JPH0359728B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a flue gas treatment method and device, and particularly to a flue gas treatment method and device that can efficiently remove SO ₃ and dust in flue gas. [Background of the Invention] Electrostatic precipitators are generally used to remove dust from coal combustion flue gas. Conventionally, the temperature of the flue gas introduced into the electrostatic precipitator was higher than the acid dew point.
However, as shown in Figure 1, the dust collection efficiency of an electrostatic precipitator varies significantly depending on the type of coal when the flue gas temperature is about 140°C. In addition, coal, whether imported or domestic, differs greatly in calorific value, ash content, sulfur content, etc. depending on the type of coal, and the difficulty of collecting dust, which is the combustion ash, also varies widely. Therefore, in order to reduce the dust concentration in flue gas emitted from coal-burning combustion equipment to above the regulatory value, electrostatic precipitator treatment must be performed according to the type of coal that generates the most difficult-to-collect dust. It is necessary to select the capacity, which makes the electrostatic precipitator large and uneconomical. (If the type of coal that generates dust that is easy to collect is burned, the capacity of the electrostatic precipitator will be excessive.) As a solution to this problem, the electrostatic precipitator should be installed at a temperature of around 380°C. Installed at a high temperature position upstream of the air preheater, where the air flows in, for example, where the dust collection performance varies widely.
Possible methods include avoiding the inlet temperature range of around 140°C, and using a back filter whose collection efficiency is not affected much by coal type. However, if the temperature of the flue gas introduced into the electrostatic precipitator is raised to about 380℃, the volume of flue gas to be treated will increase approximately 1.6 times compared to when the temperature is 140℃. As it becomes larger, heat insulation measures against high-temperature exhaust smoke become expensive. In addition, the back filter does not have sufficient reliability at present due to the fabric. Another solution is to allow the flue gas to enter the electrostatic precipitator at a temperature lower than 140°C, allowing the electrostatic precipitator to operate with higher collection efficiency than at 140°C. Conceivable. However, with this method, it is necessary to lower the exhaust temperature of the flue gas from the air preheater, which is usually installed before the electrostatic precipitator, to below 140℃. There is no effective means to improve the heat transfer efficiency of the preheater and maintain operational reliability, and if the temperature of the flue gas discharged from the air preheater is lowered to the temperature required by the electrostatic precipitator, When the flue gas falls below the dew point temperature, the generated sulfuric acid and high dust in the flue gas may cause corrosion and blockage of the air preheater, corrosion of the electrostatic precipitator, and corrosion of the electrostatic precipitator installed downstream of the electrostatic precipitator. Corrosion and blockage may occur in the exposed equipment, which may impair the operational reliability of the entire flue gas treatment system. Under these circumstances, there is a demand for a flue gas treatment method and device that can more efficiently remove SO ₃ and dust from flue gas emitted from coal combustion equipment. [Object of the Invention] The object of the present invention is to provide a single air preheater that reduces the temperature of flue gas with high heat transfer efficiency and eliminates the corrosivity of flue gas, in order to solve the problems of the prior art described above.
The flue gas mixer equalizes the temperature of the flue gas discharged from the air preheater, and the flue gas mixer has a high dust collection efficiency.
