Method for treating emissions of synthetic rutile acid digestion off-gas

Abstract

The application discloses a kind of synthetic rutile acidolysis waste gas treatment and discharge method, belong to titanium chemical industry waste gas purification technical field.The application uses four-stage coupling purification process: first, realize gaseous sublimation sulfur liquid phase phase change and early separation recovery by accurate temperature control, avoid solid sulfur generation from source;Then through dilute sulfuric acid quenching prewashing, remove mine dust, large size acid mist and recover sulfur paste;Subsequently, weak acid buffer is used to cooperate with composite lye fractional absorption, dynamically adapt intermittent waste gas pulse load, remove sulfide and hydrogen fluoride;Finally, carry out depth aerosol removal, remove submicron acid mist, residual sulfur particle and heavy metal aerosol.The application runs under micro negative pressure throughout, can guarantee long-period stable operation of device, eliminate safety hazard, realize waste gas ultra-low standard discharge and elemental sulfur resource recovery, process flow can be recycled, operation and maintenance cost is low, adapt to industrial application.

Description

Technical Field

[0001] This invention relates to the field of titanium chemical waste gas purification technology, and specifically discloses a method for treating and discharging waste gas from the acid hydrolysis of synthesized rutile. Background Technology

[0002] The current rutile synthesis reaction is carried out in a concentrated sulfuric acid intermittent acidolysis process at 180-220℃. The reaction process releases a large amount of high-temperature and high-humidity waste gas instantly. The composition of this waste gas is significantly different from that of the waste gas from the acidolysis of ilmenite. The waste gas contains a certain amount of gaseous sublimed sulfur. After the temperature drops, the gaseous sublimed sulfur easily condenses and transforms into solid sulfur particles.

[0003] Most existing acidolysis waste gas treatment methods employ a combination of cooling scrubbing and alkaline absorption, along with deep demisting. However, when treating rutile acidolysis waste gas, solid sulfur particles generated from the cooling of gaseous sublimated sulfur easily deposit within the purification process, causing blockages in pipelines and scrubbing units. Sulfur accumulation also poses a risk of spontaneous combustion, and sulfur particles are prone to escape, requiring frequent shutdowns for cleaning and maintenance, resulting in poor continuous operation. Furthermore, acidolysis is a batch-intermittent reaction, leading to drastic fluctuations in waste gas flow rate and pollutant concentration. Conventional fixed-condition purification processes struggle to adapt to pulsed impact loads, and submicron sulfuric acid mist aerosols easily penetrate the treatment units, causing acid mist tailings in the exhaust gas. Associated hydrogen fluoride and heavy metal aerosols in the waste gas are difficult to remove completely, resulting in high sulfur and fluoride loads in the liquid phase after scrubbing, increasing the pressure on subsequent wastewater treatment.

[0004] Existing publicly available solutions for rutile acidolysis waste gas purification primarily target ilmenite tail gas and do not address the phase transition process control of gaseous sublimated sulfur in rutile synthesis waste gas. These solutions mainly focus on the downstream capture of already formed solid sulfur particles, failing to inhibit solid sulfur formation at the source and thus struggling to completely resolve sulfur deposition-related issues. Attempts to treat sulfur pollutants using dry filtration and high-temperature catalytic oxidation have encountered problems such as filter media corrosion and clogging, catalyst poisoning and deactivation, and high operating costs. Therefore, it is necessary to develop a purification method that can adapt to intermittent pulsed operating conditions, prioritizing the phase transition removal of gaseous sublimated sulfur to achieve ultra-low emissions. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a method for treating and discharging waste gas from the acid hydrolysis of synthesized rutile. This method is adaptable to intermittent pulse operating conditions, prioritizes the phase transformation removal of gaseous sublimated sulfur, and achieves ultra-low emissions of waste gas.

[0006] To solve the above technical problems, the technical solution adopted by this invention is as follows: a method for treating and discharging waste gas from the acid hydrolysis of synthesized rutile, characterized in that: the high-temperature waste gas produced by the intermittent acid hydrolysis of synthesized rutile with concentrated sulfuric acid is subjected to the following steps in sequence: S1: sulfur phase change regulation and removal step; S2: rapid cooling and pre-washing step; S3: staged absorption and purification step; S4: deep aerosol removal step; and then the exhaust is completed; specifically as follows:

[0007] The original temperature of the high-temperature exhaust gas is 170-220℃, and the exhaust gas components include water vapor, gaseous sublimed sulfur, sulfuric acid mist aerosol, SO2, trace amounts of H2S, HF, titanium ore dust, and heavy metal aerosol.

