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High Efficiency Gas Removal Desulfurization process
Xiechuang. Bricebt
The desulfurization equipment developed according to the characteristics of the sintering kiln has the characteristics of convenient installation, large amount of flue gas treatment, and reduced pressure. The whole set of desulfurization tower body, internal spray structure, brackets, etc. are all made of glass fiber reinforced plastic. Because the desulfurization tower is in an environment where acid and alkali exist at the same time, the glass fiber reinforced plastic itself is an acid and alkali resistant material, which extends the service life of the equipment. It is said that FRP can be used for decades or even hundreds of years. According to our experience, it is no problem to use it for more than 10 years.
According to the ease of maintenance of the spray pipeline, it can be divided into the internal layout of the spray pipeline and the external plug-in type of the spray pipeline. The internal layout of the spray pipeline requires the suspension of the fan and people entering the desulfurization tower for maintenance,there is a support platform for maintenance under the spray pipeline; the sprinkler pipeline can be inspected and repaired outside the tower by the plug-in person without stopping the fan, which improves the efficiency and safety of maintenance.
Conclusions and suggestions: the main materials of desulfurization towers currently on the market are: glass fiber reinforced plastic, carbon steel anticorrosion, brick or granite masonry, and PP board. Generally speaking, it is recommended to choose glass fiber reinforced plastic and carbon steel anticorrosion. Description of specific materials and corresponding advantages and disadvantages.
No. | Types of desulfurization tower materials | Different material advantages and disadvantages description for selection reference |
1 | Brickwork or masonry desulfurization tower | There are many gaps, and it will leak if not handled properly. |
2 | PP board desulfurization tower | The temperature resistance is too low, and the aging is too fast, especially in the place where the ultraviolet radiation is strong, the service cycle is shorter. |
3 | Carbon steel anticorrosive desulfurization tower | Although it has been shown that many carbon steel anti-corrosion desulfurization towers cannot be used, it cannot be said that all carbon steel desulfurization towers are not good, but the anti-corrosion technology of carbon steel desulfurization towers in the brick and tile industry is not enough or to reduce costs. The anti-corrosion is too poor. If the steel plate is sandblasted to remove the rust, it is no problem to use the anti-corrosion well, but the corresponding increase in the cost is not as good as buying all-glass steel |
4 | FRP desulfurization tower | Not all FRP products are good. We have also seen many cases where FRP desulfurization towers cannot be used. It is only because some manufacturers use bad materials with low transaction prices and compressed quality. FRP itself is a corrosion-resistant material. The anti-corrosion inside the steel is also the glass fiber reinforced plastic. The service life of the selected material glass fiber reinforced plastic is absolutely no problem. |
According to the requirements of the factory and some of the technical parameters and data provided, combined with the characteristics of our company's desulfurization technology and engineering experience, a more detailed analysis has been carried out in terms of technical feasibility, safe operation, emission indicators, and engineering economics. After the demonstration, the desulfurization technical plan of this project was compiled.
1.1Project Overview
The project is located in South Africa and is a mobile tunnel kiln with a section of 11.5m. Through communication with the purchaser, a tidal exhaust fan BPCII-18#-132, according to experience, the air volume is about 180-240 thousand cubic meters, and the flue gas temperature is 40-60 degrees Celsius. (Experience value), the oxygen content is about 19%, and the daily output of South African bricks is about 260,000. According to the requirements of the purchaser, it must meet the requirements of Table 2 in GB29620-2013 "Emission Standard of Air Pollutants for Brick and Tile Industry": that is, SO2≤300mg/m3.
1.2 Design basis
"Environmental Protection Law of the People's Republic of China"
GB12348 Noise standard at the boundary of industrial enterprises
GB18599-2001 "General Industrial Solid Waste Storage and Disposal Pollution Control Standard":
GB29620-2013 "Emission Standard of Air Pollutants for Brick and Tile Industry"
GB/T 19229-2003 "Coal-fired flue gas desulfurization equipment"
Technical requirements and testing methods of HJ/T76 fixed pollution source exhaust smoke continuous detection system:
1.3 Design Principles
(1）Ensure that the flue gas sulfur dioxide meets the emission standards;
(2）Ensure the safe and stable operation of the flue gas treatment system;
(3）Adjust measures to local conditions, optimize the combination, and formulate targeted technical implementation plans;
(4）The medicament is cheap, easy to obtain, and convenient to transport, and treat waste with waste, and the desulfurization product does not cause secondary pollution;
(5）Fully consider the nature of the furnace to ensure the adaptability of the furnace desulfurization system under various operating conditions;
(6）Using advanced and mature desulfurization technology and equipment, under the premise of ensuring that the design indicators are met, combined with the actual situation of the factory, the project investment and operating costs are as low as possible;
(7）Minimize the labor load, easy to maintain and save labor.
1.4 Design Parameters
The main design parameters based on this plan are derived from the technical requirements provided by ## New Building Materials Co., Ltd., Gudian Town, Fengtai County. Part of the data not provided by the manufacturer is temporarily taken from experience values. The main original design parameters are shown in the following table.
Table 1.1 Design parameters
Item name | Parameters |
Whole production line scale | |
Fan parameters for polluting gas | BPCII-18#-132/one set |
Smoke volume (working condition) | 180,000-240,000m³/h |
Outlet flue gas temperature of tidal exhaust fan | 40-60℃ |
Daily output | 260000pcs |
Sulfur content of flue gas | |
Actual oxygen content of kiln | Based on 19% |
Annual operating time | 300days |
1.5 Technical Index Of Design
Design indicators are implemented according to corresponding environmental protection standards and requirements
The specific design technical indicators are shown in Table 1.2.
Table 1.2. Technical index of design
Item name | 技术指标（设计保证值） Technical index (design guarantee value) |
Ringelmann Blackness | ≤1级 |
Gas distribution uniformity | ≥70% |
Airflow direction | From the bottom to the top |
Net flue gas sulfur dioxide concentration (after conversion) | ≤300mg/m3 |
Pressure drop of desulfurization unit | ≤1600Pa |
Desulfurization efficiency | ≥96% |
1.6 Scope of design
The design scope of this scheme includes: desulfurization equipment and corresponding supporting systems from the outlet of the fan to the outlet of the absorption tower. Specifically including:
（1）Flue gas system；
（2） SO2 absorption system;
（3）Absorbent preparation and supply system；
（4）Gypsum dehydration system；
（5）Gypsum dehydration system；
（6）Electrical and control system；
1.7 General description of the technical solution
We guarantee that the desulfurization equipment we provide is technologically advanced, and that the manufacturing and design of all equipment meet the requirements of safe, reliable, continuous and effective operation.
●The desulfurization process adopts the sodium-calcium double alkali method.
●The desulfurization device adopts the entire production line and one tower. The flue gas processing capacity of the desulfurization device is 50% to 100% of the flue gas volume of each fan during normal operation, and the emission standard meets the requirements of the design index in 1.5.
●Adopt the plan of purchasing and supplying absorbent directly from outside the plant, without considering the installation of dry grinding or wet grinding systems in the desulfurization island.
●The average annual operating time of desulfurization equipment is considered as 300 days.
2.1 Introduction to common desulfurization processes and principles
2.1.1 Flue gas desulfurization process
According to the different desulfurization methods and product forms, there are four main types: dry desulfurization, semi-dry desulfurization, wet desulfurization and new biological desulfurization.
