Semi-coke wastewater treatment system

Abstract

The utility model discloses a semi-coke wastewater treatment system which sequentially comprises the following components in series: an ammonia distillation unit which is used for removing ammonia and acid gas in semi-coke wastewater, directly introducing the acid gas into a boiler for burning, recovering ammonia water and enabling the deaminated wastewater to flow to the downstream; the evaporation and concentration unit is used for dividing the deaminated wastewater into condensate and concentrated solution, and the concentrated solution enters the extraction unit; the extraction unit is used for extracting high-concentration organic matters such as phenols from a concentrated solution, an extraction agent is recycled, and a water phase enters the acid-base recovery unit after being subjected to steam stripping to recover the dissolved extraction agent; and the acid-base recovery unit is used for generating a sodium hydroxide solution and carbon dioxide-rich flue gas by using a lime causticization method and a calcium carbonate calcination method, and the sodium hydroxide solution and the carbon dioxide-rich flue gas are all added into the system. The system has the beneficial effects that under the condition that no chemical substance is added, the semi-coke wastewater is divided into ammonia, oil, phenol and water, all resources are recycled, and the whole set of process is low in investment, reliable in operation, low in operation cost and small in solid waste generation amount.

Description

Technical Field

[0001] The invention belongs to the field of wastewater treatment, and in particular relates to a semi-coke wastewater treatment system. Background Art

[0002] Semi-coke is a new type of coal conversion product. Due to its low price, high fixed carbon, high specific resistivity, high chemical properties and other advantages, it is widely used in industries such as calcium carbide, ferroalloys, fertilizer gasification, blast furnace injection and civilian clean coal manufacturing. In the semi-coke production process, the coal gas generated by low-temperature dry distillation to remove volatiles is not subjected to high-temperature secondary cracking, resulting in a large amount of pollutants in the semi-coke wastewater that have not been oxidized by high temperature, and its concentration is much higher than that of coking wastewater.

[0003] At present, the mainstream treatment process of semi-coke wastewater is: first add a large amount of caustic soda to the semi-coke wastewater, then use steam stripping to recover ammonia, then add acid to adjust the pH of the wastewater to acidic, and use extraction to recover phenolic substances in the wastewater, while reducing the COD value of the wastewater, achieving the purpose of recovering ammonia and phenolic substances. However, after steaming ammonia and dephenolizing, the concentrations of COD, ammonia, and phenolic substances in the wastewater are still very high, and a large amount of acid and alkali are added, which doubles the mineralization of the water phase. The wastewater treatment is very difficult, and it cannot meet the discharge standards and recycling. There is no good way to treat the remaining brine.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art. A treatment system for blue carbon wastewater is provided. An evaporation concentration unit is arranged upstream of an extraction unit to separate blue carbon wastewater into condensate and concentrate. The concentration of pollutants such as COD in the condensate is very low and can meet the discharge standard after simple biochemical treatment or be used to supplement circulating cooling water. The amount of concentrate is only 5-10% of the total water volume. The phenolic substances therein are recovered by the extraction unit, and then the carbonate alkalinity and sodium ions in the wastewater are recovered by a causticizing reaction through an acid-base recovery unit. Carbon dioxide is recovered by calcining the calcium carbonate, so that acid-base regeneration and recycling are realized in the system. Without adding any chemical substances, the blue carbon wastewater is separated into ammonia, oil, phenol and water, and all are recycled and utilized as resources. The whole process has low investment, reliable operation, low operation cost and small amount of solid waste generated, and is an ideal solution for blue carbon wastewater treatment.

[0006] In order to solve the above technical problems, the basic concept of the technical solution adopted by the present invention is: a semi-coal wastewater treatment system, which comprises, in series,

[0007] Ammonia distillation unit is used to remove ammonia and acid gases from semi-coke wastewater. The acid gases are directly passed into the boiler for burning, ammonia water is recovered, and the deammonified wastewater is circulated downstream;

[0008] The evaporation concentration unit is used to separate the deammoniation wastewater into condensate and concentrate, and the concentrate enters the extraction unit;

[0009] The extraction unit is used to extract high-concentration phenols from the concentrate, and the extractant is recycled and reused. The aqueous phase is stripped to recover the dissolved extractant and then enters the acid-base recovery unit;

[0010] The acid-base recovery unit uses lime causticization and calcium carbonate calcination to generate sodium hydroxide solution and flue gas rich in carbon dioxide, which are all recycled;

[0011] A biochemical treatment unit is also provided in the bypass of the evaporation concentration unit.

