Process for the stepwise oxidation of ammonia in a combined claus furnace

Abstract

The application provides a compound Claus furnace ammonia step-by-step oxidation decomposition process. Acid and ammonia steam are separated and operated, the main component in ammonia steam is ammonia, and the main component in acid steam is hydrogen sulfide, hydrogen cyanide and carbon dioxide. According to the theory of hydrogen sulfide step-by-step combustion to produce elemental sulfur, most of ammonia and hydrogen cyanide in acid and ammonia steam are combusted and decomposed, and the remaining small amount is catalytically cracked at high temperature, which can effectively reduce the occurrence of by-products of side reactions, slow down the corrosion of equipment and ensure the continuous and stable circulation of each unit of the entire coal gas purification system. Through the compound Claus furnace ammonia step-by-step oxidation decomposition process transformation, the dilution interference of a large amount of waste gas generated by introducing air combustion on the concentration of reactants can be avoided, the reaction rate and efficiency can be effectively improved, the compound Claus furnace ammonia step-by-step oxidation decomposition process is basically free of any side reaction, and the tail gas product is mainly nitrogen, water and carbon dioxide, which is harmless to the environment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of coal chemical industry and petroleum chemical industry, and relates to a compound Claus furnace ammonia step-by-step oxidation and decomposition process. BACKGROUND

[0002] The coal gas purification system of the Liangang coking plant is a supporting project of the 2x60 6-meter top-charging coke oven. The design coke oven gas treatment capacity is 63000 m 3 / h, the coke oven coal loading capacity and the coke discharge load steadily increased in 2020, and the actual average value of the coke oven gas production was 69370 m 3 / h, which is 10.1% higher than the design treatment capacity.

[0003] The coal gas purification system is mainly composed of five units: condensing blast, AS washing, ammonia stripping, sulfur recovery and phenol cyanide wastewater treatment. The coal gas purification process is shown in Figure 1 :

[0004] The condensing blast unit: the raw coke oven gas from the coke oven is first cooled and cooled in the primary cooler to separate the tar and ammonia water. After passing through the electric tar precipitator and the coal gas blower, the gas pressure changes from negative pressure to positive pressure.

[0005] ② The AS washing unit: the coal gas successively passes through the hydrogen sulfide washing tower, the ammonia washing tower and the naphthalene washing tower to absorb and remove hydrogen sulfide, hydrogen cyanide, ammonia and other harmful impurities in the coal gas. Finally, it enters the full-service gas pipe network for use by various users.

[0006] ③ The ammonia stripping unit: mainly responsible for the cyclic regeneration of the desulfurization rich liquid sent by the AS washing unit. The rich liquid successively passes through the acid removal tower and the ammonia stripping tower to analyze and remove hydrogen sulfide, hydrogen cyanide, carbon dioxide and part of ammonia, and then becomes a poor acid liquid that is sent back to the washing unit for spraying.

[0007] ④ The sulfur recovery unit: mainly responsible for the oxidation and decomposition of ammonia, hydrogen sulfide and hydrogen cyanide in the acid ammonia steam generated by the ammonia stripping unit and the recovery of elemental sulfur.

[0008] ⑤ The phenol cyanide wastewater unit: mainly responsible for the biochemical wastewater treatment and external sending of the ammonia stripping wastewater discharged from the fixed ammonium tower bottom of the ammonia stripping unit.

[0009] AS ammonia desulfurization method is a technology introduced from Germany in the 1980s. Its biggest advantage is that it does not need to add external absorption alkali source (sodium carbonate or potassium carbonate), and it can remove H2S and HCN in the coal gas while washing ammonia, without waste (sulfur paste) and waste liquid (by-product salt) emissions, energy saving and environmental protection, economic operation, and low cost. The principle of AS ammonia desulfurization and dehydrogen cyanation process mainly relies on ammonia produced during coking as the absorption alkali source, which is completed by acid-base neutralization reaction with acid gas (hydrogen sulfide, hydrogen cyanide, etc.). The whole reaction process is the absorption and desorption process of water and gas.

