Double-chamber kiln using low calorific value fuel and calcining method

Abstract

The present invention relates to a double-chamber kiln and a calcination method using low calorific value fuel, wherein the double-chamber kiln comprises a first kiln chamber, a second kiln chamber, a fuel pipeline and a gas exhaust heat exchanger. An exhaust gas suction beam is respectively arranged between the calcination section and the preheating section of the first kiln chamber and the second kiln chamber. The fuel pipeline and the exhaust gas suction beam are respectively connected to the gas exhaust heat exchanger, and the low calorific value gas heated by the gas exhaust heat exchanger is connected to the inserted burner arranged in the calcination zone of the first kiln chamber and the second kiln chamber. The present invention improves the effect of calcining lime with low calorific value gas by arranging the exhaust gas suction beam in the kiln chamber and using the extracted high-temperature exhaust gas to exchange heat with the low calorific value gas, so that the low calorific value fuel is fully utilized and the quality of the calcined product is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical building material production, and relates to an industrial furnace, and in particular to a double-chamber kiln using low calorific value fuel and a calcining method. Background Art

[0002] The double-chamber kiln is also called a double-chamber parallel-flow regenerative lime kiln. The fuel enters from the upper end of the calcining zone and flows in parallel with the raw materials. Since the fuel is sprayed in from the upper part of the calcining zone, the raw materials can absorb most of the heat released by the fuel here. Another important feature of the double-chamber kiln is heat storage, which uses heat storage to preheat a part of the combustion air. The thermal characteristics of parallel-flow calcination and counter-flow regenerative heat determine that the double-chamber kiln has a high thermal efficiency, and its heat energy consumption is the lowest among all types of lime kilns, including rotary kilns, sleeve kilns, etc.

[0003] During the production process of metallurgical enterprises, a large amount of blast furnace gas is generated, which is a valuable fuel resource. The calorific value of blast furnace gas is 3000-3400 kJ / Nm 3 However, due to the low calorific value fuel, it cannot be directly used to calcine limestone, so a large amount of low calorific value fuel cannot be fully utilized. In addition, the production of lime requires the purchase of high calorific value fuel, which causes a waste of resources and affects economic benefits. Summary of the invention

[0004] The purpose of the present invention is to provide a double-chamber kiln using low calorific value fuel and a calcining method, so that low calorific value fuels such as blast furnace gas can be used to calcine lime, fully utilize low calorific value fuel resources, and improve economic benefits.

[0005] According to the first aspect, an embodiment of the present application proposes a double-chamber kiln using a low calorific value fuel, comprising a double-chamber kiln body, a feeding device, a discharging device, an air supply system, a fuel pipeline and an exhaust gas emission system; the double-chamber kiln body comprises a first kiln chamber and a second kiln chamber, wherein the first kiln chamber and the second kiln chamber are respectively provided with a preheating zone, a calcining zone and a cooling zone; the calcining zone is provided with an inserted burner; it is characterized in that: an exhaust gas suction beam is respectively arranged between the calcining section and the preheating section of the first kiln chamber and the second kiln chamber; the outlet of the exhaust gas suction beam is connected to the shell side of a gas-fired exhaust gas heat exchanger, and the shell side outlet of the gas-fired exhaust gas heat exchanger is connected to the exhaust gas emission system; the fuel pipeline is connected to the tube side of the gas-fired exhaust gas heat exchanger, and the tube side outlet of the gas-fired exhaust gas heat exchanger is connected to the inserted burner.

[0006] Specifically, the double-chamber kiln is a double-chamber kiln with a hanging cylinder structure or a bull leg structure.

[0007] Specifically, the exhaust gas intake beam is a square partition structure, the interior is an exhaust gas channel, and the partition is a cooling air channel; the outlet of the cooling air channel of the exhaust gas intake beam is connected to the combustion air main pipe.

