JPH08152118A - Combustion temperature control method in melting furnace of wastes based on shaft furnace system - Google Patents

Abstract

PURPOSE: To make it possible to prevent the generation of semi-molten substances in a furnace and inhibit the growth of deposited substances on the surface of the furnace by mixing a gas whose oxygen concentration is lower than that of air with normal temperature air from an upper stage tuyere and blowing the mixed gas into a melting furnace and lowering the combustion temperature in the upper stage tuyere area than the melting temperature of ash contents. CONSTITUTION: On the downstream of a melting furnace 1 there are laid out a secondary combustion chamber 2, a waste heat boiler 3 and a dust collector 4 one by another where a stack 5 is laid out on the final stage. The melting furnace 1 is provided with a shaft 1a and a bosh 1b. What is more, the bosh 1b is provided with a lower stage tuyere 1c as well as second stage tuyeres 1d and 1e. A mixture of air and oxygen is supplied from the lower stage tuyere 1c while normal temperature air is supplied to the upper stage tuyeres 1d and 1e. In this case, a gas which is proper at a temperature and low in the concentration of oxygen, is supplied from the upper stage tuyere 1d, thereby inhibiting the generation of semi-molten substances. More specifically, low temperature exhaust gas including residual oxygen which is purified with the dust collector 4 and heat-exchanged by way of a waste heat boiler 3 is supplied into the furnace from the upper stage tuyeres 1d and 1e together with the normal temperature air.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a facility for thermally decomposing and melting general municipal waste and various industrial wastes,
In particular, the present invention relates to a temperature adjusting method for suppressing the generation of a semi-molten material by adjusting the combustion temperature of the upper tuyere portion of a shaft furnace type melting furnace by using a gas having an oxygen concentration lower than that of air.

[0002]

2. Description of the Related Art As a melting type pyrolysis furnace for melting wastes by the processes of drying, pyrolysis and combustion melting, there is, for example, the one described in Japanese Patent Publication No. 60-11766.

This is because when solid waste having a water content of 50% or more is mainly decomposed into molten slag at 1350 to 1550 ° C. and combustible gas, 50 to 300 Nm ³ of oxygen content per ton of waste is generated by air and high concentration oxygen. The furnace structure is such that the lower stage tuyeres are fed from the lower stage tuyere and the upper stage tuyere installed 300 to 1500 mm above the bottom. And, the gas blown from the upper tuyeres is less than the gas sent from the lower tuyeres in both the gas amount and the total oxygen amount contained therein, and only the air is sent from the upper tuyeres to dry the waste, From the lower tuyeres, enrich the air with high-concentration oxygen.
The incombustibles in the waste are melted by high temperature combustion with oxygen concentration of 0%.

[0004]

Air is also used in the conventional furnace as the combustion supporting gas blown from the upper tuyeres, but when the combustion temperature of the upper tuyer becomes excessive due to the object to be treated or the melting point of ash decreases. In such cases, a semi-molten ash content in the waste may be generated. This semi-molten material adheres to the inner wall surface of the furnace and gradually grows, which sometimes becomes a factor for obstructing the physical distribution such as defective loading.

Such a semi-molten material is likely to be generated especially when the combustion temperature of the filling material in the furnace at the upper tuyeres, the pyrolysis residue, the combustible gas, etc., becomes, for example, 1100 ° C. or higher. It has been confirmed.

The problems to be solved in the present invention are, in a shaft furnace type melting furnace for melting and treating waste, a decrease in the combustion ratio of the thermal decomposition residue of the waste and combustible gas in the melting furnace, and the generation of chimney exhaust gas. It is to prevent generation of semi-molten material in the furnace and growth of adhesion to the furnace wall without increasing the number.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a hearth has a lower tuyeres and an upper tuyer disposed above the bosh, and oxygen and combustion supporting gas are blown from the lower tuyeres. , Room temperature air is blown from the upper tuyeres, the pyrolysis residue and combustible gas are burned by the air blown from the upper tuyeres, and the combustion heat at this time is dried together with the combustion gas in the lower tuyeres to waste. In a shaft furnace type waste melting furnace having a plurality of stages of tuyere used as a heat source for heating, a gas having a lower oxygen concentration than air is mixed with air at room temperature from the upper stage tuyere, and the inside of the melting furnace is mixed. And the combustion temperature of the upper tuyeres is made lower than the melting temperature of the ash.

