A direct combustion incineration system and process for treating maleic anhydride plant tail gas

Abstract

A direct-fired incineration system for maleic anhydride plant tail gas, relating to the field of environmentally friendly chemical waste treatment, includes a three-stage incinerator, an ultra-high pressure waste heat boiler, a tail gas preheater, and a chimney. The three-stage incinerator comprises a high-temperature combustion section, a high-temperature oxidation section, and an ultra-clean oxidation section connected sequentially. The outlet of the ultra-clean oxidation section, the flue gas passage of the ultra-high pressure waste heat boiler, the tail gas preheater, and the chimney are connected sequentially. A main burner and an auxiliary burner are located at the top of the high-temperature combustion section. Preheated tail gas flows out of the tail gas outlet of the tail gas preheater and is divided into a first tail gas path, a second tail gas path, and a third tail gas path. The first tail gas path is connected to the high-temperature combustion section, the second tail gas path is connected to the high-temperature oxidation section, and the third tail gas path is connected to the ultra-clean oxidation section. This system enables tail gas incineration treatment of maleic anhydride plants using the n-butane process and hydrogen cyanide plants. The incineration system is highly efficient and energy-saving, eliminating the need for SNCR or SCR denitrification devices and ensuring low nitrogen emissions from the flue gas.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection treatment of chemical waste, specifically relating to a direct combustion incineration system and process for maleic anhydride plant tail gas. Background Technology

[0002] Driven by the ban on plastics, biodegradable plastics will gradually replace traditional plastics in the future, and maleic anhydride, as a raw material for biodegradable plastics, will see a continued surge in potential demand. Maleic anhydride production processes can be divided into benzene oxidation and n-butane oxidation. Currently, domestic production facilities mainly use the benzene method, but with the rapid development of my country's petrochemical industry and the improvement of refining capacity, C4 resources are gradually being comprehensively utilized, and n-butane-based maleic anhydride plants have seen rapid development in recent years.

[0003] The maleic anhydride tail gas produced by the n-butane process is characterized by its large volume, oxygen content, susceptibility to clogging and corrosion, and low calorific value. Its treatment processes mainly include direct combustion (TO) and regenerative thermal oxidation (RTO). Direct combustion offers advantages such as simple process, convenient operation, low failure rate, and high removal rate of harmful substances, meeting the high reliability requirements of maleic anhydride plants for tail gas treatment. However, it consumes a large amount of auxiliary fuel. Regenerative thermal oxidation, by adding a regenerator chamber before the oxidation chamber, can significantly reduce fuel consumption. However, it has a low removal rate of harmful substances, failing to meet environmental protection requirements. Furthermore, due to the numerous regenerator chambers, it requires constant switching of tail gas inlet and outlet via lift valve operation, resulting in cumbersome operation and a high failure rate.

[0004] Patent application number 202122010653.6, "A Combined Incineration Equipment for Maleic Anhydride Tail Gas Pipeline Regenerative Furnace and Direct-Fired Furnace," and patent application number 201911345040.9, "A Method for Treating Maleic Anhydride Production Waste Gas," introduce a combined incineration equipment for maleic anhydride tail gas pipeline regenerative furnace and direct-fired furnace. Part of the maleic anhydride tail gas enters the regenerative furnace for treatment, while the remainder enters the direct-fired furnace for treatment. The treated flue gas is mixed before being discharged. The flue gas from the direct-fired furnace dilutes the concentration of harmful substances in the flue gas from the regenerative furnace, thereby meeting environmental protection requirements. However, with the increase in equipment and operating points, the failure rate further increases, which in turn increases the frequency of maleic anhydride plant shutdowns.

[0005] The patent application number 202211620540.0, entitled "A process method for treating the tail gas of a maleic anhydride RTO furnace", sets up a flue gas scrubbing tower before the flue gas from the regenerator outlet enters the chimney in order to reduce VOCs emissions. However, other drawbacks of the regenerator cannot be avoided, and it increases wastewater discharge, further increasing the environmental pressure on enterprises. Summary of the Invention

[0006] The technical problem solved by this application is to overcome the shortcomings of existing technologies and provide a direct combustion incineration system for maleic anhydride plant tail gas. This system utilizes waste liquid from propane dehydrogenation units, polycarbonate units, and gas separation units in chemical plants as fuel for supplementary combustion of the maleic anhydride plant tail gas. This avoids fuel gas consumption and achieves the environmental goal of "treating waste with waste," making it an ideal method for treating maleic anhydride plant tail gas. Simultaneously, the system retains corresponding settings for fuel gas supplementary combustion, ensuring stable operation of the maleic anhydride tail gas direct combustion incineration unit even when the waste liquid production unit operates at reduced load or is shut down for maintenance, further improving the reliability of the direct combustion process.

[0007] The technical solution provided in this application is as follows:

[0008] A direct-fired combustion system for maleic anhydride plant tail gas includes a three-stage incinerator, an ultra-high pressure waste heat boiler, a tail gas preheater, and a chimney. The three-stage incinerator comprises a high-temperature combustion section, a high-temperature oxidation section, and an ultra-clean oxidation section connected sequentially. The high-temperature combustion section and the high-temperature oxidation section are arranged vertically from top to bottom. The outlet of the ultra-clean oxidation section is connected to the ultra-high pressure waste heat boiler, which is arranged horizontally. The tail gas preheater has a tail gas inlet, a tail gas outlet, a flue gas inlet, and a flue gas outlet. The outlet of the high-pressure waste heat boiler is connected to the flue gas inlet of the vertically arranged tail gas preheater, and the flue gas outlet at the top of the tail gas preheater is connected to the chimney. The tail gas outlet of the tail gas preheater is connected to the three-stage incinerator, forming a "U"-shaped structure. A main burner is located at the top of the high-temperature combustion section. The waste liquid and / or fuel gas are burned in the main burner and auxiliary burner to provide a heat source for the exhaust gas incineration. The exhaust gas generated by the maleic anhydride unit enters from the exhaust gas inlet of the exhaust gas preheater and flows out from the exhaust gas outlet to obtain preheated exhaust gas. The preheated exhaust gas enters the three-stage incinerator, where it is incinerated with the waste liquid and / or fuel gas. The high-temperature flue gas generated by incineration enters the ultra-high pressure waste heat boiler for waste heat recovery. The flue gas from the outlet of the ultra-high pressure waste heat boiler enters the exhaust gas preheater to heat the exhaust gas generated by the maleic anhydride unit, and then is discharged into the atmosphere through the chimney. The preheated exhaust gas is divided into a first exhaust gas, a second exhaust gas, and a third exhaust gas. The first exhaust gas is connected to the high-temperature combustion section, the second exhaust gas is connected to the high-temperature oxidation section, and the third exhaust gas is connected to the ultra-clean oxidation section.

