JP2001254901A - Method for operating heat exchanger for waste heat recovery of exhaust gas treatment facility - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prolong the service life of a heat exchanger by reducing its corrosion by high-temperature exhaust gas and to reduce the operating cost of the exchanger by making its maintenance easier. SOLUTION: In an exhaust gas treatment facility which is provided with the heat exchanger 5 on the route 2 of exhaust gas and preheats the air flowing through the exchanger 5 with the waste heat of the exhaust gas, an exhaust gas temperature regulating means 6 is provided in the preceding stage of the exchanger 5 and the temperature of the exhaust gas is regulated by means of the regulating means 6 so that the temperature of the exhaust gas at the inlet of the exchanger 5 may always become equal to or lower than the high temperature corrosion temperature of the heat transfer element of the exchanger 5. In addition, the flow rate of the air flowing through the exchanger 5 is regulated by means of the regulating means 6 so that the temperature of the exhaust gas at the outlet of the exchanger 5 may always become equal to or lower than the low temperature corrosion temperature of the heat transfer element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an operation method for preventing corrosion of a heat transfer element of a heat exchanger for recovering waste heat in an exhaust gas treatment facility.

[0002]

2. Description of the Related Art For example, a metal reduction treatment method conventionally referred to as an inmeteco method involves mixing a dusty metal oxide (iron oxide, nickel oxide, etc.) and a reducing agent (coal, coke, etc.) together with a binder. Granulated to 10-3 diameter
A pellet of 0 mm is formed, and the pellet is charged into a furnace and heated to a high temperature of about 1200 ° C. to reduce and recover the metal.
Strongly alkaline exhaust gas is discharged in a high-concentration polluted state containing metal chlorides, fluorine and the like. For this reason, there has been a case where a heat transfer element made of stainless steel or the like inside a heat exchanger provided in an exhaust gas treatment facility is conventionally corroded in a short period of time in order to recover waste heat in the exhaust gas. For this reason, in this kind of exhaust gas treatment equipment, there is a problem that a large cost is required for repairing the heat exchanger for waste heat recovery.

[0003]

SUMMARY OF THE INVENTION Accordingly, the present invention solves the above-mentioned conventional problems, reduces the corrosion of a heat exchanger due to high-temperature exhaust gas, extends its life, facilitates maintenance, and reduces operating costs. Is to reduce.

[0004]

SUMMARY OF THE INVENTION Accordingly, the present invention relates to an exhaust gas treatment equipment for providing a heat exchanger in an exhaust gas path and preheating air flowing through the heat exchanger by waste heat of the exhaust gas. The exhaust gas temperature adjusting means is provided at the preceding stage, and the exhaust gas temperature is adjusted by the temperature adjusting means so that the heat exchanger inlet temperature of the exhaust gas is always equal to or lower than the high-temperature corrosion temperature of the heat transfer element of the heat exchanger. The flow rate of air flowing through the heat exchanger is adjusted so that the temperature of the exhaust gas at the heat exchanger outlet is always equal to or higher than the low-temperature corrosion temperature of the heat transfer element of the heat exchanger.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of an exhaust gas treatment equipment according to the present invention will be described. FIG. 1 is a piping system diagram of the exhaust gas treatment equipment, and 1 indicates a rotary bed furnace provided for heating the pellets. Exhaust gas path 2 of this rotary bed furnace 1
, High-concentration exhaust gas containing sulfur, metal chlorides, fluorine, etc. in a highly contaminated state and strong alkali at around 1000 ° C. is discharged. Reference numeral 3 denotes a burner serving as a heat source for the rotary hearth furnace 1;
Is a hot water boiler provided in the exhaust gas path 2, 5 is a waste heat recovery heat exchanger provided in the exhaust gas path 2, 6 is a sprinkler tower provided in front of the heat exchanger and serving as exhaust gas temperature adjusting means,
Reference numeral 7 denotes a bag-filter type dust collector provided at the subsequent stage of the heat exchanger, 8 denotes an exhaust blower, and 9 denotes a chimney.

Reference numeral 10 denotes an air supply blower provided for supplying combustion air to the burner 3. The air supply passage of the blower has a through-flow path 11 passing through the heat exchanger 5 and a bypass path 12 thereof. And each path has an air flow adjusting damper 1
3 and 14 are provided.

