JPH07108132A - Flue gas desulfurized and method for evaluating operating performance and method for controlling thereof - Google Patents

Abstract

PURPOSE:To maximize the spray quantity to a medium temp. desulfurizing part, to obtain the simplification of a desurfurizer and the higher overall desulftrizing rate than heretofore and to obtain the optimum operating conditions by preventing combustion ash from being recycled. CONSTITUTION:In a flue gas desulfurizer where after a desulfurizing agent is used and waste gas is fed to a desulfurizer 2 at <=200 deg.C of a combustion device and the desulfurizing agent is reacted with SOx in the waste gas, the desulfurizing agent contg. the unreacted de sulfurizing agent is recovered in a low temp. part dust collector 8, after the spent desulfurizing agent contg. the unreacted desulfurizing agent recovered in the dust collector 8 is fed to a medium temp. desulfurizing part 9 at 500-900 deg.C and reacted with SOx in the waste gas, it is recovered in a high temp. part dust collector 4 upstream of the desulfurizing feeding position in the desulfurizer 2. The flue gas desulfurizer is of low temp. desulfurizing and medium temp. recycling type.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention uses as a desulfurizing agent a compound containing at least one hydroxide or a mixture of one or more alkali metal or alkaline earth metal hydroxides and oxides. The present invention relates to a desulfurization apparatus used, and more particularly to a desulfurization apparatus that improves desulfurization performance during operation of the desulfurization apparatus and a control method thereof.

[0002]

2. Description of the Related Art Sulfur oxides (hereinafter referred to as S) are contained in exhaust gas discharged from heavy oil-fired and coal-fired boilers in thermal power plants.
Acidic noxious substances such as O ₂ hereinafter) and HCl is typically 10
Since it is contained in a proportion of 0 to 3000 ppm and is considered to be a causative substance of acid rain and photochemical smog, its effective treatment means is desired. Conventionally, a wet method (for example, limestone-gypsum method) or a dry method (activated carbon method) has been carried out. However, the wet method has a high removal rate of harmful substances, but it is difficult to treat wastewater and it is necessary to reheat exhaust gas. However, there is a problem that a high removal rate cannot be obtained by the dry method because of high equipment cost and operation cost. Therefore, it is desired to develop a desulfurization method capable of obtaining a high removal rate in a low-drainage, low-cost process. As a method for desulfurizing exhaust gas from boilers, etc., in addition to the above methods, limestone is directly dispersed in high temperature gas in a furnace or flue, or a semi-dry method in which slaked lime or its slurry is sprayed into the exhaust gas to disperse acidic harmful substances. Although a dry method for removing has been proposed and has a feature of low equipment cost and operating cost, both methods have a problem of low removal rate.

FIG. 6 shows a typical flow sheet of a method of spraying slaked lime or quick lime into exhaust gas to react with SO ₂ in the exhaust gas, and removing this with a dust collector. The temperature of the exhaust gas 6 from the boiler 1 is lowered by the air heater 3, and the desulfurization tower 2
Be led to. A desulfurizing agent such as slaked lime is sprayed and supplied into the flue or the desulfurization tower 2 from the desulfurizing agent spray port 5, and at this time, water or steam is also supplied from the water / steam spray port 7 to lower the temperature of the exhaust gas, Increase humidity. At this time, water may be supplied separately from the desulfurizing agent, or may be simultaneously supplied as a slurry together with the desulfurizing agent. The reacted desulfurizing agent is collected by the dust collector 8 together with the ash in the exhaust gas and is discarded.

In such a method, the removal rate of acidic toxic substances is said to be dominated by the water content (relative humidity) in the exhaust gas. That is, in order to increase the removal rate, it is necessary to lower the temperature of the exhaust gas and increase the water content. A method of spraying water or slaked lime slurry has been proposed to increase the water concentration, but such a method of increasing the water concentration in the gas does not sufficiently improve the removal rate. If the removal rate is low, water or steam is added to the particles containing the unreacted desulfurizing agent collected by the dust collector to destroy the reaction product shell formed on the surface, and then part of this is removed. A method has also been proposed in which the removal rate is improved by spraying into the exhaust gas again (for example, U.S. Pat. No. 3,481,289, JP-A-61-35827). In such a semi-dry method, when the desulfurization reaction is completed, ash containing calcium sulfite is generated as waste. Conventionally, the waste was oxidized by heat-treating it in an oxidizing atmosphere of oxygen, but the problem is that the treatment time is long and the treatment efficiency is poor. Since it is necessary to provide a device of a system different from the combustion device, the device becomes complicated and expensive. There was a point.

In order to solve the above problems, in a desulfurization process in which one or more kinds of alkali, alkaline earth metal oxides, hydroxides or carbonates are sprayed as a desulfurizing agent in a temperature range of 200 ° C. or higher. After recovering a desulfurizing agent containing unreacted desulfurizing agent, a part of which has reacted with SO ₂ in the exhaust gas in a temperature range of 200 ° C. or lower, by a dust collector, spray supply into the exhaust gas at a temperature of 500 to 900 ° C. Then, a desulfurization process characterized by reacting with SO ₂ in exhaust gas was invented (hereinafter, this process is referred to as a low temperature desulfurization medium temperature recycling system). However, this method also recycles ash at the same time when recycling, so it is difficult to improve the desulfurization rate adequately because the amount of recycle is limited by the capacity of the dust collector in a combustion device using a fuel with a high ash content. It was
A method for recycling the desulfurizing agent blown into the furnace has also been proposed (US Pat. No. 3,481,289).
However, since the desulfurization rate itself is low unless the furnace injection overlaps with the low-temperature desulfurization, it is difficult to improve the desulfurization rate sufficiently even if it is recycled, and the ash is recycled like the low-temperature desulfurization medium-temperature recycling method. There is a problem that the amount of the reacted desulfurization agent that can be formed is limited.

