JP2547803B2 - Wet flue gas desulfurization equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a wet desulfurization apparatus, and more particularly to a wet desulfurization apparatus capable of preventing a decrease in desulfurization performance due to a stop of supply of oxidizing air.

[Conventional technology]

With the rapid development of industry, air pollution due to exhaust gas from thermal power plants, various factories, etc. has become a big problem. Among these, pollution with sulfur oxides (SOx) such as sulfurous acid gas is widespread, and various desulfurization devices have been proposed to prevent this.

The limestone-gypsum wet flue gas desulfurization system is one of them. FIG. 3 is a schematic system diagram of a conventional wet flue gas desulfurization apparatus. This apparatus comprises an absorption tower 2, a circulation tank 3 provided at the bottom of the absorption tower, a compressor 7 for feeding the oxidizing air 6 into the circulation tank, and a circulation for sending circulation slurry from the circulation tank 3 to the absorption tower 2. Limestone slurry pump that supplies limestone slurry from slurry pump 4 and limestone slurry tank 15.
14 and a limestone slurry control valve 13.

Combustion exhaust gas 1 from a boiler or the like is introduced into an absorption tower 2 by an inlet flue 8 and is brought into contact with a circulation slurry made of limestone slurry supplied by a circulation pump 4 in a gas-liquid contact to generate dust and SOx contained in the combustion exhaust gas. After being absorbed and removed, the entrained mist is removed by the demister 9 and discharged from the outlet flue 10. The oxidizing air 6 is supplied from the compressor 7 to the circulating slurry in the circulating tank 3. The oxidizing air 6
Is supplied near the blades of the stirrer 5 installed for the purpose of preventing the settling of the slurry in the circulation tank 3 and becomes fine bubbles,
It is used for the oxidation of calcium sulfite, which is generated by absorbing SOx. The gypsum obtained by oxidizing calcium sulfite is extracted from the gypsum slurry extraction tube 12 and collected.

[Problems to be solved by the invention]

In the conventional wet flue gas desulfurization apparatus described above, when the supply of the oxidizing air to the circulation tank 3 is stopped due to a failure of the compressor 7 or the like, the desulfurization performance of the wet flue gas desulfurization apparatus is deteriorated.

An object of the present invention is to provide a wet flue gas desulfurization apparatus that can continue operation without lowering desulfurization performance even when the supply of oxidizing air is stopped.

[Means for solving problems]

The present invention supplies the circulating slurry in a circulation tank provided at the bottom of the absorption tower into the absorption tower to contact with combustion exhaust gas,
In a wet flue gas desulfurization device that removes sulfur oxides from combustion exhaust gas and that feeds oxidizing air to the circulating slurry in the circulating tank, a device that detects the stop of feeding of the oxidizing air, and a circulating tank. A device for measuring pH, a device for rapidly feeding the limestone slurry into the circulation tank, and a device for controlling the feeding amount of the limestone slurry so as to maintain the pH value at a predetermined value, It is a wet flue gas desulfurization device.

[Action]

The present invention is configured to detect the stoppage of the feeding of oxidizing air, and to rapidly add the limestone slurry from the limestone slurry tank into the circulation slurry in the circulation tank to maintain the pH value of the circulation slurry at a high value. In addition, it is possible to prevent the desulfurization performance from being deteriorated due to the stop of the feeding of the oxidizing air.

 Hereinafter, the present invention will be described in detail with reference to the drawings.

〔Example〕

FIG. 1 is a schematic system diagram of a desulfurization apparatus showing one embodiment of the present invention, and FIG. 2 is a control system diagram thereof.

In FIG. 1, the absorption tower 2 has a circulation tank 3 at the bottom of the absorption tower 2, and the circulation tank 3 is provided with an agitator 5 for circulating slurry and a compressor 7 for feeding in oxidizing air 6. The circulating slurry in the circulating tank 3 is sprayed to the absorption tower 2 by the circulating slurry pump 4. The circulation tank 3 is further supplied with new limestone slurry from the limestone slurry tank 15 via the limestone slurry pump 14 and the limestone slurry flow rate control valve 13. The input slurry amount control valve 17 when the air supply is stopped is installed in a pipe different from the limestone slurry control valve 13 and detects a stop of the compressor 7 for feeding the oxidizing air 6 (not shown). ) To rapidly feed limestone.

In FIG. 1, in a normal operating state, the exhaust gas 1 is introduced from the inlet flue 2 into the absorption tower 2, and comes into gas-liquid contact with the spray from the circulation pump 4 to absorb and remove dust and sulfur oxides, and then the demister. 9 and is discharged from the outlet flue 10 into the atmosphere as clean gas 11. At that time, in the absorption tower 2,
The reactions represented by the following formulas (1) and (2) are performed.

SO ₂ + H ₂ O → H ₂ SO ₃ (1) CaCO ₃ + 2H ₂ SO ₃ → Ca (HSO ₃ ) ₂ + CO ₂ + H ₂ O (2) Next, the limestone slurry that absorbed SO ₂ was used in the circulation tank 3
Inside, it reacts with the oxidizing air 6 to produce gypsum.
The reaction is shown by the following equation.