① Dry flue gas desulfurization
Dry flue gas desulfurization refers to a desulfurization process in which the added desulfurizer is in a dry state and the desulfurization product is still in a dry state. The characteristic of this method is that the flue gas has no obvious temperature drop during the purification process, and the flue gas temperature after purification is high, which is conducive to the dilution and diffusion of the flue gas, and has the advantages of no sewage and waste acid discharge and no corrosion of equipment. But there are problems such as low desulfurization efficiency, slow reaction speed, and huge equipment.
② Wet flue gas desulfurization
Wet flue gas desulfurization is a desulfurization process in which ammonia water or sea water solution or limestone or NaOH mixed with lime is used as a desulfurizing agent slurry, and the generated desulfurization product is sulfite or sulfate dissolved or precipitated. The advantages of this technology are the convenient and cheap source of desulfurization agent, fast desulfurization reaction speed, simple equipment, high desulfurization efficiency, avoiding tower blockage and wear, and operating reliability. At present, among the existing flue gas desulfurization technologies in various countries in the world, the reasons for wet flue gas desulfurization technology account for about 85%. However, the problem is that the wastewater causes severe corrosion to the equipment and the by-product gypsum is difficult to treat, causing secondary pollution."
③Semi-dry flue gas desulfurization
Semi-dry method has some characteristics of dry method and wet method. It is a desulfurization process in which the desulfurizer desulfurizes in a dry state and regenerates in a wet state; or desulfurizes in a wet state and processes the desulfurized product in a dry state. Its advantages are that it has the advantages of fast wet desulfurization reaction speed and high desulfurization efficiency, as well as the characteristics of dry method no sewage and waste acid discharge, and easy disposal of the products after desulfurization. However, the desulfurization efficiency is low, the process is complicated, and the investment is high.
④Biological flue gas desulfurization technology
Biological desulfurization technology includes biological filtration, biological adsorption and biological trickling filtration. The three methods are all open systems, and their microbial populations change with environmental changes. It has many advantages: no catalyst and oxidant (except air), no chemical sludge treatment, little biological pollution, low energy consumption, sulfur recovery, high efficiency, and no odor. The disadvantage is that the process is difficult to control and the conditions are demanding.
Combining the actual situation of the project and the advantages and disadvantages of each desulfurization process, this project is designed to use a wet desulfurization process.
2.1.2Principles of wet flue gas desulfurization
Wet desulfurization mainly includes seawater method, ammonia method, lime (limestone)-gypsum method, double alkali method, magnesium oxide method, etc.
①Seawater desulfurization
A method to neutralize the sulfur dioxide in the flue gas by using the alkalinity of seawater to neutralize the sulfur dioxide in the flue gas. The desulfurized seawater is subjected to aeration and other treatments to reach the seawater discharge standard before being discharged to the sea. This method is mainly suitable for projects that are close to the sea and convenient for water.
② Ammonia desulfurization
The process of using ammonia as an absorbent to remove sulfur dioxide from the flue gas has high desulfurization efficiency and high absorbent utilization efficiency, but the infrastructure investment is large, the operating cost is high, recycling is difficult, and it is easy to cause secondary air pollution.
③ Lime (limestone)-gypsum method
A certain concentration of lime milk is used to absorb sulfur dioxide. The process is mature, safe and reliable in operation, with a desulfurization rate of more than 90%, abundant absorbent resources, and low cost. The waste residue can be discarded or recycled as gypsum, but it is not accurate in PH operation,in this case, the equipment is prone to fouling and clogging, and the selected liquid gas is relatively high.
④ Sodium calcium double alkali method
It uses sodium alkali to absorb sulfur dioxide and then uses lime to treat and regenerate the desulfurization solution. It absorbs the advantages of the alkali method and the lime method to avoid their shortcomings. It is developed on the basis of the improvement of two desulfurization and dust removal technologies. It has the following advantages: the sodium as the absorbent system will not produce sediment; the regeneration of the absorbent and the precipitation of desulfurization slag occur outside the absorption tower, thereby avoiding the blockage and wear of the absorption tower, improving the reliability of operation and reducing In order to reduce the operating cost, the sodium-based absorption liquid absorbs quickly, so a smaller liquid-to-gas ratio can be used to obtain a higher desulfurization rate, easy to operate, and no secondary pollution; the disadvantage is that there are many processes and the by-products can be recycled, but The quality has been reduced.
⑤ Magnesium Oxide Method
Magnesium oxide slurry is used to absorb sulfur dioxide in the flue gas to produce hydrous magnesium sulfite and a small amount of magnesium sulfate, and then the product is dehydrated, dried and heated to decompose it to obtain magnesium oxide and sulfur dioxide. Regenerated magnesium oxide can be recycled for desulfurization
In view of the actual situation of the bidding company, the sodium-calcium dual-alkali process is proposed for this plan.
The sodium-calcium double-alkali method uses Na2CO3 or NaOH solution as the first alkali to absorb flue gas SO2, and then lime is used as the second alkali to regenerate the absorption liquid. The regenerated absorption liquid can be recycled. The reaction principle is:
（1）Absorption response
2NaOH+ SO2 —— Na2SO3+ H2O
Na2CO3+ SO2 —— Na2SO3+CO2
Na2SO3+ SO2+H2O —— 2NaHSO3
In this process, since sodium alkali is used as the absorption liquid, no sediment will be generated in the absorption system. The main side reaction of this process is oxidation reaction, which produces Na2SO4:
2Na2SO3+ O2 —— 2Na2SO4
(2) Regeneration process (with lime slurry)
CaO+H2O—— Ca(OH)2
2NaHSO3 + Ca(OH)2 —— Na2SO3+CaSO3﹒1/2H2O
Na2SO3+ Ca(OH)2 ——2NaOH+CaSO3﹒1/2H2O
The NaOH solution obtained after regeneration is sent back to the absorption system for use. The obtained calcium sulfite hemihydrate can be oxidized to generate gypsum (CaSO4﹒2H2O).
In addition, during operation, because there is still some oxygen in the flue gas, there are side reactions-oxidation reactions:
2CaSO3﹒1/2H2O+O2+3H2O —— 2CaSO4﹒2H2O
2.1.3Empty tower spray desulfurization process
After the flue gas enters the desulfurization tower, it first impacts the water level at the bottom of the desulfurization tower. During the impact, part of the sulfur dioxide in the flue gas is dissolved in the aqueous solution and then flows out of the tower to react. The flue gas is initially evenly distributed; when the flue gas continues to rise through the air distributor, the flue gas is further evenly distributed, so that the wind speed of the flue gas on the same section is as consistent as possible, and the water sprayed from the spray layer falls on the air distributor and continues to flow down A water film is formed around the water outlet, and about 30-40% of the flue gas passes through the water film from under the air distributor to the top of the air distributor. The sulfur dioxide in the flue gas and the water in the process of passing through the water film The alkaline substance reacts, and a part of the particulate matter is left in the water and falls into the bottom of the tower and flows out of the tower for precipitation.
