JPS58179710A - Gasifying combustion of pulverized coal - Google Patents

Abstract

PURPOSE:To decrease the exhausting rates of generated NOX and smoke dust by producing reducing gas by gasifying pulverized coal, by feeding the air for primary combustion, which has a specified air ratio and is preheated higher than the specified temperature or is oxygen-enriched, into a combustion chamber together with water content and pulverized coal. CONSTITUTION:At the time of combustion, first, mixture of pulverized coal and water content is fed into the primary combustion chamber 2a from fuel feed pipes 5. At the same time, the air for primary combustion, which has the air ratio of 0.7-0.95 and is preheated higher than 400 deg.C or is enriched with oxygen, is fed into the primary combustion chamber 2a, from the primary combustion air feed pipes 6. Then, fuel is burned, with pulverized coal being gasified. By this method, pulverized coal is promoted to be gasified into reducing gas, and the concentration of CO and H2 is increased in a reducing chamber 2b to increase the reducing rate of NOX. Next, the gas is fed into the secondary combustion chamber 2c which is formed above the reducing chamber 2b, and unreacted reducing gas is burned in the chamber 2c by feeding the air for secondary combustion from air ports 8.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pulverized coal gasification and combustion method that can reduce as much as possible the amount of nitrogen oxides NOx and dust emissions generated by combustion.

In general, combustion is used to generate steam for commercial power generation, private power generation, heating in factory buildings, etc.

Depending on the fuel used, this combustion boiler may be a gas-fired boiler or a heavy oil-fired boiler. Coal-fired boilers and coal-fired boilers are well-known, but especially recently, coal has been reconsidered as a fuel from the standpoint of effective resource utilization, and coal-burning boilers that use it are once again in the spotlight. It has come to be used in large numbers.

As this coal combustion boiler, a pulverized coal combustion boiler is known in which raw coal is pulverized and supplied together with a slightly excessive amount of combustion air, and the pulverized coal is combusted as it is.

By the way, in conventional pulverized boilers, because the combustion temperature is low, the solid content called char in the pulverized coal reacts with oxygen in a solid state and burns, resulting in a low combustion rate. Moreover, not only does the amount of soot and dust increase, but the combustion chamber is also larger than that of a gas-fired or oil-fired boiler, resulting in an increase in the size of the boiler itself.

In addition, in the conventional pulverized coal combustion boiler as described above, a part of the reducing gas is produced by combustion with the primary combustion air, and the nitrogen oxides generated are reduced by this reducing gas, and then unburned gas is produced. A two-stage combustion method is used in which combustion is performed using air for secondary combustion. However, in this case, since it is not possible to generate sufficient reducing gas, it is not possible to sufficiently reduce the large amount of fuel NOx that is generated, resulting in lower NOx emissions compared to gas-fired boilers or oil-fired boilers. There was an inconvenience that the amount was large.

The present invention has been devised in view of the above-mentioned problems and to effectively solve the problems.The purpose of the present invention is to provide a method for burning pulverized coal as fuel in the combustion chamber of a boiler. , the air ratio is 0.7 to 0.95, and
Primary combustion air preheated to 400C or higher or oxygen-enriched, moisture and pulverized coal are supplied, the pulverized coal is gasified to generate reducing gas, NOx is reduced with the reducing gas, and unreacted It is an object of the present invention to provide a pulverized coal combustion method in which reducing gas is combusted in secondary air, thereby reducing the amount of NOx and dust emissions as much as possible.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below with reference to the accompanying drawings, which are schematic vertical sectional views showing a boiler for explaining the pulverized coal gasification and combustion method according to the present invention.

The combustion boiler 1 is formed into a substantially cylindrical shape with a rectangular cross section to form a combustion chamber 2 therein, and a large number of pipes are attached to the inner wall of the boiler to generate high-temperature steam, forming a water tube wall 3. has been done.

A combustion chamber 2 in this boiler 1 is a primary combustion chamber 2 in which pulverized coal is gasified from the upstream to the downstream direction of the combustion gas flow G.
a, a reduction chamber 2b for reducing nitrogen oxides generated in this combustion chamber, and a secondary combustion chamber 2c for completely burning unreacted reducing gas from this reduction chamber. .

Specifically, a plurality of combustion burners 4 are provided along the circumferential direction of the water tube wall 3a of the primary combustion chamber 2a in upper and lower stages.

A fuel supply pipe 5 for supplying a mixture of pulverized coal and water or steam is connected to these gases 4, and the air ratio to the supplied fuel is 07 to 0. 9
5 is connected to a primary combustion air supply pipe 6 for supplying primary combustion air maintained at It is designed to cause a gasification reaction.

C+HO-)H2+CO・・・・・・・・・(1) C0CO2 → 2CO・・・・・・・・・(2) The pulverized coal supplied here also contains a small amount of water. actively supplies water or steam to promote the gasification reaction. The amount is preferably 5 to 100% of the weight of pulverized coal.

