements reduces the efficiency of sour water filtration system by many folds.
[0026] The present disclosure provides methods for pre-treating spent quench water with an organic solvent before processing said spent quench water in a sour water filtration system. Specifically, the present disclosure provides methods for removing impurities present in said spent quench water by extracting said spent quench water with an organic solvent. The inventors observed that through this solvent extraction method, oil, grease, and other organic materials were separated out from said spent quench water. Suspended materials (TSS) were generally removed along with the organic phase if organic in nature whereas inorganic particulate matter was found to be present at the oil-water interphase. This interphase layer can be removed and is treated separately using suitable coagulants to separate out inorganic dirt and water.
[0027] In some embodiments, spent quench water generated from quenching of cracked hydrocarbon effluent is extracted with an organic solvent. In some embodiments, free oil from spent quench water is first separated in an oil separator and then this free oil-separated spent quench water is extracted with an organic solvent.
[0028] Organic solvents that can be used in the methods of the present disclosure to extract spent quench water or free oil-separated spent quench water include, but are not limited to, a paraffinic solvent, an aromatic solvent, a mixture of both paraffinic and aromatic solvents, or a mixture of paraffinic, olefin and aromatic solvents.
[0029] In some embodiments, an organic solvent is a paraffinic solvent. The paraffinic solvent can be a lower chain alkane or a higher chain alkane. In some embodiments, the paraffinic solvent is a linear, C5-C12 branched or cyclic alkane. In some embodiments, the paraffinic solvent is n-hexane.
[0030] In some embodiments, an organic solvent is an aromatic solvent. In some embodiments, an aromatic solvent includes a substituted benzene. In some embodiments, the substituted benzene is a C1-C3 alkyl-substituted benzene. In some embodiments, the substituted benzene is toluene.
[0031] In some embodiments, an organic solvent is a mixture of paraffin and aromatic compounds. In some embodiments, an organic solvent is naphtha which is a mixture of paraffinic and aromatic compounds. In some embodiments, an organic solvent is light naphtha (mixture of paraffin, naphthenes, olefins, aromatics). In some embodiments, an organic solvent is a mixture of any of the paraffinic and aromatic solvents described herein. For example, in some embodiments, an organic solvent is a mixture of an alkane and a substituted benzene. In some embodiments, an organic solvent is a mixture of n-hexane and toluene. In embodiments, where the organic solvent is a mixture of two organic solvents, the two solvents can be mixed in ratios ranging from about 1:25 to about 1:1, such as, about 1:25, 1:20, 1:15, 1:10, 1:5, 1:2, or 1:1 (v/v), including values and ranges there between. Similarly, one of ordinary skill in the art would understand that where the organic solvent is a mixture of three or more organic solvents, the solvents can be mixed in various ratios (v/v).
[0032] In some embodiments, an organic solvent is selected from a group consisting of: n-hexane, toluene, xylene, light naphtha, light kerosene, and a mixture thereof.
[0033] In some embodiments, an organic solvent is mixed with spent quench water or free oil-separated spent quench water in ratios ranging from about 1:20 to about 1:4 (v/v), including values and ranges there between. In some embodiments, the ratio of an organic solvent to spent quench water or free oil-separated spent quench water is about 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, or 1:20, including values and ranges there between. In some embodiments, the ratio of an organic solvent to spent quench water or free oil-separated spent quench water is about 1:4, 1:5, 1:8, 1:10, 1:15, or about 1:20. In some embodiments, the ratio of an organic solvent to spent quench water or free oil-separated spent quench water is about 1:10.
[0034] In some embodiments, an organic solvent is mixed with spent quench water or free oil-separated spent quench water at least for about 10 seconds. In some embodiments, an organic solvent is mixed with spent quench water or free oil-separated spent quench water for about 10 seconds to about 10 minutes, or about 10 seconds to about 5 minutes, including values and ranges there between. In some embodiments, an organic solvent is mixed with spent quench water or free oil-separated spent quench water for about 10 seconds, 30 seconds, 1 minute, 2 minutes, 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, or about 10 minutes.
[0035] In some embodiments, an organic solvent is mixed with spent quench water or free oil-separated spent quench water at a speed of 50 to 1000 rpm. In some embodiments, an organic solvent is mixed with spent quench water or free oil-separated spent quench water at a speed of 50 to 900 rpm, 50 to 800 rpm, 50 to 700 rpm, 50 to 600 rpm, 50 to 500 rpm, 50 to 400 rpm, 50 to 300 rpm, 50 to 200 rpm, 100 to 1000 rpm, 100 to 900 rpm, 100 to 800 rpm, 100 to 750 rpm, 100 to 700 rpm, 100 to 600 rpm, 100 to 500 rpm, 100 to 400 rpm, 100 to 300 rpm, 100 to 250 rpm, 100 to 200 rpm, 200 to 1000 rpm, 200 to 900 rpm, 200 to 800 rpm, 200 to 750 rpm, 200 to 700 rpm, 200 to 600 rpm, 200 to 500 rpm, 200 to 400 rpm, 200 to 300 rpm, 300 to 1000 rpm, 300 to 900 rpm, 300 to 800 rpm, 300 to 750 rpm, 300 to 700 rpm, 300 to 600 rpm, 300 to 500 rpm, 300 to 400 rpm, 400 to 1000 rpm, 400 to 900 rpm, 400 to 800 rpm, 400 to 700 rpm, 400 to 600 rpm, 400 to 500 rpm, 500 to 1000 rpm, 500 to 900 rpm, 500 to 800 rpm, 500 to 750 rpm, 500 to 700 rpm, 600 to 1000 rpm, 600 to 900 rpm, 600 to 800 rpm, 700 to 1000 rpm, 700 to 900 rpm, or 800 to 1000 rpm. In some embodiments, an organic solvent is mixed with spent quench water or free oil-separated spent quench water at a speed of 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, or 1000 rpm.
[0036] In some embodiments, an organic solvent is mixed with spent quench water or free oil-separated spent quench water at any of the speeds and time periods disclosed herein.
[0037] In some embodiments, after mixing the organic solvent with spent quench water or free oil-separated spent quench water, the mixture is allowed to settle for some time prior to the step of feeding the solvent-extracted spent quench water to the sour water filtration system. In some embodiments, the mixture is settled for about 30 minutes to about 48 hours, about 1 hour to about 48 hours, about 2 hours to about 48 hours, about 3 hours to about 48 hours, about 5 hours to about 48 hours, about 8 hours to about 48 hours, about 12 hours to about 48 hours, including values and ranges there between. In some embodiments, the mixture is settled for about 30 minutes, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 15 hours, 18 hours, 20 hours, 24 hours, 30 hours, 35 hours, 40 hours, or about 48 hours, including values and ranges there between. In some embodiments, the mixture is settled for about 5 hours, 12 hours, or about 48 hours.
[0038] In some embodiments, the mixture of the organic solvent with spent quench water or free oil-separated spent quench water is settled for about 30 minutes to about 8 hours, about 30 minutes to about 6 hours, about 1 hour to about 6 hours, or about 1 hour to about 5 hours, for a paraffinic solvent, such as an alkane (e.g., n-hexane). In some embodiments, the mixture of the organic solvent with spent quench water or free oil-separated spent quench water is settled for about 5 hours for a paraffinic solvent, such as an alkane (e.g., n-hexane).
[0039] In some embodiments, the mixture of the organic solvent with spent quench water or free oil-separated spent quench water is settled for about 8 hours to about 15 hours, about 8 hours to about 12 hours, or about 10 hours to about 12 hours, for a solvent comprising a mixture of paraffins, naphthenes, olefins and aromatics, e.g., light naphtha. In some embodiments, the mixture of the organic solvent with spent quench water or free oil-separated spent quench water is settled for about 12 hours for a solvent comprising a mixture of paraffins, naphthenes, olefins and aromatics, e.g., light naphtha.
[0040] In some embodiments, the mixture of the organic solvent with spent quench water or free oil-separated spent quench water is settled for about 24 hours to about 48 hours or about 30 hours to about 48 hours, for an aromatic solvent, such as a substituted benzene (e.g., toluene). In some embodiments, the mixture of the organic solvent with spent quench water or free oil-separated spent quench water is settled for about 48 hours, for an aromatic solvent, such as a substituted benzene (e.g., toluene).
[0041] After extraction, the mixture of spent quench water or free oil-separated spent quench water with an organic solvent separates into three layers – the top layer comprises the organic solvent with organic impurities including oil, tar, heavy aromatics, etc., the middle layer (also referred to as an interphase) comprises inorganic impurities, and the bottom layer comprises an aqueous phase.
[0042] The organic solvent with organic impurities including oil, tar, heavy aromatics, etc. is separated from the top of the oil - water separator. The inventors have found that the organic solvent containing extracted organic impurities can be reused many times with the same contaminant removal efficiency. The organic solvent comprising extracted organic impurities can be fed back to the solvent chamber and can be reused for subsequent extractions. In some embodiments, the organic solvent comprising extracted organic impurities can be reused for a subsequent extraction one time, 2 times, 3 times, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times, or 10 times. In some embodiments, the organic solvent comprising extracted organic impurities can be reused for subsequent extractions 1-4 times or 1-5 times.
[0043] The middle layer comprising inorganic impurities is separated from the mixing unit. The interphase can be treated separately with suitable coagulants e.g. PAC (poly aluminum chloride), alum, etc. to remove the adhered oils and solids from water.
[0044] The bottom aqueous layer with decreased levels of organic and inorganic impurities (also referred to herein as “solvent-extracted spent quench water”) is fed to a sour water filtration system to produce filtered spent quench water. In some embodiments, the filtered spent quench water can be fed to a sour water stripper to produce stripped spent quench water. The filtered spent quench water or the stripped spent quench water is fed to a process diluent generator (also referred to herein as “dilution steam generator”) to produce clean steam.
[0045] The methods of the present disclosure reduce the levels of organic and inorganic impurities including oil, grease, total suspended solids and total dissolved solids from spent quench water. Thus, the solvent-extracted spent quench water contains substantially reduced levels of oil, grease, total suspended solids, and total dissolved solids compared to spent quench water before solvent extraction. The methods of the present disclosure substantially reduce the turbidity and chemical oxygen demand (COD) of spent quench water compared to spent quench water before solvent extraction.
