Composite injection process for improving combustion rate of pulverized coal

Abstract

The invention relates to the field of pulverized coal combustion, and discloses a composite injection process for improving the pulverized coal combustion rate, which comprises the following steps: preparing a superheated steam flow carrying oxygen-containing micro-nano bubbles and carbon dioxide as a composite activation injection medium; the medium is sprayed into a combustion chamber in a high-speed rotating vortex form through a coaxial vortex spray gun, meanwhile, pulverized coal is sprayed into the vortex center from the center, a strong shear layer is formed between the pulverized coal and the vortex center, and according to the method, an ordered reaction area which is layered in the radial direction is constructed in the combustion chamber, the outer layer is mainly based on surface gasification of the pulverized coal, and the inner layer conducts gas combustion. And oxygen required by combustion of the inner layer comes from oxygen-containing micro-nano bubbles which are broken and released due to bearing of fluid shearing force in the shearing layer, so that accurate controlled supply of an oxidizing agent is realized. Through space decoupling and ordered regulation and control in the combustion process, the combustion rate and the burn-off rate are remarkably increased, and generation of nitric oxide is effectively inhibited.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coal combustion, in particular to a composite injection process for improving the combustion rate of coal. BACKGROUND

[0002] Coal, as a basic energy source, still occupies a core position in global industrial production and thermal power generation. Among them, coal combustion is the most widely used high-efficiency coal utilization technology. The core of this technology is to grind coal into fine particles and inject it into the industrial furnace or boiler combustion chamber with combustion-supporting gas (usually air) for suspension combustion to achieve rapid energy release.

[0003] However, the existing conventional coal combustion technology still faces some inherent technical bottlenecks in actual application. These bottlenecks are interrelated and jointly restrict the further improvement of combustion efficiency and environmental performance. A core challenge is that the mixing process of coal particles and oxidants is often not uniform and efficient, which leads to a delay in the ignition process and makes it difficult to control the stability of the entire combustion process.

[0004] Relatedly, there is also room for improvement in the combustion rate. Under the condition of limited furnace volume and coal residence time, the relatively low combustion rate will directly lead to incomplete combustion, which means that the carbon content in fly ash is high, which not only means waste of fuel energy, but also reduces the overall thermal efficiency of the system. In addition, the disorder of the combustion process often leads to uneven temperature distribution in the combustion area, which is easy to form a local area with high temperature, and this local high temperature is the main cause of the generation of thermal nitrogen oxides (NO x ).

[0005] From a deeper reaction mechanism, the existing technology generally has the problem that the coal gasification stage and the subsequent flame combustion stage overlap in space and interfere with each other. The heterogeneous gasification reaction on the surface of coal particles and the homogeneous combustion reaction of combustible gases (such as CO, H2) generated by it almost occur in the same area and compete for oxidants. This inherent competition limits the possibility of fine-tuning the combustion process and is a fundamental obstacle to improving overall combustion efficiency.

[0006] Therefore, developing a composite injection process for improving the combustion rate of coal, which aims to solve the above-mentioned problems of uneven combustion, low rate, and difficult control of pollutants, has become a technical problem to be solved in the field. SUMMARY

[0007] In response to the shortcomings of the existing technology, the present invention provides a composite injection process for improving the combustion rate of coal powder, which solves the problems existing in the existing coal powder combustion technology, such as delayed coal powder ignition, low combustion rate, disordered combustion process and easy generation of nitrogen oxides.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions: A composite injection process for increasing the combustion rate of pulverized coal comprises the following steps: Step S1: preparing a composite activated blowing medium.

[0009] The composite activation spray medium is a high-temperature, high-pressure fluid with unique physical and chemical properties, consisting of a superheated steam stream carrying oxygen-containing micro-nano bubbles and carbon dioxide. This step is specifically achieved through the following sub-steps: Sub-step S11: in a high-pressure liquid environment, dispersing oxygen in the form of micro-nano bubbles in water to form an oxygen-containing micro-nano bubble liquid.

