A submerged slurry-fed desulfurization absorption tower and a desulfurization method thereof

Abstract

The present application relates to desulfurization technical field, specifically to a kind of under-liquid slurry supply desulfurization absorption tower and desulfurization method thereof, including tower body, spray layer, oxidizing air pipe, slurry circulating pump, gypsum discharge pump and agitator, further including a under-liquid slurry supply pipeline, slurry pool is equipped in the tower body, slurry supply outlet is equipped on the under-liquid slurry supply pipeline, the slurry supply outlet is arranged on the lateral wall of slurry pool area, the slurry supply outlet position is higher than the effective stirring depth of the agitator paddle, but lower than the slurry pool liquid level position of traditional under-liquid slurry supply.The present application makes that gypsum quality is radically improved, system efficiency and energy saving are remarkable, limestone utilization rate approaches theoretical optimum value, system adaptability is strong, investment potential is big.

Description

Technical Field

[0001] This invention relates to the field of desulfurization technology, specifically to a submerged slurry desulfurization absorption tower and its desulfurization method. Background Technology

[0002] Limestone-gypsum wet desulfurization technology is currently the most widely used flue gas desulfurization technology in coal-fired power plants. Its core equipment, the absorption tower, absorbs SO2 from the flue gas by spraying limestone slurry to generate calcium sulfite, which is then forcibly oxidized to produce gypsum (CaSO4·2H2O) as a byproduct.

[0003] However, existing technologies have inherent contradictions and shortcomings: the optimal pH environment for oxidation reactions (HSO3⁻ → SO4²⁻) is 4.0-4.5, while absorption reactions (SO2 → HSO3⁻) are more efficient at higher pH values ​​(typically >5.2). Traditional absorption towers use a single slurry tank and a "top-feeding" method (adding fresh limestone slurry to the top or upper part of the slurry tank), resulting in the pH value of the entire slurry tank being maintained in a compromise range of 5.2-5.8. This model brings a series of problems:

[0004] Poor quality gypsum: Incomplete oxidation leads to excessive content of sticky calcium sulfite hemihydrate (CaSO3·1 / 2H2O) in the by-products, resulting in low purity gypsum, difficulty in dehydration, and low utilization value.

[0005] Limited desulfurization efficiency: To prevent excessive calcium sulfite hemihydrate, the overall operating pH value cannot be increased, which restricts the desulfurization capacity of the absorption tower.

[0006] High energy and material consumption: In order to meet emission standards, more slurry circulation pumps need to be operated, which leads to an increase in plant power consumption; at the same time, some limestone that has not participated in the reaction is discharged with gypsum, resulting in waste of raw materials.

[0007] High investment costs: The low upper limit of desulfurization efficiency means that the newly designed absorption tower needs a larger capacity to accommodate high-sulfur coal, which increases the initial investment.

[0008] Therefore, there is an urgent need for a new technical solution that can overcome the contradiction between the pH requirements of oxidation and absorption reactions, and ensure gypsum quality and system economy while improving desulfurization efficiency. Summary of the Invention

[0009] The purpose of this invention is to address the above-mentioned shortcomings by providing a submerged slurry desulfurization absorption tower and its desulfurization method, which fundamentally improves gypsum quality, significantly enhances system efficiency and energy saving, brings limestone utilization close to the theoretical optimal value, and has strong system adaptability and great investment potential.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: A submerged slurry desulfurization method involves supplying limestone slurry to the slurry tank of a limestone-gypsum wet desulfurization absorption tower using a submerged slurry supply method, thereby creating at least three reaction zones with different functions and pH values ​​in the vertical direction within the slurry tank. Absorption zone: Located at the top of the slurry tank, with a pH value maintained at ≥5.8, used to absorb sulfur dioxide in flue gas; Oxidation zone: Located below the absorption zone, the pH value is controlled at 4.0-4.5, and the bisulfite ions are fully oxidized by the introduced air; Diffusion zone: Located at the bottom or lower part of the slurry tank, the newly added limestone slurry is mixed with the slurry in the oxidation zone by a stirrer, which raises the pH value of the mixed slurry so that it can participate in the circulation again; The limestone slurry is supplied from the lower part of the oxidation zone, and a low pH environment in the oxidation zone is established and maintained by directly injecting limestone slurry into this area.