[0010] As shown in Figure 1 , the AS ammonia desulfurization method currently used in Lian Gang Coking Plant introduces ammonia vapor generated in the ammonia tower into the deacidification tower as heat source steam to deacidify, and finally forms mixed acid ammonia steam which enters the Claus furnace to produce sulfur, and decomposes ammonia vapor and hydrogen cyanide at the same time. The tail gas produced by the Claus furnace is combined with the raw gas system. The mixed acid ammonia steam containing NH3, H2S, HCN, and CO2 from the deacidification and ammonia vapor unit, and air controlled by the regulating valve, enter the burner at the front end of the Claus furnace. The partial oxidation method is adopted, about one third of the mixed acid ammonia steam participates in the combustion reaction, H2S and air combustion generates SO2; about two thirds of the mixed acid ammonia steam participates in the Claus reaction, and H2S and SO2 generated by combustion generate elemental sulfur. NH3 and HCN in the mixed acid ammonia steam are catalytically cracked into nitrogen, hydrogen and a small amount of carbon black in the catalyst bed of the Claus furnace at 1100°C.

[0011] The reaction of the acid ammonia steam entering the furnace in the Claus furnace is a perfect process design. However, when it is applied to the coking gas desulfurization and deamination process, it is only an ideal condition, ignoring the common sense problem, and has serious defects.

[0012] 1. There are many uncontrollable side reaction risks

[0013] In the front end of the Claus furnace, one third of the mixed acid ammonia steam is burned before it contacts the nickel catalyst (located in the middle section of the Claus furnace). Ammonia and hydrogen cyanide cannot catalytically crack under high-temperature oxygen conditions. Combustion is not selective. As long as the temperature reaches its ignition point, it will participate in the combustion reaction under the condition of coal gas ignition, generating nitric oxide.

[0014]

[0015] The nitrogen atom in nitric oxide has unpaired electrons. It can gain electrons or lose electrons, and has both oxidizing and reducing properties, and is very active in chemical properties, which can produce a series of side reactions to generate different nitrogen oxides (N Y O X ), nitric acid (HNO3), etc.

[0016]

[0017] By analyzing the Claus furnace exhaust gas, 1107g / m 3 Nitrogen oxides (NO x ) traces. Nitrogen oxides and other by-products in the tail gas are returned to the raw gas with the tail gas, washed by circulating ammonia water and lean liquid, and finally transferred to the ammonia distillation wastewater. In the wastewater sample sent to the phenol cyanide wastewater unit, 45-60g / m 3 nitrate nitrogen content.

[0018] Samples of condensed sulfur residue containing carbon deposits were collected from the interior of the Claus furnace sulfur condenser, which had been removed for maintenance. Water-soluble chemical analysis revealed traces of nitrogen oxides and sulfates. The water-soluble nitrate (HNO3) content was 2.63%, and the sulfate (H2SO4) content was as high as 31.07%. The pH of a 1% aqueous solution was 4.5, indicating strong acidity.

[0019] 2. Inhibition and harm of side reactions on catalysts

[0020] The nitrogen oxides (NO x ) and sulfates (H2SO4) are confirmed to be side reactions in the Claus furnace. Nitrogen dioxide (NO2), sulfur dioxide (SO2), and sulfur trioxide (SO3) are strong oxidizing gases, while nitric acid (HNO3) and sulfuric acid (H2SO4) are strong acids, undoubtedly corrosive to catalysts and related equipment.

[0021] The catalytic principle of nickel-cobalt-based catalysts is that under high temperature conditions, nickel oxide and cobalt oxide regenerate into metallic nickel and cobalt, which then act as catalysts. When exposed to strong acids and oxidizing gases, the catalysts cannot effectively regenerate into metallic nickel and cobalt, and their catalytic activity is inhibited or blocked. Metal oxides are generally alkaline. When exposed to strong acids such as nitric acid (HNO3) and sulfuric acid (H2SO4), the catalysts undergo acid-base dissolution reactions, causing the active substances on the catalyst surface to fall off or be lost, and the catalyst's catalytic performance is subsequently lost.

[0022] Therefore, reducing or avoiding the generation of NH3 and HCN by-products is a necessary condition to ensure the safe operation of catalysts and system equipment. However, the actual situation is that NH3 gas and acid gas are mixed into the furnace for combustion, and the proportion of NH3 entering the furnace increases. Doesn't that increase the probability of side reactions and aggravate the damage to catalysts and equipment?

