US20160313076A1 - Air preheater and method for preventing corrosion and blockage of the same - Google Patents
Air preheater and method for preventing corrosion and blockage of the same Download PDFInfo
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- US20160313076A1 US20160313076A1 US15/202,520 US201615202520A US2016313076A1 US 20160313076 A1 US20160313076 A1 US 20160313076A1 US 201615202520 A US201615202520 A US 201615202520A US 2016313076 A1 US2016313076 A1 US 2016313076A1
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- segment
- ammonium bisulfate
- air
- curing
- condensation
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
- F28F19/00—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES
- F23J15/00—Arrangements of devices for treating smoke or fumes
- F23J15/06—Arrangements of devices for treating smoke or fumes of coolers
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
- F23L15/00—Heating of air supplied for combustion
- F23L15/02—Arrangements of regenerators
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
- F23L15/00—Heating of air supplied for combustion
- F23L15/04—Arrangements of recuperators
- F23L15/045—Arrangements of recuperators using intermediate heat-transfer fluids
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
- F28D15/00—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies
- F28D15/02—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes
- F28D15/0266—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes with separate evaporating and condensing chambers connected by at least one conduit; Loop-type heat pipes; with multiple or common evaporating or condensing chambers
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES
- F23J2215/00—Preventing emissions
- F23J2215/10—Nitrogen; Compounds thereof
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES
- F23J2219/00—Treatment devices
- F23J2219/10—Catalytic reduction devices
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E20/00—Combustion technologies with mitigation potential
- Y02E20/34—Indirect CO2mitigation, i.e. by acting on non CO2directly related matters of the process, e.g. pre-heating or heat recovery
Definitions
- the invention relates to an air preheater and a method for preventing corrosion and blockage of the same.
- Conventional flue gas denitration technology employs ammonia gas as a reducing agent.
- the reducing agent reacts with sulfur trioxide in the flue gas to yield ammonia bisulfate.
- an air preheater is provided to recycle heat energy.
- the air preheater is of a regenerative type, as shown in FIG. 1 , and includes a high temperature segment, a medium temperature segment, and a low temperature segment.
- Ammonium bisulfate exhibits strong viscosity in the medium temperature segment and the low temperature segment, and tends to adsorb dust particles and, as a result, block the air preheater. This increases the gas flow resistance, lowers the heat transfer efficiency, and adversely affects operation of the air preheater.
- the air preheater is particularly practicable following a selective catalytic reduction (SCR) denitration.
- SCR selective catalytic reduction
- an air preheater comprising a flue and an air channel disposed on a downstream of a denitration device, a first segment for producing secondary air, a second segment for producing primary air, a third segment for anti-condensation of ammonium bisulfate, and a fourth segment for curing of ammonium bisulfate.
- the first segment for producing secondary air, the second segment for producing primary air, the third segment for anti-condensation of ammonium bisulfate and the fourth segment for curing of ammonium bisulfate are disposed in that order along a gas flow direction.
- the second segment for producing primary air, the third segment for anti-condensation of ammonium bisulfate, and the fourth segment for curing of ammonium bisulfate each comprise a phase-change heat exchanger.
- the phase-change heat exchanger comprises a heat absorption segment disposed in the flue, a heat release segment disposed in the air channel, an ascending tube and a downcomer which are configured to connect the heat absorption segment and the heat release segment.
- the heat release segment is disposed higher than the heat absorption segment, and the phase-change heat exchangers are provided with a cycling medium.
- a wall surface temperature of the third segment for anti-condensation of ammonium bisulfate is higher than a dew temperature of the ammonium bisulfate.
- a wall surface temperature of the fourth segment for curing of ammonium bisulfate is lower than a solidification point temperature of the ammonium bisulfate.
- the air preheater further comprises an acid-dew resistant segment disposed on a downstream of the fourth segment for curing of ammonium bisulfate.
- the acid-dew resistant segment comprises the phase-change heat exchanger, and a wall surface temperature of the acid-dew resistant segment is higher than an acid dew point temperature.
- the heat absorption segment in the second segment for producing primary air, the heat absorption segment in the third segment for anti-condensation of ammonium bisulfate, the heat absorption segment in the fourth segment for curing of ammonium bisulfate, the heat absorption segment in the acid-dew resistant segment are provided with a temperature sensor.
- the cycling medium in the second segment for producing primary air, the third segment for anti-condensation of ammonium bisulfate, the fourth segment for curing of ammonium bisulfate, and the acid-dew resistant segment is water, Freon, or heat transfer oil.
