JPH0222876B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a vertical kiln, and particularly to a vertical kiln that has been improved so as to be able to increase the co-firing rate of solid fuel such as coke.

[Background of the Invention] Vertical kilns, particularly double cylindrical vertical kilns, are widely used for the combustion of limestone, dolomite, and the like. In this double cylindrical vertical firing furnace, an outer cylinder and a middle cylinder are installed substantially coaxially in the vertical direction, and the material to be fired flows down through the space between the outer cylinder and the middle cylinder. A combustion device with a burner (usually an oil or gas-fired burner) is installed in this space between the cylinders, and the object to be fired flowing down the space between the cylinders is heated and fired by the high-temperature combustion gas of this combustion device. do.

In this double cylindrical vertical firing furnace, a solid fuel such as coke is mixed with the raw material to be fired, and the solid fuel is combusted using surplus air in the combustion gas of the combustion device, thereby reducing fuel costs. There are cases. However, in conventional double cylindrical vertical firing furnaces, when the amount of excess air in the combustion gas of the burner increases, combustion of the solid fuel starts at the upper part of the cylinder, that is, near the raw material input side, and the raw material is heated. The pre-preparation zone was shortened, the exhaust gas temperature rose, and there was a risk that stable reactor operation would become difficult.

This phenomenon will be explained with reference to the drawings. FIG. 1 is a vertical cross-sectional view showing a schematic configuration of a conventional double cylindrical vertical firing furnace. The middle cylinder 12 constitutes a furnace main body.
The part between the outer cylinder 10 and the middle cylinder 12 is the inter-cylinder part 14, and a charge tank 16, a raw material supply feeder 18, and a charging device 20 are installed at the top of the furnace body.
Raw stone, which is a material to be fired, is fed into the upper part of the cylinder part 14 by the raw material supply device consisting of the cylinder part 14.
The product is fired while gradually moving downward through the discharge device 22 and the product take-out feeder 24 to be discharged.

The middle cylinder 12 is partitioned in the middle by a partition plate 13, and is divided into a lower chamber 12a and an upper chamber 12b. Further, an air flow passage 12c is provided in the vertical direction inside the wall surface of the middle cylinder 12, and the middle cylinder 12 is configured to be cooled by the air flowing through this flow passage.

A lower combustion chamber 26 and an upper combustion chamber 28 are provided in the lower part of the intercylinder part 14 and in the upper part thereof so that the outer cylinder 10 protrudes toward the outer periphery. A lower burner 32 and an upper burner 34 are installed, to which liquid fuel such as the like is supplied via a pipe 31.

Next, a system for supplying combustion air to the combustion chambers 26 and 28 will be explained.

First, primary air and tertiary air will be explained.

Reference numeral 36 denotes a primary/working air blower that supplies primary air and working air for operating an injector 56 (to be described later), and the atmosphere flows from this blower 36 through a pipe line 38 to a heat exchanger (requioperator) 40. After being heated by exchanging heat with high-temperature combustion exhaust gas, e.g., about 700 to 800°C, discharged from the first exhaust gas outlet 42, it is introduced from the pipe 44 and installed so as to surround the furnace body. Primary/working air ring 4
6 will be introduced once. And part of it is piping 48
to the upper burner 34, and the other part to the piping 5.
0 to the lower burner 32 as primary air.

The remainder of the primary/working air is introduced from the pipe 54 into the injector 56, and is introduced into the lower chamber 12a of the middle cylinder 12.
from the gas outlet 58 communicating with the upper part of the middle cylinder lower chamber 1.
A mixed gas of the combustion gas in 2a and air sucked in from the cooling air intake port 59 is sucked in, and mixed with this mixed gas, and supplied to the lower combustion chamber 26 as tertiary air. Note that the cooling air intake port 59 is connected to the bottom of the furnace body, and the air sucked into the bottom of the furnace body from this intake port 59 rises inside the furnace body, cools the product, and raises the temperature. sucked inside.

Next, secondary air will be explained.

As described above, the middle cylinder 12 has a cooling air flow passage 12c formed inside its wall surface, and atmospheric air is sent from the secondary air fan 60 to the top of this flow passage 12c. This air flows through the flow path 12c
flows down, cools the middle cylinder 12, raises its temperature, and flows through the pipes 62, 63 from the outlets 12d, 12e.
The air is then introduced into a secondary air ring 64 installed around the furnace body, and then into pipes 66 and 68.
is supplied to the burners 32, 34 as secondary air.

Next, the flow of combustion gas will be explained. After the combustion gas generated in the lower combustion chamber 26 enters the inter-cylinder section 14, a part of it flows downward, becomes a flow parallel to the raw stone, heats it, and when it flows out of the inter-cylinder section 14, it is sucked by the injector 56. As a result of the action, it is sucked into the middle cylinder 12, mixed with the cooling air as described above, and then passed through the gas outlet 58 and the injector 56 to the lower combustion chamber 2.
It is cycled to 6.