[0023] 3. Side reactions exacerbate corrosion and shutdown failures of sulfur recovery equipment

[0024] With the increase of production load, the amount of ammonia gas combustion into the furnace will increase accordingly, the concentration of harmful nitrogen oxide (NO x ) is increasing, the activity of the catalyst is inhibited, and the ability of high temperature cracking reaction is decreased. To ensure that the tail gas contains ammonia detection is qualified, it is necessary to increase the air intake, and to realize the combustion of the side reaction.

[0025] The air consumption increases, and the concentration of SO2 produced by combustion also increases, which not only affects the control ratio of H2S:SO2, but also reduces the sulfur yield. Excess SO2 will react with nitrogen monoxide to form SO3, sulfuric acid (H2SO4) and other strong acidic substances. The water-soluble sulfuric acid content in the scale sample is as high as 31.07%. Such high sulfuric acid content will inevitably lead to corrosion of the entire sulfur recovery system equipment, especially in the tube part of the water vapor combination heat exchange, the corrosion perforation phenomenon is particularly prominent.

[0026] Due to the failure of the sulfur recovery equipment, corrosion and blockage, etc. The neck is stuck, and NH3, H2S and HCN cannot be effectively decomposed and digested. The acid ammonia steam distilled by the deacidification ammonia evaporation unit can only be returned to the raw gas system through the coal gas negative pressure pipeline, which not only increases the absorption and analysis load of each unit, but also increases the corrosion of the entire coal gas purification system equipment, forming a vicious cycle. This is the root cause of the high equipment failure rate and the serious corrosion damage of the equipment.

[0027] As described above, by simultaneously processing high-ammonia acid ammonia steam in the Claus furnace, it is impossible to control or overcome various side reactions and byproducts, resulting in long-term corrosion and damage of the system equipment and catalysts in a strong acidic environment, reducing the conversion efficiency of the Claus furnace. The average conversion efficiency of hydrogen measured from the tail gas (3.75%) is much lower than the theoretical calculated value (22%-32%), which can be used as evidence: most of the ammonia and hydrogen cyanide in the Claus furnace follow the oxidation combustion side reaction line, rather than the catalytic cracking reaction as expected. Therefore, the current problems in the coal gas purification system are not due to the selection of small equipment, but due to the need to increase the Claus furnace and other equipment. Solving the defects in the process design is the fundamental way to solve the existing problems. SUMMARY

[0028] In view of the above problems, the purpose of the present application is to provide an ammonia step-by-step oxidation decomposition process for a composite Claus furnace.

[0029] Through the research and analysis of the above technical problems, the most ideal modification route of AS ammonia desulfurization process should be how to let the by-product reaction interference of the acid gas without ammonia and hydrogen cyanide components unnecessary waste high-priced nickel-cobalt catalyst in the Claus furnace, change the Claus furnace into a single sulfur reactor, and the reaction temperature does not need to maintain above 1000℃ high temperature, normal combustion can produce sulfur. At the same time, it does not need to make too much investment change, there is no harmful to the environment of nitrogen oxides and sulfate and other by-products. In this framework, combined with the existing AS desulfurization process of the coking plant of Liansteel, a kind of compound Claus furnace ammonia step-by-step oxidation decomposition process is proposed.

[0030] The process utilizes the reaction characteristics of ammonia combustion in oxygen, which can be converted into clean and non-polluting water and nitrogen. The acid and ammonia steam are separated and operated, the dominant component in the ammonia gas is mainly ammonia, and the dominant component in the acid gas is mainly hydrogen sulfide, hydrogen cyanide and carbon dioxide. According to the theory of hydrogen sulfide step-by-step combustion to produce single sulfur, most of the ammonia and hydrogen cyanide in the acid and ammonia steam are burned and decomposed, and the remaining small part is catalytically cracked at high temperature, which can effectively reduce the by-product reaction, slow down the equipment corrosion, and ensure the continuous and stable circulation of the whole coal gas purification system. The specific process is as follows:

