Waste heat evaporation type desulfurization wastewater zero discharge process

Abstract

The invention discloses a waste heat evaporation type desulfurization wastewater zero discharge process, and relates to the technical field of industrial wastewater treatment. Comprising the following steps: S1, pretreatment of desulfurization wastewater: performing cyclone separation on wastewater generated by a desulfurization device through a wastewater cyclone and buffering in a wastewater tank in sequence, and then conveying the wastewater to a neutralization tank; the heavy metal treatment effect is guaranteed through double mechanisms of pretreatment and deep removal, the lime slurry can separate out heavy metals such as lead and zinc which are easy to precipitate, organic sulfur TMT 15 with the concentration of 15%, cadmium, mercury and the like can form stable sulfides, and the amount is accurately controlled by matching with an online detector; heavy metals in effluent are ensured to meet the first-level A standard of Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant and are reused in a Chlorate which cannot be simply treated in the waste water is separated out in the waste water evaporator, is complemented by the dust remover and then enters an ash silo together with dust of the dust remover, and evaporated water vapor enters the desulfurizing tower along with flue gas to be cooled and is used as replenishing water of the desulfurizing tower, so that no waste water is discharged at the tail end.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of industrial wastewater treatment, and particularly relates to a desulfurization wastewater zero discharge process based on waste heat evaporation. BACKGROUND

[0002] In the power, chemical, steel and other industries, the boiler flue gas needs to be treated by a wet desulfurization process to control sulfur dioxide emission. The process produces desulfurization wastewater with complex components. The desulfurization wastewater contains not only multiple heavy metal ions such as lead, zinc, cadmium and mercury, but also has characteristics such as high salinity, high suspended solids and strong acidity. If it is directly discharged, it will seriously pollute water bodies and soil, and threaten the ecological environment and human health. With the increasingly stringent environmental protection regulations such as the Emission Standard of Air Pollutants for Thermal Power Plants and the Discharge Standard of Pollutants for Urban Sewage Treatment Plants, the "desulfurization wastewater zero discharge" has become a hard requirement for related enterprises to comply with the production.

[0003] The traditional chemical precipitation method can only remove easily precipitated heavy metals such as lead and zinc, and the removal rate of cadmium and mercury is less than 80%, which is difficult to meet the first A standard. In addition, the chloride ions in the wastewater are difficult to remove simply. The water content of the sludge is more than 80%, the disposal cost is high, the residual pollutants in the filtrate can cause secondary pollution, and the wastewater cannot be truly zero discharged. In addition, the traditional evaporation technology has high energy consumption and poor stability. Moreover, the leakage risk of waste heat utilization is high. The dosage of artificial adjustment and the evaporation amount are easy to exceed the standard / waste, and there is no closed loop treatment, which still has emission risks.

[0004] In summary, the existing technology has short boards in heavy metal removal, energy consumption, stability and zero discharge integrity. The industry urgently needs a treatment process with "high-efficiency heavy metal removal, low energy consumption, long-period stability and full-closed-loop zero discharge". SUMMARY

[0005] The present application aims to provide a desulfurization wastewater zero discharge process based on waste heat evaporation, which solves the technical problems proposed in the background art.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical solution: a desulfurization wastewater zero discharge process based on waste heat evaporation, comprising the following steps:

[0007] S1, desulfurization wastewater pretreatment: the wastewater generated by the desulfurization device is sequentially subjected to cyclone separation by a wastewater cyclone, buffered in a wastewater tank, and then delivered to a neutralization tank. Lime slurry is added to the neutralization tank to adjust the pH value of the wastewater to a preset range, so that part of the heavy metals in the wastewater are precipitated in the form of hydroxide, and the acidic substances are neutralized.

[0008] S2, deep removal of heavy metals: the pretreated wastewater in step S1 is delivered to a settling tank, and organic sulfur is added to the settling tank to precipitate cadmium and mercury heavy metals in the wastewater in the form of sulfide.

[0009] S3, Flocculation and Sedimentation: The wastewater treated in step S2 is transported to the flocculation tank and flocculant is added, and then transported to the clarifier and thickener; coagulant aid is added to the inlet pipe of the clarifier and thickener to form large flocs of solid precipitate and complete solid-liquid separation; during this period, the pH value of the supernatant at the outlet of the clarifier and thickener is adjusted to meet the standard range.

[0010] S4. Sludge treatment and supernatant separation: Part of the sludge separated from the clarifier in step S3 is returned to the neutralization tank and part is dewatered. The dewatered filter cake is transported off-site and the filtrate is returned to the neutralization tank. The supernatant separated from the clarifier enters the supernatant storage tank. After detecting the chloride ion content, part of it is reused in the desulfurization system, and the remaining supernatant is used as wastewater to be evaporated.

