JPH11165030A - Method for recovering sulfuric acid and sulfur trioxide in waste gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the corrosion of an air preheater, etc., by providing a reaction zone where CaCO3 powder is added and reacted with the SO3 , etc., in the waste gas and a dust collector for collecting the unreacted CaCO3 on the downstream side of the reaction zone in a waste combustion gas passage between the outlet of the economizer of a combustion furnace and the air preheater. SOLUTION: The waste combustion gas formed by burning a sulfur-contg. fuel is passed through a denitrator 16, an air preheater 6, an electric precipitator 8 and a wet desulfurizer 9 and treated. In this case, a reaction zone 19 where CaCO3 powder is added and reacted with the SO3 , etc., in the waste gas and a dust collector 11 on the downstream side are arranged in a flue 5 extended from the economizer 4 to air preheater 6. The CaCO3 powder is introduced into the reaction zone 19 from a spray nozzle using compressed air. The introduced desulfurizing agent reacts with the SO3 , etc., in the combustion gas, and the SO3 , etc., are removed. The powder of the desulfurizing agent is recovered by the dust collector 11, introduced into a recovery hopper 12 and partly recycled as the desulfurizing agent of the wet desulfurizer 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing sulfuric acid and sulfuric anhydride contained in flue gas in a sulfur-containing fuel flue gas treatment facility such as a thermal power plant using fossil fuel as a fuel.

[0002]

2. Description of the Related Art In a thermal power plant having a structure as shown in FIG. 7 using fossil fuel containing sulfur as fuel, combustion exhaust gas generated in a combustion furnace 1 is reheated as indicated by an arrow in the figure. -It is led to the flue 5 via the superheater 3 and the economizer 4,
Denitration is performed by the denitration device 16 and heat recovery is performed by the air preheater 6.
After dust is removed by the electrostatic precipitator 8, the wet desulfurizer 9
And discharged from the chimney 10 into the atmosphere. In the drawing, reference numeral 2 denotes a burner of the combustion furnace 1, and reference numeral 7 denotes a combustion air duct. The combustion exhaust gas includes sulfur dioxide gas (SO ₂ ), sulfuric anhydride (SO ₃ ) in which a part of the sulfur sulfite gas is oxidized, and sulfuric acid (SO ₃ ) in addition to ordinary combustion exhaust gas components such as carbon dioxide, water vapor, oxygen, nitrogen, and unburned components. H ₂ SO ₄ ). Of these sulfur compounds, SO ₃ (reacts with water in the flue to produce H ₂ SO ₄ ) and H ₂ SO
₄ (hereinafter, SO ₃ and H ₂ SO ₄ are collectively referred to as SO _3, etc.) are the surfaces of the flue 5, air preheater 6, electric precipitator 8, chimney 10, etc. provided on the exhaust gas passage. High-concentration H ₂ SO ₄ is condensed and adhered to a member having a low temperature, which causes large corrosion damage. As a method for preventing such corrosion, calcium carbonate powder (CaCO ₃ ) is sprayed into flue gas in a flue gas 5 with pressurized air, and S
A method for desulfurizing and removing O ₃ in the presence of gas (Japanese Patent Laid-Open No. 9-75661), slaked lime (Ca (O
H) A method of spraying the slurry of ₂ ) into the flue 5 to remove and remove SO _{3 and the} like (JP-A-58-36623) has been proposed.

[0003] In order to prevent corrosion damage caused by SO ₃ or the like in the low temperature member of the boiler flue by the above-mentioned method, a desulfurizing agent such as CaCO ₃ (for removing SO ₃ or the like) is added to the flue. When a substance (hereinafter simply referred to as a desulfurizing agent) is introduced, there is a drawback that a sufficient effect cannot be obtained for the following reasons. (A) Since the desulfurizing agent introduction position is located downstream of the air preheater, there is no effect of preventing sulfuric acid corrosion of the air preheater (Japanese Patent Application Laid-Open No. 9-75661). (B) Since the concentration of SO ₃ or the like is small and the contact time with CaCO ₃ is short, a large amount of desulfurizing agent needs to be added in order to obtain sufficient reaction efficiency and CaCO ₃ utilization efficiency. No. 75661). (C) By adding CaCO ₃ , the amount of dust contained in the exhaust gas increases, and ash adhesion and blockage in the downstream of the flue tend to occur (Japanese Patent Application Laid-Open Nos. 9-75661 and 58-36623). .

