JPH1176749A - Exhaust gas desulfurizer and exhaust gas desulfurization method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control technique excellent in the follow-up ability to load change, capable of keeping the outlet sulfur dioxide gas concentration to equal to or below the upper limit value even in the transitional period of load change and stabilizing the purity of a by-produced gypsum in a desulfurizer for adsorbing sulfur dioxide gas in an exhaust gas by allowing an untreated exhaust gas to contact with a slurry containing a calcium compound (absorbent). SOLUTION: The sulfur dioxide gas concentration is controlled by setting the outlet SO2 concentration characteristic related with the quantity of sulfur dioxide gas and the sulfur dioxide gas concentration in the treated stack gas so as to be constant in the concentration of the unreacted absorbent in the slurry to the change of the sulfur dioxide gas quantity in the untreated stack gas, calculating the setting value of the sulfur dioxide concentration from the practical sulfur dioxide gas quantity in the untreated exhaust gas based on the outlet SO2 concentration characteristic by a computing element 32 and adjusting the charging quantity of the absorbent based on the set value by a flow rate setting part 28.

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 apparatus for controlling the concentration of outlet SO ₂ , and in particular, has good followability to load fluctuations and ensures that the upper limit of the outlet SO ₂ concentration is maintained even in the transitional period of load fluctuations. The present invention relates to a simple flue gas desulfurization apparatus capable of maintaining the value below the value and stabilizing the purity of gypsum produced as a by-product.

[0002]

2. Description of the Related Art Conventionally, as a desulfurization apparatus provided in a power plant or the like, a filling type absorption tower or a spray type or liquid column type absorption tower is used, and an absorbent composed of a calcium compound such as limestone is suspended. A wet lime-gypsum method of removing sulfur oxides (mainly sulfur dioxide) in flue gas by bringing the resulting slurry into flue gas contact with gas and liquid and producing gypsum as a by-product is known.

For example, as a single tower type, a tank oxidation type using a counter-current type liquid column type absorption tower having high gas-liquid contact efficiency is known as a small and high performance type. . Hereinafter, an example of a main body configuration of a desulfurization apparatus using such a countercurrent type liquid column type absorption tower will be described with reference to FIG.

[0004] This desulfurization apparatus has a tank 1 at the bottom to which a slurry in which an absorbent made of limestone is suspended (hereinafter referred to as an absorbent slurry) is provided. At the liquid contact part, untreated smoke exhaust A and tank 1
Column type absorption tower 2 that makes gas-liquid contact with the absorbent slurry inside
have.

[0005] Here, the absorption tower 2 is provided with a flue gas introduction section 3 for introducing untreated flue gas A at a lower portion, and a flue gas deriving section (not shown) for leading treated flue gas B. This is a so-called counter-current type absorption tower formed at the upper end thereof and into which smoke is introduced from below and flows upward.

A mist eliminator 2a is installed in the upper part of the absorption tower 2, and the accompanying mist in the flue gas generated by the gas-liquid contact is collected here, so that the mist eliminator 2a is disposed in the post-treatment flue gas B. It is configured such that a large amount of mist containing sulfurous acid gas or the like is not discharged.

[0007] The absorption tower 2 is provided with a plurality of spray pipes 4, and the spray pipes 4 are formed with a plurality of nozzles (not shown) for spraying the absorbent slurry upward in a liquid column shape. I have. A circulation pump 5 for sucking up the absorbent slurry in the tank 1 is provided outside the tank 1.
Are provided, and the absorbent slurry is fed into each spray pipe 4 via the circulation line 6.

In this case, as means for blowing the oxidizing air C as fine bubbles while stirring the slurry in the tank 1, the air C is blown near the stirring blades of the stirrer 7. A blowing pipe 8 is provided, and the absorbent slurry having absorbed the sulfurous acid gas in the tank 1 is brought into efficient contact with air to oxidize the entire amount to obtain gypsum.

That is, the absorbent slurry injected from the spray pipe 4 in the absorption tower 2 and coming into gas-liquid contact with the flue gas and flowing down while absorbing sulfurous acid gas and dust is discharged from the tank 1 by the stirrer 7 and the blowing pipe 8. It is oxidized by contact with a number of air bubbles blown while being stirred, and further causes a neutralization reaction to form a slurry containing a high concentration of gypsum. The main reactions occurring during these treatments are represented by the following reaction formulas (1) to (3).
Becomes

[0010]

Embedded image (absorption tower flue gas introduction section) SO ₂ + H ₂ O → H ⁺ + HSO ₃ ⁻ (1) (tank) H ⁺ + HSO ₃ ⁻ + 1 / 2O ₂ → 2H ⁺ + SO ₄ ²⁻ (2) 2H ^{+ _{+ SO 4 2- + CaCO 3 +}} H 2 O → CaSO 4 · 2H 2 O + CO 2 (3)

Thus, in the tank 1, a large amount of gypsum, a small amount of limestone as an absorbent and a small amount of dust collected from flue gas are usually suspended or dissolved. In this case, the slurry in the tank 1 is supplied to the solid-liquid separator 9 through a piping line 6a branched from the circulation line 6, and is filtered and taken out as gypsum D having a low moisture content. On the other hand, the filtrate from the solid-liquid separator 9 is sent out by the pump 11 via the filtrate tank 10 in this case, and a part of the filtrate is returned to the tank 1 as water constituting the absorbent slurry.
A part is discharged as desulfurization wastewater E to prevent accumulation of impurities.