[0008] The S1 step of sulfur phase change regulation and removal involves maintaining the overall exhaust gas under a slight negative pressure, indirectly cooling the exhaust gas to reduce its temperature and control it at 125-145℃. This temperature range is higher than the freezing point of elemental sulfur, causing the gaseous sublimated sulfur in the exhaust gas to undergo a phase change and condense into liquid sulfur. The formed liquid sulfur is then separated and removed.

[0009] S2: Rapid cooling and pre-washing step, the waste gas after sulfur phase change regulation and removal is rapidly cooled by contact, using 5-12wt% dilute sulfuric acid as washing liquid to cool the waste gas to 60-75℃, remove coarse mineral dust and most of the large-particle sulfuric acid mist in the waste gas, and at the same time capture the suspended liquid sulfur mist in the waste gas into the washing liquid, and separate sulfur paste from the washing liquid;

[0010] S3: The graded absorption and purification step involves treating the exhaust gas, after rapid cooling and pre-washing, with a weak acid buffer wash and an alkaline wash. The weak acid buffer wash controls the pH of the acid solution to 2.5-4.0 to buffer fluctuations in exhaust gas concentration and pre-capture residual acid mist particles. The alkaline absorption uses a composite alkaline solution with a pH of 8-11 to absorb and remove SO2, residual H2S, and HF from the exhaust gas. The spray flow rate and alkaline concentration of the washing solution are dynamically adjusted according to the time sequence of the acid hydrolysis reaction to adapt to the pulse impact of the exhaust gas caused by the intermittent reaction.

[0011] The S4 step, deep aerosol removal, involves deep aerosol removal of the waste gas after staged absorption and purification, removing submicron sulfuric acid mist, residual sulfur particles, and heavy metal aerosols, ensuring that the treated waste gas meets emission standards.

[0012] Furthermore, in step S1, the sulfur phase change regulation and removal step, the heat exchange medium used for indirect cooling is a 5-12wt% dilute sulfuric acid aqueous solution, the temperature of the heat exchange medium is maintained at 130-142℃, and the separated liquid sulfur is recovered as a by-product.

[0013] Furthermore, in step S1, the sulfur phase change control and removal step, the waste gas temperature is maintained above 120°C throughout the entire waste gas transportation process to prevent gaseous sublimated sulfur from prematurely condensing into solid sulfur during transportation.

[0014] Furthermore, in step S1, the sulfur phase change control and removal step, the process pressure difference is monitored. When the pressure difference rises to a set threshold, low-pressure superheated steam at 140-150℃ is introduced to melt and remove scale. The waste gas treatment process is not interrupted during the scale removal process.

[0015] Furthermore, in step S2, the rapid cooling pre-washing step, a portion of the dilute sulfuric acid washing liquid is discharged and sent to the acidolysis waste acid treatment system, while the other portion is supplemented with process water to maintain the concentration of dilute sulfuric acid; the separated sulfur paste is melted to recover elemental sulfur.

[0016] Furthermore, in step S3, the graded absorption and purification step, the composite alkaline solution is a mixture of sodium carbonate and sodium hydroxide. During the main acidolysis reaction burst stage, the spray flow rate is increased and the alkaline solution concentration is increased, while the spray load is reduced during feeding and the end of the reaction.

[0017] Furthermore, in step S4, the deep aerosol removal step, the collected washing liquid is recycled back to the weakly acidic buffer washing liquid phase system for reuse.

[0018] Furthermore, the entire process of steps S1 (sulfur phase change controlled removal), S2 (rapid cooling pre-washing), S3 (graded absorption purification), and S4 (deep aerosol removal) is kept under a slight negative pressure to prevent the leakage of acidic waste gas.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1. This invention achieves pre-removal of gaseous sublimation sulfur through precise temperature control, thereby preventing the precipitation and deposition of solid sulfur from the source. It solves the defects of traditional processes, such as easy clogging, easy scaling, and the need for frequent shutdowns for cleaning, eliminates the safety hazard of sulfur spontaneous combustion, and can operate continuously and stably for a long time. At the same time, it realizes the resource recovery of elemental sulfur.

[0021] 2. This invention employs a weak acid buffering and dynamically adjustable staged absorption process to effectively buffer fluctuations in exhaust gas concentration, match load changes at different reaction stages of acidolysis, and avoid pollutant penetration and tailing problems of acid mist in the exhaust gas.

