JP3752133B2 - Absorbent replenishment method in flue gas desulfurization method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for replenishing a magnesium compound used in a magnesium hydroxide desulfurization method in which sulfur oxides contained in exhaust gas are fixedly removed using a magnesium compound as a desulfurization agent.
[0002]
[Prior art]
Desulfurization process that removes sulfur oxides in exhaust gas by bringing gas exhaust into gas-liquid contact with magnesium compounds (magnesium hydroxide, etc. obtained from magnesium hydroxide, magnesium oxide, magnesium carbonate, or dolomite) And an oxidation process in which the desulfurization process liquid is oxidized to convert contained magnesium sulfite into magnesium sulfate, and a metathesis process in which magnesium sulfate undergoes a metathesis reaction with a basic calcium compound to form magnesium hydroxide and dihydrate gypsum, The magnesium hydroxide and dihydrate gypsum obtained in the metathesis process are sent directly to the desulfurization process through a storage process for temporarily storing magnesium hydroxide and dihydrate gypsum, and the contained magnesium hydroxide is used again as a desulfurization agent. Magnesium hydroxide for removing gypsum from desulfurization process or oxidation process Umm desulfurization process are well known.
[0003]
In this magnesium hydroxide desulfurization method, magnesium hydroxide used as a desulfurizing agent is circulated in the system while changing the form of magnesium sulfite, magnesium sulfate, and magnesium hydroxide again. However, in order to prevent the accumulation of dust, chlorine compounds and the like in the exhaust gas, it is necessary to partially discharge as blow water, and a part of the magnesium compound circulating in the system is discharged together with this blow water , resulting in loss.
[0004]
Conventionally, in order to replenish this loss of magnesium, magnesium hydroxide is supplied as a 30-35% by weight slurry to a recovered magnesium hydroxide tank via a line L1 as shown in FIG.
On the other hand, the concentration of the magnesium compound contained in the blown water discharged out of the system varies depending on the place where it is extracted. However, even if it is extracted from any place, its concentration is extremely low compared to the concentration of magnesium hydroxide to be replenished. Therefore, the magnesium / water balance in the system changes due to long-term operation, making it impossible to continue operation. As a countermeasure, a recovered magnesium hydroxide tank has been provided as a kind of buffer tank, but the change in the water level of the recovered magnesium hydroxide tank has become extremely large, and stable operation has been difficult.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for replenishing a magnesium-based compound that keeps the magnesium / water balance constant, which is a problem of the prior art.
[0006]
[Means for Solving the Problems]
The present invention, oxidation step of contacting a desulfurization process for removing sulfur oxides contained the magnesium compound in the exhaust gas exhaust gas and gas-liquid contacting the absorbent, a gas containing oxygen desulfurization process liquid When the oxidation step treatment liquid to a basic calcium compound and metathesis reaction include a double decomposition step of the magnesium hydroxide and gypsum, stores did Tsu had magnesium hydroxide and gypsum obtained in the double decomposition step In the desulfurization method in which the magnesium hydroxide contained in the system is sent to the desulfurization process and / or oxidation process through the storage process and used again as a desulfurization agent or neutralizer, the magnesium compound to be supplemented and the magnesium / water molar balance in the system are constant. a replenishment method of the absorbent in the flue gas desulfurization process and amount of water that replenishes in the system to be kept,
The storage step includes a storage tank that functions as a buffer for the circulating liquid containing magnesium compound in the system. (1) When the liquid level of the storage tank is higher than a specified level, the slurry containing magnesium hydroxide is desulfurized from the storage step. Supplying the magnesium compound to be replenished to the desulfurization process and / or the oxidation process when the liquid level falls below a specified level after being supplied to the process and / or the oxidation process, and (2) the liquid level of the storage tank is at a specified level. If lower, it is a method of replenishing the absorbent in the flue gas desulfurization method in which the magnesium compound to be replenished is immediately replenished to the desulfurization step and / or the oxidation step.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to the drawings.
FIG. 1 shows a storage step (recovered hydroxylation) of temporarily storing a mixed slurry of magnesium hydroxide and dihydrate gypsum produced in a metathesis tank 2 in which a metathesis reaction is carried out, in the method of replenishing a magnesium compound as an absorbent according to the present invention. A step of replenishing magnesium tank 1) with supplementary magnesium hydroxide (slurry) is shown.
In the figure, the oxidation step, the dihydrate gypsum removal step, and the like are omitted.
