CN117700008A - A zero-discharge evaporation and drying treatment process for desulfurization wastewater from coal-fired power plants - Google Patents

Abstract

The invention provides a zero-emission evaporating treatment process for desulfurization waste water of a coal-fired power plant, which utilizes the existing equipment to the maximum extent through adjusting the operation mode of the existing facilities of the coal-fired power plant, improves the stability of an evaporating system, and when a lifting pump is sent to an atomizing disk rotating at a high speed in a tower, waste liquid is stretched into a film or pulled into filaments (depending on the rotating speed and the slurry amount) due to the effect of centrifugal force, and is broken and dispersed into liquid drops at the edge of the atomizing disk to be fully mixed with hot flue gas of a boiler. The desulfurization wastewater containing soluble and suspended solid particles is evaporated under high-temperature flue gas, and the outlet temperature of an evaporation tower is 150-160 ℃. The evaporated solid entrainment matter part enters the front main flue of the electric dust collector together with the flue gas, is trapped by the electric dust collector, is mixed with fly ash of the whole plant, and part of the solid entrainment matter part flows into the bottom of the drying tower to be pumped into an ash pipe of a first electric field of the electric dust collector through a bin pump or is mixed with a slag system.

Description

A zero-discharge evaporation and drying treatment process for desulfurization wastewater from coal-fired power plants

Technical field

The invention relates to a wastewater treatment system, in particular to a zero-discharge evaporation and drying treatment process for desulfurization wastewater from coal-fired power plants.

Background technique

Coal-fired power plants burn thermal coal and convert it into electrical energy. The sulfur dioxide in the coal-fired flue gas will pollute the atmosphere. Limestone wet desulfurization has mature technology, high desulfurization efficiency and wide application range, and has become the mainstream desulfurization process today. The limestone wet desulfurization system needs to discharge a certain amount of desulfurization wastewater regularly to ensure the normal and stable operation of the desulfurization system.

During the construction of the desulfurization system, a triple-box desulfurization wastewater treatment process is generally built, and the wastewater is discharged after the treatment reaches the standard. With the improvement of environmental protection requirements, the Yellow River and Yangtze River basins are now required to complete zero discharge of desulfurization wastewater from coal-fired power plants within a time limit, and qualified power plants are also encouraged to start building zero discharge of desulfurization wastewater.

Today's mainstream zero-discharge evaporation and drying treatment process for desulfurization wastewater from coal-fired power plants is as follows.

1) Pretreatment + membrane concentration + traditional evaporation crystallization

Desulfurization wastewater is pretreated by adding alkaline substances (sodium hydroxide or lime), flocculants, gravity sedimentation and other pre-treatments to remove most of the suspended solids, heavy metals and fluoride ions, hardness, silica and other scaling substances in the wastewater. Membrane technology (DTRO/DT, NF+SWRO, FO, etc.) is used to concentrate and reduce the pretreated wastewater, fresh water is reused, concentrated water enters the subsequent traditional evaporation and crystallization system (MED&MVR), condensed water is reused, and crystallized salt Handled separately.

Defects: This technical pretreatment + membrane concentration + traditional evaporation and crystallization adds alkaline substances in the early pretreatment for softening. Adding lime is cheaper, but it brings a large amount of sludge, and the softening effect is difficult to guarantee for subsequent membranes. Technical treatments such as adding sodium hydroxide are expensive. The subsequent evaporation and crystallization system consumes a lot of energy, and the final crystallized salt does not have good sales channels, and there is a risk of being defined as hazardous waste by subsequent environmental protection regulations.

2) Flue gas waste heat concentration + secondary air drying

The flue gas after the induced draft fan enters the concentration tower. The flue gas enters the concentration tank from the lower part. The desulfurization wastewater is sprayed from the upper part. The vaporized part of the desulfurization wastewater returns to the absorption tower together with the flue gas. The concentration at the bottom of the tower is dried by secondary air. , solid particles such as crystallized salt enter the flue in front of the dust collector with the secondary air, and are collected by the dust collector to achieve the removal effect.

Defects: The flue gas waste heat concentration concentrates and reduces the desulfurization wastewater, resulting in an increase in the solid content in the desulfurization wastewater. It is difficult for the flue gas waste heat concentration system to operate stably, and it also increases the risk of secondary air drying and blockage.