- the first segment for producing secondary air is a high temperature segment of a regenerative air preheater.
- the first segment for producing secondary air comprises the phase-change heat exchanger
- the cycling medium in the second segment for producing primary air is water, Freon, or heat transfer oil.
- the reaction of the escaped ammonia and the sulfur trioxide only produces gaseous and solid ammonium bisulfate, and no liquid ammonium bisulfate is produced, thus the air preheater is effectively prevented from blockage and corrosion caused by liquid ammonium bisulfate. Therefore, the service life of the air preheater is prolonged; the heat transfer efficiency of the boiler is improved; thus ensuring the stable and safe operation of the machine set.
- the air preheater is disposed on a downstream of a denitration device using SCR denitration technology.
- the method can prevent the corrosion and blockage of the heating surface of the air preheater.
- a method for preventing an air preheater from corrosion and blockage comprising:
- the wall surface temperature of the third segment and the fourth segment can be accurately controlled, so that the ammonium bisulfate is cured on the wall surface of the pipe of the fourth segment and the wall surface of the downstream pipe of the fourth segment, then the solid ammonium bisulfate is eliminated by blowing equipment.
- the air preheater is effectively prevented from blockage and corrosion, thus ensuring the safe, reliable, and stable operation of the boiler.
- FIG. 1 is a schematic diagram of an existing air preheater
- FIG. 2 is a schematic diagram of an air preheater in accordance with one embodiment of the invention.
- FIG. 3 is a schematic diagram of an air preheater in accordance with another embodiment of the invention.
- an air preheater comprises a flue 1 and an air channel 2 disposed on the downstream of a denitration device, a first segment for producing secondary air 3 , a second segment for producing primary air 4 , a third segment for anti-condensation of ammonium bisulfate 5 , and a fourth segment for curing of ammonium bisulfate 6 disposed in that order along a gas flow direction.
- the second segment for producing primary air 4 , the third segment for anti-condensation of ammonium bisulfate 5 , and the fourth segment for curing of ammonium bisulfate 6 each comprise a phase-change heat exchanger.
- the phase-change heat exchanger comprises a heat absorption segment 7 disposed in the flue 1 , a heat release segment 8 disposed in the air channel 2 , an ascending tube 9 and a downcomer 10 which are configured to connect the heat absorption segment 7 and the heat release segment 8 .
- the heat release segment 8 is higher than the corresponding heat absorption segment 7 , and the phase-change heat exchanger is provided with a cycling medium.
- a wall surface temperature of the third segment for anti-condensation of ammonium bisulfate 5 is higher than a dew temperature of the ammonium bisulfate.
- a wall surface temperature of the fourth segment for curing of ammonium bisulfate 6 is lower than a solidification point temperature of the ammonium bisulfate.
- High-temperature flue gas (between 350 and 440° C.) in the flue 1 enters an upstream of the assembled air preheater, and passes the first segment for producing secondary air 3 , the heat-absorbing segment 7 of the second segment for producing primary air 4 , the heat-absorbing segment 7 of the third segment for anti-condensation of ammonium bisulfate 5 , and the heat-absorbing segment 7 of the fourth segment for curing of ammonium bisulfate 6 .
- the high-temperature flue gas releases heat when passing the air preheater and heats the cycling medium in the heat absorption segment 7 of all phase-change heat exchangers.
- the cycling medium in all phase-change heat exchangers absorbs heat released by the flue gas and generates a lift force because of a density difference, thus the cycling medium in the heat absorption segment 7 enters the heat release segment 8 via the ascending tube 9 , and after releasing heat to the air, the cycling medium in the heat release segment 8 is back to the heat absorption segment 7 via the downcomer 10 , hereby a self-cycle is realized and no external power is needed.
- the pipe wall temperature of the third segment for anti-condensation of ammonium bisulfate 5 and the pipe wall temperature of an upstream of the third segment for anti-condensation of ammonium bisulfate 5 are higher than the dew temperature of the ammonium bisulfate (between 0 and 200° C.)
- the pipe wall temperature of the fourth segment for curing of ammonium bisulfate 6 and the pipe wall temperature of a downstream of the fourth segment for curing of ammonium bisulfate 6 are lower than the solidification point temperature (147° C.) of the ammonium bisulfate
- the reaction of escaped ammonia and sulfur trioxide only generates gaseous and solid ammonium bisulfate in the air preheater, no liquid ammonium bisulfate is produced, and the air preheater is effectively prevented from blockage and corrosion caused by liquid ammonium bisulfate.
