A process for simultaneous purification of desulfurization waste liquid tail gas and flue gas

Abstract

This invention discloses a process for the simultaneous purification of flue gas and tail gas from desulfurization waste liquid conversion. A solution containing sodium aluminate and sodium hydroxide is used to absorb the tail gas generated during the catalytic conversion of desulfurization waste liquid. The absorbed liquid is then transported to a flue gas desulfurization tower and a denitrification agent regeneration tank for flue gas desulfurization and denitrification regeneration systems. The liquid after sulfur dioxide removal is filtered and heated; the heated liquid can then be used for further desulfurization. Simultaneously, the liquid from the denitrification agent regeneration tank is filtered and adjusted to a pH of 7-9 for flue gas recirculation denitrification. This invention converts catalytic waste gases such as hydrogen sulfide, carbonyl sulfide, carbon dioxide, and water vapor into a highly reducing and alkaline liquid, achieving simultaneous removal of multiple waste gases. This solves problems such as system deactivation in wet flue gas recirculation denitrification, reducing environmental pollution from waste gas and waste liquid.

Description

Technical Field

[0001] This invention relates to a process for the simultaneous purification of desulfurization waste liquid conversion tail gas and flue gas, specifically a process for the simultaneous purification of sulfur dioxide and nitrogen oxides in the tail gas and flue gas from the catalytic conversion of desulfurization waste liquid in coking enterprises, belonging to the field of waste gas treatment technology. Background Art

[0002] Coking plants in my country generate a large amount of desulfurization wastewater annually, which contains numerous harmful substances and cannot be directly treated biochemically. Although many methods exist for its resource recovery, the results are still far from satisfactory. Chinese Patent CN 110921953 A presents a unique device and process design for the difficult-to-treat desulfurization wastewater from coking plants, achieving resource recovery while solving the problems faced by coking plants. This patent primarily addresses the treatment scheme for desulfurization wastewater, but the high cost of tail gas treatment during catalytic conversion remains a concern. Generally, tail gas contains four main components: water vapor, hydrogen sulfide, carbon dioxide, and carbonyl sulfide. These gases are mostly acidic, and direct discharge can cause acid rain and other environmental hazards. To address this drawback, this invention couples the process with flue gas desulfurization and denitrification, achieving low-cost tail gas purification while simultaneously purifying sulfur dioxide and nitrogen oxides in the flue gas. Summary of the Invention

[0003] The present invention aims to provide a process for the simultaneous purification of desulfurization waste liquid and tail gas. Specifically, the solution after the desulfurization waste liquid is purified and converted into tail gas is used for flue gas desulfurization and denitrification. While purifying the desulfurization waste liquid and converting the tail gas, the purpose of removing multiple gases simultaneously is achieved.

[0004] The main components of the desulfurization wastewater conversion tail gas are four types: water vapor, hydrogen sulfide, carbon dioxide, and carbonyl sulfide. This invention effectively absorbs these acidic gases using a solution containing 0.3%-1% sodium aluminate and 2%-5% sodium hydroxide by mass. Sodium aluminate catalyzes the rapid alkaline absorption reaction, enabling the tail gas to meet national emission standards. This method not only improves the absorption efficiency of the waste gas but also has advantages such as low reaction temperature, low energy consumption, and few side reactions. The main component of the liquid after waste gas absorption becomes reducing sodium sulfide, which is used to reduce nitrosyl complexes and ferric ions, giving the reduced liquid the ability to remove nitrogen oxides for continued circulating flue gas denitrification. The absorption reaction formula is as follows:

[0005] COS + H2O → CO2 + H2S

[0006] 2NaOH + H2S → Na2S + 2H2O

[0007] 2NaOH + CO2 → Na2CO3 + H2O

[0008] 4NaOH + COS → Na2S + Na2CO3 + 2H2O

[0009] 5Na2S + 5Fe(II)EDTA-NO 2- + 10 H + → 5 S↓+ 2.5 N2↑+ 5 Fe(II)EDTA 2- + 5H2O+10 Na +

[0010] Na2S + 2Fe(III)EDTA - → S↓+ 2Fe(II)EDTA 2- + 2 Na +

[0011] This invention provides a process for the simultaneous purification of desulfurization wastewater tail gas and flue gas, comprising the following steps:

[0012] (1) The tail gas generated during the catalytic conversion of desulfurization waste liquid is fed into the absorption tower for absorption by the absorbent liquid, and the gas discharged from the absorption tower is collected in the enterprise's VOCs system.

