CN111664445A - Semi-coke powder circulating fluidized bed boiler based on material heat balance - Google Patents
Semi-coke powder circulating fluidized bed boiler based on material heat balance Download PDFInfo
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- CN111664445A CN111664445A CN202010661433.7A CN202010661433A CN111664445A CN 111664445 A CN111664445 A CN 111664445A CN 202010661433 A CN202010661433 A CN 202010661433A CN 111664445 A CN111664445 A CN 111664445A
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN A CARRIER GAS OR AIR
- F23C10/00—Fluidised bed combustion apparatus
- F23C10/18—Details; Accessories
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN A CARRIER GAS OR AIR
- F23C10/00—Fluidised bed combustion apparatus
- F23C10/002—Fluidised bed combustion apparatus for pulverulent solid fuel
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN A CARRIER GAS OR AIR
- F23C10/00—Fluidised bed combustion apparatus
- F23C10/02—Fluidised bed combustion apparatus with means specially adapted for achieving or promoting a circulating movement of particles within the bed or for a recirculation of particles entrained from the bed
- F23C10/04—Fluidised bed combustion apparatus with means specially adapted for achieving or promoting a circulating movement of particles within the bed or for a recirculation of particles entrained from the bed the particles being circulated to a section, e.g. a heat-exchange section or a return duct, at least partially shielded from the combustion zone, before being reintroduced into the combustion zone
- F23C10/06—Fluidised bed combustion apparatus with means specially adapted for achieving or promoting a circulating movement of particles within the bed or for a recirculation of particles entrained from the bed the particles being circulated to a section, e.g. a heat-exchange section or a return duct, at least partially shielded from the combustion zone, before being reintroduced into the combustion zone the circulating movement being promoted by inducing differing degrees of fluidisation in different parts of the bed
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN A CARRIER GAS OR AIR
- F23C10/00—Fluidised bed combustion apparatus
- F23C10/18—Details; Accessories
- F23C10/20—Inlets for fluidisation air, e.g. grids; Bottoms
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- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Fluidized-Bed Combustion And Resonant Combustion (AREA)
Abstract
The invention discloses a semi-coke powder circulating fluidized bed boiler based on material heat balance, which comprises a boiler body and a tail flue, wherein the boiler body is connected with the tail flue through a cyclone separator, a fluidized air distribution bed for providing primary air is arranged at the bottom of the boiler body, a secondary air distribution device for providing secondary air is arranged on the side wall of the boiler body, the separation efficiency of the cyclone separator is not less than 99.8%, the secondary air distribution device is provided with an upper secondary air port and a lower secondary air port, and a hearth of the boiler body is divided into a first section, a second section, a third section and a fourth section. The invention can realize the stable and high-efficiency combustion of the pure semi-coke powder on the premise of extracting the distillate and discharging low nitrogen.
Description
Technical Field
The invention relates to the field of clean coal combustion, in particular to a semi-coke powder circulating fluidized bed boiler based on material heat balance.
Background
The semi-coke is a clean coal fuel which is prepared by carrying out dry distillation on bituminous coal and has low volatile content, low sulfur and low nitrogen, high fixed carbon content and high calorific value, and the semi-coke powder is semi-coke particles with the particle size of 0-6 mm.
Like semi coke, semi coke powder also has the problems of low volatile component, difficult ignition, low burnout rate and high carbon content of fly ash after combustion, which easily causes the thermal efficiency of a boiler to be low, thereby restricting the application and popularization of the semi coke powder in the combustion field.
The current state carries out the policy of environmental protection and emission reduction, most users of thermal power thermoelectric coal-fired boiler generally face the pressure of energy conservation and emission reduction, and the advantage of semi-coke on clean emission is very obvious in practice, so that a plurality of users of coal-fired boiler generally have the rigid demand for large proportion of mixed semi-coke powder and even full-combustion semi-coke powder.
However, in the application practice of the existing circulating fluidized bed boiler, the semi-coke powder can only be co-combusted, the proportion of the co-combusted semi-coke powder is generally not more than 20%, the carbon content in ash is also higher, and the burnout rate of the semi-coke powder is lower, so that the semi-coke powder cannot be co-combusted in a large proportion at present, and cannot be fully combusted.
Disclosure of Invention
In view of the above, the present invention provides a semi-coke powder circulating fluidized bed boiler based on material heat balance, so as to achieve stable combustion of pure semi-coke and effectively improve the burnout rate of semi-coke powder.
