JP2994825B2 - Wet lime gypsum desulfurization method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for desulfurization of wet lime gypsum, and more particularly to an efficient separation of unreacted limestone and gypsum from an absorption slurry by adjusting the particle size of limestone to be supplied to recover high quality gypsum. The present invention also relates to a wet lime gypsum desulfurization method capable of greatly improving desulfurization performance by returning separated unreacted limestone to an absorption tower.

[0002]

2. Description of the Related Art FIG.
June 1985, p. 29). The flue gas 501 is washed in the absorption tower 502 of the flue gas desulfurization device. Air is supplied to the absorption tower bottom tank 503 from a line 504 to oxidize calcium sulfite in the slurry to gypsum.

The slurry in which gypsum particles and limestone particles are suspended is sprayed from an absorption tower bottom tank 503 by a spray pipe 506 by an absorption tower circulation pump 505 to absorb sulfur oxides, that is, SO ₂ , in exhaust gas. The gas after the absorption treatment is discharged out of the system through a line 507.

Limestone particles, which are the raw material for absorption, are supplied through line 508.
Is supplied to the raw material preparation tank 509, where line 5
After being mixed with the filtrate supplied from 10 to form a slurry, it is supplied to the absorption tower bottom tank 503 through a line 511.

Since limestone in excess of the SO ₂ absorption amount is supplied to increase the SO ₂ absorption capacity of the absorption tower circulation slurry,
Eventually, the slurry held in the absorption tower bottom tank 503 is a slurry in which gypsum particles and limestone particles are suspended as described above. In order to collect gypsum as a by-product, a part of the circulation tower slurry is extracted from the line 512 and the solid-liquid separation device 5 is used.
13 and the gypsum 514 is collected. The gypsum 514 contains, as impurities, limestone particles and fly ash mixed into the absorbing solution from exhaust gas. In order to increase the processing efficiency of the solid-liquid separator 513, a method is also generally employed in which the extracted absorption tower circulation slurry is once led to a thickener (not shown), concentrated, and then supplied to the solid-liquid separator 513. Have been.

A part or all of the filtrate from the solid-liquid separator 513 is sent to a raw material preparation tank 509 via a line 510, and is mixed with limestone particles.

[0007] Part of the filtrate contains impurities accumulated in the absorption system, and
In order to prevent the O ₂ absorption ability from being lowered, it is also usual to discharge the gas through the line 515 to the outside of the system.

[0008]

It is desirable to reduce the operating power cost and measure the capacity of the absorption tower by increasing the SO ₂ absorption capacity in the absorption tower for cost reduction. There is such a problem. (1) In order to enhance the SO ₂ absorption capacity, it is sufficient to supply limestone in excess of the SO ₂ absorption amount, but unreacted limestone is mixed in the recovered gypsum, which significantly impairs the quality of the gypsum. . (2) accelerate the rate of dissolution in excess limestone using instead of limestone small particle size for supplying the slurry, there is a method of increasing the absorption capacity of SO _2, utility by increasing the crushing power cost of limestone The cost of the equipment rises and the economics of the desulfurization unit is impaired. (3) A method of improving the quality of gypsum in which gypsum and limestone particles are separated and collected by a classifier such as a liquid cyclone (for example, Japanese Utility Model Application Laid-Open No. 54-10833) has been proposed. It was difficult to separate the two.

According to the present invention, unreacted limestone and gypsum are efficiently separated from the absorption slurry by adjusting the particle size of limestone to be supplied in order to solve the above problems, and high-quality gypsum is recovered. It is an object of the present invention to provide a wet lime gypsum desulfurization method capable of greatly improving desulfurization performance by returning separated unreacted limestone to an absorption tower.

[0010]

SUMMARY OF THE INVENTION The present invention relates to a wet lime gypsum desulfurization method in which a slurry containing limestone and gypsum is brought into contact with an exhaust gas in an absorption tower to absorb and remove sulfur oxides in the exhaust gas. 50% by weight cumulative diameter of the gypsum particles (hereinafter referred to as D ₅₀₎ and absorbent slurry preparation step of supplying to the slurry as an absorbent limestone particles having a larger D _50, classifying a portion of the slurry withdrawn from absorption tower An unreacted limestone separation step of supplying underflow from the classifier to the absorption tower, and supplying an overflow of the classifier to the solid-liquid separator to remove part or all of the liquid after solid-liquid separation outside the system. And a gypsum separation step of discharging the gypsum to a wet lime gypsum.