[0009] The main burner is located in the middle of the top of the high-temperature combustion section. A combustion-supporting fan is also installed at the top of the high-temperature combustion section to supply air into the high-temperature combustion section and provide oxygen for the combustion of the main burner.

[0010] The main burner uses cold air supplied by a combustion fan for combustion assistance, and controls the excess air coefficient α = 0.60 to 0.80; the heat load of the main burner accounts for 10% to 20% of the total heat load.

[0011] The auxiliary burner is located below the main burner. Multiple auxiliary burners 2 are provided, and the multiple auxiliary burners are evenly distributed tangentially in the shoulder of the high-temperature combustion section. The waste liquid or fuel gas of the auxiliary burner is assisted by the first oxygen-containing tail gas at a preheated temperature of 300℃~450℃. The oxygen content of the first oxygen-containing tail gas is 13%~15%. The heat load of the auxiliary burner 2 accounts for 20%~30% of the total heat load.

[0012] The first, second, and third exhaust gases flow tangentially into the three-stage incinerator; the direction of the tangential swirl in the auxiliary burner is the same as that of the first, second, and third exhaust gases. The first exhaust gas accounts for 10%–20% of the total exhaust gas, the second exhaust gas accounts for 10%–25%, and the third exhaust gas accounts for 55%–80%.

[0013] The combustion temperature in the high-temperature combustion section is 1300℃~1500℃, and the oxygen content is controlled between 2% and 5%; the combustion temperature in the high-temperature oxidation section is 1050℃~1200℃, and the oxygen content is controlled between 6% and 8%; the combustion temperature in the ultra-clean oxidation section is 750℃~900℃, and the oxygen content is controlled between 9% and 11%.

[0014] The ultra-high pressure waste heat boiler includes an evaporator and a superheater. High-pressure boiler feedwater enters the evaporator and exchanges heat with the high-temperature flue gas discharged from the three-stage incinerator to obtain ultra-high pressure saturated steam. Then, the ultra-high pressure saturated steam and the ultra-high pressure saturated steam generated by the maleic anhydride device are combined and enter the superheater, where they exchange heat again with the high-temperature flue gas discharged from the three-stage incinerator to obtain ultra-high pressure superheated steam.

[0015] The exhaust gas preheater is a multi-stage series tubular heat exchanger. Along the flow direction of the exhaust gas generated by the maleic anhydride unit, the exhaust gas preheater includes 1-N stages of preheaters from top to bottom. The topmost stage 1 preheater is made of 316L stainless steel, the bottommost stage N preheater is made of 304 stainless steel, and the middle preheaters are made of 20 steel. The inlet temperature of the exhaust gas preheater is 67-72℃, and the outlet temperature of the exhaust gas preheater is 300℃-450℃.

[0016] Each stage of the exhaust gas preheater consists of 2-6 modules connected in parallel. Exhaust gas enters each module in a uniform and equal manner. Each module's exhaust gas outlet is equipped with a baffle. By closing one or more baffles, the exhaust gas flow rate is increased to 40m / s to 60m / s. The high-speed flushing of exhaust gas removes crystals from the exhaust gas, preventing blockage of the exhaust gas preheater due to crystallization.

[0017] A direct combustion incineration process for maleic anhydride unit tail gas based on any one of the above-mentioned maleic anhydride unit tail gas tail gas treatment systems includes:

[0018] The main burner uses cold air for combustion assistance, with an excess air coefficient α = 0.60 to 0.80. The auxiliary burner uses the first-pass exhaust gas with an oxygen content of 13% to 15% for combustion assistance.

[0019] The exhaust gas generated by the maleic anhydride unit is preheated to 300℃~450℃ by an exhaust gas preheater to obtain preheated exhaust gas.

[0020] The preheated exhaust gas is divided into three streams: the first stream, the second stream, and the third stream. The first stream enters the high-temperature combustion section, the second stream enters the high-temperature oxidation section, and the third stream enters the ultra-clean oxidation section. The materials ejected from the main burner and auxiliary burner, along with the preheated exhaust gas, are incinerated in the three-stage incinerator. The combustion temperature in the high-temperature combustion section is 1300℃~1500℃, with an oxygen content controlled between 2% and 5%. The combustion temperature in the high-temperature oxidation section is 1050℃~1200℃, with an oxygen content controlled between 6% and 8%. The combustion temperature in the ultra-clean oxidation section is 750℃~900℃, with an oxygen content controlled between 9% and 11%.

[0021] The high-temperature flue gas generated by incineration enters the ultra-high pressure waste heat boiler for waste heat recovery. After passing through the high-pressure waste heat boiler, the flue gas temperature drops to 380℃~450℃ before entering the tail gas preheater to heat the tail gas. After the flue gas temperature in the tail gas preheater drops to 90℃~130℃, it is discharged into the atmosphere through the chimney.