[0046] In some embodiments, the oil and grease content of solvent-extracted spent quench water is substantially reduced compared to the oil and grease content of spent quench water or oil-separated spent quench water. In some embodiments, the oil and grease content of solvent-extracted spent quench water ranges from about 0 to about 100 parts per million (ppm), about 0-90 ppm, about 0-80 ppm, about 0-70 ppm, about 0-60 ppm, or about 0-50 ppm, including values and ranges there between. In some embodiments, the oil and grease content of solvent-extracted spent quench water is about 0-40 ppm, about 0-30 ppm, about 0-25 ppm, about 0-20 ppm, about 0-10 ppm, about 0-5 ppm, or about 0 ppm, including values and ranges there between. In some embodiments, the oil and grease content of solvent-extracted spent quench water is about 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, or about 100 ppm, including values and ranges there between.
[0047] In some embodiments, the methods of the present disclosure decrease the oil and grease content of spent quench water or free oil-separated spent quench water by about 40-100%, by about 50-100%, by about 60-100%, by about 70-100%, by about 75-100%, by about 80-100%, or by about 90-100%, including values and ranges there between, after solvent extraction. In other words, the oil and grease content of solvent-extracted spent quench water is about 40-100%, about 50-100%, about 60-100%, about 70-100%, about 75-100%, about 80-100%, or about 90-100%, lower compared to the oil and grease content of spent quench water or oil-separated spent quench water. In some embodiments, the methods of the present disclosure decrease the oil and grease content of spent quench water or free oil-separated spent quench water by about 75-100%, about 90-100% or by about 99%, after extraction.
[0048] In some embodiments, the methods of the present disclosure decrease the TDS content of spent quench water or free oil-separated spent quench water to about 0-50 ppm, about 0-40 ppm, about 0-30 ppm, about 0-25 ppm, about 0-20 ppm, about 0-10 ppm, or to about 0-5 ppm, including values and ranges there between, after solvent extraction. In some embodiments, the present methods decrease the TDS content of spent quench water or free oil-separated spent quench water to about 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, or to about 50 ppm, after solvent extraction.
[0049] In some embodiments, the methods of the present disclosure decrease the TDS content of spent quench water or free oil-separated spent quench water by about 60-100%, about 70-100%, about 75-100%, about 80-100%, by about 85-100%, by about 90-100%, or by about 95-100%, including values and ranges there between, after solvent extraction. In some embodiments, the methods of the present disclosure decrease the TDS content of spent quench water or free oil-separated spent quench water by about 60%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, or by about 100%, after solvent extraction.
[0050] In some embodiments, the methods of the present disclosure decrease the TSS content of spent quench water or free oil-separated spent quench water to about 0-50 ppm, about 0-40 ppm, about 0-30 ppm, about 0-25 ppm, about 0-20 ppm, about 0-10 ppm, or to about 0-5 ppm, including values and ranges there between, after solvent extraction. In some embodiments, the present methods decrease the TSS content of spent quench water or free oil-separated spent quench water to about 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, or to about 50 ppm, after solvent extraction.
[0051] In some embodiments, the methods of the present disclosure decrease the TSS content of spent quench water or free oil-separated spent quench water by about 60-100%, about 70-100%, about 75-100%, about 80-100%, by about 85-100%, by about 90-100%, or by about 95-100%, including values and ranges there between, after solvent extraction. In some embodiments, the methods of the present disclosure decrease the TSS content of spent quench water or free oil-separated spent quench water by about 60%, 70%, 75%, 80%, 85%, 90%, 95%, 99% or by about 100%, after solvent extraction.
[0052] In some embodiments, the methods of the present disclosure decrease the turbidity of spent quench water or free oil-separated spent quench water after solvent extraction. In some embodiments, the turbidity of spent quench water or free oil-separated spent quench water is decreased to about 0-50 Nephelometric Turbidity Units (NTU), about 0-45 NTU, about 0-40 NTU, about 0-30 NTU, about 0-20 NTU, about 0-15 NTU, about 0-10 NTU, or to about less than 10 NTU, including values and ranges there between, after solvent extraction. In some embodiments, the turbidity of spent quench water or free oil-separated spent quench water is decreased to about 50, 45, 40, 30, 25, 20, 15, 10, 5, or to about 0 NTU, after solvent extraction.
[0053] In some embodiments, the methods of the present disclosure decrease the turbidity of spent quench water or free oil-separated spent quench water by about 50-100%, about 60-100%, about 70-100%, about 75-100%, about 80-100%, about 85-100%, or by about 90-100%, including values and ranges there between, after solvent extraction. In some embodiments, the turbidity of spent quench water or free oil-separated spent quench water is decreased by about 50%, 60%, 70%, 75%, 80%, 85%, 90%, 95%, or by about 99%, after solvent extraction.
[0054] In some embodiments, the methods of the present disclosure decrease the Chemical Oxygen Demand (COD) of spent quench water or free oil-separated spent quench water after solvent extraction. In some embodiments, the methods of the present disclosure decrease the COD of spent quench water or free oil-separated spent quench water to about 200-1000 ppm, about 250-1000 ppm, about 300-1000 ppm, about 400-1000 ppm, about 500-1000 ppm, about 600- 1000 ppm, about 600-800 ppm, about 250-800 ppm, about 250-750 ppm, about 300-800 ppm, or to about 700-800 ppm, including values and ranges there between, after solvent extraction. In some embodiments, the methods of the present disclosure decrease the COD of spent quench water or free oil-separated spent quench water to about 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, or to about 1000 ppm, after solvent extraction.
[0055] In some embodiments, the methods of the present disclosure decrease the COD of spent quench water or free oil-separated spent quench water by about 60-100%, about 70-100%, about 75-100%, about 70-90%, or by about 80-100%, including values and ranges there between, after solvent extraction. In some embodiments, the methods of the present disclosure decrease the COD of spent quench water or free oil-separated spent quench water by about 60%, 70%, 75%, 80%, 85%, 90%, 95%, or by about 100%, after solvent extraction.
[0056] In some embodiments, the methods of the present disclosure reduce the levels of inorganic contaminants of spent quench water or free oil-separated spent quench water after solvent extraction. For example, in some embodiments, the methods of the present disclosure decrease the ion content of spent quench water or free oil-separated spent quench water after solvent extraction.
[0057] In some embodiments, the methods of the present disclosure decrease the sodium ion (Na+) content of spent quench water or free oil-separated spent quench water to about 0-0.5 ppm, about 0-0.4 ppm, about 0-0.3 ppm, about 0-0.2 ppm, or to about 0-0.1 ppm, including values and ranges there between, after solvent extraction. In some embodiments, the sodium ion content of spent quench water or free oil-separated spent quench water is decreased to about 0.5 ppm, 0.4 ppm, 0.3 ppm, 0.2 ppm, 0.1 ppm, or to about 0 ppm, after solvent extraction.
[0058] In some embodiments, the methods of the present disclosure decrease the sodium ion content of spent quench water or free oil-separated spent quench water by about 60-90%, about 60-80%, about 60-70%, about 70-90%, or by about 70-80%, including values and ranges there between, after solvent extraction. In some embodiments, the methods of the present disclosure decrease the sodium ion content of spent quench water or free oil-separated spent quench water by about 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, or by about 100%, after solvent extraction.
[0059] In some embodiments, the methods of the present disclosure decrease the ammonium ion (NH4+) content of spent quench water or free oil-separated spent quench water to about 0-5 ppm, 0-4.5 ppm, 0-4 ppm, 0-3.5 ppm, 0-3 ppm, 0-2.5 ppm, 0-2 ppm, 0-1.5 ppm, or to about 0-1 ppm, including values and ranges there between, after solvent extraction. In some embodiments, the ammonium ion content of spent quench water or free oil-separated spent quench water is decreased to about 5, 4.5, 4, 3.5, 3, 2.5, 2, 1.5, 1, or to about 0.5 ppm, after solvent extraction.
[0060] In some embodiments, the methods of the present disclosure decrease the ammonium ion content of spent quench water or free oil-separated spent quench water by about 10-50%, about 10-40%, about 10-30%, about 10-25%, about 10-20%, about 15-45%, about 15-40%, about 15-30%, about 20-50%, about 20-40%, about 20-30%, about 25-50%, or by about 30-50%, including values and ranges there between, after solvent extraction. In some embodiments, the methods of the present disclosure decrease the ammonium ion content of spent quench water or free oil-separated spent quench water by about 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, or by about 5%, after solvent extraction.
[0061] In some embodiments, the methods of the present disclosure decrease the chloride (Cl-) ion content of spent quench water or free oil-separated spent quench water to about 0-2 ppm, 0-1.5 ppm, 0 to 1 ppm, or to about 0-0.5 ppm, including values and ranges there between, after solvent extraction. In some embodiments, the chloride ion content of spent quench water or free oil-separated spent quench water is decreased to about 2, 1.8, 1.5, 1.2, 1, 0.8, 0.6, 0.5, 0.4, 0.3, 0.2, or to about 0.1 ppm after solvent extraction.
[0062] In some embodiments, the methods of the present disclosure decrease the chloride ion content of spent quench water or free oil-separated spent quench water by about 60-100%, about 70-100%, about 75-100%, about 70-90%, about 80-100%, or by about 90-100%, including values and ranges there between, after solvent extraction. In some embodiments, the methods of the present disclosure decrease the chloride ion content of spent quench water or free oil-separated spent quench water by about 60%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, or by about 100%, after solvent extraction.
[0063] In some embodiments, the methods of the present disclosure decrease the sulphate (SO42-) ion content of spent quench water or free oil-separated spent quench water to about 0-5 ppm, 0-4.5 ppm, 0-4 ppm, 0-3.5 ppm, 0-3 ppm, 0-2.5 ppm, 0-2 ppm, 0-1.5 ppm, or to about 0-1 ppm, including values and ranges there between, after solvent extraction. In some embodiments, the sulphate ion content of spent quench water or free oil-separated spent quench water is decreased to about 5, 4.5, 4, 3.5, 3, 2.5, 2, 1.5, 1, or to about 0.5 ppm, after solvent extraction.
[0064] In some embodiments, the methods of the present disclosure decrease the sulphate ion content of spent quench water or free oil-separated spent quench water by about 5-30%, 5-25%, 5-20%, 5-15%, 5-10%, 10-30%, 10-25%, 10-20%, or by about 15-30%, including values and ranges there between, after solvent extraction. In some embodiments, the methods of the present disclosure decrease the sulphate ion content of spent quench water or free oil-separated spent quench water by about 30%, 25%, 20%, 15%, 10%, or by about 5%, after solvent extraction.