Further, instead of the mixture of the low temperature oxygen concentration gas and the room temperature air, a mixture of steam and air may be blown from the upper tuyeres.

[0009]

In the melting process, room temperature air is supplied from the upper tuyeres, but the combustion temperature of solid waste, pyrolysis residue, combustible gas, etc. in the upper tuyeres is up to 1000 depending on the combustion conditions. ˜1200 ° C., and in a normal case, the melting temperature of ash may exceed 1000 to 1100 ° C.

On the other hand, the combustion temperature of the upper tuyere portion is supplied by mixing the exhaust gas of a relatively low temperature and low oxygen concentration, which has passed through a dust collector, from a heat recovery device such as a waste heat boiler and mixed with room temperature air. Can be below the melting temperature of the ash. Therefore, the generation of the semi-molten material due to the thermal decomposition residue and the combustible gas is suppressed, and the adhesion and growth on the inner wall of the furnace are prevented.

The gas to be mixed and supplied with the room temperature air is not limited to the exhaust gas from the dust collector in the system, but any gas having a lower oxygen concentration than air can be used. For example, a gas containing an inert gas can be applied. .

Even when a mixture of steam and air is blown from the tuyere of the upper stage, H ₂ O by addition of steam is added.
By controlling the combustion temperature of the upper tuyeres to be equal to or lower than the melting temperature of the ash by the endothermic reaction of + C → CO + H ₂ , it is possible to suppress the generation of the semi-molten material. And the gasification of C in the charge is promoted by the endothermic reaction due to the addition of steam,
It is also possible to improve the air permeability in the furnace.

[0013]

1 is a schematic view showing a waste treatment facility equipped with a melting furnace of the present invention.

In the figure, a melting furnace 1 into which waste is charged
A secondary combustion chamber 2 is arranged downstream of the above, and a waste heat boiler 3 as a heat recovery device and a dust collector 4 are further provided downstream thereof, and the final stage is connected to a chimney 5.

The melting furnace 1 is provided with a shaft portion 1a of equal diameter and a bosh portion 1b at the lower end, a lower stage tuyere 1c is provided at the lower end of the bosh portion 1b, and two upper stage tuyere 1d are provided above it.
1e. A mixture of air and oxygen is supplied from the lower tuyeres 1c, and room temperature air is supplied as combustion supporting gas to the upper tuyeres 1d and 1e.

A forced air blower 6 is provided for supplying air to the lower tuyeres 1c and the upper tuyeres 1d and 1e, and the temperature of the upper tuyeres 1d and 1e is adjusted to a lower temperature to make the inner wall of the semi-molten material. In order to suppress the adhesion growth to the upper part, the circulation passage 7 for supplying the low temperature exhaust gas after leaving the dust collector 4 is provided with the upper tuyeres 1d and 1e.
And the circulation blower 7a
Incorporate.

The waste material charged into the melting furnace 1 is melted from the upper layer of the shaft portion 1a through the processes of drying, pyrolysis and pyrolysis and combustion melting. Then, in the bosh portion 1b where dry distillation pyrolysis and combustion are mainly performed, a layer of residue after pyrolysis exists, and air and oxygen at room temperature from the lower tuyeres 1c, and upper tuyeres 1d, 1e. The combustion and melting process is continued by blowing room temperature air.

