A device for recovering escaped ammonia from the tail of a carbide cement kiln

Abstract

This technology relates to a device for recovering ammonia escaping from the kiln tail of a carbide slag cement kiln, comprising a flue gas spray cooler, an ammonia evaporator, and a wastewater treatment device connected in sequence. The flue gas spray cooler is located between the kiln tail exhaust fan and the chimney, employing a combination of heat transfer and composite cooling. First, the flue gas, initially at 120-150℃, is cooled to 80-90℃, then further cooled to 45-50℃ by low-temperature brine spraying, causing ammonia and water vapor to co-condense, producing clean flue gas with an ammonia concentration <8mg / Nm³ and ammonia-containing condensate of 1.5-2.5%. The ammonia-containing condensate is then heated to 80-90℃ by a serpentine tube evaporator fixed to the upper part of the rotary kiln shell using the kiln's 300-400℃ radiant heat, causing the ammonia to volatilize. The evaporate is then transported via PLC control to an 850-900℃ decomposition furnace for denitrification. After the residual water from evaporation is neutralized to pH 7-8 and further treated by a multi-media filter, the ammonia concentration in the effluent is <10ppm, achieving a reuse rate of ≥95% (60% for circulating cooling water and 40% for greening water), effectively solving the ammonia escape problem and realizing resource utilization.

Description

Technical Field

[0001] This utility model relates to the field of exhaust gas treatment technology, and in particular to a device for recovering ammonia escaped from the tail of a carbide slag cement kiln. Background Technology

[0002] Calcium carbide slag, a major industrial waste generated during the calcium carbide-based polyvinyl chloride (PVC) production process, is primarily composed of Ca(OH)2 and is an important calcium-based raw material for cement production, replacing limestone. However, in cement kilns using calcium carbide slag as a feedstock, due to the unique characteristics of the raw materials and processes, high concentrations of escaped ammonia (NH3) are present in the kiln tail flue gas. This ammonia primarily originates from the high-temperature decomposition of organic nitrogen or nitrogen-containing compounds in the raw materials, resulting in flue gas ammonia emissions far exceeding national environmental standards, posing a significant challenge to the industry.

[0003] Currently, the industry mainly relies on traditional thermal ammonia stripping or chemical absorption technologies to treat escaped ammonia, which has significant bottlenecks: First, traditional recovery technologies require a large amount of additional steam or electricity to heat and purify ammonia-containing wastewater, resulting in high energy costs that do not align with the energy conservation and emission reduction trend in the cement industry; second, the purified high-concentration ammonia gas needs to undergo complex refining and conveying processes before it can be reused for denitrification, which is complex and poses safety hazards; finally, the residual wastewater generated after evaporation and ammonia removal still contains a certain concentration of ammonia and impurities, which can easily cause secondary pollution if not properly treated, making it difficult and costly to achieve near-zero wastewater discharge.

[0004] Therefore, developing an escaped ammonia recovery device that can be deeply integrated with cement production processes, has low energy consumption, high ammonia recovery efficiency, and enables wastewater recycling is of urgent need and great significance for promoting the green and sustainable development of the carbide slag cement industry. Utility Model Content

