CN113582560B - Method for calcining limestone by using low-calorific-value fuel in double-hearth kiln - Google Patents
Method for calcining limestone by using low-calorific-value fuel in double-hearth kiln Download PDFInfo
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- CN113582560B CN113582560B CN202110809430.8A CN202110809430A CN113582560B CN 113582560 B CN113582560 B CN 113582560B CN 202110809430 A CN202110809430 A CN 202110809430A CN 113582560 B CN113582560 B CN 113582560B
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- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
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Abstract
The invention relates to a method for calcining limestone by using low-calorific-value fuel in a double-hearth kiln. The specific process comprises the following steps: state (1): the kiln chamber A is sprayed with fuel and air to be completely combusted, and the flue gas enters the kiln chamber B to preheat materials. State (2): and injecting fuel and 3-30 (v)% of air into the kiln chamber A for incomplete combustion. And burning in the second calcining area of the kiln chamber B to continuously calcine the materials. State (3): the kiln chamber B is sprayed with fuel and air to be completely combusted, and the flue gas enters the kiln chamber A to preheat materials. State (4): and (3) injecting fuel and 3-30 (v)% of air into the kiln chamber B for incomplete combustion, combusting in a second calcining zone of the kiln chamber A, and continuously calcining the materials. The invention optimizes the process of calcining limestone in the double-hearth kiln, improves the calcining effect, makes full use of low-heat value fuel, saves high-quality fuel and improves the quality of calcined products by controlling the time and calcining in sections through the second calcining zone.
Description
Technical Field
The invention belongs to the technical field of chemical building material production, relates to an industrial furnace, and particularly relates to a method for calcining limestone by using low-calorific-value fuel in a double-hearth furnace.
Background
The double-hearth kiln is also called a double-hearth parallel-flow heat accumulating type lime kiln, and fuel enters from the upper end of a calcining zone and flows in parallel with raw materials. Since the fuel is injected from the upper part of the calcining zone, the raw material can absorb most of the heat released by the fuel. Another important feature of the double-hearth kiln is heat storage, which is used to preheat a portion of the combustion air. The thermal characteristics of co-current calcination and counter-current heat storage determine that the double-hearth kiln has high thermal efficiency, the heat energy consumption is the lowest in all types of lime kilns including rotary kilns, sleeve kilns and the like, and the total heat consumption for producing lime is about 3.8 GJ/ton of lime. The double-hearth kiln has excellent performance in calcining limestone materials with small grain sizes, and the produced lime has good quality.
The calcination requires the burning of fuel in a calcining zone, and the heat is released to heat the calcined material. The decomposition temperature of the limestone is about 900 ℃, and the calcining temperature is generally 1000-1200 ℃. In order to reach the calcination temperature and produce qualified lime, fuel with a heat value above a certain value is needed. The limestone cannot be decomposed when the low-calorific-value fuel cannot reach the required combustion temperature; or the temperature is low, the limestone is not completely decomposed, and the problems of raw burning, poor quality of lime products and the like are caused. In the production process of metallurgical enterprises, a large amount of blast furnace gas is generated and is a valuable fuel resource, the heat value of the blast furnace gas is 3000-3400 kJ/Nm & lt 3 & gt, and the blast furnace gas cannot be directly used for calcining limestone due to low heat value, so that a large amount of low heat value fuel cannot be fully utilized. And high-calorific-value fuel needs to be purchased for lime production, so that resource waste is caused, and economic benefit is influenced.
Disclosure of Invention
The invention aims to provide a method for calcining limestone by using low-calorific-value fuel in a double-hearth kiln, which optimizes the limestone calcining process of the double-hearth kiln, directly uses the low-calorific-value fuel to produce lime, fully utilizes low-calorific-value fuel resources and improves economic benefits.