[0031] A kind of compound Claus furnace ammonia step-by-step oxidation decomposition process, including compound Claus furnace, the compound Claus furnace includes ammonia gas combustion area, acid gas combustion area, catalytic cracking reaction area, the front end of the compound Claus furnace is connected with oxygen pipe network, purified coke oven gas pipe network, the ammonia gas combustion area is connected with the top of free ammonia tower and fixed ammonia tower through ammonia gas pipeline, the acid gas combustion area is connected with the top of deacidification tower through acid gas pipeline, the acid gas pipeline and ammonia gas pipeline are connected with nitrogen pipe network in parallel before entering the furnace, the deacidification tower, free ammonia tower, fixed ammonia tower are connected with saturated steam pipeline; The ammonia gas pipeline and the acid gas pipeline are provided with a reducer; The compound Claus furnace is communicated with a waste heat boiler, the waste heat boiler is connected with a Claus reactor, and the Claus reactor is connected with a sulfur condenser; The compound Claus furnace ammonia step-by-step oxidation decomposition process is as follows:

[0032] The desulfurization rich liquid produced by AS washing unit enters the deacidification tower, and becomes deacidification poor liquid after resolving and removing hydrogen sulfide, hydrogen cyanide and carbon dioxide. A part of the deacidification poor liquid is cooled by heat exchanger and then sent back to the washing unit for spraying; The remaining part of the deacidification poor liquid enters the free ammonia tower and the fixed ammonia tower to remove volatile ammonia and fixed ammonium in turn, and the steam ammonia wastewater from the bottom of the fixed ammonia tower is sent to the biochemical sewage treatment. The middle and bottom positions of the deacidification tower and the bottom positions of the fixed ammonia tower and the free ammonia tower are heated by heat source, which is saturated steam reboiler (indirect steam heating). The top pressure of the free ammonia tower is controlled to be less than or equal to 50KPa, and the temperature is controlled to be less than or equal to 90℃. The top pressure of the deacidification tower is controlled to be less than or equal to 40KPa, and the temperature is controlled to be less than or equal to 80℃.

[0033] The upper part of the free ammonia tower is connected with the bottom of the deacidification tower by a pipeline, and the ammonia vapor from the upper part of the free ammonia tower enters the bottom of the deacidification tower for heating and adjusting the volatile ammonia concentration of the deacidification lean liquid, and the volatile ammonia concentration of the deacidification lean liquid is controlled to be 10-20 g / L; the hydrogen sulfide content in the ammonia vapor entering the composite Claus furnace is controlled to be ≤3.0%; and the volatile ammonia content in the acid vapor entering the composite Claus furnace is controlled to be ≤10%.

[0034] The ammonia vapor generated at the top of the fixed ammonia tower and the free ammonia tower enters the distributor cooler through the ammonia vapor pipeline, and the temperature of the cooled ammonia vapor is controlled to be ≤70℃; after vapor-liquid separation, the condensate flows back to the top of the free ammonia tower, and the ammonia vapor is introduced into the ammonia vapor combustion area of the composite Claus furnace, so that as much ammonia vapor component as possible is first combusted with oxygen to generate water, nitrogen and carbon dioxide, and a small part of hydrogen sulfide carried by the ammonia vapor is combusted to produce sulfur dioxide for producing sulfur.

[0035]

[0036] The acid vapor generated at the top of the deacidification tower enters the distributor cooler through the acid vapor pipeline, and the temperature of the cooled acid vapor is controlled to be ≤70℃; after vapor-liquid separation, the condensate flows back to the top of the deacidification tower, and the acid vapor is introduced into the acid vapor combustion area of the composite Claus furnace, so that by controlling the amount of oxygen combustion-supporting gas, a part of the combustion is used to meet one-third of the total amount of hydrogen sulfide in the acid and ammonia vapor, which is converted into sulfur dioxide, and at the same time, a part of the ammonia and hydrogen cyanide is burned, at this time, the acid vapor stops the combustion reaction due to lack of oxygen, and the remaining part of the ammonia and hydrogen cyanide is subjected to high-temperature catalytic cracking reaction in the catalytic cracking reaction area to generate nitrogen, hydrogen and a small amount of carbon black.

[0037]

[0038] The remaining two-thirds of the hydrogen sulfide in the acid and ammonia vapor is subjected to redox reaction with the sulfur dioxide produced in the previous combustion in the Claus reactor to generate elemental sulfur, which is cooled by a sulfur condenser to obtain sulfur, and the tail gas produced after being washed by ammonia stripping wastewater can be discharged or returned to the raw gas system.

[0039] .

[0040] The improvement of the present application compared with the existing process is as follows:

[0041] 1. An oxygen supply pipeline is added

[0042] An oxygen pipeline is introduced from an oxygen plant, with a maximum gas flow of 1200 m 3 / h, connected to the composite Claus furnace, and the existing air compressor gas supply device is disabled.