[0008]
In FIG. 1, a recovered magnesium hydroxide tank 1 is a tank for storing a mixed slurry of magnesium hydroxide and dihydrate gypsum produced in a metathesis tank 2, and functions as a buffer for circulating liquid containing magnesium compounds in the system. is there. The mixed slurry is sent from the recovered magnesium hydroxide tank 1 to the desulfurization tower and / or oxidation tank (not shown) via the pump and the line L5, and the contained magnesium hydroxide is used as the desulfurizing agent and / or neutralizing agent. Is done.
[0009]
Since impurities such as dust or chlorine contained in the gas accumulate in the system during a long-term operation, it is necessary to discharge the impurities accumulated as blow water out of the system. Since the magnesium compound is discharged together with the blow water in a form corresponding to the portion from which the blow water is extracted, it is necessary to replenish it. Magnesium hydroxide corresponding to the amount of magnesium contained in the blown water and discharged out of the system is replenished, but the magnesium hydroxide for replenishment usually has a predetermined amount via line L1 as a 30-35% by weight slurry. The recovered magnesium hydroxide tank 1 is supplied. Since the concentration of magnesium contained in the blown water is extremely low as compared with the concentration of magnesium in the magnesium hydroxide slurry to be replenished, the water in the system decreases and the magnesium / water molar balance cannot be maintained. In order to maintain this balance, water corresponding to blow water is supplied from the line L2 simultaneously with the supply of the supplementary magnesium hydroxide slurry so that the magnesium / water molar balance in the system is kept constant. The amount of water to be replenished can be calculated in consideration of the amount discharged out of the system as blow water, the amount supplied as calcium hydroxide slurry, the amount supplied as magnesium hydroxide slurry, and the like. When the system is in a steady state, it is sufficient to supply an amount of water proportional to the amount of magnesium hydroxide to be replenished.
[0010]
FIG. 2 shows an example in which magnesium hydroxide (slurry) is replenished to the desulfurization step (desulfurization tower 3). The means and amount to be supplied are the same as in the example of FIG. In FIG. 2, the metathesis tank 2 in FIG. 1 and the lines L3 and L4 leading to the recovered magnesium hydroxide tank 1 are omitted. In this example, a liquid level gauge is installed in the recovered magnesium hydroxide tank 1. When the position of the liquid level is lower than the specified position, the magnesium hydroxide slurry is supplemented to the desulfurization tower 3 and / or the oxidation tank (not shown) via the line L1. An amount of water in which the magnesium / water molar balance in the system is kept constant is supplied from the line L2 simultaneously with the supply of the supplementary magnesium hydroxide slurry. When the liquid level of the recovered magnesium hydroxide tank 1 is higher than the specified value, the replenishment to the desulfurization tower 3 and / or the oxidation tank is temporarily suspended, and only the mixed slurry is removed from the recovered magnesium hydroxide tank 1 via the line L6. Supply. Thereafter, when the liquid level of the recovered magnesium hydroxide tank 1 falls below the specified liquid level, the magnesium hydroxide slurry is replenished. This operation is repeated according to the liquid level position of the recovered magnesium hydroxide tank 1. This operation can be automatically performed by a computer.
[0011]
In the method of FIG. 2, a water supply line for controlling the liquid level of the desulfurization tower 3 is usually installed. In this case, although a water replenishment line may be installed independently, it can also be used together with the line L2.
[0012]
【Example】
Example 1
It implemented using the apparatus shown in FIG.
A slurry containing 1.5 wt% magnesium hydroxide is supplied from the line L3 to the recovered magnesium hydroxide tank at 87 kg / h, and a mixed slurry containing 1.5 wt% magnesium hydroxide and 30 wt% dihydrate gypsum is supplied from the line L4. Was extracted at 15 kg / h and supplied to the recovered magnesium hydroxide tank. From line L1, 30 wt% magnesium hydroxide for replenishment was 0.2 kg / h, and at the same time, 3.8 kg / h of water was supplied from line L2 to the recovered magnesium hydroxide tank. From the line L5, a slurry containing 1.5% by weight of magnesium hydroxide and 4.3% by weight of dihydrate gypsum was sent to a desulfurization tower and an oxidation tank at 106 kg / h.
The molar ratio of magnesium / water when the magnesium hydroxide slurry supplied from the lines L1 and L2 and water are added is set equal to the molar ratio of magnesium and water blown from the gypsum removal step. The change in the water level of the recovered magnesium hydroxide tank in the long-term operation was stable as shown in FIG.
