CN110260646B

CN110260646B - Cylindrical lime shaft kiln with flue gas backflow premixed combustion forward and backward flow comprehensive heat transfer

Info

Publication number: CN110260646B
Application number: CN201910435365.XA
Authority: CN
Inventors: 陈维汉; 陈云鹤; 杨海涛; 张佳鹏
Original assignee: Zhengzhou Fuding Thermal Technology Co ltd
Current assignee: Zhengzhou Fuding Thermal Technology Co ltd
Priority date: 2019-05-23
Filing date: 2019-05-23
Publication date: 2020-07-31
Anticipated expiration: 2039-05-23
Also published as: CN110260646A

Abstract

The invention relates to a concurrent and countercurrent comprehensive heat transfer cylindrical lime shaft kiln with flue gas backflow premixed combustion, which effectively solves the problems of realizing premixed combustion, and improving the utilization rate of coal gas by performing concurrent and countercurrent bidirectional heating decomposition on limestone by combustion flue gas. The upper part of the kiln chamber is provided with a feeding cone, the center of the lower part of the kiln chamber is provided with a discharging guide cone, the periphery of the lower part of the kiln chamber is provided with a lime blanking bin and a lime discharge pipe which are connected into a whole, the middle part of the kiln chamber is provided with a sleeve burner which is formed by sleeving an inner cylinder and an outer cylinder, an air distribution loop is formed between the two cylinders, the front part of one end of the lime blanking bin is contracted into an air outlet, an air inlet pipe is vertically connected to the outer cylinder wall of the sleeve burner, a gas inlet pipe is communicated with the sleeve burner and a gas outlet; a backflow flue gas inlet pipe is arranged below a gas nozzle on the inner wall of the mixed gas combustion chamber, the backflow flue gas inlet pipe is communicated with a backflow flue gas loop, a backflow flue gas distribution loop and a mixed gas injection channel, and a cooling air mixing chamber is arranged at the lower part of a lime kiln cylinder body.

Description

Cylindrical lime shaft kiln with flue gas backflow premixed combustion forward and backward flow comprehensive heat transfer

Technical Field

The invention relates to a lime calcining kiln, in particular to a cylindrical lime shaft kiln with flue gas backflow premixed combustion forward and backward flow comprehensive heat transfer for calcining lime based on gas fuel premixed combustion, limestone moving calcination decomposition and airflow flow and heat transfer direction adjustment.

Background

In the field of industrial application, the calcination of limestone into quick lime is a common industrial process, and a lime kiln is a thermal device arranged for completing the process. Depending on the type of calcination, differences in the kiln type structure, variations in the fuel and combustion modes, differences in the performance index of the burnt lime, and the like, the lime kiln type is generally selected according to the use of the lime. At present, the most used limekilns can be divided into a shaft kiln, a rotary kiln, a double-hearth kiln and a sleeve kiln according to the structural characteristics, and can be divided into a mixed combustion limekiln (solid fuel) and a gas combustion limekiln (gas fuel) according to the combustion fuel. With the increasing stricter environmental requirements, the mixed-combustion lime kiln becomes an object to be eliminated, and the gas-combustion lime kiln gradually becomes a mainstream kiln type for lime calcination.

In fact, it is most suitable to be realized by the high temperature flue gas flow with proper heating intensity and proper temperature during the decomposition process of limestone (soft burning), not to be realized in the combustion process, and not to be realized by high intensity heating (hard burning). Practice shows that in the process of heating limestone by flowing flue gas, limestone particles gradually reach proper high temperature to decompose, release carbon dioxide, and decompose at the flue gas temperature of 900-1100 ℃ to obtain better effects, such as high calcium oxide content (low overburning rate), good lime activity (soft burning) and the like. In fact, it is not easy to do this, especially in the kiln-type structures of the various limekilns mentioned above, it is difficult to achieve the above requirements in the determined fluid flow, combustion and heat transfer manners. Therefore, based on the lime decomposition mechanism, starting from the combustion, flow and heat transfer principles of lime kiln fluid, the search for a new kiln type structure becomes the main direction of lime kiln technical innovation. Therefore, on the basis of summarizing the structural characteristics and the operation practice of the lime kiln, a cylindrical lime shaft kiln which can realize premixed combustion and can realize the forward-reverse flow bidirectional heating decomposition of limestone by combustion flue gas is developed, but no public report is found so far.