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of such a situation of the prior art, and has been developed in view of the fact that sulfur contained in a combustion exhaust gas of a sulfur-containing fuel is reduced.
An object of the present invention is to provide a method for removing SO _{3 and the} like in combustion exhaust gas, which can reduce the concentration of O _{3 and the} like to lower the acid dew point and prevent corrosion in an air preheater and the like.

[0005]

SUMMARY OF THE INVENTION The present invention is directed to a denitration apparatus, an air preheater, an electric dust collector, and an exhaust gas, which are provided in order from the upstream in a flue gas passage from a combustion furnace in a flue gas produced by burning a sulfur-containing fuel. When processing through a wet desulfurization unit,
CaCO ₃ powder was added to the flue gas passage between the economizer outlet of the combustion furnace and the air preheater to add SO2 in the flue gas.
A reaction region for reacting with ₃ etc., and a dust collecting device for collecting unreacted CaCO ₃ on the downstream side of the reaction region are provided, and SO ₃ etc. in exhaust gas is reacted with CaCO ₃ in the reaction region. This is a method for removing SO ₃ or the like in exhaust gas, characterized in that CaCO ₃ removed and collected by a dust collector is recycled as part of CaCO ₃ to be added to the reaction zone.

In the method of the present invention, a part of the CaCO ₃ collected in the dust collector is used as a part of a desulfurizing agent used in a wet desulfurizer provided downstream of the flue gas passage. In addition, the utilization efficiency of unreacted CaCO ₃ can be improved. Since the reaction of CaCO ₃ particles proceeds from the surface, the reaction activity of the particles decreases as the reaction proceeds. Therefore, it is better to pulverize CaCO ₃ particles that have undergone a certain degree of reaction and use them for wet desulfurization.
Overall utilization efficiency is high.

[0007] According to the thermodynamic equilibrium calculation result, the sulfur (S) component in the combustion exhaust gas causes the following chemical reaction in an oxidizing atmosphere.

Embedded image S + O ₂ → SO ₂ (1000-1400 ° C.) SO ₂ + 1 / 2O ₂ → SO ₃ (400-10
(00 ° C.) SO ₃ + H ₂ O → H ₂ SO ₄ (400 ° C. or less) That is, the sulfur contained in the fuel is oxidized in the combustion process in the combustion furnace (formula) and mainly exists as SO ₂ . Atmospheric temperature of 400 to 500 downstream of the combustion furnace
When the temperature reaches ° C, the equilibrium completely shifts to the right side of the equation, and SO ₃ is generated stably. In addition, the ambient temperature is 400
When the temperature falls below ℃, SO ₃ and H ₂ O react to start generating H ₂ SO ₄ gas (formula).

[0008] By introducing the powder of CaCO ₃ in combustion exhaust gas at a temperature of 400 ° C. or less and comprising economizer outlet later, and CaCO ₃ is reacted with SO ₃ and the like as in Equation, SO ₃
And H ₂ SO ₄ can be removed.

(CaCO ₃ + SO ₃ → CaSO ₄ + CO ₂ ) CaCO ₃ + H ₂ SO ₄ → CaSO ₄ + H ₂ O +
CO ₂

In the method of the present invention for removing SO _{3 and the} like in flue gas in a flue by adding and mixing CaCO ₃ in the flue, technical features of the present invention are as follows (1) to (4).
It is as follows. (1) CaC between the economizer outlet and the air preheater inlet
A reaction region for adding O ₃ powder and reacting with SO ₃ etc. in the exhaust gas is provided, and CaC for desulfurization is contained in the flue gas in the flue.
O ₃ powder is added and added to react with SO ₃ or the like and removed.
By adding CaCO ₃ between the economizer and the air preheater to reduce the concentration of SO ₃ etc. in the combustion exhaust gas, the equipment in the flue after the air preheater (air preheater, electric precipitator, various Heat exchangers, wet desulfurization devices, etc.). As a result, the gas temperature at the outlet of the air preheater can be set lower than before, and the heat recovery efficiency of the exhaust gas is greatly improved. The addition position is desirably after the denitration device.