In this case, limestone (calcium compound), which is an absorbent, is supplied to the operating tank 1 from the slurry adjusting tank 12 as a slurry. Slurry adjustment tank 12
Has a stirrer 13 and is supplied with powdered limestone F from a silo (not shown) and supplied water G (such as industrial water).
Are mixed with each other to produce a slurry having a predetermined concentration suitable for transportation. The slurry inside the slurry is pressure-fed toward the tank 1 by the slurry pump 14.

A flow control valve 15 and a flow detector 16 are connected to the discharge side of the slurry pump 14, and a flow controller 17 which receives a command from a control device described later generates a detection signal of the flow detector 16. By controlling the opening degree of the flow control valve 15 while reading the information, the supply amount of the absorbent slurry is adjusted in accordance with a command from a control device as described later.

Incidentally, for example, make-up water (industrial water or the like) is appropriately supplied to the tank 1 as necessary, and the water that gradually decreases due to evaporation or the like in the absorption tower 2 is supplemented. Further, by adjusting the flow rate of makeup water to the tank 1 and the flow rate of slurry withdrawal from the piping line 6a, the tank 1
Inside, a slurry having a substantially constant solid content concentration containing gypsum and an absorbent is always maintained in a state of being within a certain range of levels.

Next, a conventional control technique of this type of desulfurization apparatus will be described. The desulfurization performance of this type of desulfurization equipment depends on the properties of the slurry in the tank 1 that comes into gas-liquid contact with the flue gas and the absorption tower 2
Is naturally affected by the amount of gas-liquid contact at For this reason, a control method for adjusting the circulation flow rate of the slurry and the input flow rate of the absorbent to the minimum necessary according to the load fluctuation during operation, etc., in order to maintain the minimum performance as much as possible and to reduce the cost, has been developed. It has been conventionally proposed.

Among them, the control based on the circulation flow rate of the slurry is problematic in that the circulation flow rate cannot be reduced so much in order to prevent the solid content from adhering to the walls of the absorption tower, the packing, and the like. Therefore, there is a problem that it is difficult to adjust the circulating flow rate by the valve.Therefore, usually, a method of basically controlling the device performance by adjusting the input flow rate of the absorbent, or adjusting the input flow rate of the absorbent and adjusting the circulating flow rate. A combined system is common.

Conventionally, such a control of the input flow rate of the absorbent is performed by sequentially changing the input flow rate of the stoichiometric equivalent which is sequentially calculated from the actual desulfurization load (the amount of sulfurous acid gas in the untreated exhaust gas). The target value is a value obtained by adding a correction amount for maintaining the actually measured value of the detected slurry pH or the outlet SO ₂ concentration or the like near the set value.

For example, FIG. 7 is a block diagram showing a configuration of a control device of a system for controlling the concentration of sulfurous acid gas (outlet SO ₂ concentration) in the exhaust gas after treatment at a constant level. Here, the flow rate of the untreated flue gas (desulfurization gas flow rate) and the concentration of the sulfite gas in the untreated flue gas (inlet SO ₂ concentration) are detected in real time by the sensors 21 and 22 and input to the multiplier 23. Multiplier 2
3 multiplies these detection values to output a value proportional to the desulfurization load (a value corresponding to the above-described stoichiometric equivalent), and inputs the value to the adder 24.

On the other hand, the outlet SO ₂ concentration is detected by the sensor 25 and input to the feedback control unit 27 together with the set value of the outlet SO ₂ concentration from the setter 26. The feedback control unit 27 calculates a value MV corresponding to the correction amount from the deviation between the detected value PV of the outlet SO ₂ concentration and the set value SV, and inputs the value MV to the adder 24. The adder 24 adds the output of the multiplier 23 and the output from the feedback control unit 27, and inputs the addition result to the absorbent slurry flow rate setting unit 28. The flow rate setting unit is configured to issue a command to, for example, the flow rate controller 17 in FIG. 6 described above so that the flow rate corresponds to the input signal.

According to the control device shown in FIG. 7, a stoichiometric equivalent of the absorbent corresponding to the load fluctuation is introduced as a basic amount, and the outlet SO ₂ concentration is feedback-controlled. Accordingly, even if there is a factor of performance deterioration such as variation in smoke emission properties, the amount of the absorbent to be charged is adjusted so that the outlet SO ₂ concentration is maintained at the set value. For this reason, in the long term, the minimum necessary amount of absorbent, which substantially matches the load, is introduced, so that a certain degree of desulfurization performance can be maintained and the cost can be reduced.

The same is true for the case where the feeding amount is adjusted so that the slurry pH is maintained at a set value (determined as an optimum value) by feedback control of the slurry pH, In this case, as a configuration of the control device, the sensor 25 in FIG.
Is a pH setting device.

That is, in general, if the pH is high, the desulfurization performance tends to be improved even if the circulating flow rate of the slurry is the same, so that the desulfurization performance is maintained at a target value or more and the amount of the absorbent introduced is kept to the minimum necessary. Has an optimum value of the slurry pH corresponding to the conditions such as the desulfurization load at that time, and if such a pH can be accurately calculated and adjusted to such a value, at least The desired desulfurization performance can be exhibited at the cost.

In addition to the above-mentioned basic control, various types of conventional desulfurizer control devices are used in addition to the basic control described above, for the purpose of further improving the followability to load fluctuations and further reducing the operating cost. Proposed. For example, JP-A-59-199020 and JP-A-59-199020
In Japanese Patent Application Laid-Open No. 199021, the relationship between the optimum pH value of the slurry corresponding to the desulfurization load and the optimal number of operating pumps is set in advance or in real time by simulation or the like, and the supply flow rate of the absorbent and the operating pump are determined based on this relationship. A method for controlling the number is disclosed.