Disclosure of Invention

In view of the above situation, in order to overcome the defects of the prior art, the invention aims to provide a concurrent and countercurrent comprehensive heat transfer cylindrical lime shaft kiln with flue gas backflow premixed combustion, which can effectively solve the problems of realization of premixed combustion, concurrent and countercurrent bidirectional heating decomposition of limestone by combustion flue gas, improvement of gas utilization rate, energy saving and environmental protection.

The technical scheme includes that the lime shaft kiln with the flue gas backflow premixed combustion forward-reverse flow comprehensive heat transfer comprises a lime kiln cylinder, a kiln chamber, a feeding conical cylinder, a flue gas outlet pipe, a lime discharge pipe, a sleeve burner, a gas inlet, an air inlet pipe, an air distribution loop, a backflow flue gas inlet pipe, a mixed gas combustion chamber, a gas ejection port, a discharge diversion cone and a lime blanking chamber, wherein the kiln chamber is an internal space surrounded by a circular lime kiln cylinder; the lime kiln comprises a lime kiln cylinder, wherein a plurality of sleeve combustors formed by coaxially sleeving an inner cylinder and an outer cylinder are arranged in the middle of the lime kiln cylinder along the circumferential direction, a space between the two cylinders forms an air distribution loop, one end, far away from the lime kiln cylinder, is closed, the front part of the other end of the lime kiln cylinder is contracted into an air outlet, an air inlet pipe is vertically connected to the outer cylinder wall of the sleeve combustor and communicated with the air distribution loop, a gas inlet pipe is communicated with the inner cylinder of the sleeve combustor, the front part of the inner cylinder is a contracted gas outlet, and one end of the sleeve combustor with the gas outlet and the air outlet is correspondingly communicated with a plurality of mixed gas injection channels along; the mixed gas injection channels are communicated with corresponding mixed gas combustion chambers which are uniformly distributed in the horizontal circumferential direction, the mixed gas combustion chambers are arranged in the lime kiln cylinder body and are separated and separated by the mixed gas combustion chambers, and a plurality of gas nozzles are uniformly distributed on the inner wall of each mixed gas combustion chamber along the circumferential direction and are used for communicating the kiln chamber; a plurality of backflow flue gas introducing pipes communicated with the kiln chamber are uniformly arranged in the lime kiln cylinder below the gas nozzle along the circumferential direction, the other end of the backflow flue gas introducing pipe is communicated with the backflow flue gas loop, is further communicated with the backflow flue gas distribution loop upwards, and is connected with the mixed gas injection channel through a backflow flue gas jet port; a plurality of cooling air mixing chambers (also called air distribution chambers, the same below) which are circumferentially arranged are arranged in the lower wall body of the lime kiln cylinder body, the cooling air mixing chambers are separated by the mixing chambers, the outer wall body of the cooling air mixing chamber is communicated with a cooling air inlet pipe, and cooling air nozzles communicated with the kiln chamber are arranged in the circumferential direction of the inner wall body of the cooling air mixing chamber; the annular bottom of the kiln chamber is uniformly provided with a contracted blanking pipe orifice with a rectangular cross section along the circumferential direction and is communicated with a lime blanking bin contracted in an inverted cone shape, and the lower part of the lime blanking bin is downwards connected with a lime discharge pipe at a contraction port; the upper part of the lime kiln cylinder body is a feeding conical cylinder which is tapered and contracted, the periphery of the upper part of the feeding conical cylinder is provided with a flue gas outlet pipe and a limestone feed inlet which are connected into a whole, and a distribution conical group is arranged in the feeding conical cylinder.

The invention has novel and unique structure, effectively improves the activity of the burnt lime, effectively reduces the over-burning rate of lime products, can control the combustion process on the basis of improving the utilization rate of gas, has simple structure, excellent performance, convenient control, energy conservation, high efficiency and low investment cost, and has obvious competitive advantage and wide market prospect compared with the traditional double-chamber lime kiln and sleeve lime kiln.

Drawings

FIG. 1 is a cross-sectional front view of the structure of the present invention.

Fig. 2 is a plan view of the structure of the present invention (cut away from the gas ejection port).

FIG. 3 is a top view of the structure of the present invention (taken from the cooling air inlet duct).

Detailed Description

The following detailed description of embodiments of the invention refers to the accompanying drawings.

