JP3193966B2 - Flue gas desulfurization apparatus and method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flue gas treatment device, and more particularly to a device for removing dust and sulfur from a dust device discharged from a combustion device such as a boiler. The present invention relates to a flue gas desulfurization apparatus and method suitable for removing substances (hereinafter, abbreviated as SO _X ). [0002] Wet flue gas desulfurization apparatus (hereinafter, referred to as desulfurization) in order to remove SO _X in the exhaust gas, although the gas-liquid contact between the exhaust gas and the absorption liquid takes place, the absorption tower ( Since the outlet gas temperature drops below the saturation temperature, for example, to about 50 ° C., the absorber outlet gas was reheated to a temperature suitable for preventing and diffusing white smoke from the chimney. Later, it is discharged from the chimney. As this reheating device, a heat exchanger that reuses the heat of the gas at the desulfurization device is generally used. FIG. 6 is a system diagram of a conventional flue gas treatment apparatus. The apparatus includes a boiler 1, an air preheater 2 for recovering heat of exhaust gas from the boiler 1, and an electric dust collector (hereinafter, referred to as EP) 3 for removing dust in the exhaust gas.
And a heat exchanger 9 that recovers the heat of the exhaust gas from which dust has been removed.
And a desulfurizer 6 for removing SO _X in the exhaust gas, and a heat exchanger 10 for reheating the desulfurized exhaust gas with heat recovered by the heat exchanger 9. Heat exchanger 9 and heat exchanger 10
Are connected by a communication pipe 11 through which a heat medium passes. As the heat exchanger 9, a system in which a heat medium is forcibly circulated by a pump, a system using a heat pipe, or the like is used. [0004] In such a configuration, the combustion exhaust gas from the boiler 1 is heat-recovered to about 150 ° C by the air preheater 2 and then sent to the EP 3 to remove soot and dust. The exhaust gas from which the dust has been removed is supplied to the suction blower (ID
F) The pressure is raised by the 4 and the desulfurization fan 5, sent to the heat exchanger 9, cooled to about 100 ° C., and then introduced into the desulfurizer 6. In the desulfurization unit 6, an absorbing solution composed of an alkali agent slurry is sprayed, and cooling, desulfurization and dust removal are performed by gas-liquid contact, and the exhaust gas at the desulfurization unit outlet is cooled to a saturation temperature of about 50 ° C. The outlet gas of the desulfurizer 6 is introduced into the heat exchanger 10, reheated to about 100 ° C. by the heat recovered by the heat exchanger 9, and discharged from the chimney 7. [0005] Recently, with the diversification of energy, the amount of dust in boiler exhaust gas has increased due to the conversion of heavy oil from boiler fuel to coal due to the conversion of heavy oil from boiler fuel to coal, and the chimney associated with stricter environmental regulations. The necessity of reducing the amount of dust emission at the 7 inlets has been required to enhance the dust removal performance of the smoke exhaust treatment device. Typically, for a coal-fired boiler, to the boiler outlet Soot dust amount of about 20 g / ^{m 3} N, it is required to dust the Soot dust amount of flue gas treatment apparatus outlet to 0.02g / ^{m 3} N, 99.9 % Dust removal performance is required. [0006] In order to obtain the above high dust-removing performance, a method of increasing the EP capacity of the flue gas treatment apparatus or an increase in the amount of spray liquid in the desulfurization apparatus is required. However, all of these methods have a problem that equipment costs and operating costs increase. It is also known that the EP performance depends on the electric resistance of dust, and that the electric resistance of dust is affected by the relative humidity of the gas.
This can be achieved by increasing the relative humidity of the exhaust gas and reducing the electrical resistance of the dust. In order to reduce the electric resistance of the dust, the capacity of the air preheater 2 is increased and the EP3
A method of lowering the inlet gas temperature of the gas, or a method of spraying water into the gas to increase the water content. However, the former method, about 2 to 3% SO _3, which is oxidized with the combustion in the boiler outlet gas is SO ₂ concentration (SO ₂ concentration 1000 ppm 20 to 30
(ppm), there is a problem that if the gas temperature is too low, the SO ₃ is condensed due to a decrease in the temperature of the low-temperature side element of the air preheater 2 and adheres to the element together with dust, causing corrosion and blockage. In the latter method, if the water is not completely evaporated, the surface of the device will be wet and cause corrosion. An object of the present invention is to provide an economical flue gas desulfurization apparatus for flue gas treatment which can solve the above-mentioned problems of the prior art, improve the dust removal performance of EP, and prevent low-temperature corrosion due to SO _3. It is to provide a method. Another object of the present invention is to solve the above-mentioned problems of the prior art and to reduce the concentration of dust at the EP outlet.
