Advanced treatment and waste heat recovery system for wet desulphurization wastewater

Abstract

The invention provides an advanced treatment and waste heat recovery system for wet desulphurization wastewater. The system comprises a precipitation assembly; a filtering device; the wastewater treated by the precipitation assembly can be discharged into the filtering device; a heat exchange device; a discharge port of the filtering device is connected with a water inlet pipe of the heat exchange device; a heat pump unit; circulating cooling water return water of the heat exchange device can be discharged into a heat exchange pipe of the heat pump unit, primary network heat supply network return water is connected into the heat pump unit, and the primary network heat supply network return water is heated by the heat pump unit and then is discharged as plant heating water. According to the advanced treatment and waste heat recovery system, the energy utilization rate can be increased, and the energy consumption and the operation cost are reduced.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, and in particular to a deep treatment and waste heat recovery system for wet desulfurization wastewater. Background Technology

[0002] In recent years, with the continuous development of industrial sulfur dioxide emission control technologies in my country, gaseous pollutants such as sulfur dioxide have basically achieved ultra-low emissions. Among them, wet desulfurization technology has gained widespread recognition due to its advantages such as small footprint, high desulfurization efficiency, and inexpensive and readily available absorbents. However, a large amount of desulfurization wastewater is generated during the desulfurization process. This wastewater has a complex composition, extremely high suspended solids content (about 4%~5%), and a high temperature.

[0003] Existing technology, as disclosed in publication number CN112794520A, presents a system and method for treating wet desulfurization wastewater in the steel industry. This invention removes impurities from the wastewater through plate and frame filtration, secondary chemical hardening, concentration and sedimentation, and filtration. Ammonia nitrogen is removed through deammoniation treatment. Following softening, nanofiltration, membrane treatment or electrodialysis, and evaporation crystallization, the resulting water, as well as high-purity sodium sulfate and sodium chloride, are obtained.

[0004] In the aforementioned prior art, the process of filtering wastewater impurities includes an ultrafiltration device. In order for the ultrafiltration device to operate stably, a heat exchanger is needed to cool the high-temperature desulfurization wastewater. In the heat exchanger, the circulating cooling water will be heated to become a low-grade heat source after completing heat exchange. In order to improve energy utilization, economic benefits and environmental value, it is urgent to preheat and recover the aforementioned low-grade heat source. Summary of the Invention

[0005] Based on the above situation, the main objective of this invention is to provide a deep treatment and waste heat recovery system for wet desulfurization wastewater, so as to solve the problems of existing wet desulfurization wastewater treatment systems that do not utilize low-grade heat sources for waste heat, resulting in low energy utilization rate and poor economic and environmental benefits.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A system for advanced treatment and waste heat recovery of wet desulfurization wastewater, comprising: Precipitation components; Filtration device; wastewater treated by the sedimentation component can be discharged into the filtration device; Heat exchange device; the outlet of the filter device is connected to the inlet pipe of the heat exchange device; The heat pump unit; the circulating cooling water return water of the heat exchange device can be discharged into the heat exchange tube of the heat pump unit, and the heat pump unit is connected to the primary heat network return water. After being heated by the heat pump unit, the primary heat network return water is discharged as heating water for the factory building.

[0007] Preferably, the sedimentation assembly includes a wastewater pre-sedimentation device, a wastewater collection device, and a high-efficiency sedimentation device; The desulfurization wastewater can be discharged into the wastewater pre-sedimentation device, which is connected to the wastewater collection device. The wastewater collection device is connected to the high-efficiency sedimentation device, and the sediment from the high-efficiency sedimentation device can be returned to the wastewater pre-sedimentation device. The wastewater pre-sedimentation device is connected to the sludge dewatering system.

[0008] Preferably, it also includes an ultrafiltration unit, a nanofiltration unit, and a reverse osmosis unit; The ultrafiltration device is connected to the heat exchange device, the nanofiltration device is connected to the ultrafiltration device, and the reverse osmosis device is connected to the nanofiltration device.

[0009] Preferably, the wastewater pre-settling device is a wastewater pre-settling tank, the bottom of the wastewater pre-settling device has a conical bottom bucket structure, and the wastewater pre-settling device is equipped with an electric variable frequency sludge scraper.

[0010] Preferably, the high-efficiency sedimentation device includes a stirring section, a transmission section, and a clarification section. The stirring section is a mechanical stirring device with a guide tube, the transmission section is a mechanical slow-speed scraper device with a guide tube, and the clarification section is a square or circular lower cone structure.