In order to achieve the purpose, the invention provides the following technical scheme:
a semi-coke powder circulating fluidized bed boiler based on material heat balance comprises a boiler body and a tail flue, wherein the boiler body is connected with the tail flue through a cyclone separator, a fluidized air distribution bed for providing primary air is arranged at the bottom of the boiler body, a secondary air distribution device for providing secondary air is arranged on the side wall of the boiler body, the separation efficiency of the cyclone separator is not less than 99.8 percent, the secondary air distribution device is provided with an upper secondary air port and a lower secondary air port, a hearth of the boiler body is divided into a first section, a second section, a third section and a fourth section, wherein,
the first section is formed by a section between the fluidization air distribution bed and the lower-layer secondary air port, the height of the first section is 3.8-4.3 m, the inner wall of the boiler in the first section is covered with a fire-resistant layer, and the average fluidization speed in the section lower than the first section is 4.0-4.5 m/s;
the second section is formed by a section of the lower secondary air port which is 3.5-4.0 m upward, and a fire-resistant layer covers the inner wall of the boiler in the second section;
the top of the second section extends upwards for 3.0-3.5 m to form a third section, the average fluidization speed of the third section is 4.0-4.5 m/s, and the inner wall of the boiler in the third section is covered with a refractory layer;
the fourth section is formed by a section between the top of the third section and the flue gas outlet of the boiler body, the average fluidization speed of the fourth section is 4.5-5.0 m/s, and all membrane walls in the fourth section are exposed.
Preferably, the bottom of boiler body is the funnel district that tip is down, the main aspects in funnel district are connected with one section and are used for expanding the expansion joint of furnace section, the top of expansion joint is connected with furnace upper portion festival section, wherein, the well lower part in funnel district constitutes first district, the well upper portion in funnel district constitutes the second district, the expansion joint constitutes the third district, furnace upper portion festival section constitutes the fourth district, the cross sectional area of expansion joint is not less than the cross sectional area of funnel district main aspects, just the cross sectional area of expansion joint is 1.05 ~ 1.15 times of furnace upper portion festival section cross sectional area.
Preferably, the distance between the upper secondary air port and the lower secondary air port is 0.7-1.0 m, the primary air accounts for 32-40% of the total air output of the hearth, and the secondary air accounts for 60-68% of the total air output of the hearth.
Preferably, the area of the fluidized air distribution bed is 35-38% of the cross section area of the upper section of the hearth, the combustion share of the bed surface of the semi-coke powder accounts for 30-35%, the air distribution resistance of the fluidized air distribution bed is 2000-2800 Pa, the upper layer air port and the lower layer air port are both bell mouths with small ends facing the hearth, the included angle between the bell mouth and the horizontal plane is 10-15 °, and the furnace inlet air speed of the secondary air is greater than the critical furnace inlet air speed, wherein the critical furnace inlet air speed is 70-75 m/s.
Preferably, the system further comprises a first opening and closing mechanism for opening and closing the upper layer secondary air opening and a second opening and closing mechanism for opening and closing the lower layer secondary air opening, when the boiler load is higher than the critical load, the second opening and closing mechanism closes the lower layer secondary air opening, and the first opening and closing mechanism opens the upper layer secondary air opening; when the boiler load is lower than the critical load, the second opening and closing mechanism opens the lower-layer secondary air opening, and the first opening and closing mechanism closes the upper-layer secondary air opening, wherein the critical load is 55% -60% of the rated load of the boiler.
Preferably, the material returning port of the cyclone separator is communicated with the first section of the hearth through a self-balancing material returning device, the self-balancing material returning device comprises a material returning bed, the material returning bed is provided with a lubricating area communicated with the material returning port of the cyclone separator and a material returning area communicated with the first section, lubricating air is introduced into the lubricating area, return air is introduced into the material returning area, and the ratio of the lubricating air to the return air is 1: 3.
Preferably, the cyclone separator comprises:
the furnace comprises a cylinder body, wherein a smoke inlet communicated with the upper part of the furnace is formed in the side surface of the cylinder body, the width of the smoke inlet is 0.7-1.0 m, the flow rate of smoke at the smoke inlet is 30-38 m/s, a smoke outlet communicated with the tail flue is formed in the top of the cylinder body, the flow rate of smoke in the cylinder body is 4.0-5.0 m/s, and the ratio of the height of the cylinder body to the diameter of the cylinder body is 1.3-1.5;
the cone is arranged at the lower end of the cylinder, the large end of the cone is connected with the cylinder, and the ratio of the height of the cone to the diameter of the cylinder is 1.6-1.9;
the central cylinder penetrates through the smoke exhaust port, the flow velocity of smoke in the central cylinder is 40m/s, and the ratio of the distance between the lower end of the central cylinder and the lower end of the central cylinder, which is embedded into the cylinder, to the height of the smoke inlet is 0.4-0.5;
the diameter of the vertical pipe is 0.6-0.7 m.
Preferably, the fluidization air distribution bed is formed by horizontally extending a rear wall membrane wall forwards, and a fluidization air cap is arranged on a connecting plate between two adjacent pipes of the membrane wall.
Preferably, a plurality of slag discharging pipes are arranged on the fluidized air distribution bed, and the slag discharging pipes penetrate through the primary air chamber and realize wall penetration sealing and free expansion through metal expansion joints.