[0010] In a specific implementation, the pressure of the high-pressure liquid phase environment is set to 5.0 MPa to 10.0 MPa. To achieve this step, a high-pressure circulating micro-nano bubble preparation system can be used, which may include a high-pressure gas-liquid mixing pump and a flotation separation tank. Liquid water and gaseous oxygen are fed into the high-pressure gas-liquid mixing pump in a predetermined proportion for forced shearing and mixing to form an oxygen supersaturated aqueous solution, which is then introduced into the flotation separation tank. By regulating the pressure in the tank, the supersaturated oxygen is stably precipitated in the form of micro-nano bubbles. The average particle size of the oxygen-containing micro-nano bubbles formed is controlled within the range of 50 nm to 10 µm. In some embodiments, in order to improve the stability of the oxygen-containing micro-nano bubbles in subsequent process steps, a non-ionic surfactant with a mass percentage concentration of 0.01% to 0.5%, such as polyoxyethylene sorbitan monooleate or polyvinyl alcohol, can be pre-added to the water.

[0011] Sub-step S12: while maintaining the high-pressure liquid phase environment, introducing carbon dioxide gas into the oxygen-containing micro-nano bubble liquid to dissolve the carbon dioxide in the oxygen-containing micro-nano bubble liquid, thereby forming a composite precursor liquid.

[0012] This step can be performed under the same pressure as sub-step S11. Carbon dioxide gas can be introduced into the pressure vessel containing the oxygen-containing micro-nanobubble liquid in a dispersed form through a gas diffuser (e.g., a porous sintered metal aeration head). Mechanical stirring or forced circulation can be used to accelerate the dissolution of the carbon dioxide gas in the liquid phase.

[0013] Sub-step S13: heating the composite precursor liquid online to change the composite precursor liquid into the composite activated spraying medium.

[0014] The composite precursor prepared in sub-step S12 is rapidly heated through an online heater (for example, a shell-and-tube or coil heat exchanger) to make it phase change into a superheated steam flow. The final state parameters of the composite activation injection medium before it is injected into the combustion chamber are: the temperature is in the range of 250°C to 400°C, and the pressure is in the range of 3.0 MPa to 8.0 MPa. In this state, the molar ratio of water vapor to carbon dioxide in the medium is in the range of 100:1 to 10:1.

[0015] Step S2: The composite activation injection medium is injected into the combustion chamber in the form of a high-speed rotating vortex.

[0016] Step S3: The pulverized coal is injected into the central region of the vortex to form a shear layer between the pulverized coal and the vortex, and combustion is carried out in the combustion chamber.

[0017] Steps S2 and S3 are implemented by using a coaxial vortex lance. The structure of the coaxial vortex lance includes a central straight pipe located at the center of the axis for conveying the pulverized coal, and an outer ring channel with spiral grooves wrapped outside the central straight pipe. The composite activation injection medium is injected out through the outer ring channel, and forms a high-speed rotating vortex under the guidance of the spiral grooves on the inner wall of the outer ring channel. The helix angle of the spiral grooves can be set to 15 degrees to 45 degrees.

[0018] To ensure that a shear layer with a significant velocity gradient is formed at the outlet of the lance, the process parameters are set as follows: the injection speed of the pulverized coal at the outlet of the central straight pipe is 20 m / s to 50 m / s; and the injection speed of the composite activation injection medium at the outlet of the outer ring channel is 100 m / s to 300 m / s. At the same time, the injection mass ratio of the composite activation injection medium to the pulverized coal is controlled in the range of 0.2:1 to 0.8:1.

[0019] Under the flow field structure and process conditions set in the present application, the combustion process in step S3 spontaneously forms a radially layered and ordered reaction region in the combustion chamber. The radially layered reaction region includes, in physical space: An outer layer region: This region is located outside the central pulverized coal jet and is mainly composed of high-speed rotating composite activation injection medium interacting with the outer surface of the pulverized coal particles. In this region, the surface gasification reactions of the pulverized coal (such as C+H2O→CO+H2 and C+CO2→2CO) are dominant.

[0020] An inner layer region: This region is located in the core of the central pulverized coal jet. In this region, the homogeneous gas combustion reactions between the combustible gas generated by the aforementioned gasification reactions and the oxidizer are dominant.