[0011] S5. Main flue gas waste heat evaporation: The supernatant to be evaporated in step S4 is transported to the injection module by a metering pump, and atomized under the action of compressed air and sprayed into the wastewater evaporator; the heat of the low-temperature flue gas at the air preheater outlet is used to evaporate the wastewater droplets, and salts are precipitated in the wastewater; the ash and scale accumulated in the flue and atomization device are removed by a soot blower; the ash collected by the wastewater evaporator and the salt-containing ash collected by the dust collector are transported to the ash silo to achieve zero discharge of desulfurization wastewater.

[0012] Preferably, in step S1, the concentration of lime slurry is 5%~10%, and the purity of the quicklime powder used is 80%; for a single 100t / h hot water boiler, the amount of desulfurization wastewater generated per hour is 600kg.

[0013] Preferably, in step S2, the organic sulfur is TMT15 with a concentration of 15%; and the amount of organic sulfur added is controlled in real time by an online heavy metal detector to ensure that the heavy metal content of the effluent meets the Class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants".

[0014] Preferably, in step S3, the flocculant is FeClSO4 with a concentration of 40%, and the coagulant aid is powdered PAM; the pH value is adjusted using a 30% hydrochloric acid solution, and the pH measuring probe is periodically cleaned using a 3%~5% diluted hydrochloric acid solution via an automatic pH meter cleaning device; the clarifier and thickener has a volume of 4m³ and adopts a continuous contact sludge treatment method, returning part of the sludge to the neutralization tank via a sludge circulation pump.

[0015] Preferably, in step S4, the volume of the supernatant storage tank is 10m³; two sludge circulation pumps and sludge conveying pumps are set up for sludge treatment, and two clean liquid reuse pumps and three-compartment discharge pumps are set up for clean liquid conveying, with one operating and one standby; the wastewater treatment capacity of the entire three-compartment treatment unit is controlled at 2m³ / h, and after the three-compartment process, the amount of supernatant to be evaporated per hour is reduced to less than 200kg.

[0016] Preferably, in step S5, three metering pumps are set up, and a two-operation-one-standby operation mode is adopted; the wastewater evaporator is installed between the air preheater outlet and the dust collector inlet, and the material is 316L, and the matching pipe valves are also made of 316L; the soot blower is a sonic soot blower that meets national standards, the silo pump is a national standard silo pump, and the ash conveying pipe is a wear-resistant pipe.

[0017] Preferably, in step S5, the flue gas temperature at the air preheater outlet is 130℃; when 200kg of supernatant to be evaporated enters the wastewater evaporator, the flue gas temperature decrease is controlled to be 5℃, the flue gas humidity increase is controlled to be 0.1%, and it does not affect the normal operation of the subsequent desulfurization and dust removal equipment; at the same time, an online monitoring instrument for flue gas temperature and humidity is set at the outlet of the wastewater evaporator to feed back the data to the control system in real time.

[0018] Preferably, in step S5, by adjusting the metering pump delivery rate of the supernatant to be evaporated, the evaporation water volume of the main flue evaporation stage is matched with the flue gas temperature and flue layout conditions. Under the premise of ensuring the safe and stable operation of the system, the amount of wastewater to be treated is reduced, thereby achieving energy saving and consumption reduction in the system. Moreover, the metering pump delivery rate adjustment range is 50~200kg / h, and the adjustment accuracy error does not exceed ±2%.

[0019] Preferably, the entire process system is equipped with a DCS automatic control system, which can realize real-time monitoring and automatic adjustment of wastewater flow, reagent dosage, and equipment operating status; when the system experiences pump failure, abnormal liquid level, or excessive flue gas parameters, it will automatically trigger an audible and visual alarm and switch to backup equipment or start an emergency shutdown procedure to ensure system safety.

[0020] Preferably, in step S4, sludge dewatering is performed using a plate and frame filter press with a filter cloth pore size of 5~10μm. After dewatering, the sludge moisture content is controlled below 60%. The filtrate generated during the dewatering process is buffered in a filtrate collection tank and then transported to a neutralization tank via a return pump to form a closed-loop treatment. At the same time, the plate and frame filter press is equipped with an automatic washing device that performs high-pressure water washing on the filter cloth every 8 hours of operation to ensure stable filtration efficiency.

[0021] Compared with related technologies, the waste heat evaporation-based zero-discharge process for desulfurization wastewater provided by this invention has the following beneficial effects:

[0022] 1. This invention provides a waste heat evaporation-based zero-discharge process for desulfurization wastewater. It ensures effective heavy metal treatment through a dual mechanism of "pretreatment + deep removal." Lime slurry causes easily precipitated heavy metals such as lead and zinc to leach out, while 15% concentration of organic sulfur TMT15 forms stable sulfides with cadmium and mercury. Combined with precise quantity control using an online detector, it ensures that the effluent heavy metals meet the Class A standard of the "Discharge Standard of Pollutants for Urban Wastewater Treatment Plants." Simultaneously, there is no wastewater discharge at the end of the process. Ash from the wastewater evaporator and salt-containing ash from the dust collector are stored in an ash storage silo. Pretreatment sedimentation, solid-liquid separation, and filtrate recirculation form a closed loop, completely eliminating leakage risks and achieving the zero-discharge goal.

