In the past 20 years, through experiments and discussions by thermal engineering professionals, the combustion control technology and waste heat recovery technology of aluminum melting furnaces have made breakthrough progress. New combustion devices represented by RCB, 1150, and HRS regenerative burners have achieved great success in improving productivity, reducing fuel consumption, and reducing turbidity emissions. This article takes a 25t top-loading circular furnace as an example to briefly introduce the structural characteristics, application performance and economic benefits of the new RCB regenerative burner.
1 Mechanism and technical performance of 25t round furnace
1.1 Mechanism and performance of circular furnace
The 25t tilting aluminum melting furnace consists of a circular furnace body, an openable spherical furnace cover, a cover opening machine, a furnace bottom tilting mechanism, a regenerative burner system, a burner air supply and an injection air system.
1.2 Main features of circular furnace
The burner of the circular furnace is installed with a downward tilt of 10° along the tangent direction of the center circle of the furnace, so that the flame goes straight into the molten pool. The internal shape of the furnace is suitable for air flow circulation and there are no dead corners of the flame to ensure good convection heating effect. Opening the lid allows for rapid charging, with the charging time for each furnace being 15 to 20 minutes, reducing labor intensity. The tilting type shortens the injection operation time and reduces the melt temperature loss. The circular furnace has a smaller specific surface area and can reduce the side heat storage and heat dissipation loss by 20% compared with the rectangular furnace.
Regenerative burners are high-speed burners configured in pairs. The 25t circular furnace uses 5 sets of RCB regenerative burners. The heating capacity of a single burner is 2.508GJ/h, and the flame injection speed Fast and periodic reversal is beneficial to furnace gas circulation.
The circular furnace adopts a steel structure frame and a fully refractory fiber-sprayed furnace cover structure. The bottom circle diameter of the furnace cover is 6233mm, the chord height is 760mm, and the total thickness of the refractory fiber is 300mm, of which the thickness of the ordinary aluminum layer is 120mm and the thickness of the high aluminum layer is 180mm. The refractory fiber spraying technology is suitable for the construction of furnace linings with complex shapes and special-shaped parts. It has the advantages of fast construction speed, low furnace construction labor intensity, light weight of the furnace cover, less heat storage, and fast temperature rise.
The RCB regenerative burner device has automatic ignition and flame monitoring devices. When the main burner is ignited, the ignition burner can be automatically closed. The burner is lined with refractory material, and corrosive media will have no adverse effect on the service life of the burner and smoke evacuator. Compared with ordinary self-preheating burner aluminum melting furnaces, the chimney and flue can be omitted, greatly simplifying the furnace structure.
2 Mechanism and working principle of regenerative burner
2.1 Mechanism and principle
Compared with regenerative furnaces, regenerative burners have the advantages of compact structure, short reversal time, low exhaust gas temperature, high heat recovery rate and small preheating temperature fluctuation. Regenerative burners generally include two similar burner bodies, two compact regenerators, a reversing valve system and a matching control system. The two regenerators are respectively in the heat storage (flowing through flue gas) or preheating (flowing through air) working state, and the reversing device allows flue gas and air to flow alternately through each regenerator. In the first half of the cycle, fuel and combustion-supporting air are introduced through the No. 1 burner, and the high-speed and high-temperature flame ejected from the No. 1 burner heats and melts the charge; the matching No. 2 burner is extracted by the suction force of the jet wind The flue gas in the furnace is heated by the regenerator in No. 2 regenerator. Due to the large specific surface area of the regenerator oil, strong heat storage capacity, excellent thermal conductivity and heat transfer performance, and small heat penetration depth, the regenerator can reach the thermal saturation state in a short period of time, which is very important for reducing pre-heating. The fluctuation of thermal temperature shortens the commutation time and reduces the size of the heat storage body. In the second half of the cycle, the reversing device switches the flow directions of flue gas and combustion air. At this time, burner No. 1 is smoking and burner No. 2 is burning. The cool air is preheated to high temperature through the No. 2 regenerator and sent to the No. 2 nozzle to participate in the combustion process. The regenerator is gradually cooled down; at the same time, the No. 1 burner extracts the flue gas from the furnace and injects the No. 1 regenerator During heating, the temperature of the flue gas removed from the regenerator is between 150 and 180°C, and the low-temperature flue gas is exhausted through the smoke exhauster. This cycle repeats over and over again to maintain the combustion process.
2.2 Comparison between regenerative burners and dividing wall burners
Both regenerative burners and partition wall burners are self-preheating burners. The waste heat recovery principle of the latter is similar to that of a heat exchanger. The burner is usually a single structure, and a single burner operates continuously [1]. The former's waste heat recovery principle is similar to that of a regenerator furnace. The burner and the regenerator appear in pairs, and the two burners alternate between smoking and combustion.