An object of the present invention is to provide a flue gas desulfurization apparatus and method which do not adversely affect the subsequent apparatus such as corrosion. Another object of the present invention is to reduce the amount of dust at the outlet of a flue gas treatment device to a value corresponding to stricter environmental regulations so as to meet the demand for higher dust removal performance of the flue gas treatment device. To provide a flue gas desulfurization apparatus and method. The above object of the present invention can be achieved by the following constitution. (1) A flue gas desulfurization device that performs cooling, desulfurization, and dust removal by introducing exhaust gas from a combustion device into gas-liquid contact with an absorbing solution composed of an alkaline slurry, and an air preheater that cools the exhaust gas. A heat exchanger for cooling the exhaust gas cooled by the air preheater to a temperature equal to or higher than the dew point of the SO ₃ concentration in the exhaust gas, and an electric device for removing dust particles in the cooled exhaust gas at the outlet of the heat exchanger. The dust collector is connected to the flue gas desulfurization device
A heat exchanger for reheating the exhaust gas with the heat recovered by the heat exchanger, and a flue gas desulfurization device including a chimney downstream of the flue gas desulfurization device. (2) heat in the exhaust gas from the combustion device is collected by an air preheater, and dust in the exhaust gas from the air preheater is removed by an electric precipitator provided downstream of the air preheater; Thereafter, a flue gas desulfurization method for removing sulfur oxides contained in the exhaust gas by gas-liquid contact with an absorbent comprising an alkali agent slurry, wherein the temperature of the exhaust gas from the air preheater is reduced by the air preheater. On the downstream side of the electric precipitator provided on the downstream side, the calorific value of the exhaust gas is recovered so as to be equal to or higher than the dew point temperature of the SO ₃ concentration in the exhaust gas, and further included in the heat recovered exhaust gas. Flue gas desulfurization for removing sulfur oxides in exhaust gas whose exhaust gas temperature is 120 ° C. or less and whose dust concentration has become 100 mg / m ³ N or less by removing dust with an electrostatic precipitator using an alkaline slurry. Method. The present invention is, of course, applicable to a system in which a medium is forcibly circulated by a pump, such as using a non-leak type gas-gas heater. It can be performed by providing a table and controlling the number of operating units. [0014] SO ₃ in the boiler exhaust gas is adsorbed by the dust in the air preheater and decreases to about 5 ppm.
At the outlet of the air preheater, the sulfuric acid dew point temperature is lower than at the inlet of the air preheater. Therefore, the lower limit value of the gas temperature caused by SO ₃ dew point corrosion (low temperature corrosion) of the heat exchanger provided at the EP inlet can be made lower than the gas temperature at the air preheater outlet, and the EP inlet gas temperature Lower
EP performance can be improved. Furthermore, always S
By controlling the heat exchange amount of the heat exchanger so as to operate at a temperature equal to or higher than the lower limit temperature at which O ₃ dew point corrosion can be prevented, it is possible to prevent flue and equipment corrosion after the EP. FIG. 5 shows the relationship between the SO ₃ concentration and the corrosion due to the dust concentration. The factor governing the SO ₃ dew point corrosion is the dust concentration in the exhaust gas. If Soot dust concentration is high relative to the SO ₃ concentration, SO ₃ is adsorbed on Gabai dust and keeps the dry adhesion surface of the device, it is possible to reduce corrosion, soot and dust against SO ₃ concentration When the concentration is low, SO ₃ is condensed into sulfuric acid with a decrease in gas temperature, adheres to the device surface, and causes corrosion. Therefore,
By knowing the concentration of dust in the EP outlet gas,
