JP2002001059A - Method and apparatus for desulfurization using granular limestone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To advance a desulfurization reaction using granular limestone smoothly by controlling the amount of new limestone to be supplied after grasping the amount of the granular limestone packed in a tank for neutralizing an absorption liquid. SOLUTION: A pressure loss when the absorption liquid which absorbed sulfur oxide in exhaust gas is oxidized and passes through the limestone packed in a neutralization tank 17 for neutralization is proportional to the difference between gravity and buoyancy acting on the granular limestone suspending in a fluidized bed. Since both the gravity and the buoyancy are proportional to the height of a limestone layer, i.e., the amount of the packed limestone, a relationship of limestone layer pressure loss ΔP=f (amount of packed limestone) is satisfied, so that the amount of the granular limestone packed in the neutralization tank can be grasped by detecting the pressure loss of the limestone layer. As a result, the difference between the level of the absorption liquid when the granular limestone is packed and the level when it is not packed is obtained, and the pressure loss when the absorption liquid passes through the limestone layer is calculated from the signal of the number of operated circulating pumps 3, so that the amount of the packed limestone can be controlled.

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 treatment system for treating combustion exhaust gas from a boiler or the like, and more particularly to an absorption medium for absorbing sulfur dioxide gas (hereinafter referred to as SO2) in exhaust gas having a size of several mm or less. The present invention relates to a preferable method for supplying limestone when granular limestone is used.

[0002]

2. Description of the Related Art Most of flue gas desulfurization systems in boiler plants are actually operated by a wet method. In the wet method, limestone finely pulverized to about several hundred meshes is usually used as an absorbent for SO2 gas. Hundreds of meshes correspond to 100 to 200 μm or less in terms of limestone particle size, and are of a fine size, so the limestone supplied to the desulfurization device is dispersed by mechanical stirring such as a stirrer, and is contained in the absorbing solution. Almost uniformly distributed.

FIG. 4 shows a system of a conventional desulfurizer. The conventional desulfurization apparatus shown in FIG. 4 mainly includes an absorption tower main body 1, a circulation tank 2, a circulation pump 3, a mist eliminator 4, an absorption tower inlet duct 5, an absorption tower outlet duct 6, a bleed pump 7, a spray section 9, and the like. Become.

Although not shown, the exhaust gas discharged from the boiler passes through an inlet duct 5 by a desulfurization fan (not shown), is introduced into the main body of the absorption tower 1, and is discharged from an outlet duct 6. During this time, the absorbing liquid containing limestone, which is sent by being pressurized by the circulation pump 3, is sprayed from the spray unit 9 into the absorption tower main body 1, and gas-liquid contact between the absorbing liquid and the exhaust gas is performed.

[0005] At this time, the absorbing liquid absorbs SO2 in the exhaust gas to generate calcium sulfite. The absorption liquid that has generated calcium sulfite accumulates in the circulation tank 2, and the oxygen contained in the oxidizing air 16 oxidizes calcium sulfite in the absorption liquid to produce gypsum.

A part of the absorbent in the circulation tank 2 where limestone and gypsum coexist is again sprayed by the circulation pump 3 into the spray section 9.
And a part is sent from the bleed pump 7 to the gypsum recovery system. Limestone, which is an absorbent, is supplied from the supply line 14 to the circulation tank 2 as limestone slurry.

[0007] As a method of controlling the supply of limestone slurry, a computing unit 13 uses a signal sent from a gas flow meter 11 (or a boiler load signal meter) and an SO2 concentration meter 12 installed in the absorption tower inlet duct 5. The required limestone amount is calculated, and feedforward control for adjusting the opening of the limestone flow control valve 15 is performed.

At the same time, a feedback control system for adjusting the opening of the limestone flow control valve 15 so that the pH in the absorption tower main body 1 is kept constant by the pH meter 10 installed in the absorption liquid extraction line 8 is also incorporated. I have.