The invention provides a method for calcining limestone by using low-calorific-value fuel in a double-hearth kiln, which comprises a hearth A and a hearth B, and alternately carries out calcination and heat storage. And the limestone at one side of the calcining zone descends to the calcining zone after being preheated in the preheating zone, and the limestone is calcined by incomplete combustion. And after the calcined flue gas and the cooled lime, high-temperature cooling air flows to a second calcining area of the kiln body on the other side to support combustion and burn completely, and the undecomposed limestone materials are continuously calcined. The calcined flue gas is preheated by the calcining zone and the preheating zone and then flows to a waste gas discharge system through an air inlet and an air-flue gas reversing valve to be discharged. The process of calcining limestone is as follows:
state (1): the inserted fuel burner of the kiln chamber A injects fuel including but not limited to 100 (v)% and feeds combustion air of which the fuel combustion requirement includes but not limited to 100 (v)% through the air inlet and the air outlet to carry out combustion-supporting combustion in the calcining zone. And the flue gas generated by combustion is delivered to the kiln chamber B through the flue gas channel, and preheats limestone materials in the kiln chamber B together with the high-temperature cooling air after lime cooling. And the cooling air volume fed into the kiln chamber A and the kiln chamber B is 3-10 (v)%, including but not limited to the air volume corresponding to fuel combustion. The state (1) is the primary calcination stage of the kiln chamber a and the secondary calcination stage of the kiln chamber B.
State (2): and continuously spraying fuel into the inserted fuel burner of the kiln chamber A, and feeding combustion-supporting air which comprises but is not limited to 3-30 (v)% of fuel combustion requirement through the air inlet and the air outlet for incomplete combustion. And the combustion flue gas enters the kiln chamber B through the flue gas channel, and enters a second calcining area of the kiln chamber B together with the high-temperature cooling air after lime cooling to carry out combustion supporting and complete combustion, and the undecomposed limestone materials are continuously calcined. The cooling air volume of the kiln chamber A is 10-20 (v)% of the air volume corresponding to fuel combustion, the preheated low-heat-value coal gas is further heated, and the cooling air volume sent into the kiln chamber B is 80-90 (v)% of the air volume corresponding to fuel combustion. The state (2) is the main cooling stage of the kiln chamber A and the main heat storage stage of the kiln chamber B.
State (3): the inserted fuel burner of the kiln chamber B sprays fuel, and combustion-supporting air including but not limited to 100 (v)% of fuel combustion requirement is fed through the air inlet and the air outlet to carry out combustion-supporting combustion. The combustion flue gas passes through the flue gas channel to reach the kiln chamber A, and preheats limestone materials in the kiln chamber A together with high-temperature cooling air after lime cooling. And the cooling air volume fed into the kiln chamber A and the kiln chamber B is 3-10 (v)%, including but not limited to the air volume corresponding to fuel combustion. The state (3) is the primary calcination stage of the kiln chamber B and the secondary calcination stage of the kiln chamber A.
State (4): and injecting fuel into an inserted fuel burner of the kiln chamber B, and feeding combustion-supporting air which comprises but is not limited to 3-30 (v)% of fuel combustion requirement through an air inlet and an air outlet to perform incomplete combustion. And the combustion flue gas enters the kiln chamber A through the flue gas channel, and enters a second calcining area of the kiln chamber A together with the high-temperature cooling air after lime cooling, so that combustion is completely supported, and the undecomposed limestone materials are continuously calcined. The cooling air volume of the kiln chamber B is 10-20 (v)% of the air volume corresponding to fuel combustion, the preheated low-heat-value coal gas is further heated, and the cooling air volume sent into the kiln chamber A is 80-90 (v)% of the air volume corresponding to fuel combustion. The state (4) is the main cooling stage of the kiln chamber B and the main heat storage stage of the kiln chamber A.
Specifically, the time interval between the processes in the states (1) and (3) includes, but is not limited to, 6-8 min, and the time interval between the processes in the states (2) and (4) includes, but is not limited to, 4-6 min.