In the present invention, the 50% weight cumulative diameter (D ₅₀ ) is defined as the total weight of particles passing through the sieve or the weight ratio of particles remaining on the sieve in a particle group having a particle size distribution. Means a particle diameter of 50%. In addition, the term “cumulative weight%” refers to the weight ratio of particles remaining on the sieve when sieving through a sieve corresponding to the particle diameter on the horizontal axis in a particle group having a particle size distribution as cumulative weight% on the vertical axis. Things.

Further, the classifier referred to in the present invention is generally a liquid cyclone, but is not limited to this.
A water fitting classifier can also be used.

[0013]

DETAILED DESCRIPTION OF THE INVENTION The present invention, limestone particles by classification device than when adjusting the slurry particle size of limestone is supplied to the absorption tower made larger than the gypsum particles size to generate the absorption tower circulating slurry in accordance with the absorption of SO ₂ Have been newly found, and this fact has been made using this fact.

The particle distribution of gypsum and limestone, which has an important effect on the separation efficiency, will be described with reference to FIGS.

FIG. 2 shows an example of the particle size distribution of gypsum in the circulation slurry of the absorption tower and the particle size distribution of various limestones supplied. D ₅₀ of the gypsum in the example of FIG. 2 is 34 .mu.m, supplied limestone are each four A _1, A _2, A ₃ and A _4, D ₅₀ were respectively 63μm, 45μm, 32μm and 14μm . Specifications and operating conditions of the D ₅₀ is discharged detachment device of gypsum, for example, the capacity of the tank, the absorption tower circulating slurry flow rate and S
Although it changes somewhat depending on the O ₂ concentration and the like, it is almost constant under those conditions.

On the other hand, the particle size of the limestone to be supplied can be almost arbitrarily selected depending on the specifications and operating conditions of the crusher. Since the particle size distribution applies to expression of a so-called Rosin-Rammler, so that the particle size distribution itself is determined by determining the D _50. Note that the supplied limestone dissolves faster as the particle size decreases as the SO ₂ is absorbed in the absorption tower, so that the limestone particles in the absorption tower circulation slurry are slightly larger than the supplied limestone particles.

In FIG. 3, the circulation slurry of the absorption tower obtained by the gypsum having the particle size distribution shown in FIG. 2 and the supplied limestone is supplied to the liquid cyclone, and how much limestone particles are generated in the underflow from the liquid cyclone. It indicates whether it is concentrated.

Under certain operating conditions of the hydrocyclone, the limestone concentration in the underflow is concentrated as the D50 of the supplied limestone becomes larger _than that of the gypsum. That is, in the range of D ₅₀ of the feed limestone is more gypsum, significantly increased the proportion of limestone in the underflow compared to the ratio in the slurry supplied to the cyclone.

Next, FIG. 4 shows the relationship between the limestone concentration in the absorbent slurry and the desulfurization performance in the wet lime gypsum desulfurization method. Exhaust gas amount, absorption liquid circulation amount, inlet exhaust gas S
If the operating conditions such as the O ₂ concentration are constant, the desulfurization rate increases as the limestone concentration increases, as shown in FIG. This is due to the effect that the dissolution rate of limestone, which is an alkali source necessary for SO ₂ absorption and neutralization, increases with the concentration of limestone.

The present invention has been made by focusing on the above-mentioned two functions and efficiently combining them.

The data shown in FIGS. 2 and 3 correspond to FIG.
Small laboratory test equipment (exhaust gas volume 20
0 m ³ N / h coal-fired exhaust gas treatment wet limestone / gypsum desulfurization unit) and the cyclone diameter is 2
The thing of 00 mm was used.

[0022]

FIG. 1 illustrates an embodiment of the present invention. The coal-fired exhaust gas having an exhaust gas amount of 200 m ³ N / h is brought into contact with a slurry in which gypsum particles and limestone particles are suspended in an absorption tower 102 from a line 101 to absorb and remove SO ₂ . Air is supplied to the absorption tower bottom tank 103 from a line 104, and oxidizes calcium sulfite generated along with the absorption of SO ₂ to gypsum.

