JPH11221432A - Limestone type desulfurization agent and production of desulfurization agent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a desulfurization agent for a fluidized bed type boiler having light desulfurization capability at a practical and low cost by producing a limestone type desulfurization agent whose CaO grade and fine pore volume are within respectively specified ranges. SOLUTION: Limestone with high CaO grade and having high fine pore volume is efficient as a desulfurization agent for a fluidized bed type boiler. A desulfurization agent having high desulfurization capability is therefore produced at a low cost by adjusting the CaO grade within a range of 40-56 wt.% and the volume of fine pores within a range of 20-300 mm<3> /g. Further, practicality of the agent is heightened by controlling the average particle diameter as 50 wt.% transmittance diameter within a range from 100 μm to 5 mm and the crushing strength within a range of 2-15 kg. In order to control the particle diameter, natural porous limestone is pulverized and sieved and, at this time, the desulfurization agent is preferably produced by mixing 4-15 wt.% of cement with 85-96 wt.% of the limestone powder having the average particle diameter as 50 wt.% transmittance diameter within a range of 1.0-500 μm, adding water to the resultant powder mixture, and granulating and curing the mixture.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION Coal is an important energy resource that accounts for about 30% of the world's energy supply. Its reserves are abundant and its prices are more stable than oil, so its demand is Significant growth is expected, mainly for use. Coal is one of the primary energy sources in Japan.
It accounts for 8% and is indispensable as an energy resource. However, coal has a C per unit calorie
O _2, SO _x, emissions of the NO _x is a number 1.5 times the oil,
There is a disadvantage that the burden on the environment is great. There are also handling problems and the need to treat coal ash remaining after combustion,
There are many issues to be solved.

[0002] The present invention relates to a desulfurizing agent for trapping SO _x generated when burning a coal of these problems, more specifically, it is in the required particle size range, high CaO quality, a range A method for producing a desulfurizing agent having a strength and pore volume, and a desulfurizing agent produced by crushing and classifying natural porous limestone and controlling the particle size, and further mixing limestone powder as a main raw material and adding cement The present invention relates to a method for producing the desulfurizing agent by granulating and curing a powder.

[0003]

2. Description of the Related Art Boilers for electric power and general industrial use are roughly classified into two types, a pulverized coal-fired boiler and a fluidized-bed boiler. The former is a method in which pulverized coal is blown into a furnace from a burner together with air to float and burn in the air, and is widely used for electric power utilities and other applications. The features of this method are that the furnace temperature is as high as 1,400 to 1,500 ° C., so that the boiler efficiency is good, and supercritical pressure steam can be obtained, so that large-capacity power generation is possible. However, on the other hand, (i)
High NOx _emissions due to high-temperature combustion, (ii) Coal types are restricted and low-grade coal cannot be used, (iii) Vast land and large amounts of water are required for post-desulfurization equipment There are disadvantages. In contrast, the latter fluidized-bed boiler has a normal pressure type,
There are various types such as pressurized type, bubbling type, circulation type, etc.For example, the normal pressure bubbling type is a method of blowing coarse coal, granular limestone, air from the lower part of the boiler and burning coal in a fluid state, In recent years, it has been put to practical use.
Features of these fluidized bed boilers, although boiler efficiency what slightly inferior compared to conventional pulverized coal boiler, requires less installation area for performing furnace desulfurization, the benefits of expansion of suppressing or coal type of the NO _X Have. In particular, the pressurized type is expected to become the mainstream of boilers in the future because it has the features of reducing the size of the boiler and being excellent in economic efficiency.

[0004] sulfur from coal during these boilers the combustion is discharged as SO _X. The wet limestone gypsum method, which is a typical treatment method, is a method in which SO _X in exhaust gas is brought into gas-liquid contact with an absorbent slurry containing limestone fine powder of several tens μm or less in an absorption tower, and is taken out as gypsum. It is commonly used for exhaust gas treatment of conventional pulverized coal boilers. On the other hand, in a fluidized-bed boiler, coal and limestone crushed products are mixed and burned to perform in-furnace desulfurization. Therefore, such a desulfurization facility is not required. However, on the other hand, to use crushed and crushed limestone of 100 μm to several mm,
The contact area with SO _X per unit weight is small, and nearly 100% is consumed in the desulfurization reaction in the wet limestone gypsum method, whereas the reaction efficiency in the fluidized bed boiler is low, about 20% of the total components of limestone. It has fatal drawbacks.

