Systems and methods for reducing sulfur dioxide-containing gas using a binary process

Abstract

A system and method for reducing sulfur dioxide-containing gas by a binary method. The system for reducing sulfur dioxide-containing gas by a binary method includes a gasifier, which is used for performing a gasification reaction of a carbon-based solid fuel and a gasifying agent, and is used for reducing SO2 in the sulfur dioxide-containing gas by a binary method using the coal gas and semicoke generated by the gasification reaction. The present invention innovatively uses the gasifier as a reduction reactor for sulfur dioxide-containing gas, and uses the two binary products, namely semicoke and coal gas, generated by gasifying the carbon-based fuel in the gasifier to perform binary reduction of SO2 in the sulfur dioxide-containing gas, strengthening the reduction effect and improving the SO2 conversion rate.

Description

Technical Field

[0001] This invention relates to the field of flue gas treatment technology, and in particular to a system and method for the binary reduction of sulfur dioxide-containing gas. Background Technology

[0002] Sulfur dioxide (SO2) is one of the major air pollutants, posing a threat to human health and contributing significantly to acid rain. Therefore, effective recovery and treatment of SO2 from flue gas is essential. Reduction of SO2 from flue gas is a crucial sulfur recovery method, and current SO2 reduction technologies mainly include direct reduction and indirect reduction methods. Direct reduction commonly uses reducing agents such as C, H2, CH4, CO, NH3, as well as coal gas and biomass pyrolysis gas. Indirect reduction methods include calcium sulfide recycling, sodium sulfide recycling, and liquid-phase electrolysis.

[0003] Using carbon as a reducing agent eliminates the need for absorbents and complex absorption systems. Furthermore, coal, coke, and even high-sulfur coal can be used as reducing agents, and the reducing agent and products are easy to store and transport. However, the reaction between carbon and SO2 is complex, produces many byproducts, requires external heating, and is greatly affected by various factors such as carbon type, reaction temperature, and C / SO2 molar ratio. Currently, most applications are limited to experimental research and have not yet been realized in industrial settings.

[0004] SO2 reduction using coal gas can utilize components such as H2, CO, and CH4 in the gas to simultaneously reduce SO2 with multiple components. However, the reaction requires a certain temperature, and most require a catalyst to improve reaction activity. The addition of a catalyst increases the cost of SO2 treatment. Furthermore, although catalytic reduction significantly lowers the reaction temperature, SO2 reduction is exothermic, and the large amount of heat released during the reaction can easily lead to high-temperature sintering and deactivation of the catalyst.

[0005] Previous studies have explored the use of activated carbon / coke and pyrolysis gas coupled reduction of SO2 to produce sulfur. This method utilizes activated carbon to adsorb SO2 from flue gas, followed by desorption to generate regenerated gas. The regenerated gas is then reduced using the pyrolysis gas from the activated carbon processing, requiring activated carbon as a catalyst. This method utilizes pyrolysis gas as a reducing agent to reduce SO2, while simultaneously providing the heat required for the reduction reaction, thus reducing external energy input. Furthermore, the use of activated carbon after adsorption and desorption of sulfur dioxide as a catalyst effectively lowers the temperature required for the reduction of SO2 by a single substance, thereby improving SO2 conversion efficiency and sulfur yield. However, the following drawbacks remain: ① Although the heat from the pyrolysis gas provides the SO2 reduction temperature, the reaction temperature is relatively low, requiring a catalyst for the reduction reaction; ② Activated carbon only acts as a catalyst and cannot perform the reduction function; ③ The pyrolysis gas inevitably contains tar, significantly impacting the quality of the reduced sulfur product, resulting in poor sulfur quality.

[0006] In summary, the existing technology has the following main drawbacks:

[0007] (1) Existing technologies basically use mono-substances as reducing agents for SO2 reduction, which has low reduction efficiency;

[0008] (2) The reduction of SO2 by a single substance requires a high reaction temperature and an external heat input;

[0009] (3) Most existing SO2 reduction reactions require the participation of catalysts to increase the reduction rate. Although the use of catalysts reduces the reaction temperature and increases the reduction efficiency, the addition of catalysts increases the operating cost. Moreover, the reduction reaction is a strongly exothermic process, which can easily cause the catalyst to sinter and deactivate at high temperature.

[0010] (4) Pyrolysis gas is used as a reducing agent, and the tar affects the quality of sulfur products. Summary of the Invention

[0011] In view of this, the main objective of the present invention is to provide a system and method for the binary reduction of sulfur dioxide-containing gas, in order to at least partially solve at least one of the aforementioned technical problems.