The corrosion of the flue and equipment after P can be prevented. Furthermore, for example, the dust concentration at the EP outlet is 1
When designing an EP under the condition of 00 mg / m ³ N, it is necessary to select an EP having the characteristic X of the EP characteristic curve in FIG. 2 under the condition of the conventional EP inlet gas temperature of 150 ° C. (A). Was. However, according to the present invention, for example, the SO ₃ concentration B is obtained for the gas temperature of A from the relationship between the gas temperature at the outlet of the air preheater and the SO ₃ concentration in FIG. _3, and the SO ₃ concentration and the dew point temperature in FIG. Since the dew point temperature C is obtained from the relationship, the EP having the characteristic of Y shown in FIG. 2 may be selected. Therefore, the equipment cost of the EP can be significantly reduced. Embodiments of the present invention will be described below in detail. FIG. 1 is a system diagram of a flue gas treatment device provided with a flue gas desulfurization device according to one embodiment of the present invention. In FIG. 1, the same portions as those in FIG. 6 are denoted by the same reference numerals, and description thereof will be omitted. 1 differs from the conventional apparatus (FIG. 6) in that a heat exchanger 8 is connected to the EP inlet, a communication pipe 12 that connects the heat exchanger 8 and the heat exchanger 10 and circulates a heat medium, Means for controlling the amount of heat exchanged in the heat exchanger 8 to control the gas temperature at the outlet of the heat exchanger 8 to a temperature at which low-temperature corrosion can be prevented, that is, the temperature detector 20 for measuring the gas temperature at the outlet of the air preheater 2 and EP3. A temperature detector 21 for measuring the gas temperature at the inlet, a calculator 23 for calculating an exchange heat quantity from the measured values of the temperature detectors 20 and 21 to reach a temperature at which low-temperature corrosion can be prevented; A flow controller 2 provided in the connecting pipe 12 for controlling a heat medium flow rate by a signal
4 is provided. In such a configuration, the exhaust gas from the boiler 1 is introduced into the heat exchanger 8 via the air preheater 2,
The exhaust gas temperature is reduced to improve the dust collection performance of the dry EP3. The gas temperature at the outlet of the heat exchanger 8 is determined by the temperature detector 20,
From the measurement value measured at 21, a computing unit 23 computes a temperature at which low-temperature corrosion of the heat exchanger 8 downstream flue and the equipment disposed in the flue is prevented, and the computing unit 23 further reduces the temperature to the temperature. The amount of heat exchanged by the heat exchanger 8 is determined so that the medium pressure is adjusted by the flow controller 24. The determination of the exchange heat quantity by the arithmetic unit 23 is as follows.
For example, it can be performed by the following two methods. First, from FIG. 3, by measuring the gas temperature at the outlet of the air preheater 2 with the temperature detector 20, the concentration of the gas SO _{3 at the} outlet of the air preheater 2, which was conventionally impossible to measure continuously with high accuracy, is continuously measured. Can be sought. 4 and FIG.
The dew point temperature of the concentration of the gas SO _{3 at the} outlet of the air preheater 2 obtained in the above can be obtained. The dew point temperature is a lower limit temperature (set value) at which low-temperature corrosion at the outlet of the heat exchanger 8 can be prevented. Therefore, the arithmetic unit 23 incorporating the relationships shown in FIGS. 3 and 4 uses the lower limit temperature of the heat exchanger 8 as a preceding signal and the temperature measured by the temperature detector 21 as a feedback signal, and The exchange heat amount (heat medium amount) at 8 is obtained. FIGS. 2, 3 and 5 show other methods.
Can be performed by the arithmetic unit 23 in which the relationship is incorporated. By measuring the temperature of the gas at the outlet of the air preheater 2 with the temperature detector 20, it can be seen from FIG.
