Method for controlling the disposal of wastewaters generated during petrochemical processes using an incinerator - Patents.com

Abstract

A process for treating waste liquids generated during a petrochemical process, the waste liquids comprising at least one first aqueous wastewater stream and at least one second organic fluid-based waste liquid stream, the method comprising the steps of: a) subjecting the at least one first aqueous wastewater stream to at least one freeze concentration stage to produce a third clean water stream and a fourth concentrated aqueous wastewater stream; and b) subjecting the at least one second organic fluid-based waste liquid stream to at least one separation stage to produce a fifth clean water stream and a fourth concentrated aqueous wastewater stream. and a sixth concentrated organic fluid-based waste stream; and c) passing the fourth concentrated aqueous wastewater stream and the sixth concentrated organic fluid-based waste stream to an incinerator and incinerating the fourth concentrated aqueous wastewater stream and the sixth concentrated organic fluid-based waste stream in the incinerator, wherein the method is controlled so that the incineration of the sixth concentrated organic fluid-based waste stream generates at least 70% of the energy required to incinerate the fourth concentrated aqueous wastewater stream.

Description

[Technical field]

[0001] The present invention relates to a method for treating wastewater generated during a petrochemical process, the wastewater comprising a first aqueous wastewater stream and a second organic fluid based wastewater stream. [Background technology]

[0002] Throughout many petrochemical processes, such as those that utilize one or more distillation or rectification steps, waste liquids are generated that include at least one aqueous wastewater stream and at least one organic fluid waste stream. Both streams must then be treated or purified or disposed of, for example, by incineration. Such petrochemical processes include, for example, the production of phenol and acetone from feed streams containing benzene and propylene via the cumene hydroperoxide process, and the utilization of cumene to produce propylene oxide.

[0003] The cumene hydroperoxide process involves the reaction of benzene with propylene to produce cumene, which is then converted to cumene hydroperoxide in the presence of molecular oxygen and then cleaved to phenol and acetone, usually using an acid catalyst. The cleavage products include the product phenol and acetone, as well as several by-products and impurities, such as acetophenone, cumene, 2-phenyl-2-propanol, etc. Usually, the product phenol and acetone are separated from the cleavage products by distillation. Furthermore, typically, unconverted cumene is recovered from the cleavage products, purified by vacuum distillation, and recycled to the process. Other by-products and impurities must be treated. For example, a plant designed to produce 200 kilotons / year of phenol generates about 1,000 kg / hour of heavy waste oil stream containing about 20 wt.% acetophenone and the balance other impurities and by-products, and about 5,000-10,000 kg / hour of wastewater stream containing methanol, acetone, phenol, cumene, etc.

[0004] Another example of a petrochemical process that generates significant amounts of waste liquids, including at least one aqueous wastewater stream and at least one organic fluid waste stream, is the utilization of cumene to produce propylene oxide. During this process, cumene is oxidized in air to obtain cumene hydroperoxide, which is used to epoxidize propylene to propylene oxide in the presence of a suitable epoxidation catalyst. During epoxidation, cumene is converted to dimethylbenzyl alcohol, which is hydrogenated with molecular hydrogen to recover cumene. After purification, the recovered cumene is recycled to the cumene oxidation step. During this process, significant amounts of organic fluid waste streams containing acetophenone, phenol, and the remainder of other impurities and by-products, as well as wastewater containing phenol and other impurities and by-products, are generated.

[0005] One option for treating waste streams is to dispose of them, for example by incineration. Such a method is disclosed, for example, in U.S. Pat. No. 6,164,087. More specifically, the method disclosed therein involves concentrating an aqueous waste stream before incinerating it with another waste stream. The purpose of concentrating an aqueous waste stream before incinerating it with another waste stream is to reduce the energy required for incineration by removing some of the water contained in the original waste stream. However, the process still requires a lot of energy for incineration. Summary of the Invention

[0006] In view of the above, it is an underlying object of the present invention to provide a method for treating waste liquids generated during a petrochemical process, the waste liquids comprising at least one aqueous wastewater stream and at least one organic fluid waste stream, in which the process utilises as much of the waste liquid components as possible by incineration, while minimising the energy required for incineration.

[0007] According to the present invention, the above object is achieved by providing a method for treating or purifying wastewater generated during a petrochemical process, the wastewater comprising at least one first aqueous wastewater stream and at least one second organic fluid waste stream, the method comprising the steps of: a) subjecting at least one first aqueous wastewater stream to at least one freeze concentration step to produce a third clean water stream and a fourth concentrated aqueous wastewater stream; b) subjecting the at least one second organic fluid waste stream to at least one separation step to produce a fifth purified product stream and a sixth concentrated organic fluid waste stream; c) passing the fourth concentrated aqueous wastewater stream and the sixth concentrated organic fluid waste stream to an incinerator and incinerating the fourth concentrated aqueous wastewater stream and the sixth concentrated organic fluid waste stream in the incinerator. wherein the method is controlled such that the incineration of the sixth concentrated organic fluid-based waste stream generates at least 70% of the energy required to incinerate the fourth concentrated aqueous wastewater stream.

[0008] By controlling the method such that the incineration of the sixth concentrated organic fluid-based waste stream generates at least 70% of the energy required to incinerate the fourth concentrated aqueous wastewater stream, at least a majority of the energy required to incinerate the fourth concentrated aqueous wastewater stream is utilized from the sixth concentrated organic fluid-based waste stream generated during the method. In other words, the sixth concentrated organic fluid-based waste stream is used as fuel for incineration, but only after one or more useful compounds contained in the second organic fluid-based waste stream have been separated. As a result, a useful portion of the second organic fluid-based waste liquid may be separated from the organic fluid-based waste liquid and then used as a raw material for a synthetic process or recycled within the method, etc., while the remaining portion of the second organic fluid-based waste liquid is used as fuel for incineration. Thus, the amount of externally supplied energy to the method can be significantly reduced or completely eliminated. Controlling the sixth concentrated organic fluid waste stream to generate at least 70% of the energy required to incinerate the fourth concentrated aqueous wastewater stream may be achieved by controlling or adjusting process parameters as appropriate, as described in more detail below.