[0013] (2) The liquid after the tail gas is removed is divided into two parts and transferred to the bottom of the flue gas desulfurization tower and the denitrification catalyst regeneration tank, respectively;

[0014] (3) The denitrification catalyst that has been deactivated by the denitrification tower is regenerated in the denitrification catalyst regeneration tank of step (2). The regenerated liquid is sent to the top of the flue gas denitrification tower for circulation denitrification in sequence through the denitrification filter, the blender and the denitrification pressurization pump.

[0015] (4) The liquid at the bottom of the flue gas desulfurization tower in step (2) is first filtered through a desulfurization filter, then crystallized and purified in an evaporator crystallizer, and the resulting secondary condensate is then reintroduced into the flue gas desulfurization tower for circulating desulfurization.

[0016] (5) Transfer the liquid at the bottom of the flue gas denitrification tower in step (3) to the denitrification catalyst regeneration tank for regeneration. After regeneration, the liquid is filtered by the denitrification filter and returned to the bottom of the flue gas denitrification tower to continue the cycle denitrification.

[0017] The specific process of the above technical solution is further explained as follows:

[0018] The tail gas generated during the catalytic conversion of desulfurization waste liquid in step (1) includes water vapor, hydrogen sulfide, carbonyl sulfide and carbon dioxide. The absorbent contains 0.3%-1% sodium aluminate and 2%-5% sodium hydroxide by mass. The solution is replenished from time to time to ensure that the absorption reaction is fully carried out.

[0019] Step (2): The liquid after tail gas removal is located at the bottom of the flue gas desulfurization tower. Its main component is sodium sulfide, which has strong reducing and alkaline properties. The amount transferred to the bottom of the flue gas desulfurization tower accounts for 50-70% of the liquid. Then, it is pumped by the desulfurization pressurization pump to the top of the flue gas desulfurization tower for spraying from top to bottom and reacting with the sulfur dioxide gas flowing from bottom to top. The remaining 30-50% of the liquid is transferred to the denitrification regeneration tank. The liquid after tail gas removal and the sulfur dioxide in the flue gas undergo the following reaction in the flue gas desulfurization tower:

[0020] 2H2O + 2Na2S + 5SO2 → 4NaHCO3 + 3S↓

[0021] The denitration catalyst in step (3) is a wet-process complexed iron catalyst. The complexed iron catalyst system consists of ferrous iron and a single or double ligand. In the system composed of ferrous iron and a single ligand, the molar ratio of the two is 1:2, and the single ligand is any one of EDTA, PBTCA, NTA, and CA. The system composed of ferrous iron and a double ligand is: Fe 2+ The molar ratio of EDTA and PBTCA is 3:1:2 or Fe 2+ The molar ratio of EDTA to NTA is 3:1:2; the concentration of complexed iron catalyst is 20 mmol / L-50 mmol / L; the liquid pH is maintained at 7-9 by a mixer to ensure the system's high-efficiency denitrification activity.

[0022] The solid obtained by filtration in step (4) is sulfur, and the solid obtained by crystallization and purification in the steam heating section is sodium carbonate.

[0023] The solid obtained from filtration in step (5) is sulfur, and the denitrification deactivated liquid consists of nitrosyl complex and ferric ions. In the denitrification regeneration tank, both nitrosyl complex and ferric ions are reduced to ferrous ions by sodium sulfide, ensuring the activity of the denitrification system. After the regeneration reaction is completed, the liquid continues to circulate for flue gas denitrification. The tail gas after denitrification is discharged into the air after being tested by a flue gas analyzer at the top of the denitrification tower and meeting the standards.

