Metal filter bag dust removal and flue gas powder injection conditioning integrated method for biomass boiler

Abstract

The application discloses a biomass boiler metal filter bag dust removal and flue gas powder injection conditioning integrated method, and particularly relates to the technical field of flue gas purification; the method is characterized in that the hydrogen chloride concentration, the sulfur dioxide concentration and the potassium-containing and chlorine-containing fly ash concentration at the metal filter bag inlet are detected, the falling ash samples between two times of ash removal are collected, the soluble chlorine of the falling ash samples is determined, the constant humidity weight gain is determined, the surface soluble chlorine difference and the constant humidity weight gain difference are obtained, the deliquescent salt conversion window is determined according to the surface soluble chlorine difference and the constant humidity weight gain difference, the inert coarse powder pre-layer is constructed on the surface of the metal filter bag, the conditioning powder is injected to the upstream of the inert coarse powder pre-layer, the conditioning powder and the potassium-containing and chlorine-containing fly ash form the reactive filter cake outside the inert coarse powder pre-layer, and the state of the reactive filter cake is determined according to the differential pressure growth rate, the differential pressure recovery rate after the ash removal and the ash sample conductivity, and the conditioning powder injection parameters and the pulse ash removal interval are adjusted according to the state of the reactive filter cake.

Description

Technical Field

[0001] This invention relates to the field of flue gas purification technology, and more specifically, to an integrated method for dust removal using metal filter bags and flue gas powder injection conditioning in biomass boilers. Background Technology

[0002] The flue gas generated during the combustion of biomass boilers typically contains fly ash, chlorides, acidic gases, and condensable salts. Flue gas purification processes often employ a combination of powder injection conditioning and baghouse dust collection. Powder injection conditioning generally involves introducing alkaline powder, adsorbent powder, or mineral powder into the flue gas before the metal filter bag inlet. This allows the powder to contact the acidic components and fly ash in the flue gas, and unreacted powder, reaction products, and fly ash are all retained by the metal filter bag. The filter cake layer formed on the surface of the metal filter bag not only retains particulate matter but also participates in the adsorption, neutralization, and deposition processes of some flue gas components. Therefore, the state of the filter cake layer affects the coordinated operation of the powder injection conditioning process and the metal filter bag filtration process.

[0003] In existing integrated processes of flue gas pulverization and conditioning in biomass boilers and dust removal using metal filter bags, the pulverization and conditioning process and the filter cake filtration process are mostly controlled by their respective operating indicators, lacking targeted regulation of the coupled deposition state between the injected powder, potassium- and chlorine-containing fly ash, and the filter cake on the surface of the metal filter bag. Summary of the Invention

[0004] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide an integrated method for dust removal by metal filter bags and flue gas powder injection conditioning for biomass boilers to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for integrating metal filter bag dust collection and flue gas powder injection conditioning in a biomass boiler includes the following steps: S1: Detect the concentrations of hydrogen chloride, sulfur dioxide, and potassium- and chlorine-containing fly ash at the inlet of the metal filter bag, and collect ash samples between two cleaning cycles; S2: The soluble chlorine content and constant humidity weight gain of the ash sample were measured to obtain the difference in soluble chlorine content on the surface and the difference in constant humidity weight gain. S3: Determine the conversion window of hygroscopic salts based on the difference in soluble chlorine on the surface and the difference in weight gain under constant humidity, and construct an inert coarse powder pre-formed layer on the surface of the metal filter bag; S4: According to the deliquescent salt conversion window, the conditioning powder is sprayed upstream of the inert coarse powder preformed layer, so that the conditioning powder and potassium- and chlorine-containing fly ash form a reactive filter cake on the outside of the inert coarse powder preformed layer. S5: Collect the pressure difference growth rate, pressure difference recovery rate after ash removal, and conductivity of the ash sample during the growth process of the reactive filter cake, and combine them with the surface soluble chlorine difference and constant humidity weight gain difference to determine the state of the reactive filter cake. S6: Divide the reactive filter cake into three stages: cake formation, cake retention, and cake removal, and adjust the conditioning powder injection parameters and pulse cleaning intervals accordingly.

[0006] In a preferred embodiment, the concentrations of hydrogen chloride, sulfur dioxide, and potassium- and chloride-containing fly ash at the inlet of the metal filter bag are detected, and ash samples are collected between two cleaning cycles. Specifically: The sampling interval is defined as the filtration operation period between two adjacent ash cleaning cycles. The concentrations of hydrogen chloride, sulfur dioxide, and potassium- and chlorine-containing fly ash in the inlet flue gas are continuously measured at the metal filter bag inlet flue. Ash samples from the corresponding sampling interval are collected during the ash discharge process in the ash hopper.

[0007] In a preferred embodiment, the soluble chlorine content of the ash sample is determined by measurement of soluble chlorine and weight gain under constant humidity, and the differences in soluble chlorine content and weight gain under constant humidity are obtained. Specifically: The ash samples collected within the sampling area were divided into front section ash samples and back section ash samples according to the order of ash discharge. The surface soluble chlorine extraction and weight gain under constant humidity conditions were determined for the front and rear ash samples, respectively. The results of surface soluble chlorine extraction and weight gain under constant humidity conditions were obtained for the front and rear ash samples. The difference between the surface soluble chlorine determination results of the first and second ash samples is defined as the surface soluble chlorine difference value. The difference between the weight gain measurements of the first and second ash samples under constant humidity conditions is defined as the constant humidity weight gain difference.

[0008] In a preferred embodiment, the deliquescent salt conversion window is determined based on the difference in soluble chlorine content on the surface and the difference in weight gain under constant humidity, and an inert coarse powder pre-formed layer is constructed on the surface of the metal filter bag, specifically as follows: The differences in soluble chlorine concentration at the inlet surface and the differences in weight gain at constant humidity were compared with each sampling interval. The sampling interval in which the differences in soluble chlorine concentration at the inlet surface continuously increased and the differences in weight gain at constant humidity increased synchronously was determined as the deliquescent salt conversion window. During the filtration operation period corresponding to the deliquescent salt conversion window, inert coarse powder is sprayed into the inlet side of the metal filter bag, so that the inert coarse powder is deposited on the surface of the metal filter bag to form a continuous inert coarse powder pre-formed layer.

[0009] In a preferred embodiment, the starting point of the sampling interval that first satisfies the effective increase among multiple consecutive sampling intervals is taken as the starting point of the hygroscopic salt conversion window, and the ending point of the sampling interval that last satisfies the synchronous increase among multiple consecutive sampling intervals is taken as the ending point of the hygroscopic salt conversion window.

[0010] In a preferred embodiment, conditioning powder is sprayed upstream of the inert coarse powder preform layer according to the hygroscopic salt conversion window, so that the conditioning powder and potassium- and chlorine-containing fly ash form a reactive filter cake on the outside of the inert coarse powder preform layer, specifically: During the filtration operation period corresponding to the hygroscopic salt conversion window, conditioning powder is continuously sprayed upstream of the inert coarse powder preformed layer. The conditioning powder is then mixed with hydrogen chloride, sulfur dioxide, and potassium- and chlorine-containing fly ash in the inlet flue gas along the flow direction of the inlet flue gas. The mixed conditioning powder and potassium- and chlorine-containing fly ash adhere to the outside of the inert coarse powder preformed layer and continue to deposit, forming a reactive filter cake.

[0011] In a preferred embodiment, the upstream of the inert coarse powder preformed layer refers to the flue gas duct area on the inlet side of the metal filter bag that the inlet flue gas passes through before reaching the inert coarse powder preformed layer.

[0012] In a preferred embodiment, the reactive filter cake is a deposit formed by the contact of conditioning powder, potassium- and chlorine-containing fly ash, and hydrogen chloride and sulfur dioxide in the inlet flue gas.