Preferably, the combustion temperature of the hearth of the boiler is 850-880 ℃.
Preferably, a superheater, an economizer and an air preheater are sequentially arranged in the tail flue from top to bottom.
Preferably, the primary air chamber is formed by horizontally extending a rear wall membrane type wall and enclosing two side membrane type walls.
Preferably, the fuel supply device is arranged on the front wall of the hearth, and the fuel supply device is connected with a plurality of blanking pipes, and fuel is uniformly fed into the first section of the hearth through the blanking pipes.
Preferably, the air preheater is made of an internally threaded pipe, and the air preheater is horizontally arranged at the lower part of the tail flue.
Preferably, the ash concentration at the upper section of the furnace is not less than 3kg/Nm3。
Preferably, the average ash concentration in the furnace is not less than 10kg/Nm3。
The semi-coke powder circulating fluidized bed boiler based on material heat balance adopts a material heat balance measure, a hearth is divided into a first section, a second section, a third section and a fourth section from bottom to top, and semi-coke and primary air are combusted in a reducing atmosphere in the first section, so that the overhigh temperature in the boiler can be inhibited, and the generation of nitrogen oxides in the boiler can be effectively reduced; in the second section, the secondary air and the semi-coke powder are combusted in an oxidizing atmosphere; the third section belongs to the intensified stable combustion stage; the fourth section belongs to a heat release area, and fine materials carried by the flue gas transfer heat to the exposed membrane wall through radiation or contact; the reasonable design of the height of each section is matched with the timely distribution of primary air and secondary air, so that the reasonable and uniform gradual release of the burning heat of the semi-coke powder can be realized, the overhigh and insufficient local temperature in a hearth can be avoided, the coking is not generated in the furnace, the heat is efficiently utilized by a water-cooled wall, and the heat balance is realized;
meanwhile, the reasonable design of the height of each section can effectively prolong the combustion time in the furnace of the semi-coke powder, and the high-efficiency cyclone separator with the separation efficiency of more than 99.8% is matched to re-send almost all unburned carbon particles into the hearth for secondary combustion, so that on one hand, large-flow material circulation in the furnace can be established, the material circulation rate is improved, on the other hand, the high-concentration ash content level in the furnace can be achieved, and finally, the balance between materials and heat in the furnace is realized, not only the low-nitrogen combustion of the semi-coke powder is realized, but also the semi-coke powder has considerable burn-off rate on the premise of effectively reducing the fly ash content of the semi-coke powder.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic view of the overall structure of a semi-coke powder circulating fluidized bed boiler disclosed in the embodiment of the present invention.
The drawings are numbered as follows:
1 is an ignition burner, 2 is a primary air chamber, 3 is a fluidized air distribution bed, 4 is a fuel supply device, 5 is a secondary air distribution device, 6 is a cyclone separator, 7 is a boiler body, 8 is a tail flue, 9 is a slag discharge pipe, 10 is a return pipe, 11 is a self-balancing type return feeder, 6-1 is a smoke inlet, 6-2 is a central cylinder, 6-3 is a cylinder, 6-4 is a cone, 6-5 is a vertical pipe, 7-1 is a first section, 7-2 is a second section, 7-3 is a third section, 7-4 is a fourth section, 8-1 is a superheater, 8-2 is an economizer, and 8-3 is an air preheater.
Detailed Description
The core of the invention is to provide a semi-coke powder circulating fluidized bed boiler based on material heat balance, so that stable combustion of pure semi-coke can be realized, and the burnout rate of semi-coke powder can be effectively improved.