Systems
[0065] The present disclosure also provides systems for removing impurities from spent quench and for cracking hydrocarbons.
[0066] In some embodiments, the system for removing impurities from spent quench water comprises (a) a quench water tower configured to receive a cracked hydrocarbon effluent from a cracking furnace; (b) a mixing unit (mixer settler) connected to the quench water tower; and (c) a sour water filtration system connected to the mixing unit (mixer settler).
[0067] In some embodiments, provided herein is a system for cracking hydrocarbons, comprising: (a) a cracking furnace to produce a cracked hydrocarbon effluent; (b) a quench water tower configured to receive the cracked hydrocarbon effluent; (c) a mixing unit (mixer settler) connected to the quench water tower; (d) a sour water filtration system connected to the mixing unit; (e) a sour water stripping unit connected to the sour water filtration system; and (f) a dilution steam generator.
[0068] In some embodiments, the mixing unit (mixer settler) comprises (i) a first inlet to receive a spent quench water, (ii) a second inlet to receive an organic solvent from a solvent chamber, (iii) mixing means to mix the spent quench water with the organic solvent, (iv) a first outlet to feed a solvent-extracted spent quench water to a sour water filtration system, (v) a second outlet to feed an interphase from the mixture (mixer settler) of the spent quench water and the organic solvent to an interphase unit, and (vi) a third outlet to feed the organic solvent layer comprising organic impurities to the solvent chamber.
[0069] In some embodiments, the spent quench water mixed with the organic solvent in the mixing unit (mixer settler) can be the free oil-separated spent quench water as described herein.
[0070] The mixing unit (mixer settler) mixes the spent quench water with the organic solvent at a speed of 50 - 1000 rpm. In some embodiments, the mixing unit (mixer settler) mixes the organic solvent with spent quench water or free oil-separated spent quench water at a speed of 50 to 900 rpm, 50 to 800 rpm, 50 to 700 rpm, 50 to 600 rpm, 50 to 500 rpm, 50 to 400 rpm, 50 to 300 rpm, 50 to 200 rpm, 100 to 1000 rpm, 100 to 900 rpm, 100 to 800 rpm, 100 to 750 rpm, 100 to 700 rpm, 100 to 600 rpm, 100 to 500 rpm, 100 to 400 rpm, 100 to 300 rpm, 100 to 250 rpm, 100 to 200 rpm, 200 to 1000 rpm, 200 to 900 rpm, 200 to 800 rpm, 200 to 750 rpm, 200 to 700 rpm, 200 to 600 rpm, 200 to 500 rpm, 200 to 400 rpm, 200 to 300 rpm, 300 to 1000 rpm, 300 to 900 rpm, 300 to 800 rpm, 300 to 750 rpm, 300 to 700 rpm, 300 to 600 rpm, 300 to 500 rpm, 300 to 400 rpm, 400 to 1000 rpm, 400 to 900 rpm, 400 to 800 rpm, 400 to 700 rpm, 400 to 600 rpm, 400 to 500 rpm, 500 to 1000 rpm, 500 to 900 rpm, 500 to 800 rpm, 500 to 750 rpm, 500 to 700 rpm, 600 to 1000 rpm, 600 to 900 rpm, 600 to 800 rpm, 700 to 1000 rpm, 700 to 900 rpm, or 800 to 1000 rpm. In some embodiments, the mixing unit (mixer settler) mixes the organic solvent with spent quench water or free oil-separated spent quench water at a speed of 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, or 1000 rpm.