[0022] 3. This invention can simultaneously and efficiently remove dust, sulfides, hydrogen fluoride, submicron acid mist and heavy metal aerosols, and the waste gas treatment is thorough and meets standards with high stability; the whole process is under micro-negative pressure with no leakage, and the washing liquid can be recycled, which greatly reduces the cost of reagents and operation and maintenance. Detailed Implementation

[0023] The present invention and its effects will be further explained below through specific embodiments.

[0024] The following examples are for illustrative purposes only and are not intended to limit the scope of protection of this invention. This invention addresses the high-temperature waste gas generated from the intermittent acidolysis of concentrated sulfuric acid during the synthesis of rutile. The waste gas temperature is 170-220℃, and it contains pollutants such as gaseous sublimed sulfur, sulfuric acid mist aerosol, SO2, HF, titanium ore dust, and heavy metal aerosol. A four-step process is employed: sulfur phase change controlled removal – rapid cooling pre-washing – staged absorption purification – deep aerosol removal. The entire process operates under slight negative pressure, making it suitable for intermittent reaction pulse waste gas conditions.

[0025] Example 1 (Optimal Intermediate Parameters)

[0026] The system treats pulsed waste gas from the main stage of the intermittent acidolysis of rutile synthesis, with an initial waste gas temperature of 190℃. S1 Sulfur Phase Change Control and Removal: The system maintains a slight negative pressure, using an 8wt% dilute sulfuric acid aqueous solution as the heat exchange medium at a temperature of 135℃. Indirect cooling controls the waste gas temperature to remain stable at 135℃, causing gaseous sublimation sulfur to condense into liquid sulfur. Liquid sulfur byproducts are recovered through gas-liquid separation. The waste gas temperature is maintained above 128℃ throughout transport, preventing premature sublimation of solid sulfur. The pressure difference is stable, eliminating the need for steam cleaning. S2 Rapid Cooling Pre-washing: The washing liquid uses 8wt% dilute sulfuric acid. Rapid cooling lowers the waste gas temperature to 68℃, removing coarse titanium ore dust and large-particle sulfuric acid mist, and capturing suspended liquid sulfur mist into the liquid phase. Part of the washing liquid is discharged to the acidolysis waste acid treatment system, replenished with process water to maintain concentration. The separated sulfur paste is melted and the elemental sulfur is recovered. S3 Staged Absorption and Purification: A weakly acidic buffer wash with pH controlled at 3.2 buffers concentration fluctuations and pre-captures residual acid mist particles; the composite alkaline solution is a mixture of sodium carbonate and sodium hydroxide, pH 9.5; during the main reaction stage, the spray flow rate and alkaline solution concentration are increased to absorb and remove SO2, trace amounts of H2S, and HF. S4 Deep Aerosol Removal: Removes submicron sulfuric acid mist, sulfur particles, and heavy metal aerosols; the collected washing liquid is recycled back to the weakly acidic buffer wash for reuse; the entire process is under slight negative pressure.

[0027] After 30 days of continuous operation, the unit showed no blockage and no risk of spontaneous combustion due to sulfur accumulation. Exhaust gas testing revealed: SO2 ≤ 15 mg / m³, HF ≤ 0.5 mg / m³, sulfuric acid mist ≤ 5 mg / m³, and no detectable heavy metal aerosols; sulfur recovery purity ≥ 98.5%.

[0028] Example 2 (lower limit parameter condition)

[0029] The treatment process begins with the initial treatment of waste gas from acidolysis, with an initial temperature of 170℃. S1: Sulfur phase change control and removal: A slight negative pressure is applied, using 5wt% dilute sulfuric acid as the heat exchange medium at 130℃. The waste gas is cooled to 125℃, liquefying gaseous sulfur into liquid sulfur, which is then separated and recovered. The waste gas transport temperature is maintained above 122℃, preventing solid sulfur precipitation and ensuring stable pressure differential. S2: Rapid cooling and pre-washing: Washing with 5wt% dilute sulfuric acid cools the waste gas to 60℃, removing mineral dust, large-particle acid mist, and suspended sulfur mist. Sulfur paste is melted to recover elemental sulfur, and a portion of the liquid phase is discharged with water added to control concentration. S3: Staged absorption and purification: Weakly acidic buffer washing (pH 2.5); composite alkali solution (pH 8.0); low initial load during feeding, reducing spray flow and alkali concentration to remove SO2, H2S, and HF. S4: Deep aerosol removal: The washing liquid is recycled, and the entire process is conducted under slight negative pressure.

[0030] The unit operated stably for 30 consecutive days. Exhaust gas testing results: SO2 ≤ 18 mg / m³, HF ≤ 0.6 mg / m³, sulfuric acid mist ≤ 6 mg / m³, sulfur recovery purity ≥ 98.0%.