Reference numeral 15 denotes a thermocouple provided to measure the temperature of the exhaust gas at the inlet of the heat exchanger, 16 denotes a thermocouple provided to measure the temperature of the exhaust gas at the outlet of the heat exchanger, and 17 denotes a thermocouple.
Is a controller for instructing the degree of opening of the watering amount adjustment valve 18 and the air volume adjustment dampers 13 and 14 of the watering tower 6. The controller controls the temperature of the heat exchanger inlet based on a temperature measurement signal obtained from the thermocouple 15. The water flow rate control valve 18 is adjusted so as to always maintain the temperature at 480 ° C. or less, and the air flow rate is controlled based on the temperature measurement signal obtained from the thermocouple 16 so that the heat exchanger outlet temperature is always maintained at 260 ° C. or more. The opening degree of the adjustment dampers 13 and 14 is adjusted.

[0008] As described above, by setting the exhaust gas inlet temperature of the exhaust gas to 480 ° C or less, the surface temperature of the heat transfer element of the heat exchanger is generally lower than 400 ° C. ) Can be removed. High-temperature corrosion is, for example, when the heat transfer element made of stainless steel is 75
It is caused by the reaction with chlorine in the exhaust gas in the temperature range of 0 to 450 ° C. to precipitate chromium.

Further, the exhaust gas outlet temperature of the exhaust gas is 260
Since the surface temperature of the heat transfer element of the heat exchanger is maintained at 150 ° C. or higher by maintaining the temperature at 150 ° C. or higher, low-temperature corrosion that can occur at 150 ° C. or lower can be prevented.
Note that low-temperature corrosion is a phenomenon in which dust in exhaust gas tends to adhere to the surface of a heat transfer element at a temperature of 150 ° C. or less, and accelerates corrosion. Therefore, according to the present invention, when there is a possibility that the surface temperature of the heat transfer element of the heat exchanger may fall into the low-temperature corrosion zone, the opening of the air volume adjusting damper 13 is reduced by a command from the controller 17 and the air volume adjusting damper 1 is simultaneously opened.
4, the temperature of the heat transfer element in the heat exchanger 5 is increased by controlling the amount of air flowing through the heat exchanger 5 to be small so that the exhaust gas exit temperature of the heat exchanger 5 is increased. Is always maintained at 260 ° C. or higher.

In this embodiment, the water spray tower 6 is shown as the exhaust gas temperature adjusting means. However, the exhaust gas may be cooled by appropriately introducing outside air into the exhaust gas path before the heat exchanger.

[0011]

As described above, according to the present invention, a heat exchanger is provided in an exhaust gas path, and in an exhaust gas treatment facility in which air flowing through the heat exchanger is preheated by waste heat of the exhaust gas, the heat exchanger is disposed upstream of the heat exchanger. Exhaust gas temperature adjusting means is provided, and the exhaust gas temperature is adjusted by the temperature adjusting means so that the heat exchanger inlet temperature of the exhaust gas is always equal to or lower than the high-temperature corrosion temperature of the heat transfer element of the heat exchanger. The flow rate of air flowing through the heat exchanger is adjusted so that the temperature at the exchanger outlet is always equal to or higher than the low-temperature corrosion temperature of the heat transfer element of the heat exchanger. An increase in maintenance costs due to the early corrosion of the exchanger is suppressed, and there is a beneficial effect of reducing operating costs.

[Brief description of the drawings]

FIG. 1 is a piping system diagram showing an embodiment of an exhaust gas treatment facility according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 rotary bed furnace 2 exhaust gas path 3 burner 5 heat exchanger 6 water spray tower (exhaust gas temperature adjusting means) 10 air supply blower 11 through flow path 12 bypass path 13, 14 air volume adjustment damper 15, 16 thermocouple 17 controller 18 water spray volume adjustment valve

Claims (1)

[Claims] 1. An exhaust gas treatment facility for providing a heat exchanger in an exhaust gas path and preheating air flowing through the heat exchanger by waste heat of exhaust gas, wherein an exhaust gas temperature adjusting means is provided in a stage preceding the heat exchanger. The exhaust gas temperature is adjusted by the temperature adjusting means so that the heat exchanger inlet temperature of the exhaust gas is always equal to or lower than the high temperature corrosion temperature of the heat transfer element of the heat exchanger, and the heat exchanger outlet temperature of the exhaust gas is always The heat exchanger for waste heat recovery in an exhaust gas treatment facility, wherein the flow rate of air flowing through the heat exchanger is adjusted so as to be equal to or higher than the low-temperature corrosion temperature of the heat transfer element of the heat exchanger. Operation method.