JPH0327803B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a steam boiler using coal as fuel, and particularly to an improvement of a spretz 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 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. ) and the equipment costs and operating costs are compared, and the biggest question is what tonnage per hour (T/H) is the equilibrium point.

In other words, in most people's view, although it depends on the quality of the coal,
It is said that 70 to 130T/H is the borderline of the equilibrium point.

Therefore, for example, when considering a 70T/H steam boiler, the equipment cost is 1.0:1.4 for Spretsuda stoker firing: pulverized coal firing, and the operating cost is 1.0:1.04 for Spretsuda stoker firing: pulverized coal firing. and
It is believed that Spretzda Stoker firing is more advantageous.

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

In addition, recent pulverized coal firing is called two-stage combustion or 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, 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 earlier, the spretz dastalker firing has the advantage of low equipment and operating costs.

However, since Spretsuda stoker firing mainly involves combustion above the stoker, the excess air ratio is inevitably higher than in pulverized coal firing, which increases the amount of air required and the resulting increase in the amount of exhaust gas. This results in an increase in exhaust gas heat loss, which results 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 limitations and problems. Ta.

In this way, although the Spretsuda 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:
It is an object of the present invention to provide a steam boiler that can reduce equipment costs and operating costs, improve boiler efficiency and reduce NOx, and 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, and a combustion chamber body provided at the lower part of the combustion chamber, from which air for coal combustion is supplied. Above it, there is a stoker that generates excess air, a spreader that is installed in a part of the combustion chamber body and that evenly projects the coal onto the stoker, and a boiler body that is connected to the combustion chamber body to communicate with the combustion chamber. and a pulverized coal burner which is installed above the spreader of the combustion chamber body and injects pulverized coal and pulverized coal combustion air in an amount less than the theoretically required amount of air.

In other words, it is based on a spretz stoker-fired boiler and is skillfully combined with a pulverized coal-fired boiler.

(Operation) Coal is uniformly projected onto the stoker by the spreader, and air for coal combustion is supplied from below the stoker, so that the entire surface above the stoker is combusted with coal.

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. This reduces the generation of NOx.

(Example) Hereinafter, an example of the present invention will be described 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 spretted stoker-fired boiler 2 and a pulverized coal burner 3.

The spretsuda 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 lower part of the combustion chamber 4, and a combustion chamber body 5.
A spreader 7 is provided below the stoker 6 to uniformly project the coal A onto the stoker 6, and a boiler main body 8 is connected to the combustion chamber body 5 to communicate with the combustion chamber 4. Coal combustion air B is supplied from the stoker 6, and surplus air C is generated above the stoker 6.

The pulverized coal burner 3 is connected to the spreader 7 of the combustion chamber body 5.
It is provided at a higher position, from which pulverized coal D 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, 10 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, 16 is a coal feeder, 17 is a mill, 18 is a cinder re-injector fan, 19 is a nozzle, and 20 is a gas recirculation fan. , 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 supplied from the forced draft fan 15 to the bottom of the stoker 6 through the air heater 11. Burns all over the top.

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.

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

On the other hand, the coal A supplied to the coal feeder 16
is crushed into pulverized coal D by the mill 17, and sent to the pulverized coal burner 3 by the pulverized coal combustion air E branched into the mill 17 from the forced draft fan 15 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 the so-called pulverized coal D is injected in an air-deficient state.

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

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

The ring degree in the reduction zone is the pulverized coal combustion air E.
It can be adjusted by increasing or decreasing the concentration of pulverized coal D.

Further, 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 drawn into the gas recirculation fan 20, mixed with the combustion air sent from the forced draft fan 15 through the air heater 11, and is sent under the stoker 6, to the pulverized coal burner 3, and to the secondary The air is blown into the combustion chamber 4 from the air nozzle 12.
Lower NOx is promoted by O ₂ operation.

The exhaust gas from the gas recirculation fan 20 is pressurized by the cinder reinjector fan 18 and introduced into the combustion chamber 4, thereby reinjecting the unburned coal that has flown to the dust collector 12 and eliminating unburned loss. 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 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 addition, in the steam boiler 1, for example, the total combustion amount
80% is stoker-fired and the remaining 20% is pulverized coal.

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

Now, let us assume that the amount of coal to be burned on the stoker 6 is 80% of the total amount, and the excess air ratio of the air for coal combustion 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 and the surplus air amount ratio is 28.

In the Spretsuda stoker-fired boiler, this surplus air is directly discharged outside the furnace as excess air, resulting in exhaust gas loss and resulting in 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.

In other words, the amount of pulverized coal burned is the remaining 20% in this case.
Now, the excess air ratio of this pulverized coal is λ=0.5.
If pulverized coal combustion air is blown into the combustion chamber, the theoretical required air ratio is 20, but since only half of that, 10, is supplied from the pulverized coal burner, the remaining 10 is insufficient. Become.

Therefore, if this shortfall of 10 is covered by a portion of the surplus air amount ratio 28 that comes up from the bottom, the surplus air amount ratio after pulverized coal combustion is reduced to 18.

This means that the excess air ratio is λ=1.18 for a total combustion amount of 100%, which can significantly reduce the overall excess air ratio and reduce exhaust gas loss.

For this reason, the boiler efficiency is improved compared to the conventional spretsuda stoker fired boiler.

In the previous example, the pulverized coal was dry pulverized coal made using a small pulverizer such as an impact mill, but it is not limited to this. It may be supplied. In this way, further reduction in NOx and equipment simplification can be achieved.

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

(1) It consists of a combustion chamber body, a stoker, a spreader, a boiler body, and a pulverized coal burner, and in particular, the surplus air generated during stoker combustion is used for pulverized coal combustion, so the overall excess air ratio is reduced. This significantly reduces exhaust gas losses and significantly improves boiler efficiency.

(2) A pulverized coal burner is installed above the stoker to burn the pulverized coal, including the pulverized coal in the coal from the stoker, in the combustion chamber above the stoker, resulting in efficient combustion. Significant reduction in NOx can be achieved.

(3) Since the stoker is provided below the pulverized coal burner, there is no problem even if the pulverized coal injected from the pulverized coal burner has a coarse particle size. because,
This is because the coarse pulverized coal falls onto the stoker and is burned together with the coal from the spreader. Therefore, even if the particle size of pulverized coal is coarse, it is possible to use a mill such as an impact mill that has low equipment costs and requires less power.

[Brief explanation of the drawing]

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... Spretsudastoker-fired boiler, 3... Pulverized coal burner, 4... Combustion chamber,
5... Combustion chamber body, 6... Stoker, 7... Spretsuda, 8... Boiler body.

Claims (1)

[Claims] 1. A combustion chamber body with a combustion chamber formed inside, a stoker installed at the bottom of the combustion chamber to which air for coal combustion is supplied from below and excess air generated above it, and a stoker that is part of the combustion chamber body. a boiler body connected to the combustion chamber body so as to communicate with the combustion chamber; and a boiler body disposed above the spreader in the combustion chamber body to spray fine powder evenly onto the stoker. A steam boiler characterized by comprising a pulverized coal burner that injects coal and air for pulverized coal combustion in an amount less than the theoretically required air amount.