[0009] According to step b) of the method of the invention, the at least one second organic fluid waste stream is subjected to at least one separation step to produce a fifth purified product stream and a sixth concentrated organic fluid waste stream. Purified product stream means in this context a stream that mainly comprises one or more compounds, which may be products of a petrochemical process, by-products of a petrochemical process and / or impurities of a petrochemical process. It is clear that only the compound or compounds separated off in at least one separation step have some value, i.e. they may be used as raw materials, catalysts, etc. in a petrochemical process or in any other process. Preferably, one compound is separated in step b), so that the fifth purified product stream mainly consists of this one compound and possibly small amounts of impurities.

[0010] As mentioned above, in step c) of the method of the invention, the method is controlled such that the incineration of the sixth concentrated organic fluid-based waste stream generates at least 70% of the energy required to incinerate the fourth concentrated aqueous wastewater stream. This may be achieved in particular by adjusting in the method at least one of the degree of concentration during the at least one freeze concentration step of step a), the degree of separation during the at least one separation step of step b) and the ratio between the fourth concentrated aqueous wastewater stream and the sixth concentrated organic fluid-based wastewater stream, so that the incineration of the sixth concentrated organic fluid-based waste stream generates at least 70% of the energy required to incinerate the fourth concentrated aqueous wastewater stream. For example, if the volume of the first aqueous wastewater stream is relatively large and therefore more energy is required for incineration, i) the degree of concentration during at least one freeze concentration stage of step a) may be increased so that more water is removed from the first aqueous wastewater stream to reduce the amount of water to be incinerated, and / or ii) the ratio between the fourth concentrated aqueous wastewater stream and the sixth concentrated organic fluid-based waste stream may be decreased so that more concentrated organic fluid-based waste stream is sent to incineration as fuel based on a given volume of the fourth concentrated aqueous wastewater stream, and / or iii) the degree of separation during at least one separation stage of step b) is decreased so that more organic fluid-based waste is present as fuel for incineration.

[0011] Considering that the initial concentration of impurities in the first aqueous wastewater stream may be higher and / or the final concentration of impurities in the first aqueous wastewater stream may be higher, it is preferred that at least two, more preferably all, of the degree of concentration during the at least one freeze concentration stage of step a), the degree of separation during the at least one separation stage of step b) and the ratio between the fourth concentrated aqueous wastewater stream and the sixth concentrated organic fluid-based waste stream are controlled in the method such that the incineration of the sixth concentrated organic fluid-based wastewater stream generates at least 70% of the energy required to incinerate the fourth concentrated aqueous wastewater stream.

[0012] In a further development of the inventive idea, it is proposed to control the method such that the incineration of the sixth concentrated organic fluid waste stream generates at least 80%, preferably at least 90%, more preferably at least 95% and most preferably at least all of the energy required to incinerate the fourth concentrated aqueous wastewater stream.

[0013] The present invention is not particularly limited with respect to the composition of the at least one first aqueous wastewater stream. However, it is preferred that the at least one first aqueous wastewater stream comprises 70-99.5% by weight of water and the remainder to 100% by weight, i.e. 0.5-30% by weight of impurities dissolved and / or dispersed in the water. Even more preferably, the at least one first aqueous wastewater stream comprises 80-95% by weight of water and the remainder to 100% by weight, i.e. 5-20% by weight of impurities dissolved and / or dispersed in the water.

[0014] The type of freeze concentration is also not particularly limited in the present invention. However, good results are obtained, particularly when at least one first aqueous wastewater stream is subjected to at least one suspension crystallization stage or at least one laminar crystallization stage in step a) for freeze concentration. The laminar crystallization stage may be a static crystallization stage or a falling film crystallization stage, with a static crystallization stage being preferred. For example, at least one first aqueous wastewater stream is subjected to one suspension crystallization stage or one static crystallization stage in step a) for freeze concentration. Alternatively, at least one first aqueous wastewater stream is subjected to two or more suspension crystallization stages in step a) for freeze concentration. Even more preferably, at least one first aqueous wastewater stream is subjected to at least one suspension crystallization stage and at least one static crystallization stage in step a) for freeze concentration, and most preferably, at least one suspension crystallization stage is carried out before the static crystallization stage.

[0015] According to a first particular preferred embodiment of the present invention, at least one first aqueous wastewater stream is subjected to at least one suspension crystallization stage in step a) for freeze concentration.Suspension crystallization has the advantage that it only requires a compact design, that it already provides a comparable high purity in one step or step, respectively, that it has a comparable low energy consumption, and that it has a comparable low installation cost.Generally, suspension crystallization is divided into two steps, firstly, the production of crystals of the compound to be purified, and secondly, the separation of the crystals from the remaining mother liquor.

[0016] In this respect, it is preferred that at least one suspension crystallization stage comprises at least one crystallization block for producing water crystals and at least one separation block for separating the crystals produced in the at least one crystallization block from the mother liquor. In one variant, the crystallization block comprises at least one scraped crystallizer for removing the heat of crystallization and a growth vessel that allows the produced crystals time to grow to a size that allows them to be separated, the separation block preferably comprising at least one wash column. In an alternative and indeed preferred variant, the crystallization block comprises a scraped crystallizer but no growth vessel. In this variant, the scraped crystallizer combines the functions of a crystallizer and a growth vessel.

[0017] According to certain preferred embodiments of the invention, the wash column comprises a cylindrical vessel, the cylindrical vessel comprising: a piston having a piston head and a piston rod, the piston head being arranged for reciprocating movement within the cylindrical container and coupled to a wash chamber within the cylindrical container above the piston head, the piston head including at least one filter means; an inlet for feeding the crystal suspension mixture produced in the crystallization block, consisting of crystals and mother liquor, into the cylindrical vessel; an outlet for draining the mother liquor from the cylindrical vessel; an outlet for discharging the crystals and / or the crystal melt from the cylindrical vessel; Includes.