[0022] In summary, this application includes at least the following beneficial technical effects:

[0023] (1) The maleic anhydride unit tail gas direct combustion incineration treatment system of the present invention uses a high-pressure waste heat boiler and a tail gas preheater to utilize the waste heat of the flue gas, so as to ensure that the incineration system is highly efficient and energy-saving.

[0024] (2) The maleic anhydride device tail gas direct combustion incineration treatment system involved in this invention uses waste liquid for supplementary combustion, which avoids the consumption of fuel gas and achieves the environmental protection goal of "treating waste with waste", thus achieving a "win-win" goal.

[0025] (3) The maleic anhydride unit tail gas direct combustion treatment system of the present invention adopts oxygen-deficient combustion, fuel staged combustion and oxygen-deficient combustion, without the need for SNCR and SCR denitrification devices, and can ensure low nitrogen emissions of flue gas.

[0026] (4) The maleic anhydride unit tail gas direct combustion incineration treatment system of the present invention has a tail gas preheater that can effectively prevent tail gas crystallization blockage of heat exchanger and corrosion problems through special tail gas flushing flow design and material selection.

[0027] (5) The maleic anhydride unit tail gas direct combustion incineration treatment system of the present invention adopts an ultra-high pressure waste heat boiler to simultaneously heat boiler feedwater and ultra-high pressure saturated steam to the steam quality required by the user, thereby ensuring the stable operation of the maleic anhydride unit and the energy recovery and utilization of the entire system.

[0028] (6) The maleic anhydride unit tail gas direct combustion incineration treatment system of the present invention can achieve complete decomposition of harmful substances in the maleic anhydride unit tail gas. Attached Figure Description

[0029] Figure 1 This is a process flow diagram for this application;

[0030] Figure 2 This is the floor plan of this application;

[0031] Figure 3 This is a front view of the elevation layout of this application;

[0032] Figure 4 Side view of the elevation layout of this application.

[0033] Explanation of reference numerals: 1. Main burner; 2. Auxiliary burner; 3. Three-stage incinerator; 31. High-temperature combustion section; 32. High-temperature oxidation section; 33. Ultra-clean oxidation section; 4. Ultra-high pressure waste heat boiler; 41. Evaporator; 42. Superheater; 5. Exhaust gas preheater; 6. Chimney; 7. Combustion fan; 8. Exhaust gas separator;

[0034] 110. Waste liquid; 111. First waste liquid; 112. Second waste liquid; 120. Fuel gas; 121. First fuel gas; 122. Second fuel gas; 411. Ultra-high pressure boiler feedwater; 412. Self-produced ultra-high pressure saturated steam; 413. Ultra-high pressure saturated steam generated by the maleic anhydride unit; 421. Ultra-high pressure superheated steam; 810. Tail gas from the maleic anhydride unit; 811. Tail gas after separation; 510. Tail gas after preheating; 511. First tail gas; 512. Second tail gas; 513. Third tail gas. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments disclosed in the present invention will be described in further detail below with reference to the accompanying drawings.

[0036] This application discloses a direct combustion incineration system for maleic anhydride plant tail gas, applicable to the incineration of large volumes of tail gas produced by n-butane process maleic anhydride plants. For industries such as hydrogen cyanide, which also produce large volumes of low-calorific-value tail gas, the process flow, oxygen-deficient combustion technology, fuel staged combustion technology, and oxygen-lean combustion-assisted combustion technology described in this invention are universally applicable in terms of technical principles. The specific embodiments described in this invention are only some examples of the invention and are used solely to explain the invention, not to limit it. Where there is no conflict, the embodiments and technical features involved in this invention can be combined.

[0037] For ease of explanation, a brief overview of the invention will be given first. For example... Figure 1 As shown, the present invention mainly includes a main burner 1, an auxiliary burner 2, a three-stage incinerator 3, an ultra-high pressure waste heat boiler 4, a tail gas preheater 5, a chimney 6, a combustion fan 7, and a tail gas separator 8. One main burner 1 is provided, and four to six auxiliary burners 2 are provided.

[0038] like Figure 2 , Figure 3 and Figure 4 As shown, the main equipment of this invention adopts a "U"-shaped arrangement, with the ends connected, resulting in a compact and economical structure. Specifically, the three-stage incinerator 3 includes a high-temperature combustion section 31, a high-temperature oxidation section 32, and an ultra-clean oxidation section 33 connected in sequence. The high-temperature combustion section 31 and the high-temperature oxidation section 32 of the three-stage incinerator 3 are arranged vertically from top to bottom, while the ultra-clean oxidation section 33 is arranged horizontally at the bottom of the high-temperature oxidation section 32. The outlet end of the ultra-clean oxidation section 33 is connected to the ultra-high pressure waste heat boiler 4, and the outlet of the high-pressure waste heat boiler 4 is connected to a vertically arranged tail gas preheater 5. The top of the tail gas preheater 5 is connected to the chimney 6.

[0039] The high-temperature combustion section 31 and high-temperature oxidation section 32 of the three-stage incinerator 3, along with the exhaust gas preheater 5, are all vertically arranged and adjacent to each other. The exhaust gas outlet height of the exhaust gas preheater 5 is flush with the top main burner 1 of the three-stage incinerator 3. The exhaust gas 510 exits directly into the three zones of the three-stage incinerator 3 from top to bottom, significantly reducing the amount of high-temperature, ultra-large exhaust gas pipelines used and greatly reducing system heat loss. The ultra-clean oxidation section 33 and the ultra-high pressure waste heat boiler 4 are horizontal structures, respectively connected to the flue gas outlet of the high-temperature oxidation section 32 and the flue gas inlet of the exhaust gas preheater 5, forming a "U"-shaped structure. This facilitates operation and maintenance and significantly reduces the amount of steel structure used. In summary, the main equipment is arranged in a "U" shape, with the "head" and "tail" connected, achieving high efficiency and energy saving, reducing land occupation, and lowering investment.