Ca (HSO ₃ ) ₂ + O ₂ → CaSO ₄ + H ₂ SO ₄ (3) CaCO ₃ + H ₂ SO ₄ → CaSO ₄ + CO ₂ + H ₂ O (4) Due to the progress of the above reaction, the concentration of sulfite ion in the circulation tank 3 Is reduced, the SO ₂ absorption amount of the circulating slurry is increased, and a high desulfurization rate can be obtained. The circulation tank 3 is replenished with new limestone slurry from the limestone slurry tank 15 by the limestone slurry pump 14 through the limestone slurry flow rate control valve 13.

When the supply of the oxidizing air is stopped, the reactions (3) and (4) become difficult to proceed in the circulation tank 3, and instead the reaction of the following formula (5) proceeds.

CaCO ₃ + Ca (HSO ₃ ) ₂ → 2CaSO ₃ + CO ₂ + H ₂ O (5) At this time, the sulfite ion concentration in the circulation tank 3 becomes high, and the desulfurization performance deteriorates. Further, the reaction of the following formula (6) proceeds and CaCO ₃ .1 / 2H ₂ O (crystalline calcium sulfite) is deposited, but the reaction rate is low.

CaCO ₃ + Ca (HSO ₃ ) ₂ + H ₂ O → 2CaSO ₃ · 1 / 2H ₂ O + CO ₂ (6) CaCO ₃ · 1 / 2H ₂ O is a solid and does not affect the desulfurization performance. If the amount of CaCO ₃ .1 / 2H ₂ O produced in the circulation tank 3 increases, the sulfite ion concentration will decrease and the desulfurization performance will be restored.
Although the reaction rate of the equation (6) is small, the reaction rate increases by increasing the pH value in the circulation tank 3.

When the stop of the oxidizing air 6 is detected, the input slurry amount control valve 17 at the time of stopping the air supply is operated, and the limestone slurry is rapidly injected into the circulation tank 3 to accelerate the reaction of the above formula (6). , Restore the desulfurization performance promptly and ensure the desulfurization performance until the function of the oxidizing air supply system is restored. FIG. 4 is a graph showing the relationship between the CaCO ₃ input amount and pH, and FIG. 5 is a graph showing the relationship between the pH of the circulating slurry and the desulfurization rate. It is shown that the pH rises when CaCO ₃ is added, and the desulfurization rate also increases in response to this.

FIG. 2 is a schematic control system diagram showing an example of an apparatus for detecting the stoppage of the supply of oxidizing air and for activating the apparatus for rapidly supplying the limestone slurry.

When the supply of oxidizing air is stopped, the limestone slurry injection control system shown in Fig. 2 detects the stop of the oxidizing air supply and activates the switch 19 by the trip signal 20 for the oxidizing air system to input the amount of limestone slurry. The control signal generator 23 is activated. On the other hand, as for the limestone slurry input amount, the pH in the circulation tank 3 is detected by the pH detector 21, and the pH signal 22 is input to the limestone slurry input control signal generator 23. Based on the output of the limestone slurry input control signal generator 23, the input slurry amount control valve 17 is operated to rapidly input the limestone slurry into the circulation tank 3. As a result, the pH in the circulation tank 3 is maintained at a predetermined value and the decrease in desulfurization rate is prevented.

〔The invention's effect〕

According to the present invention, the control circuit is activated by detecting the stoppage of the inflow of the oxidizing air for the circulation slurry, and by rapidly supplying the limestone slurry into the circulation tank so as to keep the pH in the circulation tank high, Even if the supply of oxidizing air is stopped,
It is possible to prevent deterioration of desulfurization performance. Therefore, in a boiler or the like equipped with such a flue gas desulfurization device,
The failure of the attached device does not stop the operation of the entire system,
The reliability of the wet desulfurization apparatus of the present invention is remarkably improved in terms of both operation rate and pollution prevention.

[Brief description of drawings]

FIG. 1 is a schematic system diagram of a desulfurization apparatus showing one embodiment of the present invention, FIG. 2 is a control system diagram thereof, FIG. 3 is a schematic system diagram of a conventional desulfurization apparatus, and FIG. ₃ is a diagram showing the relationship between the input amount and pH, and FIG. 5 is a diagram showing the relationship between the input amount of CaCO ₃ and the desulfurization rate. 1 ... Exhaust gas, 2 ... Absorption tower, 3 ... Circulation tank, 4 ...
... Circulation pump, 5 ... Stirrer, 6 ... Oxidizing air, 7 ...
… Compressor, 8 …… Flue inlet, 9 …… Demister, 10
…… Flue outlet, 11 …… Clean gas, 12 …… Gypsum slurry extraction pipe, 13 …… Limestone slurry flow control valve, 14 …… Limestone slurry pump, 15 …… Limestone slurry tank, 16 …… Limestone slurry, 17 …… Incoming slurry amount adjustment valve when air supply is stopped.

Claims (1)

(57) [Claims] 1. A circulation slurry in a circulation tank provided at the bottom of the absorption tower is supplied into the absorption tower to contact with combustion exhaust gas,
In a wet flue gas desulfurization device that removes sulfur oxides from combustion exhaust gas and that feeds oxidizing air to the circulating slurry in the circulating tank, a device that detects the stop of feeding of the oxidizing air, and a circulating tank. A device for measuring pH, a device for rapidly feeding the limestone slurry into the circulation tank, and a device for controlling the feeding amount of the limestone slurry so as to keep the pH value at a predetermined value. Wet flue gas desulfurization equipment that does.