Judging from the application results, the waste heat recovery rate of the partition burner does not exceed 45%; the waste heat recovery rate of the regenerative burner can reach 90%, see Table 1. The partition wall burner has achieved good results in simplifying the furnace structure, but it has large flue gas emissions and NOx emissions; the regenerative burner can simplify the furnace structure while also reducing the furnace size. The new generation of regenerative burners adopts strong flue gas circulation regeneration combustion technology and high-temperature air combustion technology. The emission of NOx is only 10% of that of traditional combustion technology, and the flue gas emission can be reduced by 30% [1, 2].
Table 1 Comparison between dividing wall type and regenerative self-preheating burners [2] Partitioning wall type burner Regenerative burner
Working principle: The heat exchange device is a non-reversing heat exchanger. The heat exchange device under continuous operating conditions is a regenerator that requires reversing. During periodic operating conditions, the heat exchange device is a regenerator that requires reversing.
Air preheating temperature/℃ 480~600 80~150℃ lower than the furnace temperature, the air can usually be preheated to 960~1080℃
Exhaust smoke temperature/℃ >700 150～180
Application life/a 3～5 >10
Waste heat acceptance rate/% 40～45 ≈90
2.3 Characteristics of regenerative burners
The regenerative burner can preheat the atmosphere to about 1000°C, which is only 80-150°C different from the furnace temperature; the flue gas emission temperature can be lower than 200°C. Compared with using cool air (which does not use flue gas waste heat), the fuel saving rate of RCB burners can be as high as 60% to 65% [3]. Due to the use of strong flue gas circulation regeneration combustion technology, its NOx emissions are very small . At the same time, due to the adoption of high waste heat recovery rate technology, when the air loss coefficient increases from 1.0 to 1.5, the unit fuel consumption of the aluminum melting furnace and the thermal efficiency of the furnace do not change much.
Another advantage of RCB burners is that they can adopt low-oxygen combustion technology. The formula for the realistic surface combustion temperature of a fuel is:
In the formula: QyDw - low-level heat generation of fuel, kJ/kg;
Q atmosphere, Q fuel - the physical heat brought into the furnace by the preheated fuel and combustion-supporting atmosphere, kJ/kg;
Vn - When the air loss coefficient is n, the product generation capacity when the fuel is burned, m3/kg;
Uniform specific heat capacity of Cy combustion gas, kJ/(m3.℃)
It can be seen from equation (1) that as the combustion air temperature increases, Q air increases and the combustion temperature increases; when the air temperature is preheated to above 1000°C, if oxygen is still supplied according to the principles of conventional combustion technology, the furnace temperature It will exceed the allowable temperature of the aluminum smelting process and even exceed the allowable use temperature of the refractory material [4]. Introducing flue gas without adding combustion response into the combustion-supporting atmosphere reduces the oxygen content in the combustion-supporting atmosphere and reduces the amount of fuel introduced. As VnCy increases, the combustion temperature decreases. By controlling the amount of smoke introduced, the furnace temperature can be controlled within the range allowed by the aluminum smelting process.
Emitted NOx is an important cause of acid rain and photochemical smog, causing great damage to the environment. The RCB burner extracts flue gas from the furnace and mixes it into the combustion-supporting air, which reduces the N2 and O2 concentrations in the combustion-supporting air and lowers the fuel combustion temperature. Due to the elimination of the high-temperature zone at the end, the production of NOx is greatly reduced, and the actual NOx emissions The capacity is only 10% of that of ordinary regenerative burners.
The RCB regenerative self-preheating burner injects very high temperature (up to about 1000°C) combustion-supporting air into the furnace, which exceeds the auto-ignition temperature of the fuel. It can ensure stable combustion without a flame stabilizing mechanism, and the flame responds to uniform high-temperature excitation. Zhongsheng, the uniformity of the furnace temperature is not affected by the shape, flame length, flame rigidity and spreadability of the traditional flame. The temperature gradient of the entire furnace is very small, and the combustion noise is extremely low.
RCB burner is a new type of combustion device with high efficiency, energy saving, low turbidity and high efficiency. It is hailed as one of the key technologies in the 21st century in Japan. It has advantages that other types of burners cannot compare with and brings excellent economic benefits. and social income.