An object of the present invention is to provide a method for treating flue gas using a flue gas treatment device having a configuration with a dust collector for removing SO ₃ and dust. [Structure of the Invention] The present invention is based on the new and extremely useful finding that when the average temperature of flue gas is lowered to 100 to 120°C, SO ₃ in flue gas is adsorbed to dust significantly better. It is completed based on the first
The invention includes a heat exchanger in which dust-containing flue gas discharged from a combustion device is introduced, heats a fluid to be heated by the flue gas, and a heat exchanger that heats a fluid to be heated by the heat exchanger, and the flue gas whose temperature is lowered by exchanging heat with the heat exchanger is introduced. In the method of treating flue gas with a dust collector, the flue gas is treated with a heat exchanger to an average temperature of 100 to
By means of supplying air in excess of that required for fuel combustion to the heat exchanger up to a temperature range of 120°C, by means of improving the heat transfer efficiency of the heat exchanger itself, and by a combination of these means. A flue gas treatment characterized in that SO ₃ in the flue gas is adsorbed to dust in the flue gas by lowering the temperature, and this dust is collected by the dust collector to remove SO ₃ from the flue gas. The method is summarized as follows. In addition, the present invention provides, as a second invention, an apparatus for performing such exhaust gas treatment, in which exhaust smoke from a combustion device is introduced, the heated fluid is heated by the exhaust smoke, and the temperature of the exhaust smoke is adjusted at the outlet part. A heat exchanger with an average temperature of 100 to 120°C, a dust collector connected to the flue gas outlet side of the heat exchanger, and a flue gas mixer installed between the heat exchanger and the dust collector. An exhaust gas treatment device comprising: In the present invention, the average temperature of flue gas at a certain location refers to the average value of temperatures measured at a number of measurement points on the cross section of the flue gas flow path at that location. That is, although the temperature distribution in the cross-sectional direction of the flue gas flow path is uneven, the average temperature refers to the normal temperature of this distributed temperature. [Embodiments of the Invention] Examples of the present invention will be described below with reference to the drawings. FIG. 2 is a system diagram showing an embodiment of a flue gas treatment device for a large-scale coal-fired boiler for commercial use. Reference numeral 1 denotes a boiler, and on its exhaust smoke outlet side there are a denitrification device 2, a rotary regenerating air preheater (in this example, a three-pass rotary regenerating air preheater) 3, an electrostatic precipitator 10, and an induced blower. 15, gas heater 16, booster blower 17,
A wet desulfurization device 18, gas mixers 31 and 32, a bag filter 19, and a chimney 20 are installed in this order. The rotary regeneration air preheater 3 heats the air supplied to the boiler 1, and has a primary air supply line 21a and a secondary air supply line 22a connected to each other. 21 and 22 are blowers, respectively. A coal mill 23 is located in the middle of the primary air supply line 21a.
is installed. A bypass flow path 22b that bypasses the rotary regeneration type air preheater 3 is provided in the secondary air supply line 22a. Bypass channel 22
A damper 25 is provided at b. Further, a heated air line 22c is branched from a portion of the secondary air supply line 22a between the air preheater 3 and the boiler 1, and is connected to the mixers 31, 3 via a damper 24.
Connected to 2. Additionally, temperature and flow rate sensors 26, 27, 28, and 29 are installed at three locations between the exhaust smoke outlet of the air preheater 3 and the secondary air supply line 22a, and their signals are input to the controller 30. The controller 30 controls the dampers 24 and 2 based on these input signals.
A signal is output to control the opening and closing of 5. In the diagram
T1 to T14 are the temperatures at each location, and the specific measurement locations are as follows. T1...Upstream part of the rotary regenerative air preheater 3. T2...Outlet part of the rotary regenerative air preheater 3. T3...Exit part of the electrostatic precipitator 10. T4...Between induced blower 15 and gas heater 16. T5...Between the gas heater 16 and booster blower 17. T6...Between the wet deflow device 18 and the mixer 31. T7...Between the mixer 31 and the gas heater 16. T8...Between the gas heater 16 and the mixer 32. T9...Between the mixer 32 and the bag filter 19. T10…Temperature of primary air before heating. T11…Temperature of the primary air after being heated by the rotary regenerative air preheater 3. T12…Secondary air temperature before being heated. T13…Secondary air temperature after being heated. T14...Temperature in line 22c branched from secondary air supply line 22a. The operation of the apparatus of this embodiment and the details of each component will be explained below in accordance with the flow of smoke exhaust. The above-mentioned temperatures T1 to T14 in this example are as shown in Table 1. After the flue gas containing dust from coal combustion discharged from the boiler 1 passes through the denitrification device 2,
The air is discharged at a temperature of about 380°C and flows into the rotary regeneration type air preheater 3. The exhaust gas that has entered the rotary regeneration type air preheater 3 exchanges heat with the air as it passes through the preheater 3, and its temperature gradually decreases. The dew point of the flue gas at the inlet of the air preheater 3 is lowered or lower, and near the exhaust smoke outlet of the air preheater 3,
When the flue gas comes into contact with the heat transfer surface whose temperature is well below the dew point, SO ₃ becomes sulfuric acid mist that condenses on the heat transfer surface and floats in the flue gas. On the other hand, during smoke evacuation,
It contains dust that has an affinity for sulfuric acid (normal content is about 10 to 30μg/), so most of the sulfuric acid floating in flue gas or attached to heat transfer surfaces is this. It is absorbed by dust and removed.
