Cracking furnace flue gas denitration system of ethylene plant

Abstract

The utility model relates to a kind of pyrolysis furnace flue gas denitration systems of ethylene device, including pyrolysis furnace, the pyrolysis furnace includes convection section and radiation section, the convection section includes upper raw material preheating section, boiler feedwater preheating section and upper mixed superheating section sequentially arranged from top to bottom, further including catalyst module and ammonia injection grid located in the pyrolysis furnace, the catalyst module is located between the upper raw material preheating section and boiler feedwater preheating section, and using Mn-based low-temperature denitration catalyst, the ammonia injection grid is connected with the pipeline for conveying ammonia air mixture outside air mixture, along the flue gas flow direction in pyrolysis furnace, the ammonia injection grid is located in the upstream of the catalyst module. Advantage lies in: can effectively reduce the transformation cost of pyrolysis furnace, shorten the transformation cycle, and can guarantee denitration effect.

Description

Technical Field

[0001] This utility model relates to the field of flue gas denitrification technology for ethylene plants, and in particular to a flue gas denitrification system for a cracking furnace in an ethylene plant. Background Technology

[0002] Traditional flue gas denitrification technologies for ethylene plants typically employ a medium-to-high temperature (350-370℃) reaction zone. NH3 reducing agent, mixed with diluted hot air, is introduced into the ammonia injection grid of the cracking furnace's convection section, where NO-containing compounds are uniformly injected. x In the flue gas, NH3 and NO x A selective catalytic reduction reaction occurs under the action of a medium-to-high temperature catalyst, with the reaction products being N2 and H2O, thereby reducing NO. x The aim is to meet national environmental protection requirements. This technology is relatively mature in China and is suitable for use during the initial construction of cracking furnaces, where SCR modules are embedded into the convection section of the furnace. However, for cracking furnaces already in operation, meeting national environmental protection requirements and reducing NO in flue gas is crucial. x If an SCR system needs to be added to the convection section of a cracking furnace, the industrial-scale modification is difficult, and the modification risk and investment cost are high.

[0003] Therefore, the existing flue gas denitrification system of the cracking furnace in ethylene plants still needs further improvement. Utility Model Content

[0004] The technical problem to be solved by this utility model is to provide a denitrification system for ethylene plant pyrolysis furnace flue gas that can effectively reduce the modification cost and shorten the modification cycle of the pyrolysis furnace, and can ensure the denitrification effect, in light of the current state of the technology.

[0005] The technical solution adopted by this utility model to solve the above-mentioned technical problems is as follows: a denitrification system for flue gas from a cracking furnace in an ethylene plant, comprising a cracking furnace, the cracking furnace including a convection section and a radiation section, the convection section including an upper feedstock preheating section, a boiler feedwater preheating section and an upper mixing superheating section arranged sequentially from top to bottom, and further including a catalyst module and an ammonia injection grid disposed in the cracking furnace, the catalyst module being located between the upper feedstock preheating section and the boiler feedwater preheating section, and employing a Mn-based low-temperature denitrification catalyst, the ammonia injection grid being connected to an external pipeline for conveying ammonia-air mixture along the flue gas flow direction inside the cracking furnace, the ammonia injection grid being located upstream of the catalyst module.

[0006] The aforementioned "catalyst module" can be understood as an integrated unit containing the catalyst and its supporting structure, typically consisting of a metal frame (such as a stainless steel frame) and catalyst monomers filled within it. For example, the module can be designed as a standard box structure for easy installation and replacement.

[0007] The aforementioned "Mn-based low-temperature denitration catalyst" uses manganese oxide as the main active component, supplemented by metal oxides such as cerium and iron or molecular sieve supports, and exhibits highly selective catalytic reduction of NO at low temperatures (120–300℃). x A catalyst for ability.

[0008] As an improvement, the catalyst module includes a catalyst mounting bracket and a catalyst disposed on the mounting bracket. The mounting bracket provides mechanical support for the catalyst, resisting vibrations and impacts caused by flue gas flow. This catalyst module can be installed as a whole or the catalyst can be replaced in modules, reducing downtime, enabling modular maintenance, and lowering maintenance costs.