[0023] 2. This invention provides a waste heat evaporation-based zero-discharge process for desulfurization wastewater. Through resource recycling, the supernatant from the clarifier is partially reused in the desulfurization system, and the filtrate is returned to the neutralization tank, achieving a closed-loop water resource system. The plate and frame filter press controls the sludge moisture content to below 60%, reducing the volume to 1 / 3 of the original, thus reducing disposal costs. The triplet can also reduce the volume of liquid to be evaporated from 600 kg / h to below 200 kg / h. In terms of energy saving, the core evaporation process utilizes the waste heat from the 130°C low-temperature flue gas at the air preheater outlet, eliminating the need for additional steam / electricity consumption. The metering pump is precisely matched to the operating conditions, and the bottom sludge return can reduce the flocculant dosage by 10%, resulting in an estimated annual energy saving of approximately 52,000 kWh.

[0024] 3. This invention provides a waste heat evaporation-based zero-discharge process for desulfurization wastewater. Key equipment adopts redundant configuration, with "1 in operation and 1 on standby" for sludge circulation pumps and clear liquid reuse pumps, and "3 units, 2 in operation and 1 on standby" for metering pumps. In case of failure, automatic switching occurs within 30 seconds, ensuring more than 8,000 hours of operation per year. The equipment is made of 316L stainless steel to resist chloride ion corrosion, and the sonic soot blower is regularly cleaned to prevent clogging. The DCS automatic control system monitors parameters such as flow rate and reagent dosage in real time. In case of abnormality, it automatically alarms with sound and light and activates emergency procedures, which greatly reduces the intensity of manual operation and maintenance and safety risks, and extends the service life of the equipment. Attached Figure Description

[0025] Figure 1 This is a flowchart of the present invention;

[0026] Figure 2 This is an extended flow chart of the desulfurization wastewater pretreatment process of the present invention;

[0027] Figure 3 This is an extended flowchart of the heavy metal deep removal process of the present invention;

[0028] Figure 4 This is an extended flow chart of the flocculation and precipitation process of the present invention;

[0029] Figure 5 This is an extended flow chart of the sludge treatment and supernatant separation of the present invention. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0031] Example 1:

[0032] Please see Figures 1-5 This invention provides a technical solution: a waste heat evaporation-based zero-discharge process for desulfurization wastewater, comprising the following steps:

[0033] S1. Pretreatment of desulfurization wastewater: The wastewater generated by the desulfurization unit is sequentially separated by a wastewater hydrocyclone and buffered in a wastewater tank before being transported to a neutralization tank. Lime slurry is added to the neutralization tank to adjust the pH value of the wastewater to a preset range, so that some heavy metals in the wastewater precipitate in the form of hydroxides and neutralize acidic substances.

[0034] In step S1, the concentration of lime slurry is 5%~10%, and the purity of the quicklime powder used is 80%; for a single 100t / h hot water boiler, the amount of desulfurization wastewater generated per hour is 600kg;

[0035] In this implementation plan, the cyclone separation effect of the wastewater hydrocyclone can preferentially remove suspended solids with a particle diameter greater than 0.1mm from the wastewater, reducing the impurity load on the subsequent neutralization tank and settling tank, and avoiding the impact of large particle impurities on the efficiency of the reagent reaction. The buffer design of the wastewater tank can balance the characteristics of "intermittent discharge and large flow fluctuation" of desulfurization wastewater with the requirements of "continuous and stable treatment" of subsequent processes, and prevent the system operating conditions from being disordered due to instantaneous interruption or excessive wastewater supply.

[0036] The selection of lime slurry with a concentration of 5% to 10% and quicklime powder with a purity of 80% is based on a dual consideration of "reaction efficiency" and "cost control": lime slurry with a concentration range of this can quickly adjust the pH value of wastewater to 8.5 to 9.5, ensuring that easily precipitated heavy metals such as lead, zinc, and copper in the wastewater are fully precipitated in the form of hydroxides, and can also efficiently neutralize acidic substances such as sulfate and sulfite in the wastewater. The pH of desulfurization wastewater is usually 4 to 6, which is acidic, thus avoiding corrosion of subsequent equipment by acidic water quality; while 80% pure quicklime powder can meet the reaction requirements while reducing the introduction of impurities and reducing the amount of subsequent sludge treatment.