3) Low temperature flash concentration + bypass flue drying

The desulfurization wastewater does not go through the pretreatment system, but is directly extracted from the desulfurization wastewater cyclone overflow. The existing low-temperature economizer outlet hot water is used as a heat source for heating. After three-effect flash concentration, the concentration rate can reach 90%. , and is automatically adjustable from 50% to 90% online. The concentrated liquid enters the spray dryer of the two units for evaporation drying or rotary sprayer (the heat source of the dryer comes from the 350°C flue between the air preheater after denitration) The hot flue gas), the generated dust and water vapor are introduced into the flue before the electrostatic precipitator along with the flue gas, and the electrostatic precipitator is used to capture chloride ions and other solid particles and metal elements, and the evaporated water vapor enters the desulfurization tower. Water vapor is generated during the flash concentration process, and after condensation, it can be recycled into desulfurization process water or water replenishment for other purposes. Defects: Low-temperature flash evaporation and concentration flash evaporation and concentration of desulfurization wastewater, using its inherent impurities as crystal nuclei for crystallization. The crystal particles are large and can easily block the subsequent evaporation and drying system. Therefore, bypass flue drying is used, but it still cannot be solved. It is prone to clogging.

To sum up, the existing technologies all have some technical problems that need to be solved and are difficult to operate stably, and they all need to set up special pretreatment process sections (① pretreatment, ② flue gas waste heat concentration, ③ low-temperature flash concentration), The project cost is high and the investment is repeated.

Contents of the invention

In order to solve the above problems, the present invention discloses a zero-discharge evaporation and drying treatment process for coal-fired power plant desulfurization wastewater. On the premise of saving a certain amount of chemicals, the turbidity of the spray water is reduced, and a self-cleaning filter is used to remove residual hard particles. particulate matter, thus reducing the solid content of the spray wastewater. Finally, a high-temperature flue gas bypass rotary atomization drying system was used to set up the necessary facilities to achieve a zero-discharge desulfurization wastewater system with low project cost, short construction period, and stable operation. .

A zero-discharge evaporation and drying treatment process for desulfurization wastewater from coal-fired power plants, including a desulfurization wastewater cyclone, a neutralization tank, a sedimentation tank, a slurry clarifier and a water outlet tank connected in sequence. The discharge end of the water outlet tank is connected to an outlet water transfer pump. Connection; the sludge in the slurry clarifier is processed and discharged through a plate and frame filter press, which is characterized by: it also includes a self-cleaning filter, a buffer box, a wastewater transfer pump and a rotary atomizer; it is filtered by setting a self-cleaning filter to remove Residual hard particles; the water outlet section filtered by the self-cleaning filter is connected to the buffer tank. The buffer tank is used for dosing liquid alkali and uses sodium hydroxide solution to reduce the generation of sedimentation substrates; one end of the buffer tank is connected to the wastewater transfer pump , in which a stainless steel Y-type filter is installed on the wastewater transfer pump. The high-temperature flue gas generated by the boiler air preheater is transported to the rotary atomizer. The bottom outlet of the rotary atomizer is connected to the flue gas outlet of the boiler air preheater. The boiler There is a cold air inlet at the bottom of the air preheater.

Furthermore, a high-temperature flue gas bypass rotary atomization drying system is used instead of hot secondary air. So far, high-temperature flue gas has been used as a bypass system to facilitate system inspection and maintenance.

Furthermore, the atomization disk is made of Hastelloy C276, and the part in contact with the wastewater is made of tungsten carbide, taking into account corrosion resistance and wear resistance during actual operation, and avoiding the impact of impurities in the wastewater and dried salt on the atomization disk. The nozzle wears too fast; wastewater forms tiny droplets under the high centrifugal force of the rotating atomizer. The atomizer uses a high-speed motor, and the connection method is direct connection. The rotation speed of the rotary atomizer needs to be above 15,000 rpm. When the desulfurization wastewater is sent to the high-speed rotating atomization disk, due to the action of centrifugal force, the waste liquid stretches into a film or It is drawn into filaments (depending on the rotation speed and the amount of slurry), and is broken and dispersed into droplets at the edge of the atomizer disk. It ensures the best atomization effect of the slurry and reduces the droplet size.

When the hot flue gas enters the drying tower through dispersion, the fine droplets atomized by the rotating atomizer come into contact with it. During the gas-liquid contact process, the water is quickly evaporated. By controlling the gas distribution, liquid flow rate, and droplet diameter Wait, before the atomized droplets reach the drying tower wall, the droplets have been dried, and the salts in the wastewater finally form powdery products. Most of the dry products fall into the bottom of the drying tower and are collected and transported, while a small part of the dry products enter the dust collector for processing along with the flue gas.

When using the rotary atomizing nozzle process in the practical application of bypass flue evaporation projects, the bypass flue evaporation usually adopts the "short and fat" high-temperature bypass flue evaporation atomization and evaporation method, and conventionally adopts a single machine and single tower design. A unit is equipped with a squat type bypass flue evaporation crystallizer. The size of a single evaporation crystallization tower is large. It needs to be moved to the open space next to the tail flue to set up a separate foundation and corresponding steel frame, which requires a certain amount of floor space.

