Limestone FGD

SO2 absorption efficiency | 99.2% and above |
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Ammonium sulfite oxidation effect | 99.0% and above |
Ammonia recovery rate | 99% |
S02 content after desulfurization | <35mg/m3 |
NOx content after desulfurization | <50mg/Nm3 |
NH3 content after desulfurization | <3mg/Nm3 |
aerosol content after desulfurization | <3mg/Nm3 |
particles content after desulfurization | <5mg/Nm3 |
PH value | 5.5-6 |
The Technology of Limestone Flue GAS Desulfurization

2CaSO3·1/2H2O+O2+3H2O=2CaSO4·2H2O
In the absorber, SO2 in flue gas reacts with CaCO3 in slurry and oxidized air to form gypsum dihydrate, and SO2 is removed. The gypsum slurry discharged from the absorption tower is recovered after dehydration by dehydration device.
After desulphurization, the flue gas is removed from water by the mist remover, and the heat exchanger heats up and enters the chimney into the atmosphere.
The Engineering System of Limestone flue gas desulfurization
It is composed of slurry preparation system, flue gas system, absorption and oxidation system, gypsum dehydration system and discharge system.
The effective volume of slurry tank shall be designed according to the the rated working condition of the unit for 6hrs slurry consumption of the desulfurization unit . The bottom of the lime silo is “conical”, “conical” bottom has a slope of at least 55°, and there is a sealed inspection/manhole door at the top of the silo. The door can be opened quickly with hinges and handles. A bag filter is arranged at the top of the discharge hopper and lime silo, and the pipeline is arranged to the lime slurry tank to prevent dust from the tank car hen unloading. Lime silo is equipped with material level meter and can also be used for remote instructions. In order to reach the top of the inspection level meter, install stairs, and provide a certain number of staircase platforms at the appropriate height.
2) Install instruments for operation control and observation on the flue ducts, such as pressure gauges, thermometer and SO2 analyzers, etc., and send signals to the DCS system.
3.1 absorption tower The absorption tower is an air tight structure, in order to ensure the integrity of the shell structure, welding connections are used as much as possible, flanged and bolted connections are used only if necessary. Manhole, passage, connecting pipe and so on need to be sealed in the place where the shell is pierced to prevent leakage. The shell of the absorption tower is designed to withstand pressure load, pipe force and torque, wind load, snow load and seismic load, as well as all other loads added to the absorption tower. The absorption tower is provided with supports and reinforcements to fully prevent the tilt and sloshing of the tower. 3.2 slurry spray system The slurry spray system in the absorption tower is composed of distribution pipe network and nozzles. The spray system can reasonably distribute the required spray quantity. The computer simulation will be used to make the flue gas flow direction uniform, and to ensure the full contact and reaction between limestone slurry and flue gas. For the selection of slurry spray pipe material, it is technically feasible and ensure the service life of 20 years. 3.3 accident flue gas cooling system The accident flue gas cooling system includes the distribution pipe network and the nozzles, and the cooling medium adopts fire-fighting process water. The system shall meet the temperature of the flue gas at the inlet of the desulfurization unit and the range of the flue gas flow, so as to ensure the lining of the absorption tower when the circulation pump is in fault.