[0013] In a preferred embodiment, the pressure differential growth rate during the reactive filter cake growth process, the pressure differential recovery rate after ash removal, and the conductivity of the ash sample are collected. The state of the reactive filter cake is determined by combining the surface soluble chlorine difference and the constant humidity weight gain difference. Specifically: During the continuous deposition of reactive filter cake, the change in filtration differential pressure with the duration of filtration operation is recorded, and the rate of differential pressure increase is determined based on the change in filtration differential pressure. After pulse cleaning is completed, record the filtration pressure difference before cleaning and the stable filtration pressure difference after cleaning. Determine the pressure difference recovery rate after cleaning based on the filtration pressure difference before cleaning and the stable filtration pressure difference after cleaning. Ash samples were collected for the corresponding filtration operation period, and their conductivity was measured to obtain the conductivity of the ash samples. The pressure difference growth rate, pressure difference recovery rate after ash removal, difference between ash sample conductivity and surface soluble chlorine, and difference in weight gain under constant humidity were compared according to the sampling interval to determine the state of the reactive filter cake.

[0014] In a preferred embodiment, the reactive filter cake is divided into a cake-forming stage, a cake-holding stage, and a cake-removing stage according to its state, and the conditioning powder injection parameters and pulse cleaning interval are adjusted accordingly. The state of the reactive filter cake where the differential pressure growth rate continues to increase and the differential pressure recovery rate remains high after dust removal is defined as the cake formation stage. During the cake formation stage, the conditioning powder is continuously injected and pulse dust removal is delayed. The state of the reactive filter cake when the pressure difference growth rate tends to be stable and the change in the conductivity of the ash sample slows down is defined as the cake preservation stage. During the cake preservation stage, the conditioning powder is stably injected and pulse cleaning is carried out at fixed intervals. The state of reactive filter cake where the differential pressure recovery rate decreases and the conductivity of the ash sample continues to increase after cleaning is defined as the cake stripping stage. During the cake stripping stage, the amount of conditioning powder injected is reduced and the pulse cleaning interval is shortened.

[0015] The technical effects and advantages of the integrated method for dust removal and flue gas powder injection conditioning of the present invention for biomass boilers are as follows: By correlating the surface soluble chlorine difference and constant humidity weight gain difference of ash samples with the pressure difference growth rate of reactive filter cake, pressure difference recovery rate after ash removal, and ash sample conductivity, the deposition evolution of potassium- and chlorine-containing fly ash, acidic gases, and conditioning powders in biomass boiler flue gas on the surface of metal filter bags can be identified in stages. The timing of inert coarse powder preform construction is determined by the hygroscopic salt conversion window, ensuring the inert coarse powder preform is located between the metal filter bag surface and the reactive filter cake, thus reducing the direct embedding of potassium- and chlorine-containing fly ash and conditioning powders into the metal. The porosity of the filter bag surface; by forming a reactive filter cake on the outside of the inert coarse powder pre-formed layer, the contact deposition process of the conditioning powder with hydrogen chloride, sulfur dioxide and potassium- and chlorine-containing fly ash is concentrated in the cleanable filter cake area; by dividing the state of the reactive filter cake into the cake formation stage, the cake retention stage and the cake peeling stage, and adjusting the conditioning powder injection parameters and pulse cleaning interval accordingly, the coordination between powder conditioning, filter cake permeability and cleaning regeneration can be improved, thereby improving the operating pressure differential stability and long-term operating reliability of the metal filter bag. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of an integrated method for dust removal and flue gas powder injection conditioning of a biomass boiler according to the present invention. Figure 2 This is a schematic diagram of an integrated device for dust removal and flue gas powder injection conditioning of metal filter bags for biomass boilers. Detailed Implementation

[0017] The technical solutions of 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] Example, Figure 1 This invention discloses an integrated method for dust removal using metal filter bags and flue gas powder injection conditioning in biomass boilers, comprising the following steps: S1: Detect the concentrations of hydrogen chloride, sulfur dioxide, and potassium- and chlorine-containing fly ash at the inlet of the metal filter bag, and collect ash samples between two cleaning cycles; S2: The soluble chlorine content and constant humidity weight gain of the ash sample were measured to obtain the difference in soluble chlorine content on the surface and the difference in constant humidity weight gain. S3: Determine the conversion window of hygroscopic salts based on the difference in soluble chlorine on the surface and the difference in weight gain under constant humidity, and construct an inert coarse powder pre-formed layer on the surface of the metal filter bag; S4: According to the deliquescent salt conversion window, the conditioning powder is sprayed upstream of the inert coarse powder preformed layer, so that the conditioning powder and potassium- and chlorine-containing fly ash form a reactive filter cake on the outside of the inert coarse powder preformed layer. S5: Collect the pressure difference growth rate, pressure difference recovery rate after ash removal, and conductivity of the ash sample during the growth process of the reactive filter cake, and combine them with the surface soluble chlorine difference and constant humidity weight gain difference to determine the state of the reactive filter cake. S6: Divide the reactive filter cake into three stages: cake formation, cake retention, and cake removal, and adjust the conditioning powder injection parameters and pulse cleaning intervals accordingly.

[0019] like Figure 2 As shown, this embodiment provides an integrated device for metal filter bag dust collection and flue gas powder injection conditioning for biomass boilers. The conditioning powder storage bin 1 is used to store inert coarse powder and conditioning powder. The powder feeding mechanism 2 is used to send inert coarse powder or conditioning powder into the pneumatic conveying pipeline 3. The pneumatic conveying pipeline 3 conveys the inert coarse powder or conditioning powder to the powder injection pipeline 4. The powder injection pipeline 4 is located upstream of the inlet flue of the metal filter bag dust collector 5. The pulse cleaning mechanism 6 is located on the upper part of the metal filter bag dust collector 5 and is used to perform pulse cleaning on the metal filter bags in the metal filter bag dust collector 5.

[0020] S1: Detect the concentrations of hydrogen chloride, sulfur dioxide, and potassium- and chloride-containing fly ash at the inlet of the metal filter bag, and collect ash samples between two cleaning cycles, including: Before testing the concentrations of hydrogen chloride, sulfur dioxide, and potassium- and chlorine-containing fly ash in the inlet flue gas, the biomass boiler must be kept in a stable combustion state, and the metal filter bags must be in normal filtration operation. The filtration operation period between two adjacent ash cleaning cycles refers to the continuous filtration time period from the completion of one pulse ash cleaning action and the stabilization of the filtration pressure difference after cleaning until the start of the next pulse ash cleaning action. The sampling interval is defined according to the filtration operation period between two adjacent ash cleaning cycles. The starting point of the sampling interval is jointly confirmed by the pulse ash cleaning completion signal and the post-cleaning filtration pressure difference stabilization signal, and the ending point of the sampling interval is confirmed by the start signal of the next pulse ash cleaning. The pulse ash cleaning completion signal can be obtained from the pulse valve's end signal; the post-cleaning filtration pressure difference stabilization signal can be obtained from the continuous slowing of the filtration pressure difference between the inlet and outlet sides of the metal filter bag; and the next pulse ash cleaning start signal can be obtained from the pulse valve's start signal.

[0021] The concentrations of hydrogen chloride, sulfur dioxide, and potassium- and chlorine-containing fly ash in the inlet flue gas were all measured within the inlet flue of the metal filter bag. The inlet flue of the metal filter bag refers to the section of the flue gas that represents the composition of the flue gas entering the metal filter bag, located before the injection point of the conditioning powder or before the gas collection point of the metal filter bag. The concentrations of hydrogen chloride and sulfur dioxide in the inlet flue gas were obtained through flue gas extraction, dust pretreatment, condensate separation, and gas concentration analysis. The flue gas extraction point was set in the stable flow region of the cross-section of the inlet flue of the metal filter bag, with the extraction pipe facing the direction of the inlet flue gas flow. The extraction process was continuous to ensure that the concentrations of hydrogen chloride and sulfur dioxide in the inlet flue gas corresponded to the sampling interval in time. The concentration of potassium- and chlorine-containing fly ash was obtained using isokinetic sampling, which means that the inlet gas velocity of the sampling nozzle is consistent with the inlet gas velocity of the flue gas at the sampling point within the inlet flue of the metal filter bag, so that the collected fly ash particles reflect the concentration of potassium- and chlorine-containing fly ash within the inlet flue of the metal filter bag. The potassium and chlorine-containing fly ash concentration is measured by fly ash particles in the inlet flue gas that contain both potassium and chlorine. The potassium and chlorine-containing fly ash concentration can be calculated by collecting fly ash particles, weighing the fly ash particles, and determining the potassium and chlorine content in the fly ash particles.

