FRP desulfurization tower series
Double-alkali desulfurization tower
Double-alkali desulfurization tower
The double-alkali method uses a sodium-based desulfurizing agent to desulfurize in a desulfurizing device. The prepared sodium carbonate solution is directly driven into the desulfurization tower to wash and remove SO2 in the flue gas. Due to the strong alkalinity of the sodium-based desulfurizer, the solubility of the reaction product after absorbing sulfur dioxide is large, which will not cause supersaturated crystals and cause scaling problems. On the other hand, the part of the desulfurization product is pumped into the regeneration tank by a regeneration pump to reduce and regenerate it with quicklime. After the regenerated sodium-based desulfurizing agent is precipitated, it is returned to the desulfurizing tower for recycling. The double-alkali desulfurization process reduces investment and operating costs, and is more suitable for desulfurization transformation of small and medium boilers.
The double-alkali method uses a sodium-based desulfurizing agent for desulfurization in the tower. Due to the strong alkalinity of the sodium-based desulfurizing agent, the solubility of the reaction product after absorbing sulfur dioxide is large, which will not cause supersaturated crystals and cause scaling problems. On the other hand, the desulfurization product is discharged into the regeneration tank for reduction and regeneration with calcium hydroxide, and the regenerated sodium-based desulfurization agent is returned to the desulfurization tower for recycling. The double-alkali desulfurization process reduces investment and operating costs, and is more suitable for dust removal and desulfurization in small and medium boilers.
The double-alkali flue gas desulfurization technology uses sodium hydroxide solution as a starting desulfurizing agent, and the prepared sodium hydroxide solution is directly driven into a desulfurization tower to wash and remove SO2 in the flue gas to achieve the purpose of flue gas desulfurization, and then the desulfurization product is desulfurized. The agent regeneration tank is reduced to sodium hydroxide and then returned to the desulfurization tower for recycling.
The desulfurization process mainly includes 5 parts:
(1) Preparation and supplement of absorbent;
(2) Spray of absorbent slurry;
(3) The mist in the tower is mixed with the smoke;
(4) Reduction of sodium base by slurry in regeneration tank;
(5) Gypsum treatment.
The dual-alkali flue gas desulfurization process is similar to other wet desulfurization reaction mechanisms such as limestone / lime. The main reaction is that the SO2 in the flue gas is first dissolved in the absorption solution and then dissociated into H + and HSO3—; SO2 (g) = = = SO2
SO2 (aq) + H2O (l) = = = H + HSO3— = = = 2H ++ SO32-;
Equation (1) is a slow response and is one of the speed control processes.
H + then neutralizes with OH- in the solution to form salts and water, which promotes the continuous absorption and dissolution of SO2. The specific reaction equation is as follows:
2NaOH + SO2 → Na2SO3 + H2O
Na2SO3 + SO2 + H2O → 2NaHSO3
The reaction product after desulfurization enters the regeneration tank and is regenerated with another base, generally Ca (OH) 2. The regeneration reaction process is as follows:
Ca (OH) 2 + Na2SO3 → 2 NaOH + CaSO3
Ca (OH) 2 + NaHSO3 → Na2SO3 + CaSO3 + H2O
(In the presence of oxygen, the following reactions also occur:
Ca (OH) 2 + Na2SO3 + O2 + H2O → NaOH + CaSO4 + H2O
The removed sulfur is precipitated in the form of calcium sulfite, calcium sulfate, and then pumped into the gypsum dehydration treatment system or directly stacked and discarded. The regenerated NaOH can be recycled.
Introduction of double alkali desulfurization process
The flue gas from the boiler is first removed by a dust collector, and then the flue gas enters the desulfurization tower from the bottom of the tower through the flue. The method of arranging a number of layers (depending on the specific conditions) of the swirl plate in the desulfurization tower. The swirl plate tower has good gas-liquid contact conditions. The lye sprayed from the top of the tower is atomized on the swirl plate to make the flue gas. The SO2 in the solution is fully absorbed and reacted with the sprayed lye. The net flue gas after desulfurization and washing is dewatered by the demister and enters the heat exchanger. The heated flue gas is discharged into the atmosphere through the chimney through the induced draft fan.
Double alkali desulfurization process:
The original double-alkali process generally had only one circulating pond. NaOH, lime, and fly ash captured during the desulfurization process were mixed in the same circulating pond. When removing the ash in the circulation tank, soot, calcium sulfite, calcium sulfate, lime slag, and unreacted lime are removed at the same time, and the cleared mixture is not easy to comprehensively use and become waste slag. In order to overcome the shortcomings of the traditional double alkali method, it has been improved. The main process is that the desulfurization solution is prepared by adding sodium hydroxide to the clear pond at one time, and pumping it into the absorption tower for desulfurization. The three products are all dissolved in water. During the desulfurization process, the fly ash mixed with flue gas is simultaneously moistened and captured by the circulating liquid, and the circulating slurry discharged from the absorption tower flows into the precipitation tank. Ash and slag are regularly removed by precipitation and can be recycled, such as making bricks. The supernatant overflows into the reaction tank and reacts with the added lime liquid. The replaced sodium hydroxide is dissolved in the circulating water, and at the same time, refractory calcium sulfite, calcium sulfate and calcium carbonate are generated. Clear.
The double-alkali flue gas desulfurization process mainly consists of five parts: absorbent preparation and supplement system, flue gas system, SO2 absorption system, desulfurization gypsum dehydration treatment system and electrical and control system.
