What technology is used for flue gas desulfurization and how effective is it?

　　 The research and development of flue gas desulfurization control technology in my country began in the early 1960s. Flue gas desulfurization process research and equipment development were carried out for coal-fired power plants, coal-fired industrial boilers and metallurgical waste gas, and laboratory small-scale tests and on-site pilot test results were obtained. Since the 1980s, a series of research, development and industrialization work have been carried out. Original * * The Science and Technology Commission organized the "Seventh Five-Year Plan" and "Eighth Five-Year Plan" research projects to conduct research on the main methods of existing desulfurization technologies in the world and conduct practical engineering device experiments. ； * * The Natural Science Foundation of China has set up a project to support basic research on desulfurization technology and has achieved many achievements. At present, the flue gas desulfurization method independently developed by our country is still in the industrial demonstration and test stage. * * During the "Ninth Five-Year Plan" period, the Ministry of Science and Technology organized a research project on "Research and Industrialization of Practical Desulfurization and Dust Prevention Technology and Equipment for Small and Medium-sized Boilers", including research on the use of new pulse corona plasma flue gas desulfurization technologies for coal-fired power plant flue gas desulfurization technology. ； At the same time, desulfurization technology projects were introduced to conduct demonstration scale tests and industrial operation applications. my country's power plant flue gas desulfurization technology started in 1961. Scientific research institutes and universities have successively invested in the research and development of flue gas desulfurization, and conducted exploratory research on flue gas desulfurization such as the wet method, semi-dry method, etc. * * Ministry of Science and Technology (formerly * * The Science and Technology Commission’s special support for desulfurization during the “Seventh Five-Year Plan”, “Eighth Five-Year Plan” and “Ninth Five-Year Plan” has made excellent progress. However, my country's self-developed flue gas desulfurization projects are still in the small and pilot stages. There are not many industrialization and industrialization technologies. 1． Rotary spray dry flue gas desulfurization pilot test In 1983, on the basis of a small test device with a flue gas processing capacity of 3,500Nm3/h, a 70,000Nm3/h pilot device was built at the Baima Power Plant in Sichuan. After nearly a year of debugging and 2,000 hours of continuous operation testing, lime was used as a desulfurizer to treat high-sulfur coal (sulfur content: 3.5%) flue gas. When the calcium-sulfur ratio is 1.4, the desulfurization rate is about 80%. After the desulfurizer is sprayed into the absorption tower, it reacts with SO2 in the flue gas to generate solid ash. The solid ash continues to dry as it falls in the tower, and finally forms dry solid dust. Part of it is separated and discharged in the tower, and the other part enters the electrostatic precipitator with the flue gas for removal. The process includes: Absorbent preparation, absorbent slurry atomization, contact mixing reaction, droplet evaporation and SO2 absorption and waste residue discharge. Main equipment: (1)Sprayer: RN-10T type, rotating speed 1000r/min, atomized slurry 10t/h. (2)Absorption tower: φ8m, cylinder height 6m. (3)Electric dust protector: Double chamber and double electric field, effective cross-sectional area 2×15.8m, single electric field length 4.5m. (4)Induced draft fan: Y4-73NO18D type, rotation speed 960r/h, capacity 143920m3/h, pressure 3300Pa. (5) Lime digester: φ600×4500mm, capacity 3-5t/h. (6) Wet ball mill: MXQG1500 type, φ1500×3000mm, output 2-7t/h (dry material). The main technical issues are the wear and tear of the high-speed rotating nozzle, which affects the atomization quality and the formation of scaling, and the durability of the slurry delivery pump. 2. Experimental research on the rotary spray dry flue gas desulfurization process began in 1987. In order to accumulate operational experience in the introduction of the Danish Niro Company's rotary spray dry flue gas desulfurization equipment, part of the flue gas was introduced from the 6.5t/h boiler of Beijing Rubber Factory No. 6, a test device for processing 2000Nm3/h flue gas volume was established, and preliminary process tests were carried out. The desulfurization equipment for the atomization of Ca(OH)2 slurry and the complete mixing reaction with flue gas includes a drying absorption tower, a high-speed centrifugal spray machine, an air flow distributor and a final product collector. The diameter of the drying absorption tower is 2m, the height is 5m, the speed of the high-speed centrifugal sprayer is 17000-27200r/min, and the slurry flow rate is 50kg/h. Ca(0H)2 is made from quicklime in the digestion tank, and the flue gas inlet temperature is 150°C. The S02 concentration to be processed is 1000-2000ppm. When the adiabatic saturation temperature is 24.6°C and the calcium-sulfur ratio is 1.2-1.8, the dehydration string is 66%-79%. 3． Hubei Songmuping Power Plant built a 5KIn3/h flue gas water-washed regenerated activated carbon desulfurization pilot plant in 1987. Activated carbon containing iodine O.5% was used as the desulfurizer and was filled in four parallel packed desulfurization towers. When the flue gas passes through the desulfurization tower, SO2 is adsorbed by the activated carbon and catalytically oxidized into sulfuric acid. The saturated desulfurization tower is washed and regenerated in five stages with dilute sulfuric acid and water of different concentrations. The residual sulfuric acid concentration in the carbon is reduced to about 3%, and then dried with steam before being put into desulfurization operation. The first and second stage wash out is 20% dilute sulfuric acid product, and the 20% dilute sulfuric acid is concentrated to obtain 70% sulfuric acid. The longest cumulative operating time of a single tower is approximately 2,000 hours, and the longest continuous operation of the entire process is 15 days. The inlet S02 concentration is greater than 3000PPm, the outlet S02 concentration is less than 350Ppm, and the desulfurization rate is 88%. The loss of the catalytic active substance iodine and the concentration of dilute sulfuric acid are serious problems and fatal weaknesses of this method, which hinder the expansion of its application. 4． Sichuan Douba Power Plant 5000Nm3/h Flue Gas Ammonium Phosphate Fertilizer Desulfurization Pilot Test In 1982, Xi'an Thermal Engineering Research Institute first explored this method. From 1983 to early 1985, the Thermal Engineering Research Institute cooperated with Sichuan Environmental Protection Research Institute to conduct a 3m3/h pilot test and determined the basic process of this method. In 1986, the ammonium phosphate fertilizer method for flue gas removal was selected as the * * “In line with the key research topics of the Seventh Five-Year Plan, a 5000Nm3/h pilot device was built at Douba Power Plant in Sichuan, and it operated continuously for more than 2000 hours at the end of 1990. * * The organization's acceptance sign confirms that the legal process is reasonable and feasible. During the pilot test, the total desulfurization efficiency of flue gas with an S02 concentration of 1600-2700Ppm was maintained at >95%, the extraction rate of phosphate rock powder was >90%, and dozens of tons of nitrogen-phosphorus compound fertilizer with an active ingredient of 37% were obtained. Dust concentration in flue gas after efficient dust removal