However, the conventional fine particle size (100 to 2)
0.5 μm instead of limestone slurry
Particle size of about 10 to 10 mm (approximately 50
In a system in which granular limestone having a size of about 100 times is used as a desulfurizing agent, the absorption liquid that has absorbed SO2 is neutralized with a site for oxidizing (the circulation tank 2 or an oxidation tank not shown but separately provided). It is divided into parts (neutralization tank not shown).

[0010] The neutralization tank is filled with granular limestone, and is neutralized by contact with the absorbing liquid by the flow of the granular limestone. Granular limestone has a particle diameter of about 50 to 100 times that of conventional limestone having a fine particle size, and therefore does not exist uniformly in all the absorbing liquids. It is held and comes into contact with the absorbing solution to cause a neutralization reaction.

One of the factors governing the desulfurization performance is the pH value of the absorbing solution, and the control of this pH value is widely used also in currently operating desulfurization plants. In the prior art using fine-grained limestone, limestone is uniformly present in the absorbing solution, and the limestone concentration in the absorbing solution determines the pH value, whereas in the granular limestone system, the limestone is filled in the neutralization tank. The amount of limestone determines the pH value. That is, in order to incorporate the pH value control function in the granular limestone system, it is necessary to know the amount of limestone filled in the neutralization tank.

For example, in the case where it becomes difficult to maintain an appropriate pH value of the absorbing solution due to some sudden change, in the related art, limestone is supplied to recover the pH of the absorbing solution, and the limestone concentration in the absorbing solution is increased. However, in the granular limestone system, excess limestone was filled in the neutralization tank, and limestone with a large particle size was entrained in the gypsum recovery system, and gypsum purity was greatly reduced. There is a concern that we cannot be satisfied.

In addition, since the limestone is excessively filled in the neutralization tank, fluidization of the limestone is weakened, and the desulfurization performance is deteriorated by circulating the unneutralized absorbent through the spray section 9, and the worst case is caused. In this case, tripping of the circulation pump 3 due to the stop of fluidization, that is, an emergency stop of the desulfurization device, may be caused.

That is, in the granular limestone system,
It is necessary to control the amount of supplied limestone after grasping the amount of limestone filled in the neutralization tank.

[0015]

When granular limestone is used in the limestone supply method according to the prior art, the purity of the formed gypsum decreases due to the incorporation of large-diameter limestone into gypsum.
And the smooth fluidization of granular limestone was not taken into account.

An object of the present invention is to maintain a supply amount of limestone to a neutralization tank so that the amount of limestone charged in the neutralization tank always exceeds a quantity required for neutralizing the absorbing solution by a certain amount or more. And a desulfurization apparatus using the same.

[0017]

The object of the present invention can be solved by the following constitution. (1) The sulfur oxides in the exhaust gas discharged from a combustion device such as a boiler are brought into contact with an absorbing solution in an absorption tower, and the absorbing solution having absorbed the sulfur oxides is oxidized in an oxidation tank, and then filled with granular limestone. Neutralized by passing through the neutralization tank
In the desulfurization method using granular limestone circulated again to the absorption section by one or more circulation pumps, the amount of limestone charged in the neutralization tank is determined by the difference between the level of the absorption liquid in the oxidation tank and the level of the absorption liquid in the neutralization tank and circulation. A desulfurization method using granular limestone that supplies limestone to a neutralization tank so that a predetermined amount of limestone is charged into the neutralization tank by detecting based on the number of operating pumps or the amount of circulating liquid.

(2) an absorption tower for bringing sulfur oxides in exhaust gas discharged from a combustion device such as a boiler into contact with an absorbing solution;
An oxidation tank that oxidizes the absorbing solution that has absorbed the sulfur oxides in the absorption tower, and a granular limestone packed layer that neutralizes the absorbing solution by passing the absorbing solution in the oxidation tank through the granular limestone packed bed. In a desulfurization apparatus equipped with a sump tank and one or more circulation pumps for circulating and supplying the absorbent passed through the neutralization tank to the absorption tower, an absorption liquid level meter in the neutralization tank, The absorption liquid level meter and the supply amount of limestone to be supplied to the neutralization tank so that a predetermined amount of limestone is charged based on the liquid level difference between the two liquid level meters and the number of operating circulating pumps or the amount of circulating liquid. A desulfurization apparatus using granular limestone provided with an arithmetic unit for calculating and a supply unit of the calculated amount of granular limestone.