[0008] Specifically, the air intake port of the exhaust gas intake beam is arranged at the lower part of the exhaust gas intake beam; the number of air intake holes of each exhaust gas intake beam is 10 to 12.

[0009] According to the second aspect, an embodiment of the present application provides a calcination method for a double-chamber kiln using a low calorific value fuel. When the first kiln chamber is calcining, the shut-off valve of the exhaust gas intake beam in the first kiln chamber is in a closed state, and the shut-off valve of the low calorific value fuel gas is in an open state; the shut-off valve of the exhaust gas intake beam in the second kiln chamber is in an open state, and the shut-off valve of the low calorific value fuel gas is in a closed state; the high-temperature exhaust gas diverted from the second kiln chamber exchanges heat with the low calorific value fuel gas entering the first kiln chamber through a fuel gas exhaust heat exchanger, and the high-temperature low calorific value fuel gas after heat exchange enters the inserted burner of the first kiln chamber for calcination. After the double-chamber kiln switches calcination, when the second kiln chamber is calcining, the shut-off valve of the exhaust gas intake beam in the second kiln chamber is in a closed state, and the shut-off valve of the low calorific value fuel gas is in an open state; the shut-off valve of the exhaust gas intake beam in the first kiln chamber is in an open state, and the shut-off valve of the low calorific value fuel gas is in a closed state; the high-temperature exhaust gas diverted from the first kiln chamber exchanges heat with the low calorific value fuel gas entering the second kiln chamber through the fuel gas exhaust heat exchanger; the high-temperature low calorific value fuel gas after heat exchange enters the inserted burner of the second kiln chamber for calcination.

[0010] Specifically, during the intermediate switching process, the shut-off valves of each exhaust gas intake beam pipeline and the fuel gas pipeline are closed.

[0011] Specifically, during the reversing and calcining stages of the double-chamber kiln, cooling air is continuously supplied to each exhaust gas intake beam, thereby ensuring the service life of the exhaust gas intake beam.

[0012] The double-chamber kiln using low calorific value fuel provided by the present invention can, by sucking a large amount of high-temperature exhaust gas formed after the combustion of the low calorific value fuel, be beneficial to adjusting the ratio of the remaining exhaust gas and the combustion-supporting air in the kiln chamber on the one hand, and can use the sensible heat of the sucked high-temperature exhaust gas to preheat the fuel, thereby increasing the combustion temperature of the low calorific value fuel, so that low calorific value fuels such as blast furnace gas can be used to calcine lime, making full use of low calorific value fuel resources and improving economic benefits. In addition, the hot air discharged from the cooling exhaust gas suction beam can be used for combustion, which can not only increase the combustion temperature and save fuel, but also reduce greenhouse gas emissions, which is beneficial to environmental protection. The present invention has a simple structure and is easy to implement, and can be used for the transformation of traditional lime double-chamber kilns. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A schematic diagram of the structure of a double-chamber kiln using a low calorific value fuel provided by the present invention;

[0014] Among them: 1 - the first kiln chamber, 2 - the second kiln chamber, 3 - the inserted burner, 4 - the fuel pipeline, 5 - the exhaust gas suction beam, 6 - the fuel gas exhaust heat exchanger, 7 - the exhaust gas induced draft fan, 8 - the chimney. Implementation

[0015] The present invention is described in detail below in conjunction with the embodiments and drawings. The protection scope of the present invention is not limited to the embodiments, and any changes made by those skilled in the art within the scope defined by the claims also fall within the protection scope of the present invention.

[0016] Limestone calcination requires fuel to burn in the calcination zone, releasing heat to heat the calcined material. The decomposition temperature of limestone is about 900℃. The higher the combustion temperature of the fuel and the greater the temperature difference with the decomposition temperature of limestone, the stronger the calcination ability. The calcination temperature of high calorific value fuel is generally 1050~1200℃, and the calcination temperature of low calorific value gas is less than 1000℃. The same size of double-chamber kiln uses fuels of different calorific values, and the output of lime is not the same, and the difference is huge. If the combustion of low calorific value fuel does not reach the required temperature, the limestone cannot be decomposed; or if the temperature is low, the limestone is not completely decomposed, resulting in problems such as raw burning and poor quality of lime products. The combustion temperature of fuels with different calorific values ​​is shown in Table 1.

