Method for effectively reducing calcium-sulfur ratio of semi-dry desulfurization process

Abstract

The invention discloses a method for effectively reducing the calcium-sulfur ratio of a semi-dry desulfurization process, and relates to the technical field of flue gas purification, and the method comprises the following steps: S1, flue gas pretreatment: introducing original flue gas into a pretreatment tower, spraying conditioning water through atomization, adjusting the flue gas temperature to 70-90 DEG C, and adjusting the relative humidity of the flue gas to 30-50% to obtain homogenized pretreated flue gas; s2, preparing an activated absorbent; s3, carrying out primary desulfurization reaction; s4, material grading and cyclic regeneration; and S5, optimization control is carried out. According to the invention, flue gas pretreatment creates an optimal initial temperature and humidity condition for the reaction; the reaction activity of the original absorbent is improved through absorbent activation; the problem of inactivation in the reaction process is solved through material grading circulation; the optimal control ensures the dynamic optimal operation of the whole system, and the four links are linked with one another and act together to generate a synergistic effect of '1 + 1gt, 2', so that the overall performance of the system is improved.

Description

Technical Field

[0001] This invention belongs to the field of flue gas purification technology, specifically, it relates to a method for effectively reducing the calcium-to-sulfur ratio in a semi-dry desulfurization process. Background Technology

[0002] Circulating fluidized bed semi-dry desulfurization technology is widely used in the treatment of flue gas from coal-fired boilers due to its advantages such as low investment and operating costs and no wastewater discharge. The core principle of this technology is to spray a calcium-based absorbent (usually quicklime) into the reaction tower, where it works together with atomized water to react with and remove sulfur dioxide (SO2) from the flue gas.

[0003] However, existing semi-dry desulfurization processes suffer from the following major technical bottlenecks: 1. High calcium-to-sulfur ratio and low absorbent utilization: To ensure compliance with emission standards, the calcium-to-sulfur molar ratio typically needs to be maintained above 1.2, or even higher, during actual operation. This means that a large amount of unreacted absorbent is wasted and discharged as solid waste, increasing raw material costs and disposal burden. 2. Encapsulation and deactivation of reaction products: The calcium sulfite / calcium sulfate generated during the reaction will encapsulate on the surface of unreacted absorbent particles, hindering further contact with SO2, leading to a rapid decline in reaction efficiency, especially in the later stages of the reaction. 3. Poor system stability and adaptability: When flue gas load or SO2 concentration fluctuates, traditional fixed feed or simple feedback control modes cannot accurately match the absorbent dosage in real time, easily causing emissions to exceed standards or excessive waste of absorbent.

[0004] While existing technologies include studies on improving the activity of quicklime by adding activators such as organic acids and inorganic salts, and practices on recycling desulfurization ash, these measures are often isolated. For example, simply adding activators without effective material recycling has limited effect on reducing the overall calcium-sulfur ratio; and simple full material recycling brings back a large number of deactivated, encapsulated coarse particles to the system, occupying reaction space but contributing very little, failing to fundamentally solve the problem of low absorbent utilization.

[0005] No effective solutions have yet been proposed to address the problems in the relevant technologies.

[0006] Therefore, in order to solve the above problems, the present invention provides a method for effectively reducing the calcium-sulfur ratio in a semi-dry desulfurization process. Summary of the Invention

[0007] In order to overcome the above-mentioned technical problems, the purpose of this invention is to provide a method for effectively reducing the calcium-sulfur ratio in a semi-dry desulfurization process.