Specifically, the temperature of the calcining zone of the kiln chamber A and the temperature of the calcining zone of the kiln chamber B after calcining in the second calcining zone of the kiln chamber B in the state (1) include, but are not limited to, 900-1000 ℃, and the temperature of the calcining zone of the kiln chamber B and the calcining zone of the kiln chamber A in the state (3) include, but are not limited to, 900-1000 ℃. And (2) cooling the material in the kiln chamber A to the temperature including but not limited to 700-900 ℃, preheating the coal gas to the temperature including but not limited to 700-800 ℃, and calcining the material in the second calcining zone of the kiln chamber B to the temperature including but not limited to 1000-1300 ℃. And (4) cooling the material in the kiln chamber B to the temperature including but not limited to 700-900 ℃, preheating the coal gas to the temperature including but not limited to 700-800 ℃, and calcining the material in the second calcining zone of the kiln chamber A to the temperature including but not limited to 1000-1300 ℃.
Specifically, the double-hearth kiln comprises a double-hearth kiln body, a feeding device, a discharging device, an air pipeline, a coal gas pipeline, a cooling fan and a waste gas discharge system. The double-chamber kiln body comprises a kiln chamber A and a kiln chamber B, wherein the upper parts of the kiln chamber A and the kiln chamber B are respectively provided with an air inlet and an air outlet, and the lower parts of the kiln chamber A and the kiln chamber B are provided with a discharge hole and a cooling air inlet. The cooling air inlet is connected with a cooling fan, the discharge port is connected with a discharging device, and a flue gas channel is arranged between the two kiln bodies. Each kiln chamber of the double-chamber kiln is internally provided with a preheating zone, a calcining zone, a cooling zone and a second calcining zone, and the second calcining zone is positioned between the calcining zone and the flue gas channel. The air inlet and outlet are connected with air pipeline and waste gas discharge system by means of air-smoke reversing valve. The calcining zone is provided with an inserted fuel burner which is connected with a gas pipeline. And allowing peripheral burners to be additionally arranged on the kiln wall of the cooling section or adding a combustion beam in the kiln for afterburning.
The invention also comprises the following options: the preheating zone of the double-hearth kiln is provided with an upper nozzle; when limestone is calcined by using low-calorific-value fuel, in the state (1) and/or the state (3), 60-70 (v)% of fuel is sprayed into the inserted fuel burner, 30-40 (v)% of fuel is sprayed into the upper nozzle, the temperature of a preheating zone is cooled by using cold gas, and meanwhile, the fuel gas is preheated. When limestone is calcined by using high-heat-value fuel or coal powder, in the state (1) and/or the state (3), 100 (v)% of fuel or coal powder is sprayed into an inserted fuel burner, an upper nozzle sprays waste gas, the introduction amount of the waste gas is determined according to the temperature of the waste gas discharged through an air inlet and an air outlet, the temperature of a preheating zone is cooled by the waste gas, the discharged waste gas is detected by a temperature sensor, when the temperature of the waste gas is higher than 150 ℃, the injection amount of the waste gas is increased, and when the temperature of the waste gas is lower than 150 ℃, the injection amount of the waste gas is reduced.
The method for calcining the limestone by using the low-heat-value fuel in the double-hearth kiln provided by the invention has the advantages that the second calcining area is arranged at the lower part of the hearth, and the limestone which is not decomposed is continuously calcined by controlling time and carrying out sectional calcining, and the lower part of the other side of the hearth is subjected to secondary combustion when the hearth at one side is calcined, so that the supply mode of the fuel and the calcining method of the limestone are optimized, the calcining effect is improved, the low-heat-value fuel is fully utilized, the high-quality fuel is saved, and the quality of calcined products is improved. The lime is produced by directly using the low-heat-value fuel, the low-heat-value fuel resource is fully utilized, and the economic benefit is improved. The hot gas after cooling lime is directly used for supporting combustion, thereby not only improving the combustion temperature and saving the fuel, but also reducing the emission of greenhouse gas and being beneficial to environmental protection.
The upper nozzle is arranged in the preheating zone, the fuel or the waste gas is sprayed according to the heat value of the fuel, the temperature of the preheating zone is cooled by using cold gas or the waste gas, and meanwhile, the fuel gas is preheated, so that the problems that the calcination temperature cannot meet the calcination requirement due to the low heat value of the fuel, the quantity of the waste gas is large, and the quantity of heat to be taken away is large are solved.
