JPS63238324A - Method of controlling temperature of waste gas from outlet of recuperator - Google Patents

Abstract

PURPOSE:To prevent dew-point corrosion of waste gas ducts as well as elements within the recuperator by actually measuring the temperature of waste gas at the outlet of the recuperator, comparing the actually measured value with a preset value, and adjusting the quantity of air passing through the recuperator based on a differential value thereby to adjust the quantity of heat extracted from sensible heat possessed by the waste gas. CONSTITUTION:Both ducts 11 and 12 are connected to each other by an air bypass duct 13, and a damper 14 is interposed within the duct 13. The temperature of a waste gas actually measured by a thermocouple 15 is inputted to a temperature adjusting meter 17 via a converter 16, and is compared with a preset value beforehand inputted by the temperature adjusting meter 17. An output corresponding to the differential value is outputted to a damper operating apparatus 18, and the opening degree of the damper 14 is adjusted. By the adjustment of the opening degree of the damper 14 quantity of air supplied to the recuperator 3 is increased or decreased. The quantity of heat extracted from the waste gas is substantially proportional to the quantity of air increased or decreased, and hence the temperature of the waste gas of the recuperator 3 can be easily controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a control method for maintaining the exhaust gas temperature at the outlet of a recuperator at a set temperature or higher.

(Prior art) In general, for example, in a metal pipe recuperator, which recovers exhaust heat from the exhaust gas of a boiler whose exhaust gas outlet temperature is as low as 150 to 350°C, if the exhaust gas temperature falls further below the above-mentioned temperature, the elements inside the recuperator There is a problem in that dew condensation occurs in the exhaust gas duct leading from the recuperator outlet to the chimney, resulting in dew point corrosion.

Therefore, conventionally, as shown in Fig. 2, a bypass duct 4 was used to connect the inlet and outlet of a recuperator 3 that was installed in the middle of the exhaust gas duct 2 of the boiler 1, and a bypass duct 4 was installed between the exhaust gas duct 2 and the bypass duct 4. A method generally adopted is to control the outlet temperature of the recuperator 3 to a specified temperature or higher by adjusting the opening degree of the damper 5.6.

In Fig. 2, 7 indicates the boiler grate, and 8 indicates the evaporator tube group.

(Problems to be Solved by the Invention) The above method attempts to change the amount of exhaust gas passing through the recuperator by adjusting the opening degree of each damper, thereby adjusting the exhaust gas temperature at the outlet of the recuperator. According to this method, it is possible to prevent dew condensation from occurring in the exhaust gas duct from the recuperator outlet to the chimney.

However, in the above method, if the amount of exhaust gas passing through the recuperator is reduced in an attempt to increase the exhaust gas temperature at the outlet of the recuperator, the exhaust gas temperature inside the recuperator further decreases, promoting dew condensation on the element surface.
The drawback was that the life of the recuperator was shortened.

Therefore, conventionally, this problem has been dealt with by using expensive materials such as glass tubes or ceramic tubes for the elements.

By the way, dew condensation occurs on the element due to the dew point when the combustion load rate decreases and the amount of exhaust gas decreases, and the location where dew condensation occurs is on the exhaust gas flow path side of the element that first comes into contact with air.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method for controlling the exhaust gas temperature at the recuperator outlet, which can prevent dew point corrosion not only in the exhaust gas duct leading from the recuperator outlet to the chimney, but also in the elements inside the recuperator. It is.

(Means for Solving the Problems) The present invention actually measures the exhaust gas temperature at the outlet of the recuperator, compares the measured value with a predetermined set value, and calculates the amount of air passing through the recuperator based on this deviation value. The gist of this is to adjust the amount of heat removed from the sensible heat held by the exhaust gas.

(Example) The method of the present invention will be explained below based on FIG.

Note that the same numerals in FIG. 1 as in FIG. 2 indicate the same or corresponding parts, and detailed explanation will be omitted.

11 is an inlet duct that supplies air to the recuperator 3;
Reference numeral 12 denotes an outlet duct for discharging air that has been heat exchanged and preheated by the recuperator 3, and the present invention connects these two ducts 11 and 12 with an air bypass duct 13, and also installs a damper in this air bypass duct 13. 1
The first feature is that the amount of air supplied to the recuperator 3 can be adjusted by interposing the recuperator 4.

The opening degree of the damper 14 is adjusted based on the exhaust gas temperature at the outlet of the recuperator 3 detected by, for example, a thermocouple 15 installed on the outlet side of the recuperator 3 of the exhaust gas duct 2. That is, the exhaust gas temperature actually measured by the thermocouple 15 is input to the temperature controller 17 via the converter 16, which compares it with a set value input in advance and outputs an output corresponding to the deviation value. is output to the damper operating device 18 to optimally adjust the opening degree of the damper 14. By adjusting the opening of the damper 14, the amount of air supplied to the recuperator 3 is increased or decreased, and the amount of heat removed from the exhaust gas is approximately proportional to this, so the exhaust gas temperature of the recuperator 3 can be easily controlled. This is the second feature of the present invention.

The temperature control method according to the present invention utilizes the air pressure loss of the recuperator, and if the air bypass duct 13 is designed based on the degree of pressure loss and the required flow rate, the structure will be simpler.

In this embodiment, the amount of air supplied to the recuperator 3 is adjusted by the air bypass duct 13 and the damper 14, but the number of rotations of the fan installed in the inlet duct 11 is controlled to adjust the air amount. Of course, the supply amount may be adjusted.

Incidentally, when the method of the present invention was applied, no dew point corrosion occurred in the recuperator element or exhaust gas duct even after 12 months of operation.

(Effects of the Invention) As explained above, the recuperator outlet exhaust gas temperature control method according to the present invention actually measures the exhaust gas temperature at the recuperator outlet, compares this measured value with a predetermined set value, and performs control based on this deviation value. This system adjusts the amount of air passing through the recuperator to adjust the amount of heat removed from the sensible heat held by the exhaust gas, so there is no condensation even at low temperatures and a small amount of exhaust gas flow, and it is suitable for glass tubes, ceramic tubes, etc. This has the great effect of extending the life of the metal tube or metallic recuperator without using expensive materials.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of the method of the present invention, and FIG. 2 is a schematic explanatory diagram of the conventional method. 3 is a recuperator, 13 is an air bypass duct, 14
is a damper, 15 is a thermocouple, and 17 is a temperature controller. Figure 1

Claims (1)

[Claims] (1) Measure the exhaust gas temperature at the outlet of the recuperator, compare this measured value with a preset value, and adjust the amount of air passing through the recuperator based on this deviation value to remove the sensible heat held by the exhaust gas. A recuperator outlet exhaust gas temperature control method characterized by adjusting the amount of heat removed.