[0043] 2. Deacidification ammonia stripping unit modification

[0044] The existing process flow of the scrubbing unit remains unchanged, and all towers maintain normal scrubbing operations. The pipelines of the deacidification and ammonia distillation units have been partially modified to separate the acid vapor and ammonia vapor produced at the top of the deacidification and ammonia distillation towers. After cooling and vapor-liquid separation in a fractionator, the vapor and ammonia vapor are introduced into their respective reaction zones in the composite Claus furnace for standby use.

[0045] The volatile ammonia evaporated from the top of the fixed ammonia tower is directly connected to the ammonia vapor pipeline at the top of the ammonia evaporation tower and enters the ammonia fractionator together. After cooling in the ammonia fractionator, the ammonia vapor temperature is controlled to ≤70°C, which facilitates ammonia vapor purification and reduces damage to the catalyst and heat loss caused by water vapor entering the furnace. The ammonia vapor condensate is refluxed to the top of the free ammonia tower.

[0046] 3. Process parameter setting

[0047] The heat source for heating points in the middle and bottom of the deacidification tower, as well as at the bottom of the free ammonia tower, was changed to saturated steam reboiler heating (indirect steam heating). The pressure at the top of the free ammonia tower was controlled to ≤50 kPa and the temperature to ≤90°C. The pressure at the top of the deacidification tower was controlled to ≤40 kPa and the temperature to ≤80°C. This facilitated the purification of acid ammonia vapor and water vapor control, and also helped increase the concentration of volatile ammonia in the deacidification lean liquid and the ammonia still.

[0048] The ammonia vapor drawn out from the upper side of the free ammonia tower is still retained for heating the bottom of the deacidification tower and adjusting the volatile ammonia concentration of the deacidification lean liquid. Its opening is flexibly adjusted according to the fluctuation of ammonia and hydrogen sulfide content in the factory gas to control the volatile ammonia content of the deacidification lean liquid at around 10-20 g / L.

[0049] Control the hydrogen sulfide content in the ammonia vapor entering the furnace to ≤3.0%; the volatile ammonia content in the acid vapor entering the furnace to ≤10%.

[0050] 4. Claus furnace transformation

[0051] The existing Claus furnace needs to be extended by 2.5 meters along the control end of the combustion device, with an outer pipe diameter of about 1.5 meters and lined with refractory insulation bricks. The extended area will be set as the ammonia gas combustion reaction zone.

[0052] The modified ammonia vapor inlet maintains the existing inlet pattern of coke oven gas, ammonia vapor, combustion-supporting gas, and protective nitrogen. The combustion of gas and oxygen controls the normal cracking reaction temperature of the composite Claus furnace and the ignition of ammonia vapor. Heat generated by the combustion of ammonia vapor and acid vapor serves as the primary supplement to maintain the Claus furnace temperature.

[0053] Beneficial effects of the present invention:

[0054] By transforming the ammonia step-by-step oxidation and decomposition process of the composite Claus furnace, the dilution interference of the reactant concentration caused by the introduction of a large amount of exhaust gas generated by the combustion-assisted air can be avoided, which can effectively improve the reaction rate and efficiency. A single Claus furnace can meet production requirements. The equipment can be operated one at a time, and there is enough time to ensure that the spare equipment is in good condition and ready for use. This can change the current situation where equipment is severely corroded and clogged, and equipment is frequently repaired and replaced. Even if two equipment are operated at the same time, it cannot meet production requirements. It can ensure the continuous stability and benign cycle of the gas purification system.

[0055] The composite Claus furnace's step-by-step ammonia oxidation and decomposition process is virtually free of side reactions, with the primary tail gas products being nitrogen, water, and carbon dioxide, harmless to the environment. Heat generated by the combustion of acid and ammonia vapors is used to supplement the Claus furnace's high temperature, reducing coke oven gas consumption and preventing contamination of sulfur products by carbon black generated by the combustion of large amounts of unsaturated hydrocarbons in the gas (caused by the lack of crude benzene recovery). This reduces carbon buildup and corrosion in the Claus furnace, achieving energy conservation and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 This is a schematic diagram of the coal gas purification process flow of the Liansteel Coking Plant;

[0057] Figure 2 This is a schematic diagram of the process flow of ammonia step-by-step oxidation and decomposition in a compound Claus furnace. DETAILED DESCRIPTION

[0058] The present invention will be further described below through specific implementation.

