Closed zero-emission heat recovery system and method

Abstract

The application discloses a novel closed zero-emission heat recovery system and method, and belongs to the chemical field.The system comprises a sulfur incinerator, a sulfur dioxide catalytic oxidizer and a heat recovery tower, the sulfur incinerator is connected with the sulfur dioxide catalytic oxidizer through a furnace gas heat recovery device, the output end of the upper part of the sulfur dioxide catalytic oxidizer is connected with the heat recovery tower through a coal economizer I, and the output end of the bottom of the heat recovery tower is connected with an evaporator through a high-temperature circulating tank.The novel heat recovery system provided by the application is taken as an example of a 800,000-ton / year sulfuric acid production device, implementation comparison is carried out to calculate that the production time is 8000h / year, and the SO2 conversion rate is 99.9%.

Description

Technical Field

[0001] This invention relates to the chemical industry, specifically to a novel closed-loop zero-emission heat recovery system and method. Background Technology

[0002] Sulfuric acid is an important basic chemical raw material and one of the most important products in the chemical industry, with a wide range of applications. Current technologies for producing sulfuric acid mainly include sulfur production from sulfur, hydrogen sulfide, pyrite, smelting flue gas, and phosphogypsum.

[0003] Industrial sulfuric acid production typically employs a "two-conversion, two-absorption" process, where two absorption towers are used for secondary SO3 absorption. However, the gas exiting the secondary absorption tower contains unabsorbed SO2, SO3, and other harmful substances, requiring desulfurization treatment before discharge. Even so, the exhaust gas still contains a large amount of harmful substances, causing environmental pollution.

[0004] Specifically, sulfuric acid production processes use solid sulfur as raw material to produce sulfuric acid. They typically employ rapid sulfur melting, liquid sulfur filtration, and mechanical atomization sulfur combustion technology, utilizing a "two-conversion, two-absorption" production process. A medium-pressure boiler and economizer are used to recover waste heat from sulfur combustion and conversion processes, generating medium-pressure superheated steam. Currently, the "two-absorption" process in sulfuric acid production involves two absorption towers for two SO3 absorption stages. In existing industrial processes, the acid temperature exiting the second absorption tower is approximately 70℃. Due to this low temperature, the heat generated by the acid production in the second absorption tower cannot be utilized by the low-temperature heat recovery system. All the heat from the acid exiting the second absorption tower is carried away by circulating water, resulting in heat waste and significant energy consumption. The gas exiting the second absorption tower does not meet emission standards and requires tail-end desulfurization treatment. Even in tail-end emissions that meet standards, the SO2 content is generally around 50 mg / Nm³. 3 ~400mg / Nm 3 For large-scale sulfuric acid production plants, the total SO2 emissions are not to be underestimated, and environmental pollution still exists. Summary of the Invention

[0005] This invention addresses the aforementioned technical problems by providing a novel closed-loop zero-emission heat recovery system and method.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A novel closed-loop zero-emission heat recovery system includes a sulfur incinerator, a sulfur dioxide catalytic oxidizer, and a heat recovery tower. The sulfur incinerator is connected to the sulfur dioxide catalytic oxidizer via a furnace gas heat recovery unit. The upper output end of the sulfur dioxide catalytic oxidizer is connected to the heat recovery tower via an economizer I. The lower output end of the heat recovery tower is connected to an evaporator via a high-temperature circulation tank.

[0008] In the technical solution of this invention: the output end of the evaporator is connected to the mixer and the evaporator feed water heater respectively, the evaporator feed water heater is connected to the demineralized water heater, and the output end of the demineralized water heater is the finished acid.

[0009] In the technical solution of this invention: the output end of the deaerator is connected to the mixer and the evaporator feedwater heater respectively; the output pipe of the demineralized water is connected to the demineralized water heater; the output pipe of the demineralized water heater is connected to the deaerator; and the output pipe of the evaporator feedwater heater is connected to the evaporator.

[0010] In the technical solution of this invention: the output end of the mixer is connected to the middle part of the heat recovery tower, and the top of the heat recovery tower is connected to the sulfur incinerator.

[0011] A novel closed-loop zero-emission heat recovery method utilizing the above-described system includes the following steps:

[0012] 1) Oxygen-enriched air enters the sulfur incinerator and burns with liquid sulfur to generate SO2. The furnace gas at the outlet of the sulfur incinerator is cooled to 400-430°C after heat exchange in the furnace gas heat recovery unit and then enters the sulfur dioxide catalytic oxidizer.