[0005] As described above, S discharged from an industrial combustion furnace is
As scavengers O _X, limestone is used in large quantities for a long time from the superior desulfurization performance and economy. For this reason, various limestones or limestone-related desulfurizing agents have been studied. For example, Japanese Patent Application Laid-Open No. Sho 58-166931 discloses a method for improving the function of removing acidic substances by immersing Portland cement clinker in water.
Japanese Patent No. 9775 discloses a method of crushing a hardened body comprising a mixture of cement and limestone and / or dolomite powder, or granulating the mixture with water to form a hardened body and contacting it with exhaust gas to remove the same. JP-A-58-166933 discloses a calcined product of a mixed powder of calcareous raw material, siliceous raw material and clayey raw material, and JP-A-59-69145 discloses kneading 25% by weight to less than 70% by weight of cement and calcium carbonate powder with water. Forming, curing and crushing later, Tokuho 6-22
No. 671 discloses a method in which limestone and / or dolomite powder is mixed with ash collected in a fluidized bed combustion furnace dust collecting apparatus and water is added to granulate the ash. In Japanese Patent Application Laid-Open No. 63-200836, limestone and / or dolomite powder or In addition, a method of mixing the ash collected in a fluidized bed combustion furnace dust collecting apparatus and granulating with a water glass aqueous solution,
JP-A-6-86329 discloses a method of using magnesium silicate, JP-A-6-50505 discloses a method of producing quicklime or calcined dolomite and sludge cake,
JP-A-9-201513 discloses a desulfurizing agent obtained by adding an alkali metal compound to a calcium carbonate-based material such as a shell.

[0006] These methods are effective in the new use of cement, siliceous or clay-based raw materials, collected ash from combustion furnaces, etc., and some of them have been found to improve desulfurization performance, but the production process is complicated. In addition, there are many problems such as poor economical efficiency due to the use of a large amount of cement or addition of chemicals such as water glass, and thus, it has not been practically used as a desulfurizing agent so far.

[0007]

In view of such circumstances, the present inventors have maximized the use of various limestone resources abundantly abundant in Japan and overseas as desulfurizing agents for fluidized bed boilers. In order to develop a practical product with excellent desulfurization performance and economic efficiency, intensive studies have been conducted on elucidation of the desulfurization mechanism, and it has been determined that limestone (calcium carbonate) having a high CaO grade and a large pore volume is effective. Was. That is, a limestone-based desulfurizing agent having a high CaO grade and a large pore volume is further used. The desulfurizing agent having a certain particle size range and an appropriate crushing strength is used. The present invention has been achieved by a simple process of obtaining a lime-based desulfurizing agent by subjecting limestone powder having a specific particle size range to granulation and hardening by using cement as a binder by performing classification and particle size control. .
That is, an object of the present invention is to provide a desulfurizing agent for a fluidized-bed boiler having excellent desulfurizing performance as a material having physical and chemical properties in a certain range, and naturally having the desulfurizing agent. An object of the present invention is to physically crush and classify porous limestone, or to granulate and harden it with high-quality limestone powder, a small amount of cement and water, and produce it at a practically low cost.

[0008]

SUMMARY OF THE INVENTION
A limestone desulfurizing agent characterized in that the CaO grade is in the range of 40 to 56% by weight and the pore volume is in the range of 20 to 300 mm ³ / g. With the desulfurizing agent having a crushing strength in a range of 100 to 5 mm and a crushing strength of 2 to 15 kg, natural porous limestone is crushed and classified to control the particle size, or the average particle size passes 50% by weight. 1.0 to 500 μm in diameter
85 to 96% by weight of limestone powder in the range of
The problem was solved by a method for producing a desulfurizing agent, characterized in that water was added to a powder mixed with ４4% by weight to granulate and harden.

