JPS6410254B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a flue gas desulfurization method for separating and removing sulfur dioxide contained in flue gas generated from a metal smelting process or the like.

[Conventional technology]

The flue gas desulfurization method using a basic aqueous aluminum sulfate solution is generally carried out according to the flow shown in FIG. That is, the exhaust gas is introduced into the absorption tower 2 through the inlet line 1, and the sulfur dioxide contained in the exhaust gas is absorbed into the basic aluminum sulfate aqueous solution introduced through the line 3, thereby producing aluminum sulfite. The exhaust gas from which the sulfur dioxide has been removed is sent to the stack through the outlet line 4 and discharged into the atmosphere. On the other hand, the aluminum sulfite aqueous solution is led to a pump tank 5 consisting of a tank and a pump, sent to an oxidation tower 6, and air line 7.
The aluminum sulfate is oxidized by the air introduced, and aluminum sulfate is produced, and the air is discharged through line 8. The aluminum sulfate aqueous solution from the oxidation tower 6 is introduced into a branch pipe (branching step) 9 by overflow, a part of which is returned to the absorption tower 2, and the remainder is sent to the neutralization tank 10. The aluminum sulfate aqueous solution introduced into the neutralization tank 10 is neutralized by the calcium carbonate introduced from the calcium carbonate slurry tank 11 to produce calcium sulfate and basic aluminum sulfate, which are sent to the filter 12 to produce sulfuric acid. Calcium 13 is separated and removed, and the liquid basic aluminum sulfate aqueous solution is circulated to the absorption tower 2 via the circulation line 3.

As shown in the above flow, normally absorption tower 2 and oxidation tower 6
Between the absorption tower 2 and the oxidation tower 6, there is a circulation system that sends the aluminum sulfite aqueous solution from the absorption tower 2 to the oxidation tower 6, and returns a part of the aluminum sulfite aqueous solution derived from the oxidation tower 6 in the branching step 9 to the absorption tower 2. A cycle is set up, and the remaining aqueous solution derived from the oxidation tower and returned to the absorption tower 2 is sent to the neutralization tank 10. When operating this, it is necessary to maintain a constant amount of liquid in the oxidation tower and absorption tower in order to balance the aqueous solution in the entire system. The gas-liquid ratio was always kept constant. In that case, the content of sulfur dioxide in the exhaust gas fluctuates, but no matter how much it fluctuates, the concentration of sulfur dioxide at the outlet of absorption tower 2 must be kept low. It is adjusted to the load amount. Therefore, except at maximum load, excess air is blown into the
There was an inconvenience that energy was wasted.

[Problem that the invention seeks to solve]

The present inventors conducted various experiments in order to blow in an amount of air corresponding to the amount of sulfur dioxide loaded. However, when changing the amount of air blown into the oxidation tower, the amount of air relative to the aqueous solution in the oxidation tower fluctuates. Even if the liquid depth in the pump tank is controlled to be constant, the amount of liquid held in the absorption tower (true amount of liquid) will fluctuate, resulting in insufficient absorption of sulfur dioxide, and reducing the concentration of sulfur dioxide in the exhaust gas at the outlet of the absorption tower. It was difficult to maintain it at a low constant value.

The present invention was achieved through further research based on the results of the above experiments, and it is possible to maintain a constant amount of liquid held in the absorption tower (true liquid amount) while adjusting the amount of air according to the amount of sulfur dioxide loaded. The purpose of the present invention is to provide a flue gas desulfurization method using a basic aluminum sulfate aqueous solution that can be blown with.

[Means for solving problems]

The present invention has been made to achieve the above-mentioned object, and its means are such that, in a flue gas desulfurization method using basic aluminum sulfate, an amount of sulfur dioxide corresponding to the amount of sulfur dioxide absorbed in an absorption tower is added to an oxidation tower. By blowing in air and correcting the liquid depth control value of the pump tank according to the apparent specific gravity determined in advance from the gas-liquid ratio of the aqueous solution and air, the amount of liquid held in the absorption tower (true liquid amount) can be adjusted. This is a flue gas desulfurization method that maintains a constant value.

[Effect]

Since the method of the present invention has the above-mentioned configuration, the amount of air corresponding to the amount of sulfur dioxide absorbed in the absorption tower is blown into the oxidation tower, and the gas-liquid ratio of the aqueous solution and air in the oxidation tower is , by correcting the liquid depth control value of the pump tank according to the apparent specific gravity determined in advance, and by changing the amount of aqueous solution in the pump tank according to the increase or decrease of the true aqueous solution in the oxidation tower. , it is possible to prevent the real aqueous solution in the absorption tower from increasing or decreasing, and the amount of liquid held in the absorption tower can be kept constant. Therefore, an energy-saving operation is possible without using a large amount of air unnecessarily. In addition, the sulfur dioxide concentration in the exhaust gas at the outlet of the absorption tower can be maintained at a low concentration below the standard value at all times.

〔Example〕

The method of the present invention will be explained below with reference to the drawings.

FIG. 1 shows an example of the method of the present invention.
Components that are the same as those in the figures are given the same reference numerals and their explanations will be omitted.