This method takes into account the problem that the rate of neutralization by the absorbent is very small compared to the rate of change in load, and the problem that the circulation flow rate of the slurry cannot be so small to prevent solids from adhering. Change the number of operating pumps according to the load,
The supply flow rate of the absorbent is adjusted so that is set to the optimum value.

Further, for example, JP-A-59-150339 discloses a carbonate concentration (unreacted absorbent concentration) in a slurry.
Are described.

[0026]

However, in the conventional control device described above, the pursuit of gypsum (calcium utilization rate), which is a by-product, is stabilized in order to further improve the ability to follow a load. Above, there were the following problems. (1) First, the pH of the slurry is fed back to adjust the input flow rate of the absorbent so as to maintain the pH at a set value. In addition, the effects of pH measurement errors and control errors become relatively large, making it difficult to stably maintain desulfurization performance and gypsum purity at predetermined values against load fluctuations and the like.

[0027] This is because in this type of desulfurization unit the outlet SO that must be kept at a minimum to comply with emission regulations
₂ If the conditions such as the circulating flow rate (gas-liquid contact capacity), desulfurization load, or the properties of exhaust gas (impurity amount) are constant, the unreacted amount existing in the slurry liquid is essentially as shown in FIG. (Eg, limestone; calcium carbonate). Further, since most of the solid content other than gypsum present in the slurry is an unreacted absorbent, the impurity concentration of the gypsum obtained by solid-liquid separation of the slurry is also substantially uniquely determined by the absorbent concentration. .

However, the relationship between the absorbent concentration and the pH is not proportional, and particularly in the case of the tank oxidation method, the reactivity of the absorbent is improved. PH changes only slightly.

That is, the slurry pH as an index for judging the desulfurization performance is not accurate, and the sensitivity becomes extremely low particularly in the case of the tank oxidation system. For this reason, even if the above-described control for adjusting the pH to a constant value is performed, the influence of a measurement error of the pH meter or the like becomes large, and in fact, the concentration of the absorbent in the slurry fluctuates from an appropriate value. As a result, desulfurization performance and gypsum purity fluctuate.

(2) In the conventional method in which the SO ₂ concentration at the outlet of the flue gas is fed back and the flow rate of the absorbent is adjusted so as to maintain this value at a constant set value independent of the load, After all, the concentration of the absorbent in the slurry is not always controlled to an appropriate value, so that it is not possible to realize high followability of the desulfurization performance to load changes and stable maintenance of gypsum purity.

For example, in the case of the constant control of the outlet SO ₂ concentration, the concentration of the absorbent at a low load is significantly smaller than that at a high load. In general, the boiler load in a power plant or the like fluctuates rapidly at, for example, about 3 to 5% / min. In comparison with this, the supply capacity of the absorbent with respect to the capacity of the absorption tower tank is reduced. Therefore, it is usually slight. Therefore, for example, when the load changes from a low load to a high load as shown in FIG. 5, the increase in the absorbent concentration (for example, the calcium carbonate concentration) in the slurry cannot keep up with the change in the load, and is shown in FIG. So the actual exit S
A phenomenon occurs in which the O ₂ concentration temporarily increases greatly and exceeds the upper limit. Further, since the concentration of the absorbent in the slurry fluctuates depending on the load, the gypsum purity cannot be stabilized.

(3) The apparatus disclosed in the above-mentioned publication is excellent in that a more appropriate control target value and a control operation amount are set by a simulation model. Due to the system, there is a problem of the above measurement error of the pH, and there is a limit in the control accuracy.

(4) In the case of the apparatus disclosed in JP-A-59-150339, since the carbonate concentration in the slurry is continuously measured, the load followability is improved and the gypsum purity is secured. Can be achieved, but there is a disadvantage in that a continuous measuring device for the carbonate concentration is required and the equipment is expensive.

The present invention has been made in view of such conventional circumstances, and in particular, has good follow-up performance with respect to load fluctuations, and can reliably maintain the outlet SO ₂ concentration at or below the upper limit even in the transitional period of load fluctuations. It is another object of the present invention to provide a simple flue gas desulfurization apparatus capable of stabilizing the purity of gypsum produced as a by-product.

[0035]

According to a first aspect of the present invention, there is provided a flue gas desulfurization apparatus for bringing untreated flue gas into contact with a slurry containing an absorbent comprising a calcium compound in an absorption tower. Thereby, in a flue gas desulfurization device that absorbs at least sulfur dioxide in untreated flue gas,
An outlet SO ₂ concentration detection means for detecting the concentration of sulfur dioxide flue gas in the processed, a load detecting means for detecting the sulfur dioxide content in the untreated flue gas to be processed and the outlet from the output of the load detecting means based on the SO ₂ concentration characteristics, and an outlet SO ₂ concentration setting means for determining the set value of sulfur dioxide concentration in the processed flue gas, this outlet SO ₂ concentration setting means, the outlet SO and set the set value ₍₂₎ a deviation output means for calculating a deviation from an actually measured value by the concentration detection means, and a stoichiometric equivalent corresponding to the sulfurous acid gas amount based on an output of the deviation output means and an output of the load detection means. An absorbent introduction amount setting means for calculating an introduction amount of the absorbent obtained by adding the correction amount corresponding to the deviation; and an absorbent is introduced into the slurry based on the introduction amount calculated by the absorbent introduction amount setting means. Sorbent The outlet SO ₂ concentration characteristic in the outlet SO ₂ concentration setting means is a relationship between a load and a set value of a concentration of sulfurous acid gas in the exhaust gas after the treatment. The concentration of the unreacted absorbent is set to be constant.

Further, the flue gas desulfurization apparatus according to claim 2, wherein the outlet SO ₂ concentration characteristics at the outlet SO ₂ concentration setting means, sulfur dioxide in the flue gas after treatment by performing desulfurization simulation based on the latest process values It is characterized in that the concentration is periodically obtained by a simulation model for estimating the concentration and is updated and set at a predetermined period.