- cycling media in the second segment for producing primary air 4 , the third segment for anti-condensation of ammonium bisulfate 5 , the fourth segment for curing of ammonium bisulfate 6 , the acid-dew resistant segment 11 is selected from water, Freon, or heat transfer oil. In actual operation, a suitable cycling medium solution is determined according to different temperatures.
- the downstream of the fourth segment for curing of ammonium bisulfate 6 is provided with an acid-dew resistant segment 11 .
- the acid-dew resistant segment 11 comprises the phase-change heat exchanger, comprising the heat absorption segment 7 , the heat release segment 8 , the ascending tube 9 and the downcomer 10 .
- the wall surface temperature of the acid-dew resistant segment 11 is higher than an acid dew point temperature (between 0 and 100° C.), thereby effectively preventing the acid dew corrosion, decreasing an energy consumption of the boiler, and saving energy and reducing emission to the largest extent.
- the air is divided into two paths after heated by the second segment for producing primary air 4 , as shown in FIGS. 2-3 , the first path is used as a primary air for a pulverizing system, and the second path is heated by the first segment for producing secondary air 3 and is used as secondary air of the boiler, which means the primary air is not heated by the first segment for producing secondary air 3 .
- Heat saved by the primary air can be used to heat materials in the third segment for anti-condensation of ammonium bisulfate 5 , the fourth segment for curing of ammonium bisulfate 6 , the acid-dew resistant segment 11 , or a combination thereof.
- the air in the acid-dew resistant segment 11 , the fourth segment for curing of ammonium bisulfate 6 , the third segment for anti-condensation of ammonium bisulfate 5 , and the second segment for producing primary air 4 is exhausted, so that no non-condensable gas exists in cycling pipes of the phase-change heat exchangers, and the blockage caused by water or gas is avoided.
- the flue gas temperature after denitration is between 350 and 440° C.
- the heat absorption segment 7 in the second segment for producing primary air 4 , the heat absorption segment 7 in the third segment for anti-condensation of ammonium bisulfate 5 , the heat absorption segment 7 in the fourth segment for curing of ammonium bisulfate 6 , the heat absorption segment 7 in the acid-dew resistant segment 11 are provided with a temperature sensor 12 adapted to detect the wall surface temperatures of the segments.
- the first segment for producing secondary air 3 is a high temperature segment of a regenerative air preheater.
- the first segment for producing secondary air 3 can also be a phase-change heat exchanger, as shown in FIG. 3
- the first segment for producing secondary air 3 also comprises the heat absorption segment 7 , the heat release segment 8 , the ascending tube 9 , and the downcomer 10
- the cycling medium in the first segment for producing secondary air 3 is water, Freon, or heat transfer oil.
- a method for preventing the air preheater from corrosion and blockage after an SCR denitration is also provided in the invention, and the method comprises:
- phase-change heat exchanger compensates for the shortcomings in the prior art, featuring high industrial value.
Abstract
An air preheater, including a flue; an air channel; a first segment for producing secondary air; a second segment for producing primary air; a third segment for anti-condensation of ammonium bisulfate; and a fourth segment for curing of ammonium bisulfate. The flue and the air channel are disposed on the downstream of a denitration device. The first segment, the second segment, the third segment and the fourth segment are disposed in that order along the gas flow direction. The first segment, the second segment, the third segment and the fourth segment each include a phase-change heat exchanger. The phase-change heat exchanger includes a heat absorption segment disposed in the flue, a heat release segment disposed in the air channel, an ascending tube and a downcomer which are configured to connect the heat absorption segment and the heat release segment.
Description
- This application is a continuation-in-part of International Patent Application No. PCT/CN2014/075792 with an international filing date of Apr. 21, 2014, designating the United States, now pending, and further claims priority benefits to Chinese Patent Application No. 201410006896.4 filed Jan. 7, 2014. The contents of all of the aforementioned applications, including any intervening amendments thereto, are incorporated herein by reference. Inquiries from the public to applicants or assignees concerning this document or the related applications should be directed to: Matthias Scholl P.C., Attn.: Dr. Matthias Scholl Esq., 245 First Street, 18th Floor, and Cambridge, Mass. 02142.
- 1. Field of the Invention
- The invention relates to an air preheater and a method for preventing corrosion and blockage of the same.
- 2. Description of the Related Art
- Conventional flue gas denitration technology employs ammonia gas as a reducing agent. The reducing agent reacts with sulfur trioxide in the flue gas to yield ammonia bisulfate. Following the denitration process, an air preheater is provided to recycle heat energy.