The amount of CaCO ₃ powder to be added to the reaction zone is such that the newly added amount is 1 to 3 equivalents to SO _{3 and the} like in the exhaust gas, and the amount to be collected and circulated by a dust collector described later is 3 to 1 equivalent.
The range is 0 equivalent. As a result, SO ₃ in the combustion exhaust gas
About 80% or more can be removed.

(2) A dust collector is provided in front of the air preheater,
Unreacted Ca containing some reaction product CaSO ₄
CO ₃ powder is separated and recovered from the gas stream. This makes it possible to reduce the dust concentration downstream of the dust collector.
It is possible to prevent the heat transfer and the pressure loss from increasing due to the attachment of the desulfurizing agent, and to reduce the burden on the air preheater and the electric dust collector. In addition, 80 to 10 of CaCO ₃ added in the reaction zone.
About 0% is collected by this dust collector.

(3) CaC recovered in (2) above
A portion of the O ₃ powder is added to the reaction zone
Recycled as part of CO ₃ . Recovered CaCO ₃
By returning a part of the powder into the reaction region and keeping the concentration of the desulfurizing agent (CaCO ₃ ) in the desulfurizing reaction region high, it is possible to increase the desulfurizing reaction efficiency and the utilization efficiency of the desulfurizing agent per unit amount.

(4) CaC recovered in (2) above
By supplying a part of the O ₃ powder, for example, 20 to 50%, as a desulfurization raw material to a wet desulfurization device installed downstream of the exhaust gas, unreacted CaCO ₃ is effectively used, and the utilization efficiency as a desulfurization agent is greatly increased. can do. As a mode of use in the desulfurization device, the Ca containing partially recovered CaSO ₄
CO ₃ is calcined to CaO, mixed with water and Ca (O
H) It is generally used as a ₂ slurry.

[0014]

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a system diagram of an exhaust gas treatment system to which a method for removing SO ₃ or the like according to a first embodiment of the present invention is applied. In FIG. 1, the point different from the conventional example shown in FIG. 7 is that the desulfurizing agent CaCO 3 is provided in the flue 5 after the economizer 4 where the concentration of SO ₃ or the like becomes large and before the air preheater 6. Reaction zone 1 between desulfurizing agent that reacts with SO ₃ etc. in exhaust gas by adding ₃ powders and SO ₃ etc.
9 and a dust collector 11 are provided in the subsequent stream, and a desulfurizing agent is added,
The point is that a removing means such as SO ₃ for recovering the unreacted desulfurizing agent and circulating the recovered desulfurizing agent is provided.

In the means for removing SO _{3 and the} like in FIG. 1, CaCO ₃ for desulfurization is added to the reaction area 19 provided in the flue 5 after the economizer 4 and before the air preheater 6 by several tens to several hundreds of μm.
m in the form of a powder from a spray nozzle with pressurized air. The introduced desulfurizing agent reacts with SO _{3 and the} like in the combustion gas until it is collected by a dust collector 11 (a dust collector using gravity, inertia, centrifugal force, etc.) installed in front of the air cooler 6. And desulfurization removal. The desulfurizing agent powder selectively collected by the dust collecting device 11 is introduced into a collecting hopper 12 by a gravity feed method, and a part of the desulfurizing agent powder is a wet desulfurizing device 9 for SO ₂ desulfurization.
Used as a desulfurizing agent. The remaining desulfurizing agent in the recovery hopper 12 is conveyed to the supply hopper 13 by a method using pneumatic force or thrust, and mixed with the desulfurizing agent newly supplied in the supply hopper 13. The desulfurizing agent in the supply hopper 13 is again introduced into the flue 5 from a spray nozzle using pressurized air (not shown) by a desulfurizing agent supply device 14 of a transport system using high-pressure air, and is used to remove SO _{3 and the} like. used.

FIG. 2 shows an SO according to a second embodiment of the present invention.
FIG. 2 is a system diagram of an exhaust gas treatment system to which a removal method such as ₃ is applied, in which an SO ₃ or other removal unit is configured to perform desulfurization during airflow conveyance and use an inertial dust collector as the dust collector 11. . A dust collector (inertial dust collector) 11 having a reaction area 19 in the flue 5 after the economizer 4 and before the air preheater 6 and having a baffle plate 17 for collecting dust therein.
Is installed so as to include most of the reaction region 19.
In the dust collector (inertial dust collector) 11, desulfurization is partially performed together with dust collection.