[0021] The realization of the layered combustion relies on a specific oxidant supply mechanism. The oxygen consumed by the gas combustion reaction in the inner layer region is mainly from the oxygen-containing micro-nano bubbles carried by the composite activated injection medium. The oxygen-containing micro-nano bubbles are broken in structure when flowing through the strong shear layer formed between the central coal powder jet and the outer vortex flow, thereby releasing the oxygen encapsulated inside to the specified region (upstream of the inner layer region) and participating in the gas combustion reaction in the inner layer region.

[0022] The present application provides a composite injection process for improving the combustion rate of coal powder. The following beneficial effects are achieved: 1. The present application uses a coaxial vortex lance to construct a central direct-current coal powder jet and an outer high-speed rotating composite activated injection medium vortex, thereby forming an inner and outer layered reaction region in the combustion chamber. This structure spatially decouples the surface gasification reaction of the outer coal powder and the combustible gas combustion reaction in the inner layer, avoids the competition for oxidant and reaction space in different reaction stages, makes the combustion process more orderly and controllable, and thus helps to improve the overall combustion rate and burnout rate.

[0023] 2. The present application pre-encapsulates oxygen in the form of micro-nano bubbles in the composite activated injection medium, realizes the hydrodynamic controlled release of the oxidant, and when the medium flows through the strong shear layer formed between the central jet and the outer vortex, the micro-nano bubbles are broken due to the fluid shear force, thereby releasing oxygen. This method ensures that the oxidant is accurately released to the inner flame zone which needs it most after the coal powder is preliminarily heated and vaporized, greatly improves the effective utilization rate of oxygen, and strengthens the combustion process.

[0024] 3. The present application sprays the medium composed of superheated water vapor and carbon dioxide in the form of high-speed rotating vortex, strengthens the heat and mass transfer process of the central coal powder jet, forms strong turbulent exchange between the high-speed rotating vortex and the coal powder flow, rapidly heats and preliminarily vaporizes the coal powder particles, and generates high-activity combustible gas. This process is equivalent to online pretreatment of the coal powder, effectively reduces the ignition threshold of the coal powder, and thus speeds up the overall combustion process. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be described below in conjunction with the description of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0026] Embodiments 1-3: Example 1: This embodiment provides a composite injection process for increasing the combustion rate of pulverized coal. The specific steps are as follows: Step S1: Preparation of composite activated spraying medium Sub-step S11 (Preparing an Oxygen-Containing Micro-Nanobubble Liquid): Oxygen is dispersed in water in the form of micro-nanobubbles in a high-pressure liquid phase environment. The pressure of the high-pressure liquid phase environment is set to 5.0 MPa. Through high-pressure gas-liquid mixing and pressure-regulated precipitation, the average particle size of the oxygen-containing micro-nanobubbles formed is controlled to 50 nm.

[0027] Sub-step S12 (forming a composite precursor solution): while maintaining a pressure of 5.0 MPa, introducing carbon dioxide gas into the oxygen-containing micro-nano bubble liquid obtained in sub-step S11 and fully dissolving it to form a composite precursor solution.

[0028] Sub-step S13 (Phase Transition): The composite precursor liquid is heated via an in-line heater to transform into a superheated water vapor stream. Before injection into the combustion chamber, the composite activated injection medium is regulated to achieve a final temperature of 250°C, a pressure of 3.0 MPa, and a molar ratio of water vapor to carbon dioxide of 100:1.

[0029] Steps S2 and S3: Coaxial vortex injection and combustion A coaxial vortex spray gun is used for spraying. The spiral channel of the outer ring channel of the spray gun has a helical rise angle of 15 degrees. The composite activated spray medium prepared in step S1 is sprayed into the combustion chamber through the outer ring channel, and the pulverized coal is sprayed into the combustion chamber through the central straight pipe.

[0030] The pulverized coal spraying velocity at the outlet of the central DC pipeline is controlled to be 20 m / s, and the spraying velocity of the composite activated injection medium at the outlet of the outer ring channel is controlled to be 100 m / s.