[0024] This invention provides a device for the simultaneous purification of desulfurization waste liquid conversion tail gas and flue gas, including a pressurizing pump, an absorption tower, a desulfurization pressurizing pump, a flue gas desulfurization tower, a desulfurization filter, an evaporator crystallizer, a denitrification pressurizing pump, a flue gas denitrification tower, a flue gas analyzer, a denitrification agent regeneration tank, a denitrification filter, and a blender;

[0025] The catalytic conversion tail gas of the desulfurization waste liquid is fed into the absorption tower. A booster pump is connected to the absorption tower. The gas outlet at the top of the absorption tower is connected to the enterprise's VOCs system. The liquid outlet at the bottom is connected to the denitrification agent regeneration tank and the bottom of the flue gas desulfurization tower, respectively. The bottom of the flue gas desulfurization tower is connected to the desulfurization booster pump. The inlet of the desulfurization filter is connected to the outlet of the flue gas desulfurization tower. The top and bottom of the desulfurization filter have liquid and solid outlets, respectively. The liquid outlet is connected to the evaporator crystallizer. The denitrification booster pump is connected to the inlet of the flue gas denitrification tower. The gas outlet at the top of the flue gas denitrification tower is connected to the flue gas analyzer. The liquid outlet at the bottom is connected to the inlet of the denitrification agent regeneration tank. The liquid outlet of the denitrification agent regeneration tank is connected to the inlet of the denitrification filter. The liquid outlet of the denitrification filter is connected to the inlet of the blender. The liquid outlet of the blender is connected to the bottom of the denitrification tower.

[0026] The beneficial effects of this invention are:

[0027] (1) The present invention uses a solution containing 0.3%-1% sodium aluminate and 2%-5% sodium hydroxide by mass to absorb the desulfurization waste liquid and catalytically convert the tail gas. While purifying the waste gas, a liquid with strong reducing and strong alkalinity is prepared without causing secondary pollution, so as to maximize the utilization of resources.

[0028] (2) The resulting strong reducing and strong alkaline liquid is used to remove sulfur dioxide and reduce the complexed iron system in the flue gas, ensuring that the system can efficiently circulate and denitrate;

[0029] (3) The present invention achieves the simultaneous removal of multiple polluting gases, reducing the pollution of the environment by waste gas and waste liquid. Attached Figure Description

[0030] Figure 1 This is a diagram of the apparatus for the simultaneous purification of desulfurization waste liquid, tail gas, and flue gas.

[0031] In the diagram: 1 is a booster pump, 2 is an absorption tower, 3 is a desulfurization booster pump, 4 is a flue gas desulfurization tower, 5 is a desulfurization filter, 6 is an evaporator crystallizer, 7 is a denitrification booster pump, 8 is a flue gas denitrification tower, 9 is a flue gas analyzer, 10 is a denitrification agent regeneration tank, 11 is a denitrification filter, and 12 is a blender. A is the catalytic conversion tail gas of desulfurization waste liquid, B is flue gas, C is a liquid containing sodium aluminate and sodium hydroxide, D is sulfur, and E is solid sodium carbonate. Detailed Implementation

[0032] The present invention will be further illustrated by the following embodiments, but is not limited to the following embodiments.

[0033] The waste gas used in this embodiment is the tail gas generated during the catalytic conversion treatment of desulfurization wastewater in a coking plant. The composition of the tail gas is as follows: CO2 60%, H2S 15%, COS 5%, and water vapor 20%. The concentration of sulfur dioxide in the flue gas is 300 ppm, and the concentration of nitrogen oxides is 600 ppm. A solution of 0.8% sodium aluminate and 3% sodium hydroxide by mass ratio was used as the absorbent (the absorbent was prepared by dissolving sodium aluminate and sodium hydroxide in water to a mass ratio of 0.8% sodium aluminate and 3% sodium hydroxide), and a 20 mmol / L Fe(II)EDTA solution was used as the complexing denitrification agent to remove various waste gases.