The flue gas passing through the air distributor continues to move upwards, and successively passes through the multi-layer spray layer arranged on the air distributor. The spray layer nozzle adopts a hollow vortex nozzle to break the water flow through the nozzle into fine water particles and water under high pressure. Fog (800-1000μm) makes the coverage of each spray layer reach 150%-200%; each spray layer is arranged crosswise, so that the entire flue gas treatment area is fully covered and there is no dead corner. In the process of passing through the spray layer in sequence, sulfur dioxide is dissolved in the water mist and the alkaline substances in the water mist undergo acid-base reaction to form soluble salts. After purification, the flue gas continues to rise, passing through the corrugated plate demister, the water droplets carried in the flue gas are blocked, but during the long-term use of the demister, some particles or crystals will adhere to the demister. If the demister is not cleaned for a long time, it will block the demister. In order to prevent the demister from clogging and increase the resistance of the desulfurization tower, a demister flushing device is installed to automatically flush the demister with process water.
The desulfurized water flows out of the desulfurization tower to the circulating pool under the action of the overflow's own gravity for further chemical reaction, and the desulfurized liquid after the reaction is again atomized and combined with the moisture exhaust flue gas for treatment, and then circulated in turn. The desulfurization wastewater flowing out of the tower first contacts the lime slurry in the return pool, and then flows into the reaction tank for reaction. Sodium sulfite and calcium hydroxide in the reaction tank react with calcium hydroxide to replace the calcium hydroxide. When the displacement reaction occurs, calcium sulfite precipitates are generated. The reacted liquid flows into the oxidation tank, and air is introduced into the oxidation tank. The air and calcium sulfite fed into the oxidation tank are forcibly oxidized to form calcium sulfate (gypsum), thereby reducing the clogging rate of spray pipes and nozzles. After forced oxidation, the desulfurized water overflows to the sedimentation tank. The supernatant of the desulfurization liquid after precipitation flows into the circulating tank through the overflow for cyclic desulfurization, and the precipitated gypsum is passed into the filter press through the slurry pump, and filtered The clear liquid will continue to flow into the pool for reaction, and the pressed filter cake will be sold or used for personal use. In the process of system operation, there is always unreacted sodium sulfite that is lost during dredging, so it is necessary to add sodium hydroxide or sodium carbonate to the pool regularly to supplement the loss of sodium and alkali.
Double alkali spraying empty tower has the following advantages:
（1）Relatively simple and convenient system, less investment;
（2）The desulfurization efficiency can meet the desulfurization efficiency requirements of the project;
（3）Relatively less prone to scaling;
（4）The absorption tower adopts spraying empty tower, which has low resistance and reliable operation.
（5）The desulfurization device also has a certain dust removal efficiency.
2.1.4Desulfurization equipment description
The whole set of equipment consists of five parts:：
（1）Flue part；（2）SO2 absorption system；（3）Absorbent preparation and supply system；（4）Process water system；（5）Electrical and control system。
（1）Flue gas system
The exhaust gas is passed into the desulfurization tower through the induced draft fan, and the part of the flue that enters the desulfurization tower from the flue through the fan will be produced and installed by the purchaser.
（2）SO2 absorption system
The flue gas from the kiln passes through the induced draft fan and enters the absorption tower at the outlet of the induced draft fan. The flue gas enters the spray absorption tower from the bottom and contacts the spray liquid countercurrently. The SO2 in the flue gas is absorbed by the absorption tower, and the sulfur dioxide removal rate of the flue gas at the outlet is above 92.8%. The clean flue gas is removed from the flue gas through a high-efficiency combined defogging device in the upper section of the tower body, and the purified flue gas enters the chimney through the flue after the tower and is discharged. The absorption tower is made of high temperature resistant glass steel.
After the desulfurization liquid fully contacts and reacts with the flue gas in the absorption tower, it flows back into the mixing tank through the drainage ditch at the bottom of the tower body, and the desulfurization liquid flowing into the mixing tank undergoes regeneration reaction with the lime slurry.
According to site conditions, the circulating mixing pool is divided into five parts: backwater area, regeneration area, oxidation area, sedimentation area, and clean water area. The reflux liquid first enters the return pool and mixes with the lime, and then enters the regeneration pool for displacement reaction; then enters the precipitation zone for precipitation, and the supernatant enters the clear pool and returns to the absorption tower through the circulating water pump. Precipitation is cleaned up regularly.
In this desulfurization equipment, the absorption tower is a countercurrent spraying empty tower, and the spraying layer is arranged in six layers (three-layer desulfurization, three-layer backwashing), which not only meets the specific surface area required to absorb SO2, but also satisfies the furnace Load and sulfur content requirements. At the same time, the pressure loss caused by spraying is reduced to a minimum. Each spray layer is equipped with multiple atomizing nozzles, which are arranged crosswise, and the coverage rate can reach 150%-250%. The nozzle adopts a vortex nozzle, and the material is a corrosion-resistant and wear-resistant silicon carbide nozzle.
The defogging device in the absorption tower is made of high-temperature resistant glass fiber reinforced plastic, mainly composed of defogging plates and anti-cleaning devices.
（3）Absorbent preparation and supply system
The desulfurization absorbent of this project adopts purchased lime powder (250 mesh, 90% sieving rate), and the lime liquid after the lime powder is dissolved by the mixing and feeding system is sent to the regeneration zone (return to the pool) for replacement reaction.
（4）Gypsum dehydration system
Set up a filter press to clean up the sediment regularly every day. The mixture of gypsum and water is fed into the filter press through a slurry pump, the clean water is returned to the pool for reuse, and the filter cake gypsum is collected for external sales or personal use.
（5）Process water system
The process water system is responsible for providing enough water for the desulfurization operation to supplement the water loss during the operation of the system to ensure the normal function of the desulfurization system. Process water is provided by self-provided wells or tap water in the plant area.
（6）Electrical and control system
In order to ensure the stability of the system's desulfurization efficiency, the feed is fed by weight, and the feed rate is adjusted for flue gas with different sulfur content. The pump is equipped with a button-type start-stop distribution box for easy operation.
3.1.1 SO2 Absorption system
The desulfurization system adopts the form of one tower for the entire project.
The absorption tower adopts multi-layer spray + combined demister desulfurization device, and the empty tower spray structure, and the desulfurization efficiency is ≥90%.
● The absorption tower includes absorption tower shell, spray system, combined demister, embedded parts and external steel structure.
● The absorption tower is made of acid and alkali resistant glass fiber reinforced plastic, which can withstand the abrasion of the flue gas fly ash and the solid suspended solids of the desulfurization process, and meet the strict anti-corrosion requirements.
● The absorption tower is designed to prevent liquid leakage. The manholes, channels, connecting pipes, etc. on the tower body are sealed at the perforated part of the shell to prevent leakage.
● The absorption tower shell is designed to withstand various loads, including the dead weight of the equipment and pipes acting on the absorption tower, the weight of the medium, the heat preservation, as well as the wind load, snow load, and seismic load.
● The bottom surface of the absorption tower can basically empty the slurry.
● The overall design of the tower facilitates the overhaul and maintenance of the components in the tower, and the spray system and supports inside the absorption tower will not accumulate dirt and scale.
● The absorption tower is equipped with a sufficient number and appropriate size of manhole doors, and walkways and platforms are set nearby.
● The design of the spray system will reasonably distribute the required spray volume, make the flue gas flow evenly, and ensure that the absorption slurry fully contacts and reacts with the flue gas.
● The nozzle selection will try to avoid rapid wear, scaling and blockage.
● The nozzle and pipe are designed as an external plug-in type, which is convenient for maintenance, flushing and replacement.