[0009] As an improvement, the catalyst has a honeycomb structure. The honeycomb structure provides a larger catalytic reaction contact area, improving denitrification efficiency. The parallel channel design reduces flue gas flow resistance and is less prone to dust accumulation, making it suitable for dusty flue gas environments. Furthermore, the honeycomb catalyst exhibits strong integrity and resistance to thermal shock and mechanical wear.

[0010] As an improvement, an induced draft fan is also included at the top of the pyrolysis furnace.

[0011] As an improvement, the orientation of the nozzles of the ammonia injection grid is aligned with the flow direction of the flue gas within the cracking furnace. The ammonia injection grid is a pipe distribution system with multiple injection holes used to uniformly inject an ammonia-air mixture into the flue gas. For example, a grid structure can be formed using multiple parallel branch pipes, with small holes or nozzles on the branch pipes, the diameter and spacing of which are designed according to the flue gas flow rate. Co-directional injection reduces ammonia flow resistance, utilizes the kinetic energy of the flue gas to achieve ammonia diffusion, and avoids localized eddies or concentration peaks. Furthermore, uniform mixing ensures that the ammonia fully participates in the reaction, reducing downstream ammonia residue.

[0012] Compared with existing technologies, the advantages of this invention are as follows: The denitrification system for the cracking furnace flue gas of this invention, by placing the Mn-based low-temperature denitrification catalyst module between the feedstock preheating section and the boiler feedwater preheating section, fully utilizes the suitable flue gas temperature in this section (typically within the low-temperature catalyst activity range), avoiding the structural modification difficulties caused by the requirement to embed traditional medium- and high-temperature SCRs in the convection section. Since the area between the feedstock preheating section and the boiler feedwater preheating section is more conducive to modular installation, the amount of modification work and downtime are significantly reduced, resulting in substantial savings in modification costs and time. Simultaneously, the Mn-based catalyst maintains high denitrification activity at lower temperatures, ensuring good NO reduction. x The purification efficiency meets environmental protection requirements, achieving a highly efficient, economical, and applicable denitrification effect suitable for retrofitting existing equipment. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the structure of the denitrification system for the pyrolysis furnace flue gas of an ethylene plant according to an embodiment of the present invention. Detailed Implementation

[0014] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0015] In the specification and claims of this utility model, terms indicating direction, such as "front," "rear," "upper," "lower," "left," "right," "side," "top," and "bottom," are used to describe various exemplary structural parts and elements of this utility model. However, the use of these terms is merely for the purpose of explanation and is based on the exemplary orientations shown in the accompanying drawings. Since the embodiments disclosed in this utility model can be arranged in different orientations, these terms indicating direction are for illustrative purposes only and should not be regarded as limitations. For example, "upper" and "lower" are not necessarily limited to directions opposite to or consistent with the direction of gravity.

[0016] Figure 1 A preferred embodiment of the denitrification system for the cracking furnace flue gas of an ethylene plant according to this invention is shown. The system is suitable for retrofitting an existing cracking furnace 1 to reduce NOx emissions. The system includes a cracking furnace 1, a catalyst module 2, an ammonia injection grid 3, and an induced draft fan.

[0017] The pyrolysis furnace 1 includes a convection section 10 and a radiation section. The convection section 10 is provided with an upper raw material preheating section 11, a boiler feedwater preheating section 12, and an upper mixing superheating section 13 from top to bottom. In order to make full use of the heat of the high-temperature flue gas in the convection section 10, the boiler feedwater is heated through the aforementioned boiler feedwater preheating section 12.

