Lime kiln off-gas treatment system

Abstract

The application discloses a lime kiln tail gas treatment system and relates to the technical field of semi-coke production. The technical points are as follows: the system comprises a vertical dryer, one side of the vertical dryer is provided with a large-inclination belt conveyor, and the diametrically opposite side of the vertical dryer is respectively provided with an air inlet pipe and an air outlet pipe; one end of the air inlet pipe, which is away from the vertical dryer, is connected with one end of a flue gas conveying pipe, the tail gas of a plurality of lime kilns is connected with the other end of the flue gas conveying pipe, the flue gas conveying pipe can input the tail gas of the plurality of lime kilns into the vertical dryer through the air inlet pipe, and the air outlet pipe is connected with a first dust collector. The application can utilize the tail gas of the lime kiln, dry the semi-coke in the vertical dryer, effectively solve the environmental protection problem, save energy, reduce emissions, reduce consumption, reduce production cost and reduce the safety risk caused by the limited space operation.

Description

Technical Field

[0001] This application relates to the field of semi-coke production technology, and in particular to a lime kiln tail gas treatment system. Background Technology

[0002] Semi-coke is essentially a type of coke with a porous structure, making it highly susceptible to moisture absorption. Undried semi-coke has a high moisture content (typically 15% to 25%), which not only increases its transport weight but also reduces its effective calorific value and fixed carbon content as fuel or reducing agent. Reducing the moisture content to 1%-5% or lower through drying processes significantly improves its quality, meeting the demands of industrial applications. In many existing calcium carbide production enterprises, semi-coke is a crucial raw material, and these enterprises typically use semi-coke drying equipment to process it.

[0003] Early calcium carbide production enterprises used horizontal dryers for drying semi-coke. These dryers consisted of an inclined drum and a mechanical rotating section. The rotating section drove the drum, and lifting plates inside the drum lifted and dropped the material to be dried. Heat from the combustion furnace passed through the dryer into the ventilation duct of the environmental protection equipment, resulting in much of the heat being released into the atmosphere without heat exchange. Furthermore, the external combustion furnace and the dryer itself continuously dissipated heat, resulting in a heat utilization rate of only about 40%. Because the heat supplied per unit time did not match the required heat, the drying quality could not be controlled. Due to high investment, high coal and electricity consumption, and large footprint, this type of dryer gradually disappeared from the production lines of various enterprises.

[0004] With the development of drying equipment, vertical dryers (also known as vertical drying kilns) gradually replaced horizontal dryers. The angle of the basin-cone structure inside a vertical dryer is designed using a critical concept, allowing the semi-coke to slide down along the outer surface of the cone and the inner surface of the basin. The sliding speed is controlled by the frequency of vibrators connected to the basin-cone structure outside the kiln via connecting rods. Therefore, the semi-coke moves in a sliding state throughout the entire vertical drying kiln, without falling or colliding with each other, even when sliding from one heat exchange unit to the next, because the design between units is continuous and compact. Consequently, the breakage rate of semi-coke is low; actual production verification shows that the breakage rate of semi-coke in a vertical dryer kiln is only 2-5%, far lower than the 10-20% breakage rate of horizontal dryers. Furthermore, vertical dryers use gravity for drying, making them a non-powered drying process. The electricity consumption during the drying process comes only from a few low-power electric vibrators. Rotary dryers, on the other hand, require a motor to drive the entire drum to rotate in order to dry the materials. The motor power ranges from tens to hundreds of kilowatts. Therefore, the power consumption of vertical dryers is much lower than that of rotary dryers.