[0006]

In the conventional low temperature desulfurization medium temperature recycling method, since the ash is also recycled at the time of recycling, the recycling amount of the unreacted desulfurizing agent is limited by the capacity of the dust collector. Therefore, an object of the present invention is to prevent the combustion ash from being recycled, thereby maximizing the spray amount of the intermediate temperature desulfurization section, simplifying the dust collector and obtaining a higher overall desulfurization rate than before. Also. The purpose of the present invention is to
In a new low-temperature desulfurization medium-temperature recycling system that prevents the combustion ash from being recycled, the establishment of a method for obtaining optimal operating conditions in order to obtain a higher overall desulfurization rate than before.

[0007]

The above object of the present invention is achieved by the following main constitutions. That is, a compound of at least one kind of metal of an alkali metal or an alkaline earth metal is used as a desulfurizing agent and is supplied to a low temperature desulfurization section of the exhaust gas passage of the combustion device at a temperature of 200 ° C. or lower to obtain S in exhaust gas.
In a flue gas desulfurization device in which a desulfurizing agent containing an unreacted desulfurizing agent is recovered by a dust collector (referred to as a low temperature part dust collector) after reacting with O ₂ , the unreacted desulfurizing agent recovered by the dust collector is included. After the used desulfurizing agent is supplied to the medium temperature desulfurization section of the exhaust gas passage at a temperature of 500 to 900 ° C. and reacted with the sulfur oxides of the exhaust gas,
This is a low-temperature desulfurization mid-temperature recycle type flue gas desulfurization device that collects by a dust collector (referred to as a high-temperature part dust collector) upstream of the desulfurization agent supply position in the low-temperature desulfurization unit.

Further, the method for obtaining the optimum operating conditions in which the total desulfurization rate of the low-temperature desulfurization / medium-temperature recycling system of the present invention is improved is as follows. That is, (a) ignoring the desulfurization reaction in the exhaust gas passage region at a temperature of 500 ° C. or lower that includes the low temperature desulfurization part of the desulfurization agent reacted in the middle temperature part, (b) is supplied to the middle temperature desulfurization part collected by the dust collector. The desulfurization rate of the desulfurizing agent with two parameters, (the number of moles of unreacted desulfurizing agent supplied) / (the number of SO ₂ moles in the exhaust gas) and the SO ₂ concentration in the exhaust gas per unit time in the medium temperature desulfurization section are two parameters. Determined from the desulfurization rate of the medium temperature desulfurization unit alone that was evaluated in advance,
(C) The desulfurization rate in the low-temperature desulfurization unit is (mol desulfurizing agent supplied) / (SO _{2 in} exhaust gas per unit time in the low-temperature desulfurization unit)
The total desulfurization rate was determined under the condition that the number of moles) (hereinafter sometimes referred to as As / S) and the relative humidity of the low temperature desulfurization section were used as parameters and the SO ₂ concentration in the exhaust gas was not used as a parameter. Is a method for evaluating the operating performance of a flue gas desulfurization device, which evaluates the operating performance of a flue gas desulfurization device.

Further, according to the present invention, the operating performance evaluation method of the flue gas desulfurization apparatus is used (As / S) per unit time in the low temperature desulfurization section and (unreacted desulfurization agent supply moles) / (SO ₂ moles of flue gas)
Of the flue gas desulfurization apparatus by changing at least one of the above. Desulfurization rate is closely related to Ab / S in each desulfurization section,
In particular, in the medium temperature desulfurization section, it was found from the characteristics of the desulfurization reaction that the desulfurization rate has a very large Ab / S dependency when the temperature and the gas are the same. In the low-temperature desulfurization medium-temperature recycling method of the present invention, the desulfurizing agent after recycling is recovered, so the low-temperature reaction of the desulfurizing agent after recycling is not considered. Further, since Ab / S in the medium temperature desulfurization section varies depending on the desulfurization rate of the low temperature desulfurization section, it is possible to accurately predict the desulfurization rate of the medium temperature desulfurization by accurately calculating the ratio of the unreacted desulfurization agent in the low temperature desulfurization agent. Will be possible. Further, the present invention, the used desulfurization agent containing the unreacted desulfurization agent recovered by the low temperature dust collector in the flue gas desulfurization apparatus, instead of the process of supplying to the intermediate temperature desulfurization section of the exhaust gas passage, the used desulfurization agent It may be applied to a flue gas desulfurization apparatus which has a process in which it is made into a slurry and then supplied to the intermediate temperature desulfurization section.

[0010]

The present invention is based on the following new findings obtained by conducting desulfurization experiments in the medium temperature desulfurization section and the low temperature desulfurization section under various conditions. (1) In the medium temperature desulfurization section, spraying the used desulfurization agent causes decomposition of hydrates on the surface of the desulfurization agent, causing cracks in the shell-like reaction layer, and exposing the unreacted portion of the desulfurization agent to exhaust gas. It As a result, in the medium temperature desulfurization section, even the used desulfurizing agent has the same reactivity as the unreacted desulfurizing agent. This means that the history of the desulfurization agent (whether a new desulfurization agent is used, whether it is a recycled desulfurization agent that once passed through the low-temperature part, or how many times the low-temperature part has been recycled) or the property does not matter. Is also shown. (2) Since the desulfurization rate in the low temperature desulfurization section is determined by the specific surface area of the desulfurization agent and the relative humidity in the low temperature desulfurization section, the desulfurization agent after desulfurization treatment in the medium temperature desulfurization section with a low specific surface area is supplied to the low temperature desulfurization section. Even so, there is almost no improvement in the desulfurization rate. (3) In the low temperature desulfurization section, if the relative humidity in the desulfurization tower and the exhaust gas composition are constant, the desulfurization rate improves in proportion to the molar ratio Ab / S of the desulfurizing agent supply amount to the SO ₂ flow rate in the exhaust gas.