Further, the dust that has adsorbed sulfuric acid becomes wet, increasing the adsorption force between particles, and becomes dust with a large particle size. Average temperature 110℃ from air preheater 3
In the flue gas emitted, most of the SO ₃ has been removed, the residual SO ₃ concentration is below 0.2 to 0.3 ppm, and the dew point temperature of the flue gas is lower than 100°C. Therefore, this flue gas exhibits almost no corrosive properties. FIG. 3 is a diagram showing the configuration of the three-pass rotary regenerative air preheater 3 used in this embodiment,
It is a view of this air preheater 3 viewed from the smoke exhaust outlet side. The process by which SO ₃ is removed from flue gas in this three-pass rotary regenerating air preheater 3 will be described in detail below while explaining the configuration of the air preheater 3. In Figure 3, smoke is emitted from the upper half of the center,
Air is supplied to the lower half, and the air is supplied to the right part of the lower half in the figure.

〔Effect of the invention〕

As mentioned above, the present invention uses a heat exchanger to convert flue gas into
After lowering the temperature to an average temperature of °C, it is treated with an electrostatic precipitator. Most of the SO ₃ in the flue gas is adsorbed to dust, and this dust is removed using an electrostatic precipitator. Most of the SO ₃ can be easily removed. Therefore, it is possible to reduce the need for anti-corrosion measures for various devices installed downstream of the electrostatic precipitator. In addition, the particles that have adsorbed SO ₃ have extremely good dust collection properties in an electrostatic precipitator, greatly improving the dust collection efficiency in the electrostatic precipitator, and making it easier for equipment installed downstream of the electrostatic precipitator to collect particles. Dust adhesion and resulting blockages are significantly reduced.
Furthermore, since the temperature of the flue gas at the exit of the heat exchanger is 100 to 120°C, which is extremely low compared to the conventional temperature (for example, 140°C), the volume of the flue gas is reduced and the amount of heat radiated to the outside of the device is reduced. Therefore, it is possible to reduce the volume of various devices installed downstream of the heat exchanger. FIG. 9 is a graph showing the relationship between the flue gas temperature measured by the test plant and the dust movement speed within the electrostatic precipitator. When flue gas flows into an electrostatic precipitator at 140°C, the dust adheres to the dust collector plate at a speed of 22 cm/sec, but when flue gas flows into the electrostatic precipitator at 100 to 120°C, it moves at around 33 cm/sec. The dust collection efficiency is significantly improved. As mentioned above, according to the present invention, the dust is in the form of moist large particles, so it is easy to collect both chemically and physically, and together with the improvement in dust collection efficiency due to the reduction in temperature, the dust collection efficiency is significantly improved. It will be improved greatly. Furthermore, in the device of the present invention, the temperature of the flue gas discharged from the heat exchanger (rotary regenerative air preheater in the above embodiment) is maintained uniformly in the cross-sectional direction (by the action of a mixer, etc.). The SO ₃ remaining in the smoke does not become sulfuric acid, so there is no need to use expensive corrosion-resistant materials for the electrostatic precipitator components. As mentioned above, FIG. 1 is a graph showing the relationship between flue gas temperature and dust collection efficiency depending on the type of coal. As shown in the figure, there are large variations in the properties of dust in flue gas generated depending on the type of coal, and there are differences in dust collection efficiency depending on the type of coal even at the same flue gas temperature. When the flue gas temperature is 140℃, the dust collection efficiency of coal A is i% and the dust collection efficiency of coal C is j
%. This difference means that a small-capacity electrostatic precipitator is sufficient to collect dust on A coal, but a large-capacity electrostatic precipitator is required to collect dust on C coal. In the case of flue gas treatment equipment when charcoal is used together, it is necessary to install a large electrostatic precipitator that can collect dust from C charcoal, and when collecting A charcoal, the capacity of the electrostatic precipitator must be This becomes excessive and results in wasted equipment. When the temperature of flue gas is lowered to 100 to 120°C as in the present invention, the dust collection efficiency of coal A is g%, the dust collection efficiency of coal C is h%, and the dust collection efficiency is but
As the temperature increased from 140℃, the temperature of A coal and C coal increased.
