JPH0355172B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved wet flue gas desulfurization method that simultaneously achieves a high desulfurization rate and produces high-purity gypsum as a by-product in a flue gas desulfurization method for removing SO ₂ from SO ₂ -containing flue gas. That is, using a slurry containing a calcium basic compound as an absorbent,
In the method of removing SO ₂ from exhaust gas and producing gypsum as a by-product, a single absorption tower is used, and the optimum liquid-gas ratio and residence time of the absorbent slurry in the absorption tower are set according to the properties of the exhaust gas. Moreover, by setting the pH of the absorbent slurry to 4 to 6, a high desulfurization rate can be obtained, and at the same time, high purity gypsum can be directly recovered from the absorbent slurry. Conventionally, calcium carbonate, calcium hydroxide, etc. are used as absorbents to react with SO ₂ and the resulting calcium sulfite is oxidized to recover gypsum (calcium sulfate), but this method achieves a high desulfurization rate. In order to perform the absorption reaction shown by the following formulas (1) and (2) in two or more absorption units, and to recover high-purity gypsum, a separate absorption unit was installed. An oxidizing device was required to carry out the reaction shown by equation (3), and high-purity gypsum was obtained in this oxidizing device by methods such as air blowing and addition of sulfuric acid. CaCO ₃ +SO ₂ +Aq→CaSO ₃・1/2H ₂ O＋C
O ₂ +Aq……(1) Ca(OH) ₂ +SO ₂ +Aq→CaSO ₃・1/2H ₂ O＋Oq
……(2) CaSO ₃・1/2H ₂ O＋1/2O ₂ +Aq→CaSO ₄
・2H ₂ O + Aq...(3) In the absorber itself, equation (3) may occur as a side reaction, but the amount of gypsum produced is not sufficient to omit the oxidizer, and the absorber has a high desulfurization rate. - It was not possible to simultaneously satisfy both requirements of producing high-purity gypsum. As a method for achieving this, a method has been invented that satisfies both by blowing air into the absorption device, but even in this case, a separate air blowing device into the absorption tower is required. The inventors of the present invention have conducted extensive research to resolve the drawbacks of flue gas desulfurization using the conventional lime-gypsum method. , provides a simplified and economical method that can simultaneously achieve high desulfurization efficiency and high purity gypsum production using only a single absorption tower. That is, the present invention has SO ₂ of 1000 ppm or less and O _{2 of} 4%.
In the wet flue gas desulfurization method with one absorption tower, which removes SO ₂ from the exhaust gas containing the above and produces gypsum as a by-product, Ca basic compound slurry is used as the absorbent, and the liquid-gas ratio is 13/m ³ in the absorption tower. As described above, we provide a wet flue gas desulfurization method characterized by obtaining a high desulfurization rate and recovering high purity gypsum directly from the absorption slurry by setting the liquid residence time to 13 hours or more and the absorption liquid slurry pH to 4 to 6. It is something to do. The process according to the invention consists of a single absorption column
SO ₂ absorption equipment (slurry concentration equipment that concentrates the absorption liquid slurry as necessary), gypsum separation equipment that separates gypsum from the absorption liquid slurry, supernatant liquid from the slurry concentration equipment or separated liquid from the gypsum separation process. It consists of an absorbent blending device that mixes a calcium basic compound, piping that connects these in sequence, and piping that connects the absorbent blending device and the absorption device. An example of an apparatus suitable for carrying out the method of the present invention will be described below with reference to the accompanying FIG. 1. The exhaust gas 1 containing SO ₂ to be treated is introduced into an absorption tower 2 having a liquid distillation section having an absorption liquid residence time depending on the characteristics of the exhaust gas. In the absorption tower 2, SO 2 is removed from the exhaust gas by an absorption liquid slurry sprayed from multi-stage sprays by a pump 3, and the SO ₂ is removed from the exhaust gas through a flow path 4.
It is sent to the chimney 5 and released into the atmosphere. The absorbent slurry PH is transferred from the absorbent blending device 6 to the pump 7.
The pH is adjusted to 4 to 6 by adjusting the flow rate of the absorbent slurry sent to the absorption tower through channel 8. A part of the absorbent slurry is sent to the concentrator 10 through the flow path 9, and the concentrated slurry is sent to the gypsum separation device 13 through the flow path 12 by the pump 11.
Separate the plaster 14. The supernatant liquid of the concentrator 10 is
The absorbent slurry is sent to the absorbent blending device 6 through the flow path 15 and mixed with the absorbent 16, thereby blending the absorbent slurry. A portion of the supernatant liquid is discharged as waste water 17. The liquid from the gypsum separation device 13 flows through the flow path 18
It is then returned to the concentrator 10. FIG. 2 shows the flow of a conventional two-absorption tower system, and devices common to those in FIG. 1 are designated by the same numbers. In this flow, compared to the case in Figure 1, the PH adjustment tank 18, oxidizer (oxidation tower 19, air 20, oxidation air fan 21), sulfuric acid equipment (sulfuric acid 22, sulfuric acid tank 23, PH meter 24), etc. are added. In need of. From the above, in the device used in the present invention,
Approximately 30% in construction cost and approximately 5% in running cost
It is possible to reduce costs. The present invention will be explained below using specific examples. Comparative Example Test results are shown for a conventional two-absorption tower system for heavy oil combustion exhaust gas. Exhaust gas to be treated: Heavy oil combustion exhaust gas Processing gas amount: 1000Nm ³ /H Absorption tower type: Spray tower type (countercurrent) 1st absorption tower
550mmφ×7000mmH (2 spray stages) 2nd
550mmφ×10000mmH (4 spray stages) Absorbent: Calcium carbonate Absorbent supply amount: 1.02 to 1.03 for absorbed SO ₂
double equivalent

