JPH02194833A - Production of dry desulfurizing agent for waste gas - Google Patents

Abstract

PURPOSE:To produce a lime-gypsum-coal ashes based hydrated hardened body having high performance by a simplified method by adding silicon dioxide and/or silicon dioxide-contg. material to a lime-gypsum-coal ashes based raw material and producing a desulfurizing agent. CONSTITUTION:In the case of producing a dry desulfurizing agent for waste gas made of a lime-gypsum-coal ashes based hydrated hardened body, silicon dioxide and/or silicon dioxide-contg. material are added to lime, gypsum and coal ashes. This mixture is kneaded while adding water thereto. The kneaded material is extrusion-molded and the molded body is aged by wet air or steam and thereafter drying treatment is performed therefor. As a result, the lime- gypsum-coal ashes based hydrated hardened body having high performance can be produced at high yield by a simplified method regardless of the kind of the utilized gypsum source.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for producing a dry desulfurization agent for exhaust gas, and more specifically, to a process for desulfurizing a lime-gypsum-coal ash (silicic acid-containing substance) hydrated and cured product. The present invention relates to a method for producing a dry desulfurization agent for exhaust gas.

[Conventional technology]

Conventionally, the removal of sulfur oxides emitted from heavy oil-fired and coal-fired boilers in thermal power plants has been carried out using wet methods such as the limestone-gypsum method or dry methods such as the activated carbon method, but there is a simplified alternative method to these methods. It is desired to develop an economical desulfurization method.

On the other hand, the present inventors have proposed a method for producing a dry desulfurization agent that makes more advanced use of the enormous amount of coal ash discharged from coal-fired boilers (Japanese Patent Application Laid-open No. 209038/1983). Desulfurization agents using this coal ash are basically 1 in Figure 6.
As shown in the diagram of the desulfurization agent production system using the stage curing crushing method, a slurry obtained by adding water to a raw material mixture consisting of slaked lime, gypsum, and coal ash is heated in a steam atmosphere, hydrated and hardened,
It is then manufactured by crushing, classifying, and drying.

In order to put the dry desulfurization method into practical use using the desulfurization agent described above, it is important to establish a technology for producing a large amount of highly active desulfurization agent at a high yield. A two-stage curing method in which the slurry obtained by adding water to the mixture is first heated with steam, hydrated and hardened, and then crushed, the crushed product is granulated to improve the product yield, and then steam-cured again. proposed a method for producing a desulfurizing agent by a method (Japanese Patent Application No. 1983-96926).

FIG. 7 is a system diagram for producing a desulfurizing agent using a two-stage curing method, and Part 8 is an overall system diagram of the desulfurization apparatus shown in FIG. In the figure, appropriate amounts of coal ash 1, slaked lime (Ca(OH)2) 2, and stone 1it (CaSO4) 3 are supplied from each silo to a mixer 4 and mixed into powder. The uniformly mixed powder is sent to a kneader 5 and kneaded with an appropriate amount of water 18 to form a slurry.
9 and is heated and hardened to a moldable hardness. This hardened material is made into an appropriate size by a crusher 7 and a crusher 8, molded into granulation nuclei by an extruder 9, and granulated by a dish-type granulator 10. The cured body granulated to a diameter of 3 to 10+ nm is subjected to secondary curing in a secondary hydration curing device 11 to which water vapor 19 is supplied, and is made into a porous cured body. This hardened material is dried in a dryer 12, and the sieved material is dried in a dryer 13.
After being screened, it is stored in a desulfurization agent silo 14 and sequentially supplied to a desulfurization absorption tower 16. Desulfurization absorption tower 16
After reacting with sulfur oxides in the boiler exhaust gas 20, the desulfurizing agent supplied to the boiler is discharged from the bottom as a used desulfurizing agent 17, a part of which is used as a substitute for gypsum. Further, the exhaust gas from which sulfur oxides have been removed is discharged to the atmosphere through line 21.

However, the above-mentioned two-stage curing method has the disadvantage that the operation is complicated, and the obtained desulfurizing agent is pulverized while being transferred through dryers and sieves, leading to a decrease in the yield of the desulfurizing agent and absorption. There was a problem in that the pressure drop inside the tower increased, and the uniform movement of the desulfurizing agent within the absorption tower was hindered, resulting in a decrease in performance.

