JPH04300626A - Device for desulfurizing flue gas and its operating method - Google Patents

Abstract

PURPOSE:To provide a device for desulfurizing, exhaust gas wherein the concn. of SO2 varied according to changes in load can be controlled easily by a simple system and a high desulfurizing rate is obtained. CONSTITUTION:In order to improve desulfurizing rate, the supply parts for supplying the desulfurizing agents such as the oxide, hydroxide or carbonate of alkali metals or alkaline earth metals are provided at not less than two places of an exhaust gas flue 7 or desulfurizing column 3: one located on the upstream side of the exhaust gas passage for supplying a desulfurizing agent (CaO) having a larger specific surface area and the other located on the downstream side thereof for supplying a desulfurizing agent (Ca(OH)2) having a smaller specific surface area. When the concn. of sulfur oxide in the exhaust gas becomes higher, the desulfurizing agent having the larger specific surface area is supplied in an increased amt. and, when the concn. thereof in the exhaust gas becomes lower, the desulfurizing agent having the smaller specific surface area is supplied in a decreased amt., whereby variations in the sulfur removing performance are reduced in case load changes should occur.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a desulfurization device that uses one or more compounds selected from alkali or alkaline earth metal oxides, hydroxides, or carbonates as a desulfurization agent, and particularly relates to a desulfurization device that improves desulfurization performance. The present invention relates to a desulfurization device that adds a chemical agent.

0002

[Prior Art] Sulfur compounds (SOx) are contained in the exhaust gas discharged from heavy oil-fired and coal-fired boilers in thermal power plants.
Acidic toxic substances such as
ppm, and is said to be a causative agent of acid rain and photochemical smog, so effective treatment means are desired. Conventionally, wet methods (e.g. limestone-gypsum method) or dry methods (activated carbon method) have been used, but while the wet method has a high removal rate of harmful substances, it is difficult to treat wastewater and requires reheating of exhaust gas. However, there were problems in that the equipment costs and operating costs were high, and a high removal rate could not be obtained with the dry method. Therefore, it is desired to develop a desulfurization method that can obtain a high removal rate with a wastewater-free, low-cost process.

[0003] In addition to the above-mentioned method, desulfurization methods for exhaust gas from boilers and the like include a semi-dry method in which slaked lime or its slurry is sprayed into the exhaust gas, and an acidic method in which limestone is directly dispersed in the high-temperature gas in the furnace or flue. Dry methods have been proposed for removing harmful substances, and are characterized by low equipment and operating costs, but all methods have the problem of low removal rates.

FIG. 6 shows a typical flow sheet of a method in which slaked lime or quicklime is sprayed into exhaust gas to react with SO2 in the exhaust gas, and then removed by a dust collector. The temperature of the exhaust gas from the boiler 1 is lowered by an air heater 2, and then guided to a desulfurization tower 3. Desulfurizing agents such as slaked lime A and quicklime B are sprayed and supplied into the flue 7 or the desulfurizing tower 3, and react with acidic harmful substances such as SO2 in the exhaust gas. At this time, water C is also supplied, thereby lowering the temperature of the exhaust gas and increasing the humidity.

At this time, even if water C is supplied separately from the desulfurizing agent,
A desulfurizing agent may be supplied simultaneously as a slurry. The reacted desulfurizing agent is collected together with the ash in the exhaust gas by the dust collector 8,
A part of it is again supplied to the desulfurization tower 3 and the SO2 in the exhaust gas is
Reacts with acidic hazardous substances such as Remaining desulfurization agent and ash D
will be discarded.

[0006] In such a method, the removal rate of acidic harmful substances is said to be dominated by the moisture (relative humidity) in the exhaust gas. That is, in order to increase the removal rate of acidic harmful substances, it is necessary to lower the temperature of the exhaust gas and increase the water concentration. In order to increase the moisture concentration, a method of spraying water or slaked lime slurry has been proposed, but such a method of increasing the moisture concentration in the gas does not sufficiently improve the removal rate of acidic harmful substances. When the removal rate of acidic harmful substances was low, water C or steam was added to the particles containing unreacted desulfurization agent collected by the dust collector 8 to destroy the shell of reaction products formed on the surface. A method has also been proposed in which the removal rate is improved by spraying a portion of this into the exhaust gas or into the furnace (for example, U.S. Pat. No. 3,431,289).
specification, JP-A-60-19019, JP-A-61-3
No. 5827).

[0007]

[Problems to be Solved by the Invention] However, water or steam is added to particles containing unreacted desulfurization agent collected by the dust collector described in the above-mentioned US patent specifications, etc. After destroying the shell of the reaction product, a part of it is sprayed into the exhaust gas or into the furnace. This method involves adding water or steam to particles containing unreacted desulfurization agent collected by a dust collector. However, since the shell of the reaction product is not completely destroyed, the recovery rate is not sufficient, especially when SO2 at the boiler outlet is removed.
If the concentration is high, a high desulfurization rate cannot be obtained.

