Denitration, dust removal and mercury removal combined system and method for coal-fired power plant

Abstract

The invention provides a denitration, dust removal and mercury removal combined system and method for a coal-fired power plant. The system comprises a mercury oxidation module, a denitration module, an electric bag composite dust removal module, a wet desulphurization module and a cooperative control module. The mercury oxidation module is used for spraying an oxidation auxiliary agent into the flue gas, so that elemental mercury in the flue gas is partially oxidized into divalent mercury; the denitration module comprises a bromination modified catalyst, and the bromination modified catalyst is used for oxidizing residual elemental mercury into divalent mercury within a preset temperature range; the electric-bag composite dust removal module comprises an electrostatic dust removal area and a cloth bag filtering area, the electrostatic dust removal area is used for capturing particulate matters, and the cloth bag filtering area is used for capturing gaseous mercury; the wet desulphurization module is used for absorbing sulfur dioxide and divalent mercury in the flue gas and converting the divalent mercury into insoluble mercuric sulfide precipitates so as to recover mercuric sulfide through solid-liquid separation. The combined demercuration device has the technical effects that the combined demercuration capability of each module can be effectively controlled, and the stability of the demercuration performance is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of atmospheric pollutant treatment in coal-fired power plants, and in particular relates to a combined denitration, dust removal and mercury removal system and method for coal-fired power plants. Background Art

[0002] Coal-fired power plants are one of the main sources of electricity supply in my country, but they are also the main source of air pollutant emissions. The main pollutants in coal-fired flue gas include nitrogen oxides (NO x ), particulate matter (PM), sulfur dioxide (SO2) and mercury (Hg). These pollutants not only cause serious harm to the environment, but also affect human health. Therefore, how to efficiently remove multiple pollutants in coal-fired flue gas has become an important technical problem in the field of environmental protection.

[0003] At present, coal-fired power plants are equipped with denitrification devices, dust removal devices and desulfurization devices to remove nitrogen oxides, particulate matter and sulfur dioxide respectively. At the same time, these devices also have a certain removal capacity for mercury.

[0004] Mercury exists in three forms in coal-fired flue gas: elemental mercury Hg 0 , oxidized mercury Hg 2+ and particulate mercury Hg p , where Hg 0 Insoluble in water, highly volatile, difficult to capture and remove, but can be partially oxidized to Hg in the SCR reactor 2+ , oxidized mercury H g2+ Easily absorbed by the desulfurization system slurry, particulate mercury Hg p Most of it is captured in the fly ash when passing through the dust collector. Therefore, elemental mercury Hg is removed as much as possible. 0 The final mercury emission concentration can be effectively reduced, that is, the elemental mercury Hg 0 Converted to oxidized mercury Hg 2+ and removed by subsequent desulfurization equipment.

[0005] In the SCR denitrification reactor, the Hg 0 Converted to Hg 2+ However, the combined mercury removal capacity of each device of the SCR denitrification reactor has not been effectively controlled and is basically in a disordered state. There is still a lack of linkage control means between systems, and it is unable to dynamically respond to complex working conditions (such as changes in coal types or fluctuations in flue gas composition), which easily leads to instability in the system's mercury removal performance. Summary of the invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art and provide a new technical solution for a combined system and method for denitrification, dust removal and mercury removal in a coal-fired power plant.

[0007] According to a first aspect of the present invention, a combined denitration, dust removal and mercury removal system for a coal-fired power plant is provided, comprising a mercury oxidation module, a denitration module, an electric bag composite dust removal module, a wet desulfurization module and a coordinated control module; wherein the furnace flue gas passes through the mercury oxidation module, the denitration module, the electric bag composite dust removal module and the wet desulfurization module in sequence and is then discharged from the chimney;

[0008] The mercury oxidation module is used to inject an oxidizing agent into the flue gas to partially oxidize the elemental mercury in the flue gas into divalent mercury;

[0009] The denitration module includes a bromination-modified catalyst, which is used to oxidize the residual elemental mercury into divalent mercury within a preset temperature range and simultaneously reduce the nitrogen oxides in the flue gas into nitrogen;