[0012] To achieve the above objectives, the technical solution of the present invention is as follows:

[0013] As one aspect of the present invention, a system for the binary reduction of sulfur dioxide-containing gas is provided, comprising:

[0014] A gasifier is used to perform gasification reactions of carbon-based solid fuels and gasifying agents, and to use the coal gas and semi-coke produced by the gasification reaction to perform binary reduction of SO2 in sulfur dioxide-containing gases.

[0015] As one aspect of the present invention, a method for reducing sulfur dioxide-containing gas using a binary method is also provided, comprising the following steps:

[0016] Step 1: The carbon-based solid fuel and gasifying agent undergo a gasification reaction in a gasifier to produce coal gas and semi-coke;

[0017] Step 2: Introduce sulfur dioxide-containing gas into the gasifier and use coal gas and semi-coke to carry out a binary reduction reaction on SO2 in the sulfur dioxide-containing gas.

[0018] Based on the above technical solution, the present invention has at least one or a portion of the following beneficial effects compared to the prior art:

[0019] (1) This invention utilizes a gasifier to reduce SO2 in SO2-containing gas, achieving the generation of a binary substance of semi-coke and coal gas and the binary reduction of SO2 by the binary substance in the same reactor, thus realizing the reduction treatment of SO2 in the gasifier; wherein, the gasifier has a high temperature, and the temperature of the gasification reaction is used to reach the SO2 flue gas reduction temperature, without the need for additional heat input; the high concentration of semi-coke in the system simultaneously acts as a reducing agent and a catalyst for reducing SO2 in coal gas, improving the SO2 conversion efficiency and eliminating the problem of catalyst deactivation;

[0020] (2) The system forms a circulating fluidized bed gasification mode by combining the gasifier, gas-solid separator and return device, achieving a high solid circulation ratio, high system carbon concentration, strong internal circulation and high heat and mass transfer rate. SO2 flue gas is introduced into the area with high system carbon concentration, so that the introduced SO2 flue gas can be quickly and completely mixed and fully contacted with high concentration carbon, coal gas and gasifying agent, etc., which enhances the reduction effect and improves the reaction efficiency.

[0021] (3) A gas inlet containing sulfur dioxide gas is also provided in the return material device so that the sulfur dioxide in the sulfur dioxide gas can directly contact the high concentration of semi-coke in the return material device to undergo an oxidation-reduction reaction, thereby improving the sulfur dioxide conversion efficiency.

[0022] (4) The gasification temperature is high, the system carbon concentration is high, the heating rate of solid fuel is fast, the carbon-based solid fuel enters the gasifier and quickly breaks down bonds to form small molecule gas. The system does not contain tar, and the reducing gas improves the quality of the final product sulfur after reacting in the Claus reactor.

[0023] (5) The waste heat of high-temperature reducing gas can be used to preheat SO2 flue gas, which improves the energy utilization rate of the system. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the binary method for reducing sulfur dioxide flue gas according to Embodiment 1 of the present invention;

[0025] Figure 2This is a schematic diagram of the binary method for reducing sulfur dioxide flue gas according to Embodiment 2 of the present invention;

[0026] Figure 3 This is a schematic diagram of the binary method for reducing sulfur dioxide flue gas according to Embodiment 3 of the present invention;

[0027] Figure 4 This is a schematic diagram of the binary method for reducing sulfur dioxide flue gas according to Embodiment 4 of the present invention.

[0028] The meanings of the reference numerals in the above figures are as follows:

[0029] 1: Gasifier; 2: Gas-solid separator; 3: Return material device; 4: Reducing gas cooling and purification unit; 5: Claus reactor; 6: Flue gas preheating device; 7: Filtration device; 8: Secondary gas-solid separator; 9: Secondary return material device; A: Reducing gas; B: Clean reducing gas; C: Biomass raw material or raw coal; D, S: SO2 flue gas; E: Sulfur; F: Low-temperature reducing gas; G: Gasifying agent. Detailed Implementation

[0030] There is no precedent in the existing technology for applying gasifiers to treat gases containing sulfur dioxide. The application of circulating fluidized bed gasifiers is limited to introducing fuel and gasifying agent into them. This invention uses a circulating fluidized bed gasifier as an SO2 reduction reactor, introducing sulfur dioxide gas at the same time as fuel and gasifying agent to achieve SO2 reduction treatment. This is one of the innovations of this invention.