3.1.1.2Design specifications：
①The diameter of the desulfurization tower is determined: the flue gas flow rate in the tower is selected from 2 to 4.5 m/s according to the sulfur content. Under the condition of ensuring the removal efficiency of the water droplets carried in the flue gas by the demister and the allowable pressure drop of the absorption system, appropriately increasing the flue gas flow rate can intensify the turbulence intensity between the flue gas and the slurry droplets, thereby increasing the difference between the two The contact area between. Higher flue gas flow rate can also appropriately reduce the geometric dimensions of the absorption tower and tower internals, and improve the cost performance. However, when the flue gas flow rate is too high, the contact time of the absorption liquid and the flue gas is short, thereby reducing its absorption efficiency; at the same time, when the flue gas flow rate is too high, it is accompanied by an increase in resistance and a reduction in the dust removal capacity of the desulfurization tower itself. Considering comprehensively, take the flue gas flow rate in the desulfurization tower=3-3.5m/s
②The design of the spray layer of the absorption tower: The design of the spray layer includes the selection and arrangement of slurry pipes and nozzles.
The arrangement of the spray layer in the absorption tower should make the sprayed droplets completely and evenly cover the entire cross section of the absorption tower, and reduce the amount of slurry flowing along the tower wall as much as possible and reduce the direct erosion and wear of the sprayed slurry on the tower wall
The nozzle should choose acid and alkali resistant materials. Nowadays, the nozzle materials on the market mainly include plastic nozzles, iron nozzles, stainless steel nozzles, and silicon carbide nozzles. Practice has proved that silicon carbide nozzles are the most suitable one.
According to the use of desulfurization towers in the past, this project is equipped with three desulfurization spray layers.
③Height determination: Taking into account the use of high-sulfur coal gangue in the later stage, the desulfurization efficiency margin needs to be considered, and 15m
④The liquid-gas ratio is 2.25, the water volume is 360m3/h, the water volume of each spray layer is 120m3/h, and three water pumps are 15kw.
⑤The design of the demister of the absorption tower: As the net flue gas after the treatment of the absorption tower entrains a large number of slurry droplets, especially when the flow rate of the absorption tower flue gas is relatively high, the amount of droplets carried by the flue gas will increase. In order to prevent water spraying in the desulfurization tower, the demister is also an indispensable part of the desulfurization tower mechanism. A layer of cleaning nozzles are arranged above and below each layer of mist eliminator to clean up the adherents on the mist eliminator in time to reduce equipment resistance and ensure the effect of the mist eliminator.
⑥The design of the flue at the outlet of the absorption tower: There are many types of flue at the outlet of the absorption tower. In this project, the outlet of the absorption tower is appropriately contracted into a cone shape, and then the outlet is sideways to avoid adverse effects on the airflow distribution of the absorption tower.
⑦The design of the nozzles and holes of the absorption tower: In order to be easy to clean, maintain, and repair, the internal structure of the absorption tower is as simple as possible, leaving no dead corners, and having enough operating space. Set up manholes and install inspection ports at corresponding positions.
⑧Material selection of desulfurization tower: The selection of desulfurization tower material is a very important aspect related to the normal and long-term use of desulfurization tower. The flue gas treatment contains SO2. When SO2 meets water, it forms sulfuric acid, which is highly corrosive. Alkaline substances are added to the absorbing liquid, so it is necessary to select materials that are both acid and alkali resistant in the selection of desulfurization tower materials and internal structural materials. The currently used desulfurization tower materials mainly include brickwork, granite, glass fiber reinforced plastic, and iron plate anti-corrosion (the glass fiber reinforced plastic material is used for anti-corrosion treatment in the tower). Now do the following analysis on the desulfurization towers of these materials:
Brick desulfurization tower: The entire tower body is built with sintered red bricks. Because it is built on site, the diameter range is wide and the construction cost is low. However, the internal structure is difficult to arrange, and the cement between the red bricks It is also suitable to be corroded by acid and alkali and has a short service life.
Granite desulfurization tower: The whole tower is built of rubble, which is acid and alkali resistant, and the construction cost is higher than that of bricks. If the entire tower body is constructed of granite, then granite is an ideal material. However, the granite is built with cement, and the cement will be corroded by acid or alkali. Especially in winter, when the cement is corroded, water freezes and expands in the gap, causing a gap between the granite and the granite. When the ice melts, the desulfurization tower Water leakage started, and due to the disappearance of the cohesive force, the continued use of the desulfurization tower has a greater safety hazard.
FRP desulfurization tower: The whole set of equipment is made of FRP, which is a good corrosion-resistant material, and has good resistance to atmosphere, water and general concentrations of acid, alkali, salt, etc. Moreover, the specific gravity of FRP is light, the surface is smooth, and the pressure is reduced, but the cost of FRP desulfurization tower is higher. After market survey feedback, FRP desulfurization tower is relatively the most successful one.
Iron plate anti-corrosion desulfurization tower: It is one of the most widely used in the market. The production cost is intermediate and the production cycle is short. Since the inner wall is anti-corrosive with FRP, it can be used normally in the short term. However, because the flue gas to be processed has a certain temperature, the expansion coefficients of FRP and iron are different, and the anti-corrosion FRP will be separated from the iron. Once the surface of the FRP leaks, the iron sheet at the leak will be corroded, and then gradually corrode the entire tower. .
The design of the circulating slurry pipeline of this system will meet the requirements of the circulating water volume of the system, and the slurry pipeline layout will have no dead zone to avoid pipeline deposition and blockage; the selection of related valves can meet the control requirements.
●Absorption tower slurry circulating pump
The absorption tower circulating pump is made of polymer lined plastic pumps with excellent anti-corrosion and wear resistance. There are three in total, which can be selected according to the situation.
Each water pump is equipped with a glass fiber reinforced plastic siphon bucket, which can save the non-return halter in the pool and reduce the probability of maintenance.
The circulating pump is a centrifugal pump, and the impeller is made of anti-corrosion and wear-resistant materials.
The circulating pump and drive motor can meet the requirements of outdoor layout.
●Circulating pool
Including mixing tank, reaction tank, sedimentation tank, clean water tank, etc. The circulating mixing pool is poured with reinforced concrete or brick masonry, and is set as an above-ground or underground pool. The specific location is agreed upon on site.
3.1.2 Absorbent preparation and supply system
●Lime powder warehouse
This location is determined by Party A and construction is carried out
●Lime powder supply tank, agitator
The lime is added to the lime dissolving tank, the agitator in the lime tank works to fully mix the lime with the water, and then the mixed liquid is supplied to the mixing tank through the valve control.
3.1.3Gypsum dehydration system
The gypsum dehydration device of this project is designed as a filter press. The gypsum slurry is passed into the plate and frame filter press through the slurry pump, and the clean water after the filter press flows into the pool for continuous recycling. The filter cakes are sold or used by themselves.
3.1.4Process water system
Provided by Party A’s own well or tap water, and lay water supply pipelines near the pool.
3.1.5Electrical System
（1）Power supply mode：
Equipped with water pump soft start, feeding frequency converter, stirring switch, etc.
3.1.6 Steel structure platform, stairs
Each spray layer of the absorption tower body is equipped with a set of platforms, and each inspection hole is equipped with an inspection platform. From the ground, a straight ladder can be used to reach the highest platform.
The minimum headroom height of platform escalators, equipment and other structures is not less than 2m, and the platform width is not less than 0.8m.
All platforms and escalators are equipped with railings on each side according to relevant industry standards. The height of the railing is designed according to specifications.