[0013] 2) A catalytic oxidation reaction occurs in the sulfur dioxide catalytic oxidizer to generate SO3. The heat of the reaction is converted into high-pressure steam through a high-temperature superheater. After a secondary catalytic oxidation reaction, medium-pressure steam is generated through a medium-temperature superheater. After another catalytic oxidation reaction, the furnace gas is cooled to 200-250°C after passing through an economizer to generate medium-pressure steam and then enters the heat recovery tower.

[0014] 3) SO3 reacts with water in the heat recovery tower to generate H2SO4 with a concentration ≥99.0wt% at a temperature of 200-220℃. This high-temperature acid is transported to the evaporator to exchange heat with the deoxygenated demineralized water to generate low-pressure steam. After heat exchange in the evaporator, part of the acid is adjusted to a sulfuric acid concentration of 97.5-98.5wt% by deoxygenated water in the mixer and returned to the heat recovery tower for spray absorption of SO3.

[0015] 4) The other part of the acid after heat exchange in the evaporator passes through the evaporator feed water heater and the demineralized water heater in sequence to produce finished acid with the acid temperature dropped to below 100℃.

[0016] 5) Pure oxygen is added to the heat recovery tower to maintain the oxygen-nitrogen ratio within the range of 0.3 to 0.5, and then sent into the sulfur incinerator by a blower as supplementary air for the liquid sulfur combustion reaction.

[0017] In the technical solution of this invention: oxygen-enriched air has an oxygen volume content of 23-33%.

[0018] In some more specific technical solutions, the technical solutions of the present invention are as follows:

[0019] 1) Through the pipeline, oxygen-enriched air (O2:N2=0.38) enters the sulfur incinerator, which is connected to equipment such as the sulfur incinerator, furnace gas heat recovery unit, sulfur dioxide catalytic oxidizer, heat recovery tower and evaporator. It burns with liquid sulfur to generate SO2. The furnace gas temperature at the outlet of the sulfur incinerator is 1253℃. After heat exchange in the furnace gas heat recovery unit, the furnace gas is cooled to ~418℃ and enters the sulfur dioxide catalytic oxidizer.

[0020] 2) A catalytic oxidation reaction occurs in the sulfur dioxide catalytic oxidizer to generate SO3. The heat of the reaction is generated into high-pressure steam through a high-temperature superheater. After a secondary catalytic oxidation reaction, medium-pressure steam is generated through a medium-temperature superheater. The furnace gas after another catalytic oxidation reaction is cooled to ~225℃ after being generated into medium-pressure steam by the economizer and then enters the heat recovery tower.

[0021] 3) SO3 reacts with water in the heat recovery tower to generate H2SO4, producing high-temperature acid at 200-220℃. This acid exchanges heat with deoxygenated demineralized water (104℃) in the evaporator to generate low-pressure steam. 4) The furnace gas at the outlet of the heat recovery tower contains 0.11% unreacted SO2, 6.8% O2, a small amount of unabsorbed SO3 and N2. Pure oxygen is added to bring the oxygen-nitrogen ratio to within the range of 0.38. The gas is then sent to the sulfur combustion furnace by a blower to continue the liquid sulfur combustion reaction.

[0022] The beneficial effects of this invention are:

[0023] The novel closed-loop zero-emission heat recovery process system and method provided by this invention, taking an 800,000-ton / year sulfuric acid production unit as an example, is implemented and compared to calculate that the production time is 8,000 hours / year and the SO2 conversion rate is 99.9%.

[0024] In terms of environmental benefits, in traditional production processes, the gas exiting the second absorption tower has a high content of SO2 and SO3, requiring the addition of a tail gas absorption system. Even after treatment, the treated gas still contains SO2 and SO3, with the SO2 emission concentration reaching the standard of 100 mg / Nm³. 3 SO3 acid mist emission concentration meets standard of 5 mg / Nm³ 3 SO2 emissions still reached 16.6 kg / h, and SO3 acid mist emissions were 0.83 kg / h. However, the process system described in this invention achieves zero emissions of tail gas, fundamentally eliminating SO2 pollution from the tail gas. This represents a significant breakthrough for sulfuric acid production equipment, and the successful development of this technology will undoubtedly bring about a major transformation in sulfuric acid industrial equipment, leading a new direction for clean production in the sulfuric acid industry. It also reduces the need for tail gas treatment devices, lowering equipment investment costs.

[0025] The novel closed-loop zero-emission heat recovery process system provided by this invention not only recovers the heat from sulfur burning and catalytic oxidation processes, but also recovers the dilution heat from the acid production process. Compared with traditional sulfuric acid production units, it recovers 48 t / h more low-pressure steam, while reducing the circulating water consumption by 6000 t / h compared with traditional sulfuric acid production units. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the novel closed-loop zero-emission heat recovery system of the present invention.

