JPH01284323A - Method and device for desulfurization by desulfurizer essentially consisting of coal ash - Google Patents

Abstract

PURPOSE:To execute efficient desulfurization by passing a desulfurizer contg. coal ash, gypsum and slaked lime or quickline through a moving bed reactor and recirculating the used desulfurizer to the exhaust gas inlet side of the reactor. CONSTITUTION:The combustion exhaust gas from a coal combustion boiler 5 is cooled by an air heater 7 and is then admitted into the moving bed reactor 1 where the gas is desulfurized by contact with the desulfurizer produced by mixing the coal ash, gypsum and slaked lime or quickline in a reaction section B. The used desulfurizer is discharged from a line 9 and the greater part is supplied through the line 8 as the used desulfurizer T to the reaction section A on the exhaust gas inlet side of the moving bed reactor 1. The unreacted slaked lime quickline are used therein. On the other hand, the remaining used desulfurizer R is sent to a desulfurizer producing device 1 and is used as a gypsum raw material.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a desulfurization method using a desulfurization agent mainly composed of coal ash, and more specifically, to a desulfurization method using a desulfurization agent mainly composed of coal ash.
The present invention relates to a desulfurization method using a desulfurization agent mainly composed of coal ash, which is suitable for increasing the utilization rate of slaked lime or quicklime in the desulfurization agent.

[Conventional technology]

Wet methods (e.g. limestone-gypsum method) are used to remove sulfur oxides discharged from heavy oil-fired and coal-fired boilers in thermal power plants.
Alternatively, it has been put into practical use by a dry method (activated carbon method). However, recently there has been a desire for a simpler and more economical desulfurization method to replace these desulfurization devices.

In addition, huge amounts of coal ash are emitted from coal-fired boilers.
These are used in cement admixtures, artificial lightweight aggregates, landfills, etc. Recently, a method of effectively utilizing coal ash that has been attracting particular attention is known to be a method of mixing coal ash as a main component with gypsum and slaked lime or quicklime, and using the cured product as a desulfurization agent after hydration reaction with water vapor. ing.

[Problem to be solved by the invention]

The inventors mixed coal ash, gypsum, slaked lime or quicklime, and optional additives, mixed with water, and then
We have proposed a desulfurization agent obtained by molding a primary cured product by granulation or the like, curing it with steam, and drying the resulting secondary cured product. FIG. 2 is a diagram showing a manufacturing process diagram of such a desulfurization agent whose main component is coal ash. This desulfurization agent contains S02 contained in combustion exhaust gas,
The results of our study have revealed that N01o, , , ■+, , o, CO2, etc. influence each other, and from the reaction aspect, it exhibits characteristics not found in conventional gas phase desulfurization agents. . For example, when 802 in the combustion exhaust gas is absorbed by the desulfurization agent, 02, H20, CO2, No, etc. in the exhaust gas are affected, and the desulfurization performance of SO2 in the exhaust gas in particular has a remarkable dependence on the No concentration. It's showing. On the other hand, the denitrification performance is influenced by the coexisting SO2 concentration, and there is a phenomenon that the higher the SO2 concentration, the higher the denitrification performance.

The desulfurization performance of the desulfurization agent is influenced by the mixing ratio of slaked lime or quicklime mixed with coal ash and the hydration reaction conditions.

Figures 3A and 3B show the X
From the comparison of the line diffraction diagrams, it has been confirmed that S02 is oxidized and fixed as stable anhydrite (a) (Figure 3B) in the used desulfurization agent, and it cannot be disposed of as is for industrial disposal. It can be thrown away as an object. However, the desulfurization agent so
2. If the proportion of slaked lime or quicklime in the desulfurizing agent is increased in order to increase the amount of absorption, the amount of unreacted slaked lime or quicklime will increase, making it impossible to dump the used desulfurizing agent as industrial waste.

In addition, in the desulfurization method using the desulfurization agent, boiler load fluctuations are dealt with by adjusting the movement speed of the desulfurization agent in a moving bed reactor, for example, but if the movement speed of the desulfurization agent is increased, The amount of slaked lime or quicklime in the reaction increases, and the used desulfurization agent extracted from the reactor may not meet the standards for disposal as industrial waste.

