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Application of Combined Swirl Plate Purification Tower in Desulfurization and Dust Removal of Heavy Oil-fired Boilers Author: Zeng Shengxue, Chen Huogui, Zhang Likui Abstract: By organically combining cyclone plate technology with other dust removal technologies, a new type of combined cyclone plate purification tower has been developed, which has achieved good results in the practice of desulfurization and dust removal for oil-fired boilers. keywords: Cyclone plate desulfurization and dust removal fuel-fired boiler exhaust gas purification tower 1. Introduction In enterprises such as dyeing and weaving, food, papermaking, chemical industry, etc., there are a number of small oil-fired boilers with evaporation capacity below 25T/h and using heavy oil as fuel. The sulfur content of heavy oil is very high. For example, the sulfur content of 180# heavy oil is as high as 2~2.6%, causing the sulfur dioxide concentration in the flue gas to be as high as more than 4000mg/Nm3. In order to effectively remove sulfur dioxide from the flue gas of heavy oil boilers, Shenzhen Best Environmental Protection Engineering Co., Ltd. has been studying the use of swirl plate technology invented by Professor Tan Tianen of Zhejiang University to control sulfur-containing exhaust gas from heavy oil boilers since 1997. In early 1999, it developed a integrated desulfurization and dust removal system. The integrated combined cyclone plate purification tower (type I and type II) has treated a large number of heavy oil boiler flue gases with varying evaporation volumes in Guangzhou and Shenzhen, and has achieved satisfactory results. To this end, the Shenzhen Municipal Environmental Protection Bureau organized an on-site promotion meeting to promote this advanced technology, and many media in Shenzhen conducted publicity and reports. 2. Principle of flue gas desulfurization in combined swirl plate purification tower. Combined swirl plate flue gas desulfurization and dust removal is essentially a typical chemical mass transfer process in which SO2 in the flue gas is transferred from the gas phase to the liquid phase. Since the desulfurization liquid is an alkali-containing aqueous solution, SO2 undergoes an acid-base neutralization reaction immediately after contact with the alkali solution in the water. Therefore, the mass transfer process resistance is mainly concentrated in the gas phase and is controlled by the gas film. According to the double-membrane theory of the mass transfer process, increasing the turbulence of the gas phase and increasing the gas-liquid contact area are beneficial to the removal of SO2. In order to increase the degree of gas phase turbulence and prevent the clogging of the purification tower, the use of swirl plates as gas-liquid contact elements has been proven to be a correct and reasonable choice both in theory and in practice.: 2.1. When the air flow makes a spiral upward motion through the swirl plate, the liquid flow part is distributed to each swirl plate blade by the air flow, forming a liquid film. ； Part of it is dispersed by the air flow into fine droplets, which rise with the air flow. During the rising process, many vortices are generated between the gas and liquid, which penetrate each other and the surface is constantly updated. This greatly enhances the gas-liquid contact area and the degree of gas phase turbulence, and strengthens the mass transfer process. 2.2. The opening ratio of the swirl plates is above 33%. The kinetic energy factor of the airflow passing through the gaps in the swirl plates is often 10~12, and some are as high as 15. Therefore, the scouring force passing through the gaps in the trays is large and will not cause clogging. This is exactly what packed towers and other types of trays cannot achieve. 3.3. The water spraying device in the cyclone plate tower is not a microhole (or small hole) sprayer. The water supply of the cyclone plate tower is directly leached into the blind area of the cyclone plate by φ40mm, φ50mm or larger diameter pipes. The water is dispersed into fine droplets by the rotating airflow, so there is no problem of clogging of the water supply device. 3. Combined cyclone plate purification tower flue gas desulfurization process The combined cyclone plate purification tower desulfurization and dust removal can use the bleaching and dyeing waste alkali water from the printing and dyeing factory, the bottle washing waste alkali water from the beverage factory, and the boiler discharge water as the absorption liquid to achieve waste treatment with waste. 