FIG. 3 shows a SO 3 according to a third embodiment of the present invention.
FIG. 2 is a system diagram of an exhaust gas treatment system to which a removal method such as ₃ is applied, wherein SO _{3 and} other removal means are configured to perform desulfurization during airflow conveyance, and to use a cyclone that is centrifugal dust collection as a dust collection device 11. It is an example. In this example, in the flue 5 after the economizer 4 and before the air preheater 6, a region having a larger cross-sectional area of the flue 5 is provided to form a reaction region 19, so that the desulfurizing agent conveyed by airflow is formed. The residence time is increased and the reaction efficiency is improved.

FIG. 4 shows an SO according to a fourth embodiment of the present invention.
FIG. 2 is a system diagram of an exhaust gas treatment system to which a removal method such as ₃ is applied, in which SO ₃ or other removal means is configured to use a reaction in a fluidized bed as a reaction system and a cyclone as a dust collector 11. In this example, a fluidized bed reactor 15 is provided in the flue 5 after the economizer 4 and before the air preheater 6, and a desulfurization reaction is performed in the reactor. The size of the input particles,
The size of the fluidized bed reactor 15 that determines the gas flow rate in the reactor is adjusted so that a fluidized bed can be formed in the reactor. Further, a gas dispersion plate 18 is provided at the bottom of the fluidized bed in order to improve the mixing state of the particles in the fluidized bed and the gas and increase the efficiency of desulfurization.

[0019]

EXAMPLES The effects of the method of the present invention are demonstrated below by way of examples. (Example) A desulfurization test (removal test of SO _{3 and the} like) was performed using a small-sized desulfurization test apparatus having the configuration shown in FIG. The test procedure is as follows. In the combustion furnace 21, kerosene is supplied from the burner 30 together with the combustion air preheated by the air preheater 31 and burned, and the combustion exhaust gas is generated at 30 Nm ³ / hr. 32 in the figure is an electric heater. Combustion furnace 21
Was added SO ₂ gas in the exhaust gas exiting the, V ₂ O ₅ system SO
₂ → The temperature of the gas is adjusted to 400 to 700 ° C. by passing through the reaction catalyst layer 22 which is also filled with an SO ₃ reaction catalyst and also serves as an air-cooling type temperature controller, to generate SO ₃ in the gas, The temperature of the gas is adjusted to 400 ° C. by the cooling type temperature controller 23 and supplied to the reactor 24.

An exhaust gas containing SO ₃ is introduced into the reactor 24 at a temperature of 400 ° C. and a gas linear velocity of 2 m / s. The desulfurizing agent CaCO ₃ powder is mixed into the exhaust gas from the supply hopper 26 just before the reactor 24 and absorbs SO _{3 and the} like in the gas while passing through the reactor 24 by air flow. Reactor 24
The dust collector 25 installed at the bottom is
The desulfurizing agent that has reacted with O ₃ or the like is collected, and the collected desulfurizing agent is sent to the collection hopper 27.

The desulfurizing agent CaC stored in the recovery hopper 27
A part of O ₃ is returned to the supply hopper 26, mixed with newly charged CaCO _3, and reused as a desulfurizing agent. The SO ₃ concentration in the gas before and after the reaction (total concentration of SO _{3 and the} like in the gas, hereinafter simply referred to as SO ₃ concentration) was measured, and the SO ₃ desulfurization reaction rate by CaCO ₃ powder in the reactor 24 was calculated by the following formula. I asked. Desulfurization reaction rate (%) = [(C ₁ -C ₂ ) / C ₁ ] × 100 C ₁ : SO ₃ concentration at reactor inlet (SO ₃ concentration measurement point 2
8) C ₂ : SO ₃ concentration at reactor outlet (SO ₃ concentration measurement point 2)
(Concentration at 9) In the conventional method, since the desulfurizing agent is not circulated, the utilization rate of the introduced CaCO ₃ is small, waste is increased, and the desulfurization efficiency is reduced.

In order to confirm the above, the reactor 24
100 ppm of SO ₃ concentration at the inlet
₃ was set to three times the equivalent of SO _{3 in} the exhaust gas (CaCO 3
₍₃₎ Injection rate 32g / h, desulfurizing agent particle size 50-150μm)
Then, a test was conducted for a case where the product was used cyclically and a case where the product was not used cyclically, and the desulfurization reaction rates were compared. When CaCO ₃ is used in a circulating manner, by recovering 80% of the desulfurizing agent introduced into the reactor 24, the concentration of the desulfurizing agent CaCO ₃ in the reactor 24 becomes approximately five times that when not circulating.