3. Application situations and energy-saving achievements of regenerative burners
The 25t round furnace uses 5 sets of RCB regenerative burners. The fuel capacity of each set of burners is 60kg/h. The low calorific value of 0# diesel is QyDw=43410kJ/kg. The aluminum charging capacity is 25t/furnace, and one furnace is smelted. The time of industrial pure aluminum is = 3.1h; while the fuel consumption of ordinary burner is B' = 80kg/t. The aluminum melting furnace adopts jet smoke exhaust technology. The jet air and combustion air each use a fan. The wind pressure of the fan is 7000Pa, and the burner reversal period is 60 to 90 seconds.
Then the actual fuel consumption per ton of aluminum smelted is:
Therefore, the fuel saving rate when using RCB burner is:
(2)
In the formula: B' - fuel consumption per ton of aluminum smelting without regenerative burners, kg/t;
B - Fuel consumption when using RCB burner, kg/t.
Substituting B=37.2B'=80 into equation (2), we get eta section=53.5%.
It can be seen from the thermal balance analysis that the fuel saving rate of using RCB burners is related to the heat storage heat of the furnace masonry and the surface heat dissipation loss of the furnace body. Since the burner absorbs waste heat from the flue gas, the heat storage of the furnace body is reduced, and the smaller the surface heat dissipation loss, the greater the waste heat of the exhaust smoke and the higher the fuel saving rate.
RCB regenerative burners are not suitable for installation and application in aluminum melting furnaces with melting front chambers, bidirectional melting furnaces and vertical aluminum melting furnaces that use flue gas waste heat to preheat the charge. In these furnace types, burner smoking will weaken the preheating effect of flue gas on the charge, resulting in a situation where the burner and the preheating section compete for heat. For chamber-type aluminum melting furnaces that do not have chimneys, flues, heat exchangers, and do not use flue gas waste heat to preheat the charge (very common in small and medium-sized enterprises), if the upper furnace wall of the molten pool can be changed to a thermally inert Using small high-strength lightweight refractory materials, the furnace top adopts a fiber spray paint structure, and is equipped with an RCB high-speed regenerative burner with a waste heat recovery rate almost close to the nominal value, which can achieve high furnace temperature, high flame ejection rate, and high efficiency in the aluminum melting furnace. The operation technology of four high and one low is high smoke temperature, high waste heat recovery rate and low inertia. It can effectively deepen the heat exchange process in the furnace, improve smelting productivity, significantly reduce fuel consumption, save site area, and achieve desired comprehensive economic results.
In the past 20 years, through experiments and discussions by thermal engineering professionals, the combustion control technology and waste heat recovery technology of aluminum melting furnaces have made breakthrough progress. New combustion devices represented by RCB, 1150, and HRS regenerative burners have achieved great success in improving productivity, reducing fuel consumption, and reducing turbidity emissions. This article takes a 25t top-loading circular furnace as an example to briefly introduce the structural characteristics, application performance and economic benefits of the new RCB regenerative burner.
1 Mechanism and technical performance of 25t round furnace
1.1 Mechanism and performance of circular furnace
The 25t tilting aluminum melting furnace consists of a circular furnace body, an openable spherical furnace cover, a cover opening machine, a furnace bottom tilting mechanism, a regenerative burner system, a burner air supply and an injection air system.
1.2 Main features of circular furnace
The burner of the circular furnace is installed with a downward tilt of 10° along the tangent direction of the center circle of the furnace, so that the flame goes straight into the molten pool. The internal shape of the furnace is suitable for air flow circulation and there are no dead corners of the flame to ensure good convection heating effect. Opening the lid allows for rapid charging, with the charging time for each furnace being 15 to 20 minutes, reducing labor intensity. The tilting type shortens the injection operation time and reduces the melt temperature loss. The circular furnace has a smaller specific surface area and can reduce the side heat storage and heat dissipation loss by 20% compared with the rectangular furnace.
Regenerative burners are high-speed burners configured in pairs. The 25t circular furnace uses 5 sets of RCB regenerative burners. The heating capacity of a single burner is 2.508GJ/h, and the flame injection speed Fast and periodic reversal is beneficial to furnace gas circulation.
The circular furnace adopts a steel structure frame and a fully refractory fiber-sprayed furnace cover structure. The bottom circle diameter of the furnace cover is 6233mm, the chord height is 760mm, and the total thickness of the refractory fiber is 300mm, of which the thickness of the ordinary aluminum layer is 120mm and the thickness of the high aluminum layer is 180mm. The refractory fiber spraying technology is suitable for the construction of furnace linings with complex shapes and special-shaped parts. It has the advantages of fast construction speed, low furnace construction labor intensity, light weight of the furnace cover, less heat storage, and fast temperature rise.