The purpose of the present invention is to be more sensitive to boiler load fluctuations, increase the utilization rate of slaked lime or quicklime,
It is an object of the present invention to provide a desulfurization method and apparatus using a desulfurization agent mainly composed of coal ash, which can effectively utilize a used desulfurization agent.

[Means to solve the problem]

The first aspect of the present invention is a desulfurization method for absorbing and removing sulfur oxides in coal combustion exhaust gas using a moving bed reactor filled with a desulfurization agent containing coal ash, gypsum, and slaked lime or quicklime. The used desulfurization agent is extracted from the bed reactor and used as at least a part of the gypsum in the raw material, and the used desulfurization agent containing unreacted slaked lime or quicklime is recycled to the exhaust gas inlet side of the moving bed reactor. It is characterized by circulation.

The second aspect of the present invention is a dry desulfurization device that desulfurizes flue gas containing coal ash discharged from a coal combustion device through a moving bed reactor filled with a desulfurizing agent, in which the moving bed reactor is connected to a first upstream side of the flue gas. A desulfurizing agent manufacturing apparatus which is divided into a reaction section and a second reaction section on the same downstream side, and in which at least a part of the used desulfurizing agent extracted from the second reaction section is used as a raw material. , a means for supplying the desulfurizing agent prepared in the desulfurizing agent manufacturing apparatus to the second reaction section, and a part of the used desulfurizing agent discharged from the second reaction section to the first reaction section. The present invention is characterized by providing means for supplying the desulfurizing agent and means for discharging the used desulfurizing agent from the first reaction section to the outside of the system.

To produce desulfurization agent from coal combustion ash, quicklime or slaked lime using spent desulfurization agent instead of gypsum, add a certain amount of water to the raw material and heat it until it has a hardness that can be molded (usually 10
After curing (heat treatment under 0° C. saturated steam for 1 to 2 hours), it is molded using a granulator to give a particle size of, for example, 10 m1 or less in diameter. As the forming method, various methods such as extrusion, plate type rolling, container transfer (concrete mixer type), etc. can be adopted. It was found that by preparing a desulfurizing agent by replacing the used desulfurizing agent with gypsum, a cured product with a larger specific surface area than when using gypsum was obtained, and hydration curing was accelerated for about 4 hours, for example. .

This is thought to be because the used desulfurization agent becomes a crystal nucleus for the formation of a hardened product.

[Effect]

The desulfurizing agent used in the present invention absorbs S02 in the flue gas when it comes into contact with the combustion exhaust gas, reacts with the calcium compound in the desulfurizing agent, and fixes it as stable anhydrite. Therefore, the used desulfurizing agent can be recycled and used as one of the raw materials for producing the desulfurizing agent.

Figure 4 shows desulfurization agent A (specific surface area: 56 m''/g) manufactured from coal ash, gypsum, and slaked lime, and desulfurization agent B (specific surface area: 76 rnz/g) manufactured from coal ash, used desulfurization agent, and slaked lime. ) is a diagram showing the relationship between the contact time with exhaust gas and the amount of SO2 absorbed.

From this figure, it can be seen that desulfurization agent B has an S02 adsorption performance equal to or higher than that of desulfurization agent A, and that the used desulfurization agent can be fully utilized as a raw material for the desulfurization agent.

On the other hand, the SO2 adsorption performance of the desulfurizing agent is influenced by the above-mentioned manufacturing conditions and also by the amount of slaked lime or quicklime added. In other words, 802 in the exhaust gas
reacts with, for example, Ca(OH)2 in the desulfurization agent raw material,
Since it is an equimolar reaction that produces CaSO4, Ca (
directly influenced by the content of OH)2. Figure 5 is a diagram showing the relationship between the Ca(OH)2 content in the desulfurizing agent and the SO2 adsorption performance. It can be seen that the reaction no longer occurs, the amount of unreacted substances increases, and the utilization rate of Ca (OH) 2 decreases.