[0010] The electric bag composite dust removal module includes an electrostatic dust removal area and a bag filter area, the electrostatic dust removal area is used to capture particulate matter, and the bag filter area is used to capture gaseous mercury; wherein the particulate matter includes particulate mercury;

[0011] The wet desulfurization module is used to absorb sulfur dioxide and divalent mercury in the flue gas and convert the divalent mercury into insoluble mercuric sulfide precipitate to recover the mercury sulfide through solid-liquid separation;

[0012] The mercury oxidation module, denitrification module, electric bag composite dust removal module, and wet desulfurization module are respectively connected to a coordinated control module, and the coordinated control module is used to adjust the injection amount of the oxidizing agent of the mercury oxidation module, the operating temperature of the denitrification module, the dust removal differential pressure of the electric bag composite dust removal module, and the precipitation reaction conditions of the wet desulfurization module.

[0013] Optionally, the catalyst surface is coated with a vanadium titanium bromide-based material to form a bromination-modified catalyst, wherein the coating thickness of the vanadium titanium bromide-based material is 10 microns to 30 microns, and the porous pore size range of the bromination-modified catalyst is about 2 nanometers to 5 nanometers.

[0014] Optionally, the electric bag composite dust removal module includes an electrostatic precipitator and a bag filter, the electrostatic precipitator is located in the electrostatic precipitator area, and the bag filter is located in the bag filter area;

[0015] A lateral spoiler unit is arranged in the electrode plate structure of the electrostatic precipitator, and the lateral spoiler unit is used to change the movement trajectory of the particulate matter; and / or a flow velocity distribution unit is arranged on the side of the bag filter close to the electrostatic precipitator, and the flow velocity distribution unit is used to adjust the flue gas flow velocity in each area of ​​the bag filter.

[0016] Optionally, the bag filter comprises a functionalized coated bag;

[0017] The surface of the functionalized coated cloth bag is covered with a modified activated carbon material, and the thickness of the modified activated carbon material is 10 microns to 50 microns.

[0018] Optionally, the mercury oxidation module is located below the first layer of catalyst of the SCR flue gas denitrification device.

[0019] Optionally, the mercury oxidation module comprises distributed multi-point nozzles to spray the oxidizing agent into the flue from multiple directions.

[0020] Optionally, the wet desulfurization module includes a mercury precipitation unit and a solid-liquid separation unit;

[0021] The mercury precipitation unit is used to add a precipitant to the slurry to cause a chemical reaction between divalent mercury and sulfide ions and generate insoluble mercuric sulfide precipitate;

[0022] The solid-liquid separation unit is used to separate solid particles and liquid in the slurry.

[0023] Optionally, the solid-liquid separation unit is a centrifugal separation device or a plate and frame filter press.

[0024] Optionally, when adding the precipitant to the slurry, a complexing agent is added to the slurry to stabilize the existence state of mercury ions; wherein the amount of the complexing agent added is 0.5 to 1 times the mass of the divalent mercury.

[0025] According to a second aspect of the present invention, a method for combined denitration, dust removal and mercury removal in a coal-fired power plant is provided, which is applied to the combined denitration, dust removal and mercury removal system in a coal-fired power plant as described in the first aspect, and comprises the following steps:

[0026] Step S1, before the flue gas flows into the SCR flue gas denitrification device, an oxidizing agent is sprayed into the flue gas through a mercury oxidation module to partially oxidize the elemental mercury in the flue gas into divalent mercury;

[0027] Step S2, the flue gas passes through the denitration module and contacts with the brominated modified catalyst to oxidize the residual elemental mercury into divalent mercury within a preset temperature range, and simultaneously reduce the nitrogen oxides in the flue gas into nitrogen;

[0028] Step S3, the oxidized flue gas enters the electric bag composite dust removal module, the particulate mercury is captured by the electrostatic dust removal area, and the gaseous mercury in the flue gas is captured by the bag filter area;

[0029] Step S4, the flue gas enters the wet flue gas desulfurization module, the slurry absorbs sulfur dioxide and divalent mercury in the flue gas, and a precipitant is added to the slurry to convert the divalent mercury into insoluble mercuric sulfide precipitate, and the mercury sulfide is recovered by solid-liquid separation;

[0030] Step S5, adjusting the injection amount of the oxidizing agent of the mercury oxidation module, the operating temperature of the denitrification module, the dust removal differential pressure of the electric bag composite dust removal module, and the precipitation reaction conditions of the wet desulfurization module through the coordinated control module.