[0011] Preferably, the limestone slurry supply outlet is located in the middle or lower middle part of the slurry pool wall of the absorption tower.

[0012] Preferably, the pH of the oxidation zone is monitored online, and the pH value of the oxidation zone is stably controlled within the range of 4.0-4.5 by adjusting the supply flow rate of limestone slurry supplied from the liquid level.

[0013] Preferably, the limestone slurry supplied from the submerged slurry is preferentially directed to the inlet side of the slurry circulation pump, and then transported by the slurry circulation pump to the spray layer above the absorption tower to participate in the desulfurization reaction.

[0014] A desulfurization absorption tower for implementing the submerged slurry desulfurization method described in any one of the above claims includes a tower body, a spray layer, an oxidation air duct, a slurry circulation pump, a gypsum discharge pump, and a stirrer. It also includes a submerged slurry supply pipeline. A slurry pool is provided inside the tower body, and a slurry supply outlet is provided on the submerged slurry supply pipeline. The slurry supply outlet is located on the side wall of the slurry pool area. The position of the slurry supply outlet is higher than the effective stirring depth of the stirrer blades, but lower than the liquid level of the slurry pool in the traditional above-water slurry supply method.

[0015] Preferably, the slurry outlet of the submerged slurry supply pipeline is located on opposite sides of the slurry pool in the tower body in the horizontal direction, as is the inlet of the gypsum discharge pump.

[0016] Preferably, the limestone slurry flowing out of the slurry outlet is directed toward or preferentially flows toward the inlet area of ​​the slurry circulation pump.

[0017] Preferably, the system further includes a control system, which is connected to a pH meter and a limestone slurry supply regulating valve located in the oxidation zone, and is used to dynamically adjust the supply of limestone slurry according to a preset pH target value in the oxidation zone.

[0018] Preferably, the operating power or rotation speed of the agitator is linked to the supply flow rate of the limestone slurry to ensure that the supplied slurry is rapidly diffused.

[0019] Preferably, the slurry outlet is provided with a slurry uniform distribution component, which includes an annular diversion pipe and multiple radial slurry distribution holes. The annular diversion pipe is connected to the submerged slurry supply pipe, and the multiple radial slurry distribution holes are evenly distributed along the circumference of the annular diversion pipe to uniformly diffuse the limestone slurry into the slurry in the lower part of the oxidation zone.

[0020] The beneficial effects of this invention are: 1. This invention fundamentally improves the quality of gypsum: It solves the problem of excessive CaSO3·1 / 2H2O. For example, practical data shows that the moisture content of gypsum can be reduced from 14.37% before the modification to 8.69%, and the purity and dehydration of gypsum are greatly improved.

[0021] 2. This invention significantly improves system efficiency and energy saving: the high pH operation in the absorption zone enhances desulfurization capacity, and can reduce the number of slurry circulation pumps in operation under the same SO2 load (e.g., from three to two), reduce the power consumption of the desulfurization and flue gas systems (e.g., the power consumption rate of the desulfurization system is reduced from 0.54% to 0.49%), and reduce the power consumption of the oxidation fan.

[0022] 3. This invention brings the limestone utilization rate close to the theoretical optimum: the optimized material flow direction makes the limestone react more fully in the system, and the SO2 emission reduction unit consumption is reduced from 1.84 kg / kg before the modification to 1.59 kg / kg, which is close to the theoretical optimum of 1.56 kg / kg.

[0023] 4. The system of the present invention has strong adaptability and great investment potential: existing units can adapt to coal with higher sulfur content; new units can reduce the design capacity of the absorption tower under the same desulfurization requirements, thereby reducing the initial investment. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the internal structure of the tower body of the present invention; Figure 2 This is a schematic diagram of the absorption tower installation structure of the present invention. Detailed Implementation