Furthermore, the high-temperature flue gas bypass rotary atomization drying system is equipped with a flushing system to complete pre-start flushing and complete pre-stop flushing.

Further, flushing is performed for about 2-10 minutes every 4-8 hours during operation, which is determined based on debugging.

Furthermore, the high-temperature flue gas bypass rotary atomization drying system is equipped with a compressed air purge system to reduce the risk of blockage.

Furthermore, the high-temperature flue gas bypass rotary atomization drying system is equipped with an oil tank and an oil filtering device.

Furthermore, the high-temperature flue gas bypass rotary atomization drying system is equipped with cooling water, and pure water (that is, demineralized water) is used as the cooling water.

Further, the rotation speed of the high-speed rotating atomizer is above 15,000 rpm.

Further, the inlet wastewater flow rate of the atomizer is 1.4m/s≤V≤2.5m/s.

The specific improvement process of the present invention is as follows:

1. Adjust the desulfurization wastewater cyclone to reduce the entry of solid particles into the existing triple box system. The solid particles in the desulfurization system will be taken away by the gypsum after accumulation;

2. Eliminate the addition of lime slurry and do not add lime slurry, which greatly reduces the entry of solid impurities and prevents the precipitation of salt substances, especially magnesium hydroxide and other substances, caused by the slurry changing from acidic to alkaline;

3. Cancel organic sulfur dosing. Organic sulfur dosing is a heavy metal removal agent added to prevent the heavy metals from being completely removed after adding lime slurry. After zero discharge, there is no wastewater discharge and no need to add;

4. According to the water quality, adjust the dosage of flocculant and coagulant aid to reduce the turbidity of the effluent.

5. In order to ensure the stable operation of the sludge system, the filter cloth of the frame filter press is forced to be replaced every 3 months, which has improved the filtration effect;

6. In order to ensure the turbidity of the effluent, a self-cleaning filter is set up to remove residual hard particles; a liquid alkali dosing is set up, and sodium hydroxide solution is used to reduce the generation of sedimentation substrates; a 2205 is set on the wastewater transfer pump. Stainless steel Y-type filter protects subsequent equipment and is easy to clean.

Beneficial effects of the present invention: According to the current situation of coal-fired power plants, the existing systems of the power plants should be utilized as much as possible to carry out system coupling, avoid duplication of investment, take stable operation as the first priority, and achieve zero discharge of desulfurization wastewater from coal-fired power plants according to local conditions.

Description of the drawings

Figure 1. Flow chart of the present invention;

Detailed ways

The present invention will be further clarified below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. It should be noted that the words "front", "back", "left", "right", "upper" and "lower" used in the following description refer to the directions in the drawings, and the words "inside" and "outside" ” refers to the direction toward or away from the geometric center of a specific part, respectively.

Comparison of three comprehensive treatment processes for desulfurization wastewater

Note: The standard coal price is 1,000 yuan/ton and the electricity price is 0.4 yuan/kW.

From the comparative analysis in the above table, it can be seen that these three processes can all meet the goal of achieving zero discharge of desulfurization wastewater.

From the perspective of one-time investment, it can be seen that this scheme has the lowest investment and scheme one has the highest investment; from the analysis of operating costs, it can be seen that this scheme has the highest high-temperature flue gas spray drying and scheme two has the lowest low-temperature flash evaporation; from the perspective of operation and maintenance, this scheme has the simplest system; from the perspective of solid-state The analysis of the impact of salt entering fly ash shows that both the solid salt in Plan 2 and this plan enter into fly ash, which may have an impact on the utilization and sales of fly ash in power plants, while the solid salt in Plan 1 can be sold separately and does not affect existing Fly ash is utilized and sold, but its sales are difficult.

Considering that the load rate of the power plant is not high and the average discharge of desulfurization wastewater is 5m ³ /h, this option will cost 150w more than the two-year operating cost of the option. Without considering financial costs, compared with this option, if option 2 is adopted, it will take 10 years to complete the operation. Recovery of excess investment, comprehensive consideration, so this solution is very suitable for existing power plants, especially power plants of 330MW and below, or those with a short construction period and rapid impact on local environmental protection policies.

