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Flue Gas Desulfurization
Technical introduction
Matured desulfurization technology includes wet, dry and semi-dry methods. Among them, limestone/lime-gypsum method is the most technically matured one in the world nowadays with the widest applications and most stable running state. Capacity of generating sets using this technology occupies about 85% of the total installed capacity of power plants and the capacity of single generator has reached over 1000MW. Boasting big flue gas processing capacity, high desulfurization rate, stable running of system, good adaptability to variety of coal and comprehensive utilization of desulfurization byproducts, the limestone/lime-gypsum wet desulfurization technology is applicable for large-sized power plants and small-sized power plants with high sulfur content.
The basic principle for limestone/lime-gypsum wet desulfurization technology is as follows: Using cheap limestone/lime/ calcium carbide residue as desulfurization absorbent, after limestone/lime/ calcium carbide residue is crushed and grinded into fine powder, it is mixed with water into adsorption slurry. Lime slurry is pumped into adsorption tower and contact fully with flue gas through slurry circulation pump and SO2 in the flue gas react with CaCO3 in the slurry and turn into calcium sulfite (and part of other pollutants such as powder dust, HCL, HF and SO3 in the flue gas are removed). And air with oxygen is pumped in from slurry pool in the lower part of adsorption tower and calcium sulfite is oxidized into calcium sulfate. After calcium sulfate reaches saturation of certain degree, it is crystallized into dihydrate gypsum (CaSO4 2H2O) and separated out. Gypsum slurry can be utilized comprehensively or sent to ash yard after it is dehydrated. Droplets of flue gas after desulfurization are removed with fog remover and then the flue gas is discharged into the atmosphere from the chimney after it is heated with GGH heater.
Control of key parameters of desulfurization island
Dust content in the flue gas at inlet: Over high dust content in the flue gas will result in deteriorated operations of the system, which is shown as low adsorption rate and difficult dehydration of conveyor, and deteriorated operations of the system will be corrected for a long time.
PH value of slurry in the adsorption tower: PH value shall be controlled within an appropriate range. A too low value will result in loss of adsorption ability and a too high value will result in serious consequence of sedimentation and blockage.
Concentration of slurry in the adsorption tower: Concentration of slurry in the adsorption tower shall be controlled within a proper range. A too low concentration will result in difficult crystallization of gypsum in the slurry and difficult dehydration of conveyor and a too high concentration will result in increased abrasion of the system.
Reactivity of limestone: Generally mineral containing high grade of lime shall be used and its degree of fineness shall be qualified.
Temperature of flue gas at outlet.
Content of SO2 in the flue gas at outlet: Maximum discharge concentration of SO2 shall be monitored all the time, and in case of deviation, factors such as load of furnace, content of SO2 in the flue gas at inlet and PH value of pulp shall be analyzed comprehensively.
Composition of the system
Limestone/lime-gypsum wet desulfurization system (FGD) is a complete technical system mainly composed of nine systems-limestone/lime slurry preparation system, flue gas system, windshield air-tight system, SO2 adsorption system, gypsum slurry dehydration system, exhaustion system, air compression system, technical water system and waste water treatment.
Main equipment of desulfurization island is mainly composed of booster fan, adsorption tower, adsorption circulation pump, oxidization fan, fog remover, gypsum-water cyclone, gypsum vacuum dehydration conveyor and so on. And the desulfurization island is also equipped with electrical and thermal control equipment and auxiliary equipment such as DCS, fire control and fire alarm equipment.
Characteristics of the system
With adoption of advanced and reliable single-circuit sprinkle tower and no component in the air-liquid contact area in the adsorption tower, running resistance in the tower can be reduced effectively and sedimentation and blockage in the tower in abnormal working conditions can be prevented effectively. Adopting simulation of computer, combining experience of many similar projects, configuration of desulfurization tower and components in the tower are optimized and stable flowing of flue gas and uniform sprinkling in the desulfurization tower are guaranteed. Slurry concentration, calcium-sulfur ratio and liquid-gas ratio are optimized to ensure stable transmission media, sufficient contact between gas and liquid in the tower, highly efficient and stable running of the system and reach the best desulfurization effects.
Designed flow-rate of flue gas in the tower is high, which effectively reduces diameter of adsorption tower, improves efficiency of transmission media and reduces cost.
By verification of impact of reaction area¡¯s height on performance of the system, distance between sprinkle layers is calculated to reach the best reaction effects, which ensures its design not only satisfies performance requirement, but facilitates working personnel¡¯s repair and maintenance of slurry sprinkle layers and nozzle.
Unique nozzle arrangement way is adopted. Rational arrangement of sprinkle system at each floor enables sufficient covering over effective intersecting surface of the tower, uniform sprinkling, big contact area and contact rate between gas and liquid. Desulfurization efficiency is improved effectively and slurry quantity sprinkled on wall of the tower is reduced as much as possible.
Forced oxidization way is adopted on site and lateral low-speed mixer matching with advanced air gun further increases specific surface area of oxidized air. Thanks to unique design of oxidized air gun with automatic cleaning function, sedimentation and blockage can be prevented effectively.
Material is selected rationally, which ensures service life of the system and reduces total investment and cost for use.
Matured technology and high reliability of running of the equipment.
Technical specification
High desulfurization efficiency (over 95%)
High utilization rate of the system (over 98%)
Big treatment capacity of flue gas by a single tower and big desulfurization volume of SO2
Good distribution effect of gas in the tower without bias current
Good adaptation to variety of coal.
Good adaptation to load of boiler
Dust content in flue gas after treatment has been greatly reduced
Low energy consumption for running of the system
Need for land has been reduced due to compactly configured equipment
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