[0025] like Figure 1 and 2As shown, a submerged slurry supply desulfurization absorption tower, in practical application, includes a tower body 1, a spray layer 2, an oxidation duct 3, a slurry circulation pump 4, a gypsum discharge pump 5, and an agitator 6, plus a submerged slurry supply pipe 7. The slurry pool 11 inside the tower body 1 is the main site of the desulfurization reaction. The slurry outlet 71 on the submerged slurry supply pipe 7 is located on the side wall of the slurry pool 11 area, higher than the effective stirring depth of the agitator 6 blades, ensuring that the injected limestone slurry can be fully diffused by the stirring flow of the agitator 6, while being lower than the slurry pool surface of traditional surface-supply slurry, thus achieving submerged slurry supply. During operation, the limestone slurry is injected into the lower part of the oxidation zone 112 through the submerged slurry supply pipe 7 from the slurry outlet 71, cooperating with other components to complete the zoned desulfurization reaction. This design provides hardware support for the submerged slurry supply desulfurization method, solves the problem that traditional absorption towers cannot achieve precise zoned slurry supply, and improves the desulfurization performance of the absorption tower. As one specific embodiment of the submersible slurry supply pipeline 7, it can be made of corrosion-resistant fiberglass pipe, which is fixed to the side wall of the tower body 1 by means of flange connection, so as to facilitate installation and maintenance.

[0026] like Figure 1 As shown, in practical use, the slurry outlet 71 of the submerged slurry supply pipe 7 is positioned horizontally on opposite sides of the gypsum discharge pump 5 in the slurry pool of the tower body. When limestone slurry is injected from the slurry outlet 71, it flows towards the inlet of the gypsum discharge pump 5 under the action of the agitator 6, mixing thoroughly with the slurry during the process. The gypsum discharge pump 5 then discharges the gypsum-containing slurry from the opposite side, preventing the newly injected limestone slurry from being directly discharged and improving the utilization rate of the limestone slurry. This design optimizes the slurry flow path, solves the problem of mutual interference between slurry supply and discharge and material waste, and improves the material circulation efficiency of the absorption tower. As a specific implementation of the relative positions of the slurry outlet 71 and the inlet of the gypsum discharge pump 5, they can be horizontally symmetrically distributed at 180 degrees on the sidewall of the slurry pool of the tower body.

[0027] like Figure 1 As shown, in practical use, by setting a flow guiding device at the slurry outlet 71, the limestone slurry flowing out of the slurry outlet 71 is directed or preferentially flows towards the inlet area of ​​the slurry circulation pump 4. In this way, fresh limestone slurry can be quickly drawn into the slurry circulation pump 4 and transported to the spray layer 2, participating in the desulfurization reaction in a timely manner, reducing the residence time of the slurry in the pool, and improving the utilization efficiency of alkaline substances. This design further optimizes the slurry circulation path, solves the problem of limestone slurry circulation lag, and enhances the timeliness of the desulfurization reaction. As a specific implementation of the flow guiding device, it can be a funnel-shaped flow guide hood installed at the slurry outlet 71 to guide the slurry flow towards the inlet of the slurry circulation pump 4.

[0028] like Figure 1As shown, in practical use, the absorption tower is equipped with a control system. This control system is connected to a pH meter located in oxidation zone 112 and a limestone slurry supply regulating valve. The pH meter monitors the pH value of oxidation zone 112 in real time and transmits the data to the control system. The control system compares the monitored value with the preset pH target value of 4.0-4.5 and dynamically adjusts the opening of the limestone slurry supply regulating valve based on the difference, thereby controlling the supply of limestone slurry. When the pH value is lower than the lower limit of the target value, the regulating valve opening increases, and the slurry supply increases; when the pH value is higher than the upper limit of the target value, the regulating valve opening decreases, and the slurry supply decreases. This design achieves automatic and precise control of the pH value in oxidation zone 112, solving the problems of large errors and untimely reactions in manual control, and ensuring the stable and efficient operation of the desulfurization reaction. As a specific implementation of the control system, it can be a PLC control system, which uses a control program to achieve the linkage adjustment of pH value and slurry supply.

[0029] like Figure 1 As shown, in practical use, the operating power or speed of the agitator 6 is linked to the supply flow rate of the limestone slurry. When the supply flow rate of the limestone slurry increases, the control system automatically increases the operating power or speed of the agitator 6 to enhance the mixing intensity and ensure that the large amount of limestone slurry supplied can be rapidly diffused and fully mixed with the slurry in the tank; when the supply flow rate decreases, the operating power or speed of the agitator 6 is reduced to reduce energy consumption. This design realizes the coordinated work of the agitator 6 and the slurry supply system, solving the problems of insufficient slurry mixing or excessive energy consumption when the supply flow rate changes, and improving the energy efficiency and operational stability of the absorption tower. As a specific implementation of the linkage control, it can be achieved by setting a corresponding curve between the supply flow rate and the agitator power in the control system, and automatically adjusting the agitator power according to the real-time supply flow rate.