The average particle size of the granulated material as a limestone-based desulfurizing agent is a 50% by weight passage diameter through a dry sieve, and the average particle size of the limestone powder as a raw material is a microtrack particle size obtained by a laser diffraction / scattering method. Analyzer (Leeds + Northrup H
RA9320-X100). The CaO grade is a value measured on a sample after drying at 110 ° C. The crushing strength is an average particle size of 2.0 to
It refers to the maximum value of the granulated product having a diameter of 2.8 mm immediately before the granule is broken when stress is applied from two opposite directions. The pore volume is defined as the mercury intrusion method (Pasca manufactured by FISONS Instruments).
l 140-440), the pore size is 0.001-10
It refers to the sum of the volumes in the μm range.

In the present invention, the natural porous limestone is a limestone formed by fossil fragments of calcium carbonate such as coral and foraminifera, and formed after 65 million years ago since the new Cenozoic. It is often found in warm and tropical regions such as Okinawa and Indonesia. For physical crushing, a jaw crusher, an impact crusher, a hammer mill, a roll crusher, and the like are suitable, but are not particularly limited. Classification is a vibration sieve,
Sifting such as a probability sieve is efficient and advantageous in terms of cost.

[0011] Limestone powder is obtained by pulverizing natural high-quality limestone by a physical method using a roller mill, a ball mill, or the like. A synthetic product obtained by a chemical reaction generally called light tankal can also be used. Calcium carbonate industrially recovered as a by-product can also be used. In physically ground limestone powder, the average particle size is 1 to 5
The thickness is preferably 00 μm, preferably 10 to 300 μm.
If the average particle size is less than 1 μm, the pulverization cost is high and it is not practical. On the other hand, when the average particle diameter exceeds 500 μm, granulation becomes difficult and desulfurization efficiency is lowered, which is not preferable.
Cement is not particularly limited in its kind, and desired properties can be achieved with ordinary Portland cement. However, the use of colloid cement or early-strength cement is effective in early expression of crushing strength and improvement in strength. The usage amount is 15
-4% by weight is desirable. If the content is less than 4% by weight, sufficient strength cannot be obtained, and a large amount of fine powder is generated during transportation and use, which causes various problems such as generation of dust during handling and powdering in a boiler. On the other hand, if it exceeds 15% by weight,
The increase in cost not only makes it unsuitable for practical use, but also reduces the amount of desulfurization.

The granulator used in the present invention is not particularly limited, such as a drum or pan type rolling granulator, a stirring granulator, an extrusion granulator, a briquetting machine and the like.
In granulation, limestone powder and cement are mixed at a predetermined ratio, and then water is gradually added. After the whole becomes uniform, granulation is performed according to the procedure according to each model.

The average particle size of the granulated product is preferably in the range of 100 μm to 5 mm, more preferably 200 μm to 3 mm. A circulating fluidized bed boiler having a relatively small particle size of 1 mm or less is used. On the other hand, those having a large average particle size are mainly used for bubbling type fluidized bed boilers. If the average particle size is smaller than 100 μm, the amount of fine powder increases, which increases the amount of dust collection, increases the load on the filter, and may affect the turbine. In addition, it is necessary to have the same flow behavior as that of coal. If the average particle size exceeds 5 mm, the balance of the flow state is lost, leading to a decrease in desulfurization efficiency and a trouble of the apparatus.

The CaO grade is preferably at least 40% by weight,
It is more preferably at least 50% by weight. If the content is lower than 40% by weight, the desulfurization efficiency decreases, so that a desulfurizing agent must be additionally used, and the amount of ash increases, which is not preferable. On the other hand, the main component of limestone is calcium carbonate, and the theoretical value of CaO grade is 56.08%. Since natural limestone containing some MgO or SiO ₂ or the like In addition, 56%
Never exceed. 2-15 kg in crush strength
And more preferably 4 kg or more. 2kg
If it is less than, fine powder is generated during transportation, and furthermore, powdering during use in a boiler is remarkable, which also adversely affects filters and turbines. A strength exceeding 15 kg is difficult for natural limestone, and it is considered that it is technically difficult to apply the material by granulation, and so far, it has not been manufactured. In terms of pore volume, the current limestone crushed product is 3.7
mm ³ / g, and high desulfurization efficiency cannot be expected at such a value. The pore volume of natural porous limestone is 20-6
0 mm ³ / g, the pore volume of granulated limestone powder is 80 mm ³
/ G or more, the surface area per unit particle weight increases, and the desired effect can be obtained. However, granules having a pore volume exceeding 300 mm ³ / g have not been produced so far.

