JPH0116887Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to pulverized coal two-stage combustion equipment for boilers, general industrial furnaces, etc. that can reduce nitrogen oxides in exhaust gas.

[Conventional technology] In the wake of the first and second oil shocks,
With the shift from petroleum-based fuels to coal, especially for thermal power plants, not only are new oil-fired power plants no longer permitted to be built, but existing facilities are also required to reduce their oil consumption. ing.

On the other hand, with regard to the prevention of environmental pollution accompanying the expansion of economic activities, significant improvements have been made due to progress in technological development, coupled with the strengthening of various laws and regulations.
In many areas, the current environmental concentration of nitrogen oxides (hereinafter referred to as _NOx ) exceeds the environmental standard values required for maintaining health.

Under these circumstances, it is particularly important to take measures to reduce NO _x during coal combustion, which emits essentially higher concentrations of NO _x than the conventionally used oil combustion.

In a conventional pulverized coal combustion furnace, as shown in Fig. 2, coal stored in bunker a is sent to pulverizer d via coal feeder b via coal feeder chute c according to the load.
For example, in the case of a ball mill, the powder is agitated with steel balls in a rotating drum and crushed by impact. The pulverized pulverized coal is passed through the cold air (thick line arrow) from the forced draft fan outlet, and the hot air (dashed line arrow) from the air preheater to dry the moisture contained in the pulverized coal so that the temperature at the pulverizer outlet remains constant. The coal is mixed while being adjusted by a damper i, and is carried out from a pulverizer d by air pressurized by a primary ventilation fan e. At this time, coarse powder with a large particle size is separated by a coarse powder separator f. is separated and only the fine powder is sent to the burner of the pulverized coal combustion furnace.

When burning pulverized coal in a pulverized coal combustion furnace, in order to reduce the amount of NO _x produced mainly by oxidation of nitrogen compounds contained in the pulverized coal, the pulverized coal is used as a fuel in a main burner and a secondary combustion burner. The NO _x produced by combustion in the main burner is
can be reduced and denitrated by injecting secondary fuel into the wake of the main combustion zone.

[Problems to be solved by the invention] In this case, the conventional method of transporting pulverized coal to the main burner and the secondary combustion burner using primary air having a normal oxygen concentration is used. When the coal supply amount is varied, as shown in Figure 3, the weight ratio (A/C) between the amount of primary air (A: Air) and the amount of pulverized coal transported (C: Coal) is small when the load is small. It is large when the load is large, and changes to become small when the load is large.

Therefore, when the load is small and the amount of coal supplied is small, the A/C will be high and the amount of primary air will be large, so the oxygen concentration in the secondary fuel injection section will be high and the NO _x generated in the main combustion zone will be reduced. Appropriate conditions for the reduction reaction cannot be obtained, and a sufficient denitrification effect cannot be obtained.

[Means for Solving the Problems] The present invention is aimed at solving the drawbacks of the conventional pulverized coal combustion method described above and suppressing NO _x emissions. That is, it is equipped with a main burner and a secondary combustion burner, and the secondary fuel from the pulverized coal mill for secondary fuel is injected into the downstream part of the main burner combustion zone, and the decomposition products are used to generate energy in the main burner combustion zone. In a two-stage pulverized coal combustion facility designed to reduce the generated nitrogen oxides, the pipe connected to the forced draft fan outlet is branched into two, one of which is passed through an air preheater to form a hot air pipe. The hot air pipe and the other cold air pipe are merged and connected to the main burner pulverizer, and the hot exhaust gas pipe branched from the high temperature gas inlet side of the air preheater and the low temperature gas outlet side of the air preheater are connected to the main burner pulverizer. The cold exhaust gas pipes branched from the downstream part of the induced draft fan are connected to the secondary fuel pulverized coal machine after being merged with each other by adjusting the flow rate with a damper, and the cold air pipe and the cold exhaust gas pipe are connected with a damper. The present invention relates to a two-stage pulverized coal combustion equipment, which is characterized in that the pulverized coal is connected by a conduit having a pulverized coal.

[Function] After the high and low temperature exhaust gases at the inlet and outlet of the air preheater of the pulverized coal two-stage combustion furnace with low oxygen content are mixed and brought to the optimum temperature, they are sent to the pulverized coal machine for secondary fuel. and used for transporting secondary fuel.

Therefore, even when the load is small, the oxygen concentration does not become excessive, and the NO _x emission concentration can be suppressed.

[Example] Hereinafter, an example of the present invention will be described based on the drawings.