[0071] ADVANTAGES/BENEFITS: The methods and systems of the present disclosure provides advantages, including but not limited to, the following:
1) Efficient and faster separation of impurities including oil, grease, tar, TDS, TSS, and inorganic contaminants from spent quench water upstream of the sour water filtration system.
2) Reduced clogging of filter elements due to the removal of organic and inorganic impurities from spent quench water.
3) Improved run length of water filtration system (pre-filters, filters and coalesce s) thereby reduction of revenue cost incurred for replacement of elements
4) Improved run length of dilution steam generators (DSG) by at least 50%, thereby savings in operating costs.
5) Used solvents are regenerable.
[0072] Additional embodiments and features of the present disclosure will be apparent to one of ordinary skill in art based upon description provided herein. The embodiments herein provide various features and advantageous details thereof in the description. Descriptions of well-known/conventional methods/steps and techniques are omitted so as to not unnecessarily obscure the embodiments herein. Further, the disclosure herein provides for examples illustrating the above described embodiments, and in order to illustrate the embodiments of the present disclosure certain aspects have been employed. The examples used herein for such illustration are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the following examples should not be construed as limiting the scope of the embodiments herein.

EXAMPLES:
Example 1
[0073] Cracked hydrocarbon effluent was quenched in a quench water tower to produce quenched effluent and spent quench water. Part of oil rich portion of spent quench water was separated as a side cut from the bottom of quench water tower and after separation of free oil in oil-water separator, the remaining oil-rich spent quench water (referred as “spent quench water” for the rest of this Example) was extracted with the organic solvents according to the invention as follows before treatment through pre-filter, filter and coalescer.
[0074] For removal of oil and suspended solids from spent quench water, three different types of solvents, i.e., paraffins (n-Hexane), aromatics (Toluene) and mixture of paraffins, naphthenes, olefins and aromatics (Light Naphtha, ~10% aromatics) were selected for solvent extraction studies.
[0075] During the study, following parameters were monitored to check the quality of spent quench water before and after treatment with organic solvents. The description included in parenthesis refers to the standard industry test or method used to measure the given parameter. As these tests/methods are known in the art and readily available to one of ordinary skill in the art, they are not described in detail here.

