JP2003210935A - Wet-type flue-gas desulfurization equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide wet-type flue-gas desulfurization equipment provided with an absorption tower having a structure in which scattering of mist of liquid absorbent is not increased, even when a gas flow-rate in a gas-liquid contact part is increased. <P>SOLUTION: This equipment comprises a spray section, an absorption tower discharging cleaned gas from a flue-gas outlet, a liquid-absorbent tank placed below the absorption tower, and a circulation system for supplying the absorbent from the tank to the spray section. In the spray section, the absorbent containing desulfurization agent for absorbing sulfur oxides in the flue gas introduced from a flue-gas inlet is sprayed from spray nozzles provided in a plurality of stages in the gas-flow direction. In the absorption tower, a gas flow-path is formed to allow flue-gas to flow in the unperpendicular direction from a flue-gas inlet having a comparatively narrow width to the outlet. The spray section is placed in the flue-gas inlet of the tower, and a mist eliminator is placed in the flue-gas outlet. The sectional area of the gas flow-path above the tank is made larger than that of the flue gas inlet. The tank is placed below the absorption tower on the side of the inlet trail-flow and outlet forward- flow. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas purifying apparatus, and more particularly to a wet flue gas desulfurization apparatus equipped with an absorption tower suitable for efficiently removing sulfur oxides from boiler exhaust gas.

[0002]

2. Description of the Related Art Among the air pollution that has become a global problem, particularly in the case of acid rain, sulfur oxides and nitrogen oxides in combustion gas emitted when fossil fuel is burned in a boiler in a thermal power plant Things are one of the factors. Therefore, a wet limestone-gypsum desulfurization method has been widely put into practical use as a method for removing this sulfur oxide. FIG. 2 shows an absorption tower used in a wet limestone-gypsum desulfurization method for removing sulfur oxides from a conventional exhaust gas from a thermal power plant boiler. The boiler exhaust gas 1 is absorbed from the absorption tower 12 from the side of the absorption tower 12.
Be guided inside. In the absorption tower 12, a required amount of limestone, which serves as an absorbent for removing sulfur oxides, is supplied from the limestone supply line 13 into the absorption tower 12, and the absorption liquid containing this limestone is circulated by the circulation pump 14 and the circulation pump. A plurality of spray nozzles 16 arranged above the absorption tower 12 are sprayed as fine droplets through the line 15 and come into countercurrent contact with the boiler exhaust gas 1. At this time, the sulfur oxides in the boiler exhaust gas 1 are absorbed in the absorbing liquid by the reaction shown below.

SO ₂ + H ₂ O → H ₂ SO ₃ (1) CaCO ₃ + 2H ₂ SO ₃ → Ca (HSO ₃ ) ₂ + CO ₂ + H ₂ O (2) The absorption liquid that has absorbed the sulfur oxide is in the absorption tower 12. In the tank part, the oxygen is blown into the lower part of the absorption tower 12 through the air blowing line 17 to be oxidized by oxygen in the air, and the following reaction proceeds to produce gypsum (calcium sulfate). Ca (HSO ₃ ) ₂ + O ₂ + 2H ₂ O → CaSO ₄・ 2H ₂ O + H ₂ SO ₄ (3) CaCO ₃ + H ₂ SO ₄ + H ₂ O → CaSO ₄・ 2H ₂ O + CO ₂ (4) Recover the generated gypsum. Therefore, a part of the absorbing liquid is sent to a gypsum recovery facility (not shown) via the extraction pump 18 and the extraction line 19, and the gypsum is recovered. On the other hand, the treated exhaust gas 1 after the removal of sulfur oxides is discharged from the upper part of the absorption tower 12 to the outside of the tower, but the fine droplets sprayed from the spray nozzle 16 are partly entrained in the exhaust gas flow and out of the system. The mist eliminator 20 is installed above the spray section in order to prevent the discharge of the fine droplets entrained in the exhaust gas flow.

This system uses gas-liquid contact by a spray method, and has less gas pressure loss than other gas-liquid contact methods such as a wet wall method, a submerged bubbling method, and a packed tower method, and sulfur oxide It has the advantages that it can efficiently collect soot and dust during absorption, and that gypsum deposits in the absorption liquid, but the possibility of clogging is low due to the simple structure. On the other hand, this system uses the spray nozzle 16
There are also disadvantages such as large pump power for fine atomization and entrainment of liquid. In order to improve the economical efficiency of the wet flue gas desulfurization device, it is effective to reduce the pump power and reduce the facility cost and the operating cost. It is necessary to increase the reactivity of the absorbed liquid.