[0019]

The pressure loss (hereinafter, sometimes referred to as pressure loss) when the absorbent passes through the granular limestone layer filled in the neutralization tank is determined by the gravity and buoyancy acting on the limestone floating in the fluidized bed. It is possible to organize as the difference of. At this time, since both gravity and buoyancy are proportional to the limestone layer height, that is, the limestone filling amount, the relationship of gravity and buoyancy = f (limestone filling amount) is established.

On the other hand, since the pressure loss of the granular limestone layer can be arranged as the difference between gravity and buoyancy, the relationship of limestone layer pressure loss △ P = f (limestone filling amount) is established, and the pressure loss when passing through the limestone layer is established. Increases in proportion to the height of the limestone layer, ie the limestone loading. Therefore, by detecting the pressure loss of the limestone layer, it becomes possible to grasp the amount of granular limestone filled in the neutralization tank.

[0021]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a granular limestone supply system of a deflower according to an embodiment of the present invention. The granular limestone system is divided into a part that oxidizes the absorbing solution that has absorbed SO2 (an oxidation tank (same as the circulation tank 2)) and a part that neutralizes limestone by fluidization (neutralization tank 17).

The desulfurization apparatus shown in FIG. 1 mainly includes an absorption tower main body 1, a circulation tank 2, a circulation pump 3, a mist eliminator 4, an absorption tower inlet duct 5, an absorption tower outlet duct 6, a bleed pump 7, and a spray section 9. It also comprises a neutralization tank 17 to which the absorbing liquid from the circulation tank 2 is sent. Exhaust gas discharged from a boiler (not shown) passes through an inlet duct 5 by a desulfurization fan (not shown), is introduced into the absorption tower main body 1, and is discharged from an outlet duct 6.

During this time, the absorbing liquid pressurized by the circulation pump 3 is sprayed from the spray section 9 in the absorption tower main body 1, and gas-liquid contact between the absorbing liquid and the exhaust gas is performed. At this time, the absorbing liquid absorbs SO2 in the exhaust gas and generates sulfurous acid. The absorbing solution that has generated sulfurous acid accumulates in the circulation tank 2, and the oxygen contained in the oxidizing air 16 supplied to the circulation tank 2 oxidizes the sulfurous acid in the absorbing solution to generate sulfuric acid.

The absorption liquid in the circulation tank 2 is sent into the neutralization tank 17 due to the level difference ΔH between the level of the absorption liquid and the level of the absorption liquid in the neutralization tank 17, and is filled in the neutralization tank 17. The granulated limestone is fluidized and reacts with sulfuric acid contained in the absorbing solution to produce gypsum.

The absorption liquid is extracted while the particulate limestone is selectively retained in the neutralization tank 17 among the absorption liquid and the particulate limestone, which are components in the neutralization tank 17, and a part thereof is circulated by a circulation pump. 3 again sends it to the spraying section 9 and the other absorbing liquid is sent from the bleed pump 7 to the gypsum recovery system. Limestone, which is an absorbent, is supplied to the neutralization tank 17 through the supply line 14 as limestone slurry or solid limestone.

The supply of limestone to the neutralization tank 17 is controlled in a batch system. Since it is sufficient that the neutralization tank 17 is filled with limestone necessary for satisfying the neutralization performance, limestone is supplied so as to always maintain a higher filling amount.

The amount of limestone charged in the neutralization tank 17 is
It is calculated by the calculator 13 from the signal from the liquid level meter 19 of the absorbing liquid in the inside, the liquid level meter 20 of the absorbing liquid in the circulation tank 2 and the signal of the number of operating circulation pumps 3.

As a result, the neutralization tank 17 is not filled with limestone more than necessary, and the operation of the desulfurization device is not hindered by the excessive supply of limestone.

The above is the purpose of the present invention. Hereinafter, a method for detecting the amount of limestone charged into the neutralization tank 17 and a method for controlling the liquid level in the neutralization tank 17 will be described in detail.