– pH of the liquid (IS 3025 part-11)
– Conductivity of the liquid (IS 3025 part-14)
– Oil and Grease, O&G, of the liquid (IS 3025 part-39)
– Total suspended solid, TSS, of the liquid (IS 3025 part-17)
– Total dissolved solid, TDS, of the liquid (IS 3025 part-16)
– Chemical oxygen demand, COD, of the liquid (IS 3025 part-58)
– Water soluble ions using ion chromatography (In-housed developed method)
– Distillation of separated oils, SIMDIST, (ASTM D 2887)
– Elemental (C, H, N, S) analysis of separated oil (ASTM D 5373)

[0076] Lab scale solvent extraction study of spent quench water was done using glass separating funnel of one liter capacity with an arrangement of stopper and stopcock.
[0077] Solvent Extraction: Selected solvents (n-Hexane, Toluene, and Light Naphtha, LN) were added to the spent quench water sample kept in the separating funnel by maintaining the solvent to feed ratio of 1:10 (v/v). The system was mixed vigorously for 30 seconds (minimum) and kept for settling. Organic and aqueous phases separated immediately after the mixing. Entire operation was done at ambient temperature.
[0078] After desired settling of the entire mixture to separate dissolved organic solvents from the aqueous phase, the oil free aqueous portion was taken out from the bottom of the separating funnel whereas the organic phase containing oil and other organic impurities was collected after removal of coagulated materials at the inter phase. All three samples were analyzed to determine impurity and oil concentrations in the treated water (solvent-extracted spent quench water) as well as the organic phase. Typical physical properties of three solvents used in the study are mentioned in Table 1.
Table 1: Typical Properties of Solvents Used for Extraction

Sr. No. Solvent Source BP
(?) d
(g/cc) Composition (wt. %) Mw
n-P+ n-O i-P Napthenes Aromatics
1. n-Hexane
(paraffin) Analytical Grade (99% pure), S D Fine Chem. 68 0.66 100 0 0 0 86
2. Toluene
(aromatic) Analytical Grade
(99% pure), Merck 110 0.87 0 0 0 100 92
3. Light Naphtha
(10% aromatic + 90% paraffin/olefin) Commercial Grade IBP = 56
FBP = 110 0.73 6.9 34.7 48.1 10.3 -

[0079] Observations: Appearance of the spent quench water sample was hazy and dirty yellow colored with suspended particulates matters and floated oil at the top. After mixing the organic solvent with spent quench water, the organic phase immediately separated out from the emulsion and appeared at the top with dark orange color. Coagulated light brown particulates matters was found at the interphase (IP). Slight hazy aqueous phase became cleared after approx. 4-5 hrs. incase of n-Hexane solvent and required longer time with increasing aromaticity of solvents. Collected samples of aqueous and organic phases were analyzed for desire properties.

[0080] Results and Discussion:
[0081] Oil & Suspended Solid Removal Efficiency of Different Solvents: To check efficiency of removal of contaminants / impurities from the spent quench water, three solvents e.g. n-Hexane, Toluene and Light Naphtha were separately taken by maintaining solvent to feed ratio of 1:10 (v/v). The extracted waters along with untreated water were analyzed after 4 hrs. of settling for determination of O&G, TDS, TSS, pH, Conductivity, turbidity and COD.
[0082] Table 2 shows all three solvents were efficient in removing emulsified and suspended oils from spent quench water. Haziness of the oil free aqueous phase was due to presence of ppm level of solvents in the aqueous phase which was cleared completely after settling of about 5 hr., 12hr. & ~48 hr. in case of n-hexane, light naphtha and toluene, respectively.
Table 2: Parameters of Spent Quench Water prior to and after solvent extraction
Sr. No. Sample Appearance O&G (ppm) pH Conduct-
-ivity (µs/cm2) TDS (ppm) TSS (ppm) Turbidity
(NTU) COD (ppm) Inter Phase Material
(ppm)
1. Spent Quench Water Dirty yellow, Hazy
Sight oily layer at top and suspended materials 401 5.10 59 15 150 567 4100 NA
2. n-Hexane Extracted Water Clear,
Transparent aft. 5 hr.
No oil & suspended materials 0 5.13 60 5 0 <10 340 31
3. Toluene Extracted Water Clear,
Transparent aft. ~48 hr.
No oil & suspended materials 0 5.07 62 5 0 <10 690 32
4. Light Naphtha Extracted Water Clear,
Transparent after 12 hr.
No oil & suspended materials 0 5.04 61 5 0 <10 750 32

[0083] Characterization of Separated Oil: Oil and gas (O&G) separated by solvent extraction was quantified by removing of solvent and characterization of the oil was done through SARA (Table 3A), SIMDIST (FIG. 2) and CHNS (Table 3B) analysis.
Table 3A: SARA Analysis

Table 3B: CHNS Analysis

[0084] Table 3A-3B and FIG. 2 show that separated oil is aromatic in nature. Significant amount of resin was also present. Boiling range of the oil is 210 – 510? with ~65% in the diesel range material.
[0085] Ion Analysis of Spent Quench Water prior to and after extraction: Cations and anions present in the solvent-extracted and untreated spent quench water were analyzed using ion chromatographic techniques. IC results showed the presence of sodium, ammonium, chloride and sulphate at very low ppm level.