Flue gas desulfurization is divided into dry and wet methods. The dry method is such as dry desulfurization in the furnace, activated carbon adsorption desulfurization, and the wet method is such as the mainstream gypsum desulfurization, ammonia desulfurization, double alkali desulfurization, seawater desulfurization, magnesium oxide desulfurization, sodium sulfite desulfurization, etc. The choice needs to be based on your specific conditions such as flue gas flow and sulfur dioxide content. We use the gypsum method for desulfurization, which has good desulfurization efficiency, but the cost of desulfurization is high. The desulfurized gypsum has no use, and the cement plant does not need it. It can only be stored in a yard. In addition, the system is highly corrosive.

Gypsum method desulfurization has better desulfurization efficiency, but the desulfurization cost is higher. The desulfurized gypsum is dried and calcined to produce various products to increase added value.: Dry calcium sulfate dihydrate (i.e. raw gypsum) is used as cement retarder in the cement industry ； Semi-hydrated gypsum (i.e. plaster of paris) has cement-like gelling properties. The process of drying to remove free water is called drying, and the process of removing crystal water is called calcining. According to different calcining methods, β-type hemihydrate gypsum and α-type hemihydrate gypsum can be obtained respectively. β-type semi-hydrated gypsum is obtained by heating and dehydrating under gas phase conditions. It is also called building gypsum. It is mainly used to make gypsum boards, gypsum blocks, or is processed into stucco gypsum after adding additives. ； α-type semi-hydrated gypsum is obtained by cooking and drying saturated steam under pressure. It is also called high-strength gypsum and is mainly used for mold manufacturing in the ceramic and pharmaceutical industries.