The desulfurizing agent of the present invention can be produced by a simple process of physically crushing and classifying naturally occurring porous limestone having specific physical and chemical characteristics. Also, in the granulated product, limestone powder is used as a raw material, so that the pore volume is large, and only cement is used as a binder, and the amount used is 15% or less, which is advantageous in terms of cost. There is no decrease in CaO quality. As a result, not only is it possible to achieve a much higher desulfurization rate than the currently used limestone crushed products, but also the raw material cost is low, the manufacturing process is simple, and the economic efficiency is excellent. It has the feature of being extremely high.

[0016]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples. In the various measurements, a sample having a particle size of 100 mesh to 3 mm was taken out by a dry sieve except for the crushing strength and used as a measurement sample.

Measurement of crushing strength From a sample of 100 mesh to 3 mm, the particle size is 2.0 to 2.8.
Twenty-five mm-sized grains were selected, the maximum value was measured until a force was applied from the vertical direction to breakage, and the average value was defined as the crushing strength of the sample. However, in the case of a granulated product, a sample which passed 7 days after granulation was used as a measurement sample.

[0018] The adsorption test method samples 5g of SO ₂ gas was loaded into a tube furnace maintained at 900 ° C., SO ₂
A gas (mixed gas with air having a concentration of 1000 ppm) was allowed to flow at 2 liter / minute for 30 minutes to react, and the amount of S adsorbed was analyzed according to JIS M8217 (method for determining sulfur in iron ore).

Example 1 Porous limestone from Indonesia (40-70 mm) 10k
g was crushed to -7 mm with a jaw crusher, and further crushed to -3 mm with a roll crusher. From this pulverized product, one having a desired particle size was taken out using a circular vibrating sieve.
Granular product has CaO grade of 55.8% and crush strength of 5.3k
g, and the pore volume was 31 mm ³ / g.

EXAMPLE 2 18 kg of limestone powder having an average particle size of 25 μm and 2 kg of ordinary Portland cement were put into a batch type drum-type rolling granulator (capacity: 130 liters), and 3.5 kg of water was rotated while rotating the drum at 3000 rpm. It was added slowly. After 7 minutes, the granules were taken out. The CaO grade of the granulated product is 54.1
%, Crush strength is 2.9 kg, pore volume is 280 mm ³ /
g.

Example 3 36 kg of limestone powder having an average particle size of 25 μm and 4 kg of ordinary Portland cement were put into a batch type drum-type rolling granulator (capacity: 130 liters), and 6.0 kg of water was rotated while rotating the drum at 3000 rpm. It was added slowly. After 9 minutes, the granules were taken out. The CaO grade of the granulated product is 54.5
%, Crush strength 2.2 kg, pore volume 263 mm ³ /
g.

Example 4 30 kg of limestone powder having an average particle diameter of 450 μm and 2.4 kg of early-strength cement were charged into a batch-type drum type rolling granulator (capacity: 130 liters), and water was added while rotating the drum at 3000 rpm. 12 kg were added slowly. After 8 minutes, the granules were taken out. The CaO grade of the granulated product was 53.1%, the crushing strength was 6.3 kg, and the pore volume was 251 mm ³ / g.

EXAMPLE 5 45 kg of limestone powder having an average particle diameter of 450 μm and 2 kg of early-strength cement were put into a batch-type drum-type rolling granulator (capacity: 130 liters), and 5.1 kg of water was rotated while rotating the drum at 3000 rpm. It was added slowly. After 5 minutes, the granules were taken out. The CaO grade of the granulated product was 54.8%, the crushing strength was 5.0 kg, and the pore volume was 225 mm ³ / g.

