COMPLEX CLEANING SYSTEM FOR HEAT EXCHANGER
The purpose of the present disclosure is to solve the problems of a difficult operation or occurrence of corrosion damage to equipment caused by the attachment of ammonium sulfate salt, which is generated when unreacted ammonia (NH3 slip) and sulfur trioxide (SO3) in exhaust gas are bonded with each other when a selective catalytic reduction (SCR) is used to eliminate nitrogen oxides that are contained in the exhaust gas generated during the combustion of a boiler or the like, to a heat exchanger of an air preheater (APH) or the like installed at the rear of an SCR device and blocks a passage of the exhaust gas such that the pressure inside the boiler is increased. To this end, a dry ice cleaning device is installed at the front of an exhaust gas inlet in an air preheater such that the blocking of a heat exchanger caused by ammonium sulfate salt or the like is removed by spraying dry ice pellets, and at the same time, high-temperature steam spraying device is installed at a cold end of the air preheater so as to spray the steam in the same direction as that of air supplied to a boiler, thereby removing contaminants more effectively. Furthermore, in order to effectively prevent blocking which occurs in a cold end of the air preheater, dry ice is sprayed to the front of an exhaust gas inlet of the air preheater and also, to the front of a supply air inlet of the air preheater which is an opposite direction thereof, such that a cleaning effect is increased.
The present disclosure relates to a method of cleaning a heat exchanger, and more particularly, to a complex cleaning system for the heat exchanger, which is to solve the problems of a difficult operation or shutdown caused by the attachment of ammonium bisulfate, which is generated when unreacted ammonia and sulfur trioxide in exhaust gas are bonded with each other when a selective catalytic reduction (SCR) method is used to eliminate nitrogen oxide that are contained in the exhaust gas generated during combustion of a boiler or the like, to a heat exchanger of an air preheater or the like installed at the rear of the SCR device and blocks a passage of the exhaust gas.
BACKGROUND ARTNitrogen oxide, as a pollutant causing environmental harm, which is contained in the exhaust gas generated when coal, oil, gas, or combustible materials, etc. burn in a combustion engine, should be eliminated before being exhausted in air.
To eliminate nitrogen oxide contained in the exhaust gas, a selective non-catalytic reduction (SNCR) method directly spraying a reducer such as ammonia into a boiler, or a selective catalytic reduction (SCR) method spraying a reducer at the rear of the boiler, has been used. The SCR method is mainly used because the SNCR method has low denitrification efficiency.
The SCR method is a method to convert nitride oxide (NOx) contained in the exhaust gas into nitrogen and water by passing through catalyst after blending nitride oxide with the reducer such as ammonia.
Generally, the exhaust gas generated by combustion of coal or heavy oil in the boiler contains sulfur dioxide (SO2) and sulfur trioxide (SO3). Sulfur dioxide is partially oxidized to sulfur trioxide during passing through denitrification catalyst, as the following chemical equation 1, and as such, a concentration of sulfur trioxide in the exhaust gas is increased after passing through the SCR device.
2SO2+O2→2SO3 [Chemical Equation 1]
Meanwhile, water exists in the exhaust gas, while ammonia supplied to the SCR device is partially reacted with sulfur trioxide and water to form ammonium bisulfate, as the following chemical equation 2.
NH3+SO3+H2O→NH4HSO4 [Chemical Equation 2]
Ammonium bisulfate decreases activity of catalyst, corrodes the rear facilities of the SCR device, and increases loss of pressure in the boiler due to blocking a hole for catalyst and a passage for the exhaust gas in the heat exchanger. For this reason, during operation of the SCR device, a discharge concentration of unreacted ammonia is normally limited to be equal to or smaller than 2 to 3 ppm. However, in spite of this limitation, during operation of the SCR device, a blocking problem in heat exchangers of various equipments occurs frequently.