[0018] In a further development of the idea of ​​the invention, it is proposed that the separation block comprises a circulation conduit for circulating the melt, arranged outside the cylindrical vessel, i.e. that the cylindrical vessel is connected to a circulation conduit for circulating the melt, arranged outside the cylindrical vessel, which communicates with the washing chamber and with means for partial melting and disintegration of the crystal bed, arranged in the washing chamber, for limiting the movement of the crystal bed compressed in the washing chamber by the piston and for directing the washing liquid entering the cylindrical vessel from the circulation conduit so as to distribute the washing liquid uniformly over the entire cross section of the washing column.

[0019] Preferably, at least one first aqueous wastewater stream is subjected to at least two, for example two, suspension crystallization stages in step a) for freeze concentration, especially if a high concentration of the first aqueous wastewater stream is to be obtained. Such a two-stage suspension crystallization allows a concentration about 10% higher than a one-stage suspension crystallization. Each of the two suspension crystallization stages comprises a crystallizer, both crystallizers may have the same or different design. The first suspension crystallization stage comprises, in addition to its crystallizer, a wash column as described above, the slurry obtained in the crystallizer of the first suspension crystallization stage is transferred to the wash column and the crystals obtained in the crystallizer of the first suspension crystallization stage are separated from the mother liquor. The crystals and / or the crystal melt are respectively removed as a third clean water stream, while the mother liquor obtained as the filtrate of the wash column is transferred to the crystallizer of the second suspension crystallization stage, which further comprises a thickener. The slurry obtained in the crystallizer of the second suspension crystallization stage is transferred to the thickener. The slurry is compressed in the thickener into a packed crystal bed, similar to the wash column, but the crystal bed is not washed in situ, or at least not completely, in the wash column. The crystal bed obtained in the thickener, after passing through a means for disintegrating the crystal bed, is transferred to the crystallizer of the first suspension crystallization stage, while at least a part of the concentrate obtained as the thickener filtrate is removed as a fourth concentrated aqueous wastewater stream, while another part of the concentrate is optionally returned to the crystallizer of the second suspension crystallization stage.

[0020] According to a second particularly preferred embodiment of the present invention, the at least one first aqueous wastewater stream is subjected in step a) for freeze concentration to at least one laminar crystallization stage, which may be at least one falling film crystallization stage or preferably at least one static crystallization stage.

[0021] According to a third particular preferred embodiment of the present invention, at least one first aqueous wastewater stream is subjected to at least one suspension crystallization stage and at least one laminar crystallization stage in step a) for freeze concentration, the laminar crystallization stage may be at least one falling film crystallization stage or preferably at least one static crystallization stage. More preferably, at least one first aqueous wastewater stream is subjected to one suspension crystallization stage followed by one laminar crystallization stage in step a) for freeze concentration, the laminar crystallization stage being more preferably a static crystallization stage. The advantage of this embodiment is that the feed stream can be very highly concentrated, i.e. the first aqueous wastewater stream can be treated to produce a third clean water stream and a fourth highly concentrated aqueous wastewater stream, even if the first aqueous wastewater stream has a relatively high viscosity. During suspension crystallization, the viscosity of the slurry increases exponentially with increasing concentration, so that an upper limit is set for the concentration in the suspension crystallization stage. If the mother liquor obtained in the suspension crystallization stage is subjected to a static crystallization stage, the concentration of the resulting fourth concentrated aqueous wastewater stream can be further increased. Thus, the suspension crystallization stage preferably comprises a crystallizer and a wash column as described above, the slurry obtained in the crystallizer of the suspension crystallization stage being transferred to the wash column, in which the crystals obtained in the crystallizer of the suspension crystallization stage are separated from the mother liquor. The crystals and / or the crystal melt are respectively removed as a third clean water stream, while the mother liquor obtained as the filtrate of the wash column is transferred to the static crystallizer of the static crystallization stage. The mother liquor obtained is removed from the static crystallizer after crystallization as the fourth concentrated aqueous wastewater stream, whereas the crystals and / or the crystal melt obtained in the static crystallization stage of the static crystallization stage are transferred to the feed to the crystallizer of the suspension crystallization stage.

[0022] Depending on the downstream use of the purified water, the third purified water stream obtained after the final stage of at least one freeze concentration stage preferably contains less than 1,000 ppm, more preferably less than 100 ppm, even more preferably less than 50 ppm, and most preferably less than 10 ppm of dissolved and / or dispersed impurities. Such a purified water stream may be used in the same process as the purified water or in a different process.

[0023] Furthermore, the fourth concentrated aqueous wastewater stream preferably comprises less than 90% by weight of water, more preferably less than 80% by weight of water, even more preferably less than 75% by weight, most preferably at most 70% by weight of water, the remainder up to 100% by weight being impurities dissolved and / or dispersed in water. The impurities may be of organic and / or inorganic nature and may also comprise insoluble substances such as salt(s) and / or finely dispersed organic phase droplets. For example, the impurities may be organic fluids, inorganic liquids, and / or inorganic solids such as salt(s). The content of organic fluids in the fourth concentrated aqueous wastewater stream is preferably at most 30% by weight, since otherwise the viscosity of the mother liquor during freeze concentration would be too high for the efficient mass transfer required during freeze concentration as well as an inappropriate depression of the freezing point.

[0024] In a further development of the inventive idea, it is proposed that the second organic fluid-based waste stream comprises 5-99.5% by weight, preferably 10-30% by weight, of one or more organic compounds separated by at least one separation stage during step b), and the remainder up to 100% by weight being one or more dissolved and / or dispersed impurities. Such a content of compounds separated by at least one separation stage during step b) is high enough that the desired compounds can be separated with sufficiently low effort by at least one separation stage during step b), but reasonably low enough that sufficient fuel remains for incineration.

