Zero-discharge treatment method for desulfurization wastewater of thermal power plant

Abstract

The invention discloses a thermal power plant desulfurization wastewater zero discharge treatment method, which comprises: S1, carrying out triple-effect flash evaporation concentration treatment on desulfurization wastewater so as to reduce the amount, and storing the concentrated liquid after concentration in a concentrated liquid box; and S2, treating the concentrated liquid obtained in the step S1 by adopting a triple box process, enabling the treated water to enter a clarification tank for gravity settling, enabling clear water at the upper part to overflow to a wastewater collection box, and discharging sludge generated at the bottom to a gypsum dehydration belt through a sludge discharge pump. According to the invention, twice reduction of desulfurization wastewater is realized through triple-effect flash evaporation concentration and a triple-box process, so that the amount of desulfurization wastewater needing to be treated by a flue gas bypass system is reduced, the problems of pipeline pollution and blockage and frequent fault of an atomizer in the treatment process are reduced, and the reduced wastewater can be stored in a wastewater collection box during deep adjustment of a unit, so that the treatment efficiency of the unit is improved. Zero discharge of the desulfurization wastewater is realized, chloride ions in the slurry of the desulfurization absorption tower are controllable after zero discharge of the desulfurization wastewater, and the risks of slurry poisoning and gypsum diarrhoea of the absorption tower are reduced.

Description

Technical Field

[0001] The invention relates to the technical field of desulfurization wastewater treatment in thermal power plants, and in particular to a zero-discharge treatment method for desulfurization wastewater in thermal power plants. Background Art

[0002] The desulfurization wastewater from thermal power plants (usually from wet desulfurization systems, such as the limestone-gypsum method) has the characteristics of high salinity, high suspended matter, heavy metals and strong acidity. Its treatment needs to comprehensively consider environmental protection requirements and economic efficiency.

[0003] Conventional treatment solutions usually take the "three-tank" process as the core, combining neutralization, flocculation, sedimentation and other steps to achieve standard discharge or partial reuse. The advantages are mature technology, low investment and operation costs, and the ability to effectively remove heavy metals and suspended solids to meet basic discharge requirements; however, the disadvantages are also obvious, such as 1. Large amount of wastewater, difficult recycling, and non-compliant discharge; 2. Cl - 、SO 4 2- Soluble salts such as chlorinated salts cannot be removed, limiting reuse; 3. Sludge containing heavy metals needs to be managed as hazardous waste, and the disposal cost is high; 4. Some COD and additives (such as corrosion inhibitors) are difficult to degrade;

[0004] "Zero emission" requires a combination of multiple processes to completely remove soluble salts and recycle water resources, and finally dispose of them in the form of solid salt or mixed salt; the technical routes include:

[0005] 1. Membrane + thermal method: zero discharge of desulfurization wastewater is achieved through three steps of "pretreatment → membrane reduction → thermal curing". The pretreatment process mainly includes chemical softening, heavy metal removal, and fine filtration to ensure the stable operation of the membrane system. Membrane reduction mainly includes reverse osmosis (RO), electrodialysis (ED), and high-pressure reverse osmosis (DTRO). Thermal curing mainly includes mechanical vaporization (MED), mechanical vapor recompression (MVR), and crystallization salt separation.

[0006] The advantage is that it can be treated thoroughly, but the disadvantages are high cost, high chloride ion corrosion, membrane fouling, difficulty in handling impure salts, and high energy consumption;

[0007] 2. Flue gas bypass technology, which uses the heat energy of high-temperature flue gas at the tail of the boiler to achieve wastewater evaporation and pollutant solidification;

[0008] The advantage is that it uses the high-temperature flue gas at the tail of the boiler, and the treatment cost is low; however, the disadvantage is that the treatment efficiency is low, and the treatment volume is usually ≤5m 3 / h, and large power plants require multiple sets of parallel connection, high chloride ion corrosion, system pipelines are easily blocked by dirt, and are related to unit load. They cannot be processed under deep adjustment conditions and the processing capacity is unstable.

[0009] Therefore, seeking appropriate technical solutions to solve the problems of wastewater volume and pollution blockage is an important measure to ensure zero wastewater discharge. Summary of the invention

[0010] The purpose of the present invention is to solve the above-mentioned shortcomings and provide a zero-discharge treatment method for desulfurization wastewater in a thermal power plant.

[0011] In order to solve the above technical problems, the present invention adopts the following technical solution: A method for zero-discharge treatment of desulfurization wastewater from a thermal power plant, comprising the following steps:

[0012] S1. Desulfurization wastewater is reduced by three-effect flash concentration treatment, and the concentrated concentrate is sent to the concentrate tank for storage;

[0013] S2. The concentrated liquid obtained in S1 is treated by the "triple tank" process. The treated water enters the clarifier for gravity sedimentation. The clean water above overflows to the wastewater collection tank, and the sludge generated at the bottom is discharged to the gypsum dehydration belt through the sludge pump;

[0014] S3. The clean water collected in the wastewater collection box in S2 is sent to the flue gas bypass system for spray drying, and the salt is captured along with the fly ash.

