JPS61157333A - Method for controlling temperature of exhaust gas at outlet of boiler - Google Patents

Abstract

PURPOSE:To adjust temp., by providing a boiler outlet duct in the exhaust gas flow passage reaching the terminal outlet of a boiler from the firing furnace of the boiler through the spaces between the water tube groups of the boiler and adjusting the opening degrees of dampers attached to the duct and the boiler outlet. CONSTITUTION:The exhaust gas issued from the firing furnace 14 of a boiler enters an exhaust gas flow passage 30 from an introducing port 22 to heat the water tube groups 20 of the boiler and flowed out to an exhaust gas main flow passage 38 from an outlet duct 52 having a damper 50 mounted therein and a terminal outlet duct 36 having a damper 34 mounted therein and flowed through a denitration apparatus 40 to remove NOx. At this time, the relation between the opening degrees of the dampers 34, 50 and the temp. of the outlet exhaust gas is preliminarily calculated and the opening degrees of the dampers are automatically controlled by the temp. sensor provided to the upstream side of the denitration apparatus to control temp.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a boiler outlet exhaust gas temperature control method, and particularly to an exhaust gas temperature control method suitable for use in boiler equipment equipped with a denitrification device on the boiler outlet side.

[Conventional technology]

The boiler has a furnace that burns fuel and an exhaust gas flow path that heats a group of boiler water tubes with high-temperature combustion exhaust gas obtained from the furnace, and when the exhaust gas flows through the exhaust gas flow path, Heat exchange is performed to obtain heated steam. In addition, the exhaust gas discharged from the boiler outlet contains nitrogen oxides (NO
x), a denitrification device is installed in the exhaust gas path to remove nitrogen oxides. As a denitrification device, a dry denitrification device is usually used, and since the effective temperature range is generally determined for the catalyst, the temperature of the exhaust gas flowing through the denitrification device NK is adjusted so that it falls within the effective temperature range of the catalyst. There is a need.

[Problem that the invention seeks to solve]

However, if the boiler fuel is of a certain type and the exhaust gas temperature is within the effective temperature range of the denitrification equipment catalyst, there will be no problem. There was a problem in that the exhaust gas temperature and the nitrogen oxide concentration at the boiler outlet differed, resulting in the temperature falling outside the effective temperature range of the denitrification device catalyst. This is because when petroleum pitch is used as fuel, the NOx concentration in the exhaust gas must be kept high and the exhaust gas outlet temperature must be kept high, but when using heavy oil as fuel, the NOx concentration in the exhaust gas is relatively low. Moreover, since efficient combustion is important, it is necessary to heat the exhaust gas at a low temperature. This is because there is a large difference in exhaust gas temperature due to the combustion of both fuels, and it is impossible to use a denitrification catalyst that covers these differences.

[Failure to solve the problem]

The present invention focuses on the above-mentioned conventional problems, and allows the boiler outlet exhaust gas temperature to be adjusted to be within the effective temperature range of the denitrification device catalyst regardless of the fuel type, thereby making it possible to effectively perform the denitrification action. It is an object of the present invention to provide a boiler outlet exhaust gas temperature control method.

In order to achieve the above object, the boiler outlet exhaust gas temperature control method of the present invention further includes providing a boiler outlet duct in the middle of the exhaust gas flow path from the boiler furnace to the boiler outlet at the end, passing between the boiler water tube groups, The opening degree of the damper provided in the duct and the damper provided at the outlet of the terminal boiler are adjusted to adjust the outlet exhaust gas temperature.

[Effect]

With the above configuration, the temperature gradient of the exhaust gas flow path in the boiler is used to transfer the low temperature exhaust gas from the conventional end outlet duct and the high temperature gas from the outlet duct installed upstream from the damper. By adjusting the temperature and mixing, the desired temperature can be adjusted.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a sectional view of a boiler used to implement the boiler outlet exhaust gas temperature control method. The boiler 1° has a burner 12 placed on one end side, and uses heavy oil or petroleum pitch as fuel.
The combustion is performed in a furnace 14 facing the burner 12. Further, a compartment adjacent to the furnace 14 is provided in the boiler 1°, and a header 16 is disposed at the bottom of this compartment, and an air-water drum 18 is disposed at the top, both of which are connected by a group of water pipes 20. It is connected. Then, the upper part of the partition wall 21 between the furnace 14 and the compartment is opened, and from the furnace 14,
ヮ, Yuka 7゜1. 2□Good. 1. A superheater 24 is installed inside the 2□ 1, and an air/water drum 18
It is assumed that the steam from the

Moreover, the pressure inside the compartment is between a first buffer 26A that hangs downward from the air-water drum 18 substantially parallel to the partition wall 21 and has an open lower end, and a space between the first buffer 26A and the water-cooled wall 28, which is the outer wall of the boiler. A second buffer 26B is provided which stands up from the header 16 and has an open upper end, and these buffers 26A.

