JPH0498012A - Coal firing boiler - Google Patents

Abstract

PURPOSE:To considerably reduce NOx without use of other fuel than coal by a method wherein coal is separated into coarse and fine particles, coarse particles are fed into a furnace through a main burner and fine particles are fed through an upper burner. CONSTITUTION:Pulverized coal crushed by coal pulverizers 7 is pneumatically conveyed to cyclones 12 through pulverized coal pipes 8. The air used for pneumatic conveyers is heated up to 300-350 deg.C. In the cyclones 12, the pulverized coal is separated into coarse and fine particles by centrifugal force. The ultra- fine coal separated is sent to an upper burner 4 through an ultra-fine coal pipe 14 together with volatile matters, steam and hot-air. On the other hand, the coarse particle coal which is left in the cyclones 12 is sent to a main burner 3 through coarse particle coal pipes 13 together with hot-air and steam, and fed into a furnace 2 together with combustion air (secondary air) to be burnt. As the zone around the upper burner 4 is an reducing atmosphere and the exhaust gas has an adequate temperature, NOx generated in the zone around the main burner 3 is reduced and considerably diminished. Unburnt carbon components are completely burnt by supplying air from an additional air nozzle 5.

Description

DETAILED DESCRIPTION OF THE INVENTION: Industrial Application Field The present invention relates to a coal-fired boiler used for business or industrial purposes, and particularly to its combustion equipment.

[Conventional technology]

Coal is increasingly being used as an abundant fossil fuel to replace oil. However, exhaust gas emitted from boilers that use coal as fuel generally has a higher concentration of NOx than boilers that use other fossil fuels such as oil and natural gas. Particularly in recent years, it has become widespread on a global scale, and there is a strong social demand for its reduction.

FIG. 2 shows a fuel system diagram of a conventional boiler that uses coal as the main fuel and oil as the two-stage combustion fuel, in response to the above-mentioned demand. In the coal-fired boiler (1) in this figure,
Coal is pulverized into fine powder by pulverized coal W (7), and the pulverized coal pipe (8) transports it from the main burner (3) to the furnace (2).
) and burn it. An upper burner (4) is provided downstream (above) of this king burner (3), and fuel oil sent from the fuel oil supply system (9) through the fuel oil pump 0■ and the control valve (10) is supplied to this upper burner (3). Upper burner (4)
Then put it into the furnace (2). As a result, a reducing atmosphere is formed in the upper part of the king combustion zone around the king burner (3), and NOx generated in the main burner zone is decomposed. And furthermore,
The fuel is completely combusted in the furnace by injecting air necessary for completing combustion from an additional air port (5) provided above the upper burner (4).

[Problem to be solved by the invention]

The conventional coal-fired boiler explained with reference to FIG. 2 performs so-called two-stage combustion, in which fuel oil is injected downstream of the combustion zone to form a reducing atmosphere, in order to significantly reduce NOx contained in the exhaust gas. It has already been proven to be effective.

However, this method requires fuel oil in addition to coal.

In an attempt to obtain the same effect by injecting coal instead of fuel oil, even if the coal is directly injected downstream of the main burner as in the case of fuel oil, the time required to complete the combustion of coal will be shorter than that of fuel oil. Because the length of the coal is relatively long, the amount of unburned coal increases significantly.

The present invention aims to significantly reduce NOx in a coal-fired boiler without using any fuel other than coal.

[Means for Solving the Problems] In order to solve the above-mentioned conventional problems, the present invention separates pulverized coal that is transported by hot air into coarse particles and fine powder, and transfers the coarse particles to the main burner. The present invention proposes a coal-fired boiler characterized in that the fine powder is introduced into the furnace from an upper burner provided above the ball burner.

(Function) In the present invention, fine powdered coal with a short combustion time and volatile matter in the coal, as well as traces of NO emitted from within the coal, are
Since H2C (hydrogen gas), which is effective in reducing x, is injected downstream (above) the main burner, NOx can be reduced without increasing unburned content.

〔Example〕

An embodiment of the present invention is shown in FIG.

The pulverized coal pulverized by the pulverizer (7) is conveyed by air through a pulverized coal pipe (8) and sent to cyclone 0. This pulverized coal conveying air is heated to about 300 to 350°C by an air preheater (not shown).

Therefore, the moisture and volatile matter contained in coal are
It evaporates and evaporates due to the hot air that transports the pulverized coal.

In this way, pulverized coal, volatile matter, hot air, and phlegm air flow through the pulverized coal pipe (8). This mixture is Cyclone 02
) is separated into two parts.