[0015] Furthermore, in the step S1, the specific steps of the triple-effect flash concentration are as follows:

[0016] S1.1. The desulfurization wastewater is first sent into the first-effect evaporator pipeline for surface heat exchange. Under the heating effect, the water in the desulfurization wastewater evaporates;

[0017] S1.2, introducing the steam generated by the evaporation of water in step S1.1 into the second-effect evaporator as a heating source to evaporate the water in the desulfurization wastewater entering the second-effect evaporator;

[0018] S1.3. Introduce the steam generated by the evaporation of water in step S1.2 into the third-effect evaporator as a heating source to continue evaporating the water in the desulfurization wastewater entering the third-effect evaporator, and send the concentrated concentrate into the concentrate tank for storage.

[0019] Furthermore, in the "triple-tank" process, three reaction boxes, flocculation boxes and clarification tanks are connected in series, and heavy metal precipitation and flocculation separation of desulfurization wastewater are completed step by step through the reaction box and the flocculation tank, and the treated water enters the clarification tank for gravity sedimentation.

[0020] Furthermore, the sludge generated in step S2 is conveyed to the gypsum dehydration belt, dehydrated together with the gypsum discharge slurry to form gypsum, and is processed in the form of gypsum.

[0021] Furthermore, the condensed water after evaporation and condensation is used as raw water for chemical water production or water replenishment for desulfurization process.

[0022] Furthermore, the S3 step specifically includes:

[0023] S3.1, extract 300-400℃ high temperature flue gas from the boiler air preheater;

[0024] S3.2, desulfurization wastewater is sprayed into the evaporation tower and atomized by high-speed rotating atomizing nozzle;

[0025] S3.3, the desulfurization wastewater enters the evaporation tower and is atomized by the high-speed rotating atomizing nozzle. After contacting with the high-temperature flue gas, it evaporates instantly, and the dissolved salt is converted into solid particles;

[0026] S3.4. The evaporated flue gas returns to the main flue, and the solid particles formed by evaporation and the fly ash in the flue gas are captured by the dust collector.

[0027] Furthermore, in the step S3.2, a high-speed rotating atomizing nozzle is used to form the desulfurization wastewater into droplets of 20-50 μm.

[0028] Furthermore, after the desulfurization wastewater contacts and evaporates with the high-temperature flue gas, the water enters the flue gas in the form of water vapor and returns to the main flue for discharge. The salt in the desulfurization wastewater forms micron-sized particles and mixes into the fly ash. The heavy metals in the desulfurization wastewater are converted into stable oxides / sulfates and solidified in the fly ash. After being captured by the dust collector, they are sent to the ash system for treatment.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) The present invention utilizes triple-effect flash evaporation concentration technology to firstly significantly reduce the amount of desulfurization wastewater, and by utilizing the steam generated during the flash evaporation process, it saves energy waste and realizes the recycling of condensed water;

[0031] (2) The present invention uses the "triple-tank" process to complete the heavy metal precipitation and flocculation separation of desulfurization wastewater in steps, and performs clarification separation, thereby achieving cement separation, further achieving the reduction of desulfurization wastewater, and only clear water enters the flue gas bypass system, solving the problems of pipeline system blockage and frequent failure of high-speed rotary atomizers, and ensuring the reliable operation of the atomizer;

[0032] (3) The present invention effectively solves the problem of solid waste treatment in the zero-discharge process of desulfurization wastewater by discharging the bottom sludge onto the gypsum dehydration belt after cement separation. The bottom sludge and the slurry discharged from the gypsum discharge pump are dehydrated together to form gypsum, which is further processed in the form of gypsum.

[0033] (4) The present invention achieves a double reduction of desulfurization wastewater through three-effect flash concentration and a "triple box" process, thereby reducing the amount of desulfurization wastewater that needs to be treated by the flue gas bypass system and the problems of pipeline blockage and frequent failure of the atomizer during the treatment process. During the deep adjustment of the unit, the reduced wastewater (clean water with a turbidity of less than 10PPM) can be stored in a wastewater collection box, achieving zero discharge of desulfurization wastewater. After zero discharge of desulfurization wastewater, the chloride ion of the desulfurization absorption tower slurry can be controlled, reducing the risk of absorption tower slurry poisoning and gypsum loosening. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. In the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present invention.

[0035] The various raw materials used in the following examples and comparative examples, unless otherwise specified, are products well known in the art.