Flue gas desulfurization is mainly an environmentally friendly technology used by large coal-burning plants such as power plants. The existing flue gas desulfurization technology is broadly classified into wet method, semi-dry (wet) method, and dry method. The principle is relatively simple. The main thing is that SO2 in the flue gas reacts with CaCO3 slurry or alkaline solution, and S atoms are replaced. The desulfurization efficiency is highest in the wet method and the lowest in the dry method. The capital investment is just the opposite. The limestone-gypsum method among the wet methods is the most mature technology currently, with the highest desulfurization efficiency, the most stable operation, and the desulfurization by-products are easy to dispose. Therefore, it is the most widely used. Most of the existing thermal power companies in my country use this technology. You can check the specific process online. This method can achieve fully automated control. However, the investment in the project is large, and the project covers a large area, which ordinary enterprises cannot afford. The double-alkali method in the wet method is also a widely used technology. Although the desulfurization efficiency is not as good as the limestone-gypsum method, the initial capital investment of this method is smaller and the area is smaller. However, after the desulfurization facility is operated, the operating cost is higher due to the need to continuously replenish the alkali solution.

Circulating fluidized bed flue gas desulfurization technology abbreviation: CFB-FGD The flue gas from the boiler air preheater with a temperature of about 120 to 180°C enters the circulating fluidized bed absorption tower from the bottom through the venturi tube. Set up a set of venturi pipe outlet expansion section * * device, creating a good desulfurization reaction temperature. The main chemical reaction principles of circulating fluidized bed flue gas desulfurization technology are as follows: 　　In the vertical gas-solid two-phase flow system in nature, in the circulating fluidized bed state (gas velocity 4~6m/s), a gas-solid sliding velocity equivalent to tens to hundreds of times of the sliding velocity of a single particle can be obtained. Since the reaction process between SO2 and calcium hydroxide particles in the circulating fluidized bed is a chemical reaction process controlled by external diffusion, the large sliding speed between gas and solid strengthens the mass transfer and heat transfer rate between gas and solid and the mixing of gas and solid, thereby meeting the condition requirements for the efficient reaction of sulfur dioxide and calcium hydroxide. 　　The huge surface area and intensely turbulent particles in the fluidized bed of the absorption tower provide a fundamental guarantee for the rapid vaporization and rapid controllable cooling of the injected water, thereby creating good chemical reaction temperature conditions (20~30°C above the dew point), converting the reaction between sulfur dioxide and calcium hydroxide into an ionic reaction that is completed instantly. 　　The intense turbulence of the particles leads to constant collisions between particles, so that the surface of the desulfurizer calcium hydroxide particles is constantly renewed, and the desulfurization ash is continuously recycled. * * Improved utilization of calcium hydroxide. 　　In the circulating fluidized bed, the reaction between SO2 and Ca(OH)2 generates the by-product CaSO3·1/2H2O. It also reacts with SO3, HF and HCl to generate the corresponding by-products CaSO4·1/2H2O, CaF2, CaCl2, etc. The main chemical reaction equations are as follows: 　　Ca(OH)2+ SO2=CaSO3·1/2 H2O +1/2 H2O Ca(OH)2+ SO3=CaSO4·1/2 H2O +1/2 H2O CaSO3·1/2 H2O+ 1/2O2=CaSO4·1/2 H2O Ca(OH)2+ CO2=CaCO3 + H2O Ca(OH)2+ 2HCl=CaCl2·2H2O 2Ca(OH)2+ 2HCl=CaCl2·Ca(OH)2·2H2O Ca(OH)2+ 2HF=CaF2 + 2H2O Technical features 1. High desulfurization efficiency, over 95% ； 　　2. Simple process, easy operation, high system reliability ； 　　3. The flue gas does not need to be reheated ； 　　4. It can remove SO3 at the same time, and the chimney does not need to be anti-corrosion. ； 　　5. Desulfurization by-products are in dry state and no waste water is produced. ； 　　6. Small footprint, low investment and low maintenance costs. 　　Process Flow A typical CFB-FGD system consists of a pre-electrostatic precipitator, absorbent preparation, absorption tower, desulfurization ash recycling, water injection system, desulfurization dust collector and instrument control system. 　　Fujian XX Environmental Protection Co., Ltd. is the only domestic environmental protection enterprise with this mature technology.

Personally, I think the effect of using super gravity desulfurization and dust removal is very good. Hahaha, the size of the equipment is also relatively small.