JPS61243206A - Steam boiler - Google Patents

Abstract

PURPOSE:To reduce the cost of facility and operating cost and to improve a low Nox state as well as an efficiency of boiler by a method wherein a fine powdered coal burner is arranged at a position above a spreader in a combustion chamber, and both fine powdered coals and air for fine powdered coal combustion less than a theoretical required volume of air are injected from the burner. CONSTITUTION:On the stoker 6, a part of the coal-combustion air B as a surplus air C to be not in use for combustion is generated. The coal A to be supplied to a coal feeder 16 is ground by a mill 17 and made as a fine powdered coal D, fed to the fine powdered coal burner 3 by the fine powdered coal air E passed air E passed from an extrusion air blower 15 through an air heater 11 and branched and fed to the mill 17, then injected into the combustion chamber 4. In this case, the fine powdered coal combustion air E is made less than the theoretical required air volume and the fine powdered coal D is injected under a less volume of air. The fine powdered coal D is ignited together with the fine powder coal air E injected simultaneously and the surplus air C generated on the stoker 6, thereby a reducing zone is generated. Therefore, a low NOx can be attained by this reducing zone.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a steam boiler using coal as fuel, and particularly to improvements in a spreader stoker fired boiler.

(Prior art) Recently, due to the problem of soaring oil prices and price instability, coal, which is expected to be inexhaustible and stable in supply and is inexpensive, has been reconsidered as a fuel, and as an alternative fuel. It is rapidly becoming popular.

In the Old Coal Age, coal was the main ingredient, and oil was used under special conditions.

Therefore, coal-fired boilers using coal as fuel were commonly used, with large boilers using pulverized coal firing and small and medium sized boilers using stoker firing.

However, in recent years, boilers have become larger and the economic balance between pulverized coal-fired and stoker-fired has shifted upwards. The equipment costs and operating costs are compared with
The biggest issue is whether the tonnage per hour (T/H) is an equilibrium point.

In other words, from Dairyoku's point of view, depending on the quality of the coal, 70 to 1
It is said that 30 T/H is the borderline of the equilibrium point.

Therefore, for example, when considering a 70 T/H steam boiler, the equipment cost is 1.0:1.4 for spreader stoker firing: pulverized coal firing, and the operating cost is t for spreader stoker firing: pulverized coal firing. o: t, o4, and spreader stoker firing is considered to be more advantageous.

By the way, pulverized coal firing has the advantage of high boiler efficiency.

In addition, in recent pulverized coal firing, two-stage combustion is called three-stage combustion, and first, the excess air ratio when ejecting from the pulverized coal burner is kept lower than the theoretically required amount of air, and then the pulverized coal is ejected from the burner. It is possible to suppress the generation of NOx by adding secondary air immediately after this, or by injecting pulverized coal to the top of the stage to form a reduction zone and injecting tertiary air. can.

However, as mentioned above, pulverized coal firing has the drawbacks of high equipment costs and the fact that the mill requires a large amount of power, leading to high electricity bills and high operating costs.

On the other hand, as mentioned above, spreader stoker firing has the advantage of low equipment and operating costs.

However, in spreader stoker firing, the combustion is mainly on the stoker, so the excess air ratio is inevitably higher than in pulverized coal firing, which increases the amount of air required and the resulting reduction in the amount of exhaust gas. As a result, exhaust gas heat loss increases, resulting in a decrease in boiler efficiency.

Furthermore, since the excess oxygen rate also increases, the NOx value also increases.

However, in order to reduce NOx, it is possible to suppress this by guiding recirculated gas from the flue and supplying it with air under the stoker, but this has its limits and is a problem. Ta.

As described above, while the spreader stoker-fired boiler has advantages over the pulverized coal-fired boiler in terms of equipment costs and operating costs, it is inferior to the pulverized coal-fired boiler in terms of boiler efficiency and low NOx.

(Problems to be Solved by the Invention) The present invention was devised in view of the above-mentioned problems and to solve them, and its purpose is to reduce equipment costs and operating costs, and The object of the present invention is to provide a steam boiler that improves boiler efficiency and reduces NOx, and that can be easily applied to large boilers.

(Means for Solving the Problems) The steam boiler of the present invention includes a combustion chamber body in which a combustion chamber is formed, a stoker provided at the lower part of the combustion chamber, and a part of the combustion chamber body. The stoker is equipped with a spreader that uniformly projects the coal onto the stoker, and a boiler body that is connected to the combustion chamber body so as to communicate with the combustion chamber. Air for coal combustion is supplied from below the stoker and the stoker is heated. In a spreader stoker fired boiler in which surplus air is generated, a pulverized coal burner is provided at a position above the spreader of the combustion chamber body,
The feature lies in the structure in which pulverized coal and air for pulverized coal combustion in an amount less than the theoretically required amount of air are injected from here.