[0037] The design process is designed for a single 100t / h hot water boiler with a desulfurization wastewater volume of 600kg per hour, which further ensures the matching between the process scale and the boiler water production intensity. This avoids energy waste caused by excessive treatment capacity and prevents wastewater accumulation caused by insufficient treatment capacity, laying the foundation for the stable operation of the entire system.

[0038] S2, Deep removal of heavy metals: The wastewater pretreated in step S1 is transported to a settling tank, and organic sulfur is added to the settling tank to precipitate cadmium and mercury in the wastewater in the form of sulfides.

[0039] In step S2, the organic sulfur is TMT15 with a concentration of 15%; and the amount of organic sulfur added is controlled in real time by an online heavy metal detector to ensure that the heavy metal content of the effluent meets the Class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants".

[0040] In this implementation plan, 15% organic sulfur TMT15 is selected as the deep heavy metal removal agent. Its core advantage lies in its specific reaction with "difficult-to-precipitate heavy metals" such as cadmium and mercury: compared with lime pretreatment which can only remove easily precipitated heavy metals, TMT15 can form sulfide precipitates with cadmium and mercury ions with extremely high stability constants, which solves the problem of insufficient cadmium and mercury removal in traditional processes.

[0041] By adjusting the dosage of organic sulfur in real time using an online heavy metal detector, precise "on-demand" control is achieved: the detector collects a water sample from the sedimentation tank outlet every 5 minutes. If the heavy metal content is close to the upper limit of the Class A standard, the dosage is automatically increased; if the content is far below the standard, the dosage is reduced. This avoids waste of reagents and prevents the risk of exceeding the treatment standard due to insufficient dosage. Ultimately, it ensures that the heavy metal content of the effluent strictly complies with the Class A standard of the "Discharge Standard of Pollutants for Urban Wastewater Treatment Plants", meeting the water quality requirements for subsequent supernatant reuse or evaporation treatment.

[0042] S3, Flocculation and Sedimentation: The wastewater treated in step S2 is transported to the flocculation tank and flocculant is added, and then transported to the clarifier and thickener; coagulant aid is added to the inlet pipe of the clarifier and thickener to form large flocs of solid precipitate and complete solid-liquid separation; during this period, the pH value of the supernatant at the outlet of the clarifier and thickener is adjusted to meet the standard range.

[0043] In step S3, the flocculant is FeClSO4 with a concentration of 40%, and the coagulant aid is powdered PAM; the pH value is adjusted using a 30% hydrochloric acid solution, and the pH measuring probe is periodically cleaned by an automatic pH meter spraying device using a 3%~5% diluted hydrochloric acid solution; the clarifier and thickener has a volume of 4m³ and adopts a continuous contact sludge treatment method, returning part of the sludge to the neutralization tank through a sludge circulation pump;

[0044] In this implementation scheme, 40% FeClSO4 is used as a flocculant. The ferric hydroxide colloid generated after its hydrolysis has extremely strong adsorption properties, effectively capturing tiny heavy metal sulfide precipitates and residual suspended solids in wastewater. Combined with powdered PAM coagulant aid, it promotes the aggregation of tiny colloidal particles into large-particle flocs with a diameter greater than 100 μm through a "bridging effect," significantly shortening the settling time and improving solid-liquid separation efficiency. The flocculation mechanism of 40% FeClSO4 (polyferric sulfate) is as follows: hydrolysis generates polynuclear hydroxyl complexes such as Fe(OH)2⁺ and Fe(OH)3, which, through adsorption bridging, bridging small-sized particles (1-10 μm) in wastewater. The heavy metal sulfide precipitates (such as CdS and HgS) and suspended matter are encapsulated to form initial flocs; the subsequently added powdered PAM (anionic, molecular weight 8 million-12 million) bridges the initial flocs, causing them to aggregate into large flocs with a diameter ≥100μm, increasing the settling velocity to 20-30m / h (the settling velocity is only 5-8m / h without PAM), which greatly shortens the solid-liquid separation time of the clarifier and concentrator; the pH value is adjusted to 6-9 with 30% hydrochloric acid solution, which can avoid the supernatant pH value being too high (>9) causing premature precipitation and scaling of salts (such as CaCO3) in the subsequent evaporator, or the pH value being too low (<6) causing corrosion of the supernatant storage tank and metering pump;

[0045] Adjusting the pH of the supernatant at the outlet of the clarifier to 6-9 using a 30% hydrochloric acid solution can prevent acidic water from corroding subsequent supernatant storage tanks and reuse pipelines, or alkaline water from causing salt scaling during evaporation. At the same time, regularly cleaning the pH measurement probe with a 3%-5% diluted hydrochloric acid solution can prevent scale formation on the probe surface due to calcium carbonate and ferric hydroxide, avoid measurement errors, and ensure the accuracy of pH control.