Even if the upper tuyeres 1d and 1e are operated under the condition that the air at room temperature is supplied, the upper tuyeres 1d and 1e are operated.
Depending on the combustion conditions, the combustion temperature of solid waste, pyrolysis residue, combustible gas, etc. in parts d and 1e may be up to 1000.
It may be about 1200 ° C. On the other hand, as described in the section of the prior art, in the normal case, the melting temperature of ash is 100
It is about 0 to 1100 ° C., and in such a temperature range, generation of a semi-molten product and adhesion to the inner wall of the furnace may occur.

On the other hand, according to the experience of the present inventors, the residue after dry distillation could be burned under the condition of 500 to 600 ° C. or higher if oxygen content was present.

From the above, it is possible to suppress the generation of the semi-molten material by supplying the gas having a low oxygen concentration at an appropriately low temperature from the upper tuyeres 1d and 1e. In the present invention, the waste heat boiler 3 is used. The low-temperature exhaust gas containing the residual oxygen that has been heat-exchanged via the dust collector 4 and has been cleaned by the dust collector 4 is supplied into the furnace from the upper tuyeres 1d and 1e together with room temperature air.

When such exhaust gas is blown, even if the temperature in the furnace fluctuates to some extent during the operating period, the formation of semi-molten material and the prevention of adhesion to the inner wall of the furnace and the melting and combustibility in the furnace are prevented. Dust collector 4 so as not to affect the
It is of course possible to set the amount of circulating exhaust gas after exiting.

That is, the combustion gas discharged from the melting furnace 1 and discharged through the secondary combustion chamber 2 is heat-exchanged by the waste heat boiler 3, and the combustion gas as the primary fluid and the waste heat recovery as the secondary fluid are recovered. Dust collector 4 depending on the amount of heat transfer with fluid (steam, etc.)
The temperature of the exhaust gas flowing to the side is determined. Therefore, the recirculation amount of the exhaust gas discharged from the dust collector 4 is appropriately set and the upper tuyeres 1
By mixing and blowing from d and 1e into room temperature air,
It is possible to adjust the temperature inside the furnace at the blowing part.

Further, in order not to impair combustibility in the melting furnace 1 due to blowing of exhaust gas, the temperature of the upper tuyeres 1d and 1e is 1000 ° C. or less with respect to the production temperature range of the semi-molten material of 1000 to 1100 ° C. It is preferable to maintain the degree. Such setting of the temperature is, for example, when the exhaust gas temperature exiting the dust collector 4 is about 150 to 200 ° C., the exhaust gas amount is 0 to 50% with respect to the blowing amount of the room temperature air from the upper tuyeres 1d and 1e. It is possible to set within a range.

As described above, the clean exhaust gas discharged from the dust collector 4 has a temperature of 1000 ° C. in the upper tuyeres 1d and 1e depending on the setting of the quantity ratio with the room temperature air.
Exhaust gas that can be maintained at the level below can be supplied to the melting furnace 1 from the circulation flow path 7. For this reason, the combustion temperature of the filling material in the furnace, the pyrolysis residue, the combustible gas, etc. should be kept at 1000 ° C.
It can be suppressed to the following level, and generation of a semi-molten material and adhesion and growth on the inner wall of the furnace can be prevented.

Here, in the operation of adjusting the temperature by supplying the exhaust gas from the dust collector 4 together with the air at room temperature from the upper tuyere 1d, 1e, the circulating exhaust gas amount can be made constant during operation. However, it goes without saying that various measures such as controlling the blowing amount according to the situation inside the furnace are possible.

In such control, for example, the unloading state of the melt in the furnace and the temperature in the furnace are monitored, and if there is a tendency that a phenomenon such as the formation of semi-molten ash content occurs, the circulation blower 7a.
Is operated to supply cooling exhaust gas from the upper tuyeres 1d and 1e together with air at room temperature. In this operation, the amount of exhaust gas is set as described above, and any condition that can prevent the production of semi-molten material and the growth of adhesion to the inner wall of the furnace may be used.

In the example of FIG. 1, the lower tuyeres 1c have one stage, but they may have a plurality of stages, and instead of the upper tuyeres 1d and 1e having two stages, one stage or three or more stages. May be

FIG. 2 shows an example in which the gas for controlling the combustion temperature in the furnace is air to which steam is added.

