JP2001017825A - Flue gas desulfurization method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus for a flue gas desulfurization method capable of excellent responding to load fluctuation, and preventing appliance corrosion by restricting the lowest value of the pH of the absorption tower and decreasing the amount of usage of an absorbent slurry at the time of low load operation while keeping the pH of an absorption tower at a proper value. SOLUTION: To keep the desulfurization efficiency constant, the actual desulfurization ratio is calculated from the difference between the SO2 concentration 2 in a flue gas at an inlet of an absorption tower and the SO2 concentration 3 in the flue gas at an outlet of the absorption tower in relation to the flue gas flow rate 1 introduced into the absorption tower. The desulfurization agent supply amount of a desulfurization agent necessary to be supplied to an absorption solution to keep the desulfurization ratio constant is calculated based on the deviation of the calculated actual desulfurization ratio from the desulfurization ratio set value. The deviation of the pH 20 of the absorption solution from the lowest pH set value of the absorption solution is calculated and the desulfurization agent supply amount of the desulfurization agent necessary to be supplied to the absorption solution to keep the pH of the absorption solution at a prescribed value or higher is calculated. The higher amount of these two calculated desulfurization agent supply amounts is selected as the amount of the desulfurization agent to be supplied to the absorption solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flue gas desulfurization method and apparatus for reducing sulfur oxides contained in flue gas from a boiler or the like, and in particular, it is required to reduce utility and to further improve additional followability. To a method and an apparatus for flue gas desulfurization.

[0002]

2. Description of the Related Art An absorption control system of a desulfurization device for absorbing and removing sulfur oxides in exhaust gas by bringing a known desulfurizing agent made of limestone slurry into contact with an exhaust gas discharged from a combustion device such as a conventional boiler in an absorption tower. As shown in FIG.

The output signal of the exhaust gas flow rate 31 and the inlet S of the absorption tower
The output signal of the O ₂ concentration 32 is input to the multiplier 41 to obtain an inlet SO ₂ amount signal 46, and the output of the inlet SO ₂ concentration 32 and the output signal of the outlet SO ₂ concentration 33 are output to a subtractor 35 and a divider. 37, an actual desulfurization rate signal 36 is obtained, a deviation between the signal 36 and the desulfurization rate setter 34 is obtained by a subtractor 38, and this deviation signal is inputted to a controller 39 to be proportionally integrated. The signal 44 is output.

The amount of SO _{2 at the} inlet 46 and the desulfurization rate 36 are multiplied by a multiplier 4
The required limestone slurry amount 45 is obtained by multiplying the demand signal 47 by multiplying the demand signal 47 by the demand signal 47 and the desulfurization rate correction signal 44 previously obtained by the multiplier 43.

[0005] The deviation between the required limestone slurry amount 45 and the actual limestone slurry amount 48 is proportionally corrected by a controller 49, and the limestone slurry supply amount is adjusted by opening and closing the limestone slurry control valve 50. At this time, the required amount of limestone slurry by the limestone slurry required amount setting unit 51 is added to the adder 52.
Is added to the required amount of limestone slurry 45 and used for calculating the deviation from the actual amount of limestone slurry 48. In FIG. 2, A / H is an automatic / manual switch.

An invention similar to the above-mentioned prior art is described in Japanese Patent Application Laid-Open No. Sho 59-102425. The prior art in order to control the supply amount of the absorbent as desulfurization rate does not fall below a specified value for variations of SO ₂ amount by the load change in the boiler, the absorption tower inlet SO ₂ concentration and flow rate, the absorbing solution This is a method in which the pH of the absorbing liquid circulated from the circulation tank storing the water to the absorption tower is used as a control element.

[0007]

However, in the control method shown in FIG. 2, since the pH of the absorption tower is not taken in as a control element, the desulfurization rate of the exhaust gas is kept constant at a low load of the power plant using the boiler. When the operation of narrowing the pH of the absorbing solution in the absorption tower for control is started, there is nothing to limit it, and the absorbing solution in the absorption tower is extremely low in pH.
There was a case to operate in H.