[0012] Furthermore, the sodium hydroxide solution generated by the acid-base recovery unit is added back to the ammonia distillation unit; the calcium salt generated by the acid-base recovery unit becomes a mud cake after crystallization, precipitation and dehydration, and the mud cake is calcined to produce calcium oxide and carbon dioxide. The calcium oxide remains in the acid-base recovery unit, and the flue gas rich in carbon dioxide returns to the extraction unit.

[0013] Furthermore, the sodium hydroxide solution generated by the acid-base recovery unit is filtered and added to the wastewater discharged from the deacidification and ammonia distillation tower before entering the evaporation and concentration unit.

[0014] Furthermore, the calcium oxide produced by the calcined mud cake is recycled in the lime slaking device and reacts with water to form a calcium hydroxide solution.

[0015] Furthermore, the flue gas rich in carbon dioxide is introduced into the acidification tower of the extraction unit after dust removal.

[0016] Furthermore, the wastewater needs to enter the acidification tower before entering the extraction tower. The wastewater is fully contacted with the carbon dioxide-rich gas inside the acidification tower, and the pH value of the wastewater is reduced from alkaline to weakly acidic.

[0017] Furthermore, a portion of the concentrated liquid treated by the extraction unit will be diverted to the biochemical treatment unit to reduce the concentration of chloride ions.

[0018] Furthermore, the lime digestion device discharges the fluoride ions contained in the raw sewage in the form of calcium fluoride, thereby reducing the fluoride ion concentration in the system to less than 40 mg / l.

[0019] Furthermore, a filtering unit is provided upstream of the ammonia distillation unit for filtering and removing solid matter and petroleum in the wastewater.

[0020] Furthermore, the condensate produced by the evaporation concentration unit also enters the biochemical treatment unit and can be used to supplement the circulating cooling water after treatment.

[0021] Compared with the prior art, the present invention has the following beneficial effects: without adding any chemical substances, the semi-coke wastewater is separated into ammonia, oil, phenol and water, all of which are recycled and utilized as resources; the whole process has low investment, reliable operation, low operating cost and small amount of solid waste generated.

[0022] The process is simple, the effect is remarkable, and it is suitable for popularization and use.

[0023] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings are part of the present invention and are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute an improper limitation of the present invention. Obviously, the drawings described below are only some embodiments. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the accompanying drawings:

[0025] Figure 1 It is a schematic diagram of the process flow of the semi-coke wastewater treatment system according to an embodiment of the present invention.

[0026] In the figure, 1: ammonia distillation unit, 101: pretreatment filter, 102: intermediate storage tank 1, 103: deacidification ammonia distillation tower, 104: intermediate storage tank 2;

[0027] 2: Evaporation and concentration unit; 3: Biochemical treatment unit;

[0028] 4: extraction unit, 401: intermediate storage tank three, 402: acidification tower, 403: intermediate storage tank four, 404: extraction tower, 405: stripping tower, 406: extraction agent recovery tower;

[0029] 5: Acid and alkali recovery unit, 501: Intermediate storage tank five, 502: Causticizing crystallization precipitation device, 503: Intermediate storage tank six, 504: Alkali filter, 505: Recovery alkali storage tank, 506: Sludge dewatering machine, 507: Calcination device, 508: Lime digestion device, 509: Lime milk storage tank.

[0030] It should be noted that these drawings and textual descriptions are not intended to limit the conceptual scope of the present invention in any way, but are intended to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0032] In the description of the present invention, it should be noted that the directions or positional relationships indicated by terms such as “upper”, “lower”, “front”, “back”, “left”, “right”, “vertical”, “inside” and “outside” are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0033] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0034] like Figure 1 The figure shows a semi-coke wastewater treatment system, which includes, in series, an ammonia distillation unit 1, an evaporation concentration unit 2, a biochemical treatment unit 3, an extraction unit 4, and an acid-base recovery unit 5.