[0027] Among them, 1 is the sulfur incinerator, 2 is the furnace gas heat recovery unit, 3 is the high-temperature superheater, 4 is the sulfur dioxide catalytic oxidizer, 5 is the medium-temperature superheater, 8 is the economizer, 9 is the heat recovery tower, 10 is the high-temperature circulating tank, 12 is the evaporator, 13 is the mixer, 14 is the evaporator feedwater heater, 15 is the demineralized water heater, and 17 is the deaerator. Detailed Implementation

[0028] The present invention will be further described below with reference to embodiments, but the scope of protection of the present invention is not limited thereto:

[0029] like Figure 1 A novel closed-loop zero-emission heat recovery system includes a sulfur incinerator 1, a sulfur dioxide catalytic oxidizer 4, and a heat recovery tower 9. The sulfur incinerator 1 is connected to the sulfur dioxide catalytic oxidizer 4 via a furnace gas heat recovery unit 2. The upper output end of the sulfur dioxide catalytic oxidizer 4 is connected to the heat recovery tower 9 via an economizer 18. The bottom output end of the heat recovery tower 9 is connected to an evaporator 12 via a high-temperature circulation tank 10.

[0030] The output end of the evaporator 12 is connected to the mixer 13 and the evaporator feed water heater 14 respectively. The evaporator feed water heater 14 is connected to the demineralized water heater 15. The output end of the demineralized water heater 15 is the finished acid.

[0031] The output of the deaerator 17 is connected to the mixer 13 and the evaporator feedwater heater 14 respectively. The output pipe of the demineralized water is connected to the demineralized water heater 15, and the output pipe of the demineralized water heater 15 is connected to the deaerator 17. The output pipe of the evaporator feedwater heater 14 is connected to the evaporator 12.

[0032] The output end of the mixer 13 is connected to the middle of the heat recovery tower 9, and the top of the heat recovery tower 9 is connected to the sulfur incinerator 1.

[0033] A method for achieving zero-emission heat recovery using the above system is as follows:

[0034] 1) Oxygen-enriched air (23% ≤ O2 content ≤ 33%) enters the sulfur incinerator 1 and burns with liquid sulfur to generate SO2. The outlet gas temperature of the sulfur incinerator 1 is as high as 1250℃. After heat exchange by the gas heat recovery unit 2, the gas temperature is reduced to 400-430℃ and enters the sulfur dioxide catalytic oxidizer 4.

[0035] 2) A catalytic oxidation reaction occurs in the sulfur dioxide catalytic oxidizer 4 to generate SO3. The reaction heat is converted into high-pressure steam by the high-temperature superheater 3. After a secondary catalytic oxidation reaction, medium-pressure steam is generated by the medium-temperature superheater 5. The furnace gas after another catalytic oxidation reaction is cooled to 200-250°C after the economizer 8 generates medium-pressure steam and enters the heat recovery tower.

[0036] 3) SO3 reacts with water in heat recovery tower 9 to generate H2SO4 (concentration ≥99.0%) at a temperature of 200-220℃. This high-temperature acid is transported to evaporator 12 to exchange heat with deoxygenated water to generate low-pressure steam. Part of the medium-temperature acid (temperature 160-190℃) after heat exchange in evaporator 12 is adjusted to a sulfuric acid concentration of about 98% by deoxygenated water in mixer 13 and returned to heat recovery tower 9 for spray absorption of SO3.

[0037] 4) The other part of the medium-temperature acid (temperature 160-190℃) after heat exchange in evaporator 12 passes through evaporator feed water heater 14 and demineralized water heater 15 in sequence to produce finished acid with acid temperature dropped to below 100℃.

[0038] Performance testing:

[0039] The novel closed-loop zero-emission heat recovery process system provided by this invention mainly includes a sulfur incinerator, a furnace gas heat recovery unit, a sulfur dioxide catalytic oxidizer, a heat recovery tower, and an evaporator. Traditional production processes require a larger number of reaction towers, including a drying tower and first / second absorption towers. A comparison of the main equipment for the two production processes is shown in Table 1.

[0040] Table 1 Comparison of Main Equipment in Different Process Systems

[0041]

[0042]

[0043] As can be seen from the table above, the main equipment required by this invention is less than that of traditional processes, reducing the floor space required, and the main reactor is smaller than that of traditional processes, reducing investment costs.

[0044] (2) Power consumption

[0045] The novel closed-loop zero-emission heat recovery process system provided by this invention eliminates the need for a dry-suction acid cooler and recovers and utilizes the heat of reaction, reducing the amount of circulating water used in traditional production processes. Furthermore, this system eliminates the need for dry-suction acid circulation pumps and primary and secondary suction acid circulation pumps, reducing annual power consumption by 265.6 x 10⁻⁶. 4 kWh.