[0008] When the operation of the desulfurization apparatus is continued while the absorption liquid in the absorption tower is kept at a low pH, the activity of the absorbent slurry is degraded, and the pH does not recover even when the load on the plant begins to rise. May not be able to follow the load change. Further, the corrosion of equipment in the absorption tower may be a problem due to the low pH of the absorbing solution.

In the desulfurization system shown in FIG. 2, the control method for keeping the desulfurization rate of the exhaust gas constant is effective in reducing the amount of the absorbent slurry used at a low load, but follows the power plant and protects equipment materials. Was not taken into account.

Further, in the invention described in Japanese Patent Application Laid-Open No. Sho 59-102425, there is disclosed a method of controlling the supply amount of an absorbent which takes in the pH of an absorbing solution in an absorption tower as a control element. although the lack of temporary desulfurization rate with respect to fluctuations is eliminated, since always controlled to a constant value by feedback control of the absorbing solution pH, the desulfurization rate varies in accordance with the change of the absorption tower inlet sO ₂ concentration Inevitable.

An object of the present invention is to reduce the amount of absorbent slurry used during low-load operation while maintaining the absorption tower pH at an appropriate value, and to improve the follow-up performance when the load changes. Solving the problem of equipment corrosion.

[0012]

The above object of the present invention is attained by appropriately switching the means for controlling the desulfurization rate of the flue gas desulfurization unit and the means for maintaining the absorption tower pH at a predetermined minimum value or more. Can be achieved.

That is, the present invention relates to a flue gas desulfurization method for removing sulfur oxides in exhaust gas from a combustion device such as a boiler by bringing the sulfur oxides into contact with an absorbent containing a desulfurizing agent.
Is adjusted based on the difference between the SO ₂ concentration in the exhaust gas before and after the desulfurization treatment with respect to the amount of the exhaust gas to be desulfurized while adjusting the supply amount of the desulfurizing agent to the absorption liquid so that the pH is equal to or higher than the set minimum pH. A flue gas desulfurization method of adjusting the supply amount of a desulfurizing agent into an absorbing solution such that a desulfurization rate is maintained within a predetermined range, or a sulfur oxide in an exhaust gas from a combustion device such as a boiler including a desulfurizing agent. In the flue gas desulfurization method of removing by contact with the absorbent, the desulfurization is performed so that the desulfurization rate calculated based on the difference between the amount of exhaust gas to be desulfurized and the concentration of SO _{2 in} the exhaust gas before and after the desulfurization is constant is constant. The desulfurizing agent supply amount to be supplied and the desulfurizing agent supply amount to be supplied to the absorbing solution so that the pH of the absorbing solution is equal to or higher than the set minimum pH are selected and supplied to the absorbing solution. The desulfurizing agent supply A flue gas desulfurization process to.

Further, the present invention relates to a flue gas desulfurization apparatus provided with an absorption tower for removing sulfur oxides contained in exhaust gas from a combustion apparatus such as a boiler by contacting with an absorbent containing a desulfurizing agent. Flow meter for the exhaust gas to be discharged, a concentration meter for SO _{2 in} the exhaust gas at the inlet of the absorption tower, a concentration meter for SO _{2 in} the exhaust gas at the outlet of the absorption tower, and the exhaust gas SO at the inlet and the outlet of the absorption tower with respect to the measured value of the exhaust gas flow meter. ₍₂₎ A desulfurization rate calculator for calculating the actual desulfurization rate from the difference between the measured values of the densitometers, and a desulfurizing agent necessary for keeping the desulfurization rate constant based on the deviation between the calculated actual desulfurization rate and the set value of the desulfurization rate. A first desulfurizing agent supply amount calculator for calculating the amount of water to be supplied to the absorbing solution, and p for measuring the pH of the absorbing solution.
H meter and the minimum p of the absorbing solution for which the measured value of the pH meter is set.
The second desulfurizing agent supply amount calculator for supplying the necessary desulfurizing agent to the absorbing liquid so as to have a H or more, and the larger desulfurizing agent supply amount obtained by the two desulfurizing agent supply amount calculators is selected. And a high-signal selector.

