JPS6228365B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of mixing exhaust gas with combustion air as a method for suppressing nitrogen oxides (NOx) generated from a boiler. Generated from coke oven gas in a co-fired boiler that uses heavy oil and coke oven gas (including other fuel gases that contain _NH3 and have high NOx emission characteristics).
In order to suppress NOx, recirculated gas was conventionally mixed using the method shown in Figure 1. In Figure 1, 1 is a strong pressure ventilation fan for combustion air, 3 is a recirculation gas line, 2 is an air + gas supply line to the heavy oil burner, 4 is an air + gas supply line to the coke oven gas burner, and 5 is a duct , 6 is a mixer. However, if the mixed amount of circulating gas is increased too much, the ignition point of the heavy oil flame tends to move away from the burner tip, resulting in unstable combustion. Therefore, the amount of recirculated gas mixed is suppressed to an extent that the heavy oil burner flame does not blow out, but this results in a problem that the NOx generated by the coke oven gas burner becomes high. The present invention was made for the purpose of suppressing generated NOx to a minimum by mixing an amount of recirculated gas suitable for each burner, such as a heavy oil burner or a coke oven gas burner, into combustion air. In the case of the system shown in FIG. 1, the amount of recirculated gas mixed is suitable for the heavy oil burner, and additional recirculated gas is required to minimize NOx generated in the coke oven gas burner. Therefore, if additional recirculated gas is mixed in after the combustion air is branched for the coke oven gas burner, NOx generated by the coke oven gas burner can be kept to a minimum. The present invention has been made with attention to this point, and it is possible to oxidize nitrogen by mixing exhaust gas from the outlet of the boiler or combustion furnace with the combustion air of a boiler or combustion furnace that supplies two or more types of fuel from separate burners. In this method, two or more exhaust gas mixing sections for combustion air are installed, and the first mixing section is installed in the air duct common to each burner, and the burner is used for fuel with low NOx generation. Mix the appropriate amount of exhaust gas, then install a second mixing section in the branched air passage, and mix the amount of exhaust gas suitable for the burner for fuel with higher NOx generation and the amount of mixed exhaust gas input in the first mixing section. By adding the difference between
The present invention relates to a recirculating gas mixing method characterized by minimizing NOx. FIG. 2 is a diagram showing an embodiment of the method of the present invention. In FIG. 2, the same reference numerals as in FIG. 1 indicate the same parts as in FIG. In Fig. 2, an amount of recirculating gas suitable for a burner using a fuel (such as heavy oil) that generates low NOx is added to the combustion air sent from the high-pressure fan 1 to the line 3.
branch duct 5 to the burner for fuel with high NOx generation (e.g. coke oven gas).
Recycle gas is additionally mixed in from line 7. This ensures that the amount of recirculated gas suitable for the various fuel burners in the co-fired boiler is mixed into the combustion air to each burner (e.g. 30-40% for heavy oil burners, 40-50% for coke oven gas burners). %, 0% for blast furnace gas burner), NOx generated is kept to a minimum. Although FIG. 2 shows an example in which two types of fuel are simultaneously combusted, it goes without saying that the method of the present invention can also be applied to cases in which three or more types of fuel are combusted simultaneously. Example In a power generation boiler with an evaporation rate of 1130 t/h, three types of fuel having the following properties were used and exhaust gas was mixed with combustion air in the manner shown in FIG. 2. The conditions at this time were as follows.

[Table] Under the above conditions, first, a recirculation gas amount of approximately 19% of the air flow rate was injected from line 3, and an additional recirculation gas amount of approximately 6% of the air flow rate was injected from line 7. The generated amount is 80 ppm (O ₂ 4% conversion), and the amount of recirculated gas from line 3 is changed to approximately 13% of the air flow rate, and the additional recirculated gas amount from line 7 is changed to approximately 12% of the air flow rate. The amount of NOx generated was 77ppm (converted to 4% O ₂ ). For comparison, when the entire amount of recirculated gas was injected from line 3 in the conventional manner shown in Fig. 1,
The amount of NOx generated was 88 ppm (converted to 4% O ₂ ).

[Brief explanation of the drawing]

Figure 1 shows the conventional recirculation mixing system;
The figure shows an example of an embodiment of the method of the present invention.

Claims (1)

[Claims] 1 Mix exhaust gas from the outlet of the boiler or combustion furnace with combustion air from a boiler or combustion furnace that supplies two or more types of fuel from separate burners,
In a method of reducing nitrogen oxides (NOx),
Equipped with two or more exhaust gas mixing sections for combustion air, the first mixing section is installed in the air duct common to each burner, mixes the exhaust gas in an amount suitable for the burner for fuel with low NOx generation, and then branches out. By installing a second mixing section in the air duct, and adding the difference between the exhaust gas mixture amount suitable for the burner for fuel with higher NOx generation and the exhaust gas mixture input in the first mixing section, Optimize the amount of recirculated gas mixed in each burner, and reduce the amount of gas generated in the boiler or combustion furnace.
A recirculating gas mixing method characterized by the lowest NOx.