[0005] Furthermore, in a vertical dryer, the semi-coke particles are completely dispersed within the drying kiln under the guidance of the heat exchange device, ensuring that the outer surface of each particle is in complete contact with the hot air. This large heat exchange surface results in high thermal efficiency. In contrast, in a rotary dryer, only up to 50% of the semi-coke's outer surface is in contact with hot air, leading to significantly lower thermal efficiency compared to the vertical dryer. Additionally, the vertical dryer utilizes internal refractory brick insulation, greatly reducing energy loss. Rotary kilns struggle to achieve the same insulation effect as vertical dryers, and their air leakage is far more severe. Therefore, the heat consumption of a dynamic vertical dryer is significantly lower than that of a rotary dryer, achieving 50% energy savings.

[0006] Although existing vertical dryers can save up to 20% of coal consumption compared to rotary dryers in completing the same semi-coke drying task, they still rely on the heat generated from burning semi-coke powder as the main heat source for the drying process. If the coal consumption required for the operation of vertical dryers can be further reduced, it will not only achieve the effects of energy saving, emission reduction, and consumption reduction, but also reduce production costs and increase profits for enterprises. Utility Model Content

[0007] This application provides a lime kiln tail gas treatment system that can use the tail gas of the lime kiln to provide heat energy for a vertical dryer, thereby reducing the demand for coal in the process of drying semi-coke. This not only achieves the effect of energy saving and emission reduction, but also reduces the production cost of enterprises.

[0008] The above-mentioned objective of this application is achieved through the following technical solution: A lime kiln exhaust gas treatment system includes a vertical dryer, with a steeply inclined belt conveyor on one side of the vertical dryer. The steeply inclined belt conveyor is used to transport semi-coke from the carbon material receiving bin to the upper port of the vertical dryer. An air inlet pipe and an air outlet pipe are respectively provided on opposite radial sides of the vertical dryer. The end of the air inlet pipe away from the vertical dryer is connected to one end of the flue gas conveying pipe, and the exhaust gas from multiple lime kilns is connected to the other end of the flue gas conveying pipe. The flue gas conveying pipe can input the exhaust gas from multiple lime kilns into the vertical dryer through the air inlet pipe. The air outlet duct is connected to the first dust collector.

[0009] Furthermore, the number of air inlet pipes and air outlet pipes are equal, and there are not less than two of each. Multiple air inlet pipes and multiple air outlet pipes are installed sequentially on the side wall of the vertical dryer on the corresponding side in a vertical direction. Multiple air inlet pipes are connected to the same air inlet manifold, and the side of the air inlet manifold away from the air inlet pipe is connected to the flue gas conveying pipe; Multiple air outlet pipes are connected to the same outlet manifold, and the side of the outlet manifold away from the air outlet pipe is connected to the first dust collector through an exhaust gas pipe.

[0010] Furthermore, there are four air inlet pipes and four air outlet pipes. The four air outlet pipes are located in the middle area of ​​one side wall of the vertical dryer, and the four air inlet pipes are distributed in pairs at the upper and lower ends of the other opposite side wall of the vertical dryer.

[0011] Furthermore, a second dust collector is installed on the flue gas conveying pipe, which can remove dust from the exhaust gas of the lime kiln before it reaches the air inlet manifold.

[0012] Furthermore, a hot air pipe is added between the flue gas conveying pipe and the exhaust gas pipe, and an electromagnetic control valve is installed on the hot air pipe.

[0013] Furthermore, an auxiliary heat source is connected to the flue gas conveying pipe.

[0014] Furthermore, the auxiliary heat source is a fluidized bed furnace, and the hot air outlet of the fluidized bed furnace is connected to the flue gas conveying pipe via a tee.