FIG. 1 is a diagram schematically showing the equipment of the present invention,
Inside the boiler 1, a main burner 2, an intermediate air blowing hole 3, a secondary combustion burner 4, and a two-stage combustion air hole 5 are provided in order from upstream to downstream, and a smoke pipe connected to the top of the boiler 1 is provided. A secondary superheater 7, a reheater 8, a primary superheater 9, an economizer 10, an air preheater 11, and an induced draft fan 12 are installed in the path 6 in this order from the upstream side, and are connected to a chimney 13. Bunka 14a, 14
b, coal feeder 15a, 15b, pulverizer 16a, 1
6b and connected to the outlet of the forced draft fan 17, a hot air pipe 19 is branched from the pipe 18, passes through the air preheater 11, and is connected to the downstream side of the pipe 18 again. A pipe line 21 connected to the pipe line 18 via a primary ventilation fan 20 is connected to a pulverizer 16a for the main burner 2 of the boiler 1, and the boiler 1 is connected to the discharge side of the pulverizer 16a. A conduit 22 for feeding pulverized coal by primary air is provided to the main burner 2 provided in the main burner 2 . Further, a hot exhaust gas pipe 23 is provided to take out a part of the high temperature combustion exhaust gas from the inlet of the air preheater 11, and an exhaust gas recirculation fan 24 is provided in the pipe 23, and the pipe downstream of the exhaust gas recirculation fan 24 A cold exhaust gas pipe 25 provided on the downstream side of the induced draft fan 12 for taking out part of the low-temperature combustion exhaust gas is connected to the pipe 23, and a pipe 29 connected to the pipe 23 via a primary draft fan 28 is connected to the pipe 23. A pipe line that is connected to another pulverized coal machine 16b for secondary fuel and sends pulverized coal for secondary combustion together with circulating exhaust gas to the secondary combustion burner 4 provided in the boiler 1 on the discharge side of the pulverized coal machine 16b. 30
is provided. In the figure, 31 is a pipe connected to the downstream side of the air preheater 11 of the pipe line 19 and sends preheated combustion air to the main burner 2 of the boiler 1, intermediate air blowing hole 3, and second-stage combustion air hole 5. 32 is a conduit connecting the conduit 18 and the conduit 25; 34 is a conduit connecting the conduit 23 between the exhaust gas recirculation fan 24 and the control damper 27 and the conduit 31; Reference numeral 35 indicates control dampers provided in the conduits 25, 32, and 34, respectively.

The cold air sent through the cold air pipe 18 and the hot air sent through the hot air pipe 19 and air preheater 11 from the forced draft fan 17 outlet are transferred to the pulverizer 16a.
The temperature of the air for conveying pulverized coal at the outlet is adjusted and mixed so as to be constant, and the air is sent to the pulverized coal machine 16a through the primary ventilation fan 20 and the pipe line 21, and then the pulverized coal pulverized by the pulverized coal machine 16a is mixed. When sending the pulverized coal to the main burner 2 of the boiler 1 and burning it, the air preheater 1
A damper 27 mixes high-temperature exhaust gas discharged by an exhaust gas recirculation fan 24 from a hot exhaust gas pipe 23 provided on the upstream side of the cooling exhaust gas pipe 25 and low-temperature exhaust gas discharged from an induced draft fan 12 from a cold exhaust gas pipe 25. After the adjustment, the pulverized coal for secondary combustion pulverized by the pulverizer 16b is conveyed to the burner 4 for secondary combustion by the exhaust gas for secondary combustion whose pressure is increased by the primary ventilation fan 28, and the pulverized coal for secondary combustion is pulverized by the pulverizer 16b. It is injected from the burner 4 into the downstream part of the combustion zone of the main burner 2.

NO _x produced by combustion in the main burner 2 is a reducing substance produced when pulverized coal injected into the downstream part of the combustion zone of the main burner 2 is thermally decomposed by hot gas produced by the combustion in the main burner 2. (Hydrogen gas: H ₂ ,
Carbon monoxide: CO, carbon: C, etc.). Thereafter, the unburned matter is completely combusted by air supplied from the second-stage combustion air hole 5, becomes combustion gas, undergoes heat exchange with the secondary superheater 7, etc., is induced by the induced draft fan 12, and is discharged from the chimney. .

In the equipment of the present invention, the secondary fuel injected into the boiler 1 from the secondary combustion burner 4 is combusted from the main burner 2 within the boiler 1 without being combusted near the burner, unlike in the case of the main burner 2. When mixed with the main stream of gas, it is decomposed by the residual oxygen contained in the main stream and a reducing substance is generated, and NO _x is reduced by the reducing substance, achieving a sufficient denitrification effect. be done.