- Typically, the air preheater is of a regenerative type, as shown in
FIG. 1 , and includes a high temperature segment, a medium temperature segment, and a low temperature segment. Ammonium bisulfate exhibits strong viscosity in the medium temperature segment and the low temperature segment, and tends to adsorb dust particles and, as a result, block the air preheater. This increases the gas flow resistance, lowers the heat transfer efficiency, and adversely affects operation of the air preheater. - In view of the above-described problems, it is one objective of the invention to provide an air preheater that has good corrosion resistant property. The air preheater is particularly practicable following a selective catalytic reduction (SCR) denitration.
- To achieve the above objective, in accordance with one embodiment of the invention, there is provided an air preheater, comprising a flue and an air channel disposed on a downstream of a denitration device, a first segment for producing secondary air, a second segment for producing primary air, a third segment for anti-condensation of ammonium bisulfate, and a fourth segment for curing of ammonium bisulfate. The first segment for producing secondary air, the second segment for producing primary air, the third segment for anti-condensation of ammonium bisulfate and the fourth segment for curing of ammonium bisulfate are disposed in that order along a gas flow direction. The second segment for producing primary air, the third segment for anti-condensation of ammonium bisulfate, and the fourth segment for curing of ammonium bisulfate each comprise a phase-change heat exchanger. The phase-change heat exchanger comprises a heat absorption segment disposed in the flue, a heat release segment disposed in the air channel, an ascending tube and a downcomer which are configured to connect the heat absorption segment and the heat release segment. The heat release segment is disposed higher than the heat absorption segment, and the phase-change heat exchangers are provided with a cycling medium. A wall surface temperature of the third segment for anti-condensation of ammonium bisulfate is higher than a dew temperature of the ammonium bisulfate. A wall surface temperature of the fourth segment for curing of ammonium bisulfate is lower than a solidification point temperature of the ammonium bisulfate.
- In a class of this embodiment, the air preheater further comprises an acid-dew resistant segment disposed on a downstream of the fourth segment for curing of ammonium bisulfate. The acid-dew resistant segment comprises the phase-change heat exchanger, and a wall surface temperature of the acid-dew resistant segment is higher than an acid dew point temperature.
- Preferably, the heat absorption segment in the second segment for producing primary air, the heat absorption segment in the third segment for anti-condensation of ammonium bisulfate, the heat absorption segment in the fourth segment for curing of ammonium bisulfate, the heat absorption segment in the acid-dew resistant segment are provided with a temperature sensor.
- In a class of this embodiment, the cycling medium in the second segment for producing primary air, the third segment for anti-condensation of ammonium bisulfate, the fourth segment for curing of ammonium bisulfate, and the acid-dew resistant segment is water, Freon, or heat transfer oil.
- Preferably, the first segment for producing secondary air is a high temperature segment of a regenerative air preheater.
- Preferably, the first segment for producing secondary air comprises the phase-change heat exchanger, and the cycling medium in the second segment for producing primary air is water, Freon, or heat transfer oil.
- Advantages of the air preheater according to embodiments of the invention are summarized as follows:
- In the air preheater, the reaction of the escaped ammonia and the sulfur trioxide only produces gaseous and solid ammonium bisulfate, and no liquid ammonium bisulfate is produced, thus the air preheater is effectively prevented from blockage and corrosion caused by liquid ammonium bisulfate. Therefore, the service life of the air preheater is prolonged; the heat transfer efficiency of the boiler is improved; thus ensuring the stable and safe operation of the machine set.
- It is another objective of the invention to provide a method for preventing the air preheater from corrosion and blockage. The air preheater is disposed on a downstream of a denitration device using SCR denitration technology. The method can prevent the corrosion and blockage of the heating surface of the air preheater.
- To achieve the above objective, in accordance with another embodiment of the invention, there is provided a method for preventing an air preheater from corrosion and blockage, the method comprising:
-
- a) introducing flue gas in a flue to an upstream of the air preheater, and allowing the flue gas to pass a first segment for producing secondary air, a second segment for producing primary air, a third segment for anti-condensation of ammonium bisulfate and a fourth segment for curing of ammonium bisulfate in that order; introducing air in an air channel to a downstream of the air preheater, and allowing the air to pass the fourth segment for curing of ammonium bisulfate, the third segment for anti-condensation of ammonium bisulfate, the second segment for producing primary air, and the first segment for producing secondary air;
- b) adjusting a wall surface temperature of the third segment for anti-condensation of ammonium bisulfate to be higher than a dew temperature of the ammonium bisulfate, and adjusting a wall surface temperature of the fourth segment for curing of ammonium bisulfate to be lower than a solidification point temperature of the ammonium bisulfate;
- c) gasifying the ammonium bisulfate in the flue prior to and in the third segment for anti-condensation of ammonium bisulfate; curing the ammonium bisulfate in and after the fourth segment for curing of ammonium bisulfate, the ammonium bisulfate being cured on a wall surface of a pipe of the fourth segment and a wall surface of a downstream pipe of the fourth segment; and
- d) eliminating solid ammonium bisulfate on the wall surface of the pipe of the fourth segment and on the wall surface of the downstream pipe of the fourth segment.