[Problems to be Solved by the Invention] Furthermore, the present inventors have found that when a used desulfurization agent containing Ca5Oa produced by absorbing SO□ in exhaust gas is used as a gypsum source, the curing speed and hardness of the raw material kneaded material will increase. They have found that the desulfurization performance can be improved, and have proposed a method for producing a desulfurization agent using a one-stage curing method as shown in FIG. This manufacturing method involves extruding a mixture of lime, used desulfurization agent, coal ash, and water, followed by steam curing, and drying to obtain the desulfurization agent. Desulfurizing agent is obtained. This is Ca(OH)z
In order for CaSO4 and coal ash to form a hydrated body, 5i02 etc. need to be eluted from the coal ash.
The spent desulfurization agent contains SiO that has already been removed (from coal ash).
This is thought to be because □min etc. exist in an active state and quickly react with the newly added Ca(OH)2 and water.

According to this method, once waste desulfurization agent (spent desulfurization agent) is started to be extracted from the -degree desulfurization absorption tower, there is no need to prepare, for example, wet flue gas desulfurization byproduct gypsum (exhaust desulfurization gypsum) as a gypsum source. . However, when starting the desulfurization equipment, a used desulfurization agent is not available, so a gypsum source such as waste desulfurization gypsum is used. In this case, in the one-stage curing method, the hydration hardening rate of the raw material kneaded material is slow;
Although it is necessary to adopt a stage curing method, it would be unreasonable in terms of equipment to have to install a two-stage curing device just for startup. Therefore, it is desired to develop a technology that can produce a high-performance desulfurization agent in a single curing operation even when de-sulfurized gypsum or the like is used as a gypsum source, as in the case where a used desulfurization agent is used.

The first object of the present invention is to produce a lime-gypsum-coal ash-based hydrated body with a simplified method that is not affected by the type of gypsum source used and has high performance. A second object of the present invention is to provide a method for producing a dry desulfurization agent, and a second object of the present invention is to produce a dry desulfurization agent for exhaust gas made of a hydrated lime-gypsum-coal ash-based desulfurization agent having high performance at a high yield. The goal is to provide a way to do so.

[Means to solve the problem]

The first aspect of the present invention is a method for producing a dry desulfurization agent for exhaust gas using a lime-gypsum-coal ash-based hydrated material as a desulfurization agent, in which silicon dioxide and/or silicon dioxide and/or
Alternatively, a desulfurizing agent is produced by adding a silicon dioxide-containing substance.

The desulfurization agent is prepared by adding water to a mixture of lime, gypsum, and coal ash and adding silicon dioxide and/or a silicon dioxide-containing material, kneading the mixture, extruding the kneaded product, and curing it in a wet air or steam. It is preferable to obtain it by a method of drying.

The second aspect of the present invention is a method for producing a dry desulfurization agent by hydrating and curing a kneaded material consisting of lime, gypsum, coal ash, and water, characterized in that bentonite is added to the kneaded material.

(Example] Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 1 is a production system diagram of a desulfurizing agent showing an embodiment of the first invention. In this figure, the solid line indicates the use of degassed gypsum as a gypsum source during startup, and the dashed line indicates the subsequent use of spent desulfurization agent.

The usage proportions of slaked lime (Ca(OH)z), removed gypsum (Ca SO4 equivalent), coal ash, and silicon dioxide, which are raw materials for the production of desulfurization agents, are 15 to 40 parts by weight and 5 to 2 parts by weight, respectively.
Preferably, it is 0 parts by weight, 40 to 80 parts by weight, and 1 to 10 parts by weight.

In the present invention, silicon dioxide-containing substances such as silica gel, silica sol, natural zeolite, acid clay, hentonite, etc. can be used in addition to the fine powder of silicon dioxide.

Further, in the present invention, excreted gypsum is preferably used as a gypsum source, but any form of gypsum dihydrate (CaSO42H20), gypsum hemihydrate (Ca SOa ・'AHz O), or anhydrite (CaSO4) may be used. It can also be used.

