Pulverized coal classifying flameless combustion device with coupling concentration and dilution separationTechnical Field
The invention belongs to the technical field of coal combustion, and particularly relates to a pulverized coal classifying flameless combustion device with coupling concentration and dilution separation.
Background
As the emission requirements for nitrogen oxides become more stringent, controlling NOx emissions has now become an important area of research in the environmental protection field. The development of new low nitrogen combustion technology and burner design is urgent for the ultra low emission limit requirements of 50mg/m3 in the NOx emission standard.
Flameless combustion (MILD combustion) is favored as an advanced combustion technology because of its stable combustion process and low NOx emissions. The technology forms strong internal circulation of the flue gas in the furnace by entrainment of the high-temperature flue gas by high-speed jet flow, greatly dilutes fuel and oxidant, enlarges combustion area, reduces peak temperature and oxygen concentration, and thus inhibits the generation of NOx. However, flameless combustion mainly has two problems in application, namely 1) the oxidant needs to be preheated at high temperature and sprayed at high speed, so that additional energy consumption and cost are increased, and 2) the fuel jet and the oxidant jet cannot form stable flame propagation before being intersected by each other due to a non-premixed combustion mode, so that obvious flame floating exists near an outlet of the combustor, and combustion stability is affected.
Disclosure of Invention
The invention aims to solve the problems, and provides the pulverized coal classifying flameless combustion device with coupling concentration separation, which reduces the energy consumption and the cost of the flameless combustion technology by an oxidant injection mode with the cooperation of outside preheating and inside speed increasing on one hand and shortens the ignition delay and the flame floating distance by the concentration separation of pulverized coal airflow on the other hand.
The invention provides a pulverized coal classifying flameless combustion device with coupling concentration separation, which comprises a combustion chamber, a primary air spray pipe, a secondary air spray pipe and a tertiary air spray pipe, wherein the primary air spray pipe is used for conveying pulverized coal and primary air into the combustion chamber, and the secondary air spray pipe and the tertiary air spray pipe are respectively used for conveying secondary air and tertiary air into the combustion chamber, wherein the secondary air and the tertiary air are respectively high-speed oxidant air flow and high-temperature oxidant air flow;
the secondary air jet pipe is coaxially arranged inside the tertiary air jet pipe, the primary air jet pipe is uniformly distributed around the tertiary air jet pipe, and a separation mechanism is arranged in the primary air jet pipe and is used for separating initial pulverized coal airflow (primary air carrying pulverized coal) into concentrated pulverized coal airflow and dilute pulverized coal airflow, wherein the concentrated pulverized coal airflow is closer to the middle oxidant airflow (secondary air and tertiary air).
Specifically, the separation mechanism comprises a first separation stop block which is arranged on the inner wall of one side of the primary air nozzle far away from the tertiary air nozzle in the transverse direction, and is positioned at the middle part of the primary air nozzle or closer to the outlet end of the primary air nozzle in the axial direction, so that the initial pulverized coal airflow is divided into two pulverized coal airflows.
Further, the cross section of the first separation stop block is triangular, and the first separation stop block is provided with an upper inclination angle theta 1 and a lower inclination angle theta 2 relative to the inner wall surface of the primary air spray pipe, wherein the upper inclination angle theta 1 is closer to the inlet end of the primary air spray pipe, and the angle theta 1 is 120-150 degrees, and the angle theta 2 is 135-160 degrees.
Specifically, the separation mechanism further comprises a second separation stop block which is arranged at the middle part of the primary air spray pipe in the transverse direction and is closer to the outlet of the primary air spray pipe than the first separation stop block in the axial direction, so that the separation degree is further enhanced.
Further, the section of the second separation stop block is rectangular, and the inclination theta 3 of the section of the second separation stop block relative to the primary air spray pipe is 5-25 degrees.
Specifically, the secondary air spray pipe adopts a tapered spray pipe structure and comprises an inlet section, a contraction section and an outlet section which are sequentially communicated, wherein the diameter ratio of the outlet section to the inlet section is 1/3-1/2. The high-temperature smoke is intensively sucked in by internal high-speed jet flow in the combustion chamber, so that the oxidant is diluted and the pulverized coal particles are preheated, and the flameless combustion state is realized.
