Method for removing so3 in flue gas by charge coagulation

Abstract

The application relates to the field of coal-fired flue gas treatment, and discloses a method for removing SO3 in coal-fired flue gas through charging and coagulation, which comprises the following steps: step S1, a pre-charging step: making the SO3 aerosol carry a first polarity charge; step S2, a generating and injecting step: atomizing an alkaline solution into alkaline droplets carrying a second polarity charge; step S3, a coagulation step: using the traveling wave electric field to drive the relative movement of the two kinds of particles; step S4, obtaining a real-time feedback signal reflecting the coagulation efficiency; and step S5, dynamically adjusting the operation parameters based on the feedback signal. Through the traveling wave electric field, the SO3 aerosol carrying opposite polarity charges and the alkaline droplets are subjected to electric field forces in opposite directions, the relative movement between the two kinds of particles is driven, the particle coagulation is changed from a passive process depending on slow Brownian diffusion into a capture process dominated by an external electric field, and then the collision frequency and coagulation rate between submicron particles are improved.

Description

Technical Field

[0001] This invention relates to the field of coal-fired flue gas treatment, specifically a method for electro-condensing and removing SO3 from coal-fired flue gas. Background Technology

[0002] During combustion in coal-fired power plants and other combustion devices, sulfur in the fuel is oxidized to sulfur dioxide (SO2), of which a portion (approximately 1%-5%) is further catalytically oxidized to sulfur trioxide (SO3). As the flue gas is transported and cooled along the flue, gaseous SO3 reacts rapidly with water vapor (H2O) present in the flue gas to form gaseous sulfuric acid (H2SO4). When the flue gas temperature drops below the sulfuric acid dew point, the gaseous sulfuric acid rapidly condenses through homogeneous nucleation, forming numerous extremely small droplets. These ultrafine sulfuric acid droplets suspended in the flue gas are known as SO3 aerosols. These aerosols are not only a major cause of blue smoke from chimneys and visual pollution, but their strong acidity and high corrosiveness also cause severe low-temperature acid corrosion to air preheaters, flue gas ducts, and downstream equipment, jeopardizing their safe operation.

[0003] To remove pollutants from flue gas, industrial applications commonly employ end-of-pipe dust collection equipment such as electrostatic precipitators (ESPs) or bag filters (FFs). However, these devices generally have low removal efficiency for SO3 aerosols. The fundamental reason is that the particle size of SO3 aerosols is mainly concentrated in the submicron range of 0.1-1.0 µm, which falls precisely within the penetration zone of electrostatic precipitators. Particles within this range are difficult to effectively charge through diffusion, and their extremely small size results in very low electromigration velocity in an electric field, making them prone to escaping with the airflow. For bag filters, highly viscous and strongly acidic SO3 aerosols easily cause filter bag caking and corrosion, shortening filter bag life and increasing operating resistance. Therefore, existing technologies generally face technical bottlenecks such as low removal efficiency for submicron-sized SO3 aerosols, poor adaptability, and unstable operation. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for electrostatic condensation and removal of SO3 from coal-fired flue gas, which solves the problems of low collection efficiency, poor adaptability, and unstable operation of existing dust removal technologies for submicron-sized SO3 aerosols.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for electrostatic condensation and removal of SO3 from coal-fired flue gas, comprising the following steps:

[0006] First, the SO3 aerosols native to the flue gas are charged with a first polarity charge through corona discharge. Then, alkaline droplets carrying opposite polarity (second polarity) charges are generated and injected using electrohydrodynamic atomization as coagulation nuclei. Next, a traveling wave electric field drives the two types of opposite polarity particles to undergo violent relative motion to achieve efficient coagulation. Finally, an adaptive resonant closed-loop control system dynamically adjusts key operating parameters based on real-time monitoring of the coagulation efficiency, ensuring that the system continuously operates in its optimal state.

[0007] Specifically, the technical solution of this method includes:

[0008] Pre-charging step: Flue gas containing SO3 aerosol is guided to the pre-charging zone. Within this zone, a stable corona discharge is generated by applying a negative DC high voltage to the discharge electrodes. As the SO3 aerosol and ultrafine dust in the flue gas flow through this zone, they are processed into a unified particle group carrying a primary polarity (e.g., negative polarity) charge under the combined effects of electric field charging and diffusion charging.