Here, when the load on the pulverizer 16b decreases,
Since the ratio of the gas that conveys the pulverized coal to the amount of pulverized coal changes as shown in FIG.
If air is used as the carrier gas in the same way as in a, the amount of air will exceed the appropriate amount at low load, and combustion will proceed too much near the jet port of the secondary combustion burner 4, resulting in sufficient reduction of NO _x . I can't.
However, in the present invention, the pulverized coal for secondary combustion is mixed with the exhaust gas taken out from the inlet of the air preheater 11 and the outlet of the induced draft fan 12, and the circulating exhaust gas has a low oxygen concentration. Machine 16b
Since the oxygen concentration is low, even if the load decreases, combustion will not proceed too much in the vicinity of the nozzle, and NO _x can be sufficiently reduced. . The control damper 27 is connected to the pulverizer 1 for secondary combustion as described above.
In order to keep the carrier gas temperature at the 6b outlet constant,
Cold exhaust gas at the outlet of the induced draft fan 12 and air preheater 11
Used to adjust the mixing ratio with the hot exhaust gas at the inlet. Further, the control dampers 26 and 33 are dampers for switching between the gas at the outlet of the induced draft fan 12 and the air at the outlet of the forced draft fan 17, and when the pulverized coal machine 16b for secondary combustion is stopped during operation of the boiler 1, the pulverized coal is It is operated so that low temperature air can be used when the aircraft 16b is cooled down. If the control damper 33 is opened, the air at the outlet of the forced draft fan 17 can be mixed with the circulating exhaust gas for conveying the secondary fuel.

The pulverized coal two-stage combustion equipment of the present invention is not limited to the above-mentioned embodiments, and can be applied to combustion furnaces other than boilers that use pulverized coal as fuel.
Of course, various changes may be made without departing from the gist of the present invention.

[Effects of the invention] As described above, according to the pulverized coal two-stage combustion equipment of the invention, (i) NO _x generated by combustion in the main burner of the boiler;
is reduced by the decomposition products of pulverized coal injected from a secondary combustion burner, and the hot exhaust gas at the inlet of the air preheater and the cold exhaust gas at the outlet of the induced draft fan are mixed to produce circulating exhaust gas at an appropriate temperature with a low oxygen concentration. The pulverized coal is transported and supplied to the secondary combustion burner, so even when the load is small, combustion near the secondary combustion burner nozzle does not progress too much as in the conventional case, and the secondary combustion burner It is possible to maintain the reduction ability of NOx to the maximum extent, and the emission concentration of _NOx can be suppressed.

(ii) The temperature of the circulating exhaust gas that conveys the pulverized coal to the secondary combustion burner can be adjusted by mixing the hot exhaust gas at the air preheater inlet and the cold exhaust gas at the induced draft fan outlet, so the pulverized coal can be dried at the same time. can be done.

(iii) The piping line for utilizing circulating exhaust gas has a relatively simple structure, and _the
Because the _NOx removal effect is remarkable, the denitrification equipment that was previously required is no longer necessary
Ammonia, catalysts, etc. for reducing NO _x are also not required. Therefore, construction costs for boilers and the like are significantly reduced.

(iv) Since it is easy to install the circulating gas piping line, add a burner, and modify it, it can be used even with conventional boilers.

etc., exhibits various excellent effects.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of one embodiment of the equipment of the present invention, Figure 2 is an explanatory diagram of a pulverized coal supply section used in a conventional pulverized coal combustion furnace, and Figure 3 is an illustration of the load and A/C of the pulverizer.
(Air/Coal). 1 is a boiler, 2 is a main burner, 4 is a burner for secondary combustion, 5 is an air hole for two-stage combustion, 7 is a secondary superheater,
8 is a reheater, 9 is a primary superheater, 10 is an economizer, 11 is an air preheater, 12 is an induced draft fan, 14
a, 14b are bunkers, 15a, 15b are coal feeders,
16a and 16b are pulverized coal machines, 17 is a forced draft fan,
18, 19, 21, 22, 23, 25, 29, 3
0, 31, 32, 34 are pipes, 20, 28 are primary ventilators, 24 are exhaust gas recirculation fans, 26, 2
7, 33, and 35 indicate control dampers.

Claims (1)

[Scope of utility model registration request] Equipped with a main burner and a secondary combustion burner, secondary fuel from a pulverized coal machine for secondary fuel is injected into the downstream part of the main burner combustion zone, and the decomposition products are generated in the main burner combustion zone. In a two-stage pulverized coal combustion facility designed to reduce nitrogen oxides, the pipe connected to the forced draft fan outlet is branched into two, one of which is passed through an air preheater to form a hot air pipe, and the hot air is The pipe and the other cold air pipe are merged and connected to the main burner pulverizer, and the hot exhaust gas pipe branched from the high temperature gas inlet side of the air preheater and the cold gas outlet side of the air preheater are induced drafts. The cold exhaust gas pipes branched from the downstream part of the machine are connected to the secondary fuel pulverized coal machine after being merged with each other by adjusting the flow rate with a damper, and the cold air pipe and the cold exhaust gas pipe are further provided with a damper. A two-stage pulverized coal combustion facility that is connected by a pipe.