[0008] Furthermore, the SO2 concentration in the exhaust gas also changes due to changes in the boiler load and the sulfur content in the coal that is the fuel, but in the conventional technology, when the SO2 changes, the supply amount of the desulfurizing agent is adjusted. was used to control the SO2 concentration at the chimney outlet. However, with this method, the amount of desulfurization agent supplied is not constant, and the content of unreacted desulfurization agent in particles collected by the dust collector fluctuates, making it difficult to control desulfurization performance when recycled. The problem was that it became difficult.

[0009] As described above, the above-mentioned conventional technology does not take into consideration the clogging of the pores of the desulfurizing agent due to SO2 absorption.
There have been problems in that the removal rate (desulfurization rate) of acidic harmful substances is low and the equipment cost is high. Furthermore, it was difficult to control changes in S02 concentration due to load fluctuations.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a flue gas desulfurization apparatus which is a simple system, can easily control changes in S02 concentration due to load fluctuations, and can obtain a high desulfurization efficiency.

[0011]

[Means for Solving the Problems] The above objects of the present invention are achieved by the following main configurations. In other words, in a flue gas desulfurization equipment that adds at least one compound selected from alkali or alkaline earth metal oxides, hydroxides, or carbonates to the combustion flue gas as a desulfurization agent, it is added to two or more locations in the flue gas path. Flue gas desulfurization with a desulfurization agent supply section, a supply section for the desulfurization agent with a larger specific surface area on the upstream side of the exhaust gas path, and a supply section for the desulfurization agent with a smaller specific surface area on the downstream side of the exhaust gas path. When the concentration of sulfur oxides in the exhaust gas increases, the amount of desulfurization agent with a large specific surface area is increased, and when the concentration of sulfur oxides in the exhaust gas decreases, the amount of desulfurization agent with a small specific surface area is increased. This is a method of operating the flue gas desulfurization equipment to increase the supply amount.

Here, the ratio of the specific surface area of the desulfurizing agent measured by the N2BET method is (desulfurizing agent with larger specific surface area)/(
Desulfurization performance is improved by setting the desulfurization agent with a smaller specific surface area to 1.5 or more. Furthermore, as desulfurizing agents with different specific surface areas, for example, multiple slaked limes with different specific surface areas can be used, but quicklime (CaO) is used as a desulfurizing agent with a larger specific surface area, and slaked lime ( Ca(OH)2) can also be used.

[0013]

[Operation] In the conventional technology, the pores of the desulfurizing agent that has reacted with SO2 in the exhaust gas are blocked by the reaction products (here, calcium sulfite and/or calcium sulfate), resulting in poor contact between the SO2 and the desulfurizing agent. , no further desulfurization occurred. However, a desulfurizing agent with a large specific surface area or a large pore volume has less pore clogging even in an atmosphere with a high SO2 concentration. Therefore, in an atmosphere with high SO2 concentration near the boiler outlet, a desulfurizing agent with a large specific surface area is used to reduce the SO2 concentration in the exhaust gas.
After lowering the SO2 concentration, using a desulfurizing agent with a small specific surface area and further absorbing SO2 in the exhaust gas reduces pore clogging and increases the desulfurization rate. Further, there is little change in desulfurization performance due to fluctuations in SO2 concentration at the boiler outlet.

[0014]

EXAMPLES The present invention will be explained in more detail by the following examples, but is not limited thereto.

Example 1 The case of desulfurizing exhaust gas from a coal-fired boiler using slaked lime and quicklime prepared by heating it as a desulfurizing agent will be described using an example in which an apparatus according to the present invention is applied. In FIG. 1, exhaust gas from a boiler 1 is lowered in temperature by an air heater 2, and is led to a desulfurization tower 3. A part of the slaked lime A is supplied to the heating device 4 and heated to 600° C. to become quicklime B. Slaked lime A and quicklime B are sprayed and supplied from line 5 and line 6 into the flue 7 or desulfurization tower 3, respectively. Slaked lime A and quicklime B react with acidic toxic gases such as SO2 in the flue gas in the flue 7 or the desulfurization tower 3, and the reacted desulfurization agent is collected in the dust collector 8 along with the ash in the flue gas and unreacted desulfurization agent. collected. However, slaked lime A needs to be supplied to an area downstream of quicklime B where the SO2 concentration is low. When spraying the desulfurization agent, in order to further improve the desulfurization rate, it is also possible to lower the temperature of the exhaust gas and increase the humidity by supplying water C from the line 9 into the flue 7 or the desulfurization tower 3. At this time, water C may be supplied at the same location as the desulfurizing agent, or may be supplied at a different location. A part of the particles D (hereinafter referred to as collected particles) collected by the dust collector 8 and containing unreacted and reacted desulfurizing agent and ash is discarded, and the remainder is returned to the flue 7 or It is also possible to spray it into the desulfurization tower 3 and cause it to react again with acidic toxic gas such as SO2 in the exhaust gas. However, in this case, it is preferable to supply it together with slaked lime A from the viewpoint of desulfurization performance.

