Flue gas denitration and heat storage method and device for natural gas industrial heating furnace

Abstract

The invention provides a flue gas denitration and heat storage method and device for a natural gas industrial heating furnace. The device comprises an air blower, a rotary air door, a low-temperature heat storage section A, a medium-temperature denitration and heat storage section A, a high-temperature heat storage section A, a burner cavity A, a burner cavity B, a high-temperature heat storage section B, a medium-temperature denitration and heat storage section B, a low-temperature heat storage section B, an induced draft fan, a natural gas valve A for reduction and a natural gas valve B for reduction. The heat storage sections, the combustion cavities and the natural gas valves for reduction are divided into two rows, and two working modes of regeneration preheating and denitration heat storage are achieved. NOx in the flue gas in the denitration heat storage mode and metal-form active Wuzhihao in the denitration material are subjected to denitration reaction, NO is converted into N2, and active metal is converted into oxide. In the regeneration preheating mode, reducing natural gas reacts with metal oxide to be regenerated into a metal form; air flows through the inert channel to be preheated. The method and the device use part of natural gas as a denitration agent, and have the advantages of compact equipment and low operation cost.

Description

Technical Field

[0001] This invention belongs to the field of low-NOx combustion and flue gas purification in natural gas industrial furnaces, specifically relating to a method and apparatus for flue gas denitrification and heat storage in a natural gas industrial heating furnace. Background Technology

[0002] Natural gas industrial furnaces are widely used in industries such as metal heat treatment and building materials. Due to the heat treatment requirements of the heated objects, natural gas furnaces generally have high combustion temperatures, resulting in correspondingly high flue gas temperatures. To fully utilize the heat in the high-temperature flue gas, regenerative burners are often used. Regenerative burners utilize ceramic regenerators to alternately absorb and release heat. During heat absorption, the regenerator recovers waste heat from the flue gas, reducing flue gas losses. During heat release, air is introduced into the regenerator to absorb the flue gas heat and preheat ambient air. Regenerative combustion can reduce the flue gas temperature to below 180℃, significantly reducing heat loss and improving fuel energy utilization efficiency.

[0003] Industrial heating furnaces mostly use clean and readily available natural gas as fuel. Although natural gas contains trace amounts of nitrogen, the large amount of nitrogen introduced by the air required for combustion reacts with oxygen at high temperatures to produce nitrogen oxides (NOx), primarily in the form of NO. In the initial stages of emissions, NO typically accounts for over 90%. NOx damages the deep respiratory tract, irritates the lungs, and can also contribute to photochemical smog and acid rain.

[0004] Regenerative industrial furnaces generally struggle to simultaneously meet the demands of high heating temperatures and low NOx emissions. With increasingly stringent environmental regulations, strict NOx emission control is essential. Besides improving combustion organization and implementing low-NOx combustion methods such as flue gas recirculation, further NOx removal typically requires the installation of ammonia injection denitrification devices at the tail end. However, ammonia is a flammable, explosive, and highly irritating gas. Implementing ammonia injection denitrification necessitates additional auxiliary equipment and corresponding fire-fighting facilities for conventional industrial furnaces. Furthermore, the transportation of ammonia poses risks to residents along the route, significantly increasing fixed investment and operating costs. This approach places a greater safety and economic burden on small and medium-sized enterprises, making the development of novel ammonia removal methods and processes highly valuable.

[0005] This invention proposes a low-NOx combustion process and device for a natural gas regenerative industrial heater that addresses non-ammonia-injection denitrification in regenerative burners. This process further reduces the NOx content in flue gas without using ammonia-injection denitrification. Summary of the Invention

[0006] The purpose of this invention is to provide a method and apparatus for flue gas denitrification and heat storage in a natural gas industrial heating furnace, so as to achieve low-cost denitrification without ammonia injection during stable operation and reduce the concentration and total amount of nitrogen oxide emissions from flue gas.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method and apparatus for flue gas denitrification and heat storage in a natural gas industrial heating furnace, as follows: Figure 1 As shown, the system includes: 1. Blower; 2. Rotary damper; 3. Low-temperature heat storage section A; 4. Medium-temperature denitrification heat storage section A; 5. High-temperature heat storage section A; 6. Burner cavity A; 7. Burner cavity B; 8. High-temperature heat storage section B; 9. Medium-temperature denitrification heat storage section B; 10. Low-temperature heat storage section B; 11. Exhaust fan; 12. Natural gas valve A for reduction; 13. Natural gas valve B for reduction. Components 3, 4, and 5 constitute the A-row heat storage denitrification system; components 10, 9, and 8 constitute the B-row heat storage denitrification system. The two rows have the same materials and structure but different operating modes. The low-temperature and high-temperature sections only have heat storage functions and use inert heat storage materials. A 104-hole channel is opened at the bottom of the denitrification channel, through which natural gas for reduction is injected. Sufficient space is provided above and below the medium-temperature denitrification heat storage section for the switching position of the baffle in channel 101.