[0046] The 4m³ clarifier and thickener adopts the "continuous contact sludge treatment" method. 10% to 15% of the bottom sludge is returned to the neutralization tank through a sludge circulation pump. The active flocculants in the returned sludge enhance the flocculation effect of the wastewater in the neutralization tank, which can reduce the amount of flocculant added later by about 10% and reduce operating costs. At the same time, the continuous treatment mode avoids water quality fluctuations caused by intermittent sedimentation and ensures the stability of the supernatant water quality.

[0047] S4. Sludge treatment and supernatant separation: Part of the sludge separated from the clarifier in step S3 is returned to the neutralization tank and part is dewatered. The dewatered filter cake is transported off-site and the filtrate is returned to the neutralization tank. The supernatant separated from the clarifier enters the supernatant storage tank. After detecting the chloride ion content, part of it is reused in the desulfurization system, and the remaining supernatant is used as wastewater to be evaporated.

[0048] In step S4, the volume of the supernatant storage tank is 10m³; two sludge circulation pumps and sludge transfer pumps are installed for sludge treatment, and two clean liquid reuse pumps and three-unit discharge pumps are installed for clean liquid transfer, with one in operation and one on standby; the wastewater treatment capacity of the entire three-unit treatment unit is controlled at 2m³ / h, and after the three-unit process, the amount of supernatant to be evaporated per hour is reduced to less than 200kg;

[0049] In step S4, sludge dewatering is performed using a plate and frame filter press. The filter cloth of the filter press has a pore size of 5~10μm, and the moisture content of the sludge after dewatering is controlled below 60%. The filtrate generated during the dewatering process is buffered in a filtrate collection tank and then transported to a neutralization tank through a return pump to form a closed-loop treatment. At the same time, the plate and frame filter press is equipped with an automatic washing device, which performs high-pressure water washing on the filter cloth every 8 hours of operation to ensure stable filtration efficiency.

[0050] In this implementation plan, the 10m³ supernatant storage tank can provide sufficient buffer space for "supernatant reuse" and "wastewater to be evaporated": when the demand for reuse in the desulfurization system increases, the storage tank can quickly replenish and divert the flow; when the load of the evaporation process is low, the storage tank can temporarily store the supernatant to prevent the supernatant from flowing back to the front end due to the inability to process it in time, thus balancing the water distribution of the entire system.

[0051] The sludge separated by the clarifier and thickener is divided into two parts: ① 10%-15% of the sludge is returned to the neutralization tank via a sludge circulation pump. The residual Fe(OH)3 colloid and unreacted TMT15 in the sludge can continue to participate in the heavy metal precipitation reaction in the neutralization tank. Actual measurements show that this can reduce the amount of lime slurry added in the neutralization tank by 5%-8% and the amount of TMT15 added in the settling tank by 3%-5%, thus reducing reagent costs; ② 85%-90% of the dewatered sludge is pre-concentrated in the sludge thickening tank before entering the plate and frame filter press, increasing the sludge solids content from 3%-5% to 15%-20%, thus reducing the filter press processing time. The filter cloth of the filter press is cleaned by an automatic washing device every 8 hours of operation, which can maintain the filter cloth filtration flux at 80-100L / (m²・h) (if not cleaned, the filter cloth flux will drop below 30L / (m²・h), resulting in a decrease in filter press efficiency).

[0052] The sludge circulation pump, sludge transfer pump, clear liquid reuse pump, and triple box discharge pump all adopt a "1 in operation, 1 standby" operation mode, which is a key design based on system reliability: if the main pump stops due to mechanical failure or wear, the standby pump can automatically switch and start within 30 seconds to ensure uninterrupted sludge transfer and stable clear liquid transfer, greatly reducing the risk of system downtime and ensuring an annual operating time of more than 8,000 hours.

[0053] The wastewater treatment capacity of the entire triplex unit is controlled at 2 m³ / h, matching the "low-load, high-efficiency treatment" with the amount of desulfurization wastewater generated at the front end. Through multi-stage reaction and concentration, the amount of supernatant to be evaporated per hour is reduced from the initial 600 kg to below 200 kg, significantly reducing the treatment load of the subsequent main flue gas waste heat evaporation and reducing the energy consumption of the metering pump and the waste heat consumption of the flue gas. The design basis for controlling the triplex unit's treatment capacity to 2 m³ / h is that a single 100 t / h hot water boiler generates 600 kg of desulfurization wastewater per hour. The treatment capacity of 2 m³ / h ensures that the wastewater reacts fully in the neutralization tank, settling tank, and flocculation tank, avoiding insufficient reaction between the reagents and wastewater due to insufficient residence time. After treatment in the triplex unit, the amount of supernatant is reduced from 600 kg / h to below 200 kg / h. The reduced 400 kg / h of supernatant is recycled to the desulfurization system through the supernatant reuse pump, which reduces both the evaporator load and the fresh water consumption of the desulfurization system.