[0005] The purpose of this invention is to address the shortcomings of existing technologies, such as the need for traditional ammonia recovery technologies to consume large amounts of steam or electricity for heating and purifying ammonia-containing wastewater, resulting in high energy costs that do not align with the energy conservation and emission reduction trends in the cement industry; the need for complex refining and conveying processes before the purified high-concentration ammonia can be reused for denitrification, which is both complex and poses safety hazards; and the need for residual wastewater after evaporation and ammonia removal to still contain a certain concentration of ammonia and impurities, which can easily cause secondary pollution if not properly treated, making it difficult and costly to achieve near-zero wastewater discharge. Therefore, this invention proposes a device for recovering ammonia escaping from the kiln tail of a carbide slag cement kiln.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A device for recovering ammonia escape from the tail of a carbide slag cement kiln includes a flue gas spray cooler, an ammonia evaporator and a wastewater treatment device connected in sequence. It also includes a kiln tail high-temperature fan, a kiln tail dust collector, a kiln tail exhaust fan, and a kiln tail chimney. The flue gas spray cooler is located between the kiln tail exhaust fan and the kiln tail chimney, and adopts a structure combining heat transfer and composite cooling. It includes a heat exchanger and a spray tower. The heat exchanger is used to cool the high-temperature humid flue gas at 120-150℃ to 80-90℃. The spray tower is used to deeply cool the flue gas to 45-50℃ through low-temperature brine spraying, so that ammonia and water vapor co-condense, and output clean flue gas with an ammonia concentration of <8mg / Nm³ and ammonia-containing condensate with an ammonia concentration of 1.5-2.5%. The kiln tail exhaust fan is connected to the kiln tail dust collector, and the kiln tail dust collector is connected to the kiln tail high-temperature fan. It also includes a cement rotary kiln, a decomposition furnace, and a preheater. The ammonia evaporator is fixed to the upper 1 / 3 of the cement rotary kiln cylinder by a ring support. It is a serpentine tube evaporator. The inner wall of the serpentine tube evaporator is coated with a PTFE nano-coating. The material is Hastelloy C-276. It is used to heat the ammonia-containing condensate to 80-90°C using the radiant heat of the kiln body at 300-400°C to volatilize the ammonia. It is equipped with a PLC closed-loop controller to transport the volatilized ammonia to the decomposition furnace at 850-900°C for reuse and denitrification. The decomposition furnace is connected to the high-temperature fan at the kiln tail through multiple preheaters. The wastewater treatment device is used to treat the residual water from the ammonia evaporator. It includes a neutralization tank and a multi-media filter. The neutralization tank is used to add Ca(OH)2 to adjust the pH of the wastewater to 7-8. The multi-media filter is filled with quartz sand and activated carbon to filter the neutralized wastewater. The ammonia concentration of the treated effluent is <10ppm, achieving a reuse rate of ≥95%, of which 60% is reused for circulating cooling water and 40% is reused for greening water in the plant area. The neutralization tank is equipped with a nested retractable stirring paddle, the total length of which is adjustable to accommodate tank depths of 1-2.5m.

[0007] Furthermore, the spray tower of the flue gas spray cooler includes a shell, an upper annular cover is fixedly installed on the top of the shell, a lower annular cover is fixedly installed on the bottom of the shell, an air inlet is fixedly connected to one side of the lower annular cover, an exhaust port is fixedly connected to one side of the upper annular cover, connecting plates are fixedly installed at the bottom of the upper annular cover and the top of the lower annular cover, and multiple hollow tubes are fixedly connected between the two connecting plates. A cooling water outlet is fixedly connected to the upper side of one side of the shell, and a cooling water inlet is fixedly connected to the lower side of one side of the shell.

[0008] Furthermore, the annular support of the ammonia evaporator is made of high-temperature resistant alloy material and can rotate together with the rotary kiln cylinder.

[0009] Furthermore, the serpentine evaporator is arranged with a multi-layer spiral coil structure to maximize the heat exchange area.

[0010] Furthermore, multiple limiting plates are fixedly installed inside the housing, and the limiting plates are used to limit the hollow tube.

[0011] Furthermore, the top of the upper annular shield is fixedly connected to an upper shield, the top of the upper shield is fixedly connected to a liquid inlet, a hollow plate is fixedly installed inside the upper shield, multiple nozzles are fixedly connected to the bottom of the hollow plate, the top of the hollow plate is fixedly connected to the bottom of the liquid inlet, the bottom of the lower annular shield is fixedly connected to a lower shield, the bottom of the lower shield is fixedly connected to a drain outlet, a fixing plate is fixedly installed inside the lower shield, and multiple liquid inlet pipes are fixedly passed through the inside of the fixing plate, the liquid inlet pipes are used in conjunction with the multiple hollow pipes.

[0012] In this application, firstly, the high-temperature humid flue gas (120-150℃) from the cement rotary kiln, driven by the high-temperature fan at the kiln tail, passes sequentially through the kiln tail dust collector and the kiln tail exhaust fan before entering the aforementioned flue gas spray cooler. In this cooler, the flue gas first undergoes preliminary cooling via a heat exchanger ("heat transfer" stage), with the temperature dropping to 80-90℃; then it enters the spray tower, where it undergoes deep spray cooling by low-temperature brine sprayed from nozzles ("composite cooling" stage), further reducing the temperature to 45-50℃. Under these low-temperature conditions, gaseous ammonia (NH3) in the flue gas undergoes co-condensation with water vapor, thereby being captured and entering the liquid phase. This process ultimately produces two products: firstly, clean flue gas with an ammonia concentration below 8 mg / Nm³, which is discharged through the kiln tail chimney in compliance with standards; and secondly, ammonia-containing condensate water with an ammonia concentration of approximately 1.5-2.5%, which has captured the escaped ammonia.