To this end, in some power plants, a real-time high-pressure water cleaning device is further provided at the heat exchanger, particularly the air preheater, which includes a soot blower as shown in
Furthermore, as shown in
To this end, the same inventors as this disclosure had disclosed a dry ice cleaning device installed at the front of an exhaust gas inlet of an air preheater to eliminate pollutants by spraying dry ice pellets. (KR Patent Application Publication No. 10-2011-0096603)
When only ammonium bisulfate exists as a contaminant, the contaminant is attached at a middle part of the air preheater, thereby being easily removed only using the dry ice pellets. However, when the other contaminants occur due to a decline of fuel quality, it may be hard to remove these contaminants. In particular, when the ambient temperature extremely drops due to severe cold in winter season, as shown in
Korea Patent Laid-open Publication No. 10-2011-0096603
Technical ProblemAs described above, the present disclosure provides a complex cleaning method to effectively remove contaminants from a thermal element, while solving the problems of a damage of the thermal element by spraying high-pressure water and decline of performance and durability of an electric precipitator connected to the rear of an air preheater, due to high content of water contained in an exhaust gas.
Technical SolutionThe present disclosure may be applied to various industrial plants and combustion engines using SCR, more particular power plants or industrial boilers, but is not limited thereto. Hereafter, an air preheater as a heat exchanger will be described as an example, but the present disclosure is not intended to be limited thereto.
When a thermal element of an air preheater is contaminated by only ammonium bisulfate, a layer of ammonium bisulfate is mainly attached at a middle of the air preheater, thereby easily removing the layer of ammonium bisulfate only using dry ice pellets. When various contaminants, however, are accumulated naturally or due to a decline of fuel quality, it is hard to eliminate the contaminants. In particular, when an ambient temperature extremely drops due to severe cold in winter season, it often happens that ammonium bisulfate bonded to dust is frozen with water at the cold end of the air preheater, and as such, it is necessary to complement the cleaning by the sole dry ice.
To this end, the illustrated embodiment of the present disclosure provides a method of effectively eliminating the contaminants attached on the thermal element of the heat exchanger, by alternately or simultaneously operating a high-temperature steam spraying device and a dry ice spraying device, which are installed.
Furthermore, according to the illustrated embodiment of the present disclosure, dry ice and high-temperature steam are sprayed to not only an exhaust gas inlet, which is an original spraying position but also a supply air inlet, namely a cold end, in an opposite spraying direction with respect to an original spraying direction, thereby improving cleaning effect.
In an aspect of the present disclosure, the present invention provides the complex cleaning method for the air preheater to effectively remove the contaminants, for example, ammonium bisulfate and dust, formed on a surface of the air preheater by alternately or simultaneously spraying the high-temperature steam and spraying the dry ice to the air preheater. In more detail, the complex cleaning method according to the illustrated embodiment of the present disclosure includes spraying the high-temperature steam to the air preheater at a temperature of 90° C. to 500° C., preferably, 90° C. to 400° C. and a pressure of 10 kg/cm2 g to 30 kg/cm2 g, preferably, 20 kg/cm2 g; spraying the dry ice pellets to the inlet of the air preheater in parallel with a surface of the thermal element at a pressure of 0.5 kg/cm2 g to 20 kg/cm2 g and a speed of 200 m/sec and 400 m/sec, while each dry ice pellet having a diameter equal to or smaller than 3 mm, preferably, between 0.1 mm and 3 mm; and removing the contaminants formed on the thermal element.
Preferably, when the temperature is equal to or smaller than 400° C. and the pressure is equal to or smaller than 20 kg/cm2 g in the described method, time-worn of the air preheater may be minimized and the contaminants may be effectively eliminated.
Preferably, when cleaning by the steam, the high-temperature steam spraying device is installed at the cold end of the air preheater so as to spray the steam to the air preheater in the same direction 9 as a direction of air supplied to the boiler, or in a direction opposite to the direction of air supplied to the boiler toward the exhaust gas inlet of the air preheater. Meanwhile, when cleaning by the dry ice pellets, the dry ice spraying device is installed at the front of the exhaust gas inlet of the air preheater so as to spray the dry ice to the air preheater in the same direction 8 as a flow direction of the exhaust gas, or in a direction opposite to the flow direction of the exhaust gas toward a supply air inlet.
More preferably, the steam is sprayed to the cold end of the air preheater in the same direction 9 as the direction of the supply air and the dry ice pellets are sprayed to the air preheater in a direction of the exhaust gas supplied to the air preheater, namely, the direction 8 of the exhaust gas.
Cleaning using the steam and cleaning using the dry ice pellets may be simultaneously performed. Alternatively, after cleaning using the steam, cleaning using the dry ice pellets may be performed, whereas after cleaning using the dry ice pellets, cleaning using the steam may be sequentially performed.