[0040] The high-temperature combustion section 31 of the three-stage incinerator 3 is equipped with a main burner 1 and an auxiliary burner 2 at its top. Waste liquid 110 is burned in the main burner 1 and auxiliary burners 2 to provide a heat source for the combustion of ultra-high flow tail gas. The maleic anhydride unit tail gas is supplemented by combustion through the waste liquid. After entering the unit, the waste liquid 110 is divided into two streams. The first stream, waste liquid 111, enters the main burner 1 through a waste liquid gun for combustion. The main burner 1 uses cold air provided by the combustion fan 7 for oxygen-deficient combustion, which suppresses NOx formation. The second stream, waste liquid 112, is burned through waste liquid guns on 4 to 6 auxiliary burners 2 to provide heat for tail gas combustion. The auxiliary burners 2 use the first stream tail gas 511 for oxygen-deficient combustion, meaning the oxygen content of the first stream tail gas 511 is 13% to 15%. NOx formation is suppressed through fuel staging and oxygen-deficient combustion technology. NOx formation is suppressed through oxygen-deficient combustion, fuel staging, and oxygen-deficient combustion technology.

[0041] The main burner 1 is installed at the top of the three-stage incinerator 3. The main burner 1 includes a combustion air inlet, a waste liquid gun, a gas gun, a flame stabilizer, an air swirl generator, a flame detector, and an ignition system. The main burner 1 uses cold air supplied by the combustion air fan 7 for combustion assistance, controlling the excess air coefficient α to be 0.60–0.80, i.e., employing oxygen-deficient combustion to suppress NOx emissions. The heat load of the main burner 1 accounts for 10%–20% of the total heat load. The swirling high-temperature flue gas generated by the main burner 1 enters the high-temperature combustion section 31 of the three-stage incinerator 3, igniting the waste liquid or gas injected by the auxiliary burner 2.

[0042] Four to six auxiliary burners 2 are tangentially swirled and evenly distributed at the shoulder of the high-temperature combustion section 31 of the three-stage incinerator 3. Each auxiliary burner includes a waste liquid gun, a gas gun, and a flame stabilizer. The waste liquid or gas from the auxiliary burners 2 is aided by preheated oxygen-containing tail gas 511 at 300℃~450℃. NOx formation is suppressed through fuel staging and lean-oxygen combustion technology. The heat load of the auxiliary burners 2 accounts for 20%~30% of the total heat load. The tangentially swirled and evenly distributed auxiliary burners 2 generate high-temperature flue gas that swirls at the front end of the high-temperature combustion section 31. The oxygen-containing tail gas 511 also tangentially swirls into the front end of the high-temperature combustion section 31. The high-temperature flue gas generated by the main burner 1 also swirls at high speed into the front end of the high-temperature combustion section 31, forming multiple swirles. The high-temperature flue gas and the tail gas reinforce and entrain each other, achieving thorough mixing of the three.

[0043] The exhaust gas from the maleic anhydride unit, specifically the waste liquid 110, can be replaced with fuel gas or other high-calorific-value waste gas. The main burner 1 and auxiliary burner 2 can handle multiple or multiple streams of waste liquid 110. The first stream of waste liquid 111 accounts for 30% to 50% of the total waste liquid 110.

[0044] By configuring the main burner 1 and auxiliary burner 2 as described above, staged combustion of fuel is achieved, preventing the main burner 1 from being overloaded. Furthermore, since the main burner 1 and auxiliary burner 2 are located at different positions on the axis of the three-stage incinerator 3, high-temperature singularities are eliminated, suppressing the formation of NOx.

[0045] The high-temperature flue gas generated by combustion is sequentially mixed with the second exhaust gas 512 and the third exhaust gas 513 in a swirling motion to ensure the complete decomposition of harmful substances in the exhaust gas. When the flow rate of waste liquid 110 generated by other devices is insufficient or the supply stops, supplementary fuel gas is used for combustion. The fuel gas 120 enters the device in two paths: the first path fuel gas 121 enters the main burner for combustion through a gas spray gun, and the second path fuel gas 122 is burned through gas guns on 4 to 6 auxiliary burners 2.

[0046] The flue gas in the high-temperature combustion section 31 comes from the main burner 1, the auxiliary burner 2, and the first tail gas 511, and is used to treat the waste liquid generated by each device. The combustion temperature is 1300℃~1500℃, and the oxygen content is controlled between 2% and 5% to meet the requirements of pyrolysis combustion of the waste liquid. The second tail gas 512 flows into the high-temperature oxidation section in two layers and is mixed with the high-speed jet flue gas in the high-temperature combustion section 31 for combustion. The combustion temperature in the high-temperature oxidation section 32 is 1050℃~1200℃, and the oxygen content is controlled between 6% and 8% to ensure that the components after pyrolysis of the waste liquid are fully combusted. The third tail gas 513 flows into the purification oxidation section 33 in five layers and is mixed with the high-speed jet flue gas in the high-temperature oxidation section 32 for combustion. The combustion temperature in the ultra-clean oxidation section 33 is 750℃~900℃, and the oxygen content is controlled between 9% and 11% to achieve complete oxidation.

[0047] The high-temperature flue gas from the outlet of the three-stage incinerator 3 enters the ultra-high pressure waste heat boiler 4 for waste heat recovery. The ultra-high pressure waste heat boiler 4 can heat various heat media for use in power generation by the user's turbine unit or heating network. Conventionally, the ultra-high pressure waste heat boiler 4 consists of an evaporator 41 and a superheater 42. High-pressure boiler feedwater 411 enters the evaporator 41 to generate ultra-high pressure saturated steam 412, which then merges with a large amount of ultra-high pressure saturated steam 413 generated by the maleic anhydride unit and enters the superheater 42 for reheating, ultimately producing ultra-high pressure superheated steam 421 for user use. The flue gas from the outlet of the ultra-high pressure waste heat boiler 4 enters the tail gas preheater 5 to heat the tail gas before being discharged into the atmosphere through the chimney 6. In addition, the ultra-high pressure waste heat boiler 4 can also heat heat transfer oil or molten salt and other heat media. The above-mentioned ultra-high pressure waste heat boiler 4 reheats the steam generated by the maleic anhydride unit from external steam.