Detectors 14 and 15 are installed in the exhaust gas inlet line 1 and outlet line 4, and the meter 16 continuously measures the amount of exhaust gas and the sulfur dioxide concentration. 2
Calculate the amount of sulfur dioxide absorbed by the aqueous solution. A signal based on this calculation operates the regulator 17 of the air line 7 to blow into the oxidation tower 6 an amount of air corresponding to the absorbed sulfur dioxide.

In the oxidation tower 6, the gas-liquid state of the aqueous solution changes depending on the amount of air blown in from the air line 7, so its apparent specific gravity changes. Therefore, the apparent specific gravity for various gas-liquid ratios is stored in advance in the microcomputer, and the set value of the liquid depth to be controlled by the pump tank 5 is corrected with the apparent specific gravity value according to the gas-liquid ratio at that time. By changing the amount, the amount of liquid held in the absorption tower 2 (true amount of liquid) is kept constant. That is, for example, when the amount of air blown into the oxidation tower 6 is increased, the apparent liquid volume within the oxidation tower 6 does not change, but the amount of air within the oxidation tower 6 increases, so that the true liquid inside the oxidation tower 6 increases. quantity decreases. As a result, if the liquid depth in the pump tank 5 is not controlled (maintained constant) as in the conventional case, the true liquid amount in the absorption tower 2 will increase, but in this embodiment Since the liquid depth of the pump tank 5 is controlled so that the excess aqueous solution in the absorption tower 2 can be collected into the pump tank 5, the amount of liquid held in the absorption tower 2 (true liquid amount) is kept constant. be done.

Then, through the operations described above, while keeping the true liquid volume in the absorption tower 2 constant, air is supplied to the oxidation tower according to the sulfur dioxide load a, as shown in an example in Fig. 2. Since the blowing amount b can be changed, there is no need to blow in wasteful air, the amount is significantly reduced, and operation with excellent energy saving effects is possible.

On the other hand, in the conventional method, as shown in Fig. 3, in order to keep the liquid volume constant and keep the sulfur dioxide concentration in the exhaust gas discharged from the absorption tower low,
Regardless of the sulfur dioxide load a, a constant amount of air b must be blown in at the highest load, which results in a large amount of wasted energy being consumed.

〔Effect of the invention〕

As described above, even if the amount of air blown into the oxidation tower changes, the method of the present invention corrects the liquid depth control value of the pump tank in accordance with the increase or decrease in the amount of air blown into the absorption tower. Increases and decreases in the amount of liquid held in the oxidation tower can be prevented by controlling the liquid depth of the pump tank, and the true amount of liquid in the absorption tower can be maintained constant regardless of changes in the amount of liquid in the oxidation tower. Since the absorption reaction of sulfur dioxide is carried out smoothly and stably in the absorption tower, the aqueous solution is drawn out to the neutralization tank stably, and the liquid volume is unbalanced, resulting in a drop in the flue gas at the exit of the absorption tower. The amount of blown air can be changed according to the amount of sulfur dioxide absorbed without increasing the sulfur dioxide concentration in the aqueous solution or decreasing the aluminum ion concentration in the aqueous solution, which has a large energy saving effect.

[Brief explanation of drawings]

Fig. 1 is a schematic explanatory diagram of the method of the present invention, Fig. 2 is a diagram showing an example of the sulfur dioxide load and blown air amount in the method of the present invention, and Fig. 3 is a diagram showing the sulfur dioxide load and the sulfur dioxide load in the conventional method. A diagram showing an example of the amount of blown air, and FIG. 4 is a schematic diagram showing the flow of flue gas desulfurization using basic aluminum sulfate. 1... Inlet line, 2... Absorption tower, 3... Circulation line, 4... Outlet line, 5... Pump tank, 6... Oxidation tower, 7... Air line, 8... Air outlet line, 9
... Branch pipe (branching process), 10... Neutralization tank, 11... Calcium carbonate slurry tank, 12... Filter machine, 13...
Calcium sulfate, 14, 15...detector, 16...meter, 17...regulator, a...sulfur dioxide load, b...blow air amount.

Claims (1)

[Claims] 1. Introducing exhaust gas containing sulfur dioxide into an absorption tower and contacting it with a basic aluminum sulfate aqueous solution,
The above sulfur dioxide is absorbed into the above aqueous solution to form an aluminum sulfite aqueous solution, and the aluminum sulfite aqueous solution discharged from the above absorption tower is received in a pump tank, and sent to an oxidation tower, where air is blown into the aluminum sulfite solution. A part of the discharged aluminum sulfate aqueous solution is returned to the above-mentioned absorption tower through a branching process, and the remaining aqueous solution is sent to a neutralization tank, where calcium carbonate is added to produce calcium sulfate and basic aluminum sulfate. Separate the calcium sulfate into solid and liquid using a filtration machine,
In a flue gas desulfurization method using a basic aluminum sulfate aqueous solution in which a liquid basic aluminum sulfate aqueous solution is circulated to the absorption tower, an amount of air corresponding to the amount of sulfur dioxide absorbed in the absorption tower is blown into the oxidation tower. according to the apparent specific gravity determined in advance from the gas-liquid ratio of the aqueous solution and air in the oxidation tower.
A flue gas desulfurization method characterized by maintaining a constant amount of liquid in an absorption tower by correcting a liquid depth control value in a pump tank.