[0036] A method for zero-discharge treatment of desulfurization wastewater from a thermal power plant comprises the following steps:

[0037] S1. Desulfurization wastewater is reduced by three-effect flash concentration treatment. The specific operation process includes:

[0038] S1.1. The desulfurization wastewater is first sent into the first-effect evaporator pipeline for surface heat exchange. Under the heating effect, the water in the desulfurization wastewater evaporates;

[0039] S1.2, introducing the steam generated by the evaporation of water in step S1.1 into the second-effect evaporator as a heating source to evaporate the water in the desulfurization wastewater entering the second-effect evaporator;

[0040] S1.3, introducing the steam generated by the evaporation of water in step S1.2 into the third-effect evaporator as a heating source to continue evaporating the water in the desulfurization wastewater entering the third-effect evaporator, and the condensed water after evaporation and condensation is used as raw water for chemical water production or water for desulfurization process, and the concentrated concentrate is sent to the concentrate tank for storage;

[0041] S2. The concentrated solution obtained in S1 is treated by a "triple tank" process, through three series-connected reaction boxes, flocculation boxes and clarification tanks, and the heavy metal precipitation and flocculation separation of the desulfurization wastewater are completed step by step through the reaction box and the flocculation tank. The treated water enters the clarification tank for gravity sedimentation, and the clean water above overflows to the wastewater collection tank. The sludge generated at the bottom is discharged to the gypsum dehydration belt through the sludge discharge pump, and is dehydrated together with the slurry discharged by the gypsum discharge pump to form gypsum, and is treated in the form of gypsum;

[0042] S3, the clean water collected in the wastewater collection box in S2 is sent to the flue gas bypass system for high-speed rotary atomization spray drying, and the salt is captured along with the fly ash;

[0043] S3.1, extract 300-400℃ high temperature flue gas from the boiler air preheater;

[0044] S3.2, desulfurization wastewater is sprayed into the evaporation tower;

[0045] S3.3. Use an atomizing nozzle to form the desulfurization wastewater into droplets of 20-50μm. The desulfurization wastewater enters the evaporation tower and evaporates instantly after contacting with the high-temperature flue gas. After the desulfurization wastewater contacts and evaporates with the high-temperature flue gas, the water enters the flue gas in the form of water vapor and returns to the main flue for discharge. The salt in the desulfurization wastewater forms micron-sized particles and mixes with the fly ash. The heavy metals in the desulfurization wastewater are converted into stable oxides / sulfates and solidified in the fly ash. They are captured by the dust collector and sent to the ash slag system for treatment.

[0046] S3.4. The evaporated flue gas returns to the main flue, and the solid particles formed by evaporation and the fly ash in the flue gas are captured by the dust collector.

[0047] Comparative Example 1:

[0048] A large coal-fired power plant uses limestone wet desulfurization technology, vacuum belt conveyor gypsum dehydration technology, and a desulfurization wastewater flue gas bypass evaporation "zero discharge" system with a designed output of 7.5t / h; each unit dehydrates for about 8 hours a day, and produces about 20t of desulfurization wastewater per hour during dehydration, with a solid content of 4% to 6%. According to the design, it can meet the need for zero discharge of desulfurization wastewater.

[0049] In actual operation, the treatment capacity of the zero-discharge desulfurization wastewater system is significantly affected by the boiler load. The boiler can reach the designed output when it is fully loaded, and the output drops sharply to zero when the load is less than 50%. With the substantial development of new energy installations, the utilization hours of coal-fired units have dropped drastically, the unit load rate has continued to decline, and deep peak regulation and even start-stop peak regulation have become the norm. In the first half of 2024: the average load rate of thermal power units nationwide is about 50% to 55% (a decrease of 2 to 3 percentage points from the same period in 2023). The average load rate of thermal power in 2024 is 50% to 53%, and it may drop to 48% to 50% in 2025. The treatment capacity of the zero-discharge system for desulfurization wastewater has seriously declined, resulting in insufficient treatment of desulfurization wastewater. The untreated desulfurization wastewater can only be returned to the absorption tower, resulting in excessive chloride ions in the absorption tower slurry, slurry poisoning and gypsum loosening have become the norm; due to the presence of solids, heavy metals and other sludge-loaded substances in the wastewater, the pipeline system and atomizer are seriously blocked, the atomizer fails frequently, and the operating reliability is reduced, further reducing the wastewater treatment capacity. When the wastewater cannot be treated, it will trigger a series of environmental risks, which seriously restricts the safe and stable operation of the unit.