Also in this example, the melting furnace 1 has the same structure as that of the previous example, the furnace top is connected to the secondary combustion chamber, and each member is the same as that shown in FIG. It is indicated by a code.

A mixture of air and oxygen is supplied to the lower tuyeres 1c as in the previous example, and the upper tuyeres 1d and 1e are supplied.
Is supplied with a mixture of steam added to normal temperature air as combustion supporting gas. In the example shown in the figure, the upper tuyeres 1d and 1e are connected to an air-fuel mixture supply path in which an air supply path 11 for room temperature air and a steam supply path 12 for steam are joined. Flowmeters 11a and 12a and control valves 11b and 12b for adjusting the flow rate are provided in the air supply path 11 and the steam supply path, respectively, and the flow rate adjusting valves 11b and 12b are used to mix air and steam. A ratio is set to allow blowing into the furnace.

Here, not only is the gas diluted before the upper tuyeres 1d and 1e due to the blowing of water vapor, but H
_{2 O + C → CO + H} 2 -2610Kcal / Kg (C)
The gas is cooled by the endothermic reaction of the main body. When such steam is blown in, due to fluctuations in the composition of the charging material in the melting furnace 1, the amount of heat required for drying the charging material is insufficient, and the temperature of the exhaust gas from the furnace top is lowered. Therefore, when the calorific value is insufficient, the melting temperature at the bottom of the furnace lowers, and the lowering of the exhaust gas temperature easily causes clogging of the exhaust gas pipe due to the deposition of tar. Need to control.

The mixing ratio of air and water vapor depends on the reaction with the water vapor of the pyrolysis residue in the combustion state estimated by detecting the in-furnace ventilation resistance and the gas temperature at the top of the furnace during combustion. Control so that optimum combustion including consumption and reduction of ventilation resistance in the furnace can be obtained. For this control, an in-reactor ventilation differential pressure gauge 13 for detecting the pressure difference between the upper and lower portions of the shaft portion 1a of the melting passage 1 and an exhaust gas thermometer 14 for detecting the temperature of the exhaust gas from the furnace top toward the secondary combustion chamber are provided. .

When the calorific value of the charged material is large, the water content of the charged material is small and the combustible content ratio is large. At this time, since the attached water content is small, the solid temperature in the combustion region rises. Therefore, since the combustion gas temperature rises and the amount of heat required for drying is small, the furnace top exhaust gas temperature rises. When the combustible content ratio is large, the amount of pyrolysis residue generated by pyrolysis also increases.
From such a relationship between the furnace top gas temperature and the pyrolysis residue, if the steam addition ratio is increased so as to maintain the furnace top exhaust gas temperature at an appropriate value, the consumption of the pyrolysis residue without raising the temperature in the combustion zone Is possible.

On the other hand, when the calorific value of the charged material is small,
The water content of the charge is high and the combustible content is low,
The solid temperature rises in the combustion zone. Therefore, since the combustion gas temperature decreases and a large amount of heat is required for drying, the furnace top exhaust gas temperature decreases. When the combustible content ratio is small, the amount of pyrolysis residue generated by pyrolysis decreases. Therefore, as in the case where the calorific value of the charged material is large, in order to maintain the furnace top exhaust gas temperature at an appropriate value, it is sufficient to control so that the rate of addition of steam is reduced.

When the ventilation resistance in the furnace during combustion is detected to be large, the furnace top gas temperature is changed by increasing the steam addition ratio within the proper range.
That is, by blowing steam into the furnace, H ₂ O + C →
Since the reaction of CO + H ₂ occurs, the gasification of C in the charge can be promoted and the air permeability can be improved. Therefore, in the period when the ventilation resistance is high, the ventilation ratio in the furnace can be reduced by increasing the mixing ratio of water vapor and blowing in, and the unloading property of the furnace interior contents can be secured, and at the same time, blow-through etc. The phenomenon can also be suppressed.