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The semi-coke powder circulating fluidized bed boiler based on material heat balance comprises a boiler body 7 and a tail flue 8, wherein the boiler body 7 is connected with the tail flue 8 through a cyclone separator 6, as shown in figure 1, a fluidized air distribution bed 3 for providing primary air is arranged at the bottom of a hearth of the boiler body 7, the fluidized air distribution bed 3 is connected with a primary air chamber 2, a secondary air distribution device 5 for providing secondary air is also arranged on the side wall of the boiler body 7, a superheater 8-1, an economizer 8-2 and an air preheater 8-3 are sequentially arranged in the tail flue 8 from top to bottom, in the semi-coke powder circulating fluidized bed boiler in the embodiment, the separation efficiency of the cyclone separator 6 is not less than 99.8%, particles captured by the cyclone separator are sent back to the hearth to be re-combusted, the secondary air distribution device 5 is provided with an upper secondary air port and a lower secondary air port, the furnace of the boiler body 7 is divided into a first section 7-1, a second section 7-2, a third section 7-3 and a fourth section 7-4, please refer to fig. 1:
a first section 7-1 is formed by a section between the fluidized air distribution bed 3 and the lower secondary tuyere in the hearth, the height of the first section 7-1 is in a range of 3.8 m-4.3 m (including two end values), the average fluidization speed in the first section 7-1 is 4.0 m/s-4.5 m/s (including two end values), the first section 7-1 is a section in which primary air and semi-coke breeze fuel are subjected to reductive combustion atmosphere, the section can also be called as a reduction zone, and the reductive combustion atmosphere can effectively inhibit the generation of fuel type nitrogen oxides;
a second section 7-2 is formed by a region between 3.5m and 4.0m (including two end values) upward of the lower secondary air inlet, the second section 7-2 is an oxidation zone, the average fluidization speed in the second section 7-2 is 4.5m/s to 5.2m/s (including two end values), secondary air enters a hearth from the second section, and the second section 7-2 is enabled to reach an oxidative combustion atmosphere;
the third section 7-3 is formed by extending the top of the second section 7-2 upwards by 3.0 m-3.5 m (including two end values), the third section 7-3 is a stable combustion zone, and the superficial fluidization velocity in the third section 7-3 is 4.0 m/s-4.5 m/s;
the section between the top of the third section 7-3 and the flue gas outlet of the boiler body 7 forms a fourth section 7-4, the superficial fluidization velocity of the fourth section 7-4 is 4.5 m/s-5.0 m/s, and the fourth section 7-4 is a main heat transfer zone.
In the semi-coke powder circulating fluidized bed boiler disclosed in the above embodiment, the inner walls of the boiler in the first section 7-1, the second section 7-2 and the third section 7-3 are all covered with a refractory layer, and the fourth section 7-4 is a main heat transfer area, so that the membrane wall in the fourth section 7-4 is a fully-naked membrane wall which is not covered with the refractory layer, and flue gas carries high-concentration fine particle materials to transfer heat through radiation or contact.
Actually, the semi-coke powder circulating fluidized bed boiler based on material heat balance disclosed in the above embodiment adopts a material heat balance measure, the furnace chamber is divided into a first section 7-1, a second section 7-2, a third section 7-3 and a fourth section 7-4 from bottom to top, and in the first section 7-1, semi-coke and primary air are combusted in a reducing atmosphere, so that not only can the over-high temperature in the boiler be inhibited, but also the generation of nitrogen oxides in the boiler can be effectively reduced; in the second section 7-2, secondary air and semi-coke powder are combusted in oxidizing atmosphere; the third section 7-3 belongs to the intensified stable combustion stage; the fourth section 7-4 belongs to a heat release area, and fine materials carried by the flue gas transfer heat to the exposed membrane wall through radiation or contact; the reasonable design of the height of each section is matched with the timely distribution of primary air and secondary air, so that the burning heat of semi-coke powder can be reasonably and uniformly released step by step, ideal staged burning is realized, the over-high or over-low local temperature in a hearth is effectively avoided, coking in the furnace is prevented, the heat is efficiently utilized by a water-cooled wall, and the heat balance is achieved;
meanwhile, the reasonable design of the height of each section can effectively prolong the combustion time in the furnace of the semi-coke powder, and the high-efficiency cyclone separator with the separation efficiency of more than 99.8% is matched to re-send almost all unburned carbon particles into the hearth for secondary combustion, so that on one hand, large-flow material circulation in the furnace can be established, the material circulation rate is improved, on the other hand, the high-concentration ash content level in the furnace can be achieved, and finally, the balance between materials and heat in the furnace is realized, not only is the low-nitrogen full combustion of the semi-coke powder realized, but also the semi-coke powder has considerable burn-off rate on the premise of effectively reducing the fly ash content of the semi-coke powder.
Referring to fig. 1, in the semi-coke dust circulating fluidized bed boiler based on material heat balance disclosed in this embodiment, the bottom of the boiler body 7 is a funnel area, the small end of the funnel area faces downward, the large end of the funnel area is connected with an expansion joint with one end used for expanding the cross sectional area of the furnace, the upper section of the furnace is connected above the expansion joint, the cross sectional area of the expansion joint is not smaller than the cross sectional area of the large end of the funnel area, and the cross sectional area of the expansion joint is 1.05 to 1.15 times of the cross sectional area of the upper section of the furnace, the middle lower part of the funnel area forms a first section 7-1, the middle upper part of the funnel area forms a second section 7-2, the expansion joint forms a third section 7-3, the upper section of the furnace forms a fourth section 7-4, and by means of the structural design, the third section 7-3 forms an expansion region, the expansion area enables the flow velocity of the smoke gas flowing out of the second section 7-2 to tend to be stable, so that a stable combustion area is formed in the third section 7-3, the stable combustion area is beneficial to prolonging the combustion time of the fuel in the hearth, and the burnout rate of the semi-coke powder is improved on the premise of staged combustion of the fuel and staged and reasonable release of heat.