[0009] Generation and Injection Steps: This step utilizes an electrohydrodynamic atomization (EHDA) system to generate and inject alkaline condensate nuclei carrying a secondary polarity (e.g., positive polarity) charge. The core innovation of this system lies in:

[0010] Charge-to-mass ratio control: An alkaline solution (such as sodium hydroxide solution or ammonia) is atomized into submicron-sized droplets carrying positive charges through a nozzle under the influence of a strong electric field. The charge-to-mass ratio of these droplets (…) The parameter is a key physical property and can be actively controlled by adjusting operating parameters. Its physical relationship can be represented by the following formula:

[0011] ;

[0012] In the formula, The charge of the droplet. For the mass of the droplet, Let be the droplet radius. Since the droplet radius... Controlled by the injection voltage and liquid flow rate of the EHDA system, alkaline condensation nuclei with a specific charge-to-mass ratio can be generated by adjusting these two parameters.

[0013] Phase-synchronized pulse injection linked to the traveling wave electric field: The injection of condensate nuclei is not continuous, but rather employs a pulsed method synchronized with the subsequent operation of the traveling wave electric field. The system monitors the potential phase of the traveling wave electric field at the nozzle location in real time. This phase is described by the following equation:

[0014] ;

[0015] In the formula, The electric field angular frequency, For wave vector, For nozzle position coordinates. Only when the real-time phase... When the system reaches a preset trigger window corresponding to a potential trough, the EHDA is triggered to perform a brief pulse injection. This ensures that newly generated condensed nuclei are always introduced during the most favorable electric field phase.

[0016] Coagulation Step: Flue gas containing the two types of oppositely charged particles is introduced into a traveling wave electric field region. This traveling wave electric field consists of multiple electrode arrays arranged along the airflow direction and is powered by an N-phase (N≥3) AC power supply, thereby constructing a potential wave propagating along the airflow direction within the channel. SO3 aerosols carrying the first polarity charge and alkaline droplets carrying the second polarity charge experience opposite electric forces in the traveling wave electric field due to their opposite charge polarities. Combined with the significant difference in their charge-to-mass ratios, this results in violent, asynchronous reciprocating motion under the electric field's influence, i.e., significant relative velocity. This macroscopic relative motion, actively applied by an external electric field, greatly increases the collision frequency between the oppositely charged particles, achieving highly efficient electro-induced sweeping coagulation and rapidly increasing particle size.

[0017] Real-time monitoring steps: A coalescence efficiency monitoring unit is installed downstream of the traveling wave electric field region. Since the coalescence process is electrically a neutralization process of opposite polarity charges, a real-time feedback signal that directly reflects the degree of completion of the coalescence reaction can be obtained by non-contactly measuring the net space charge density carried by the flue gas after coalescence. The closer the net space charge density is to zero, the higher the coalescence efficiency.

[0018] The adaptive resonant optimization control steps are as follows: A closed-loop control system is established with the optimization objective of minimizing the absolute value of the real-time feedback signal. This system receives the aforementioned real-time feedback signal and, based on an optimization algorithm (such as the perturbation-observation method), continuously and dynamically adjusts two key operating parameters:

[0019] Driving frequency of traveling wave electric field :

[0020] EHDA system injection voltage Its function is to change the mass-charge ratio of basic condensation nuclei. );

[0021] By optimizing these two parameters in two-dimensional space, the system can automatically find and lock the frequency-charge-mass ratio resonance matching point under the current flue gas conditions, which maximizes the relative motion between SO3 aerosols and alkaline condensation nuclei and the condensation efficiency.

[0022] This invention provides a method for electrostatic condensation and removal of SO3 from coal-fired flue gas. It has the following beneficial effects:

[0023] 1. This invention applies opposite electric field forces to SO3 aerosols and alkaline droplets carrying opposite polarity charges using a traveling wave electric field, actively driving relative motion between the two particle groups. This transforms particle agglomeration from a passive process dependent on slow Brownian diffusion into a capture process dominated by an external electric field, thereby increasing the collision frequency and agglomeration rate between submicron particles.

[0024] 2. By employing a pulsed injection method synchronized with the potential of the traveling wave electric field, this invention ensures that alkaline condensation nuclei are always introduced at the specific electric field phase (such as the potential trough) where energy utilization is most efficient. This allows the injected particles to obtain the maximum initial acceleration, maximizing the conversion efficiency of electric field energy to particle sweeping kinetic energy and avoiding energy waste and reduced condensation efficiency caused by injection at non-optimal phases.

