JP3705838B2 - Smoke removal equipment - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method and apparatus for efficiently and economically treating exhaust gas from a coal-fired combustion apparatus.
[0002]
[Prior art]
Environmental regulations for thermal power plants that use coal as fuel are becoming stricter year by year, and in particular, it is required to achieve soot and soot emission concentrations as low as heavy oil thermal power.
Conventionally, as shown in FIG. 5 , as a method for treating coal-fired exhaust gas, exhaust gas from a coal-fired combustion device, for example, a coal-fired boiler 10, is introduced into a denitration device 12 for denitration treatment, and then an air preheater (GAH) 14. And then into a dry electrostatic precipitator 16 (hereinafter sometimes referred to as DEP) to collect the collected exhaust gas, and the collected exhaust gas is recovered by a medium circulation type gas / gas heater (GGH) 18 as heat. After being introduced into the vessel 20 and cooled, it is introduced into the dedusting tower 22 and sprayed with water for dedusting, and then introduced into the desulfurization device 24 for desulfurization, and then a medium circulation type gas / gas heater (GGH) 18. There is known a method of introducing the reheater 26 into the chimney 28 by reheating it. It is also known that a heat pipe is used instead of the medium circulation type gas / gas heater.
[0003]
In the method shown in FIG. 5 , the method of increasing the performance of the electrostatic precipitator (DEP) 16 is the simplest way to reduce the dust concentration, but this method has the following drawbacks.
(1) For mere performance improvement, the dust collection area of DEP may be excessive depending on the type of coal (1.5 to 2 times that of a general type of coal). I need.
(2) In the heat recovery unit 20 of the medium circulation type gas / gas heater 18 usually installed in the downstream of the DEP 16, the neutralization ability of the acid is reduced due to the decrease in the concentration of the dust in the exhaust gas, and the portion below the acid dew point Corrosion occurs.
[0004]
Since the method shown in FIG. 5 has such a problem, a wet electrostatic precipitator 30 (hereinafter referred to as WEP) is provided at the outlet of the desulfurizer 24 as shown in FIG. 6 without reducing the outlet concentration of DEP. A system to reduce the concentration of dust is put into practical use.
Although the method of FIG. 6 can be stably operated to keep the dust concentration in the exhaust gas low, there is a disadvantage inferior in economic efficiency.
As an alternative to the system shown in FIG. 6 , as shown in FIG. 7 , a system is proposed in which the heat recovery unit 20 of the gas / gas heater 18 is installed upstream of the DEP 16 (see Japanese Patent Laid-Open No. 3-70907).
The system of FIG. 7 has the following excellent points.
(1) Since the exhaust gas temperature at the outlet of DEP16 is as low as 80 to 110 ° C. and the electric resistance value of dust is also low, the dust collection performance at DEP16 is improved.
(2) Even if the concentration of the dust at the outlet of the DEP 16 is lowered, the heat recovery unit 20 of the gas / gas heater is located upstream of the DEP, so that the acid is neutralized by the dust and there is no concern about corrosion.
(3) Since the dust collection performance of DEP16 is improved and the dust concentration at the DEP outlet is lowered, the amount of dust mixed into the desulfurization unit 24 is reduced, and the by-product gypsum quality can be ensured to be a predetermined quality even without a dust removal tower. .
(4) Further, dust can be reduced to a low concentration (for example, 5 mg / m ³ N or less) without installing WEP.
[0005]
However, the method shown in FIG. 7 has the following drawbacks.
(A) Corrosion of DEP16 and measures against dust adhesion are necessary When the exhaust gas temperature becomes low, the fluidity of the collected dust generally deteriorates. Accordingly, dust is attached to or adhered to the dust collection electrode, discharge electrode, hopper, etc. in the electrostatic precipitator 16, so that countermeasures are required (such as enhanced thermal insulation, aeration, change of structure of discharge electrode, etc.). necessary).
(B) Corrosion countermeasure of boiler induction fan (IDF) is necessary IDF is installed downstream of DEP from the viewpoint of preventing impeller wear, but after DEP in this system, temperature is low and soot concentration is low. Corrosion due to the flying of SO ₃ or sulfuric acid fume that has passed through the DEP to the IDF is concerned, and some countermeasures such as the use of a corrosion-resistant material are necessary, resulting in high costs.
(C) Measures for long-term stable operation of the gas / gas heater heat recovery unit 20 are necessary. The soot concentration is about two orders of magnitude higher than before (10g-20g / m ³ N), so the heat recovery unit 20 is blocked by soot. Sufficient consideration should be given to preventive measures.
In general, a steel ball spraying method is used as a measure to prevent clogging. However, when high concentrations of dust are generated, a large amount of dust adheres to the surface of the heat transfer tube of the heat recovery device 20, so that the impact force caused by the drop of the steel balls is reduced. The removal effect is reduced.
[0006]
[Problems to be solved by the invention]
Thermal power plant environmental countermeasure facilities often consist of two lines as the power generation output increases. This may be due to manufacturing limitations, but it is also due to the consideration that one-line operation is possible in case of trouble.