[0011] Preferably, the discharge outlet of the clarification section can be connected to the wastewater pre-sedimentation device.

[0012] Preferably, the filtration device is a multi-media filter, and the filter media of the filtration device are quartz sand and anthracite.

[0013] Preferably, the quartz sand has a particle size of 0.5-0.8 mm, and the anthracite has a particle size of 0.8-1.6 mm.

[0014] Preferably, the heat pump unit is a lithium bromide absorption heat pump unit or a mechanical heat pump unit.

[0015] Preferably, the nanofiltration device is a low-pressure, anti-fouling organic composite nanofiltration membrane device.

[0016] The beneficial effects of this invention are as follows: On the one hand, this invention recovers and utilizes the low-grade heat generated during wastewater treatment, converting this heat into high-grade heat energy that can be used for factory heating through a heat pump unit. This not only improves energy utilization efficiency but also reduces energy consumption and operating costs, resulting in significant economic benefits. Simultaneously, this waste heat recovery and utilization method also reduces the environmental impact of waste heat emissions, enhancing its environmental value.

[0017] On the other hand, the wastewater in this application directly enters the pre-sedimentation device for sedimentation, which removes pollutants in the wastewater to the greatest extent and reduces the risk of clogging of subsequent equipment. At the same time, the sediment after hardening in the high-efficiency sedimentation device is returned to the pre-sedimentation device and sent to the sludge dewatering system together with the suspended solids after sedimentation. This can improve the solids content and sedimentation effect of the sludge, which is conducive to improving the treatment effect of subsequent deep treatment of wastewater.

[0018] Other beneficial effects of the present invention will be explained in detail through the introduction of specific technical features and technical solutions in specific embodiments. Those skilled in the art should be able to understand the beneficial technical effects brought about by these technical features and technical solutions through the introduction of these technical features and technical solutions. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a wet desulfurization wastewater deep treatment and waste heat recovery system according to the present invention.

[0020] Figure 2 This is a schematic diagram of a sedimentation component in a wet desulfurization wastewater deep treatment and waste heat recovery system according to the present invention.

[0021] Explanation of reference numerals in the attached figures: 1. Sedimentation unit; 11. Wastewater pre-sedimentation device; 12. Wastewater collection device; 13. High-efficiency sedimentation device; 2. Filtration device; 3. Heat exchange device; 4. Heat pump unit; 5. Ultrafiltration device; 6. Nanofiltration device; 7. Reverse osmosis device. Detailed Implementation

[0022] The present invention is described below based on embodiments, but the present invention is not limited to these embodiments. In the following detailed description of the present invention, some specific details are described in detail, but well-known methods, processes, procedures, and elements are not described in detail in order to avoid obscuring the essence of the present invention.

[0023] Furthermore, those skilled in the art should understand that the accompanying drawings provided herein are for illustrative purposes only and are not necessarily drawn to scale.

[0024] Unless the context explicitly requires it, the words "comprising," "including," and similar terms throughout the specification and claims should be interpreted as encompassing rather than being exclusive or exhaustive; that is, meaning "including but not limited to."

[0025] In the description of this invention, it should be understood that the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0026] Reference Figure 1 The present invention provides a deep treatment and waste heat recovery system for wet desulfurization wastewater, including a sedimentation component 1, a filtration device 2, a heat exchange device 3, a heat pump unit 4, an ultrafiltration device 5, a nanofiltration device 6, and a reverse osmosis device 7.

[0027] The sedimentation unit 1 first pretreats the wet desulfurization wastewater by adding chemicals to remove most of the suspended solids, hardness substances, and heavy metal ions. After treatment by the sedimentation unit 1, the wastewater enters the filtration unit 2, which further filters out residual fine particulate matter and other impurities, achieving initial purification. Subsequently, the wastewater flows into the heat exchange unit 3, which regulates the temperature to create suitable conditions for subsequent ultrafiltration and other processes. Simultaneously, the heat pump unit 4 works in conjunction with the heat exchange unit 3 to recover waste heat from the circulating cooling water during the heat exchange process. After treatment by the heat exchange unit 3, the wastewater enters the ultrafiltration unit 5, which retains colloids and other substances in the wastewater, further improving water quality. Next, the wastewater enters the nanofiltration unit 6, which performs salt separation to achieve the separation of different salts. Wastewater from the product water end of nanofiltration unit 6 then enters reverse osmosis unit 7, which concentrates the wastewater to obtain product water that meets the standards for reuse. The concentrated water from nanofiltration unit 6 and reverse osmosis unit 7 can be used for purposes such as flushing slag in the plant area.