[0025] 3. By setting up a coagulation efficiency monitoring unit and establishing an adaptive resonance optimization closed-loop control, this invention can evaluate the coagulation effect in real time. When the flue gas temperature, flow rate and other operating conditions change, the control system can automatically adjust the traveling wave electric field driving frequency and the coagulation nucleus-charge-mass ratio, dynamically track and lock the optimal operating point, thereby ensuring that the system always maintains a high-efficiency and stable operating state in the ever-changing industrial environment. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the method flow of the present invention;

[0027] Figure 2 This is a schematic diagram illustrating the synchronization relationship between the pulsed injection and the traveling wave electric field phase in step S2 of the present invention. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] To better understand the present invention, the above content will be described in detail below with reference to specific embodiments.

[0030] Please see the appendix Figure 1 and attached Figure 2 This invention provides a method for electrocoagulation and removal of SO3 from coal-fired flue gas, comprising the following steps:

[0031] Step S1, Pre-charging step: Treat the flue gas containing SO3 aerosol so that the SO3 aerosol carries a first polar charge;

[0032] Step S2, Generation and Injection Step: Using electrohydrodynamic atomization, the alkaline solution is atomized into alkaline microdroplets carrying a second polarity charge, and the alkaline microdroplets are injected into the flue gas treated in step S1. The polarity of the second polarity charge is opposite to that of the first polarity charge.

[0033] Step S3, Coagulation Step: The flue gas mixed with the SO3 aerosol carrying the first polarity charge and the alkaline droplets carrying the second polarity charge is flowed through the traveling wave electric field region. The traveling wave electric field drives the two types of particles to move relative to each other, thereby coagulating to form particles with increased particle size.

[0034] Step S4: Monitor the flue gas after step S3 in real time to obtain a real-time feedback signal reflecting the condensation efficiency.

[0035] Step S5: Based on the real-time feedback signal, the operating parameters are dynamically adjusted through adaptive resonance optimization closed-loop control to ensure that the coagulation efficiency is at the optimal efficiency point.

[0036] In one embodiment, step S1 of the method of the present invention is to pretreat the raw flue gas containing SO3 aerosol so that it carries a preset first polarity charge.

[0037] Specifically, the raw flue gas originating from the tail flue of a boiler or similar combustion device is first guided to a pre-charging unit before entering the subsequent condensation section. This pre-charging unit can be a conventional electrostatic precipitator or a specially designed charger, for example, it contains an electric field region composed of discharge electrodes and dust collection electrodes. The discharge electrodes can be linear electrodes, needle electrodes, serrated wire electrodes, or combinations thereof, while the dust collection electrodes are typically flat, honeycomb, or cylindrical structures. In this embodiment, a wire-plate structure is preferred, in which multiple sets of corona wires are arranged parallel between two grounded dust collection plates to form a uniform charging area, ensuring that particles are fully charged as the flue gas flows through.

[0038] In this method, a negative DC high voltage is applied to the discharge electrode, typically set between -30kV and -80kV. This high voltage allows the electric field strength around the discharge electrode to exceed the gas breakdown threshold, thereby generating a stable corona discharge phenomenon.

[0039] The corona discharge process ionizes gas molecules (such as O2, H2O) in the flue gas, generating a large number of free electrons and negative ions (such as O2, H2O). 2- O -Driven by a strong electric field, these ions migrate toward the dust collection electrode, thus forming a space charge region filled with negative ions throughout the space between the electrodes.

[0040] When flue gas containing SO3 aerosols and ultrafine dust particles with a particle size in the submicron range (e.g., less than 1 μm) flows through the space charge region at a set process flow rate (e.g., 5 m / s to 20 m / s), the particles will collide with these high concentrations of negative ions.

[0041] The particle charging mechanism in this process is mainly dominated by electric field charging and diffusion charging. These two mechanisms enable the particle surface to rapidly accumulate negative charges within a very short residence time (e.g., 0.1 to 0.5 seconds) until it approaches its saturation charge under the electric field conditions.

[0042] To describe this charging process more precisely, the particle's charge... Over time rate of change It can be represented by the following comprehensive model, and the mathematical formula is:

[0043] ;

[0044] In the formula, Indicates the electric field charge rate. To represent the diffusion charging rate, and for particles with relatively large diameters, electric field charging plays a dominant role, the final achievable saturation charge is... This can be described by the Pauthenier formula, expressed as:

[0045] ;

[0046] In the formula, Where is the particle radius, For charging field strength, The vacuum permittivity, is the relative permittivity of the particle; Pi is the mathematical constant of a circle.