[0030] like Figure 1As shown, in practical applications, a slurry distribution component is installed at the slurry outlet 71 of the submerged slurry supply pipe 7. This component includes an annular distribution pipe and multiple radial slurry distribution holes. The annular distribution pipe is connected to the outlet end of the submerged slurry supply pipe 7, and the multiple radial slurry distribution holes are evenly distributed along the circumference of the annular distribution pipe. The hole diameter can be set to 15-30 mm according to the slurry flow rate requirements. During operation, limestone slurry is transported to the annular distribution pipe through the submerged slurry supply pipe 7. Under pressure, the slurry is evenly sprayed out from each radial slurry distribution hole and diffuses in different directions at the bottom of the oxidation zone 112. Compared with single-point slurry supply, the annular distribution method allows the limestone slurry to be integrated into the slurry in the pool more quickly and evenly, avoiding excessively high or low concentrations of alkaline substances in local areas. With the stirring action of the agitator, the newly injected limestone slurry can complete the initial mixing with the slurry in the oxidation zone 112 within 30-60 seconds, ensuring a uniform pH distribution in the oxidation zone 112. This design solves the problems of local pH fluctuations and slurry mixing lag caused by single-point slurry supply, further improving the stability of pH control in the oxidation zone (112), while reducing the load on the agitator 6 and reducing energy consumption. As a specific implementation of the slurry distribution component, the annular distribution pipe can be made of 316L stainless steel and connected to the submersible slurry supply pipe 7 through a flange for easy disassembly and cleaning later; the radial slurry distribution holes can be chamfered to reduce slurry flow resistance and avoid blockage.

[0031] Working principle: In the slurry tank 11 of the limestone-gypsum wet desulfurization absorption tower, the traditional liquid-top slurry supply method is abandoned, and the limestone slurry is supplied by the liquid-bottom slurry supply method. This makes the slurry tank 11 internally form three reaction zones with different functions and pH values ​​in the vertical direction: absorption zone 111, oxidation zone 112, and diffusion zone 113. The absorption zone 111 is located above the slurry tank 11, with a pH value maintained at ≥5.8. After the flue gas containing sulfur dioxide enters from the top of the absorption tower, it comes into contact with the slurry in the absorption zone 111. The sulfur dioxide reacts with the alkaline substances in the slurry, thus absorbing the sulfur dioxide in the flue gas. The oxidation zone 112 is located below the absorption zone 111, with a pH value controlled at 4.0-4.5. Oxidizing air is introduced into this zone through the oxidation duct 3. Under the low pH environment, bisulfite ions react fully with oxygen and are oxidized to sulfate ions. The diffusion zone 113 is located at the lower part or bottom of the slurry tank 11. The agitator 6 operates continuously to fully mix the newly added limestone slurry with the slurry flowing down from the oxidation zone 112, raising the pH value of the mixed slurry so that it can participate in the circulating desulfurization reaction again. The limestone slurry is supplied to the lower part of oxidation zone 112. By directly injecting limestone slurry into this area, the acidic substances produced by the reaction in oxidation zone 112 are neutralized. Simultaneously, the injection volume is controlled to avoid excessively high pH values, thereby establishing and maintaining a low pH environment in oxidation zone 112. This design achieves precise zoned control of the desulfurization reaction, solving the problem of mutual interference between absorption and oxidation reaction environments and low reaction efficiency in traditional desulfurization processes, thus improving overall desulfurization efficiency. As a specific embodiment of the agitator 6, it can be a side-entry agitator, using inclined blades to form a composite axial and radial mixing flow, enhancing the slurry mixing effect.