In other words, it is mainly a spreader stoker-fired boiler and is skillfully combined with a pulverized coal-fired boiler.

(Function) Coal is uniformly projected onto the stoker by the spreader, and coal combustion air is supplied from below the stoker to burn the coal over the entire surface above the stoker.

□ At this time, all of the air for coal combustion is not used for combustion above the stoker, and surplus air is generated.

On the other hand, from the pulverized coal burning burner, pulverized coal and air for pulverized coal combustion in an amount less than the theoretically required amount of air are injected.

In other words, pulverized coal is injected into the combustion chamber in an air-deficient state, and this deficiency is compensated for by surplus air generated above the stoker and combusted, forming a reduction zone above the stoker.

Combustion gas generated by combustion of coal and pulverized coal is led to the boiler body to generate steam.

In the combustion chamber, the excess air generated above the stoker is used to burn the pulverized coal, which reduces the overall excess air ratio, reduces exhaust gas heat loss, and forms a reduction zone above the stoker. Therefore, the generation of NOx can be suppressed.

(Example) Embodiments of the present invention will be described below based on the drawings.

The drawing is a schematic diagram showing the general structure of a steam boiler according to an embodiment of the present invention.

The main parts of the steam boiler 1 include a spreader stoker-fired boiler 2 and a pulverized coal burner 3.

The spreader stoker-fired boiler 2 includes a combustion chamber body 5 in which a combustion chamber 4 is formed, a reverse feed type stoker 6 provided at the bottom of the combustion chamber 4, and a part of the combustion chamber body 5. It includes a spreader 7 that uniformly projects coal A onto the stoker 6, and a boiler body 8 connected to the combustion chamber body 5 to communicate with the combustion chamber 4. Coal combustion air B is supplied from below the stoker 6. is supplied, and surplus air C is generated above the stoker 6.

The pulverized coal burner 3 is provided at a position above the spreader 7 of the combustion chamber body 5, from which pulverized coal and pulverized coal combustion air E in an amount less than the theoretically required amount of air are injected.

In the figure, 9 is a superheater, 1O is an economizer, 11 is an air heater, 12 is a dust collector, 13 is an induced draft fan, 14 is a chimney,
15 is a forced draft fan, 116 is a coal feeder, 17 is a mill, 18 is a cinder reinjector fan, 19 is a nozzle, 20 is a gas recirculation fan, and 21 is a secondary air nozzle.

Coal A is uniformly projected onto the stoker 6 by the spreader 7, and coal combustion air B is sent to the forced draft fan 15.
The coal A is supplied from the coal A through the air heater 11 to the bottom of the stoker 6, and burns on the entire surface above the stoker 6.

At this time, above the stoker 6, a part of the coal combustion air B is not used for combustion and is generated as surplus air C.

The combustion gas generated by combustion is transferred to the combustion chamber 4 → superheater 9 →
The steam is discharged through the boiler body 8 → economizer 10 → dust collector 12 → induced draft fan 13 → chimney 14, and steam is generated in the boiler body 8.

On the other hand, the coal A supplied to the coal feeder 16 is
The charcoal is pulverized and made into pulverized coal according to step 7, and then passed through forced ventilation machine 15.
The air is sent to the pulverized coal burner 3 by the pulverized coal combustion air E branched into the mill 17 through the air heater 11.
From here it is injected into the combustion chamber 4.

At this time, the air E for pulverized coal combustion is kept below the theoretically required amount of air, and so-called pulverized coal is injected in an air-deficient state.

The pulverized coal injected into the combustion chamber 4 is combusted by the simultaneously injected pulverized coal combustion air E and the surplus air C generated above the stoker 6, thereby forming a reduction zone.

Therefore, reduction in NOx can be achieved by this reduction zone.

The degree of reduction in the reduction zone can be adjusted by increasing or decreasing the amount of air E for combustion of fine powder and charcoal to change the concentration of the fine powder and charcoal.

The degree of reduction can also be changed by adjusting the secondary air branched into the secondary air nozzle 21 from the forced draft fan 15 through the air heater 11 and supplying it to the combustion chamber 4.

A part of the exhaust gas that has passed through the dust collector 12 is sent to the gas recirculation fan 2.
0, mixed with the combustion air sent from the forced draft fan 15 via the air heater 11, and blown into the combustion chamber 4 from under the stoker 6, from the pulverized coal burner 3, and from the secondary air nozzle 21. Low NOx reduction due to low 02 operation is promoted.