[0031] A technical effect of the present invention is:

[0032] In the embodiment of the present application, the combined denitrification, dust removal and mercury removal system and method of the coal-fired power plant is based on the mercury removal capacity of the SCR flue gas denitrification device, by adding a mercury oxidation module to improve the mercury oxidation capacity of the catalyst; the electrostatic dust removal area of ​​the electric bag composite dust removal module captures particulate mercury, and the bag filter area captures gaseous mercury; and the injection amount of the oxidizing agent of the mercury oxidation module, the operating temperature of the denitrification module, the dust removal differential pressure of the electric bag composite dust removal module and the precipitation reaction conditions of the wet desulfurization module are dynamically adjusted through the collaborative control module, thereby achieving efficient linkage between modules. Compared with the solution in the prior art where the modules operate independently and lack a collaborative mechanism, this solves the problem of unstable processing efficiency caused by parameter mismatch, and at the same time improves the adaptability under complex working conditions, so that the combined mercury removal capacity of each module can be better controlled to ensure the stability of the mercury removal performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic structural diagram of a combined denitration, dust removal and mercury removal system for a coal-fired power plant according to an embodiment of the present invention;

[0034] Figure 2 The present invention is a schematic flow chart of a combined method for denitrification, dust removal and mercury removal in a coal-fired power plant according to an embodiment of the present invention.

[0035] In the figure: 1. Mercury oxidation module; 2. Denitrification module; 3. Electric bag composite dust removal module; 4. Wet desulfurization module; 5. Coordinated control module. DETAILED DESCRIPTION

[0036] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present application.

[0037] The embodiments of the present application will be described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and should not be construed as limitations on the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present application.

[0038] The term "first" or "second" in the specification and claims of this application may include one or more of the features explicitly or implicitly. In the description of this application, unless otherwise specified, "plurality" means two or more. In addition, "and / or" in the specification and claims means at least one of the connected objects, and the character " / " generally means that the objects connected before and after are in an "or" relationship.

[0039] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0040] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0041] According to a first aspect of the present invention, see Figure 1 , provides a combined denitration, dust removal and mercury removal system for a coal-fired power plant, comprising a mercury oxidation module 1, a denitration module 2, an electric bag composite dust removal module 3, a wet desulfurization module 4 and a coordinated control module 5; wherein the furnace flue gas passes through the mercury oxidation module 1, the denitration module 2, the electric bag composite dust removal module 3, and the wet desulfurization module 4 in sequence and is then discharged from the chimney, that is, the modules are connected in sequence through a flue gas flow path;

[0042] The mercury oxidation module 1 is used to inject an oxidizing agent into the flue gas to partially oxidize the elemental mercury in the flue gas into divalent mercury;

[0043] The denitration module 2 includes a bromination-modified catalyst, which is used to oxidize the residual elemental mercury into divalent mercury within a preset temperature range and simultaneously reduce the nitrogen oxides in the flue gas into nitrogen;

[0044] The electric bag composite dust removal module 3 includes an electrostatic dust removal area and a bag filter area, wherein the electrostatic dust removal area is used to capture particulate matter, and the bag filter area is used to capture gaseous mercury; wherein the particulate matter includes particulate mercury;

[0045] The wet desulfurization module 4 is used to absorb sulfur dioxide and divalent mercury in the flue gas and convert the divalent mercury into insoluble mercuric sulfide precipitate, so as to recover the mercury sulfide through solid-liquid separation;

[0046] The mercury oxidation module 1, the denitration module 2, the electric bag composite dust removal module 3, and the wet desulfurization module 4 are respectively connected to the coordinated control module 5, and the coordinated control module 5 is used to adjust the injection amount of the oxidizing agent of the mercury oxidation module, the operating temperature of the denitration module, the dust removal differential pressure of the electric bag composite dust removal module, and the precipitation reaction conditions of the wet desulfurization module. At the same time, the coordinated control module 5 can combine the existing SCR temperature (that is, the operating temperature of the denitration module), the efficiency of the electric bag dust collector, the desulfurization slurry of the wet desulfurization module and other online monitoring parameters to efficiently capture and control mercury according to the concentration of mercury.