In order to set such a ventilation differential pressure in the furnace and the exhaust gas temperature as detection targets and to properly set the mixing ratio of air and water vapor, a control system surrounded by the one-dot chain line in FIG. Any internal ventilation pressure difference is controlled so as to be maintained within an appropriate range.

That is, the gas flow differential pressure in the melting furnace 1 is detected by the gas flow differential pressure gauge 13 in the furnace and sent to the exhaust gas temperature target value setting circuit 15 to compare the preset gas flow differential pressure with the actual value. The target value of the exhaust gas temperature is increased or decreased according to the deviation, and the target value is sent to the exhaust gas temperature controller 16 within a preset upper limit and lower limit.
On the other hand, the exhaust gas temperature is detected by the exhaust gas thermometer 14 and is discharged and sent to the gas temperature controller 16. The target value set by the exhaust gas temperature target value setting circuit 15 is compared with the actual value, and steam is added according to the deviation. The target value of the ratio is increased or decreased and sent to the steam addition ratio (amount) setting circuit 17. Also, the upper tuyeres 1d,
The amount of air blown from 1e is also sent to the steam addition ratio (amount) setting circuit 17, and the target value of the steam addition amount is determined so as to be the target value of the steam addition ratio. As a result, even if the amount of air blown from the upper tuyeres 1d and 1e varies, the steam addition ratio can be controlled. In addition, the target value of the amount of added steam is sent to the controller 18 for adding amount of steam to perform feedback control.

As described above, either only the exhaust gas temperature fluctuates depending on the composition of the charge, the furnace ventilation differential pressure only varies, or both the exhaust gas temperature and the furnace ventilation differential pressure vary. Also in this case, by controlling the steam addition ratio, it becomes possible to simultaneously maintain the exhaust gas temperature and the in-furnace ventilation pressure difference within an appropriate range.

Here, even in the case where the air added with steam is blown from the upper tuyeres 1d and 1e, it is possible to suppress the generation of the semi-molten material. Then, by appropriately setting the mixing ratio of water vapor and air in accordance with the above control, it is possible to prevent the generation of semi-molten material and the adhesion to the inner wall of the furnace, and at the same time affect the melt flammability in the furnace. It is of course not to do so.

That is, as in the case of the example shown in FIG. 1, since the combustibility in the melting furnace 1 due to the blowing of the air to which steam is added is not impaired, 1000 to 1100 ° C.
Upper tuyeres 1d and 1e for the temperature range of semi-molten product
It is preferable to maintain the temperature of the part at about 1000 ° C. or lower. According to the knowledge of the present inventors, such a temperature can be set by keeping the temperature of the exhaust gas at the furnace top at 150 ° C. or higher. The amount of heat of drying can be secured, and at the same time, the precipitation of tar can be prevented.

Further, by controlling the mixing ratio of water vapor and air and the flow rate of these mixtures so that the combustion temperature of the upper tuyeres 1d and 1e can be maintained at about 1000 ° C. or less, the same as in the previous example. Moreover, the combustion temperature of the filling material in the furnace, the thermal decomposition residue, the combustible gas, and the like can be suppressed to about 1000 ° C. or less, and the generation of semi-molten material and the adhesion and growth on the inner wall of the furnace can be prevented.

Further, the fluctuation of the amount of the thermal decomposition residue of the combustible components in the charge is known from the correlation between the in-furnace ventilation differential pressure and the furnace top exhaust gas, and based on this, an appropriate mixing ratio of steam and air is obtained. As a result, the generated thermal decomposition residue can be consumed by the reaction with steam, and the quantitative fluctuation of the generated thermal decomposition residue can be suppressed. And, in addition to this, by the reaction of H ₂ O + C → = CO + H ₂ by blowing in steam,
The gasification of C in the charge can be promoted. Therefore, the consumption of the generated pyrolysis residue by steam and the gasification of C further promote the improvement of the air permeability in the furnace. As a result, it is possible to sufficiently ensure the drying of the charge and the unloading property of the dry distillate, and it is also possible to prevent blow-through.