[0028] Specifically, the drain outlet of the filter device 2 is connected to the inlet pipe of the heat exchange device 3, which can transfer the desulfurization wastewater after preliminary filtration to the heat exchange device 3. The heat exchange device 3 is an ultrafiltration inlet heat exchanger, which can complete the heat exchange between the cooling water and the desulfurization wastewater inside.

[0029] At this time, the temperature of the filtered inlet water is 55-60℃, taking 60℃ as an example in this embodiment. The inlet water that can be connected to the heat exchange tube of the heat exchange device 3 is 25-35℃, taking 30℃ as an example in this embodiment. This can cool the desulfurization wastewater to be treated to 30-40℃, taking 35℃ as an example in this embodiment. The return water temperature of the circulating cooling water after heating is 45-50℃, taking 50℃ as an example in this embodiment. A low-grade heat source is formed. This circulating cooling water return water can enter the heat exchange pipe of the heat pump unit 4. The heat pump unit 4 can utilize the heat of this low-grade heat source as waste heat. After the waste heat utilization is completed, the 25-35℃ return water (taking 30℃ as an example in this embodiment) enters the circulating cooling water system to provide circulating cooling water to the heat exchange device 3 again.

[0030] The inlet and outlet of the heat pump unit 4 are connected to the primary heat network return water and the plant heating water, respectively. The temperature of the primary heat network return water is 35-45℃, and the temperature of the plant heating water is 65-75℃. In this embodiment, the primary heat network return water is 40℃ and the plant heating water is 70℃. Although the temperature of the low-grade heat source is not high, the volume of circulating cooling water returned by the heat exchange device 3 is large. The large volume of circulating cooling water returns provides a significant heat source supply to the heat pump unit 4. Combined with the high energy transfer efficiency of the heat pump unit 4, the primary heat network return water can be heated to a high temperature for plant heating, making full use of the waste heat from the low-grade heat source. This improves the energy utilization rate in the wet desulfurization wastewater treatment process and enhances the economic benefits and environmental value of the overall production system.

[0031] As one embodiment, heat pump unit 4 can be either a lithium bromide absorption heat pump unit or a mechanical heat pump unit. The lithium bromide absorption heat pump unit is driven by thermal energy and achieves heat transfer through the absorption and release process of lithium bromide-water solution. It can work under low-grade heat source conditions, making full use of energy, and its operation is relatively stable with low noise. The mechanical heat pump unit relies on mechanical compression to improve the heat grade. It has the advantages of compact structure and convenient installation, and can be flexibly selected according to the actual site and energy supply conditions.

[0032] Reference Figure 2 In one embodiment, the sedimentation component 1 includes a wastewater pre-sedimentation device 11, a wastewater collection device 12, and a high-efficiency sedimentation device 13. Desulfurization wastewater can be discharged into the wastewater pre-sedimentation device 11, where the sludge from the desulfurization wastewater naturally settles, and the clear water at the top overflows into the wastewater collection device 12. During this process, alkaline solution and coagulant aid can be added to the wastewater pre-sedimentation device 11 to make the desulfurization wastewater alkaline, thereby improving the sedimentation effect.

[0033] Furthermore, the wastewater pre-settling device 11 is a wastewater pre-settling tank with a conical bottom structure. An electric variable frequency scraper is installed inside the tank, and the sludge discharge port of the wastewater pre-settling pipe is connected to a sludge dewatering system for direct treatment of the discharged sludge. The conical bottom structure of the wastewater pre-settling tank allows sludge to accumulate at the bottom of the tank via the conical slope, facilitating subsequent discharge. The electric variable frequency scraper continuously scrapes away sludge from the side walls of the wastewater pre-settling tank, placing the dispersed sludge at the discharge port, thus improving sludge discharge efficiency. It should be noted that the structure of the wastewater pre-settling tank and the electric variable frequency scraper are existing technologies and will not be described further in this application.

[0034] Wastewater collection device 12 is a wastewater collection tank, and the wastewater is transferred to the high-efficiency sedimentation device 13 by a lift pump.