EXAMPLE 6 15.8 kg of limestone powder having an average particle size of 25 μm and 2.2 kg of ordinary Portland cement were put into a batch-type agitation type granulator (capacity: 50 liters), and 2.52 kg of water was stirred at 1400 rpm. It was added slowly. After that, while reducing the rotation speed from 1200 rpm to 300 rpm, 23
After a minute the granulation was completed. The obtained granulated product has a CaO grade of 53.9%, a crushing strength of 6.7 kg, and a pore volume of 148.
mm ³ / g.

Example 7 15.8 kg of limestone powder having an average particle diameter of 450 μm and a high-strength cement were placed in a batch-type agitation type granulator (capacity: 50 liters).
2 kg of water and stirring at 1400 rpm.
52 kg were added slowly. Thereafter, the number of rotations was set to 1200
Granulation was completed after 23 minutes while reducing the rpm from 300 rpm to 300 rpm. The CaO grade of the obtained granules is 54.0.
%, Crush strength is 13.9 kg, pore volume is 104 mm ³
/ G.

Example 8 88 kg of limestone powder having an average particle size of 25 μm and 12 kg of ordinary Portland cement were charged into a batch-type stirring granulator (capacity: 200 liters), and 13.2 kg of water was gradually added while stirring at 1400 rpm. . After that, the number of revolutions
The granulation was completed after 16 minutes after being lowered to 00 rpm. The CaO grade of the obtained granules is 54.4%, and the crushing strength is 6.5.
kg, and the pore volume was 189 mm ³ / g.

Example 9 17.6 kg of limestone powder having an average particle size of 25 μm, 2.4 kg of ordinary Portland cement, and 1.6 kg of water were mixed in advance, and formed into an almond mold having a long diameter of 2 cm using a briquetting machine. This molded product was crushed by a pin mill to obtain a granulated product. The CaO grade of the granulated product was 54.8%, the crushing strength was 6.4 kg, and the pore volume was 125 mm ³ / g.

Example 10 48 kg of limestone powder having an average particle diameter of 450 μm, 2.0 kg of early-strength cement, and 2.0 kg of water were mixed in advance and formed by a flat roll of a briquetting machine. This molded product was crushed by a pin mill to obtain a granulated product. Granulated CaO
The grade was 54.5%, the crushing strength was 2.2 kg, and the pore volume was 122 mm ³ / g.

Comparative Example 1 10 kg of limestone (40-20 mm) from Torigatayama, Kochi Prefecture was crushed to -7 mm with a jaw crusher and further crushed to -3 mm with a roll crusher. From this pulverized product, one having a desired particle size was taken out using a circular vibrating sieve. The CaO grade of the granular product is 55.4%, the crush strength is 11.0 kg,
The pore volume was 3.7 mm ³ / g.

COMPARATIVE EXAMPLE 2 39 kg of limestone powder having an average particle size of 25 μm and an early-strength cement 1 were placed in a batch-type drum type rolling granulator (capacity: 130 liters).
5.8 kg of water was gradually added while rotating the drum at 3000 rpm. After 8 minutes, the granules were taken out. The CaO grade of the granulated product was 55.2%, the crushing strength was 1.6 kg, and the pore volume was 278 mm ³ / g.

COMPARATIVE EXAMPLE 3 39 kg of limestone powder having an average particle diameter of 450 μm and 1 kg of early-strength cement were put into a batch drum type rolling granulator (capacity: 130 liters), and 5.4 kg of water was rotated while rotating the drum at 3000 rpm. Was added. After 8 minutes, the granules were taken out. The CaO grade of the granulated product is 55.2%, and the crushing strength is 1.
2 kg, and the pore volume was 252 mm ³ / g.

Comparative Example 4 36 kg of limestone powder having an average particle size of 670 μm and 4 kg of ordinary Portland cement were charged into a batch drum type rolling granulator (capacity: 130 liters), and 5.55 kg of water was rotated while rotating the drum at 3000 rpm. It was added slowly. 12
After a minute, the granules were removed. The CaO grade of the granulated product is 5
4.2%, crush strength 5.6kg, pore volume 169m
m ³ / g.