[0047] In the embodiment of the present application, the combined denitrification, dust removal and mercury removal system and method of the coal-fired power plant is based on the mercury removal capacity of the SCR flue gas denitrification device, by adding a mercury oxidation module to improve the mercury oxidation capacity of the catalyst; the electrostatic dust removal area of ​​the electric bag composite dust removal module captures particulate mercury, and the bag filter area captures gaseous mercury; and the injection amount of the oxidizing agent of the mercury oxidation module, the operating temperature of the denitrification module, the dust removal differential pressure of the electric bag composite dust removal module and the precipitation reaction conditions of the wet desulfurization module are dynamically adjusted through the collaborative control module, thereby achieving efficient linkage between modules. Compared with the solution in the prior art where the modules operate independently and lack a collaborative mechanism, this solves the problem of unstable processing efficiency caused by parameter mismatch, and at the same time improves the adaptability under complex working conditions, so that the combined mercury removal capacity of each module can be better controlled to ensure the stability of the mercury removal performance.

[0048] It should be noted that elemental mercury Hg 0 Oxidation to Hg 2+ The reaction equation of (divalent mercury) is shown below:

[0049]

[0050] In the above reaction process, there are two key factors: catalyst and halogen element concentration (i.e. flue gas components). Under the condition that the mercury oxidation performance of the catalyst itself is constant, as the concentration of HCl / HBr in the flue gas increases, the catalyst's oxidation efficiency of elemental mercury increases rapidly. Therefore, by increasing the concentration of halogen elements in the SCR flue gas denitrification device, Hg 0 Converted to Hg 2+ proportion.

[0051] Optionally, the catalyst surface is coated with a vanadium titanium bromide-based material to form a bromination-modified catalyst, wherein the coating thickness of the vanadium titanium bromide-based material is 10 microns to 30 microns; the porous pore size range of the bromination-modified catalyst is about 2 nanometers to 5 nanometers, which matches the physical size of mercury molecules, thereby enhancing the catalyst's adsorption capacity for mercury molecules.

[0052] In the above embodiment, since the mercury oxidation performance is affected by two factors, the flue gas components and the catalyst, wherein the flue gas components have been sprayed with an oxidizing agent through the mercury oxidation module to achieve mercury oxidation capability, the catalyst can also achieve mercury oxidation capability through a demercuration catalyst, that is, the demercuration catalyst can be a bromination modified catalyst. The coating thickness of the brominated vanadium titanium-based material is 10 microns to 30 microns, which can ensure high oxidation efficiency while reducing the pressure drop of the catalyst.

[0053] Optionally, the electric bag composite dust removal module includes an electrostatic precipitator and a bag filter, the electrostatic precipitator is located in the electrostatic precipitator area, and the bag filter is located in the bag filter area;

[0054] A lateral spoiler unit is arranged in the electrode plate structure of the electrostatic precipitator, and the lateral spoiler unit is used to change the movement trajectory of the particulate matter; and / or a flow velocity distribution unit is arranged on the side of the bag filter close to the electrostatic precipitator, and the flow velocity distribution unit is used to adjust the flue gas flow velocity in each area of ​​the bag filter.

[0055] It should be noted that after the flue gas is treated by the mercury oxidation module, most of the elemental mercury (Hg 0 ) has been converted into divalent mercury (Hg 2+ At this time, the flue gas still contains a large amount of particulate matter (PM) and a small amount of gaseous mercury (Hg 0 , Hg 2+ , Hg p The main function of the electric bag composite dust removal module is to remove particulate mercury and gaseous mercury in the flue gas through the synergistic effect of electrostatic capture and bag filtration.