[0034] like Figure 1 As shown, a process for the simultaneous removal of sulfur dioxide and nitrogen oxides from desulfurization waste liquid conversion tail gas and flue gas includes a pressurizing pump 1, an absorption tower 2, a desulfurization pressurizing pump 3, a flue gas desulfurization tower 4, a desulfurization filter 5, an evaporator crystallizer 6, a denitrification pressurizing pump 7, a flue gas denitrification tower 8, a flue gas analyzer 9, a denitrification agent regeneration tank 10, a denitrification filter 11, and a blender 12;

[0035] The specific steps of this embodiment include the following:

[0036] The catalytic conversion tail gas of the desulfurization waste liquid is fed into the absorption tower 2. The pressurization pump 1 is connected to the absorption tower 2. The gas outlet at the top of the absorption tower 2 is connected to the enterprise's VOCs system, and the liquid outlet at the bottom is connected to the denitrification agent regeneration tank 10 and the bottom of the flue gas desulfurization tower 4, respectively. The bottom of the flue gas desulfurization tower 4 is connected to the desulfurization pressurization pump 3. The inlet of the desulfurization filter 5 is connected to the outlet of the flue gas desulfurization tower 4. The top and bottom of the desulfurization filter 5 are respectively provided with liquid and solid outlets. The liquid outlet is connected to the evaporator crystallizer 6. The denitrification pressurization pump 7 is connected to the inlet of the flue gas denitrification tower 8. The gas outlet at the top of the flue gas denitrification tower 8 is connected to the flue gas analyzer 9. The liquid outlet at the bottom of the flue gas denitrification tower 8 is connected to the inlet of the denitrification agent regeneration tank 10. The liquid outlet of the denitrification agent regeneration tank 10 is connected to the inlet of the denitrification filter 11. The liquid outlet of the denitrification filter 11 is connected to the inlet of the blender 12. The liquid outlet of the blender 12 is connected to the bottom of the flue gas denitrification tower 8.

[0037] The process flow is as follows: The catalytic conversion tail gas A from the desulfurization waste liquid is fed into absorption tower 2, where it reacts with liquid C containing sodium aluminate and sodium hydroxide, which is pumped to the top of absorption tower 1 by a pressurized pump. The remaining gas is collected in the enterprise's VOCs system through the gas outlet at the top of absorption tower 2. The liquid after absorbing the waste gas flows from the bottom liquid outlet of absorption tower 2 into flue gas desulfurization tower 4 and denitrification agent regeneration tank 10, respectively. Flue gas desulfurization tower 4 is pumped to the top by a desulfurization pressurized pump 3, where the liquid is sprayed from top to bottom to react with sulfur dioxide in the flue gas B flowing upwards. The liquid absorbing sulfur dioxide flows from the bottom liquid outlet of flue gas desulfurization tower 4 into desulfurization filter 5, where the filtered solid is sulfur D, which can be directly sold externally. The filtered liquid flows from the top liquid outlet of desulfurization filter 5 into evaporator crystallizer 6, where it is heated and crystallized to obtain sodium carbonate solid E, which can also be sold externally. Unreacted gas from flue gas desulfurization tower 4 continues to be fed into flue gas denitrification tower 8 for removal. The gas outlet at the top of flue gas denitrification tower 8 is connected to flue gas analyzer 9. After passing inspection, the gas is discharged into the atmosphere. The liquid after nitrogen oxide removal enters the denitrification agent regeneration tank 10 from the bottom outlet of flue gas denitrification tower 8. The denitrification agent regeneration tank 10 regenerates the deactivated complexed iron denitrification liquid and then passes it into denitrification filter 11 for filtration. The sulfur D obtained from the filtration is taken out from the lower port of denitrification filter 11 and can be sold externally. The filtrate enters the blender 12 from the lower port of denitrification filter 11 to adjust the solution pH. After pH adjustment, the liquid enters the bottom of flue gas denitrification tower 8 from the outlet of blender 12, and then is transported to the top of flue gas denitrification tower 8 by denitrification booster pump 7 for circulating denitrification.