[0022] When continuously monitoring the concentrations of hydrogen chloride, sulfur dioxide, and potassium- and chlorine-containing fly ash in the inlet flue gas, the data obtained within the sampling interval are saved according to the monitoring time. The time records for these data are consistent with the start and end points of the sampling interval. If an interval monitoring method is used, the time between adjacent monitoring points is used as the data retention time, and all monitoring points within the sampling interval are used to form inlet flue gas hydrogen chloride concentration sequences, sulfur dioxide concentration sequences, and potassium- and chlorine-containing fly ash concentration sequences. If a continuous online monitoring method is used, the continuous online monitoring results are saved at the same time intervals to form inlet flue gas hydrogen chloride concentration sequences, sulfur dioxide concentration sequences, and potassium- and chlorine-containing fly ash concentration sequences. Inlet flue gas hydrogen chloride concentration sequences, sulfur dioxide concentration sequences, and potassium- and chlorine-containing fly ash concentration sequences corresponding to the same sampling interval are considered as the same set of inlet flue gas monitoring results.

[0023] During the ash hopper discharge process, ash samples corresponding to the sampling interval are collected. The ash hopper discharge process refers to the process where deposits on the surface of the metal filter bags are removed by the cleaning action, enter the ash hopper, and are discharged through the ash hopper discharge port. To ensure that the ash samples correspond to the sampling intervals, after confirming the start point of the sampling interval, the path for residual ash from the previous sampling interval to enter the sampling container is closed or isolated. After the sampling interval ends and the next pulse cleaning is completed, the ash sample collection path is opened, allowing the ash discharged from the ash hopper discharge port to enter the collection container corresponding to the sampling interval. The collection container is kept dry before use, and the empty container's mass is recorded. The collection container is sealed after the ash samples enter to prevent environmental moisture from altering the moisture content of the ash samples. The start time of ash sample collection is defined as the start of ash discharge from the ash hopper discharge port corresponding to the sampling interval, and the end time of ash sample collection is defined as the ash hopper discharge port ceasing to discharge ash corresponding to the sampling interval.

[0024] After the ash samples are collected, they are homogenized and then aliquoted for storage. Homogenization can be performed by gently turning the samples over in a sealed container. For aliquoting, the ash samples are placed in a sealed container, and the starting and ending points of the sampling interval, the sequence number of the inlet flue gas hydrogen chloride concentration, sulfur dioxide concentration, potassium- and chlorine-containing fly ash concentration, and the ash sample number are recorded on the outside of the sealed container.

[0025] S2: The soluble chlorine content and constant humidity weight gain of the ash samples were determined to obtain the surface soluble chlorine difference and constant humidity weight gain difference, including: Read the starting point, ending point, and ash sample number of the sampling interval, and confirm that the ash sample number corresponds to the inlet flue gas hydrogen chloride concentration sequence, sulfur dioxide concentration sequence, and potassium- and chlorine-containing fly ash concentration sequence within the same sampling interval. Ash samples collected within the sampling interval are segmented according to the order of ash discharge. The ash portion that first enters the collection container after ash discharge begins is defined as the first ash sample, and the ash portion that last enters the collection container before the end of ash discharge is defined as the second ash sample. The segmentation can be based on the median of the cumulative ash discharge mass. Ash collected before the cumulative ash discharge mass reaches the median of the total ash sample mass is classified as the first ash sample, and ash collected after the cumulative ash discharge mass reaches the median of the total ash sample mass is classified as the second ash sample. The first and second ash samples are placed in sealed containers and the same sampling interval number is recorded.

[0026] When performing surface soluble chlorine extraction on a front-end ash sample, the sample is gently spread in a dry, clean, flat-bottomed container to form a uniform sample layer. The thickness of the sample layer is determined based on the particle size of the ash sample and the spreading area, ensuring continuous contact between the sample layer surface and the sampling scraper. For example, the sample layer thickness can be set to 3 mm to 10 mm. The surface layer in the surface soluble chlorine extraction determination refers to the exposed particle layer of the sample layer away from the bottom of the flat-bottomed container. The surface layer can be obtained by scraping parallel to the exposed surface of the sample layer with a sampling scraper. The scraping depth is determined based on the sample layer thickness and the particle size of the ash sample, ensuring that the scraped material mainly comes from the exposed particle layer of the sample layer. For example, the scraping depth can be set to 0.5 mm to 2 mm. After weighing the obtained surface layer of the front-end ash sample, it is added to a measured amount of deionized water for extraction. The extraction process is carried out using a closed oscillation or closed stirring method, allowing the water-soluble chlorides in the surface layer of the front-end ash sample to enter the extraction solution. After settling or filtration, the extract yields a soluble chlorine extract from the surface layer of the ash sample. The soluble chlorine content of the surface layer of the ash sample is determined by chloride ion selective electrode determination, ion chromatography, or silver nitrate titration. The soluble chlorine content of the surface layer of the ash sample is expressed as the chloride ion mass per unit mass of the surface portion of the ash sample.

[0027] When determining the soluble chlorine extraction from the surface layer of the ash sample in the later stage, the same spreading thickness, scraping depth, extraction water volume, extraction time, and measurement method as for the earlier stage ash sample were used. The later stage ash sample was gently spread in a dry, clean, flat-bottomed container, and the surface layer was obtained by scraping parallel to the exposed surface of the sample layer with a sampling scraper. The surface layer of the later stage ash sample was weighed and added to the same volume of deionized water as the surface layer of the earlier stage ash sample for extraction. After the soluble chlorine extraction solution from the surface layer of the later stage ash sample underwent the same static sedimentation or filtration treatment, chloride ion determination was performed to obtain the soluble chlorine determination result for the surface layer of the later stage ash sample. The soluble chlorine determination result for the surface layer of the later stage ash sample is expressed as the chloride ion mass per unit mass of the surface layer of the later stage ash sample. The soluble chlorine determination results for the surface layer of the earlier and later stage ash samples were recorded using the same units and the same decimal places.

[0028] When determining the weight gain of the ash sample under constant humidity conditions, a weight gain test sample of equal mass is taken from the ash sample. The initial mass of the weight gain test sample is weighed before the measurement. Constant humidity conditions refer to the environmental conditions under which the relative humidity of the air inside the measuring container is maintained within a preset humidity range for the set measurement time. Constant humidity conditions can be formed by setting a saturated salt solution, humidity regulating liquid, or humidity-controlled airflow in a sealed container. The preset humidity range is determined based on the hygroscopic risk of salts in the biomass boiler flue gas and the storage state of the ash sample. The preset humidity range should be higher than the humidity of the ash sample storage environment but lower than the humidity that would cause liquid water to condense directly on the sample surface. For example, the preset humidity range can be set to a relative humidity of 70% to 90%. The measurement time is determined based on the time required for the mass change of the weight gain test sample to slow down, and the measurement time should cover the main stage of the hygroscopic mass increase of the weight gain test sample. For example, the measurement time can be set to 2 hours to 24 hours. After the initial mass of the ash sample is placed under constant humidity conditions for the measurement time, the final mass is weighed. The difference between the final mass and the initial mass of the ash sample is converted into the mass increase per unit mass of the ash sample, thus obtaining the mass increase result of the ash sample under constant humidity conditions.