[0025] The present invention is not particularly limited with respect to the chemical nature of the organic compound or compounds separated by at least one separation step during step b), for example, the compounds may be selected from the group consisting of phenol, cumene, acetophenone, 1,3-butylene glycol, acrylic acetate, acrylonitrile, and any combination of two or more of the above compounds.

[0026] The at least one separation stage used in step b) depends on the compounds to be separated by the at least one separation stage during step b), for example, the at least one separation stage to which the second organic fluid waste stream is subjected in step b) is selected from the group consisting of layer crystallization, distillation, extraction, and any combination of two or more of the above methods.

[0027] Depending on the downstream application of the product obtained in step b) or its saleable grade, respectively, it is preferred that the fifth product stream obtained after the last of at least one separation step in step b) contains less than 2,000 ppm, more preferably less than 1,000 ppm, even more preferably less than 100 ppm, even more preferably less than 50 ppm and most preferably less than 10 ppm of dissolved and / or dispersed impurities.

[0028] The temperature at which the fourth concentrated aqueous wastewater stream and the sixth concentrated organic fluid waste stream are incinerated in the incinerator during step c) should be high enough to completely decompose the hydrocarbons and other impurities, but as low as possible to minimize the energy demand of the process. In view of this, it is preferred that the fourth concentrated aqueous wastewater stream and the sixth concentrated organic fluid waste stream are incinerated in the incinerator during step c) at a temperature of at least 900°C, preferably between 900 and 1,100°C, more preferably between 900 and 1,000°C, most preferably between 900 and 950°C. This may be achieved by appropriately adjusting the ratio between the fourth concentrated aqueous wastewater stream and the sixth concentrated organic fluid waste stream, i.e. by adjusting said ratio so that the incineration takes place at least at 900°C, preferably between 900 and 1,100°C, more preferably between 900 and 1,000°C, most preferably between 900 and 950°C.

[0029] For this reason, it is preferred that the sixth concentrated organic fluid waste stream has a reasonably high heat of combustion, with good results being obtained when the sixth concentrated organic fluid waste stream has a heat of combustion of at least 2,000 kJ / kg, more preferably at least 2,500 kJ / kg, and most preferably at least 2,800 kJ / kg.

[0030] As mentioned above, the ratio of the fourth concentrated aqueous wastewater stream to the sixth concentrated organic fluid-based wastewater stream is preferably controlled in the process and may be varied in response to variations in the composition of the at least one first aqueous wastewater stream and the at least one second organic fluid-based wastewater stream. In general, however, good results are obtained when the fourth concentrated aqueous wastewater stream and the sixth concentrated organic fluid-based wastewater stream are fed to the incinerator in step c) in a volumetric ratio of between 2:1 and 10:1, preferably between 4:1 and 8:1, more preferably between 5:1 and 7:1, for example about 6:1.

[0031] Another aspect of the invention is a plant for treating or purifying wastewater generated during a petrochemical process, the wastewater comprising a first aqueous wastewater stream and a second organic fluid waste stream, the plant comprising: a) a source for a first aqueous wastewater stream; b) a source for a second organic fluid waste stream; c) at least one freeze concentration stage having an inlet line for feeding the first aqueous wastewater stream to the at least one freeze concentration stage, and an outlet line for removing a third clean water stream produced in the freeze concentration stage, and an outlet line for removing a fourth concentrated aqueous wastewater stream produced in the freeze concentration stage; d) at least one separation stage having an inlet line for feeding the second organic fluid waste stream to the at least one separation stage, an outlet line for removing a fifth purified product stream produced by the at least one separation stage, and an outlet line for removing a sixth concentrated organic fluid waste stream produced by the at least one separation stage; e) an incinerator having an inlet line for supplying a fourth concentrated aqueous wastewater stream and an inlet line for supplying a sixth concentrated organic fluid waste stream to the incinerator; and f) a control unit embodied in such a way that the incineration of the sixth concentrated organic fluid waste stream generates at least 70% of the energy required to incinerate the fourth concentrated aqueous waste stream. Includes.

[0032] Preferably, the control unit includes at least one of a measuring device for determining the concentration of the fluid stream treated in the at least one freeze concentration stage, a measuring device for determining the degree of separation during the at least one separation stage, and a device for controlling the ratio between the fourth concentrated aqueous wastewater stream and the sixth concentrated organic fluid waste stream fed to the incinerator.

[0033] According to a preferred embodiment of the invention, the at least one freeze concentration stage comprises at least one suspension crystallization stage and / or at least one static crystallization stage.

[0034] Preferably, the at least one separation step is selected from the group consisting of a laminar crystallization step, a distillation step, an extraction step, and any combination of two or more of the foregoing steps.

[0035] According to a particular preferred embodiment of the invention, at least one freeze concentration stage comprises at least one suspension crystallization stage comprising at least one crystallization block for producing water crystals and at least one separation block for separating the crystals produced in the at least one crystallization block from the mother liquor, the crystallization block comprising at least one crystallizer and the separation block comprising at least one wash column. In one variant, the crystallization block comprises at least one scraped crystallizer for removing the heat of crystallization and a growth vessel that allows time for the produced crystals to grow to a size that allows them to be separated. In an alternative and in fact preferred variant, the crystallization block comprises a scraped crystallizer but no growth vessel. In this variant, the scraped crystallizer combines the functions of a crystallizer and a growth vessel.

[0036] Further, it is preferred that the separation block comprises at least one washing column. More preferably, the at least one washing column comprises a cylindrical vessel, the cylindrical vessel comprising: a piston having a piston head and a piston rod, the piston head being arranged for reciprocating movement within the cylindrical container and coupled to a wash chamber within the cylindrical container above the piston head, the piston head including at least one filter means; an inlet line for feeding the crystal suspension mixture produced in the crystallization block, consisting of crystals and mother liquor, into the cylindrical vessel; an outlet line for draining the mother liquor from the cylindrical vessel; an outlet line for discharging the crystals and / or the crystal melt from the cylindrical vessel; Includes.