[0048] Specifically, the evaporator 41 heats and evaporates the boiler feedwater 411 to generate ultra-high pressure saturated steam 412 of 8.0–12 MPa.g. This ultra-high pressure saturated steam 412, along with a large amount of ultra-high pressure saturated steam 413 generated by the maleic anhydride unit, merges into the superheater 42 for reheating, ultimately heating the steam to 500°C–540°C for use by the user's turbine unit for power generation. In unconventional cases, the ultra-high pressure waste heat boiler can also heat heat transfer oil or molten salt, among other heat transfer media.

[0049] After passing through the high-pressure waste heat boiler 4, the flue gas temperature drops to 380℃~450℃ before entering the tail gas preheater 5 to heat the tail gas. After the flue gas temperature in the tail gas preheater 5 drops to 90℃~130℃, it is discharged into the atmosphere through the chimney 6.

[0050] The ultra-high pressure waste heat boiler 4 adopts a modular design, and different modules can realize the function of heating various heat media for users' turbine units to generate electricity or for use in heating networks.

[0051] The ultra-high pressure waste heat boiler 4 includes a boiler chemical dosing system, a boiler sampling system, and a boiler blowdown system.

[0052] The exhaust gas preheater 5 is a multi-stage series tubular heat exchanger, typically with 5 or 6 stages. Each stage consists of 2 to 6 modules connected in parallel, ensuring uniform exhaust gas flow between modules and consistent heat exchange. To address the issue of exhaust gas crystallization and blockage, an exhaust gas flushing flow design is employed to prevent blockage due to crystallization. Specifically, each module's exhaust gas outlet in the exhaust gas preheater 5 is equipped with a baffle. By closing one or more baffles, the exhaust gas velocity is increased to 40 m / s to 60 m / s. This high-speed flushing action removes any crystals from the exhaust gas. After being separated by a separator, the maleic anhydride unit's exhaust gas first enters the first-stage exhaust gas preheater, which is made of 316L stainless steel to prevent low-temperature corrosion. The final stage is made of 304 stainless steel, while the intermediate 3rd and 4th stages are made of 20 stainless steel. The exhaust gas inlet temperature is 67-72℃, the exhaust gas preheater outlet temperature is 300℃-450℃, and the preheated exhaust gas enters the three-stage incinerator in three separate streams.

[0053] The implementation principle of this embodiment is as follows:

[0054] Both the main burner 1 and the auxiliary burner 2 are gas-liquid combined burners. When the waste liquid is insufficient or absent, the maleic anhydride unit's tail gas is supplemented by fuel gas combustion. The high-temperature flue gas generated from the combustion of waste liquid and / or fuel gas enters the three-stage incinerator 3 and is mixed with the remaining tail gas to oxidize and decompose the harmful components in the tail gas.

[0055] The tail gas 810 generated by the maleic anhydride unit is first separated into liquid and liquid components by a gas-liquid separator 8. After separating the polymer absorbent and condensate, the separated tail gas 811 is obtained. The separated tail gas 811 enters the tail gas preheater 5 for preheating. After five stages of preheating (illustrated as stage 5 or 6), the tail gas 510 is preheated to 300℃~450℃. The tail gas 510 is divided into three streams and enters the three-stage incinerator 3. The first stream of tail gas 511 enters the high-temperature combustion section 31 tangentially, where the combustion temperature is 1300℃~1500℃ and the oxygen content is between 2% and 5%. The waste liquid undergoes pyrolysis and combustion under low-oxygen conditions to aid combustion of the fuel in the auxiliary burner 2. The second tail gas 512 enters tangentially into the high-temperature oxidation section 32 and is mixed and combusted with the high-temperature flue gas from the outlet of the high-temperature combustion section 31. The combustion temperature is 1050℃~1200℃ and the oxygen content is between 6% and 8%. The third tail gas 513 enters tangentially into the ultra-clean oxidation section 33 and is mixed and combusted with the flue gas from the outlet of the high-temperature oxidation section 32. The combustion temperature is 750℃~900℃ and the oxygen content is between 9% and 11%. The tail gas completes complete oxidation and combustion.

[0056] The flue gas from the outlet of the three-stage incinerator 3 enters the ultra-high pressure waste heat boiler 4 for heat recovery, and simultaneously generates ultra-high pressure superheated steam for user use. The flue gas from the outlet of the ultra-high pressure waste heat boiler 4 enters the tail gas preheater 5 to heat the maleic anhydride unit's tail gas, and finally is discharged into the atmosphere through the chimney 6.

[0057] Example 1

[0058] The tail gas of the maleic anhydride unit was treated by supplementing combustion with waste liquid from other devices. The composition and state parameters of the tail gas of the maleic anhydride unit to be treated are shown in Table 1.

[0059] Table 1. Components and states of the tail gas from the maleic anhydride unit to be treated.