Further, a cyclone is arranged in the tertiary air spray pipe and comprises a cyclone inner ring, guide vanes and a cyclone outer ring, wherein the guide vanes are arranged between the cyclone inner ring and the cyclone outer ring, and the inclination angles of the guide vanes are 15-25 degrees. By adding the cyclone, the mixing of the pulverized coal and the oxidant at the outlet of the burner is enhanced, the problem of flame floating caused by slow preheating of pulverized coal particles is relieved, and flame propagation is promoted.
Further, a fourth air nozzle is arranged on the downstream side wall of the combustion chamber and is used for conveying fourth air into the combustion chamber. The fourth air spray pipe is positioned at the upstream of the smoke internal circulation area, so that on one hand, the air classification technology is used as a part of the air classification technology, NOx emission is reduced, on the other hand, the air flow momentum of the downstream recirculation area can be improved, the recirculation area is further enlarged, and the flameless combustion state is promoted to be realized more quickly.
Specifically, the distribution position of the four-time air jet pipes corresponds to the primary air jet pipes, and the inclination angle alpha of the four-time air jet pipes relative to the wall surface of the combustion chamber is 30-45 degrees.
Specifically, the primary air accounts for 5% -10%, the secondary air accounts for 60% -70%, the tertiary air accounts for 5% -10%, and the quaternary air accounts for 20% -25%. Under the multi-layer staged combustion, the furnace in the main reaction zone presents a weak reducing atmosphere, the oxidation process of Fuel nitrogen (Fuel-N) is inhibited, and more coke particles remain in the main reaction zone, which is beneficial to promoting heterogeneous reduction of NOx, thereby further reducing NOx emission.
The beneficial effects are that:
1. The pulverized coal direct-current burner is arranged as the shade-separating burner provided with the blunt body so as to separate pulverized coal particles before entering a hearth into two pulverized coal flows with different shades, wherein the concentrated pulverized coal side is closer to a high-temperature oxidant jet flow (tertiary air), so that more pulverized coal is ensured to be intensively sucked into a high-temperature area for combustion, the contact of the pulverized coal particles and the oxidant is promoted, the preheating time of the pulverized coal particles is reduced, stable flame is formed at an outlet of the burner, and the flame floating distance is shortened. For the inferior coal with low volatile matters, the setting can improve ignition and combustion of the inferior coal, and has a stronger application range.
2. The high-temperature high-speed oxidant spray pipe is arranged as the composite spray pipe with the inner side at normal temperature and high-speed spray and the outer side at high temperature and low-speed spray, so that coal dust is contacted with the outer side high-temperature oxidant, thereby promoting ignition and flame propagation of coal dust particles, and further sucking the high-temperature flue gas to dilute the oxidant and preheat the coal dust particles through the inner side high-speed jet flow so as to realize a flameless combustion state. Compared with the traditional mode of full preheating and high-speed oxidant injection, the invention only needs to preheat and accelerate part of the oxidant so as to reduce the process energy consumption and cost in the flameless combustion process.
Drawings
FIG. 1 is a schematic diagram of a pulverized coal classifying flameless combustion device according to an embodiment of the present invention;
FIG. 2 is a top view of a pulverized coal staged flameless combustion device in accordance with an embodiment of the present invention;
3 a-3 c are schematic structural diagrams of a primary air nozzle, a first separation block and a second separation block according to an embodiment of the present invention;
FIG. 4 is a schematic structural diagram of a secondary air nozzle and a tertiary air nozzle in an embodiment of the present invention;
FIG. 5 is a schematic diagram of a fourth wind nozzle according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of the flue gas circulation of a pulverized coal staged flameless combustion device in accordance with an embodiment of the present invention;
the air-fuel separation device comprises a primary air spray pipe 1, a secondary air spray pipe 2, a tertiary air spray pipe 3, a quaternary air spray pipe 4, a combustion chamber 5, a first separation stop block 11, a first separation stop block 12, a second separation stop block 31 and a cyclone.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention.
Referring to fig. 1, the embodiment provides a pulverized coal classifying flameless combustion device with coupling concentration separation, which mainly comprises a combustion chamber 5, and a primary air nozzle 1, a secondary air nozzle 2, a tertiary air nozzle 3 and a quaternary air nozzle 4 which are communicated with the combustion chamber 5, wherein the primary air nozzle 1 is used for conveying pulverized coal and primary air into the combustion chamber 5, and the secondary air nozzle 2, the tertiary air nozzle 3 and the quaternary air nozzle 4 are respectively used for conveying secondary air, tertiary air and quaternary air into the combustion chamber 5.