[0029] When determining the weight gain of the subsequent gray section sample under constant humidity conditions, the same sample mass, preset humidity range, measurement time, and weighing conditions as the preceding gray section sample were used. The initial mass of the subsequent gray section sample was weighed before entering the constant humidity conditions, and the final mass was weighed after the measurement time was reached under constant humidity conditions. The difference between the final mass and the initial mass of the subsequent gray section sample was converted into the mass increase per unit mass of the subsequent gray section sample, yielding the weight gain measurement result under constant humidity conditions for the subsequent gray section sample. The weight gain measurement results of the preceding and subsequent gray section samples under constant humidity conditions were recorded using the same units. During the weighing process, the time from removing the preceding and subsequent gray section samples from the constant humidity conditions to completing the weighing was kept consistent to minimize the deviation caused by changes in external air humidity in the weight gain measurement results under constant humidity conditions.

[0030] The surface soluble chlorine difference is obtained by subtracting the surface soluble chlorine measurement result of the preceding ash-discharged sample from the surface soluble chlorine measurement result of the following ash-discharged sample. A positive surface soluble chlorine difference indicates that the following ash-discharged sample has a higher surface soluble chlorine measurement result compared to the preceding ash-discharged sample within the sampling interval; a negative surface soluble chlorine difference indicates that the following ash-discharged sample has a lower surface soluble chlorine measurement result compared to the preceding ash-discharged sample within the sampling interval; a zero surface soluble chlorine difference indicates that the preceding and following ash-discharged samples within the sampling interval have the same surface soluble chlorine measurement result. The surface soluble chlorine difference is recorded together with the sampling interval number, the preceding ash-discharged sample number, and the following ash-discharged sample number.

[0031] The constant humidity weight gain difference is obtained by subtracting the weight gain of the initial ash removal sample from the weight gain of the later ash removal sample under constant humidity conditions. A positive constant humidity weight gain difference indicates that the later ash removal section has a higher constant humidity condition than the earlier ash removal section within the sampling interval; a negative constant humidity weight gain difference indicates that the later ash removal section has a lower constant humidity condition than the earlier ash removal section within the sampling interval; and a zero constant humidity weight gain difference indicates that the earlier and later ash removal sections within the sampling interval have the same constant humidity condition.

[0032] S3: Determine the deliquescent salt conversion window based on the difference in soluble chlorine content and the difference in weight gain under constant humidity, and construct an inert coarse powder pre-layer on the surface of the metal filter bag, including: Each sampling interval corresponds to a difference in surface soluble chlorine and a difference in weight gain under constant humidity. Before comparison, multiple sampling intervals are arranged in chronological order of their start and end points. The differences in surface soluble chlorine and weight gain under constant humidity for each sampling interval are then entered into the same time series, forming a set of comparison data within the same sampling interval. If there are missing values ​​for surface soluble chlorine and weight gain under constant humidity, the corresponding sampling interval is not included in the determination of the deliquescent salt conversion window. Sampling intervals before and after the missing value sampling interval maintain their original time order and are included in the comparison.

[0033] A sustained increase in the surface soluble chlorine difference refers to a situation where, after arranging the sampling intervals sequentially, the surface soluble chlorine difference in the later sampling interval is greater than that in the earlier sampling interval, and this increasing trend appears across multiple consecutive sampling intervals. The number of consecutive sampling intervals is determined based on the cleaning frequency of the metal filter bags and the stability of the ash samples. The determination method is as follows: Under stable combustion conditions in the biomass boiler without the injection of inert coarse powder, several sampling intervals are selected as reference sampling intervals. The natural fluctuation range of the surface soluble chlorine difference within the reference sampling intervals is calculated, and then the number of consecutive sampling intervals that can eliminate misjudgments based on the natural fluctuation range is selected. For example, the number of consecutive sampling intervals can be set to 3. When the surface soluble chlorine difference in the later sampling interval is greater than that in the earlier sampling interval, and the increase is greater than the natural fluctuation range of the surface soluble chlorine difference within the reference sampling interval, it is confirmed that the surface soluble chlorine difference has effectively increased between two adjacent sampling intervals.

[0034] Synchronous increase in the constant humidity weight gain difference refers to a situation where, within the same sampling interval where the difference in surface soluble chlorine concentration effectively increases, the constant humidity weight gain difference in a later sampling interval is greater than that in a previous sampling interval, and this upward trend occurs across multiple consecutive sampling intervals with the same constant humidity weight gain difference. The determination of synchronous increase in the constant humidity weight gain difference involves using a reference sampling interval to determine the natural fluctuation range of the constant humidity weight gain difference, and then comparing the increase in the constant humidity weight gain difference between two adjacent sampling intervals with the natural fluctuation range of the constant humidity weight gain difference. If the constant humidity weight gain difference in a later sampling interval is greater than that in a previous sampling interval, and the increase is greater than the natural fluctuation range of the constant humidity weight gain difference within the reference sampling interval, then a synchronous increase in the constant humidity weight gain difference between two adjacent sampling intervals is confirmed. After both the surface soluble chlorine difference and the constant humidity weight gain difference increase synchronously, the starting point of the sampling interval that first meets the effective increase among multiple consecutive sampling intervals is taken as the starting point of the hygroscopic salt conversion window, and the ending point of the sampling interval that last meets the synchronous increase among multiple consecutive sampling intervals is taken as the ending point of the hygroscopic salt conversion window. The filtration operation period between the starting point and the ending point of the hygroscopic salt conversion window is the filtration operation period corresponding to the hygroscopic salt conversion window.

[0035] Inert coarse powder refers to powder that maintains its solid particle form within the temperature range of the flue gas inlet of the metal filter bag and mainly forms an interparticle support structure on the surface of the metal filter bag. Inert coarse powder can be selected from coarse particles screened from kaolin, diatomaceous earth, quartz sand powder, ceramic powder, or biomass boiler burnt-out ash. Before use, the inert coarse powder is dried and screened. The particle size of the inert coarse powder is determined based on the pore size of the metal filter bag surface, the particle size of potassium- and chlorine-containing fly ash, and the powder conveying capacity. The particle size determination method is as follows: measure the particle size distribution of potassium- and chlorine-containing fly ash, and then select particles with a particle size larger than the main particle size of the potassium- and chlorine-containing fly ash that can be conveyed to the surface of the metal filter bag with the inlet flue gas as inert coarse powder. To prevent inert coarse powder from directly entering the internal pores of the metal filter bag, the median particle size of the inert coarse powder can be larger than the median particle size of the potassium- and chlorine-containing fly ash. For example, the median particle size of the inert coarse powder can be set to 2 to 5 times the median particle size of the potassium- and chlorine-containing fly ash.

[0036] When inert coarse powder is injected into the inlet side of the metal filter bag during the filtration operation period corresponding to the deliquescent salt conversion window, the inert coarse powder enters the inlet flue gas from the flue on the inlet side of the metal filter bag and moves to the surface of the metal filter bag with the flow direction of the inlet flue gas. The injection position of the inert coarse powder is set at the inlet flue of the metal filter bag near the air inlet area of ​​the metal filter bag, so that the inert coarse powder completes lateral diffusion before entering the metal filter bag. The injection direction of the inert coarse powder can form an angle with the flow direction of the inlet flue gas, so that the inert coarse powder can be dispersed into the inlet flue gas cross section. The injection amount of inert coarse powder is determined according to the filtration area of ​​the metal filter bag and the duration of the deliquescent salt conversion window. The determination method is as follows: determine the required inert coarse powder deposition mass per unit filtration area based on the filtration area of ​​the metal filter bag, and then convert it into the inert coarse powder injection mass per unit time based on the duration of the deliquescent salt conversion window. The required inert coarse powder deposition mass per unit filtration area is determined by a short-time pre-spray test, which ends with the formation of a continuous inert coarse powder pre-layer on the surface of the metal filter bag. For example, the required amount of inert coarse powder deposited per unit filtration area can be set to 20 to 150 grams per square meter of metal filter bag filtration area.

