A thermal power plant flue gas SO 3 System and method for coordinating treatment of desulfurization wastewater

Abstract

The present invention provides a system and method for the coordinated treatment of flue gas SO3 and desulfurization wastewater in a thermal power plant. The coordinated treatment system includes: a desulfurization wastewater magnesium extraction module, which prepares magnesium hydroxide powder by adding an alkaline solution to the desulfurization wastewater, and collects the desulfurization wastewater after demagnesization; an in-furnace SO3 removal module, which removes SO3 by adding magnesium hydroxide powder prepared by the desulfurization wastewater magnesium extraction module to the SCR reactor and / or air preheater; a bypass flue gas desulfurization wastewater spray drying module, which extracts high-temperature flue gas from the outlet of the SCR reactor, dries the desulfurization wastewater after demagnesization, and discharges the treated smoke to a dust collector. The system can simultaneously perform the coordinated treatment of flue gas SO3 and desulfurization wastewater, and has the characteristics of low initial investment, low comprehensive operating cost, simple process, and high production flexibility.

Description

[Technical field]

[0001] The present invention relates to the technical field of coal-fired boiler wastewater and flue gas treatment, in particular to a thermal power plant flue gas SO 3 A system and method for coordinated treatment of desulfurization wastewater. [Background technology]

[0002] With the increasing efforts in environmental protection, SO in flue gas from thermal power plants has 3 Gas treatment and desulfurization wastewater treatment are increasingly valued. However, because their physical properties and production processes are completely different, their technical routes for treatment are different, and their treatment is isolated and separated.

[0003] First, let's look at the SO in the flue gas. 3 Gas treatment. Although SO 3 The content of the gas is very small, accounting for only 1-5% of the total sulfur, but the harm is not small. From a macroscopic perspective, it is the main cause of acid rain and an important component of atmospheric secondary aerosols (secondary aerosols contribute 30-77% to PM2.5 in China's atmospheric environment). From a microscopic perspective, it is one of the main causes of colored smoke plumes in power plants, which will lead to an increase in the acid dew point of flue gas, corrosion, dust accumulation, and blockage of low-temperature equipment such as APH (air preheater), reduce boiler efficiency, and even endanger the safe operation of the unit.

[0004] SO in flue gas 3 From SO 2 Oxidation of SO 2 / SO 3 There are two sources of conversion: one is high-temperature conversion (in the furnace), about 0.5-2.5%, and the other is catalytic conversion (in SCR), about 0.5-1.5%. The specific total amount varies depending on the type of coal burned. But overall, my country has a small reserve of low-sulfur coal, and there are many thermal power plants burning high-sulfur coal. At this stage, SO 3 The content is relatively high, generally 30-80 mg / m 3 .

[0005] At present, the removal of flue gas SO 3 There are three main methods: furnace method, out-of-furnace method and tail removal method.

[0006] The furnace method usually involves spraying alkaline absorbents from the top of the furnace. Commonly used alkaline absorbents include alkali metals such as sodium and potassium, and alkaline earth metal absorbents such as calcium and magnesium. This type of furnace method has three main disadvantages. First, the reagent consumption is large, because SO is removed under high temperature. 3 At the same time, some SO 2 The large amount of reagent consumption will also reduce the quality of fly ash; secondly, alkaline absorbent absorbs and removes SO 3The sulfate generated later often reduces the ash melting point, causing coking in the furnace; thirdly, it can only remove SO in the furnace. 3 , SO generated in the SCR reactor 3 Without removal capability, overall efficiency cannot be guaranteed.

[0007] The tail method mainly focuses on the dust collector and desulfurization island, such as adding a low-temperature electrostatic precipitator, modifying the wet desulfurization system, adding a wet electrostatic precipitator, and changing the electrostatic precipitator to an electric bag precipitator or a bag precipitator. In general, this model has a positive impact on SO 3 The removal effect is significant, but the investment is huge, the operating costs are high, and it has no effect on improving the dust accumulation and clogging problems of ammonium bisulfate (ABS) of APH.

[0008] The off-furnace method is a recently developed method. It mainly adds different alkaline absorbents at the inlet of SCR reactor and APH (air preheater) simultaneously or separately to remove sulfur (SO 3 ). At present, the main absorbents are magnesium hydroxide, calcium hydroxide, sodium bicarbonate, sodium carbonate, natural alkali, etc. The removal rates are magnesium hydroxide (75.3%), sodium bicarbonate (69.7%), calcium hydroxide (55.1%) and sodium carbonate (52.8%), respectively. The effect of natural alkali is close to that of sodium carbonate. These alkaline absorbents also have some defects. For example, magnesium hydroxide is expensive, sodium bicarbonate is prone to coking and causes "poisoning" of SCR catalysts, calcium hydroxide will change the dust resistivity and affect the dust removal efficiency of the tail electrostatic precipitator, and this type of absorbent can only be in the form of dry powder, which needs to be ground and refined, increasing the cost; and sodium carbonate is not suitable for APH (air preheater) desulfurization because it will produce some sodium bisulfate. Sodium bisulfate, like ammonium bisulfate (ABS), has high viscosity and is easy to cause dust accumulation and blockage in APH.

[0009] Next, let’s look at the treatment of desulfurization wastewater.

[0010] The wastewater generated in the boiler flue gas wet desulfurization (limestone / gypsum method) process mainly comes from the desulfurization absorption tower discharge water, gypsum dehydration process cleaning water and cleaning system.