[0031] The injection mass ratio of composite activated injection medium to pulverized coal is controlled to be 0.2:1.

[0032] Through the above process, radially layered reaction areas are formed in the combustion chamber, with the outer layer being dominated by surface gasification reaction and the inner layer being dominated by gas combustion reaction.

[0033] Example 2: This embodiment provides a composite injection process for increasing the combustion rate of pulverized coal. The specific steps are as follows: Step S1: Preparation of composite activated spraying medium Sub-step S11 (Preparing an Oxygen-Containing Micro-Nanobubble Liquid): Oxygen is dispersed in water in the form of micro-nanobubbles in a high-pressure liquid phase environment. The pressure of the high-pressure liquid phase environment is set to 7.5 MPa. Through high-pressure gas-liquid mixing and pressure-regulated precipitation, the average particle size of the oxygen-containing micro-nanobubbles formed is controlled to 5 µm.

[0034] Sub-step S12 (forming a composite precursor solution): while maintaining a constant pressure of 7.5 MPa, introducing carbon dioxide gas into the oxygen-containing micro-nano bubble liquid obtained in sub-step S11 and fully dissolving it to form a composite precursor solution.

[0035] Sub-step S13 (Phase Transition): The composite precursor liquid is heated via an in-line heater to transform into a superheated water vapor stream. Before injection into the combustion chamber, the composite activated injection medium is regulated to a final temperature of 325°C, a pressure of 5.5 MPa, and a molar ratio of water vapor to carbon dioxide of 55:1.

[0036] Steps S2 and S3: Coaxial vortex injection and combustion A coaxial vortex spray gun is used for spraying. The spiral channel of the outer ring channel of the spray gun has a helical rise angle of 30 degrees. The composite activated spray medium prepared in step S1 is sprayed into the combustion chamber through the outer ring channel, and the pulverized coal is sprayed into the combustion chamber through the central straight pipe.

[0037] The pulverized coal spraying velocity at the outlet of the central DC pipeline is controlled to be 35 m / s, and the spraying velocity of the composite activated injection medium at the outlet of the outer ring channel is controlled to be 200 m / s.

[0038] The injection mass ratio of composite activated injection medium to pulverized coal is controlled to be 0.5:1.

[0039] Through the above process, radially layered reaction areas are formed in the combustion chamber, with the outer layer being dominated by surface gasification reaction and the inner layer being dominated by gas combustion reaction.

[0040] Example 3: This embodiment provides a composite injection process for increasing the combustion rate of pulverized coal. The specific steps are as follows: Step S1: Preparation of composite activated spraying medium Sub-step S11 (Preparing an Oxygen-Containing Micro-Nanobubble Liquid): Oxygen is dispersed in water in the form of micro-nanobubbles in a high-pressure liquid phase environment. The pressure of the high-pressure liquid phase environment is set to 10.0 MPa. Through high-pressure gas-liquid mixing and pressure-regulated precipitation, the average particle size of the oxygen-containing micro-nanobubbles formed is controlled to 10 µm.

[0041] Sub-step S12 (forming a composite precursor solution): while maintaining a pressure of 10.0 MPa, introducing carbon dioxide gas into the oxygen-containing micro-nano bubble liquid obtained in sub-step S11 and fully dissolving it to form a composite precursor solution.

[0042] Sub-step S13 (Phase Transition): The composite precursor liquid is heated via an in-line heater to transform into a superheated water vapor stream. Before injection into the combustion chamber, the composite activated injection medium is regulated to achieve a final temperature of 400°C, a pressure of 8.0 MPa, and a molar ratio of water vapor to carbon dioxide of 10:1.

[0043] Steps S2 and S3: Coaxial vortex injection and combustion A coaxial vortex spray gun is used for spraying. The spiral channel of the outer ring channel of the spray gun has a helical rise angle of 45 degrees. The composite activated spray medium prepared in step S1-3 is sprayed into the combustion chamber through the outer ring channel, and the pulverized coal is sprayed into the combustion chamber through the central straight pipe.

[0044] The pulverized coal spraying velocity at the outlet of the central DC pipeline is controlled to be 50 m / s, and the spraying velocity of the composite activated injection medium at the outlet of the outer ring channel is controlled to be 300 m / s.