Further, the amount of flammable dust (fine thermal decomposition residue) scattered by the consumption of the generated thermal decomposition residue by steam, improvement of air permeability, and suppression of quantitative fluctuation of the generated thermal decomposition residue. And the fluctuation can be suppressed. For this reason, the combustion fluctuation in the secondary combustion chamber for completely burning the gas generated from the melting furnace 1 is also suppressed, and the generation of residual unburned CO and clinker is also suppressed.

[0044]

The present invention has the following effects.

1) A gas having a lower oxygen concentration than that of air (generally an inert gas, a gas containing water vapor, etc.) is mixed with room temperature air from the upper tuyeres and supplied, whereby a thermal decomposition residue or flammability is generated. It is possible to prevent the combustion temperature of the generated gas and the like from becoming excessively high, to prevent the generation of a semi-molten ash content, to prevent the adhesion and growth on the inner wall of the furnace, and to prevent the operation of preventing the load drop.

2) As the blown low oxygen concentration gas,
If the temperature is adjusted using the exhaust gas after heat exchange and dust collection of the combustion gas from the melting furnace, the total amount of exhaust gas will not increase as compared to using a gas for cooling from outside the system,
Equipment that effectively uses exhaust gas can be obtained.

3) When a mixture of water vapor and air is blown in, the carbon content in the charge can be gasified in addition to the temperature adjustment by the endothermic reaction, so that the air permeability in the furnace can be improved. In addition, it is possible to maintain the load unloading property of the charge satisfactorily and prevent accidents such as blow-by.

[Brief description of drawings]

FIG. 1 is a schematic view showing a waste melting treatment facility to which a temperature adjusting method for a melting furnace of the present invention is applied.

FIG. 2 is a schematic view showing an example in which a mixture of air and water vapor is blown from the upper tuyeres.

[Explanation of symbols]

 1 Melting Furnace 1a Shaft 1b Bosh 1c Lower Tuyer 1d Upper Tuyer 1e Upper Tuyer 2 Secondary Combustion Chamber 3 Waste Heat Boiler (Heat Recovery Device) 4 Dust Collector 5 Chimney 6 Push Blower 7 Circulation Blower 11a Circulation Blower 11 Air supply path 12 Steam supply path 13 In-furnace ventilation differential pressure gauge 14 Exhaust gas thermometer

Claims (2)

[Claims] 1. A hearth has a lower stage tuyeres and an upper stage tuyeres arranged above the bosh section. Oxygen and combustion supporting gas are blown from the lower stage tuyeres and the room temperature is supplied from the upper stage tuyeres. A plurality of tuyeres in which air is blown and the pyrolysis residue and combustible gas are burned by the air blown from the upper tuyeres, and the heat of combustion is used as a heat source for drying waste together with the combustion gas in the lower tuyeres. In a shaft furnace type waste melting furnace equipped with, a gas having an oxygen concentration lower than that of air is mixed with room temperature air from the upper stage tuyeres and blown into the inside of the melting furnace to burn the upper stage tuyeres. A method for adjusting the combustion temperature in a shaft furnace type waste melting furnace in which the temperature is lower than the melting temperature of ash. 2. A hearth has a lower tuyere and an upper tuyere arranged above the bosh, oxygen and combustion supporting gas are blown from the lower tuyere, and room temperature is supplied from the upper tuyere. A plurality of tuyeres in which air is blown and the pyrolysis residue and combustible gas are burned by the air blown from the upper tuyeres and the combustion heat is used as a heat source for drying waste together with the combustion gas in the lower tuyeres. In a melting furnace for waste, a shaft furnace method for mixing steam into the air blown into the upper tuyeres and blowing the mixture into the inside of the melting furnace to lower the combustion temperature of the upper tuyeres below the melting temperature of ash For adjusting combustion temperature in waste melting furnace in Japan.