[0035] The high-efficiency precipitation device 13 is configured in stages, and may include a primary high-efficiency precipitation device 13 and a secondary high-efficiency precipitation device 13. An alkaline solution can be added to the primary high-efficiency precipitation device 13 to adjust the pH; a sodium carbonate solution is added to the secondary high-efficiency precipitation device 13 to remove Ca. 2+ Mg 2+ This is used to remove hardness from wastewater.

[0036] The alkaline solution can be a sodium hydroxide solution, with a concentration in the range of 25%–35%, preferably 30%–32%, to adjust the pH of the wastewater to 9.5–10.5, preferably 9.8–10. The sodium carbonate solution concentration should be in the range of 10%–30%, preferably 15%–20%. The hardness in the wastewater is mainly non-carbonate hardness, i.e., permanent hardness, such as calcium and magnesium ions. The hardness removal principle in this step is to introduce carbonate ions into the wastewater, which then combine with calcium ions to form calcium carbonate precipitate. The chemical reaction formula is: Ca... 2+ +CO3 2- →CaCO3↓, carbonate ions and magnesium ions combine to form magnesium carbonate precipitate. The chemical reaction formula is: Mg 2+ +CO3 2- →MgCO3↓.

[0037] In addition, flocculants and coagulants can be added to the two-stage high-efficiency sedimentation device 13 to enhance the flocculation and sedimentation effect.

[0038] To further enhance the flocculation effect, both stages of high-efficiency sedimentation devices 13 include a stirring section, a transmission section, and a clarification section. The stirring section is a mechanical agitator with a guide tube, the transmission section is a mechanical slow-speed scraper with a guide tube, and the clarification section has a square or circular lower conical structure. The stirring section uses the guide tube to achieve directional flow of wastewater, ensuring thorough mixing and reaction of the reagents and wastewater. The transmission section drives the slow-speed scraper to gently agitate the sediment, preventing caking and promoting settling. The square or circular lower conical structure of the clarification section facilitates the concentration and discharge of sediment. The sediment from the high-efficiency sedimentation device 13 can be returned to the wastewater pre-sedimentation device 11, achieving sludge recycling and improving treatment efficiency. Specifically, the sewage outlet of the clarification section can be returned to the sewage pre-sedimentation device through a pipeline, and the sediment after hardening is returned to the wastewater pre-sedimentation device 11. The wastewater pre-sedimentation device 11 is connected to the sludge dewatering system. The suspended solids after sedimentation in the wastewater pre-sedimentation device 11 and the high-efficiency sedimentation device 13 are sent to the sludge dewatering system for treatment, which can improve the solids content and sedimentation effect of the sludge.

[0039] The coagulant can be one or more of the following: aluminum chloride, aluminum sulfate, ferric chloride, ferric sulfate, polyaluminum chloride, polyaluminum sulfate, polyferric chloride, and polyferric sulfate solution. The coagulant is used in solution form, and the concentration of the solution should be in the range of 3% to 5%, preferably 4% to 5%.

[0040] The flocculant can be a nonionic or anionic flocculant, such as one or more nonionic or anionic polyacrylamide solutions. The flocculant is used in solution form, and the concentration of the solution should be in the range of 0.05% to 0.15%, preferably 0.08% to 0.1%.

[0041] As one embodiment, wastewater discharged from the high-efficiency sedimentation device 13 can be sent to the filtration device 2, which is a multi-media filter, and the filter media of the multi-media filter is quartz sand and / or anthracite.

[0042] The combination of quartz sand and anthracite can fully leverage the advantages of both. Specifically, quartz sand has a particle size of 0.5-0.8mm, which has good interception capacity and can effectively intercept fine particulate impurities in wastewater; anthracite has a particle size of 0.8-1.6mm and a large porosity, which can further filter and adsorb organic matter and other impurities in wastewater. The two work together to significantly improve the filtration effect, further optimizing the water quality of the wastewater after treatment by filtration device 2 and providing good water quality conditions for subsequent treatment processes.

[0043] After treatment by filtration device 2 and heat exchange device 3, wastewater with a lower temperature and some impurities removed is obtained. The wastewater then passes through ultrafiltration device 5, nanofiltration device 6, and reverse osmosis device 7 for further treatment. After the above treatment, the outlet of reverse osmosis device 7 discharges central low-salt purified water (product water) and neutral high-salt purified water (concentrate), while nanofiltration device 6 discharges a portion of neutral high-salt purified water. The neutral low-salt purified water can be directly recycled, and the neutral high-salt purified water is used for slag flushing in the plant area, completing the deep treatment and reuse of wet sulfur-containing wastewater.