From the above results, as an air flow spray desulfurization device that uses the desulfurizing agent most effectively, the desulfurizing agent was sprayed in each of the low temperature desulfurizing section and the medium temperature desulfurizing section, and the medium temperature desulfurizing section was reacted in the low temperature desulfurizing section. A device for spraying a desulfurizing agent is used. In addition to this, the recycling ratio by collecting dust downstream of each desulfurization unit (amount sprayed from the low temperature part dust collector to the middle temperature part / amount discarded from the low temperature part dust collector)
Therefore, it is possible to obtain a desulfurizer having higher performance than the conventional one. In addition, the used desulfurization agent sprayed in the medium temperature desulfurization unit improves the dust collection rate in the high temperature dust collection unit, and almost no combustion ash is mixed, so the amount of ash flowing through the entire equipment is the same as when not recycled. become,
When a fuel with a high ash content is used, it is possible to operate with a dust collector having a smaller capacity than the conventional method. Further, according to the present invention, it is possible to determine in advance the operating conditions of the desulfurization device together with the operating conditions of the combustion device, and it is also possible to easily predict the change in the desulfurization performance due to the change in the operating conditions of the desulfurization device. It enables the most efficient operation of the desulfurization system as a whole.

The operation performance evaluation method of the flue gas desulfurization apparatus of the present invention (low temperature desulfurization medium temperature recycling method) will be described in detail below. In the low temperature desulfurization medium temperature recycling method of the present invention, the conditions (1) to (3) are set, the desulfurization rate in each temperature range is calculated according to the conditions, and the total desulfurization rate is obtained based on the desulfurization rate. Total desulfurization rate = Middle-temperature desulfurization section desulfurization rate + (1-Medium-temperature desulfurization section desulfurization rate) x Low-temperature desulfurization section desulfurization rate The reason why the components of the used desulfurization agent recovered by the dust collector and recycled to the middle-temperature desulfurization section change The low temperature desulfurization medium temperature recycling method is as follows. First, a new desulfurizing agent (unreacted desulfurizing agent) 1 is added to the low temperature desulfurization section
Is supplied and only desulfurization is performed in the low-temperature desulfurization section Recycling desulfurization agent 1 = low-temperature desulfurization section desulfurization agent 1 Next, desulfurization in the medium-temperature desulfurization section by the recycling desulfurization agent 1 and low-temperature desulfurization by the new desulfurization agent 2 supplied next When desulfurization is performed in the recycle section: Recycle desulfurization agent 2 = Recycle desulfurization agent 1 + Low temperature desulfurization section desulfurization agent 2 Further, desulfurization in the medium temperature desulfurization section by the recycle desulfurization agent 2 and desulfurization in the low temperature desulfurization section by the new desulfurization agent 3 Recycle Desulfurization agent 3 = Recycling desulfurization agent 2 + Low temperature desulfurization part desulfurization agent 3

Thus, the total desulfurization rate changes in the desulfurizing agent components recycled to the medium temperature desulfurization section in the first 2-3 cycles. However, the desulfurizing agent component is stabilized in the 5th to 6th cycles. Therefore, the total desulfurization rate is also calculated after the recycled desulfurization agent component is stabilized. Therefore, at a specific recycle ratio, the amount of unreacted desulfurization agent in the recycled desulfurization agent (for example, the amount of slaked lime) is constant (deviation <0.0000).
Convergence is determined by whether or not 1). Then, the conditions (1) to (3) of the present invention are applied to this convergence calculation (claim 3).
And requirements (a) to (c) of the invention according to claim 7) are taken into consideration.

Thus, Ab / S in the medium temperature desulfurization section and Ab / S in the low temperature desulfurization section satisfying the convergence conditions at various recycle ratios are obtained, and they are experimentally obtained in advance based on these Ab / S. The desulfurization rate in each desulfurization section is calculated by the following formula, and the total desulfurization rate is obtained using the calculated desulfurization rate. Ab in the low temperature desulfurization section of the desulfurizer under standard conditions
/ S and each desulfurization rate η _L in the low temperature desulfurization section and the medium temperature desulfurization section,
The relationship of η _M is calculated by the following equations (1), (2)
I asked from. Desulfurization rate η in hot desulfurization section and medium temperature desulfurization section
_L , η _M η _L = a (θ) × (As / S) ^{b (θ)} ... (1) η _M = c × (As / S) ^d (2) However, a (θ) and b (θ) are functions of the relative humidity θ, and c and d are constants.

Under normal pressure, at a temperature of 100 ° C. or higher, the relative humidity is negligible even in a saturated state of water vapor (for example, at 500 ° C., under normal pressure, in a saturated water vapor state, the relative humidity becomes 0.30%. It's just too much.)
There is no concept of relative humidity. As described above, since the relative humidity θ affects only the low temperature desulfurization section, the equation (1) takes into consideration the functions a (θ) and b (θ) depending on the relative humidity only in the low temperature desulfurization section. . Further, under the condition that the relative humidity is constant, it can be said that the relationship between Ab / S and the desulfurization rate can be approximated by a linear expression. However, in general, the relative humidity in the low temperature desulfurization section is controlled by the amount of water spray and is substantially constant (the standard condition is the operating condition in the following examples of the present invention), and therefore the functions a (θ) and b ( θ) is treated as a constant and the change in desulfurization rate due to relative humidity is not taken into consideration. Desulfurization rate η
It has been found that the estimated value and the actual measured value, which are predicted using the values approximated by the calculation formulas (1) and (2), can be estimated with an error of about ± 1%. Further, according to the SO ₂ concentration in the exhaust gas, the total desulfurization rate can be controlled by controlling the fresh desulfurizing agent supply amount to the low temperature desulfurization section in the low temperature desulfurization medium temperature recycling type flue gas desulfurization apparatus. .