[Table] In the conventional method using two absorption towers (no air blowing into the absorption towers), a large amount of calcium sulfite remains in the solid content of the absorbent slurry at the outlet of the absorption tower, as shown in the comparative example. Therefore, in order to obtain high-purity gypsum, an oxidation device for turning calcium sulfite into gypsum is required. Alternatively, in order to prevent calcium sulfite from remaining in the absorbent slurry at the outlet of the absorption tower, it becomes necessary to blow air into the absorption tower. On the other hand, the present inventors found that when using a single absorption tower, the gypsum production rate in the absorption tower (the rate at which absorbed and removed SO ₂ is converted to gypsum) is expressed by the following relational expression: I found out that it can be done. Y=K×O ₂ 〓×P _SO2 〓×L〓×H・T〓/[SO ₂ ] Y: Gypsum production rate (-) O ₂ : Oxygen concentration in gas (-) P _SO2 : SO in gas ₂ Concentration (ppm) L: Circulating liquid volume (m ³ /H) L = L / G × G L / G: Liquid gas ratio (m ³ /m ³ ) G: Processing gas volume (m ³ /H) H. T: Absorption tower liquid residence time (Hr) [ _SO2 ]: Absorbed SO2 _amount (Kg-mol/H) K: 0.1 to 0.4 α: 0.8 to 1.0 β: -0.1 to 0.5 γ: 1 to 1.2 θ: 0.2 to 1.0 However, absorption liquid slurry PH = 4 to 6 Example 1 The test results when the method of the present invention was applied to heavy oil combustion exhaust gas are shown. Exhaust gas to be treated: Heavy oil combustion exhaust gas Processing gas amount: 1000Nm ³ /H Absorption tower type: Spray tower (countercurrent) 550mmφ×
15000mmH (6 spray stages) Absorbent: Calcium carbonate Absorbent supply amount: 1.02 to 1.05 for absorbed SO ₂
double equivalent

【table】

[Table] In other words, the examples show that when a single absorption tower is used, the lower the SO ₂ concentration and the higher the O ₂ concentration, liquid-gas ratio, and absorption tower liquid residence time, the more gypsum formation occurs. and at least SO ₂ 1000ppm or less,
For exhaust gas containing 4% or more _O2 , liquid gas ratio 13
/m ³ or more, absorption tower liquid residence time 13 hours or more, and absorption liquid slurry PH = 4 to 6, the solid content in the absorption liquid slurry at the absorption tower outlet can be made into high purity gypsum of 95% or more. be. Under these conditions, a high desulfurization rate of over 95% has also been achieved. Furthermore, when comparing Example 1 and Comparative Example, it is found that under similar exhaust gas properties and operating conditions, the desulfurization performance achieved a high desulfurization rate of 95% or more.
The gypsum ratio in the solid content of the absorption liquid slurry at the outlet of the absorption tower is a very low value in the two-layer absorption tower system. That is, the above-mentioned relational expression indicating the gypsum production rate holds true in the case of one absorption tower, and cannot be considered from a two-absorption tower system. Examples 2 and 3 below show cases in which the method of the present invention is applied to coal combustion exhaust gas. Example 2 Exhaust gas to be treated: Coal combustion exhaust gas Processing gas amount: 553000Nm ³ /H4 humidity Absorption tower type: Spray tower (countercurrent) 9.7mφ×
35.5mH Absorbent: Calcium carbonate Absorbent supply amount: 1.05 times equivalent to absorbed SO ₂

【table】

[Table] Example 3 Exhaust gas to be treated: Coal combustion exhaust gas Processing gas amount: 1336000Nm ³ /H4 moisture Absorption tower type: Spray tower (countercurrent) 14.0mφ×
33.1mH Absorbent: Calcium carbonate Absorbent supply amount: 1.05 times equivalent to absorbed SO ₂

[Table] As described above, from Examples 2 and 3, the effects of the method of the present invention are clear.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram showing an example of an apparatus suitable for implementing the method of the present invention, and FIG. 2 is a conceptual diagram of an apparatus in a conventional method. 1: Exhaust gas, 2: Absorption tower, 3: Absorption tower circulation pump, 4: Flue, 5: Chimney, 6: Absorbent preparation tank, 7: Absorbent supply pump, 8, 9, 12, 1
5, 18: Piping, 10: Slurry concentrator, 1
1: pump, 13: solid-liquid separator, 14: gypsum,
16: Absorbent, 17: Drainage, 18: PH adjustment tank, 1
9: Oxidation tower, 20: Air, 21: Oxidation air fan, 22: Sulfuric acid, 23: Sulfuric acid tank, 24: PH meter.

Claims (1)

[Claims] 1 In the wet flue gas desulfurization method using one absorption tower, which removes SO ₂ from flue gas containing 1000 ppm or less of SO _{2 and} 4% _or more of O 2 and produces gypsum as a by-product, Ca is used as an absorbent.
Using a basic compound slurry, in an absorption tower,
Liquid-gas ratio 13/ ^m3 or more, liquid residence time 13Hr or more,
A wet flue gas desulfurization method characterized by obtaining a high desulfurization rate by setting the absorption liquid slurry to pH 4 to 6 and at the same time recovering high purity gypsum directly from the absorption liquid slurry.