[0047] For ultrafine particles with even smaller diameters, the effect of diffusion charging is more significant, and their charge... The process of change over time can be approximated by White's formula, expressed as:

[0048] ;

[0049] In the formula, Boltzmann's constant, For flue gas temperature, For elementary charge, This refers to the ion concentration. The average thermal velocity of the ions. For time.

[0050] Using the above method, the electrically neutral SO3 aerosols and dust particles in the original flue gas can be converted into particles carrying a uniform first polarity (negative polarity in this embodiment) charge.

[0051] After completing the unipolar (negative polarity) charging of SO3 aerosols in flue gas, the method of the present invention proceeds to step S2, namely: generating and injecting alkaline condensation nuclei carrying opposite polarity (second polarity) charges.

[0052] Specifically, this method employs an electrohydrodynamic atomization (EHDA) system, which mainly includes multiple atomizing nozzles, a precision liquid delivery device, and a high-voltage DC power supply. The atomizing nozzles can be a single metal capillary or an array of multiple micro-nozzles to accommodate different flue gas volumes. The precision liquid delivery device, such as a micro-injection pump or a constant-flow pump, is used to precisely control the flow rate and deliver the working liquid to the atomizing nozzles.

[0053] The positive terminal of the high-voltage DC power supply is connected to the atomizing nozzle, and the negative terminal is grounded to establish a strong electric field between the nozzle tip and the grounded electrode. In this embodiment, the applied voltage (defined as the injection voltage) The voltage range is typically between +5kV and +20kV. In one specific embodiment, the grounding electrode can be a ring-shaped electrode, coaxially arranged with the atomizing nozzle and located at a certain distance downstream of the nozzle outlet. This helps to concentrate the electric field lines, stabilize the Taylor cone shape, and guide the initial path of the jet.

[0054] Specifically, during operation, an alkaline solution, such as a 5% to 20% sodium hydroxide (NaOH) solution, ammonia, or other alkaline liquids capable of neutralizing acidic substances, is delivered to the nozzle tip via a liquid delivery device. At the nozzle tip, the liquid is subjected to electrostatic pressure generated by a strong electric field. Capillary pressure generated by its own surface tension The combined effect of these factors can be expressed by the following formula:

[0055] ;

[0056] ;

[0057] In the formula, The vacuum permittivity, Let be the normal electric field strength at the liquid surface at the nozzle tip. For liquid surface tension, Let be the radius of curvature of the liquid surface.

[0058] When the applied voltage is high enough, the electrostatic pressure... Sufficient to overcome capillary pressure When the electric field is applied, the liquid at the nozzle tip is stretched into a stable cone shape, known as a Taylor cone. At the tip of the Taylor cone, an extremely fine liquid jet extends out, which breaks up under the influence of electrostatic instability, forming a series of uniformly sized droplets distributed in the submicron range (e.g., 100 nm to 800 nm).

[0059] Furthermore, due to the aforementioned formation process, these alkaline droplets carry a large amount of positive charge at the moment of formation, and their charge... Approaching the physical maximum stable charge, i.e., the Rayleigh limit. The formula can be:

[0060] ;

[0061] In the formula, Where is the droplet radius, these alkaline microdroplets carrying a high density of surface charge become the condensation nuclei in the subsequent electrocoagulation process. Furthermore, these generated condensation nuclei possess a charge-to-mass ratio... In this invention, it is actively controllable: by combining the droplet mass (the formula is: ;in, (for liquid density) and Rayleigh limit Its charge-to-mass ratio can be derived:

[0062] ;

[0063] From the above equation, we can see that the charge-to-mass ratio of the condensate nucleus is equal to its radius. A definite function. And the radius. The key operating parameter of the EHDA system, namely injection voltage The synergistic effect with liquid flow rate. Therefore, the method of the present invention can actively and quantitatively change the radius of the generated droplets by adjusting these two operating parameters. This allows for precise control and the acquisition of condensation nuclei with specific charge-to-mass ratios. Therefore, alkaline droplets carrying a second polarity (positive polarity) charge and with a controllable charge-to-mass ratio, generated using the above method, are subsequently injected into flue gas containing negatively charged SO3 aerosols, preparing for the next step of heteropolar condensation in a traveling wave electric field.