[0016]

The present invention will be explained in more detail by the following examples, but it should not be construed as being limited thereto. Example 1 A case in which slaked lime is used as a desulfurizing agent to desulfurize exhaust gas from a coal-fired boiler will be described using an application example of the present invention to a desulfurization apparatus. In FIG. 1, coal is blown into the boiler 1, and then the temperature of the exhaust gas 6 is lowered by the air heater 3. Then, the coal ash in the exhaust gas is subjected to the high temperature dust collector 4
After being removed in step 1, the exhaust gas in which the slaked lime in the feeder 10 is sprayed from the spray port 5 is guided to the desulfurization tower 2. In the desulfurization tower 2 in which water is sprayed from the water spray port 7, the exhaust gas reacts with the desulfurization agent, and the reacted desulfurization agent is collected by the dust collector 8. Here, the cyclone is used for the dust collector 4 and the electric dust collector is used for the dust collector 8. However, it is sufficient to use the electric dust collector for the dust collector 4 and the dust collecting type filter dust collector for the dust collector 8. Performance is obtained. In particular, when a dust storage type filter dust collector is used for the dust collector 8, a part of the used desulfurizing agent recovered by the filter causes a desulfurization reaction, which leads to an improvement in the total desulfurization rate.

Using this apparatus, the desulfurization performance when A charcoal (sulfur content in coal: 2.5%, ash content: 12%) was burned was measured. However, slaked lime was used as the desulfurizing agent, and 2.0 times the molar ratio of slaked lime (hereinafter abbreviated as Ca / S = 2.0) was added to SO ₂ in the exhaust gas generated during combustion. At this time, the coal ash recovery amount (kg / min) and the slaked lime supply amount (kg / min) per unit time in the high temperature dust collector 4
Were about the same. Further, when water was sprayed so that the temperature inside the desulfurization tower 2 became 60 ° C, the partial pressure of water vapor in the gas was about 17% of the atmospheric pressure (relative humidity was about 85%, and the partial pressure of water vapor was about 10% before water spraying). )Met. After removing water in the gas at the outlet of the boiler 1 before spraying the desulfurizing agent,
_{When 2} concentrations were measured, it was 2000 ppm. After the desulfurizing agent is sprayed and before recycling, the dust collector 8
After removing water in the gas at the outlet, the SO ₂ concentration was measured and found to be 600 ppm. That is, 70% of SO _{2 in} the exhaust gas was removed.

After the above reaction is completed, the ash recovered from the dust collector 8 contains S in the exhaust gas per mol of the desulfurizing agent.
The reacted desulfurization agent having an O ₂ absorption amount (hereinafter, abbreviated as S / Ca) of 35.0% was contained. All of the reacted desulfurization agents are fed by the feeder 10 to the medium temperature desulfurization section 9 of the boiler (gas temperature 65
0 ° C). The above process is repeated and performed continuously. When the desulfurization rate becomes steady, S / Ca of the reacted desulfurization agent recovered by the dust collector 8 is 0.32 to 0.33, and the reacted desulfurization after the recycling reaction with the ash recovered by the dust collector 4 S / of a mixture of agents (abbreviated as a recycled recycling agent)
Ca is 0.42 to 0.43 (incombustible S and Ca in fuel
Was considered). As a result, the total desulfurization rate (above, total desulfurization rate) of the medium temperature desulfurization section and the low temperature desulfurization section was about 84 to 86%. In addition, the weight of the ash and the reacted desulfurization agent recovered by the dust collector was about 1.6 times greater when recycled, compared to when not recycled.

Comparative Example 1 As shown in FIG. 5, the dust collector 4 used in Example 1 using exactly the same coal as the fuel in the same combustion apparatus as in Example 1.
The characteristics were compared with those of the example 1 by utilizing the conventional technique which does not have the above.
Slaked lime was used as the desulfurization agent, and water was sprayed in the desulfurization tower 2 so that the temperature inside the tower became 60 ° C. As a result, the partial pressure of water vapor in the gas is about 17% of atmospheric pressure (about 8% relative humidity).
The water vapor partial pressure was 5%, and the water vapor partial pressure before water spraying was about 10%). After removing water in the gas at the boiler outlet 1 before spraying the desulfurizing agent, the SO ₂ concentration was measured to be 2000 pp
It was m. After the spraying of the desulfurizing agent and before the recycling, the SO ₂ concentration was measured at the outlet of the dust collector 8 after removing water in the gas, and it was 600 ppm. That is, 70% of SO _{2 in} the exhaust gas was removed. The ash recovered from the dust collector 8 after the above reaction was completed contained the reacted desulfurizing agent having S / Ca of 35.0%. A part of the desulfurized agent after the reaction is fed by the feeder 10 to the middle temperature desulfurization section 9 of the boiler (gas temperature 650 ° C.)
Supply to. At this time, an experiment was conducted with a recycling ratio of 0.5. The above process is repeated and performed continuously. When the desulfurization rate becomes steady, the desulfurization rate of the entire system is 79-80.
%Met. The weight of the powder collected by the dust collector 8 was about 1.6 times that of the case without recycling. This indicates that if the amount of collected dust is constant, the device of Example 1 according to the present invention can obtain a higher desulfurization rate.