It should be noted that, according to the sizes of the first section 7-1 and the second section 7-2, those skilled in the art can know that the heights of the first section 7-1 and the second section 7-2 are substantially equal, and the middle upper portion of the funnel region refers to a position above the midpoint in the height direction of the funnel region, or a position above the substantially midpoint in the height direction; the lower-middle portion of the funnel region means a position below the midpoint in the height direction of the funnel region, or a position substantially below the midpoint in the height direction.
Preferably, the distance between the upper secondary air port and the lower secondary air port is 0.7-1.0 m, the primary air accounts for 32-40% (including two end values) of the total air supply of the hearth, the secondary air accounts for 60-68% (including two end values) of the total air supply of the hearth, the fluidized air distribution bed 3 is of a low-wind-resistance and small-wind-quantity structure, the area of the fluidized air distribution bed 3 is 35-38% of the cross-sectional area of the upper section of the hearth, the bed-surface combustion share of the semi-coke powder accounts for 30-35%, the air distribution resistance of the fluidized air distribution bed 3 is 2000-2800 Pa, the secondary air distribution devices 5 are arranged on the front wall and the rear wall of the boiler body 7, the primary air and the secondary air are supplied in proper positions to enable the semi-coke powder to be completely combusted in a graded manner, the upper secondary air port and the lower secondary air port are horn ports with small ends facing the hearth, the included angle between the horn ports and the horizontal plane, the furnace entering air speed of the secondary air is larger than the critical furnace entering air speed, and the critical furnace entering air speed is 70-75 m/s.
As is well known to those skilled in the art, the flow rate of flue gas in a hearth of a boiler greatly changes under high load and low load, so that the fuel can be subjected to oxygen-enriched combustion at a proper position only by properly changing the feeding position of secondary air according to the load condition of the boiler; when the load of the boiler is lower than the critical load, the second opening and closing mechanism opens the secondary air port at the lower layer, and the first opening and closing mechanism closes the secondary air port at the upper layer, namely, only the secondary air port at the lower layer supplies secondary air at the low load, wherein the critical load is 55-60% of the rated load of the boiler.
Through adjusting the position of going into the stove to the overgrate air, not only can make the fuel release the heat step by step through the staged combustion, can also effectively restrain the formation of nitrogen oxide and sulphide simultaneously, improve fume emission's cleanliness factor.
Referring to fig. 1, the material returning port of the cyclone separator 6 is connected to the first section 7-1 of the furnace through a material returning device and a material returning pipe 10, wherein the material returning device has high air pressure (20 kPa-30 kPa) and low flow rate(10m3/min-18m3Min), wherein the self-balancing material returning device 11 comprises a material returning bed, the material returning bed is provided with a lubricating area communicated with a material returning port of the cyclone separator 6 and a material returning area communicated with the first section 7-1, a lubricating air cap is arranged in the lubricating area, a material returning air cap is arranged in the material returning area, and the lubricating air introduced into the lubricating area and the material returning air introduced into the material returning area are matched according to the ratio of 1:3 to ensure that the lubricating air can provide sliding kinetic energy for circulating materials, and the materials are smoothly pushed into the first section 7-1 of the hearth through the material returning air.
Further, the cyclone separator 6 specifically comprises a cylinder 6-3, a cone 6-4, a central cylinder 6-2 and a vertical pipe 6-5, a smoke inlet 6-1 communicated with the upper part of the hearth is arranged on the side surface of the cylinder 6-3, the smoke inlet 6-1 is usually rectangular, the width of the smoke inlet 6-1 is 0.7 m-1.0 m (namely the span size of the smoke inlet in the horizontal direction), the smoke flow rate at the smoke inlet 6-1 is adjusted to be 30 m/s-38 m/s through the height of the smoke inlet 6-1 (namely the span size of the smoke inlet in the vertical direction), a smoke outlet communicated with the tail flue 8 is arranged at the top of the cylinder 6-3, the smoke flow rate in the cylinder 6-3 is 4.0 m/s-5.0 m/s, the diameter of the cylinder 6-3 is determined by the flow rate, the height of the cylinder 6-3 is 1.3-1.5 times of the diameter of the cylinder;
the cone 6-4 is arranged at the lower end of the cylinder 6-3, the large end of the cone 6-4 is connected with the cylinder 6-3, and the height of the cone 6-4 is 1.6-1.9 times of the diameter of the cylinder, preferably 1.85 times of the diameter of the cylinder; the central cylinder 6-2 penetrates through the smoke exhaust port, the diameter of the central cylinder 6-2 is determined by the smoke flow velocity of 40m/s of the central cylinder 6-2, and the ratio of the distance of the lower end of the central cylinder 6-2 embedded into the cylinder 6-3 to the height of the smoke inlet 6-1 is 0.4-0.5, preferably 0.42; the riser 6-5 is connected to the small end of the cone, as shown in fig. 1, the diameter of the riser 6-5 is 0.6-0.7 m, the cyclone 6 thus designed has a separation efficiency of not less than 99.8%, and the ash concentration in the upper part of the furnace (fourth zone) is not less than 3kg/Nm3Almost all particles can be captured and sent into the hearth again for burning, so that the circulation rate of the materials is greatly improved, the residence time of the fuel in the hearth is effectively prolonged, and the burnout rate of the semi coke powder is improved.