The invention has simple structure and easy implementation, can be used for calcining limestone and dolomite and producing lime, and can also be used for other high-temperature combustion equipment.
Drawings
FIG. 1 is a schematic structural view of a lime double-chamber kiln according to the present invention;
FIG. 2 is a schematic structural view of another embodiment of the present invention;
wherein: 1-air-smoke reversing valve, 2-fuel ring pipe, 3-plug-in fuel nozzle, 4-kiln body, 5-gas inlet and outlet, 6-upper nozzle, 7-discharge outlet, 8-cooling air inlet, 9-lime bin, 10-smoke channel, 11-three-way valve, 12-valve, 15-cooling fan, 16-preheating zone, 17-calcining zone, 18-cooling zone, 19-second calcining zone, 20-air pipeline, 21-gas pipeline.
Detailed Description
The present invention will be described in detail with reference to the following examples and drawings. The scope of protection of the invention is not limited to the embodiments, and any modifications made by those skilled in the art within the scope defined by the claims also belong to the scope of protection of the invention.
Example 1
A double-chamber kiln for producing lime is shown in figure 1 and comprises a double-chamber kiln body 4, a feeding device, a discharging device, an air pipeline 20, a gas pipeline 21, a cooling fan 15 and an exhaust gas discharge system. The double-chamber kiln body comprises a kiln chamber A and a kiln chamber B, wherein the upper parts of the kiln chamber A and the kiln chamber B are respectively provided with an air inlet and outlet 5, and the lower parts of the kiln chamber A and the kiln chamber B are provided with a discharge hole 7 and a cooling air inlet 8. The cooling air inlet is connected with a cooling fan 15, the discharge port is connected with a lime bin 9, and a flue gas channel 10 is arranged between the two kiln bodies. Each kiln chamber of the double-chamber kiln is provided with a preheating zone 16, a calcining zone 17, a cooling zone 18 and a second calcining zone 19, and the second calcining zone 19 is positioned between the calcining zone 17 and the flue gas channel 10. The inlet and outlet 5 is connected to the exhaust gas system and the air line 20 via the air-flue gas reversing valve 1. The calcining zone 17 is provided with plug-in fuel burners 3, to which plug-in fuel burners 3 fuel lines 21 are connected via the fuel ring pipe 2.
The method for calcining limestone by using low-calorific-value fuel in the double-hearth kiln provided by the invention comprises the following steps: limestone materials on one side to be calcined descend to a calcining zone 17 after being preheated in a preheating zone 16, coal gas fuel is sprayed out of a plug-in fuel burner 3, air in an air pipeline 20 enters a kiln chamber from an air inlet and an air outlet 5 through an air-flue gas reversing valve 1, and incomplete combustion is carried out to calcine limestone. The calcined smoke and the high-temperature cooling air after lime cooling enter the second calcining area 19 of the kiln body on the other side to support combustion and burn completely, and the undecomposed limestone materials are continuously calcined. After calcined flue gas preheats limestone through the calcining zone 17 and the preheating zone 16, the temperature is reduced to 150 ℃, and the calcined flue gas is discharged to a waste gas discharge system through the air inlet and outlet 5 and the air-flue gas reversing valve 1. The lime fully calcined in the calcining zone and the second calcining zone is cooled in the cooling zone and then is discharged out of the kiln through a discharge port 7.
The specific process for calcining limestone by the double-hearth kiln comprises the following steps:
state (1): the inserted fuel burner 3 of the kiln chamber A sprays fuel, air which is 100 (v)% of the fuel combustion requirement is fed in through the air inlet and outlet 5, namely one time of S (S represents the air quantity required by the complete combustion of the fuel), and combustion-supporting combustion is carried out to generate high temperature of 950-1000 ℃. In the second calcining area 19 of the kiln chamber A, the high temperature of 1250 ℃ is reserved in the secondary combustion process, the flue gas enters the kiln chamber B through the flue gas channel 10, and the flue gas and the high-temperature cooling air after lime cooling preheat the limestone material in the kiln chamber B. The cooling air volume sent into the kiln chamber A and the kiln chamber B is 5 (v)% of the air volume corresponding to fuel combustion, namely 5% S. The process was run for 8 min. This stage is the primary calcination stage of chamber a and the secondary calcination stage of chamber B.