Example 2 Under the same apparatus and exhaust gas conditions as in Example 1, the used desulfurizing agent recovered by the dust collector 8 was slurried and sprayed to the intermediate temperature desulfurizing section. The total desulfurization rate was about 86 to 88% by actual measurement, and although the operation was more complicated than that in Example 1, the desulfurization rate was slightly higher than that in Example 1. Example 3 Under the same equipment and exhaust gas conditions as in Example 1, a case was investigated in which magnesium hydroxide (Mg (OH) ₂ ) was used as a desulfurizing agent. Magnesium hydroxide absorbs CO ₂ during low temperature desulfurization to form MgCO _3
Since the decomposition temperature of ₃ is as low as around 500 ° C, the decomposition reaction can be caused again by performing the medium temperature desulfurization. Therefore, it is more advantageous than slaked lime for recycling. Under the condition that the molar ratio of MgCO _{3 to} SO ₂ in the exhaust gas was 2.0 times (Mg / S = 2), the total desulfurization rate was about 86%. Although the cost of the desulfurization agent was higher than that of slaked lime, it was possible to obtain a higher desulfurization rate than that of Example 1.

Example 4 B coal (with a sulfur content of 1.0%
%, Ash content 12%), the desulfurization performance was measured. However, slaked lime was used as the desulfurizing agent, and 2.0 mol of slaked lime (Ca / S = 2.0) was added in a molar ratio to SO ₂ in the exhaust gas generated during combustion. At this time, the amount of coal ash recovered per unit time in the high temperature dust collector 4 (kg / mi
n) and slaked lime supply rate (kg / min) are about 2.
5 times. After removing water in the gas at the boiler outlet 1 before spraying the desulfurizing agent, the SO ₂ concentration was measured and found to be 800 ppm. After the start of spraying the desulfurizing agent and before recycling, the water content in the gas was removed at the outlet of the dust collector 8 and the SO ₂ concentration was measured.
It was 0 ppm. That is, 7 out of SO _{2 in} the exhaust gas
0% has been removed.

After the above reaction is completed, the ash recovered from the dust collector 8 contains the reacted desulfurization agent having an SO ₂ absorption amount (S / Ca) of 35.0% per mol of the desulfurization agent. Was there. All of the reacted desulfurization agent is fed to the medium temperature desulfurization section 9 (gas temperature 650 ° C.) of the boiler by the feeder 10. The above process is repeated and performed continuously. S / C of the reacted desulfurization agent recovered by the dust collector 8 when the desulfurization rate becomes steady
a is 0.33, and S / Ca of the mixture of the ash recovered by the dust collector 4 and the reacted recycle agent after the recycling reaction is 0.
It was 43 (non-combustible S and Ca in fuel were taken into consideration).
As a result, the total desulfurization rate (hereinafter, total desulfurization rate) including the intermediate temperature desulfurization section and the low temperature desulfurization section was about 86%. In addition, the weight of the ash and the reacted desulfurization agent recovered by the dust collector was about 1.3 times as much as when they were recycled.

Comparative Example 2 Using the same apparatus as in Comparative Example 1 and using the same coal B as in Example 4, various characteristics of Example 4 were compared. The ash recovered from the dust collector 8 before the recycling contained the reacted desulfurization agent having an SO ₂ absorption amount (S / Ca) of 35.0% per mol of the desulfurization agent. A part of the reacted desulfurizing agent is supplied to the medium temperature desulfurizing section 9 (gas temperature 650 ° C.) of the boiler by the feeder 10. At this time, an experiment was conducted with a recycling ratio of 0.33. The above process is repeated and performed continuously. When the desulfurization rate becomes steady, the desulfurization rate of the entire system is 76-7.
It was 7%. Further, the weight of the powder collected by the dust collector 8 was about 1.3 times that of the case where it was not recycled. This means that if the amount of collected dust is constant, the fourth embodiment according to the present invention will be described.
It is possible to obtain a higher desulfurization rate than the apparatus of Comparative Example 2 and the smaller the ratio of sulfur content to ash content (S / ash) in the fuel, the more the desulfurization process of the present invention is compared with the prior art. It shows that the same capacity dust collector (combining the dust collectors 4 and 8) exhibits higher desulfurization performance.

Embodiment 5 This embodiment and subsequent embodiments are embodiments of the control device of the flue gas desulfurization apparatus of the present invention. In addition to the flue gas desulfurization apparatus of FIG. 1 described in the first embodiment, a feeder 10 ′ for supplying fresh desulfurizing agent to the flue immediately before the desulfurization tower 2 is added to the apparatus of the present embodiment shown in FIG. , A supply amount control device 11 for the desulfurizing agent in the feeders 10, 10 ', and an air flow rate measuring device 1 for the air supply passage of the boiler 1.
2. Boiler outlet SO ₂ concentration measuring device 1 at the boiler 1 outlet
3. Low-temperature part dust collector outlet SO ₂ concentration measuring device 14 at the outlet of the dust collector 8 and desulfurization tower inlet SO ₂ at the inlet of the desulfurization tower _2.
Each of the concentration measuring devices 15 is provided. The desulfurizing agent supply amount control device 11 calculates the desulfurizing agent supply amount based on the SO ₂ concentration and the air flow rate data measured by the respective measuring devices.
Control.

Using this apparatus, the desulfurization performance when A charcoal (sulfur content in coal: 2.5%, ash content: 12%) was burned was measured. However, slaked lime was used as the desulfurization agent, Ca / S, the temperature inside the desulfurization tower 2 by water spraying into the desulfurization tower 2, and the partial pressure of water vapor in the gas were the same as in Example 1. After removing water in the gas at the outlet of the boiler 1 before spraying the desulfurizing agent, the SO ₂ concentration was measured and found to be 2000 ppm. After the desulfurizing agent is sprayed and before the recycling is performed, after removing the moisture in the gas at the outlet of the dust collector 8,
The SO ₂ concentration was 600 ppm as in Example 1.
That is, 70% of SO _{2 in} the exhaust gas has been removed (hereinafter, this condition is referred to as standard operating condition).