[0031] This invention uses a circulating fluidized bed gasifier as a reduction reactor for sulfur dioxide-containing gas. Utilizing the circulating fluidized bed gasification process, SO2 is simultaneously reduced by the binary substances of semi-coke and coal gas within the same reactor, improving SO2 conversion rate. The circulating fluidized bed gasifier features a high solids circulation ratio, high system carbon concentration, strong internal circulation, and high heat and mass transfer rates. Introducing sulfur dioxide-containing gas into the high-carbon-concentration region allows for rapid and complete mixing of the introduced sulfur dioxide with the high-concentration carbon, coal gas, and gasifying agent, enhancing the reduction effect and improving reaction efficiency. Using a circulating fluidized bed gasifier as a reduction reactor… The gasifier features a high gasification temperature, utilizing the gasification reaction temperature to reach the reduction temperature of sulfur dioxide-containing gases without requiring additional heat input. The high concentration of semi-coke within the system simultaneously acts as a reducing agent and a catalyst for SO2 reduction from coal gas, improving SO2 conversion efficiency and eliminating catalyst deactivation issues. The high gasification temperature and high carbon concentration in the system result in rapid heating of solid fuels. Upon entering the gasifier, carbon-based solid fuels rapidly break down bonds, forming small-molecule gases. The system is tar-free, improving the quality of the final sulfur product. Furthermore, the waste heat from the high-temperature reducing gas can be used to preheat sulfur dioxide-containing gases, enhancing the system's energy utilization rate.

[0032] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0033] As one aspect of the present invention, a system for the binary reduction of sulfur dioxide-containing gas is provided, comprising:

[0034] A gasifier is used to perform gasification reactions of carbon-based solid fuels and gasifying agents, and to use the coal gas and semi-coke produced by the gasification reaction to perform binary reduction of SO2 in sulfur dioxide-containing gases.

[0035] In embodiments of the present invention, the system further includes a gas-solid separator and a return material device, wherein the gas-solid separator and the return material device form a circulating fluidized bed gasification mode with the gasifier; wherein...

[0036] A gas-solid separator is used to separate the gas and solid products discharged from the gasifier.

[0037] The return material device is used to collect the semi-coke separated by the gas-solid separator and return it to the gasifier.

[0038] In an embodiment of the present invention, an SO2 inlet for introducing sulfur dioxide gas is provided on the gasifier, and the SO2 inlet is located at the bottom of the gasifier.

[0039] In an embodiment of the present invention, a return port connected to the return device is provided on the gasifier, and a throat is provided on the gasifier below the return port;

[0040] The inner diameter at the throat is smaller than the inner diameter of the gasifier.

[0041] In this embodiment of the invention, a throat is provided below the return port of the gasifier. The airflow velocity at the throat is high, which on the one hand reduces the back mixing of solid particles returning from the return port and solid particles in the upper part of the gasifier furnace to the lower part of the furnace, thereby increasing the concentration of solid particles in the upper part of the furnace. On the other hand, it accelerates the carrying of heat to the upper part of the furnace and reduces the radiation of heat to the bottom of the furnace.

[0042] In an embodiment of the present invention, a secondary air inlet for introducing sulfur dioxide gas is provided on the gasifier, and the height h1 between the secondary air inlet and the bottom of the gasifier furnace satisfies: h≤h1≤0.5H; where h is the height from the return port to the bottom of the gasifier furnace, and H is the height of the gasifier furnace.

[0043] In this embodiment of the invention, the secondary air inlet is located above the return feed inlet and the throat. This area has a high concentration of both carbon and coal gas. The SO2 flue gas introduced through the secondary air inlet rapidly contacts and reacts with the coal gas already generated in the gasifier and the high-concentration carbon returned from the return feed device, thus improving the reduction reaction rate and efficiency. The throat design allows the large amount of heat released by the SO2 reduction reaction to be quickly carried to the upper part of the furnace, blocking the transfer of heat to the lower part of the furnace and preventing coking at the bottom of the furnace, where the ash concentration is high, due to high temperature.

[0044] In an embodiment of the present invention, the lower part of the gasifier furnace is configured as a conical section with a gradually decreasing inner diameter; the inner diameter of the bottom of the conical section is d2, and the inner diameter of the gasifier is d, wherein 0.2d≤d2≤0.8d.

[0045] In this embodiment of the invention, the bottom of the gasifier is designed as a conical section, which increases the bottom fluidization velocity and can quickly remove the large amount of heat released by the SO2 reduction reaction, thus ensuring the stability of the system operation.

[0046] In an embodiment of the present invention, the return device includes a gas inlet for causing SO2 in the sulfur dioxide-containing gas input from the gas inlet to undergo an oxidation-reduction reaction with the semi-coke.

