JPS58198606A - Low nox combustion of powdered coal - Google Patents

Abstract

PURPOSE:To reduce NOX and to control the discharge of an unburned part of coal by a method wherein the combustion conditions of high fuel ratio coal and low fuel ratio coal are specified. CONSTITUTION:Burners 2 and 3 for burning powdered coal are arranged up and down, respectively, in a furnace 1 and the high fuel ratio powdered coal 4 and the low fuel ratio powdered coal 7 are injected from burners 2 and 3, respectively. Then the coal 4 is burned in a condition in which the quantity of air is in excess while the coal 7 is burned in a condition in which the quantity of air is made insufficient by a blow of an exhaust gas 9. Consequently, as the combustion zone B of the low fuel ratio coal 7 is in a low oxygen condition and NH3 and HCN generate therein, NOX generated in the combustion zone A of the high fuel ratio coal 4 is reduced to N2 by the NH3 and HCN generated in the zone B. Further, the high fuel ratio coal 4 which is not so well combustible is burned in such a manner that is stays long within the furnace so that the amount of discharge of the unburned part of the coal is reduced and the unburned part of the low fuel ratio coal 7 is also burned sufficiently due to the excess oxygen in the combustion zone A.

Description

DETAILED DESCRIPTION OF THE INVENTION This 'rJ11.
Low NO of powdered coal! The way it burns is the way it burns.

The mainstream combustion method in coal-fired boilers/F-* that uses stone coal as fuel is pulverized coal combustion, in which fuel coal is pulverized and ejected into a furnace for combustion. Pulverized coal combustion often uses a premix combustion method in which the pulverized coal is transported by combustion air. The pulverized coal ejected from the burner into the furnace is ignited,
Combustion is completed through the processes of thermal decomposition, gaseous combustion and solid combustion. The initial combustion region is a region where ignition thermal decomposition progresses, and the region transitions to the combustion region of the released volatile matter. Coal with a high volatile content has good combustibility because it approaches the combustion of gas, and the combustion flame containing this volatile content promotes solid combustion, making it possible to achieve stable combustion overall. Conventional fuel coal has used coal with a high volatile content, but as coal imports have become more dependent on overseas countries, there has been a tendency to use many types of coal as fuel, including those with low volatile content. . Generally, the ratio of fixed carbon content to volatile content contained in coal is called the fuel ratio, but low fuel ratio coal, which has a higher volatile content than fixed carbon content, must be burned in a relatively low temperature range. is possible, but
High fuel ratio coal, which has a lower volatile content than fixed carbon content, needs to be burned in a high temperature range in order to achieve solid combustion. In particular, coal combustion with a high fixed carbon content has the disadvantage that it cannot be completely combusted, leaving a large amount of unburned carbon. ·Also,
The amount of NOx generated during pulverized coal combustion is 100M
It can be broadly divided into fuel NOx, which is produced when the phosphorus content (hereinafter referred to as N content) in the combustion air is oxidized during the combustion process, and thermal NOX, which is produced by the oxidation of the N content in the combustion air.
80 to 90% of the NOX-producing seaweed is produced by fuel NOX. Therefore, in order to suppress NOX generation in pulverized coal combustion, it is necessary to reduce fuel NOX.

The low NOx combustion method currently in use is that the nitrogen content in coal is released together with volatile matter during thermal decomposition, oxidizes, and produces NOx in contact with titanium.
and cyanide (HCN) and ammonia (NHI).
) etc. are formed. It has been reported that these nitrogen adducts reduce NOX to N in a low-oxygen atmosphere and low-temperature region. There have been reports of a method in which waste sludge is crushed and burned in a fine powder R combustion burner. Although this method is effective for charcoal with a high volatile content, it has the disadvantage that the bulk fuel ratio increases the unburned content, and the combustion rate of the unburned content (solid) is slow, so the furnace However, even if low NOx can be achieved, there is a disadvantage that there is a large amount of unburned matter. Therefore low NO
X. There is a need for a combustion method that simultaneously achieves low unburned content.

The present invention was made in an attempt to correct the above-mentioned drawbacks.
The purpose of this is to reduce NOx and suppress emissions of unburned substances.

In other words, in the method of pulverized coal combustion in a boiler or the like, the current value of the present invention is such that at least two pulverized coal injection parts are provided in the vertical direction within the furnace, and the volatile content is lower than the fixed carbon content. Pulverized coal with a low volatile content is ejected from below, and pulverized coal with a high volatile content compared to fixed carbon content is ejected from above, and the pulverized coal with a low volatile content is injected with air in an amount greater than the theoretical combustion air amount. There is a low NOx combustion method for pulverized coal in which pulverized coal is burned in an excess amount and has a high volatile content, and is combusted in an insufficient amount of air that is less than the theoretical combustion air amount.