[0017] Table 1 Combustion temperature of fuels with different calorific values

[0018] fuel <![CDATA[Calorific value (kcal / m 3 ).]]> Theoretical combustion temperature (℃) Calcination temperature (℃) Output (t) natural gas 8400 1950 1200 600 Pulverized coal 6000 1800 1190 600 Converter gas 1200 1610 1050 400 Blast furnace gas 840 1390 950 --

[0019] The double-chamber kiln is equipped with two kiln chambers, each of which is equipped with a preheating zone, a calcining zone and a cooling zone. The preheating zone, calcining zone and cooling zone are arranged in sequence from top to bottom. The combustion air in one kiln chamber is heated by the preheating zone and then mixed with the fuel in the calcining zone. The airflow flows downward with the limestone to heat and calcine. The flue gas and the air after the lime is cooled at the bottom merge in the connecting channel between the two kiln chambers, enter the other kiln chamber, and move upward together with the air after the lime is cooled in the kiln chamber, preheating the limestone flowing downward in the countercurrent and reducing the exhaust gas emission temperature. The exhaust gas stores heat in the limestone in the preheating section of one kiln chamber, and the combustion air takes away the heat through the preheating zone of another kiln chamber. This repeated switching ensures that the exhaust gas can be reduced to below 150°C. By comparing the exhaust gas volume and exhaust gas temperature after the combustion of fuels with different calorific values, it is known that the exhaust gas temperature of high calorific value fuel is about 110-120°C, and the exhaust gas temperature of low calorific value coal gas is about 180-200°C. The lower the calorific value, the higher the exhaust gas temperature. At the same time, it can be found that the ratio of the combustion air volume to the exhaust gas volume of high calorific value coal gas is about 45-50%, and the ratio of the combustion air volume to the exhaust gas volume of low calorific value coal gas is less than 30%. The lower the calorific value of the coal gas, the lower the ratio of the combustion air volume to the exhaust gas volume.

[0020] There are two main reasons why the exhaust gas temperature of a double-chamber kiln burning low calorific value gas is high. The first is that the combustion air volume is insufficient, which cannot fully cool the temperature of the preheated limestone. After the direction is changed, the limestone cannot fully absorb the heat of the exhaust gas and reduce the exhaust gas temperature. The second is that the calcination temperature of the low calorific value gas is low, and the heat cannot be quickly absorbed by the decomposition reaction of the limestone, resulting in a high exhaust gas temperature when entering the other kiln chamber. Table 2 lists the exhaust gas parameters of fuels with different calorific values.

[0021] Table 2 Exhaust gas parameters of fuels with different calorific values

[0022] fuel <![CDATA[Calorific value (kcal / m 3 ).]]> Output (t / d) <![CDATA[Combustion air volume (m 3 / h)]]> <![CDATA[Exhaust gas volume (m 3 / h)]]> Exhaust gas temperature (℃) Air exhaust ratio / % natural gas 8400 600 29370 65900 ＜110 44.56 Pulverized coal 6000 600 31830 68300 ＜120 46.6 Converter gas 1200 400 14360 49300 180 29.1 Blast furnace gas 840 400 14460 54960 More than 200 26.3

[0023] The waste gas generated during the calcination of limestone in a double-chamber kiln is cooled by heat storage in the limestone in the preheating section, and then the heat is taken away by the combustion air. In a double-chamber kiln with low calorific value fuel, the volume and temperature of the waste gas are much greater than those of the waste gas generated by high calorific value fuel. In this way, the combustion air cannot fully cool the limestone, causing the downstream equipment to not work properly. If a part of the waste gas is diverted and led out in the calcination section and preheating section, and the ratio of the remaining waste gas to the combustion air is adjusted, the outlet temperature of the waste gas can be reduced.