As shown in fig. 1, fig. 2 and fig. 3, the invention relates to a lime shaft kiln with flue gas backflow premixed combustion forward and backward flow comprehensive heat transfer cylinder, which comprises a lime kiln cylinder 1, a kiln chamber 2, a feeding cone cylinder 3, a flue gas outlet pipe 3-1, a lime discharge outlet pipe 5, a sleeve burner 6, a gas inlet 7, an air inlet pipe 8, an air distribution loop 8-1, a backflow flue gas inlet pipe 9, a mixed gas combustion chamber 10, a gas ejection port 11, a discharge guide cone 15 and a lime blanking bin 16, wherein the kiln chamber 2 is an internal space enclosed by the circular lime kiln cylinder 1, the upper part of the kiln chamber 2 is the feeding cone cylinder 3 which is connected into a whole, the center of the lower part is provided with the discharge guide cone 15, the periphery of the discharge guide cone 15 is provided with a blanking pipe opening 4 which is connected into a whole, and the periphery of the lower part of the lime kiln cylinder 1 is provided with the lime blanking bin; a plurality of sleeve combustors 6 formed by coaxially sleeving an inner cylinder and an outer cylinder are arranged in the middle of a lime kiln cylinder 1 along the circumferential direction, the space between the two cylinders forms an air distribution loop 8-1, one end far away from the lime kiln cylinder 1 is closed, the front part of the other end is contracted into an air outlet 8-2, the air inlet pipe 8 is vertically connected to the outer cylinder wall of the sleeve combustor 6 and communicated with the air distribution loop 8-1, a gas inlet pipe 7 is communicated with the inner cylinder of the sleeve combustor 6, the front part of the inner cylinder is a contracted gas outlet 7-1, and one end of the sleeve combustor 6 with the gas outlet 7-1 and the air outlet 8-2 is correspondingly communicated with a plurality of mixed gas injection channels 6-1 along the middle of the lime kiln cylinder; the mixed gas injection channel 6-1 is communicated with corresponding mixed gas combustion chambers 10 which are uniformly distributed in the horizontal circumferential direction, the mixed gas combustion chambers 10 are arranged in the lime kiln cylinder body and are separated by the mixed gas combustion chamber partition 10-1, and a plurality of gas nozzles 11 are uniformly distributed on the inner wall of each mixed gas combustion chamber 10 along the circumferential direction and are used for communicating the kiln chamber 2; a plurality of backflow flue gas introducing pipes 9 communicated with the kiln chamber 2 are uniformly arranged in the lime kiln cylinder 1 below the gas nozzle 11 along the circumferential direction, the other end of the backflow flue gas introducing pipe 9 is communicated with a backflow flue gas loop 9-1, is further communicated with a backflow flue gas distribution loop 6-3 upwards, and is connected with a mixed gas injection channel 6-1 through a backflow flue gas jet 6-2; a plurality of cooling air mixing chambers (also called air distribution chambers, the same below) 13 which are arranged in the circumferential direction are arranged in the lower wall body of the lime kiln cylinder 1, the cooling air mixing chambers 13 are separated by mixing chamber partitions 13-1, the outer wall body of each cooling air mixing chamber 13 is communicated with a cooling air inlet pipe 12, and cooling air nozzles 14 communicated with the kiln chamber 2 are arranged in the circumferential direction of the inner wall of each cooling air mixing chamber 13; uniformly arranging contracted blanking pipe orifices 4 with rectangular cross sections on the annular bottom of the kiln chamber 2 along the circumferential direction, and communicating with a lime blanking bin 16 contracted in an inverted cone shape, wherein the lower part of the lime blanking bin 16 is downwards connected with a lime discharge pipe 5 at the contraction opening; the upper part of the lime kiln cylinder body is provided with a feeding cone cylinder 3 which is tapered and contracted, the periphery of the upper part of the feeding cone cylinder 3 is provided with a flue gas outlet pipe 3-1 and a limestone feed inlet which are connected into a whole, and a distribution cone group 3-2 is arranged in the feeding cone cylinder 3.

The lime kiln barrel 1, the feeding conical barrel 3 and the flue gas outlet pipe 3-1 which are connected in a shrinkage mode at the upper portion, the lime discharging outlet pipe 5 at the lower portion and the lime blanking bin 16 formed by conical shrinkage at the lower portion are all formed by welding heat-resistant steel plates, and fire-resistant spraying layers are arranged on the inner wall surfaces of the lime kiln barrel 1.