The desulfurization equipment developed according to the characteristics of the sintering kiln has the characteristics of convenient installation, large amount of flue gas treatment, and reduced pressure. The whole set of desulfurization tower body, internal spray structure, brackets, etc. are all made of glass fiber reinforced plastic. Because the desulfurization tower is in an environment where acid and alkali exist at the same time, the glass fiber reinforced plastic itself is an acid and alkali resistant material, which extends the service life of the equipment. It is said that FRP can be used for decades or even hundreds of years. According to our experience, it is no problem to use it for more than 10 years.
According to the ease of maintenance of the spray pipeline, it can be divided into the internal layout of the spray pipeline and the external plug-in type of the spray pipeline. The internal layout of the spray pipeline requires the suspension of the fan and people entering the desulfurization tower for maintenance,there is a support platform for maintenance under the spray pipeline; the sprinkler pipeline can be inspected and repaired outside the tower by the plug-in person without stopping the fan, which improves the efficiency and safety of maintenance.
Conclusions and suggestions: the main materials of desulfurization towers currently on the market are: glass fiber reinforced plastic, carbon steel anticorrosion, brick or granite masonry, and PP board. Generally speaking, it is recommended to choose glass fiber reinforced plastic and carbon steel anticorrosion. Description of specific materials and corresponding advantages and disadvantages.
No. | Types of desulfurization tower materials | Different material advantages and disadvantages description for selection reference |
1 | Brickwork or masonry desulfurization tower | There are many gaps, and it will leak if not handled properly. |
2 | PP board desulfurization tower | The temperature resistance is too low, and the aging is too fast, especially in the place where the ultraviolet radiation is strong, the service cycle is shorter. |
3 | Carbon steel anticorrosive desulfurization tower | Although it has been shown that many carbon steel anti-corrosion desulfurization towers cannot be used, it cannot be said that all carbon steel desulfurization towers are not good, but the anti-corrosion technology of carbon steel desulfurization towers in the brick and tile industry is not enough or to reduce costs. The anti-corrosion is too poor. If the steel plate is sandblasted to remove the rust, it is no problem to use the anti-corrosion well, but the corresponding increase in the cost is not as good as buying all-glass steel |
4 | FRP desulfurization tower | Not all FRP products are good. We have also seen many cases where FRP desulfurization towers cannot be used. It is only because some manufacturers use bad materials with low transaction prices and compressed quality. FRP itself is a corrosion-resistant material. The anti-corrosion inside the steel is also the glass fiber reinforced plastic. The service life of the selected material glass fiber reinforced plastic is absolutely no problem. |
According to the requirements of the factory and some of the technical parameters and data provided, combined with the characteristics of our company's desulfurization technology and engineering experience, a more detailed analysis has been carried out in terms of technical feasibility, safe operation, emission indicators, and engineering economics. After the demonstration, the desulfurization technical plan of this project was compiled.
1.1Project Overview
The project is located in South Africa and is a mobile tunnel kiln with a section of 11.5m. Through communication with the purchaser, a tidal exhaust fan BPCII-18#-132, according to experience, the air volume is about 180-240 thousand cubic meters, and the flue gas temperature is 40-60 degrees Celsius. (Experience value), the oxygen content is about 19%, and the daily output of South African bricks is about 260,000. According to the requirements of the purchaser, it must meet the requirements of Table 2 in GB29620-2013 "Emission Standard of Air Pollutants for Brick and Tile Industry": that is, SO2≤300mg/m3.
1.2 Design basis
"Environmental Protection Law of the People's Republic of China"
GB12348 Noise standard at the boundary of industrial enterprises
GB18599-2001 "General Industrial Solid Waste Storage and Disposal Pollution Control Standard":
GB29620-2013 "Emission Standard of Air Pollutants for Brick and Tile Industry"
GB/T 19229-2003 "Coal-fired flue gas desulfurization equipment"
Technical requirements and testing methods of HJ/T76 fixed pollution source exhaust smoke continuous detection system:
1.3 Design Principles
(1）Ensure that the flue gas sulfur dioxide meets the emission standards;
(2）Ensure the safe and stable operation of the flue gas treatment system;
(3）Adjust measures to local conditions, optimize the combination, and formulate targeted technical implementation plans;
(4）The medicament is cheap, easy to obtain, and convenient to transport, and treat waste with waste, and the desulfurization product does not cause secondary pollution;
(5）Fully consider the nature of the furnace to ensure the adaptability of the furnace desulfurization system under various operating conditions;
(6）Using advanced and mature desulfurization technology and equipment, under the premise of ensuring that the design indicators are met, combined with the actual situation of the factory, the project investment and operating costs are as low as possible;
(7）Minimize the labor load, easy to maintain and save labor.
1.4 Design Parameters
The main design parameters based on this plan are derived from the technical requirements provided by ## New Building Materials Co., Ltd., Gudian Town, Fengtai County. Part of the data not provided by the manufacturer is temporarily taken from experience values. The main original design parameters are shown in the following table.
Table 1.1 Design parameters
Item name | Parameters |
Whole production line scale | |
Fan parameters for polluting gas | BPCII-18#-132/one set |
Smoke volume (working condition) | 180,000-240,000m³/h |
Outlet flue gas temperature of tidal exhaust fan | 40-60℃ |
Daily output | 260000pcs |
Sulfur content of flue gas | |
Actual oxygen content of kiln | Based on 19% |
Annual operating time | 300days |
1.5 Technical Index Of Design
Design indicators are implemented according to corresponding environmental protection standards and requirements
The specific design technical indicators are shown in Table 1.2.
Table 1.2. Technical index of design
Item name | 技术指标（设计保证值） Technical index (design guarantee value) |
Ringelmann Blackness | ≤1级 |
Gas distribution uniformity | ≥70% |
Airflow direction | From the bottom to the top |
Net flue gas sulfur dioxide concentration (after conversion) | ≤300mg/m3 |
Pressure drop of desulfurization unit | ≤1600Pa |
Desulfurization efficiency | ≥96% |
1.6 Scope of design
The design scope of this scheme includes: desulfurization equipment and corresponding supporting systems from the outlet of the fan to the outlet of the absorption tower. Specifically including:
（1）Flue gas system；
（2） SO2 absorption system;
（3）Absorbent preparation and supply system；
（4）Gypsum dehydration system；
（5）Gypsum dehydration system；
（6）Electrical and control system；
1.7 General description of the technical solution
We guarantee that the desulfurization equipment we provide is technologically advanced, and that the manufacturing and design of all equipment meet the requirements of safe, reliable, continuous and effective operation.
●The desulfurization process adopts the sodium-calcium double alkali method.
●The desulfurization device adopts the entire production line and one tower. The flue gas processing capacity of the desulfurization device is 50% to 100% of the flue gas volume of each fan during normal operation, and the emission standard meets the requirements of the design index in 1.5.
●Adopt the plan of purchasing and supplying absorbent directly from outside the plant, without considering the installation of dry grinding or wet grinding systems in the desulfurization island.
●The average annual operating time of desulfurization equipment is considered as 300 days.
2.1 Introduction to common desulfurization processes and principles
2.1.1 Flue gas desulfurization process
According to the different desulfurization methods and product forms, there are four main types: dry desulfurization, semi-dry desulfurization, wet desulfurization and new biological desulfurization.