[0056] In the above-mentioned embodiment, the uneven flow velocity at the inlet of the electrostatic precipitator is mainly considered. At this time, the dust removal effect is poor in the area with high flue gas flow velocity, which also affects the mercury removal efficiency. In order to improve the efficiency of the dust removal area, a lateral spoiler unit is added to the plate structure of the electrostatic precipitator to change the movement trajectory of the particles. Through this spoiler method, the probability of collision between the particles and the plate is increased, thereby improving the electrostatic capture efficiency.

[0057] And / or, the flue gas is first adjusted by the flow velocity distribution unit before entering the bag filter. That is, the flow velocity distribution unit can automatically adjust the flue gas flow velocity in each area according to the distribution of the flue gas inlet flow velocity, thereby avoiding the occurrence of wear and tear caused by excessive local load on the bag filter.

[0058] Optionally, the bag filter comprises a functionalized coated bag;

[0059] The surface of the functionalized coated cloth bag is covered with a modified activated carbon material, and the thickness of the modified activated carbon material is 10 microns to 50 microns.

[0060] In the above embodiment, the surface of the functionalized coated cloth bag is coated with a modified activated carbon material, which is resistant to gaseous mercury (especially Hg 2+ ) has a high adsorption capacity, and the coating thickness is controlled in the range of 10-50 microns to significantly improve the adsorption capacity while balancing the pressure drop of the functionalized coated bag.

[0061] Optionally, the mercury oxidation module is located below the first layer of catalyst of the SCR flue gas denitrification device.

[0062] In the above embodiment, a mercury oxidation module (i.e., an oxidizing agent injection unit) is added below the first layer of catalyst of the SCR flue gas denitrification device. Since mercury and ammonia compete for adsorption, the concentration of ammonia adsorbed in the first layer of catalyst is relatively high, which will affect the ability of the oxidizing agent to oxidize mercury. Therefore, the mercury oxidation module is placed below the first layer, so as to better ensure the mercury oxidation module's ability to oxidize mercury.

[0063] Optionally, the mercury oxidation module comprises distributed multi-point nozzles to spray the oxidizing agent into the flue from multiple directions.

[0064] In the above embodiment, the distributed multi-point nozzles can spray the oxidizing agent into the flue from multiple directions to achieve uniform coverage of the oxidizing agent. The oxidizing agent mainly refers to a substance that can be decomposed into halogen elements, and the present invention uses hydrogen bromide gas.

[0065] Optionally, the wet desulfurization module includes a mercury precipitation unit and a solid-liquid separation unit;

[0066] The mercury precipitation unit is used to add a precipitant to the slurry to cause a chemical reaction between divalent mercury and sulfide ions and generate insoluble mercuric sulfide precipitate;

[0067] The solid-liquid separation unit is used to separate solid particles and liquid in the slurry.

[0068] Exemplarily, the wet desulfurization module is located downstream of the electric bag composite dust removal module to absorb sulfur dioxide in the flue gas and dissolve divalent mercury. Considering that divalent mercury is present in the wastewater after dissolution and then enters the gypsum, affecting the use of the desulfurization gypsum, the present invention adds a mercury precipitation unit and a solid-liquid separation unit to convert the divalent mercury in the slurry into a solid phase and separate it.

[0069] Specifically, the mercury precipitation unit adds a precipitant (such as sodium sulfide Na2S) to the slurry to make Hg 2+ It reacts chemically with sulfur ions to form insoluble mercuric sulfide (HgS) precipitation. The solid-liquid separation equipment uses a centrifugal separation device or a plate and frame filter press.

[0070] A bypass is introduced between the desulfurization slurry circulation pumps to lead out the slurry and flow it into the separation unit. The separation unit is equipped with a stirring device to ensure that the mercury ions in the slurry are fully mixed with the precipitant, thereby improving the reaction efficiency. The solid particles in the slurry are separated from the liquid through the separation unit, and the separated clear liquid is returned to the slurry pump and then to the absorption tower for recycling.