[0015]

According to the present invention, in order to keep the desulfurization rate of the exhaust gas constant while limiting the pH of the absorbent in the absorption tower, the amount of the desulfurizing agent (limestone slurry, etc.) is controlled to keep the desulfurization rate of the exhaust gas constant. When the pH of the absorption liquid in the absorption tower is reduced below the set minimum limit value, the desulfurizing agent is supplied to the absorption liquid so that the pH of the absorption liquid in the absorption tower becomes the minimum value or more. The control is switched to As a result, the pH in the absorbing solution is always maintained at or above the minimum value, and there is no response delay at the time of load change or corrosion of equipment.

Further, has been the invention described in JP-A-59-102425, but always controlled to a constant value by feedback control of the absorption liquid pH, the desulfurization rate varies in accordance with the change of the absorption tower inlet SO ₂ concentration I do. On the other hand, in the present invention, although the pH of the absorbing solution fluctuates according to the change in the SO ₂ concentration at the inlet of the absorbing tower, the pH of the absorbing solution is not less than a predetermined value (minimum value) as a measure against the boiler load fluctuation and as a measure against corrosion by equipment. It is characterized in that the desulfurizing agent is supplied to the absorbing liquid as much as possible. Moreover, in the present invention since the feedback control by the desulfurization rate calculated from the SO ₂ concentration in the absorption tower doorway for desulfurization rate, always controlled to a constant value.

As a result, in the present invention, the desulfurization rate can be controlled to be constant over the entire load range of the boiler. As a result, the amount of limestone, industrial water, and the like can be reduced because the operation of narrowing the absorbent can be performed in a low load region. Further, according to the above-described control of the present invention, even when the pH of the absorbent is lowered by narrowing down the absorbent, functions such as load followability are achieved because the pH is not lowered below a certain value by the pH limiting circuit.

[0018]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a limestone slurry demand control system diagram. An output signal of the exhaust gas flow absorption tower inlet SO ₂
The output of the concentration 2 is input to the multiplier 13 and the total S in the exhaust gas is
The O ₂ amount signal 14 is obtained in advance. In addition, the absorption tower inlet SO
_{2 The} density signal is input to a function generator 5 defined as follows, and the value calculated by the function generator 5 and the value of the outlet SO ₂ set value bias setter 4 are added and selected by an adder 5a. value is output as the outlet SO ₂ setpoint 6.

Definition of the function generator 5: inlet SO ₂ × (1-desulfurization rate) A signal obtained by subtracting the value of the outlet SO ₂ set value 6 and the value of the inlet SO ₂ concentration 2 by the subtractor 7 is divided by the inlet SO ₂ concentration. The value obtained by dividing by the vessel 8 becomes the required desulfurization rate 9.

At the same time, the outlet SO ₂ set value 6 and the outlet SO ₂
The deviation from the concentration is calculated by the subtractor 7, and the deviation is calculated by the controller 1
The integral is corrected by 0, and the limestone slurry required amount correction value 12 is output. Next, the total SO ₂ amount 14 obtained by multiplying the exhaust gas flow rate 1 by the inlet SO ₂ concentration 2 and the signal 12
Is multiplied by the multiplier 13 and the required desulfurization rate 9 is further multiplied by the multiplier 13 to obtain a required amount of limestone slurry flow rate (set value) 15 calculated so that the desulfurization rate becomes constant.

The deviation between the limestone slurry flow set value 15 and the actual limestone slurry amount 16 is corrected by the controller 19, and the limestone slurry flow control valve 28 is opened and closed to control the amount of limestone. At this time, the required amount of limestone slurry by the limestone slurry required amount bias setting unit 17 is added to the limestone slurry flow rate set value 15 by the adder 18 and used for calculating the deviation from the actual limestone slurry amount 16.

Further, an absorption tower pH control signal 24 in which the deviation between the absorption tower pH 20 and the pH value of the minimum pH setting device 21 of the absorption liquid in the absorption tower is always integrated and corrected by a controller 23 via a subtractor 22 is always used. Output. The signal obtained from the signal 24 and the signal from the controller 19 from the control system for maintaining the desulfurization rate obtained by the above-described method is used as a high signal selector 26.
When the signal of the controller 19 is narrowed down extremely on the side of the constant outflow rate control, the control is switched to the absorption tower pH control signal 24 and the control is switched to the minimum pH holding control.