Table 4: IC Data of Treated and Untreated Spent Quench Water

Sr. No. Sample Details Cations (ppm) Anions (ppm)
Na+ NH4+ Cl- SO42-
1. Quench Water prior to extraction 0.4 1.8 5.2 2.9
2. Solvent-extracted Quench Water 0.1 1.5 0.1 2.8

[0086] Recycling of Spent Solvent: After solvent extraction, most of the contaminants transferred from aqueous phase to the 10% organic phase used during extraction. To reduce the solvent quantity and make the process energy efficient, the spent solvent was recycled after extraction of contaminants from the spent quench water. In the laboratory, total 5 recycles of impurity-rich solvent were conducted by taking fresh spent quench water every time. 100% removal of oil, grease and TSS was observed in every cycle. The TDS content was also reduced in every cycle. See Table 5.

Table 5: Spent Solvent Recycle Data

Recycle No. Fresh Quench Water Sample
(ml) Vol. of Fresh Light Naphtha Used
(ml) Light Naphtha Recovered to Recycle
(ml) Appearance of Aq. Phase TDS
(ppm) TSS (ppm)
after 30 min. After 12 hr.
- - - - Light yellow, Hazy
with floated oil & Suspended particulates matters Light yellow, Hazy
with floated oil & partly precipitated Suspended particulates matters 15 150
0 200 20 0 Slight hazy, Colourless Clear Colourless 5 0
1 200 0 20 Slight hazy, Colourless Clear Colourless 5 0
2 200 0 20 Slight hazy, Colourless Clear Colourless 5 0
3 200 0 20 Slight hazy, Colourless Clear Colourless 5 0
4 200 0 20 Slight hazy, Colourless Clear Colourless 5 0

INCORPORATION BY REFERENCE
[0087] All references, articles, publications, patents, patent publications, and patent applications cited herein are incorporated by reference in their entireties for all purposes.
[0088] However, mention of any reference, article, publication, patent, patent publication, and patent application cited herein is not, and should not be taken as, an acknowledgment or any form of suggestion that they constitute valid prior art or form part of the common general knowledge in any country in the world.