Further, the remainder of the combustion gas in the combustion chamber 26 is
The lower bridge 70 installed at the lower bridge 70 raises the inside of the rear inter-tube section 14, which is evenly distributed within the inter-tube section 14, and forms a counterflow with the falling raw ore to heat it.

The combustion gas generated in the upper combustion chamber 28 rises in the rear inter-cylinder part 14, which is evenly distributed within the cylinder part 14 by the upper bridge 72, and heats the raw stone.

A part of the combustion gas that rose inside the cylinder part 14 to heat and burn the raw stone is transferred to the middle cylinder upper chamber 12.
From the high-temperature gas outlet port 74 communicating between the cylinder part 14 and the middle cylinder upper chamber 12b, the gas enters the middle cylinder upper chamber 12b, rises, reaches the exhaust gas outlet 42, and then enters the above-mentioned requicuperator 40 from the pipe line 76 and enters the primary cylinder upper chamber 12b. After exchanging heat with the working air, the pipes 78, 80 and the exhaust gas fan 82
The dust is introduced into a dust collector 84 through which it is subjected to dust removal processing and then released into the atmosphere.

On the other hand, the remainder of the combustion gas rising inside the cylinder part 14 rises in the upper part of the cylinder part 14, preheats the raw stone, and then reaches the second exhaust gas outlet 86 at the top of the furnace body, and then passes through the pipe. 80, and is sent to a dust collector 84 via an exhaust gas fan 82.

Therefore, raw ore input into the furnace from the top of the furnace body is transported to the preheating zone A above the port 74 and to the port 7.
4 and the upper combustion chamber 28, an intermediate firing zone C between the upper combustion chamber 28 and the lower combustion chamber 26, and a lower firing zone between the lower combustion chamber 26 and the lower end of the middle cylinder 12. After being sufficiently fired through the zone (co-current firing zone) D, the cooling zone E is placed below the lower end of the middle cylinder 12.
After cooling, it is discharged from the bottom of the furnace body.

In such a double cylindrical vertical kiln, when solid fuel such as coke is mixed with raw stone and co-fired, the solid fuel co-firing rate is set to about 30% or less, and almost all of the solid fuel is in the above-mentioned calcination zone B. The furnace is operated to burn at That is, in the lower combustion chamber 26, normally,
Combustion occurs in an excess air condition with an air ratio of 1.6 to 1.8, producing combustion gas at a temperature of approximately 1250 to 1350°C.
In addition, in the upper combustion chamber 28, the air ratio of the primary air is 0.1,
The air ratio of the secondary air is set to about 0.4, and about 30 to 50% of the lower stage combustion amount is combusted. Then, O ₂ in the combustion gas near the high temperature gas extraction port 74
After the concentration reaches about 5-6%, the solid fuel mixed with the raw ore is preheated in the preheating zone A, and then transferred to the upper firing zone B.
Alternatively, in the lower part of the preheating zone A, the combustion gas is combusted by excess air in the combustion gas.

However, in order to further increase the co-combustion rate of solid fuel such as coke and further reduce the amount of oil or gas used, which is relatively expensive compared to solid fuel, the combustion of the upper stage burner 34 must be stopped. The coke combustion zone from lower A to upper calcination zone B
O ₂ concentration increases and coke combustion begins in the upper part of the furnace, making it impossible to operate the furnace.
However, when the combustion of the upper stage burner 34 is stopped, the combustion heat of only the coke is insufficient for calcination, and only the area around the coke is sintered, and the other parts of the ore are not sufficiently sintered, resulting in uneven sintering. and product quality deteriorates. In order to prevent uneven firing, it is necessary to input an extra amount of heat from the lower combustion chamber 26, which results in an increase in heat consumption.

For this reason, in the conventional vertical kiln, the solid fuel co-firing rate had to be kept low, and relatively expensive oil or gas had to be used that much more, resulting in high energy costs.

[Object of the Invention] The object of the present invention is to solve the problems of the above-mentioned conventional technology, and to achieve stable operation even when the co-firing rate of solid fuel such as coke is increased, and to achieve excellent results without inputting excess heat. The object of the present invention is to provide a vertical kiln that can fire products of high quality.