At this time, the relationship between the desulfurization rate in the low temperature desulfurization section and Ca / S (FIG. 3) and the relationship between Ca / S and the desulfurization rate in the intermediate temperature desulfurization section (FIG. 4) were determined. As in Example 1, the ash recovered from the dust collector 8 during the standard operating conditions contained the reacted desulfurization agent having an SO ₂ absorption amount (S / Ca) of 35.0% per mol of the desulfurization agent. It was The reacted desulfurization agent is collected in batches at regular intervals (here, 3 hours), and all the collected desulfurization agents are fed by the feeder 10 at the same temperature interval as the batch (here, 3 hours) to the boiler middle temperature desulfurization section 9 (gas. Temperature 650
℃). The above process is repeated and performed continuously. At this time, Table 1 shows an analysis of S / Ca and C / Ca of the used desulfurizing agent collected by the dust collector 8.

[0027]

[Table 1] Comparison of this result and the experimental results of FIGS. 3 and 4 with the estimated value using the value approximated by the formula of desulfurization rate η = a × (Ca / S) ^{b in} the low temperature desulfurization section and the intermediate temperature desulfurization section is also compared. They are also shown together. It was found that the estimated value and the actually measured value can be estimated with an error of about ± 1%.

Further, under such conditions, when the desulfurization apparatus is in a steady state, Ca / S in the low temperature desulfurization section becomes 2.5 times, and the slaked lime is supplied by the information from the inlet SO ₂ concentration measuring device 15 of the desulfurization tower 2. When the system was operated with the amount controlled, the total desulfurization rate (=
(Boiler outlet SO ₂ concentration-dust collector outlet SO ₂ concentration) / boiler outlet SO ₂ concentration) was about 82% in the rising state (the state where the used desulfurizing agent at the outlet has not been recycled). Total desulfurization rate after recycling used desulfurization agent 8
Stabilized to 5 to 86% (this desulfurization rate is hereinafter referred to as standard desulfurization rate). Conventional desulfurization agent (here slaked lime) supply rate is about 70%
However, by using the control method utilizing the present invention, the desulfurization rate was sufficiently high from the rising state. As a result of the above, by using the desulfurization apparatus control method of the present invention, the desulfurization rate is stabilized when the overall desulfurization rate of the low temperature desulfurization medium temperature recycling type flue gas desulfurization apparatus is unstable, such as at the time of starting the apparatus. It has become possible. It should be noted that, in all of the following Examples, since the SO ₂ concentration in the exhaust gas from the boiler fuel can be treated as a constant, the SO ₂ concentration function should not be included in the calculation of the desulfurization rate in the intermediate temperature desulfurization section. did.

Example 6 Under the same apparatus and exhaust gas conditions as in Example 5, the used desulfurizing agent recovered by the dust collector was slurried and sprayed in the medium temperature range. With the same control method as in Example 5, the total desulfurization rate in the standing state was about 85%, the total desulfurization rate in the steady state was about 86 to 88%, and the operation is more complicated than that in Example 5, but The desulfurization rate was slightly higher than that of Example 5. Example 7 Under the same apparatus and exhaust gas conditions as in Example 5, a study was also conducted on the case where magnesium hydroxide (Mg (OH) ₂ ) was used as the desulfurizing agent. Under the same control as in Example 5, the rising desulfurization rate was 83% and the total desulfurization rate was about 86%. Although the cost of the desulfurization agent was higher than that of slaked lime, it was possible to obtain a higher desulfurization rate than that of Example 5.

Example 8 In order to reduce the output of the combustion apparatus from the steady operation of the apparatus of Example 5, both the coal supply rate and the air flow rate were reduced to 60% (batch interval was 3 hours). Here, S at the exit of boiler 1
When the supply amount of slaked lime in the low temperature desulfurization section and the medium temperature desulfurization section with respect to the O ₂ flow rate is fixed and controlled at Ca / S = 2.0 (control condition), the slaked lime content is changed with respect to the SO ₂ concentration at the desulfurization tower 2 inlet. When the supply amount is controlled, that is, Ca / in the low temperature desulfurization section
The case where the slaked lime supply amount was controlled so that S was Ca / S = 2.5 (control condition) was compared. In the control condition,
Since the supply amount of the desulfurizing agent in the medium-temperature desulfurization unit is the same as in the steady state, Ca / S in the medium-temperature desulfurization unit is 1.67 times (medium-temperature desulfurization unit C
Since a / S = 2.0 and Ca / S = 1.2 in Table 1), the value is considerably higher than the standard desulfurization rate (about 90 to 92).
%), And the desulfurizing agent used for low temperature desulfurization is wasted accordingly. On the other hand, the total desulfurization rate can be suppressed to (about 86 to 88%) if controlled by the control condition method. Moreover, when the operation is returned to the steady operation after the operation for 6 hours in the reduced output state, the total desulfurization rate becomes 80 to 82% because the Ca / S of the intermediate temperature desulfurization section becomes about 0.7 under the control conditions. Then 84-8
The total desulfurization rate was 6% and was stable in the range of 84 to 88% regardless of the output fluctuation of the output device of the combustion device.

According to the operation performance evaluation method of the flue gas desulfurization apparatus of this example, the unreacted lime / total supply desulfurization agent was measured by measuring the sulfur concentration and carbon concentration in the desulfurization agent after exhaust gas desulfurization in the low temperature desulfurization section. The flue gas desulfurization device may be controlled by accurately obtaining the molar ratio (obtained by subtracting the sulfur equivalent of the fuel (obtained by measuring the carbon concentration) from the sulfur concentration in the total solid content). In addition, even when slurry was formed during the recycling to the medium temperature desulfurization section of the reacted desulfurization agent, the same examination as above was performed by changing the desulfurization rate of the low temperature desulfurization section. It was confirmed that the estimation can be performed with the same accuracy. In the above examples, slaked lime was used as the desulfurizing agent, but calcium oxide, calcium carbonate, magnesium carbonate, sodium hydroxide or the like may be used.