[0011] Its main features are as follows:

[0012] (1) The wastewater is slightly acidic, with a pH value between 5 and 7. The suspended solids are very high (mainly gypsum particles), up to tens of thousands of mg / L;

[0013] (2) The total dissolved solids (TDS) content is high (about 20,000-90,000 mg / L), the calcium ion, magnesium ion, sodium ion, chloride ion, sulfate ion, sulfite ion, etc. are high, and the heavy metal, fluoride, ammonia nitrogen, COD and other indicators exceed the standard, making it difficult to recover the salt in the wastewater. Affected by solubility, the calcium ion content is below 1000 mg / L, while the magnesium ion content is relatively high, with the lowest being above 4000 mg / L;

[0014] (3) The emission scale is small. According to the Technical Manual of Wet Flue Gas Desulfurization in Thermal Power Plants, when the chlorine content of coal is 0.05%, the Cl content in the slurry should be maintained at - The concentration does not exceed 20000mg / L. Under this condition, the design values ​​of the desulfurization wastewater volume of 300MW, 600MW and 1000MW units are 4m 3 / h、7m 3 / h and 12m 3 According to on-site measurements, the actual emissions of most power plants are about 70% higher on average, that is, 7m 3 / h、12m 3 / h and 20m 3 / h.

[0015] With the improvement of national and local environmental protection standards, the requirements for near-zero discharge of desulfurization wastewater are increasing, and the relevant technologies are developing rapidly. From the perspective of the nature of the treated products, the near-zero discharge technology of desulfurization wastewater can be divided into salt separation process and salt mixing process. Both technical routes can be simplified into three modules: pretreatment → concentration reduction → solidification and crystallization.

[0016] Analyze the salt separation process. The salt separation process is to first temper the wastewater (pH) and fully soften it to remove calcium and magnesium ions that may affect the normal operation of the concentration and reduction module; then enter the concentration and reduction module for further treatment of the wastewater, which can be a membrane concentration or a thermal concentration; finally enter the crystallizer to perform crystallization and salt separation on the treated concentrated tail liquid. The clean water and condensate generated in the whole process are reused, and some concentrated water and mother liquor may need to be discharged or concentrated and dried by thermal methods for mixed salt treatment.

[0017] In general, the salt separation process requires the addition of a large amount of alkaline reagents and produces a large amount of salt-containing sludge. In addition, the process chain of salt separation is very long, and the system is large and complex. More importantly, the added value of the finished inorganic salt is low and it is impossible to form large-scale production. Therefore, the characteristics of large investment and high operation and maintenance costs have greatly limited the application of the salt separation process.

[0018] Accordingly, the mixed salt process is more widely used. The mixed salt process is to extract the high-temperature flue gas from the SCR outlet, use the high-temperature flue gas to dry the wastewater or the concentrated and reduced wastewater, and the formed mixed salt ash directly enters the dust collector with the flue gas and mixes with the fly ash. However, in order to prevent dust accumulation and blockage of APH, the extraction amount of high-temperature flue gas should generally not exceed 3%.

[0019] Taking a 2×350MW thermal power unit as an example, the flue gas volume at the SCR outlet of a single unit under BMCR working conditions is about 1408666kg / h, and the flue gas temperature is 360℃. If 3% of the flue gas volume is extracted, about 42,000 kg / h, it can dry about 2.6m 3 / h wastewater. According to the current amount of wastewater generated, 3% of the flue gas volume is obviously not enough to directly dry all the wastewater. Therefore, the existing mixed salt industrial route requires the wastewater to be concentrated and reduced first, and then thermally solidified and crystallized. The problems faced in the concentration and reduction process are the same as those in the technical route of the salt separation process. Therefore, the mixed salt process also has the characteristics of large investment and high operation and maintenance costs.

[0020] In summary, at present, flue gas SO 3 The treatment of flue gas SO is isolated and separated from the zero-emission treatment system of desulfurization wastewater, which deviates from the development principle of "comprehensive utilization of energy" advocated by the country. 3 During the treatment process, a large amount of alkaline absorbents are consumed. Although magnesium hydroxide has the best effect, sodium carbonate or calcium hydroxide with obvious side effects are often used as absorbents due to cost reasons. On the other hand, in the wastewater treatment process, a large amount of alkaline agents are used to remove magnesium ions, and the cost remains high. Moreover, a large amount of magnesium ions are discarded, causing secondary pollution.

[0021] The consequence of the isolation and separation of the two is the need to build two sets of governance systems, duplicate construction, increased investment, repeated dosing, serious waste, increased production costs, complex processes, and increased operation and maintenance costs.

[0022] Therefore, it is necessary to study a flue gas SO 3 A system and method for co-processing desulfurization wastewater is provided to address the deficiencies of the prior art to solve or alleviate one or more of the above problems. [Summary of the invention]

[0023] In view of this, the present invention provides a flue gas SO 3 The system and method for coordinating the treatment of desulfurized wastewater can be used in industrial and mining enterprises with coal-fired boilers such as thermal power plants and paper mills, and can simultaneously treat flue gas SO 3 The coordinated treatment with desulfurization wastewater has the characteristics of low initial investment, low comprehensive operating cost, simple process and great production flexibility.

[0024] On the one hand, the present invention provides a system and method for the coordinated treatment of flue gas SO3 and desulfurization wastewater, the coordinated treatment system comprising:

[0025] The desulfurization wastewater magnesium extraction module prepares magnesium hydroxide powder by adding alkaline solution to the desulfurization wastewater, and collects the desulfurization wastewater after magnesium removal;

[0026] SO in furnace 3 Removal module, which removes SO by adding magnesium hydroxide powder prepared by the desulfurization wastewater magnesium extraction module into the SCR reactor and / or APH 3 ;

[0027] The bypass flue gas desulfurization wastewater spray drying module extracts the high-temperature flue gas from the outlet of the SCR reactor, dries the desulfurization wastewater after magnesium removal, and discharges the treated smoke into the dust collector.