[0013] Subsequently, the collected ammonia-containing condensate is transported to an ammonia evaporator. The ammonia evaporator is fixed to the upper third of the cement rotary kiln shell via a high-temperature resistant annular support, utilizing the high-temperature radiant heat of the kiln surface (300-400℃) as a heat source. The ammonia-containing condensate enters a serpentine evaporator made of Hastelloy C-276 material with a PTFE nano-coating lining, where it is heated to 80-90℃. At this temperature, the dissolved ammonia in the water is re-evaporated and released. Through precise control by a PLC closed-loop controller, the released high-concentration ammonia is stably transported to the high-temperature zone at the inlet of the decomposition furnace (temperature 850-900℃), where it participates as a reducing agent in SNCR (Selective Non-Catalytic Reduction) or SCR (Selective Catalytic Reduction) denitrification reactions, thereby achieving in-situ recovery and utilization of ammonia resources.

[0014] Finally, the residual evaporation water (with a significantly reduced ammonia concentration) after ammonia removal enters the wastewater treatment unit for final treatment. The wastewater first enters a neutralization tank, where Ca(OH)2 is added to adjust its pH to a neutral range of 7-8. The neutralized wastewater then enters a multi-media filter filled with quartz sand and activated carbon for further filtration and purification, removing suspended solids and other impurities, ultimately resulting in an effluent ammonia concentration below 10 ppm. The treated water achieves a comprehensive reuse rate of ≥95%, with approximately 60% reused in the circulating cooling water system and approximately 40% reused for irrigation of the plant's green areas, realizing the recycling of water resources. The entire system effectively solves the problem of ammonia escape from the kiln tail and achieves dual resource recovery of ammonia and water.

[0015] Beneficial effects: Physical cooling and condensation: Utilizing the property that ammonia is easily soluble in water, the high-temperature humid flue gas is cooled to below the dew point, so that water vapor and ammonia gas are condensed together into ammonia-containing wastewater.

[0016] Waste heat evaporation to recover ammonia: The waste heat of the rotary kiln cylinder is used to heat ammonia-containing wastewater, evaporate ammonia gas, and reuse it for denitrification.

[0017] Wastewater harmless treatment: The hot water after evaporation is treated and reused or used for greening, achieving zero discharge. Attached Figure Description

[0018] Figure 1 This is a process diagram of an ammonia recovery device for the tail end of a carbide slag cement kiln proposed in this utility model. Figure 2 This is a three-dimensional structural diagram of the flue gas spray cooler in the ammonia recovery device at the tail of a carbide slag cement kiln proposed in this utility model. Figure 3 This is an exploded view of the flue gas spray cooler in the ammonia recovery device at the tail of a carbide slag cement kiln proposed in this utility model. Figure 4 This is an exploded view of the upper protective cover and the upper annular protective cover in the ammonia recovery device at the tail of a carbide slag cement kiln proposed in this utility model. Figure 5 This is an exploded view of the lower annular cover and the lower cover in a carbide slag cement kiln tail escape ammonia recovery device proposed in this utility model.

[0019] In the diagram: 1. Flue gas spray cooler; 2. Ammonia evaporator; 3. Wastewater treatment device; 4. Cement rotary kiln; 5. Decomposition furnace; 6. Kiln tail high-temperature fan; 7. Kiln tail dust collector; 8. Kiln tail exhaust fan; 9. Kiln tail chimney; 10. Preheater; 101. Shell; 102. Exhaust port; 103. Upper protective cover; 104. Liquid inlet; 105. Upper annular protective cover; 106. Cooling water outlet; 107. Cooling water inlet; 108. Lower annular protective cover; 109. Liquid outlet; 110. Lower protective cover; 111. Air inlet; 112. Hollow tube; 113. Limiting plate; 114. Nozzle; 115. Hollow plate; 116. Liquid inlet pipe; 117. Fixing plate; 118. Connecting plate. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention.

[0021] In one embodiment: Refer to Figure 1-5 The specific implementation of a recycling device is achieved in the following manner. The core of the device consists of a flue gas spray cooler 1, an ammonia evaporator 2, and a wastewater treatment device 3 connected in sequence, and works in conjunction with the main cement production line equipment.