The O ₃ concentration is determined, and the dust concentration in the gas that can prevent corrosion at the SO ₃ concentration is determined from FIG. This dust concentration becomes the EP outlet gas dust concentration capable of preventing low-temperature corrosion, and the EP inlet gas temperature (set value) for achieving the dust concentration is determined from the EP characteristic curve Y in FIG. Therefore, the arithmetic unit 23 incorporating the relations of FIGS. 2, 3 and 5 uses the EP inlet gas temperature as a leading signal and the EP inlet gas temperature measured by the temperature detector 21 as a feedback signal to the heat exchanger 8. Can be calculated. In the above embodiment, the dew point temperature of the gas at the outlet of the air preheater is obtained by calculation, but it goes without saying that the same operation can be performed by installing a dew point meter. FIG. 7 is a system diagram of a flue gas treatment apparatus provided with a flue gas desulfurization apparatus according to another embodiment of the present invention. The difference of the present invention from FIG. 1 is that the control of the heat exchange amount of the heat exchanger 8 is performed by measuring the dust concentration of the EP outlet gas and the gas temperature of the EP inlet. That is, a temperature detector 21 is provided. In such a configuration, the determination of the exchange heat quantity by the arithmetic unit 23 is performed as follows. First, a dust concentration meter 2
The dust concentration of the EP outlet gas is measured by 2. SO ₃ capable of preventing SO ₃ dew point corrosion at the dust concentration
The concentration is determined from FIG. 5, and the dew point temperature of the SO ₃ concentration is determined from FIG. The dew point temperature becomes the lower limit value (set value) of the gas temperature at the outlet of the heat exchanger 8. Therefore, using the lower limit temperature as a leading signal and the measurement value of the temperature detector 21 as a feedback signal, the arithmetic unit 23 incorporating the relationship of FIGS. 4 and 5 can obtain the heat exchange amount of the heat exchanger 8. The medium pressure is adjusted to a medium pressure corresponding to the heat exchange amount by a flow rate adjuster 24 provided in the communication pipe 12. According to the present invention, the EP inlet gas temperature can be reduced to a temperature at which low-temperature corrosion due to SO ₃ can be prevented, so that EP performance can be improved and SO3 low-temperature corrosion can be prevented. . In addition, the heat recovered by the heat exchanger is used for reheating the gas.
This is economical because the equipment cost can be reduced. Further, according to the present invention, even if the concentration of dust at the EP outlet is reduced, there is no danger of adverse effects such as corrosion on subsequent devices, and the exhaust gas treatment device outlet can be installed without increasing equipment costs. The amount of dust can be reduced to strict environmental regulation values.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a system diagram of a flue gas treatment apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing an EP characteristic curve. FIG. 3 is a graph showing an air preheater outlet gas temperature and SO3 concentration. FIG. 4 is a diagram showing the relationship between SO ₃ concentration and dew point temperature. FIG. 5 is a diagram showing the relationship between SO ₃ concentration and corrosion due to dust concentration. FIG. 7: System diagram of a flue gas treatment apparatus according to another embodiment of the present invention [Description of symbols] 1 Boiler 2 Air preheater 3 Electric precipitator 6 Desulfurizer 7 Chimney 8 Heat exchanger 9 Heat exchanger DESCRIPTION OF SYMBOLS 10 Heat exchanger 11 Communication pipe 12 Communication pipe 20 Temperature detector 21 Temperature detector 22 Dust concentration meter 23 Computing unit 24 Flow rate controller

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B01D 53/50 B01D 53/34 ZAB B01D 53/77 B03C 3/01 B03C 3/02

Claims (1)

(57) [Claims] A flue gas desulfurization device that performs cooling, desulfurization, and dust removal by introducing exhaust gas from a combustion device and making gas-liquid contact with an absorbing solution composed of an alkaline slurry, an air preheater that cools the exhaust gas, A heat exchanger for cooling the exhaust gas cooled by the preheater to a temperature equal to or higher than the dew point of the SO ₃ concentration in the exhaust gas, and an electric precipitator for removing dust and dust in the cooled exhaust gas at the outlet of the heat exchanger Before
Provided on the upstream side of the Kihaikemuri desulfurization unit, a heat exchanger for reheating the flue gas by heat recovered in the heat exchanger, the chimney the
A flue gas desulfurization device provided downstream of the flue gas desulfurization device. 2. The amount of heat in the exhaust gas from the combustion device is recovered by an air preheater, and dust in the exhaust gas from the air preheater is removed by an electric dust collector provided on the downstream side of the air preheater. A flue gas desulfurization method for removing sulfur oxides contained therein by gas-liquid contact with an absorbent comprising an alkali agent slurry, wherein the temperature of exhaust gas from the air preheater is downstream of the air preheater. On the downstream side of the electrostatic precipitator provided in the above, the calorific value of the exhaust gas is recovered so as to be equal to or higher than the dew point temperature at the SO ₃ concentration in the exhaust gas, and the dust contained in the exhaust gas thus recovered is further removed. By removing with an electric dust collector, the exhaust gas temperature is 120 ° C or less and the dust concentration is 100 mg /
A flue gas desulfurization method characterized by removing sulfur oxides in exhaust gas that has become m ³ N or less with an alkaline slurry.