COMPLEX CLEANING SYSTEM FOR HEAT EXCHANGER

Abstract

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 (NH.sub.3 slip) and sulfur trioxide (SO.sub.3) 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.

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/cm.sup.2 g to 30 kg/cm.sup.2 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/cm.sup.2 g to 20 kg/cm.sup.2 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.

Description

DESCRIPTION OF DRAWINGS

[0028] FIG. 1 illustrates a layout of a general power plant or boiler installed conventional antipollution control facilities wherein a coal economizer provided at the rear of the boiler, a selective catalytic reduction (SCR) provided at the rear of the coal economizer, and an air preheater provided at the rear of the SCR.

[0029] FIG. 2 illustrates a conventional system for eliminating ammonium bisulfate in an air preheater using a soot blower and a water washing system.

[0030] FIG. 3 illustrates a drain system for eliminating water during water washing.

[0031] FIG. 4 illustrates a conventional system for eliminating ammonium bisulfate in an air preheater including a dry ice cleaning device instead of the water washing system shown in FIG. 2.

[0032] FIG. 5 illustrates a process for eliminating ammonium bisulfate using dry ice pellets.

[0033] FIG. 6 illustrates blocking an exhaust gas path at a cold end of the air preheater, with ammonium bisulfate coupled to dust frozen with water when ambient temperature rapidly drops in winter season.

[0034] FIG. 7 illustrates a system operating a dry ice cleaning device and a high-temperature steam spraying system which are installed together.

DETAILED DESCRIPTION OF MAIN ELEMENTS

[0035] 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 MODE

[0036] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to accompanying drawings.

[0037] As shown in FIG. 5, dry ice pellets are sprayed from a cleaning device by air having a high-pressure or low-pressure to hit a surface of a thermal element of an air preheater. The dry ice pellets causes ammonium bisulfate to be rapidly frozen at ultralow temperature (78 C.), such that ammonium bisulfate contracts due to a temperature difference with ambient temperature, thereby a number of cracks are occurred. The dry ice pellets penetrate into ammonium bisulfate through the cracks while sublimating to expand equal to or greater than 800 times in its volume, thereby lifting to remove only ammonium bisulfate. According to the same process, dust or the other contaminants as well as ammonium bisulfate are separated to be eliminated and materials frozen at ultralow-temperature are easily separated to be discharged to the rear of the air preheater.

[0038] FIG. 7 shows a system improving the conventional dry ice cleaning device of FIG. 4, as adding a high-temperature steam spraying device 6 having two spraying positions, an exhaust gas inlet, namely the original spraying position, and a supply air inlet, namely a cold end of the air preheater. In the high-temperature steam spraying device 6, as a steam temperature and pressure are increased, cleaning efficiency is excellent, whereas it is possible to damage the thermal element, such that the steam is sprayed at a temperature equal to or smaller than 400 C. and a pressure equal to or smaller than 20 kg/cm.sup.2 g. The steam has a pressure at about a tenth part of an operation pressure of high-pressure water, for example 150 kg/cm.sup.2 g to 200 kg/cm.sup.2 g, in the conventional cleaning using the high-pressure water, and as such the thermal element is not damaged compared with the conventional cleaning.

[0039] 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 DISCLOSURE

[0040] Various embodiments have been described in the best mode for carrying out the disclosure.