[0046] Table 2 Comparison of power consumption of different process systems

[0047]

[0048] (4) Steam production

[0049] Table 3 Comparison of Steam Production in Different Process Systems

[0050]

[0051] The novel closed-loop zero-emission heat recovery process system provided by this invention not only recovers heat from sulfur combustion and catalytic oxidation processes, but also recovers dilution heat from acid production processes for the production of low-pressure steam, while simultaneously reducing the amount of circulating water used in traditional production processes. Therefore, this process system demonstrates significant advantages.

[0052] (5) Exhaust emissions

[0053] Table 4. Exhaust gas emissions and composition of traditional sulfuric acid production systems

[0054]

[0055] In traditional production processes, the gas exiting the second absorption tower has a high content of SO2 and SO3, requiring the addition of a tail gas absorption system. As shown in the table above, even after treatment, the treated exhaust gas still contains SO2 and SO3, with SO2 emissions still reaching 16593.87 Nm³. 3 The process system described in this invention achieves zero emissions of tail gas, fundamentally eliminating SO2 pollution from tail gas. This represents a significant breakthrough for sulfuric acid production equipment, and the successful development of this technology will undoubtedly bring about a major transformation in sulfuric acid industrial equipment, leading a new direction for clean production in the sulfuric acid industry.

Claims

1. A closed-loop zero-emission heat recovery system, characterized in that: The system includes a sulfur incinerator (1), a sulfur dioxide catalytic oxidizer (4), and a heat recovery tower (9). The sulfur incinerator (1) is connected to the sulfur dioxide catalytic oxidizer (4) via a furnace gas heat recovery unit (2). The upper output end of the sulfur dioxide catalytic oxidizer (4) is connected to the heat recovery tower (9) via an economizer (8). The bottom output end of the heat recovery tower (9) is connected to the evaporator (12) via a high-temperature circulation tank (10). The output end of the evaporator (12) is connected to the mixer (13) and the evaporator feed water heater (14), respectively. The evaporator feed water heater (14) is connected to the demineralized water heater (15), and the output end of the demineralized water heater (15) is the finished acid. The output of the deaerator (17) is connected to the mixer (13) and the evaporator feedwater heater (14) respectively. The output pipe of the demineralized water is connected to the demineralized water heater (15), and the output pipe of the demineralized water heater (15) is connected to the deaerator (17). The output pipe of the evaporator feedwater heater (14) is connected to the evaporator (12). The output end of the mixer (13) is connected to the middle of the heat recovery tower (9), and the top of the heat recovery tower (9) is connected to the sulfur incinerator (1).

2. A method for achieving closed-loop zero-emission heat recovery using the system described in claim 1, characterized in that: The method includes the following steps: 1) Oxygen-enriched air enters the sulfur incinerator (1) and burns with liquid sulfur to generate SO2. The furnace gas at the outlet of the sulfur incinerator (1) is cooled to 400-430°C after heat exchange by the furnace gas heat recovery unit (2) and then enters the sulfur dioxide catalytic oxidizer (4). 2) A catalytic oxidation reaction occurs in the sulfur dioxide catalytic oxidizer (4) to generate SO3. The reaction heat is generated into high-pressure steam through the high-temperature superheater (3). After the secondary catalytic oxidation reaction, medium-pressure steam is generated through the medium-temperature superheater (5). After the furnace gas undergoes another catalytic oxidation reaction, it is cooled to 200-250°C after the economizer (8) generates medium-pressure steam and enters the heat recovery tower. 3) SO3 reacts with water in the heat recovery tower (9) to generate H2SO4 with a concentration ≥99.0wt% at a temperature of 200~220℃. The high-temperature acid is transported to the evaporator (12) to exchange heat with the deoxygenated demineralized water to generate low-pressure steam. After heat exchange in the evaporator (12), part of the acid is adjusted to a sulfuric acid concentration of 97.5~98.5wt% by deoxygenated water in the mixer (13) and returned to the heat recovery tower (9) for spray absorption of SO3. 4) The other part of the acid after heat exchange in the evaporator (12) passes through the evaporator feed water heater (14) and the demineralized water heater (15) in sequence to produce finished acid with the acid temperature dropped to below 100℃; 5) Pure oxygen is added to the heat recovery tower (9) to keep the oxygen-nitrogen ratio in the range of 0.3 to 0.5, and then sent to the sulfur incinerator by a blower as supplementary air for the liquid sulfur combustion reaction.

3. The method according to claim 2, characterized in that: Oxygen-enriched air is air with an oxygen content of 23-33% by volume.

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