[0054] Sludge dewatering uses a plate and frame filter press with a filter cloth pore size of 5~10μm, which can filter out more than 95% of solid particles in sludge. The moisture content of the dewatered sludge is strictly controlled below 60% - the reduced moisture content can reduce the sludge volume to 1 / 3 of the original volume, significantly reducing the cost of sludge transportation and disposal. The filtrate produced by dewatering is buffered in the filtrate collection tank and then returned to the neutralization tank, forming a closed loop process of "wastewater treatment-filtrate return", avoiding secondary pollution caused by direct discharge of filtrate, and improving water resource utilization.

[0055] The plate and frame filter press is equipped with an automatic high-pressure water flushing device that flushes the filter cloth every 8 hours of operation. This thoroughly removes blockages from the filter cloth pores, maintains the filter cloth's filtration throughput, and prevents a decrease in dewatering efficiency or overload of the filter press due to filter cloth blockage.

[0056] S5. Main flue gas waste heat evaporation: The supernatant to be evaporated in step S4 is transported to the injection module via a metering pump, atomized under the action of compressed air, and then sprayed into the wastewater evaporator; the heat of the low-temperature flue gas at the air preheater outlet is used to evaporate the wastewater droplets, and salts are precipitated in the wastewater; the soot blower removes the ash and scale accumulated in the flue and atomization device; the ash collected by the wastewater evaporator and the salt-containing ash collected by the dust collector are both transported to the ash silo to achieve zero discharge of desulfurization wastewater;

[0057] In step S5, three metering pumps are set up, with a 2-operation-1-standby operation mode; the wastewater evaporator is installed between the air preheater outlet and the dust collector inlet, and is made of 316L material, and the matching pipes and valves are also made of 316L material; the soot blower is a sonic soot blower that meets national standards, the silo pump is a national standard silo pump, and the ash conveying pipe is a wear-resistant pipe.

[0058] In step S5, the flue gas temperature at the air preheater outlet is 130℃; when 200kg of supernatant to be evaporated enters the wastewater evaporator, the flue gas temperature decrease is controlled to be 5℃ and the flue gas humidity increase is controlled to be 0.1%, without affecting the normal operation of subsequent desulfurization and dust removal equipment; at the same time, an online monitoring instrument for flue gas temperature and humidity is set at the outlet of the wastewater evaporator to provide real-time feedback data to the control system.

[0059] In step S5, by adjusting the metering pump flow rate of the supernatant to be evaporated, the evaporation water volume in the main flue gas evaporation stage is matched with the flue gas temperature and flue gas layout conditions. Under the premise of ensuring the safe and stable operation of the system, the amount of wastewater to be treated is reduced, thereby achieving energy saving and consumption reduction in the system. The metering pump flow rate adjustment range is 50~200 kg / h, and the adjustment accuracy error does not exceed ±2%.

[0060] In this implementation plan, the metering pumps adopt a "3-unit configuration, 2 in operation and 1 in standby" operating mode. This not only meets the maximum demand of 200 kg / h for conveying the supernatant to be evaporated, but also allows for immediate switching to the standby pump in case of main pump failure, ensuring uninterrupted evaporation. Simultaneously, the frequency conversion control design of the metering pumps enables continuous adjustment of the conveying capacity from 50 to 200 kg / h, with an adjustment accuracy error not exceeding ±2%. This provides a precise control basis for subsequent "evaporation rate matching with flue gas waste heat." The 316L stainless steel material, verified by chloride ion corrosion testing, exhibits an annual corrosion rate of ≤0.02 mm under conditions of chloride ion concentration ≤8000 mg / L in wastewater and flue gas temperature 120-140℃, far lower than ordinary 304 stainless steel. The ash conveying pipeline uses a ceramic-lined composite steel pipe with a wear resistance coefficient of 0.5, capable of withstanding wear caused by long-term conveying of salt-containing ash, extending the pipeline replacement cycle to over 5 years.

[0061] The wastewater evaporator and its supporting pipes and valves are made of 316L stainless steel, primarily due to its excellent corrosion resistance. Even after pretreatment, the desulfurization wastewater still contains a certain concentration of chloride ions. The molybdenum element in 316L stainless steel can form a passivation film, effectively resisting chloride ion corrosion and preventing flue gas pollution or wastewater overflow caused by corrosion leaks, thus extending the equipment's service life. Meanwhile, the sonic soot blower, meeting national standards, can automatically run every two hours, using sonic vibrations to remove accumulated ash and scale from the inner wall of the flue and the atomizing device, preventing ash buildup from affecting heat transfer in the flue gas and avoiding uneven wastewater atomization caused by blockage of the atomizing device.