The method of adding silicon dioxide is not particularly limited as long as it is mixed uniformly with other raw materials, but if the removed gypsum is supplied in the form of a slurry, it may be added and mixed at the same time when preparing the removed gypsum slurry. , preferably supplied as a slurry.

The amount of water used when kneading the raw material mixture consisting of slaked lime, silicon dioxide, gypsum and coal ash with water may be 35 to 50 parts by weight per 100 parts by weight (dry basis) of the raw material mixture. preferable.

The optimal amount of water to add varies depending on the amount of silicon dioxide added, but for example, even if the water content is as low as 35% due to the addition of a small amount of silicon dioxide, it will be more effective than a two-stage cured product (45% water addition) that does not contain silicon dioxide. A desulfurizing agent with high performance can be obtained.

The hardness of a kneaded product obtained by adding a predetermined amount of water to a raw material mixture is evaluated by the penetration degree. Here, the penetration rate refers to the distance that a needle penetrates when a predetermined load is applied to a needle of a predetermined thickness for a predetermined period of time, and the smaller this value is, the harder the sample is. FIG. 2 shows the change in the penetration degree of the kneaded product when the kneaded material was kneaded by changing the amount of silicon dioxide added under constant conditions in which the amount of water added was 35% and the kneading time was 2 minutes. The penetration depth is determined by measuring the penetration depth (M) of a needle when a load of 50 g is applied to the needle for 5 seconds. When 2% of silicon dioxide is added, the penetration becomes 150 or less, which can withstand molding operations such as extrusion, and as the amount added increases, the penetration gradually decreases, and when 5% is added, a molded product with hardness is obtained. .

Therefore, it was shown that the amount of silicon dioxide added is preferably 1% or more, and more preferably 5% or more to obtain a hydrated cured product having high hardness.

The kneaded material having a predetermined hardness is supplied to an extruder and is extruded into a columnar broken product having a diameter of 2 to 10 mm+ and a length of approximately 5 to 30 mm. The appropriate size of the desulfurizing agent is determined not only by the desulfurizing performance but also by taking into account the pressure loss and the like when the gas to be treated is supplied to the absorption tower.

The obtained extruded product is steam-cured after fine particles are removed if necessary, and then dried to obtain a desulfurization agent.

Examples 1 to 3 Slaked lime (Ca(OH)z) 30 parts by weight of the heavy wall and 16 parts by weight of removed gypsum (CaSO4 base), specific surface area 150r
Add and mix 3 parts by weight, 5 parts by weight, and 10 parts by weight of silicon dioxide powder having yf/g (Examples 1 to 3), respectively, and the remainder when the total amount of coal ash is 100 parts by weight. Add water to the mixture at 3 parts per 100 parts by weight of the dry mixture.
5 parts by weight were added and kneaded for 2 minutes. The kneaded material was made into a hole with a diameter of 6
It was extruded and molded using a mold with a plate thickness of 3.2 mm and a plate thickness of 3.2 mm. At this time, no mutual adhesion between particles was observed, and a cylindrical extrusion molded product was obtained. The extrudate was placed in a container with a wire mesh bottom and steam-cured in steam at 100°C for 9 hours.
The obtained cured product was heated and dried at 130°C for 2 hours to obtain a desulfurization agent.

The crushing strength and specific surface area of the obtained desulfurizing agent were measured and shown in Table 1, and it was shown from this table that as the amount of silicon dioxide added increased, both the hardness and specific surface area increased. Also, the particle size is 6 mm diameter x 10 mm
4 g of the sample was placed on a perforated plate in a reaction tube with a diameter of 30 mm, and a gas having the following composition was flowed at a flow rate of 12 ff/min at a temperature of 130'C. SOz: 110
00PP, NO: 200ppm, CO2: 12%, 0
□: 6%, N20: 10%, N2: remainder. When the utilization rate of CaO was determined by extracting the sample after a predetermined time and analyzing the amount of alkali remaining, the CaO utilization rate at a reaction time of 50 hours was 80.9% (Sin, addition amount = 3%), 92 .5% (5%) and 97% (10%).