Further, the flue gas desulfurization apparatus according to claim 3 has a plurality of pumps for circulating the slurry in the absorption tower,
The simulation model, and sets the outlet SO ₂ concentration characteristic for each number of operating this pump is configured to also set the pump operation number characteristic showing the optimal number of operating the pump to the load variation by the desulfurization simulation, Further, the outlet SO ₂ concentration setting means selects a corresponding one of the outlet SO ₂ concentration characteristics according to the actual number of operating pumps, and based on the selected characteristics, determines the concentration of the sulfur dioxide gas in the treated flue gas. The apparatus is characterized in that it is configured to perform setting and further includes a pump control unit that starts and stops the pump based on the characteristic of the number of operating pumps.

Further, the flue gas desulfurization method according to claim 4 has a plurality of pumps for circulating the slurry in the absorption tower,
The outlet SO ₂ concentration characteristics are set for each number of operating pumps, and the outlet SO ₂ concentration setting means selects a corresponding one of the outlet SO ₂ concentration characteristics according to the actual number of operating pumps. It is configured to set the concentration of sulfurous acid gas in the exhaust gas after treatment based on the selected characteristics, and based on the characteristics of the number of operating pumps indicating the optimal number of operating pumps with respect to load fluctuations, starting and stopping the pumps 2. The flue gas desulfurization apparatus according to claim 1, further comprising a pump control means for performing the following.

In the flue gas desulfurization method according to the fifth aspect, at least sulfurous acid in the untreated flue gas is brought into contact with the untreated flue gas and a slurry containing an absorbent comprising a calcium compound in an absorption tower. In the flue gas desulfurization method for absorbing gas, the amount of the sulfur dioxide gas and the amount of the treated flue gas are adjusted so that the concentration of the unreacted absorbent in the slurry becomes constant with respect to the variation in the amount of the sulfur dioxide gas in the untreated flue gas. An outlet SO ₂ concentration characteristic that is a relationship with the sulfur dioxide gas concentration in the gas is set, and based on the outlet SO ₂ concentration characteristics, the set value of the sulfur dioxide gas concentration is obtained from the actual sulfur dioxide gas amount in the untreated exhaust gas. The concentration of the sulfurous acid gas is controlled by adjusting the input amount of the absorbent based on the set value.

Further, in the flue gas desulfurization method according to claim 6, at least sulfurous acid in the untreated flue gas is brought into contact with a slurry containing an absorbent comprising a calcium compound in an absorption tower. in flue gas desulfurization method of absorbing gas, detecting the sulfur dioxide quantity of the untreated flue gas to be treated and the concentration of sulfur dioxide in the process after the flue gas, the predetermined outlet SO ₂ concentration from the detected value of the sulfur dioxide amount Determine the set value of the sulfur dioxide concentration in the smoke after treatment based on the characteristics, calculate the deviation between the set value and the detected value of the sulfur dioxide concentration, and calculate the deviation and the detected value of the sulfur dioxide gas amount. Based on the stoichiometric equivalent corresponding to the sulfurous acid gas amount, calculate the input amount of the absorbent by adding the correction amount corresponding to the deviation, based on the calculated input amount in the slurry Add absorbent And so, the outlet SO ₂ concentration characteristics as characteristics showing the relationship between the sulfurous acid gas amount and the sulfur dioxide concentration, the concentration of unreacted absorbent in said slurry to variations in the sulfur dioxide amount is constant It is characterized by setting so that:

According to a seventh aspect of the present invention, in the flue gas desulfurization method, the slurry is circulated in the absorption tower by a plurality of pumps, and the outlet SO ₂ concentration characteristics are set for each number of operating pumps. , the actual pump operation number, the corresponding characteristic and select one of the outlet SO ₂ concentration characteristics, to set the sulfur dioxide concentration in flue gas during post processing based on the selected characteristic, and a load fluctuation The start and stop of the pump are performed based on a pump operating number characteristic indicating an optimum operating number of the pumps.

[0042]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a control device of the flue gas desulfurization device of the present embodiment. Note that the same components as those of the conventional device shown in FIGS. 6 and 7 are denoted by the same reference numerals, and redundant description will be omitted.

This control device is specifically composed of various sensors and a control device main body.
Simulation model 3 for performing desulfurization simulation
1, an arithmetic unit 32 for outputting a set value of the outlet SO ₂ concentration based on the exit SO ₂ density characteristics which are computed by the simulation model 31 (the outlet SO ₂ concentration setting means),
The main feature is that a calculator 33 (pump control means) that outputs a set value of the number of operating pumps based on the characteristic of the number of operating pumps set by the simulation model 31 is provided.

The simulation model 31 includes a setting input 31a for setting the lower limit of the gypsum purity and the upper limit of the outlet SO ₂ concentration.
And 31b, performs a desulfurization simulation based on the latest detection signal 31c of various process values, the pump operation number characteristics and a certain period the process of outputting the outlet SO ₂ concentration characteristics of each pump operation number (for example, once / hour) Is repeated.

Here, the process value 31c includes the gas flow rate of the untreated flue gas, the concentration of sulfur dioxide in the untreated flue gas (inlet SO ₂ concentration), and the concentration of the sulfur dioxide gas in the treated flue gas (outlet S).
O ₂ concentration), CaCO ₃ concentration of the absorption tower slurry, the latest data of the slurry circulation flow rate, etc. are input.