[0045] The injection mass ratio of composite activated injection medium to pulverized coal is controlled to be 0.8:1.

[0046] Through the above process, radially layered reaction areas are formed in the combustion chamber, with the outer layer being dominated by surface gasification reaction and the inner layer being dominated by gas combustion reaction.

[0047] Comparative Examples 1-3: Comparative Example 1: Compared with Example 2, the difference is that the outer ring channel does not spray the composite activation spray medium, but instead sprays preheated air at the same temperature (325°C) as a combustion aid. The other process conditions are the same as those in Example 2.

[0048] Comparative Example 2: Compared with Example 2, the difference is that the composite activated injection medium prepared here does not contain "oxygen-containing micro-nano bubbles", but instead mixes gaseous oxygen with superheated water vapor and a fluid containing dissolved carbon dioxide before injection into the combustion chamber. The remaining process conditions are the same as those in Example 2.

[0049] Comparative Example 3: Compared to Example 2, the difference lies in that the outer annular channel of the coaxial lance used lacks spiral grooves, allowing the composite activated injection medium to be ejected in a straight flow parallel to the central pulverized coal stream, eliminating the formation of high-speed rotating vortices and strong shear layers. All other process conditions are the same as in Example 2.

[0050] Test Example 1: Performance testing and results: In order to verify the beneficial effects of the technical solution of the present invention, performance tests were carried out on Examples 1-3 and Comparative Examples 1-3 on the same laboratory-scale combustion test bench.

[0051] Experimental test method: After each experimental condition (corresponding to Examples 1-3 and Comparative Examples 1-3) had been running stably for 60 minutes, data acquisition and sample collection began. The specific test method was as follows: The burnout rate test collects bottom ash samples from the ash hopper below the test bench, while fly ash samples are collected from the cyclone separator after the combustion chamber outlet. The bottom ash and fly ash are weighed separately. The carbon content of each sample is then determined using the muffle furnace ignition method, in accordance with the national standard GB / T212-2008, "Industrial Analysis Methods of Coal." The comprehensive burnout rate is calculated based on the initial coal feed rate, the ash content of the raw coal, and the mass and carbon content of the collected ash samples.

[0052] Flue gas component concentration test: Insert a sampling probe of a flue gas analyzer (for example, Testo350 flue gas analyzer) into the cross section of the flue gas where the gases are evenly mixed at the combustion chamber outlet. During the stable operation of each working condition, continuously monitor and record the CO2 and nitrogen oxides (NO x The final result is the average value within the 30-minute stabilization period. x The emission concentration is converted to a dry flue gas benchmark with an O2 content of 6% in accordance with the standard.

[0053] Experimental test results: The performance test data of Examples 1-3 and Comparative Examples 1-3 are summarized in the following table.

[0054] Table 1 Performance test results of the embodiments and comparative examples

[0055] Result analysis: From the test results in Table 1, it can be seen that the processes adopted in Examples 1, 2 and 3 are significantly higher than those in Comparative Examples 1, 2 and 3 in terms of burnout rate and CO2 concentration of combustion products, while NO x The emission concentration is significantly lower than that of the control group.

[0056] This performance improvement is directly related to the specific combustion mechanism constructed by the process. By adopting a coaxial vortex spray gun, the composite activated blowing medium forms a high-speed rotating vortex and wraps the central coal powder jet, constructing a radially layered reaction area in the combustion chamber. The outer layer of high-temperature medium rich in water vapor and carbon dioxide enhances the heat and mass transfer to the central coal powder, and causes a preliminary surface gasification reaction, providing highly active combustible gas components for subsequent combustion. Comparative Example 3 did not use a spiral groove and failed to form this layered vortex structure. Its burnout rate and CO2 concentration were significantly lower than those of the embodiment, proving the decisive role of this flow field structure in improving combustion efficiency.