[0037] After inert coarse powder is carried into the surface of the metal filter bag by the inlet flue gas, it adheres and deposits on the surface of the metal filter bag through inertial impaction, interception, and filtration. A continuously covered inert coarse powder pre-formed layer refers to the formation of a continuous particle deposition layer of inert coarse powder on the surface of the metal filter bag along the filtration direction of the inlet flue gas, where the surface of the metal filter bag is no longer directly exposed to potassium- and chlorine-containing fly ash in the inlet flue gas. Continuous coverage can be determined by the increase in filtration pressure difference before and after pre-spraying the inert coarse powder and the change in particulate matter at the outlet side of the metal filter bag. If the increase in filtration pressure difference reaches the deposition pressure difference range determined by the short-term pre-spray test, for example, if the particulate matter concentration at the outlet side of the metal filter bag is not higher than the allowable fluctuation range of the outlet side particulate matter concentration before the short-term pre-spray test, it is confirmed that the inert coarse powder pre-formed layer has been formed.

[0038] S4: Conditioning powder is sprayed upstream of the inert coarse powder preform layer according to the deliquescent salt conversion window, so that the conditioning powder and potassium- and chlorine-containing fly ash form a reactive filter cake on the outside of the inert coarse powder preform layer, including: The upstream of the inert coarse powder preformed layer refers to the flue gas duct area on the inlet side of the metal filter bag that the inlet flue gas passes through before reaching the inert coarse powder preformed layer. The conditioning powder injection position is set upstream of the inert coarse powder preformed layer and spaced apart from the inlet side of the metal filter bag, so that the conditioning powder can be dispersed before reaching the inert coarse powder preformed layer after entering the inlet flue gas. The conditioning powder injection position is determined by obtaining the inlet flue gas velocity in the flue gas duct on the inlet side of the metal filter bag, and then determining the flue gas duct distance between the conditioning powder injection position and the inlet side of the metal filter bag according to the inlet flue gas velocity and the residence time required for the dispersion of the conditioning powder. The residence time required for the dispersion of the conditioning powder is determined by short-term injection observation, and the short-term injection observation ends when the concentration difference of the conditioning powder in the cross-section of the flue gas duct on the inlet side of the metal filter bag tends to stabilize. For example, the concentration of conditioning powder is collected at different measuring points on the cross-section of the flue on the inlet side of the metal filter bag. When the difference between the highest and lowest concentrations of conditioning powder obtained from two consecutive short-term injections is less than the preset fluctuation range, it is determined that the difference in the concentration of conditioning powder tends to be stable. The residence time required for the dispersion of conditioning powder can be set to 0.5 seconds to 3 seconds.

[0039] Conditioning powder is a solid powder capable of contact adsorption, neutralization, or surface coating with hydrogen chloride, sulfur dioxide, or potassium- and chlorine-containing fly ash in the inlet flue gas. Conditioning powder can be selected from sodium bicarbonate powder, calcium hydroxide powder, calcium oxide powder, calcium carbonate powder, activated carbon powder, or alkaline mineral powder. The particle size of the conditioning powder is determined based on the particle size of the inert coarse powder, the particle size of the potassium- and chlorine-containing fly ash, and the porosity retention requirements of the inert coarse powder pre-formed layer. The determination method for the conditioning powder particle size is as follows: measure the particle size distribution of the inert coarse powder and the particle size distribution of the potassium- and chlorine-containing fly ash, and then select a conditioning powder particle size that can enter the outer side of the inert coarse powder pre-formed layer with the inlet flue gas without extensively penetrating the inert coarse powder pre-formed layer into the surface pores of the metal filter bag. To ensure that the conditioning powder mainly deposits on the outer side of the inert coarse powder pre-formed layer, the median particle size of the conditioning powder can be smaller than the median particle size of the inert coarse powder but larger than the bulk particle size of the potassium- and chlorine-containing fly ash fine particles. For example, the cumulative mass proportion of potassium- and chlorine-containing fly ash in the particle size distribution reaches the fine particle size range of the main distribution range; the median particle size of the tempered powder can be set to 20% to 80% of the median particle size of the inert coarse powder.

[0040] During the filtration operation period corresponding to the deliquescent salt conversion window, the conditioning powder is fed into the upstream of the inert coarse powder preforming layer via powder feeding, pneumatic conveying, and nozzle dispersion. The powder feed rate is determined according to the inlet flue gas hydrogen chloride concentration sequence, sulfur dioxide concentration sequence, and potassium- and chlorine-containing fly ash concentration sequence. When determining the powder feed rate, the acidic gas load is obtained based on the inlet flue gas hydrogen chloride and sulfur dioxide concentration sequences within the same sampling interval, and the particle load is obtained by combining the potassium- and chlorine-containing fly ash concentration sequence. The basic injection rate of the conditioning powder is determined by the greater of the amount required for the conditioning powder to contact the acidic gas and the amount required for the conditioning powder to coat the surface of the potassium- and chlorine-containing fly ash. The basic injection rate of the conditioning powder is converted into the injection rate per unit time under continuous injection conditions based on the duration of the deliquescent salt conversion window. The injection rate per unit time is continuously output during the filtration operation period corresponding to the deliquescent salt conversion window and is updated in segments according to changes in the inlet flue gas hydrogen chloride concentration sequence, sulfur dioxide concentration sequence, and potassium- and chlorine-containing fly ash concentration sequence.

[0041] After the conditioning powder enters the upstream of the inert coarse powder preformed layer, it moves along the inlet flue gas flow direction and comes into contact with and mixes with hydrogen chloride, sulfur dioxide, and potassium- and chlorine-containing fly ash in the inlet flue gas. This contact mixing is achieved through inlet flue gas flow carrying, nozzle jet diffusion, and flue cross-section diffusion. To prevent the conditioning powder from concentrating in localized metal filter bag areas, the powder injection direction can form an angle with the inlet flue gas flow direction, and multiple injection points can be distributed along the flue cross-section on the inlet side of the metal filter bag. The number and location of injection points are determined according to the flue cross-section dimensions on the inlet side of the metal filter bag and the inlet flue gas velocity distribution. This is achieved by measuring the inlet flue gas velocity distribution and then including areas with higher and lower inlet flue gas velocities within the injection coverage area, ensuring that the conditioning powder reaches different areas outside the inert coarse powder preformed layer after entering the inlet flue gas. The mixture after contact mixing includes conditioning powder, hydrogen chloride after contact with conditioning powder, sulfur dioxide after contact with conditioning powder, and potassium- and chlorine-containing fly ash that has been in contact with conditioning powder.

[0042] After the conditioned powder and potassium- and chlorine-containing fly ash, after contact mixing, reach the outer side of the inert coarse powder preformed layer, they are retained on the outer side by the inlet flue gas filtration. The outer side of the inert coarse powder preformed layer refers to the side of the inert coarse powder preformed layer facing away from the metal filter bag surface and towards the inlet flue gas. The adhesion and deposition of the conditioned powder and potassium- and chlorine-containing fly ash on the outer side of the inert coarse powder preformed layer successively undergoes particle contact, particle embedding, and particle accumulation. Particle contact refers to the conditioned powder and potassium- and chlorine-containing fly ash reaching the outer side of the inert coarse powder preformed layer and contacting the surface of the inert coarse powder particles. Particle embedding refers to the conditioned powder and potassium- and chlorine-containing fly ash entering the surface gaps between the inert coarse powder particles and being retained on the outer side of the inert coarse powder preformed layer by the inlet flue gas filtration. Particle accumulation refers to the continuous deposition of the conditioned powder and potassium- and chlorine-containing fly ash on the outer side of the inert coarse powder preformed layer, forming a deposition layer covering the outer side of the inert coarse powder preformed layer.

[0043] Reactive filter cake is a deposited layer formed by the contact of conditioning powder, potassium- and chlorine-containing fly ash, and hydrogen chloride and sulfur dioxide in the inlet flue gas. The formation process begins with the appearance of a continuous deposited layer on the outside of the inert coarse powder pre-formed layer and continues to thicken during filtration. The formation of reactive filter cake can be confirmed by changes in filtration pressure differential, changes in particulate matter at the outlet of the metal filter bag, and the composition of ash in the ash hopper. Changes in filtration pressure differential confirm continuous deposition on the outside of the inert coarse powder pre-formed layer; changes in particulate matter at the outlet of the metal filter bag confirm the retention of conditioning powder and potassium- and chlorine-containing fly ash; and the composition of ash in the ash hopper is confirmed by the joint detection of characteristic components of the conditioning powder and potassium- and chlorine-containing fly ash.