[0028] According to the above aspects and any possible implementation, an implementation is further provided, wherein the desulfurization wastewater magnesium extraction module comprises:

[0029] The primary buffer tank is used to settle the desulfurization wastewater discharged from the desulfurization island;

[0030] The first magnesium extraction unit is used to collect the supernatant discharged from the primary buffer tank, and add alkaline solution and flocculant to carry out the first magnesium hydroxide precipitation;

[0031] The second magnesium extraction unit is used to collect the supernatant discharged from the first magnesium extraction unit, and add an alkaline solution and a flocculant to perform a second magnesium hydroxide precipitation;

[0032] The filter pressing and drying unit is used to collect the sediments from the primary buffer tank, the first magnesium extraction unit and the second magnesium extraction unit, and perform filter pressing and drying to prepare magnesium hydroxide powder.

[0033] According to the above aspects and any possible implementation, there is further provided an implementation, wherein the first magnesium extraction unit comprises a first magnesium extraction and dosing device and a first base agent storage device;

[0034] The first base agent storage device is used to store alkaline solution and flocculant;

[0035] The first magnesium extraction and dosing device is used to collect the supernatant discharged from the primary buffer tank, and add the alkaline solution and flocculant in the first alkaline agent storage device to the supernatant discharged from the primary buffer tank.

[0036] According to the above aspects and any possible implementation, there is further provided an implementation, wherein the second magnesium extraction unit comprises a second magnesium extraction and dosing device, a second base agent storage device, a high efficiency filter and a backwashing device;

[0037] The second base agent storage device is used to store alkaline solution and flocculant;

[0038] The second magnesium extraction and dosing device is used to collect the supernatant discharged from the first magnesium extraction unit, and add the alkaline solution and flocculant in the second alkaline agent storage device to the supernatant discharged from the first magnesium extraction and dosing device;

[0039] The high-efficiency filter and the backwashing device are both arranged in the second magnesium extraction and dosing device, and the filtering effect is: SS<200mg / L.

[0040] According to the above aspects and any possible implementation, further provided is an implementation, wherein the SO 3 The removal module includes:

[0041] First SO 3 The removal unit is located at the flue gas inlet of the SCR reactor and performs the first SO removal by adding magnesium hydroxide powder produced by the pressure filter drying unit. 3 Remove;

[0042] Second SO 3 The removal unit is located at the flue gas inlet of APH, and the magnesium hydroxide powder produced by the pressure filter drying unit is added for the second SO 3 Remove;

[0043] The first SO 3 Removal unit and second SO 3 The removal units can work separately or simultaneously.

[0044] According to the above aspects and any possible implementation, an implementation is further provided, wherein the bypass flue gas desulfurization wastewater spray drying module comprises:

[0045] SDE, providing space for bypass flue gas discharged from the SCR reactor to enter;

[0046] The secondary buffer tank is used to collect the supernatant discharged from the second magnesium extraction unit and enter the SDE through spraying for drying.

[0047] According to the above aspects and any possible implementation method, a thermal power plant flue gas SO 3 Co-processing with desulfurization wastewater, the method comprises the following steps:

[0048] S1: The magnesium extraction module of desulfurization wastewater prepares magnesium hydroxide powder. By adding alkaline solution, magnesium ions are replaced with magnesium hydroxide. Magnesium hydroxide is an insoluble solid. After extraction, it is dried using waste heat or residual heat as a raw material for removing SO 3 absorbent;

[0049] S2: The bypass flue gas desulfurization wastewater spray drying module extracts high-temperature flue gas from the SCR outlet, dries the wastewater that has not been concentrated and reduced, and discharges the treated smoke to the dust collector to complete the zero-emission treatment of desulfurization wastewater;

[0050] S3: SO in the furnace 3 The removal module adds the prepared magnesium hydroxide dry powder to remove SO in the SCR reactor and APH respectively. 3 , complete the SO in the flue gas 3 Remove.

[0051] According to the above aspects and any possible implementation, an implementation is further provided, wherein S1 specifically includes:

[0052] S11: The desulfurization wastewater discharged from the desulfurization island is subjected to sedimentation treatment in the primary buffer tank;

[0053] S12: collecting the supernatant discharged from the primary buffer tank in the first magnesium extraction unit, adding an alkaline solution and a flocculant, and performing the first magnesium hydroxide precipitation;

[0054] S13: collecting the supernatant discharged from the first magnesium extraction unit in the second magnesium extraction unit, adding an alkaline solution and a flocculant, and performing a second magnesium hydroxide precipitation;

[0055] S14: collecting and aggregating the sediments from the primary buffer tank, the first magnesium extraction unit and the second magnesium extraction unit, filtering and drying them to prepare magnesium hydroxide powder.

[0056] According to the above aspects and any possible implementation, an implementation is further provided, wherein S3 specifically includes:

[0057] S31: SCR reactor receives SO generated by boiler furnace 3 of smoke;

[0058] S32: First SO 3 The removal unit is located at the flue gas inlet of the SCR reactor, and magnesium hydroxide powder produced by the filter press drying unit is added for the first SO 3 Remove;

[0059] S33: Flue gas discharged from the SCR reactor enters the APH;

[0060] S34: Second SO 3 At the entrance of APH, the magnesium hydroxide powder produced by the filter press drying unit is added to the removal unit for the second SO 3 Removal of SO in flue gas 3 Remove;

[0061] The S22 and S24 can be performed separately or simultaneously.

[0062] According to the above aspects and any possible implementation manner, an implementation manner is further provided, wherein S2 specifically includes:

[0063] S21: bypass flue gas discharged from the SCR reactor enters the SDE;

[0064] S22: collecting the supernatant discharged from the second magnesium extraction unit in the secondary buffer tank and entering the SDE by spraying;

[0065] S23: Drying treatment is then carried out to achieve zero discharge of desulfurization wastewater.