The exhaust gas from the gas recirculation 7 amp 20 is pressurized by the cinder reinjector fan 18 and introduced into the combustion chamber 4, whereupon the unburned coal that has flown to the dust collector 12 is reinjected to eliminate unburned losses. is prevented.

The mill 17 does not need to be made entirely of pulverized coal as in conventional pulverized coal-fired boilers, so it can be small, and there is no problem even if the grains are somewhat rough. This is because the coarse grained pulverized coal can fall onto the stoker 6 and be combusted, so it will not go unburned. Further, even if the fine particles of pulverized coal reach the dust collector 12 unburned, they are re-blown into the combustion chamber 4 by the cinder reinjector fan 18 and burned.

In the steam boiler 1, for example, 80% of the total combustion amount is subjected to stoker combustion, and the remaining 20% is combusted by pulverized coal.

This will be explained in a simplified manner to make it easier to understand.

Now, the amount of coal to be burned on stoker 6 is 80% of the total amount.
% and the excess air ratio of coal combustion air is λ = 1.35, the total air amount ratio is 108, whereas the theoretically required air amount ratio (actually consumed air amount ratio) is 80. ,
The surplus air amount ratio is 28.

In a spreader stoker fired boiler, this surplus air is directly discharged outside the furnace as excess air, resulting in exhaust gas loss and causing low boiler efficiency.

However, in the steam boiler 1, a portion of this surplus air is consumed for combustion of pulverized coal that is blown into the upper part.

That is, the amount of pulverized coal combustion is the remaining 20% in this case, and if this pulverized coal is now blown into the combustion chamber with pulverized coal combustion air with an excess air ratio of λ = 0.5, the theoretically required air The quantity ratio is 20, but from the pulverized coal burner it is half that, 10.
Since only 1O is supplied, there is a shortage of 1O remaining.

Therefore, if this shortage of 10 is covered by a part of the surplus air amount ratio 28 coming up from below, the surplus air amount ratio after pulverized coal combustion is reduced to 18.

This means that the excess air ratio is λ = 100% of the total combustion amount.
1 and 1.8, the overall excess air ratio can be significantly reduced and exhaust gas loss can be reduced.

For this reason, boiler efficiency is improved compared to conventional spreader stoker fired boilers.

(Effects of the Invention) As described above, according to the present invention, the following excellent effects can be achieved.

(1) A spreader stoker firing boiler is equipped with pulverized coal and a burner, from which pulverized coal and air for pulverized coal combustion that is less than the theoretically required amount of air are injected, and the excess air generated by so-called stoker combustion is used to burn pulverized coal As a result, the overall excess air ratio is significantly reduced and exhaust gas losses are reduced, resulting in improved boiler efficiency compared to conventional spreader stoker fired boilers.

(2) Since a pulverized coal burner is provided to burn pulverized coal in the combustion chamber above the stoker, a reduction zone is formed here, making it possible to reduce NOx.

(3) Since the spreader stoker-fired boiler is configured with a pulverized coal burner, equipment costs and operating costs do not increase significantly, and therefore it can be easily applied to large boilers.

(4) If a part of the exhaust gas is mixed with combustion air and introduced into the combustion chamber, further reduction in NOx can be achieved.

(5) In the above example, it was explained that pulverized coal is made using a small pulverizer, but as an alternative, it is possible to further reduce NOx and save equipment by supplying water/coal slurry from a pulverized coal burner. The advantage is even greater because it can be simplified.

[Brief explanation of drawings]

The drawing is a schematic diagram showing the general structure of a steam boiler according to an embodiment of the present invention. 1... Steam boiler 2... Spreader stoker fired boiler 3...
... Pulverized coal burner 4 ... Combustion chamber 5 ... Combustion chamber body 6 ... Stoker 7 ... Spreader 8 ... Boiler body 1 other person

Claims (1)

[Claims] A combustion chamber body with a combustion chamber formed inside, a stoker provided at the bottom of the combustion chamber, a spreader provided in a part of the combustion chamber body to uniformly project coal onto the stoker, and a In a spreader stoker-fired boiler, the boiler body is connected to the combustion chamber body for communication, and air for coal combustion is supplied from below the stoker, and surplus air is generated above the stoker. A steam boiler characterized in that a dry pulverized coal burner or a water/coal slurry burner is provided above the spreader, and pulverized coal and air for pulverized coal combustion in an amount less than the theoretically required amount of air are injected from the burner. .