Using this apparatus, the desulfurization performance was measured when coal A (sulfur content in coal was 1.9%) was burned. However, slaked lime A (specific surface area 10.3 m by N2BET method)
2/g: Hereinafter simply referred to as specific surface area) and quicklime B (
(specific surface area: 29.7 m2/g) were added at a molar ratio of 1.0 times, respectively, and a total of 2.0 times the SO2 contained in the exhaust gas at the boiler outlet, and water C was added at a weight ratio of 3% of the exhaust gas. Slaked lime A and quicklime B were sprayed and supplied into the flue 7 and the desulfurization tower 3 through lines 5 and 6, respectively. Particles collected by the dust collector 8 are not recirculated,
All were discarded.

[0017] At the boiler outlet and the dust collector outlet,
After removing moisture from the gas, the SO2 concentration was measured and found to be 1540 ppm. In other words, when the SO2 concentration in the exhaust gas was measured, it was 1540p.
pm and 155 ppm. In other words, S in the exhaust gas
90% of O2 removed (hereinafter referred to as 90% desulfurization rate)
It means that it was done.

Example 2 Using the same apparatus as in Example 1, the desulfurization rate was measured under the same conditions. However, by adjusting the amount of slaked lime supplied to the heating device 4, the total amount of slaked lime A and quicklime B supplied (
(on a molar basis), the supply ratio of slaked lime A and quicklime B was varied under constant conditions.

The results are shown in FIG. 2(a). The higher the proportion of quicklime B, the higher the desulfurization rate, but in the case of charcoal A, it was found that there was almost no effect when the proportion of quicklime B was 60% or more.

Similar studies were conducted on coals with other sulfur contents other than coal A, and it was found that, in general, the higher the sulfur content of coal, the higher the mixing ratio of quicklime B needs to be. Desulfurization performance is improved by adding quicklime B with large pore volume to the upstream side where SO2 concentration is high.
This is presumed to be because quicklime B has a larger pore volume and is less likely to be clogged even at a high SO2 concentration.

Example 3 Using the same apparatus as in Example 1, the desulfurization rate was measured under the same conditions. However, two types of slaked lime A having different specific surface areas were used as desulfurizing agents. Slaked lime I has a specific surface area of 26.8m2
/g, and slaked lime II with a specific surface area of 10.3 m2/g was used. The total supply amount of slaked lime I and slaked lime II was kept constant, and the supply ratio of slaked lime I and slaked lime II was varied. Figure 3 shows the relationship between the supply ratio and desulfurization performance at that time.
Shown below. As in Example 2, the higher the proportion of slaked lime I, the higher the desulfurization rate, but in the case of A charcoal, it was found that when the proportion of slaked lime I was 60% or more, there was almost no effect.

Example 4 Using the same apparatus as in Example 1, the desulfurization rate was measured under the same conditions. However, two types of slaked lime A were used: slaked lime II with a small specific surface area (specific surface area 10.3 m2/g) and slaked lime with several types of larger specific surface areas. Then, each slaked lime is extracted from the SO2 contained in the exhaust gas.
They were added in a molar ratio of 1.0 times each, and a total of 2.0 times. The relationship between the specific surface area and desulfurization performance of slaked lime, which has a larger specific surface area than slaked lime II, is shown in (a) in FIG. It was found that when the specific surface area of slaked lime, which has a large specific surface area, is 15 m2/g or less, the desulfurization rate decreases.

Similar studies were conducted on coals other than coal A with different sulfur contents, and from the viewpoint of desulfurization performance, the specific surface area ratio of two types of slaked lime with different specific surface areas was more than 1.5 times. That's what I found out.

Example 5 Using the same apparatus as in Example 1, desulfurization rates were measured for coals with different sulfur contents under the same conditions. The relationship between the SO2 concentration at the boiler outlet and the desulfurization performance is shown in (a) in FIG. It can be seen that the change in desulfurization rate due to fluctuations in SO2 concentration at the boiler outlet is small and control is easy.