[0018] Catalyst module 2 is located between the upper raw material preheating section 11 and the boiler feedwater preheating section 12. The flue gas temperature at this location is typically between 120°C and 300°C, suitable for the activity range of the Mn-based low-temperature denitrification catalyst. Catalyst module 2 adopts a modular design, including a catalyst mounting rack and the catalyst arranged on the rack. The catalyst unit is an Mn-based low-temperature denitrification catalyst, specifically with manganese oxide as the main active component, and cerium oxide and iron oxide added as co-catalysts. The catalyst has a honeycomb structure with a large specific surface area, effectively promoting contact between the flue gas and the catalyst, and improving denitrification efficiency. Specifically, the Mn-based low-temperature denitrification catalyst can be the catalyst described in application number CN201611002394, "A Method for Preparing a Honeycomb Mn-Based Low-Temperature Denitrification Catalyst." The radiant section of the cracking furnace 1 uses the heat released from burning liquid or gaseous fuel to further heat the material obtained after preheating the cracking raw material in the convection section 10 to induce a cracking reaction. The structural design and layout within the radiant section can utilize existing technologies.

[0019] The ammonia injection grid 3 is located upstream of the catalyst module 2, arranged perpendicular to the flue gas flow direction within the cracking furnace 1. The ammonia injection grid 3 is connected to an external ammonia-air mixing pipeline, which uses a flow control valve to adjust the ammonia-air mixing ratio. The ammonia injection grid 3 consists of a grid structure composed of multiple parallel branch pipes, with multiple nozzles on each branch pipe. The nozzle spacing can be evenly distributed according to the flue gas flow rate. The nozzle orientation is consistent with the flue gas flow direction within the cracking furnace 1 to reduce flow resistance and utilize the kinetic energy of the flue gas to promote ammonia diffusion, ensuring uniform mixing of ammonia and flue gas. An induced draft fan is located at the top of the cracking furnace 1 to extract flue gas and guide it sequentially through the ammonia injection grid 3 and catalyst module 2 before finally discharging it. The induced draft fan's airflow is adjustable to maintain a stable negative pressure environment within the cracking furnace 1.

[0020] After ammonia and air are mixed, the mixture is sent to the ammonia injection grid 3 through a pipeline. The ammonia injection grid 3 evenly distributes the mixture into the flue gas, reducing the NO content in the flue gas. x Ammonia is captured in the denitrification catalyst, and NO is reduced to nitrogen and water, thus ensuring that the NO concentration at the flue gas outlet meets emission standards.

[0021] This embodiment fully utilizes the temperature range between the raw material preheating section 11 and the boiler feedwater preheating section 12, avoiding the difficulty of embedding the convection section 10 required for traditional medium- and high-temperature SCR retrofits. During the retrofit, only the catalyst module 2 and the ammonia injection grid 3 need to be installed by opening holes in this area, resulting in a short retrofit cycle and low cost. Simultaneously, the Mn-based low-temperature catalyst maintains high activity at lower temperatures, achieving a denitrification efficiency of over 80%, meeting environmental protection requirements.

Claims

1. A denitrification system for flue gas from a cracking furnace in an ethylene plant, comprising a cracking furnace (1), the cracking furnace (1) comprising a convection section (10) and a radiation section, the convection section (10) comprising, from top to bottom, an upper feedstock preheating section (11), a boiler feedwater preheating section (12), and an upper mixing superheating section (13), characterized in that: It also includes a catalyst module (2) and an ammonia injection grid (3) installed in the cracking furnace (1). The catalyst module (2) is located between the upper raw material preheating section (11) and the boiler feedwater preheating section (12) and uses a Mn-based low-temperature denitrification catalyst. The ammonia injection grid (3) is connected to an external pipeline for conveying ammonia-air mixture along the flue gas flow direction inside the cracking furnace (1). The ammonia injection grid (3) is located upstream of the catalyst module (2).

2. The denitrification system for pyrolysis furnace gas of an ethylene plant according to claim 1, characterized in that: The catalyst module (2) includes a catalyst mounting rack and a catalyst arranged on the catalyst mounting rack.

3. The denitrification system for pyrolysis furnace gas of an ethylene plant according to claim 2, characterized in that: The catalyst has a honeycomb structure.

4. The denitrification system for pyrolysis furnace gas of an ethylene plant according to claim 1, characterized in that: It also includes an induced draft fan located on top of the pyrolysis furnace (1).

5. The denitrification system for pyrolysis furnace gas of an ethylene plant according to claim 1, characterized in that: The orientation of the nozzles of the ammonia injection grid (3) is consistent with the direction of flue gas flow inside the pyrolysis furnace (1).

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