[0009] The basic unit structure of the medium-temperature denitrification heat storage section is as follows: Figure 2 As shown, it consists of a denitrification channel 102 and a heat storage channel 103, which are isolated but thermally conductive. The denitrification channel is filled with NixMny / Al2O3 denitrification material, with x and y ranging from 0.91 to 0.98 and 0.02 to 0.09, respectively, and adopts a porous or honeycomb structure. An opening is made on the bottom side of the denitrification channel as an inlet for the natural gas used for reduction. The heat storage channel is filled with an inert heat storage material, such as ceramic or medium-to-high temperature resistant metal, and adopts a porous or honeycomb structure. A baffle plate in channel 101 controls the entry of air or flue gas into the corresponding channel. One denitrification channel and one heat storage channel constitute a basic unit, and the medium-temperature denitrification heat storage section contains one or more units.

[0010] Its key feature is that the entire combustion device comprises two rows of regenerative denitrification bodies, A and B, which are made of the same material and have the same structure. Both rows can operate in two modes: "regeneration preheating" and "denitrification heat storage," but their operating modes are always different at any given time. The "regeneration preheating" mode preheats the air while simultaneously regenerating the denitrification material. The "denitrification heat storage" mode absorbs heat from the exhaust gas to achieve heat storage, while the denitrification material undergoes a denitrification reaction.

[0011] To achieve the above functions, taking column A "Regeneration Preheating" and column B "Denitrification Heat Storage" as an example, the details are as follows:

[0012] (1) The process flow of "regeneration preheating" in column A is as follows: The damper of the rotary damper is in position L. At the same time, the damper of the channel of the 4th medium-temperature denitrification heat storage section A closes the denitrification channel to prevent air from entering. The blower pushes the air through the channel when the damper is in position L and sends it into the heat storage denitrification body of column A. The air first undergoes preliminary preheating in the 3rd low-temperature heat storage section A, and the air is heated to between 470 and 510°C. Then the air enters the inert channel of the 4th medium-temperature denitrification heat storage section A for further preheating. Valve 12 is opened to introduce natural gas for reduction into the denitrification channel, which reacts with the active substances in the form of metal oxides in the denitrification material in a regeneration reaction: CH4 + 4NiO → 4Ni + CO2 + 2H2O, and the reaction temperature is 470 to 510°C.

[0013] The gases discharged from the heat storage and denitrification channels of the intermediate-temperature denitrification heat storage section A (section 4) mix and enter the high-temperature heat storage section A (section 5), where they are further preheated to a temperature above 600°C. Then, the air enters the burner located in the burner chamber A (section 6), where it undergoes a combustion reaction with the fuel natural gas, providing heat to the object being heated. Note: Burner chamber A (section 6) is merely a space reserved for the burner and is not a specific burner. The method and structure of the burner are not within the scope of this invention.

[0014] (2) The process flow of the "denitrification and heat storage" in column B is as follows: The natural gas combustion system in column B is in a stopped state, and the high-temperature flue gas enters the high-temperature heat storage section B through the burner cavity B (7). It exchanges heat with the inert heat storage material, cooling the flue gas to 480-520℃. Valve 13 is closed, and the channel baffle of the medium-temperature denitrification and heat storage section B (9) is controlled to close the inert channel, preventing the flue gas from entering the inert channel, and instead allowing it to enter the denitrification channel entirely. The NO in the flue gas reacts with the active substances in the metal form of the denitrification material in the following denitrification reaction: 2NO + 2Ni → 2NiO + N2, with a reaction temperature of 480-520℃. The flue gas discharged from the medium-temperature denitrification and heat storage section B (9) enters the low-temperature heat storage section B (10), where it exchanges heat with the inert heat storage material, and finally cools down to below 180℃. The low-temperature flue gas is discharged into the atmosphere through the other side of the two-way damper (2) and under the suction of the induced draft fan (11).

[0015] The above describes the operating modes of column A ("regeneration preheating") and column B ("denitrification heat storage"). By switching the bidirectional damper and rotating the baffle position 90° to position R, the direction of air and flue gas is changed. Simultaneously, the functions of the denitrification heat storage bodies in columns A and B are switched, alternating the corresponding regeneration or denitrification reaction; the channel closed by baffle 101 is switched; and the on / off states of natural gas valves 12 and 13 for reduction are switched, thereby achieving "denitrification heat storage" in column A and "regeneration preheating" in column B. This further reduces nitrogen oxide emissions without adding an ammonia injection denitrification device to the flue gas.

[0016] The mass hourly space velocity (MSV) of the denitrification material should not exceed 100 h⁻¹; the average conversion rate of the denitrification material should not be less than 30%. The margin coefficients for the flow rate of the natural gas used for reduction and the amount of denitrification material should both be between 1.1 and 1.4. The remaining natural gas from the reaction is mixed with air and enters the combustion zone in a premixed manner.