① Dry flue gas desulfurization
Dry flue gas desulfurization refers to a desulfurization process in which the added desulfurizer is in a dry state and the desulfurization product is still in a dry state. The characteristic of this method is that the flue gas has no obvious temperature drop during the purification process, and the flue gas temperature after purification is high, which is conducive to the dilution and diffusion of the flue gas, and has the advantages of no sewage and waste acid discharge and no corrosion of equipment. But there are problems such as low desulfurization efficiency, slow reaction speed, and huge equipment.
② Wet flue gas desulfurization
Wet flue gas desulfurization is a desulfurization process in which ammonia water or sea water solution or limestone or NaOH mixed with lime is used as a desulfurizing agent slurry, and the generated desulfurization product is sulfite or sulfate dissolved or precipitated. The advantages of this technology are the convenient and cheap source of desulfurization agent, fast desulfurization reaction speed, simple equipment, high desulfurization efficiency, avoiding tower blockage and wear, and operating reliability. At present, among the existing flue gas desulfurization technologies in various countries in the world, the reasons for wet flue gas desulfurization technology account for about 85%. However, the problem is that the wastewater causes severe corrosion to the equipment and the by-product gypsum is difficult to treat, causing secondary pollution."
③Semi-dry flue gas desulfurization
Semi-dry method has some characteristics of dry method and wet method. It is a desulfurization process in which the desulfurizer desulfurizes in a dry state and regenerates in a wet state; or desulfurizes in a wet state and processes the desulfurized product in a dry state. Its advantages are that it has the advantages of fast wet desulfurization reaction speed and high desulfurization efficiency, as well as the characteristics of dry method no sewage and waste acid discharge, and easy disposal of the products after desulfurization. However, the desulfurization efficiency is low, the process is complicated, and the investment is high.
④Biological flue gas desulfurization technology
Biological desulfurization technology includes biological filtration, biological adsorption and biological trickling filtration. The three methods are all open systems, and their microbial populations change with environmental changes. It has many advantages: no catalyst and oxidant (except air), no chemical sludge treatment, little biological pollution, low energy consumption, sulfur recovery, high efficiency, and no odor. The disadvantage is that the process is difficult to control and the conditions are demanding.
Combining the actual situation of the project and the advantages and disadvantages of each desulfurization process, this project is designed to use a wet desulfurization process.
2.1.2Principles of wet flue gas desulfurization
Wet desulfurization mainly includes seawater method, ammonia method, lime (limestone)-gypsum method, double alkali method, magnesium oxide method, etc.
①Seawater desulfurization
A method to neutralize the sulfur dioxide in the flue gas by using the alkalinity of seawater to neutralize the sulfur dioxide in the flue gas. The desulfurized seawater is subjected to aeration and other treatments to reach the seawater discharge standard before being discharged to the sea. This method is mainly suitable for projects that are close to the sea and convenient for water.
② Ammonia desulfurization
The process of using ammonia as an absorbent to remove sulfur dioxide from the flue gas has high desulfurization efficiency and high absorbent utilization efficiency, but the infrastructure investment is large, the operating cost is high, recycling is difficult, and it is easy to cause secondary air pollution.
③ Lime (limestone)-gypsum method
A certain concentration of lime milk is used to absorb sulfur dioxide. The process is mature, safe and reliable in operation, with a desulfurization rate of more than 90%, abundant absorbent resources, and low cost. The waste residue can be discarded or recycled as gypsum, but it is not accurate in PH operation,in this case, the equipment is prone to fouling and clogging, and the selected liquid gas is relatively high.
④ Sodium calcium double alkali method
It uses sodium alkali to absorb sulfur dioxide and then uses lime to treat and regenerate the desulfurization solution. It absorbs the advantages of the alkali method and the lime method to avoid their shortcomings. It is developed on the basis of the improvement of two desulfurization and dust removal technologies. It has the following advantages: the sodium as the absorbent system will not produce sediment; the regeneration of the absorbent and the precipitation of desulfurization slag occur outside the absorption tower, thereby avoiding the blockage and wear of the absorption tower, improving the reliability of operation and reducing In order to reduce the operating cost, the sodium-based absorption liquid absorbs quickly, so a smaller liquid-to-gas ratio can be used to obtain a higher desulfurization rate, easy to operate, and no secondary pollution; the disadvantage is that there are many processes and the by-products can be recycled, but The quality has been reduced.
⑤ Magnesium Oxide Method
Magnesium oxide slurry is used to absorb sulfur dioxide in the flue gas to produce hydrous magnesium sulfite and a small amount of magnesium sulfate, and then the product is dehydrated, dried and heated to decompose it to obtain magnesium oxide and sulfur dioxide. Regenerated magnesium oxide can be recycled for desulfurization
In view of the actual situation of the bidding company, the sodium-calcium dual-alkali process is proposed for this plan.
The sodium-calcium double-alkali method uses Na2CO3 or NaOH solution as the first alkali to absorb flue gas SO2, and then lime is used as the second alkali to regenerate the absorption liquid. The regenerated absorption liquid can be recycled. The reaction principle is:
（1）Absorption response
2NaOH+ SO2 —— Na2SO3+ H2O
Na2CO3+ SO2 —— Na2SO3+CO2
Na2SO3+ SO2+H2O —— 2NaHSO3
In this process, since sodium alkali is used as the absorption liquid, no sediment will be generated in the absorption system. The main side reaction of this process is oxidation reaction, which produces Na2SO4:
2Na2SO3+ O2 —— 2Na2SO4
(2) Regeneration process (with lime slurry)
CaO+H2O—— Ca(OH)2
2NaHSO3 + Ca(OH)2 —— Na2SO3+CaSO3﹒1/2H2O
Na2SO3+ Ca(OH)2 ——2NaOH+CaSO3﹒1/2H2O
The NaOH solution obtained after regeneration is sent back to the absorption system for use. The obtained calcium sulfite hemihydrate can be oxidized to generate gypsum (CaSO4﹒2H2O).
In addition, during operation, because there is still some oxygen in the flue gas, there are side reactions-oxidation reactions:
2CaSO3﹒1/2H2O+O2+3H2O —— 2CaSO4﹒2H2O
2.1.3Empty tower spray desulfurization process
After the flue gas enters the desulfurization tower, it first impacts the water level at the bottom of the desulfurization tower. During the impact, part of the sulfur dioxide in the flue gas is dissolved in the aqueous solution and then flows out of the tower to react. The flue gas is initially evenly distributed; when the flue gas continues to rise through the air distributor, the flue gas is further evenly distributed, so that the wind speed of the flue gas on the same section is as consistent as possible, and the water sprayed from the spray layer falls on the air distributor and continues to flow down A water film is formed around the water outlet, and about 30-40% of the flue gas passes through the water film from under the air distributor to the top of the air distributor. The sulfur dioxide in the flue gas and the water in the process of passing through the water film The alkaline substance reacts, and a part of the particulate matter is left in the water and falls into the bottom of the tower and flows out of the tower for precipitation.