- Advantages of the method according to embodiments of the invention are summarized as follows:
- Using the method, the wall surface temperature of the third segment and the fourth segment can be accurately controlled, so that the ammonium bisulfate is cured on the wall surface of the pipe of the fourth segment and the wall surface of the downstream pipe of the fourth segment, then the solid ammonium bisulfate is eliminated by blowing equipment. As a result, the air preheater is effectively prevented from blockage and corrosion, thus ensuring the safe, reliable, and stable operation of the boiler.
- The invention is described hereinbelow with reference to the accompanying drawings, in which:
-
FIG. 1 is a schematic diagram of an existing air preheater; -
FIG. 2 is a schematic diagram of an air preheater in accordance with one embodiment of the invention; and -
FIG. 3 is a schematic diagram of an air preheater in accordance with another embodiment of the invention. - In the drawings, the following reference numbers are used: 1. Hue; 2. Air channel; 3. First segment for producing secondary air; 4. Second segment for producing primary air; 5. Third segment for anti-condensation of ammonium bisulfate; 6. Fourth segment for curing of ammonium bisulfate; 7. Heat absorption segment; 8. Heat release segment; 9. Ascending tube; 10. Downcomer; 11. Acid-dew resistant segment; and 12. Temperature sensor.
- For further illustrating the invention, experiments detailing an air preheater and a method for preventing corrosion and blockage of the same after selective catalytic reduction (SCR) denitration are described below. It should be noted that the following examples are intended to describe and not to limit the invention.
- As shown in
FIG. 2 , an air preheater comprises aflue 1 and anair channel 2 disposed on the downstream of a denitration device, a first segment for producingsecondary air 3, a second segment for producingprimary air 4, a third segment for anti-condensation ofammonium bisulfate 5, and a fourth segment for curing ofammonium bisulfate 6 disposed in that order along a gas flow direction. The second segment for producingprimary air 4, the third segment for anti-condensation ofammonium bisulfate 5, and the fourth segment for curing ofammonium bisulfate 6 each comprise a phase-change heat exchanger. The phase-change heat exchanger comprises aheat absorption segment 7 disposed in theflue 1, aheat release segment 8 disposed in theair channel 2, an ascendingtube 9 and adowncomer 10 which are configured to connect theheat absorption segment 7 and theheat release segment 8. Theheat release segment 8 is higher than the correspondingheat absorption segment 7, and the phase-change heat exchanger is provided with a cycling medium. A wall surface temperature of the third segment for anti-condensation ofammonium bisulfate 5 is higher than a dew temperature of the ammonium bisulfate. A wall surface temperature of the fourth segment for curing ofammonium bisulfate 6 is lower than a solidification point temperature of the ammonium bisulfate. - High-temperature flue gas (between 350 and 440° C.) in the
flue 1 enters an upstream of the assembled air preheater, and passes the first segment for producingsecondary air 3, the heat-absorbingsegment 7 of the second segment for producingprimary air 4, the heat-absorbingsegment 7 of the third segment for anti-condensation ofammonium bisulfate 5, and the heat-absorbingsegment 7 of the fourth segment for curing ofammonium bisulfate 6. The high-temperature flue gas releases heat when passing the air preheater and heats the cycling medium in theheat absorption segment 7 of all phase-change heat exchangers. The cycling medium in all phase-change heat exchangers absorbs heat released by the flue gas and generates a lift force because of a density difference, thus the cycling medium in theheat absorption segment 7 enters theheat release segment 8 via the ascendingtube 9, and after releasing heat to the air, the cycling medium in theheat release segment 8 is back to theheat absorption segment 7 via thedowncomer 10, hereby a self-cycle is realized and no external power is needed. Because the pipe wall temperature of the third segment for anti-condensation ofammonium bisulfate 5 and the pipe wall temperature of an upstream of the third segment for anti-condensation ofammonium bisulfate 5 are higher than the dew temperature of the ammonium bisulfate (between 0 and 200° C.), and the pipe wall temperature of the fourth segment for curing ofammonium bisulfate 6 and the pipe wall temperature of a downstream of the fourth segment for curing ofammonium bisulfate 6 are lower than the solidification point temperature (147° C.) of the ammonium bisulfate, the reaction of escaped ammonia and sulfur trioxide only generates gaseous and solid ammonium bisulfate in the air preheater, no liquid ammonium bisulfate is produced, and the air preheater is effectively prevented from blockage and corrosion caused by liquid ammonium bisulfate. Therefore, a flue gas temperature is decreased; an air leakage is reduced; a service life of the air preheater is prolonged; a heat transfer efficiency of a boiler is improved; and finally a stable and safe operation of a machine set is ensured. Preferably, cycling media in the second segment for producingprimary air 4, the third segment for anti-condensation ofammonium bisulfate 5, the fourth segment for curing ofammonium bisulfate 6, the acid-dewresistant segment 11 is selected from water, Freon, or heat transfer oil. In actual operation, a suitable cycling medium solution is determined according to different temperatures. - Preferably, when the pipe wall temperature of the downstream of the fourth segment for curing of
