JP4507404B2 - Boiler flue gas treatment system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a boiler flue gas treatment system for removing high sulfuric anhydride (SO ₃ ) contained in exhaust gas discharged from a boiler, recovering this using a magnesium hydroxide gypsum method, and removing SO _2. Is.
[0002]
[Prior art]
Traditionally, the removal of SOx in the boiler flue gas, for SO ₂ is to spray the absorption liquid in the absorption column, but by contacting the exhaust gas with a gas-liquid be absorbed removing SO ₂ have been made, Ya this wet desulfurization The semi-dry type desulfurization apparatus cannot absorb and remove SO ₃ , and if it is released to the atmosphere, it causes purple smoke due to sulfuric acid mist.
[0003]
Such being the case, the SO _3, it has been made for absorbing and removing SO ₃ by injecting an alkaline agent to the flue.
[0004]
As absorber SO _2, with Mg (OH) _2, after absorption oxidation, there is a process for recovering gypsum as a by-product by adding CaO or Ca (OH) _2.
[0005]
[Problems to be solved by the invention]
However, neutralization of a high SO ₃ content gas has a problem that unreacted CaO or Ca (OH) ₂ is discarded and becomes uneconomical. Further, the magnesium hydroxide gypsum method has a problem that CaO or Ca (OH) ₂ is separately required as a replenisher.
[0006]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a boiler flue gas treatment system that can solve the above problems and simplify the system by efficiently using an absorbent and a replenisher in removing SO ₃ and SO ₂ from exhaust gas. There is to do.
[0007]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the invention of claim 1 is to absorb the boiler exhaust gas after adding SO ₃ in the exhaust gas by adding an absorbent composed of powdered quicklime or slaked lime to the exhaust gas from the boiler. It is introduced into a desulfurization unit together with an agent, and is contacted with a slurry using magnesium hydroxide as a desulfurization agent in the desulfurization unit, so that SO ₂ is absorbed and removed. This is a boiler flue gas treatment system that uses magnesium oxide to recover gypsum and reuse magnesium hydroxide as a desulfurization agent.
[0008]
The invention according to claim 2 is the boiler flue gas treatment system according to claim 1, wherein in the desulfurization apparatus, air is blown into the slurry which has become SO ₂ by absorbing SO ₂ and is oxidized to magnesium sulfate.
[0009]
In the invention of claim 3, quick lime or slaked lime is added so as to be equimolar or more with respect to S content in the exhaust gas, and unreacted quick lime or slaked lime is supplied as a replenisher to the aging tank via a desulfurization apparatus to desulfurize The boiler flue gas treatment system according to claim 1, wherein a substitution reaction is performed with magnesium sulfate afterwards.
[0010]
According to a fourth aspect of the present invention, the gypsum and magnesium hydroxide produced by the substitution reaction in the aging tank are separated in particle size by a gypsum separator such as a hydrocyclone to separate the gypsum and the magnesium hydroxide. It is a boiler flue gas treatment system.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
[0012]
FIG. 1 shows a block diagram of a boiler flue gas treatment system of the present invention.
[0013]
In FIG. 1, reference numeral 10 denotes a heavy oil-fired small to medium-sized boiler, and exhaust gas discharged from the boiler 10 is passed through a denitration device 11 for denitration. The temperature of this part is 300-400 degreeC.
[0014]
An absorbent injection line 14 for adding an absorbent made of powdered quicklime (CaO) or slaked lime (Ca (OH) ₂ ) to the duct 13 connecting the denitration device 11 and the downstream gas-air heater (GAH) 12. Is connected.
[0015]
The gas-air heater 12 is connected to a bag filter type or electric dust collection type dust collector 16 through a duct 15, and exhaust gas from the dust collector 16 is discharged from the chimney 18 to the atmosphere.
[0016]
Quick lime or slaked lime as an absorbent to be injected into the duct 13 on the inlet side of the gas-air heater 12 is an amount that is expected to be excessive with respect to the amount of (SO ₂ + SO ₃ ) in the exhaust gas, for example, Ca for S content. Is added so as to be at least equimolar.
[0017]
When an absorbent of quicklime or slaked lime is added to the exhaust gas in the temperature range of 300 to 400 ° C., sulfuric anhydride (SO ₃ ) can be efficiently removed according to the following neutralization reaction.
[0018]
CaO + SO ₃ → CaSO ₄
Or
Ca (OH) ₂ + SO ₃ → CaSO ₄ + H ₂ O
The exhaust gas is heat-exchanged with boiler combustion air by the gas-air heater 12, the temperature is lowered and supplied to the desulfurization device 16, and contacted with the slurry of magnesium hydroxide as the desulfurization agent supplied from the line 17. The SO ₂ is absorbed and removed and exhausted from the chimney 18.
[0019]
In this case, in order to prevent white smoke in the exhaust of the chimney 18, a gas-gas heater is installed before and after the desulfurization device 16, and flows into the desulfurization device 16 with the preceding gas-gas heater. By recovering heat from the exhaust gas and reheating it to a temperature equal to or higher than the saturated water vapor temperature of the exhaust gas to be exhausted by a subsequent gas-gas heater, white smoke can be prevented. That is, the temperature of the exhaust gas exiting the gas-air heater 12 is set to 170 ° C., and the exhaust gas is recovered by heat at about 70 to 80 ° C. with the preceding gas-gas heater, and the temperature is further lowered by the desulfurization device 16 to become saturated steam. However, by reheating this with a gas-gas heater at the latter stage and heating it above the saturated water vapor temperature of the exhaust gas, even if exhausted from the chimney 18, it will not become below the saturated vapor temperature. Can be prevented.
[0020]
An electric dust collector may be provided between the desulfurization device 16 and the chimney 18.
[0021]
Now, a slurry using magnesium hydroxide (Mg (OH) ₂ as a desulfurizing agent is supplied from the line 17 to the desulfurization device 16 and brought into gas-liquid contact with the exhaust gas.
[0022]
This magnesium hydroxide has a particle size of 1 to 2 μm and reacts with SO ₂ in the exhaust gas as shown in the following formula to desulfurize the exhaust gas.
[0023]
Mg (OH) ₂ + SO ₂ → MgSO ₃ + H ₂ O
Magnesium sulfite produced by desulfurization is oxidized into magnesium sulfate by the air blown into the slurry from the air blowing line 20 into the desulfurization apparatus 16 as shown in the following formula.
[0024]
MgSO ₃ + 1 / 2O ₂ → MgSO ₄
Further, unreacted absorbent made of quick lime or slaked lime added with exhaust gas before the gas air heater 12 and calcium sulfate absorbed SO ₃ flow into the desulfurization apparatus 16, and this is a slurry line 21 together with the slurry of the desulfurization agent. Is introduced into the aging tank 22.
[0025]
In the aging tank 22, magnesium sulfate and unreacted absorbent (CaO or Ca (OH) ₂ ) generated by desulfurization are converted into gypsum and magnesium hydroxide by a substitution reaction as shown in the following formula.
[0026]
MgSO ₄ + CaO + H ₂ O → CaSO ₄ + Mg (OH) ₂
The slurry subjected to the substitution reaction in the aging tank 22 is supplied from a line 23 to a gypsum separator 24 made of hydrocyclone or the like.
[0027]
The gypsum separator 24 can be separated into gypsum and magnesium hydroxide by a simple centrifugal separation operation such as a hydrocyclone.
[0028]
The separated gypsum 25 is recovered as a by-product, and magnesium hydroxide is not shown in the figure, but is separated from the waste water 27 by a solid-liquid separator, and is passed from the line 26 to the desulfurizer 16 as a magnesium hydroxide desulfurizing agent. Return and reuse.
[0029]
In this way, the sulfuric acid that is contained in the exhaust gas at a high concentration, which causes purple smoke, is neutralized with quick lime or slaked lime, and unreacted quick lime or slaked lime is directly fed into the desulfurization apparatus, and this is treated with the magnesium hydroxide gypsum method By using it as a calcium salt, magnesium hydroxide as a desulfurizing agent can be used repeatedly without the need for fresh quicklime or the like.
[0030]
In addition, by installing a wet electric dust collector, a gas-gas heater or the like in this flue gas desulfurization system, it is possible to implement more severe environmental measures.
[0031]
【The invention's effect】
In short, according to the present invention, the sulfuric acid that is contained in the exhaust gas at a high concentration and causes purple smoke is neutralized with quick lime or slaked lime, and unreacted quick lime or slaked lime is directly fed to the desulfurization apparatus, By using it as a calcium salt in the magnesium oxide gypsum method, the system can be simplified.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Boiler 12 Gas-air heater 14 Absorbent addition line 16 Desulfurization apparatus 22 Aging tank