[0038] The first step involves feeding the catalytic conversion tail gas from the desulfurization wastewater into an absorption tower. The spray absorption liquid used in the absorption tower is a solution containing 0.8% sodium aluminate and 3% sodium hydroxide by mass. The tail gas reacts with the solution to produce sodium sulfide and sodium carbonate, and the remaining tail gas is collected by the company's VOCs collection system. The liquid-to-gas ratio is 3, the tail gas velocity is 2.6 m / s, and the amount of spray absorption liquid added is 240 m³ / s. 3 / h.

[0039] The second step involves transferring the obtained sodium sulfide and sodium carbonate liquids, which have strong reducing properties, to the flue gas desulfurization tower and the denitrification agent regeneration tank, respectively. The liquid at the bottom of the flue gas desulfurization tower is pumped to the top via a desulfurization pressurization pump, where it is sprayed from top to bottom to wash away sulfur dioxide gas at a concentration of 300 ppm. After the reaction, the liquid enters the desulfurization filter for filtration.

[0040] In the third step, sulfur is generated in the liquid from which sulfur dioxide is removed. This sulfur is filtered through a desulfurization filter and sold as sulfur paste. The filtered liquid is then sent to an evaporator crystallizer for heating and crystallization to obtain solid sodium carbonate, which can also be sold. The secondary condensate obtained from the evaporator crystallizer can be fed into the bottom of the flue gas desulfurization tower for continued circulating desulfurization.

[0041] The fourth step involves continuing to pass the remaining exhaust gas from the flue gas desulfurization tower into the flue gas denitrification tower for further removal. The deactivated complexed iron denitrification liquid (containing deactivated complexed iron catalyst) at the bottom of the tower is transported to a denitrification agent regeneration tank for regeneration. This tank consists of a strongly reducing liquid sodium sulfide solution reacting with nitrosyl complex Fe(II)EDTA-NO and ferric ions to generate a complexed denitrification system with ferrous active components. The concentration of the active component Fe(II)EDTA is 20 mmol / L. After filtration through a denitrification filter, the liquid is adjusted to pH 8 using dilute sulfuric acid in a mixer before being transported to the bottom of the denitrification tower. A denitrification pressurization pump then performs a top-to-bottom rinsing process on the top of the tower, resulting in a nitrogen oxide concentration of 600 ppm. The remaining exhaust gas is then tested by a flue gas analyzer and discharged in compliance with standards (SO2 concentration of 8 ppm and nitrogen oxide concentration of 25 ppm).

[0042] The desulfurization waste liquid conversion tail gas and flue gas synchronous purification process provided by this invention converts catalytic waste gases such as hydrogen sulfide, carbonyl sulfide, carbon dioxide and water vapor into liquids with strong reducing and strong alkalinity, realizing the simultaneous removal of multiple waste gases, solving the problem of system deactivation in wet circulating denitrification of flue gas, and reducing the pollution of waste gas and waste liquid to the environment.