According to the present disclosure, when the dry ice pellets are sprayed to the air preheater, the dry ice pellets hit the thermal element of the air preheater to be smashed, and then ammonium bisulfate covered on the surface of the thermal element is rapidly frozen by particles of smashed dry ice pellets at a temperature range of 0° C. to −78.5° C., and as such, cracks occurs in the layer of ammonium bisulfate. In this case, the smashed dry ice pellet particles penetrate into the cracks in the layer of ammonium bisulfate while the dry ice particles sublimate, thereby ammonium bisulfate is separated from the thermal element. The other contaminants such as dust accumulated on the surface of the thermal element of the air preheater are separated by the same process described above, thereby cleaning of the thermal element is performed.
Advantageous EffectsThe complex cleaning method according to the present disclosure may be conveniently performed during operation mode, namely, without suspension of plant operation which was a prior problem, and do not damage an air preheater or an electrostatic precipitator. Furthermore, spraying high-temperature steam has a lower pressure than that of spraying high-pressure water, and water amount for spraying the high-temperature steam is very small compared with spraying the high-pressure water, and as such, water content in an exhaust gas is not increased. Accordingly, additional waste water disposal facilities are not required because contaminants are not discharged additionally.
Meanwhile, CO2 collected from the exhaust gas of the power plant may be recycled to generate dry ice, thereby being advantageous in terms of utilization of CO2 and cost reduction.
1: rotation direction of air preheater, 2: air preheater, 3: dry ice pellet spraying nozzle, 4: dry ice pellet spraying device, 5: dry ice pellet sizer, 6: high-temperature steam spraying device, 7: supply air outlet, 8: exhaust gas inlet, 9: supply air inlet, 10: exhaust gas outlet
BEST MODEHereinafter, the embodiments of the present disclosure will be described in detail with reference to accompanying drawings.
As shown in
Although method of cleaning the air preheater has been disclosed according to the embodiments of the present disclosure in detail with reference to the accompanying drawings, it will be understood that these embodiments are illustrative and that the scope of the inventive subject matter is not limited to them.
MODE FOR DISCLOSUREVarious embodiments have been described in the best mode for carrying out the disclosure.
Claims
1. A method of complex cleaning for a heat exchanger comprising:
- spraying high-temperature steam to the heat exchanger at a temperature of 90° C. to 500° C. and a pressure of 10 kg/cm2 g to 30 kg/cm2 g;
- spraying dry ice pellets to an inlet of the heat exchanger in parallel with a surface of a thermal element at a pressure of 0.5 kg/cm2 g to 20 kg/cm2 g and a speed of 200 m/sec to 400 m/sec, each dry ice pellet having a diameter of 0.1 mm to 3 mm; and
- eliminating contaminants formed on the surface of the thermal element,
- wherein,
- in spraying the high-temperature steam, the high-temperature steam is sprayed to an exhaust gas inlet of the heat exchanger or to a supply air inlet of the heat exchanger opposite to the exhaust gas inlet; and
- in spraying the dry ice pellets, the dry ice pellets are sprayed to the exhaust gas inlet of the heat exchanger or to the supply air inlet of the heat exchanger opposite to the exhaust gas inlet.
2. The method according to claim 1, wherein spraying the high-temperature steam and spraying the dry ice pellets are performed simultaneously or sequentially.
3. The method according to claim 1, wherein spraying the dry ice pellets comprises:
- rapidly freezing a layer of ammonium bisulfate covered on the surface of the thermal element of the heat exchanger at 0° C. to −78.5° C. using dry ice pellet particles shattered by hitting the thermal element to have cracks in the layer of ammonium bisulfate;
- infiltrating the shattered dry ice pellet particles into the cracks of the layer of ammonium bisulfate; and
- separating and removing ammonium bisulfate from the surface of the thermal element by sublimation of the dry ice particles.
4. The method according to claim 1, wherein the heat exchanger is an air preheater.
Type: Application
Filed: Jun 23, 2014
Publication Date: Jan 19, 2017
Inventors: Dae Woo KIM (Incheon), Do Jeung KIM (Seoul), Tae-Hee LEE (Incheon), Song-yl JAEONG (Gyeonggi-do), Dong-won KIM (Gyeonggi-do), Sae-Rom JOO (Gyeonggi-do)
Application Number: 15/039,001