[0059] like Figure 2 As shown, a composite Claus furnace ammonia stepwise oxidation and decomposition process includes a composite Claus furnace, which includes an ammonia vapor combustion area, an acid vapor combustion area, and a catalytic cracking reaction area. The front end of the composite Claus furnace is connected to an oxygen pipeline network and a purified coke oven gas pipeline network. The ammonia vapor combustion area is connected to the top of a free ammonia tower and a fixed ammonia tower via an ammonia vapor pipeline. The acid vapor combustion area is connected to the top of a deacidification tower via an acid vapor pipeline. The acid vapor pipeline and the ammonia vapor pipeline are connected in parallel to a nitrogen pipeline network before entering the furnace. The deacidification tower, the free ammonia tower, and the fixed ammonia tower are connected to a saturated steam pipeline. A fractionator is provided on the ammonia vapor pipeline and the acid vapor pipeline. The composite Claus furnace is connected to a waste heat boiler, which is connected to a Claus reactor, and the Claus reactor is connected to a sulfur condenser. The composite Claus furnace ammonia stepwise oxidation and decomposition process is as follows:

[0060] The desulfurization rich solution produced by the AS washing unit enters the deacidification tower, and becomes deacidification lean solution after resolving and removing hydrogen sulfide, hydrogen cyanide and carbon dioxide. Part of the deacidification lean solution is cooled by the heat exchanger and then sent back to the washing unit for washing and spraying. The remaining deacidification lean solution enters the free ammonia tower and the fixed ammonia tower to remove volatile ammonia and fixed ammonium, respectively. The steam ammonia waste water from the bottom of the fixed ammonia tower is sent to the biochemical sewage treatment. The middle and bottom of the deacidification tower, and the bottom of the fixed ammonia tower and the free ammonia tower are heated by a heat source, which is a saturated steam reboiler (indirect steam heating). The pressure at the top of the free ammonia tower is controlled to be less than or equal to 50 KPa, and the temperature is controlled to be less than or equal to 90℃. The pressure at the top of the deacidification tower is controlled to be less than or equal to 40 KPa, and the temperature is controlled to be less than or equal to 80℃.

[0061] The upper side of the free tower ammonia is connected to the bottom of the deacidification tower by a pipeline. The ammonia vapor from the upper side of the free tower ammonia enters the bottom of the deacidification tower to heat the bottom of the deacidification tower and adjust the volatile ammonia concentration of the deacidification lean solution. The volatile ammonia concentration of the deacidification lean solution is controlled to be 10-20 g / L. The hydrogen sulfide content in the ammonia vapor entering the composite Claus furnace is controlled to be less than or equal to 3.0%. The volatile ammonia content in the acid vapor entering the composite Claus furnace is controlled to be less than or equal to 10%.

[0062] The ammonia vapor produced at the top of the fixed ammonia tower and the free ammonia tower enters the ammonia vapor pipeline and is cooled by the ammonia vapor pipeline. The temperature of the cooled ammonia vapor is controlled to be less than or equal to 70℃. After vapor-liquid separation, the condensed liquid flows back to the top of the free ammonia tower, and the ammonia vapor is introduced into the ammonia vapor combustion area of the composite Claus furnace. In the ammonia vapor combustion area, as much ammonia vapor component as possible is completely combusted with oxygen to generate water, nitrogen and carbon dioxide, and a small amount of sulfur dioxide produced by the combustion of a small amount of hydrogen sulfide carried by the ammonia vapor. No side reactions occur.

[0063]

[0064] The acid vapor produced at the top of the deacidification tower enters the acid vapor pipeline and is cooled by the acid vapor pipeline. The temperature of the cooled acid vapor is controlled to be less than or equal to 70℃. After vapor-liquid separation, the condensed liquid flows back to the top of the deacidification tower, and the acid vapor is introduced into the acid vapor combustion area of the composite Claus furnace. In the acid vapor combustion area, by controlling the amount of oxygen combustion-supporting gas, a portion of the combustion is used to convert one-third of the hydrogen sulfide in the acid and ammonia vapor into sulfur dioxide, and a portion of the ammonia and hydrogen cyanide is also combusted. At this time, the acid vapor stops the combustion reaction due to lack of oxygen, and the remaining ammonia and hydrogen cyanide undergo high-temperature catalytic cracking reaction in the catalytic cracking reaction area to generate nitrogen, hydrogen and a small amount of carbon black.

