JP2573589C - - Google Patents

Description

Description: BACKGROUND OF THE INVENTION (Industrial application field) The present invention relates to a flue gas treatment device, and particularly to the removal of dust and sulfur oxides (hereinafter abbreviated as SOx) discharged from a combustion device such as a boiler. The present invention relates to a smoke exhaust treatment device suitable for performing (Prior Art) In a wet-type flue gas desulfurization device (hereinafter, referred to as a desulfurization device), gas-liquid contact between the exhaust gas and an absorbent is performed to remove SOx in the exhaust gas. Because the outlet gas temperature drops below the saturation temperature, for example, to about 50 ° C., the absorber outlet gas is reheated to a temperature suitable for white smoke prevention and diffusion from the chimney, and then from the chimney. Has been exhausted. 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. This apparatus includes a boiler 1, an air preheater 2 for recovering heat of exhaust gas from the boiler 1, an electric precipitator (hereinafter referred to as EP) 3 for removing dust in exhaust gas, and a dust collector. A heat exchanger 9 for recovering the heat of the exhaust gas from which the sulfur has been removed, a desulfurization device 6 for removing SOx in the exhaust gas, and a heat exchanger 10 for reheating the desulfurized exhaust gas with the heat recovered by the heat exchanger 9. Consists of The heat exchanger 9 and the 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. In such a configuration, the combustion exhaust gas from the boiler 1 is sent to the EP 3 after heat recovery to about 150 ° C. by the air preheater 2, and the dust is removed. The exhaust gas from which the dust has been removed is pressurized by an intake blower (IDF) 4 and a desulfurization fan 5, sent to a heat exchanger 9, cooled to about 100 ° C., and then introduced into a 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 desulfurization device 6 is introduced into the heat exchanger 10,
The heat recovered by the heat exchanger 9 is reheated to about 100 ° C. and discharged from the chimney 7. Recently, with the diversification of energy, the amount of dust in boiler exhaust gas has increased due to the conversion of boiler fuel from heavy oil to coal, and the need to reduce the amount of dust emission at the entrance of chimney 7 due to the tightening of environmental regulations. There is a demand for advanced dust removal performance of flue gas treatment equipment.
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 0.02 g / m ³ N,
Dust removal performance of 99.9% or more is required. (Problems to be Solved by the Invention) In order to obtain the high dust removal performance as described above, it is necessary to increase the EP capacity of the flue gas treatment apparatus and increase the amount of spray liquid in the desulfurization apparatus. However, both have the problem that equipment costs and operating costs increase. Also, it is known that the EP performance depends on the electric resistance of dust, and it is known that the electric resistance of dust is affected by the relative humidity of gas. This can be achieved by 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, since the boiler outlet gas is SO ₃ which is oxidized with the combustion present from about 2 to 3% (20 to 30 ppm in SO ₂ concentration 1000 ppm) of SO ₂ concentration, too low a gas temperature As a result, there is a problem that SO ₃ agglomerates due to a decrease in the temperature of the low-temperature side element of the air preheater 2, adheres to the element together with dust, and causes 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. SUMMARY OF THE INVENTION It is an object of the present invention to provide an economical flue gas treatment apparatus which solves the above-mentioned problems of the prior art, improves the dust removal performance of EP, and can prevent low-temperature corrosion due to SO ₃ . (Means for Solving the Problems) An object of the present invention is to provide a heat exchanger at the EP inlet and to set the gas temperature at the outlet (EP inlet) of the heat exchanger to the flue downstream of the heat exchanger (after the EP). And means for controlling the temperature at which low-temperature corrosion of equipment can be prevented. That is, the first aspect of the present invention is to provide an air preheater for recovering the calorific value of exhaust gas from a boiler or the like.
A dust collector for removing soot and dust contained in exhaust gas, and a wet flue gas desulfurization apparatus for removing sulfur oxides, the flue for guiding the exhaust gas from the electrostatic precipitator in the wet flue gas desulfurization system And heat exchange for reheating for reheating exhaust gas from the wet flue gas desulfurization unit.
In a flue gas treatment device having a heat exchanger, the heat of the exhaust gas is provided downstream of the air preheater.