When configuring the system shown in FIG. 7 with two series are as shown in FIG. 32 is an attracting fan, and 34 is a booster fan. The method shown in FIG. 8 has the following problems.
(A) Desulfurization unit single-system operation It is highly likely that the single-system operation due to a trouble will be performed in the environmental countermeasure facility is the desulfurization unit 24 that is likely to increase pressure loss due to scaling caused by calcium. When performing the desulfurization piece series operation by the method of FIG. 8 , the heat recovery unit 20 side of the gas / gas heater must be operated in two series, and the reheater 26 side must be operated in one series. (1) Heat recovery of the stop series Some countermeasures are required for the vessel, and (2) exhaust gas temperature after reheating on the operation side is low (heat exchange amount is about half).
(B) Whole system single series operation Since there is the above-mentioned problem in the desulfurization single system operation, the whole system including denitration can be considered to be a single series operation, but in this case, there is the following problem. That is, the amount of exhaust gas to be processed is a planned amount, but the temperature is low because the load is low. This is because denitration performance is deteriorated in denitration using a catalyst, and when such operation is planned from the beginning, it is necessary to increase the amount of catalyst in advance.
[0007]
The present invention has been made in view of the above-mentioned various points, and an object of the present invention is to provide a method and apparatus for eliminating smoke that are all excellent in terms of economy and excellent in economy.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the flue gas treatment method of the present invention performs denitration treatment of coal combustion exhaust gas, introduces it into an air preheater, recovers heat, and then pulses the cooled exhaust gas after heat recovery. After being collected in a charge-type electrostatic precipitator and collected, it was introduced into a heat recovery unit using a Teflon (registered trademark) tube of a medium circulation type gas / gas heater, cooled, and then cooled. The exhaust gas is desulfurized by the wet lime gypsum method , and then introduced into the recirculator of the medium circulation type gas / gas heater so as to be reheated and led to the chimney .
[0009]
The flue gas treatment apparatus of the present invention includes a denitration apparatus for denitrating coal combustion exhaust gas, an air preheater for exchanging heat between the denitrated exhaust gas and combustion air, and collecting exhaust gas from the air preheater. Pulse-charge-added electric dust collector, medium circulation type gas / gas heater heat recovery unit that recovers the heat of the exhausted exhaust gas, and wet lime gypsum desulfurization process that desulfurizes the exhaust gas from this heat recovery unit A recirculator of the medium circulation type gas / gas heater for reheating the desulfurized exhaust gas, and a chimney for discharging the reheated exhaust gas to the atmosphere, and the heat of the medium circulation type gas / gas heater The collector is characterized by including a Teflon (registered trademark) tube.
[0010]
Also, through the heat recovery unit of the gas-gas heater is divided into a plurality sections with respect to the gas flow, it is preferable to connect the cleaning water supply pipe in each compartment.
In this case , it is preferable to connect each section of the heat recovery unit of the gas / gas heater and the desulfurization apparatus via a used washing water pipe.
[0011]
[Action]
The exhaust gas from the coal-fired combustion device is introduced into the denitration device to remove NOx in the exhaust gas, then introduced into the air preheater to preheat the combustion air, and then the cooled exhaust gas after heat recovery is pulse charged After introducing into the electric dust collector of the type and collecting the dust, it is introduced into the heat recovery unit of the medium circulation type gas / gas heater and cooled, and then the cooled exhaust gas is introduced into the desulfurization unit and SOx in the exhaust gas is introduced. After removing the gas, it is introduced into a recirculator of a medium circulation type gas / gas heater and reheated to be led to a chimney.
Since the electrostatic precipitator is a pulse charging type, high dust collection efficiency can be obtained without increasing the precipitator area of the precipitator even with high resistance ash.
In addition, the heat recovery unit of the gas / gas heater is made of heat- and acid-resistant synthetic resin tubes such as Teflon (registered trademark) tubes, so there is no risk of corrosion and the dust concentration at the outlet of the electrostatic precipitator is low. can do.
[0012]
【Example】
EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to the following Example at all, It can change suitably and can implement.
FIG. 1 shows an embodiment of an apparatus for carrying out the smoke treatment method of the present invention. Exhaust gas from a coal fired combustion apparatus, for example, a coal fired boiler 10 is introduced into a denitration apparatus 12 and denitrated, then introduced into an air preheater 14 for heat recovery, and then the cooled exhaust gas after heat recovery is pulsed. After being introduced into the charge-type dry electrostatic precipitator 16a and collected, it is introduced into the heat recovery unit 20a of the medium-circulating gas / gas heater 18a that circulates a medium, for example, water.
[0013]
The pulse-charge-type dry electrostatic precipitator 16a in the present invention is an electric precipitator that generates corona discharge using a pulsed high voltage generated by electrical switching or the like alone or together with a DC voltage. A dry-type electrostatic precipitator that can achieve high performance stably against ash.