The Features of Limestone flue gas desulfurization(FGD)
Mature technology, wide applicationHigh operation reliability
Rich absorbent resources
Low straight investment
90%-95% desulphurization efficiency
Adaptable to the variety of coal and load
Limestone/Limestone-Gypsum Desulfurization Process
1.Working Principle
Limestone/limestone-gypsum flue gas desulfurization uses limestone or lime as the desulfurization absorbent. Limestone is crushed and ground into powder and mixed with water to form absorption slurry. When limestone is used as absorbent, lime powder is digested and added with water to form absorbent slurry. In the absorption tower, the absorbent slurry is contacted and mixed with the flue gas, and the sulfur dioxide in the flue gas is removed by chemical reaction with the calcium carbonate in the slurry and the blown-in oxidized air. The final reaction product is gypsum.
2.Reaction Process
1.Absorption
SO2 + H2O—> H2SO3
SO3 + H2O—> H2SO4
2.Neutralization
CaCO3 + H2SO3 —> CaSO3+CO2 + H2O
CaCO3 + H2SO4 —> CaSO4+CO2 + H2O
CaCO3 +2HCl—> CaCl2+CO2 + H2O
CaCO3 +2HF —>CaF2+CO2 + H2O
3.Oxidization
2CaSO3+O2—>2 CaSO4
4.Crystallization
CaSO4+ 2H2O —>CaSO4 ·2H2O
3.System Composition
The desulfurization system mainly consists of flue gas system, absorption and oxidation system, limestone/ limestone slurry preparation system, by-product treatment system, wastewater treatment system, emergency slurry tank system, utility system (process water, compressed air, etc.) and electrical control system, etc.
4.Technological Process
Boiler/ Kiln-> Dust Collector-> Induced Draft Fan-> Absorption Tower-> Chimney<br />
The flue gas from the boiler or kiln enters the absorption tower after dust removal under the action of the induced draft fan. The absorption tower is a countercurrent spraying empty tower structure, which integrates the absorption and oxidation functions. The upper part is the absorption zone, the lower part is the oxidation zone, and the flue gas after dust removal is in reverse contact with the circulating slurry in the absorption tower. The system is generally equipped with 3-5 sets of slurry circulating pumps, and each circulating pump corresponds to an atomized spray layer. When only one unit is running or the load is low, 1-2 spray layers can be stopped. At this time, the system still maintains high liquid-gas ratio, thus achieving the required desulphurization effect. The secondary demister is installed in the upper part of the absorption zone, and the free water in the flue gas of the demister outlet is not more than 75mg/Nm3. The slurry after absorbing SO2 enters the circulating oxidation zone, in which calcium sulfite is oxidized into gypsum crystals by the blown-in air. At the same time, fresh limestone slurry is supplied from the absorbent preparation system to the absorption oxidation system to supplement the depleted limestone so as to make the absorbent slurry maintain at a certain pH value. When the reaction product slurry reaches a certain density, it is discharged into the desulphurization by-product system, and then dehydrated to form gypsum.
5.Application Field
Flue gas desulfurization for coal-fired power generation boilers, cogeneration boilers, central heating boilers, sintering machines, pellet kilns, coking furnaces, glass kilns, etc.
Friendly reminder: The process has the most extensive application, mature technology, good adaptability to flue gas load and variety of coal types, as well as the high desulphurization efficiency. It is especially suitable for high sulfur coal and strict environmental protection emission requirements, but the system is relatively complex, the cost of investment is high, and the chimney needs anti-corrosion treatment
Special Topics on Desulfurization Process Selection
The following table mainly focuses on the comparison of several desulfurization processes that are widely used.
S.l No. | Item | DSI FGD | Semi-dry FGD | Wet FGD |
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1 | electrical consumption | no | low | high |
2 | water consumption | 60%-85% | 60%-85% | 80%-99% |
3 | desulfurization efficiency | The maintenance of the equipment is simple and the cost is very low. | Low, equipment maintenance is simple, but compared with dry desulphurization, semi-dry tower interior needs maintenance and maintenance. | High, wet desulphurization equipment corrosion is serious, maintenance rate is high. |
4 | maintenance and repair cost | High, the equipment in the high temperature operation, will not produce the knot, the operation is stable. | Low, equipment maintenance is simple, but compared with dry desulphurization, semi-dry tower interior needs maintenance and maintenance. | High, wet desulphurization equipment corrosion is serious, maintenance rate is high. |
5 | availability of equipment | High, the equipment in the high temperature operation, will not produce the knot, the operation is stable. | A little high, the equipment runs at medium and low temperature, due to the characteristics of water content, internal consolidation is easy to appear, resulting in parking maintenance and so on. | High, Because of its high desulphurization efficiency, some equipment problems will not affect the flue gas treatment with low sulfur content under normal maintenance. |
Analysis of Operating Cost
2. Power consumption of desulfurization system
3. Consumption calculation
3.1 Consumption and costs of desulfurizer
3.2 Electricity charges
3.3 Labor costs
3.4 Water consumption costs
The design data, specific parameters related to the list, operation cost and implementation plan need to be calculated according to the actual situation.