ammonium bisulfate 6 is too low, an acid dew corrosion happens, thus along the flue gas flow direction, the downstream of the fourth segment for curing ofammonium bisulfate 6 is provided with an acid-dewresistant segment 11. The acid-dewresistant segment 11 comprises the phase-change heat exchanger, comprising theheat absorption segment 7, theheat release segment 8, the ascendingtube 9 and thedowncomer 10. The wall surface temperature of the acid-dewresistant segment 11 is higher than an acid dew point temperature (between 0 and 100° C.), thereby effectively preventing the acid dew corrosion, decreasing an energy consumption of the boiler, and saving energy and reducing emission to the largest extent. - In addition, the air is divided into two paths after heated by the second segment for producing
primary air 4, as shown inFIGS. 2-3 , the first path is used as a primary air for a pulverizing system, and the second path is heated by the first segment for producingsecondary air 3 and is used as secondary air of the boiler, which means the primary air is not heated by the first segment for producingsecondary air 3. Heat saved by the primary air can be used to heat materials in the third segment for anti-condensation ofammonium bisulfate 5, the fourth segment for curing ofammonium bisulfate 6, the acid-dewresistant segment 11, or a combination thereof. - Prior to starting the assembled air preheater, the air in the acid-dew
resistant segment 11, the fourth segment for curing ofammonium bisulfate 6, the third segment for anti-condensation ofammonium bisulfate 5, and the second segment for producingprimary air 4 is exhausted, so that no non-condensable gas exists in cycling pipes of the phase-change heat exchangers, and the blockage caused by water or gas is avoided. When the boiler is operated at a rated load, the flue gas temperature after denitration is between 350 and 440° C. and is gradually stable, and water volumes in the cycling pipes of the acid-dewresistant segment 11, the fourth segment for curing ofammonium bisulfate 6, the third segment for anti-condensation ofammonium bisulfate 5, and the second segment for producingprimary air 4 are adjusted according to the flue gas temperature after denitration, a temperature of the primary air, and a temperature of the secondary air; correspondingly, steam pressures in the phase-change heat exchangers are adjusted and determined, then saturation temperatures are determined, and wall surface temperatures of the segments are determined. Preferably, theheat absorption segment 7 in the second segment for producingprimary air 4, theheat absorption segment 7 in the third segment for anti-condensation ofammonium bisulfate 5, theheat absorption segment 7 in the fourth segment for curing ofammonium bisulfate 6, theheat absorption segment 7 in the acid-dewresistant segment 11 are provided with atemperature sensor 12 adapted to detect the wall surface temperatures of the segments. - Preferably, in the example, as shown in
FIG. 2 , the first segment for producingsecondary air 3 is a high temperature segment of a regenerative air preheater. Optionally, the first segment for producingsecondary air 3 can also be a phase-change heat exchanger, as shown inFIG. 3 , the first segment for producingsecondary air 3 also comprises theheat absorption segment 7, theheat release segment 8, the ascendingtube 9, and thedowncomer 10, and the cycling medium in the first segment for producingsecondary air 3 is water, Freon, or heat transfer oil. - A method for preventing the air preheater from corrosion and blockage after an SCR denitration is also provided in the invention, and the method comprises:
-
- a) introducing flue gas from the
flue 1 to an upstream of the air preheater, and allowing the flue gas to pass the first segment for producingsecondary air 3, the second segment for producingprimary air 4, the third segment for anti-condensation ofammonium bisulfate 5, and the fourth segment for curing ofammonium bisulfate 6 in that order; introducing air from the air channel to a downstream of the air preheater, and allowing the air to pass the fourth segment for curing ofammonium bisulfate 6, the third segment for anti-condensation ofammonium bisulfate 5, the second segment for producingprimary air 4, and the first segment for producingsecondary air 3; - b) adjusting the wall surface temperature of the third segment for anti-condensation of
ammonium bisulfate 5 to be higher than a dew temperature of the ammonium bisulfate, and adjusting the wall surface temperature of the fourth segment for curing ofammonium bisulfate 6 to be lower than a solidification point temperature of the ammonium bisulfate; - c) gasifying the ammonium bisulfate in the
flue 1 prior to and in the third segment for anti-condensation of ammonium bisulfate and an upstream of the third segment for anti-condensation of ammonium bisulfate; curing the ammonium bisulfate in and after the fourth segment for curing ofammonium bisulfate 6, the ammonium bisulfate being cured on a wall surface of a pipe of the fourth segment and a wall surface of a downstream pipe of the fourth segment; and - d) eliminating solid ammonium bisulfate on the wall surface of the pipe of the fourth segment and on the wall surface of the downstream pipe of the
fourth segment 6.
