JPH04135617A - Dry desulfurizing method with spout fluidized bed - Google Patents

Abstract

PURPOSE:To increase the rate of desulfurization of waste combustion gas and the rate of utilization of granules of a desulfurizing agent by feeding the desulfurizing agent together with the waste gas from the bottoms of the conical parts of a desulfurizer and forming spout beds in the conical parts. CONSTITUTION:Granules of a desulfurizing agent are sent from a hopper 13 to a feed pipe 17 leading to the bottoms of the conical parts 2 of a desulfurizer 1, a fluidizing medium is also sent from a hopper 14 to the pipe 17 as required and they are fed into the conical parts 2 with carrier gas 19. Waste gas enters the conical parts 2 together with the granules from a feed pipe 4 and moves toward the top of the desulfurizer 1 while violently mixing with the granules. Since the gas is decelerated at the outlets of the conical parts 2, large granules are separated from flows of the gas and drop again to form spout beds. Since the granules are agitated by the gas, the film resistance of the gas is reduced and the desulfurization of the gas is accelerated. The residence time of the large granules is longer than that of the small granules and the rate of utilization of Ca in the large granules, that is, the rate of reaction of S is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method and apparatus for efficiently desulfurizing by a dry method using a spouted fluidized bed.

[Conventional technology] Sulfur compounds (SOx), HCl, NO
Acidic toxic substances such as x usually have a concentration of 100 to 3. OOOpp
Since it is considered to be a causative agent of acid rain and photochemical smog, 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 prevents white smoke from coming from chimneys. In order to do this, it is necessary to reheat the exhaust gas, which results in high equipment and operating costs, and the dry method has the problem that a high removal rate cannot be obtained. Therefore, it is desired to develop a desulfurization method that can obtain a high removal rate with a wastewater-free, low-cost process.

In addition to the above-mentioned methods, desulfurization methods for exhaust gas from boilers include a semi-dry method in which slaked lime or its slurry is sprayed into the exhaust gas, and a method in which limestone is directly supplied to high-temperature gas in a furnace or flue to remove acidic harmful substances. A dry method has been proposed to remove . Although the above methods are characterized by low equipment and operating costs, they all have the problem of low removal rate of acidic harmful substances.

In contrast, calcium-based desulfurization agents are present in low-temperature exhaust gas.
For example, the method of mainly removing sulfur compounds using a dry method by supplying slaked lime or quicklime is being reconsidered. A typical flow sheet for this method is shown in FIG. The temperature of the exhaust gas from the boiler 51 is lowered by the air heater 52, and the temperature is lowered by the desulfurization device 55.
guided by.

A desulfurizing agent such as slaked lime is supplied by spraying into the boiler 51, flue 53 or desulfurizing device 55 from five desulfurizing agent supply pipes,
At this time, water is also supplied from the water spray nozzle 54 to lower the temperature of the waste and increase the humidity. This water removal may be supplied separately from the desulfurizing agent, or the 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 56 and disposed of through the collection dust pipe 61.

[Problems to be Solved by the Invention] In the prior art described above, since the surface of the desulfurizing agent is fresh near the inlet of the desulfurization device 55, the removal rate of acidic harmful substances is affected by the moisture (relative humidity) in the exhaust gas. It is said that In this way, in order to increase the removal rate of acidic harmful substances under conditions where the desulfurization agent is highly active in the early stage of the reaction,
It is necessary to lower the temperature of the exhaust gas and increase the moisture content.

Methods of spraying water or slaked lime slurry have been proposed, but
Such a method of increasing the water concentration in the gas does not sufficiently improve the removal rate of acidic harmful substances. In other words, from the intermediate part to the vicinity of the outlet of the desulfurization device 55, more than 50% of the acidic harmful substances are usually removed by the desulfurization agent.
The concentration of acidic toxic substances has decreased from several thousand ppm to several hundred ppm. At such concentrations of acidic harmful substances, the reaction rate decreases because the desulfurizing agent reacts to a certain extent with the low concentration of acidic harmful substances. Therefore, in this reaction region, it is important to reduce the film resistance of the desulfurizing agent or to lengthen the residence time of the desulfurizing agent. Conventionally,
In order to increase the removal rate of acidic harmful substances to 80% or more, it is necessary to set the residence time on the gas side to 10 seconds or more, or to increase the height of the desulfurization device 55 to several tens of meters or more.
The dimensions of the desulfurization device 55 tend to become too large. (
For example, EPA First Combined FG
D SO2 Control Symposium.

1988.10. ST, Louis, JP-A-61-28
No. 7421).

In addition, in order to improve the utilization rate of the desulfurizing agent, the dust collector 56
When recycling the particles containing the unreacted desulfurization agent collected by the dust collector 56, the amount of particles that must be treated by the dust collector 56 increases, and the processing capacity of the dust collector 56 must be increased. Furthermore, since recycling equipment is also required, there is a problem in that equipment costs and operating costs increase.