3.1. Flue gas desulfurization process flow chart 3.2. The process flow chart illustrates that the flue gas containing sulfur dust is inhaled, and after being pressurized by the induced draft fan, it enters the purification tower at a certain speed. In the purification tower, through a series of effects such as impact, washing, leaching and liquid film, the larger dust particles in the flue dust and a considerable part of the SO2 acid gas are removed here to a certain extent. This process is called the first-level purification. Because the flue gas temperature is relatively high (200~220oC), a large amount of steam is generated during this process. The generated steam rises together with the initially purified flue gas, and repeatedly mixes with the leached desulfurization liquid on multiple gas-liquid contact elements - cyclone plates, so that the dust and SO2 acid gas in the flue gas can be basically removed. This process is called the second-level purification. The purified flue gas then passes through the cyclone demister to remove liquid foam and mist droplets, and is discharged directly from the top of the purification tower or into the chimney. The desulfurization liquid carrying dust particles flows out from the bottom of the tower and returns to the pool. The dust particles sink to the bottom of the pool by gravity, and the absorbent liquid is pumped into the tower for recycling. In order to maintain a certain pH value in the circulating fluid, lye or alkali is regularly added to the pool. A float is used in the pool to keep the liquid level constant, and evaporated water can be automatically replenished. According to its specific gravity, part of the circulating fluid is discharged to the water treatment station for treatment. The chemical reaction formula of the process is as follows: SO2 (gas) → SO2 (liquid) 2NaOH + SO2 → Na2SO3 + H2O Na2SO3 + SO2 + H2 O → 2NaHSO3 Because there is oxygen in the flue gas, part of Na2SO3 is oxidized 2Na2SO3 + O2 → 2Na2SO4 4. Some examples of combined swirl plate purification towers for treating heavy oil boiler flue gas are taken from Shenzhen Vita (Guangming) Food and Beverage Co., Ltd. The company is a large-scale enterprise that produces a variety of bottled, soft-packaged, and carton-packed beverages. Its products are sold to Hong Kong, Macao, Southeast Asia, and the Pearl River Delta. Its boiler workshop has three heavy oil-fired boilers with an evaporation capacity of 6T/h. They operate all year round and directly emit fuel fumes, causing serious pollution to the surrounding environment. Entrusted by it, our company assumed the task of flue gas desulfurization and dust removal of the company's heavy oil boiler in August 2002. After on-site investigation, it was found that there was about 30m3/h bottle washing waste alkali water with a pH of 8 to 11 in its bottle washing workshop. It was decided to use the bottle washing waste alkali water as a desulfurization and dust removal liquid to purify the sulfur dioxide in the boiler flue gas and achieve the design plan of "treating waste with waste". After the project was completed and put into operation, the Municipal Environmental Protection Bureau conducted multiple random monitoring (monitoring results are shown in Tables 1, 2, and 3), and the purification effect was very gratifying. Vita (Bright) Food and Beverage Co., Ltd. Pollution Source and Waste Gas Monitoring List Table 1 Date before project treatment and after treatment 2002.7.16 2002.12.13 2003.1.15 Boiler 1#3#1#2# Chimney height 25M25M20M20M Monitoring times 112312 Measured emission concentration 33269 1076 Converted emission concentration 5701219211513 Emission rate 1.040.020.030.030.040.01 Measured emission concentration 193314314316160157 Emission rate 0.6021. 011.011.021.030.381 Actual measured emission concentration 1.6×1032118175857 Converted emission concentration 2.75×103433735124123 Emission rate 4.990.070.120. 050.370.14 Smoke blackness (Ringelmann level) 111111 Standard dry flue gas flow (m3/h) 3.12×1033.22×1033.22×1033.22×1036.42×1032.43×103 Assessment and monitoring status table organized by Shenzhen Environmental Protection Bureau on February 24, 2003 Table 2 Parameter name Fuel O2 (%) Actual measured excess air coefficient Specified excess air coefficient Flue gas temperature (℃) Flue gas moisture content (%) 1# before boiler chimney treatment 180# Heavy oil 10.21.941.21767.531# after boiler chimney treatment 180# Heavy oil 10.82.061.27612.45 Table 3 Monitoring items (before treatment) smoke dust nitrogen oxides sulfur dioxide flue gas blackness (Ringelmann level) measured emission concentration 1002562.69×10314.32×103 converted emission concentration 162-4.20×103--emission rate 0.4321.1111.2--measured emission concentration 102260 2.71×103-4.32×103 converted emission concentration 165-4.38×103--emission rate 0.4411.1211.7--actual measured emission concentration 982672.84×103-4.32×103 converted emission concentration 158-4.59×103--emission rate 0. 4231.1512.3--Monitoring items (after treatment) smoke dust nitrogen oxides sulfur dioxide flue gas blackness (Ringelmann level) measured emission concentration 2122111813.24×103 converted emission concentration 36-203--emission rate 0.0680.7160.382--measured emission concentration 172 24104-3.24×103 converted emission concentration 29-179--emission rate 0.0550.7260.337--measured emission concentration 2022089-3.24×103 converted emission concentration 34-153--emission rate 0.0650.7130.288--monitoring method: The minimum detection limit for smoke gravimetric method is 2 mq/m3. The nitrogen oxide constant potential electrolysis method is 1 mq/m3. The sulfur dioxide constant potential electrolysis method is 1 mq/m3. Flue gas blackness Ringelmann smoke degree 0 Ringelmann level Some heavy oil boiler flue gas desulfurization and dust removal projects completed by our company in recent years are shown in the table below. Before and after flue gas treatment, Ringelmann blackness dust mg/m3SO2mg/m3 Ringelmann blackness dust mg/m3SO2mg/m3 Shenzhen Haichao Industry and Trade Co., Ltd. 6T/h>130028000120..673.87 Alkaline water 1#8T/h in the first phase