JPH0395302A - Method of reducing thermal nox in combustion discharged gas of boiler - Google Patents

Abstract

PURPOSE:To form a flow of combustion discharged gas near a furnace bottom part, eliminate an accumulation of hot gas near the furnace bottom part and further substantially reduce thermal NOx by a method wherein a part of the combustion discharged gas is blown into a part near the bottom part of a boiler furnace. CONSTITUTION:A part of combustion discharged gas 5 is taken out of a discharged gas duct 4 through a discharged gas taking-out pipe 9. The taken-out combustion discharged gas 5 is blown from a discharged gas intake 8 arranged at a furnace bottom part 6 of a boiler furnace 1, resulting in that a flow 12 caused by the blown combustion discharged gas 5 is formed and then a hot gas is prevented from being accumulated in the furnace bottom part 6. Accordingly, the hot gas is accumulated at the furnace bottom part to eliminate a problem that a thermal NOx is generated. In addition, since the combustion discharged gas 5 blown near the furnace bottom part 6 from the discharged gas intake 8 shows a low temperature and a concentration of O2 is also low, it decreases a flame temperature of the burner 2 and thus an effect of reducing the thermal NOx can be expected. The burner 2 is mounted near the furnace bottom part 6 and then a height size of the furnace 1 can be made low.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for reducing thermal NOx in boiler combustion exhaust gas in a gas-fired boiler, an oil-fired boiler, or the like.

[Conventional technology Fig. 3 shows an example of a boiler furnace 1 such as a gas-fired boiler or an oil-fired boiler, which is equipped with burners 2 on the lower side of the boiler furnace l for injecting a plurality of gases or oils as fuel. ing. In the figure, 3 indicates the furnace rear heat transfer section, 4 indicates the exhaust gas duct for the combustion exhaust gas 5, and 6 indicates the bottom of the furnace.

NOx generated in gas-fired or oil-fired boiler furnaces
Thermal NOx (T
hera+al NOx), and the generation of the thermal NOx largely depends on the flame temperature and the residence time of the hot gas. That is, when the flame temperature is high, thermal NOx increases, and when the residence time of high-temperature gas is long, thermal NOx increases.

[Problems to be Solved by the Invention] The bottom 6 of the boiler furnace t, such as the gas-fired boiler or oil-fired boiler described above, usually has a horizontal surface, and the flame of the burner 2 is not brought too close to the bottom of the furnace. As a result, a space is created between the furnace bottom 6 and the burner 2, which makes it easy for gas to accumulate in the furnace bottom 6, resulting in a gas retention area 7.

The high temperature gas heated by the burner 2 remains in the gas retention section 7 for a long time, which is a significant factor in the generation of thermal NOx.

The present invention was made by focusing on the above-mentioned conventional problems.
The purpose is to reduce thermal NOx by eliminating the stagnation of high-temperature gas that occurs at the bottom of a gas-fired or oil-fired boiler furnace.

[Means for Solving the Problems] The present invention provides a gas-fired or oil-fired boiler in which gas or oil is injected into the boiler furnace from a burner provided on the side of the boiler furnace for combustion, and the present invention provides a method for combustion downstream of the boiler furnace. A boiler combustion exhaust gas system characterized in that a part of the exhaust gas is branched, and the branched combustion exhaust gas is blown into the boiler furnace from near the bottom of the boiler furnace to form a flow of combustion exhaust gas near the bottom of the boiler furnace. The present invention relates to a thermal NOx reduction method.

[Function] When a part of the flue gas is blown into the vicinity of the bottom of the boiler furnace to form a flow of the flue gas near the bottom of the furnace, the formation of a stagnation portion of high temperature gas near the bottom of the furnace is prevented. Furthermore, the flame temperature of the burner is also lowered by blowing the combustion exhaust gas.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 show an example of an apparatus for carrying out the method of the present invention, and parts with the same reference numerals as in FIG. 3 represent the same parts.

As shown in FIGS. 1 and 2, an exhaust gas inlet 8 is formed near the bottom 6 of a boiler furnace l such as a gas-fired boiler or oil-fired boiler, and combustion exhaust gas is injected into the downstream exhaust gas duct 4. 5 is connected to an exhaust gas take-off pipe 9 for taking out the branched part, and the end of the exhaust gas take-off pipe 9 is connected to a flow rate adjusting tambour lO.
It is connected to the exhaust gas inlet 8 via an introduction fan 1l.

As described above, a part of the combustion exhaust gas 5 is taken out from the exhaust gas duct 4 through the exhaust gas take-out pipe 9, and the taken out combustion exhaust gas 5 is passed through the exhaust gas inlet 8 provided at the bottom 6 of the boiler furnace l. By blowing into the vicinity of 6, the flow 12 of the blown combustion exhaust gas 5 is formed, thereby preventing high-temperature gas from staying at the bottom 6 of the furnace.

Therefore, due to the retention of high temperature gas, thermal NOx
Problems that occur are prevented.

Further, since the combustion exhaust gas 5 blown into the vicinity of the furnace bottom 6 from the exhaust gas inlet 8 has a low temperature and a low O2 concentration, the flame temperature of the burner 2 is lowered, and the effect of reducing thermal NOx can be expected as a result.

Furthermore, as described above, since the temperature near the furnace bottom 6 can be lowered by blowing in the combustion exhaust gas 5, the burner 2 can be installed close to the furnace bottom 6 and the height dimension of the furnace 1 can be reduced. You can also do it.

Note that the method for reducing thermal NOx in boiler combustion exhaust gas of the present invention is not limited to the above-mentioned embodiments,
Of course, various changes can be made without departing from the spirit of the invention.

[Effects of the Invention] As explained above, according to the method for reducing thermal NOx in boiler combustion exhaust gas of the present invention, by blowing a part of the combustion exhaust gas into the vicinity of the bottom of the boiler furnace, combustion is reduced near the bottom of the furnace. Because it forms a flow of exhaust gas, it eliminates the accumulation of high-temperature gas near the bottom of the furnace and reduces thermal NO.
An excellent effect can be achieved in which X can be significantly reduced.

[Brief explanation of drawings]

Fig. 1 is a side view showing an example of an apparatus for carrying out the method of the present invention, Fig. 2 is a view from the 1-1 arrow in Fig. 1, and Fig. 3 is an example of a conventional gas-fired or oil-fired furnace. FIG. 1 is a boiler furnace, 2 is a burner, 4 is an exhaust gas duct, 5 is a combustion exhaust gas, 6 is a furnace bottom, 8 is an exhaust gas inlet, 9 is an exhaust gas outlet pipe, 10 is a flow rate adjustment damper, 11 is an introduction fan, 12 is a combustion Shows the flow of exhaust gas. Patent applicant Ishikawajima Harima Heavy Industries Co., Ltd.

Claims (1)

[Claims] 1) In a gas-fired or oil-fired boiler in which combustion is performed by injecting gas or oil into the boiler furnace from a burner provided on the side of the boiler furnace, a part of the combustion exhaust gas downstream of the boiler furnace is branched, and the branching is performed. A method for reducing thermal NOx in boiler combustion exhaust gas, characterized in that a flow of combustion exhaust gas is formed near the bottom of the boiler furnace by blowing the combustion exhaust gas into the boiler furnace from near the bottom of the boiler furnace.