[0064] At this point, the physical properties of the final generated droplets can be controlled by precisely adjusting the key operating parameters of the electrohydrodynamic atomization (EHDA) system.

[0065] In one embodiment of the present invention, the key operating parameters mainly include two: the injection voltage applied to the atomizing nozzle. The flow rate of the alkaline solution supplied by the precision liquid delivery device, and the combined changes in these two parameters, directly affect the stability of the Taylor cone jet mode at the nozzle tip, the jet diameter, and the state of the jet after breakup. The physical principle is that changes in the injection voltage and liquid flow rate ultimately affect the radius of the generated alkaline droplets. Above. And the radius of the droplet Its charge and quality All of them have definite physical relationships.

[0066] As mentioned earlier, the charge of microdroplets Its Rayleigh limit Related, while the Rayleigh limit is the radius The function; simultaneously, the mass of the droplet Also determined by its radius and liquid density The charge-to-mass ratio of a droplet is determined by its radius. There exists a definite functional relationship, namely the simplified formula for the charge-to-mass ratio derived above:

[0067] ;

[0068] Therefore, based on the above relationships, the method of the present invention can adjust the injection voltage by sending commands to the high-voltage power supply and liquid delivery device of the EHDA system. And the liquid flow rate. In this way, the radius of the generated droplets can be actively and quantitatively changed. This allows for precise control and the acquisition of condensation nuclei with specific charge-to-mass ratios.

[0069] Based on the active control of the charge-to-mass ratio of the condensation nuclei, the method of the present invention includes a method for injecting condensation nuclei, which achieves synergistic effect by linking the generation of condensation nuclei with the operating state of the subsequent traveling wave electric field.

[0070] Specifically, this method employs a pulsed injection approach synchronized with the traveling wave electric field phase. This pulsed injection generates the driving signal for the traveling wave electric field and controls the operation of the electrohydrodynamic atomization (EHDA) system. Specifically, it acquires or calculates the potential phase of the traveling wave electric field at any location in space in real time. The potential distribution of the traveling wave electric field along the airflow direction (z-axis) is shown. It can be described by the following formula:

[0071] ;

[0072] In the formula, The potential amplitude, Angular frequency ( , (driving frequency) wave vector ( , (for spatial wavelength) For time, These are the position coordinates along the airflow direction.

[0073] During pulse injection, the axial position coordinates of the EHDA nozzle can be controlled via the control system. Based on this, continuously monitor the real-time potential phase at this point: In the formula, The real-time potential phase representing the nozzle position; This represents the angular frequency of the traveling wave electric field. For time; The wave vector (or wave number) represents the electric field of a traveling wave.

[0074] Furthermore, one or more trigger phase windows can be preset; for example, a phase window can be set to... This window corresponds to the trough of the traveling wave potential or its vicinity. When the system monitors the real-time phase... When the preset trigger phase window is entered, a trigger command can be sent to the high-voltage power supply of the EHDA system. This command causes the power supply to output a high-voltage pulse within a very short time (e.g., milliseconds), thereby driving the EHDA nozzle to eject a discrete cloud of positively charged alkaline droplets. Outside the phase window, the EHDA system is in a non-ejection state. This control logic can be expressed by the following equation:

[0075] ;

[0076] In the formula, This is a trigger signal; a value of 1 indicates that injection is triggered, and a value of 0 indicates that injection is not triggered. Represents modulo operation; This indicates the pre-set trigger phase window; Indicates the starting phase of the trigger phase window. This indicates the end phase of the trigger phase window.

[0077] Therefore, this phase-synchronized pulse injection method ensures that each newly formed basic condensation nucleus is always introduced at a predetermined, optimal electric field phase. For example, after injection at a potential trough, the particles will immediately be subjected to the strong electric field force generated by the subsequent potential peak, thereby obtaining maximum initial acceleration and sweeping momentum. This avoids the energy waste and reduced condensation efficiency caused by injection at an inoptimal phase.

[0078] After the alkaline condensation nuclei are injected into the flue gas using the phase synchronization method described above, the mixture of flue gas and condensation nuclei then enters the traveling wave electric field region. At this point, the present invention proceeds to step S3, which involves using the traveling wave electric field to drive electro-induced sweeping condensation between particles.