In the present invention, the desulfurizing agent is used by filling a moving bed reactor. An example of this moving bed reactor is shown in FIG. The desulfurizing agent is supplied from the desulfurizing agent port a provided at the upper part of the moving bed reactor 1, and is supplied from the desulfurizing agent port a provided at the lower part.

is discharged from. The desulfurizing agent forming the moving bed adsorbs sulfur oxides by contacting the combustion exhaust gas supplied from the exhaust gas port, and the desulfurized exhaust gas is discharged from the exhaust gas outlet b°. By controlling the desulfurization agent movement speed in the reactor 1,
Stable desulfurization performance can be maintained against daily load changes in the boiler. In the moving bed reactor 1, there is a difference in the adsorption amount of SO2 between the inlet-side desulfurizing agent and the outlet-side desulfurizing agent for the flue gas, and the adsorption amount distribution is shown in FIG. 6a. According to this, the amount of SO2 adsorbed by the desulfurizing agent on the exhaust gas inlet side is larger than the adsorbed amount of the desulfurizing agent on the exhaust gas outlet side.

In other words, Ca in the desulfurization agent on the inlet side where SO2 concentration is high
The utilization rate of (OH)2 is also increasing. This is also supported by the relationship between the alkali utilization rate and reaction time (Figure 10) when the SO2 concentration in the exhaust gas is changed. Therefore, as shown in the moving bed reactor 1 in FIG. By supplying most of the agent and bringing it into contact with combustion exhaust gas, 802 reacts with unreacted quicklime or slaked lime in the used desulfurizing agent at a high reaction rate, and the unreacted slaked lime or quicklime in the used desulfurizing agent is removed. The used desulfurization agent can be disposed of as industrial waste.

〔Example〕

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

FIG. 1 is a system diagram of a desulfurization treatment apparatus showing one embodiment of the present invention. This device includes a boiler 5 that burns coal, an air heater 7 that cools combustion exhaust gas, and a first reaction section A and a desulfurizer that removes sulfur oxides from the exhaust gas, respectively, on the exhaust gas inlet side and exhaust gas outlet side. A moving bed reactor 1 provided with a second reaction part B, a part of the used desulfurization agent,
A desulfurization agent production device 11 that produces desulfurization agent from coal ash, slaked lime, water, and other additives, a line 18 that disposes the used desulfurization agent from the first reaction section A outside the system, and a second reaction section A line 10 that introduces a part of the used desulfurizing agent B (used desulfurizing agent R) into the desulfurizing agent manufacturing device 11, and a line 10 that introduces a part of the used desulfurizing agent B (used desulfurizing agent R) into the desulfurizing agent manufacturing device 11, and a line 10 that introduces the desulfurizing agent manufactured in the desulfurizing agent manufacturing device 11 into the upper part of the second reaction section B. a line 17 that introduces the remainder of the used desulfurizing agent (spent desulfurizing agent T) from the second reaction section B into the upper part of the first reaction section A, and a line 8 that introduces the remainder of the spent desulfurizing agent from the second reaction section B into the upper part of the first reaction section A, and a line 8 that It consists of a dust collector 12 that performs this, and a chimney 13 that discharges the dust-removed exhaust gas to the outside of the system.

In such a configuration, the flue gas from the boiler 5 enters the air heater tube through line 6 and is cooled there before being introduced into the moving bed reactor 1 through line 14. The desulfurizing agent initially filled into the moving bed reactor 1 is manufactured by the desulfurizing agent manufacturing process shown in FIG. 2 described above in the desulfurizing agent manufacturing apparatus 11. The desulfurizing agent is supplied to the upper part of the second reaction section B provided in the moving bed reactor 1 through the line 17. The desulfurizing agent and the exhaust gas come into gas-solid contact in a cross flow in the second reaction section B, thereby performing desulfurization and denitration. The reacted spent desulfurization agent is discharged from line 9, and most of it passes through line 8 as spent desulfurization agent T to moving bed reactor 1.
The unreacted slaked lime in the used desulfurizing agent T is consumed and then discharged to the outside of the system as waste desulfurizing agent 19 through line 18. Since this waste desulfurization agent 19 does not contain unreacted slaked lime, it can be used as a gypsum raw material for the desulfurization agent, and can also be thrown away as is as industrial waste.