[0047] In this embodiment of the invention, the sulfur dioxide-containing gas enters the system in two parts. One part of the sulfur dioxide-containing gas enters through the SO2 air inlet at the bottom of the gasifier or the secondary air inlet in the lower part of the gasifier, while the other part enters from the bottom of the return material device. The high-temperature semi-coke concentration in the return material device allows the sulfur dioxide in the gas to quickly and fully contact the high-concentration semi-coke, resulting in a redox reaction that generates a sulfur-containing gas primarily composed of elemental sulfur. This sulfur dioxide-containing gas also serves as the return air to maintain the return material and system circulation. The generated sulfur-containing gas returns to the gasifier along with the high-temperature carbon (i.e., semi-coke).

[0048] In an embodiment of the invention, the system further includes a Claus reactor for reacting H2S in the gas separated by the gas-solid separator with SO2 in the sulfur dioxide-containing gas via a Claus reaction.

[0049] In embodiments of the present invention, the system further includes a flue gas preheating device for heat exchange between the gas separated by the gas-solid separator and the sulfur dioxide-containing gas. That is, waste heat is recovered from the reducing gas separated by the gas-solid separator to cool the reducing gas, while simultaneously preheating the sulfur dioxide-containing gas, thereby improving the system's energy utilization rate.

[0050] In an embodiment of the present invention, the system further includes a filtration device for filtering the gas separated by the gas-solid separator.

[0051] In embodiments of the present invention, the gas-solid separator includes a primary gas-solid separator and a secondary gas-solid separator; the return material device includes a primary return material device and a secondary return material device;

[0052] The primary gas-solid separator is used to perform primary gas-solid separation on the products discharged from the gasifier, and the secondary gas-solid separator is used to perform secondary gas-solid separation on the gas separated from the primary gas-solid separator.

[0053] The primary return device is used to collect the solid particles separated by the primary gas-solid separator, and uses the semi-coke in the solid particles to carry out an oxidation-reduction reaction on SO2 in the sulfur dioxide-containing gas, and then returns the material to the gasifier.

[0054] The secondary return device is used to return the solid particles separated by the secondary gas-solid separator to the gasifier.

[0055] As one aspect of the present invention, a method for reducing sulfur dioxide-containing gas using a binary method is also provided, comprising the following steps:

[0056] Step 1: The carbon-based solid fuel and gasifying agent undergo a gasification reaction in a gasifier to produce coal gas and semi-coke;

[0057] Step 2: Introduce sulfur dioxide-containing gas into the gasifier and use coal gas and semi-coke to carry out a binary reduction reaction on SO2 in the sulfur dioxide-containing gas.

[0058] In this embodiment of the invention, the carbon-based solid fuel includes either coal or biomass, or a mixture of the two; the particle size of the carbon-based solid fuel is 0 mm to 12 mm.

[0059] The vaporizing agent includes one of the following: air, oxygen-enriched air, and oxygen, or a combination of one of the above three with water vapor.

[0060] In this embodiment of the invention, carbon-based solid fuel and gasifying agent undergo a gasification reaction in a gasifier, with the temperature inside the gasifier being 900℃~1200℃; the fluidization velocity at the bottom of the gasifier is 1.5m / s~5m / s. The gasification reaction produces coal gas containing components such as H2, CO, CH4, and CO2.

[0061] In embodiments of the present invention, the sulfur dioxide-containing gas may be, but is not limited to, sulfur dioxide flue gas, wherein the volume percentage of sulfur dioxide is 3% to 25%.

[0062] In an embodiment of the present invention, after step 2 is completed, the method further includes:

[0063] Step 3: Introduce sulfur dioxide-containing gas into the return material device and use semi-coke to reduce the SO2 in the sulfur dioxide-containing gas.

[0064] In a preferred embodiment of the present invention, the method for reducing SO2 flue gas using a binary method includes the following steps:

[0065] Step 1: Carbon-based solid fuel is added from the lower part of the gasifier furnace and reacts with the gasifying agent introduced from the bottom of the furnace to produce gas containing components such as H2, CO, CH4, and CO2. The main reactions occurring in the gasifier include:

[0066] C m H n →C+CH4+H2

[0067] C + O₂ → CO + CO₂

[0068] C + H₂O → CO + H₂

[0069] Step 2: SO2 flue gas is introduced from both the return feed device and the gasifier, and the circulating fluidized bed gasifier is used as the SO2 reduction reactor to achieve efficient SO2 reduction.