[0044] S5: Collect the pressure differential growth rate, pressure differential recovery rate after ash removal, and conductivity of the ash sample during the reactive filter cake growth process. Combine this with the surface soluble chlorine difference and the constant humidity weight gain difference to determine the state of the reactive filter cake, including: Filtration differential pressure refers to the difference between the pressure at the inlet side and the pressure at the outlet side of the metal filter bag. During the continuous deposition of reactive filter cake, the filtration differential pressure is recorded at the same time intervals within each sampling interval, establishing a correspondence between the recorded filtration differential pressure and the filtration operation period. The same time interval is determined based on the deposition rate of the reactive filter cake and the rate of change of the metal filter bag pressure differential. The determination method is as follows: before the continuous injection of conditioning powder, a reference filtration operation period is selected, and the shortest time required for a identifiable change in filtration differential pressure to occur within the reference filtration operation period is recorded. Then, the recording time interval is set to be no greater than the shortest time. For example, the same time interval can be set to 30 seconds to 5 minutes.

[0045] The differential pressure growth rate is determined based on the change in filtration differential pressure during filtration operation. Filtration differential pressure records within the same sampling interval are read sequentially. The filtration differential pressure at the later recording time is subtracted from the filtration differential pressure at the previous recording time to obtain the incremental filtration differential pressure between adjacent recording times. This incremental filtration differential pressure between adjacent recording times is then divided by the filtration operation time interval between adjacent recording times to obtain the segmented differential pressure growth rate between adjacent recording times. The arithmetic mean of multiple segmented differential pressure growth rates within the same sampling interval is used to obtain the differential pressure growth rate for the corresponding sampling interval. If a pulse cleaning action occurs within the same sampling interval, the filtration differential pressure record after the pulse cleaning action is not included in the calculation of the differential pressure growth rate before the pulse cleaning action, to avoid the instantaneous pressure drop caused by pulse cleaning affecting the differential pressure growth rate of the continuous deposition process of the reactive filter cake.

[0046] The pre-cleaning filtration differential pressure is obtained before the pulse cleaning begins. Before the next pulse cleaning start signal appears, the stable filtration differential pressure record closest to the next pulse cleaning start signal is read, and the stable filtration differential pressure record closest to the next pulse cleaning start signal is determined as the pre-cleaning filtration differential pressure.

[0047] The stable filtration differential pressure after dust removal is obtained after the pulse dust removal is completed. Filtration differential pressure is recorded again after the pulse dust removal completion signal appears. When the variation amplitude of multiple consecutive filtration differential pressure records is lower than the natural fluctuation amplitude of the filtration differential pressure during the reference filtration operation period, the average value of the multiple consecutive filtration differential pressure records is determined as the stable filtration differential pressure after dust removal. The number of consecutive filtration differential pressure records is determined according to the filtration differential pressure recording time interval; for example, it can be set to 3 to 6.

[0048] The differential pressure recovery rate after dust removal is determined based on the filtration differential pressure before dust removal and the stable filtration differential pressure after dust removal. The difference between the filtration differential pressure before dust removal and the stable filtration differential pressure after dust removal is subtracted to obtain the pressure drop after dust removal. This drop is then divided by the filtration differential pressure before dust removal to obtain the differential pressure recovery rate. The differential pressure recovery rate is recorded as a percentage. If there is an abnormal fluctuation in the filtration differential pressure before dust removal, the last stable filtration differential pressure record before the abnormal fluctuation is taken as the filtration differential pressure before dust removal. Abnormal fluctuations are identified when the filtration differential pressure exceeds the natural fluctuation range of the filtration differential pressure during a reference filtration operation period within a recording time interval.

[0049] The conductivity of the ash sample is obtained by collecting ash samples from the corresponding filtration operation period and measuring the conductivity of the leachate. The ash sample from the corresponding filtration operation period refers to the sediment sample that has been continuously deposited in the sampling interval by the reactive filter cake and has entered the ash hopper after pulse cleaning. When collecting ash samples from the corresponding filtration operation period, the ash sample collection path and sampling interval number are followed to ensure that the ash sample corresponds to the pressure difference increase rate, pressure difference recovery rate after cleaning, surface soluble chlorine difference, and constant humidity weight gain difference within the same sampling interval. After ash sample collection, it is sealed and gently homogenized, and then a fixed mass of ash sample is added to a fixed volume of deionized water. The fixed mass and fixed volume are determined based on the salt content of the ash sample and the conductivity measurement range, ensuring that the conductivity of the leachate falls within the stable reading range of the conductivity measuring instrument. For example, the fixed mass can be set to 1 gram to 10 grams, and the fixed volume can be set to 50 milliliters to 500 milliliters.

[0050] After mixing the ash sample with deionized water, leaching is performed using a closed-loop oscillation or closed-loop stirring method. The leaching time is determined based on the time it takes for soluble salts in the ash sample to enter the aqueous phase. The method is as follows: different leaching times are set for the same ash sample, and the conductivity of the leachate is measured. When the change in conductivity of the leachate corresponding to adjacent leaching times is lower than the preset reading fluctuation range, the shorter leaching time is taken as the leaching time. For example, the leaching time can be set from 10 minutes to 60 minutes. After leaching, the leachate is allowed to settle or filtered to remove the influence of suspended particles on the conductivity measurement. Before conductivity measurement, the temperature of the leachate is adjusted to the same measurement temperature, and deionized water is used as a blank control to read the background conductivity. The conductivity of the ash sample is obtained by subtracting the background conductivity from the conductivity of the leachate and is recorded using the corresponding sampling interval number.

[0051] When determining the state of the reactive filter cake, the pressure differential growth rate, pressure differential recovery rate after cleaning, ash sample conductivity, surface soluble chloride difference, and constant humidity weight gain difference within the same sampling interval are entered into the same comparison record. Corresponding comparisons are performed in the order of the starting and ending points of the sampling interval. The pressure differential growth rate characterizes the change in deposition resistance of the reactive filter cake on the surface of the metal filter bag; the pressure differential recovery rate after cleaning characterizes the degree of peeling of the reactive filter cake after pulse cleaning; the ash sample conductivity characterizes the change in soluble salt content in the reactive filter cake; the surface soluble chloride difference characterizes the change in chloride migration on the surface of the ash within the sampling interval; and the constant humidity weight gain difference characterizes the change in moisture absorption weight gain of the ash within the sampling interval. The pressure differential growth rate, pressure differential recovery rate after cleaning, ash sample conductivity, surface soluble chloride difference, and constant humidity weight gain difference of the current sampling interval are compared with the corresponding data of the previous sampling interval to generate the determination result of the reactive filter cake's state.

[0052] The determination of the reactive filter cake's state includes at least the direction of change in the differential pressure growth rate, the direction of change in the differential pressure recovery rate after ash removal, the direction of change in the conductivity of the ash sample, the direction of change in the difference in surface soluble chlorine, and the direction of change in the difference in weight gain under constant humidity. The direction of change is determined by the difference between the data from the subsequent sampling interval and the data from the previous sampling interval. When the data from the subsequent sampling interval is greater than the data from the previous sampling interval and the difference is greater than the corresponding data's natural fluctuation range, the direction of change is recorded as increasing; when the data from the subsequent sampling interval is less than the data from the previous sampling interval and the absolute value of the difference is greater than the corresponding data's natural fluctuation range, the direction of change is recorded as decreasing; when the absolute value of the difference between the data from the subsequent sampling interval and the data from the previous sampling interval is not greater than the corresponding data's natural fluctuation range, the direction of change is recorded as stable. The corresponding data's natural fluctuation range is obtained through a reference filtration operation period during which the biomass boiler is stably burning and no conditioning powder is injected.