[0079] Specifically, the physical structure of this traveling wave electric field section mainly consists of multiple electrode arrays arranged sequentially along the airflow direction. These electrode arrays can be installed on the inner wall of the flue gas channel or span the entire channel. The electrodes can be rod-shaped, ring-shaped, or parallel plate-shaped electrodes, and their specific form and size are determined according to the channel geometry and process requirements. In this embodiment, multiple sets of parallel rod-shaped electrodes are preferably used, with a fixed spatial spacing between each set of electrodes.

[0080] To construct the traveling wave electric field, these electrode arrays are powered by a multiphase AC power supply. In one specific embodiment, this power supply is an N-phase AC power supply, where N is an integer greater than or equal to 3. Preferably, a three-phase or four-phase AC power supply can be used, as this type of power supply is a mature technology in the industrial field. Specifically, the N-phase voltages have the same amplitude, but their phases lag behind each other by a fixed angle (e.g., 120° for a three-phase power supply; 90° for a four-phase power supply).

[0081] The electrode array is connected sequentially to the output terminals of the N-phase power supply. For example, if a three-phase power supply (phases A, B, and C) is used, then the first, fourth, seventh, and so on groups of electrodes are connected to phase A, the second, fifth, and eighth, and so on groups of electrodes are connected to phase B, and the third, sixth, and ninth, and so on groups of electrodes are connected to phase C.

[0082] Therefore, through this kind of excitation, the periodic changes in potential on each electrode group are sequentially transmitted in space, thereby constructing a periodically changing potential field that propagates in space along the airflow direction (defined as the z-axis) inside the channel, i.e., a traveling wave electric field. Thus, the potential distribution of this electric field... It can be described by the following formula:

[0083] ;

[0084] In the formula, Angular frequency ( , The driving frequency is determined by the AC power supply. wave vector ( , (The wavelength is spatial, determined by the physical arrangement of the electrode array). For time, These are the position coordinates along the airflow direction; It represents the magnitude of the electric potential.

[0085] The aforementioned traveling wave electric field forms the physical basis for the subsequent implementation of electro-induced sweeping condensation, and its field strength, frequency, and wavelength provide adjustable variables for the subsequent adaptive resonant control system.

[0086] After the traveling wave electric field is constructed, particles carrying two opposite polarities of charge (i.e., negatively charged SO3 aerosol and positively charged alkaline condensation nuclei) enter the electric field region. Since the traveling wave electric field applies different electric forces to charged particles with different properties, it drives violent relative motion between particles on a macroscopic scale, thereby achieving efficient collisional condensation.

[0087] Specifically, when a charge-carrying quantity is When a particle enters the traveling wave electric field region, the electric force it experiences... It is its charge quantity and the electric field strength at that point The product of the electric field strength and the electric potential, where the electric field strength is the electric potential. Spatial gradient:

[0088] ;

[0089] In the formula, Represents the electric field intensity vector of a traveling wave; Represents electric potential The negative gradient; electric potential For position coordinates The partial derivative represents the rate of change of electric potential along the direction of airflow; It is a unit vector along the direction of airflow;

[0090] Therefore, the electric force on the particle for:

[0091] ;

[0092] In the formula, It is a unit vector along the direction of airflow; This represents the amount of charge carried by the particle.

[0093] Regarding the two types of particles in this method: SO3 aerosol (carrying a negative charge) ) and basic condensate nuclei (carrying positive charges) At any time and at any location, the direction of the electric force is opposite.

[0094] Therefore, the motion of particles in flue gas is determined by the net external force acting on them. The Lagrange method is used to describe the motion of a single particle; its equations of motion follow Newton's second law, primarily considering electric force and fluid resistance.

[0095] ;

[0096] in, For particle mass, For particle velocity, For the aforementioned traveling wave electric field force, This refers to the fluid resistance of the flue gas to the particles. Fluid resistance... The Stokes drag formula is typically used to describe this, with slip corrections applied for submicron particles. The formula is expressed as:

[0097] ;

[0098] In the formula, The dynamic viscosity of the flue gas. The particle diameter is For the flue gas velocity, This is the slip correction factor. The calculation formula is:

[0099] ;

[0100] In the formula, The mean free path of gas molecules, , , This is an empirical constant.

[0101] Furthermore, because SO3 aerosols and alkaline condensates have opposite polarities and significant differences in mass, particle size, and charge, their charge-to-mass ratios are completely different. Therefore, under the same traveling wave electric field, the motion responses (i.e., acceleration and velocity) of these two types of particles differ greatly. This directly leads to violent and large-amplitude relative motion between the two particle groups on a macroscopic scale.