With continuing reference to fig. 1, the fluidized air distribution bed 3 is formed by extending a rear wall film-type wall forward horizontally, a fluidized air cap is arranged on a connecting plate between two adjacent pipes of the film-type wall, a water-cooling heating surface or an additional heating surface is arranged in a hearth according to needs, the ignition burner 1 is arranged at the rear part of the fluidized air distribution bed 3, is hung on a steel beam above the boiler body 7 through a spring hanger and freely expands downwards together with the hearth, the primary air chamber 2 is formed by extending the rear wall film-type wall horizontally and enclosing the film-type walls at two sides, a plurality of slag discharging pipes 9 are arranged on the fluidized air distribution bed 3, and the slag discharging pipes 9 pass through the primary air chamber 2 and realize wall-penetrating sealing and free expansion through metal expansion joints.
The fuel supply device 4 is arranged on the front wall of the hearth, and the fuel supply device 4 is connected with a plurality of blanking pipes (2 and 3 for example), and the fuel uniformly falls into the first section 7-1 of the hearth from the blanking pipes for oxygen-deficient combustion.
The air preheater 8-3 in the back flue 8 is made of an internally threaded pipe, and the air preheater 8-3 is horizontally disposed at the lower portion of the back flue 8.
The semi-coke powder circulating fluidized bed boiler disclosed in the above embodiment realizes stable combustion of pure semi-coke and achieves a high burnout rate mainly based on the following technical measures:
the material heat balance measures are taken, high-rate circulation of materials in the furnace is realized through the high-efficiency cyclone separator, the ash amount level with high concentration in the furnace is reached, and by means of reasonable layout of positions of primary air and secondary air in the hearth and subdivision of one to four sections in the hearth, staged combustion of semi-coke powder and gradual release of heat are realized, and the generation of a local overtemperature phenomenon is controlled; compared with a coal-fired boiler with the same tonnage, the height of the boiler is integrally increased, so that the burning time of the semi-coke powder in a hearth is prolonged, three basic elements of the temperature, the oxygen amount and the burning time of the semi-coke powder are guaranteed, and the balance of materials and heat in the boiler is realized;
the heat medium strengthening measures are that the average gray scale in the whole hearth reaches 10kg/Nm by means of the fluidized bed and the efficient cyclone separator through the internal circulation and the external circulation of the hearth3Above, effectively strengthen the heat transfer ability of diaphragm type wall in the furnace, reached the heat mediumThe purpose of strengthening;
atmosphere construction measures, namely the semi-coke powder is subjected to staged combustion through reasonable proportion of primary air and secondary air and the air supply position, and the temperature in the furnace can be controlled at a low temperature level of 850-880 ℃ by combining the material return of the cyclone separator and the slag discharge of the slag discharge pipe, so that coking in the furnace is effectively prevented; meanwhile, the high-rate material circulation can actually provide enough unburned carbon, so that the first section is provided with enough reducing agent, the generation of combustion type nitrogen oxides is effectively inhibited, and a low-nitrogen atmosphere is created; in fact, limestone is sprayed into the hearth along with the secondary tuyere, limestone powder has proper temperature to desulfurize flue gas at the position, and meanwhile, the utilization rate of the limestone powder is improved due to high-rate material circulation, so that a proper desulfurization atmosphere is created in the section.
The semi-coke powder circulating fluidized bed boiler based on material heat balance realizes stable combustion of pure semi-coke powder, the boiler operates safely, reliably and stably, the thermal efficiency of the boiler is not lower than 91%, and the emission of original nitrogen oxides in flue gas is lower than 100mg/Nm3Emission, original SO of flue gas2And (4) near zero emission.
Operation case one
The semi-coke powder circulating fluidized bed hot water boiler with the model number of QXF116-1.6/130/70 (the heat supply amount is 116MW, the working pressure is 1.6MPa, the water outlet temperature is 130 ℃ and the water return temperature is 70 ℃), the rated load is 116MW, the rated water outlet temperature is 130 ℃ and the rated water return temperature is 70 ℃, semi-coke powder is used as fuel, a hearth is designed according to the reasonable section height, the first section height is 4 meters, the second section height is 3.5 meters, the third section height is 3.5 meters, the fourth section height is 22.5 meters, primary air accounts for 35 percent of the total air volume, secondary air accounts for 65 percent of the total air volume, and graded low-nitrogen combustion is realized.