[0037] According to a further particular preferred embodiment of the invention, the at least one freeze concentration stage comprises at least two, more preferably two, suspension crystallization stages. Preferably, each of the at least two suspension crystallization stages comprises a suspension crystallizer, both suspension crystallizers may have the same or different design. The first suspension crystallization stage comprises, in addition to its crystallizer, a wash column as described above and a line connecting the crystallizer to the wash column such that the slurry obtained in the crystallizer of the first suspension crystallization stage is transferred to the wash column, the crystals obtained in the crystallizer of the first suspension crystallization stage being separated from the mother liquor. The wash column comprises a removal line for the crystals and / or crystal melt, respectively, and a line connecting the wash column to the second suspension crystallization stage such that the mother liquor obtained as filtrate of the wash column is transferred to the crystallizer of the second suspension crystallization stage. The second suspension crystallization stage further comprises a concentrator and a line connecting the crystallizer to the concentrator such that the slurry obtained in the crystallizer of the second suspension crystallization stage is transferred to the concentrator. The thickener comprises a line connecting it to the crystallizer of the first suspension stage, such that the crystal bed obtained in the thickener is transferred to the crystallizer of the first suspension crystallization stage after passing through the means for disintegration of the crystal bed.Furthermore, the thickener comprises a line for removing the concentrate obtained in the thickener as a filtrate, said line may be divided into a removal line and a recirculation line, such that at least a part of the concentrate obtained as the filtrate of the thickener is removed as a fourth concentrated aqueous wastewater stream, while optionally another part of the concentrate is returned to the crystallizer of the second suspension crystallization stage.

[0038] According to a further particular preferred embodiment of the present invention, at least one freeze concentration stage comprises at least one suspension crystallization stage and at least one laminar crystallization stage, the laminar crystallization stage may be at least one falling film crystallization stage or preferably at least one static crystallization stage. More preferably, at least one freeze concentration stage comprises one suspension crystallization stage and one laminar crystallization stage downstream thereof, the laminar crystallization stage being more preferably a static crystallization stage. Preferably, the suspension crystallization stage comprises a suspension crystallizer as described above and a washing column. The washing column comprises a removal line for the crystals and / or crystal melt, respectively, and a line connecting the washing column with the second static crystallization stage, so that the mother liquor obtained as filtrate of the washing column is transferred to the crystallizer of the second suspension crystallization stage. The freeze concentration stage further comprises a line connecting the static crystallizer of the second static crystallization stage to the crystallizer of the first suspension crystallization stage such that the crystals and / or crystal melt obtained in the crystallizer of the second static crystallization stage are transferred to the crystallizer of the first suspension crystallization stage or to the feed to the crystallizer of the first suspension crystallization stage.Furthermore, the crystallizer of the second static crystallization stage comprises a removal line for removing the mother liquor obtained in the crystallizer of the second static crystallization stage as a fourth concentrated aqueous wastewater stream.

[0039] Next, specific embodiments according to the present invention will be described with reference to the accompanying drawings. [Brief description of the drawings]

[0040] [Figure 1] FIG. 1 is a schematic diagram of a method and plant for treating waste liquids generated during a petrochemical process, the waste liquids comprising at least one first aqueous wastewater stream and at least one second organic fluid waste stream, according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram of the freeze concentration stage of a method and plant according to one embodiment of the present invention. [Diagram 3] FIG. 2 is a schematic diagram of a freeze concentration stage of a method and plant according to another embodiment of the present invention. [Figure 4] FIG. 2 is a schematic diagram of a freeze concentration stage of a method and plant according to yet another embodiment of the present invention. [Diagram 5] FIG. 2 is a schematic diagram of a freeze concentration stage of a method and plant according to yet another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] In the method according to the invention shown in FIG. 1, a feedstock 2 is fed to a petrochemical main process 4, where the feedstock 2 is processed to a main product 6. During the method, a first aqueous wastewater stream 8, a second organic fluid waste stream 10 and optionally further waste products 12 are also generated. For example, the main process 4 is a process for producing cumene hydroperoxide, and the feedstock 2 is benzene and propylene which end up in cumene hydroperoxide as the main product 6. In this case, the first aqueous wastewater stream 8 contains methanol, acetone, phenol, cumene and other compounds, whereas the second organic fluid waste stream 10 contains acetophenone and the further waste products 12 contain other by-products. The further waste products 12 are disposed of in an apparatus 14 and / or subjected to primary treatment. The first aqueous wastewater stream 8 is led to a freeze concentration stage 24, where the first aqueous wastewater stream 8 is separated into a third clean water stream 26 and a fourth concentrated aqueous wastewater stream 28. The third clean water stream 26 is directed to the disposal and / or primary treatment device 14, while the fourth concentrated aqueous wastewater stream 28 is directed to the incinerator 16. Additionally, the second organic fluid waste stream 10 is directed to a separation stage 30 where it is separated into a fifth purified product stream 32 and a sixth concentrated organic fluid waste stream 34. The fifth purified product stream 32 is combined with the main product 6 after a portion of the by-products 36 has been removed therefrom, while the sixth concentrated organic fluid waste stream 34 is directed to the incinerator 16. According to the invention, the method is controlled by a control unit (not shown) such that the incineration of the sixth concentrated organic fluid-based waste stream 34 generates at least 70% of the energy required for incinerating the fourth concentrated aqueous wastewater stream 28, so that at least the majority of the energy required for incineration of the fourth concentrated aqueous wastewater stream 28 is utilized from the sixth concentrated organic fluid-based waste stream 34 generated during the main process 4. In other words, the sixth concentrated organic fluid-based waste stream 34 is used as fuel for incineration, but only after the useful compound or compounds contained in the second organic fluid-based waste stream 10 have been separated.As a result, a useful portion of the second organic fluid-based waste liquid 10 may be separated from the second organic fluid-based waste liquid 10 and then used as a feedstock for a synthesis process or recycled within the method, etc., while the remaining portion of the second organic fluid-based waste liquid 10 is used as fuel for incineration. Thus, the amount of externally supplied energy to the method can be significantly reduced or completely eliminated. The control of generating at least 70% of the energy required to incinerate the fourth concentrated aqueous wastewater stream 28 by the sixth concentrated organic fluid-based waste liquid stream 34 may be achieved in the method by adjusting at least one of the degree of concentration during the freeze concentration step 24, the degree of separation during the separation step 30, and the ratio between the fourth concentrated aqueous wastewater stream 28 and the sixth concentrated organic fluid-based waste liquid stream 34, such that the incineration of the sixth concentrated organic fluid-based waste liquid stream 34 generates at least 70% of the energy required to incinerate the fourth concentrated aqueous wastewater stream 28.