[0062] The air preheater outlet flue gas temperature is designed to be 130℃. When 200kg of supernatant to be evaporated is injected into the evaporator, the flue gas temperature is precisely controlled to decrease by 5℃ and the humidity increases by 0.1%. This parameter design is based on a balance between "waste heat utilization" and "protection of subsequent equipment": the waste heat of the 130℃ flue gas can fully meet the heat required for the evaporation of 200kg of wastewater without the need for additional steam or electricity consumption; while the 5℃ temperature drop and 0.1% humidity increase can prevent excessively low flue gas temperature from causing condensation and corrosion in the subsequent dust collector, and will not affect the desulfurization efficiency of the desulfurization system due to excessively high humidity. To ensure the stable operation of the entire boiler flue gas treatment system, the specific parameter control logic is as follows: If the online monitoring instrument detects that the flue gas temperature is below 125℃, the DCS system automatically reduces the metering pump's delivery rate from 200kg / h to below 150kg / h until the flue gas temperature rises back to above 128℃; if the detected flue gas humidity is above 0.8%, one operating metering pump is suspended, and both pumps are resumed operation once the humidity drops below 0.5%. This parameter control can prevent excessively low flue gas temperature from causing condensation on the dust collector filter bags, while also preventing excessively high humidity from affecting the stability of the slurry concentration in the desulfurization tower.

[0063] The wastewater evaporator outlet is equipped with an online monitoring instrument for flue gas temperature and humidity, which can feed the data back to the DCS control system in real time. If the flue gas temperature is below 125℃, the system automatically reduces the metering pump's delivery rate. If the humidity is above 8%, the evaporation process is suspended and restarted after the flue gas parameters return to normal. This "dynamic adjustment" achieves precise matching between the evaporation water volume and the waste heat of the flue gas and the flue conditions. While ensuring system safety, it reduces unnecessary wastewater connection and transportation energy consumption, achieving an annual energy saving of approximately 52,000 kWh. The wastewater evaporator is equipped with three sets of atomizing nozzles with an atomization angle of 60° and a droplet diameter controlled between 50-100 μm. The nozzle spacing is 1.2m, and they are evenly distributed along the flue section to ensure that the atomized droplets cover more than 95% of the contact area with the flue gas. This avoids the local waste heat of the flue gas not being utilized or the local droplets not being completely evaporated. Incompletely evaporated droplets will form a "wet wall," causing salt to accumulate on the inner wall of the evaporator and increasing the cleaning load of the soot blower.

[0064] The entire process system is equipped with a DCS automatic control system, which can realize real-time monitoring and automatic adjustment of wastewater flow, reagent dosage, and equipment operating status. When the system experiences pump failure, abnormal liquid level, or excessive flue gas parameters, it will automatically trigger an audible and visual alarm and switch to backup equipment or start an emergency shutdown procedure to ensure system safety.

[0065] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, the phrase "comprising an element defined as..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0066] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A waste heat evaporation-based zero-discharge process for desulfurization wastewater, characterized in that: Includes the following steps: S1. Pretreatment of desulfurization wastewater: The wastewater generated by the desulfurization unit is sequentially separated by a wastewater hydrocyclone and buffered in a wastewater tank before being transported to a neutralization tank. Lime slurry is added to the neutralization tank to adjust the pH value of the wastewater to a preset range, so that some heavy metals in the wastewater precipitate in the form of hydroxides and neutralize acidic substances. S2, Deep removal of heavy metals: The wastewater pretreated in step S1 is transported to a settling tank, and organic sulfur is added to the settling tank to precipitate cadmium and mercury in the wastewater in the form of sulfides. S3, Flocculation and Sedimentation: The wastewater treated in step S2 is transported to the flocculation tank and flocculant is added, and then transported to the clarifier and thickener; coagulant aid is added to the inlet pipe of the clarifier and thickener to form large flocs of solid precipitate and complete solid-liquid separation; during this period, the pH value of the supernatant at the outlet of the clarifier and thickener is adjusted to meet the standard range. S4. Sludge treatment and supernatant separation: Part of the sludge separated from the clarifier in step S3 is returned to the neutralization tank and part is dewatered. The dewatered filter cake is transported off-site and the filtrate is returned to the neutralization tank. The supernatant separated from the clarifier enters the supernatant storage tank. After detecting the chloride ion content, part of it is reused in the desulfurization system, and the remaining supernatant is used as wastewater to be evaporated. S5. Main flue waste heat evaporation: The supernatant to be evaporated in step S4 is transported to the injection module by a metering pump, and then atomized and sprayed into the wastewater evaporator under the action of compressed air. The wastewater droplets are evaporated by utilizing the heat from the low-temperature flue gas at the air preheater outlet, and salts are precipitated out of the wastewater. The accumulated ash and scale in the flue and atomizing device are removed by a soot blower. The ash collected by the wastewater evaporator and the salt-containing ash captured by the dust collector are transported to the ash silo to achieve zero discharge of desulfurization wastewater.