[0015] In summary, this application includes at least one of the following beneficial technical effects: This application utilizes the exhaust gas from lime kilns in calcium carbide enterprises, which is then uniformly fed into a vertical dryer via a flue gas pipeline and an inlet pipe. The waste heat from the lime kiln exhaust gas is used to dry the carbon material (i.e., semi-coke) within the dryer. After sufficient heat exchange with the carbon material, the lime kiln exhaust gas is discharged through an outlet pipe to the first dust collector. The first dust collector filters the used lime kiln exhaust gas to meet emission standards before it is released. Because this application utilizes the exhaust gas, which has a certain temperature, from the lime kiln to replace the hot air generated by burning coal in traditional technology, it not only achieves energy conservation and emission reduction while ensuring the normal operation of the vertical dryer, but also reduces the enterprise's production costs. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the overall structure of this application; Figure 2 This is a schematic diagram of the internal structure of the vertical dryer of this application; Figure 3 This is a schematic diagram of the flow direction of the internal flue gas in the vertical dryer of this application during use (the arrow in the diagram indicates the flow direction of the flue gas).

[0018] Attached reference numerals: 1. Vertical dryer; 2. Inclined belt conveyor; 3. Inlet pipe; 4. Outlet pipe; 5. Flue gas conveying pipe; 6. First dust collector; 7. Inlet collector pipe; 8. Outlet collector pipe; 9. Tail gas pipe; 10. Fluidized bed furnace. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are also within the scope of protection of this application.

[0020] like Figure 1 and Figure 2 As shown, this application discloses a lime kiln exhaust gas treatment system, which includes a vertical dryer 1. A steep-angle belt conveyor 2 is provided on one side of the vertical dryer 1. The steep-angle belt conveyor 2 is used to transport semi-coke in the carbon material receiving bin to the upper port of the vertical dryer 1. An air inlet pipe 3 and an air outlet pipe 4 are respectively provided on opposite sides of the vertical dryer 1 in the radial direction. The end of the air inlet pipe 3 away from the vertical dryer 1 is connected to one end of the flue gas conveying pipe 5. The exhaust gas from multiple lime kilns is connected to the other end of the flue gas conveying pipe 5. The flue gas conveying pipe 5 can input the exhaust gas from multiple lime kilns into the vertical dryer 1 through the air inlet pipe 3. The air outlet duct 4 is connected to the first dust collector 6.

[0021] In the above embodiments, the vertical dryer 1 of this application is specifically selected based on the manufacturer's drying capacity of semi-coke per unit time. For example, to achieve a drying capacity of 20 tons of carbon material (i.e., semi-coke) per hour, the vertical dryer 1 is preferably configured with an outer cylinder diameter of 4.0 meters, an inner cylinder diameter of 1.8 meters, and a height of 28 meters. The inner and outer baffle plates and cylinder wall are made of Q355B manganese steel with a wall thickness ≥12mm; the baffle plates are made of Q355B steel with a thickness ≥12mm; the drying section flange thickness is ≥16mm; and the sealing bolts must be grade 8.8 or higher. A buffer silo is installed at the top of the vertical dryer 1. The buffer silo is equipped with a high and low level gauge, ensuring the low level is higher than the receiving cone, effectively preventing wear on the receiving cone and avoiding material drop and damage. The annular space between the inner and outer baffle plates is divided into 8 independent chambers, with each adjacent chamber separated by a partition made of Q355B manganese steel with a thickness ≥16mm. Temperature sensing elements are installed at sections 1-8 of the equipment body to monitor the internal temperature of the dryer. A material distributor is installed at the top of the vertical dryer 1 to ensure more uniform material distribution. During normal operation, the raw material is continuously fed from the charcoal receiving hopper to the upper port of the vertical dryer 1 by a steep-angle belt conveyor 2. The discharge end of the vertical dryer 1 has 8 independent discharge areas, which can discharge independently and have a rapid discharge function.