[0008] The objective of this invention can be achieved through the following technical solutions: A method for effectively reducing the calcium-to-sulfur ratio in a semi-dry desulfurization process includes the following steps: S1. Flue gas pretreatment: The raw flue gas is introduced into the pretreatment tower, and conditioning water is sprayed in through atomization to adjust the flue gas temperature to 70℃-90℃ and the relative humidity of the flue gas to 30%-50% to obtain homogeneous pretreated flue gas. S2. Preparation of Activated Absorbent: Quicklime is slaked to produce hydrated lime powder, and the hydrated lime powder is surface-wetted with an activation solution containing carboxylates or phosphates to obtain an activated absorbent. S3, Primary desulfurization reaction: The homogeneous pretreated flue gas is fed into the circulating fluidized bed desulfurization tower from the bottom, and at the same time, part of the activated absorbent is injected from above the Venturi section of the desulfurization tower through the first feeder to carry out the primary desulfurization reaction under strong turbulence conditions. S4. Material Classification and Recycling: The gas-solid mixture discharged from the top of the desulfurization tower is separated into fine and coarse particles by gas-solid separation. The separated solid material enters the pneumatic classifier and is separated into fine and coarse particles. The fine particles are directly returned to the Venturi section of the desulfurization tower to participate in the recycling reaction. The coarse particles are sent to a fluidized bed supplementary activator to regenerate by contacting supplementary atomized water and activating liquid to obtain a regenerated absorbent. Then, it is sent to the secondary reaction zone above the primary reaction zone in the desulfurization tower by a second feeder. S5. Optimized control: Real-time monitoring of SO2 concentration and flow rate of the original flue gas, and dynamic adjustment of the total feed amount of the activated absorbent, so that the total calcium-sulfur ratio of the system is controlled between 1.00 and 1.10.

[0009] As a preferred embodiment of the present invention, in step S1, a dispersant comprising 0.01%-0.1% of the water mass is added to the conditioning water, wherein the dispersant is sodium polyacrylate or lignin sulfonate.

[0010] As a preferred embodiment of the present invention, in step S2, the activation solution is a sodium citrate solution or sodium pyrophosphate solution with a concentration of 0.5%-5%, and the amount of activation solution added is 1%-5% of the mass of quicklime powder.

[0011] As a preferred embodiment of the present invention, in step S3, the flow velocity at the throat of the Venturi section of the desulfurization tower is 25-40 m / s, and the flow velocity in the empty tower of the primary reaction zone is 3.5 m / s-5.5 m / s.

[0012] As a preferred embodiment of the present invention, in step S4, the pneumatic classifier separates solid particles with a particle size less than or equal to 15 μm into fine particles and solid particles with a particle size greater than 15 μm into coarse particles.

[0013] As a preferred embodiment of the present invention, in step S4, the operating temperature inside the supplementary activator is 50℃-70℃, and the residence time of the solid material is 3-10min.

[0014] As a preferred embodiment of the present invention, in step S4, the secondary reaction zone is located 2-5 meters above the primary reaction zone of the desulfurization tower, and the empty tower flow velocity in this zone is 2.0-3.5 m / s.

[0015] As a preferred technical solution of the present invention, the optimization control is achieved through a feedforward-feedback composite control system: the base speed of the first feeder and the second feeder is rapidly adjusted in a feedforward manner according to the SO2 concentration and flow rate of the original flue gas; and PID fine-tuning is performed in a feedback manner according to the measured SO2 concentration value at the outlet of the desulfurization tower.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. In this invention, through the “optimized control” step, the system can always accurately control the total calcium-sulfur ratio within an ultra-low range of 1.00-1.10, which significantly reduces the consumption of quicklime compared to traditional processes (usually >1.2), directly reducing operating costs and reducing the yield of desulfurization byproducts.

[0017] 2. In this invention, a "pneumatic classifier" is used to separate and treat fine particles (highly active, incompletely reacted) and coarse particles (lowly active, encapsulated): fine particles directly and rapidly circulate to participate in the reaction, while coarse particles are regenerated by a "supplementary activator" and then sent to the secondary reaction zone for deep utilization. This classification strategy is highly targeted and maximizes the reaction potential of each absorbent particle, thereby maintaining high desulfurization efficiency even at low calcium-sulfur ratios.

[0018] 3. In this invention, "flue gas pretreatment" creates the best initial temperature and humidity conditions for the reaction; "absorbent activation" enhances the reactivity of the original absorbent; "material classification and circulation" solves the deactivation problem during the reaction process; and "optimized control" ensures the dynamic optimal operation of the entire system. These four links are interconnected and work together to produce a synergistic effect of "1+1>2", achieving a leap in the overall performance of the system.