The lime kiln barrel 1 is also internally provided with heavy load-bearing bricks and light insulating bricks 1-1 which are high temperature resistant, and the space in the heavy load-bearing bricks forms a kiln chamber 2.

The gas nozzles 11 are a plurality of rectangular or circular channels which are uniformly distributed along the horizontal circumference of the lime kiln cylinder 1 and are communicated with the kiln chamber 2, the channels are in a structural form with gradually enlarged cross sections, and the gas nozzles are gradually enlarged along the cross section of the kiln chamber 2 to form a downward spraying state when being discharged.

One end of the backflow flue gas inlet pipe 9 is communicated with the kiln chamber 2 and is the same as the structure of the fuel gas jet port 11, while the other end is communicated with the backflow flue gas loop 9-1, is further communicated with the backflow flue gas distribution loop 6-3 upwards, and is connected with the mixed gas jet channel 6-1 through the backflow flue gas jet port 6-2.

The backflow flue gas ejection port 6-2 is a multi-nozzle structure which is uniformly distributed along the circumferential direction and surrounds the narrowest part of the mixed gas ejection channel 6-1, the cross section of the nozzle is rectangular or circular, and the ejection direction is radial or has a certain inclination angle with the radial direction.

The material distribution cone group 3-2 is a member formed by combining a cone and an annular cone which are arranged up and down, and is made of heat-resistant and wear-resistant metal materials.

The lime blanking pipe mouth 4 is arranged on the annular bottom of the kiln chamber 2, is circumferentially and uniformly arranged with a contraction-shaped opening with a rectangular cross section, is formed by welding wear-resistant steel, and the lower part of the lime blanking pipe mouth is a lime blanking bin 16.

When the lime kiln is implemented, the gas consumption of the lime kiln is 15000m³H, air quantity primary air 10500 m³H, 4500 m cooling air³The sleeve combustor 6, the air inlet pipe 8 and the cooling air inlet pipe 12 are uniformly distributed and matched with 8 inlet pipes, limestone and burnt lime are fully piled in a hearth from top to bottom, the porosity is 0.34, and a central air flow adjusting channel only passes through air flow; the furnace bottom is closed, 3000Pa outlet pressure is arranged at an outlet, the diameter of a cooling air inlet pipe is 100mm, and the width of a nozzle is 60mm and the height is 77 mm.

Firstly, limestone is filled in a lime kiln chamber 2, then coal gas and primary air are respectively connected from a coal gas inlet pipe 7 and an air inlet pipe 8 of a combustor 6, the coal gas enters a mixer injection channel 6-1 through a coal gas nozzle 7-1, the air also enters the mixer injection channel 6-1 through an air distribution loop 8-1 and an air nozzle 8-2, the coal gas and the air are fully mixed and then enter a mixed gas combustion chamber 10 for preheating combustion, the high-temperature flue gas after combustion is injected into the middle part of the lime kiln chamber 2 through a fuel gas nozzle 11 at the upper part of the mixed gas combustion chamber 10 and then penetrates through a limestone accumulation layer, and then a part of the high-temperature flue gas flows upwards, and a part of the high-temperature flue gas flows downwards under the action of a backflow flue gas introduction; then, relative to the gas nozzle 11, a part of hot flue gas flowing upwards along the kiln chamber is heated and decomposed into limestone, and a part of hot flue gas flowing downwards along the kiln chamber is heated and decomposed into limestone and then enters the return flue gas loop 9-1 through the return flue gas inlet 9; the part of the backflow flue gas can upwards enter a backflow flue gas distribution loop 6-3 which is distributed on the upper part of the backflow flue gas loop along the circumferential direction of the backflow flue gas loop 9-1 and surrounds the mixer injection channel 6-1, the backflow flue gas is injected into the mixer injection channel 6-1 through a backflow flue gas injection port 6-2 distributed on the periphery of the backflow flue gas distribution loop, is fully mixed with the coal gas jet flow and the air jet flow in the channel, and then enters a gas mixing combustion chamber 10 for preheating and combustion, so that the combustion process of controlling temperature and oxygen through the backflow of the flue gas is realized; a cooling air system is also arranged at the lower part of the lime kiln chamber 2, cooling air enters from a cooling air inlet pipe 12, passes through a cooling air distribution chamber 13 and is sprayed into the lime kiln chamber 2 through a cooling air spraying port 14, and the cooling air system has the functions of cooling burnt lime and mixing and burning part of incompletely burnt coal gas; the burnt lime gradually moves downwards and is gradually cooled in the sequential operation process of a lime discharging pipe opening 4 of the lime kiln, the cooled lime is distributed in a ring groove at the bottom of the lime kiln under the action of a lime kiln discharging guide cone 15, and the lime sequentially falls into a lime discharging bin (or called a lime hopper) 16 with a conical contraction structure at the lower part of the lime kiln through the discharging pipe opening 4; the smoke flowing upwards in the kiln chamber 2 of the lime kiln finally enters a lime kiln feeding cone cylinder 3 at the top, and the discharged smoke enters a lime kiln smoke outlet 3-1 through a lime kiln distributing cone combination 3-2 and is discharged outside the kiln body. It can be seen from the implementation process that the uniform constant temperature decomposition of limestone of 950-1100 ℃ is realized by the circumferentially uniform adjustable premixed combustion mode of the combustion device, and the forward and reverse flow combined limestone heating decomposition of limestone and the uniform controllable combustion of high temperature, low oxygen and low nitrogen of the lime kiln combustion device are realized by the aid of the function of injecting flue gas reflux by the combustion device. Therefore, the implementation of the technology can effectively improve the activity of the burnt lime, effectively reduce the over-burning rate of the lime product and realize the control of the combustion process on the basis of improving the utilization rate of the coal gas by 30 percent. The lime kiln with the structure has the advantages of simple structure, excellent performance, convenient control, energy conservation, high efficiency, investment cost saving, energy conservation and environmental protection, obvious competitive advantage and wide market prospect compared with the traditional double-chamber lime kiln and the sleeve lime kiln, and remarkable economic and social benefits, and the investment cost can be saved by more than 40%.