[0071] Optionally, the solid-liquid separation unit is a centrifugal separation device or a plate and frame filter press.

[0072] Optionally, when adding the precipitant to the slurry, a complexing agent is added to the slurry to stabilize the existence state of mercury ions; wherein the amount of the complexing agent added is 0.5 to 1 times the mass of the divalent mercury.

[0073] In the above embodiment, a complexing agent is added to the slurry to stabilize the existence state of mercury ions, which can improve the efficiency of mercury precipitation, thereby preventing the mercury ions from being secondary oxidized or reduced in the slurry.

[0074] In a specific implementation, the collaborative control module is based on the online monitoring system to collect the concentrations of nitrogen oxides (NOx), particulate matter (PM) and mercury (Hg) in the flue gas, as well as the operating status parameters of the module, including the injection amount of the oxidizing agent, the operating temperature of the denitrification module (i.e., the temperature of the SCR catalytic device), the electrostatic precipitator electric field voltage, the dust removal differential pressure, the bag filter adsorption efficiency and the pH value of the wet desulfurization slurry (wherein, the mercury concentration test adopts the activated carbon adsorption method monitoring equipment of the US standard EPA-30A), and the above data is transmitted to the collaborative control module in real time through sensors and analytical instruments. The collaborative control module is used to adjust the operating parameters, and typical parameters include the injection amount of the oxidizing agent, the operating temperature of the denitrification module, the electrostatic precipitator efficiency of the electric bag composite dust removal module, the adsorption performance of the bag filter and the comprehensive control of the wet desulfurization reaction conditions to ensure the flue gas treatment requirements under different coal types and different working conditions, and achieve the best pollutant removal effect.

[0075] Specifically, regarding the control of the injection amount of the oxidizing agent: the higher the injection amount of the oxidizing agent, the higher the oxidation efficiency of mercury. The coordinated control module controls the injection amount of the oxidizing agent according to the elemental mercury (Hg 0 ) real-time concentration, dynamically adjust the injection amount of the oxidant. At the same time, considering that the unit has different operating temperatures under different loads, the mercury oxidation efficiency also varies at different temperatures. When the SCR temperature is high, the injection amount of the oxidant should be appropriately reduced to reduce the operating cost; when the SCR temperature is low, the injection amount of the oxidant should be increased to compensate for the decrease in oxidation efficiency.

[0076] Regarding the control of the electric field voltage of electrostatic precipitators: In order to optimize the particle capture effect, the collaborative control module can dynamically adjust the intensity of the electric field according to the particle concentration and particle size distribution. For example, when the particle concentration is high and the particle size is large, the electric field voltage is appropriately increased to enhance the capture ability; when the particle concentration is low, the electric field voltage is reduced to save energy.

[0077] Regarding the regulation of bag filter adsorption efficiency, the present invention adds pressure gauges before and after the bag filter, and determines whether bag cleaning is needed through test data of the pressure difference change of the bags in the flue gas. When the pressure difference on the bag surface exceeds the set threshold, the collaborative control module will start the pulse spray device for cleaning. The adsorption performance of the bag filter area is crucial to the removal efficiency of gaseous mercury.

[0078] Regarding the adjustment of wet flue gas desulfurization reaction conditions: the coordinated control module dynamically adjusts the reaction conditions of the slurry by monitoring the circulation rate of the slurry and the amount of precipitant added. 2+ When the concentration increases, the collaborative control module will automatically increase the amount of precipitant added; it can also improve the contact efficiency between the slurry and the flue gas by adjusting the circulation rate of the slurry (6-15m / s).