[0017] The beneficial effects of this invention are as follows:

[0018] The medium-temperature heat storage body used in this invention has the functions of storing flue gas heat, denitrification, and regeneration. The direction of the fluid is controlled by the rotation of the rotating baffle and the opening and closing of the partition door, allowing flue gas or air to flow along designated channels, thus achieving efficient denitrification. This process has a compact structure and a high degree of system integration; it can be used alone or in conjunction with other low-NOx combustion organization methods.

[0019] This invention targets industrial heating furnaces using natural gas, employing a small amount of natural gas fuel as a reducing agent without requiring a new reducing agent system, thus avoiding the need for ammonia or urea in ammonia injection denitrification processes. The technical modification is simple, and the increase in costs for equipment, reducing agents, and supporting fire protection is minimal.

[0020] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall structure and process of the present invention;

[0022] Figure 2 This is a schematic diagram of the basic unit of the medium-temperature denitrification heat storage section of the present invention;

[0023] Figure reference numerals: 1 Blower, 2 Rotary damper, 3 Low-temperature heat storage section A, 4 Medium-temperature denitrification heat storage section A, 5 High-temperature heat storage section A, 6 Burner cavity A, 7 Burner cavity B, 8 High-temperature heat storage section B, 9 Medium-temperature denitrification heat storage section B, 10 Low-temperature heat storage section B, 11 Exhaust fan, 12 Natural gas valve for reduction A, 13 Natural gas valve for reduction B, 101 Channel baffle, 102 Denitrification channel, 103 Heat storage channel Detailed Implementation

[0024] The following specific examples illustrate the implementation methods and beneficial effects of the present invention. Taking a medium-sized natural gas heating furnace as an example, the natural gas flow rate for combustion is 210 m³ / h. 3 / h, air flow rate 2520m³ 3 / h, A and B column burner switching time 30s, flue gas approximately 2740m³ / h.3 / h; Initial NOx concentration in flue gas 220 mg / m³ 3 This does not meet the latest provincial emission standards. The designed final NOx concentration after denitrification is 80 mg / L. 3 / h, emission reduction of 63.6%. Using the scheme of this invention, operating at an average conversion rate of 50%, the margin coefficient for both the reduction natural gas and denitrification materials is taken as 1.2. The flow rate of the reduction natural gas is approximately 0.175 m³ / h. 3 / h, which is only 0.08% of the fuel natural gas; the amount of Ni used in denitrification materials is 0.2kg.

[0025] Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention; in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0026] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0027] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0028] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method and apparatus for flue gas denitrification and heat storage in a natural gas industrial heating furnace, comprising a blower, a rotary damper, a low-temperature heat storage section A, a medium-temperature denitrification heat storage section A, a high-temperature heat storage section A, a burner cavity A, a burner cavity B, a high-temperature heat storage section B, a medium-temperature denitrification heat storage section B, a low-temperature heat storage section B, an induced draft fan, a natural gas valve A for reduction, and a natural gas valve B for reduction. Its characteristics are: A blower drives the flue gas, and a rotating baffle guides the flow of the flue gas. A catalytic heat storage body is installed inside the refractory material along the flow direction of the flue gas. By opening and closing the partition door, a denitrification chamber is formed for denitrification, which controls the catalytic denitrification process. An ammonia spray gun is installed on the denitrification chamber.

2. According to claim 1, the medium-temperature denitrification and heat storage section consists of a denitrification channel and an inert channel, wherein the denitrification channel is filled with denitrification material and the inert channel is filled with inert heat storage material.

3. According to claims 1 and 2, the medium-temperature denitrification heat storage section is characterized in that... Both columns A and B have two operating modes: denitrification heat storage and regeneration preheating. However, the operating modes of columns A and B are always different. In the denitrification heat storage mode, medium-temperature flue gas enters the denitrification channel, where NOx reacts with the metal denitrification material within the range of 470–520℃, converting NO into N2, and the active metal in the denitrification material is converted into oxides. In the regeneration preheating mode, air enters the inert channel for preheating, and reducing natural gas enters the denitrification channel within the range of 470–510℃, reacting with the oxide-form denitrification material to generate a metallic form, thereby regenerating the denitrification material.

4. According to claims 1 and 3, the characteristic is that Natural gas is supplied to the bottom of each denitrification channel. In the regeneration preheating mode, the corresponding natural gas valve for reduction is opened, and a small amount of natural gas is injected to reduce and regenerate the denitrification material. In the denitrification heat storage mode, the valve is closed.

5. According to claims 2 and 3, a channel baffle is provided between the denitrification channel and the inert channel to close or open the channel, and to prevent or allow air or flue gas to enter a specific channel according to its working mode.

6. The low-NOx combustion method and apparatus for a regenerative industrial heating furnace according to claim 1, characterized in that... Low-temperature heat storage sections and high-temperature heat storage sections are set before and after the medium-temperature denitrification heat storage section to absorb heat from flue gas or preheat air, so that the medium-temperature denitrification heat storage section meets the temperature conditions required for the reaction.

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