[0024] The present invention provides a double-chamber kiln using low calorific value fuel, wherein the double-chamber kiln is a hanging cylinder structure or a bracket structure. Figure 1 As shown, the double-chamber kiln includes a double-chamber kiln body, a feeding device, a discharging device, an air supply system, a fuel pipeline 4 and an exhaust gas exhaust system. Specifically, the double-chamber kiln body includes a first kiln chamber 1 and a second kiln chamber 2. A preheating zone, a calcining zone and a cooling zone are respectively provided in the first kiln chamber 1 and the second kiln chamber 2, and an inserted burner 3 is provided in the calcining zone of each kiln chamber. An exhaust gas suction beam 5 is respectively provided between the calcining section and the preheating section of the first kiln chamber 1 and the second kiln chamber 2. Specifically, two exhaust gas suction beams can be provided in the first kiln chamber, and two exhaust gas suction beams can be provided in the second kiln chamber.

[0025] The outlet of the exhaust gas suction beam 5 is connected to the shell side of the gas exhaust heat exchanger 6, and the shell side outlet of the gas exhaust heat exchanger 6 is connected to the exhaust gas discharge system composed of the exhaust gas induced draft fan 7 and the chimney 8. The fuel pipeline 4 is connected to the tube side of the gas exhaust heat exchanger 6, and the tube side outlet of the gas exhaust heat exchanger 6 is connected to the plug-in burner 3.

[0026] Specifically, the exhaust gas intake beam 5 can be a square partition structure, with an exhaust gas channel inside and a cooling air channel in the partition. The outlet of the cooling air channel in the exhaust gas intake beam 5 is connected to the combustion air main pipe. The air temperature of the exhaust gas intake beam after the partition cooling is increased and can be used as combustion air for calcining lime.

[0027] In order to prevent limestone from blocking the air intake port, the air intake port of the exhaust gas intake beam 5 can be set at the lower part of the exhaust gas intake beam. The number of air intake holes of an air intake beam is generally 10-12, and the size of the air intake hole is determined according to the output and the amount of exhaust gas. In addition, the number of exhaust gas intake beams set in each kiln chamber can be determined according to the output and the amount of exhaust gas.

[0028] According to the data analysis of a double-chamber kiln with a production of 400t / d and burning blast furnace gas (calorific value 840 kcal / m3), the combustion air volume is 14460 m 3 / h, according to the air exhaust ratio of 45%, the main exhaust gas flow rate is 32000 m 3 / h, the exhaust gas volume discharged through the exhaust gas suction beam is 22960 m 3 / h. The exhaust gas duct needs thermal insulation protection.

[0029] An effective way to solve the problem that the double-chamber kiln cannot burn low calorific value gas is to increase the combustion temperature. By increasing the temperature of low calorific value coal gas, the combustion temperature can be effectively increased. The gas exhaust heat exchanger 6 can effectively reduce the exhaust gas temperature and increase the coal gas temperature.

[0030] The exhaust gas temperature between the calcining section and the preheating section of the double-chamber kiln can reach 500 to 600°C, and the diverted exhaust gas can be used to preheat the low calorific value gas. 3 ) double-chamber kiln data analysis, the exhaust gas volume is 22960 m 3 / h, temperature 600℃, blast furnace gas flow rate 18850 m 3 / h. Heat is exchanged through the fuel gas exhaust heat exchanger 6, which adopts a tube-sheet structure, with coal gas passing through the tube side and high-temperature exhaust gas passing through the shell side.

[0031] The preheating temperature of blast furnace gas can be calculated using formula (1).