[0057] This process carries oxygen in the form of oxygen-containing micro-nano bubbles and achieves controlled release through the action of flow field mechanics. In the strong shear layer formed between the central jet and the outer vortex, the micro-nano bubbles rupture due to the huge fluid shear force, and the oxygen encapsulated inside is released in the designated area. This release mechanism enables oxygen to be accurately supplied to the inner layer area where the initial gasification has been completed for homogeneous gas combustion, avoiding premature mixing of the oxidant and the original coal powder. Comparative Example 2 mixes oxygen in the form of ordinary gas, and its NO x The emission concentration is much higher than that in the embodiment, which confirms the controlled oxygen release mechanism of micro-nano bubbles, which is very effective in suppressing NO in the combustion process. x The generation of plays a key role.

[0058] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A composite injection process for increasing the combustion rate of pulverized coal, characterized in that: The following steps are involved: S1. Prepare a composite activated blowing medium, wherein the composite activated blowing medium is a superheated water vapor flow carrying oxygen-containing micro-nano bubbles and carbon dioxide; S2, spraying the composite activated blowing medium into the combustion chamber in the form of a high-speed rotating vortex; S3. Spraying pulverized coal into the central area of ​​the vortex to form a shear layer between the pulverized coal and the vortex, and burning in the combustion chamber.

2. A composite injection process for increasing the combustion rate of pulverized coal according to claim 1, characterized in that: The step S1 includes the following sub-steps: S11. In a high-pressure liquid environment, dispersing oxygen in water in the form of micro-nano bubbles to form an oxygen-containing micro-nano bubble liquid; S12, while maintaining the high-pressure liquid phase environment, introducing carbon dioxide gas into the oxygen-containing micro-nano bubble liquid to dissolve the carbon dioxide in the oxygen-containing micro-nano bubble liquid, thereby forming a composite precursor liquid; as well as S13, heating the composite precursor liquid online to change the composite precursor liquid into the composite activated spraying medium.

3. A composite injection process for increasing the combustion rate of pulverized coal according to claim 2, characterized in that: In the sub-step S11, the pressure of the high-pressure liquid environment is 5.0 MPa to 10.0 MPa, and the average particle size of the oxygen-containing micro-nano bubbles is in the range of 50 nm to 10 μm.

4. The composite injection process for increasing the combustion rate of pulverized coal according to claim 1, characterized in that: The molar ratio of water vapor to carbon dioxide in the composite activated blowing medium is in the range of 100:1 to 10:1, the temperature of the composite activated blowing medium before being injected into the combustion chamber is in the range of 250°C to 400°C, and the pressure is in the range of 3.0MPa to 8.0MPa.

5. The composite injection process for increasing the combustion rate of pulverized coal according to claim 1, characterized in that: The implementation of step S2 and step S3 is to use a coaxial vortex spray gun, and the coaxial vortex spray gun includes: a central, straight-through pipeline for conveying the pulverized coal; An outer ring channel with spiral grooves is wrapped around the outside of the central straight flow pipe.

6. A composite injection process for increasing the combustion rate of pulverized coal according to claim 5, characterized in that: The helix angle of the spiral groove is 15 degrees to 45 degrees.

7. The composite injection process for increasing the combustion rate of pulverized coal according to claim 5, characterized in that: The pulverized coal has a spraying velocity of 20 to 50 m / s at the outlet of the central direct current pipeline; and the composite activated injection medium has a spraying velocity of 100 to 300 m / s at the outlet of the outer ring channel.

8. The composite injection process for increasing the combustion rate of pulverized coal according to claim 1, characterized in that: The injection mass ratio of the composite activated injection medium to the coal powder is in the range of 0.2:1 to 0.8:

1.

9. The composite injection process for increasing the combustion rate of pulverized coal according to claim 1, characterized in that: In step S3, the combustion process forms a radially layered reaction region in the combustion chamber, and the radially layered reaction region includes: an outer region in which surface vaporization reactions predominate; An inner region, in which the gas combustion reaction is dominant.

10. A composite injection process for increasing the combustion rate of pulverized coal according to claim 9, characterized in that: The oxygen consumed by the gas combustion reaction in the inner layer region mainly comes from the rupture of the oxygen-containing micro-nano bubbles in the shear layer due to the shear force of the fluid.

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