In this way, when the amount of limestone slurry is narrowed to control the desulfurization rate of the exhaust gas to be constant, and the pH of the absorbing solution in the absorption tower falls below the set minimum limit value, the absorption tower pH limiting circuit is used. And operates so as to keep the pH of the absorbing solution in the absorption tower at the minimum value. As a result, the pH of the absorbent is always maintained at or above the minimum value, so that there is no delay in response to load changes or corrosion of equipment.

[0024]

According to the present invention, since the desulfurization rate constant control and the means for maintaining the minimum pH of the absorption tower are effectively switched, the effect of reducing the amount of absorbent slurry used in the desulfurization rate constant control is maintained. In addition, there is an effect that load followability and equipment corrosion problems can be improved.

[Brief description of the drawings]

FIG. 1 shows a desulfurization rate constant control circuit with a PH limiting circuit according to the present invention.

FIG. 2 shows a conventional desulfurization rate constant control circuit.

[Explanation of symbols]

1 Boiler outlet exhaust gas amount 2 Desulfurization inlet S
O ₂ concentration 3 Desulfurization outlet SO ₂ concentration 4 Outlet SO ₂ concentration set value bias setter 5 Function generator 5a Adder 6 Outlet SO ₂ set value 7 Subtractor 8 Divider 9 Desulfurization rate 10 Controller 11 Automatic / manual setter 12 Limestone slurry demand correction value 13 Multiplier 14 Total SO ₂ quantity 15 Limestone slurry demand 16 Limestone slurry flow rate 17 Limestone slurry demand bias setter 18 Adder 19 Controller 20 Absorber tower pH 21 Minimum pH
Setting device 22 Subtractor 23 Controller 24 Absorption tower pH control signal 25 Limestone slurry final signal 26 High signal selector 27 Limestone slurry flow control valve 28 Limestone slurry flow control valve

Claims (3)

[Claims] In a flue gas desulfurization method for removing sulfur oxides in exhaust gas from a combustion device such as a boiler by contacting the same with an absorbent containing a desulfurizing agent, the pH of the absorbent is equal to or higher than a set minimum pH. while adjusting the supply amount into the absorbent liquid of the desulfurization agent, a desulfurization rate is calculated based on the sO ₂ concentration differences in the exhaust gas before and after the desulfurization treatment for the exhaust gas amount of the desulfurization process is maintained within a predetermined range as A flue gas desulfurization method characterized in that the amount of the desulfurizing agent supplied to the absorbing solution is adjusted as described above. 2. A flue gas desulfurization method for removing sulfur oxides in exhaust gas from a combustion device such as a boiler by bringing the sulfur oxides into contact with an absorbent containing a desulfurizing agent. SO
_{(2) The} amount of desulfurizing agent supplied to the absorbing solution and the pH of the absorbing solution so that the desulfurization rate calculated based on the difference between the concentrations is constant.
The desulfurizing agent supply amount to be supplied to the absorbing solution is adjusted so as to be equal to or more than the set minimum pH. A flue gas desulfurization method characterized by the above-mentioned. 3. A flue gas desulfurization device having an absorption tower for removing sulfur oxides in exhaust gas from a combustion device such as a boiler by bringing the sulfur oxide into contact with an absorbent containing a desulfurizing agent. a flow meter, the absorption tower inlet gas in SO ₂ concentration meter and the concentration of SO ₂ meter of the absorption tower outlet in exhaust gas, the absorption tower inlet and outlet gas SO ₂ concentration meter for measurement of the exhaust gas flowmeters A desulfurization rate calculator that calculates the actual desulfurization rate from the difference between the measured values, and a deviation between the calculated actual desulfurization rate and the desulfurization rate set value.
A first desulfurizing agent supply amount calculator for calculating the amount of desulfurizing agent required to keep the desulfurization rate constant to the absorbing solution, a pH meter for measuring the pH of the absorbing solution, and a measured value of the pH meter A second desulfurizing agent supply amount calculator for supplying a necessary desulfurizing agent to the absorbing solution so that the pH is equal to or higher than the set minimum pH of the absorbing solution; and the desulfurization obtained by the two desulfurizing agent supply amount calculators, respectively. A flue gas desulfurization apparatus comprising: a high signal selector for selecting a larger amount of the agent supplied.