[0079] According to the second aspect of the present invention, see Figure 2 , provides a combined denitration, dust removal and mercury removal method for a coal-fired power plant, which is applied to the combined denitration, dust removal and mercury removal system for a coal-fired power plant as described in the first aspect, comprising the following steps:

[0080] Step S1, before the flue gas flows into the SCR flue gas denitrification device, an oxidizing agent is sprayed into the flue gas through a mercury oxidation module to partially oxidize the elemental mercury in the flue gas into divalent mercury;

[0081] Step S2, the flue gas passes through the denitration module and contacts with the brominated modified catalyst to oxidize the residual elemental mercury into divalent mercury within a preset temperature range, and simultaneously reduce the nitrogen oxides in the flue gas into nitrogen;

[0082] Step S3, the oxidized flue gas enters the electric bag composite dust removal module, the particulate mercury is captured by the electrostatic dust removal area, and the gaseous mercury in the flue gas is captured by the bag filter area;

[0083] Step S4, the flue gas enters the wet flue gas desulfurization module, the slurry absorbs sulfur dioxide and divalent mercury in the flue gas, and a precipitant is added to the slurry to convert the divalent mercury into insoluble mercuric sulfide precipitate, and the mercury sulfide is recovered by solid-liquid separation;

[0084] Step S5, adjusting the injection amount of the oxidizing agent of the mercury oxidation module, the operating temperature of the denitrification module, the dust removal differential pressure of the electric bag composite dust removal module, and the precipitation reaction conditions of the wet desulfurization module through the coordinated control module.

[0085] In the above-mentioned embodiment, a collaborative control module is used to dynamically adjust the injection amount of the oxidizing agent, the SCR catalytic temperature, the electric bag composite dust removal parameters and the wet desulfurization conditions, thereby realizing efficient linkage between modules. Compared with the solution in the prior art where the modules operate independently and lack a collaborative mechanism, it solves the problem of unstable processing efficiency caused by parameter mismatch and improves the adaptability under complex working conditions.

[0086] Moreover, the present invention adopts limestone slurry to absorb SO2, and at the same time, by dynamically adjusting the pH value of the slurry, the circulation rate and the amount of precipitant added, the divalent mercury in the slurry is converted into mercuric sulfide precipitation and separated and recovered, thereby solving the problems of mercury accumulation and secondary pollution in wet flue gas desulfurization waste liquid and realizing the resource utilization of mercury.

[0087] In addition, the present invention optimizes the design of electrostatic dust removal and bag filtration of the electric bag composite dust removal module. The electrostatic dust removal area is used to capture large particles and particulate mercury, and the bag filtration area deeply removes gaseous mercury through a functionalized adsorption coating. Compared with the technical solution of traditional dust collectors that can only efficiently capture particulate matter, this solves the problem of low gaseous mercury removal efficiency and significantly improves the overall mercury capture efficiency.

[0088] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present invention, but the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A combined system for denitrification, dust removal and mercury removal in a coal-fired power plant, characterized in that: It includes a mercury oxidation module, a denitration module, an electric bag composite dust removal module, a wet desulfurization module and a coordinated control module; wherein the furnace flue gas passes through the mercury oxidation module, the denitration module, the electric bag composite dust removal module and the wet desulfurization module in sequence and is then discharged from the chimney; The mercury oxidation module is used to inject an oxidizing agent into the flue gas to partially oxidize the elemental mercury in the flue gas into divalent mercury; The denitration module includes a bromination-modified catalyst, which is used to oxidize the residual elemental mercury into divalent mercury within a preset temperature range and simultaneously reduce the nitrogen oxides in the flue gas into nitrogen; The electric bag composite dust removal module includes an electrostatic dust removal area and a bag filter area, the electrostatic dust removal area is used to capture particulate matter, and the bag filter area is used to capture gaseous mercury; wherein the particulate matter includes particulate mercury; The wet desulfurization module is used to absorb sulfur dioxide and divalent mercury in the flue gas and convert the divalent mercury into insoluble mercuric sulfide precipitate to recover the mercury sulfide through solid-liquid separation; The mercury oxidation module, denitrification module, electric bag composite dust removal module, and wet desulfurization module are respectively connected to a coordinated control module, and the coordinated control module is used to adjust the injection amount of the oxidizing agent of the mercury oxidation module, the operating temperature of the denitrification module, the dust removal differential pressure of the electric bag composite dust removal module, and the precipitation reaction conditions of the wet desulfurization module.