[0053] S6: Divide the reactive filter cake into three stages according to its state: cake formation, cake retention, and cake removal. Adjust the conditioning powder injection parameters and pulse cleaning interval, including: The cake-forming stage, cake-holding stage, and cake-removing stage are determined according to the order of sampling intervals, which are determined by the starting and ending points of each interval. Before determining the stage, the natural fluctuation range of the differential pressure growth rate, the natural fluctuation range of the differential pressure recovery rate after ash removal, and the natural fluctuation range of the ash sample conductivity are obtained during a reference filtration operation period in which the biomass boiler is stably burning and no conditioning powder is injected. The pulse ash removal interval during the reference filtration operation period is then determined as the baseline pulse ash removal interval.

[0054] A continuously increasing differential pressure growth rate means that, after arranging the sampling intervals sequentially, the differential pressure growth rate of the later sampling interval is greater than that of the previous sampling interval, and the difference in differential pressure growth rate between two adjacent sampling intervals is greater than the natural fluctuation range of the differential pressure growth rate. This increasing trend appears in multiple consecutive sampling intervals. The number of consecutive sampling intervals is determined based on the metal filter bag cleaning frequency and the stability of the differential pressure growth rate record; for example, it can be set to three. A high differential pressure recovery rate after cleaning means that the differential pressure recovery rate after cleaning is not lower than the difference between the average differential pressure recovery rate after cleaning and the natural fluctuation range of the differential pressure recovery rate after cleaning during the reference filtration operation period. The state of the reactive filter cake with a continuously increasing differential pressure growth rate and a high differential pressure recovery rate after cleaning is defined as the cake-forming stage, and the starting point of the sampling interval that first meets the requirement of a continuously increasing differential pressure growth rate is taken as the starting point of the cake-forming stage.

[0055] During the cake-forming stage, the conditioning powder is continuously injected, and the pulse cleaning is delayed. Maintaining continuous injection of the conditioning powder means adhering to the injection rate per unit time determined based on the inlet flue gas hydrogen chloride concentration sequence, sulfur dioxide concentration sequence, and potassium- and chlorine-containing fly ash concentration sequence, ensuring uninterrupted injection from the start to the end of the cake-forming stage. The end of the cake-forming stage is defined as the sampling interval after the start of the cake-forming stage, where, when comparing the pressure difference growth rate of the subsequent sampling interval in sequence, the absolute value of the difference between the pressure difference growth rate of the previous sampling interval and the subsequent pressure difference growth rate is not greater than the natural fluctuation range of the pressure difference growth rate, and the pressure difference recovery rate after cleaning is not lower than the difference between the average pressure difference recovery rate after cleaning and the natural fluctuation range of the pressure difference recovery rate after cleaning during the reference filtration operation period. Delayed pulse cleaning means extending the reference pulse cleaning interval when the pressure difference recovery rate after cleaning remains high and the filtration pressure difference has not reached the upper limit of the allowable filtration pressure difference of the metal filter bag. The extension range is determined based on the difference between the rate of increase in differential pressure and the natural fluctuation range of the rate of increase in differential pressure during the cake-forming stage. The larger the difference, the smaller the extension range; the closer the difference is to the natural fluctuation range of the rate of increase in differential pressure, the larger the extension range. For example, the extension range can be set to 10% to 30% of the reference pulse cleaning interval.

[0056] A stable pressure differential growth rate means that the absolute value of the difference between the pressure differential growth rate of the subsequent sampling interval and that of the previous sampling interval is not greater than the natural fluctuation range of the pressure differential growth rate, and this stable state occurs across multiple consecutive sampling intervals. A slowdown in the change of ash sample conductivity means that the absolute value of the difference between the ash sample conductivity of the subsequent sampling interval and that of the previous sampling interval gradually decreases, and the absolute value of this difference is not greater than the natural fluctuation range of the ash sample conductivity. The reactive filter cake state where the pressure differential growth rate stabilizes and the change in ash sample conductivity slows is defined as the cake-holding stage, and the starting point of the sampling interval that first satisfies both the stable pressure differential growth rate and the slowdown in the change of ash sample conductivity is taken as the starting point of the cake-holding stage.

[0057] During the cake-holding phase, a stable injection of conditioning powder is maintained, and pulse cleaning is performed at fixed intervals. Maintaining a stable injection of conditioning powder means using the injection rate per unit time of the most recent sampling interval before entering the cake-holding phase as the injection rate per unit time during the cake-holding phase, and only making small updates based on the segmented changes in the inlet flue gas hydrogen chloride concentration sequence, sulfur dioxide concentration sequence, and potassium- and chlorine-containing fly ash concentration sequence during the reference filtration operation period. The magnitude of the small updates is determined based on the natural fluctuation range of the inlet flue gas hydrogen chloride concentration sequence, sulfur dioxide concentration sequence, and potassium- and chlorine-containing fly ash concentration sequence during the cake-holding phase; for example, it can be set to 5% to 15% of the injection rate per unit time during the cake-holding phase. The fixed interval is determined based on the average of the actual pulse cleaning intervals of the most recent multiple sampling intervals before the start of the cake-holding phase, and the number of multiple sampling intervals is determined based on the number of consecutive sampling intervals covered when the pressure difference growth rate tends to stabilize.

[0058] A decrease in differential pressure recovery rate after dust removal means that the differential pressure recovery rate after dust removal in the subsequent sampling interval is less than that in the previous sampling interval, and the decrease is greater than the natural fluctuation range of the differential pressure recovery rate after dust removal. A continuous increase in ash sample conductivity means that the ash sample conductivity in the subsequent sampling interval is greater than that in the previous sampling interval, and the increase is greater than the natural fluctuation range of the ash sample conductivity, with the increasing trend appearing in multiple consecutive sampling intervals. The state of the reactive filter cake characterized by a decrease in differential pressure recovery rate after dust removal and a continuous increase in ash sample conductivity is defined as the cake stripping stage, and the starting point of the sampling interval that first meets the condition of a decrease in differential pressure recovery rate after dust removal is taken as the starting point of the cake stripping stage.

[0059] During the cake removal stage, the amount of conditioning powder injected should be reduced and the pulse cleaning interval shortened. Reducing the amount of conditioning powder injected means lowering the injection rate per unit time from the base rate during the cake retention stage to a rate that still covers the acidic gas load corresponding to the hydrogen chloride and sulfur dioxide concentration sequences in the inlet flue gas. The reduction amount is determined by the combined effect of the continuous increase in ash sample conductivity and the decrease in differential pressure recovery rate after cleaning. A larger continuous increase in ash sample conductivity and a larger decrease in differential pressure recovery rate after cleaning result in a larger reduction amount; conversely, a reduction amount smaller if the continuous increase in ash sample conductivity is close to the natural fluctuation range of ash sample conductivity and the decrease in differential pressure recovery rate after cleaning is close to the natural fluctuation range of differential pressure recovery rate after cleaning. For example, the reduction amount can be set to 10% to 40% of the injection rate per unit time during the cake retention stage. Shortening the pulse cleaning interval means advancing the start time of the next pulse cleaning based on a fixed interval, and recording the shortened pulse cleaning interval together with the start and end points of the cake removal stage, the reduced injection volume per unit time, and the corresponding sampling interval number. The end point of the cake removal stage refers to the sampling interval where, after the start of the cake removal stage, when comparing the sampling intervals in sequence, the absolute value of the difference between the post-cleaning differential pressure recovery rate of the next sampling interval and the post-cleaning differential pressure recovery rate of the previous sampling interval is not greater than the natural fluctuation range of the post-cleaning differential pressure recovery rate, and the absolute value of the difference between the ash sample conductivity of the next sampling interval and the ash sample conductivity of the previous sampling interval is not greater than the natural fluctuation range of the ash sample conductivity.

[0060] The above embodiments are only used to illustrate the technical methods of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical methods of the present invention without departing from the spirit and scope of the technical methods of the present invention.