The RCB regenerative burner device has automatic ignition and flame monitoring devices. When the main burner is ignited, the ignition burner can be automatically closed. The burner is lined with refractory material, and corrosive media will have no adverse effect on the service life of the burner and smoke evacuator. Compared with ordinary self-preheating burner aluminum melting furnaces, the chimney and flue can be omitted, greatly simplifying the furnace structure.
2 Mechanism and working principle of regenerative burner
2.1 Mechanism and principle
Compared with regenerative furnaces, regenerative burners have the advantages of compact structure, short reversal time, low exhaust gas temperature, high heat recovery rate and small preheating temperature fluctuation. Regenerative burners generally include two similar burner bodies, two compact regenerators, a reversing valve system and a matching control system. The two regenerators are respectively in the heat storage (flowing through flue gas) or preheating (flowing through air) working state, and the reversing device allows flue gas and air to flow alternately through each regenerator. In the first half of the cycle, fuel and combustion-supporting air are introduced through the No. 1 burner, and the high-speed and high-temperature flame ejected from the No. 1 burner heats and melts the charge; the matching No. 2 burner is extracted by the suction force of the jet wind The flue gas in the furnace is heated by the regenerator in No. 2 regenerator. Due to the large specific surface area of the regenerator oil, strong heat storage capacity, excellent thermal conductivity and heat transfer performance, and small heat penetration depth, the regenerator can reach the thermal saturation state in a short period of time, which is very important for reducing pre-heating. The fluctuation of thermal temperature shortens the commutation time and reduces the size of the heat storage body. In the second half of the cycle, the reversing device switches the flow directions of flue gas and combustion air. At this time, burner No. 1 is smoking and burner No. 2 is burning. The cool air is preheated to high temperature through the No. 2 regenerator and sent to the No. 2 nozzle to participate in the combustion process. The regenerator is gradually cooled down; at the same time, the No. 1 burner extracts the flue gas from the furnace and injects the No. 1 regenerator During heating, the temperature of the flue gas removed from the regenerator is between 150 and 180°C, and the low-temperature flue gas is exhausted through the smoke exhauster. This cycle repeats over and over again to maintain the combustion process.
2.2 Comparison between regenerative burners and dividing wall burners
Both regenerative burners and partition wall burners are self-preheating burners. The waste heat recovery principle of the latter is similar to that of a heat exchanger. The burner is usually a single structure, and a single burner operates continuously [1]. The former's waste heat recovery principle is similar to that of a regenerator furnace. The burner and the regenerator appear in pairs, and the two burners alternate between smoking and combustion.
Judging from the application results, the waste heat recovery rate of the partition burner does not exceed 45%; the waste heat recovery rate of the regenerative burner can reach 90%, see Table 1. The partition wall burner has achieved good results in simplifying the furnace structure, but it has large flue gas emissions and NOx emissions; the regenerative burner can simplify the furnace structure while also reducing the furnace size. The new generation of regenerative burners adopts strong flue gas circulation regeneration combustion technology and high-temperature air combustion technology. The emission of NOx is only 10% of that of traditional combustion technology, and the flue gas emission can be reduced by 30% [1, 2].
Table 1 Comparison between dividing wall type and regenerative self-preheating burners [2] Partitioning wall type burner Regenerative burner
Working principle: The heat exchange device is a non-reversing heat exchanger. The heat exchange device under continuous operating conditions is a regenerator that requires reversing. During periodic operating conditions, the heat exchange device is a regenerator that requires reversing.
Air preheating temperature/℃ 480~600 80~150℃ lower than the furnace temperature, the air can usually be preheated to 960~1080℃
Exhaust smoke temperature/℃ >700 150～180
Application life/a 3～5 >10
Waste heat acceptance rate/% 40～45 ≈90
2.3 Characteristics of regenerative burners
The regenerative burner can preheat the atmosphere to about 1000°C, which is only 80-150°C different from the furnace temperature; the flue gas emission temperature can be lower than 200°C. Compared with using cool air (which does not use flue gas waste heat), the fuel saving rate of RCB burners can be as high as 60% to 65% [3]. Due to the use of strong flue gas circulation regeneration combustion technology, its NOx emissions are very small . At the same time, due to the adoption of high waste heat recovery rate technology, when the air loss coefficient increases from 1.0 to 1.5, the unit fuel consumption of the aluminum melting furnace and the thermal efficiency of the furnace do not change much.
