JPS6237607A - Starting procedure of burning device - Google Patents

Abstract

PURPOSE:To enable to reduce the generation of NOx to a lower extent at the starting time of a boiler by effecting two-stage burning in such a manner that air amount supplied to burner stacks ignited at the starting time is throttled and air is supplied to burner stacks above said burner stacks. CONSTITUTION:Burning air discharged from a forced draft fan 2 is heat- exchanged with exhaust gas at an air preheater 5 and its temp. is raised up and flows into wind boxes 7, 8, 9 respectively and supplied to each burner after air flow amount is controlled by wind box dampers 12, 13, 16. A part of exhaust gas is recirculated and supplied to said burners by a gas mixing fan 4 and realizes low NOx by reduction of oxygen partial pressure and unburnt combustibles in exhaust gas are burnt by air supplied from AAP 10, 11 and therefore two stage burning is effected. Thereby, burner parts locating at the downstream neat burners which are in ignited condition are used as after air ports and even at the starting time of a boiler, effective two-stage burning is possible and the generation of NOx is able to be reduced.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for starting a combustion device, and in particular, a method for starting a boiler suitable for reducing nitrogen oxide emissions during hot startup in a boiler device. Regarding.

<Prior art and its problems> For example, in a gas-fired boiler, the boiler is stopped for a certain period of time, such as during the night, and then restarted before the fluid in the boiler has completely cooled down. Nitrogen oxides (N.

x) The tM degree may exceed the specified value.

In other words, when restarting a boiler after it has been shut down, first of all, there is a risk that gas fuel may remain in the furnace, so the furnace must be purged for a certain period of time using, for example, approximately 25% of the amount of air at maximum load. However, after a certain amount of time, the burner is ignited and the boiler is started after the ignition conditions are satisfied. However, this method supplies the same amount of air as the purge condition to the burner when the boiler is started, resulting in an excessive amount of air supply and an increase in so-called thermal NOx, which may temporarily exceed the regulation value. Sometimes I put it away.

For this reason, several types of methods have been proposed as NOx reduction measures, but the reality is that they all have advantages and disadvantages, and no fundamental solution to the problem has been reached.

First, in equipment that uses a burner with three nozzles, the middle nozzle is cut to perform stratified combustion, which reduces NOx, but there is a limit to the reduction of NOx itself, and it is not always possible to achieve the specified reduction. Unable to achieve quantity.

In addition, in a device having an after air bow (AAP) in the furnace, the amount of air supplied to the AAP and the amount of air supplied to the burner are adjusted respectively to reduce the amount of air supplied to the burner and reduce the amount of NOx generated. A method has also been proposed in which unburned matter generated by low-oxygen combustion is combusted by air supplied from an AAP. In this method, the two-stage combustion method, which is carried out at the boiler's rated load, is carried out from the time of startup. However, because the distance between the burner and the AAP is long, the effect of the two-stage combustion is low at startup, and the cannot obtain the effect of

<Objective of the present invention> The present invention was constructed in view of the above-mentioned problems, and an object of the present invention is to provide a method that can suppress the amount of NOx generated even when starting a boiler.

<Summary of the present invention> In short, the present invention reduces the amount of air supplied to the burner stage that is ignited at startup, and supplies air to the burner stage directly above this burner stage, thereby making it more effective for two adjacent burner stages. This method uses two-stage combustion.

<Examples> Examples of the present invention will be specifically described below with reference to the drawings.

FIG. 1 is a control system diagram of air and exhaust gas of a gas-fired boiler for carrying out the method according to the present invention. In this figure, the control state when the boiler is operated at rated load will be explained as follows.

In the figure, combustion air exchanges heat with exhaust gas in an air preheater 5 through a forced draft fan (FDP) 2 to raise its temperature, and is then distributed and supplied to burners in each stage. That is, after the flow rate is controlled by the wind box damper 12.14.16, it flows into the wind box 7.8.9, and then flows into each burner (
(not shown). A portion of the exhaust gas is recirculated and supplied to this burner by a gas mixing fan 4 to lower the oxygen partial pressure and reduce NOx, and the unburned part is combusted by air supplied from AAPIo and 11. However, two-stage combustion is implemented. 13.15.17 is a damper that adjusts the amount of exhaust gas mixed into the air supplied to the burner; 19.21 is a damper that adjusts the amount of exhaust gas mixed into the air supplied to the AAPIOll; 18.
20 is a damper that adjusts the amount of air supplied to the AAPIOll, and 22 is a damper that adjusts the amount of exhaust gas supplied from the bottom of the furnace. Note that the exhaust gas discharged from the furnace 1 is induced by an induced draft fan (IDF) 3 and is discharged from the chimney 6 in balance with the combustion air.