[0019] 4. In this invention, a "feedforward-feedback composite control system" is adopted, which can respond quickly to changes in inlet flue gas parameters (feedforward) and then make fine adjustments based on outlet accuracy (feedback), making the system more adaptable to load fluctuations and more stable outlet SO2 concentration, thus achieving safe and stable operation under low calcium-sulfur ratio. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0022] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention: Example 1

[0023] A method for effectively reducing the calcium-to-sulfur ratio in a semi-dry desulfurization process comprises the following steps: S1. Flue Gas Pretreatment: Raw flue gas at 130℃ and SO2 concentration of 2200mg / Nm³ is introduced into the pretreatment tower. Conditioning water without dispersant is sprayed in via atomization to adjust the flue gas temperature to 80℃ and the relative humidity to 40%, resulting in homogeneous pretreated flue gas.

[0024] S2. Preparation and activation of absorbent: Quicklime is slaked into hydrated lime powder with an average particle size of approximately 20 μm. A 2.8% sodium citrate solution is prepared as the activation solution, and the solution is sprayed and impregnated at 3% of the mass of the hydrated lime powder to obtain the activated absorbent.

[0025] S3, First-stage reaction: The homogeneous pretreated flue gas is fed into the circulating fluidized bed desulfurization tower from the bottom. The flow velocity at the throat of the Venturi section of the desulfurization tower is designed to be 32.5 m / s, and the flow velocity in the empty tower of the first-stage reaction zone is 4.5 m / s. Approximately 70% of the total amount of activated absorbent obtained in step (2) is injected from above the Venturi section through the first feeder to carry out the first-stage desulfurization reaction.

[0026] S4. Material Recycling and Classification: The gas-solid mixture discharged from the top of the desulfurization tower is separated by a cyclone separator, and the solid material enters the pneumatic classifier. Fine particles with a diameter ≤15μm are directly returned to the Venturi section for recycling. Coarse particles with a diameter >15μm are fed into a fluidized bed supplementary activator, where they are held at 60℃ for 6 minutes and regenerated by contact with supplementary atomized water and a small amount of 1% sodium citrate solution to obtain regenerated absorbent. This regenerated absorbent is fed into the secondary reaction zone, located 3.5 meters above the primary reaction zone, through a second feeder. The empty tower velocity in this zone is controlled at 2.75 m / s.

[0027] S5. Feeding optimization control: Real-time monitoring of flue gas SO2 concentration and flow rate, and dynamic adjustment of the speed of the first and second feeders by a feedforward-feedback composite control system to control the total feed rate.

[0028] After testing, the system achieved an average desulfurization efficiency of 98.5% after stable operation, and the outlet SO2 concentration consistently met the standards. The actual average calcium-sulfur ratio of the system was 1.05. Example 2

[0029] A method for effectively reducing the calcium-to-sulfur ratio in a semi-dry desulfurization process comprises the following steps: S1. Flue Gas Pretreatment: Raw flue gas at 110℃ and SO2 concentration of 1800mg / Nm³ is introduced into the pretreatment tower. Conditioning water with 0.01% sodium polyacrylate is sprayed in via atomization to adjust the flue gas temperature to 70℃ and the relative humidity to 30%.

[0030] S2. Preparation and activation of absorbent: Prepare a 0.5% sodium citrate solution as the activation solution and impregnate it with 1% of the mass of quicklime powder.

[0031] S3, First-stage reaction: The flow velocity at the throat of the Venturi section of the desulfurization tower is designed to be 25 m / s, and the flow velocity in the empty tower of the first-stage reaction zone is controlled to be 3.5 m / s.

[0032] S4. Material Circulation and Graded Reuse: The operating temperature of the supplementary activator is controlled at 50℃, and the residence time of solid materials is 3 minutes. The regenerated absorbent is fed 2 meters above the primary reaction zone, and the empty tower flow rate in the secondary reaction zone is controlled at 2.0 m / s.

[0033] S5. Feeding optimization control: The control logic is the same as in Example 1.

[0034] Tests showed that under these relatively mild process parameters, the system operated stably, with an average desulfurization efficiency of 97.8% and an average calcium-to-sulfur ratio of 1.08. The results indicate that even at the lower limit of the parameters, the proposed method can still achieve a lower calcium-to-sulfur ratio and higher desulfurization efficiency than traditional processes. Example 3

[0035] A method for effectively reducing the calcium-to-sulfur ratio in a semi-dry desulfurization process comprises the following steps: S1. Flue Gas Pretreatment: High-temperature, high-sulfur flue gas with a temperature of 150℃ and an SO2 concentration of 2800mg / Nm³ is introduced into the pretreatment tower. Conditioning water with 0.1% lignin sulfonate added is injected through atomization to adjust the flue gas temperature to 90℃ and the relative humidity to 50%.