Specifically, the primary air spray pipe 1, the secondary air spray pipe 2 and the tertiary air spray pipe 3 are all arranged at the upstream of the combustion chamber 5, wherein the secondary air spray pipe 2 is coaxially arranged inside the tertiary air spray pipe 3, the primary air spray pipes 1 are uniformly distributed around the tertiary air spray pipe 3, and the quaternary air spray pipes 4 are arranged on the downstream side wall of the combustion chamber 5. Further, a separation mechanism is arranged in the primary air spray pipe 1 and is used for separating the initial pulverized coal airflow into a high-speed concentrated pulverized coal airflow and a low-speed thin pulverized coal airflow, wherein the high-speed concentrated pulverized coal airflow is closer to the middle oxidant jet. The initial pulverized coal airflow refers to primary air carrying pulverized coal, and the separated high speed and low speed, and the concentration and the dilution are relative to the initial pulverized coal airflow.
As an example, referring to fig. 2 and 3a, the primary air nozzles 1 are four in number and symmetrically arranged around the tertiary air nozzle 3, and meanwhile, two separation blocks are installed inside the primary air nozzle 1, after the initial pulverized coal airflow encounters the first separation block 11, the original pulverized coal airflow is divided into two pulverized coal airflows due to the existence of a blunt body, and the separation degree of the two airflows is further enhanced after the two airflows pass through the second separation block 12, so that a high-speed concentrated pulverized coal airflow (inwards) and a low-speed light pulverized coal airflow (outwards) are formed at the outlet of the combustor (i.e. the primary air nozzle 1), wherein the high-speed concentrated pulverized coal airflow is closer to the oxidant jet (secondary air and tertiary air) in the middle, is easily sucked into the main reaction zone and then reacts with the oxidant, thereby promoting pulverized coal ignition and shortening ignition delay. For low-volatile pulverized coal, pulverized coal particles are difficult to ignite, more pulverized coal can be ensured to enter a high-temperature zone in a concentrated manner through a concentration separation method, the pulverized coal particles are promoted to contact with more oxygen, and the combustion stability is improved.
Referring to fig. 3a, the first separation stopper 11 is disposed on an inner wall of the primary air nozzle 1 on a side away from the tertiary air nozzle 3 in a lateral direction while being located at a middle portion of the primary air nozzle 1 or closer to an outlet end of the primary air nozzle 1 in an axial direction, and the second separation stopper 12 is disposed at a middle portion of the primary air nozzle 1 in a lateral direction while being closer to an outlet end of the primary air nozzle 1 than the first separation stopper 11 in an axial direction, thereby achieving further enhancement of the separation degree. Referring to fig. 3b and 3c, the first separation stopper 11 has a triangular cross section having an upper slope θ1 and a lower slope θ2 with respect to the inner wall surface of the primary air nozzle 1, wherein the upper slope θ1 is closer to the inlet end of the primary air nozzle 1, θ1 is 120 ° to 150 °, θ2 is 135 ° to 160 °, and the second separation stopper 12 has a rectangular cross section with respect to the slope θ3 of the cross section of the primary air nozzle 1, is 5 ° to 25 °. In addition, other blunt body structures can be adopted to realize the concentration separation of the coal powder airflow so as to promote the coal powder ignition and shorten the ignition delay.
Specifically, the middle oxidant nozzle is divided into an inner side nozzle and an outer side nozzle, namely a secondary air nozzle 2 and a tertiary air nozzle 3, wherein the secondary air nozzle 2 is used for conveying normal-temperature high-speed oxidant jet flow (the normal-temperature is about 303K, the jet speed is >100 m/s), and the tertiary air nozzle 3 is used for conveying preheated low-speed oxidant flow (the preheating temperature is >1000K, and the jet speed is about 26 m/s). The reason for this is that the outside preheated oxidant gas stream first contacts the high velocity concentrated pulverized coal gas stream to promote ignition and flame propagation of pulverized coal particles, and then strong internal circulation entrainment of high temperature flue gas is generated in the combustion chamber 5 by the inside high velocity jet stream, thereby diluting the oxidant and preheating pulverized coal particles to achieve a flameless combustion state. Compared with the traditional method of full preheating and high-speed injection of oxidant jet, only partial oxidant is accelerated and preheated, so that energy consumption and cost are greatly reduced.