Specific construction parameters:

Under full load, each furnace extracts about 44000Nm ³ /h flue gas from the denitrification outlet air preheater inlet. The drying tower is equipped with an inlet baffle to adjust the flue gas volume. The flue gas enters the tower in a uniform and swirling flow through the flue gas distributor at the top of the tower. (According to the flow field conditions in the tower, the flue gas flow field can be flexibly adjusted to fill the entire drying tower, and the contact time between flue gas and liquid droplets can be increased, etc.). After the desulfurization wastewater is conditioned and clarified by the triple box, it enters the wastewater tank buffer and is sent to the high-speed rotating atomization disk in the tower through the lift pump. Due to the action of centrifugal force, the waste liquid stretches into a film or is pulled into filaments (depending on rotation speed and slurry volume), break and disperse into droplets at the edge of the atomization disk, and fully mix with the hot flue gas of the boiler. Desulfurization wastewater containing soluble and suspended solid particles is evaporated under high-temperature flue gas, and the evaporation tower outlet temperature is 150 to 160°C. Part of the evaporated solid entrainment enters the main flue in front of the electrostatic precipitator along with the flue gas, is captured by the electrostatic precipitator, and is mixed with the fly ash of the whole plant. Part of it flows into the bottom of the drying tower and is sent to the first electric field of the electrostatic precipitator through the silo pump. in the ash pipe, or mixed with the slag system.

Main equipment list:

The technical means disclosed in the solution of the present invention are not limited to the technical means disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features.

Claims (10)

1. A zero-discharge evaporation and drying treatment process for desulfurization wastewater from coal-fired power plants, including a desulfurization wastewater cyclone, a neutralization tank, a sedimentation tank, a slurry clarifier and a water outlet tank connected in sequence. The discharge end of the water outlet tank is connected to the water outlet. The transfer pump is connected; the sludge in the slurry clarifier is processed and discharged through a plate and frame filter press, which is characterized by: it also includes a self-cleaning filter, a buffer tank, a wastewater transfer pump and a rotary atomizer; it is filtered by setting a self-cleaning filter , remove residual hard particles; the water outlet section filtered by the self-cleaning filter is connected to the buffer box. The buffer box is used for liquid alkali dosing, using sodium hydroxide solution to reduce the generation of suspended matter; one end of the buffer box is connected to the wastewater transfer pump The wastewater transfer pump is equipped with a stainless steel Y-type filter. The high-temperature flue gas generated by the boiler air preheater is transported to the rotary atomizer. The bottom outlet of the rotary atomizer is connected to the flue gas outlet of the boiler air preheater. There is a cold air inlet at the bottom of the boiler air preheater. 2. A zero-discharge evaporation and drying treatment process for desulfurization wastewater from coal-fired power plants according to claim 1, characterized in that: the existing triple box treatment equipment is used to change its operation mode and adjust the desulfurization for the purpose of removing suspended solids. The wastewater cyclone reduces the entry of solid particles; cancels the dosing of lime slurry to reduce the entry of impurities and the precipitation of salts; cancels the dosing of organic sulfur; adjusts the dosage of flocculant and coagulant aids to reduce the turbidity of the effluent; It is mandatory to replace the filter cloth of the frame filter press every three months; set up a self-cleaning filter to remove residual hard particles. 3. A zero-discharge evaporation and drying treatment process for coal-fired power plant desulfurization wastewater according to claim 1, characterized in that: the atomization disk is made of Hastelloy C276, and the part in contact with the wastewater is made of tungsten carbide, taking into account actual operation Corrosion resistance and wear resistance during the process to prevent impurities in waste water and dried salt from wearing out the atomizer plate nozzle too quickly. 4. A zero-discharge evaporation and drying treatment process for coal-fired power plant desulfurization wastewater according to claim 1, characterized in that: the high-temperature flue gas bypass rotary atomization drying system is equipped with a flushing system to complete pre-start flushing and complete pre-stop flushing . 5. A zero-discharge evaporation and drying treatment process for desulfurization wastewater from coal-fired power plants according to claim 4, characterized in that: flushing is performed for about 2-10 minutes every 4-8 hours of operation, which is determined based on debugging. 6. A zero-discharge evaporation and drying treatment process for desulfurization wastewater from coal-fired power plants according to claim 1, characterized in that: the high-temperature flue gas bypass rotary atomization drying system is equipped with a compressed air purge system. 7. A zero-discharge evaporation and drying treatment process for coal-fired power plant desulfurization wastewater according to claim 1, characterized in that: the high-temperature flue gas bypass rotary atomization drying system is equipped with an oil tank and an oil filtering device. 8. A zero-discharge evaporation and drying treatment process for coal-fired power plant desulfurization wastewater according to claim 1, characterized in that: the high-temperature flue gas bypass rotary atomization drying system is provided with cooling water, and pure water (i.e., demineralized water) is used as the Cooling water. 9. A zero-discharge evaporation-drying treatment process for coal-fired power plant desulfurization wastewater according to claim 1, characterized in that: the rotation speed of the high-speed rotating atomizer is above 15,000 rpm. 10. A zero-discharge evaporation-drying treatment process for desulfurization wastewater from coal-fired power plants according to claim 1, characterized in that: the inlet wastewater flow rate of the atomizer is 1.4 m/s≤V≤2.5m/s.