State (2): the inserted fuel burner 3 of the kiln chamber A continuously sprays fuel, and combustion-supporting air with the fuel combustion requirement of 10 (v)% is fed through the air inlet and outlet 5 to carry out incomplete combustion, namely 10% S. The flue gas (containing 90% of fuel gas) after combustion is delivered to the kiln chamber B through the flue gas channel 10, and is delivered to a second calcining area 19 of the kiln chamber B together with the high-temperature cooling air after lime cooling for complete combustion supporting, the high temperature of 1300 ℃ is generated, and the undecomposed limestone materials are continuously calcined. The cooling air volume of the kiln chamber A is 10 (v)% of the air volume corresponding to the combustion of the fuel, and the preheated low-heat value coal gas is further heated. The cooling air volume fed into the kiln chamber B is 90 (v)% of the air volume corresponding to fuel combustion. The process was run for 4min and then the commutation was performed. The state is a main cooling stage of a kiln chamber A and a main heat storage stage of a kiln chamber B.
State (3): and (3) injecting fuel into an inserted fuel burner 3 of the reversing kiln chamber B, feeding combustion-supporting air (one time S) with the fuel combustion requirement of 100 (v)% through an air inlet and an air outlet 5, and carrying out combustion-supporting combustion to generate high temperature of 950-1000 ℃. In the second calcining area 19 of the kiln chamber B, the high temperature of 1250 ℃ is reserved in the secondary combustion process, the flue gas enters the kiln chamber A through the flue gas channel 10, and the flue gas and the high-temperature cooling air after lime cooling preheat the limestone material in the kiln chamber A. The cooling air volume sent into the kiln chamber A and the kiln chamber B is 5 (v)% of the air volume corresponding to fuel combustion. The process was run for 8 min. This state is the primary calcination stage of chamber B and the secondary calcination stage of chamber a.
State (4): the inserted fuel burner 3 of the kiln chamber B continuously sprays fuel, and combustion-supporting air with the fuel combustion requirement of 10 (v)% is fed through the air inlet and outlet 5 for incomplete combustion. The combustion flue gas passes through the flue gas channel 10 to the kiln chamber A, and is delivered to a second calcining area 19 of the kiln chamber A together with the high-temperature cooling air after lime cooling for combustion supporting, the high temperature of 1300 ℃ is generated, and the undecomposed limestone materials are continuously calcined. The cooling air volume of the kiln chamber B is 10 (v)% of the air volume corresponding to the fuel combustion, and the preheated low-heat value coal gas is further heated. The cooling air quantity sent into the kiln chamber A is 90 (v)% of the air quantity corresponding to fuel combustion. The process was run for 4min and then the commutation was performed. The state is a main cooling stage of a kiln chamber B and a main heat storage stage of a kiln chamber A.
The method for calcining limestone by using low-calorific-value fuel in the double-hearth kiln has the advantages that: the heat dissipation is not excessive, and the top temperature is always lower than 150 ℃. Secondly, the yield can be improved, and the calorific value of the coal gas before entering the kiln can be prepared into fixed calorific values which are suitable for the kiln, such as 700 kilocalories, 800 kilocalories, 900 kilocalories or 1000 kilocalories, and the like, regardless of the calorific value of the coal gas. And thirdly, in the state (2), the amount of the combustion-supporting air at the top of the kiln can be selected at will, and is only more than 1% S, for example, 50% S (if too much, the combustion-supporting air reacts with the coal gas and is not beneficial to cooling), so that the coal gas is always pressed by the combustion-supporting air, and the coal gas is prevented from entering the top of the kiln. The durations of states 1 and 3 and states 2 and 4 include, but are not limited to, a 2:1 relationship. When states 1 and 3 and states 2 and 4 have a 2:1 duration relationship, the calcining zone of one kiln chamber, for example, has been calcined for 8 minutes, while the second calcining zone of the other kiln chamber has been calcined for 4 minutes. The quantity of lime cooling air at the bottom is elastic, 0.1S when the quantity is low, 0.9S when the quantity is high, but the quantity of the total lime cooling air is still 0.7S on average. Sixthly, the content of nitrogen oxide in the waste gas is low, and a denitration system is not required to be opened. And allowing peripheral burners to be additionally arranged on the kiln wall of the cooling section or adding a combustion beam in the kiln for afterburning.