Further, the remaining used desulfurizing agent R discharged from the line 9 is sent to the desulfurizing agent manufacturing device 11 via the line 10,
It is used as a raw material for desulfurizing agents to produce desulfurizing agents. A manufacturing process diagram of a desulfurizing agent using the used desulfurizing agent R is shown in FIG. 1A. The used desulfurization agent R is kneaded with coal ash, slaked lime or quicklime, and additives for accelerating the hydration reaction (eg, gypsum or cement), and then subjected to steam curing and drying. The produced desulfurization agent is on line 17
is again supplied to the upper part of the second reaction section B in the moving bed reactor 1. The spent desulfurization agent from the second reaction section B is
The spent desulfurization agents T and R are again divided and subjected to the above operations,
That is, it can be recycled, or it can be thrown away after being brought to a stable state, or it can also be used as a raw material for desulfurization agents.

On the other hand, the exhaust gas desulfurized and denitrated in the moving bed reactor 1 is removed by a dust collector 12, and is discharged from the chimney 13 through a line 16 to the outside of the system.

The used desulfurizing agent T may be supplied to the first reaction section A as it is as shown in FIG. 7, or may be supplied to the first reaction section A after adjusting the particle size depending on the conditions. You can also do that. In addition, the first
The reaction section A and the second reaction section B may be provided by partitioning the same container with a partition plate such as a perforated plate, or separate reaction sections A and B may be formed in a moving bed reactor.

Furthermore, the used desulfurizing agent T can be immersed in an aqueous acid solution as shown in FIG. 8, stabilized by adjusting the pH, and then discarded.

As explained above, in one embodiment of FIG.
Most of the used desulfurization agent is extracted for the purpose of dumping.
A part of it can be introduced into the desulfurizing agent manufacturing device 11 and used as a raw material for the desulfurizing agent.

With this configuration, it is possible to maintain a high utilization rate of the slaked lime added to the raw material, and it is possible to operate efficiently by reducing the amount of gypsum used in producing the desulfurization agent.

The desulfurization agent in the present invention is preferably produced by appropriately mixing 60 to 80 parts by weight of coal ash, 2 to 10 parts by weight of gypsum, and 5 to 35 parts by weight of slaked lime, but it is also used by mixing the used desulfurization agent R. In some cases, gypsum and coal ash are unnecessary or reduced.

The ratio of R and T when using the used desulfurizing agent R depends on the amount of slaked lime or quicklime added, but when the amount of slaked lime added is about 30% by weight of the raw material mixture, the used desulfurizing agent By appropriately replenishing coal ash and slaked lime so that R is 10 to 30% by weight, the balance of the entire system can be maintained. In this way, the amount of used desulfurizing agent T discharged to the outside of the system can be reduced to, for example, about 50% of the amount of used desulfurizing agent extracted from the second reaction section B. Furthermore, in order to reduce the amount of used desulfurizing agent T, the amount of slaked lime or quicklime added during desulfurizing agent production is reduced, and Ca(OH)2 or CaO
It is only necessary to increase the utilization rate of

Figure 9 shows 77 parts by weight of coal ash, 8 parts by weight of gypsum, and 1 part by weight of slaked lime.
A desulfurization agent is prepared by mixing 5 parts by weight, and this desulfurization agent is supplied to a moving bed reactor to perform a desulfurization test.
The used desulfurizing agents T with different utilization rates were prepared, an elution test was conducted, and the results of measuring the pH in the liquid at that time are shown. Desulfurization test is SO2: 11000pp, No.
: 200 ppm, 26% by weight of 02, 10% by weight of CO2, 10% by weight of H2, the remaining amount of N2 (conducted using simulated combustion exhaust gas at a temperature of 140°C. The elution test was carried out using 5g of sample (spent desulfurization agent). immersed in 150ml of distilled water,
The reaction was carried out at a temperature of 25° C. with stirring.

From the results in Figure 9, the Ca(OH)z utilization rate is 77 ca.