[0066] Compared with the prior art, the present invention can achieve the following technical effects:

[0067] (1) No need to perform precise pretreatment of wastewater, which greatly reduces the difficulty of pretreatment;

[0068] (2) Using magnesium ions in wastewater to remove SO from flue gas 3 , increasing the added value of magnesium ions in wastewater;

[0069] (3) Magnesium hydroxide is the best desulfurization (SO 3 ) absorbent, compared with other absorbents, has the best desulfurization efficiency without side effects.

[0070] Of course, any product implementing the present invention does not necessarily need to achieve all of the above-mentioned technical effects at the same time.

Brief Description of the Drawings

[0071] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0072] Figure 1 It is a structural diagram of a collaborative processing system provided by an embodiment of the present invention.

[0073] Among them, in the figure:

[0074] 1- primary buffer tank for desulfurization wastewater; 2- magnesium dosing box for desulfurization wastewater; 3- secondary sedimentation tank for magnesium extraction from desulfurization wastewater; 4- sludge filter press; 5- fluidized bed dryer; 6- magnesium hydroxide powder bin; 7- SCR (denitrification reactor); 8- APH (air preheater); 9- SDE (spray drying tower); 10- secondary buffer tank for desulfurization wastewater; 11- desulfurization wastewater inlet pipe; 12- desulfurization wastewater drainage pipe 13- desulfurization wastewater sludge discharge pipe; 21- alkali agent storage tank 22- magnesium dosing box drainage pipe; 23- magnesium hydroxide solid phase Main discharge pipe; 31-demagnesiumization wastewater drainage pump; 32-demagnesiumization wastewater drainage pipe; 33-magnesium hydroxide solid phase auxiliary discharge pipe; 34-sludge pump 41-sludge discharge pipe; 42-demudification wastewater drainage pump; 43-demudification wastewater drainage pipe; 51-dry powder discharge pipe; 61-dry powder main regulating valve; 62-dust-containing hot air pipe; 63-dry powder blower; 64-dry powder conveying pipe; 65-SCR bin nozzle; 66-APH bin regulating valve; 67-APH bin nozzle; 71-SCR outlet flue gas main flue; 72-bypass flue discharge pipe. [Specific implementation method]

[0075] In order to better understand the technical solution of the present invention, the embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0076] It should be clear that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0077] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "said" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0078] A thermal power plant flue gas SO 3 A coordinated treatment system with desulfurization wastewater, the coordinated treatment system comprising:

[0079] The desulfurization wastewater magnesium extraction module prepares magnesium hydroxide powder by adding alkaline solution to the desulfurization wastewater, and collects the desulfurization wastewater at the same time;

[0080] SO in furnace 3 Removal module, by adding magnesium hydroxide powder prepared by desulfurization wastewater magnesium extraction module into SCR reactor and / or air preheater to remove SO 3 ;

[0081] The bypass flue gas desulfurization wastewater spray drying module extracts the high-temperature flue gas from the outlet of the SCR reactor, dries the desulfurization wastewater after magnesium removal, and discharges the treated flue dust to the dust collector. In order to prevent dust accumulation and blockage of the APH (air preheater), the extraction amount of the high-temperature flue gas at the outlet of the SCR is generally not more than 3% in the existing technology, and the SO 3 After the removal module desulfurizes the high-temperature flue gas, the extraction volume can reach up to 8% without affecting the boiler. At the same time, the APH (air preheater) will not be ash-accumulated or blocked.

[0082] The desulfurization wastewater magnesium extraction module comprises:

[0083] The primary buffer tank is used to settle the desulfurization wastewater discharged from the desulfurization island;

[0084] The first magnesium extraction unit is used to collect the supernatant discharged from the primary buffer tank, and add an alkaline solution and a flocculant to perform the first magnesium hydroxide precipitation, wherein the alkaline solution is a sodium hydroxide solution or other waste alkaline solution;

[0085] The second magnesium extraction unit is used to collect the supernatant discharged from the first magnesium extraction unit, and add an alkaline solution and a flocculant to perform a second magnesium hydroxide precipitation;

[0086] The filter pressing and drying unit is used to collect the sediments from the primary buffer tank, the first magnesium extraction unit and the second magnesium extraction unit, and perform filter pressing and drying to prepare magnesium hydroxide powder.

[0087] The first magnesium extraction unit includes a first magnesium extraction and dosing device and a first base agent storage device;

[0088] The first base agent storage device is used to store alkaline solution and flocculant;

[0089] The first magnesium extraction and dosing device is used to collect the supernatant discharged from the primary buffer tank, and add the alkaline solution and flocculant in the first alkaline agent storage device to the supernatant discharged from the primary buffer tank.

[0090] The second magnesium extraction unit includes a second magnesium extraction and dosing device, a second base agent storage device, a high efficiency filter and a backwashing device;

[0091] The second base agent storage device is used to store alkaline solution and flocculant;

[0092] The second magnesium extraction and dosing device is used to collect the supernatant discharged from the first magnesium extraction unit, and add the alkaline solution and flocculant in the second alkaline agent storage device to the supernatant discharged from the first magnesium extraction and dosing device;

[0093] The high-efficiency filter and the backwashing device are both arranged in the second magnesium extraction and dosing device, and the filtering effect is: SS<200mg / L.

[0094] The SO 3 The removal module includes:

[0095] First SO 3 The removal unit is located at the flue gas inlet of the SCR reactor and performs the first SO removal by adding magnesium hydroxide powder produced by the pressure filter drying unit. 3 Remove;

[0096] Second SO 3 The removal unit is located at the flue gas inlet of APH, and the magnesium hydroxide powder produced by the pressure filter drying unit is added for the second SO 3 The two desulfurization processes can be carried out separately or simultaneously, that is, the second desulfurization is carried out at the same time as the first desulfurization, and the system can maintain stability at the same time, or the first desulfurization is carried out first, and after the first desulfurization is completed, the flue gas enters the APH for the second desulfurization.