Since the difference in dust collection efficiency with charcoal is very small,
There is almost no difference in the capacity of the electrostatic precipitator required when collecting dust from charcoal or when collecting dust from C charcoal.
There is no need to provide an electric precipitator with excessive capacity. For these reasons, according to the present invention, the capacity of the electrostatic precipitator can be significantly small, and the electrostatic precipitator can be downsized. In the present invention, the flue gas discharged from the electrostatic precipitator has a low temperature and a low dust content and SO ₃
Both contents are extremely low, and the volume is reduced due to the low temperature, which reduces the corrosion resistance and blockage measures required for various equipment installed downstream of the electrostatic precipitator. Can be made smaller. Furthermore, it has the effect of reducing water evaporation loss in the desulfurization equipment. In addition, since the exhaust gas outlet temperature of a heat exchanger such as a rotary regenerative air preheater is reduced to 100 to 120°C, the amount of heat exchanged in the heat exchanger can be improved. For example, when increasing the amount of passing air to improve heat transfer efficiency, surplus heated air can be obtained in addition to the heated air required for combustion, and this surplus heated air can be used as a heat source for various heating purposes. be able to. Further, due to the above-mentioned various effects, according to the present invention, it is possible to achieve a significant reduction in the equipment cost and operating cost of the device, and to improve the reliability of the device operation.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between coal type, flue gas temperature, and dust collection efficiency, FIG. 2 is a system diagram of an apparatus according to an embodiment of the present invention, and FIG. Figures 4a and 4b are cross-sectional views of the heat transfer element, Figures 5a, b and c are views showing the installation structure of the split multi-blade guide plates 4 and 5, respectively.
The figure shows a schematic diagram of the rotary regeneration air preheater, flue gas mixer, inlet duct, and electrostatic precipitator, and Figure 7 shows how the SO ₃ content in flue gas decreases in an embodiment of the present invention. FIG. 8 is a system diagram of a different example device, and FIG. 9 is a graph showing the relationship between flue gas temperature and dust movement speed in an electrostatic precipitator. 1...Boiler, 2...Denitrification device, 3...Rotary regeneration type air preheater, 4, 5...Divided multi-blade guide plate,
6, 7... Rotating shaft, 8... Smoke exhaust mixer, 9... Inlet duct, 10... Electric precipitator, 11a, 11b
... Distribution plate, 12 ... Guide vane, 13 ... Hopper section, 14 ... Heater, 15 ... Induced blower, 1
6... Gas heater, 17... Boost blower, 18...
...Wet desulfurization equipment, 19...Bag filter, 20
... Chimney, 21, 22 ... Blower, 21a ... Primary air supply line, 22a ... Secondary air supply line, 22b ... Bypass passage, 22c ... Heating air line, 23 ... Coal mill, 24 ... ... Branch damper, 25 ... Bypass damper, 26, 27, 2
8, 29... Temperature and flow rate sensor, 30... Controller, 31, 32... Mixer.

Claims (1)

[Scope of Claims] 1. A single heat exchanger into which dust-containing flue gas discharged from a combustion device is introduced and heats a fluid to be heated by the flue gas, and a heat exchanger that exchanges heat with the heat exchanger to lower the temperature. A method for treating flue gas with a dust collector into which the flue gas is introduced, wherein the flue gas is heated to an average temperature of 100 to
By lowering the temperature to a range of 120°C, SO ₃ in the flue gas is adsorbed to dust in the flue gas, and this dust is collected by the dust collector to remove SO ₃ from the flue gas. A flue gas treatment method characterized by: 2. A heat exchanger into which flue gas from a combustion device is introduced, heats a fluid to be heated by the flue gas, and brings the temperature of the flue gas to an average temperature of 100 to 120 °C at the outlet; A flue gas treatment device comprising: a dust collector connected to a smoke outlet side; and a flue gas mixer installed between the heat exchanger and the dust collector. 3. The device according to claim 2, wherein the precipitator is an electrostatic precipitator. 4. The apparatus according to claim 2, wherein the dust collector is an electric dust collector and a bag filter, and the bag filter is installed downstream of the electric dust collector. 5. The device according to claim 4, characterized in that a wet desulfurization device is installed between the electrostatic precipitator and the bag filter.