Table 1 Examples 4 to 6 A desulfurizing agent was produced in the same manner as in Example 1 except that the steam curing period was changed from 9 hours to 15 hours, and the crushing strength and specific surface area of the obtained desulfurizing agent were measured. and the result in the second
Shown in the table. The utilization rate of CaO is 88.6% (SiO□
Addition amount 3%), 93.1% (5%), 97.0% (10
%)Met.

Table 2 Examples 7 to 10 A desulfurizing agent prepared by adding 5% silicon dioxide and steam curing for 9 hours in the same manner as in Example 2 was heated until the alkaline content contained therein was almost consumed. It was converted into a spent desulfurization agent by contacting with 802-containing gas.

Next, 38 parts by weight of this used desulfurization agent (16 parts by weight as Ca'S O4), 30 parts by weight of slaked lime, and 32 parts by weight of coal ash.
40 parts by weight of hot water was added to the mixture consisting of parts by weight, and the steam curing time was 9.15.
Examples 7 to 10), and desulfurization agents were prepared in the same manner as in Example 1, and desulfurization was performed. The CaO utilization rate at desulfurization reaction time of 50 hours was 86.3%.
, 92.9%, 95.5% and 93.9%.

Comparative Example 1 Slaked lime (Ca(OH)z) 30 parts by weight, removed gypsum (C
To a mixture consisting of 16 parts by weight of a SO4 base) and 54 parts by weight of coal ash, 35 parts by weight of water (the amount added to the dry powder) was added and kneaded for 2 minutes. Pour the kneaded material into a hole with a hole diameter of 6 mm.
Although extrusion was performed using a mold with a plate thickness of 3.2 mm, mutual adhesion between particles occurred immediately after extrusion, and a cylindrical extruded product could not be obtained.

Comparative Example 2 A kneaded material having the same raw material composition and moisture content as Comparative Example 1 was steam-cured for 2 hours (primary curing) until it became moldable, then extruded and further 9
Steam curing (secondary curing) was performed for an hour. The obtained two-stage cured product was dried at 130° C. for 2 hours to prepare a desulfurization agent, and desulfurization was performed in the same manner as in Example 1. The CaO utilization rate after a desulfurization reaction time of 50 hours was measured and found to be 70.1%, which was significantly inferior in performance to the one containing silicon dioxide.

Examples 11 to 13 and Comparative Example 3 FIG. 3 is a production system diagram of a desulfurizing agent showing an example of the second invention. In the figure, coal ash, slaked lime, gypsum, and bentonite are supplied in appropriate amounts from each silo and mixed into powders in a mixer. The uniformly mixed powder is sent to a kneader, where an appropriate amount of water is added to form a slurry, and heated with steam in a hydration curing device to form a hydration-cured product. The hydration-cured primary permanently cured product is crushed by a coarse crusher or a crusher to a size that can be processed by an extrusion molding machine, and after extrusion molding, it is granulated by dish-shaped granulation. The granules are sent to a secondary hydration curing device, where they are hydrated and hardened with steam to make them active, and then sent to a dryer to remove surface moisture, and the sieved material is screened in a machine. , particle size 3-10IIT [
No. 11 is used as a desulfurization agent and sent to the absorption tower. The desulfurizing agent sent to the upper part of the absorption tower comes into contact with the exhaust gas and absorbs S02 in the exhaust gas while moving to the lower part. The desulfurizing agent that has lost its absorption capacity is extracted from the bottom, and a portion of this is reused as used desulfurizing agent.

Figure 4 shows desulfurization agent B obtained by adding bentonite,
The measurement results of the crushing strength of C and D (Examples 11 to 13) and desulfurization agent A (Comparative Example 3) obtained without adding bentonite are shown. In addition, FIG. 5 shows the desulfurizing agents A, B,
The results of measuring the absorption performance of C and D are shown. These figures show that the addition of bentonite increases the strength and performance of the desulfurizing agent, and that the greater the amount added, the more effective it is.