[0070] ① A portion of the SO2 flue gas is fed into the gasifier from the return feeder, where it comes into direct contact with the high concentration of semi-coke inside the return feeder, resulting in an oxidation-reduction reaction that improves reaction efficiency. The main reactions that occur include:

[0071] Main reaction:

[0072] C + SO₂ → S + CO₂

[0073] Side reactions:

[0074] C+2S→CS2

[0075] C + CO₂ → 2CO

[0076] CO+S→COS

[0077] ②Another portion of the SO2 flue gas is introduced into the gasifier, where it reacts simultaneously with the incompletely reacted solid carbon particles and gases such as H2, CO, and CH4. This process achieves the simultaneous reduction of SO2 by the binary substances of solid carbon and gas. The main reactions occurring in the gasifier include:

[0078] C + SO₂ → S + CO₂

[0079] CO + SO₂ → S + CO₂

[0080] CH4 + SO2 → S + H2O

[0081] H2 + SO2 → H2S

[0082] CO+S→COS

[0083] COS + H₂O → H₂S

[0084] Preferably, a portion of the SO2 flue gas is introduced from a secondary air inlet located in the lower part of the gasifier. The secondary air inlet is located above the return material inlet, where the carbon concentration and gas concentration are both relatively high. Introducing SO2 flue gas from this location increases the SO2 reduction rate and reduction efficiency.

[0085] The high concentration of high-temperature carbon particles in the circulating fluidized bed, under the conditions of excess carbon, sufficient H2 and high temperature in the gasifier, SO2 is mainly reduced to hydrogen sulfide (H2S), and there are also small amounts of elemental sulfur, COS and other substances.

[0086] A mixture of gases containing H2S, H2, CO, CH4, CO2 and other components, as well as carbon particles, enters the gas-solid separator from the top of the circulating fluidized bed gasifier. Gas-solid separation is carried out here. Most of the solid particles are collected by the gas-solid separator and returned to the gasifier via the return device to continue participating in the reaction. The remaining reducing gas enters the subsequent purification and cooling process.

[0087] (5) The purified and cooled clean reducing gas enters the Claus reactor, and SO2 flue gas is introduced into the Claus reactor at the same time. The clean reducing gas and SO2 flue gas undergo the Claus reaction with a molar ratio of H2S to SO2 of 2:1 to generate elemental sulfur, which becomes the sulfur product.

[0088] The technical solution of the present invention will be further described below with reference to specific embodiments. However, it should be noted that the following embodiments are only used to illustrate the technical solution of the present invention, but the present invention is not limited thereto.

[0089] Example 1

[0090] Figure 1 This is a schematic diagram of the binary method for reducing SO2 flue gas according to Embodiment 1 of the present invention.

[0091] like Figure 1 As shown, in this embodiment, the gasifier 1, gas-solid separator 2, and return material device 3 are a circulating fluidized bed gasification method.

[0092] 0-10mm raw coal C is added from the middle and lower part of gasifier 1 and reacts with gasifying agent G introduced from the bottom of gasifier 1 to generate coal gas containing components such as H2, CO, CH4 and CO2. The temperature at the bottom of gasifier body 1 is 965℃.

[0093] The vaporizing agent G is a mixture of oxygen and water vapor.

[0094] SO2 flue gas S with an SO2 content of 18% is divided into two parts and enters gasifier 1. One part of SO2 flue gas S enters from the bottom of gasifier 1, i.e. SO2 inlet, and the other part of SO2 flue gas S enters from the bottom of return material device 3. The SO2 flue gas S entering gasifier 1 reacts with the semi-coke remaining in the gasification reaction and the generated coal gas. SO2 is reduced by the semi-coke and coal gas to generate reducing gas containing H2S, H2, CO, CH4 and CO2.

[0095] The reducing gas, carrying some solid particles, leaves from the top of the gasifier 1 and enters the gas-solid separator 2. Most of the solid particles are separated and enter the return device 3, where they react with the SO2 flue gas introduced here. The reaction products are returned to the middle and lower part of the gasifier 1 through the return device 3. The remaining reducing gas A leaves the gas-solid separator 2 and enters the reducing gas cooling and purification unit 4. After being cooled and purified, it forms clean reducing gas B and leaves the reducing gas cooling and purification unit 4.

[0096] The temperature of reducing gas A is 900℃. The temperature of clean reducing gas B is 630℃.

[0097] Clean reducing gas B and SO2 flue gas D enter Claus reactor 5 at a molar ratio of H2S to SO2 of 2:1 to carry out the Claus reaction and produce sulfur E.

[0098] It is worth mentioning that SO2 flue gas D and SO2 flue gas S have the same composition, which will not be repeated in the following Examples 2-4.