The vertical meandering flow path formed by 26B is referred to as the exhaust gas flow path 30.
It is said that The end of the exhaust gas passage 30 is connected to the second buffer 26
A lower header 16 surrounded between B and the water cooling wall 28
An opening 32 is formed in the water cooling wall 28 at this position, and a damper 34 is inserted into this opening 32.
It is connected to a terminal outlet duct 36 containing a. This terminal outlet duct 36 serves as a boiler outlet for exhaust gas, and is connected to an exhaust gas main flow path 38 . A denitrification device 40 is disposed downstream of the exhaust gas main flow path 38.

In contrast to such a boiler IOK, the present embodiment particularly has a boiler 10.
An outlet opening 42 is also formed on the upstream side of the exhaust gas passage 30 in the water cooling wall 28, specifically, in the water cooling wall 28 corresponding to the upper end opening of the second buffer 26.

This outlet opening 42 is connected to the water cooling wall 2 as shown in FIGS.
Boiler tube 4 with fins for water cooling wall with window 44 provided in 8
6 facing out, and is formed by cutting out the fins 48 between the tubes 46 (hatched portion in Figure 2). Such outlet opening 42
An outlet duct 52 also having a built-in damper 50 is connected thereto, and this duct 52 is connected to the exhaust gas main flow path 38 .

The connection position between this duct 52 and the exhaust gas main flow path 38 is
□The location is upstream of the denitrification device 40.

A method for controlling the boiler outlet exhaust gas temperature in the boiler 10 having such a configuration is performed as follows. First, normal operation is performed by closing the damper 50 of the additional outlet duct 52 and fully opening the damper 34 of the terminal outlet duct 36 of the exhaust gas flow path 30 provided at the bottom. At this time, the boiler water tube group 20
The heated exhaust gas flows out from the terminal duct 36 into the exhaust gas main flow path 38 and passes through the denitrification device 40 to remove nitrogen oxides. The temperature of the outlet exhaust gas flowing out from this terminal outlet duct 36 is approximately 32°C when heavy oil or petroleum pitch is used as fuel.
The temperature range is from 2°C to 220°C. It is sufficient if this temperature range is the effective temperature range of the catalyst of the denitrification device f40, but if it is lower than the effective temperature range, the additional outlet duct 52 on the upstream side
The damper 50 in is opened, and the damper 34 in the terminal outlet duct 36 is operated in the closing direction. The exhaust gas temperature at the location of the additional outlet duct 52 is 415°C ~
Since the temperature is in the range of 300°C, high-temperature exhaust gas is mixed in, and immediately before the denitrification device 1i40, the exhaust gas temperature becomes higher than the exhaust gas temperature when only the terminal outlet duct 36 flows, and falls within the catalyst effective temperature range. This allows the exhaust gas temperature to be adjusted. Therefore, in this embodiment, the exhaust gas temperature to the denitrification device 40 is controlled by the damper 34,
By adjusting the opening degree of 50°C, it is possible to control the temperature within the range of 220°C to 415°C. Specifically, the damper 34,
The relationship between the opening degree of 50 and the outlet exhaust gas temperature is determined in advance,
The opening degree v4 of the dampers 34 and 50 may be automatically adjusted using a temperature sensor provided immediately upstream of the denitrification device 40.

According to such an embodiment, the paper exhaust gas outlet temperature can be controlled in a simple manner by simply modifying a part of the water cooling wall 28 of the boiler 0 without installing extra equipment such as a heat exchanger. be able to. Further, regardless of the load on the boiler 0, by simply controlling the opening degrees of the dampers 34 and 50, the exhaust gas temperature can be controlled to the optimum temperature for the dry denitrification device 40 for NOx removal installed at the boiler outlet.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to discharge a desired amount of exhaust gas from the most downstream position and its upstream position in the exhaust gas flow path from the boiler furnace to the outlet, and to control the temperature by mixing the exhaust gas using the temperature gradient. It has excellent effects.

[Brief explanation of drawings]

FIG. 1 is a structural sectional view of a boiler to which the control method according to the present invention is applied, FIG. 2 is a front view of the outlet opening, and FIG. 3 is a sectional view of the outlet opening. 10...Boiler, 14...Furnace, 20...Boiler water pipe (group, 26A, 26B°°°) Tsufa, 2
8...Water cooling wall, 30...Exhaust gas flow path, 34.50.
...Damper, 36152...Outlet duct, 38...
Exhaust gas main flow path, 40... denitrification device.

Claims (1)

[Claims] (1) A boiler outlet duct is further provided in the middle of the exhaust gas flow path from the boiler furnace to the boiler outlet at the end, passing between the boiler water tube groups, and a damper provided in the duct and a damper provided at the end boiler outlet. A boiler outlet exhaust gas temperature control method characterized by adjusting the outlet exhaust gas temperature by adjusting the opening degree of the boiler outlet exhaust gas temperature.