FIG. 6 shows the results of the desulfurization test. The plot (○) in the figure indicates the measurement result of the SO ₃ concentration before and after the reactor 24 when the desulfurizing agent was not circulated, and the plot (□) indicates the result when the desulfurizing agent was circulated. When the desulfurizing agent CaCO ₃ was not used in circulation, the desulfurization reaction rate was 80%, but it increased to 93% by using the desulfurization agent in circulation.

[0024]

According to the method of the present invention, SO2 contained in combustion exhaust gas from a combustion facility such as a thermal power plant using fossil fuel such as heavy oil, orimulsion, or coal as fuel is used.
The concentration of ₃ etc. (SO ₃ and H ₂ SO ₄ ) can be reduced and the acid dew point can be lowered, thereby preventing corrosion in the flue equipment after the air preheater. As a result, there is no fear of corrosion, and the temperature of the outlet gas of the air preheater can be set low, so that heat can be recovered to a lower temperature and the overall energy efficiency in a thermal power plant or the like can be increased. Further, since the amount of SO ₃ released into the atmosphere is significantly reduced, generation of purple smoke can be prevented.

[Brief description of the drawings]

FIG. 1 is a system diagram of an exhaust gas treatment system to which a method for removing SO ₃ or the like according to a first embodiment of the present invention is applied.

FIG. 2 is a system diagram of an exhaust gas treatment system to which a method for removing SO ₃ or the like according to a second embodiment of the present invention is applied.

FIG. 3 is a system diagram of an exhaust gas treatment system to which a method for removing SO ₃ or the like according to a _third embodiment of the present invention is applied.

FIG. 4 is a system diagram of an exhaust gas treatment system to which a method for removing SO ₃ or the like according to a fourth embodiment of the present invention is applied.

FIG. 5 is a flowchart of a small-sized desulfurization test apparatus used in the examples.

FIG. 6 is a graph showing test results in Examples.

FIG. 7 is a system diagram showing one example of a flue gas treatment system in a conventional thermal power plant.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshimitsu Ichinose 5-717-1, Fukahori-cho, Nagasaki-shi, Nagasaki Sanishi Heavy Industries, Ltd. Nagasaki Research Laboratory (72) Inventor Masashi Hishida 2-5-2, Marunouchi, Chiyoda-ku, Tokyo No. 1 Mitsuhishi Heavy Industries, Ltd. (72) Katsuyuki Ueda, Inventor 1-1, Akunoura-cho, Nagasaki, Nagasaki Prefecture Mitsubishi Heavy Industries, Ltd. Nagasaki Shipyard (72) Inventor Junji Aiba 1-1, Akunoura-cho, Nagasaki, Nagasaki Prefecture No.Mitsubishi Heavy Industries, Ltd.Nagasaki Shipyard

Claims (2)

[Claims] 1. A flue gas produced by burning a sulfur-containing fuel is treated by passing it through a denitration device, an air preheater, an electric precipitator, and a wet desulfurization device provided in order from the upstream in a flue gas passage from a combustion furnace. In doing so, a reaction zone in which calcium carbonate powder is added to the flue gas passage between the coal economizer outlet of the combustion furnace and the air preheater to react with sulfuric acid and sulfuric anhydride in the flue gas, and after the reaction zone A dust collector for collecting unreacted calcium carbonate on the flow side is provided, and sulfuric acid and sulfuric anhydride in exhaust gas are removed by reacting with calcium carbonate in the reaction area, and the calcium carbonate collected by the dust collector is removed. A method for removing sulfuric acid and sulfuric anhydride from exhaust gas, wherein the sulfuric acid and sulfuric acid in the exhaust gas are circulated and used as a part of calcium carbonate added to the reaction zone. 2. A method according to claim 1, wherein a part of the calcium carbonate collected in said dust collecting device is used as a part of a desulfurizing agent used in a wet desulfurizing device provided downstream of a flue gas passage. Item 4. The method for removing sulfuric acid and sulfuric anhydride from exhaust gas according to item 1.