[0099] Example 2

[0100] Figure 2 This is a schematic diagram of the binary method for reducing SO2 flue gas in Example 2 of this paper.

[0101] like Figure 2 As shown, in this embodiment, the gasifier 1, gas-solid separator 2, and return material device 3 are a circulating fluidized bed gasification system. The gasifier 1 in this embodiment 2 has a throat at its lower part.

[0102] The 0-10mm biomass feedstock C is added from the middle and lower part of the gasifier 1 and reacts with the gasifying agent G introduced from the bottom of the gasifier 1 to generate coal gas containing components such as H2, CO, CH4 and CO2. The temperature at the bottom of the gasifier 1 is 940℃.

[0103] Sulfur dioxide flue gas S with an SO2 content of 20% is divided into two parts and enters gasifier 1. One part of the SO2 flue gas S enters from the upper middle part of gasifier 1, i.e., the secondary air inlet, while the other part of the SO2 flue gas S enters from the bottom of return material device 3. The SO2 flue gas S entering gasifier 1 reacts with the semi-coke remaining from the gasification reaction and the generated coal gas. The SO2 is reduced by the semi-coke and coal gas, which are binary substances, to generate reducing gas containing H2S, H2, CO, CH4, and CO2.

[0104] The reducing gas carrying some solid particles leaves from the top of the gasifier 1 and enters the gas-solid separator 2. Most of the solid particles are separated and enter the return device 3, where they react with the SO2 flue gas S introduced here. The reaction products are returned to the middle and lower part of the gasifier 1 by the return device 3, and the remaining reducing gas A leaves the gas-solid separator 2.

[0105] The temperature of reducing gas A is 910℃.

[0106] In this embodiment, a flue gas preheating device 6 is added, which adopts an indirect heat exchange method between SO2 flue gas S and reducing gas A to preheat SO2 flue gas S and simultaneously cool reducing gas A. SO2 flue gas S enters the flue gas preheating device 6 and exchanges heat with reducing gas A, raising the temperature of SO2 flue gas S to 550°C. Afterward, SO2 flue gas S enters the gasifier 1 and the return material device 3 to undergo a reduction reaction.

[0107] The temperature of the low-temperature reducing gas F at the outlet of the flue gas preheating device 6 is 650°C. It then enters the filtration device 7 to remove dust from the low-temperature reducing gas F, forming clean reducing gas B which leaves the filtration device 7.

[0108] The temperature of the clean reducing gas B is 600℃.

[0109] Clean reducing gas B and SO2 flue gas D enter Claus reactor 5 at a molar ratio of H2S to SO2 of 2:1 to carry out the Claus reaction and produce sulfur E.

[0110] Example 3

[0111] Figure 3 This is a schematic diagram of the binary method for reducing SO2 flue gas according to Embodiment 3 of the present invention.

[0112] like Figure 3 As shown, in this embodiment, the gasifier 1, gas-solid separator 2, and return material device 3 are a circulating fluidized bed gasification system. The bottom of the gasifier 1 is a conical section design.

[0113] 0-10mm raw coal C is added from the middle and lower part of gasifier 1 and reacts with gasifying agent G introduced from the bottom of gasifier 1 to generate coal gas containing components such as H2, CO, CH4 and CO2, while semi-coke is produced at the same time. The temperature at the bottom of gasifier 1 is 980℃.

[0114] The vaporizing agent G is oxygen.

[0115] SO2 flue gas with an SO2 content of 18.0% is divided into two parts and enters gasifier 1. One part of the SO2 flue gas S enters from the bottom of return material device 3.

[0116] Another portion of the SO2 flue gas S enters from the bottom of gasifier 1 and reacts with the carbon remaining from the gasification reaction and the generated coal gas. The SO2 is reduced by the binary substances of solid carbon and coal gas to generate reducing gas containing H2S, H2, CO, CH4, and CO2. The SO2 flue gas S, along with oxygen, serves as the fluidizing medium in the gasifier.

[0117] The reducing gas carrying some solid particles leaves from the top of the gasifier 1 and enters the gas-solid separator 2. Most of the solid particles are separated and enter the return device 3, where they react with the SO2 flue gas introduced here. The reaction products are returned to the middle and lower part of the gasifier body 1 by the return device 3, and the remaining reducing gas A leaves the gas-solid separator 2.

[0118] The temperature of reducing gas A is 930℃.