Claims

1. A cylindrical lime shaft kiln with flue gas backflow premixed combustion forward and backward flow comprehensive heat transfer comprises a lime kiln cylinder body (1), a kiln chamber (2), a feeding conical cylinder (3), a flue gas outlet pipe (3-1), a lime discharge pipe (5), a sleeve burner (6), a coal gas inlet (7), an air inlet pipe (8), an air distribution loop (8-1), a backflow flue gas inlet pipe (9), a mixed gas combustion chamber (10), a gas ejection port (11), a discharging diversion cone (15) and a lime blanking bin (16), and is characterized in that the kiln chamber (2) is an internal space enclosed by the circular lime kiln cylinder body (1), the feeding conical cylinder (3) is connected into a whole at the upper part of the kiln chamber (2), the discharging diversion cone (15) is arranged at the center of the lower part, and a discharging pipe orifice (4) is connected into a whole at the periphery of the discharging diversion cone (15), a lime blanking bin (16) and a lime discharge outlet pipe (5) which are connected into a whole are arranged on the periphery of the lower part of the lime kiln cylinder body (1); a plurality of sleeve combustors (6) formed by coaxially sleeving an inner cylinder and an outer cylinder are arranged in the middle of a lime kiln cylinder (1) along the circumferential direction, the space between the two cylinders forms an air distribution loop (8-1), one end far away from the lime kiln cylinder (1) is closed, the front part of the other end is contracted into an air outlet (8-2), an air inlet pipe (8) is vertically connected to the outer cylinder wall of the sleeve combustor (6), communicated with an air distribution loop (8-1), a gas inlet pipe (7) is communicated with an inner cylinder of a sleeve combustor (6), the front part of the inner cylinder is provided with a contracted gas outlet (7-1), one end of a sleeve combustor (6) with a gas jet port (7-1) and an air jet port (8-2) is correspondingly communicated with a plurality of mixed gas jet channels (6-1) along the middle part of the lime kiln cylinder; the mixed gas injection channel (6-1) is communicated with corresponding horizontal circumferential gas mixing combustion chambers (10) which are uniformly distributed, the gas mixing combustion chambers (10) are arranged in the lime kiln cylinder body and are separated from each other by gas mixing combustion chamber partitions (10-1), and a plurality of gas nozzles (11) are uniformly distributed on the inner wall of each gas mixing combustion chamber (10) along the circumferential direction and are used for communicating the kiln chamber (2); the gas nozzles (11) are a plurality of rectangular or circular channels which are uniformly distributed along the horizontal circumference of the lime kiln cylinder body (1) and are communicated with the kiln chamber (2), the channels are in a structural form with gradually enlarged cross sections, and gradually enlarge along the cross section of the kiln chamber (2) to form a downward spraying state when in outlet, a plurality of backflow flue gas introducing pipes (9) communicated with the kiln chamber (2) are uniformly arranged in the lime kiln cylinder body (1) below the gas nozzles (11) along the circumferential direction, the other end of the backflow flue gas introducing pipe (9) is communicated with a backflow flue gas loop (9-1) and then is upwards communicated with a backflow flue gas distribution loop (6-3), and is connected with a mixed gas spraying channel (6-1) through a backflow flue gas spraying port (6-2), the backflow flue gas spraying port (6-2) is a multi-nozzle structure which is uniformly distributed along the circumferential direction and surrounds the narrowest part of the mixed gas spraying channel (6-1), the cross section of the nozzle is rectangular or circular, and the spraying direction is radial or has a certain inclination angle with the radial direction; a plurality of cooling air mixing chambers (13) which are arranged in the circumferential direction are arranged in the lower wall body of the lime kiln cylinder body (1), the cooling air mixing chambers (13) are separated by mixing chamber partitions (13-1), the outer wall body of each cooling air mixing chamber (13) is communicated with a cooling air inlet pipe (12), and cooling air nozzles (14) communicated with the kiln chamber (2) are arranged in the circumferential direction of the inner wall of each cooling air mixing chamber (13); the annular bottom of the kiln chamber (2) is uniformly provided with a contractive blanking pipe orifice (4) with a rectangular cross section along the circumferential direction and is communicated with a lime blanking bin (16) with an inverted cone-shaped contraction, and the lower part of the lime blanking bin (16) is downwards connected with a lime discharge pipe (5) at the contraction opening; the upper part of the lime kiln cylinder body is provided with a feeding conical cylinder (3) which is tapered and contracted, the periphery of the upper part of the feeding conical cylinder (3) is provided with a flue gas outlet pipe (3-1) and a limestone feed inlet which are connected into a whole, and a distribution cone group (3-2) is arranged in the feeding conical cylinder (3).