[0032] The limestone slurry supply outlet is located in the middle or lower part of the slurry tank wall of the absorption tower. When the supply outlet is located in the middle of the slurry tank wall, the injected limestone slurry can quickly enter the lower part of oxidation zone 112 and participate in pH adjustment in a timely manner; if located in the lower part, it can more directly supplement alkaline substances to oxidation zone 112, while reducing the load on the agitator by utilizing the natural flow of the slurry. This design further optimizes the supply position of limestone slurry, ensuring that it can accurately act on oxidation zone 112, solving the problem of pH control lag caused by unreasonable supply position, and improving the pH stability of oxidation zone 112. As a specific implementation of the supply outlet, it can be a diffuser-type outlet with multiple diversion holes, so that the limestone slurry can be injected more evenly into the lower part of oxidation zone 112.

[0033] An online pH monitoring device is installed in oxidation zone 112 to acquire real-time pH data. The monitoring data is transmitted to the control system, which automatically adjusts the flow rate of the limestone slurry supplied from the submerged system based on a preset pH range of 4.0-4.5. When the pH value is detected to be below 4.0, the slurry flow rate is increased to supplement more alkaline limestone slurry; when the pH value is above 4.5, the slurry flow rate is decreased to avoid excessive alkaline substances. This design achieves dynamic and precise control of the pH value in oxidation zone 112, solving the problems of strong lag and low control accuracy in manual adjustment, and ensuring the efficient progress of the oxidation reaction. As a specific implementation of the online pH monitoring device, an immersion pH meter can be used, installed on the side wall of oxidation zone 112 through a waterproof sealing structure to ensure the accuracy and stability of the monitoring data.

[0034] The limestone slurry supplied submerged is preferentially directed to the inlet side of the slurry circulation pump 4. When the slurry circulation pump 4 operates, a negative pressure is created at the inlet side, drawing in the slurry from the lower part of the oxidation zone 112, which is mixed with the newly injected limestone slurry, and then transporting it to the spray layer 2 at the top of the absorption tower. The spray layer 2 atomizes the slurry and sprays it out, ensuring full contact with the rising flue gas and participation in the desulfurization reaction. This design shortens the circulation path of the limestone slurry, allowing fresh alkaline slurry to quickly participate in the absorption reaction, solving the problems of slurry circulation lag and low utilization rate of alkaline substances in traditional processes, and improving the desulfurization reaction rate. As a specific implementation of the slurry guiding method, a guide plate can be installed at the slurry outlet 71, with the angle of the guide plate designed to direct the limestone slurry towards the inlet area of ​​the slurry circulation pump 4.

[0035] Example 1 Before the renovation of Wanzhou Power Plant in October 2024, the power consumption rate of the desulfurization system (desulfurization system power consumption / power generation) was 0.54%. After the renovation of the two units was completed in 2025, the power consumption rate dropped to 0.49% in the first quarter of 2026. Based on the power generation of 9.8 billion kWh in 2025, the annual savings are 3.92 million kWh (9.8 * 100,000,000 * (0.54 - 0.49%) = 3,920,000 kWh = 3.92 million kWh). The savings amount to 1.764 million yuan (3.92 million kWh * 0.45 yuan / kWh = 1.764 million yuan).

[0036] In 2024, before the renovation of Units 1 and 2, the gypsum moisture content was 14.37% and 11.8% respectively. After the renovation was completed in 2026, the gypsum moisture content dropped to 8.69% and 9.2% respectively. The significant reduction in gypsum moisture content indicates improved gypsum quality, which in turn indicates improved absorber slurry quality and enhanced desulfurization capacity.

[0037] In 2025, both Units 1 and 2 will be operating at full capacity. For Unit 1, without modifications, the SO2 concentration at the inlet is 1271 mg / m³, requiring the operation of three slurry circulation pumps. For Unit 2, with the slurry supply pipeline modified, the SO2 concentration at the inlet is 1243 mg / m³, requiring only the operation of two slurry circulation pumps. This indicates an increase in desulfurization efficiency.

[0038] Before the renovation of Wanzhou Power Plant in October 2024, the SO2 emission reduction unit consumption was 1.84 (the amount of limestone powder needed to consume 1 kg of SO2; the smaller the value, the more energy-efficient it is; the theoretical optimal value is 1.56, but due to various practical reasons, the control standard is below 1.79). After the renovation of the two units was completed in 2025, the SO2 emission reduction unit consumption dropped to 1.66 from January to March 2026. From January to March 2026, the purity of limestone powder was 95.9%. After deducting the impact of purity, the emission reduction unit consumption dropped to 1.66 * 95.9% = 1.59, which basically reached the theoretical optimal value.