As described above, the above-mentioned conventional technology does not give sufficient consideration to the reaction with the desulfurizing agent particles when the concentration of acidic harmful substances decreases, resulting in a problem that the desulfurization rate becomes low and the equipment cost increases. there were.

Therefore, an object of the present invention is to make the device more compact by reducing the film resistance of the desulfurizing agent or increasing the residence time of the desulfurizing agent, and to remove the unreacted desulfurizing agent collected by the dust collector. The objective is to significantly reduce the amount of recycled particles and obtain a high desulfurization rate with a simple system.

[Means for Solving the Problems] The above objects of the present invention are achieved by the following method.

That is, the lower part of the desulfurization equipment is a cone part having at least one cone structure, and at the same time, the combustion exhaust gas containing acidic harmful substances is supplied from the lower part of the desulfurization equipment, and at the same time, the desulfurization agent is supplied from the lower part of the cone part. This is a dry desulfurization method using a spout fluidized bed that forms a spout head in a cone portion, or an apparatus for carrying out the method.

[Function] The lower part of the desulfurization tower has at least one cone structure, and acidic harmful substances such as sulfur dioxide gas are supplied from the lowest part thereof, and at the same time, a desulfurization agent such as a calcium-based compound is supplied. When scum and desulfurizing agent particles are blown up from the bottom of the cone section to the top, the gas is decelerated when it exits the cone section, so large desulfurizing agent particles are separated from the gas flow and form a so-called spout bed where they fall back to the bottom. Form. By forming the spout bed in this way, the flow of the gas and the desulfurizing agent particles in the reactor becomes non-uniform, and the mixing of the scum and the desulfurizing agent particles can be increased. therefore,
The film resistance of the desulfurization agent is reduced, and the residence time of the desulfurization agent is increased, so the equipment becomes more compact, the removal rate of acidic harmful substances increases, and the utilization rate of the desulfurization agent also increases. Furthermore, if a spout bed cannot be formed using the desulfurizing agent alone, a fluidizing medium may be added.

Here, the desulfurization reaction with SO2 gas will be described using slaked lime (hereinafter referred to as Ca(○H)2) as an example of the desulfurization agent. The desulfurization reaction is as shown below.

Ca (OH)2+S O;= Ca S○3+H7○
(1) Ca(○H)2 +S O2+1/202
−+CaS○4+H20k1) Formula is calcium sulfite (
Equation (2) is a reaction in which gypsum (Ca SO 4) is produced. When the above method is adopted, the desulfurizing agent reacts while being blown up from the cone portion by the exhaust gas. Since the exhaust gas is decelerated by the mud coming out of the cone, large desulfurizing agent particles are separated from the gas flow and fall back to the bottom, forming a so-called spout bed. Under such conditions, the desulfurizing agent particles are agitated by the gas, so the gas film resistance becomes small and the desulfurizing reaction is promoted. Moreover, the residence time of the desulfurizing agent with large particles is longer than that of the desulfurizing agent with small particles, and the Ca utilization rate of the large particles also increases. At the early stage of the reaction when the SO2 concentration is high, the reactions of equations (1) and (2) occur quickly, but after the middle part of the desulfurization equipment where the SO2 concentration is low, by adopting this method, the reactions of the gas and In order to increase the relative velocity of particles,
This is also desirable in order to reduce film resistance. In addition, in this method of forming a spout bed, since the mixing characteristics of the desulfurizing agent with oxygen (02) in the exhaust gas also increase at the same time, (
The production rate of gypsum (CaSO,) according to equation 2) is also improved.

As described above, the present invention is suitable for reactions that produce inert compounds on the surface of the desulfurizing agent.

[Examples] The present invention will be explained in more detail by the following examples, but the invention is not limited thereto. An embodiment of the invention is shown in FIG. This process is based on SO in exhaust gas.
2, a desulfurization device 1 that removes gas, a dust removal device 6 that separates desulfurization agent particles and dust after reaction from exhaust gas, and a desulfurization agent hopper 1.
It consists of a supply facility for desulfurizing agent particles such as No. 3, and associated equipment. The exhaust gas containing SO2 gas is sent to the exhaust gas supply port 4.
from the cone part 2 through the gas on-off valve 3 together with the desulfurizing agent particles.
to go into. Here, the desulfurization agent particles and the exhaust gas move toward the upper part of the desulfurization apparatus 1 while being mixed vigorously.