Claims

1. A method for integrating metal filter bag dust removal and flue gas powder injection conditioning in a biomass boiler, characterized in that, Includes the following steps: S1: Detect the concentrations of hydrogen chloride, sulfur dioxide, and potassium- and chlorine-containing fly ash at the inlet of the metal filter bag, and collect ash samples between two cleaning cycles; S2: The soluble chlorine content and constant humidity weight gain of the ash sample were measured to obtain the difference in soluble chlorine content on the surface and the difference in constant humidity weight gain. S3: Determine the conversion window of hygroscopic salts based on the difference in soluble chlorine on the surface and the difference in weight gain under constant humidity, and construct an inert coarse powder pre-formed layer on the surface of the metal filter bag; S4: According to the deliquescent salt conversion window, the conditioning powder is sprayed upstream of the inert coarse powder preformed layer, so that the conditioning powder and potassium- and chlorine-containing fly ash form a reactive filter cake on the outside of the inert coarse powder preformed layer. S5: Collect the pressure difference growth rate, pressure difference recovery rate after ash removal, and conductivity of the ash sample during the growth process of the reactive filter cake, and combine them with the surface soluble chlorine difference and constant humidity weight gain difference to determine the state of the reactive filter cake. S6: Divide the reactive filter cake into three stages: cake formation, cake retention, and cake removal, and adjust the conditioning powder injection parameters and pulse cleaning intervals accordingly.

2. The integrated method for dust removal and flue gas powder injection conditioning of a biomass boiler using metal filter bags according to claim 1, characterized in that, The concentrations of hydrogen chloride, sulfur dioxide, and potassium- and chloride-containing fly ash at the inlet of the metal filter bag were measured, and ash samples were collected between two cleaning cycles. Specifically: The sampling interval is defined as the filtration operation period between two adjacent ash cleaning cycles. The concentrations of hydrogen chloride, sulfur dioxide, and potassium- and chlorine-containing fly ash in the inlet flue gas are continuously measured at the metal filter bag inlet flue. Ash samples from the corresponding sampling interval are collected during the ash discharge process in the ash hopper.

3. The integrated method for metal filter bag dust removal and flue gas powder injection conditioning in a biomass boiler according to claim 1, characterized in that, The soluble chlorine content and constant humidity weight gain of the ash samples were determined to obtain the differences in soluble chlorine content and constant humidity weight gain on the surface. Specifically: The ash samples collected within the sampling area were divided into front section ash samples and back section ash samples according to the order of ash discharge. The surface soluble chlorine extraction and weight gain under constant humidity conditions were determined for the front and rear ash samples, respectively. The results of surface soluble chlorine extraction and weight gain under constant humidity conditions were obtained for the front and rear ash samples. The difference between the surface soluble chlorine determination results of the first and second ash samples is defined as the surface soluble chlorine difference value. The difference between the weight gain measurements of the first and second ash samples under constant humidity conditions is defined as the constant humidity weight gain difference.

4. The integrated method for dust removal and flue gas powder injection conditioning of a biomass boiler using metal filter bags according to claim 1, characterized in that, The conversion window for hygroscopic salts was determined based on the difference in soluble chlorine content on the surface and the difference in weight gain under constant humidity. An inert coarse powder pre-formed layer was then constructed on the surface of the metal filter bag, specifically as follows: The differences in soluble chlorine concentration at the inlet surface and the differences in weight gain at constant humidity were compared with each sampling interval. The sampling interval in which the differences in soluble chlorine concentration at the inlet surface continuously increased and the differences in weight gain at constant humidity increased synchronously was determined as the deliquescent salt conversion window. During the filtration operation period corresponding to the deliquescent salt conversion window, inert coarse powder is sprayed into the inlet side of the metal filter bag, so that the inert coarse powder is deposited on the surface of the metal filter bag to form a continuous inert coarse powder pre-formed layer.

5. The integrated method for dust removal and flue gas powder injection conditioning of a biomass boiler using metal filter bags according to claim 4, characterized in that, The starting point of the sampling interval that first satisfies the effective increase among multiple consecutive sampling intervals is taken as the starting point of the hygroscopic salt conversion window, and the ending point of the sampling interval that last satisfies the synchronous increase among multiple consecutive sampling intervals is taken as the ending point of the hygroscopic salt conversion window.

6. The integrated method for dust removal and flue gas powder injection conditioning of a biomass boiler using metal filter bags according to claim 1, characterized in that, Conditioning powder is sprayed upstream of the inert coarse powder preform layer according to the hygroscopic salt conversion window, so that the conditioning powder and potassium- and chlorine-containing fly ash form a reactive filter cake on the outside of the inert coarse powder preform layer, specifically: During the filtration operation period corresponding to the hygroscopic salt conversion window, conditioning powder is continuously sprayed upstream of the inert coarse powder preformed layer. The conditioning powder is then mixed with hydrogen chloride, sulfur dioxide, and potassium- and chlorine-containing fly ash in the inlet flue gas along the flow direction of the inlet flue gas. The mixed conditioning powder and potassium- and chlorine-containing fly ash adhere to the outside of the inert coarse powder preformed layer and continue to deposit, forming a reactive filter cake.

7. The integrated method for dust removal and flue gas powder injection conditioning of a biomass boiler using metal filter bags according to claim 6, characterized in that, The upstream of the inert coarse powder preformed layer refers to the flue gas duct area on the inlet side of the metal filter bag that the inlet flue gas passes through before reaching the inert coarse powder preformed layer.

8. The integrated method for dust removal and flue gas powder injection conditioning of a biomass boiler using metal filter bags according to claim 6, characterized in that, The reactive filter cake is a deposit layer formed by the contact of conditioning powder, potassium- and chlorine-containing fly ash, and hydrogen chloride and sulfur dioxide in the inlet flue gas.

9. The integrated method for dust removal and flue gas powder injection conditioning of a biomass boiler using metal filter bags according to claim 1, characterized in that, The pressure differential growth rate, pressure differential recovery rate after ash removal, and conductivity of the ash sample were collected during the reactive filter cake growth process. The state of the reactive filter cake was determined by combining the surface soluble chlorine difference and the constant humidity weight gain difference. Specifically: During the continuous deposition of reactive filter cake, the change in filtration differential pressure with the duration of filtration operation is recorded, and the rate of differential pressure increase is determined based on the change in filtration differential pressure. After pulse cleaning is completed, record the filtration pressure difference before cleaning and the stable filtration pressure difference after cleaning. Determine the pressure difference recovery rate after cleaning based on the filtration pressure difference before cleaning and the stable filtration pressure difference after cleaning. Ash samples were collected for the corresponding filtration operation period, and their conductivity was measured to obtain the conductivity of the ash samples. The pressure difference growth rate, pressure difference recovery rate after ash removal, difference between ash sample conductivity and surface soluble chlorine, and difference in weight gain under constant humidity were compared according to the sampling interval to determine the state of the reactive filter cake.

10. The integrated method for dust removal and flue gas powder injection conditioning of a biomass boiler using metal filter bags according to claim 1, characterized in that, The reactive filter cake is divided into three stages based on its state: cake formation, cake retention, and cake removal. The parameters for injecting conditioning powder and the pulse cleaning interval are adjusted accordingly. The state of the reactive filter cake where the differential pressure growth rate continues to increase and the differential pressure recovery rate remains high after dust removal is defined as the cake formation stage. During the cake formation stage, the conditioning powder is continuously injected and pulse dust removal is delayed. The state of the reactive filter cake when the pressure difference growth rate tends to be stable and the change in the conductivity of the ash sample slows down is defined as the cake preservation stage. During the cake preservation stage, the conditioning powder is stably injected and pulse cleaning is carried out at fixed intervals. The state of reactive filter cake where the differential pressure recovery rate decreases and the conductivity of the ash sample continues to increase after cleaning is defined as the cake stripping stage. During the cake stripping stage, the amount of conditioning powder injected is reduced and the pulse cleaning interval is shortened.

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