[0022] When the vertical dryer 1 is in use, the semi-coke to be dried is first conveyed to the top buffer silo of the vertical dryer 1 via a steeply inclined belt conveyor 2. A rotating distributor installed in the top buffer silo of the vertical dryer 1 evenly distributes the semi-coke inside the dryer. The carbon material falls in a creeping motion through the annular space between the inner and outer baffles, traveling approximately 12.5 meters per hour. The material is almost stationary, effectively reducing breakage defects caused by wear. When the material reaches the bottom silo of the vertical dryer 1, it is transferred from each independent discharge area to the discharge belt, which is then used to transport it to the next process. In addition to the vertical dryer 1, calcium carbide production enterprises also have lime kilns. Lime kilns generate exhaust gas of over 200 degrees Celsius during operation. This heat is often discharged directly through the chimney after treatment, which is clearly a waste of thermal energy. Therefore, this application innovatively sends the exhaust gas generated by the lime kiln in the calcium carbide enterprise into the vertical dryer 1 through five flue gas conveying pipes and air inlet pipe 3. The waste heat of the lime kiln exhaust gas is used to dry the carbon material (i.e., semi-coke) in the vertical dryer 1. After sufficient heat exchange with the carbon material, the lime kiln exhaust gas is discharged to the first dust collector 6 through the air outlet pipe 4. After the first dust collector 6 filters the used lime kiln exhaust gas to meet the standards, it is then discharged to the outside. (As for the specific heat exchange method and principle between the hot air and the material in the vertical dryer 1, these are all existing technologies, just like its structure (for example, similar vertical dryers 1 are disclosed in patent documents with application numbers 201520689200.2 and 202211446672.6). These contents are all known to those skilled in the art, so this application will not elaborate on the relevant details here.) Compared with the existing technology, this application utilizes the exhaust gas with a certain temperature discharged from the lime kiln to replace the traditional method of using hot air generated by burning coal to provide a heat source for drying charcoal materials in the vertical dryer 1. While ensuring the normal operation of the vertical dryer 1, it can not only achieve the effect of energy saving and emission reduction, but also reduce the production cost of enterprises.

[0023] If the lime kiln and the vertical dryer 1 are far apart, a pressurizing fan needs to be installed on the flue gas conveying pipe 5 to ensure that all the exhaust gas can be sent to the vertical dryer 1 for disposal in accordance with the process requirements.

[0024] Furthermore, such as Figure 1 and Figure 2 As shown, the number of air inlet pipes 3 and air outlet pipes 4 are equal and each is not less than two. Multiple air inlet pipes 3 and multiple air outlet pipes 4 are installed in sequence along the vertical direction on the side wall of the vertical dryer 1 on the corresponding side. Multiple air inlet pipes 3 are all connected to the same air inlet manifold 7, and the side of the air inlet manifold 7 away from the air inlet pipes 3 is connected to the flue gas conveying pipe 5. Multiple air outlet pipes 4 are connected to the same outlet manifold 8. The side of the outlet manifold 8 away from the air outlet pipes 4 is connected to the first dust collector 6 through the exhaust gas pipe 9.

[0025] In the above embodiments, the inlet manifold 7 can distribute the flue gas in the flue gas conveying pipe 5 to each inlet pipe 3. Multiple inlet pipes 3 are arranged vertically on one side wall of the vertical dryer 1, thus forming a multi-compartment synchronous heating zone within the vertical dryer 1, ensuring the semi-coke is fully dried during its descent. To ensure the smooth discharge of gas entering the vertical dryer 1 after drying, this application provides the same number of outlet pipes 4 on the side of the vertical dryer 1 opposite to the inlet pipes 3. The side of the outlet pipes 4 furthest from the vertical dryer 1 is connected to the same outlet manifold 8. The outlet manifold 8 can uniformly transport the flue gas discharged from multiple outlet pipes 4 to the exhaust gas pipe 9, and then from the exhaust gas pipe 9 to the first dust collector 6 for centralized treatment.

[0026] Furthermore, such as Figure 2 and Figure 3 As shown, there are four air inlet pipes 3 and four air outlet pipes 4. The four air outlet pipes 4 are located in the middle area of ​​one side wall of the vertical dryer 1, and the four air inlet pipes 3 are distributed in pairs at the upper and lower ends of the other opposite side wall of the vertical dryer 1.