[0035] In an embodiment of the present invention, the ammonia evaporation unit 1 is used to remove ammonia and acidic gases from the semi-coke wastewater. The acidic gases are directly introduced into the boiler and burned, the ammonia water can be recovered, and the remaining wastewater flows to the downstream unit. A pretreatment filter 101 is provided at the front end of the ammonia evaporation unit 1 to remove suspended solids with a diameter greater than 5 microns in the wastewater to prevent blockage of the deacidification ammonia evaporation tower 103 and subsequent processes. The intermediate storage tank 1 102 is arranged between the pretreatment filter 101 and the deacidification ammonia evaporation tower 103 for temporarily storing wastewater and adjusting the water volume. The intermediate storage tank 2 104 is arranged after the deacidification ammonia evaporation tower 103 for temporarily storing wastewater after deacidification and ammonia removal. The intermediate storage tank 2 104 is provided with a pH value detection device to adjust the amount of alkali solution added according to the detected pH value.

[0036] Adding alkali solution to the intermediate storage tank 104 can adjust the pH value of the wastewater to weak alkalinity, so that the phenolic substances in the wastewater exist in the form of sodium phenol salts, reducing the volatility of the phenolic substances and preventing the loss of phenolic substances in subsequent units.

[0037] In the embodiment of the present invention, the evaporation concentration unit 2 is an evaporator, specifically, the evaporator is a multiple effect evaporator or an MVR evaporator. By introducing steam into the deacidification and ammonia removal wastewater in the evaporator, liquid water is continuously evaporated, and the phenolic substances in the wastewater are retained in the concentrated solution during this process, and the concentration of the phenolic substances is greatly increased, reaching 10-20 times the concentration of the phenolic substances in the deacidification and ammonia removal wastewater, which is easier to extract the phenolic substances.

[0038] In the embodiment of the present invention, the biochemical treatment unit 3 is used to treat the condensate generated by the evaporation concentration unit 2. The COD value of the condensate is lower than 1000 mg / L. Only simple biochemical treatment is needed to reduce the COD value of this part of wastewater to 50 mg / L. After the treatment is completed, it can be directly used as supplementary water for circulating cooling water.

[0039] In the embodiment of the present invention, the concentrated liquid produced by the evaporation concentration unit 2 is transported to the extraction unit 4. An intermediate storage tank 3 401 is provided at the front end of the extraction unit 4 for temporarily storing the weakly alkaline concentrated liquid.

[0040] The acidification tower 402 is arranged after the intermediate storage tank three 401. The concentrated liquid is introduced into the top of the acidification tower 402, and the flue gas rich in CO2 is introduced into the bottom of the acidification tower 402. After the concentrated liquid and the gas flow in opposite directions in the tower and fully contact each other, the CO2 dissolves in the concentrated liquid and reacts with the sodium phenol salt therein to convert the sodium phenol salt into phenol, and the pH of the concentrated liquid is gradually reduced to about 5.5. The intermediate storage tank four 403 arranged after the acidification tower 402 is used to temporarily store these weakly acidic phenol-containing wastewaters.

[0041] The extraction unit 4 further includes an extraction tower 404, a stripping tower 405, and an extractant recovery tower 406. The oil phase extracted from the extraction tower 404 and sent to the extractant recovery tower 406 is called dirty extractant, and the oil phase extracted from the extractant recovery tower 406 and sent back to the extraction tower 404 is called clean extractant.

[0042] Phenol-containing wastewater enters from the top of the extraction tower 404, and the extractant is introduced from the bottom of the extraction tower 404. After the phenol-containing wastewater and the extractant flow in opposite directions and fully contact each other in the tower, the extractant that has dissolved most of the phenolic substances in the wastewater rises to the upper part of the extraction tower 404 and becomes a dirty extractant, and the wastewater containing a small amount of extractant flows to the lower part of the extraction tower 404.

[0043] The top of the stripping tower 405 receives the wastewater produced from the bottom of the extraction tower 404, and fresh water vapor is introduced into the bottom of the stripping tower 405. After the wastewater and steam flow in opposite directions inside the stripping tower 405 and fully contact each other, the steam containing the extractant is produced from the upper part of the stripping tower 405, and the wastewater is produced from the lower part of the stripping tower 405. The produced wastewater is cooled and sent to subsequent units for treatment.

[0044] The top of the extractant recovery tower 406 receives the dirty extractant extracted from the upper part of the extraction tower 404, and the bottom of the extractant recovery tower 406 receives two kinds of steam, one is the steam containing the extractant extracted from the upper part of the stripping tower 405, and the other is fresh water vapor. After the liquid and the steam flow in the opposite direction inside the extractant recovery tower 406 and fully contact, the clean extractant on the upper layer is sent back to the extraction tower 404 for continued use; the phenol-containing solution on the lower layer can be directly sold after being extracted.