[0097] The bypass flue gas desulfurization wastewater spray drying module includes:

[0098] SDE, providing space for bypass flue gas discharged from the SCR reactor to enter;

[0099] The secondary buffer tank is used to collect the supernatant discharged from the second magnesium extraction unit and enter the SDE through spraying for drying.

[0100] In addition, the SCR reactor and APH in this application are common equipment in existing coal-fired boilers, among which:

[0101] The SCR reactor (denitrification reactor) is used to receive the flue gas SO generated by the boiler furnace. 3 ;

[0102] APH (air preheater, full name air preheater) is used to receive high-temperature flue gas from the SCR reactor.

[0103] A thermal power plant flue gas SO 3 Co-processing with desulfurization wastewater, including the above-mentioned co-processing method, the method comprises the following steps:

[0104] S1: Magnesium extraction module for desulfurization wastewater to prepare magnesium hydroxide powder. By adding alkaline solution, the alkaline solution is sodium hydroxide solution or other alkaline solution, the magnesium ions are replaced with magnesium hydroxide, which is an insoluble solid. After extraction, it is dried using waste heat or residual heat as a means of removing SO 3 absorbent;

[0105] S2: The bypass flue gas desulfurization wastewater spray drying module extracts high-temperature flue gas from the SCR outlet, dries the wastewater that has not been concentrated and reduced, and discharges the treated smoke to the dust collector to achieve zero discharge of desulfurization wastewater;

[0106] S3: SO in the furnace 3 The removal module removes SO by adding prepared magnesium hydroxide dry powder. 3 , first remove the SO generated in the furnace 3 , and then remove the SO generated by SCR 3 , complete the SO in high temperature flue gas 3 of removal.

[0107] The S1 specifically includes:

[0108] S11: The desulfurization wastewater discharged from the desulfurization island is subjected to sedimentation treatment in the primary buffer tank;

[0109] S12: collecting the supernatant discharged from the primary buffer tank in the first magnesium extraction unit, adding an alkaline solution and a flocculant, and performing the first magnesium hydroxide precipitation;

[0110] S13: collecting the supernatant discharged from the first magnesium extraction unit in the second magnesium extraction unit, adding an alkaline solution and a flocculant, and performing a second magnesium hydroxide precipitation;

[0111] S14: collecting and aggregating the sediments from the primary buffer tank, the first magnesium extraction unit and the second magnesium extraction unit, filtering and drying them to prepare magnesium hydroxide powder.

[0112] The S3 specifically includes:

[0113] S31: SCR reactor receives SO 3 of smoke;

[0114] S32: First SO 3 The removal unit is located at the flue gas inlet of the SCR reactor, and magnesium hydroxide powder produced by the filter press drying unit is added for the first SO 3 Remove;

[0115] S33: Flue gas discharged from the SCR reactor enters the APH;

[0116] S34: Second SO 3 At the entrance of APH, the removal unit adds magnesium hydroxide powder produced by the filter press drying unit for the second SO 3 Removal of SO in flue gas 3 Remove.

[0117] The S2 specifically includes:

[0118] S21: bypass flue gas discharged from the SCR reactor enters the SDE;

[0119] S22: collecting the supernatant discharged from the second magnesium extraction unit in the secondary buffer tank and entering the SDE by spraying;

[0120] S23: Drying treatment is then carried out to achieve zero discharge of desulfurization wastewater.

[0121] like Figure 1 As shown, the present invention provides a system comprising a desulfurization wastewater magnesium extraction module, a bypass flue gas desulfurization wastewater spray drying module, a furnace SO 3 The removal module consists of:

[0122] (1) The magnesium extraction module is used to prepare magnesium hydroxide powder. By adding high-concentration sodium hydroxide solution or other alkaline solution, magnesium ions are replaced with magnesium hydroxide. Magnesium hydroxide is an insoluble solid. After extraction, it is dried using waste heat or residual heat as a raw material for removing SO 3 absorbent.

[0123] (2) The bypass flue gas desulfurization wastewater spray drying module extracts high-temperature flue gas from the SCR outlet, dries the wastewater that has not been concentrated and reduced, and discharges the treated smoke to the dust collector. The module includes a wastewater buffer tank, a spray pump and pipeline, a spray drying tower (including tower body, flue gas distributor, nozzle), a flue gas damper door and regulating valve, and a bypass flue, etc.;

[0124] (3) SO in the furnace 3 The removal module removes SO by adding a dosage (magnesium hydroxide powder) 3 Including absorbent silo, spray gun, booster fan, pipeline, the module is divided into two independent subsystems. Subsystem ① is located at the entrance of SCR, mainly to remove SO generated in the furnace. 3 Subsystem ② is at the APH inlet, mainly to remove SO generated by SCR 3 The two systems can be flexibly combined according to the situation and can be merged or installed separately.

[0125] After the desulfurization wastewater is discharged from the desulfurization island, it is subjected to gravity sedimentation treatment in the primary buffer tank. The precipitate is sludge mainly composed of calcium sulfate, which is discharged to a special filter press through a sludge pipeline. The supernatant enters the magnesium extraction and dosing box. The magnesium removal agent is an alkali solution such as sodium hydroxide. At the same time, a flocculant is added to accelerate the sedimentation of magnesium hydroxide. Most of the magnesium hydroxide settles in this box and is discharged to a special filter press through a sludge pipeline. The supernatant enters the next sedimentation tank. The tank is equipped with a high-efficiency filter to collect the remaining magnesium hydroxide and discharge it to a special filter press through a sludge pipeline. The supernatant flows into the secondary buffer tank.