Comparative Example 1 Using the flue gas desulfurization equipment based on the conventional technology shown in FIG.
Desulfurization rates were measured for coals with different sulfur contents under the same conditions as in Examples 1 and 5. However, the desulfurization agent used in Example 1
and slaked lime A and quicklime B similar to 5 are mixed,
Half of the amount was sprayed and supplied into the flue 7 and the desulfurization tower 3 through lines 5 and 6, respectively. The results are shown in FIG. 5(b).

The desulfurization rate is lower than that of the desulfurization apparatus according to the present invention, and the difference is particularly large when the SO2 concentration at the boiler outlet is high. Furthermore, the desulfurization rate changes greatly due to fluctuations in the SO2 concentration at the boiler outlet, making control difficult.

Comparative Example 2 Using the apparatus based on the prior art shown in FIG. 6, the desulfurization rate was measured for charcoal A under the same conditions as in Example 2 while varying the supply amounts of slaked lime A and quicklime B. However, the desulfurization agent was a mixture of slaked lime A and quicklime B similar to those in Comparative Example 1, and half the amount was sprayed into the flue 7 and the desulfurization tower 3 through lines 5 and 6, respectively. The results are shown in FIG. 2(b). The overall desulfurization rate is lower than that of the desulfurization apparatus according to the present invention.

Comparative Example 3 Using the apparatus based on the prior art shown in FIG. 6, the desulfurization rate was measured for charcoal A under the same conditions as in Example 4 when two types of slaked lime B were used. However, the desulfurization agent was a mixture of slaked lime A and quicklime B similar to those in Comparative Example 1, and half the amount was sprayed into the flue 7 and the desulfurization tower 3 through lines 5 and 6, respectively. The results are shown in (b) in Figure 4.
). The overall desulfurization rate is lower than that of the desulfurization device according to the present invention.

[0029]

According to the present invention, a desulfurizing agent having a large specific surface area and a large pore volume causes less pore clogging even in an atmosphere with a high SO2 concentration. Therefore, in an atmosphere with a high SO2 concentration near the boiler outlet, a desulfurizing agent with a large specific surface area is used to lower the SO2 concentration in the exhaust gas, and after lowering the SO2 concentration, a desulfurizing agent with a small specific surface area is used to further reduce the exhaust gas. By absorbing the SO2 inside, the clogging of pores is reduced and the desulfurization rate is also increased. In addition, by controlling the amount of desulfurization agent with a large specific surface area added in an atmosphere with high SO2 concentration near the boiler outlet in response to changes in SO2 concentration due to changes in the boiler load, the desulfurization performance will change due to changes in SO2 concentration. can be made smaller.

[Brief explanation of drawings]

FIG. 1 is a flow sheet of a desulfurization apparatus in an example of the present invention.

FIG. 2 is a diagram showing the relationship between quicklime supply ratio and desulfurization rate.

FIG. 3 is a relationship diagram of the supply ratio of slaked lime having a large specific surface area in an example of the present invention.

FIG. 4 is a diagram showing the relationship between the specific surface area of slaked lime having a large specific surface area and the desulfurization rate.

FIG. 5 is experimental data showing the relationship between SO2 concentration at the boiler outlet and desulfurization rate.

FIG. 6 is a diagram showing a flow of a conventional technique.

[Explanation of symbols]

1 Boiler 3 Desulfurization tower 4 Heating device 7 Flue 8 Dust collector A Slaked lime B Quicklime C Water D Collection particles

Claims (4)

[Claims] Claim 1. In a flue gas desulfurization device in which at least one compound selected from oxides, hydroxides, or carbonates of alkali or alkaline earth metals is added to combustion flue gas as a desulfurization agent, A desulfurizing agent supply section is provided in at least two locations, and a desulfurizing agent supply section with a larger specific surface area is provided on the upstream side of the exhaust gas path, and a desulfurizing agent supply section with a smaller specific surface area is provided on the downstream side of the exhaust gas path. A flue gas desulfurization device characterized by: [Claim 2] The desulfurizing agent has a specific surface area ratio measured by the N2BET method of (desulfurizing agent with a larger specific surface area)/(desulfurizing agent with a smaller specific surface area) = 1.5 or more. The flue gas desulfurization device according to claim 1. 3. Claim 1, wherein the desulfurizing agent with a larger specific surface area is quicklime (CaO), and the desulfurizing agent with a smaller specific surface area is slaked lime (Ca(OH)2).
The flue gas desulfurization equipment described. [Claim 4] When the concentration of sulfur oxides in the exhaust gas increases, the supply amount of the desulfurizing agent having a large specific surface area is increased,
2. The method of operating a flue gas desulfurization apparatus according to claim 1, wherein the supply amount of the desulfurization agent having a small specific surface area is increased when the concentration of sulfur oxides in the flue gas becomes low.