[0032] (1)

[0033] in, t m is the blast furnace gas preheating temperature, °C; v f is the exhaust gas flow rate, 22960m 3 / h; t f1 is the exhaust gas inlet temperature, 600°C; c f1 is the specific heat capacity of the exhaust gas inlet, 1.55 kJ / (m 3 ℃); t f2 is the exhaust gas outlet temperature, 150°C; cf2 is the specific heat capacity of the exhaust gas outlet, 1.436 kJ / (m 3 ℃); v m is the blast furnace gas flow rate, 18850m 3 / h; c m is the specific heat capacity of blast furnace gas, 1.506 kJ / (m 3 ·℃).

[0034] Through calculation, it can be obtained that the preheating temperature of blast furnace gas can reach 598℃. The combustion temperature t of blast furnace gas can be calculated by the theoretical combustion formula (see formula 2): i .

[0035] (2)

[0036] In the formula, Q is the calorific value of blast furnace gas, 840*4.18kJ / m 3 ; t m is the blast furnace gas preheating temperature, 598°C; c m is the specific heat capacity of blast furnace gas, 1.506 kJ / (m 3 ℃); v a is the gas volume generated by unit fuel combustion under a certain air coefficient, 1.6m 3 / m 3 ; c y is the specific heat capacity of flue gas, 1.616 kJ / (m 3 ·℃).

[0037] Through calculation, we know that the combustion temperature of blast furnace gas is 1706℃, which is slightly lower than the combustion temperature of coal powder and higher than the combustion temperature of converter gas. Through the above calculation, we know that the calcination temperature can reach about 1100℃, which can fully meet the calcination requirements of limestone.

[0038] The operation process of the double-chamber kiln using low calorific value fuel provided by the present invention is as follows:

[0039] When the first kiln chamber 1 is calcining, the shut-off valve of the exhaust gas intake beam 5 in the first kiln chamber 1 is in a closed state, and the shut-off valve of the low calorific value fuel gas is in an open state; the shut-off valve of the exhaust gas intake beam 5 in the second kiln chamber 2 is in an open state, and the shut-off valve of the low calorific value fuel gas is in a closed state. The high-temperature exhaust gas diverted from the second kiln chamber 2 exchanges heat with the low calorific value fuel gas entering the first kiln chamber 1 through the fuel gas exhaust heat exchanger 6, and the high-temperature low calorific value fuel gas after heat exchange enters the insert burner of the first kiln chamber 1 for calcining.

[0040] After the double-chamber kiln is switched to calcination, when the second kiln chamber 2 is calcining, the shut-off valve of the exhaust gas intake beam 5 in the second kiln chamber 2 is in a closed state, and the shut-off valve of the low calorific value fuel gas is in an open state; the shut-off valve of the exhaust gas intake beam 5 in the first kiln chamber 1 is in an open state, and the shut-off valve of the low calorific value fuel gas is in a closed state. The high-temperature exhaust gas diverted from the first kiln chamber 1 exchanges heat with the low calorific value fuel gas entering the second kiln chamber 2 through the fuel gas exhaust heat exchanger 6; the high-temperature low calorific value fuel gas after heat exchange enters the plug-in burner of the second kiln chamber 2 for calcination.

[0041] During the intermediate reversing process, the shut-off valves connecting the exhaust gas intake beam pipelines and the fuel gas pipelines are closed. During the reversing and calcining stages of the double-chamber kiln, cooling air is continuously supplied to each exhaust gas intake beam 5, thereby ensuring the service life of the exhaust gas intake beam 5.

[0042] Through theoretical calculation and analysis of the data of the currently operating double-chamber kiln, after adding the air intake beam and the gas heat exchanger, the output of the double-chamber kiln burning blast furnace gas can reach 400-450 tons / day. The activity and raw overburning rate of lime can reach the average level of the double-chamber kiln, which can fully meet the needs of various customers.