In addition, the high-efficiency cyclone separator ensures that high-concentration materials exist in the hearth, the ash concentration in the hearth is higher than 3kg/Nm3, and high air pressure (25kPa) and small flow rate (15 m) are adopted3Min) the self-balancing material returning device returns the circulating material to the hearth.
The boiler operates stably, the temperature field in the hearth is balanced at 880 ℃, and the material layer resistance is 6.5 kPa-7.0 kPa; the hearth differential pressure is 1200Pa, so that the over-high or over-low local temperature in the hearth is effectively avoided, and the combustion and heat transfer of the boiler are ensured; the arrangement of the tail coal economizer and the air preheater is reasonable, the exhaust gas temperature is 122 ℃, and the thermal efficiency of the boiler reaches 92%.
The high-efficiency cyclone separator with the separation efficiency of more than 99.8 percent establishes large-flow material circulation in a hearth, the temperature in the hearth is 880 ℃, and the oxygen content is 3 percent; a desulfurization and denitrification atmosphere is created; limestone is added into the furnace for desulfurization, so that the utilization rate of the limestone is improved. 70mg/Nm of original emission amount of nitrogen oxides in flue gas3Original SO of flue gas2Discharge amount of 3mg/Nm3。
Operation case two
130t/h semi-coke powder circulating fluidized bed boiler with rated load of 130t/h and rated pressure of 9.8MPa, wherein the hearth is designed according to the height of a reasonable section, the height of a first section is 7-1 and 4.2 meters, the height of a second section is 3.8 meters, the height of a third section is 7-3 and 3.5 meters, the height of a fourth section is 7-4 and 23.5 meters, and the area of a fluidized air distribution bed is 12m2The sectional area of the upper section of the hearth is 32.2m2The fluidized air distribution bed accounts for 37.3 percent of the area of the section of the upper hearth, the primary air accounts for 32 percent of the total air volume, and the secondary air accounts for 68 percent of the total air volume, so that the low-nitrogen staged combustion is realized.
The secondary air is arranged in two layers, the first section of the hearth is below the lower secondary air, the upper secondary air is arranged at a position 0.7m above the lower secondary air, the upper secondary air and the lower secondary air are adjusted in real time according to the height of the load, and the wind speed of the secondary air is 80 m/s. In order to improve the separation efficiency, 2 high-efficiency separators with the diameter of 5400mm are designed for the boiler, the separation efficiency of the cyclone separator is more than 99.8 percent, the ash concentration in a hearth reaches 5kg/Nm3, and high air pressure (30kPa) and small flow rate (18 m)3Min) the self-balancing material returning device returns the circulating material to the hearth.
The boiler operates stably, the temperature field in the hearth is balanced at 870 ℃, and the resistance of the material layer is 6.5 kPa-7.0 kPa; the hearth differential pressure is 1500Pa, so that the combustion and heat transfer of the boiler are ensured; the tail part is sequentially provided with a superheater, an economizer and an air preheater from top to bottom, and the exhaust gas temperature is 128 ℃; the heat efficiency of the boiler reaches 91.6 percent.
Adopts high-efficiency cyclone separation with separation efficiency of more than 99.8 percentSeparating from the device, establishing large-flow material circulation in the hearth, wherein the temperature in the hearth is 870 ℃, and the oxygen content is 3%; a desulfurization and denitrification atmosphere is created; limestone is added into the furnace for desulfurization, so that the utilization rate of the limestone is improved. The original nitrogen oxide in the flue gas is lower than 80mg/Nm3Emission, original SO of flue gas2And (4) near zero emission.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (10)
1. A semi-coke powder circulating fluidized bed boiler based on material heat balance comprises a boiler body and a tail flue, wherein the boiler body is connected with the tail flue through a cyclone separator, a fluidized air distribution bed for providing primary air is arranged at the bottom of the boiler body, and a secondary air distribution device for providing secondary air is arranged on the side wall of the boiler body, and is characterized in that the separation efficiency of the cyclone separator is not less than 99.8 percent, the secondary air distribution device is provided with an upper secondary air port and a lower secondary air port, a hearth of the boiler body is divided into a first section, a second section, a third section and a fourth section, wherein,
the first section is formed by a section between the fluidization air distribution bed and the lower-layer secondary air port, the height of the first section is 3.8-4.3 m, the inner wall of the boiler in the first section is covered with a fire-resistant layer, and the average fluidization speed in the section lower than the first section is 4.0-4.5 m/s;
the second section is formed by a section of the lower secondary air port which is 3.5-4.0 m upward, and a fire-resistant layer covers the inner wall of the boiler in the second section;
the top of the second section extends upwards for 3.0-3.5 m to form a third section, the average fluidization speed of the third section is 4.0-4.5 m/s, and the inner wall of the boiler in the third section is covered with a refractory layer;
the fourth section is formed by a section between the top of the third section and the flue gas outlet of the boiler body, the average fluidization speed of the fourth section is 4.5-5.0 m/s, and all membrane walls in the fourth section are exposed.