Example 2
Another embodiment of the present invention is shown in fig. 2, and comprises a double-chamber kiln body 4, a feeding device, a discharging device, an air pipeline 20, a gas pipeline 21, a cooling fan 15 and an exhaust gas discharge system. The double-chamber kiln body comprises a kiln chamber A and a kiln chamber B, wherein the upper parts of the kiln chamber A and the kiln chamber B are respectively provided with an air inlet and outlet 5, and the lower parts of the kiln chamber A and the kiln chamber B are provided with a discharge hole 7 and a cooling air inlet 8. The cooling air inlet is connected with a cooling fan 15, the discharge port is connected with a lime bin 9, and a flue gas channel 10 is arranged between the two kiln bodies. Each kiln chamber of the double-chamber kiln is provided with a preheating zone 16, a calcining zone 17, a cooling zone 18 and a second calcining zone 19, and the second calcining zone 19 is positioned between the calcining zone 17 and the flue gas channel 10. The inlet and outlet 5 is connected to the exhaust gas system and the air line 20 via the air-flue gas reversing valve 1. The preheating zone is provided with an upper nozzle 6, the calcining zone 17 is provided with an inserted fuel burner 3, and the upper nozzle 6 is positioned at the upper part 3m of the inserted fuel burner 3. The fuel pipeline 21 is divided into two paths, one path is connected to the plug-in fuel burner 3 through the fuel ring pipe 2, and the connecting pipeline is provided with a valve 12; the other path is connected to the upper nozzle 6 through a three-way valve 11, and the other path of inlet of the three-way valve is connected to the flue gas outlet of the air-flue gas reversing valve 1 at the upper parts of the kiln body A and the kiln body B. The other structure is the same as embodiment 1.
The operation of this example was divided into two cases, (i) when limestone was calcined using low calorific value fuel, 70 (v)% of fuel was injected from the plug-in fuel burner 3, 30 (v)% of fuel was injected from the upper nozzle (6) in the state (1) and/or the state (3), and the temperature of the preheating zone was cooled with cold gas while preheating the fuel gas. The problem of large heat quantity brought away due to the fact that the fuel heat value is low in calcination temperature and cannot meet calcination requirements and the waste gas quantity is large when low-heat-value fuel is calcined is solved. And secondly, when limestone is calcined by using high-calorific-value fuel or pulverized coal, in the state (1) and/or the state (3), 100 (v)% of fuel is sprayed into the inserted fuel burner 3, the upper nozzle 6 sprays waste gas, and the introduction amount of the waste gas is determined according to the temperature of the waste gas discharged from the gas inlet 5 and the gas outlet 5. Cooling the temperature of the preheating zone by using waste gas, detecting the temperature of the discharged waste gas by using a temperature sensor, and increasing the spraying amount of the waste gas of the upper nozzle 6 when the temperature of the waste gas is higher than 150 ℃; when the exhaust gas temperature is lower than 150 ℃, the exhaust gas injection amount of the upper nozzle 6 is reduced. The problem of the temperature of kiln thorax exhaust gas is high, takes away heat many is solved. The other structure and operation are the same as those of embodiment 1.