[0042] Figure 2 is a schematic diagram of a freeze concentration stage 24 of a method and plant according to an embodiment of the present invention, such as the method and plant described above in Figure 1. The freeze concentration stage 24 comprises a suspension crystallizer 38 for producing water crystals, a wash column 40 for separating the crystals produced in at least one crystallization block from the mother liquor, an inlet line 42 for feeding the first aqueous wastewater stream to the freeze concentration stage 24, an outlet line 44 for removing the third clean water stream produced in the freeze concentration stage 24, and an outlet line 46 for removing the fourth concentrated aqueous wastewater stream produced in the freeze concentration stage 24. The freeze concentration stage 24 further comprises a feed tank 48, which is connected to the inlet 42 and to a feed line 50 leading to the suspension crystallizer 38. The suspension crystallizer 38 is further provided with a circulation line 52 including a pump 54. A slurry line 56 leads from the circulation line 52 to the wash column 40. The wash column 40 is also connected to a concentrate line 58, which is divided into an outlet line 46 and a return line 60. During operation of the plant, a first aqueous wastewater stream is transferred via an inlet line 42 to a feed tank 48 and from the feed tank 48 via a feed line 50 to the suspension crystallizer 38, where water crystals are formed to obtain a slurry containing water crystals and mother liquor. The slurry is recirculated via a circulation line 52, from which a part of the slurry is transferred via a slurry line 56 to the wash column 40. The water crystals are separated from the mother liquor in the wash column 40 and are removed from the freeze concentration stage 24 as a melt via an outlet line 44 as a third clean water stream. The mother liquor obtained in the wash column 40 is transferred from the wash column 40 via a concentrate line 58, from which a part is removed via an outlet line 46 as a fourth concentrated aqueous wastewater stream and another part is transferred via a return line 60 to the feed tank 48.

[0043] Figure 3 is a schematic diagram of a freeze concentration stage 24 according to another embodiment of the invention, comprising two suspension crystallization stages. Each of the two suspension crystallization stages comprises a suspension crystallizer 38, 38', the first suspension crystallization stage being embodied as described above with reference to Figure 2, with the difference that the concentrate line 58 is not divided into an outlet line 46 and a return line 60. Here, the concentrate line 58 leads to a feed tank 48' of a second suspension crystallization stage, which further comprises a thickener 62. The feed tank 48' of the second suspension crystallization stage is connected to a feed line 50' leading to the suspension crystallizer 38'. Furthermore, the suspension crystallizer 38' is provided with a circulation line 52' comprising a pump 54'. A slurry line 56' leads from the circulation line 52' to the thickener 62. Also connected to the thickener 62 is a concentrate line 58' which splits into an outlet line 46' and a return line 60'. The thickener 62 is further connected to a line 64 which leads to the circulation line 52 of the first suspension crystallization stage. During operation of the plant, the first aqueous wastewater stream is transferred via the inlet line 42 to the feed tank 48 of the first suspension crystallization stage, where it is treated as described above with reference to FIG. 2, except that the mother liquor obtained in the washing column 40 is not partially withdrawn and partially fed to the feed tank 48. Here, the mother liquor obtained in the washing column 40 is transferred from the washing column 40 via the concentrate line 58 to the feed tank 48' of the second suspension crystallization stage. From there, the mother liquor or the feed, respectively, is pumped via the feed line 50' to the suspension crystallizer 38', where water crystals are formed to obtain a slurry comprising water crystals and mother liquor. The slurry is recycled via circulation line 52' from which a part of the slurry is transferred via slurry line 56' to thickener 62. The crystal bed obtained in the thickener, after passing through a means for disintegrating the crystal bed, is transferred via line 64 to the circulation line 52 of the first suspension crystallization stage. The concentrate obtained in the thickener 62 as filtrate is transferred from the thickener 62 via concentrate line 58' from where a part is removed as the fourth concentrated aqueous wastewater stream via outlet line 46' and another part is transferred via return line 60' to the feed tank 48'.

[0044] 4 is a schematic diagram of a freeze concentration stage 24 according to another embodiment of the invention, which includes one static crystallization stage. The static crystallization stage includes a static crystallizer 66, a feed tank 48, an inlet line 42, a feed line 50, an outlet line 44 for the third clean water stream, and an outlet line 46 for removing the fourth concentrated aqueous wastewater stream. During operation of the plant, the first aqueous wastewater stream is transferred to the feed tank 48 via the inlet line 42 and from the feed tank 48 via the feed line 50 to the static crystallizer 66, where water crystals are formed on the cooling plate contained in the static crystallizer 66, obtaining a crystal layer and a mother liquor. After the crystallization is completed, the mother liquor is removed from the static crystallizer 66 as the fourth concentrated aqueous wastewater stream via the outlet line 46, and then the crystal layer is melted and the melt is removed as the third clean water stream via the outlet line 44.