- a) introducing flue gas from the
- Advantages of the air preheater and the method are summarized as follows:
-
- 1. Using the method, the wall surface temperature of the third segment and the fourth segment can be accurately controlled, so that the ammonium bisulfate is cured on the wall surface of a heat exchanger, meanwhile avoiding condensation of the ammonium bisulfate on the wall surface of the heat exchanger; then the solid ammonium bisulfate is eliminated by the blowing equipment. As a result, the air preheater is effectively prevented from blockage and corrosion, thus ensuring the safe, reliable, and stable operation of the boiler, and the corrosion caused by the ammonium bisulfate in a medium temperature segment and a low temperature segment of the regenerative air preheater is completely prevented.
- 2. The acid-dew
resistant segment 11 is provided, and the wall surface temperature of the acid-dewresistant segment 11 is controlled so as to prevent the acid dew corrosion, decrease the energy consumption of the boiler, and save energy and reduce emission to the largest extent. - 3. The phase-change heat exchanger is employed, and the flue gas temperature is decreased to a lower level than the flue gas temperature of the regenerative air preheater.
- 4. The air is directly divided into two paths following the second segment for producing
primary air 4, and the primary air does not enter the first segment for producingsecondary air 3, thus the heat is saved. - 5. The air leakage problem of the regenerative air preheater in the prior art is solved by using the phase-change heat exchanger.
- Therefore, the phase-change heat exchanger compensates for the shortcomings in the prior art, featuring high industrial value.
- Unless otherwise indicated, the numerical ranges involved in the invention include the end values. While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.
Claims (7)
1. An air preheater, comprising:
a flue;
an air channel;
a first segment for producing secondary air;
a second segment for producing primary air;
a third segment for anti-condensation of ammonium bisulfate; and
a fourth segment for curing of ammonium bisulfate;
wherein
the flue and the air channel are disposed on a downstream of a denitration device;
the first segment for producing secondary air, the second segment for producing primary air, the third segment for anti-condensation of ammonium bisulfate and the fourth segment for curing of ammonium bisulfate are disposed in that order along a gas flow direction;
the second segment for producing primary air, the third segment for anti-condensation of ammonium bisulfate, and the fourth segment for curing of ammonium bisulfate each comprise a phase-change heat exchanger; the phase-change heat exchanger comprises a heat absorption segment disposed in the flue, a heat release segment disposed in the air channel, an ascending tube and a downcomer which are configured to connect the heat absorption segment and the heat release segment; the heat release segment is disposed higher than the heat absorption segment, and the phase-change heat exchanger is provided with a cycling medium; and
a wall surface temperature of the third segment for anti-condensation of ammonium bisulfate is higher than a dew temperature of the ammonium bisulfate;
a wall surface temperature of the fourth segment for curing of ammonium bisulfate is lower than a solidification point temperature of the ammonium bisulfate.
2. The air preheater of claim 1 , wherein the air preheater further comprises an acid-dew resistant segment disposed on a downstream of the fourth segment; the acid-dew resistant segment also comprises the phase-change heat exchanger, and a wall surface temperature of the acid-dew resistant segment is higher than an acid dew point temperature.