[0027] In the above embodiments, the vertical dryer 1 of this application preferably has a 4-inlet, 4-outlet design for its air inlet and outlet, which makes the airflow in and out of the vertical dryer 1 more uniform, the material heated more evenly, and the drying efficiency improved. This effectively solves the possibility of ignition and red-hot material caused by excessively high temperatures due to localized hot air baking. Figure 3 The diagram shows the flow trajectory of the flue gas inside the vertical dryer 1 during operation. The vertical dryer 1 can be divided into three longitudinal zones. The flue gas entering the vertical dryer 1 through the two upper air inlets 3 first contacts the semi-coke falling from its upper port and undergoes heat exchange. The flue gas blowing out from the two upper air inlets 3 cools down after contacting this semi-coke and flows downwards. The two lower air inlets 3 directly contact the semi-coke that is about to be discharged from the vertical dryer 1. At this point, the semi-coke has a low moisture content and has already been heated by the flue gas from above. Therefore, the flue gas entering through the two lower air inlets 3 will continue to flow upwards. The higher it flows, the higher the moisture content of the semi-coke it comes into contact with, and the flue gas entering through the two lower air inlets 3 will stop rising. According to production research, the flue gas introduced by the two upper air inlets 3 and the flue gas introduced by the two lower air inlets 3 will just converge in the middle area of ​​the vertical dryer 1. The four air outlets 4 of this application are located in this area. Therefore, the four air outlets 4 of this application are set in the middle of the four air inlets 3 in the vertical direction, which helps to discharge all the flue gas that has completed the drying task into the vertical drying kiln in a unified manner.

[0028] In actual use, in order to ensure that the flue gas is discharged smoothly from the vertical dust collector, a fan can be installed on the exhaust duct 9 to provide power for the flow of flue gas.

[0029] Furthermore, a second dust collector is installed on the flue gas conveying pipe 5, which can remove dust from the tail gas of the lime kiln before it reaches the air inlet collection pipe 7.

[0030] In the above embodiments, to prevent dust carried in the exhaust gas from the lime kiln from affecting the quality of the semi-coke in the vertical dryer 1, this application specifically adds a second dust collector to the flue gas conveying pipe 5 to remove dust from the flue gas before it enters the vertical dryer 1. The first dust collector 6 and the second dust collector in this application can be a bag filter, an electrostatic precipitator, or a cyclone dust collector. The specific type of dust collector can be flexibly selected according to the actual production environment, and this application does not further limit this selection.

[0031] Furthermore, a hot air pipe is added between the flue gas conveying pipe 5 and the exhaust gas pipe 9, and an electromagnetic control valve is installed on the hot air pipe.

[0032] In the above embodiments, for the vertical dryer 1, due to the use of low-temperature drying principle and the thorough heat exchange caused by the hot air passing through the material multiple times, the initial temperature of the hot air in the first dust collector 6 is generally only around 80°C. This results in significant energy savings in spring, summer, and autumn, but condensation is easily caused in winter (especially in northern regions). Through repeated research and experimentation, in addition to ensuring proper insulation of the dust collector, this application proposes a DN250 hot air pipe bypassing the flue gas conveying pipe 5 near the inlet pipe 3 of the vertical dryer 1. This pipe connects to the exhaust gas pipe 9 of the vertical dryer 1, and an electric regulating valve is installed on this hot air pipe. The opening degree is controlled by the electric regulating valve to ensure that the temperature of the hot air entering the first dust collector 6 is around 90°C in winter. By increasing the temperature of the hot air entering the first dust collector 6, condensation can be effectively avoided. When spring arrives and the temperature rises, the electric regulating valve can be closed, and all flue gas will again directly enter the dryer, thus restoring the hot air efficiency.

[0033] Furthermore, such as Figure 1 As shown, an auxiliary heat source is connected to the flue gas conveying pipe 5.