[0031] Example 3 (Parameter Upper Limit Condition)

[0032] The system treats high-concentration pulsed waste gas from a vigorous acidolysis reaction, with an initial waste gas temperature of 220℃. S1: Sulfur Phase Change Control and Removal: Under slight negative pressure, using 12wt% dilute sulfuric acid as the heat exchange medium at 142℃, the waste gas temperature is controlled at 145℃. Gaseous sulfur undergoes phase change to liquid sulfur, which is then separated and recovered. The waste gas transport temperature is >125℃. When the operating pressure difference reaches the threshold, 145℃ low-pressure superheated steam is introduced for online melting and scale removal without interrupting waste gas treatment. S2: Rapid Cooling and Pre-washing: Washing with 12wt% dilute sulfuric acid, cooling the waste gas to 75℃, capturing mineral dust, sulfuric acid mist, and sulfur mist. Sulfur paste is melted to recover elemental sulfur, and waste acid is discharged while water is added to maintain concentration. S3: Staged Absorption and Purification: Weakly acidic buffer washing at pH 4.0; composite alkaline solution at pH 11.0; increasing the spray flow rate and alkaline solution concentration during the peak stage of the main reaction to remove SO2, H2S, and HF. S4: Deep Aerosol Removal: The washing liquid is refluxed and circulated throughout the process under slight negative pressure.

[0033] After 30 days of continuous operation, the pressure differential returned to normal after online descaling, with no potential for blockage. Exhaust gas testing results: SO2 ≤ 12 mg / m³, HF ≤ 0.4 mg / m³, sulfuric acid mist ≤ 4 mg / m³, sulfur recovery purity ≥ 98.2%.

[0034] Comparative Example 1 (Traditional titanium ore waste gas treatment process)

[0035] Without the S1 sulfur phase change control step, the initial exhaust gas temperature was 190℃. Direct water spraying for rapid cooling, conventional acid-base washing, and demisting were performed without phase change temperature control or dynamic spray adjustment. All other raw material conditions remained consistent with Example 1. Operating results: Gaseous sublimated sulfur directly condensed into solid sulfur particles at low temperatures, causing deposit blockages in pipelines and washing units; the pressure differential increased significantly after 7 days of operation, requiring manual shutdown and cleaning; there was a risk of spontaneous combustion due to sulfur accumulation; acid mist trailed in the exhaust gas, and submicron sulfuric acid mist and heavy metal removal were incomplete. Exhaust gas detection: SO2 35-50 mg / m³, HF 2.0-3.5 mg / m³, sulfuric acid mist 15-25 mg / m³; there was no sulfur recovery, and the wastewater had high sulfur and fluoride loads, making long-term continuous operation of the unit impossible.

[0036] Comparative Example 2 (removing the S1 phase transition step and retaining all steps S2-S4)

[0037] The initial temperature and composition of the exhaust gas were the same as in Example 1, but the sulfur phase change control and removal in S1 were omitted. The high-temperature exhaust gas directly entered the rapid cooling pre-washing. The process parameters and micro-negative pressure conditions in S2, S3, and S4 were exactly the same as in Example 1. Operating results: Gaseous sublimated sulfur rapidly cooled and condensed in the rapid cooling unit, generating a large number of solid sulfur particles. Some escaped with the tail gas, while others deposited on the packing and pipes. Scaling and blockage occurred after 30 days of operation, requiring shutdown for cleaning. The tail gas contained excessive sulfuric acid mist and sulfur particles, incomplete removal of heavy metal aerosols, and decreased SO2 and HF removal efficiency, making efficient sulfur recovery impossible. The overall treatment effect was significantly inferior to that of the embodiments of this invention.

[0038] As can be seen from the comparison, this invention uses S1 to perform liquid-phase phase change pre-removal of sublimed sulfur, avoiding solid sulfur deposition from the source. Combined with weak acid buffering, dynamic graded absorption and deep aerosol removal, it is suitable for intermittent pulsed exhaust gas. The device can operate continuously for a long time, eliminating the risk of sulfur spontaneous combustion. It has high pollutant removal efficiency and realizes the recovery of sulfur by-products, reducing the pressure on reagent and wastewater treatment.