3. The air preheater of claim 2 , wherein the heat absorption segment in the second segment for producing primary air, the heat absorption segment in the third segment for anti-condensation of ammonium bisulfate, the heat absorption segment in the fourth segment for curing of ammonium bisulfate, the heat absorption segment in the acid-dew resistant segment each are provided with a temperature sensor.
4. The air preheater of claim 2 , wherein the cycling medium in the second segment, in the third segment, in the fourth segment, and in the acid-dew resistant segment is water, Freon, or heat transfer oil.
5. The air preheater of claim 1 , wherein the first segment for producing secondary air is a segment of a regenerative air preheater.
6. The air preheater of claim 1 , wherein the first segment for producing secondary air comprises the phase-change heat exchanger, and the cycling medium in the second segment for producing primary air is water, Freon, or heat transfer oil.
7. A method for preventing corrosion and blockage of an air preheater, the air preheater being disposed on a downstream of a denitration device, the method comprising:
1) introducing flue gas in a flue to an upstream of the air preheater, and allowing the flue gas to pass a first segment for producing secondary air, a second segment for producing primary air, a third segment for anti-condensation of ammonium bisulfate and a fourth segment for curing of ammonium bisulfate in that order; introducing air in an air channel to a downstream of the air preheater, and allowing the air to pass the fourth segment for curing of ammonium bisulfate, the third segment for anti-condensation of ammonium bisulfate, the second segment for producing primary air, and the first segment for producing secondary air;
2) adjusting a wall surface temperature of the third segment for anti-condensation of ammonium bisulfate to be higher than a dew temperature of the ammonium bisulfate, and adjusting a wall surface temperature of the fourth segment for curing of ammonium bisulfate to be lower than a solidification point temperature of the ammonium bisulfate;
3) gasifying the ammonium bisulfate in the flue prior to and in the third segment for anti-condensation of ammonium bisulfate; curing the ammonium bisulfate in and after the fourth segment for curing of ammonium bisulfate, the ammonium bisulfate being cured on a wall surface of a pipe of the fourth segment and a wall surface of a downstream pipe of the fourth segment; and
4) eliminating solid ammonium bisulfate on the wall surface of the pipe of the fourth segment and on the wall surface of the downstream pipe of the fourth segment.
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CN201410006896.4 | 2014-01-07 | ||
CN201410006896.4A CN103982906B (en) | 2014-01-07 | 2014-01-07 | Be applicable to the Combined air preheater after SCR denitration and corrosion-and blocking-prevention method |
PCT/CN2014/075792 WO2015103823A1 (en) | 2014-01-07 | 2014-04-21 | Combined air preheater suitable for post-scr denitration, and anti-corrosion and anti-blocking method |
Related Parent Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/CN2014/075792 Continuation-In-Part WO2015103823A1 (en) | 2014-01-07 | 2014-04-21 | Combined air preheater suitable for post-scr denitration, and anti-corrosion and anti-blocking method |
Publications (1)
Publication Number | Publication Date |
---|---|
US20160313076A1 true US20160313076A1 (en) | 2016-10-27 |
Family
ID=51274982
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US15/202,520 Abandoned US20160313076A1 (en) | 2014-01-07 | 2016-07-05 | Air preheater and method for preventing corrosion and blockage of the same |
Country Status (5)
Country | Link |
---|---|
US (1) | US20160313076A1 (en) |
JP (1) | JP6157757B2 (en) |
KR (1) | KR101767365B1 (en) |
CN (1) | CN103982906B (en) |
WO (1) | WO2015103823A1 (en) |
Cited By (1)
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CN108413439A (en) * | 2018-04-23 | 2018-08-17 | 华北电力科学研究院有限责任公司 | Adjust the device and method of four points of storehouse air preheater exit gas temperatures |
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CN107191963B (en) * | 2017-07-10 | 2023-07-25 | 东方电气集团东方锅炉股份有限公司 | Rotary air preheater and method for preventing ammonium bisulfate from being blocked by rotary air preheater |
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- 2014-04-21 JP JP2016562051A patent/JP6157757B2/en not_active Expired - Fee Related
- 2014-04-21 WO PCT/CN2014/075792 patent/WO2015103823A1/en active Application Filing
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Also Published As
Publication number | Publication date |
---|---|
JP6157757B2 (en) | 2017-07-05 |
WO2015103823A1 (en) | 2015-07-16 |
CN103982906B (en) | 2016-04-06 |
JP2017501370A (en) | 2017-01-12 |
KR101767365B1 (en) | 2017-08-10 |
KR20160103101A (en) | 2016-08-31 |
CN103982906A (en) | 2014-08-13 |
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