In the above configuration, the present invention controls the amount of air supplied to the burner stage to be ignited and the amount of air supplied to the downstream burner stage adjacent to this burner stage at the time of startup of the boiler, thereby reducing the amount of NOx generated at the time of startup. This method is designed to reduce

This will be explained in detail below.

In FIG. 1, an example will be described in which the burner at the lowest stage is ignited when the boiler is started.

First, start FDP2 and damper 12.14.16
．． Fully open at 18.20. As a result, the inside of the furnace is purged for about 5 minutes with an air amount of about 5% of the maximum load. Ignition conditions are established by purging the furnace.

Once the dampers 16, 18, and 20 are fully closed, the dampers 12, 14 are opened 50%. In this state, the lowest burner is ignited, and the dampers 12 and 14 are set so that the air ratio becomes approximately 0.6 and the remaining air is supplied to the wind box 8.
Adjust each. In this state, each of the lowermost burners is ignited one after another. As a result, the amount of fuel supplied to the lowest burner increases, but each damper 12 and 14 is adjusted in accordance with the number of burners ignited so that the air ratio is maintained at about 0.6. In this way, the amount of air supplied to the ignition burner is adjusted to achieve low oxygen combustion, thereby reducing the amount of NOx generated even when the boiler is started. Further, in this case, since air is supplied from the downstream burner (upper stage burner) close to the burner being lit, the unburned matter is burnt well by this air, and effective two-stage combustion can be performed. In other words, since the burners in each stage are originally placed close to each other, the air supply port of the burner group located in the upper stage of the burner that is ignited (extinguished) can be used as an AAP, and the Since the unburned content of the burner can be burnt well, effective two-stage combustion becomes possible.

Note that as the number of ignitions of the lowest burner increases, the concentration of exhaust gas on the downstream side of the economizer increases and exhaust gas recirculation becomes possible, so after this state is reached, the combustion is switched to normal two-stage combustion. That is, the air ratio for the burner at the lowest stage is increased from 0.6 to 0.8, and thereafter the burners at each stage are sequentially ignited to enter rated operation.

FIG. 2 shows changes in the air supply amount, air ratio, Nox concentration, etc. during this period. That is, by adjusting the flow rate distribution while keeping the total amount of air supplied to the ignited burner and the upper burner portion constant, the Nox value can be significantly reduced from about 60 ppm to about 15 ppm. During this time, the air ratio of the burner being ignited is set to about 0.6 as described above, and if the burners in the other stages are also ignited and are in a parallel state, the air ratio is set to about 0.8.

<Effects> Since the present invention is configured as described above, the downstream burner section close to the burner being ignited can be used as a lid air port, and effective two-stage combustion is possible even when the boiler is started. The amount of NOx generated can be reduced.

Furthermore, since there is no need for special equipment to carry out this method, it can be carried out immediately on existing equipment.

[Brief explanation of drawings]

Fig. 1 is a system diagram showing the air supply and exhaust gas control of a gas-fired boiler for carrying out the method according to the present invention, and Fig. 2 shows the operating status of the boiler, NOx concentration, burner air ratio, LN
It is a diagram showing the relationship between G flow rate, air flow rate, and boiler load. 1... Boiler furnace 7.8.9... Wind box 12.1
4.16.18.20...Damper Figure 2

Claims (3)

[Claims] (1) In a method of starting a combustion device in which burner groups are arranged in multiple stages in the direction of exhaust gas flow, at startup, the burner group of the stage to be ignited and the downstream burner group that is extinguished adjacent to this burner group are A method for starting a combustion device characterized by supplying air to each burner group and performing two-stage combustion using both burner groups. (2) The total air supply amount to the burner group in the ignition stage and the extinguished downstream burner group adjacent to this burner group is constant, and even when the number of ignited burners in the burner group in the ignition stage is increasing, the ignition A method for starting a combustion apparatus according to claim 1, characterized in that the amount of air supplied to both burner groups is adjusted so that the air ratio to each burner in the burner group is constant. (3) The amount of air supplied to the burner group in the second stage is adjusted so that the air ratio is approximately 0.6.
2) The method for starting the combustion device described in section 2).