[0032]

EFFECTS OF THE INVENTION According to the present invention, the disadvantage of increasing the capacity of the dust collector, which is generated by the conventional low temperature desulfurization medium temperature recycling method performed to obtain a sufficient desulfurization rate, is compensated, and the generated powder is It becomes possible to further improve the desulfurization rate compared to the amount. Furthermore, if the above characteristics are used to reduce the amount of desulfurizing agent supplied / SO ₂ flow rate in the exhaust gas (Ab / S), the amount of desulfurizing agent supplied can be reduced as compared with the case of using the conventional recycling method, and sufficient total desulfurization can be achieved. It is possible to achieve both the rate and the reduction of operating cost. Further, according to the present invention, in the operating method of the flue gas desulfurization apparatus of the low temperature desulfurization medium temperature recycling method of the present invention performed to obtain a sufficient desulfurization rate, it is possible to calculate the total desulfurization rate under any condition, Rather than controlling the desulfurization agent supply method by the molar ratio with the conventional boiler outlet SO ₂ flow rate,
The low temperature desulfurization unit Ab / S in the steady state is calculated, and the low temperature desulfurization unit A is calculated.
By controlling b / S to be constant, the desulfurization rate can be controlled to a sufficiently high value even when the desulfurization apparatus is in a standing state. As a result, it has become possible to stabilize the desulfurization rate of the entire apparatus in any state.

[Brief description of drawings]

FIG. 1 is a flow sheet and a schematic view of a desulfurization device according to a first embodiment of the present invention.

FIG. 2 is a flow sheet and a schematic diagram of a desulfurization apparatus according to a fifth embodiment of the present invention.

FIG. 3 is a diagram of test results showing the relationship between the desulfurization rate of the low temperature desulfurization section and Ca / S in the method for operating the desulfurization apparatus of Example 5 of the present invention.

FIG. 4 is a diagram of test results showing the relationship between the desulfurization rate of the intermediate temperature desulfurization section and Ca / S in the operating method of the desulfurization apparatus of Example 5 of the invention.

FIG. 5 is a schematic diagram of a desulfurization apparatus including a conventional low temperature desulfurization medium temperature recycling process.

FIG. 6 is a schematic view of a conventional dry desulfurization apparatus of a method of spraying a desulfurizing agent onto a typical airflow layer.

[Explanation of symbols]

1 ... Boiler, 2 ... Desulfurization tower, 3 ... Air heater, 4 ... High temperature dust collector, 5 ... Desulfurizing agent spray port, 6 ... Exhaust gas, 7 ... Water spray port, 8 ... (Low temperature part) dust collector, 9 ... Medium temperature Desulfurization unit, 10,
10 '... Feeder, 11 ... Desulfurizing agent supply amount control device, 12
... Blower amount measuring device, 13 ... Boiler outlet SO ₂ concentration measuring device, 14 ... Low temperature part dust collector outlet SO ₂ concentration measuring device, 1
5 ... SO ₂ concentration measuring device at desulfurization tower inlet

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location B01D 53/34 ZAB (72) Inventor Sakaguchi Anei 3-36 Takaracho, Kure-shi, Hiroshima Babcock Hitachi Ltd. Kure Institute

Claims (10)