Another advantage of RCB burners is that they can adopt low-oxygen combustion technology. The formula for the realistic surface combustion temperature of a fuel is:
In the formula: QyDw - low-level heat generation of fuel, kJ/kg;
Q atmosphere, Q fuel - the physical heat brought into the furnace by the preheated fuel and combustion-supporting atmosphere, kJ/kg;
Vn - When the air loss coefficient is n, the product generation capacity when the fuel is burned, m3/kg;
Uniform specific heat capacity of Cy combustion gas, kJ/(m3.℃)
It can be seen from equation (1) that as the combustion air temperature increases, Q air increases and the combustion temperature increases; when the air temperature is preheated to above 1000°C, if oxygen is still supplied according to the principles of conventional combustion technology, the furnace temperature It will exceed the allowable temperature of the aluminum smelting process and even exceed the allowable use temperature of the refractory material [4]. Introducing flue gas without adding combustion response into the combustion-supporting atmosphere reduces the oxygen content in the combustion-supporting atmosphere and reduces the amount of fuel introduced. As VnCy increases, the combustion temperature decreases. By controlling the amount of smoke introduced, the furnace temperature can be controlled within the range allowed by the aluminum smelting process.
Emitted NOx is an important cause of acid rain and photochemical smog, causing great damage to the environment. The RCB burner extracts flue gas from the furnace and mixes it into the combustion-supporting air, which reduces the N2 and O2 concentrations in the combustion-supporting air and lowers the fuel combustion temperature. Due to the elimination of the high-temperature zone at the end, the production of NOx is greatly reduced, and the actual NOx emissions The capacity is only 10% of that of ordinary regenerative burners.
The RCB regenerative self-preheating burner injects very high temperature (up to about 1000°C) combustion-supporting air into the furnace, which exceeds the auto-ignition temperature of the fuel. It can ensure stable combustion without a flame stabilizing mechanism, and the flame responds to uniform high-temperature excitation. Zhongsheng, the uniformity of the furnace temperature is not affected by the shape, flame length, flame rigidity and spreadability of the traditional flame. The temperature gradient of the entire furnace is very small, and the combustion noise is extremely low.
RCB burner is a new type of combustion device with high efficiency, energy saving, low turbidity and high efficiency. It is hailed as one of the key technologies in the 21st century in Japan. It has advantages that other types of burners cannot compare with and brings excellent economic benefits. and social income.
3. Application situations and energy-saving achievements of regenerative burners
The 25t round furnace uses 5 sets of RCB regenerative burners. The fuel capacity of each set of burners is 60kg/h. The low calorific value of 0# diesel is QyDw=43410kJ/kg. The aluminum charging capacity is 25t/furnace, and one furnace is smelted. The time of industrial pure aluminum is = 3.1h; while the fuel consumption of ordinary burner is B' = 80kg/t. The aluminum melting furnace adopts jet smoke exhaust technology. The jet air and combustion air each use a fan. The wind pressure of the fan is 7000Pa, and the burner reversal period is 60 to 90 seconds.
Then the actual fuel consumption per ton of aluminum smelted is:
Therefore, the fuel saving rate when using RCB burner is:
(2)
In the formula: B' - fuel consumption per ton of aluminum smelting without regenerative burners, kg/t;
B - Fuel consumption when using RCB burner, kg/t.
Substituting B=37.2B'=80 into equation (2), we get eta section=53.5%.
It can be seen from the thermal balance analysis that the fuel saving rate of using RCB burners is related to the heat storage heat of the furnace masonry and the surface heat dissipation loss of the furnace body. Since the burner absorbs waste heat from the flue gas, the heat storage of the furnace body is reduced, and the smaller the surface heat dissipation loss, the greater the waste heat of the exhaust smoke and the higher the fuel saving rate.
RCB regenerative burners are not suitable for installation and application in aluminum melting furnaces with melting front chambers, bidirectional melting furnaces and vertical aluminum melting furnaces that use flue gas waste heat to preheat the charge. In these furnace types, burner smoking will weaken the preheating effect of flue gas on the charge, resulting in a situation where the burner and the preheating section compete for heat. For chamber-type aluminum melting furnaces that do not have chimneys, flues, heat exchangers, and do not use flue gas waste heat to preheat the charge (very common in small and medium-sized enterprises), if the upper furnace wall of the molten pool can be changed to a thermally inert Using small high-strength lightweight refractory materials, the furnace top adopts a fiber spray paint structure, and is equipped with an RCB high-speed regenerative burner with a waste heat recovery rate almost close to the nominal value, which can achieve high furnace temperature, high flame ejection rate, and high efficiency in the aluminum melting furnace. The operation technology of four high and one low is high smoke temperature, high waste heat recovery rate and low inertia. It can effectively deepen the heat exchange process in the furnace, improve smelting productivity, significantly reduce fuel consumption, save site area, and achieve desired comprehensive economic results.