NUMBERED EMBODIMENTS OF THE DISCLOSURE
1. A method for removing impurities from spent quench water, comprising:
a. providing spent quench water from quenching of a cracked hydrocarbon effluent in a quench water tower;
b. mixing said spent quench water with an organic solvent, wherein impurities from said spent quench water are extracted by the organic solvent to produce a solvent-extracted spent quench water; and
c. feeding the solvent-extracted spent quench water to a sour water filtration system.
2. A method for removing impurities from spent quench water, comprising:
a. providing spent quench water from quenching of a cracked hydrocarbon effluent in a quench water tower;
b. separating free oil from said spent quench water to provide free oil-separated spent quench water;
c. mixing said spent quench water or said free oil-separated spent quench water with an organic solvent, wherein impurities from said spent quench water or said free oil-separated spent quench water are extracted by the organic solvent to produce a solvent-extracted spent quench water; and
d. feeding the solvent-extracted spent quench water to a sour water filtration system.
3. A method for cracking hydrocarbons, comprising:
a. mixing a hydrocarbon stream with a steam stream to produce a mixed hydrocarbon stream;
b. cracking the mixed hydrocarbon stream in a cracking furnace to produce a cracked effluent;
c. quenching the cracked effluent in a quench water tower with quench water to produce a quenched effluent stream and a spent quench water;
d. mixing said spent quench water with an organic solvent, wherein impurities from said spent quench water are extracted by the organic solvent to produce a solvent-extracted spent quench water;
e. feeding the solvent-extracted spent quench water to a sour water filtration system to produce filtered spent quench water;
f. feeding the filtered spent quench water to a sour water stripper to produce stripped spent quench water; and
g. feeding the stripped spent quench water to a dilution steam generator to produce a clean steam stream.
4. A method for cracking hydrocarbons, comprising:
a. mixing a hydrocarbon stream with a steam stream to produce a mixed hydrocarbon stream;
b. cracking the mixed hydrocarbon stream in a cracking furnace to produce a cracked effluent;
c. quenching the cracked effluent in a quench water tower with quench water to produce a quenched effluent stream and a spent quench water;
d. separating free oil from said spent quench water to provide free oil-separated spent quench water;
e. mixing said spent quench water or said free oil-separated spent quench water with an organic solvent, wherein impurities from said spent quench water or said free oil-separated spent quench water are extracted by the organic solvent to produce a solvent-extracted spent quench water;
f. feeding the solvent-extracted spent quench water to a sour water filtration system to produce filtered spent quench water;
g. feeding the filtered spent quench water to a sour water stripper to produce stripped spent quench water; and
h. feeding the stripped spent quench water to a dilution steam generator to produce a clean steam stream.
5. The method of any one of embodiments 1 to 4, wherein the organic solvent is selected from the group consisting of: a paraffinic solvent, an aromatic solvent, an olefinic solvent and a mixture thereof.
6. The method of embodiment 5, wherein the paraffinic solvent is a C5-C12 alkane.
7. The method of embodiment 5 or 6, wherein the paraffinic solvent is n-hexane.
8. The method of embodiment 5, wherein the aromatic solvent is a substituted benzene.
9. The method of embodiment 8, wherein the substituted benzene is a C1-C3 alkyl substituted benzene.
10. The method of embodiment 8 or 9, wherein the substituted benzene is toluene.
11. The method of any one of embodiments 1 to 10, wherein the organic solvent is selected from the group consisting of: hexane, toluene, xylene, naphtha, light kerosene and a mixture thereof.
12. The method of embodiment 11, wherein the naphtha is light naphtha.
13. The method of any one of embodiments 1 to 11, wherein the organic solvent is a mixture of hexane and toluene.
14. The method of any one of embodiments 1 to 13, wherein the impurities comprise oil, grease, dissolved solids, and suspended solids.
15. The method of any one of embodiments 1 to 14, wherein the organic solvent is mixed with said spent quench water or said free oil-separated spent quench water in a ratio ranging from about 1:20 to about 1:4 (v/v).
16. The method of embodiment 15, wherein the ratio of the organic solvent to said spent quench water or said free oil-separated spent quench water is about 1:4, 1:5, 1:8, 1:10, 1:15, or 1:20.
17. The method of embodiment 15 or 16, wherein the ratio of the organic solvent to said spent quench water or said free oil-separated spent quench water is about 1:10.
18. The method of any one of embodiments 1 to 17, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water is carried out at least for 10 seconds.
19. The method of any one of embodiments 1 to 18, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water is carried out for about 10 seconds to about 5 minutes.
20. The method of any one of embodiments 1 to 19, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water is carried out for about 1 minute.
21. The method of any one of embodiments 1 to 20, wherein after mixing the organic solvent with said spent quench water or said free oil-separated spent quench water, the mixture is settled for about 2 hours to about 48 hours, prior to the step of feeding the solvent-extracted spent quench water to the sour water filtration system.
22. The method of embodiment 21, wherein the mixture is settled for about 5 hours, prior to the step of feeding the solvent-extracted spent quench water to the sour water filtration system.
23. The method of embodiment 21, wherein the mixture is settled for about 12 hours, prior to the step of feeding the solvent-extracted spent quench water to the sour water filtration system.
24. The method of embodiment 21, wherein the mixture is settled for about 48 hours, prior to the step of feeding the solvent-extracted spent quench water to the sour water filtration system.
25. The method of any one of embodiments 1 to 24, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the oil and grease content of said water to about 0-50 ppm.
26. The method of any one of embodiments 1 to 25, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the oil and grease content of said water to about 0-40 ppm, about 0-30 ppm, about 0-25 ppm, about 0-20 ppm, about 0-10 ppm, about 0-5 ppm, or to about 0 ppm.
27. The method of any one of embodiments 1 to 26, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the oil and grease content of said water by about 75-100%.
28. The method of any one of embodiments 1 to 27, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the oil and grease content of said water by about 90-100%.
29. The method of any one of embodiments 1 to 28, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the oil and grease content of said water by about 99%.
30. The method of any one of embodiments 1 to 29, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the total dissolved solids content of said water to about 0-20 ppm.
31. The method of any one of embodiments 1 to 30, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the total dissolved solids content of said water to about 10 ppm.
32. The method of any one of embodiments 1 to 31, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the total dissolved solids content of said water to about 5 ppm.
33. The method of any one of embodiments 1 to 32, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the total dissolved solids content of said water to about 0 ppm.
34. The method of any one of embodiments 1 to 33, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the total dissolved solids content of said water by about 60-100%.
35. The method of any one of embodiments 1 to 34, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the total dissolved solids content of said water by about 70%.
36. The method of any one of embodiments 1 to 35, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the total dissolved solids content of said water by about 75%.
37. The method of any one of embodiments 1 to 36, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the total suspended solids content of said water to about 0-20 ppm.
38. The method of any one of embodiments 1 to 37, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the total suspended solids content of said water to about 10 ppm.
39. The method of any one of embodiments 1 to 38, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the total suspended solids content of said water to about 5 ppm.
40. The method of any one of embodiments 1 to 39, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the total suspended solids content of said water to about 0 ppm.
41. The method of any one of embodiments 1 to 40, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the total suspended solids content of said water by about 75-100%.
42. The method of any one of embodiments 1 to 41, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the total suspended solids content of said water by about 90-100%.
43. The method of any one of embodiments 1 to 42, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the total suspended solids content of said water by about 99%.
44. The method of any one of embodiments 1 to 43, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases turbidity of said water to about 0-20 Nephelometric Turbidity Units (NTU).
45. The method of any one of embodiments 1 to 44, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases turbidity of said water to about 0-10 NTU.
46. The method of any one of embodiments 1 to 45, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases turbidity of said water to about 0-5 NTU.
47. The method of any one of embodiments 1 to 46, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases turbidity of said water by about 75-100%.
48. The method of any one of embodiments 1 to 47, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases turbidity of said water by about 90-100%.