It was found that samples with high pH decreased and were stable. In addition, a test was conducted on the used desulfurizing agent T with a utilization rate ηcao of 100% in accordance with industrial waste emission regulations and Environment Agency Notification No. 13, and the results are shown in Table 1. The results confirmed that it is possible to dispose of it in a landfill.

Table 1 [Effects of the Invention] According to the present invention, by supplying the used desulfurization agent to the exhaust gas inlet side of the moving bed reactor, the utilization rate of slaked lime or quicklime in the desulfurization agent can be increased. Or the amount of quicklime used can be reduced. In addition, by using a portion of the used desulfurization agent as a substitute for gypsum, which is the raw material for the desulfurization agent, it is possible to effectively utilize the large amount of used desulfurization agent that is generated, reducing the amount of used desulfurization agent that is thrown away, reducing raw material costs, and reducing waste disposal. processing costs can be reduced. Furthermore, when molded desulfurization agents are manufactured using used desulfurization agents, the hydration and curing time (manufacturing time) can be shortened compared to when plaster is used.
Moreover, it has other effects such as high strength. Therefore, the desulfurization method of the present invention has excellent economic efficiency and excellent responsiveness to boiler load fluctuations.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of a desulfurization treatment equipment showing one embodiment of the present invention, Fig. 1A is a diagram explaining the desulfurization agent manufacturing process and the used desulfurization agent circulation system, and Fig. 2 is a coal ash Figure 3A is a manufacturing process diagram of a desulfurizing agent whose main component is
Ray diffraction diagram, Figure 3B is the X-ray diffraction diagram of the used desulfurization agent, Figure 4
The figure shows desulfurization agent A made from coal ash, gypsum, and slaked lime.
Figure 5 shows the relationship between the contact time of desulfurizing agent B produced from coal ash, used desulfurizing agent, and slaked lime with the exhaust gas and the amount of SO2 adsorbed.
Figure 6 is a cross-sectional view of the moving bed reactor, Figure 6a is a diagram showing the SO2 adsorption amount distribution from the exhaust gas inlet side to the outlet side in the moving bed reactor, Figure 7 is a diagram showing the relationship between the adsorption performance. Figure 8 and Figure 8 are diagrams showing other examples of the stabilization treatment method for used desulfurizing agent T, and Figure 9 shows the elution test results of used desulfurizing agent T with different Ca (OH)2 utilization rates. 10 are diagrams showing the relationship between the reaction time of the desulfurizing agent and the alkali utilization rate. l...Moving bed reactor, 5...Boiler, 7...Air heater, 11...Desulfurizing agent manufacturing device, 12...Dust collector, 13...Chimney, 19...Waste desulfurizing agent . Agent Patent Attorney Takenaga Kawakita Figure 3A 2e Contact time with exhaust gas (h) Ca(OH)z content (%) Elapsed time (h)

Claims (2)

[Claims] (1) In a desulfurization method in which sulfur oxides in coal combustion exhaust gas are absorbed and removed using a moving bed reactor filled with a desulfurization agent containing coal ash, gypsum, and slaked lime or quicklime, from the moving bed reactor Take out the used desulfurization agent,
The main component is coal ash, which is used as at least a part of the gypsum in the raw material, and the spent desulfurization agent containing unreacted slaked lime or quicklime is recycled to the exhaust gas inlet side of the moving bed reactor. A desulfurization method using a desulfurization agent. (2) In a dry desulfurization device that desulfurizes flue gas containing coal ash discharged from a coal combustion device through a moving bed reactor filled with a desulfurizing agent, the moving bed reactor is the same as the first reaction section on the upstream side of the flue gas. a second reaction section on the downstream side, and a desulfurization agent manufacturing apparatus in which at least a part of the used desulfurization agent extracted from the second reaction section is used as a raw material, and the desulfurization agent means for supplying the desulfurizing agent prepared in the manufacturing device to the second reaction section; and means for supplying a portion of the used desulfurizing agent discharged from the second reaction section to the first reaction section. 1. A desulfurization apparatus using a desulfurization agent mainly composed of coal ash, characterized in that a means for discharging the used desulfurization agent from the first reaction section out of the system is provided.