Furthermore, in order to sufficiently carry out the above gasification reaction, it is necessary to maintain the temperature within the combustion chamber at a high temperature within a range that does not deteriorate the durability of the combustion chamber structure and the economical efficiency of the boiler performance. For this purpose, the primary combustion air is preheated to 400° C. or higher, or the primary combustion air is enriched with oxygen by 5% or more and 80% or less of the weight of the primary combustion air.

Since the reaction temperature inside the primary combustion chamber 2a is high as described above, the ash generated by the reaction will melt, but in order to remove this molten ash in the direction of gravity, the molten ash collector 7 is installed at one time.
Also provided in the lower part of the next combustion chamber 2a, the combustion chamber water pipe wall 3aK
: Designed to collect molten ash that flows down.

A reduction chamber 2b for reducing nitrogen oxides in the gas is formed downstream of the primary combustion chamber 2a. This reduction chamber 2b contains the reducing gas (H2
, Co), which has a size that can sufficiently reduce nitrogen oxides in the gas and maintain the gas residence time for frying.
Nitrogen oxides generated by combustion within the primary combustion chamber 2a can be effectively reduced.

Furthermore, a secondary combustion chamber 2c is provided downstream of the reduction chamber 2b to burn unreacted reducing gas in the gas flowing from the reduction chamber 2b. Specifically, the water pipe wall 3c of the secondary combustion chamber 2c has an air amount sufficient to burn the unreacted reducing gas, that is, an air amount equivalent to the total required air amount minus the air amount for primary combustion. A secondary air supply port 8 is provided for supplying secondary combustion air to completely burn the unreacted reducing gas.

It should be noted that the amount of nitrogen acid compounds, ie, thermal NOx, generated by the secondary combustion is very small compared to the amount of nitrogen oxides (mainly fuel NOx) generated in the primary combustion chamber 2a.

Next, a method according to the present invention will be explained.

First, from the fuel supply pipe 5, the air ratio is 07~
095 and preheated to 400° C. or higher or oxygen-enriched primary combustion air is supplied to burn the pulverized coal while gasifying it as described above.

In the present invention, as described above, the primary combustion chamber is maintained at a high temperature and water is supplied, thereby promoting reduction gasification of pulverized coal and reducing the Co and H2 concentrations in the reduction chamber 2b. In particular, an increase of 62111 degrees will increase the reduction rate of nitrogen oxides. In addition, this reduction chamber 2b is set to a size that can maintain a gas residence time long enough to sufficiently reduce nitrogen oxides in the gas.
Coupled with the above reasons, most of the #1 nitrogen oxides (mainly fuel N0x) generated in the second breath of the primary combustion chamber are reduced in the reduction chamber 2b.

Next, the gas flows into the secondary combustion chamber 2c formed above the reduction chamber 2b. Secondary combustion air is supplied into this secondary combustion chamber 2c through a secondary combustion air port 8, and unreacted reducing gas is completely combusted and discharged as it is to the outside of the boiler. It turns out. At this time, since the thermal No. generated by this secondary combustion is very small, the total amount of nitrogen oxides finally discharged from this boiler 1 can be reduced as much as possible compared to the conventional example. .

Further, since the exhaust gas discharged from the boiler 1 does not contain any ash that causes soot and dust, the dust collector provided in the exhaust gas flue can be downsized.

In summary, according to the method according to the present invention, the following excellent effects can be achieved.

(1) Since the concentration of reducing gases such as H2 and Co is higher than before, the total amount of nitrogen oxides (NOx) emitted can be reduced to the same level as gas-fired boilers and oil-fired boilers.

(2) Unlike conventional methods, pulverized coal is not burned in a solid state, but most of it is gasified before being combusted, making it possible to increase combustion efficiency and making the combustion chamber and boiler itself more compact. It is possible to promote the development of

(3) Since the method is simple, it can be easily applied to existing boilers without major changes.

[Brief explanation of drawings]

The figure is a schematic vertical sectional view showing a boiler for explaining the pulverized coal gasification and combustion method according to the present invention. In the figure, 2 is a combustion chamber, 2a is a primary combustion chamber, 2b is a reduction chamber, 2c is a secondary combustion chamber, 4 is a combustion burner, 5 is a fuel supply pipe, 6 is a primary combustion air supply pipe, 1 is a molten ash collection device,
8 is an air port for secondary combustion, and G is a combustion gas flow. Patent applicant: Ishikawajima Harima Heavy Industries Co., Ltd. Agent Patent attorney: Nobuo Kinutani

Claims (1)

[Claims] In a method of burning pulverized coal as fuel in a combustion chamber of a boiler, the combustion chamber has an air ratio of 0.7 to 0.095, and
Primary combustion air preheated to 400°C or higher or oxygen-enriched, moisture and pulverized coal are supplied, the pulverized coal is gasified to generate reducing gas, NOx is reduced with the reducing gas, and unreacted A pulverized coal gasification combustion method characterized by burning reducing gas in secondary air.