Referring to fig. 4, the secondary air jet pipe 2 adopts a tapered jet pipe structure, and comprises an inlet section, a contraction section and an outlet section which are sequentially communicated, wherein the diameter ratio of the outlet section to the inlet section is 1/3-1/2. Further, a cyclone 31 is arranged in the tertiary air spray pipe 3, the cyclone 31 consists of a cyclone inner ring, guide vanes and a cyclone outer ring, the cyclone outer ring is fixedly assembled on the inner wall of the tertiary air spray pipe 3, and the middle of the cyclone inner ring is provided with a secondary air spray pipe 2. The reason for this arrangement is that the high temperature oxidant air flow passes through the turbine guide vane to generate a stronger reflux zone near the burner outlet, so as to ensure the full mixing of the pulverized coal and the high temperature oxidant, promote the contact of the pulverized coal particles and the oxidant, promote the ignition and flame propagation of the pulverized coal particles, and meanwhile, the circulating flue gas in the reflux zone dilutes the concentration of the oxidant, thereby being beneficial to inhibiting the generation of NOx. Illustratively, the number of guide vanes is six, the thickness of the vanes is about 1mm, the height is about 20mm, and the inclination angle of the vanes is 15-25 degrees.
Compared with the traditional flameless combustion process that the oxidant is directly preheated and sprayed at a high speed (the preheating temperature is about 1573K and the spraying speed is about 65 m/s), the invention only needs to preheat and accelerate part of the oxidant to realize flameless combustion. Specifically, the oxidant is injected into the hearth in two parts, namely, one part of the oxidant is injected into the hearth through the secondary air jet pipe 2 to realize high-speed injection (the injection speed is more than 100 m/s), and the other part of the oxidant is injected into the hearth through the tertiary air jet pipe 3 to realize high-temperature injection (the preheating temperature is more than 1000K) and is combined with the cyclone, so that stable flame is formed at the outlet of the burner. The secondary air high-speed injection is used for promoting strong smoke circulation in the furnace and promoting flameless combustion, the tertiary air high-temperature and rotational flow is used for promoting flame propagation, shortening the flame floating distance and improving the combustion stability.
Specifically, referring to fig. 6, a fourth air nozzle 4 is disposed on the downstream side wall of the combustion chamber 5 for delivering fourth air to a recirculation zone downstream in the combustion chamber 5, and the injection of oxidant jets increases the momentum of the recirculated flue gas jet, which facilitates the continued expansion of the flue gas recirculation zone while ensuring adequate burnout of unburnt char particles upstream of the furnace. For example, referring to fig. 2 and 5, the number of the four-way wind nozzles 4 is 4, and each is provided corresponding to one burner (i.e., the primary wind nozzle 1) at an inclination angle α of 30 ° to 45 ° with respect to the side wall of the combustion chamber 5.
Specifically, the first, second, third and fourth wind form all oxidants, the gas components are air, wherein the primary wind accounts for 5% -10%, the secondary wind accounts for 60% -70%, the tertiary wind accounts for 5% -10%, and the fourth wind accounts for 20% -25%. The ratio of the air flow to the air flow may be a ratio of mass flow or volume flow, wherein the air flow is ejected at a low speed at normal temperature (the temperature is about 303K, and the ejection speed is about 26 m/s). Referring to fig. 6, under multi-layered staged combustion, a weakly reducing atmosphere is present in the primary reaction zone furnace, the oxidation process of Fuel nitrogen (Fuel-N) is inhibited, and more coke particles remain in the primary reaction zone, which is advantageous for promoting heterogeneous reduction of NOx, thereby further reducing NOx emissions.
In summary, the pulverized coal direct-current burner is arranged as a double-blunt-body thick-thin separation burner so as to promote pulverized coal ignition and improve combustion uniformity, the high-temperature high-speed oxidant spray pipe is arranged as a composite spray pipe with inner side normal-temperature high-speed spray and outer side high-temperature low-speed spray so as to reduce energy consumption and cost, the cyclone 31 is arranged in the oxidant outer side spray pipe, the cyclone strength of the oxidant is improved, the flame stability at the outlet of the burner is enhanced, the problem of flame floating is further relieved, and the four-time air spray pipe 4 is arranged on the downstream side wall of the combustion chamber 5 so as to further reduce NOx emission.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.