[0126] The magnesium hydroxide filter press can be a centrifugal or plate and frame type, etc. The filter press includes magnesium hydroxide particles and wastewater sludge. The moisture content of the filter cake is controlled below 70% and sent to the sludge dryer. The dryer can be a belt type, fluidized bed type dryer, etc., preferably a fluidized bed dryer. After the filter cake is further dehydrated to a dry powder below 20% in the dryer, it enters the silo. The drying heat source can be a heat source not lower than 75°C such as hot water from a low-temperature economizer or boiler steam, preferably a waste heat source such as a low-temperature economizer. The engineering silo can be used only as a backup, and the powder can be directly pressurized by the blower and sent to the pre-SCR desulfurization (SO 3 ) system and APH pre-desulfurization (SO 3 ) system for desulfurization. The two systems can be combined into one or installed separately. The desulfurization system consists of a blower, an air duct, a regulating valve and an injector. The alkali (magnesium) sulfur ratio is a key control point and is not higher than 2.5. The desulfurization efficiency is not less than 80%. The amount of alkali (magnesium) powder added is mainly determined by the pressure difference of APH and the inlet and outlet temperature difference. The flow-through material is a normal temperature wear-resistant material, preferably a ceramic material.

[0127] The wastewater from the secondary buffer tank is pumped into the bypass flue gas spray drying tower (SDE) through a spray pump. The bypass flue gas is taken from the SCR outlet. The wastewater is quickly dried by the high-temperature flue gas in the tower, and the generated crystal salt is mixed evenly with the fly ash before entering the dust collector inlet with the bypass flue gas, achieving zero discharge treatment of wastewater. The amount of flue gas extracted is determined by the wastewater treatment amount and the flue gas inlet temperature. Up to 8% of the flue gas can be extracted without affecting the APH and other tail flues, which can meet the general needs of most projects.

[0128] The specific workflow is as follows:

[0129] The wastewater discharged from the desulfurization island FGD enters the primary buffer tank 1 of the desulfurization wastewater along the wastewater inlet pipe 11, which also serves as a regulating tank. The total suspended solids TSS of the wastewater is relatively high. After adding conventional agents such as flocculants, most of the TSS settles. The supernatant flows into the magnesium dosing box 2 along the drainage pipe 12, and the settled sludge is discharged to the filter press 4 along the sludge discharge pipe 13. The flow material is 316L, and the buffer tank is lined with carbon steel rubber or glass flakes.

[0130] The supernatant in the magnesium extraction dosing tank 2 reacts with the alkali solution added from the alkali agent storage tank 21 to generate magnesium hydroxide. The alkali solution is a solution of sodium hydroxide, calcium hydroxide, etc., preferably sodium hydroxide. The pH value of the dosing tank 2 is not less than 10. The agent storage tank also includes conventional agents such as flocculants. The supernatant is discharged to the secondary sedimentation tank for magnesium removal through the drain pipe 22. Because the supernatant still contains a large amount of magnesium hydroxide particles, in order to recover Mg as much as possible, 2+ , secondary sedimentation is required. The sediment sludge mainly composed of magnesium hydroxide particles is discharged to the filter press 4 through the magnesium hydroxide solid phase main discharge pipe 23. The flow material is carbon steel lined with rubber or plastic.

[0131] The secondary sedimentation tank 3 for magnesium extraction contains a high-efficiency filter and is equipped with a backwashing device. The filtering effect is adjustable, and SS < 200 mg / L is recommended to reduce the frequency of backwashing. The filtered clear liquid is pressurized by the magnesium removal wastewater discharge pump 31 and pumped into the secondary buffer tank 10 along the magnesium removal wastewater discharge pipe 32. The sediment magnesium hydroxide particles are discharged to the filter press 4 along the magnesium hydroxide solid phase auxiliary discharge pipe 33. The sludge pump 34 is a shared equipment. The pump valve flow material is 316L, and the rest is carbon steel lined with rubber or plastic.

[0132] The sludge and magnesium hydroxide particles in the primary buffer tank 1, magnesium dosing box 2, and magnesium secondary sedimentation tank 3 are collected in the filter press 4. The filter press can be centrifugal or plate-frame type, preferably plate-frame type. The moisture content of the filter cake is not higher than 70%, and it is sent to the dryer 5 through the sludge discharge pipe 41 for thermal drying. The filtrate is pressurized by the drainage pump 42 and discharged back to the primary buffer tank 1 along the drainage pipe 43. The pump valve flow material is 316L, and the rest is carbon steel lined with rubber or plastic.

[0133] The dryer 5 is a thermal dryer, which can be a fluidized bed, belt type or other type, preferably a fluidized bed dryer. The dried magnesium hydroxide particles are in powder form with a moisture content of less than 20%. The hot air and dry powder are discharged to the magnesium hydroxide powder bin 6 along the discharge pipe 51, and there is no need to install a dust collector. The heat source is hot water, steam or hot air at a temperature not lower than 75°C, preferably hot water from a low-temperature economizer. If there is no low-temperature economizer, it is preferred to configure a separate air-water heat exchanger after the APH.