[0022] High-temperature, humid flue gas at 120-150℃ from the cement rotary kiln 4, driven by the high-temperature fan 6 at the kiln tail, first passes through the kiln tail dust collector 7 for dust collection, and then is transported to the flue gas spray cooler 1 by the kiln tail exhaust fan 8. The flue gas spray cooler 1 is located in the flue between the kiln tail exhaust fan 8 and the kiln tail chimney 9, and adopts a two-stage treatment of heat transfer and composite cooling. The flue gas first enters a plate heat exchanger, where it indirectly exchanges heat with circulating cooling water, reducing its temperature to 80-90℃. The pre-cooled flue gas enters the shell 101 of the spray tower through the inlet 111. The core component of the spray tower includes multiple layers of vertically arranged hollow tubes 112. These hollow tubes 112 are fixed between the upper annular cover 105 and the lower annular cover 108 by upper and lower connecting plates 118, and are further positioned by limiting plates 113 inside the shell 101 to ensure structural stability. A cryogenic brine circulator supplies refrigerant to the inner cavity of the shell 101 through the cooling water inlet 107, and finally flows out through the cooling water outlet 106. During the ascent of the flue gas within the tower, it comes into full contact with the cryogenic brine droplets sprayed from the nozzles 114. The top of the upper annular shroud 105 is fixedly connected to an upper shroud 103, and the top of the upper shroud 103 is fixedly connected to a liquid inlet 104. The nozzles 114 are connected to the liquid inlet 104 at the top through a hollow plate 115. Brine enters through the liquid inlet 104 and is distributed to each nozzle 114 via the hollow plate 115. A fixing plate 117 is fixedly installed inside the lower shroud 110. Multiple liquid inlet pipes 116 are fixedly inserted through the interior of the fixing plate 117. The liquid inlet pipes 116 are used in conjunction with multiple hollow pipes 112, deeply cooling the flue gas to 45-50°C. The ammonia gas in the flue gas co-condenses with the water vapor, forming ammonia-containing droplets that fall. The liquid collects at the bottom of the tower, is collected by the lower shroud 110, and then discharged from the drain port 109. The ammonia concentration of this condensate is between 1.5% and 2.5%. The ammonia concentration of the purified flue gas is less than 8 mg / Nm³, and it is discharged through the exhaust port 102 on the side of the upper annular shroud 105, and then discharged through the kiln tail chimney 9 to meet emission standards.

[0023] The system also includes multiple preheaters 10, and the collected ammonia-containing condensate is pumped to the ammonia evaporator 2 via a corrosion-resistant pump. The main body of the ammonia evaporator 2 is a serpentine evaporator, with pipes made of Hastelloy C-276 material and coated with a PTFE nano-coating on the inner wall to resist corrosion from the ammonia water. The ammonia evaporator 2 is fixedly installed in the upper third of the cylinder of the cement rotary kiln 4 via a ring support made of high-temperature resistant alloy, and can rotate with the kiln. The evaporator's pipes are arranged in a multi-layer spiral coil structure to maximize its heating area. During operation, the surface temperature of the cement rotary kiln 4 is 300-400℃, continuously radiating heat to the ammonia-containing condensate in the coils, maintaining its temperature stably at 80-90℃, thereby promoting the efficient volatilization and precipitation of dissolved ammonia gas. The volatilized ammonia gas is led to the inlet of the decomposition furnace 5 through an insulated pipe. A PLC closed-loop controller monitors the NOx concentration signal at the inlet of the decomposition furnace 5 in real time, and adjusts the flow rate of ammonia-containing condensate delivered to the evaporator accordingly, thereby precisely controlling the supply of ammonia and ensuring that it is used for denitrification reaction in the high-temperature range of 850-900℃.

[0024] This application can be used in the field of exhaust gas treatment, or in other fields applicable to this application.

[0025] In another embodiment: Reference Figure 1-5 A device for recovering ammonia escaping from the tail end of a carbide slag cement kiln is described. This device is used in the field of tail gas treatment. The residual evaporation water produced after ammonia removal through evaporation has a significantly reduced ammonia concentration and is then pumped into a wastewater treatment unit 3 for final treatment. The wastewater first enters a neutralization tank. A nested, retractable agitator adjusts its blade length between 1 and 2.5 meters according to the actual depth of the tank to ensure uniform mixing. Ca(OH)2 slurry is added to the tank via an automatic dosing device to adjust the pH of the wastewater to a neutral range of 7-8. The neutralized wastewater overflows by gravity into a multi-media filter filled with a double layer of quartz sand and activated carbon to remove suspended particles and residual impurities. The final effluent ammonia concentration is below 10 ppm, achieving a reuse rate of over 95%. Approximately 60% of the treated water is reused as makeup water for the plant's circulating cooling water system, and approximately 40% is used for irrigation of the plant's green spaces, achieving a closed-loop recycling of water resources.

[0026] However, as is well known to those skilled in the art, the working principles and wiring methods of the ammonia evaporator 2, decomposition furnace 5, kiln tail exhaust fan 8, kiln tail high temperature fan 6, kiln tail dust collector 7, and preheater 10 are all conventional methods or common knowledge, and will not be elaborated here. Those skilled in the art can make any selections according to their needs or convenience.