[0102] This relative motion, actively driven by an external electric field, can significantly increase the collision frequency between particles of opposite polarity, thereby accelerating the agglomeration process. This mechanism transforms particle agglomeration from a passive process dependent on slow Brownian diffusion or turbulent shearing into an active sweeping and capture process dominated by the electric field, thus enabling the removal of submicron-sized SO3 aerosols.

[0103] After completing the electro-sweeping agglomeration of particles, the method of this invention proceeds to step S4, which involves real-time monitoring of the efficiency of the agglomeration process to provide a basis for subsequent closed-loop control. Specifically, the agglomeration process is electrically manifested as a neutralization process of opposite polarity charges. That is, negatively charged SO3 aerosols collide and react with positively charged alkaline agglomeration nuclei to form large particles that are electrically neutral or have a significantly reduced charge. Therefore, by measuring the net space charge density remaining in the flue gas after agglomeration, the degree of completion of the agglomeration reaction can be directly determined. The closer the net space charge density is to zero, the more complete the charge neutralization and the higher the agglomeration efficiency.

[0104] In this embodiment of the invention, a condensation efficiency monitoring unit is installed downstream of the traveling wave electric field region within the flue gas channel. In a preferred embodiment, the monitoring unit may specifically be a non-contact space charge density sensor. Therefore, when flue gas carrying a net charge flows through these induction electrodes, equal and opposite charges are induced on the electrode surface through electrostatic induction, thereby forming a detectable induced current in the external measurement circuit connected to the electrodes. The magnitude of the induced current is related to the net space charge density of the flue gas flowing through it. They are directly proportional, and the expression is:

[0105] ;

[0106] In the formula, The induced current is measured in real time; The real-time net space charge density of the flue gas flowing through the sensor area is the algebraic sum of the positive and negative charge densities. For the flue gas velocity; This represents the effective sensing area of ​​the sensing electrode.

[0107] The measuring circuit will measure the induced current. After signal conditioning (such as amplification and filtering), a real-time feedback signal proportional to the net space charge density is output. .

[0108] The real-time feedback signal This can then serve as the input for implementing the next step of adaptive resonant closed-loop control. Therefore, in this way, the method of the present invention can continuously evaluate the coagulation efficiency online, thus providing a foundation for achieving dynamic optimization of the system.

[0109] Upon receiving real-time feedback signals Then, the method of the present invention implements step S5, which, by constructing an adaptive resonance optimization closed-loop control, ensures that the changes in the entire condensation operation are always at the optimal efficiency point.

[0110] Specifically, the ultimate optimization goal of this closed-loop control is to optimize the feedback signal. absolute value Minimize. Specifically, this control logic can be executed by, for example, a programmable logic controller (PLC), a field-programmable gate array (FPGA), or an industrial control computer. This is achieved by receiving feedback signals. As input, and based on the set optimization algorithm, two key operating parameters are dynamically adjusted as output:

[0111] The driving frequency of the multiphase AC power supply applied to the traveling wave electric field electrode array .

[0112] Injection voltage applied to the electrohydrodynamic atomization (EHDA) nozzle Adjusting this voltage, as mentioned earlier, will change the radius of the generated basic condensation nuclei. This indirectly controls its charge-to-mass ratio. .

[0113] In one specific implementation, the optimization algorithm employs a perturbation-observation method or a similar hill-climbing algorithm, which are well-known techniques in the field of control. The control process is as follows: For a preset time period, one of the control parameters (e.g., drive frequency) is adjusted... Apply a small, pre-set perturbation. After the disturbance is applied, the feedback signal from the downstream monitoring unit will be sampled and analyzed immediately. The changes.

[0114] If the disturbance causes the absolute value of the feedback signal to decrease A decrease indicates that the adjustment is in the correct direction towards the optimal point. Therefore, in the next control cycle, the parameter will continue to be adjusted in this direction.

[0115] Conversely, if the disturbance leads to An increase indicates that the adjustment has deviated from the optimal point. Therefore, in the next control cycle, the adjustment will be made in the opposite direction.