[0060] Temperature ℃ 70 ℃ Inlet pressure 10 Kpa.G Low heating value 92.8 kcal / kg Normal traffic 670000 kg / h quality score Nitrogen 75.33 wt% oxygen 15.38 wt% n-Butane 0.58 wt% carbon monoxide 1.11 wt% carbon dioxide 1.59 wt% water 5.957 wt% Acetic acid 0.03 wt% acrylic acid 0.02 wt% DBP and other organic compounds 0.003 wt%

[0061] Using the incineration treatment system described in this invention, the tail gas treatment steps of the maleic anhydride unit are as follows:

[0062] The exhaust gas 810 generated by the maleic anhydride unit first passes through a gas-liquid separator 8 to separate the polymer absorbent and condensate. The separated exhaust gas 811 then enters the exhaust gas preheater 5 and is preheated to 430°C. The preheated exhaust gas 510 is divided into three streams and enters the three-stage incinerator 3. The first stream of exhaust gas 511 enters the high-temperature combustion section 31 tangentially, accounting for 15.51% of the total exhaust gas 810. The second stream of exhaust gas 512 enters the high-temperature oxidation section 32 tangentially, accounting for 22.25% of the total exhaust gas 810. The third stream of exhaust gas 513 enters the ultra-clean oxidation section 33 tangentially, accounting for 62.24% of the total exhaust gas 810.

[0063] The maleic anhydride unit's tail gas incineration system uses waste liquid 110 for supplementary combustion. The lower heating value of the waste liquid is 10435 kcal / kg. After entering the unit, the waste liquid 110 is divided into two streams. The first stream, waste liquid 111, enters the main burner 1 for combustion via a waste liquid gun. The main burner 1 uses cold air provided by the combustion fan 7 for combustion assistance, controlling the excess air coefficient α = 0.75. Oxygen-deficient combustion technology is used to suppress NOx formation. The first stream of waste liquid accounts for approximately 42.2% of the total waste liquid 110. The second stream of waste liquid 112 is burned via waste liquid guns on 6 auxiliary burners 2, using the first stream of tail gas 511 for oxygen-deficient combustion. NOx formation is suppressed through fuel grading and oxygen-deficient combustion technology. The second stream of waste liquid 112 accounts for approximately 57.8% of the total waste liquid 110.

[0064] The high-temperature flue gas generated by the main burner 1, auxiliary burner 2, and the first exhaust gas 511 enters the high-temperature combustion section 31, where the combustion temperature is 1400℃ and the oxygen content is 3.12%, satisfying the pyrolysis combustion of the waste liquid. The second exhaust gas 512 flows into the high-temperature oxidation section 32 in two layers, where it is mixed and burned with the high-speed jet flue gas from the high-temperature combustion section 31, where the combustion temperature is 1100℃ and the oxygen content is 6.8%. The third exhaust gas 513 flows into the purification oxidation section 33 in five layers, where it is mixed and burned with the high-speed jet flue gas from the high-temperature oxidation section 32, where the combustion temperature is 850℃ and the oxygen content is 9.56%, thus completing the complete oxidation combustion of the exhaust gas.

[0065] The high-temperature flue gas from the outlet of the three-stage incinerator 3 enters the ultra-high pressure waste heat boiler 4 for heat recovery. The ultra-high pressure waste heat boiler is divided into an evaporator 41 and a superheater 42. High-pressure boiler feedwater 411 with a pressure of 12 MPa.g or higher enters the evaporator 41 to generate ultra-high pressure saturated steam 412 with a pressure of 11.8 MPa.g, with a production of about 48 to 65 t / h. Then, it is combined with ultra-high pressure saturated steam 413 with a production of about 215 to 252 t / h generated by the maleic anhydride unit and enters the superheater 422 for heating to 540°C, finally generating ultra-high pressure superheated steam 421 for user use.

[0066] After the flue gas from the high-pressure waste heat boiler 4 is cooled to 400°C, it enters the tail gas preheater 5 to be heated. After the flue gas temperature in the tail gas preheater 5 is reduced to 120°C, it is discharged into the atmosphere through the chimney 6. The flue gas emission data are shown in Table 2.

[0067] Table 2 Flue Gas Emission Data

[0068] Temperature ℃ 120 ℃ Emission flow 690000 <![CDATA[Nm 3 / h]]> Volume fraction Nitrogen 73.72 mol% oxygen 9.56 mol% carbon dioxide 4.20 mol% water 12.52 mol% carbon monoxide 3.58 <![CDATA[mg / m 3 ]]> nitrogen oxides 3.77 <![CDATA[mg / m 3 ]]> VOCs 0.89 <![CDATA[mg / m 3 ]]> Particulate matter 1.22 <![CDATA[mg / m 3 ]]>

[0069] Example 2

[0070] The maleic anhydride unit tail gas is treated using fuel gas for afterburning. The composition and state parameters of the maleic anhydride unit tail gas to be treated are the same as in Table 1. Using the incineration treatment system described in this invention, the maleic anhydride unit tail gas treatment steps are similar to those in Example 1, with the following significant differences:

[0071] The maleic anhydride unit's tail gas incineration system uses fuel gas 120 for supplemental combustion, with a calorific value of 2500 kcal / Nm³. 3 ~28000kcal / Nm 3 After entering the device, fuel gas 120 is divided into two streams. The first stream, fuel gas 121, enters the main burner 1 for combustion via a gas gun. The main burner 1 uses cold air provided by the combustion fan 7 for combustion assistance, controlling the excess air coefficient α = 0.60 to 0.80. It employs oxygen-deficient combustion technology to suppress NOx formation. The first stream of fuel gas 121 accounts for approximately 20% to 40% of the total fuel gas 120. The second stream of fuel gas 122 is combusted via gas guns on 4 to 6 auxiliary burners 2. It uses the exhaust gas 511 from the first stream for oxygen-deficient combustion. NOx formation is suppressed through fuel grading and oxygen-deficient combustion technology. The second stream of fuel gas 122 accounts for approximately 60% to 80% of the total fuel gas 120.

[0072] Comparative Example 1

[0073] The difference between the processing method and that of Example 1 is:

[0074] In Comparative Example 1, no auxiliary burner 2 was installed. All waste liquid 110 entered the main burner 1 for combustion. The main burner 1 used cold air provided by the combustion fan 7 for combustion assistance, and the excess air coefficient α was controlled to be 0.75 (consistent with Example 1).