The characteristic of the number of operating pumps is, for example, the relationship between the load and the number of operating pumps as shown in FIG.
This is a characteristic indicating the minimum required number of operating pumps according to the load. Further, the outlet SO ₂ concentration characteristic is, for example, a relationship between the load and the outlet SO ₂ concentration as shown in FIG. 1, and even if conditions such as the load and the number of operating pumps fluctuate, the amount of CaCO _{3 in} the absorption tower slurry is changed. The density is set to be constant.

The simulation model 31 is realized, for example, as follows. That is, the performance of the desulfurization device is generally represented by the following equations (4) and (5).

[0048]

Yso ₂ out = f (G, Yso ₂ in, [CaCO ₃ ], L, k) (4) ηso ₂ = g (G, Yso ₂ in, [CaCO ₃ ], L, k) (5) )

Here, Yso ₂ out is the concentration of SO _{2 at the} outlet of the desulfurizer, Yso ₂ in is the concentration of SO _{2 at the} inlet of the desulfurizer, G is the amount of processing gas, and [CaCO ₃ ] is the amount of CaCO ₃ in the slurry of the absorption tower.
₃ Concentration, L is the slurry circulation flow rate, f and g are functions representing the characteristics of the desulfurizer, ηso ₂ is the desulfurization rate, and k is the activity value (dissolution rate) of the absorbent.

That is, the concentration of SO _{2 at the} outlet of the desulfurization device can be obtained via the function f with respect to the above input value. This function f is described in JP-A-59-199021 or JP-A-63-1990.
It may be realized by a chemical reaction model as shown in Japanese Patent Application Laid-Open No. 229126, and the characteristics of the actual desulfurization device to be controlled under various operating conditions are measured and modeled by a method such as statistical processing. Is also possible.

[0051] In the prior application publication mentioned above, instead of CaCO ₃ concentration of the absorption tower slurry, although the absorption tower pH is a variable, which contributes essentially neutralization reaction in the absorption tower to CaCO ₃ Concentration is a variable that more directly affects desulfurization performance than pH.

[0052] In this control method, the concentration of unreacted limestone in the absorption tower slurry, i.e. for determining the set value of the outlet SO ₂ concentration such that the CaCO ₃ concentration constant, CaCO ₃ concentration is fixed for example to a constant value Then, the outlet SO ₂ concentration at each load is calculated by the simulation model. This constant value may be determined, for example, as follows.

That is, as a constraint on the operation of the desulfurization apparatus, it is generally necessary to ensure gypsum purity. CaCO ₃ in the absorption tower slurry is extracted together with the gypsum from the absorption tower.
Since it becomes an impurity in gypsum, the upper limit of the CaCO ₃ concentration for securing the gypsum purity is determined in consideration of the concentration of other impurities (dust and impurities in limestone, etc.).
If the operation is performed with the upper limit set to the above-mentioned constant value, it is possible to reduce the number of circulating pumps of the absorption tower and to save energy while keeping the outlet SO ₂ concentration below the target value.

The set value of the outlet SO ₂ concentration at each load needs to be set for each of the properties of the exhaust gas (properties of the boiler fuel) and the circulating flow rate (the number of operating circulating pumps of the absorption tower). Although it is possible to determine the set value based on the calculation or the actual machine operation data measurement result, in order to avoid the trouble of storing and selecting the set value for each fuel property and circulating flow rate, the processing of the simulation model 31 must be performed. It is preferable that the optimum value under the latest condition is determined and set every time at a constant cycle.

As described above, in the simulation model 31, the above calculations are performed under various load conditions, and the limestone concentration is maintained at the above-mentioned constant value which does not fall below the lower limit of the gypsum purity. Target value for outlet SO ₂ concentration load (ie, outlet SO ₂ concentration characteristics)
But is set for each pump volume, yet, the minimum necessary pump operation number commensurate with the load (i.e., the pump operation number characteristic) is determined in a range not exceeding the upper limit of the outlet SO ₂ concentration.

Next, the arithmetic unit 32 (outlet SO ₂ concentration setting means) receives the signal 32 a of the actual number of pumps operated and the signal 23 a of the desulfurization load output from the multiplier 23, and sets it by the simulation model 31. Exit SO ₂
The set value of the outlet SO ₂ concentration is output based on the concentration characteristics.

In this case, since the outlet SO ₂ concentration characteristic is set for each number of operating pumps as described above, the arithmetic unit 32 receives the signal 32 indicating the number of operating pumps.
The outlet SO ₂ concentration characteristic corresponding to “a” is selected, and the output value of the outlet SO ₂ concentration is determined from the input desulfurization load signal based on this characteristic. For example, when the outlet SO ₂ concentration characteristic as shown in FIG. 1 is selected, the signal of the desulfurization load is equivalent to 40 ppm when it is equivalent to 100%, and is equivalent to 20 ppm when it is equivalent to 50%.

The computing unit 33 (pump control means)
Receives the signal 33a of the power generation amount command (boiler load),
The set value of the number of operating pumps is output based on the characteristic of the number of operating pumps set by the simulation model 31. For example, when the pump operation number characteristic as shown in FIG.
If it is equivalent to 0 to 100%, it becomes three, and if it is equivalent to 0 to 40%, it becomes two. The output of the calculator 33 is
The pump is input to a pump drive control unit 34 (pump control means) that controls the drive of the pumps, and the pumps are controlled by the pump drive control unit 34 to operate the number of pumps according to the set value at the rated constant rotation speed.

In this case, since the power generation command 33a in which the change in the load variation appears first is used as the load signal input to the arithmetic unit 33, the response to the load variation is further improved. In this case, the signal 33a of the power generation amount command is also input to the adder 24 for correcting the input amount of the limestone slurry (absorbent slurry). If there is a sudden load change, the absorbent slurry is preceded. It is configured to increase and correct the input amount.