[0050] For the comparative example 1 above, the zero-discharge treatment method for desulfurization wastewater from a thermal power plant of the present application is adopted for treatment. After the desulfurization wastewater of 20 t / h and a solid content of 4% to 6% is concentrated by triple-effect flash evaporation, it becomes a concentrated solution of 3 to 5 t / h and a solid content of 20% to 30%, which is stored in a concentrated solution tank, thus completely solving the problem of the "amount" of desulfurization wastewater; the "triple-tank" process further reduces the desulfurization wastewater to 2.6 to 4 t / h and clean water below 10 PPM;

[0051] After three-effect flash evaporation concentration and pretreatment precipitation, the 20t / h desulfurization wastewater with a solid content of 4% to 6% becomes 2.6 to 4t / h and 10PPM of clean water, which is transported to the flue gas bypass for evaporation treatment, which completely solves the "volume" and "fouling blockage" problems in the desulfurization wastewater treatment process, and the atomizer failure rate is reduced from 2 times / month to 0.1 times / month. During the deep adjustment of the unit, the wastewater can be stored in the wastewater collection tank and treated in time when the treatment conditions are met, achieving zero discharge of desulfurization wastewater; after zero discharge of desulfurization wastewater, the chloride ions in the desulfurization absorption tower slurry can be controlled, reducing the risk of absorption tower slurry poisoning and gypsum loosening.

[0052] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

Claims

1. A method for zero-discharge treatment of desulfurization wastewater from a thermal power plant, characterized in that: The steps include: S1. Desulfurization wastewater is reduced by three-effect flash concentration treatment, and the concentrated concentrate is sent to the concentrate tank for storage; S2. The concentrated liquid obtained in S1 is treated by the "triple tank" process. The treated water enters the clarifier for gravity sedimentation. The clean water above overflows into the wastewater collection tank, and the sludge generated at the bottom is discharged to the gypsum dehydration belt through the sludge pump; S3. The clean water collected in the wastewater collection box in S2 is sent to the flue gas bypass system for spray drying, and the salt is captured along with the fly ash.

2. The method for zero-discharge treatment of desulfurization wastewater from a thermal power plant according to claim 1, characterized in that: In the step S1, the specific steps of the triple-effect flash concentration are as follows: S1.

1. The desulfurization wastewater is first sent into the first-effect evaporator pipeline for surface heat exchange. Under the heating effect, the water in the desulfurization wastewater evaporates; S1.2, introducing the steam generated by the evaporation of water in step S1.1 into the second-effect evaporator as a heating source to evaporate the water in the desulfurization wastewater entering the second-effect evaporator; S1.

3. Introduce the steam generated by the evaporation of water in step S1.2 into the third-effect evaporator as a heating source to continue evaporating the water in the desulfurization wastewater entering the third-effect evaporator, and send the concentrated concentrate into the concentrate tank for storage.

3. The method for zero-discharge treatment of desulfurization wastewater from a thermal power plant according to claim 2, characterized in that: In the "triple tank" process, three reaction tanks, flocculation tanks and clarification tanks are connected in series, and heavy metal precipitation and flocculation separation of desulfurization wastewater are completed step by step through the reaction tank and flocculation tank. The treated water enters the clarification tank for gravity sedimentation.

4. The method for zero-discharge treatment of desulfurization wastewater from a thermal power plant according to claim 3, characterized in that: The sludge generated in step S2 is conveyed to the gypsum dehydration belt, dehydrated together with the gypsum discharge slurry to form gypsum, and is processed in the form of gypsum.

5. The method for zero-discharge treatment of desulfurization wastewater from a thermal power plant according to claim 2, characterized in that: The condensed water after evaporation and condensation is used as raw water for chemical water production or as make-up water for desulfurization process.

6. The method for zero-discharge treatment of desulfurization wastewater from a thermal power plant according to any one of claims 1 to 5, characterized in that: The S3 step specifically includes: S3.1, extract 300-400℃ high temperature flue gas from the boiler air preheater; S3.2, desulfurization wastewater is sprayed into the evaporation tower and atomized by high-speed rotating atomizing nozzle; S3.3, the desulfurization wastewater enters the evaporation tower and is atomized by the high-speed rotating atomizing nozzle. After contacting with the high-temperature flue gas, it evaporates instantly, and the dissolved salt is converted into solid particles; S3.

4. The evaporated flue gas returns to the main flue, and the solid particles formed by evaporation and the fly ash in the flue gas are captured by the dust collector.

7. The method for zero-discharge treatment of desulfurization wastewater from a thermal power plant according to claim 6, characterized in that: In the step S3.2, a high-speed rotating atomizing nozzle is used to form the desulfurization wastewater into droplets of 20-50 μm.

8. The method for zero-discharge treatment of desulfurization wastewater from a thermal power plant according to claim 6, characterized in that: After the desulfurization wastewater comes into contact with the high-temperature flue gas and evaporates, the moisture enters the flue gas in the form of water vapor and returns to the main flue for discharge. The salt in the desulfurization wastewater forms micron-sized particles and mixes into the fly ash. The heavy metals in the desulfurization wastewater are converted into stable oxides / sulfates and solidified in the fly ash. After being captured by the dust collector, they are sent to the ash system for treatment.