[Claims] 1. Sulfur oxidation in exhaust gas by using a compound of at least one metal of an alkali metal or an alkaline earth metal as a desulfurizing agent and supplying the compound to a low temperature desulfurization section of an exhaust gas passage of a combustion device at a temperature of 200 ° C. or lower. In a flue gas desulfurization device that recovers a desulfurizing agent containing an unreacted desulfurizing agent with a dust collector after the reaction with a substance, the used desulfurizing agent containing the unreacted desulfurizing agent recovered with the dust collecting device is used in the exhaust gas passage. Temperature 500 ~ 900 ℃
The flue gas desulfurization apparatus characterized in that after being supplied to the medium-temperature desulfurization section and reacted with the sulfur oxides of the exhaust gas, it is recovered at the upstream side of the desulfurizing agent supply position in the low-temperature desulfurization section. 2. Sulfur oxidation in exhaust gas by using a compound of at least one metal of an alkali metal or an alkaline earth metal as a desulfurizing agent and supplying it to a low temperature desulfurization section of an exhaust gas passage of a combustion device at a temperature of 200 ° C. or lower. In a flue gas desulfurization device in which a desulfurizing agent containing an unreacted desulfurizing agent is collected by a dust collector after reacting with a substance, water is added to a used desulfurizing agent containing an unreacted desulfurizing agent collected by the dust collecting device. After making it into a slurry state,
The flue gas desulfurization is characterized in that the temperature of the exhaust gas passage is supplied to a medium-temperature desulfurization unit of 500 to 900 ° C., reacted with the sulfur oxides of the exhaust gas, and then recovered at a portion upstream of the desulfurizing agent supply position in the low-temperature desulfurization unit. apparatus. 3. Use of a compound of at least one metal of an alkali metal or an alkaline earth metal as a desulfurizing agent, and supply the compound to a low temperature desulfurization section of an exhaust gas passage of a combustion device at a temperature of 200 ° C. or lower to oxidize sulfur in exhaust gas. After reacting with the substance, the desulfurizing agent containing the unreacted desulfurizing agent is collected by the dust collector, and the used desulfurizing agent containing the unreacted desulfurizing agent collected by the dust collecting apparatus is used at the exhaust gas passage temperature of 500 to 900 ° C. Supply to the medium temperature desulfurization section of
In a flue gas desulfurization device that recovers the sulfur oxides of the exhaust gas at a portion upstream of the desulfurizing agent supply position in the low temperature desulfurization section, (a) a temperature 500 including the low temperature desulfurization section of the desulfurization agent reacted in the intermediate temperature section. The desulfurization rate of the desulfurization agent supplied to the intermediate temperature desulfurization section recovered by the dust collector (b) per unit time (unreacted) 2 of the desulfurizing agent supply mole number) / (sulfur oxide mole number in the exhaust gas) and the sulfur oxide concentration in the exhaust gas
Determined from the desulfurization rate of the medium-temperature desulfurization section alone, which has been evaluated in advance as one parameter, (c) the desulfurization rate in the low-temperature desulfurization section is (mol desulfurizing agent supply moles) per unit time in the low-temperature desulfurization section / The total desulfurization rate is calculated under the condition that (the number of moles of sulfur oxides in the exhaust gas) and the relative humidity of the low temperature desulfurization part are used as parameters, and that the concentration of sulfur oxides in the exhaust gas is not used as a parameter. A method for evaluating the operational performance of a flue gas desulfurization device, characterized by evaluating the operational performance of 4. The method for evaluating operational performance of a flue gas desulfurization apparatus according to claim 3, wherein (desulfurizing agent supply mole number) / (sulfur oxide mole number in exhaust gas) per unit time and low temperature in the low temperature desulfurization section. It is possible to control the total desulfurization rate of the flue gas desulfurization unit by changing at least one of (the number of moles of unreacted desulfurizing agent supplied) / (the number of moles of sulfur oxides in the exhaust gas) per unit time in the desulfurization section. A method for controlling a flue gas desulfurization device characterized. 5. The method for evaluating operational performance of a flue gas desulfurization apparatus according to claim 3, wherein at least one of the low temperature desulfurization section and the intermediate temperature desulfurization section in a steady state during recycling of the desulfurization agent is used per unit time. (Desulfurizing agent supply mole number) / (low temperature desulfurization unit inlet sulfur oxide inflow mole number) is estimated, and the estimated mole ratio is set to a value estimated from the beginning of operation, so that the flue gas desulfurization apparatus is brought into a steady state faster. A method for controlling a flue gas desulfurization apparatus, which is characterized by the above. 6. The unreacted lime / total supply by measuring the sulfur concentration and carbon concentration in the desulfurization agent after exhaust gas desulfurization in the low temperature desulfurization section by the method for evaluating the operation performance of the flue gas desulfurization apparatus according to claim 3. A method for controlling a flue gas desulfurization device, characterized in that the molar ratio of a desulfurizing agent is accurately obtained. 7. Sulfur oxidation in exhaust gas by using a compound of at least one metal of an alkali metal or an alkaline earth metal as a desulfurizing agent and supplying it to a low temperature desulfurization section of an exhaust gas passage of a combustion device at a temperature of 200 ° C. or lower. After reacting with the substance, the desulfurizing agent containing the unreacted desulfurizing agent is collected by the dust collector, and water is added to the used desulfurizing agent containing the unreacted desulfurizing agent collected by the dust collecting apparatus to form a slurry state. After that, the temperature of the exhaust gas path is 500 ~
In a flue gas desulfurization device that is supplied to a medium-temperature desulfurization unit at 900 ° C. and reacted with sulfur oxides of exhaust gas, and then is recovered in an upstream portion of a desulfurizing agent supply position in the low-temperature desulfurization unit, (a) reacted in the middle-temperature portion. The desulfurization rate of the desulfurization agent supplied to the intermediate temperature desulfurization section recovered by the dust collector is the intermediate temperature desulfurization, ignoring the desulfurization reaction in the exhaust gas passage region at a temperature of 500 ° C or less including the low temperature desulfurization section of the desulfurization agent. Medium-temperature desulfurization evaluated in advance using two parameters: (number of moles of unreacted desulfurization agent supplied) / (number of moles of sulfur oxides in exhaust gas) per unit time and concentration of sulfur oxides in exhaust gas (C) The desulfurization rate in the low temperature desulfurization section is determined from the desulfurization rate of the single part, and the (desulfurizing agent supply mole number) / (sulfur oxide mole number in exhaust gas) per unit time in the low temperature desulfurization section and the low temperature Relative humidity of the desulfurization part was determined as a parameter. Sulfur oxides concentration in the exhaust gas is not a parameter, determine the overall desulfurization rate on the condition that the operating performance evaluation method of flue gas desulfurization apparatus and evaluating the operation performance of the flue gas desulfurization system. 8. The method for evaluating operational performance of a flue gas desulfurization apparatus according to claim 7, wherein (desulfurizing agent supply mole number) / (sulfur oxide mole number in exhaust gas) per unit time and low temperature in the low temperature desulfurization section. It is possible to control the total desulfurization rate of the flue gas desulfurization unit by changing at least one of (the number of moles of unreacted desulfurizing agent supplied) / (the number of moles of sulfur oxides in the exhaust gas) per unit time in the desulfurization section. A method for controlling a flue gas desulfurization device characterized. 9. The method for evaluating operational performance of a flue gas desulfurization apparatus according to claim 7, wherein at least one of the low temperature desulfurization section and the medium temperature desulfurization section at a desulfurization section in a steady state during desulfurization agent recycling (Desulfurizing agent supply mole number) / (low temperature desulfurization unit inlet sulfur oxide inflow mole number) is estimated, and the estimated mole ratio is set to a value estimated from the beginning of operation, so that the flue gas desulfurization apparatus is brought into a steady state faster. A method for controlling a flue gas desulfurization apparatus, which is characterized by the above. 10. The unreacted lime / total supply by measuring the sulfur concentration and carbon concentration in the desulfurizing agent after exhaust gas desulfurization in the low temperature desulfurization section by the method for evaluating the operation performance of the flue gas desulfurization apparatus according to claim 7. A method for controlling a flue gas desulfurization device, characterized in that the molar ratio of a desulfurizing agent is accurately obtained.