[0043] By adding suction beams and gas heat exchangers, the calcination temperature of low calorific value gas can be effectively increased, the exhaust temperature of waste gas can be reduced, and the limestone products can meet the corresponding requirements.

Claims

1. A double-chamber kiln using low calorific value fuel, comprising a double-chamber kiln body, a feeding device, a discharging device, an air supply system, a fuel pipeline (4) and an exhaust gas discharge system; the double-chamber kiln body comprises a first kiln chamber (1) and a second kiln chamber (2), wherein the first kiln chamber (1) and the second kiln chamber (2) are respectively provided with a preheating zone, a calcining zone and a cooling zone; the calcining zone is provided with an inserted burner (3); the characteristics are: An exhaust gas intake beam (5) is respectively arranged between the calcining section and the preheating section of the first kiln chamber (1) and the second kiln chamber (2); the outlet of the exhaust gas intake beam (5) is connected to the shell side of a gas exhaust heat exchanger (6), and the shell side outlet of the gas exhaust heat exchanger (6) is connected to an exhaust gas emission system; the fuel pipeline (4) is connected to the tube side of the gas exhaust heat exchanger (6), and the tube side outlet of the gas exhaust heat exchanger (6) is connected to an insert burner (3); the calcining method of the double-chamber kiln is: When the first kiln chamber (1) is calcining, the shut-off valve of the exhaust gas intake beam (5) in the first kiln chamber (1) is in a closed state, and the shut-off valve of the low calorific value fuel gas is in an open state; the shut-off valve of the exhaust gas intake beam (5) in the second kiln chamber (2) is in an open state, and the shut-off valve of the low calorific value fuel gas is in a closed state; the high-temperature exhaust gas diverted from the second kiln chamber (2) exchanges heat with the low calorific value fuel gas entering the first kiln chamber (1) through the fuel gas exhaust heat exchanger (6), and the high-temperature low calorific value fuel gas after heat exchange enters the insert burner of the first kiln chamber (1) for calcining; After the double-chamber kiln is switched to calcination, when the second kiln chamber (2) is calcining, the shut-off valve of the exhaust gas intake beam (5) in the second kiln chamber (2) is in a closed state, and the shut-off valve of the low calorific value fuel gas is in an open state; the shut-off valve of the exhaust gas intake beam (5) in the first kiln chamber (1) is in an open state, and the shut-off valve of the low calorific value fuel gas is in a closed state; the high-temperature exhaust gas diverted from the first kiln chamber (1) exchanges heat with the low calorific value fuel gas entering the second kiln chamber (2) through the fuel gas exhaust heat exchanger (6); the high-temperature low calorific value fuel gas after heat exchange enters the plug-in burner of the second kiln chamber (2) for calcination; The exhaust gas intake beam (5) is a square partition structure, the interior of which is an exhaust gas channel, and the partition is a cooling air channel; the outlet of the cooling air channel of the exhaust gas intake beam (5) is connected to the combustion air main pipe.

2. The double-chamber kiln using low calorific value fuel according to claim 1, characterized in that: The double-chamber kiln is a double-chamber kiln with a hanging cylinder structure or a bull leg structure.

3. The double-chamber kiln using low calorific value fuel according to claim 1 is characterized in that: The air intake port of the exhaust gas intake beam (5) is arranged at the lower part of the exhaust gas intake beam (5); the number of air intake holes of each exhaust gas intake beam (5) is 10 to 12.

4. The double-chamber kiln using low calorific value fuel according to claim 1 is characterized in that: During the intermediate switching process, the shut-off valves of the exhaust gas intake beam (5) pipeline and the fuel gas pipeline are closed.

5. The double-chamber kiln using low calorific value fuel according to claim 1 is characterized in that: During the reversing and calcining stages of the double-chamber kiln, cooling air is continuously supplied to each exhaust gas intake beam (5), thereby ensuring the service life of the exhaust gas intake beam (5).

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