[0039] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for treating and discharging waste gas from the acid hydrolysis of synthesized rutile, characterized in that: The high-temperature waste gas produced by the intermittent acid hydrolysis of rutile synthesis with concentrated sulfuric acid is subjected to the following steps in sequence: S1: sulfur phase change regulation and removal step; S2: rapid cooling and pre-washing step; S3: staged absorption and purification step; S4: deep aerosol removal step; and then the exhaust is completed. The details are as follows: The original temperature of the high-temperature exhaust gas is 170-220℃, and the exhaust gas components include water vapor, gaseous sublimated sulfur, sulfuric acid mist aerosol, SO2, trace amounts of H2S, HF, titanium ore dust, and heavy metal aerosol. The S1 step of sulfur phase change regulation and removal involves maintaining the overall exhaust gas under a slight negative pressure, indirectly cooling the exhaust gas to reduce its temperature and control it at 125-145℃. This temperature range is higher than the freezing point of elemental sulfur, causing the gaseous sublimated sulfur in the exhaust gas to undergo a phase change and condense into liquid sulfur. The formed liquid sulfur is then separated and removed. S2: Rapid cooling and pre-washing step, the waste gas after sulfur phase change regulation and removal is rapidly cooled by contact, using 5-12wt% dilute sulfuric acid as washing liquid to cool the waste gas to 60-75℃, remove coarse mineral dust and most of the large-particle sulfuric acid mist in the waste gas, and at the same time capture the suspended liquid sulfur mist in the waste gas into the washing liquid, and separate sulfur paste from the washing liquid; The S3 step, a graded absorption and purification step, involves subjecting the exhaust gas, after rapid cooling and pre-washing, to a weakly acidic buffer wash followed by an alkaline wash. The weakly acidic buffered scrubbing solution maintains a pH of 2.5-4.0 to buffer fluctuations in exhaust gas concentration and pre-capture residual acid mist particles. The alkaline absorption solution uses a composite alkaline solution with a pH of 8-11 to absorb and remove SO2, residual H2S, and HF from the exhaust gas. The scrubbing flow rate and alkaline concentration are dynamically adjusted according to the time sequence of the acidolysis reaction to adapt to the pulse impact of the exhaust gas caused by the intermittent reaction. The S4 step, deep aerosol removal, involves deep aerosol removal of the waste gas after staged absorption and purification, removing submicron sulfuric acid mist, residual sulfur particles, and heavy metal aerosols, ensuring that the treated waste gas meets emission standards.

2. The method for treating and discharging waste gas from the acid hydrolysis of synthetic rutile according to claim 1, characterized in that: In step S1, the sulfur phase change controlled removal step, the heat exchange medium used for indirect cooling is a 5-12wt% dilute sulfuric acid aqueous solution, the temperature of the heat exchange medium is maintained at 130-142℃, and the separated liquid sulfur is recovered as a by-product.

3. The method for treating and discharging waste gas from the acid hydrolysis of synthetic rutile according to claim 1, characterized in that: In step S1, the sulfur phase change control and removal step, the waste gas temperature is maintained above 120°C throughout the entire waste gas transportation process to prevent gaseous sublimated sulfur from prematurely condensing into solid sulfur during transportation.

4. The method for treating and discharging waste gas from the acid hydrolysis of synthetic rutile according to claim 1, characterized in that: In step S1, the sulfur phase change control and removal step, the process pressure difference is monitored. When the pressure difference rises to a set threshold, low-pressure superheated steam at 140-150℃ is introduced to melt and remove scale. The waste gas treatment process is not interrupted during the scale removal process.

5. The method for treating and discharging waste gas from the acid hydrolysis of synthetic rutile according to claim 1, characterized in that: In step S2, the rapid cooling and pre-washing step, a portion of the dilute sulfuric acid washing liquid is discharged into the acidolysis waste acid treatment system, while the other portion is supplemented with process water to maintain the concentration of dilute sulfuric acid; the separated sulfur paste is melted to recover elemental sulfur.

6. The method for treating and discharging waste gas from the acid hydrolysis of synthetic rutile according to claim 1, characterized in that: In step S3, the graded absorption and purification step, the composite alkaline solution is a mixture of sodium carbonate and sodium hydroxide. During the main acidolysis reaction burst stage, the spray flow rate is increased and the alkaline solution concentration is increased. During the feeding and final reaction stages, the spray load is reduced.

7. The method for treating and discharging waste gas from the acid hydrolysis of synthetic rutile according to claim 1, characterized in that: In step S4, the deep aerosol removal step, the collected washing liquid is recycled back to the weakly acidic buffer washing liquid phase system for reuse.

8. The method for treating and discharging waste gas from the acid hydrolysis of synthetic rutile according to any one of claims 1-7, characterized in that: Throughout the S1 step (sulfur phase change controlled removal), S2 step (rapid cooling pre-washing), S3 step (graded absorption purification), and S4 step (deep aerosol removal), a slight negative pressure is maintained to prevent the leakage of acidic waste gas.