2. The cylindrical lime shaft kiln with the functions of flue gas backflow premixing combustion forward-reverse flow comprehensive heat transfer according to claim 1, characterized in that a lime kiln cylinder body (1), a feeding conical cylinder (3) and a flue gas outlet pipe (3-1) which are connected in a shrinkage mode at the upper part, a lime discharge pipe (5) at the lower part and a lime blanking bin (16) formed by conical shrinkage at the lower part are all formed by welding heat-resistant steel plates, and the inner wall surfaces of the lime kiln cylinder body and the lime blanking bin are all provided with a fireproof spraying coating.

3. The cylindrical lime shaft kiln with the functions of flue gas backflow, premixed combustion, forward flow and reverse flow comprehensive heat transfer as claimed in claim 1, wherein a heavy load-bearing brick and a light insulating brick (1-1) which are resistant to high temperature are further built in a lime kiln cylinder body (1), and a kiln chamber (2) is formed in the space in the heavy load-bearing brick.

4. The cylindrical lime shaft kiln with flue gas backflow premixed combustion forward and backward flow comprehensive heat transfer as claimed in claim 1, wherein one end of the backflow flue gas introducing pipe (9) is communicated with the kiln chamber (2) and is the same as the structure of the gas jetting port (11), and the other end of the backflow flue gas introducing pipe is communicated with the backflow flue gas loop (9-1), is further communicated with the backflow flue gas distribution loop (6-3) upwards, and is connected with the mixed gas jetting channel (6-1) through the backflow flue gas jetting port (6-2).

5. The vertical lime kiln with flue gas recirculation, premixed combustion, forward flow and reverse flow comprehensive heat transfer as claimed in claim 1, wherein said distribution cone group (3-2) is a member composed of a cone and an annular cone arranged up and down, and is made of heat-resistant and wear-resistant metal material.

6. The cylindrical lime shaft kiln with the functions of flue gas backflow, premixed combustion, forward flow and reverse flow comprehensive heat transfer as claimed in claim 1, wherein the lime blanking pipe orifice (4) is a contraction-shaped opening with a rectangular cross section, is arranged on the annular bottom of the kiln chamber (2), is circumferentially and uniformly arranged, is formed by welding wear-resistant steel materials, and the lower part of the lime blanking pipe orifice is a lime blanking bin (16).