The characteristics of this example are: firstly, a group of upper nozzles 6 are additionally arranged above the original plug-in fuel burner 3 by a distance of about 3 meters. When high-calorific-value gas or coal powder is used for calcining lime, low-temperature waste gas is mixed through the upper nozzle 6; when lime is calcined using low calorific value gas, the gas is introduced through the upper nozzle 6. And secondly, air is always blown into the kiln body, and air is supplied for calcination and the calcined lime is cooled through two cooling air inlets (a cooling air inlet of the kiln chamber A and a cooling air inlet of the kiln chamber B) and a combustion-supporting air inlet (a combustion-supporting air inlet of the kiln chamber A or a combustion-supporting air inlet of the kiln chamber B).
In practical application, the lower part of the kiln chamber A and the kiln chamber B can be provided with corresponding lower nozzles. Specifically, lower nozzles may be provided for the kiln chamber a and the kiln chamber B below the flue gas channel 10 for injecting fuel gas and burning in the second calcining zone 19 facing the kiln chamber.
Claims (5)
1. A method for calcining limestone by using low-calorific-value fuel in a double-hearth kiln is characterized by comprising the following steps: the double-chamber kiln comprises a kiln chamber A and a kiln chamber B, and calcination and heat storage are alternately carried out; the limestone at one side of the calcining zone is preheated in the preheating zone (16) and then descends to the calcining zone (17) for incomplete combustion and calcining the limestone; the calcined smoke and the high-temperature cooling air after lime cooling enter a second calcining area (19) of the kiln body on the other side to support combustion and burn completely, and the undecomposed limestone materials are continuously calcined; after calcined flue gas preheats limestone through a calcining zone (17) and a preheating zone (16), the calcined flue gas is discharged to a waste gas discharge system through an air inlet and outlet (5) and an air-flue gas reversing valve (1); the process for calcining the limestone comprises the following steps:
state (1): 100% of fuel is sprayed into an inserted fuel burner (3) of the kiln chamber A, combustion-supporting air with 100% of fuel combustion requirement is fed into the kiln chamber A through an air inlet and an air outlet (5), and combustion-supporting combustion is carried out in a calcining zone (17); flue gas generated by combustion reaches a kiln chamber B through a flue gas channel (10), and preheats limestone materials in the kiln chamber B together with high-temperature cooling air after lime cooling; the cooling air volume sent into the kiln chamber A and the kiln chamber B is 3-10% of the air volume corresponding to fuel combustion; the state (1) is a main calcining stage of a kiln chamber A and a secondary calcining stage of a kiln chamber B;
state (2): continuously spraying fuel into an inserted fuel burner (3) of the kiln chamber A, and feeding combustion-supporting air with fuel combustion requirement of 3-30% through an air inlet and an air outlet (5) for incomplete combustion; the combustion flue gas passes through a flue gas channel (10) to the kiln chamber B, and is delivered to a second calcining area (19) of the kiln chamber B together with the high-temperature cooling air after lime cooling to carry out combustion supporting and complete combustion, and the undecomposed limestone materials are continuously calcined; the cooling air volume of the kiln chamber A is 10-20% of the air volume corresponding to fuel combustion, the preheated low-calorific-value gas is further heated, and the cooling air volume sent into the kiln chamber B is 80-90% of the air volume corresponding to fuel combustion; the state (2) is a main cooling stage of the kiln chamber A and a main heat storage stage of the kiln chamber B;
state (3): fuel is sprayed into an inserted fuel burner (3) of the kiln chamber B, and combustion-supporting air with the fuel combustion requirement of 100% is fed into the kiln chamber B through an air inlet and an air outlet (5) to carry out combustion-supporting combustion; the combustion flue gas passes through a flue gas channel (10) to reach a kiln chamber A, and preheats limestone materials in the kiln chamber A together with high-temperature cooling air after lime cooling; the cooling air volume sent into the kiln chamber A and the kiln chamber B is 3-10% of the air volume corresponding to fuel combustion; the state (3) is a main calcining stage of the kiln chamber B and a secondary calcining stage of the kiln chamber A;
state (4): injecting fuel into an inserted fuel burner (3) of the kiln chamber B, and feeding combustion-supporting air with fuel combustion requirement of 3-30% through an air inlet and an air outlet (5) for incomplete combustion; the combustion flue gas passes through a flue gas channel (10) to the kiln chamber A, and is delivered to a second calcining area (19) of the kiln chamber A together with the high-temperature cooling air after lime cooling, combustion is completely supported, and the undecomposed limestone materials are continuously calcined; the cooling air volume of the kiln chamber B is 10-20% of the air volume corresponding to fuel combustion, the preheated low-calorific-value gas is further heated, and the cooling air volume sent into the kiln chamber A is 80-90% of the air volume corresponding to fuel combustion; the state (4) is the main cooling stage of the kiln chamber B and the main heat storage stage of the kiln chamber A.