[0027] The above description is only a preferred embodiment of the present utility model, but the protection scope of the present utility model is not limited thereto. Any equivalent substitutions or changes made by those skilled in the art within the technical scope disclosed in the present utility model, based on the technical solution and the inventive concept of the present utility model, should be included within the protection scope of the present utility model.

Claims

1. A calcium carbide slags cement kiln off-take ammonia recovery apparatus, characterized in that, It consists of a flue gas spray cooler (1), an ammonia evaporator (2), and a wastewater treatment device (3) connected in sequence; It also includes a kiln tail high-temperature fan (6), a kiln tail dust collector (7), a kiln tail exhaust fan (8), and a kiln tail chimney (9). The flue gas spray cooler (1) is located between the kiln tail exhaust fan (8) and the kiln tail chimney (9), and adopts a structure combining heat transfer and composite cooling. It also includes a heat exchanger and a spray tower. The heat exchanger is used to cool the high-temperature humid flue gas. The spray tower is used to deeply cool the flue gas by spraying with low-temperature brine, so that ammonia and water vapor co-condense. The kiln tail exhaust fan (8) is connected to the kiln tail dust collector (7), and the kiln tail dust collector (7) is connected to the kiln tail high-temperature fan (6). It also includes a cement rotary kiln (4), a decomposition furnace (5) and a preheater (10). The ammonia evaporator (2) is fixed to the upper 1 / 3 area of ​​the cylinder of the cement rotary kiln (4) by a ring bracket. It adopts a serpentine tube evaporator. The inner wall of the serpentine tube evaporator is coated with a PTFE nano-coating and equipped with a PLC closed-loop controller for transporting the volatilized ammonia to the decomposition furnace (5) for reuse and denitrification. The decomposition furnace (5) is connected to the kiln tail high-temperature fan (6) through multiple preheaters. The wastewater treatment device (3) is used to treat the residual water from the evaporation of the ammonia evaporator (2). It includes a neutralization tank and a multi-media filter. The neutralization tank is used to add Ca(OH)2 to adjust the pH of the wastewater. The multi-media filter is filled with quartz sand and activated carbon to filter the neutralized wastewater. The neutralization tank is equipped with a nested retractable stirring paddle, the total length of which is adjustable.

2. A calcium carbide slags cement kiln tail gas ammonia recovery device according to claim 1, characterized in that, The spray tower of the flue gas spray cooler (1) includes a shell (101), an upper annular cover (105) is fixed to the top of the shell (101), a lower annular cover (108) is fixed to the bottom of the shell (101), an air inlet (111) is fixedly connected to one side of the lower annular cover (108), an exhaust hole (102) is fixedly connected to one side of the upper annular cover (105), a connecting plate (118) is fixedly installed at the bottom of the upper annular cover (105) and the top of the lower annular cover (108), a plurality of hollow tubes (112) are fixedly connected between the two connecting plates (118), a cooling water outlet (106) is fixedly connected to the upper side of one side of the shell (101), and a cooling water inlet (107) is fixedly connected to the lower side of one side of the shell (101).

3. A calcium carbide slags cement kiln tail gas ammonia recovery device according to claim 1, characterized in that, The ring support of the ammonia evaporator (2) is made of high-temperature resistant alloy material and can rotate together with the rotary kiln (4) cylinder.

4. A calcium carbide slags cement kiln tail gas ammonia recovery device according to claim 1, characterized in that, The serpentine evaporator is arranged with a multi-layer spiral coil structure to maximize the heat exchange area.

5. A calcium carbide slags cement kiln tail gas ammonia recovery device according to claim 2, characterized in that, Multiple limiting plates (113) are fixedly installed inside the housing (101), and the limiting plates (113) are used to limit the hollow tube (112).

6. A calcium carbide slags cement kiln tail gas ammonia recovery device according to claim 2, characterized in that, The upper annular shield (105) is fixedly connected to the top of the upper shield (103), and the top of the upper shield (103) is fixedly connected to the liquid inlet (104). A hollow plate (115) is fixedly installed inside the upper shield (103), and multiple nozzles (114) are fixedly connected to the bottom of the hollow plate (115). The top of the hollow plate (115) is fixedly connected to the bottom of the liquid inlet (104). The bottom of the lower annular shield (108) is fixedly connected to the lower shield (110), and the bottom of the lower shield (110) is fixedly connected to the drain port (109). A fixing plate (117) is fixedly installed inside the lower shield (110), and multiple liquid inlet pipes (116) are fixedly passed through the fixing plate (117). The liquid inlet pipes (116) are used in conjunction with multiple hollow pipes (112).

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