[0036] S2. Preparation and activation of absorbent: Prepare a 5% sodium pyrophosphate solution as the activation solution, and impregnate it with 5% of the mass of quicklime powder.

[0037] S3, First-stage reaction: The throat velocity of the desulfurization tower venturi section is designed to be 40 m / s, and the empty tower velocity in the first-stage reaction zone is controlled to be 5.5 m / s.

[0038] S4. Material Circulation and Graded Reuse: The operating temperature of the supplementary activator is controlled at 70℃, and the residence time of solid materials is 10 minutes. The regenerated absorbent is fed 5 meters above the primary reaction zone, and the empty tower flow rate in the secondary reaction zone is controlled at 3.5 m / s.

[0039] S5. Feeding optimization control: The control logic is the same as in Example 1.

[0040] Tests showed that under these more stringent process parameters, the system demonstrated excellent removal capabilities for high-concentration SO2 flue gas. The average desulfurization efficiency was 98.2%, and the average calcium-to-sulfur ratio was 1.02. This indicates that the proposed solution, when operating at its maximum parameter limits, can not only stably handle more severe flue gas conditions but also exhibits higher calcium utilization efficiency (lower calcium-to-sulfur ratio).

[0041] Comparative Example 1 Compared with Example 1, the pneumatic classification and supplementary activation steps in step S4 are omitted. All solid materials separated from the cyclone separator are directly returned to the Venturi section of the desulfurization tower for recycling. Other steps and parameters are consistent with Example 1.

[0042] Testing showed that the initial desulfurization efficiency of the system reached 97%, but after several hours of operation, the efficiency showed a slow but continuous downward trend. To maintain the SO2 concentration at the outlet, the feed rate of the absorbent needed to be continuously increased. Ultimately, the average calcium-to-sulfur ratio of the system rose to 1.38, and the absorbent consumption was about 31% higher than in Example 1. Shutdown inspection revealed that the circulating material had a high proportion of coarse particles, and the surface was covered by a dense product layer.

[0043] Comparative Example 2 Compared with Example 1, this comparative example changes the optimized control in step S5 to a fixed calcium-sulfur ratio control, i.e., setting a fixed calcium-sulfur ratio (e.g., 1.05) for feeding, without feedforward-feedback composite control logic. It operates when the SO2 concentration in the inlet flue gas fluctuates within the range of 1800-2600 mg / Nm³.

[0044] Testing revealed that the system could not respond quickly to changes in flue gas concentration. During periods of low SO2 concentration, the feed was relatively excessive; during periods of high concentration, the feed was relatively insufficient, leading to significant fluctuations in the outlet SO2 concentration, with occasional momentary exceedances. Although the average calcium-to-sulfur ratio throughout the process was approximately 1.05, compared to Example 1, emission stability was significantly worse, resulting in lower control quality.

[0045] Table 1: Summary of Effects of Examples and Comparative Examples project Average calcium-sulfur ratio Average desulfurization efficiency <![CDATA[Outlet SO2 concentration stability]]> Process feature description Example 1 1.05 98.5% high Intermediate parameter values, complete process Example 2 1.08 97.8% high Minimum parameter value, complete process Example 3 1.02 98.2% high Maximum parameter value, complete process Comparative Example 1 1.38 High initially, then decays. Low Non-graded regeneration Comparative Example 2 Approximately 1.05 98.0% Low (high volatility) No intelligent control Effect Analysis: 1. As can be seen from the conclusions drawn from Examples 1-3, the complete technical solutions of the present invention can stably achieve the target of a calcium-to-sulfur ratio of less than 1.10, and the desulfurization efficiency is maintained above 97.5%; 2. As can be seen from Comparative Example 1, the lack of the core step of "material classification and replenishment activation" will directly lead to a significant decline in system performance and a sharp increase in the calcium-sulfur ratio to 1.38. 3. Comparative Example 2 shows that even with good process design, it is difficult to achieve stable and efficient low calcium-sulfur ratio operation under fluctuating conditions if the "optimization control" steps are not precisely matched.