[0045] Through the above arrangement, the semi-coke wastewater is pretreated, deacidified and deammonified, and the pH value is adjusted in the ammonia evaporation unit 1, which is beneficial to the treatment of the evaporation concentration unit 2. In the evaporation concentration unit 2, on the one hand, a concentrated solution with a high concentration of phenolic substances is obtained, and on the other hand, a condensate that is easy to be treated by the biochemical treatment unit 3 is obtained. The concentrated solution produced reduces the amount of wastewater transported to the extraction unit 4, and reduces the amount of extractant used in the extraction unit 4.

[0046] In the embodiment of the present invention, an intermediate storage tank 501 is provided at the front end of the acid-base recovery unit 5 for temporarily storing the wastewater treated by the extraction unit 4. The wastewater after the extraction contains chloride ions, sulfate ions and other unknown substances. Since the water circulation in the system will cause the chloride ions and other harmful substances to accumulate continuously, in order to avoid corrosion or scaling of equipment and pipelines, 10%-30% of the wastewater needs to be diverted back to the biochemical treatment unit 3, and the remaining 70-90% of the wastewater is sent to the subsequent equipment for further treatment.

[0047] The causticizing crystallization precipitation device 502 is arranged after the intermediate storage tank five 501. In the causticizing crystallization precipitation device 502, NaCO3 in the wastewater reacts with Ca(OH)2 in the lime milk to generate NaOH and CaCO3. After precipitation, the sludge produced by the causticizing crystallization precipitation device 502 is sent to the sludge dewatering machine 506, and the filtrate containing NaOH produced by it is sent to the intermediate storage tank six 503.

[0048] The sludge dewatering machine 506 dehydrates the bottom sludge and separates it into filtrate and mud cake with low water content. The filtrate is sent to the intermediate storage tank 6 503, and the mud cake is discharged from the slag discharge port of the sludge dewatering machine 506.

[0049] It should be noted that the main component of the mud cake is CaCO3, and it also contains a small amount of CaSO4 and CaF2.

[0050] The acid-base recovery unit 5 further includes a calcining device 507 , a lime digestion device 508 , and a dust collector 510 .

[0051] The mud cake produced by the sludge dewatering machine 506 is transported to the calcining device 507. The calcining temperature of the calcining device 507 is controlled to be less than 1000°C. CaCO3 is decomposed to generate CaO and CO2. The calcined solid matter is sent to the lime digestion device 508, and the generated smoke is sent to the dust collector 510.

[0052] In the lime slaking device 508, CaO in the solid matter reacts with water transported from the intermediate storage tank 6 503 to form a lime milk solution, and the undecomposed CaSO4 and CaF2 after calcination are discharged from the system through slagging.

[0053] The dust collector 510 receives the dust-containing gas produced by the calcining device 507, and the solid matter is collected and transported out for treatment, while the flue gas mainly containing CO2 after the dust is removed is sent back to the acidification tower 402 in the extraction unit 4 for utilization.

[0054] In addition, the acid-base recovery unit 5 further includes a lime milk storage tank 509 , an alkali solution filter 504 , and a recovered alkali solution storage tank 505 .

[0055] The lime milk storage tank 509 is arranged after the lime slaking device 508, and is used to store the lime milk solution and receive the NaOH-containing solution from the intermediate storage tank 6 503 at the same time.

[0056] The alkali solution filter 504 is used to filter the solution produced from the intermediate storage tank 6 503.

[0057] The recovered alkali solution storage tank 505 is used to temporarily store the solution to be transported to the ammonia distillation unit 1 .

[0058] Through the above settings, most of the F in the semi-coal wastewater is removed. - , and strictly control the F - The concentration is less than 40mg / L, ensuring F - It will not corrode equipment and pipes in the system. At the same time, it makes full use of substances such as calcium carbonate produced in the wastewater treatment process, reduces the use of fresh tap water, and reduces the system operation cost.