[0116] Thus, through a process of perturbation, observation, and decision-making, it is periodically applied to the driving frequency. and injection voltage Regarding these two control parameters, in a preferred embodiment, the two-dimensional optimization process can employ an alternating optimization strategy: first, fix... By perturbation Find the current optimal frequency Then fix for Then through perturbation Find the current optimal voltage Repeat this alternating process until a feedback signal is received. The absolute value converges to a minimum. In this way, the method of the present invention can be applied in a two-dimensional parameter space ( ) to perform continuous optimization search in order to lock in the global or local optimal working point.

[0117] Therefore, this invention can specify a driving frequency that enables negatively charged SO3 aerosols and positively charged alkaline condensation nuclei to generate maximum relative velocity in a traveling wave electric field under specific flue gas conditions (such as temperature, flow rate, particulate matter concentration, etc.), thereby achieving the highest condensation efficiency. ratio of charge to mass The combination point;

[0118] Finally, the present invention performs the end-of-pipe dust removal stage. At this time, the agglomerated and grown particles are collected with the flue gas in the downstream bag filter or electrostatic precipitator, thereby completing the SO3 removal process.

Claims

1. A method for removing SO3 from coal-fired flue gas by electrostatic condensation, characterized in that, Includes the following steps: Step S1, Pre-charging step: Treat the flue gas containing SO3 aerosol so that the SO3 aerosol carries a first polar charge; Step S2, Generation and Injection Step: Using electrohydrodynamic atomization, the alkaline solution is atomized into alkaline microdroplets carrying a second polarity charge, and the alkaline microdroplets are injected into the flue gas treated in step S1. The polarity of the second polarity charge is opposite to that of the first polarity charge. Step S3, Coagulation Step: The flue gas mixed with the SO3 aerosol carrying the first polarity charge and the alkaline droplets carrying the second polarity charge is flowed through the traveling wave electric field region. The traveling wave electric field drives the two types of particles to move relative to each other, thereby coagulating to form particles with increased particle size. Step S4: Monitor the flue gas after step S3 in real time to obtain a real-time feedback signal reflecting the condensation efficiency. Step S5: Based on the real-time feedback signal, the operating parameters are dynamically adjusted through adaptive resonance optimization closed-loop control to ensure that the coagulation efficiency is at the optimal efficiency point. The real-time monitoring specifically involves: measuring the net space charge density of the flue gas through a condensation efficiency monitoring unit, and using a signal proportional to the net space charge density as the real-time feedback signal; In step S5, the adaptive resonance optimization closed-loop control uses an optimization algorithm to minimize the absolute value of the real-time feedback signal as the optimization objective.

2. The method for electrostatic condensation and removal of SO3 from coal-fired flue gas according to claim 1, characterized in that, In step S5, the dynamic adjustment of operating parameters includes: the driving frequency of the multiphase AC power supply applied to the traveling wave electric field electrode array; and the injection voltage used to change the physical properties of the alkaline microdroplets.

3. The method for electrostatic condensation and removal of SO3 from coal-fired flue gas according to claim 2, characterized in that, The injection voltage and the liquid flow rate of the alkaline solution are used to change the radius of the generated alkaline droplets, thereby precisely controlling their charge-to-mass ratio.

4. The method for electrostatic condensation and removal of SO3 from coal-fired flue gas according to claim 1, characterized in that, In step S2, the alkaline droplets are injected using a pulsed injection method that is synchronized with the potential phase of the traveling wave electric field.

5. The method for electrostatic condensation and removal of SO3 from coal-fired flue gas according to claim 4, characterized in that, The pulse injection method specifically involves monitoring the real-time potential phase of the traveling wave electric field at the atomizing nozzle position, and triggering pulse injection when the real-time potential phase enters a preset trigger phase window corresponding to a potential trough.

6. The method for electrostatic condensation and removal of SO3 from coal-fired flue gas according to claim 1, characterized in that, In step S2, the alkaline solution is a sodium hydroxide solution or ammonia solution with a mass fraction of 5% to 20%.

7. The method for electrostatic condensation and removal of SO3 from coal-fired flue gas according to claim 1, characterized in that, In step S3, the traveling wave electric field is constructed by an N-phase AC power supply, where N is an integer greater than or equal to 3.

8. The method for electrostatic condensation and removal of SO3 from coal-fired flue gas according to claim 1, characterized in that, Step S1 specifically includes: applying a negative polarity DC high voltage to the discharge electrode to generate corona discharge, so that the SO3 aerosol is saturated with negative charge under the action of electric field charging and diffusion charging, and the negative charge is the first polarity charge.

Images