That is, in the cyclone 112), by flowing the above-mentioned mixture in a spiral shape, centrifugal force is used to separate coarse particles and ultrafine particles in the pulverized coal.

The separated ultra-fine coal is sent to an upper burner (4
). On the other hand, the coarse particles of coal remaining without being separated by the cyclone 02) are transported along with hot air and water air to the main burner (3) by the coarse and pulverized coal pipe 03), from where they are supplied with combustion air (secondary air). (This supply system is not shown) is put into the furnace (2) and burned.

At this time, the combustion form around the main burner (3) is considered to be almost the same as combustion in a conventional coal-fired boiler. The NOx generated here reaches the vicinity of the upper burner (4) through exhaust gas ↓, but from the upper burner (4), it is mixed with ultra-fine coal, which is the fuel, volatile matter, and water atom. Since air with insufficient oxygen concentration is injected to complete the combustion of powdered coal, the air ratio near this upper burner (4) is 0.
．． It becomes a reducing atmosphere of 8 to 0.9. Furthermore, by setting the installation position of this upper burner (4) at an appropriate position from the main burner (3), it is possible to set the nearby exhaust gas temperature to the optimum value for NOx. . This 2
Due to two factors, namely a reducing atmosphere and a suitable waste gas temperature, the NOx generated in the ball burner area is reduced and significantly reduced.

This NOx-reduced exhaust gas contains coal that has not yet been completely burned. Therefore, the unburned carbon is completely combusted by air introduced from an additional air port (5) provided above the upper burner (4). At time 2, of the remaining unburned carbon, the portion of the main burner (3) has almost finished burning between the main burner (3) and the Adinoyonal Airport (5).
The particles are sufficiently small. Also, the amount input from the upper burner (4) is Motomo Cyclo 7 G
2) The ultrafine powder and volatile matter separated by c. Therefore, the time required to complete these combustions is short. In this way, near the furnace outlet (5), not only NOx l is sufficiently reduced, but also the unburned coal content is reduced.

The particle size of the ultrafine coal fed from the upper burner (4) must be 70 μm (200 to 23,511 esh) or less.

This particle size is different from conventional pulverizer (fixed separator and M
This can be achieved with either one with R3).

However, if you look at the particle size distribution of the pulverized coal coming out of the pulverized coal machine, depending on the separator model, it contains 15 to 30% or more of particles coarser than 70μ, so as in this example,
Ultrafine powder (almost 100% 70μ) for upper burner (4)
(below) must be separated using a cyclone 07J or the like.

As a parameter for determining the effect of lowering NOx, it is preferable to use the air ratio (ratio between the actual air amount and the theoretical air amount) in each part of the boiler furnace (2). The target air ratio of each part in this example is roughly as follows. That is, 0.8 to 0.9 at the main burner section and 0 at the overfire air outlet.
．． 9-1.0, 0.85-0.9 at upper burner exit
5. 1.15-1.2 at the additional airport exit
That's about it. These target air ratios are controlled and adjusted by changing the amount of air supplied to each burner and additional air port by changing the opening degree of a damper installed in each duct. Further, the fuel input ratio is targeted to be (main burner) = (upper burner) = 90% = 10%.

〔Effect of the invention〕

According to the present invention, ultra-low NOx can be achieved by a two-stage combustion method in a coal-fired boiler without using fuel F4 other than coal (for example, oil or gas). Therefore, there is no need to install a fuel system other than coal, which is the main fuel, so the fuel system is simple and economical with ultra-low NOx.
A coal combustion system is realized.

[Brief explanation of drawings]

FIG. 1 is a fuel system diagram of a coal-fired boiler according to an embodiment of the present invention, and FIG. 2 is a fuel system diagram of an example of a conventional coal-fired boiler. (1) Coal-fired boiler, (2) Furnace. (3)...Main burner, (4)...Upper burner (
5)...Additional airport (6)...Chimney, (7)...Pulverized coal machine (8)...Pulverized coal pipe, (9)...Fuel oil supply system 00)...Fuel oil Pump (11)...Control valve a...Cyclone 0J...Coarse pulverized coal pipe side/Ultra pulverized coal pipe Q9...Furnace outlet Ka2 diagram

Claims (1)

[Claims] Coal that is pulverized and transported by hot air is separated into coarse particles and fine powder, and the coarse particles are fed into the furnace from the main burner, and the fine powder is fed into the upper burner installed above the main burner. A coal-fired boiler characterized in that the coal is fed into the furnace.