[0065]

[0066] The remaining two-thirds of the hydrogen sulfide in the acid and ammonia vapor undergoes redox reaction with the sulfur dioxide produced in the previous combustion in the Claus reactor to generate elemental sulfur. The sulfur is cooled by a sulfur condenser to obtain sulfur. The tail gas produced after the ammonia washing treatment can be discharged or returned to the raw gas system.

[0067] .

[0068] The process technical performance and indexes after the modification are as follows:

[0069] (1) Performance of the compound Claus furnace

[0070] The combustion of air is stopped, which can greatly reduce the tail gas production by 50%. Compared with the chemical reaction of the process gas, the concentration ratio of the reactants is improved, which can improve the chemical reaction rate and reaction efficiency, and ensure the rapid and sufficient chemical reaction of the Claus furnace.

[0071] The modified compound Claus furnace has the capacity of processing 3000 m 3 / h of acid ammonia steam, that is, it can simultaneously process 1500 m 3 / h of ammonia gas and acid gas, and the sulfur recovery system realizes one open and one standby.

[0072] (2) Tail gas production and composition

[0073] The maximum tail gas production of the modified compound Claus furnace is less than 4500 m 3 / h, and 90-95% of the tail gas is water, nitrogen and carbon dioxide, of which the water vapor accounts for about 60-70%.

[0074] The generated tail gas can be discharged after ammonia and wastewater washing treatment, or can be returned to the raw coal gas system. Discharging can effectively reduce the concentration of carbon dioxide accumulated in the coal gas purification system, enhance the washing and absorption and resolution efficiency of hydrogen sulfide and hydrogen cyanide in lean and rich liquid, and be beneficial to the decomposition and recovery of hydrogen sulfide and hydrogen cyanide.

[0075] (3) Improve the quality of sulfur

[0076] Using oxygen for combustion, ammonia gas is fully decomposed to generate a large amount of heat to maintain the furnace temperature, which can correspondingly reduce the use amount of coke oven gas, and the unsaturated hydrocarbons in the coal gas can also be fully burned to generate carbon dioxide, effectively avoiding the generation of carbon black, reducing the pollution to sulfur, and improving the quality of sulfur from the current 99% to 99.95%. The maximum theoretical production of industrial sulfur is 8-10 tons / day. The elemental sulfur can meet the requirements of the superior product grade index: elemental sulfur content ≥ 99.95%; ash content ≤ 0.03%; acidity ≤ 0.003%.

[0077] (4) Reduce the accumulation and blockage of equipment

[0078] The full combustion and decomposition of the raw gas and fuel gas with the participation of oxygen effectively avoids the production of carbon black, reduces the fatal damage of the graphite of the waste heat boiler caused by high temperature and carbon deposition, and the hardening and clogging of the furnace tube. Before the transformation, the furnace needs to be stopped for half a year for dredging and maintenance of the furnace tube, which has a great impact on the service life of the Claus furnace wall and catalyst. After the transformation, such factors are basically excluded.

[0079] In summary, through the transformation of the ammonia step-by-step oxidation and decomposition process of the composite Claus furnace, the dilution and interference of a large amount of waste gas produced by the introduction of air combustion on the reactant concentration are avoided, the reaction rate and efficiency can be effectively improved, the single operation of the Claus furnace can meet the production requirements, the equipment realizes one open and one standby, and there is enough time to ensure that the standby equipment is in good condition, which changes the current situation of serious corrosion and blockage of equipment, frequent equipment maintenance and replacement, and the inability to meet the production requirements of two simultaneous operations, and ensures the continuous and stable operation of the coal gas purification system.

[0080] The ammonia step-by-step oxidation and decomposition process of the composite Claus furnace basically has no side reactions, and the tail gas product is mainly nitrogen, water and carbon dioxide, which is harmless to the environment. The heat generated by the full combustion and decomposition of acid and ammonia vapor is used as a high-temperature supplement for the Claus furnace, reducing the consumption of coke oven gas combustion and avoiding the pollution of carbon black produced by the combustion of a large amount of unsaturated hydrocarbons in the coal gas (caused by the absence of crude benzene recovery) to the sulfur product, reducing the carbon deposition and corrosion of the Claus furnace, and achieving energy saving and environmental protection.