[0013]
Example 2
It implemented using the apparatus shown in FIG.
A mixed slurry containing 1.5% by weight of magnesium hydroxide and 4.5% by weight of dihydrate gypsum was supplied to the desulfurization tower at a rate of 102 kg / h from line L6. From line L1, magnesium hydroxide for replenishment was supplied at a concentration of 30% by weight at 0.2 kg / h, and at the same time 3.8 kg / h of water was supplied from line L2 to the desulfurization tower. The molar ratio of magnesium / water when the magnesium hydroxide slurry and water supplied from the lines L1 and L2 are combined is set equal to the molar ratio of magnesium and water blown from the gypsum removal step. The change in the water level of the recovered magnesium hydroxide tank in the long-term operation was gentle as shown in FIG.
[0014]
Comparative Example 1
It implemented using the apparatus shown in FIG.
A slurry containing 1.5 wt% magnesium hydroxide is supplied from the line L3 to the recovered magnesium hydroxide tank at 87 kg / h, and a mixed slurry containing 1.5 wt% magnesium hydroxide and 30 wt% dihydrate gypsum is supplied from the line L4. Was extracted at 15 kg / h and supplied to the recovered magnesium hydroxide tank. The liquid level of the recovered magnesium hydroxide tank was low, and 30 wt% magnesium hydroxide for replenishment was temporarily supplied from the line L1 to the recovered magnesium hydroxide tank at 2.0 kg / h. A slurry containing 2.0% by weight of magnesium hydroxide and 4.3% by weight of dihydrate gypsum was sent to the desulfurization tower at 78 kg / h from the line L5. As a result, the balance of the flow rate was lost, and the liquid level of the recovered magnesium hydroxide tank suddenly increased. The liquid level exceeded a specified position and the replenishment of the magnesium hydroxide slurry was stopped, but the liquid level of the recovered magnesium hydroxide tank rose and then began to drop. This phenomenon was repeated.
As shown in FIG. 3, the vertical amplitude of the recovered magnesium hydroxide tank in the long-term operation was considerably large.
[0015]
【The invention's effect】
In the method of the present invention, when the magnesium salt contained in the blown water and discharged outside the system is supplemented as magnesium hydroxide, water is added so that the magnesium / water molar balance in the system is maintained within a certain range. Since the water balance in the system is kept constant, the operation of the desulfurization apparatus is stabilized.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a method for replenishing a recovered magnesium hydroxide tank with magnesium hydroxide slurry and water according to the present invention.
FIG. 2 is a diagram showing an example of a method for replenishing a desulfurization tower with magnesium hydroxide slurry and water according to the present invention.
FIG. 3 is a diagram showing a change in liquid level of a recovered magnesium hydroxide tank.
FIG. 4 is a diagram showing a conventional magnesium hydroxide slurry replenishment method.
[Explanation of symbols]
1 recovered magnesium hydroxide tank 2 metathesis tank 3 desulfurization tower L1-L6 piping

Claims (1)

A desulfurization process that removes sulfur oxides contained in the exhaust gas by contacting the exhaust gas with the exhaust gas using a magnesium compound as an absorbent, an oxidation process that contacts the desulfurization process liquid with a gas containing oxygen, and an oxidation process treatment desulfurizing liquid basic calcium compound to the metathesis reaction include a double decomposition step of the magnesium hydroxide and gypsum, via a storage step of storing did Tsu had magnesium hydroxide and gypsum obtained in the double decomposition step In the desulfurization method in which magnesium hydroxide contained in the process and / or oxidation process is used again as a desulfurizing agent or neutralizing agent, the magnesium compound to be replenished and the amount in which the magnesium / water molar balance in the system is kept constant a replenishment method of the absorbent in the flue desulfurization how to replenish the water in the system,
The storage step includes a storage tank that functions as a buffer for the circulating liquid containing magnesium compound in the system. (1) When the liquid level of the storage tank is higher than a specified level, the slurry containing magnesium hydroxide is desulfurized from the storage step. Supplying the magnesium compound to be replenished to the desulfurization process and / or the oxidation process when the liquid level falls below a specified level after being supplied to the process and / or the oxidation process, and (2) the liquid level of the storage tank is at a specified level. A method of replenishing an absorbent in a flue gas desulfurization method in which when it is lower, the magnesium compound to be replenished is immediately replenished to the desulfurization step and / or the oxidation step .

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