In this embodiment, the flow controller 17 (shown in FIG. 6) and the like described in the prior art correspond to the absorbent charging means of the present invention, and the sensors 21, 22 and the multiplier 23 detect the load of the present invention. The means is that the sensor 25 is connected to the outlet SO of the present invention.
₍₂₎ Concentration detecting means, the adder 24 and the flow rate setting unit 28 constitute an absorbent input amount setting means, and the feedback control unit 27 constitutes a deviation output means.

Next, the operation of the control device for the above-mentioned flue gas desulfurization device will be described. With the control device as described above, the control target value of the outlet SO ₂ concentration is changed according to the load condition and the like by the functions of the simulation model 31 and the calculator 32 (outlet SO ₂ concentration setting means). The input flow rate of limestone is adjusted by the feedback control, and the limestone concentration (absorbent concentration) in the slurry is maintained substantially constant. In other words, the outlet SO ₂ concentration control is performed so that the limestone concentration in the slurry is substantially constant, and the operation is performed within a range where the outlet SO ₂ concentration does not exceed the upper limit value.

For example, in FIG. 3, the limestone concentration is held at the value indicated by reference numeral S1. When the load is 100%, the limestone concentration is controlled to the point indicated by reference numeral A, and when the load is 50%, the control is performed at the point indicated by reference numeral B. Is done. The fact that the limestone concentration is kept constant means that the amount of unreacted limestone is kept constant because the capacity of the absorption tower tank is kept constant. However, this amount does not need to be changed. Therefore, even if a sudden load increase, never input amount increasing limestone is delayed greatly, less variation in the measured value of the outlet SO ₂ concentration, as shown in FIG. 4, for example.

On the other hand, for example, in the case of the conventional outlet SO ₂ concentration constant control, for example, when the load is 100%, the control is performed at the point indicated by the symbol A in FIG.
In the case of, the limestone concentration (the amount of limestone possession) fluctuates greatly from S1 to S2, for example, it is controlled to the point indicated by the symbol C.

Therefore, for example, when the load is suddenly increased from 100% to 100% from the state indicated by reference symbol C at a load of 50%, it is impossible to immediately increase the limestone possession from S2 to S1. there, the actual state of the apparatus becomes in the vicinity of the point indicated by the temporary code D, it exceeds the upper limit outlet sO ₂ concentration is greatly increased.

In the case of this example, since the limestone concentration is maintained at a constant level, the purity of the gypsum produced as a by-product is stable at a lower limit or more.

In the apparatus of this embodiment, a simulation model 31 capable of faithfully simulating the behavior of the desulfurization apparatus is provided.
Is used to determine the above-described outlet SO ₂ concentration characteristic, and feedback control is performed so that the outlet SO ₂ concentration target value is based on this characteristic. For this reason, the control accuracy is high, and the followability to the load fluctuation and the stabilization of the gypsum purity are more highly realized.

In the apparatus of this embodiment, the number of operating pumps (optimum number of operating pumps according to the load) is set by the simulation model 31. Based on these characteristics, the computing unit 33 and the pump driving unit 34 (pump control means) The operation of ()) starts and stops the pump. For this reason, the pump power is reduced in the case of a low load as compared with the case where the maximum circulation flow rate (100% operating state) is always maintained.

Also, the present apparatus can control the outlet SO ₂ concentration to
Since the limestone concentration in the slurry is indirectly controlled to maintain the desulfurization performance and the like against load fluctuation, the above-described problem of the conventional pH control is also solved.

The present invention is not limited to the above-described embodiment, and may have various aspects. For example, the outlet SO ₂ concentration characteristic of the present invention does not necessarily need to be periodically updated and set by a simulation model. In a plant where the condition variation such as the smoke emission property is small, for example, as shown in FIG. or by certain outlet SO ₂ concentration characteristic obtained by actual performance measurements may be configured to set the outlet SO ₂ concentration. Further, when there is little demand for energy saving, it is not necessary to control the number of operating circulation pumps. In this case, the control device has an extremely simple configuration as shown in FIG.

Further, the control method of the present invention is not necessarily required to be automatically performed by the control device, and the whole or a part of the control process may be performed by a manual operation including manual calculation. Further, the present invention is not limited to a tank oxidation type desulfurization apparatus, and the same effects can be obtained even when applied to a type of desulfurization apparatus in which an oxidation tower is installed separately from an absorption tower.

[0071]

In the flue gas desulfurization apparatus according to the first aspect, the outlet SO ₂ concentration setting means determines the sulfur dioxide gas concentration in the treated flue gas based on a predetermined outlet SO ₂ concentration characteristic from the output of the load detecting means. The set value of the outlet SO ₂ concentration is determined, the deviation output means outputs the difference between the set value and the actually measured value of the outlet SO ₂ concentration, and the absorbent setting means sets the difference between the set value and the load detection means. Based on the output, the stoichiometric equivalent corresponding to the amount of sulfurous acid gas, the amount of the absorbent added by adding the correction amount corresponding to the deviation is calculated, the absorbent input means, based on this input amount Add the absorbent into the slurry. The outlet SO ₂ concentration characteristic is set so that the concentration of the unreacted absorbent in the slurry is constant with respect to load fluctuation.

For this reason, according to the present apparatus, the control target value of the outlet SO ₂ concentration is changed in accordance with the load condition by the function of the outlet SO ₂ concentration setting means, and the feed amount of the absorbent is adjusted by the feedback control based on this. Adjusted to keep the absorbent concentration in the slurry substantially constant. In other words, the outlet SO ₂ concentration control is performed so that the absorbent concentration in the slurry becomes substantially constant.