[0075] The first exhaust gas, 511, accounts for 5.2% of the total exhaust gas (810). The high-temperature combustion section 31 has a combustion temperature of 1400℃ and an oxygen content of 5.26%. The second exhaust gas, 512, accounts for 14.53% of the total exhaust gas (810). The high-temperature oxidation section 32 has a combustion temperature of 1100℃ and an oxygen content of 8.31%. The third exhaust gas, 513, accounts for 81.27% of the total exhaust gas (810). The purification oxidation section 33 has a combustion temperature of 780℃ and an oxygen content of 10.32%.

[0076] The flue gas emission data are shown in Table 3.

[0077] Table 3 Flue Gas Emission Data

[0078]

[0079]

[0080] Comparative Example 1 eliminated the auxiliary burner, and all waste liquid entered the main burner for combustion. Although the main burner was still controlled for oxygen-deficient combustion (excess air coefficient α = 0.75), the amount of nitrogen oxides generated increased significantly due to excessive heat concentration. Since all waste liquid was assisted by cold air supplied by the combustion fan 7, the amount of cold air introduced increased, and the combustion temperature of the purification oxidation section 33 decreased from 850℃ to 780℃. The decrease in combustion temperature led to a decrease in the combustion removal rate, and the emission concentrations of carbon monoxide, VOCs, and particulate matter all increased significantly.

[0081] Comparative Example 2

[0082] The difference between the processing method and that of Example 1 is:

[0083] In contrast to Case 1, where no auxiliary burner 2 was installed, all waste liquid 110 entered the main burner 1 for combustion. The main burner 1 used cold air provided by the combustion fan 7 for combustion assistance, eliminating the first exhaust gas 511. The combustion temperature of the high-temperature combustion section 31 was controlled to 1400℃ and the oxygen content to 6.35% by the cold air provided by the combustion fan 7. At this time, the excess air coefficient α = 1.48.

[0084] The second exhaust gas, 512, accounts for 12.58% of the total exhaust gas (810). The high-temperature oxidation section (32) has a combustion temperature of 1100℃ and an oxygen content of 8.96%. The third exhaust gas, 513, accounts for 87.42% of the total exhaust gas (810). The purification oxidation section (33) has a combustion temperature of 750℃ and an oxygen content of 11.13%.

[0085] Table 2 Flue Gas Emission Data

[0086]

[0087]

[0088] Comparative Example 2, based on Comparative Example 1, changed the main burner from anaerobic combustion to oxygen-rich combustion and eliminated the first exhaust gas path. The combustion temperature of the high-temperature combustion section 31 was controlled to 1400℃ by controlling the cold air supplied by the combustion fan. Due to excessive heat concentration and the main burner's α = 1.48, the amount of nitrogen oxides generated increased sharply. Simultaneously, the main burner's combustion state was changed from anaerobic combustion (α = 0.75) to oxygen-rich combustion (α = 1.48), leading to a further increase in the amount of cold air introduced. This further reduced the combustion temperature of the purification oxidation section to 750℃, resulting in a further decrease in the combustion removal rate and a significant increase in the emission concentrations of carbon monoxide, VOCs, and particulate matter.

[0089] The contents not described in detail in this application specification are common knowledge to those skilled in the art.

[0090] The present application has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present application. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and implementation methods of the present application without departing from the spirit and scope of the present application, and all such modifications and improvements fall within the scope of the present application. The scope of protection of the present application is determined by the appended claims.

Claims

1. A direct combustion incineration system for maleic anhydride plant tail gas, characterized in that: It includes a three-stage incinerator (3), an ultra-high pressure waste heat boiler (4), a tail gas preheater (5), and a chimney (6); The three-stage incinerator (3) includes a high-temperature combustion section (31), a high-temperature oxidation section (32), and an ultra-clean oxidation section (33) connected in sequence. The high-temperature combustion section (31) and the high-temperature oxidation section (32) are arranged vertically from top to bottom. The outlet end of the ultra-clean oxidation section (33) is connected to the ultra-high pressure waste heat boiler (4). The ultra-clean oxidation section (33) and the ultra-high pressure waste heat boiler (4) are arranged horizontally. The tail gas preheater (5) is provided with a tail gas inlet, a tail gas outlet, a flue gas inlet, and a flue gas outlet. The outlet of the high-pressure waste heat boiler (4) is connected to the flue gas inlet of the vertically arranged tail gas preheater (5). The flue gas outlet at the top of the tail gas preheater (5) is connected to the chimney (6). The tail gas outlet of the tail gas preheater (5) is connected to the three-stage incinerator (3) to form a "U" shaped structure. The top of the high-temperature combustion section (31) is equipped with a main burner (1) and an auxiliary burner (2), where waste liquid and / or fuel gas are burned in the main burner (1) and the auxiliary burner (2) to provide a heat source for exhaust gas incineration; The exhaust gas generated by the maleic anhydride unit enters through the exhaust gas inlet of the exhaust gas preheater (5) and flows out through the exhaust gas outlet to obtain preheated exhaust gas (510). The preheated exhaust gas (510) enters the three-stage incinerator (3) and is incinerated with waste liquid and / or fuel gas. The high-temperature flue gas generated by incineration enters the ultra-high pressure waste heat boiler (4) for waste heat recovery. The flue gas from the outlet of the ultra-high pressure waste heat boiler (4) enters the exhaust gas preheater (5) to heat the exhaust gas generated by the maleic anhydride unit, and then is discharged into the atmosphere through the chimney (6). The preheated exhaust gas (510) is divided into a first exhaust gas (511), a second exhaust gas (512) and a third exhaust gas (513). The first exhaust gas (511) is connected to the high-temperature combustion section (31), the second exhaust gas (512) is connected to the high-temperature oxidation section (32), and the third exhaust gas (513) is connected to the ultra-clean oxidation section (33). The main burner (1) is located in the middle of the top position of the high-temperature combustion section (31). A combustion-supporting fan (7) is also provided at the top position of the high-temperature combustion section (31). The combustion-supporting fan (7) is used to introduce air into the high-temperature combustion section (31) to supply oxygen for the combustion of the main burner (1). The main burner (1) uses cold air supplied by the combustion fan (7) for combustion assistance, and controls the excess air coefficient α = 0.60~0.80; the heat load of the main burner (1) accounts for 10%~20% of the total heat load; The auxiliary burner (2) is located below the main burner (1). Multiple auxiliary burners (2) are provided, and the multiple auxiliary burners (2) are evenly distributed tangentially in the shoulder of the high-temperature combustion section (31). The waste liquid or fuel gas of the auxiliary burner (2) is assisted by the first oxygen-containing tail gas (511) at a preheated temperature of 300℃~450℃. The oxygen content of the first oxygen-containing tail gas (511) is 13%~15%. The heat load of the auxiliary burner 2 accounts for 20%~30% of the total heat load. Each stage of the exhaust gas preheater (5) consists of 2-6 modules connected in parallel. The exhaust gas enters each module in a uniform and equal amount. Each module's exhaust gas outlet is equipped with a baffle. By closing one or more baffles, the exhaust gas flow rate is increased to 40 m / s to 60 m / s. The exhaust gas crystals are cleaned by high-speed flushing of the exhaust gas, preventing the exhaust gas preheater (5) from becoming blocked due to crystallization.