[0134] The magnesium hydroxide powder bin 6 is provided with a cyclone separator and a storage tank. The storage tank is provided with a thermostat to prevent the dry powder from absorbing water and hardening. The heat source comes from the heat source outlet of the dryer 5. The powder bin storage tank is provided with a main regulating valve 61 to control the amount of dry powder added. The hot air from the dryer 5 is discharged from the cyclone and enters the dry powder conveying pipe 64 along the hot air pipe 62, and then is conveyed to the desulfurization (SO 3 ) system, the air supply pressure is provided by the air supply fan 63. To ensure the desulfurization rate, the SCR front dry powder injector and the APH front dry powder injector are respectively set. The two injectors can be installed together or independently, preferably independently. Desulfurization (SO 3 ) The system consists of a blower 63, a pipeline 64, regulating valves 65 and 67, and dry powder injectors 66 and 68, wherein injector 66 is installed at the inlet of SCR and injector 68 is installed at the inlet of APH. The total desulfurization efficiency is not less than 80%, and the alkali (magnesium) sulfur ratio is the key control point, which is not higher than 2.5. The amount of alkali (magnesium) powder added is mainly determined by the pressure difference and the inlet and outlet temperature difference of APH. The flow-through material is a normal temperature wear-resistant material, and the injector needs to withstand a high temperature of 500°C, preferably a ceramic material.

[0135] SO 3The flue gas with about 50% reduced content is divided into two flue gases from the outlet of the SCR reactor 7, of which the main flue gas flows along the main flue 71 to the APH (air preheater) 8. The flue gas for wastewater drying enters the SDE (spray drying tower) 9 along the bypass flue 72, and the flue gas volume is controlled by the bypass flue gas regulating valve 73. The amount of extracted flue gas is determined by the wastewater treatment volume and the flue gas inlet temperature. A maximum of 8% of the flue gas can be extracted without affecting the APH and other tail flues.

[0136] Although the flue gas volume entering APH (air preheater) 8 is reduced, due to SO 3 The removal system works, and its acid dew point temperature is reduced to below 100°C, the ash accumulation is mainly ordinary ash accumulation, the ABS ash accumulation strength is suppressed, and the heat exchange efficiency is maintained. Therefore, the smoke temperature of the smoke exhaust main pipeline 81 can be reduced to 110°C at the lowest. The heat storage element of APH (air preheater) 8 can be DU plate or NF plate, preferably DU plate.

[0137] The wastewater in the secondary buffer tank 10 of desulfurization wastewater comes from the supernatant of the magnesium extraction sedimentation tank 3, and its pH is about 10. Therefore, the secondary buffer tank also has a conditioning function, and the pH value can be adjusted to neutral by adding acid. The conditioned wastewater is pressurized by the spray water pump 101 and pumped into the SDE (spray drying tower) 9 along the spray pipe 102 for drying. The flow material is 316L or higher.

[0138] The bypass flue gas taken from the SCR enters the SDE (spray drying tower) 9 to dry the desulfurization wastewater from the secondary buffer tank 10. The SDE is composed of a tower body, a nozzle and a flue gas distributor. The nozzle can be a pressure type, an airflow type or a centrifugal nozzle, preferably a centrifugal nozzle, preferably 2205 lined with silicon carbide or other ceramics and other wear-resistant and corrosion-resistant materials. The tower body and the flue gas distributor are both ordinary carbon steel. The flue gas is dispersed through the flue gas distributor in the tower body and fully mixed with the wastewater atomized by the nozzle, and the wastewater is completely evaporated and dried in the tower body. The temperature of the dried flue gas is reduced to above 120°C, and it is discharged to the flue gas exhaust main pipeline 81 through the flue gas exhaust pipe 91, mixed with the flue gas at the APH outlet, and finally discharged to the dust collector to achieve zero wastewater discharge.

[0139] The key point of the present invention is to use alkali solution to recover magnesium ions in wastewater and produce magnesium hydroxide without secondary pollution. Magnesium hydroxide is a flue gas desulfurization (SO 3 ) is one of the best absorbents. It increases the added value of magnesium salts; at the same time, it uses flue gas waste heat to produce magnesium hydroxide dry powder, and the mixed sludge is dried together, so there is no secondary pollution in the production process; in addition, the magnesium ions in the wastewater are used to remove SO in the furnace flue gas. 3 , which improves the denitrification efficiency of SCR and ensures that SCR can still work normally at low load, extending the working life of the catalyst; finally, the magnesium ions in the wastewater are used to remove SO in the SCR flue gas. 3, can reduce the flue gas acid dew point temperature, inhibit ABS ash accumulation intensity, and increase the heat exchange efficiency by about 5-10% under the condition that the heat exchange area of ​​APH (air preheater) remains at the conventional design. The additional heat is used for zero discharge treatment of desulfurization wastewater. Therefore, there is no need to concentrate and reduce the wastewater, which greatly reduces the investment and operation and maintenance costs of zero discharge of wastewater.

[0140] The above is a detailed introduction to a flue gas SO3 and desulfurization wastewater coordinated treatment system and method provided by the embodiment of the present application. The description of the above embodiment is only used to help understand the method and its core idea of ​​the present application; at the same time, for those skilled in the art, according to the idea of ​​the present application, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

[0141] For example, certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that hardware manufacturers may use different nouns to refer to the same component. This specification and claims do not use differences in names as a way to distinguish components, but use differences in the functions of components as the criteria for distinction. As mentioned throughout the specification and claims, "including" and "comprising" are open-ended terms, so they should be interpreted as "including / including but not limited to". "Approximately" means that within an acceptable error range, those skilled in the art can solve the technical problem within a certain error range and basically achieve the technical effect. The subsequent description of the specification is a preferred embodiment of the present application, but the description is for the purpose of illustrating the general principles of the present application, and is not used to limit the scope of the present application. The scope of protection of the present application shall be determined by the definition of the attached claims.

[0142] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a product or system including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such a product or system. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the product or system including the elements.

[0143] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0144] The above description shows and describes several preferred embodiments of the present application, but as mentioned above, it should be understood that the present application is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the application concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art do not deviate from the spirit and scope of the present application, and should be within the scope of protection of the claims attached to the present application.