The fact that the concentration of the absorbent is kept constant means that the amount of the unreacted absorbent is kept constant. In this apparatus, it is necessary to change this amount even if the load fluctuates. Absent. Therefore, even if there is a sudden increase in the load, the increase in the amount of the absorbent introduced does not greatly delay, and for example, as shown in FIG. 4, the fluctuation of the measured value of the outlet SO ₂ concentration decreases, and the load following ability is markedly improved. improves. Further, since the concentration of the absorbent is kept constant, there is an effect that the purity of the gypsum by-produced becomes stable.

Further, the present apparatus can control the outlet SO ₂ concentration to
Since the limestone concentration in the slurry is indirectly controlled to maintain the desulfurization performance and the like against load fluctuation, the above-described problem of the conventional pH control is also solved.

Further, in the flue gas desulfurization apparatus according to the _{second aspect,} the outlet SO ₂ concentration characteristics of the outlet SO ₂ concentration setting means may be determined by performing a desulfurization simulation based on the latest process value to obtain a sulfur dioxide gas in the treated flue gas. The concentration is periodically obtained by a simulation model for estimating the concentration, and is updated and set at a predetermined period. For this reason, the accuracy of the control is increased, and the followability to the load fluctuation and the stabilization of the gypsum purity are more highly realized.

Further, in the flue gas desulfurization apparatus according to the third aspect,
The characteristics of the number of operating pumps (optimum operating number according to the load) are set by the simulation model, and the pump is started and stopped by the operation of the pump control means based on these characteristics. Therefore, there is an effect that the operating power of the pump is reduced.

Further, in the flue gas desulfurization apparatus according to the fourth aspect,
The pump control means starts and stops the pump based on, for example, a preset number-of-operating-units characteristic (optimal operating number according to load). Therefore, there is an effect that the operating power of the pump is reduced.

In the flue gas desulfurization method according to the fifth aspect, the amount of the sulfurous acid gas and the amount of the treated sulfurous acid are controlled so that the concentration of the unreacted absorbent in the slurry becomes constant with respect to the variation in the amount of sulfurous acid gas in the untreated flue gas. Outlet SO, which is related to the concentration of sulfur dioxide in post-smoke
₂ Set the concentration characteristics, and based on the outlet SO ₂ concentration characteristics,
The set value of the sulfur dioxide concentration is obtained from the actual amount of the sulfur dioxide in the untreated exhaust gas, and the amount of the absorbent is adjusted based on the set value to control the sulfur dioxide concentration.

For this reason, the control target value of the outlet SO ₂ concentration is changed in accordance with the load condition, and the amount of the absorbent to be introduced is adjusted by the control based on this, so that the absorbent concentration in the slurry is maintained substantially constant. You. Therefore, load followability is improved,
The purity of by-produced gypsum becomes stable,
The above-described problem in the case of the conventional pH control is also solved.

In the flue gas desulfurization method according to the sixth aspect, the amount of the sulfurous acid gas and the amount of the treated sulfurous acid are controlled so that the concentration of the unreacted absorbent in the slurry becomes constant with respect to the variation in the amount of sulfurous acid gas in the untreated flue gas. Outlet SO, which is related to the concentration of sulfur dioxide in post-smoke
₍₂₎ Set a concentration characteristic, determine a set value of the sulfur dioxide concentration in the exhaust gas after treatment based on the outlet SO ₂ concentration characteristic from the detected value of the sulfur dioxide gas amount, and determine the set value and the sulfur dioxide concentration. A deviation from the detected value is calculated, and based on the deviation and the detected value of the sulfurous acid gas amount, an absorption obtained by adding a correction amount corresponding to the deviation to a stoichiometric equivalent corresponding to the sulfurous acid gas amount. The dosage of the agent is calculated, and the absorbent is injected into the slurry based on the calculated dosage.

For this reason, the control target value of the outlet SO ₂ concentration is changed in accordance with the load condition, and the amount of the absorbent adsorbed is adjusted by the feedback control based on this, so that the absorbent concentration in the slurry is maintained substantially constant. Is done. Therefore, the load following ability is remarkably improved, the purity of the gypsum by-produced becomes stable, and the above-mentioned problem of the conventional pH control is solved.

In the flue gas desulfurization method according to the seventh aspect, the start and stop of the pump are determined based on the pump operation number characteristics (optimum operation number corresponding to the load) set in advance or appropriately set by a real-time simulation model. I do. Therefore, there is an effect that the operating power of the pump is reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of a control device of a flue gas desulfurization device of the present invention.

FIG. 2 is a block diagram showing another example of the control device of the flue gas desulfurization device of the present invention.

FIG. 3 shows a relationship between an absorbent concentration and an outlet SO ₂ concentration.
It is a figure explaining an operation of the present invention.

FIG. 4 is a diagram for explaining the operation (load followability) of the present invention.

FIG. 5 is a diagram for explaining a conventional problem (load followability).

FIG. 6 is a diagram illustrating an example of a main body configuration of the flue gas desulfurization device.

FIG. 7 shows an example of a control technique of a conventional flue gas desulfurization apparatus (exit S
FIG. 4 is a diagram showing O ₂ concentration constant control).

[Explanation of symbols]

5 Circulating pump 17 Flow rate controller (absorbent charging means) 21, 22 Sensor (load detecting means) 23 Multiplier (load detecting means) 24 Adder (absorbent charging amount setting means) 25 Sensor (outlet SO ₂ concentration detecting means) 27) feedback control section (deviation output means) 28 flow rate setting section (absorbent input amount setting means) 31 simulation model 32 computing unit (outlet SO ₂ concentration setting means) 33 computing unit (pump control means) 34 pump drive control section ( Pump control means)

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Susumu Okino 4-6-22 Kannonshinmachi, Nishi-ku, Hiroshima-shi, Hiroshima Inside Hiroshima Research Laboratory, Mitsubishi Heavy Industries, Ltd.