Claims (4)

After adding an absorbent made of quick lime powder or slaked lime to the exhaust gas from the boiler to absorb and remove SO ₃ in the exhaust gas, the boiler exhaust gas is introduced into the desulfurization apparatus together with the absorbent, and magnesium hydroxide is used in the desulfurization apparatus. is contacted with the slurry to desulfurizing agent SO ₂ removed by absorption, desulfurizing agent of magnesium hydroxide together with the desulfurizing agent and the absorbent is a substitution reaction with aging tank to gypsum and magnesium hydroxide, to recover the gypsum Boiler flue gas treatment system characterized by being reused as The boiler flue gas treatment system according to claim 1, wherein air is blown into a slurry that has become SO ₂ absorbed into magnesium sulfite in a desulfurization apparatus and oxidized to magnesium sulfate. Add quick lime or slaked lime so as to be equimolar or more with respect to the S content in the exhaust gas, supply unreacted quick lime or slaked lime as a replenisher to the aging tank via a desulfurization device, and replace with magnesium sulfate after desulfurization The boiler flue gas treatment system according to claim 1. The boiler flue gas treatment system according to claim 2, wherein gypsum and magnesium hydroxide produced by a substitution reaction in an aging tank are separated in particle size by a gypsum separator such as a hydrocyclone to separate gypsum and magnesium hydroxide.

Images