2. The maleic anhydride unit tail gas direct combustion incineration treatment system according to claim 1, characterized in that: The first exhaust gas (511), the second exhaust gas (512) and the third exhaust gas (513) flow tangentially into the three-stage incinerator (3); the direction of the tangential swirl of the auxiliary burner (2) is the same as the direction of the tangential swirl of the first exhaust gas (511), the second exhaust gas (512) and the third exhaust gas (513).

3. The maleic anhydride unit tail gas direct combustion incineration treatment system according to claim 1, characterized in that: The combustion temperature in the high-temperature combustion section (31) is 1300℃~1500℃, and the oxygen content is controlled between 2% and 5%; the combustion temperature in the high-temperature oxidation section (32) is 1050℃~1200℃, and the oxygen content is controlled between 6% and 8%; the combustion temperature in the ultra-clean oxidation section (33) is 750℃~900℃, and the oxygen content is controlled between 9% and 11%. The first exhaust gas (511) accounts for 10% to 20% of the preheated exhaust gas (510), the second exhaust gas (512) accounts for 10% to 25% of the preheated exhaust gas (510), and the third exhaust gas (513) accounts for 55% to 80% of the preheated exhaust gas (510).

4. The maleic anhydride unit tail gas direct combustion incineration treatment system according to claim 1, characterized in that: The ultra-high pressure waste heat boiler (4) includes an evaporator (41) and a superheater (42). The high pressure boiler feedwater (411) enters the evaporator (41) and exchanges heat with the high temperature flue gas discharged from the three-stage incinerator (3) to obtain ultra-high pressure saturated steam (412). Then, the ultra-high pressure saturated steam (412) and the ultra-high pressure saturated steam (413) generated by the maleic anhydride device are combined and enter the superheater (42), and exchange heat again with the high temperature flue gas discharged from the three-stage incinerator (3) to obtain ultra-high pressure superheated steam (421).

5. The maleic anhydride unit tail gas direct combustion incineration treatment system according to claim 1, characterized in that: The exhaust gas preheater (5) is a multi-stage series tube heat exchanger. Along the flow direction of the exhaust gas generated by the maleic anhydride device, the exhaust gas preheater (5) includes 1-N stages of preheaters from top to bottom. The uppermost stage 1 preheater is made of 316L stainless steel, the lowermost stage N preheater is made of 304 stainless steel, and the middle preheaters are made of 20 steel. The inlet temperature of the exhaust gas preheater (5) is 67~72℃, and the outlet temperature of the exhaust gas preheater (5) is 300℃~450℃.

6. A process for direct combustion incineration of maleic anhydride unit tail gas based on a direct combustion incineration system for maleic anhydride unit tail gas according to any one of claims 1-5, characterized in that, include: The main burner (1) uses cold air for combustion, with an excess air coefficient α = 0.60~0.

80. The auxiliary burner (2) uses the first exhaust gas (511) with an oxygen content of 13%~15% for combustion. The exhaust gas generated by the maleic anhydride unit is preheated to 300℃~450℃ by the exhaust gas preheater (5) to obtain preheated exhaust gas (510); The preheated exhaust gas (510) is divided into a first exhaust gas (511), a second exhaust gas (512), and a third exhaust gas (513). The first exhaust gas (511) enters the high-temperature combustion section (31), the second exhaust gas (512) enters the high-temperature oxidation section (32), and the third exhaust gas (513) enters the ultra-clean oxidation section (33). The materials sprayed from the main burner (1) and the auxiliary burner (2) and the preheated exhaust gas (510) are incinerated in the three-stage incinerator (3). The combustion temperature in the high-temperature combustion section (31) is 1300℃~1500℃, and the oxygen content is controlled between 2% and 5%. The combustion temperature in the high-temperature oxidation section (32) is 1050℃~1200℃, and the oxygen content is controlled between 6% and 8%. The combustion temperature in the ultra-clean oxidation section (33) is 750℃~900℃, and the oxygen content is controlled between 9% and 11%. The high-temperature flue gas generated by incineration enters the ultra-high pressure waste heat boiler (4) for waste heat recovery. After passing through the high pressure waste heat boiler (4), the flue gas temperature drops to 380℃~450℃ and then enters the tail gas preheater (5) to heat the tail gas. After the flue gas temperature drops to 90℃~130℃ in the tail gas preheater (5), it is discharged into the atmosphere through the chimney (6).

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