[0046] In summary, this invention systematically solves the technical problems of high calcium-to-sulfur ratio and low absorbent utilization in semi-dry desulfurization processes by providing a complete technical solution that includes pretreatment, activation, staged regeneration, and intelligent control. It achieves excellent and stable results under various parameter boundaries and typical conditions.

[0047] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for effectively reducing the calcium to sulfur ratio in a semi-dry desulfurization process, characterized by: The method comprises the following steps: S1, flue gas pretreatment: introducing the original flue gas into a pretreatment tower, and adjusting the temperature of the flue gas to 70-90 DEG C and the relative humidity of the flue gas to 30-50% by spraying the conditioning water, to obtain homogeneous pretreated flue gas; S2, preparation of activated absorbent: digesting the quicklime to obtain slaked lime powder, and performing surface infiltration treatment on the slaked lime powder by using an activation liquid containing carboxylate or phosphate, to obtain the activated absorbent; S3, primary desulfurization reaction: introducing the homogeneous pretreated flue gas from the bottom into a circulating fluidized bed desulfurization tower, and spraying part of the activated absorbent from above the Venturi section of the desulfurization tower by a first feeder, to perform the primary desulfurization reaction under strong turbulent flow conditions; S4, material grading and cyclic regeneration: after the gas-solid mixture discharged from the top of the desulfurization tower is separated, the separated solid material enters a pneumatic classifier and is separated into fine particle material and coarse particle material; wherein the fine particle material is directly returned to the Venturi section of the desulfurization tower to participate in the cyclic reaction; the coarse particle material is introduced into a fluidized bed type supplementary activator to contact with supplementary atomized water and activation liquid for regeneration treatment, to obtain regenerated absorbent, and then is introduced into the secondary reaction zone above the primary reaction zone in the desulfurization tower by a second feeder; S5, optimization control: real-time monitoring of the SO2 concentration and flow rate of the original flue gas, and dynamic adjustment of the total feeding amount of the activated absorbent based on the SO2 concentration and flow rate of the original flue gas, so that the total calcium-sulfur ratio of the system is controlled to be 1.00-1.

10.

2. A method for effectively reducing the Ca / S ratio in a semi-dry desulphurization process according to claim 1, characterized in that: In step S1, the conditioning water is added with a dispersant in an amount of 0.01%-0.1% of the mass of the water, and the dispersant is sodium polyacrylate or lignosulfonate.

3. A method of effectively reducing the calcium to sulfur ratio in a semi-dry desulfurization process as claimed in claim 1, characterized in that: In step S2, the activation liquid is a sodium citrate solution or a sodium pyrophosphate solution with a concentration of 0.5%-5%, and the addition amount of the activation liquid is 1%-5% of the mass of the slaked lime powder.

4. The method as claimed in claim 1, wherein the method is effective in reducing the Ca / S ratio in a semi-dry desulphurization process. In step S3, the throat flow velocity of the Venturi section of the desulfurization tower is 25-40 m / s, and the empty tower flow velocity of the primary reaction zone is 3.5-5.5 m / s.

5. The method as claimed in claim 1, wherein the method is effective in reducing the Ca / S ratio in a semi-dry desulphurization process. In step S4, the pneumatic classifier separates the solid particles with a particle size of less than or equal to 15 μm into fine particle material, and separates the solid particles with a particle size of greater than 15 μm into coarse particle material.

6. A method of effectively reducing the Ca / S ratio in a semi-dry desulphurization process as claimed in claim 1, wherein: In step S4, the operating temperature in the supplementary activator is 50-70 DEG C, and the residence time of the solid material is 3-10 min.

7. A method of effectively reducing the calcium to sulfur ratio in a semi-dry desulfurization process as claimed in claim 1, wherein: In step S4, the secondary reaction zone is located 2-5 m above the primary reaction zone of the desulfurization tower, and the empty tower flow velocity of the secondary reaction zone is 2.0-3.5 m / s.

8. A method of effectively reducing the Ca / S ratio in a semi-dry desulphurization process as claimed in claim 1, wherein: The optimization control is realized by a feedforward-feedback compound control system: the base speed of the first feeder and the second feeder is adjusted in a feedforward manner according to the SO2 concentration and flow rate of the original flue gas; and PID fine adjustment is performed in a feedback manner according to the measured SO2 concentration at the outlet of the desulfurization tower.

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