The slurry comes into contact with exhaust gas by being sprayed from an absorption tower bottom tank 103 by an absorption tower circulation pump 105 from a spray pipe 106 at the top of the absorption tower 102. The gas after the absorption treatment is discharged out of the system through the line 107.

The limestone particles it from being granularity prepared so that a larger gypsum particles in the D ₅₀ of the absorption slurry line 108
Is supplied to the raw material preparation tank 109, where the line 1
After being mixed with the filtrate supplied from 10 to form a slurry, it is supplied to the absorption tower bottom tank 103 through a line 111.

The absorption tower circulation slurry is withdrawn from the line 112 and supplied to the hydrocyclone 113. The underflow of the hydrocyclone 113 is entirely returned to the absorption bottom tank 103 through the line 114 by the line 114. On the other hand, the overflow is extracted from the line 115 and supplied to the solid-liquid separator 116 to collect the gypsum 117. In this embodiment, a centrifuge was used as the solid-liquid separation device 116.

A part of the filtrate from the solid-liquid separator 116 is sent from a line 110 to a raw material preparation tank 109, and the remainder is discharged from a line 118 to the outside of the system.

The flow rate of the slurry and underflow supplied to the cyclone 113 in this example is constant at 0.5, and was changed D ₅₀ of the limestone supplied, the results shown in Table 1 were obtained. Limestone of the same production area and the same composition was used.

Although FIG. 1 shows an embodiment using the hydrocyclone 113, the classifier is not limited to the hydrocyclone, and it is of course possible to use a classifier such as a water fitting classifier. is there.

[Table 1]

Comparative Example In order to clarify the effect of the present invention, the results obtained when the hydrocyclone 113 is bypassed in the embodiment of FIG. 1 are shown in Table 2. The operating conditions of the absorption tower, other limestones, and the test limestone are the same as in the example.

[Table 2]

The effects of the present invention are clear when the examples and comparative examples are compared. That is, according to the example, the recovered gypsum purity is high and the high desulfurization rate is maintained despite the coarse particle size of the limestone, whereas the desulfurization rate is as high as that of the example in the comparative example. Nevertheless, the recovered gypsum purity is significantly reduced.

[0031]

According to the present invention, by adjusting the particle size distribution of the supplied limestone, it is possible to achieve a remarkable effect of improving the desulfurization rate and maintaining the gypsum to be recovered at a high purity.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is a table showing an example of a particle size distribution of gypsum in a circulation slurry of an absorption tower and a particle size distribution of supplied limestone.

FIG. 3 shows how the limestone particles are concentrated in the underflow from the liquid cyclone by supplying the circulation slurry of the absorption tower obtained by the gypsum having the particle size distribution shown in FIG. 2 and the supplied limestone to the hydrocyclone FIG.

FIG. 4 is a table showing the relationship between desulfurization performance and limestone concentration in circulating slurry.

FIG. 5 is an explanatory view of one embodiment of a conventional wet lime gypsum desulfurization method.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenji Inoue 4-6-22 Kanon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries, Ltd. Hiroshima Research Laboratory (72) Inventor Shizuka Nakamura 4-chome Kanon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture No. 6 No. 22 Mitsubishi Heavy Industries, Ltd. Hiroshima the laboratory (56) reference Patent flat 3-238023 (JP, a) JP Akira 63-156522 (JP, a) (58 ) investigated the field (Int.Cl. ⁶ B01D 53/50 B01D 53/77

Claims (1)

(57) [Claims] 1. A wet lime gypsum desulfurization method in which a slurry containing limestone and gypsum is brought into contact with an exhaust gas in an absorption tower to absorb and remove sulfur oxides in the exhaust gas, wherein 50% by weight of gypsum particles contained in the slurry are accumulated. An absorption slurry preparation step of supplying limestone particles having a larger diameter with a 50% weight cumulative diameter to the slurry as an absorbent, extracting a part of the slurry from the absorption tower, supplying the slurry to a classification device, and removing the slurry from the classification device An unreacted limestone separation step of returning the flow to the absorption tower, and a gypsum separation step of supplying an overflow of the classification device to a solid-liquid separation device and discharging a part or all of the liquid after the solid-liquid separation to the outside of the system. A wet lime gypsum desulfurization method characterized by the above-mentioned.