When the reaction process between the sulfur oxides in the exhaust gas and the sprayed absorption liquid is considered microscopically, the diffusion of sulfur oxides in the gas boundary film on the gas side at the boundary between the gas and the liquid affects the absorption rate. It has an effect, and on the liquid side, diffusion in the liquid boundary film affects the absorption rate. The absorption rate on the liquid side in the absorption reaction of the sulfur oxide into the absorption liquid at the boundary between the gas and the liquid can be increased as the alkali is stronger, but for that purpose, as an absorbent, Chemicals such as caustic soda (NaOH), which is more expensive than limestone, or a large amount of limestone may be used, but this is not preferable because the cost of the absorbent increases.

On the other hand, on the gas side at the boundary between gas and liquid, if the gas flow velocity at the gas-liquid contact portion is increased, the diffusion of sulfur oxide on the gas side is increased, and the absorption rate of sulfur oxide into the absorbing liquid is increased. Has been found to increase. Further, if the gas flow velocity at the gas-liquid contact portion is increased, the cross-sectional area of the absorption tower becomes smaller, so that the absorption tower 12 can be made compact and the equipment cost can be reduced. However, when the gas flow velocity at the gas-liquid contact portion is increased, the entrainment of the absorbing liquid increases, the load of the mist eliminator 20 in the absorbing tower 12 increases, and the mist cannot be removed completely, and the absorbing liquid moves outside the absorbing tower 12. There is a problem of scattering.

[0007]

In the above prior art, when the gas flow velocity at the gas-liquid contact portion is increased in order to increase the absorption rate of the sulfur oxide in the exhaust gas into the absorption liquid,
There is a problem that the scattering of mist (microdroplets) increases, the load on the mist eliminator increases, and further, the absorbing liquid mist scatters outside the absorption tower. An object of the present invention is to provide a wet flue gas desulfurization apparatus having an absorption tower structure that does not increase the scattering of the absorbing liquid mist even when the gas flow velocity at the gas-liquid contacting portion is increased.

[0008]

The above objects of the present invention can be achieved by the following constitutions. That is, a desulfurizing agent-containing absorption liquid for absorbing sulfur oxides in the exhaust gas introduced from the exhaust gas inlet portion is provided with a spray portion sprayed from a spray nozzle provided in a plurality of stages in the exhaust gas flow direction, and purified gas is discharged from the exhaust gas outlet portion. In the wet flue gas desulfurization apparatus having an absorption tower and a circulation system that circulates the absorption liquid from the absorption liquid tank to the absorption tank and the spray section provided in the lower part of the absorption tower, the absorption tower has a relatively narrow front Equipped with a gas flow path in which the exhaust gas flows from the narrowed exhaust gas inlet portion toward the exhaust gas outlet portion in a non-vertical direction, the spray portion is arranged at the exhaust gas inlet portion of the absorption tower, and the mist eliminator is arranged at the exhaust gas outlet portion, The cross-sectional area of the gas flow path located above the absorbent tank is made larger than the cross-sectional area of the gas flow path at the exhaust gas inlet, and the absorbent tank Which is a wet flue gas desulfurization apparatus disposed in the absorption tower bottom of the upstream side of the outlet portion. At this time, by making the rear part of the exhaust gas introducing part an inclined bottom part, the absorbed liquid after spraying easily flows into the absorption liquid tank.

The spray direction of the absorbing liquid in the spray section of the wet flue gas desulfurization apparatus of the present invention may be countercurrent, cocurrent or a combination of countercurrent and cocurrent with respect to the gas flow.

[0010]

[Function] After the gas-liquid contact is made efficiently in the high gas flow velocity range of the absorption tower, and the gas flow is contacted in the high gas flow velocity range by providing a relatively low gas flow rate region in the wake, the absorbing liquid mist is generated. Even if it is entrained in the gas flow and scattered to the downstream side, part of the absorbing liquid mist falls by gravity in the low gas flow velocity region and is collected in the absorbing liquid tank provided at the bottom of the absorption tower. Since the mist load of the mist eliminator provided on the side is the same as the conventional one, there is no fear that mist scattering outside the absorption tower will increase. Further, the horizontal absorption tower type wet flue gas desulfurization apparatus of the present invention does not need to increase the tower height, and if it is a self-supporting structure, the equipment cost can be reduced.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic structural diagram of an absorption tower used in the wet flue gas desulfurization apparatus of the embodiment of the present invention. The absorption tower of this embodiment is a so-called horizontal absorption tower in which the exhaust gas 1 is introduced into the absorption tower 2 from the horizontal direction and discharged horizontally. The absorption tower 2 is provided with a spray nozzle 6 for absorbing liquid at the inlet of the boiler exhaust gas 1 provided on the side wall thereof, and the absorbing liquid is supplied to the spray nozzle 6 from the circulation line 5. Since the inlet of the absorption tower 2 has a narrow frontage and is in a high gas flow velocity range, by spraying the absorbing liquid here, the sulfur oxide in the exhaust gas and the absorbing liquid can be efficiently brought into contact with each other, and The sulfur oxides are effectively removed. Absorption liquid that has absorbed sulfur oxides is absorption tower 2
In the tank part, the oxygen is oxidized by oxygen in the air blown into the lower part of the absorption tower 2 through the air blowing line 7, the above reaction proceeds, and gypsum (calcium sulfate) is produced.