[0059] Example 1

[0060] In the embodiment of the present invention, the raw water volume is 6m 3 / h, after oil separation and filtration, directly enters the ammonia distillation unit 1. The steam pressure used in the ammonia distillation unit 1 is about 1.0MPa, and the steam temperature is about 185℃; the ammonia-containing steam extracted from the side of the ammonia distillation tower is condensed to obtain ammonia water with an ammonia concentration of about 15%, and acidic gases such as carbon dioxide and hydrogen sulfide are discharged from the top. Sodium hydroxide solution is added to the wastewater after ammonia distillation, and the pH value of the wastewater entering the concentration unit is controlled at 11-12. The water quality of the wastewater after deacidification and ammonia distillation, evaporation concentration, extraction, biochemical treatment and other units is as shown in the following table.

[0061]

[0062]

[0063] The salt content of the condensate is less than 100mg / l, which is very high-quality make-up water for circulating cooling water and can be fully reused.

[0064] Example 2

[0065] In the embodiment of the present invention, the raw water volume is 100m 3 / h, has been oil-separated and filtered, and directly enters the ammonia distillation unit 1. The steam pressure used in the ammonia distillation unit 1 is 0.4-0.5MPa, and the steam temperature is 145-155℃; the ammonia-containing steam extracted from the side of the ammonia distillation tower is condensed to obtain ammonia water with an ammonia concentration of about 15%, and acidic gases such as carbon dioxide and hydrogen sulfide are discharged from the top. Sodium hydroxide solution is added to the wastewater after ammonia distillation, and the Ph value of the wastewater flowing into the concentration unit is controlled to be 11-12. The water quality of the wastewater after deacidification and ammonia distillation, evaporation concentration, extraction, biochemical treatment and other units is as shown in the following table.

[0066]

[0067] The above description is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as above in the preferred embodiment, it is not used to limit the present invention. Any technician familiar with this patent can make some changes or modifications to equivalent embodiments of equivalent changes by using the technical content suggested above without departing from the scope of the technical solution of the present invention. The implementation scheme in the above embodiment can be further combined or replaced. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the solution of the present invention.

Claims

1. A blue carbon wastewater treatment system, characterized in that: The ammonia distillation unit is connected in series to remove ammonia and acid gases from the semi-coke wastewater. The acid gases are directly introduced into the boiler for burning, the ammonia water is recovered, and the wastewater after deammoniation flows downstream; The evaporation concentration unit is used to separate the deammoniation wastewater into condensate and concentrate, and the concentrate enters the extraction unit; The extraction unit is used to extract high-concentration phenols from the concentrate, and the extractant is recycled and reused. The aqueous phase is stripped to recover the dissolved extractant and then enters the acid-base recovery unit; The acid-base recovery unit uses lime causticization and calcium carbonate calcination to generate sodium hydroxide solution and rich carbon dioxide, and all flue gas is recycled; A biochemical treatment unit is also provided in the bypass of the evaporation concentration unit.

2. A blue carbon wastewater treatment system according to claim 1, characterized in that The sodium hydroxide solution generated by the acid-base recovery unit is added to the wastewater after deacidification and ammonia evaporation and before evaporation and concentration; the calcium salt generated by the acid-base recovery unit becomes a mud cake after crystallization, precipitation and dehydration, and then calcined to produce calcium oxide and flue gas rich in carbon dioxide. The calcium oxide is used to prepare lime milk and then used for wastewater causticization; the flue gas rich in carbon dioxide is passed into the acidification tower of the extraction unit after dust removal.

3. A blue carbon wastewater treatment system according to claim 1, characterized in that: When the wastewater is treated in the extraction unit, it needs to enter the acidification tower before entering the extraction tower. The wastewater is fully contacted with the flue gas rich in carbon dioxide inside the acidification tower, and the pH value of the wastewater is reduced from alkaline to weakly acidic.

4. A blue carbon wastewater treatment system according to claim 1, characterized in that: The biochemical treatment unit is used to treat the condensate produced by the evaporation and concentration unit, and simultaneously treat the concentrated liquid after extraction diverted from the extraction unit. Both are used to supplement circulating cooling water after treatment.

5. A blue carbon wastewater treatment system according to claim 1, characterized in that: The acid-base recovery unit is provided with a lime digestion device, which discharges the fluoride ions contained in the raw sewage in the form of calcium fluoride through slag discharge, thereby making the fluoride ion concentration in the system less than 40 mg / l.

6. A blue carbon wastewater treatment system according to claim 1, characterized in that: A filtering unit is arranged upstream of the ammonia distillation unit for filtering and removing solid substances and petroleum in the wastewater.

Images