A heat exchanger for heat recovery that circulates a heat medium to the heat exchanger for reheating by collecting the amount.
, The electrostatic precipitator is sequentially provided, and the heat exchanger for heat recovery and the wet exhaust
The detection means of the exhaust gas temperature is provided between the smoke desulfurization system, the heat as further exhaust gas temperature of the heat exchanger outlet for the heat recovery low temperature corrosion in the downstream side of the dust collector becomes a temperature that does not occur A control device for adjusting the heat exchange amount of the heat exchanger for recovery is provided. The second of the present invention is the first invention, the flue for guiding the exhaust gas from the electrostatic precipitator before Symbol wet flue gas desulfurization apparatus is characterized in that the fan is provided. Needless to say, the present invention can be applied to a system in which a heat exchanger is forcibly circulated by a pump using a heat exchanger. In this case, a plurality of pumps are provided and the number of operating units can be controlled. . (Operation) Since SO ₃ in the boiler exhaust gas is adsorbed by the dust in the air preheater and drops to about 5 ppm, the sulfuric acid dew point temperature at the outlet of the air preheater is lower than that at the inlet of the air preheater. Therefore, the lower limit value of the gas temperature caused by the 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 outlet of the air preheater. The temperature can be lowered and the performance of the EP can be improved. Further, by controlling the heat exchange amount of the heat exchanger so that the operation can always be performed at a temperature equal to or higher than the lower limit temperature at which the SO ₃ dew point corrosion can be prevented, the flue and equipment after the EP can be prevented from being corroded. 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 coagulated into sulfuric acid as the gas temperature decreases, adheres to the device surface, and causes corrosion. Therefore, by ascertaining the concentration of dust in the EP outlet gas, it is possible to prevent the flue and equipment from corroding after the EP. Furthermore, for example, when designing an EP at a dust concentration of 100 mg / m ³ N at the EP outlet, under the condition of the conventional EP inlet temperature of 150 ° C. (A), the EP is the value of I in the EP characteristic curve of FIG. It was necessary to select an EP having characteristics. However,
According to the present invention, for example, the SO ₃ concentration B is determined 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 concentration C is obtained from the relationship, the EP having the characteristic of the characteristic curve II shown in FIG. 2 may be selected. Therefore, the equipment cost of the EP can be significantly reduced. (Examples) Hereinafter, the present invention will be described in detail based on examples. FIG. 1 is a system diagram of a flue gas treatment apparatus according to one embodiment of the present invention. In the figure, the same parts as those in FIG. 6 are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 1, the point different from the conventional apparatus (FIG. 6) is that a heat exchanger 8 is connected to the inlet of EP3, a communication pipe 12 connecting the heat exchanger 8 and the heat exchanger 10 and circulating 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 air preheater 2 outlet and the EP
A temperature detector 21 for measuring the gas temperature at the three inlets; an arithmetic unit 23 for calculating the amount of heat exchanged from the measured value of the temperature detector to a temperature at which low-temperature corrosion can be prevented; and a signal from the arithmetic unit 23 That is, a flow controller 24 provided in the communication pipe 12 for adjusting the heat medium amount 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, and the temperature of the exhaust gas is reduced to improve the dust collection performance of the EP 3. The heat exchanger 8 outlet gas temperature is calculated by the calculator 23 from the measured values measured by the temperature detectors 20 and 21 to a temperature at which low-temperature corrosion of the heat exchanger 8 downstream flue and equipment is prevented, Further, the amount of heat exchanged in the heat exchanger 8 is determined by the calculator 23 so as to reach the above-mentioned temperature, and the medium pressure is adjusted by the flow controller 24. The determination of the amount of heat exchanged by the arithmetic unit 23 can be performed, for example, 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 SO ₃ gas at the outlet of the air preheater 2, which has conventionally been impossible to measure continuously with high accuracy, is calculated. It can be determined continuously. Further, the dew point temperature of the gas SO ₃ concentration at the outlet of the air preheater 2 obtained in FIG. ₃ can be obtained from FIG. 