[0039] The specific embodiments described herein are merely illustrative examples of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the scope defined by this invention.

Claims

1. A method for submerged slurry desulfurization, characterized in that: In the slurry tank (11) of the limestone-gypsum wet desulfurization absorption tower, limestone slurry is supplied by a submerged slurry supply method, so that at least three reaction zones with different functions and pH values ​​are formed in the vertical direction within the slurry tank (11): Absorption zone (111): Located above the slurry tank (11), with a pH value maintained at ≥5.8, used to absorb sulfur dioxide in flue gas; Oxidation zone (112): Located below the absorption zone (111), the pH value is controlled at 4.0-4.5, and the bisulfite ions are fully oxidized by the introduced air; Diffusion zone (113): Located at the lower part or bottom of the slurry tank (11), the newly added limestone slurry is mixed with the slurry in the oxidation zone (112) by the agitator (6) to increase the pH value of the mixed slurry so that it can participate in the circulation again; The limestone slurry is supplied from the lower part of the oxidation zone (112), and a low pH environment in the oxidation zone (112) is established and maintained by directly injecting limestone slurry into the zone.

2. The submersible slurry desulfurization method according to claim 1, characterized in that, The limestone slurry supply outlet is located in the middle or lower part of the slurry pool wall of the absorption tower.

3. The submersible slurry desulfurization method according to claim 1, characterized in that, The pH of the oxidation zone (112) was monitored online, and the pH value of the oxidation zone (112) was stably controlled within the range of 4.0-4.5 by adjusting the flow rate of limestone slurry supplied by the liquid-supply slurry.

4. The submersible slurry desulfurization method according to claim 1, characterized in that, The limestone slurry supplied by the submerged slurry is preferentially directed to the inlet side of the slurry circulation pump (4), and then transported to the spray layer (2) above the absorption tower via the slurry circulation pump (4) to participate in the desulfurization reaction.

5. A desulfurization absorption tower for implementing the submerged slurry desulfurization method according to any one of claims 1-4, comprising a tower body (1), a spray layer (2), an oxidation duct (3), a slurry circulation pump (4), a gypsum discharge pump (5), and a stirrer (6), characterized in that, It also includes a submerged slurry supply pipe (7), and a slurry pool (11) is provided inside the tower body (1). The submerged slurry supply pipe (7) is provided with a slurry supply outlet (71). The slurry supply outlet (71) is located on the side wall of the slurry pool (11) area. The position of the slurry supply outlet (71) is higher than the effective stirring depth of the agitator (6) blade, but lower than the liquid level of the slurry pool in the traditional above-liquid slurry supply.

6. The submersible slurry supply desulfurization absorption tower according to claim 5, characterized in that, The slurry outlet (71) of the submerged slurry supply pipe (7) is located on opposite sides of the slurry pool in the tower body in the horizontal direction, along with the inlet of the gypsum discharge pump (5).

7. A submersible slurry supply desulfurization absorption tower according to claim 5, characterized in that, The limestone slurry flowing out from the slurry outlet (71) is directed toward or preferentially flows toward the inlet area of ​​the slurry circulation pump (4).

8. A submersible slurry supply desulfurization absorption tower according to claim 5, characterized in that, It also includes a control system, which is connected to a pH meter and a limestone slurry supply regulating valve located in the oxidation zone (112) for dynamically adjusting the limestone slurry supply according to the preset pH target value of the oxidation zone (112).

9. A submersible slurry supply desulfurization absorption tower according to claim 5, characterized in that, The operating power or speed of the agitator (6) is linked to the supply flow rate of the limestone slurry to ensure that the supplied slurry is rapidly diffused.

10. A desulfurization absorption tower according to claim 5, characterized in that, The slurry outlet (71) is provided with a slurry distribution component, which includes an annular diversion pipe and multiple radial slurry distribution holes. The annular diversion pipe is connected to the submerged slurry supply pipe, and the multiple radial slurry distribution holes are evenly distributed along the circumference of the annular diversion pipe to uniformly diffuse limestone slurry into the slurry in the lower part of the oxidation zone (112).

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