Claims

1. A process for simultaneous purification of desulfurization wastewater conversion tail gas and flue gas, characterized in that... Includes the following steps: (1) The tail gas generated during the catalytic conversion of desulfurization waste liquid is fed into the absorption tower for absorption by the absorbent liquid, and the gas discharged from the absorption tower is collected in the enterprise's VOCs system. The tail gas generated during the catalytic conversion of desulfurization waste liquid includes water vapor, hydrogen sulfide, carbonyl sulfide and carbon dioxide. The absorbent contains 0.3%-1% sodium aluminate and 2%-5% sodium hydroxide by mass. The absorbent is replenished from time to time to ensure that the absorption reaction is fully carried out. (2) The liquid after the tail gas is removed is divided into two parts and transferred to the bottom of the flue gas desulfurization tower and the denitrification catalyst regeneration tank, respectively; The liquid after exhaust gas removal is mainly composed of sodium sulfide, which has strong reducing and alkaline properties. The amount of liquid transferred to the bottom of the flue gas desulfurization tower accounts for 50-70%, and then it is pumped by the desulfurization pressurization pump to the top of the flue gas desulfurization tower for spraying from top to bottom and reacting with the sulfur dioxide gas flowing from bottom to top; the remaining 30-50% of the liquid is transferred to the denitrification regeneration tank. (3) The denitrification catalyst that has been deactivated by the denitrification tower is regenerated in the denitrification catalyst regeneration tank of step (2). The regenerated liquid is sent to the top of the flue gas denitrification tower for denitrification in sequence through the denitrification filter, the blender and the denitrification pressurization pump. The denitration catalyst is a wet-process complexed iron catalyst. The complexed iron catalyst system consists of ferrous iron and a single or dual ligand. In the system composed of ferrous iron and a single ligand, the molar ratio is 1:2, and the single ligand is any one of EDTA, PBTCA, or NTA. The system composed of ferrous iron and a dual ligand is: Fe... 2+ The molar ratio of EDTA and PBTCA is 3:1:2 or Fe 2+ The molar ratio of EDTA and NTA is 3:1:2; the concentration of complexed iron catalyst is 20 mmol / L-50 mmol / L; the pH of the liquid is maintained at 7-9 by a mixer to ensure the system's high-efficiency denitrification activity. (4) The liquid at the bottom of the flue gas desulfurization tower in step (2) is first filtered through a desulfurization filter, then crystallized and purified in an evaporator crystallizer, and the resulting secondary condensate is then reintroduced into the flue gas desulfurization tower for circulating desulfurization. (5) Transfer the liquid at the bottom of the flue gas denitrification tower in step (3) to the denitrification catalyst regeneration tank for regeneration. After regeneration, the liquid is filtered by the denitrification filter and returned to the bottom of the flue gas denitrification tower to continue the cycle denitrification.

2. The simultaneous purification process for desulfurization wastewater conversion tail gas and flue gas according to claim 1, characterized in that: The solid obtained by filtration in step (4) is sulfur, and the solid obtained by crystallization and purification in the steam heating section is sodium carbonate.

3. The simultaneous purification process for desulfurization wastewater conversion tail gas and flue gas according to claim 1, characterized in that: The solid obtained by filtration in step (5) is sulfur, and the denitrified liquid is nitrite complex and ferric ions.

4. A device for simultaneous purification of desulfurization wastewater conversion tail gas and flue gas, used in the simultaneous purification process of desulfurization wastewater conversion tail gas and flue gas as described in any one of claims 1 to 3, characterized in that: Includes booster pumps, absorption towers, desulfurization booster pumps, flue gas desulfurization towers, desulfurization filters, evaporation crystallizers, denitrification booster pumps, flue gas denitrification towers, flue gas analyzers, denitrification agent regeneration tanks, denitrification filters, and blenders; The catalytic conversion tail gas of desulfurization waste liquid is fed into the absorption tower. A pressurization pump is connected to the absorption tower. The gas outlet at the top of the absorption tower is connected to the enterprise's VOCs system. The liquid outlet at the bottom is connected to the denitrification agent regeneration tank and the bottom of the flue gas desulfurization tower, respectively. The bottom of the flue gas desulfurization tower is connected to the desulfurization pressurization pump. The inlet of the desulfurization filter is connected to the outlet of the flue gas desulfurization tower. The top and bottom of the desulfurization filter have liquid and solid outlets, respectively. The liquid outlet is connected to the evaporator crystallizer. The denitrification pressurization pump is connected to the inlet of the flue gas denitrification tower. The gas outlet at the top of the flue gas denitrification tower is connected to the flue gas analyzer. The liquid outlet at the bottom is connected to the inlet of the denitrification agent regeneration tank. The liquid outlet of the denitrification agent regeneration tank is connected to the inlet of the denitrification filter. The liquid outlet of the denitrification filter is connected to the inlet of the blender. The liquid outlet of the blender is connected to the bottom of the denitrification tower.

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