The heat recovery unit 20a of the gas / gas heater 18a is composed of a heat-resistant / acid-resistant synthetic resin tube, for example, a Teflon (registered trademark) tube. The exhaust gas cooled by the heat recovery unit 20a is treated with a wet lime gypsum desulfurization device 24. And then desulfurized, and then introduced into a recirculator 26 of a medium circulation type gas / gas heater, reheated and discharged from the chimney 28. The gas / gas heater 18a includes a heat recovery unit 20a and a reheater 26.
[0014]
As shown in FIGS. 2 and 3, the heat recovery unit 20a of the gas / gas heater is divided into a plurality of sections 40 by a damper 36 and a partition plate 38 with respect to the gas flow, and a cleaning water supply pipe 42 is connected to each section 40. Each section 40 and the wet lime gypsum desulfurization device 24 are connected via a used washing water pipe 44 .
[0015]
FIG. 4 is a graph showing the relationship between fly ash electrical resistance and dust collection efficiency when there is no pulse charge and when there is pulse charge in a dry electrostatic precipitator.
[0016]
【The invention's effect】
Since this invention is comprised as mentioned above, there exist the following effects.
(1) Since the heat recovery unit of the gas / gas heater is made of Teflon (registered trademark) having excellent corrosion resistance, there is no concern about corrosion and the dust concentration at the outlet of the electric dust collector can be reduced.
(2) Since the electrostatic precipitator employs a pulse charging system, high dust collection efficiency can be obtained without increasing the precipitator area of the precipitator even with high resistance ash (see FIG. 4) . ).
(3) Since the dust concentration at the inlet of the desulfurization apparatus is low and can be further collected by the desulfurization apparatus, the dust concentration at the smoke outlet can be reduced without installing a wet electric dust collector.
(4) When the concentration of dust in the heat recovery unit of the gas / gas heater is low and the heat exchange tube is Teflon (registered trademark) , the surface is smoother than that of the steel pipe, so it is difficult for dust to adhere, and a simple removal device. By adding only (water washing device etc.), it is possible to prevent the gas / gas heater from being clogged or increased in pressure loss due to soot and dust.
(5) Since there is little dust flying to the desulfurizer, high-quality gypsum can be produced as a by-product without installing a dedusting tower. For this reason, the dedusting tower can be omitted, the apparatus is simplified, and the cost becomes economical.
(6) The electric dust collector outlet where the boiler induction fan is installed has a high gas temperature and is above the acid dew point temperature, so there is no concern about corrosion and there is no need to use a corrosion resistant material for the induction fan.
(7) Regarding the operation in the two-line operation, the desulfurization apparatus that is expected to have the highest frequency of the single-line operation is located on the most downstream side including the gas / gas heater, and the single-line operation can be easily performed.
[Brief description of the drawings]
FIG. 1 is a system diagram showing an embodiment of a flue gas treatment apparatus of the present invention.
2 is an elevational sectional view showing an example of a heat recovery unit of the gas / gas heater in FIG. 1. FIG.
FIG. 3 is a cross-sectional view of the same plane .
FIG. 4 is a graph showing the results of measurement of fly ash electrical resistance and dust collection efficiency with and without pulse charge in an electrostatic precipitator.
FIG. 5 is a system diagram showing an example of a conventional smoke treatment apparatus.
FIG. 6 is a system diagram showing an example of a conventional flue gas treatment apparatus.
FIG. 7 is a system diagram showing an example of a conventional flue gas treatment apparatus.
FIG. 8 is a system diagram of a device in which the devices shown in FIG. 7 are connected in two lines.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Coal-fired boiler 12 Denitration apparatus 14 Air preheater 16a Dry type electric dust collector 18a Gas / gas heater 20a Heat recovery machine 22 Dedusting tower 24 Desulfurization device 26 Reheater 28 Chimney 30 Wet electric dust collector 32 Induction fan 34 Booster fan 36 Damper 38 Partition plate 40 Section 42 Washing water supply pipe 44 Used washing water pipe

Claims (1)

A denitration device for denitrating coal combustion exhaust gas;
An air preheater for exchanging heat between the denitrated exhaust gas and the combustion air;
A pulse charge addition type electric dust collector that collects the exhaust gas from the air preheater;
A heat recovery device for a medium circulation type gas / gas heater that recovers the heat of the exhausted exhaust gas;
A wet lime gypsum desulfurization device for desulfurizing exhaust gas from the heat recovery device;
A reheater of the medium circulation type gas / gas heater for reheating the desulfurized exhaust gas;
It consists of a chimney that discharges the reheated exhaust gas to the atmosphere,
The heat recovery device of the medium circulation type gas / gas heater includes a Teflon (registered trademark) tube ,
The heat recovery unit of the gas / gas heater is divided into a plurality of compartments for the gas flow, and a wash water supply pipe is connected to each compartment,
A smoke exhausting treatment apparatus, wherein each section of the heat recovery unit of the gas / gas heater is connected to a desulfurization apparatus through a used washing water pipe .

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