2. The waste heat evaporation-based zero-discharge process for desulfurization wastewater according to claim 1, characterized in that: In step S1, the concentration of lime slurry is 5%~10%, and the purity of the quicklime powder used is 80%; for a single 100t / h hot water boiler, the amount of desulfurization wastewater generated per hour is 600kg.

3. The waste heat evaporation-based zero-discharge process for desulfurization wastewater according to claim 1, characterized in that: In step S2, the organic sulfur is TMT15 with a concentration of 15%; and the amount of organic sulfur added is controlled in real time by an online heavy metal detector to ensure that the heavy metal content of the effluent meets the Class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants".

4. The waste heat evaporation-based zero-discharge process for desulfurization wastewater according to claim 1, characterized in that: In step S3, the flocculant is FeClSO4 with a concentration of 40%, and the coagulant aid is powdered PAM; the pH value is adjusted using a 30% hydrochloric acid solution, and the pH measuring probe is periodically cleaned using a 3%~5% diluted hydrochloric acid solution via an automatic pH meter cleaning device; the clarifier and thickener has a volume of 4m³ and adopts a continuous contact sludge treatment method, returning part of the sludge to the neutralization tank via a sludge circulation pump.

5. The waste heat evaporation-based zero-discharge process for desulfurization wastewater according to claim 1, characterized in that: In step S4, the volume of the supernatant storage tank is 10m³; two sludge circulation pumps and sludge transfer pumps are set up for sludge treatment, and two clean liquid reuse pumps and three-compartment discharge pumps are set up for clean liquid transfer, with one in operation and one on standby; the wastewater treatment capacity of the entire three-compartment treatment unit is controlled at 2m³ / h, and after the three-compartment process, the amount of supernatant to be evaporated per hour is reduced to less than 200kg.

6. The waste heat evaporation-based zero-discharge process for desulfurization wastewater according to claim 1, characterized in that: In step S5, three metering pumps are set up, operating in a 2-on-1-standby mode; the wastewater evaporator is installed between the air preheater outlet and the dust collector inlet, and is made of 316L stainless steel, as are the matching pipes and valves; the soot blower is a sonic soot blower that meets national standards, the silo pump is a national standard silo pump, and the ash conveying pipeline is a wear-resistant pipeline.

7. The waste heat evaporation-based zero-discharge process for desulfurization wastewater according to claim 1, characterized in that: In step S5, the flue gas temperature at the air preheater outlet is 130℃. When 200kg of supernatant to be evaporated enters the wastewater evaporator, the flue gas temperature decrease is controlled to be 5℃ and the flue gas humidity increase is controlled to be 0.1%, without affecting the normal operation of subsequent desulfurization and dust removal equipment. At the same time, an online monitoring instrument for flue gas temperature and humidity is installed at the outlet of the wastewater evaporator to provide real-time feedback data to the control system.

8. The waste heat evaporation-based zero-discharge process for desulfurization wastewater according to claim 1, characterized in that: In step S5, by adjusting the metering pump delivery rate of the supernatant to be evaporated, the evaporation water volume of the main flue evaporation stage is matched with the flue gas temperature and flue layout conditions. Under the premise of ensuring the safe and stable operation of the system, the amount of wastewater to be treated is reduced, thereby achieving energy saving and consumption reduction in the system. The metering pump delivery rate adjustment range is 50~200kg / h, and the adjustment accuracy error does not exceed ±2%.

9. The waste heat evaporation-based zero-discharge process for desulfurization wastewater according to claim 1, characterized in that: The entire process system is equipped with a DCS automatic control system, which can realize real-time monitoring and automatic adjustment of equipment operating status such as wastewater flow rate, reagent dosage, ash conveying frequency, and soot blowing frequency; When the system experiences pump failure, abnormal liquid level, or excessive flue gas parameters, it will automatically trigger an audible and visual alarm and switch to backup equipment or initiate an emergency shutdown procedure to ensure system safety.

10. The waste heat evaporation-based zero-discharge process for desulfurization wastewater according to claim 1, characterized in that: In step S4, sludge dewatering is performed using a plate and frame filter press. The filter cloth of the filter press has a pore size of 5~10μm, and the moisture content of the sludge after dewatering is controlled below 60%. The filtrate generated during the dewatering process is buffered in the filtrate collection tank and then transported to the neutralization tank through a return pump to form a closed-loop treatment. At the same time, the plate and frame filter press is equipped with an automatic washing device, which performs high-pressure water washing on the filter cloth every 8 hours of operation to ensure stable filtration efficiency.

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