[0034] In the above embodiments, the main function of the auxiliary heat source is to ensure that the production capacity of the vertical dryer 1 is not significantly affected when there is insufficient tail gas from the lime kiln.

[0035] Furthermore, such as Figure 1 As shown, the auxiliary heat source is a fluidized bed furnace 10, and the hot air outlet of the fluidized bed furnace 10 is connected to the flue gas conveying pipe 5 through a tee.

[0036] In the above embodiments, the fluidized bed furnace 10 is the main equipment for providing hot air for drying semi-coke in the existing vertical dryer 1. In the implementation of the system of this application, the original fluidized bed furnace 10 can be retained, and its outlet can be connected to the flue gas conveying pipe 5 via a tee. Under normal circumstances, when the amount of tail gas from the lime kiln is sufficient, the fluidized bed furnace 10 does not need to operate. Only under special circumstances (such as when a lime kiln is under maintenance) when the tail gas from the lime kiln alone is insufficient to maintain the output of the vertical dryer 1, will the fluidized bed furnace 10 be started. This improves the stability of the vertical dryer 1 during operation.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A lime kiln exhaust gas treatment system, comprising a vertical dryer (1), wherein a steep-angle belt conveyor (2) is provided on one side of the vertical dryer (1), the steep-angle belt conveyor (2) being used to transport semi-coke from the carbon material receiving hopper to the upper port of the vertical dryer (1), characterized in that: The vertical dryer (1) is provided with an air inlet pipe (3) and an air outlet pipe (4) on opposite sides of the radial direction. The air inlet pipe (3) is connected to one end of the flue gas conveying pipe (5) at the end away from the vertical dryer (1). The exhaust gas from multiple lime kilns is connected to the other end of the flue gas conveying pipe (5). The flue gas conveying pipe (5) can input the exhaust gas from multiple lime kilns into the vertical dryer (1) through the air inlet pipe (3). The air outlet pipe (4) is connected to the first dust collector (6).

2. The lime kiln tail gas treatment system according to claim 1, characterized in that: The number of air inlet pipes (3) and air outlet pipes (4) are equal, and there are not less than two of each. Multiple air inlet pipes (3) and multiple air outlet pipes (4) are installed in sequence along the vertical direction on the side wall of the vertical dryer (1) on the corresponding side. Multiple air inlet pipes (3) are connected to the same air inlet manifold (7), and the side of the air inlet manifold (7) away from the air inlet pipes (3) is connected to the flue gas conveying pipe (5); Multiple air outlet pipes (4) are connected to the same outlet manifold (8), and the side of the outlet manifold (8) away from the air outlet pipes (4) is connected to the first dust collector (6) through the exhaust gas pipe (9).

3. The lime kiln tail gas treatment system according to claim 2, characterized in that: The number of air inlet pipes (3) and air outlet pipes (4) are both four. The four air outlet pipes (4) are located in the middle area of ​​one side wall of the vertical dryer (1), and the four air inlet pipes (3) are distributed in pairs at the upper and lower ends of the other opposite side wall of the vertical dryer (1).

4. The lime kiln tail gas treatment system according to claim 3, characterized in that: A second dust collector is installed on the flue gas conveying pipe (5). The second dust collector can remove dust from the tail gas of the lime kiln before it reaches the air inlet collection pipe (7).

5. The lime kiln tail gas treatment system according to claim 2, characterized in that: A hot air pipe is added between the flue gas conveying pipe (5) and the tail gas pipe (9), and an electromagnetic control valve is installed on the hot air pipe.

6. The lime kiln tail gas treatment system according to any one of claims 1 to 5, characterized in that: The flue gas conveying pipe (5) An auxiliary heat source is connected to the top.

7. The lime kiln tail gas treatment system according to claim 6, characterized in that: The auxiliary heat source is a fluidized bed furnace (10), and the hot air outlet of the fluidized bed furnace (10) is connected to the flue gas conveying pipe (5) through a tee.

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