of May 1999.13713863069.42532.05 Alkali-containing wastewater from weaving and dyeing 2#8T/h in the second phase of March 2001>13623 913041.6602 Textile and dyeing alkali-containing wastewater 2001 December first phase 3#10T/h>140641500105221 Textile and dyeing alkali-containing wastewater 20016 June second phase 1#10T/h>139840100100268 Textile and dyeing alkali-containing wastewater 2 0019 month 2#10T/h>13913870094175 Textile and dyeing alkali-containing wastewater20019 month 5#10T/h>1387370009034.8 Textile and dyeing alkali-containing wastewater20019 Shenzhen Vita (Guangming) Food and Beverage Co., Ltd. 6T/h 3 units 15702750117.338.3 Bottle washing alkali-containing wastewater December 5, 2002. Comparison of operating parameters and performance between combined cyclone plate purification tower and other absorption equipment. In addition to integrating desulfurization and dust removal, the combined cyclone plate purification tower has many unparalleled advantages that other purification devices have.: 5.1. The desulfurization and dust removal efficiency is high, usually reaching more than 90%. 5.2. The air flow resistance is small, and the air flow resistance of the entire tower is within 600Pa. Therefore, you can choose a fan with lower wind pressure to save power. 5.3. Handle large airflow. With the same tower diameter and the same air flow resistance, the gas volume it can handle is twice that of the packed tower. For packed towers, the general empty tower velocity is below 2~2.5m/s. If this value is exceeded, liquid blocking and flooding will often occur. ； In the combined cyclone plate purification tower, the air flow rotates upward, the air volume increases, and the rotation intensifies. If the air flow resistance is not considered, it will only be beneficial to desulfurization and dust removal, and there will be no liquid blocking or liquid flooding. 5.4. The liquid-to-gas ratio is small, accounting for 60% of the liquid volume used by other desulfurization and dust removal equipment. Our company has used it many times and found that as the liquid-gas ratio increases, the desulfurization and dust removal efficiency increases. However, when the liquid-gas ratio increases to a certain value, the airflow resistance will rise rapidly as the liquid-gas ratio increases, with 0.6~0.8 being the best (see figure). 5.5. Never blocked. The tray opening rate is as high as 33%, and the air flow through the holes has strong scouring force. ； In addition, the pipes supplying liquid to the blind plate area of the swirl plate are ф40mm~ф50mm and will not be blocked. 5.6. The gas flow temperature is high and the fluctuation range is large. It can handle both high-temperature gases and normal-temperature gases. Oil-fired boiler flue gas purification, the flue gas temperature entering the tower is 220oC, and the flue gas temperature leaving the tower is 65oC ； Diesel generator flue gas purification, the flue gas temperature entering the tower is 400oC, and the flue gas temperature leaving the tower is 70oC ； Rock grinding dust gas and spraying organic waste gas are normal temperature gases. 5.7. It has a simple structure, convenient manufacturing, stable operation, and can be automatically controlled without the need for additional personnel to operate. Operating parameters and performance comparison table between combined cyclone plate purification tower and other absorption equipment Name Combined cyclone plate tower Packing tower Spray tower Liquid-gas ratio 0.5~0.8 L/m31~10 L/m30.6~1.0 L/m3 Spray density kinetic energy factor 10~156~8 m3/ m2.h Pressure loss < 600 Pa 500 Pa/m < 600 Pa Air velocity in tower 4.0～5.0 m/s2.0～2.5 m/s0.2～2.0 m/s has a simple structure, is easy to make, is easy to make, is easy to make, has a strong handling capacity, is low, is strong, has a large operating elasticity, is generally fluid resistance, is small, is small, is energy consuming, generally has a uniform distribution of atmospheric liquids, is not uniform, is not easy to be uniform, and has equipment functions that can simultaneously absorb, remove dust, and cool down. When the gas contains high dust content, it is easy to block. Cooling operation status is reliable. Packing is easy to clog. Nozzle is easy to clog. Good purification effect. General general anti-corrosion. Easy anti-corrosion. Easy anti-corrosion. Easy anti-corrosion. Maintenance. Infrequent. More often. More often. 6. Conclusion The combined swirl plate purification tower has not only achieved success in desulfurization and dust removal of flue gas from heavy oil boilers, but has also achieved good results in treating other types of waste gas. Our company uses this technology to treat various power diesel generator black smoke, canteen stove fire smoke, stone grinding dust, cupola kiln flue gas and even organic waste gas projects. All of them operate stably, have reliable quality, and pass the first acceptance. The purified exhaust gas emission concentration is lower than * * and provincial and municipal standard allowable values. The advanced desulfurization and dust removal equipment, the combined cyclone plate purification tower, will play a greater role with the rapid development of my country's economic construction. Author's affiliation: Shenzhen Best Environmental Protection Engineering Co., Ltd. This post was last edited by youngor on 2008-1-12 17:05 ]