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 relationship of FIG. 3 and FIG. 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. Further, another method can be performed by the arithmetic unit 23 in which the relationships shown in FIGS. 2, 3 and 5 are incorporated. By measuring the temperature of the gas at the outlet of the air preheater 2 with the temperature detector 20, the SO ₃ concentration of the gas at the outlet of the air preheater 2 is determined from FIG. _{3, and} from FIG. The dust concentration in the inside is required. This dust concentration becomes the dust concentration of the EP3 outlet gas that can prevent low-temperature corrosion, and the EP3 inlet gas temperature (set value) for achieving the dust concentration is determined from the EP characteristic curve II in FIG. Therefore, the arithmetic unit 23 incorporating the relationships shown in FIGS. 2, 3 and 5 uses the EP3 inlet gas temperature as a preceding signal, and uses the temperature detector 2
The exchange heat quantity of the heat exchanger 8 can be obtained using the EP3 inlet gas temperature measured in 1 as a feedback signal. In the above embodiment, the dew point temperature of the gas at the outlet of the air preheater 2 was 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 according to another embodiment of the present invention. The difference of the present invention from FIG. 1 is that the exchange heat quantity of the heat exchanger 8 is controlled by measuring the gas concentration at the outlet of the EP3 and the gas temperature at the inlet of the EP3. That is, a temperature detector 21 is provided at the entrance. In such a configuration, the determination of the amount of exchanged heat by the computing unit 23 is performed as follows. First, the dust concentration of the EP outlet gas is measured by the dust concentration meter 22. The SO ₃ concentration that can prevent the SO ₃ dew point corrosion at the dust 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 determines the heat exchange amount of the heat exchanger 8. The medium pressure is adjusted to the medium pressure corresponding to the heat exchange amount by the flow rate adjuster 24 provided in the communication pipe 12. (Effects of the Invention) According to the present invention, the gas temperature at the inlet of the electrostatic precipitator can be reduced to a temperature at which low-temperature corrosion due to SO ₃ can be prevented, so that the performance of the electric precipitator can be improved, SO ₃ low temperature corrosion can also be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a system diagram of a flue gas treatment apparatus according to one embodiment of the present invention, FIG. 2 is a diagram showing an EP characteristic curve, and FIG. FIG. 4 is a diagram showing a relationship between temperature and SO ₃ concentration, FIG. 4 is a diagram showing a relationship between SO ₃ concentration and dew point temperature, FIG. 5 is a diagram showing a relationship between SO ₃ concentration and corrosion by dust concentration, and FIG. The figure is a system diagram of a smoke exhaust treatment device according to the prior art, and FIG. 7 is a system diagram of a smoke exhaust treatment device according to another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1 ... Boiler, 2 ... Air preheater, 3 ... Electric precipitator (EP), 6 ... Desulfurization apparatus, 7 ...
Chimney, 8, 9, 10 ... heat exchanger, 11, 12 ... connecting pipe, 20, 21 ... temperature detector, 22 ... dust concentration meter, 23 ... arithmetic unit, 24 ... flow rate controller.

Claims (1)

Claims: 1. An air preheater for recovering calorific value of exhaust gas from a boiler or the like, an electric dust collector for removing dust contained in the exhaust gas, and a wet exhaust gas for removing sulfur oxides. A flue gas desulfurization device, and a flue that guides exhaust gas from the electrostatic precipitator to the wet flue gas desulfurization device,
In a flue gas treatment device having a heat exchanger for reheating to reheat exhaust gas from the wet flue gas desulfurization device , the calorie of the exhaust gas is recovered on the downstream side of the air preheater.
A heat recovery heat exchanger for circulating a heat medium through the reheating heat exchanger;
While providing a duster sequentially, the heat exchanger for heat recovery and the wet flue gas desulfurization device
The detection means of the exhaust gas temperature is provided between the the heat recovery as further exhaust gas temperature of the heat exchanger outlet for the heat recovery low temperature corrosion in the downstream side of the dust collector becomes a temperature that does not occur
A flue gas treatment device comprising a control device for adjusting a heat exchange amount of a heat exchanger for expropriation . 2. The flue gas treatment apparatus according to claim 1, wherein
That the flue leading the flue gas to the wet flue gas desulfurization unit has a fan
Characteristic smoke exhaust treatment device.