If the water vapor concentration required for the reaction is not reached here, water may be sprayed at the inlet of the desulfurization device 1. This desulfurization equipment 1
The reacted desulfurizing agent and waste gas pass through the outlet pipe 5 to the dust removal device 6.
to go into. More than 99% of the dust in the exhaust gas is separated here, and the purified exhaust gas is disposed of outside the system through the exhaust gas duct 9.

On the other hand, the dust separated by the dust removing device 6 enters the separator 8, and the dust with small particle size is discharged from the waste duct 9 to the outside of the system. The large particle size dust passes through the media duct 10 and enters the fluidized media hopper 14 .

Desulfurization agent particles, for example finely divided limestone, quicklime or slaked lime, are sent from the desulfurization agent hopper 13 through a feed device 15 to a particle feed pipe 17 leading to the lower part of the cone section 2 of the desulfurization device 1 . If a fluidized medium is also required, the fluidized bed hopper 1
4 and the supply device 16 to the particle supply pipe 17, and one carrier gas passes through the particle on-off valve 18 to the desulfurization device 1.
is supplied to the cone section 2 at the bottom of the . The fluidized medium or the particles collected by the dust removal device 1 are mixed in the particle supply pipe 17 and then supplied to the desulfurization device 1. When such a method is adopted, the desulfurizing agent reacts while being blown up from the cone portion 2 by the gas. Since the gas is decelerated when it exits the cone portion 2, large particles are separated from the waste flow and form a so-called spout bed where they fall again towards the bottom. In the spout bed, the particles are stirred by the gas, so the gas film resistance is reduced and the desulfurization reaction is promoted. Moreover, the residence time of large-particle desulfurizing agents is longer than that of small-particles, and the Ca utilization rate (S reaction rate of desulfurizing agent) of large particles also increases.

The supply amount of the fluidized medium is determined by detecting the interlayer pressure below the desulfurization device 1 using a differential pressure detector 1 installed in a pipe connecting the desulfurization device 1 and the particle supply pipe 17.
1, and the controller 12 controls opening and closing of the supply device 16.

During startup, shutdown, or load control, the gas on-off valve 3 and particle on-off valve 18 are controlled to always form an optimal spout bed. In particular, it is important to set the gas flow velocity in the cone section 2 to 7 m/s or more. If such conditions are adopted, a stable spout bed will be formed, the residence time of the particles will be increased, and the desulfurization rate will also be greatly improved.

Further, by providing a wear-resistant material such as a ceramic plate to the cone portion 2, wear in this portion can also be reduced.

FIG. 2 shows an embodiment in which exhaust gas is supplied from the lower part of the desulfurization apparatus 1 and desulfurization agent is supplied from the lower part of the cone part 2. In this embodiment, since the exhaust gas does not pass through the cone portion 2, the pressure loss in this portion is reduced. water supply pipe 2
Water is sprayed from 0 to the exhaust gas supply port 4 of the desulfurization apparatus 1 using the spray nozzle 22, and the water vapor partial pressure is set to the level required for the reaction.

Here, the exhaust gas moves to the lower part of the desulfurization apparatus 1 while fully reacting with the desulfurization agent. A temperature detector 24 is installed at the outlet of the desulfurization equipment 1, and the set temperature here is 10 to 10, which is the saturation temperature.
A water pump 21 installed in the water supply pipe 20 to maintain a temperature of 50°C.
A controller 23 controls the supply amount. If the exhaust gas temperature at the outlet of the desulfurization device 1 drops too much, water will condense in the dust removal device 6 and desulfurization agent particles will adhere, causing blockage problems, so temperature monitoring in this part is especially important. .

FIG. 3 shows an embodiment in which part of the particles collected by the dust removal device 6 is recycled to the desulfurization agent hopper 13 and supplied to the desulfurization device 1. In FIGS. 1 and 2, the desulfurizing agent and the particles collected by the dust removing device 6 are line-mixed in the particle supply pipe 17, but in this embodiment, the particles are mixed in the desulfurizing agent hopper 13. As a result, the desulfurizing agent and the dust particles are better mixed. In this case, the amount of particles collected by the dust removing device 6 to be supplied to the desulfurizing agent hopper 13 is
This can be controlled by controlling the amount of particles discharged outside the system.

FIG. 4 shows the results of comparing the particle residence time of the conventional downflow (desulfurization agent and gas are supplied downward from the top of the desulfurization apparatus 1) and the present invention. As a result of using industrial slaked lime as the particles, the particle residence time of the present invention is increased by 20 to 40% compared to the particle residence time of the conventional method at a superficial velocity of 25 cm/s. Therefore, if the present invention is used, the desulfurization rate and the Ca utilization rate of the desulfurization agent can also be improved.