In the example of FIG. 1, the absorption tower 2 is supplied to the spray nozzle 6 from the circulation line 5 at the horizontal exhaust gas inlet of the absorption tower 2, and the absorption solution is sprayed from the nozzle 6. The spray absorption liquid and the boiler exhaust gas 1 are gas-liquid contacted at a high flow rate at a narrow inlet part of the absorption tower 2, and the tower cross-sectional area is widened so that the gas flow rate after the gas-liquid contact is relatively low. In the area within 2, the scattered mist is dropped by gravity into the liquid reservoir below the absorption tower 2. As a result, the amount of mist at the inlet of the horizontal flow mist eliminator 10 installed at the outlet of the absorption tower 2 can be reduced, and the mist scattered outside the absorption tower 2 can be reduced as much as possible.

Further, in the illustrated example, in the spray direction of the absorbing liquid of the spray nozzle 6, the upstream side of the exhaust gas flow is cocurrent with the exhaust gas flow and the downstream side thereof is countercurrent, so that the ejector effect is provided on the upstream side of the exhaust gas flow. Thus, the exhaust gas is rectified and introduced at an appropriate spray rate of the absorbing liquid and an appropriate flow rate of the exhaust gas. Further, by making the spray direction of the absorbing liquid of the spray nozzle 6 countercurrent to the exhaust gas flow on the downstream side of the exhaust gas flow, the spray absorbing droplets corrode the ducts and equipment disposed downstream of the spray portion. It has the effect of preventing this. Further, if the above-mentioned problems do not occur, the spraying direction of the absorbing liquid and the exhaust gas flow direction may be only countercurrent or cocurrent.

[0014]

According to the present invention, the amount of scattered mist does not increase even if the gas flow rate in the absorption tower spray section is increased, so that the scattered mist can be removed by the current mist eliminator. Further, by increasing the gas flow velocity in the absorption tower spray section, the absorption tower spray section can be made compact, and the facility cost of the flue gas desulfurization apparatus can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic structural diagram of an absorption tower of a wet flue gas desulfurization apparatus according to an embodiment of the present invention.

FIG. 2 is a structural diagram showing an absorption tower of a conventional wet flue gas desulfurization apparatus.

[Explanation of symbols] 1 ... Exhaust gas, 2 ... Absorption tower, 3 ... Limestone supply line, 5 ...
Circulation line, 6 ... Spray nozzle, 7 ... Air blowing line, 10 ... Mist eliminator

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shigeru Nozawa             Babcock Hitachi 6-9 Takaracho, Kure City, Hiroshima Prefecture             Kure Office Co., Ltd. F-term (reference) 4D002 AA02 AC01 BA02 BA16 CA01                       DA05 DA16 DA35 EA02 EA12                       FA03

Claims (3)

[Claims] 1. A purification unit that sprays a desulfurizing agent-containing absorption liquid for absorbing sulfur oxides in exhaust gas introduced from an exhaust gas inlet from spray nozzles provided in a plurality of stages in the exhaust gas flow direction, and purifies from an exhaust gas outlet In a wet flue gas desulfurization apparatus equipped with an absorption tower for discharging gas, an absorption liquid tank provided under the absorption tower, and a circulation system for circulating the absorption liquid from the absorption liquid tank to the spray section, the absorption tower is Is equipped with a gas flow path in which the exhaust gas flows in a non-vertical direction from the exhaust gas inlet part where the exhaust gas is relatively narrow, and the spray part is arranged at the exhaust gas inlet part of the absorption tower, and the mist eliminator is installed at the exhaust gas outlet part. Place and
The cross-sectional area of the gas channel located above the absorbent tank is made larger than the cross-sectional area of the gas channel at the exhaust gas inlet, and the absorbent tank is on the downstream side of the exhaust gas inlet and before the exhaust gas outlet. A wet flue gas desulfurization device, which is arranged below the absorption tower on the side. 2. A wet flue gas desulfurization apparatus according to claim 1, wherein the spray direction of the absorbing liquid in the spray section is countercurrent to the gas flow, cocurrent or a combination of countercurrent and cocurrent. . 3. The wet flue gas desulfurization apparatus according to claim 1, wherein the rear portion of the exhaust gas inlet portion has an inclined bottom portion.