[0044] As one embodiment, nanofiltration device 6 is a low-pressure antifouling organic composite nanofiltration membrane device. The low-pressure antifouling organic composite nanofiltration membrane used in nanofiltration device 6 has unique membrane materials and membrane structure. Its membrane surface undergoes special antifouling treatment, which can effectively reduce the adhesion and deposition of pollutants in wastewater on the membrane surface, thereby reducing the risk of membrane fouling and extending the service life of the membrane.

[0045] Those skilled in the art will understand that, without conflict, the above-mentioned preferred solutions can be freely combined and superimposed.

[0046] It should be understood that the above embodiments are merely exemplary and not restrictive. Various obvious or equivalent modifications or substitutions that can be made by those skilled in the art regarding the above details without departing from the basic principles of the present invention will be included within the scope of the claims of the present invention.

Claims

1. A system for advanced treatment and waste heat recovery of wet desulfurization wastewater, characterized in that, include: Precipitation component (1); Filter device (2); Wastewater treated by the sedimentation component (1) can be discharged into the filtration device (2); Heat exchange device (3); the outlet of the filter device (2) is connected to the inlet pipe of the heat exchange device (3); Heat pump unit (4); the circulating cooling water return water of the heat exchange device (3) can be discharged into the heat exchange tube of the heat pump unit (4), the heat pump unit (4) is connected to the primary heat network return water, the primary heat network return water is heated by the heat pump unit (4) and discharged as heating water for the factory building.

2. The deep treatment and waste heat recovery system for wet desulfurization wastewater as described in claim 1, characterized in that, The sedimentation assembly (1) includes a wastewater pre-sedimentation device (11), a wastewater collection device (12), and a high-efficiency sedimentation device (13); The desulfurization wastewater can be discharged into the wastewater pre-sedimentation device (11), which is connected to the wastewater collection device (12). The wastewater collection device (12) is connected to the high-efficiency sedimentation device (13), and the sediment from the high-efficiency sedimentation device (13) can be returned to the wastewater pre-sedimentation device (11). The wastewater pre-sedimentation device (11) is connected to the sludge dewatering system.

3. The deep treatment and waste heat recovery system for wet desulfurization wastewater as described in claim 1, characterized in that, It also includes an ultrafiltration unit (5), a nanofiltration unit (6), and a reverse osmosis unit (7); The ultrafiltration device (5) is connected to the heat exchange device (3), the nanofiltration device (6) is connected to the ultrafiltration device (5), and the reverse osmosis device (7) is connected to the nanofiltration device (6).

4. The deep treatment and waste heat recovery system for wet desulfurization wastewater as described in claim 2, characterized in that, The wastewater pre-settling device (11) is a wastewater pre-settling tank. The bottom of the wastewater pre-settling device (11) is a cone-shaped bucket structure, and the wastewater pre-settling device (11) is equipped with an electric variable frequency sludge scraper.

5. The deep treatment and waste heat recovery system for wet desulfurization wastewater as described in claim 2, characterized in that, The high-efficiency sedimentation device (13) includes a stirring part, a transmission part and a clarification part. The stirring part is a mechanical stirring device with a guide tube, the transmission part is a mechanical slow scraper device with a guide tube, and the clarification part is a square or circular lower cone structure.

6. The deep treatment and waste heat recovery system for wet desulfurization wastewater as described in claim 5, characterized in that, The discharge outlet of the clarification section can be connected to the sewage pre-sedimentation device.

7. The deep treatment and waste heat recovery system for wet desulfurization wastewater as described in claim 1, characterized in that, The filter device (2) is a multi-media filter, and the filter media of the filter device (2) are quartz sand and anthracite.

8. The deep treatment and waste heat recovery system for wet desulfurization wastewater as described in claim 7, characterized in that, The quartz sand has a particle size of 0.5-0.8 mm, and the anthracite has a particle size of 0.8-1.6 mm.

9. The deep treatment and waste heat recovery system for wet desulfurization wastewater as described in claim 1, characterized in that, The heat pump unit (4) is selected as either a lithium bromide absorption heat pump unit (4) or a mechanical heat pump unit (4).

10. The deep treatment and waste heat recovery system for wet desulfurization wastewater as described in claim 1, characterized in that, The nanofiltration device (6) is a low-pressure, anti-fouling organic composite nanofiltration membrane device.

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