2. The semi-coke pulverized-coal circulating fluidized bed boiler based on the material-heat balance as claimed in claim 1, wherein the bottom of the boiler body is a funnel area with a downward small end, the large end of the funnel area is connected with an expansion joint for expanding the cross section of the furnace, an upper section of the furnace is connected above the expansion joint, wherein the middle lower part of the funnel area constitutes the first section, the middle upper part of the funnel area constitutes the second section, the expansion joint constitutes the third section, the upper section of the furnace constitutes the fourth section, the cross sectional area of the expansion joint is not less than the cross sectional area of the large end of the funnel area, and the cross sectional area of the expansion joint is 1.05-1.15 times the cross sectional area of the upper section of the furnace.
3. The semi-coke powder circulating fluidized bed boiler based on the material heat balance as claimed in claim 1, wherein the distance between the upper layer secondary air port and the lower layer secondary air port is 0.7 m-1.0 m, the primary air accounts for 32% -40% of the total air supply of the hearth, and the secondary air accounts for 60% -68% of the total air supply of the hearth.
4. The semi-coke powder circulating fluidized bed boiler based on the material heat balance as claimed in claim 3, wherein the fluidized air distribution bed has an area of 35-38% of the cross-sectional area of the upper section of the furnace chamber, the bed surface combustion share of the semi-coke powder accounts for 30-35%, the air distribution resistance of the fluidized air distribution bed is 2000Pa-2800Pa, the upper layer air port and the lower layer air port are both bell mouths with small ends facing the furnace chamber, the included angle between the bell mouth and the horizontal plane is 10-15 °, and the secondary air inlet speed is greater than the critical inlet speed, wherein the critical inlet speed is 70-75 m/s.
5. The semi-coke powder circulating fluidized bed boiler based on the material heat balance is characterized by further comprising a first opening and closing mechanism for opening and closing the upper-layer secondary air port and a second opening and closing mechanism for opening and closing the lower-layer secondary air port, wherein when the boiler load is higher than the critical load, the second opening and closing mechanism closes the lower-layer secondary air port, and the first opening and closing mechanism opens the upper-layer secondary air port; when the boiler load is lower than the critical load, the second opening and closing mechanism opens the lower-layer secondary air opening, and the first opening and closing mechanism closes the upper-layer secondary air opening, wherein the critical load is 55% -60% of the rated load of the boiler.
6. The semi-coke powder circulating fluidized bed boiler based on the material heat balance as claimed in claim 1, wherein the material return port of the cyclone separator is communicated with the first section of the furnace through a self-balancing material return device, the self-balancing material return device comprises a material return bed, the material return bed is provided with a lubricating area communicated with the material return port of the cyclone separator and a material return area communicated with the first section, lubricating air is introduced into the lubricating area, material return air is introduced into the material return area, and the ratio of the lubricating air to the material return air is 1: 3.
7. The semi-coke powder circulating fluidized bed boiler based on the material heat balance as claimed in claim 1, wherein the cyclone comprises:
the furnace comprises a cylinder body, wherein a smoke inlet communicated with the upper part of the furnace is formed in the side surface of the cylinder body, the width of the smoke inlet is 0.7-1.0 m, the flow rate of smoke at the smoke inlet is 30-38 m/s, a smoke outlet communicated with the tail flue is formed in the top of the cylinder body, the flow rate of smoke in the cylinder body is 4.0-5.0 m/s, and the ratio of the height of the cylinder body to the diameter of the cylinder body is 1.3-1.5;
the cone is arranged at the lower end of the cylinder, the large end of the cone is connected with the cylinder, and the ratio of the height of the cone to the diameter of the cylinder is 1.6-1.9;
the central cylinder penetrates through the smoke exhaust port, the flow velocity of smoke in the central cylinder is 40m/s, and the ratio of the distance between the lower end of the central cylinder and the lower end of the central cylinder, which is embedded into the cylinder, to the height of the smoke inlet is 0.4-0.5;
the diameter of the vertical pipe is 0.6-0.7 m.
8. The semi-coke powder circulating fluidized bed boiler based on material heat balance as claimed in claim 1, characterized in that the fluidized air distribution bed is formed by a rear wall membrane wall extending horizontally forward, and a fluidizing air cap is arranged on a connecting plate between two adjacent pipes of the membrane wall.
9. The semi-coke powder circulating fluidized bed boiler based on the material heat balance as claimed in claim 8, characterized in that a plurality of slag discharging pipes are arranged on the fluidized air distribution bed, and the slag discharging pipes pass through the primary air chamber and realize the sealing and free expansion of the through wall through metal expansion joints.
10. The semi-coke powder circulating fluidized bed boiler based on the material heat balance as claimed in any one of claims 1 to 9, characterized in that the combustion temperature of the hearth of the boiler is 850 ℃ to 880 ℃.
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