Figure 5 shows the relationship between reaction temperature and desulfurization rate. water vapor concentration 1
As a result of reacting a simulated gas with SO2: 2,000 ppm and slaked lime at a Ca/S molar ratio of -3 at It can be seen that the desulfurization equipment has a higher desulfurization rate. Particularly in the present invention, when the reaction temperature is set at 50° C., it can be seen that a desulfurization rate of 90% or more is achieved.

FIG. 6 shows the relationship between reaction temperature and Ca utilization rate under the same reaction conditions as in FIG. 5. Under the same reaction conditions,
Similar to the desulfurization rate, the Ca utilization rate is higher in the present invention than in the conventional method (downflow method). This is thought to be due to the longer particle residence time in the present invention.

FIG. 7 shows the relationship between the superficial velocity and the molar ratio of Ca5O,/CaS3 under the same reaction conditions as in FIG. Superficial velocity of conventional method (downflow method): 25 cm
If the Ca S O4/Ca S O3 ratio at /s is 1, then in the conventional method, when the superficial velocity is increased to 75 cm, /'S, it decreases to 0.5 or less. However, in the present invention, the superficial velocity is reduced to 50% due to the good miscibility of gas and particles.
Even if set to cm/s, CaS O4/'Ca
It can be seen that the S O3 ratio is 1 or more, which means that the probability that the reaction of formula (2) will occur is greater than in the conventional method.

As described above, by using the present invention, it becomes possible to efficiently remove harmful acidic scum from exhaust gas.

Suitable desulfurizing agents used in this embodiment are alkali metal or alkaline earth metal compounds such as slaked lime, caustic potash, caustic soda, and sodium sulfate.

[Effects of the Invention] According to the present invention, the exhaust gas containing S02 and the desulfurizing agent particles can be mixed vigorously, and the residence time of the particles can be increased, so compared to the conventional method, the S02
High values can be obtained for both the gas desulfurization rate and the desulfurization agent particle utilization rate.

[Brief explanation of drawings]

Figures 1, 2, and 3 are flow sheets of the desulfurization process in an example of the present invention, Figure 4 is a diagram showing the relationship between particle residence time and superficial velocity, and Figure 5 is reaction temperature and desulfurization rate. Figure 6 is a diagram showing the relationship between reaction temperature and Ca utilization rate, Figure 7 is superficial velocity and Ca SO < / Ca
A diagram of experimental data showing the SO3 ratio and a flow sheet of a conventional desulfurization process are shown in FIG. Fig. 1 1 Desulfurization device, 2... Cone part, 4... Exhaust gas supply port, 6... Dust removing device, 13... Desulfurizing agent hopper, 14...
... Fluidized medium hopper, 19... Carrier gas applicant Babcock Hitachi Co., Ltd. Agent Patent attorney Takayoshi Matsunaga 1 person Exhaust gas supply port 14 Fluidized medium hopper superficial velocity (am/s) Fig. Fig. Fig. Diagram Reaction temperature ('C)

Claims (9)

[Claims] (1) The lower part of the desulfurization apparatus is a cone part having at least one cone structure, and at the same time, the combustion exhaust gas containing acidic harmful substances is supplied from the lower part of the desulfurization apparatus, and the desulfurization agent is supplied from the lower part of the cone part, A dry desulfurization method using a spout fluidized bed, characterized in that a spout bed is formed in the cone portion. (2) The dry desulfurization method using a spout fluidized bed according to claim 1, characterized in that a fluidized medium is added to the desulfurization agent. (3) The dry desulfurization method using a spout fluidized bed according to claim 2, characterized in that at least a portion of the particles collected in a dust collector subsequent to the desulfurization device is separated and used as a fluidized medium. (4) The dry desulfurization method using a spout fluidized bed according to claim 1, characterized in that the supply amount of the fluidized medium is controlled so that the bed pressure loss of the spout bed is constant. (5) The dry desulfurization method using a spout fluidized bed according to claim 1, characterized in that the gas flow velocity in the cone portion is 7 m/s or more. (6) The dry desulfurization method using a spout fluidized bed according to claim 1, characterized in that moisture is supplied to the desulfurization device, and the amount of water supplied is controlled by the temperature of the gas at the outlet of the desulfurization device. (7) A cone section having at least one cone structure is provided at the bottom of the desulfurization device, a combustion exhaust gas supply port containing acidic harmful substances is provided at the bottom of the desulfurization device, and a desulfurization agent supply port is provided at the bottom of the cone section. A dry desulfurization device having a spout fluidized bed, characterized in that a spout bed is formed in a cone portion. (8) The dry desulfurization device having a spout fluidized bed according to claim 7, characterized in that a wear-resistant material is installed in the cone section at the bottom of the desulfurization device. (9) The dry desulfurization device having a spout fluidized bed according to claim 7, wherein on-off valves for flue gas and for supplying a fluidized medium for forming a spout bed are respectively attached to the cone portion at the bottom of the desulfurization device.