The flue gas passing through the air distributor continues to move upwards, and successively passes through the multi-layer spray layer arranged on the air distributor. The spray layer nozzle adopts a hollow vortex nozzle to break the water flow through the nozzle into fine water particles and water under high pressure. Fog (800-1000μm) makes the coverage of each spray layer reach 150%-200%; each spray layer is arranged crosswise, so that the entire flue gas treatment area is fully covered and there is no dead corner. In the process of passing through the spray layer in sequence, sulfur dioxide is dissolved in the water mist and the alkaline substances in the water mist undergo acid-base reaction to form soluble salts. After purification, the flue gas continues to rise, passing through the corrugated plate demister, the water droplets carried in the flue gas are blocked, but during the long-term use of the demister, some particles or crystals will adhere to the demister. If the demister is not cleaned for a long time, it will block the demister. In order to prevent the demister from clogging and increase the resistance of the desulfurization tower, a demister flushing device is installed to automatically flush the demister with process water.
The desulfurized water flows out of the desulfurization tower to the circulating pool under the action of the overflow's own gravity for further chemical reaction, and the desulfurized liquid after the reaction is again atomized and combined with the moisture exhaust flue gas for treatment, and then circulated in turn. The desulfurization wastewater flowing out of the tower first contacts the lime slurry in the return pool, and then flows into the reaction tank for reaction. Sodium sulfite and calcium hydroxide in the reaction tank react with calcium hydroxide to replace the calcium hydroxide. When the displacement reaction occurs, calcium sulfite precipitates are generated. The reacted liquid flows into the oxidation tank, and air is introduced into the oxidation tank. The air and calcium sulfite fed into the oxidation tank are forcibly oxidized to form calcium sulfate (gypsum), thereby reducing the clogging rate of spray pipes and nozzles. After forced oxidation, the desulfurized water overflows to the sedimentation tank. The supernatant of the desulfurization liquid after precipitation flows into the circulating tank through the overflow for cyclic desulfurization, and the precipitated gypsum is passed into the filter press through the slurry pump, and filtered The clear liquid will continue to flow into the pool for reaction, and the pressed filter cake will be sold or used for personal use. In the process of system operation, there is always unreacted sodium sulfite that is lost during dredging, so it is necessary to add sodium hydroxide or sodium carbonate to the pool regularly to supplement the loss of sodium and alkali.
Double alkali spraying empty tower has the following advantages:
（1）Relatively simple and convenient system, less investment;
（2）The desulfurization efficiency can meet the desulfurization efficiency requirements of the project;
（3）Relatively less prone to scaling;
（4）The absorption tower adopts spraying empty tower, which has low resistance and reliable operation.
（5）The desulfurization device also has a certain dust removal efficiency.
2.1.4Desulfurization equipment description
The whole set of equipment consists of five parts:：
（1）Flue part；（2）SO2 absorption system；（3）Absorbent preparation and supply system；（4）Process water system；（5）Electrical and control system。
（1）Flue gas system
The exhaust gas is passed into the desulfurization tower through the induced draft fan, and the part of the flue that enters the desulfurization tower from the flue through the fan will be produced and installed by the purchaser.
（2）SO2 absorption system
The flue gas from the kiln passes through the induced draft fan and enters the absorption tower at the outlet of the induced draft fan. The flue gas enters the spray absorption tower from the bottom and contacts the spray liquid countercurrently. The SO2 in the flue gas is absorbed by the absorption tower, and the sulfur dioxide removal rate of the flue gas at the outlet is above 92.8%. The clean flue gas is removed from the flue gas through a high-efficiency combined defogging device in the upper section of the tower body, and the purified flue gas enters the chimney through the flue after the tower and is discharged. The absorption tower is made of high temperature resistant glass steel.
After the desulfurization liquid fully contacts and reacts with the flue gas in the absorption tower, it flows back into the mixing tank through the drainage ditch at the bottom of the tower body, and the desulfurization liquid flowing into the mixing tank undergoes regeneration reaction with the lime slurry.
According to site conditions, the circulating mixing pool is divided into five parts: backwater area, regeneration area, oxidation area, sedimentation area, and clean water area. The reflux liquid first enters the return pool and mixes with the lime, and then enters the regeneration pool for displacement reaction; then enters the precipitation zone for precipitation, and the supernatant enters the clear pool and returns to the absorption tower through the circulating water pump. Precipitation is cleaned up regularly.
In this desulfurization equipment, the absorption tower is a countercurrent spraying empty tower, and the spraying layer is arranged in six layers (three-layer desulfurization, three-layer backwashing), which not only meets the specific surface area required to absorb SO2, but also satisfies the furnace Load and sulfur content requirements. At the same time, the pressure loss caused by spraying is reduced to a minimum. Each spray layer is equipped with multiple atomizing nozzles, which are arranged crosswise, and the coverage rate can reach 150%-250%. The nozzle adopts a vortex nozzle, and the material is a corrosion-resistant and wear-resistant silicon carbide nozzle.
The defogging device in the absorption tower is made of high-temperature resistant glass fiber reinforced plastic, mainly composed of defogging plates and anti-cleaning devices.
（3）Absorbent preparation and supply system
The desulfurization absorbent of this project adopts purchased lime powder (250 mesh, 90% sieving rate), and the lime liquid after the lime powder is dissolved by the mixing and feeding system is sent to the regeneration zone (return to the pool) for replacement reaction.
（4）Gypsum dehydration system
Set up a filter press to clean up the sediment regularly every day. The mixture of gypsum and water is fed into the filter press through a slurry pump, the clean water is returned to the pool for reuse, and the filter cake gypsum is collected for external sales or personal use.
（5）Process water system
The process water system is responsible for providing enough water for the desulfurization operation to supplement the water loss during the operation of the system to ensure the normal function of the desulfurization system. Process water is provided by self-provided wells or tap water in the plant area.
（6）Electrical and control system
In order to ensure the stability of the system's desulfurization efficiency, the feed is fed by weight, and the feed rate is adjusted for flue gas with different sulfur content. The pump is equipped with a button-type start-stop distribution box for easy operation.
3.1.1 SO2 Absorption system
The desulfurization system adopts the form of one tower for the entire project.
The absorption tower adopts multi-layer spray + combined demister desulfurization device, and the empty tower spray structure, and the desulfurization efficiency is ≥90%.
● The absorption tower includes absorption tower shell, spray system, combined demister, embedded parts and external steel structure.
● The absorption tower is made of acid and alkali resistant glass fiber reinforced plastic, which can withstand the abrasion of the flue gas fly ash and the solid suspended solids of the desulfurization process, and meet the strict anti-corrosion requirements.
● The absorption tower is designed to prevent liquid leakage. The manholes, channels, connecting pipes, etc. on the tower body are sealed at the perforated part of the shell to prevent leakage.
● The absorption tower shell is designed to withstand various loads, including the dead weight of the equipment and pipes acting on the absorption tower, the weight of the medium, the heat preservation, as well as the wind load, snow load, and seismic load.
● The bottom surface of the absorption tower can basically empty the slurry.
● The overall design of the tower facilitates the overhaul and maintenance of the components in the tower, and the spray system and supports inside the absorption tower will not accumulate dirt and scale.
● The absorption tower is equipped with a sufficient number and appropriate size of manhole doors, and walkways and platforms are set nearby.
● The design of the spray system will reasonably distribute the required spray volume, make the flue gas flow evenly, and ensure that the absorption slurry fully contacts and reacts with the flue gas.
● The nozzle selection will try to avoid rapid wear, scaling and blockage.
● The nozzle and pipe are designed as an external plug-in type, which is convenient for maintenance, flushing and replacement.