Claims (7)

[Claims] 1. A flue gas desulfurization device for absorbing at least sulfur dioxide in untreated flue gas by bringing untreated flue gas and a slurry containing an absorbent comprising a calcium compound into contact in an absorption tower. an outlet SO ₂ concentration detection means for detecting the sulfur dioxide concentration in the rear flue, a load detecting means for detecting the sulfur dioxide content in the untreated flue gas to be processed and the outlet SO from the output of the load detecting means based on ₂ density characteristics, and an outlet SO ₂ concentration setting means for determining the set value of sulfur dioxide concentration in the processed flue gas, this outlet SO ₂ concentration setting means, the outlet SO ₂ and set the set value A deviation output means for calculating a deviation from an actually measured value by the concentration detection means, and a stoichiometric equivalent corresponding to the sulfur dioxide gas amount based on an output of the deviation output means and an output of the load detection means. Means for setting the amount of the absorbent added by adding the correction amount corresponding to the deviation, and the absorbent in the slurry based on the amount of the input calculated by the amount setting means for the absorbent. and a absorbent dosing means for introducing the outlet SO ₂ concentration characteristics at the outlet SO ₂ concentration setting means is a relationship between the set value of the concentration of sulfur dioxide load and after processing the flue gas, to the load variation Wherein the concentration of the unreacted absorbent in the slurry is set to be constant. 2. The outlet SO ₂ concentration characteristic of the outlet SO ₂ concentration setting means is periodically obtained by a simulation model for performing a desulfurization simulation based on the latest process value and estimating a sulfur dioxide gas concentration in the exhaust gas after treatment. 2. The flue gas desulfurization apparatus according to claim 1, wherein the flue gas desulfurization apparatus is updated and set at a predetermined cycle. 3. A simulation model comprising a plurality of pumps for circulating the slurry in the absorption tower, wherein the simulation model sets the outlet SO ₂ concentration characteristic for each number of operating pumps and performs load fluctuation by the desulfurization simulation. Pump operating number characteristic indicating the optimal operating number of the pumps with respect to the outlet SO ₂
Concentration setting means selects the corresponding characteristic of said outlet SO ₂ concentration profile by actual pump operation number, a configuration for setting the concentration of sulfur dioxide flue gas in the post-processing based on the selected characteristic 3. The flue gas desulfurization apparatus according to claim 2, further comprising a pump control unit that starts and stops the pump based on the characteristic of the number of operating pumps. 4. A pump having a plurality of pumps for circulating the slurry in the absorption tower, wherein the outlet S
While setting the O ₂ concentration characteristics, the outlet SO ₂ concentration setting means selects a corresponding characteristic among the outlet SO ₂ concentration characteristics according to the actual number of pumps operated, and performs a post-processing based on the selected characteristics. It is configured to set the concentration of sulfurous acid gas in flue gas, and provided with pump control means for starting and stopping the pump based on a pump operating number characteristic indicating an optimal operating number of the pump with respect to a load change. The flue gas desulfurization device according to claim 1, wherein: 5. A flue gas desulfurization method for absorbing at least sulfur dioxide in untreated flue gas by bringing untreated flue gas into contact with a slurry containing an absorbent comprising a calcium compound in an absorption tower. An outlet which is a relationship between the amount of the sulfurous acid gas and the concentration of the sulfurous acid gas in the post-treatment flue gas so that the concentration of the unreacted absorbent in the slurry becomes constant with respect to the variation in the amount of the sulfite gas in the treated flue gas. An SO ₂ concentration characteristic is set, and a set value of the sulfur dioxide gas concentration is obtained from the actual amount of the sulfur dioxide gas in the untreated exhaust gas based on the outlet SO ₂ concentration characteristic, and the absorbent is charged based on the set value. A flue gas desulfurization method comprising controlling the sulfur dioxide gas concentration by adjusting the amount. 6. A flue gas desulfurization method for absorbing at least sulfur dioxide in untreated flue gas by bringing untreated flue gas and a slurry containing an absorbent comprising a calcium compound into contact in an absorption tower. detecting the sulfur dioxide content in the untreated flue gas to be treated and the concentration of sulfur dioxide in the rear flue, the sulfite sulfur dioxide amount based from the detection value to a predetermined outlet SO ₂ concentration characteristic after processing the flue gas A set value of the gas concentration is determined, a deviation between the set value and the detected value of the sulfur dioxide gas concentration is calculated, and a chemical corresponding to the sulfur dioxide gas amount is calculated based on the deviation and the detected value of the sulfur dioxide gas amount. Calculating the amount of the absorbent to be added by adding a correction amount corresponding to the deviation to the stoichiometric equivalent, and introducing the absorbent into the slurry based on the calculated amount of the input; ₂ Density characteristics The characteristics indicating the relationship between the sulfurous acid gas amount and the sulfurous acid gas concentration are set so that the concentration of the unreacted absorbent in the slurry is constant with respect to the fluctuation of the sulfurous acid gas amount. Flue gas desulfurization method. 7. The slurry is circulated in the absorption tower by a plurality of pumps, and the outlet SO ₂ concentration characteristic is set for each number of operating pumps. ₂ Select the corresponding characteristic from the concentration characteristics, set the concentration of sulfurous acid gas in the exhaust gas after treatment based on the selected characteristic, and operate the pump indicating the optimal number of the pumps to operate with respect to load fluctuation. 7. The flue gas desulfurization method according to claim 5, wherein starting and stopping of the pump are performed based on the number characteristic.