FIG. 2 shows the relationship between the limestone filling amount Q in the neutralization tank 17 and the liquid level difference ΔH in the neutralization tank 17. △ H in the figure
0 is the liquid level difference between the circulating tank 2 and the neutralizing tank 17 when the neutralizing tank 17 is not filled with limestone,
This value corresponds to the pressure loss when the absorbent passes through the communication pipe 18 from the circulation tank 2 which is also an oxidation tank to the neutralization tank 17.

Incidentally, this value can be grasped by adjustment at the time of trial operation. Next, the neutralization tank 17 is filled with limestone, and by measuring the liquid level difference ΔH each time, the relationship between the limestone layer height and the liquid level difference ΔH can be grasped.

Attention is paid to the point that the liquid level difference ΔH1 is obtained.
7 is the pressure loss of the absorbent when passing through the limestone layer of (7)
H1− △ H0) causes a pressure loss of the limestone layer.

The amount of limestone filling at this time is Q1, that is, the amount of limestone filling in the neutralization tank 17 is determined by detecting the liquid level difference ΔH between the circulation tank 2 and the neutralization tank 17. Becomes possible.

At the same time, when the actual operation state of the desulfurization unit is taken into consideration, it is possible to operate the desulfurization unit with the circulating liquid amount to the spray unit 9 lower than the planned condition depending on the gas amount and the SO2 load. Also exists. In this case, an operation is also performed to cut the number of operating circulating pumps 3 which is usually a plurality of units.

Since the liquid level difference ΔH is a pressure loss of the absorbent, it differs depending on the amount of circulating liquid, that is, the number of operating circulating pumps 3. It is necessary to understand the relationship of the difference ΔH.

As described above, it is possible to detect the amount of limestone charged in the neutralization tank 17.
Control of supply amount of limestone necessary for performance and control of filling amount of neutralization tank 17 such as interlock necessary for structure (protection to prevent limestone from being overfilled into neutralization tank and overflowing) The interlock controls the limestone in the neutralization tank so that it does not exceed a certain amount.).

Next, a method for supplying granular limestone into the neutralization tank 17 will be described. In the conventional method, the amount of SO2 absorption is calculated based on the gas amount and the SO2 concentration, and fine limestone corresponding to the calculated amount is intermittently supplied to the circulation tank which is also a neutralization tank. In the desulfurization system of the present invention, limestone can be batch-supplied to the neutralization tank 17. FIG. 3 shows an explanatory diagram of limestone batch supply.

As described above, the amount of limestone charged in the neutralization tank 17 can be detected by the liquid level difference ΔH between the circulation tank 2 and the neutralization tank 17, so that the sulfuric acid in the absorption liquid is neutralized. What is necessary is just to always maintain the limestone layer height or more necessary to satisfy the required performance.

That is, the minimum limestone layer height required for neutralization of the absorbent is set to the minimum level, and a predetermined limestone layer height is added as a batch from the required limestone layer height. Limestone should be supplied into the neutralization tank 17.

In FIG. 3, when the limestone filling amount Q1 corresponds to the required minimum limestone layer height and the liquid level difference ΔH1 corresponding to the limestone filling amount Q1 is reached, the granular limestone is removed from the neutralization tank 17.
Start supplying.

Then, the supply of the limestone is stopped when the liquid level difference ΔH2, which is known in advance and corresponds to the filling amount Q2 corresponding to the maximum limestone layer height, is reached. That is, the limestone filling amount (Q2-Q1) is the limestone supply amount for one batch.

Here, consider the batch supply of fine limestone in the prior art. In the prior art, since fine limestone is supplied, the concentration of limestone in the absorbent is uniform. For this reason, the limestone concentration in the absorbing solution after one batch supply is greatly increased.

However, since the formed gypsum is used as a raw material such as a gypsum board, the gypsum purity is usually specified. Therefore, after one batch is supplied, the limestone concentration is greatly increased and the gypsum purity is maintained. It is feared that it cannot be done.

On the other hand, the granular limestone system of the present invention utilizes granular limestone having a particle size of several mm or less. Therefore, some fine limestone migrates from the surface of the granular limestone into the absorbing solution, but most of the granular limestone is removed from the neutralization tank 17.
Remains selectively in the interior.