3.1.1.2Design specifications：
①The diameter of the desulfurization tower is determined: the flue gas flow rate in the tower is selected from 2 to 4.5 m/s according to the sulfur content. Under the condition of ensuring the removal efficiency of the water droplets carried in the flue gas by the demister and the allowable pressure drop of the absorption system, appropriately increasing the flue gas flow rate can intensify the turbulence intensity between the flue gas and the slurry droplets, thereby increasing the difference between the two The contact area between. Higher flue gas flow rate can also appropriately reduce the geometric dimensions of the absorption tower and tower internals, and improve the cost performance. However, when the flue gas flow rate is too high, the contact time of the absorption liquid and the flue gas is short, thereby reducing its absorption efficiency; at the same time, when the flue gas flow rate is too high, it is accompanied by an increase in resistance and a reduction in the dust removal capacity of the desulfurization tower itself. Considering comprehensively, take the flue gas flow rate in the desulfurization tower=3-3.5m/s
②The design of the spray layer of the absorption tower: The design of the spray layer includes the selection and arrangement of slurry pipes and nozzles.
The arrangement of the spray layer in the absorption tower should make the sprayed droplets completely and evenly cover the entire cross section of the absorption tower, and reduce the amount of slurry flowing along the tower wall as much as possible and reduce the direct erosion and wear of the sprayed slurry on the tower wall
The nozzle should choose acid and alkali resistant materials. Nowadays, the nozzle materials on the market mainly include plastic nozzles, iron nozzles, stainless steel nozzles, and silicon carbide nozzles. Practice has proved that silicon carbide nozzles are the most suitable one.
According to the use of desulfurization towers in the past, this project is equipped with three desulfurization spray layers.
③Height determination: Taking into account the use of high-sulfur coal gangue in the later stage, the desulfurization efficiency margin needs to be considered, and 15m
④The liquid-gas ratio is 2.25, the water volume is 360m3/h, the water volume of each spray layer is 120m3/h, and three water pumps are 15kw.
⑤The design of the demister of the absorption tower: As the net flue gas after the treatment of the absorption tower entrains a large number of slurry droplets, especially when the flow rate of the absorption tower flue gas is relatively high, the amount of droplets carried by the flue gas will increase. In order to prevent water spraying in the desulfurization tower, the demister is also an indispensable part of the desulfurization tower mechanism. A layer of cleaning nozzles are arranged above and below each layer of mist eliminator to clean up the adherents on the mist eliminator in time to reduce equipment resistance and ensure the effect of the mist eliminator.
⑥The design of the flue at the outlet of the absorption tower: There are many types of flue at the outlet of the absorption tower. In this project, the outlet of the absorption tower is appropriately contracted into a cone shape, and then the outlet is sideways to avoid adverse effects on the airflow distribution of the absorption tower.
⑦The design of the nozzles and holes of the absorption tower: In order to be easy to clean, maintain, and repair, the internal structure of the absorption tower is as simple as possible, leaving no dead corners, and having enough operating space. Set up manholes and install inspection ports at corresponding positions.
⑧Material selection of desulfurization tower: The selection of desulfurization tower material is a very important aspect related to the normal and long-term use of desulfurization tower. The flue gas treatment contains SO2. When SO2 meets water, it forms sulfuric acid, which is highly corrosive. Alkaline substances are added to the absorbing liquid, so it is necessary to select materials that are both acid and alkali resistant in the selection of desulfurization tower materials and internal structural materials. The currently used desulfurization tower materials mainly include brickwork, granite, glass fiber reinforced plastic, and iron plate anti-corrosion (the glass fiber reinforced plastic material is used for anti-corrosion treatment in the tower). Now do the following analysis on the desulfurization towers of these materials:
Brick desulfurization tower: The entire tower body is built with sintered red bricks. Because it is built on site, the diameter range is wide and the construction cost is low. However, the internal structure is difficult to arrange, and the cement between the red bricks It is also suitable to be corroded by acid and alkali and has a short service life.
Granite desulfurization tower: The whole tower is built of rubble, which is acid and alkali resistant, and the construction cost is higher than that of bricks. If the entire tower body is constructed of granite, then granite is an ideal material. However, the granite is built with cement, and the cement will be corroded by acid or alkali. Especially in winter, when the cement is corroded, water freezes and expands in the gap, causing a gap between the granite and the granite. When the ice melts, the desulfurization tower Water leakage started, and due to the disappearance of the cohesive force, the continued use of the desulfurization tower has a greater safety hazard.
FRP desulfurization tower: The whole set of equipment is made of FRP, which is a good corrosion-resistant material, and has good resistance to atmosphere, water and general concentrations of acid, alkali, salt, etc. Moreover, the specific gravity of FRP is light, the surface is smooth, and the pressure is reduced, but the cost of FRP desulfurization tower is higher. After market survey feedback, FRP desulfurization tower is relatively the most successful one.
Iron plate anti-corrosion desulfurization tower: It is one of the most widely used in the market. The production cost is intermediate and the production cycle is short. Since the inner wall is anti-corrosive with FRP, it can be used normally in the short term. However, because the flue gas to be processed has a certain temperature, the expansion coefficients of FRP and iron are different, and the anti-corrosion FRP will be separated from the iron. Once the surface of the FRP leaks, the iron sheet at the leak will be corroded, and then gradually corrode the entire tower. .
The design of the circulating slurry pipeline of this system will meet the requirements of the circulating water volume of the system, and the slurry pipeline layout will have no dead zone to avoid pipeline deposition and blockage; the selection of related valves can meet the control requirements.
●Absorption tower slurry circulating pump
The absorption tower circulating pump is made of polymer lined plastic pumps with excellent anti-corrosion and wear resistance. There are three in total, which can be selected according to the situation.
Each water pump is equipped with a glass fiber reinforced plastic siphon bucket, which can save the non-return halter in the pool and reduce the probability of maintenance.
The circulating pump is a centrifugal pump, and the impeller is made of anti-corrosion and wear-resistant materials.
The circulating pump and drive motor can meet the requirements of outdoor layout.
●Circulating pool
Including mixing tank, reaction tank, sedimentation tank, clean water tank, etc. The circulating mixing pool is poured with reinforced concrete or brick masonry, and is set as an above-ground or underground pool. The specific location is agreed upon on site.
3.1.2 Absorbent preparation and supply system
●Lime powder warehouse
This location is determined by Party A and construction is carried out
●Lime powder supply tank, agitator
The lime is added to the lime dissolving tank, the agitator in the lime tank works to fully mix the lime with the water, and then the mixed liquid is supplied to the mixing tank through the valve control.
3.1.3Gypsum dehydration system
The gypsum dehydration device of this project is designed as a filter press. The gypsum slurry is passed into the plate and frame filter press through the slurry pump, and the clean water after the filter press flows into the pool for continuous recycling. The filter cakes are sold or used by themselves.
3.1.4Process water system
Provided by Party A’s own well or tap water, and lay water supply pipelines near the pool.
3.1.5Electrical System
（1）Power supply mode：
Equipped with water pump soft start, feeding frequency converter, stirring switch, etc.
3.1.6 Steel structure platform, stairs
Each spray layer of the absorption tower body is equipped with a set of platforms, and each inspection hole is equipped with an inspection platform. From the ground, a straight ladder can be used to reach the highest platform.
The minimum headroom height of platform escalators, equipment and other structures is not less than 2m, and the platform width is not less than 0.8m.
All platforms and escalators are equipped with railings on each side according to relevant industry standards. The height of the railing is designed according to specifications.