[0119] Preferably, the present invention includes a flue gas preheating device 6, which uses an indirect heat exchange method between SO2 flue gas and gasification reducing gas to preheat SO2 flue gas S and simultaneously cool the reducing gas A. SO2 flue gas S enters the flue gas preheating device 6, where it exchanges heat with the reducing gas A, raising the temperature of SO2 flue gas S to 550°C. Afterward, SO2 flue gas S enters the gasifier 1 and the return material device 3 to undergo a reduction reaction.

[0120] The temperature of the low-temperature reducing gas F at the outlet of the flue gas preheating device 6 is 650°C. It then enters the filtration device 7 to remove dust from the low-temperature reducing gas F, forming clean reducing gas B which leaves the filtration device 7.

[0121] The temperature of the clean reducing gas B is 600℃.

[0122] Clean reducing gas B and SO2 flue gas D enter reactor 5 at a molar ratio of H2S to SO2 of 2:1 to carry out the Claus reaction and produce sulfur E.

[0123] Example 4

[0124] Figure 4 This is a schematic diagram of the binary method for reducing SO2 flue gas according to Embodiment 4 of the present invention.

[0125] like Figure 4 As shown, the embodiment of the present invention adopts a circulating fluidized bed partial gasification method, which includes a gasifier 1, a gas-solid separator 2, a return material device 3, a secondary gas-solid separator 8, and a secondary return material device 9.

[0126] 0-10mm raw coal C is added from the middle and lower part of gasifier 1 and undergoes a partial gasification reaction with the gasifying agent G introduced from the bottom of gasifier 1 to generate coal gas containing components such as H2, CO, CH4, CO2 and tar, while semi-coke is produced at the same time. The gasifying agent G is air, and the temperature at the bottom of gasifier 1 is 920℃.

[0127] SO2 flue gas with a SO2 content of 17% is divided into two parts and enters gasifier 1. One part of the SO2 flue gas S enters from the bottom of return device 3. The high concentration of high-temperature carbon in return device 3 causes the SO2 flue gas introduced here to quickly and fully contact the high-concentration high-temperature carbon and undergo an oxidation-reduction reaction, generating sulfur-containing gas mainly composed of elemental sulfur. The sulfur-containing gas also serves as return air to maintain return and system circulation. The generated sulfur-containing gas returns to the gasifier body along with the high-temperature carbon.

[0128] Another portion of the SO2 flue gas S enters from the bottom of the gasifier 1, but it is not limited to this. It can also enter entirely from the gasifier 1, including from the SO2 air inlet at the bottom of the gasifier 1 and / or from the secondary air inlet in the middle of the gasifier 1.

[0129] SO2 flue gas S enters from the bottom of gasifier 1 and reacts with some of the carbon remaining from the gasification reaction and the generated coal gas. SO2 is reduced by the binary substances of solid carbon and coal gas to generate reducing gas containing H2S, H2, CO, CH4 and CO2. SO2 flue gas S, together with gasifying agent G, serves as the fluidizing medium of the gasifier.

[0130] The reducing gas, carrying some solid particles, leaves from the top of the gasifier 1 and enters the gas-solid separator 2. Some solid particles are separated and enter the return device 3, where they react with the SO2 flue gas S introduced here. The reaction products are returned to the middle and lower part of the gasifier 1 by the return device 3. The remaining reducing gas with some solid particles enters the secondary gas-solid separator 8 for further collection of solid particles. The collected solid particles are returned to the middle and upper part of the gasifier 1 by the secondary return device 9. These solid particles undergo catalytic cracking and adsorption removal of tar in the gas within the gasifier 1. The remaining reducing gas A leaves the secondary gas-solid separator 8.

[0131] The temperature of reducing gas A is 910℃.

[0132] Preferably, the present invention includes a flue gas preheating device 6, which uses an indirect heat exchange method between SO2 flue gas and gasification reducing gas to preheat SO2 flue gas S and simultaneously cool the reducing gas. SO2 flue gas S enters the flue gas preheating device 6 and exchanges heat with reducing gas A, raising the temperature of SO2 flue gas S to 550°C. Afterward, SO2 flue gas S enters the gasifier 1 and the return material device 3 to undergo a reduction reaction.

[0133] The temperature of the low-temperature reducing gas F at the outlet of the flue gas preheating device 6 is 650°C. It then enters the filtration device 7 to remove dust from the low-temperature reducing gas F, forming clean reducing gas B which leaves the filtration device 7.

[0134] The temperature of the clean reducing gas B is 630℃.

[0135] Clean reducing gas B and SO2 flue gas D enter Claus reactor 5 at a molar ratio of H2S to SO2 of 2:1 to carry out the Claus reaction and produce sulfur E.