2. The combined denitrification, dust removal and mercury removal system for a coal-fired power plant according to claim 1, characterized in that: The catalyst surface is coated with vanadium titanium bromide based material to form a bromination modified catalyst, wherein the coating thickness of the vanadium titanium bromide based material is 10 microns to 30 microns, and the porous pore size range of the bromination modified catalyst is about 2 nanometers to 5 nanometers.

3. The combined denitrification, dust removal and mercury removal system for a coal-fired power plant according to claim 1, characterized in that: The electric bag composite dust removal module includes an electrostatic precipitator and a bag filter, the electrostatic precipitator is located in the electrostatic precipitator area, and the bag filter is located in the bag filter area; A lateral spoiler unit is arranged in the electrode plate structure of the electrostatic precipitator, and the lateral spoiler unit is used to change the movement trajectory of the particulate matter; and / or a flow velocity distribution unit is arranged on the side of the bag filter close to the electrostatic precipitator, and the flow velocity distribution unit is used to adjust the flue gas flow velocity in each area of ​​the bag filter.

4. The combined denitrification, dust removal and mercury removal system for a coal-fired power plant according to claim 3, characterized in that: The bag filter includes a functionalized coated bag; The surface of the functionalized coated cloth bag is covered with a modified activated carbon material, and the thickness of the modified activated carbon material is 10 microns to 50 microns.

5. The combined denitrification, dust removal and mercury removal system for a coal-fired power plant according to claim 1, characterized in that: The mercury oxidation module is located below the first layer of catalyst of the SCR flue gas denitration device.

6. The combined denitrification, dust removal and mercury removal system for a coal-fired power plant according to claim 1, characterized in that: The mercury oxidation module includes distributed multi-point nozzles to spray oxidation aids into the flue from multiple directions.

7. The combined denitrification, dust removal and mercury removal system for a coal-fired power plant according to claim 1, characterized in that: The wet desulfurization module includes a mercury precipitation unit and a solid-liquid separation unit; The mercury precipitation unit is used to add a precipitant to the slurry to cause a chemical reaction between divalent mercury and sulfide ions and generate insoluble mercuric sulfide precipitate; The solid-liquid separation unit is used to separate solid particles and liquid in the slurry.

8. The combined denitrification, dust removal and mercury removal system for a coal-fired power plant according to claim 7, characterized in that: The solid-liquid separation unit is a centrifugal separation device or a plate and frame filter press.

9. The combined denitrification, dust removal and mercury removal system for a coal-fired power plant according to claim 8, characterized in that: When the precipitant is added to the slurry, a complexing agent is added to the slurry to stabilize the existence of mercury ions; wherein the amount of the complexing agent added is 0.5 to 1 times the mass of the divalent mercury.

10. A combined method for denitrification, dust removal and mercury removal in a coal-fired power plant, characterized in that: The combined denitrification, dust removal and mercury removal system for a coal-fired power plant as claimed in any one of claims 1 to 9 comprises the following steps: Step S1, before the flue gas flows into the SCR flue gas denitrification device, an oxidizing agent is sprayed into the flue gas through a mercury oxidation module to partially oxidize the elemental mercury in the flue gas into divalent mercury; Step S2, the flue gas passes through the denitration module and contacts with the brominated modified catalyst to oxidize the residual elemental mercury into divalent mercury within a preset temperature range, and simultaneously reduce the nitrogen oxides in the flue gas into nitrogen; Step S3, the oxidized flue gas enters the electric bag composite dust removal module, the particulate mercury is captured by the electrostatic dust removal area, and the gaseous mercury in the flue gas is captured by the bag filter area; Step S4, the flue gas enters the wet flue gas desulfurization module, the slurry absorbs sulfur dioxide and divalent mercury in the flue gas, and a precipitant is added to the slurry to convert the divalent mercury into insoluble mercuric sulfide precipitate, and the mercury sulfide is recovered by solid-liquid separation; Step S5, adjusting the injection amount of the oxidizing agent of the mercury oxidation module, the operating temperature of the denitrification module, the dust removal differential pressure of the electric bag composite dust removal module, and the precipitation reaction conditions of the wet desulfurization module through the coordinated control module.

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