49. The method of any one of embodiments 1 to 48, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases turbidity of said water by about 99%.
50. The method of any one of embodiments 1 to 49, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the chemical oxygen demand (COD) of said water to about 600-800 ppm.
51. The method of any one of embodiments 1 to 50, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the COD of said water to about 700-800 ppm.
52. The method of any one of embodiments 1 to 51, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the COD of said water to about 700 ppm.
53. The method of any one of embodiments 1 to 52, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the COD of said water to about 300-400 ppm.
54. The method of any one of embodiments 1 to 53, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the COD of said water by about 60-100%.
55. The method of any one of embodiments 1 to 54, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the COD of said water by about 70-90%.
56. The method of any one of embodiments 1 to 55, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the COD of said water by about 80%.
57. The method of any one of embodiments 1 to 56, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the sodium ion content of said water to about 0-0.2 ppm.
58. The method of any one of embodiments 1 to 57, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the sodium ion content of said water by about 60-80%.
59. The method of any one of embodiments 1 to 58, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the sodium ion content of said water by about 75%.
60. The method of any one of embodiments 1 to 59, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the ammonium ion content of said water to about 1-1.5 ppm.
61. The method of any one of embodiments 1 to 60, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the ammonium ion content of said water by about 10-50%.
62. The method of any one of embodiments 1 to 61, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the ammonium ion content of said water by about 15-30%.
63. The method of any one of embodiments 1 to 62, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the chloride ion content of said water to about 0-0.5 ppm.
64. The method of any one of embodiments 1 to 63, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the chloride ion content of said water by about 70-100%.
65. The method of any one of embodiments 1 to 64, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the chloride ion content of said water by about 90-100%.
66. The method of any one of embodiments 1 to 65, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the chloride ion content of said water by about 99%.
67. The method of any one of embodiments 1 to 66, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the sulphate ion content of said water to about 2.5 ppm.
68. The method of any one of embodiments 1 to 67, wherein the step of mixing the organic solvent with said spent quench water or said free oil-separated spent quench water decreases the sulphate ion content of said water by about 5-15%.
69. The method of any one of embodiments 1 to 68, wherein the organic solvent is a solvent recycled from a prior extraction process.
70. The method of any one of embodiments 1 to 69, wherein the organic solvent is a solvent recycled from one prior extraction process.
71. The method of any one of embodiments 1 to 69, wherein the organic solvent is a solvent recycled from two, three, or four prior extraction processes.
72. A system for removing impurities from spent quench water, comprising:
a. a quench water tower configured to receive a cracked hydrocarbon effluent from a cracking furnace;
b. a mixing unit (mixer-settler) connected to the quench water tower, wherein the mixing unit comprises (i) a first inlet to receive a spent quench water, (ii) a second inlet to receive an organic solvent from a solvent chamber, (iii) mixing means to mix the spent quench water with the organic solvent, (iv) a first outlet to feed a solvent-extracted spent quench water to a sour water filtration system, (v) a second outlet to feed an interphase from the mixture of the spent quench water and the organic solvent to interphase treatment compartment, and (vi) a third outlet to feed the organic solvent layer comprising organic impurities to the solvent chamber; and
c. a sour water filtration system connected to the mixing unit (mixer-settler).
73. A system for cracking hydrocarbons, comprising:
a. a cracking furnace to produce a cracked hydrocarbon effluent;
b. a quench water tower configured to receive the cracked hydrocarbon effluent;
c. a mixing (mixer-settler) unit connected to the quench water tower, wherein the mixing unit comprises (i) a first inlet to receive a spent quench water, (ii) a second inlet to receive an organic solvent from a solvent chamber, (iii) mixing means to mix the spent quench water with the organic solvent, (iv) a first outlet to feed a solvent-extracted spent quench water to a sour water filtration system, (v) a second outlet to feed an interphase from the mixture of the spent quench water and the organic solvent to an interphase treatment compartment, and (vi) a third outlet to feed the organic solvent layer comprising organic impurities to the solvent chamber;
d. a sour water filtration system connected to the mixing unit (mixer-settler);
e. a sour water stripping unit connected to the sour water filtration system; and
f. a dilution steam generator.
74. The system of embodiment 72 or 73, wherein the mixing unit mixes the spent quench water with the organic solvent at a speed of 50 - 1000 rpm.
,CLAIMS:1. A method for removing impurities from spent quench water, comprising:
a. providing spent quench water from quenching of a cracked hydrocarbon effluent in a quench water tower;
b. mixing said spent quench water with an organic solvent, wherein impurities from said spent quench water are extracted by the organic solvent to produce a solvent-extracted spent quench water; and
c. feeding the solvent-extracted spent quench water to a sour water filtration system.
2. The method as claimed in claim 1, wherein free oil is separated from said spent quench water prior to the mixing with an organic solvent
3. The method of as claimed in claim 1 or 2, wherein the organic solvent is selected from the group consisting of: a paraffinic solvent, an aromatic solvent, an olefinic solvent and a mixture thereof.
4. The method as claimed in claim 3, wherein the paraffinic solvent is a C5-C12 alkane and the aromatic solvent is a substituted benzene.
5. The method of as claimed in any one of claims 1-4, wherein the organic solvent is selected from the group consisting of: hexane, toluene, xylene, naphtha, light kerosene and a mixture thereof.
6. The method as claimed in any one of claims 1-5, wherein the organic solvent is light naphtha or a mixture of hexane and toluene.
7. The method of as claimed in any one of claims 1-6, wherein the organic solvent is mixed with said spent quench water in a ratio ranging from about 1:20 to about 1:4 (v/v).
8. The method as claimed in any one of claims 1-7, wherein the ratio of the organic solvent to said spent quench water is about 1:10.
9. The method as claimed in any one of claims 1-8, wherein after mixing the organic solvent with said spent quench water, the mixture is settled for about 2 hours to about 48 hours, prior to the step of feeding the solvent-extracted spent quench water to the sour water filtration system.
10. The method as claimed in any one of claims 1-9, wherein the step of mixing the organic solvent with said spent quench water decreases the oil and grease content of said water to about 0-50 ppm; decreases the total dissolved solids content of said water to about 0-20 ppm; decreases the total dissolved solids content of said water to about 10 ppm; and/or decreases the total suspended solids content of said water to about 0-20 ppm.
11. The method as claimed in any one of claims 1-10, wherein the step of mixing the organic solvent with said spent quench water decreases turbidity of said water to about 0-20 Nephelometric Turbidity Units (NTU); decreases the chemical oxygen demand (COD) of said water to about 600-800 ppm; decreases the sodium ion content of said water to about 0-0.2 ppm; decreases the ammonium ion content of said water to about 1-1.5 ppm; decreases the chloride ion content of said water to about 0-0.5 ppm; and/or decreases the sulphate ion content of said water to about 2.5 ppm.
12. The method as claimed in any one of claims 1-11, wherein the organic solvent is a solvent recycled from a prior extraction process.
13. A method for cracking hydrocarbons, comprising:
a. mixing a hydrocarbon stream with a steam stream to produce a mixed hydrocarbon stream;
b. cracking the mixed hydrocarbon stream in a cracking furnace to produce a cracked effluent;
c. quenching the cracked effluent in a quench water tower with quench water to produce a quenched effluent stream and a spent quench water;
d. removing impurities from said spent quench water as claimed in any one of claims 1-25 to produce stripped spent quench water; and
e. feeding the stripped spent quench water to a dilution steam generator to produce a clean steam stream.
14. A system for removing impurities from spent quench water, comprising:
a. a quench water tower configured to receive a cracked hydrocarbon effluent from a cracking furnace;
b. a mixing unit (mixer-settler) connected to the quench water tower, wherein the mixing unit comprises (i) a first inlet to receive a spent quench water, (ii) a second inlet to receive an organic solvent from a solvent chamber, (iii) mixing means to mix the spent quench water with the organic solvent, (iv) a first outlet to feed a solvent-extracted spent quench water to a sour water filtration system, (v) a second outlet to feed an interphase from the mixture of the spent quench water and the organic solvent to interphase treatment compartment, and (vi) a third outlet to feed the organic solvent layer comprising organic impurities to the solvent chamber; and
c. a sour water filtration system connected to the mixing unit (mixer-settler).