Claims

1. A system for coordinating the treatment of flue gas SO3 and desulfurization wastewater from a thermal power plant, characterized in that: The collaborative treatment system comprises: a desulfurization wastewater magnesium extraction module, which prepares magnesium hydroxide powder by adding an alkaline solution to the desulfurization wastewater and collects the desulfurization wastewater after magnesium removal; The SO3 removal module in the furnace removes SO3 by adding magnesium hydroxide powder prepared by the desulfurization wastewater magnesium extraction module into the SCR reactor and / or APH; The bypass flue gas desulfurization wastewater spray drying module extracts the high-temperature flue gas from the outlet of the SCR reactor, dries the desulfurization wastewater after magnesium removal, and discharges the treated smoke to the dust collector; The desulfurization wastewater magnesium extraction module includes: a primary buffer tank for sedimentation treatment of the desulfurization wastewater discharged from the desulfurization island; The first magnesium extraction unit is used to collect the supernatant discharged from the primary buffer tank, and add alkaline solution and flocculant to carry out the first magnesium hydroxide precipitation; The second magnesium extraction unit is used to collect the supernatant discharged from the first magnesium extraction unit, and add an alkaline solution and a flocculant to perform a second magnesium hydroxide precipitation; The filter pressing and drying unit is used to collect the sediments from the primary buffer tank, the first magnesium extraction unit and the second magnesium extraction unit, and perform filter pressing and drying to prepare magnesium hydroxide powder; The first magnesium extraction unit includes a first magnesium extraction and dosing device and a first base agent storage device; The first base agent storage device is used to store alkaline solution and flocculant; The first magnesium extraction and dosing device is used to collect the supernatant discharged from the primary buffer tank, and add the alkaline solution and flocculant in the first alkaline agent storage device to the supernatant discharged from the primary buffer tank; The second magnesium extraction unit includes a second magnesium extraction and dosing device, a second base agent storage device, a high efficiency filter and a backwashing device; The second base agent storage device is used to store alkaline solution and flocculant; The second magnesium extraction and dosing device is used to collect the supernatant discharged from the first magnesium extraction unit, and add the alkaline solution and flocculant in the second alkaline agent storage device to the supernatant discharged from the first magnesium extraction and dosing device; The high-efficiency filter and the backwashing device are both arranged in the second magnesium extraction and dosing device, and the filtering effect is: SS < 200 mg / L; The in-furnace SO3 removal module comprises: a first SO3 removal unit, located at the flue gas inlet of the SCR reactor, for performing the first SO3 removal on the flue gas by adding magnesium hydroxide powder produced by the pressure filter drying unit; The second SO3 removal unit is located at the flue gas inlet of APH, and performs a second SO3 removal on the flue gas by adding magnesium hydroxide powder produced by the pressure filter drying unit; The first SO3 removal unit and the second SO3 removal unit work separately or simultaneously; The bypass flue gas desulfurization wastewater spray drying module includes: an SDE, which provides a space for the bypass flue gas discharged from the SCR reactor to enter; The secondary buffer tank is used to collect the supernatant discharged from the second magnesium extraction unit and enter the SDE through spraying for drying.

2. A method for the coordinated treatment of flue gas SO3 and desulfurization wastewater from a thermal power plant, comprising the coordinated treatment system according to claim 1, characterized in that: The method comprises the following steps: S1: The magnesium extraction module of desulfurization wastewater prepares magnesium hydroxide powder. By adding alkaline solution, magnesium ions are replaced with magnesium hydroxide. Magnesium hydroxide is an insoluble solid. After extraction, it is dried using waste heat or residual heat and used as an absorbent for removing SO3; S2: The bypass flue gas desulfurization wastewater spray drying module extracts high-temperature flue gas from the SCR outlet, dries the wastewater that has not been concentrated and reduced, and discharges the treated smoke to the dust collector to complete the zero-emission treatment of desulfurization wastewater; S3: The prepared magnesium hydroxide dry powder is added to the SO3 removal module in the furnace to remove the SO3 in the SCR reactor and APH respectively, thus completing the removal of SO3 in the flue gas.

3. The collaborative processing method according to claim 2, characterized in that: The S1 specifically includes: S11: performing sedimentation treatment on the desulfurization wastewater discharged from the desulfurization island in the primary buffer tank; S12: collecting the supernatant discharged from the primary buffer tank in the first magnesium extraction unit, adding an alkaline solution and a flocculant, and performing the first magnesium hydroxide precipitation; S13: collecting the supernatant discharged from the first magnesium extraction unit in the second magnesium extraction unit, adding an alkaline solution and a flocculant, and performing a second magnesium hydroxide precipitation; S14: collecting and aggregating the sediments from the primary buffer tank, the first magnesium extraction unit and the second magnesium extraction unit, filtering and drying them to prepare magnesium hydroxide powder.

4. The collaborative processing method according to claim 3, characterized in that: The S3 specifically includes: S31: the SCR reactor receives the flue gas containing SO3 generated by the boiler furnace; S32: The first SO3 removal unit is at the flue gas inlet of the SCR reactor, and magnesium hydroxide powder produced by the filter press drying unit is added to remove SO3 for the first time; S33: Flue gas discharged from the SCR reactor enters the APH; S34: The second SO3 removal unit is at the inlet of the APH, and the magnesium hydroxide powder produced by the filter press drying unit is added to perform the second SO3 removal, thereby completing the SO3 removal in the flue gas; The S32 and S34 are performed separately or simultaneously.

5. The collaborative processing method according to claim 4, characterized in that: The S2 specifically includes: S21: bypass flue gas discharged from the SCR reactor enters the SDE; S22: collecting the supernatant discharged from the second magnesium extraction unit in the secondary buffer tank and entering the SDE by spraying; S23: Drying treatment is then carried out to achieve zero discharge of desulfurization wastewater.

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