[0136] This embodiment uses a partial gasification fluidized bed gasifier as the SO2 reduction reactor. No external steam is required. The partial gasification produces coal gas with a high hydrogen content, which promotes the reduction of SO2 to H2S. Furthermore, the reactor and process can achieve complete removal of tar, improving the quality of the final product, sulfur. At the same time, the system can simultaneously produce semi-coke products, resulting in superior system and process economic performance.

[0137] As those skilled in the art will know, the system and method described in this application are also applicable to the reduction treatment of sulfur dioxide in other gases containing sulfur dioxide. Therefore, the application of this system and method to treat sulfur-containing gases is also within the scope of protection of this invention.

[0138] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. 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 system for the binary reduction of sulfur dioxide-containing gas, characterized in that, include: A gasifier is used for gasification reaction of carbon-based solid fuel and gasifying agent, and for binary reduction of SO2 in sulfur dioxide-containing gas using the gas and semi-coke produced by the gasification reaction; wherein the gasifier is a circulating fluidized bed gasifier, and the gasifier is provided with an SO2 inlet for introducing sulfur dioxide-containing gas. The system also includes a gas-solid separator and a return material device, which together with the gasifier form a circulating fluidized bed gasification mode. Among them, the gas-solid separator is used to separate the gas and solid products discharged from the gasifier; A return material device is used to collect the semi-coke separated by the gas-solid separator and return it to the gasifier; the return material device includes a gas inlet for causing SO2 in the sulfur dioxide-containing gas input from the gas inlet to undergo an oxidation-reduction reaction with the semi-coke. The gasifier is provided with a return port connected to the return device, and a throat is provided on the gasifier below the return port; the inner diameter of the throat is smaller than the inner diameter of the gasifier; a secondary air inlet for introducing sulfur dioxide gas is provided on the gasifier, and the secondary air inlet is located above the return port and the throat. The system also includes a Claus reactor for reacting H2S in the gas separated by the gas-solid separator with SO2 in the sulfur dioxide-containing gas via a Claus reaction.

2. The system as described in claim 1, characterized in that, The SO2 air inlet is located at the bottom of the gasifier.

3. The system as described in claim 2, characterized in that, The height h1 between the secondary air inlet and the bottom of the gasifier furnace chamber satisfies: h ≤ h1 ≤ 0.5H; where h is the height from the return material inlet to the bottom of the gasifier furnace chamber, and H is the height of the gasifier furnace chamber.

4. The system as described in claim 1, characterized in that, The system also includes a flue gas preheating device for exchanging heat between the gas separated by the gas-solid separator and the sulfur dioxide-containing gas.

5. The system as described in claim 1, characterized in that, The system also includes a filtration device for filtering the gas separated by the gas-solid separator.

6. The system as described in claim 1, characterized in that, The gas-solid separator includes a primary gas-solid separator and a secondary gas-solid separator; the return material device includes a primary return material device and a secondary return material device; The primary gas-solid separator is used to perform primary gas-solid separation on the products discharged from the gasifier, and the secondary gas-solid separator is used to perform secondary gas-solid separation on the gas separated from the primary gas-solid separator. The primary return device is used to collect the solid particles separated by the primary gas-solid separator, and to use the semi-coke in the solid particles to carry out an oxidation-reduction reaction on SO2 in the sulfur dioxide-containing gas, and then return the material to the gasifier. The secondary return device is used to return the solid particles separated by the secondary gas-solid separator to the gasifier.

7. A method for binary reduction of sulfur dioxide-containing gas using the system according to any one of claims 1-6, characterized in that, Includes the following steps: Step 1: The gasification reaction of carbon-based solid fuel and gasifying agent is carried out in a gasifier to generate coal gas and semi-coke. The gasifier is equipped with an SO2 inlet for introducing sulfur dioxide gas. Step 2: Introduce sulfur dioxide-containing gas into the gasifier, and use coal gas and semi-coke to carry out a binary reduction reaction on SO2 in the sulfur dioxide-containing gas; wherein, the gasifier is a circulating fluidized bed gasifier; The method further includes: Step 3: Introduce sulfur dioxide-containing gas into the return material device, and use the semi-coke separated by the gas-solid separator to reduce the SO2 in the sulfur dioxide-containing gas. The gas-solid separator and the return material device together with the gasifier form a circulating fluidized bed gasification mode.

8. The method as described in claim 7, characterized in that, The sulfur dioxide-containing gas is sulfur dioxide flue gas, wherein the volume percentage of sulfur dioxide is 3% to 25%. The temperature inside the gasifier is 900℃~1200℃; The particle size of the carbon-based solid fuel is 0 mm to 12 mm.

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