Desulfurization agents produced by conventional methods without the addition of bentonite have low strength because they come into contact with live steam, and as a result, when screened with a sieve at the dryer outlet, there is a large amount of desulfurization agents with a diameter of 3 mm or less, resulting in low absorption. Become. In addition, it becomes pulverized when moving inside the absorption tower, which causes an increase in the pressure loss of the absorption tower and prevents the desulfurization agent from moving uniformly within the tower. Furthermore, since the dryer also dries the desulfurizing agent in the under three cylinders, the hot air used for drying is wasted, reducing utility. However, in this example, the strength and performance of the desulfurizing agent are improved by adding hentonite, and the above-mentioned conventional problems can be prevented. Although it is not possible to guess which component of bentonite is responsible for such an effect, a similar effect is obtained when the pure component SiO□ is added. However, since the price of bentonite is about 1/10 of the price of SiO□, the manufacturing cost can be kept low according to this embodiment.

〔Effect of the invention〕

According to the first production method of the present invention, a high-performance desulfurization agent can be obtained by a one-stage curing method even if deionized gypsum or the like is used as a gypsum source at the start-up of desulfurization agent production. Therefore, there is no need to install a two-stage curing device only for startup, which is highly economical.

According to the second manufacturing method of the present invention, it is possible to increase the strength of the desulfurizing agent and the absorption performance, so that the following effects can be obtained.

(1) The desulfurization agent is less likely to be pulverized during movement through the drying device and absorption tower, increasing the yield of usable desulfurization agent.

(2) Since the amount of fine powder inside the absorption tower is reduced, the pressure loss is lowered, and the desulfurization agent inside the absorption tower can be moved smoothly, allowing effective SO□ absorption operation.

(3) Since the drying equipment also dries the fine powder of the desulfurizing agent, the hot air used to be wasted in terms of utility, but the drying equipment reduces the amount of fine powder and allows more efficient drying.

(4) Since not only the strength but also the performance increases, the curing time of the secondary hydration curing equipment can be shortened, the amount of steam can be reduced, the equipment can be made more compact, and the running cost can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a production system diagram of a desulfurizing agent showing one embodiment of the first invention, FIG. 2 is a diagram showing the relationship between the amount of silicon dioxide added and the penetration degree, and FIG. 3 is a diagram showing the relationship between the amount of silicon dioxide added and the penetration FIG. 4 is a diagram showing the relationship between the amount of bentonite added and crushing strength; FIG. 5 is a diagram showing the relationship between the amount of bentonite added and absorption performance; Figure 6 is a desulfurizing agent manufacturing system diagram using the conventional one-stage curing crushing method, Figure 7 is a desulfurizing agent manufacturing system diagram using the conventional two-stage curing method, and Figure 8 is a diagram showing the desulfurizing agent production system in the conventional technology using the two-stage curing method. The overall system diagram, Figure 9, shows 1
It is a system diagram of the production of a desulfurization agent by a stage curing method. 1...Coal ash, 2...Slaked lime, 3...Gypsum, 4.
... Continuous mixer, 5... Continuous kneading machine, 6... - Jieiwa hardening device, 7... Coarse crusher, 8... Crushing machine, 9...
- Extrusion molding machine, 10... Dish-type granulator, 11... Secondary hydration curing device, 12... Dryer, 13... Sieving machine, 14... Desulfurizing agent silo, 15... Desulfurization fan, 16... Desulfurization absorption tower, 17... Used desulfurization agent, 1
8...Water supply fan, 19...Water vapor, 20...
Boiler exhaust gas, 21...processed gas.

Claims (3)

[Claims] (1) In a method for producing a dry desulfurization agent for exhaust gas using a hydrated lime-gypsum-coal ash-based desulfurization agent, silicon dioxide and/or a silicon dioxide-containing substance is added to the lime-gypsum-coal ash-based raw material. A method for producing a dry desulfurizing agent for exhaust gas, which comprises adding the desulfurizing agent. (2) Lime, gypsum and coal ash with silicon dioxide and/or
Or a claim characterized in that water is added to a mixture to which a silicon dioxide-containing substance is added and kneaded, the kneaded product is extruded and cured in a humid air or steam, and then a drying treatment is performed (
1) The method for producing a dry desulfurization agent for exhaust gas as described above. (3) Production of a dry desulfurization agent for exhaust gas in a method of producing a dry desulfurization agent by hydrating and curing a kneaded material consisting of lime, gypsum, coal ash, and water, characterized in that bentonite is added to the kneaded material. Method.