[0045] Figure 5 is a schematic diagram of a freeze concentration stage 24 according to another embodiment of the invention, comprising one suspension crystallization stage and one static crystallization stage. The suspension crystallization stage is embodied as described above with reference to Figure 2, with the difference that the concentrate line 58 is not divided into an outlet line 46 and a return line 60. Here, the concentrate line 58 leads to a feed tank 48' of the static crystallization stage. The static crystallization stage further comprises a static crystallizer 66, an outlet line 46 for the fourth concentrated aqueous wastewater stream, and a line 68 for transferring the crystal melt of intermediate purity obtained after melting the crystal layer formed on the cooled surface of the static crystallizer to the feed tank of the suspension crystallization stage. During operation of the plant, the first aqueous wastewater stream is transferred via an inlet line 42 to the feed tank 48 of the first suspension crystallization stage, where it is treated as described above with reference to Figure 2, except that the mother liquor obtained in the washing column 40 is not partially withdrawn and partially fed to the feed tank 48. Here, the mother liquor obtained in the washing column 40 is transferred from the washing column 40 via a concentrate line 58 to the feed tank 48' of the static crystallization stage. From there, the mother liquor or feed, respectively, is fed via a feed line 50' to a static crystallizer 66, in which water crystals form on cooled plates contained in the static crystallizer 66 to obtain a crystal layer and a mother liquor. The mother liquor is removed as a fourth concentrated aqueous wastewater stream via an outlet line 46, and the molten crystal layer obtained in the static crystallizer 66 is removed from the static crystallizer 66 and transferred via a line 68 to the feed tank 48 of the suspension crystallization stage. [Explanation of symbols]

[0046] 2 Raw materials 4. Main / Petrochemical Processes 6 Main products 8 First Aqueous Wastewater Stream 10 Second organic fluid waste stream 12 More waste 14 Disposal and / or primary treatment equipment 16 Incinerator 18 fuel 20 Gas 22 Ash 24 Freeze concentration step 26 The third clean water stream 28 Fourth concentrated aqueous waste stream 30 Separation Stage 32 Fifth refined product stream 34 Sixth concentrated organic fluid waste stream 36 By-products 38, 38' Suspension Crystallizer 40 Washing column 42 Entrance Line 44 Outlet line for third clean water stream 46, 46' Outlet line for fourth concentrated aqueous wastewater stream 48, 48' Supply Tank 50, 50' supply line 50 52, 52' Circulation Line 54, 54' Pump 56, 56' Slurry Line 58, 58' Concentrate Line 60, 60' return line 62 Concentrator 64 lines 66 Static crystallizer 68 Line

Claims

1. A method for treating wastewater generated during a petrochemical process (4), the wastewater comprising at least one first aqueous wastewater stream (8) and at least one second organic fluid waste stream (10), the method comprising the steps of: a) subjecting at least one first aqueous wastewater stream (8) to at least one freeze concentration stage (24) to produce a third clean water stream (26) and a fourth concentrated aqueous wastewater stream (28); b) subjecting the at least one second organic fluid waste stream (10) to at least one separation stage (30) to produce a fifth purified product stream (32) and a sixth concentrated organic fluid waste stream (34), the second organic fluid waste stream (10) comprises 5-99.5% by weight of one or more organic compounds, the remainder up to 100% by weight being one or more dissolved and / or dispersed impurities, said one or more organic compounds separated by at least one separation stage (30) during step b) and being selected from the group consisting of phenol, cumene, acetophenone, 1,3-butylene glycol, acrylic acetate, acrylonitrile, and any combination of two or more of the foregoing compounds; at least one separation stage (30) to which the second organic fluid waste stream (10) is subjected in step b) is selected from the group consisting of layer crystallization, distillation, extraction, and any combination of two or more of the above methods; the fifth purified product stream (32) obtained in step b) contains less than 2,000 ppm dissolved and / or dispersed impurities; subjecting the at least one second organic fluid waste stream (10) to at least one separation stage (30) to produce a fifth purified product stream (32) and a sixth concentrated organic fluid waste stream (34); c) passing the fourth concentrated aqueous wastewater stream (28) and the sixth concentrated organic fluid waste stream (34) to an incinerator (16) and incinerating the fourth concentrated aqueous wastewater stream and the sixth concentrated organic fluid waste stream (28, 34) in the incinerator (16); wherein the incineration of the sixth concentrated organic fluid-based waste stream (34) is controlled to generate at least 70% of the energy required to incinerate the fourth concentrated aqueous wastewater stream (28).

2. 2. The method of claim 1, wherein during the method at least one of the degree of concentration during the at least one freeze concentration stage (24) of step a), the degree of separation during the at least one separation stage (30) of step b) and the ratio between the fourth concentrated aqueous wastewater stream (28) and the sixth concentrated organic fluid-based wastewater stream (34) is adjusted such that the incineration of the sixth concentrated organic fluid-based wastewater stream (34) generates at least 70% of the energy required to incinerate the fourth concentrated aqueous wastewater stream (28).

3. 3. The method of claim 1 or 2, wherein the incineration of the sixth concentrated organic fluid waste stream (34) is controlled to generate at least 80%, preferably at least 90%, more preferably at least 95%, and most preferably at least all of the energy required to incinerate the fourth concentrated aqueous wastewater stream (28).

4. 4. The method according to any one of claims 1 to 3, wherein the at least one first aqueous wastewater stream (8) comprises 70 to 99.5% by weight, preferably 80 to 95% by weight of water and 0.5 to 30% by weight, preferably 5 to 20% by weight of dissolved and / or dispersed impurities.