An embodiment of the present invention will be described below with reference to the drawings. 1 is the furnace of the boiler; 2 and 3 are burners for pulverized coal combustion installed in the vertical direction of the furnace 1; Combustion air 5 (preferably preheated air) is mixed in an ejector 6 and ejected from the burner 2 in an excess amount of air that is greater than the theoretical combustion air amount. In addition, pulverized coal (low fuel ratio coal) 7 with a high volatile content compared to fixed carbon content and combustion air 8 are mixed in the ejector 1O, and air with a temperature below the theoretical combustion air certificate is sent from the burner 3 along with the exhaust gas 9. It is ejected in insufficient quantity. 1
1 is installed in the exhaust gas passage of the furnace 1 and exhaust gas 9t211
In addition, A is the combustion zone of burner 2, and B is the combustion zone of burner 3.

Now, since high fuel ratio coal is combusted in the lower combustion chamber of the furnace 1, the combustion time (residence time in the furnace 1) is lengthened to reduce the emissions of unburned matter. Possible.In the combustion zone, high-temperature combustion with excess oxygen concentration releases the N content in the high fuel ratio coal, which is oxidized and generates NOx. The amount of NHL and HCN generated varies depending on the type of coal, but it is small and large and medium-sized coals directly turn into NOx.

Next, from burner 3, low fuel ratio coal 7 with a m-ring content is used.
is supplied. As for combustion conditions, combustion is performed at a low air ratio in which the amount of combustion air is less than the theoretical amount of combustion air relative to the amount of coal supplied. Combustion at such a low air ratio, that is, oxygen conditions, suppresses the combustion rate and is NO! This suppresses the generation of NH8°HCN under low oxygen atmosphere conditions compared to high oxygen conditions. Exhaust gas9 due to low oxygen combustion
is circulated to the burner 3, and is ejected into the furnace 1 together with the low fuel ratio coal 7 and combustion air 8 together with the premixed fuel by the ejector.

In this exhaust gas circulation system, the exhaust gas 9 is ejected from the burner 3 so as to surround the combustion zone B, eliminating the diffusion of oxygen from the outside, and making it possible to always burn under low oxygen conditions in the combustion zone B of low fuel ratio coal 7. In the combustion zone B of this low fuel ratio coal 7, NH, HCN are generated 9,
In addition, due to the low oxygen conditions, N0XUNHs and HCN produced in the combustion zone of high fuel ratio coal 4 are
, r (reduced, jIl is finally discharged from the furnace l)
OX can be suppressed. In addition, the unburned content is also relatively low in combustibility and has a high fuel ratio.
The unburned sea bream of the low fuel ratio coal produced under low oxygen combustion in combustion zone B is also left over from combustion in the combustion zone! The cables allow sufficient combustion within the furnace l, and also suppress the removal of unburned substances.

According to Fujomei, by efficiently burning cylinder fuel ratio coal and at the same time performing low oxygen combustion of low fuel ratio coal, it is possible to generate from southern fuel ratio coal and reduce it to 'fcN OX't N *. , low NOx%, low unburned fuel, and the effect of achieving low unburned fuel.

[Brief explanation of drawings]

Figure - shows low NO of heather % light imitated powder coal! The center of the combustion bed ll1A
B5 indicating moth? , Figure 1. 1...Furnace, 2j3...Burner, 4...*Powdered coal (
High fuel ratio coal), 5... 9 for combustion! air, 7... value powder (low fuel ratio coal), 8... air for combustion. Many page continuations Akira Takao Hishinuma 3-1-1 Saiwaimachi, Hitachi City Stock % Formula 1 Applicant Babcock Hitachi Co., Ltd. 2-6-2 Otemachi, Chiyoda-ku, Tokyo

Claims (1)

[Claims] L In the method of combustion of pulverized coal in a boiler etc., the pulverized coal is ejected at at least two places in the vertical direction inside the st furnace, and pulverized coal with a lower content of volatile matter than fixed carbon is added from below. , the pulverized coal with a volatile content compared to the fixed carbon content is spouted from above, and the pulverized coal with a low volatile content is heated in a state with an excess amount of air more than that of a combustion air violet. Pulverized coal that burns and has a high volatile content is salt-
The low NO of pulverized coal is expressed as a percentage when it is combusted in a state where the amount of air is insufficient, which is less than the amount of combustion air! Combustion method.