2. The method for calcining limestone in a dual-chamber kiln using a low calorific value fuel according to claim 1, wherein: the interval time of the states of Tst and Tst is 6-8 min, and the interval time of the states of (2) and (4) is 4-6 min.
3. The method for calcining limestone in a dual-chamber kiln using a low calorific value fuel according to claim 1, wherein: the temperature of the calcined zone (17) of the kiln chamber A after calcination and the calcined zone (19) of the kiln chamber B after calcination in the state (1) is 900-1000 ℃, and the temperature of the calcined zone of the kiln chamber B after calcination and the calcined zone (19) of the kiln chamber A in the state (3) is 900-1000 ℃; in the state (2), the material in the kiln chamber A is cooled to 700-900 ℃, the coal gas is preheated to 700-800 ℃, and the temperature of the calcined material in the kiln chamber B in the second calcining zone (19) is 1000-1300 ℃; and in the state (4), the material in the kiln chamber B is cooled to 700-900 ℃, the coal gas is preheated to 700-800 ℃, and the temperature of the calcined material in the second calcining zone (19) of the kiln chamber A is 1000-1300 ℃.
4. The method for calcining limestone in a dual-chamber kiln using a low calorific value fuel according to claim 1, wherein: the double-chamber kiln comprises a double-chamber kiln body (4), a feeding device, a discharging device, an air pipeline (20), a gas pipeline (21), a cooling fan (15) and a waste gas discharge system; the double-chamber kiln body comprises a kiln chamber A and a kiln chamber B, wherein the upper parts of the kiln chamber A and the kiln chamber B are respectively provided with an air inlet and outlet (5), and the lower parts of the kiln chamber A and the kiln chamber B are provided with a discharge hole (7) and a cooling air inlet (8); the cooling air inlet is connected with a cooling fan (15), the discharge port is connected with a discharge device, and a flue gas channel (10) is arranged between the two kiln bodies; each kiln chamber of the double-chamber kiln is internally provided with a preheating zone (16), a calcining zone (17), a cooling zone (18) and a second calcining zone (19), and the second calcining zone (19) is positioned between the calcining zone (17) and the flue gas channel (10); the air inlet and outlet (5) is connected with an air pipeline (20) and an exhaust emission system through an air-flue gas reversing valve (1); the calcining zone (17) is provided with an inserted fuel burner (3), and the inserted fuel burner (3) is connected with a gas pipeline; and peripheral burners are additionally arranged on the kiln wall of the cooling section, or a combustion beam is additionally arranged in the kiln for afterburning.
5. The method for calcining limestone in a dual-chamber kiln using a low calorific value fuel according to claim 1, wherein: the preheating zone of the double-hearth kiln is provided with an upper nozzle (6); when limestone is calcined by using low-calorific-value fuel, in the state (1) and/or the state (3), 60-70% of fuel is sprayed into the corresponding inserted fuel burner (3), and 30-40% of fuel is sprayed into the corresponding upper nozzle (6); when limestone is calcined by using high-heat-value fuel or coal powder, in the state (1) and/or the state (3), 100% of fuel or coal powder is sprayed into the corresponding inserted fuel burner (3), waste gas is sprayed into the corresponding upper nozzle (6), and the introduction amount of the waste gas is determined according to the temperature of the waste gas discharged through the gas inlet and outlet (5).
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