5. At least one first aqueous wastewater stream (8) is subjected in step a) for freeze concentration (24) to at least one suspension crystallization stage, the at least one suspension crystallization stage comprising at least one crystallization block for producing water crystals and at least one separation block for separating the crystals produced in the at least one crystallization block from the mother liquor, the crystallization block comprising at least one scraped crystallizer (38, 38'), the separation block comprising at least one wash column (40), preferably the wash column (40) being a cylindrical vessel, a piston having a piston head and a piston rod arranged for reciprocating movement within the cylindrical container and associated with a washing chamber within the cylindrical container above the piston head, the piston head including at least one filter means; an inlet for feeding the crystal suspension mixture produced in the crystallization block, consisting of crystals and mother liquor, into the cylindrical vessel; an outlet for draining the mother liquor from the cylindrical vessel; an outlet for discharging the crystals and / or the crystal melt from the cylindrical vessel; 5. The method of claim 1 , further comprising a cylindrical vessel comprising:

6. 6. The method according to claim 5, wherein the cylindrical vessel is connected to a circulation conduit for circulating the melt, arranged outside the cylindrical vessel, the circulation conduit communicating with the washing chamber and with means for partial melting and disintegration of the crystal bed arranged in the washing chamber, the means being for limiting the movement of the crystal bed compressed in the washing chamber by the piston and for directing the washing liquid from the circulation conduit into the cylindrical vessel so as to distribute the washing liquid uniformly over the entire cross section of the washing column.

7. 7. The method according to any one of claims 1 to 6, wherein the at least one first aqueous wastewater stream (8) is subjected to at least one static crystallization stage in step a) for freeze concentration (24).

8. 8. The method according to claim 1, wherein the at least one first aqueous wastewater stream (8) is subjected in step a) for freeze concentration (24) to i) at least two suspension crystallization stages or ii) to at least one suspension crystallization stage and at least one static crystallization stage, the at least one static crystallization stage being downstream of the at least one suspension crystallization stage.

9. 9. The method according to any one of claims 1 to 8, wherein the second organic fluid waste stream (10) comprises 10-30 wt. % of the organic compound(s) separated by at least one separation stage (30) during step b), and the remainder up to 100 wt. % being dissolved and / or dispersed impurities(s).

10. 10. The process according to any one of the preceding claims, wherein the fifth purified product stream (32) obtained in step b) contains less than 1,000 ppm, preferably less than 100 ppm, more preferably less than 50 ppm, and most preferably less than 10 ppm of dissolved and / or dispersed impurities.

11. 11. The method according to any one of claims 1 to 10, wherein the ratio between the fourth concentrated aqueous wastewater stream (28) and the sixth concentrated organic fluid-based waste liquid stream (34) is adjusted such that the incineration of the fourth concentrated aqueous wastewater stream (28) and the sixth concentrated organic fluid-based waste liquid stream (34) is carried out at a temperature of at least 900°C, preferably between 900 and 1,100°C, more preferably between 900 and 1,000°C, most preferably between 900 and 950°C.

12. A plant for carrying out the method according to any one of claims 1 to 11, wherein the waste liquid comprises a first aqueous wastewater stream (8) and a second organic fluid waste liquid stream (10), the plant comprising: a) a source (4) for a first aqueous wastewater stream (8); b) a source (4) for a second organic fluid waste stream (10); c) at least one freeze concentration stage (24) having an inlet line (42) for feeding the first aqueous wastewater stream (8) to the at least one freeze concentration stage (24), an outlet line (44) for removing a third clean water stream (26) produced in the freeze concentration stage (24), and an outlet line (46, 46') for removing a fourth concentrated aqueous wastewater stream (28) produced in the at least one freeze concentration stage (24); d) at least one separation stage (30) having an inlet line for feeding the second organic fluid waste stream (10) to the at least one separation stage (30), an outlet line for removing a fifth purified product stream (32) produced in the at least one separation stage (30), and an outlet line for removing a sixth concentrated organic fluid waste stream (34) produced in the at least one separation stage (30); e) an incinerator (16) having an inlet line for supplying a fourth concentrated aqueous wastewater stream (28) and an inlet line for supplying a sixth concentrated organic fluid waste stream (34) to the incinerator (16); f) a control unit embodied in such a way that the incineration of the sixth concentrated organic fluid waste stream (34) produces at least 70% of the energy required to incinerate the fourth concentrated aqueous waste stream (28). The plant includes:

13. 13. The plant according to claim 12, wherein the control unit comprises at least one of a measuring device for determining the concentration of the fluid stream treated in the at least one freeze concentration stage (24), a measuring device for determining the degree of separation during the at least one separation stage (30), and a device for controlling the ratio between the fourth concentrated aqueous wastewater stream (28) and the sixth concentrated organic fluid waste stream (34) fed to the incinerator (16).

14. 14. A plant according to claim 12 or 13, wherein the at least one freeze concentration stage (24) comprises at least one suspension crystallization stage and / or at least one static crystallization stage, and preferably the at least one separation stage (30) is selected from the group consisting of a laminar crystallization stage, a distillation stage, an extraction stage and any combination of two or more of the above stages.

15. At least one freeze concentration stage (24) comprises at least one suspension crystallization stage comprising at least one crystallization block for producing water crystals and at least one separation block for separating the crystals produced in the at least one crystallization block from the mother liquor, the crystallization block comprising at least one crystallizer (38, 38'), the separation block comprising at least one wash column (40), preferably the wash column (40) comprising a cylindrical vessel, the cylindrical vessel comprising: a piston having a piston head and a piston rod arranged for reciprocating movement within the cylindrical container and associated with a washing chamber within the cylindrical container above the piston head, the piston head including at least one filter means; an inlet line for feeding the cylindrical vessel with the crystal suspension mixture produced in the crystallization block, consisting of crystals and mother liquor; an outlet line for draining the mother liquor from the cylindrical vessel; an outlet line for discharging the crystals and / or the crystal melt from the cylindrical vessel; 15. A plant according to any one of claims 12 to 14, comprising:

16. 16. The plant according to any one of claims 12 to 15, wherein the at least one freeze concentration stage (24) comprises i) at least two suspension crystallization stages, or ii) at least one suspension crystallization stage and at least one static crystallization stage.

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