[Structure and operation of the invention] In order to achieve this object, the vertical firing furnace of the present invention combines low-temperature combustion gas with a low O ₂ concentration with high-temperature combustion gas extracted from a high-temperature section in the furnace. After replacing and heating, O2 is blown into the firing zone of the furnace body again to suppress the O ₂ concentration in the firing zone to, for example, about 5 to 6%, and to bring the temperature of the firing zone to a temperature that allows sufficient firing. It is constructed so that it can be maintained, and is installed vertically inside of which the material to be fired flows down, and a furnace body equipped with a combustion device for heating the material to be fired, and a furnace body above the combustion device. a first gas exhaust means for extracting exhaust gas from an intermediate part of the furnace body; and a second gas exhaust means for extracting exhaust gas from an upper part of the furnace body.
a heat exchanger into which the exhaust gas from the first gas exhaust means is introduced to the heat source side, and the first gas exhaust means and/or the second gas exhaust means that have passed through the heat exchanger. and an exhaust gas circulation system that heats a part of the exhaust gas from the furnace through the heat exchanger and then blows it into the firing zone of the furnace body. be.

That is, in order to suppress the O ₂ concentration in the upper firing zone B and maintain it above a predetermined temperature, high-temperature combustion gas is extracted from the high-temperature gas extraction port 74 using an induction fan, and this high-temperature combustion gas is circulated to the upper combustion chamber. It would be better if you let them do it,
A fan that can stably suck in a large amount of high-temperature gas over a long period of time (for example, a fan that can withstand high-temperature gas of 750 to 850 degrees Celsius, a wind pressure of 300 to 500 mm, and an air volume of 4000 to 8000
Characteristics of the order of m ³ /h are required. ) cannot be provided at a cost that can be used industrially with today's technological level, and therefore, simply circulating high-temperature combustion gas using a normal fan cannot provide stable furnace operation over a long period of time. I can't do it.

According to the present invention, the high temperature combustion gas taken out from the high temperature gas extraction port and the low temperature combustion gas are exchanged with each other and are blown into the furnace.
There are no such technical difficulties and the intended purpose can be achieved.

[Embodiments of the Invention] The present invention will be described in further detail below with reference to embodiments shown in the drawings.

FIG. 2 is a configuration diagram of an embodiment device of the present invention,
Components that are the same or corresponding to those of the prior art device of FIG. 1 are designated with the same reference numerals.

In this embodiment apparatus, the structure of the furnace main body is the same as that of the conventional apparatus shown in FIG. After being fired by the combustion heat of the coke mixed with the combustion gas and raw materials, it is cooled and discharged from the bottom of the furnace body. Also,
Similarly, exhaust gas is discharged through two systems: a low-temperature exhaust gas outlet 86 at the top of the furnace body and a high-temperature exhaust gas outlet 76 communicating with the port 74. It mixes with tertiary air due to the suction action of the lower combustion chamber 26.
circulating to. Furthermore, the liquid fuel is also supplied from the pump 30 to the burners 32 and 34 as in FIG. It is supplied to the burners 32, 34 via a ring 64.

In the embodiment shown in FIG. 2, an exhaust gas ring 88 is installed to surround the furnace body, and a pipe 89 is provided for blowing exhaust gas from the exhaust gas ring 88 into the upper combustion chamber 28. ing. Exhaust gas heated to a high temperature in the following manner is introduced into the exhaust gas ring 88.

That is, the high temperature gas extraction port 74 and the middle cylinder upper chamber 1
2b and taken out from the first exhaust gas outlet 42 constituting the first gas exhaust means, the high temperature exhaust gas is introduced into the requioperator 40, which is the first heat exchanger, through the pipe line 76, and is then introduced into the furnace body. After exchanging heat with the circulating exhaust gas, it is introduced from the pipe line 78 into a recuperator 90, which is a second heat exchanger, and after heating the primary working air, it passes through the pipe line 91 and is transferred to the second gas exhaust means. The exhaust gas from the second exhaust gas outlet 86 constituting the exhaust gas fan 8 passes through the pipe 80.
2. A part of the exhaust gas sent out from the exhaust gas fan 82 at a temperature of, for example, 140 to 200°C is sent from a pipe 83 to a dust collector 84, but the rest is introduced into the requipulator 40 from a pipe 92, and is heated to a temperature of, for example, 700 to 800°C by the exhaust gas fan 82. After being heated to ℃, the conduit 94
to the exhaust gas ring 88 and then to the pipe 89
The air is blown into the upper combustion chamber 28 from above.

Since high temperature and low O ₂ concentration gas is blown in in this way, the O ₂ concentration in the upper firing zone B is suppressed to a low concentration of, for example, 5 to 6%, and the solid fuel is combusted in the upper part of the preheating zone A. This enables stable operation of the reactor over a long period of time. In addition, since the upper firing zone B is maintained at a sufficiently high temperature, the amount of oil or gas burned in the upper and lower combustion chambers 28 and 26 is reduced by increasing the mixing ratio of solid fuel to the raw ore. Also, sufficient firing is performed in the upper firing zone B, and no uneven firing occurs. Moreover, since there is no need to input extra heat, there is no increase in heat consumption. In this way, the co-combustion rate of solid fuel can be increased and the amount of oil or gas combusted can be reduced.