COMPARATIVE EXAMPLE 5 17.5 kg of limestone powder having an average particle diameter of 450 μm was added to a batch type stirring granulator (volume: 50 liters) in an amount of 50 kg.
5 kg was added and water was stirred at 1400 rpm.
46 kg were added slowly. Thereafter, the number of rotations was set to 1200
Granulation was completed after 25 minutes while reducing the rpm from 300 rpm to 300 rpm. The CaO grade of the obtained granules is 54.9.
%, Crush strength 1.7 kg, pore volume 104 mm ³ /
g.

COMPARATIVE EXAMPLE 6 15.8 kg of limestone powder having an average particle diameter of 670 μm and an early-strength cement were placed in a batch-type agitation granulator (50 liters in capacity).
2 kg of water and stirring at 1400 rpm.
5 kg was added slowly. After that, the number of rotations was 1200 r
Granulation was completed after 22 minutes while reducing the rpm from 300 rpm to 300 rpm. CaO grade of the obtained granules is 54.3%,
The crushing strength is 13.2 kg and the pore volume is 142 mm ³ / g.
Met.

Comparative Example 7 19.8 kg of limestone powder having an average particle size of 25 μm, 0.2 kg of ordinary Portland cement and 1.5 kg of water were mixed in advance and formed into an almond type having a long diameter of 2 cm using a briquetting machine. This molded product was crushed by a pin mill to obtain a granulated product. The CaO grade of the granulated product was 55.3%, the crushing strength was 0.8%, and the pore volume was 96 mm ³ / g.

Comparative Example 8 30 kg of low-grade limestone powder having an average particle diameter of 450 μm and 2.4 kg of early-strength cement were charged into a batch-type drum-type rolling granulator, and water was added while rotating the drum at 3000 rpm.
kg was added slowly. After 9 minutes, the granules were taken out. The granulated material has a CaO grade of 35.2% and a crushing strength of 5.1 k.
g, and the pore volume was 167 mm ³ / g.

COMPARATIVE EXAMPLE 9 17.6 kg of low-grade limestone powder having an average particle size of 25 μm, 2.4 kg of ordinary Portland cement and 1.6 kg of water were mixed in advance, and the long diameter was 2 cm using a briquetting machine.
Into an almond mold. This molded product was crushed by a pin mill to obtain a granulated product. The CaO grade of the granulated product is 30.8
%, Crush strength is 6.1 kg, pore volume is 124 mm ³ /
g.

Reference Example An SO ₂ gas adsorption test was performed on the samples of the examples and the comparative examples. Table 1 shows the adsorption amount of S.

[0039]

[Table 1]

[0040]

The desulfurizing agent of the present invention can achieve a much higher desulfurization rate than crushed limestone products currently used, and furthermore, the raw materials are inexpensive, the production process is simple and the economic efficiency is excellent. In this respect, it has the feature of being extremely practical, and has great significance not only in industry but also in global environmental protection.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Hiroshi Tanaka No. 2-1, Hirai, Hinodecho, Nishitama-gun, Tokyo Nippon Steel Mining Co., Ltd.

Claims (4)

[Claims] 1. A limestone desulfurizing agent having a CaO grade in the range of 40 to 56% by weight and a pore volume in the range of 20 to 300 mm ³ / g. 2. An average particle diameter of 100 μm at a passing diameter of 50% by weight.
The limestone desulfurizing agent according to claim 1, wherein the limestone-based desulfurizing agent is in a range of m to 5 mm and a crushing strength is in a range of 2 to 15 kg. 3. The method for producing a limestone desulfurizing agent according to claim 2, wherein the particle size of natural porous limestone is controlled by physical pulverization and classification. 4. An average particle size of from 1.0 to 50% by weight when passed.
The limestone desulfurizing agent according to claim 2, wherein water is added to a powder obtained by mixing 15 to 4% by weight of cement with 85 to 96% by weight of limestone powder in a range of 500 µm to granulate and harden. Manufacturing method.