Absorbent preparation and supplement system
When the desulfurization device is started, sodium hydroxide is used as an absorbent. The sodium hydroxide dry powder is added to the lye tank, and water is added to prepare the sodium hydroxide lye. The lye is pumped into the return tank and pumped into the desulfurization tower. Desulfurization, in order to regenerate and reduce the desulfurized product after being desulfurized with a sodium-based desulfurizing agent, a pulping tank is required. Lime powder (particles less than 10mm in diameter) is added to the pulping tank. After adding water, a lime slurry is prepared. The lime slurry is driven into a regeneration tank and reacts with sodium sulfite and sodium sulfate. During the entire operation, many solid residues and other particulate matter produced by desulfurization are precipitated and then removed by a grabber for secondary treatment by the user. Part of the sodium hydroxide will be lost in the discharged residue, so sodium hydroxide can be replenished regularly in the lye tank to ensure the normal operation of the entire desulfurization system and compliance with the flue gas emissions. In order to avoid the regeneration of calcium sulphite and calcium sulphate that are also driven into the desulfurization tower, it is easy to cause scaling and clogging in the pipeline and the tower. A waterfall gas device is specially installed for forced oxidation. The full-scale sedimentation tank fully precipitates to ensure that large particles are not hit back to the tower.
In the flue gas system, the boiler flue gas enters the dust removal and desulfurization tower through the flue, and the low temperature flue gas after dust removal and desulfurization enters the main flue through two stages, and is discharged into the atmosphere from the chimney.
SO2 absorption system
The flue gas enters the absorption tower and flows upward, and the slurry sprayed downward is washed in a countercurrent manner, and the gas and liquid are in full contact. The desulfurization tower adopts a method of built-in several layers of swirl plates, and a nozzle is arranged in the uppermost layer of the desulfurization swirl plates in the tower. The sprayed sodium hydroxide solution is sprayed onto the water distributor of the cyclone central shaft through the spraying layer, and then the lye is spread evenly. Under the guidance of the cyclone, the flue gas rises and spreads evenly. The alkaline liquid phase cut on the swirl plate further atomizes the alkaline liquid, fully absorbs acid gases such as SO2, SO3, HCl and HF, and generates NaSO3 and NaHSO3, while consuming sodium hydroxide as an absorbent. The sodium hydroxide lye added for replenishment enters the return tank and is pumped into the absorption tower to circulate and absorb SO2 together with the sodium hydroxide solution regenerated by lime.
A two-stage swirl plate (or baffle) demister is installed at the exit of the absorption tower to remove the water mist brought out by the flue gas during the washing process. In this process, the smoke and other solid particles carried by the flue gas are also captured by the demister, and they are flushed regularly to avoid clogging the demister.
Desulfurization product processing system
The final desulfurization product of the desulfurization system is still gypsum slurry (about 20% solids content), and the specific composition is CaSO3, CaSO4, and partially oxidized sodium salt NaSO4. It is discharged from the drainage pipe at the bottom of the sedimentation tank, or it is fished out by the grab. Because the solid product is doped with various ash and NaSO4, which seriously affects the quality of gypsum, it is generally discarded.
Electrical and control systems
The power supply of the desulfurization device is led out from the switchboard of the boiler room and connected to the switchboard of the desulfurization electrical control room via the power cable. In the desulfurization electrical control room, the low-voltage power distribution is powered by the power center motor control center. The dust removal pump, lye pump, and lime slurry pump are all designed for one use and one backup to ensure system continuity.
Desulfurization agent feeding solution preparation equipment for desulfurization system realizes on-site control, centralized control of control panel, and can realize manual or automatic operation.
During normal operation, the vertical control panel automatically controls the operation of each pump to control the supply of lime slurry and sodium hydroxide solution in the desulfurization system. When the boiler load changes, you can manually set the liquid adding time according to the PH feedback value to achieve automatic operation. . Specific electrical principles refer to the electrical control principle drawings.
Solve the problem of secondary pollution:
Using sodium hydroxide as a desulfurizing agent, the reaction rate of sulphur dioxide absorption in the desulfurization tower is fast and the desulfurization efficiency is high, but the desulfurization product Na2SO4 is difficult to handle, which is very likely to cause serious secondary pollution problems. A double-alkali method is used for the flue gas desulfurization process. The product after absorbing sulfur dioxide with sodium hydroxide is regenerated with lime, and only a small amount of Na2SO4 is brought into the gypsum slurry.
Compared with the limestone or lime wet desulfurization process, the double alkali method has the following advantages in principle
(1) Desulfurization with NaOH. The circulating water is basically an aqueous solution of NaOH. During the circulation process, there is no corrosion and blockage of pumps, pipes and equipment, which is convenient for equipment operation and maintenance.
(2) The regeneration of the absorbent and the precipitation of the desulfurization slag occur outside the tower, which avoids blockage and abrasion in the tower, improves the reliability of the operation, and reduces the operating cost; at the same time, an efficient plate tower or packed tower can be used instead of the Tower to make the system more compact and improve desulfurization efficiency;
(3) Sodium-based absorption liquid absorbs SO2 fast, so a smaller liquid-gas ratio can be used to achieve higher desulfurization efficiency, generally above 90%;
For the integrated technology of desulfurization and dust removal, the utilization rate of lime can be improved.
Disadvantages: Na2SO3 oxidation side reaction product Na2SO4 is difficult to regenerate, and NaOH or Na2CO3 needs to be continuously added to increase the consumption of alkali. In addition, the presence of Na2SO4 will also reduce the quality of gypsum.
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