In addition, in the recuperator 90, the air blown from the primary/working air blower 36 through the pipe 38 is heated to, for example, about 400 to 500°C, and then
The next working air ring 46 is supplied. Primary/
From the working air ring, a portion of the air is supplied to the burners 32, 34 as primary air, and the remaining air is supplied to the injector 56 as working air, as in the conventional device shown in FIG.

In Fig. 2, 1 to 5 are members for supplying raw materials to the top of the kiln, 1 is an ore tank, 2 is a solid fuel tank, and 3 and 4 are cutouts provided at the bottom of tanks 1 and 2. The feeder 5 is a belt conveyor. Further, 6 is a belt conveyor for conveying the product discharged from the bottom of the furnace body.

The present invention is not limited to the above embodiments, and may be implemented in various other forms without departing from the spirit thereof. For example, in the above embodiment device, the requiperators 40, 9
0 in series, and the primary side requiperator 4
In the present invention, the exhaust gas that is circulated is heated at
90 may be installed in parallel, with one recuperator heating the circulating exhaust gas and the other recuperator heating the primary/working air.

An appropriate blowing space may be formed in the outer cylinder 10 separately from the upper combustion chamber so that the exhaust gas heated by the recuperator is blown into the vicinity of the upper combustion chamber.

Two exhaust gas fans may be installed, one fan attracting the exhaust gas that has passed through the recuperator, and the other fan attracting the exhaust gas from the low-temperature exhaust gas outlet.

In addition to oil-fired burners, gas-fired or pulverized coal-fired burners may be used.

Note that the present invention can also be applied to various types of vertical firing furnaces other than the double cylindrical vertical firing furnace.

[Effects of the Invention] As detailed above, the vertical firing furnace of the present invention has an O ₂
Low concentration combustion gas is heated with high temperature combustion gas and then circulated to the firing zone.
The O ₂ concentration in the firing zone can be suppressed to a value of, for example, about 5 to 6%, and the firing zone can be maintained at a temperature level necessary for sufficient firing. Therefore, by increasing the mixing ratio of solid fuel such as coke to the raw ore and reducing the amount of oil or gas burned, it is possible to operate the furnace stably over a long period of time, and it is possible to significantly reduce fuel costs. It is said that

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a conventional device, and FIG. 2 is a configuration diagram of an embodiment device. 10...Outer cylinder, 12...Middle cylinder, 14...Inter-cylinder part, 26...Lower combustion chamber, 28...Upper combustion chamber,
30...Liquid fuel pump, 36...Primary/working air blower, 40...Requiperator, 42...First exhaust gas outlet, 46...Primary/working air ring, 56...Injector, 64... Secondary air ring, 74...High temperature gas take-off port, 82...Exhaust gas fan, 84...Dust collector, 86...Second exhaust gas take-out port, 88...Exhaust gas ring, 90...Requiperator.

Claims (1)

[Scope of Claims] 1. A furnace body which is installed in the vertical direction, through which a material to be fired flows down, and which is equipped with a combustion device for firing the material to be fired, and a furnace body above the combustion device. A first gas exhaust means for extracting exhaust gas from the middle part of the furnace body, a second gas exhaust means for extracting exhaust gas from the upper part of the furnace body, and a heat source in which the exhaust gas from the first gas exhaust means is introduced into the heat source side. After heating a part of the exhaust gas from the exchanger and the first gas exhaust means and/or the second gas exhaust means that has passed through the heat exchanger, it is heated in the firing zone of the furnace main body. A vertical kiln characterized by being equipped with a blowing exhaust gas circulation system. 2. As the heat exchanger, first and second heat exchangers are installed which are connected in series and through which exhaust gas passes sequentially from the first gas discharge means, and the gas in the circulation system is heated to the first heat exchanger. Claim 1, characterized in that there is provided a system for heating primary air for combustion with an exchanger, heating primary air for combustion with the second heat exchanger, and supplying the heated air to the combustion device. Vertical firing furnace. 3. The furnace main body has an outer cylinder and a middle cylinder installed substantially coaxially in the vertical direction, and the material to be fired flows down through the cylinder space between the two cylinders, and a lower combustion device is installed at the bottom of the cylinder space. is provided, an upper stage combustion device is provided in an inter-cylinder section above the lower stage combustion device, and the exhaust gas circulation system is connected to the upper stage combustion device or a portion in the vicinity thereof so as to be able to blow exhaust gas. A vertical firing furnace according to claim 1 or 2.