Claims

1. A composite Claus furnace ammonia stepwise oxidation decomposition process, characterized by: The composite Claus furnace comprises an ammonia combustion area, an acid vapor combustion area, and a catalytic cracking reaction area. The front end of the composite Claus furnace is connected to an oxygen network and a purified coke oven gas network. The ammonia combustion area is connected to the top of a free ammonia tower and a fixed ammonia tower through an ammonia pipeline. The acid vapor combustion area is connected to the top of a deacidification tower through an acid vapor pipeline. The acid vapor pipeline and the ammonia pipeline are connected in parallel to a nitrogen network before entering the furnace. The deacidification tower, free ammonia tower, and fixed ammonia tower are connected to a saturated steam pipeline. A fractionator is provided on the ammonia pipeline and the acid vapor pipeline. The composite Claus furnace is connected to a waste heat boiler, which is connected to a Claus reactor, which is connected to a sulfur condenser. The stepwise oxidation and decomposition process of ammonia in the composite Claus furnace is as follows: The desulfurized rich liquid produced by the AS scrubbing unit enters the deacidification tower, where hydrogen sulfide, hydrogen cyanide, and carbon dioxide are resolved and removed to form deacidified lean liquid. A portion of the deacidified lean liquid is cooled in a heat exchanger and then returned to the scrubbing unit for washing and spraying. The remaining deacidified lean liquid enters the free ammonia tower and the fixed ammonia tower to remove volatile ammonia and fixed ammonium in sequence. The ammonia vapor wastewater at the bottom of the fixed ammonia tower is sent to biochemical wastewater treatment. The heat source for heating the middle and bottom of the deacidification tower, as well as the bottom of the fixed ammonia tower and the free ammonia tower, is a saturated steam reboiler. The pressure at the top of the free ammonia tower is controlled to be ≤50KPa and the temperature to be ≤90℃. The ammonia produced at the top of the fixed ammonia tower and the free ammonia tower is passed through the ammonia pipeline into the fractionator for cooling. After vapor-liquid separation, the ammonia is introduced into the ammonia combustion area of ​​the composite Claus furnace. In the ammonia combustion area, as many ammonia components as possible are first completely combusted with oxygen to generate water, nitrogen, and carbon dioxide. Part of the hydrogen sulfide carried by the ammonia is burned to generate sulfur dioxide gas. The pressure at the top of the deacidification tower is controlled to be ≤40KPa and the temperature is ≤80℃. The acid vapor generated at the top of the deacidification tower enters the fractionator through the acid vapor pipeline for cooling. After vapor-liquid separation, it is introduced into the acid vapor combustion area of ​​the composite Claus furnace. In the acid vapor combustion area, by controlling the amount of oxygen-assisted combustion, partial combustion is used to meet the requirement that one-third of the total amount of acid and ammonia vapor is burned to convert hydrogen sulfide into sulfur dioxide. At the same time, a portion of ammonia and hydrogen cyanide is also burned. At this time, the acid vapor combustion reaction stops due to lack of oxygen. The remaining ammonia and hydrogen cyanide undergo high-temperature catalytic cracking reaction in the catalytic cracking reaction area to produce nitrogen, hydrogen and carbon black. The remaining two-thirds of hydrogen sulfide in the acid and ammonia vapor undergoes an oxidation-reduction reaction with sulfur dioxide produced in the early combustion in the Claus reactor to produce elemental sulfur, which is then cooled in a sulfur condenser to obtain sulfur. The generated tail gas is returned to the raw gas system or discharged after appropriate wastewater washing treatment; The upper side of the free ammonia tower is connected to the bottom of the deacidification tower through a pipeline. The ammonia gas drawn from the upper side of the free ammonia tower enters the bottom of the deacidification tower for heating the bottom of the deacidification tower and adjusting the volatile ammonia concentration of the deacidification lean liquid. The volatile ammonia concentration of the deacidification lean liquid is controlled to be 10-20 g / L; the hydrogen sulfide content in the ammonia gas entering the composite Claus furnace is controlled to be ≤3.0%; and the volatile ammonia content in the acid vapor entering the composite Claus furnace is controlled to be ≤10%.

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