Therefore, even after a large amount of limestone is supplied in one batch, a large amount of limestone is not mixed into the gypsum recovery system, and the limestone purity can be maintained.

[0046]

According to the present invention, the amount of limestone filling in the neutralization tank is determined based on the level difference between the oxidation tank and the neutralization tank and the number of operating circulation pumps, and the limestone is supplied in batches, whereby granular limestone is supplied. Enables smooth operation of a desulfurization unit using

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment according to the present invention.

FIG. 2 is a diagram illustrating a pressure loss when passing through a limestone layer.

FIG. 3 is a diagram illustrating a pressure loss when passing through a limestone layer.

FIG. 4 is a diagram showing a conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Absorption tower main body 2 Circulation tank 3 Circulation pump 4 Mist eliminator 5 Absorption tower entrance duct 6 Absorption tower exit duct 7 Bleed pump 8 Absorbent extraction line 9 Spray part 10 pH meter 11 Gas flow meter 12 SO2 concentration meter 13 Calculator 14 Limestone supply line 15 Limestone flow control valve 16 Oxidation air 17 Neutralization tank 18 Communication pipe 19, 20 Level meter

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kozo Obata 6-9 Takara-cho, Kure-shi, Hiroshima Prefecture Inside the Babcock Hitachi Co., Ltd. (72) Inventor Takanori Nakamoto 6-9 Takara-cho, Kure-shi, Hiroshima Prefecture Babcock Hitachi Co., Ltd. F-term in the Kure office (reference) 4D002 AA02 AC01 BA02 CA01 DA05 DA16 EA07 EA12 EA13 EA14 FA03 GA02 GA03 GB05 GB06 GB09 GB20

Claims (5)

[Claims] Claims 1. After contacting sulfur oxides in exhaust gas discharged from a combustion device such as a boiler with an absorbing solution in an absorption tower and oxidizing the absorbing solution having absorbed the sulfur oxides in an oxidation tank,
Neutralization by passing through a neutralization tank filled with granular limestone, and again in a desulfurization method using granular limestone circulated by one or more circulation pumps to the absorption section, the amount of limestone in the neutralization tank is reduced by the oxidation tank. Detects based on the liquid level difference between the absorption liquid level and the absorption liquid level in the neutralization tank and the number of operating circulation pumps or the amount of circulating liquid, and neutralizes so that a predetermined amount of limestone is filled in the neutralization tank. A desulfurization method using granular limestone that supplies limestone to a tank. 2. The desulfurization method using granular limestone according to claim 1, wherein a predetermined amount of limestone is supplied in excess of the amount of limestone necessary for neutralizing the absorbent in the neutralization tank. 3. The desulfurization method using granular limestone according to claim 1, wherein the limestone is supplied into the neutralization tank in a batch system. 4. The desulfurization using granular limestone according to claim 1, wherein the limestone is supplied into the neutralization tank by giving a control width to the liquid level difference between the absorption liquid level in the oxidation tank and the absorption liquid level in the neutralization tank. Method. 5. An absorption tower for bringing sulfur oxides in exhaust gas discharged from a combustion device such as a boiler into contact with an absorption liquid, an oxidation tank for oxidizing the absorption liquid having absorbed the sulfur oxides in the absorption tower, A neutralization tank provided with a granular limestone packed bed for neutralizing the absorbed liquid by passing the absorbing liquid in the oxidation tank through the granular limestone packed bed; and circulating the absorbing liquid passed through the neutralizing tank to the absorption tower. A desulfurization apparatus provided with one or more circulation pumps for performing the following operations: an absorption liquid level meter in a neutralization tank, an absorption liquid level meter in an oxidation tank, and a liquid level difference between the two liquid level meters and circulation. A calculator for calculating a supply amount of limestone to be supplied to the neutralization tank so that a predetermined amount of limestone is charged based on the number of operating pumps or a circulating fluid amount; and a granular limestone for supplying the calculated amount of granular limestone. Using granular limestone provided with a supply means Apparatus.